The experiment set-up comprises three main parts: a semi-cylinder model, a water circulating flume, and a PIV system. As shown in Fig. 1, the flume dimensions were length = 11 m, width = 0.6 m, height = 6 m. An aluminum semi-cylinder model with a length of 0.6 m and a radius of 0.025 m, used as the model of the half-buried pipeline. The model was fixed in the flume at a distance of 5 m away from the outfall, as shown in Fig. 2(a). The PIV system consists of a highspeed camera (Photron FASTCAM Mini WX50) and a laser device. The laser device was mounted on the flume at the position above the pipeline model so that the laser light plane (as shown in Fig. 2(b)) could be cast into the flume. The laser light plane was perpendicular to the lengthwise direction of the pipeline model and parallel to the flow direction in the flume. The highspeed camera was placed at the side of the flume aiming at the laser light plane with the axis view perpendicular to the laser light plane.

Fig. 1. The dimensions of the flume

Fig. 2. Experiment set-up: (a) Front view; (b) Top view.

#### 2.2 Experimental Method

Three tests were taken in this study, and the test conditions are shown in Table 1. The water depth was kept constant in the tests at 0.3 m. The mean velocity of the flow was calculated based on the flow discharge in each test.

Table 1. Test conditions.

The procedure of each test is described below:

(1) Running the water pump, and adjusting the flow discharge to the designated value in each test.

A total of 3000 images of each test were used to obtain the time-averaged flow field around the pipeline model by the PIV technique. The details of the PIV technique and the calculation principle can be found in Guan et al. (2019). It is worth noting that, as shown in Fig. 3., the origin of coordinates adopted in this study is located at the center of the semi-cylinder bottom; the X-axis and the Y-axis of the coordinates are parallel to the longitudinal and vertical axis of the flume, respectively. u and v are the horizontal velocity and vertical velocity of the flow, respectively.

Fig. 3. Two-dimensional coordinates

### 3 Experimental Results and Discussion

#### 3.1 Characteristics of Time-Averaged Flow Field

The time-averaged flow field around the half-buried pipeline model in three tests was calculated by the PIV technique. The time-averaged flow features of each test, including the distribution of streamlines, the average kinetic energy (AKE), and the vorticities, were presented in Fig. 4.

As shown in Fig. 4(a), three vortices could be observed around the pipeline model. To better distinguish the vortices, these vortices were defined as:

By comparing the streamline distributions of the three tests, it can be found that as the Reynolds number increases, Vup gradually disappears, Vdp becomes unstable, but Vwp exists all the time. It can be deduced that with the increase of the approaching flow velocity, the backflow zone in front of the pipeline is compressed, causing the Vup becomes smaller and disappear eventually. In the meantime, the area of the Vdp is contracted to cause a unstable status. Moreover, with the increase of the Reynolds number of the flow, the Vwp exists all the time during the experiment, and its position remains unchanged.

The different distributions of AKE, as shown in Fig. 4(b), indicate that with the increase of Reynolds number of the flow, the wake zone is compressed and becomes smaller, especially in the vertical direction. In the meantime, as the Reynolds number increases, the difference between the AKE of pipeline wake and the AKE of undisturbed flow grows significantly.

The time-averaged vorticities at different flow Reynolds number are shown in Fig. 4(c). The two-dimensional distribution of the vorticities shows that the area with relatively large vorticities mainly appears downstream of the pipeline model near the Vdp and Vwp. The maximum vorticity appears on the top of the pipeline model. With the increase of flow Renolds number, the maximum vorticity increases, and the area with relatively large vorticities extends downstream. It may because that the pipeline's existence constrains the vertical development of the area of relatively large vorticities above the pipeline, but the horizontal extension of this area receives fewer restrictions. Thus, the area of relatively large vorticities tends to extend significantly downstream in the horizontal direction rather than in the vertical direction.

Fig. 4. Time-averaged flow field around the half-buried pipeline at different Reynolds number. (a) Streamlines distributions; (b) AKE distributions; (c) Vorticities distributions.

#### 3.2 Characteristics of Wake Turbulence Structure

Figure 5 shows the characteristics of the wake turbulence structure in three tests, including the Reynolds shear stresses, turbulence intensities, and turbulence kinetic energy (TKE).

As shown in Fig. 5(a), the areas with considerable Reynolds shear stress, situated downstream of the half-buried pipeline model, can be classified as the upper region behind the top of the pipeline and the lower region near the bed surface. It is found that the Reynolds shear stress in the upper region is much greater than that in the lower region, which is different from the Reynolds shear stresses of flow around the singlecylinder, where the Reynolds shear stresses of the upper and lower shear layers are almost equal in magnitude. In addition, the comparison of the Reynolds shear stresses at different Reynolds number indicates that as the flow Reynolds number increases, the maximum value of Reynolds shear stress as well as the kinetic energy of the flow increase.

Figure 5(a) and Fig. 5(c) show the turbulence intensity at different Reynolds number in the axis-X direction (TIx) and in the axis-Y direction (TIy), respectively. It can be observed that with the increase of the flow Reynolds number, TIx and TIy in the half-buried pipeline wake increase, and the triangular-shaped region with relatively high TIx and TIy value at the pipeline wake is expanded. TIx and TIy of the area upstream of the pipeline above the bed surface developed as the flow Reynolds number increased. Moreover, similar to the turbulence intensity distribution around submerged weir in the downstream direction and vertical direction (Guan et al. 2014), TIx are more than twice TIy by comparing turbulence intensities of the same point at the same Reynolds number. The triangular-shaped region of relatively high TIx is broader than that of TIy. The main reason is that the flow velocity in the horizontal direction (u) is much higher than that in the vertical direction (v), resulting in a more significant turbulent intensity TIu. Furthermore, the flow above the half-buried pipeline is constrained vertically. u is more affected than v in the wake flow of the pipeline.

The distribution pattern of TKE in the flow field of each test, as shown in Fig. 5(d), is similar to that of TIu. The outline of the high TKE zone and the high TIu zone at the wake of the pipeline are almost the same. Similar to the development rules of TIx and TIy, with the increase of the flow Reynolds number, the maximum TKE increases, and the area of the high TKE region develops. Especially the turbulence intensity at the upstream side of the half-buried pipe near the bed surface increases significantly when the Reynolds number increases. It indicates that the flow structure of the upstream side of the half-buried pipeline becomes turbulent at high flow velocity conditions, which may lead to the potential scour in front of the pipeline, and may eventually result in the suspension of the submerged pipeline above the scoured bed threatening the safety of the pipeline. The scour problem of the submerged half-buried pipeline needs to be further studied in the future.

Fig. 5. Turbulence structure around the half-buried pipeline at different Reynolds number. (a) Reynolds shear stresses distributions; (b) TIx distributions; (c) TIy distributions; (d) TKE distributions.

### 4 Conclusion

This experimental study investigated the flow field patterns and the turbulent structures around the half-buried pipelines at different Reynolds number using the PIV technique. The flow structures studied include the streamlines, the average kinetic energy, the vorticities, the Reynolds shear stress, the turbulence intensities, and the turbulence kinetic energy. The main conclusions are summarized as follows:

the turbulence intensity at the upstream side of the half-buried pipe near the bed surface strengthens significantly under high Reynolds number conditions.

Acknowledgements. This work was supported by the National Natural Science Foundation of China (Project No. 52122109), and the first author would like to thank China Scholarship Council (CSC) for the financial support of this research.

#### References

Ahmed F, Rajaratnam N (1998) Flow around bridge piers. J. Hydraul. Eng. 124(3):288–300

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# Field Measurements of Flow Velocities in Propeller Jets

Irene Cantoni1 , Arne Van Der Hout2(&) , Erik Jan Houwing3 , Alfred Roubos4 , and Michel Ruijter3

1 Civil Engineering and Geosciences, TUDelft, Delft, The Netherlands 2 Deltares, Harbour, Coastal and Offshore Engineering, Delft, The Netherlands<EMAIL_ADDRESS>3 Rijkswaterstaat, GPO, Utrecht, The Netherlands 4 Port or Rotterdam Authority, Port Development, Rotterdam, The Netherlands

Abstract. Propellers of ships generate high velocities adjacent to quay walls, jetties and locks. Generally, a bottom protection is installed in order to prevent instability due to scour. Although design guidance exist, propeller-induced loads are far from fully understood and have predominantly been derived on the basis of model tests. The validation of the existing design methods is lacking, especially for specific types of bow thrusters. In this research, field measurements of flow velocities induced by a 4-channel bow thruster system against a vertical quay wall have been performed. Test results showed a flow characterized by low mean velocities and large fluctuations, with the extent of reflected flow limited to few meters from the quay wall and inflow beneath the suction points playing a role.

Keywords: Propeller jet Bow thruster Quay wall Field measurement Bed protection

### 1 Introduction

Use of transverse thrusters, such as bow thrusters, is common during berthing procedures. Bow thruster-induced wash can cause scour (Roubos, et al., 2014), creating therefore the need for a bottom protection. Due to the interaction between propeller, ship hull and lateral restrictions such as quay walls and sea bed, the flow pattern of the jet is quite complex and is characterized by turbulence and high flow velocities near the bed. An accurate understanding of the propeller-induced flow field is fundamental for engineers, in order to quantify scour and to design an adequate bed protection (Hamill and Kee, 2016).

While an unconfined jet has received attention from several studies, fewer research has been focused on the flow field induced by propellers when confinement elements, such as vertical quay walls or proximity to the sea bed, are present (Wei and Chiew, 2019). Most of the research on propeller induced flow has been based on Albertson et al., who used axial momentum theory to investigate the flow field of a plain-water jet (Albertson et al., 1950).

General features of jets are: diffusion, mixing layers and a great amount of turbulence derived by decelerating flow (Verhagen, 2001). Using the results of Albertson et al., several others developed semi-empirical equations to describe the velocity field within a propeller jet, slightly modifying Albertson's equations. Fuehrer and Römisch (1987), Blaauw and van de Kaa (1978), Hoffmans and Verheij (2011) and Schmidt (2000) based their research on scale models, while Blokland (1996) conducted field measurements. Similar to the present research, Schmidt (2000) and Blokland (1996) investigated reflection of a propeller jet against a vertical quay wall, although they did consider a different type of (bow) thruster than investigated here. Based on Blaauw and van de Kaa, and Fuehrer and Römisch research, BAW (2010) and PIANC (2015) design guidelines have been developed.

In the most recent years, a series of studies identified discrepancies between expected theoretical values as computed using general design guidelines and scale or numerical models. Location of the maximum flow velocities and flow patterns were different than expected (Deltares, 2015). Another study, conducted in Hamburg by Danish Hydraulics (Köppen and Best, 2014), pointed the attention on current guidelines to be overly conservative. Furthermore, guidelines don't provide a clear indication with regard to the width of a bottom protection, which is often designed based on vessel characteristics instead on the extent of the flow velocities (PIANC, 2015).

This has created the need to increase knowledge about propeller jets, especially when reflecting from a vertical quay wall. Both the research community and industry show interest in the topic, with the final goal of achieving optimized bottom protection designs. This study is the result of a collaboration between Port of Rotterdam Authority, Rijkswaterstaat, Deltares, TU Delft, Rotterdam Municipality, Boskalis, Deme and CROW.

In November 2018, pilot measurements on this topic were conducted using a tug at the Antarcticakade, a quay wall for inland barges with a nautical water depth of approximately 7–9 m in the Port of Rotterdam (Deltares, 2018). During that measurement campaign, flow velocities in the propeller jet have been measured using a single upward looking Acoustic Doppler Current Profiler (ADCP). Measurement results indicated the applied set-up was adequate to measure propeller jets, being practical and applicable. Measurements carried out in the present research represent a follow-up study, using a similar test setup and taking place at the same location, with objective of obtaining a better understanding of the flow velocities that occur near the bed and to verify the applicability of design methods presently in use.

#### 2 Field Measurements Methodology

For conducting the measurements, an inland motor vessel, MTS Vorstenbosch, was utilized (see Fig. 1, left panel). It was considered representative for ultimate design situations, since this inland vessel is the largest in the Netherlands. The quay wall at the Antarcticakade consists a sheet pile vertical quay wall, and it has a bed protection of a 20 m wide and 0.85 m thick layer of loose rocks 10–60 kg. For the first 10 m from the quay wall, the protection is penetrated with colloidal concrete (see Fig. 2).

