**10. New perspectives on the development of natural cholesterol-lowering products**

Cardiovascular friendly natural products are those nutritional supplements, which can provide potential health benefits in cardiovascular diseases (CVD). Experimental, epidemio‐ logical and clinical data indicates that dietary nutrients and supplements have profound cardioprotective effects in the primary as well as secondary prevention of coronary heart disease [88]. Except for the aforementioned several cholesterol-lowering natural products, the plant alkaloid berberine has recently been introduced to the filed of lipid-lowering products. Berberine has shown a moderate or comparable cholesterol- and triacylglycerol-lowering effect in humans [89]. More importantly, recent studies have demonstrated that berberine combined with plant stanols improves cholesterol-lowering efficacy through a synergistic action on cholesterol absorption and reducing plasma triacylglycerols in animals [90], [91], with the efficacies are comparable or even better cholesterol-lowering drugs, statins. The product has been patent-protected and at the preclinical stage. Clinical trials are warranted before moving this potentially highly effective natural product to the lipid-lowering market.

#### **10.1. Current status in the development of cholesterol-lowering products**

An initial approach to control the modifiable risk factors of hyperlipidemia relies on the changes of diet, lifestyle, and other factors such as smoking. When all these fail, pharmaceutical intervention is necessary. Many of the current available drugs are those either inhibit choles‐ terol synthesis, or increase synthesis of bile acids and excretion. The majority of the current research focuses on lowering the "bad" LDL cholesterol, with less attention on increasing "good" HDL cholesterol. A treatment with a combination that can lower LDL cholesterol and increase HDL cholesterol would certainly provide more benefits than single approach for the treatment of hyperlipidemia, atherosclerosis and cardiovascular disease.

#### *10.1.1. Lowering LDL cholesterol*

Health Canada has recently reconsidered the classification of food products with disease risk reduction claims or therapeutic claims in light of clarified principles for the classification of foods at the Food-Natural Health Product interface (http://www.hc-sc.gc.ca/fn-an/labeletiquet/claims-reclam/assess-evalu/sat-mono-poly-fat-gras-eng.php). Health Canada has concluded that the results of the updated literature review are consistent with the 2002 report provided by the Institute of Medicine (IOM), which forms the basis of the US and Canada dietary guidance, on the replacement of saturated fat with unsaturated fat for blood cholesterol lowering. In other words, scientific evidence exists in support of the therapeutic claim linking the replacement of saturated fat with unsaturated fat to a reduction of blood cholesterol. It is stated that the claim is relevant and generally applicable to the Canadian population as a high proportion of the Canadian population is hyperlipidemic. It is allowed now by the Health Canada's to put therapeutic claim statements such as "Replacing saturated fats with polyun‐ saturated and monounsaturated fats (from vegetable oils) helps lower/reduce cholesterol" in vegetable oils and foods containing vegetable oils when specific conditions for the food

Olive oil can reduce LDL and raise high-density lipoprotein cholesterol and decrease lipid damage due to oxidative stress. In addition, olive oil reduces inflammatory and thrombogenic

Tea catechin-especially (-)-epigallocatechin-3-gallate-inhibits the expression of soluble adhesion molecules including vascular adhesion molecule-1 and intercellular adhesion molecule-1, endothelial cell inflammatory markers, decreased oxidized LDL, and prevents the

Certainly, there are more natural products available, for instance a number of antioxidants and phenolic compounds, to lower blood cholesterol levels. However, the big challenges that the natural products have been facing in the past years lie in their relatively lower efficacies as compared with the cholesterol-lowering drugs. The apparent advantages of natural products are their better safety profiles. In order to promote the market share of cholesterol-lowering natural products in competing with the drugs, it is critical to develop new products that can offer better efficacies than the current natural products, without losing safety or introducing increased toxic or severe side effects. Considering that the majority of the current natural products fall into the same category of cholesterol absorption inhibitor, the future direction of research and development of cholesterol-lowering products, novel distinct pathways or targets should be focused. Herewith, we will provide some brief thoughts on new approaches that we believe worth to tackle into, with a hope that the new mind in the research and development direction and focus would help to discover and develop novel natural products with significantly improved cholesterol-lowering efficacy working through distinct mecha‐

nisms than the currently available natural products, without apparent side effects.

carrying the claim are met.

**9.7. Green tea products**

development of atherosclerosis and[87].

status, endothelial dysfunction, and blood pressure[86].

200 Using Old Solutions to New Problems - Natural Drug Discovery in the 21st Century

**9.6. Olive oil**

Statins drugs, which are currently widely prescribed, lower LDL cholesterol primarily via inhibiting cholesterol biosynthesis and a secondary effect of increase LDL receptor and LDL clearance. However this family of drugs has shown several undesirable side-effects. Niacin, can also lower LDL cholesterol but not efficiently as statin but it is only one drug proved to increase HDL cholesterol with very less side effects. Therefore, a combination of niacin and statins might be superior to these drugs alone for lowering lipid levels. The scientific evidence of long-term safety and tolerability of these combination therapies are key determinants for good compliance and cardiovascular benefits.

Proprotein convertase subtilisin kexin-9 (PCSK9) is a sterol-responsive protein that accelerates LDLR turnover in the liver. When PCSK9 transcription is reduced, there will be subsequently increases LDLR levels helping to maintain cholesterol homeostasis. The transcription of PCSK9 is increased by SREBP-2, which also regulate the transcription of many other genes. Therefore, a pharmacologically specific inhibitor of PCSK9 will have atherogenic effect by increasing LDLR levels without affecting other genes regulated by SREBP-2.