Fig. 1. Measurement location with the Vorstenbosch (left); Schematic representation of a 4 channel bow thruster, illustrating the working principle of the system (Right, source: vethpropulsion.com).

Fig. 2. Cross section of the Antarcticakade, with bottom protection characteristics highlighted.

The MTS Vorstenbosch is equipped with two 4-channel bow thruster systems (see Fig. 1, right panel). This vessel was selected, since for this type of thruster no clear design guidelines are yet available. Due to the shape of the bow of the vessel, the length of the thruster channel and the bow thruster inlet and outlet locations are different for each bow thruster. By applying different combinations of power for both bow-thrusters, it was therefore possible to test a wide variety of conditions. The characteristics of the vessel are listed in Table 1. For the most backward placed propeller (bow thruster 1), the wall clearance was equal to 4.23 times the propeller diameter Dt, and for the most forward propeller (bow thruster 2) the wall clearance was 2.32 times Dt.

Table 1. Characteristics of the Vorstenbosch

To measure flow velocities, two Acoustic Doppler Current Profilers (ADCP) and two Acoustic Doppler Velocimeters (ADV) were installed (Nortek, 2017). While ADCPs measures an array of flow velocities, ADV sensors have a fairly small measurement volume (cylinder of 14 mm diameter and 14 mm height) with high sampling rate of 64 Hz. The ADCP measures the flow velocity in an array of cells by combining information of 4 acoustic beams, assuming a uniform flow within each measurement cell. The size of these measurement cells increases with increasing distance from the instrument. Due to the highly turbulent flow within a propeller jet, it was assessed that the assumption of uniform flow would not be met when the distance from the instrument would be too large. Therefore, here only the measurement results of the second cell of the ADCP are presented (located 0.5 m from sensor head), with a measurement volume that can be visualized as a pyramid trunk with a lateral area of 0.23 m base1 0. 41 m base2 0.20 m height (total approximate volume: 0.016 m3 ) and a sampling rate of 8 Hz.

The instruments were mounted on a frame that was positioned on the sea bed, perpendicularly to the quay wall. One ADCP and one ADV were situated close to each other at the end of the frame near the quay, where maximum velocities are expected. One ADV was located in the middle of the frame, with the objective of being close to the bow thruster inlets and monitor the inflow. Finally, the last ADCP has been mounted at the external end of the frame, at \*14 m from the quay wall. ADCPs were mounted horizontally, therefore looking underneath the ship's hull.

Three different ship positions have been considered. Firstly, the ship has been positioned with the axis of the bow thrusters symmetrical with respect to the measurement frame. Then, tests have been performed with the ship positioned 5 m ahead in respect to the first position, and 5 m behind it. Figure 3 (left panel) shows the three different adopted ship positions and their relative position to the measurement frame. A general reference system is adopted, with the positive x axis pointing perpendicularly away from the quay wall, y axis along the quay wall (positive towards the bow of the vessel), and z representing the vertical dimension in the water column (positive upwards). To acquire insight in the spatial distribution of the flow, it is assumed that mean flow patterns are stationary and that the results of individual tests at different ship positions can be combined. Since moving the vessel was more efficient than installing additional instruments, this approach was adopted as a practical compromise. An illustration of the measurement points with respect to the vessel is depicted in Fig. 3 (right panel).

As a general measurement protocol, each bow-thruster was activated for 2 minutes for 4 applied power steps (25%, 50%, 75% and 100%), then both bow-thrusters were activated simultaneously also applying the same 4 power steps. The three tests were repeated for three different ship positions. Tests were then repeated both a low and high tide, to investigate influence of different keel clearances. To assess the influence of the changing water level, and identify eventual recirculation patterns, one test with a longer duration of 30 min was performed during the rising tide. In addition, one test where the ship is de-berthing was performed using both bow-thrusters at 100% of power, to allow a comparison of stationary tests with a realistic maneuver. Table 2 lists an overview of all performed tests.

Fig. 3. The horizontal lines indicate the position of the frame on which the instrument where mounted with respect to vessel for the different considered ship positions (left); Illustration of the position of the instrument. ADVs are shown as triangles and cell 2 of ADCPs as circles. Inflow and outflow coordinates of both bow thrusters are illustrated, as well as a schematic outline of the ship (right).

Table 2. Measurement protocol for tests

### 3 Test Results

#### 3.1 General Flow Patterns

To investigate general flow patterns, the mean flow velocity and standard deviation for each step of applied power was calculated. Test 1, where bow thruster 1 was used at low tide for ship position 1, is taken as a base case; results are shown in Fig. 4 (left panel).

Observing the measured flow velocities for each instrument, it is possible to notice some general flow patterns. Instruments located near to the quay wall (ADCP1 and ADV1) recorded an increase in mean flow velocity with increase in applied power. Mean horizontal flow velocity appeared to be in the same order of magnitude for these two instruments, however the ADV recorded larger fluctuations. Also, the instrument located beneath the suction points (ADV2) showed an increase in mean flow velocity with an increase in applied power, but velocity magnitude was lower than recorded by the two instruments near the quay wall, and the trend seems different. The last instrument (ADCP2), located 14 m from the quay wall, recorded low mean flow velocities and the increase of applied power did not correspond to an increase in mean flow velocities.

These general observations are valid for most of the tests: mean flow velocities were usually in the order of magnitude of 1 m/s. The instruments near the quay wall presented a clear relation between an increase in applied power and an increase in velocities, whereas the instrument located beneath the suction points, despite recording an increase of velocity with increase of applied power, showed lower mean flow velocities. ADCP2 did not show a relation between use of bow thrusters and recorded velocities.

However, the data from the two instruments near the quay wall was not always consistent: the ADV often recorded higher mean flow velocities than the ADCP, and a larger variability, expressed by higher standard deviations. This behavior is especially evident in tests where the flow had more space to develop (larger keel and/or wall clearance). It is hypothesized that the relative low flow velocities measured by the ADCP is caused by the relatively large size of measurement cell compared to the turbulent structures present in the flow. However, this could not be confirmed during data processing and should be investigated further.

Concerning the spatial distribution of the flow: by assuming that placing the ship at a different position and combining individual test results is equivalent to have extra measurement points in the corresponding location, it is possible to gain an insight on the spatial distribution of the flow. This assumption was based on the uniformity of the measuring location. Test in different ship positions were performed with comparable water levels. A check conducted during post-processing gave confidence that the flow during the test was stationary enough to capture the small variations, as well as it did the absence of recirculation patterns during test 10. The only uncertainty on the validity of this assumption is represented by the variability of the sheet pile wall. Nonetheless, the results from the tests conducted with the ship located in position 2 and 3, consistently shown flow velocities significantly lower than the ones recorded for tests with the ship in position 1, giving a clear indication of the extent of the flow along the quay wall.

As observable in Fig. 4 (right panel), measurements do not show a clear return flow underneath the ship as there is a large variability in flow direction. Measurement points further away from the outlet do not seem to measure the reflected jet but show that the flow near the inflow point was directed towards the suction points of the bow thrusters. A comparison of flow direction recorded by the instrument located between the two suction points (ADV2), confirms that at this location (\*10 m from the quay wall) the flow was dominated by the inflow and not by the reflected jet from the quay wall. This became particularly evident when comparing tests where different bow thrusters were used. Depending on which one is activated, the flow was directed towards the respective suction point (Fig. 5).

Fig. 4. Results from test 1 (use of bow thruster 1, ship position 1, low water). Horizontal mean velocity and standard deviation for each subtest are presented for each instrument. Non reliable data is colored in grey (left); Mean horizontal velocity magnitude and dominant direction for bow thruster 1 induced flow field at 50% of applied power. Tests 1, 5 and 7 (low water) have been combined. Dotted lines: range in direction, corresponding to ±st. Dev of direction (right).

Fig. 5. Comparison of mean velocity and dominant direction measured by ADV2 for 100% of applied power in test 1 (bow thruster 1) and test 2 (bow thruster 2). Suction points of both bow thruster projections on the bed are shown.

#### 3.2 Influence of Wall Clearance

To investigate impact of different wall clearances, the tests using one or the other bow thrusters were compared. The two bow thrusters differ in channel length, and hence in the resulting wall clearance. Wall clearances of the bow thrusters are, relative to the propeller diameter, respectively 2.32 Dt for bow thruster 1 and 4.23 Dt for bow thruster 2. For both bow thrusters however, also the relative position of the instruments with respect to the outlet was different. It was assumed that for this set-up, this difference was not relevant. Figure 6 shows that when low water tests are compared, no significant differences can be observed between the use of one or the other bow thruster, despite the asymmetric shape of the bow. For this condition, the influence of wall clearance seems small. When assessing the influence of under keel clearance however, the results are different for bow thruster 1 and bow thruster 2. This suggests that the impact of the under keel clearance is depending on the wall clearance and vice versa (Fig. 6).

Fig. 6. Comparison of horizontal flow velocity mean magnitude and standard deviation for each step of applied power for test 1 (bow thruster 1) and test 2 (bow thruster 2), at low water.

#### 3.3 Influence of Under Keel Clearance

Comparing the tests conducted at low or high tide, it is possible to observe the influence of under keel clearance on bed velocities. The results, as it can be observed in Fig. 7, vary depending on which bow thruster is used. Observing the data collected by ADV1, the use of bow thruster 1 seems to result in lower values of mean horizontal flow velocities with a larger under keel clearance. On the contrary, when bow thruster 2 is used, ADV1 records larger mean horizontal flow velocities with a larger under keel clearance, as well as an increase in turbulence.

This is though not reflected by measurements from ADCP1, which recorded similar velocities for both cases. It is also worth noting how, for bow thruster 2, the difference in mean horizontal flow velocity between low and large under keel clearance recorded by ADV1 increased with the increase in applied power (Fig. 7, right). In contrast for bow thruster 1, the difference remained fairly constant (Fig. 7, left). From this result, it therefore appears that the influence of under keel clearance on the bed velocities also depends on wall clearance.

Fig. 7. Comparison for bow thruster 1 of horizontal mean flow velocity and standard deviation for each step of applied power for test 1 (low water) and test 11 (high water) (left); Same for bow thruster 2 for test 2 (low water) and test 12 (high water) (right).

#### 3.4 Use of Multiple Bow Thrusters

Simultaneous use of the bow thrusters was also investigated during this research. Figure 8 (left panel) compares the results of tests 1, 2 and 3. In these tests, bow thruster 1, bow thruster 2 and both bow thrusters have been used during low tide. It seems that the use of both bow thruster simultaneously resulted in significantly higher flow velocities as could be expected. It should be noted that test 3 has been conducted only for the first two steps of applied power. This comparison is also possible for tests 11, 12 and 13, where respectively bow thruster 1, 2 and both bow thrusters simultaneously were used, but during high tide (Fig. 8, right panel). While tests 1, 2 and 3, presented above, were conducted at low water and with a fairly constant water depth, tests 11, 12 and 13 were carried out at high water and with larger variation in water level. There was, in fact, a difference of approximately 30 cm between water depth in test 11 and in test 13.

Figure 8 (right panel) shows that differences between use of bow thruster 1 and bow thruster 2 were more significant than the difference between the use bow thruster 2 or both bow thrusters at the same time. It is also worth noting the discrepancies in data recorded by the two instruments located near the quay wall (ADV1 and ADCP1), and the fact that velocities recorded by ADV1 during test 13 did not increase constantly with the increase in applied power, differently than in the other tests. The reason for this was unclear. Consequently, simultaneous use of both bow thrusters do not seem to lead to differences in mean flow velocities larger than the ones between the use of each bow thruster singularly for large keel clearances.

Fig. 8. Comparison of horizontal flow velocity mean magnitude and standard deviation for each step of applied power for test 1 (bow thruster 1) and test 2 (bow thruster 2), and test 3 (both bow thrusters) at low water (left); Same for test 11 (bow thruster 1) and test 12 (bow thruster 2), and test 13 (both bow thrusters) at high water (right).

### 4 Comparison with Guidelines

Results from field measurements were compared to the theoretical predictions using the formulae suggested by commonly used guidelines.

#### 4.1 Maximum Velocities at the Bottom

The maximum velocities at the bottom have been estimated on the basis of both the Dutch and the German method suggested by PIANC. Equations suggested by the guidelines are based on the efflux velocity V0, which depends on the power of the bow thruster Pt, water density qw, and propeller diameter Dt as:

$$V\_0 = 1.15 \left(\frac{P\_t}{\rho\_w D\_t^2}\right)^{0.33} \tag{1}$$

Furthermore, the maximum velocities Vmax, which can be expected at the corner between the quay and the bed, can be calculated according to German method from:

$$V\_{\max} = a\_L 1.9 \, V\_0 \left(\frac{L}{D\_p}\right) \tag{2}$$

where aL is an empirical coefficient chosen based on wall and under keel clearance and L is the wall clearance. Following Dutch method, Vmax is calculated using the following equations, with ht the height of the thruster above the bed:

$$V\_{\max} = V\_0 \frac{D\_t}{h\_t} \qquad \qquad \qquad \qquad \qquad \qquad \frac{L}{h\_t} < 1.8 \tag{3}$$

Vmax ¼ 2:8 V0 Dt L þ ht for L ht [ 1:8 ð4Þ

The data obtained from measurements are compared to the theoretical predictions in Fig. 9 (left and right panel) for both bow thrusters and respectively for a keel clearance of \*1 m, and \*2.7 m. This comparison shows that both formulae are generally conservative compared to the measured velocities, with the exception of data measured during use of bow thruster 2 at high water (test 12, see Fig. 9, right panel). Furthermore, it is possible to observe how sensitivity the methods are to variations in wall and under keel clearance. This could also be because some of the considered wall and under keel clearance ratio falls outside the range of values for which the formulae have been developed and validated.

Fig. 9. Comparison between maximum velocities on the bed, as calculated with Dutch and German method, and measured maximum velocities from ADV1 and ADCP2 with a small UKC in Test 1 and Test 2 (left); Same for a larger UKC in Test 11 and Test 12 (right). Unreliable data (low correlation) depicted in grey.

#### 4.2 Relative Turbulence Intensity

Relative turbulence intensity is a parameter that is often used to give an indication of turbulence level and can be calculated as r ¼ ffiffiffiffi u02 p u , ratio between the root-mean-square of turbulent fluctuations u', and mean velocity u. . Previous literature focused mainly on unrestricted flow; moreover, several methods (full scale measurements, scale models, analytical relations) were used. This resulted in a quite large typical range for relative turbulence intensity. Current guidelines indicate 0.25–0.4 as a typical range of values for r in propellers jet (PIANC, 2015). Figure 10 shows the data collected during the field measurements and shows that values are generally larger. This is mainly since the measured flow was characterized by low mean flow velocities and large fluctuations. The instruments near the quay wall record relative turbulence intensity levels even in the order of magnitude of 1.

Fig. 10. Relative turbulence intensity measured by each instrument for each step of applied power. Comparison between bow thruster 1 (test 1) and bow thruster 2 (test 2). Unreliable data are depicted in grey. Reference lines indicate lower- and upper-bound values expected from literature.

#### 4.3 Use of Multiple Propellers

According to literature, two approaches were adopted to take into account the use of multiple propellers: either linear superposition (PIANC, 2015) or proportionality to square root of number of propellers used (Schiereck, 2016). As observable from Fig. 11 both theories result to be generally conservative. Data collected during test 22 by the ADV is an exception (Fig. 11, right panel) and measurement results seem to be close to theoretical values obtained by multiplying theoretical velocities of one propeller by ffiffiffi 2 p .

Fig. 11. Comparison of linear superposition theory and proportionality to sq. Root of no of used propellers, with data from ADV1 and ADCP1 during test 13 (both bow thrusters, high water) (left). Same during test 3 and test 22 (both bow thrusters, low water) (right). Unreliable data in grey.

#### 5 Discussion

#### 5.1 Assessment of the Measurement Set-Up and Protocol

The measurement set-up used includes some limitations. Firstly, the efflux velocity of the thruster V0 could not be measured directly with the used measurement setup. In the comparison of the measurement results with the design guidelines, the theoretical value of V0 has been estimated based on Eq. (1) and the applied power as read from the instrument panel in the ship cabin. It is possible however that the actual efflux velocity in the field tests was lower than this theoretical value and that part of the conservatism shown in Section 4 is originating from the uncertainty in actual efflux velocity. It is therefore advised to measure V0 directly in future research to verify the validity of Eq. (1) for these types of 4-channel bow thrusters.

Secondly, the limited amount of measuring points and the low spatial resolution result in a fragmented knowledge of the spatial patterns of the flow. ADCPs should have provided more insight on the extent of the reflected flow, but due to the high level of turbulence caused by the reflected jet, the cells more distant from the instrument were considered not reliable due to their relatively large measurement volume. Furthermore, in some tests there is a clear discrepancy between the two instruments placed near the quay wall. Despite their vicinity, ADV1 and ADCP1 are often showing different results. Namely, the ADV records higher mean flow velocities and larger fluctuations than the ADCP. Moreover, velocities corresponding to pressure fluctuations recorded by the ADCP appear to be larger than the recorded flow velocities. This could raise the suspicion that the ADCP, that averages the flow over measuring volume, it is not able to capture the turbulent flow caused by the bow thrusters. Therefore, we consider the flow measured by the ADVs to be more reliable, although the ACDP data can still valuable in a qualitative way, e.g. for relative comparison between different tests and showing trends in the data.

Despite the discrepancies and uncertainties above mentioned, the used measurement set-up was able to clearly determine three different zones in the bow thrustersinduced flow on the bed. These zones fit in the framework identified by Schmidt and we adapted it for 4-channel type bow thrusters. Figure 12 illustrates these zones of the flow induced by the reflection of bow thrusters against a vertical quay wall.

Fig. 12. Zones of reflected jet identified by the tests analyzed in this paper. Adapted by the authors from Schmidt (2000).

Furthermore, the used set-up confirmed the two assumptions that were made during testing. The first assumption was that activating the bow thrusters with the ship moored at the quay would be representative of realistic mooring operations. To test this hypothesis, a test was performed with the ship de-berthing, both bow thrusters activated at 100% of power. Results from this test show that mean velocities of the dynamic situation are comparable with the ones from the static one (see Fig. 13). Since the guidelines provide calculations for the mean velocity, the focus on the dynamic test was on the moving mean. These values were comparable with the ones in the static tests. The higher instantaneous velocities recorded by ADV1 shown in Fig. 13 may be partly influenced by measurement errors and should be investigated further. Stationarity checks conducted on the static tests ensured that the mean over each subtest is representative. Therefore, the results from tests 1–9 and 11–22 are considered representative for a realistic berthing or de-berthing situation.

Fig. 13. Time series of recorded horizontal flow velocities during test 23 (de-berthing maneuver, both bow thrusters activated at maximum power). Both instantaneous and moving mean over 1 min are shown.

#### 5.2 Contextualization in the Theoretical Framework

From comparison with Dutch and German calculation methods of near-bed flow velocities recommended by PIANC guidelines, data collected in this study identified the guidelines as conservative in most cases, especially the ones were the maximum absolute velocities were recorded and are, therefore, determinant for design. On the other side, data recorded by ADV1 in some tests, namely test 12 and 22, resulted in maximum velocities at the bottom slightly larger than the expected ones. Both in test 12 and test 22, bow thruster 2 was used: in test 12 on its own, in test 22 simultaneously with bow thruster 1. Bow thruster 2 is characterized by a larger wall clearance, equal to 4.23 Dt, while bow thruster 1 is located at 2.32 Dt from the quay wall. Most of the research upon which the guidelines have been based considered situations where the flow was less restricted than in the case presented in the present study: (Blaauw and Van de Kaa, 1978) conducted physical scale modelling for ducted and non-ducted propellers, measuring the velocities as the ship was moving in relatively unrestricted waters. (Schmidt, 2000) studied propeller jets against a quay wall in a stationary situation, evaluating different wall and keel clearances. Wall clearance studied by Schmidt were between 7.3- and 4-times Dt, while height of the thruster in the water column was either 2.2- or 2.4-times Dt. In the present study, height of the bow thruster changed more gradually within the tests, covering values between 1.21 Dt and 2.45 Dt. The results of the present study for the situation with a height of the bow thruster of 2.45 Dt and a wall clearance of 4.23 Dt fall within the range explored in Schmidt experiments. As Fig. 9 illustrates, maximum velocities recorded by the ADV present a similar trend to the one forecasted following the German method. However, the maximum velocities recorded by the ADV were slightly larger than expected. For the test with an under keel and wall clearance outside the range taken into account by the studies upon which the guidelines were drafted, the results showed the guidelines to be over conservative.

In combination with the aforementioned smaller wall clearances associated with the bow thruster system, the results of the present study show how the flow develops in a more restricted environment compared to previous studies and shows that for these conditions the design guidelines are conservative. Already a physical scale model research performed by Deltares (2015) found that formulae in literature being generally conservative for small wall clearances, with the exception of larger distances between quay wall and ship (9.5 Dt). Blokland (1996) as well, using field measurements, found higher flow velocities than expected from calculations for wall clearances between 3.2 Dt and 16 Dt.

These results support the hypothesis that currently generally used guidelines do not reflect influence of wall and keel clearance accurately enough for restricted situations, which are outside the range of tested conditions on which the theoretical formulations used in design guidelines are based. These conclusions are relevant, since the situation of small wall clearance considered in the present field measurements is representative for most inland vessels, which are usually characterized by a blunt hull shape that results in a small distance between the wall and the bow thruster's outlet.

#### 5.3 Impact on Bottom Protection Design

When using measured flow velocities in the commonly used stability formulae to determine a suitable rock size required for bed protection, results vary greatly according to which tests are chosen as representative for design conditions. Concerning stability formulas such as Izbash and Pilarczyk, one should consider that these formulations have not been specifically developed for propeller jets. For propeller-jet induced damage, and stability in general, turbulence has been previously identified as a mechanism which might be even more important than mean flow velocity, for instance by Verhagen (2001) and Hofland (2005). As observed in Paragraph 4, low values of mean flow velocities and high relative turbulence intensities were present near the bed. The resulting calculations of rock stability for these conditions suggested that some damage would occur at the Antarcticakade for the most severe conditions. However, surveys conducted after the measurements did show an absence of damage (no displaced rocks) and also the instruments did not show any signs of impact due to moving loose material. This leads to think that a more precise representation of the physical phenomena should be sought.

### 6 Conclusions

From the measurements conducted at the Antarcticakade quay wall, bow thrusterinduced flow on the bed seems to be characterized by fairly low mean flow velocities in combination with a high relative turbulence level. In contrast to research that was previously conducted, no clear return flow underneath the vessel was observed. The extent of the reflected flow from the quay wall seemed to be limited to a few meters. In addition, the flow pattern below the vessels seems to be largely influenced by the suction points of the 4-channel bow thruster system. Furthermore, the measured flow velocities for small wall and under keel clearances showed to be much lower than predicted by methods that are presently used in the design of bottom protections. For larger keel and wall clearances, a better match with general design guidelines was found, but the maximum velocities were slightly larger than expected. Consequently, the design guidelines for bottom protection seem to be conservative for berths facilitating inland vessels in situations with small under keel clearances (approximately < 2 Dt) and small wall clearances (approximately < 4 Dt). It is however important to note how more restricted situations are more relevant for design, since they cause the largest absolute flow velocities. These results are in agreement with previous scale model tests conducted by Deltares (2015). It is highly recommended that additional tests be performed to derive more insight into the relation between the flow velocities near quay walls and small under keel and wall clearances.

Acknowledgements. On behalf of the Delft University of Technology, Deltares, Port of Rotterdam, and Rijkswaterstaat the authors of this paper would like to thank all companies involved for their support, funding and hospitality. In particular, VT and Shell are gratefully acknowledged for their support and for providing a fully laden Vorstenbosch for this test.

### References

Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# Field Observation and Experimental Study on the Interaction Between Ship Waves And Vertical Wave Dissipation Revetment

Liehong Ju, Jingxin Huang, and Junning Pan(&)

Laboratory of Hydrology-Water Resource and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing, China<EMAIL_ADDRESS>
Abstract. With China's economic development, many inland waterways adopt vertical revetment structure to save land resources, but this structure is not conducive to wave attenuation. According to the measurement results of the ship wave data of typical ship types in Sunan Canal sailing at different speeds collected in field observation, the maximum wave height in front of the vertical revetment wall was less than 1.0 m under normal navigation conditions, while the navigation administration boats can form a wave height of nearly 1.8 m in front of the vertical revetment wall at the maximum speed. In channels with heavy freight and fast ship speed, the ship waves formed by ships, superposed with the reflected waves by vertical impervious revetment, would result in severe water surface fluctuation, affecting the safety of ship navigation and the stability of revetment structure. Based on the regulation project of Sunan Canal, this paper put forward two types of vertical wave dissipation revetment, namely round-hole caisson structure and grid-type structure. And their wave dissipation effects are compared and optimized through 2-D wave test. Finally, the 3-D physical model tests of ship wave and revetment were carried out, and the effects of reducing ship wave height of round-hole caisson structure and grid structure are compared. The results show that these two vertical wave dissipation structures can reduce the maximum ship wave height in front of the revetment wall by about 20–25%. The relevant research results of this paper can serve as a reference for similar projects.

Keywords: Wave dissipation revetment Ship wave Field observation Physical model test

### 1 Introduction

Jiangsu Province boosts abundant canals and developed water transportation since ancient times (Sun 2007), occupying about one fourth of China's shipping mileage, tonnage of transportation vessels, annual cargo transportation volume and turnover. In response to the economic development and shipping needs in recent years, many canals have carried out waterway regulation by dredging channels and building revetments to improve the efficiency of canals.

The interaction between ship waves and revetment is a traditional hydrodynamic issue. Revetment structure is one of the important facilities of inland waterway engineering, which can alleviate the scouring of bank slope by water flow and ship waves, thus playing an important role in ensuring the stable and unobstructed waterways. Choosing an appropriate revetment structure is the primary task of revetment engineering design. The revetment structures are generally divided into slope type and vertical type. Slope revetment structure is more commonly used and has a long history, which tends to be more ecological and diversified in recent years (Li et al. 2019). Compared with the slope structure, the vertical revetment requires less land resources but has weaker ability of dissipating ship waves. In order to reduce wave reflection and dissipate waves, people set holes in vertical structures on the wave-ward side, often with perforated caissons. The caisson type breakwaters was first proposed by Jarlan in the 1960s. Subsequently, many domestic and foreign scholars have carried out a lot of experimental research and theoretical analysis on the wave dissipation effect and mechanical characteristics of perforated caissons, and achieved fruitful results (Chen et al. 2001; Shi et al. 2011) while the researchers are focusing more numerical simulation in recent years (Cai et al. 2022). The main mechanism of wave dissipation by using perforated caissons is to introduce part of the wave energy into the caissons through the holes opened on the wave-ward side of the vertical structure, and weaken the reflected waves through the dissipation of waves in the caisson and the influence of phase difference, so as to realize the wave dissipation effect.

The main hydrodynamic force in the canal is ship waves. Throughout the long history of studies on ship waves, many achievements have been made in theoretical research on Kelvin's ship-wave pattern (Ursell 1959) and empirical formulas have been developed through field observation and experiments (Blaauw et al. 1984; Pilarczyk 1984; Robert and Sorensen 1986; Zhou and Chen 1995). In recent years, the research on ship waves mostly focuses on numerical simulation (Zhou et al. 2013).

Relying on the regulation project of Sunan Canal, the field observation was carried out to collect the ship wave under different conditions. Then, 2-D wave tests were carried out to explore different vertical revetment wave dissipation structures and propose the reasonable types of structure accordingly. Finally, 3-D tests of ship waves and different wave dissipation revetments were carried out to verify the effect of vertical revetment on dissipating ship waves.

### 2 Field Observation of Ship Waves

#### 2.1 Basic Information About Field Observation of Ship Waves

The field observation on the ship waves in Sunan Canal was mainly conducted at two sites: ① Zhenjiang section of Sunan Canal. The revetment spacing on both sides of the channel is 90 m, and the water level during observation was 2.3 m; ② Yixing beltway section of Wushen Line. The revetment spacing on both sides of the channel is 70 m, and the water level during observation was 2.1 m. The upstream and downstream shorelines of the two observation locations are straight. The canal section of the ship wave field observation sites is shown in Fig. 1.

Fig. 1. Schematic diagram of ship wave field observation

The wave gauges which adopted for field ship wave surface measuring are 2 m high. During wave surface measuring, the computer-controlled acquisition system was used, the data collection frequency is 20 20 Hz. The layout of wave height gauges is shown in Fig. 2. The distance between the ship and the shoreline was measured by infrared rangefinder.

Ship types at two sites: 500 ton–1000 ton cargo ships, navigation administration boats.

Ship waves were measured mainly in two scenarios: ① when the canal is under temporary control, and individual vessels pass the canal separately at a constant speed, record the water surface fluctuation process when the vessel passes through the observation points; ② when the canal is open for normal navigation without control measures, record the water surface fluctuation process for a period of time (0.5 hours).

#### 2.2 Main Results of Ship Wave Field Observation

Figure 2 shows the typical water surface fluctuation process in field under normal navigation conditions, while Fig. 3 shows the same process when the navigation administration boat (NA boat) passes through at high speed. Among them, wave gauge 1# was deployed adjacent to the revetment wall, while the distance between wave gauges 2#, 3#, 4# and 5# and the revetment wall were 0.6 m, 1.6 m, 3.1 m and 5.1 m, respectively. The results of the maximum wave height and the maximum runup on the revetment wall measured by wave gauges under normal navigation conditions are shown in Table 1, while those obtained when the NA boat passes through are shown in Table 2.

Fig. 2. Typical water surface fluctuation process under normal navigation condition

Fig. 3. Typical water surface fluctuation process when the NA boat passes through at a high speed

Table 2. Maximum wave height and runup on the revetment wall measured at two sites (NA boat)

Under normal navigation conditions, the average value of the maximum wave height of different measurement times at the measuring points on the revetment wall was 0.49 m and the maximum wave height was 0.84 m; the average runup of wave on the revetment wall was 0.30 m, and the maximum runup was 0.53 m. The wave height formed by a single cargo ship passing through the observation point was small due to its small speed; when the NA boat passed through the observation point at a high speed, the wave was much higher. The maximum wave height of the observation points on the revetment wall was 1.73 m and the maximum runup height of the wave surface was 1.17 m.

#### 3 2-D Test of Vertical Wave Dissipation Revetment

#### 3.1 Section of Vertical Revetment Wave Dissipation Structure

According to the hydrological, geological and topographic data of the regulated channel, two types of vertical wave dissipation structures were adopted: round-hole caisson structure and grid-type structure. See Fig. 4 for the section and front of the round-hole caisson wave dissipation structure (the elevation unit in the drawing is m, and other marked units are mm). The top elevation of round-hole caisson structure was +4.1 m and the bottom elevation was −1.9 m. The circular holes were 150 mm in diameter, arranged in three rows, with a transverse spacing of 800 mm and a longitudinal spacing of 1000 mm. The elevation of the center point of the top row was +2.6 m and that of the bottom row was +0.6 m. See Fig. 5 for the section and front of the grid-type wave dissipation structure. The upper and lower elevations of grid openings were 3.7 m and 1.3 m respectively, the grid width was 400 mm, and the column width between grids was 600 mm.

Fig. 4. Round-hole caisson wave dissipation structure

Fig. 5. Grid-type wave dissipation structure

### 3.2 Test Conditions

The physical model test of wave section was carried out in the wave tank, which was 170 m long, 1.2 m wide and 1.6 m deep. One end of the flume was equipped with a wave maker and the other end a wave dissipation slope. The test was designed according to Froude's law of similarity, and the geometric scale of the model was 1:5. Regular wave is adopted for the section test wave, with the test wave period including 2.0 s and 3.0 s, and the test wave height including 0.3 m and 0.5 m. During the test, capacitive sensors were adopted to measure the wave surface, which was automatically collected by computer control at the sampling frequency of 40 Hz; the reflection coefficient was analyzed by multipoint method.

### 3.3 Test Results and Analysis

(1) Test results of round-hole caisson wave dissipation structure

The opening ratio of round-hole caisson wave dissipation structure has a great influence on its wave dissipation effect. In the section test, the reflection coefficients of perforated caisson under different opening ratio were measured to analyze the influence of opening ratio on the reflection coefficient. The caisson opening ratio (n) is equal to the ratio of the hole area in the opening area to the total area. When n = 0.15, the transverse spacing of holes was 40 cm, the longitudinal spacing was 30 cm and the hole diameter was 15 cm. When n = 0.22, the transverse spacing of holes was 40 cm, the longitudinal spacing was 20 cm and the hole diameter was 15 cm. When n = 0.26, the transverse spacing of holes was 40 cm, the longitudinal spacing was 30 cm and the hole diameter was 20 cm. When n = 0.39, the transverse spacing of holes was 40 cm, the longitudinal spacing was 20 cm and the hole diameter was 20 cm. See Fig. 6 for comparison of reflection coefficient test results of wave dissipation structure with different opening ratio.

The results show that when the water level is 2.5 m, the wave period is 2 s and the wave height is 0.3 m, the reflection coefficients of the round-hole caisson revetment wave dissipation structure are 0.94, 0.71, 0.61, 0.59 and 0.57 respectively under opening ratio of 0.02, 0.15, 0.22, 0.26 and 0.39, indicating that the decreasing trend of reflection coefficient slows down when the opening ratio is greater than 0.26.

(2) Test results of grid-type wave dissipation structure Considering the structural design of the grid-type structure, the test was made with two kinds of opening structures. One structure was with an opening ratio of about 0.40, grid width of 90 cm (solid part), grid spacing of 60 cm (cavity part), while the other was with an opening ratio of about 0.33, grid width of 100 cm (solid part) and grid spacing of 50 cm (cavity part). The top and bottom elevations of the grid structure are shown in Fig. 5. The test results of reflection coefficients of the two grid-type structures under the action of different waves with the water level of 2.5 m are shown in Table 3.

Fig. 6. Variation of wave reflection coefficient of round-hole caisson under different opening ratio

Table 3. Test results of wave reflection coefficient of different grid-type structures

The test results show that the two grid structures have similar wave dissipation effects. Under the action of forward waves, the wave reflection coefficient of the gridtype wave dissipation structure was larger than that of the round-hole caisson wave dissipation structure.

#### 4 3-D Test of Ship Waves and Revetment

#### 4.1 Test Conditions

The bottom width of the test channel is 46 m, and the spacing of the fronts of the revetment wall is 90 m. See Fig. 7 for the section. The test water level is the average navigable water level, i.e. +2.5 m.

Fig. 7. Channel section of the 3-D test of ship waves and revetment

The test ship includes 1000 t cargo ship and 500 t cargo ship. See Table 4 for the type and size of ship for the 3-D test.

Table 4. Ship type and size for the 3-D test of ship waves and revetment

Five types of different revetment structures were tested, including:

REVETMENT 1: vertical impervious structure; REVETMENT 2: round-hole caisson structure (opening ratio n = 0.02); REVETMENT 3: round- hole caisson structure (opening ratio n = 0.26); REVETMENT 4: grid-type structure (opening ratio n = 0.4); REVETMENT 5: riprap slope structure (slope gradient 1:2).

#### 4.2 Model Test Design

The test was carried out in a water tank with a length of 50 m, a width of 6.0 m and a height of 0.8 m. The revetment structure is simulated within a 20 m section in the middle. The ends of the water tank are the acceleration and deceleration areas of the test ship, as shown in Fig. 8. The geometric scale of the 3-D ship waves and revetment wave dissipation test model is 1:20.

Fig. 8. Layout of the 3-D ship wave and revetment test model

The model ship is self-propelled with remote control, with the designed maximum speed of 2.5 m/s.

The wave height is measured by using capacitive wave surface sensors, and sample collection is controlled by computer at the sampling frequency of 40 Hz. The layout position of wave gauge is the same as that in the field observation.

Particle imaging analysis technology is adopted for the measurement of ship speed trajectory: install position identification devices on the ship model, erect high-definition camera devices above the water tank, and calculate the motion trajectory and speed of the ship through video analysis software.

During the test, accelerate the model ship to a certain speed before the test section and stabilize it, and then drive it into the model test section at a uniform speed. Measure the ship speed by using the particle imaging system and collect the wave surface process of each measuring point by the wave surface acquisition system. See Fig. 9 for test photos.

Fig. 9. Photos of 3-D ship wave and revetment test

#### 4.3 Model Test Results

(1) Comparison between the test results and field observation results The fourth condition of field observation of NA boats in Table 5 was redemonstrated in the 3-D test. During the ship wave re-demonstration test, the revetment wall is a vertical impervious structure. See Fig. 10 for the comparison between the waveform change at the revetment wall measured in the laboratory and the field observation results. In general, the waveform changes of the ship waves were basically identical, from the larger "bow waves" caused by the ship to the "stern waves" with relatively small wave height. The peak shape and interval of the "bow waves" simulated in the laboratory were basically consistent with those measured during field observation. However, the water reduction phenomenon of the bow wave front was greater than that in the field observation, which was mainly due to the difference between the near shore terrain of the channel at the field observation site and the simulated terrain in that the water at the field was deeper while that in the near shore of the laboratory was shallow. The comparison between the maximum wave height at the revetment wall generated by 1000 t cargo and 500 t cargo ship sailing at different speeds in the laboratory and the field observation results is shown in Fig. 11 (22 m from the center line along the edge of the channel). It can be seen that the trend of maximum wave height is close to the speed variation.

Fig. 10. Comparison of wave surface fluctuation process between field observation and test

Fig. 11. Comparison of ship wave height between test and field observation

(2) Comparison of wave dissipating effect of different revetment structures In the test, the wave height in front of the revetment wall was measured under different ship speeds and offshore distance. The comparison of the maximum wave height in front of the revetment wall in different routes is shown in Fig. 12

Fig. 12. Comparison of the maximum ship wave height in front of the revetment wall of different revetment structures when the vessel is sailing in the middle of the channel

The test results show that the maximum wave height was similar in the case of vertical impervious revetment structure and round-hole caisson structure (opening ratio n = 0.02), followed by grid-type structure (opening ratio n = 0.4) and roundhole caisson structure (opening ratio n = 0.26), and the smallest height was generated with riprap slope structure. The maximum wave height in front of the revetment wall of the round-hole caisson structure (opening ratio n = 0.26) and the grid-type structure (opening ratio n = 0.4) was reduced by about 20–25%, while that of the riprap slope structure was reduced by about 40%.

### 5 Main Conclusions

Vertical revetment is a structure that saves land resources, but it can hardly reduce the wave reflection. In the waterway with busy shipping and fast vessel speed, the interaction between vertical impervious revetment structure and ship waves often leads to severe water surface fluctuation, which will affect navigation safety. In addition, the larger wave height is also unfavorable to the stability and safety of revetment. Through field observation, 2-D wave test and 3-D ship wave and revetment test, this study came to the following conclusions:

#### References

Blaauw HG, van der Knaap FCM, de Groot MT, Pilarczyk KW (1984) Design of Bank Protection of Inland Navigation Fairways. Delft Hydraulic Laboratory. Publication No. 320

Pilarczyk KW (1984) Prototype tests of slope protection systems. Hartel Canel, The Netherlands

Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# Meshed Remote Operation as the Default Mode: From Technical Challenge to Society Opportunnities

Anges Peil(&) and Michiel Coopman

De Vlaamse Waterweg, Hasselt, Belgium<EMAIL_ADDRESS>
Abstract. This paper describes the choice of the Flemish waterway authority – De Vlaamse Waterweg – for a new vision on remote operation of its inland waterway infrastructure. From now on, remote control is the default operation mode. As of 2019, a new vision was approved to remotely control all our movable structures (ca.330) by 2032 from 3 remote control centres. The innovative aspect is that they will function as a fully interconnected meshed network and can be used as a back-up for each other. At first glance this may seem a purely technical challenge. It is however shown that by pursuing this goal, it compels us to rethink large parts of our organisation in regards with change management, business processes, roles and responsibilities, training and technical management. At the same time, we see society opportunities revealing themselves. This paper is aimed at sharing our experiences and as a call-to action for other waterway authorities, academic institutions and private companies to help envision and built the future waterway-systems.

Keywords: Future of inland waterway governance Remote operation Change management Innovation Traffic management

### 1 Introduction

De Vlaamse Waterweg NV is an Inland Waterway Authority in Belgium that manages almost all inland waterways and infrastructure, excluding the ports, in Flanders, the northern region of Belgium. Flanders has approximately 1,000 kms of navigable waterways within an area of 13,625 km2 . The organization of shipping- and water management requires approx. 330 bridges, locks, weirs, pumping stations, etc.

De Vlaamse Waterweg has a long history developing remote control systems for bridges, locks and weirs. As with most inland waterway authorities, these systems were implemented using a project-based approach, clustering the operation of infrastructure per waterway or section of a waterway.

We have come to a point that we have outgrown this stage. From now on, remote control is the default operation mode. As of 2019, a new vision was approved to remotely control all our movable structures (ca.330) by 2032 from 3 remote control centres. The innovative aspect is that they will function as a fully interconnected meshed network and can be used as a back-up for each other.

What started as a purely technical story, has evolved into a future full of opportunities. We found that by formulating such a progressive vision and actually getting to work with it, it opened up a lot of new sometimes unexpected challenges but most of all, a lot of unexpected new opportunities. Opportunities for our organisation, for our employees, but above all for society, the logistics sector and shipping in general.

This paper is aimed at sharing our experiences and as a call-to action for other waterway authorities, academic institutions and private companies to help envision and built the future waterway-systems.

### 2 Towards a Meshed Network

Up until 2019, De Vlaamse Waterweg had a vision of clustering the operation of movable infrastructures per waterway or specific sections of waterways. A total of 13 stand-alone Remote Operation Centers (ROC's) were envisioned. Some of them have already been built and in operation for decades, some of them are in the finale stage of construction and some of them will forever remain on the drawing table.

During 2019, a number of evolutions made that De Vlaamse Waterweg adjusted this vision: the logistics sector is evolving towards supply chain approach and there is a desire to sail more efficiently (fuel consumption, loading and unloading,…); the 13 corridors have different opening hours and traffic intensity which makes the workload for the employees very different and which increases the risk of less readability of the waterway for the skipper; the Flemish Government imposed staff reduction, …. Based on these evolutions, the Board of Directors chose at the end of 2019 for the new vision where De Vlaamse Waterweg will operate its infrastructure from 3 major ROC's, aiming at 2032 to accomplish this.

From a technical viewpoint, the vision of evolving towards 3 major ROC's starting from several pre-existing stand-alone minor ROC's sparked the idea to approach this in a different way than before. First off, there is the question of availability, redundancy and disaster recovery. By centralising the operations, the impact of an incident in one of the ROC's scales along with the size of the ROC. This will become a major concern in the final state. Secondly, the path towards this finale state of 3 major ROC's, will have to accommodate for the current situation of several minor ROC's and allow for a flexible and smooth migration, preferably with some sort of fall-back plan and stable intermediate situation, all while ensuring continuous service.

These considerations lead to the idea to make both the existing ROC's and the future major ROC's, interoperable and redundant such that they form a meshed network. The idea is that all the operating desks and involved technical systems are interoperable, no matter where they are located.

In doing so it will become possible during the transition stage, to remain in operation until the day of migration and then to turn the switch as a matter of speech. This allows to detach the operational and organizational decision from the technical timeline. And in case of incident or emergency, it will be just as easy to fall-back or to move operations towards one of the other ROC's.

#### Lessons Learned and Recommendations:

### 3 Change Management

The new vision from 2019 (to serve 330 infrastructure works from 3 control centres) introduced technical, organisational, communicative, … challenges within De Vlaamse Waterweg. Between 2019 and 2022, this new vision was translated into a new approach in various areas: ensuring redundancy across the 3 control centres, building long-distance stable network connections, extensive standardization, improving cybersecurity, drawing new organizational charts and business processes, developing a central approach to water management, providing professional training to operators, drafting an implementation plan with a view up to 2032, …

#### 3.1 Working with Ambassadors

We think that supportive communication and a precise insight in the stakeholders of your change is essential for success. Therefore we make extensive use of various forms of communication and interaction with our stakeholders.

At the end of 2021, an community of ambassadors was set up to extend the diversity in our guiding coalition to Remote control. The community of ambassadors are a group of volunteers within our organization committed to the transformation effort. They promote remote control and share feedback of the business engagement they experience.

This community officially started at a digital (because of COVID-19 measures) seminar attended by approximately 1/10th of the employees of De Vlaamse Waterweg. The Managing Director and the Operations Director shared the change story with the participants to create a sense of urgency. Besides the importance of remote control for society and shipping, the importance for their own employees, the professionalization of the operation, the new opportunities created for collaboration within the organization, the opportunities to standardize processes,… Were discussed in an interactive way.

#### 3.2 Communication

This was followed with an intensive communication through various media. A onepager was created to promote the change story on various ways throughout the organization explaining the 'what-why-how'. A seperate page Remote control was created on the intranet of De Vlaamse Waterweg. Here colleagues can easily find all the latest information about remote control an get access to the digital workplaces.

#### 3.3 Focus Groups

We use co-creation and interaction to activate our organisation for Remote control. Dedicated 'focus groups are regularly organized to capture expertise of our operators and their managers. This on numerous strategic subjects such as the organizational chart within a control centre, on the manuals with the operational guidelines, on solving personnel related bottlenecks, etc. The unique concept of collaboration across different functions ensures support and acceptance of the entire transition among staff members and valuable insight we otherwise would miss. The game rules are: a focus group delivers input and advice from the field, makes proposals for solutions, … But does not have decision-power. The existing decision-making bodies, both at management level and for consultations with the trade unions, will be retained. In the focus groups, the proposals made by the employees are treated with respect, they are explored in depth, and the "why" question is the most frequently asked question in such a focus group: "why are you saying this", "why is this important to you", etc.

#### Lessons Learned and Recommendations:

### 4 Tools

#### 4.1 Training Simulator

De Vlaamse Waterweg NV has set up the AWATAR project. AWATAR stands for Automation of Waterways: Training and Reference. The 3 main goals of AWATAR are, to establish and maintain the technical and operational reference, to allow for standardized and professional training, facilitate, professionalize and mature the way remote control is implemented.

We made virtual 3D models of several lock and bridges, together with models of ships, cars, pedestrians, … inside a gaming engine. We connected these virtual models with real PLC and SCADA software and simulated different camera-viewpoints, traffic situations and weather conditions.

This allows us to discuss and try very different HMI designs, camera-view points, functional behaviour, operational procedures, … all without disturbing any real-life operation and in great detail. For the development of the simulator, we organized multiple participation sessions, workshops and feedback-loops with both engineers and operators. We used Virtual Reality Glasses to design the operator desk.

The simulator offers the possibility to employees to train various types of infrastructure (e.g. lift bridge, swing bridge, rolling bridge, …) and various scenarios in a short period of time. In addition to the normal traffic flow, various weather conditions can be rolled out (rain, fog, etc.), incidents can occur, etc. This allows the operator to practice his skills in a safe environment on generic structures. On the work floor, training is then given on the specific structures in the remote control center.

#### 4.2 Learning Environment

A digital learning platform was set up, tailored to operators. this learning platform uses 12 clickable tiles. The information offered depends on the theme. sometimes a short explanation is given and a link is made to existing tools or internet pages, e.g. for water management, a link is made to the website www.waterinfo.be of the Flemish Government.

In the case of more complex subjects, such as 'navigation regulations and signaling', a video film provides a verbal guide to help colleagues navigate through the complex regulations. Basic information can be found, for example, behind the tile 'naming of waterways' or 'languages' where the most common nautical terms are translated into the languages mainly used by skippers in Flanders. The digital learning platform also offers a 'do the test' tile where colleagues can see on the basis of a test on which subjects they should best learn more.

The website https://www.visuris.be/ developed by De Vlaamse Waterweg, in accordance with a number of agreements at the scale of the European Union, is also a source of information.

#### Lessons Learned and Recommendations:

#### 5 Technical Implementation

The formulation of the new vision towards large, meshed ROC's requires a mature technology management.

#### 5.1 Research and Development Center

The changing functional needs of the organization require an specific approach from both the technology and the technical organization. The technical realization evolves towards a continuous-life-cycle-approach with a more centrally coordinated organizational unit. To achieve all this, the need for a proper and in-company research and development centre (R&DC) was identified. Beforehand, the technologies implemented in a ROC were mostly contractor-developments and as such, contractorspecific. These technical systems used to be integrated on the spot, in a live environment.

As of the creation the R&DC, contractors are obliged to develop their systems in cooperation with the waterway authority. A systematic development cycle is used, going from functional requirements to technical requirements to proof-of-concept, prototyping and testing, with multiple feedback loops. Only when this cycle is successfully complement, real-life integration is allowed. Furthermore, a developmentversion is kept, to test future alternations and updates. The idea is to gradually implement and standardize all systems for the whole infrastructure and keep them evolving at the same pace of technological development, in contrast with just using the new technologies in new projects.

#### 5.2 Innovation

New functionalities are requested to support the operation of and between the remote control centres. A different balance is sought between decentralization and centralization of the infrastructure, between standardization and customization. Demands on availability are increasing, but can be partly mitigated by the network synergies when compared to classic redundancy solutions. The scalability and multi-deployability of the systems are a critical point of attention. Technical systems evolve towards an almost completely network-driven operation.

In 2022, in our R&DC, we successfully accomplished a fully functional prototype of 2 ROC's who function redundant for each other. We found that almost all technical systems to we used this date, like the Supervisory Control And Data Acquisitionsystem (SCADA), Video-management-system (VMS), Automatic Identification System (AIS) now have the capability to function within a network, as they are becoming more and more IP-based. As a general design approach, we make sure to make as little adaptations as possible on the local infrastructure. It is the overarching systems that offer these functionalities. The only system that we have found that poses problems in realizing the needed new functions, is the VHF-system. Different sections of waterway have different settings of the VHF-equipment and the number of sections this equipment can handle is limited. However this is not problematic for now, since the goal of the network of ROC's is to operate mainly predefined sections of waterways and only switch-over in case of major incidents. In such a case, whole sections of waterways will be redistributed across the remaining ROC's and not isolated specific structures. The work-around for now, is to work with redundant VHF equipment within the ROC to allow for some flexibility on this part and to go for manual configuration in case of larger incidents and thus switch-overs.

#### 5.3 Procurement Management

In order to realize a performant and uniform technological standard across all our infrastructure and across the whole life-cycle of our systems, we had to rethink our procurement management. Contracts are no longer aligned with geographical borders (a specific waterway, a specific ROC, ..) or made to measure for a specific project. Contracts are now framework-contracts focussing on technological-system-borders and include often not only new implementations but also updates, replacements, maintenance etc. during several years. This allows to attract specialised contractors and built a long-term cooperation. The challenge of course, is to coordinate between these different framework contracts while realizing large projects and making sure these different technical systems can fully cooperate. Another reason why the R&DC is a crucial piece of the puzzle.

### 5.4 Project Management

In order to achieve the goal of remote control as a default mode for our ca. 330 works, a complex task is set out for our organisation as a whole, in regards of project management. As of now, all projects on the movable assets become part of the larger puzzle. The full potential is only reached when all pieces of the puzzle come together and the picture becomes clear. Following the timeline of one project can already be a challenging task but now the timeline of all these projects influence one another. A dedicated team is assigned this daunting task.

#### Lessons Learned and Recommendations:

### 6 Opportunities

#### 6.1 Service

Remote control offers the opportunity to let the service model of De Vlaamse Waterweg evolve in a future-oriented way. In this matter, too, the involvement of the sector is of great importance. In its service developments, the Flemish Waterway wants to take into account the various players and their possibilities. Companies, logistics players, independent skippers, ... Should be given time and the opportunity to adapt and organize their way of working. By organizing specific board groups, the input of the sector is captured.

Today, the operating hours of navigable waterways in Flanders are very diverse. It must be noted that there is also a large variety of vessels on these waterways. On some waterways there is mainly commercial shipping, other waterways have mainly recreational boating.

It seems logical to state that operating hours anywhere can expand to 24/7 once the remote control centers are up and running. However, for various reasons, it seems that it is not appropriate to decide this as such and requires further investigation. On the side of the waterway manager, for example, an adapted intervention strategy will have to be worked out if waterways are navigated 24/7, which means that more technicians need to be available to solve technical failures. Against this desired higher availability, there is also a higher cost of operation. On the side of the skipper, attention should be paid to the possible shift in the competitive position of independent skippers who have to take into account rest periods versus companies with many skippers who can sail in shifts.

### 6.2 Integrating with RIS Smart Shipping and Smart Logistics

By moving from a fragmented approach to an overarching integrated strategy and stateof-the-art overall remote control system, full integration with RIS, Smart Shipping and Smart Logistics, and the physical internet becomes possible. Data from the infrastructure will be gathered and turned into useful information.

The opportunities for the logistics sector and shipping are created by embracing innovative technologies and integrating them within the day-to-day operations. We provide the necessary tools to shipping to plan their journey as effective as possible and the systems in the remote control centres support the operators in offering an optimal locking process.

### 6.3 Water Management

Remote operation of water-controlling structures is somewhat different form operating locks and bridges. The former focusses on a large area and tries to optimise the water management across this whole area. The operating time of each structure is rather short. The latter focusses on one specific structure and takes a larger amount of time (not taking into account traffic management). The main advantage of remote operation on water-controlling structure is exactly that you can oversee the whole area by gathering and using all available data from all the involved structures and basins. It allows to build a decision-support system based on real-time information and predictions. Climate-change is putting more stress on our infrastructure resulting from more extreme weather and water conditions. Making sure we use the full potential of our infrastructure and basins is a way to mitigate the effects with fairly reasonable effort.

#### Lessons Learned and Recommendations:

### 7 Conclusions

The strategy towards all-out meshed remote-control makes a digital evolution possible. As such, this originally technical story will contribute to prosperity and well-being in Flanders. Organizations must dare to dream and dare to seize technical evolutions as a basis for the many opportunities to improve the future for the shipping and logistics sector, while at the same time responding efficiently and effectively to the impact of climate change.

Acknowledgements. The authors would like to thank and honor all operators, colleagues, management, contractors and stakeholders of De Vlaamse Waterweg for their work and contributions in the development and realization of the new remote operation vision.

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# Presenting the Work of PIANC TG234 "INfrastructure for the Decarbonisation of IWT"

Mark Van Koningsveld1(&) and Gernot Pauli2

1 Delft University of Technology, Delft, The Netherlands<EMAIL_ADDRESS>2 Self employed, Berlin, Germany<EMAIL_ADDRESS>
Abstract. PIANC provides guidance and technical advice for sustainable waterborne transport infrastructure. To address the challenge of making inland navigation infrastructure sustainable, a Task Group "Infrastructure for the decarbonisation of Inland Water Transport" (TG234) was set up in January 2021. The objective of the TG was to identify knowledge gaps and major challenges that need to be urgently addressed and advise PIANC on further actions, such as setting up a working group. A report was to be delivered in early 2022. The TG involved a range of international experts who met every three months on-line. They jointly participated in the following activities: sharing experiences in their area of expertise; gathering, organising, and discussing literature; discussing the perspective to be taken while reporting; contributing an overview of the developments either in their country or organisations and of course in the various discussions. A final report was produced that took the perspective of the waterway manager, highlighting a number of key questions that need to be answered in the transition to reduced/zero emissions. With the state-of-art knowledge gathered by the group, it became possible to identify the existing knowledge gaps and the major challenges that need to be addressed. The report can guide PIANC in evaluating the best way forward to address the decarbonisation of IWT infrastructure.

Keywords: Inland waterway transport Decarbonisation IWT infrastructure Alternative fuels

### 1 Introduction

The availability of zero-emission fuels infrastructure, including onshore electric power supply, will be key to enable zero-emission vessels and increase the competitiveness of IWT as a whole, at a time when other modes of transport are reducing their ecological footprint. To address the challenge of making inland navigation infrastructure sustainable, PIANC Task Group TG234 "Infrastructure for the decarbonisation of Inland Water Transport" was set up in January 2021. The objective of the TG is in line with the declaration of PIANC, namely developing approaches to decarbonise the operation of port and navigation infrastructure (i.e. move to net-zero emissions), whilst at the same time enabling the reduction of greenhouse gas emissions from vessels by providing the necessary facilities, infrastructure and, where appropriate, incentives. For this purpose TG234 was tasked to identify knowledge gaps and major challenges that need to be urgently addressed and advise PIANC on further actions. The findings of TG234 have been written down in a final report that has been submitted to INCOM (PIANC 2022). The report serves as a coarse knowledge base to guide further steps towards a rational approach to developing infrastructure for the decarbonisation of IWT.

### 2 Approach

The steps taken by the TG to identify knowledge gaps and challenges are listed here briefly. As suggested in the Terms of Reference (TOR dated October 1st 2020) and to provide first insights into the decarbonisation of IWT, TG234 compiled key developments per country/organisation that participated in the TG. Similarly, main developments per energy carrier were also compiled. These compilations or briefing notes form an integral part of the report and are summarized in Chapter 3. Next, attention was given to the questions that an actor striving for decarbonisation would have. A comprehensive list of questions was drawn up in Chapter 4 and an approach was suggested over how to answer them in Chapter 5. Some conclusions are drawn in Chapter 6.

### 3 Key Developments Related to Decarbonisation of Infrastructure

A feasible starting point for the members of TG234 was to create briefing notes on key developments on zero emission IWT as they observed them in their own countries/organisations. In the following, short summaries per briefing note are included. Next to the key developments per organisation or country, briefing notes were also made of a number of promising new energy carriers. It is clear that the work done so far is not yet comprehensive at global scale, but it provides an inspiring first step.

#### 3.1 Key Developments per Country or Organization

Short Report Decarbonisation IWT Europe. In 2019, the European Union presented the European Green Deal with the aim of ensuring that the continent is greenhouse gases (GHG) emission-free by 2050. In July 2021, the European Commission adopted a set of proposals (Fit for 55 package) to make the EU's climate, energy, transport and taxation policies fit for reducing net GHG emissions fit for reducing net GHG emissions by at least 55% by 2030. The initiatives include Alternative Fuels Infrastructure Regulation (AFIR), the Renewable Energy Directive (RED) and the Energy Taxation Directive (ETD). AFIR supports the deployment of alternative fuels infrastructure, including refueling points for natural gas and hydrogen. Member States are required to set up national policy frameworks to establish markets for alternative fuels and report their progress. RED deals with the promotion of energy from renewable sources and has set a binding target to produce 40% of energy from renewable sources by 2030. The ETD aims to ensure the proper functioning of the EU internal market by ensuring that energy taxation is aligned with climate objectives.

Short Report Decarbonisation IWT CCNR. The Central Commission for the Navigation of the Rhine (CCNR) has drawn up a roadmap (Adopted on 9 December 2021) to lay the foundation for a common approach to the energy transition and emissions reduction by all stakeholders. This roadmap should be understood as the primary CCNR instrument for climate change mitigation and setting transition pathways for the fleet (new and existing vessels), suggesting, planning, and implementing measures directly adopted or not by the CCNR, and monitoring intermediate and final goals set by the Mannheim Declaration. In 2021, CCNR published the results of indepth studies over financial instruments to be seen as part of a broad discussion process at Rhine, European and international level. It mandated its committees to feed the study results into the PLATINA3 project, desiring an action plan for the further development of a European funding and financing instrument to be drawn up and detailed. CCNR regularly organizes workshops on innovative technologies.

Short Report Decarbonisation IWT Austria. The current political ambitions to decarbonise IWT in Austria are higher than those on European level. The Mobility Masterplan 2030 and Government Programme 2021–2027 make concrete recommendations while also committing to endeavours such as installing shore power units. Implementation projects prepared by the Austrian waterway company, Viadonau, include the installation of shore power supply for cargo vessels at selected existing and future berths, and implementation plans for cruise vessels are underway. CCNR and Viadonau have set up an international conference aiming at international harmonisation of technical standards and the operational and billing systems of a future shore power system along the European waterways.

Short Report Decarbonisation IWT France. In order to meet the GHG emissions reduction targets in the transport sector, policies have been set up for the inland navigation sector. The "Mobility orientation Act" of 2019 eased the establishment of low emission zones (ZFEs) while the "National hydrogen plan" of 2018 aims at achieving mass-production of green hydrogen as a fuel for mobility. A bill entitled "Delivery of a vessel certificate for a restricted navigation", that was introduced in 2019 allowing green vessels to derogate from the EU technical regulations if they operate on a limited journey in an area of local (national) interest, has proven efficient. As a result, the French inland fleet will welcome hydrogen and GNC powered vessels in the coming years.

Short Report Decarbonisation IWT Germany. The Federal Climate Protection Law (Bundes-Klimaschutzgesetz – KSG), amended by the German Federal Parliament in 2021, aims to achieve GreenHouse Gas (GHG) neutrality in Germany by 2045. The Federal Ministry for Digital and Transport (BMDV) will support climate friendly inland navigation with subsidies for decarbonisation and development of inland waterway infrastructure as well as with research and development. It has commissioned work, to be published in 2023, to develop energy efficiency indices for inland navigation together with a proposal for their practical implementation. German IWT companies are already investing in climate neutral vessels. The report concludes that IWT in Germany has a chance to survive, when it will be innovative and when there will be an adequate regulation for GHG emissions from transport, including carbon prizing, that honours the inherent energy efficiency of IWT.

Short Report Decarbonisation IWT Netherlands. The targets for emissions reduction in the Netherlands have been drafted in the Dutch Green Deal on Maritime and Inland Shipping and Ports (2019), signed by various governmental authorities, trade associations, ports, sector representatives and research institutes, each with a list of planned actions. Numerous initiatives have been launched e.g., investing in shore power facilities for around 500 state berths, a national ban on degassing while sailing (to be introduced step by step), examining blending biofuel obligation in inland shipping vessels. The Dutch national government has set up a supporting system for innovations such as fully emission-free powered ships for the inland shipping sector. Funding schemes have been put in place for greening of the Dutch fleet. Another initiative to stimulate the decarbonization of the fleet is a new labelling system for inland vessels' emissions performance. Attention will be given to the necessary bunkering infrastructure and the safety requirements and legal framework to facilitate the introduction of new energy carriers in the inland waterway sector in the coming year.

#### 3.2 Key Developments Per Carrier

Short Report Hydrogen for Propulsion. Pressurized hydrogen storage is currently furthest developed for mobile applications (inland shipping) and is the most applied method in current hydrogen vessel projects. Liquid hydrogen could be an option as a mid-term solution when liquefaction plants are built and the fuel price comes down. Bunkering can take place via four different configurations: truck-to-ship, ship-to-ship, bunker stations and swapping of tank-containers and depends on the physical state in which hydrogen (pressurized, liquid or hydrogen carrier) is stored on board inland navigational vessels. The most feasible scenario for the short-term is swapping pressurized hydrogen in swappable containerized containment systems (tube-containers) at container terminals. Regulations for the use of hydrogen on board of-, and bunkering of hydrogen to inland navigational vessels are still under development. The availability of hydrogen as a fuel for vessels relates to hydrogen fuel production as well as to provision of bunkering infrastructure in a sufficient number of ports in the operating area. Strategic engagement of a large industrial player (gas producer, utility company, oil or energy major), who is not only aiming at supplying (moderate amounts of) green hydrogen to inland waterway vessels but also to large consumers along the Inland Waterways, is required for a breakthrough.

Short Report Biofuel for Propulsion. Rapeseed methyl ester, also known as OLEO100, is a biofuel produced exclusively from rapeseed oil. It can be used in its pure form and does not need to be mixed with a fossil fuel. It has an energy density comparable to that of diesel (slightly lower). Similar to diesel/gasoil, OLEO100 is used in internal combustion engines and can be mixed with diesel, it is therefore compatible with existing conventional propulsion systems. It is mainly used by heavy road vehicles, but it is being tested for application on inland vessels. Currently, refuelling is done either by refuelling trucks or directly by drums delivered to the refuelling station. It can be regarded as a conventional fuel when it comes to existing rules. OLEO100 is not considered harmful for human nor the environment, no specific policies are needed. Infrastructure changes required are minor and costs are therefore negligible compared to other alternative fuels. If available on location, OLEO100 refuelling specifics are comparable to those of conventional fuels; since comparable energy density and viscosity means comparable volumes and refuelling times. The main challenge is the longterm availability of this fuel if it is widely adopted.

Short Report Methanol for Propulsion. Methanol is a climate neutral fuel, when it is produced from renewable energy and can be used as fuel for combustion engines or for fuel cells. Methanol has a low energy density compared to gasoil/diesel fuel. Otherwise, it is rather similar to diesel/gasoil and be used for all applications. Bunkering is possible from bunkering vessels, tank trucks and fixed tank stations. The required safety distances are also similar to diesel/gasoil. Safety risks during methanol transport are well understood and safety measures in place. Technical requirements and standards for methanol as fuel on inland navigation vessels are under development in Europe. Infrastructure costs are on the same level as for diesel/gasoil and low in comparison to other alternative/climate neutral fuels. More refuelling (bunkering) stops are needed because of low energy density. The main challenge is the high cost for methanol itself, when it is produced from renewable energy. Otherwise, methanol could become a standard fuel for inland navigation.

Short Report Battery Electric Propulsion. A battery electric propulsion system consists in general of rechargeable batteries, electric switch board and an electric propulsion system. Because of low energy density, battery electric propulsion is most suitable for ships that travel short distances (between stops). Fixed batteries require electric charging points at mooring places and exchangeable batteries require cranes, e.g., on container terminals with nearby charging point. Infrastructure costs are high as many charging points are needed and as rechargeable batteries for inland navigation vessels require a high-capacity power supply. Battery fires are rare, but hard to control. Technical requirements and standards for rechargeable batteries exist or are under development. In Europe, national and EU policies support the implementation of charging points at suitable locations of the inland waterway network. Battery costs are expected to further decrease, and energy density will increase, allowing battery electric propulsion becoming a technical and economically feasible alternative for certain inland navigation tasks. According to the latest RWS studies on the safety aspects of new energy carriers, the surrounding safety zones between the location of the battery containers and the surrounded buildings can be as low as 5 m. The most important recommendation is the location awareness for energy services. This is particularly important in case of shipping accidents.

### 4 Relevant Questions for Waterway Managers

#### 4.1 General

From Chapter 3 it can be concluded that the path to decarbonisation of IWT is different for different corridors and in different countries. While a relatively short list of potential energy carriers appears to emerge when discussing decarbonisation, which carrier (or a mix of carriers) is likely to emerge as preferred depends on a whole range of local situations. In practice, it is seen that vessels owners and bunker station operators have a strong influence on the alternative energy carriers they would like to use (bottom-up). But at the same time, the question whether a selected alternative energy carrier is going to be successful at the corridor scale can depend on a range of policy measures and subsidy schemes (top town). While momentum for change appears to be stronger bottom-up, TG234 considered that a top-down approach could provide a stronger rational framework. So while fully aware of the bottom-up as well as the top-down perspective, TG234 decided to take on the perspective of a waterway manager that faces the need for decarbonisation of his/her waterway. By discussing step-by-step the kind of questions that arise, a structured approach to decarbonisation emerges.

#### 4.2 List of Questions

TG234 foresees that a waterway manager that seeks to decarbonise his/her network encounters the questions listed below:

#### What are the most promising technologies (or energy carriers) for the decarbonisation of IWT?

The impact on the infrastructure for the decarbonisation varies substantially with the different energy carriers. As was shown in the short reports of the previous chapter, biofuel for decarbonisation allows for continuous use of the existing refuelling infrastructure, whereas a switch to electric propulsion would require building a totally new infrastructure. Furthermore, none of the future energy carriers is suitable for all transport tasks. Therefore, the waterway manager is well advised to get a good understanding of the different technologies or energy carriers for the decarbonisation of IWT. This will also help him or her to efficiently consider the following questions.\

#### What is the overall transport challenge in my network (amount of cargo, number of passengers, from where to where, now and in the future)?

It is important to consider what the transport challenge is in the network. The type and amount of cargo that needs to be transported, in combination with the origin and destination of this cargo, determines the demand for transport and also the location of the bunkering infrastructure of the new energy carriers. It is also important to assess whether or not there are alternative transport modes that are likely to compete with inland shipping.

#### What is the state of the water transport network and of the fleet that operates on it (proportion of vessels of given type/classification, now and in the future, alternative transport modes)?

When it is clear what the transport demand is depending on future traffic flows and the vessels required to transport it, it becomes important to assess the potential for transport over water.

Looking at the state of the water transport network will reveal the vessel classes (PIANC 2020) that will be able to fulfil the transport demand. The maximum vessel class that can operate on a waterway is typically restricted by a maximum available air draught (e.g., due to the presence of fixed bridges), a maximum allowable width, length and draught (e.g., due to the presence of locks) and the presence of other width and depth bottlenecks (Van Dorsser et al. 2020; CCNR 2021c; Vinke et al. 2022). Other aspects that can come into play are traffic intensity and environmental aspects like wind and current. The state of the waterway, the available water depth and the ambient current conditions influence the amount of energy that is associated with the transport function.

The waterway classification determines the maximum size of the vessels that can use it. Beyond that it is important to know the composition of the fleet that is available to perform the transport function on the waterway network. Not all vessels that are part of the fleet will be of the maximum size. Smaller vessels will need more trips to transport the same amount of cargo compared to larger ships. Older vessels might still have older engines that may perform less when it comes to emissions. Also, it is important to assess the availability of alternative transport modes, e.g., road, rail, pipeline. When alternatives are available and capable to accommodate a significant modal shift, this will put more pressure on the inland shipping sector to adopt/convert to other energy carriers.

#### What is the energy consumption that is associated with the transport challenge, given the current and future state of the network as well as of the fleet and the waterway conditions in the future considering impacts of climate change? (Emission hotspots?)

When the transport demand (volumes, origins, destinations), the state of the waterway network (e.g., water depths, currents), and the state of the fleet (composition, engine ages, etc.) are known, the associated energy demand for transport can be estimated using vessel resistance algorithms (Bolt 2003; Vehmeijer 2021; Segers 2021; Van Koningsveld et al. 2021; Rijkswaterstaat, 2022a, b) (Fig. 1).

Fig. 1. Methodology for estimating emissions for IWT vessels (image modified from Segers, 2021, by TU Delft Ports and Waterways is licenced under CC BY-NC-SA 4.0)

For modern waterway networks that are already actively used, the availability of Automatic Identification System (AIS) data can be an important source of input. Depending on the country of origin, digital information on the state of the waterway network may also be openly available.

AIS data, combined with waterway network data, can be utilised to provide a promising first estimate of the energy demand that is associated with the transport function. To estimate future demands, growth/shrinkage scenarios can be of use.

Table 1. General SFC and emission factors of CO2, PM10 and NOx for diesel fuel and different engine construction year classes (source: Ligetink et al. 2019 and modified based on the emission standards described at DieselNet (2021)).

It is useful to take the energy consumption (kWh) as a basis for analysis, since empirical information is typically available to estimate the associated fuel consumption, via so-called Specific Fuel Consumption factors (g/kWh) (Table 1). When assumptions are made on partial engine loads and engine ages also CO2 and environmental pollutant emissions can be estimated (Hulskotte 2013; Smart Freight Centre 2019; Wijaya et al. 2020).

It may be worthwhile to validate these coarse estimates with actual energy consumption, fuel use and emissions. Also, it will be useful to document the current locations and capacities of bunker facilities.

With the above method so-called energy consumption, fuel use and emission footprints can be generated for individual vessels. Overall patterns can be generated by aggregating the footprints of individual vessels that together represent the traffic on a corridor (Jiang et al. 2022).

Such heatmaps, created from individual contributions, can be used to identify hotspots and identify root causes. This information can be used to design policies to reduce emissions (Segers 2021). On the long term such policies will probably involve zero emission energy carriers, but in the years before those other measures may be necessary in an effort to reduce emissions.

More coarse methods to estimate energy consumption, fuel use and emissions may also be used. Various methods are available that estimate fuel use per tonne kilometre (tkm) based on empirical data. While these methods are easier to use, especially in situations of limited data availability, they are less useful to test new situations. The most practical way forward as such is a trade-off.

#### What type of energy carriers can replace the current ones, what quantities of fuel are needed where, and how will these fuels affect range, payload, velocity, etc.?

Once the total energy demand, fuel use and emissions, as well as the locations and capacities of current bunker facilities are known, it becomes possible to estimate the required volumes in case alternative energy carriers would be considered.

Alternative energy carriers will have a different energy content than more traditionally available options. Also, other energy carriers may involve alternative energy conversion systems. For each energy carrier/energy conversion combination it should be investigated what the potential influence on sailing range, payload amount and sailing velocity is. If only the sailing range is affected, an increased number of bunker stops is the main transport efficiency impact. If the range remains the same but the amount of payload is affected, the main transport efficiency impact is an increased number of trips required to transport the same amount of cargo.

Where for the previous question AIS data could be used as a basis for quantification of the current state, testing the effectiveness of alternative policies requires simulation. A common approach for this these days is the use of agent-based meso-scale simulation models (Van Koningsveld and Den Uijl 2020; Jiang et al. 2022). With such models the effect of changes to the vessels (the agents) can be assessed beforehand.

A typical question is of course what performance indicators are most suitable. Given that a known amount of cargo needs to be transported a typical measure of transport performance is the unit of tonne kilometre (tkm), or the tons of cargo times the km of distance over which it needs to be transported. Obviously, an important indicator is the cost of transport. When we are interested in energy, fuel and emission efficiency respective units of kWh/tkm, g fuel/tkm and g emission/tkm become relevant.

It is good to realise that in the cost and emission units the efficiency of the transport chain becomes visible. Let's imagine that 3.000 tons of cargo need to be transported over 100 km. Then the transport performance can be expressed as 3.000 100 = 300.000 tkm. This performance is irrespective of vessel size. But now let's assume this cargo is transported with a vessel that has a capacity of 3.000 tons or a vessel that has a capacity of 1.500 tons. In the first case the cargo can be transported by 1 full trip to the destination and 1 empty trip back to the origin. In the second case 2 full trips and 2 empty trips are needed to transport the same amount of cargo.

Depending on local circumstances and vessel properties this will result in different emission patterns: there is good chance that the second option will have a poorer total efficiency in terms of e.g., g CO2/tkm, at the same time the emission source in terms of g CO2/s or g CO2/km can be lower since the emission will be spread out over time. While for CO2 the totals are likely to be of interest, the actual peak values may be of interest for other environmental pollutants like fine particle emissions such as PM10. It will also be interesting to see what the cost effects are the situation will be complicated further when aspects like ambient current and available water depth are included. It is clear that the total performance of the IWT mode is complex. An increasingly popular approach these days is that the effects of policies are tested in simulation models or digital twins. It is necessary to do this since relying on intuition or coarse empirical data may yield unreliable results. Especially since the use of alternative energy carriers can affect things like sailing range (refuelling more often, and possibly taking longer/shorter), amount of payload that can be carried (more trips required) and perhaps the velocity profile that can be achieved. Information on refuelling/charging times and waiting times will influence the cost competitiveness of a suggested solution.

#### Where should we position bunkering points or refuelling stations? What are the charging/fuelling times and the waiting times at refuelling stations?

Insight in the total energy demand over the network tells the waterway manager something about the capacity requirements of the bunker stations/charging stations on the network. Insight in the range of vessels for different energy carrier/energy converter combinations will tell the waterway managers something about the maximum interdistance of the bunker stations/bunker vessel.

How this all works out in detail will depend on the current vessel mix, and scenarios for possible future vessel mixes as well as on scenarios for the energy carrier mix that is assumed to be used on the network.

It is good to realise that also developments in other transport modes will be of interest, as well as developments in other corridors. In the end the selected solution (or mix of solutions) must be price competitive compared to available alternatives. Unless the other transport modes lack the capacity to accommodate a modal shift, poor price competitiveness will lead to the decline of the IWT mode.

#### How can the estimated demand for alternative fuels (electricity, hydrogen, methanol, etc.) be supplied over the network?

Insights in potential locations and capacities of alternative fuel bunker points are already an important step forward. But the availability (and cost) of alternative energy carriers may also be a deciding factor. When the supply of sufficient amounts of a given energy carrier is problematic, a preferred energy carrier, while potentially suitable, might not become the implemented solution. Availability of certain energy carriers can vary significantly from one location to the next. This is at least one of the reasons why it is not possible to point to any one energy carrier as a preferred solution that fits all.

#### What are the standards or existing regulations that must be followed?

Next to demand for and the potential supply of alternative energy carriers, another important factor for likely success or failure of an energy carrier is the presence/ absence of regulations. Mandatory safety margins for example, may pose inhibiting restrictions on the implementation of a given energy carrier.

### 5 Suggested Approach to Answer the Questions

The questions posed in Chapter 4 are key for any waterway manager to contemplate while decarbonising the IWT mode. TG234 suggests that these questions should be addressed first before detailed guidance can be provided on the actual dimensions of the required energy-related infrastructure components. It makes a big difference if you are dealing with a very busy shipping corridor that supports a wide range of vessels and substantial cargo flows, or a much smaller waterway that caters to a limited number of vessels and only one cargo type. Or if you are dealing with a waterway system that has substantial current vs one that has more calm conditions. In any case, waterway managers need a good understanding of the most promising technologies and energy carriers for the decarbonisation of IWT. Therefore, PIANC could compile the information that allows waterway managers to gain this understanding without having to do their own research.

### 6 Conclusions

The report concludes that PIANC could consider setting up a WG that focuses on the methodological approaches in the field of decarbonisation of inland waterway infrastructure that are at different development stages at an international level. A subsequent PIANC WG could work on coupling guidelines with the currently lacking standards in the field. A complicating factor is that insights on decarbonization are still very much under development. As a result it may not be easy to collate best practices since these are continuously being developed and updated. An alternative could be to approach the decarbonisation challenge with a Permanent Task Group/Strategic Initiative, such as the Permanent Task Group on Climate Change.

Acknowledgements. The report on which the paper is based has been produced by an international Task Group convened by InCom, comprising the following members (in alphabetical order): Cees Boon, Peng Chuandsheng, Nathaly Dasburg-Tromp, Turi Fiorito, Man Jiang, Mark van Koningsveld (chair), Hugo Lopes, Ulf Meinel, Hyumin Oh, Baptiste Panhaleux, Gernot Pauli (co-chair) and Poonam Taneja.

#### References

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# The Application of Beidou High-Precision Positioning Technology in the Deformation Monitoring of Ship Locks

Haizun Huang1(&) , Shihua Qin2 , Chihua Wang1 , Weixun Fang2 , Yulong Wang1 , Hao Gong3 , Dongjie Ning1 , and Jian Shi3

1 Guangxi Beibu Gulf Port Big Data Technology Co., Ltd., Nanning, China

<EMAIL_ADDRESS><EMAIL_ADDRESS>2 Guangxi Xijiang Development and Investment Group Co., Ltd.,

Nanning, China 3 Shanghai Huace Navigaition Technology Ltd., Shanghai, China<EMAIL_ADDRESS>
Abstract. Accompanying the construction of inland navigation projects is the generation of high slopes, whose stability has always been an important safety issue of great concern during the process. The safety incidents involving high slope instability often cause huge economic losses and even casualties. Therefore, it is of particular importance to monitor high slopes, to identify safety hazards and to predict the occurrence of safety accidents in advance through the tendency of changing. Once the project is completed, effective monitoring is also essential during the operation of the locks in order to avoid safety accidents such as the collapse of ship locks and other main structures.

Based on the BeiDou high-precision positioning technology, this paper investigates the application of the automated displacement monitoring system in the construction and operation of navigation projects. The system mainly consists of sensor subsystem, data transmission subsystem, data processing and control subsystem as well as other auxiliary support subsystems. The system collects static satellite data from fiducial points and monitoring points, carries out baseline vector solution to realize millimeter-level displacement monitoring, and effectively monitors high slope displacement during construction according to the storage, management, query, statistics and analysis of the monitoring data, as well as timely detects abnormal situations about the displacement. When there is slope instability, early warning will be issued by grading so that measures could be implemented in advance to avoid safety accidents. When applied during the operation of ship locks, it can monitor the displacement of the lock chamber's main work persistently to ensure its normal operation.

This paper takes the construction site of certain ship lock project as the object and sets up 1 fiducial point and 10 monitoring points. The real-time displacement monitoring of the site's high slopes throughout the construction period is carried out, the main functions of the monitoring system are tested and the monitoring data and results are briefly analyzed. After the completion of the project, the monitoring system is applied during the operation of the ship lock and the deformation of the lock chamber is constantly monitored and analyzed. Keywords: BeiDou high-precision positioning technology Ship lock Automated monitoring system

### 1 Background

Deformation monitoring is the periodic and repeated measurement of the observation points set on deformed bodies in order to determine the changes of their spatial location and the characteristics of their internal structure over time [1]. Throughout the construction and during the operation, the engineering structures should be continuously monitored in order to keep track of the deformation, identify problems in time and ensure their security.

The deformation monitoring of the lock includes the main work such as the lock head, the lock chamber [2], and the foundation pit [3]. The fill behind the lock chamber walls gradually increases in height during the construction, covering the original observation points. Therefore, they must be increased in height as well to enable continuous monitoring. Due to the phased construction of the lock chamber wall, its surrounding area is excavated and back filled every now and then, making it necessary to frequently change the monitoring route for settlement measurements and thus it would compromise the continuity and accuracy of the monitoring. What's more, the release of water within the lock chamber during the operation phase will affect the observation points during the construction phase, also creating difficulties for deformation monitoring.

Since its establishment, the BeiDou system has been widely used in various fields like navigation and positioning. Its advantages of high accuracy, high efficiency, allweather service and no need for line of sight in static relative positioning have led many researchers to choose it over the conventional methods such as triangulation, trilateration and triangulateration. And it has brought fruitful results both in theory and practice. It is also increasingly widely used in the deformation monitoring of precision engineering.

Therefore, this paper carries out research on the automated displacement monitoring in the main work of ship locks based on the BeiDou high-precision positioning technology.

#### 2 The Principle of BeiDou High-Precision Measurement

Four satellites are required in the BeiDou positioning technology. The distance from each of the two satellites to the user machine is the radius of two spheres intersecting at two points. Suppose the distances from the 4 satellites to the user machine are R1, R2, R3 and R4 respectively [4].

$$R\_1 = c(t\_\mathbf{r} + \mathbf{d}t\_\mathbf{r} - t\_\mathbf{s1}) = \sqrt{\left(\mathbf{x}\_1 - \mathbf{x}\right)^2 + \left(\mathbf{y}\_1 - \mathbf{y}\right)^2 + \left(z\_1 - z\right)^2} \tag{1}$$

$$R\_2 = c(\mathbf{t\_r} + \mathbf{d\_r} - \mathbf{t\_{s2}}) = \sqrt{(\mathbf{x\_2} - \mathbf{x})^2 + (\mathbf{y\_2} - \mathbf{y})^2 + (z\_2 - z)^2} \tag{2}$$

$$R\_3 = c(t\_t + \mathbf{d}t\_r - t\_{\mathbf{s}3}) = \sqrt{\left(\mathbf{x}\_3 - \mathbf{x}\right)^2 + \left(\mathbf{y}\_3 - \mathbf{y}\right)^2 + \left(z\_3 - z\right)^2} \tag{3}$$

$$R\_2 = c(t\_\mathbf{r} + \mathbf{d}t\_\mathbf{r} - t\_{\mathbf{s}4}) = \sqrt{(\mathbf{x}\_4 - \mathbf{x})^2 + (\mathbf{y}\_4 - \mathbf{y})^2 + (z\_4 - z)^2} \tag{4}$$

where xi, yi and zi are the coordinates of the i-th satellite; c is the speed of light; tr is the signal arrival time measured by the receiver; dtr is the clock bias between the receiver and the satellite; tsi is the signal emission time measured by the satellite.