#### *10.1.2. Increasing HDL levels*

Low HDL-cholesterol (HDL-C) is a strong and independent cardiovascular risk marker. Niacin is the only drug proved to increase HDLC but associated with flushing as a side-effect. Niacininduced flushing involves both PGD2 from mast cells and serotonin from platelets. The possibility of administering or formulating niacin together with flavonoid luteolin was recently shown to inhibit niacin flush in rats. Further investigation on inhibitors on side-effect can warrant an effective medicine for CVD[92]. Aleglitazar, a dual PPARα/γ agonist, proven has beneficial effects on both lipid and glucose parameters [93]. Activation of PPARα may increase ApoA1, apolipoprotein of HDL and increased the synthesis of LPL which hydrolyzes VLDL, IDL and LDL. PPARα agonist, with good safety profile, may have a therapeutic role in modifying cardiovascular risk factors.

#### *10.1.3. CETP inhibition*

Besides established strategies to increase HDL-C, e.g. with nicotinic acid, CETP (Cholesteryl ester transfer protein)-inhibition is a promising new therapeutic option. The failure of torcetrapib, the first CETP-inhibitor, seems to be attributed to "off-target" effects. Treatment with the newer CETP-inhibitors dalcetrapib and anacetrapib has been shown to be efficacious and safe - but their usefulness in clinical practice remains to be determined in ongoing clinical trials [94].

#### *10.1.4. Inhibition of cannabinoid receptors*

G protein-coupled cannabinoid receptor, CB-1 of the endocannabinoid system, plays a crucial role in regulating feeding pattern, lipid metabolism, and energy homeostasis. CB-1 receptors are located in the central nervous system and peripheral tissues including adipocytes, pancreas, gut, liver, and muscle. Rimonabant, a selective CB-1 antagonist drug to be developed for weight loss via increasing energy expenditure actually also increases HDL-cholesterol and triglycerides.However, the clinical efficacy and safety of these new antiobesity compounds are yet to be determined. Additional cannabinoid receptor blockers have been developed and are in testing [95].

#### *10.1.5. Nuclear receptor modifiers*

Identification of nuclear receptor LXR and FXR as regulatorof genes in bile acid and cho‐ lesterol metabolism has providedpotential new targets for screening cholesterol-lowering drugsby manipulating bile acid synthesis, transport, and absorption. Therapies targeted to LXR and FXR would be ideal for drug developmentbecause nuclear receptors are acti‐ vated by natural and syntheticligands, which could be identified by high-throughput screening [96].

#### *10.1.6. Acyl-coenzyme A: Cholesterol acyltransferas (ACAT) inhibitors*

a pharmacologically specific inhibitor of PCSK9 will have atherogenic effect by increasing

Low HDL-cholesterol (HDL-C) is a strong and independent cardiovascular risk marker. Niacin is the only drug proved to increase HDLC but associated with flushing as a side-effect. Niacininduced flushing involves both PGD2 from mast cells and serotonin from platelets. The possibility of administering or formulating niacin together with flavonoid luteolin was recently shown to inhibit niacin flush in rats. Further investigation on inhibitors on side-effect can warrant an effective medicine for CVD[92]. Aleglitazar, a dual PPARα/γ agonist, proven has beneficial effects on both lipid and glucose parameters [93]. Activation of PPARα may increase ApoA1, apolipoprotein of HDL and increased the synthesis of LPL which hydrolyzes VLDL, IDL and LDL. PPARα agonist, with good safety profile, may have a therapeutic role in

Besides established strategies to increase HDL-C, e.g. with nicotinic acid, CETP (Cholesteryl ester transfer protein)-inhibition is a promising new therapeutic option. The failure of torcetrapib, the first CETP-inhibitor, seems to be attributed to "off-target" effects. Treatment with the newer CETP-inhibitors dalcetrapib and anacetrapib has been shown to be efficacious and safe - but their usefulness in clinical practice remains to be determined in ongoing clinical

G protein-coupled cannabinoid receptor, CB-1 of the endocannabinoid system, plays a crucial role in regulating feeding pattern, lipid metabolism, and energy homeostasis. CB-1 receptors are located in the central nervous system and peripheral tissues including adipocytes, pancreas, gut, liver, and muscle. Rimonabant, a selective CB-1 antagonist drug to be developed for weight loss via increasing energy expenditure actually also increases HDL-cholesterol and triglycerides.However, the clinical efficacy and safety of these new antiobesity compounds are yet to be determined. Additional cannabinoid receptor blockers have been developed and are

Identification of nuclear receptor LXR and FXR as regulatorof genes in bile acid and cho‐ lesterol metabolism has providedpotential new targets for screening cholesterol-lowering drugsby manipulating bile acid synthesis, transport, and absorption. Therapies targeted to LXR and FXR would be ideal for drug developmentbecause nuclear receptors are acti‐ vated by natural and syntheticligands, which could be identified by high-throughput

LDLR levels without affecting other genes regulated by SREBP-2.

202 Using Old Solutions to New Problems - Natural Drug Discovery in the 21st Century

*10.1.2. Increasing HDL levels*

modifying cardiovascular risk factors.

*10.1.4. Inhibition of cannabinoid receptors*

*10.1.3. CETP inhibition*

trials [94].

in testing [95].

screening [96].

*10.1.5. Nuclear receptor modifiers*

ACAT 1 and ACAT2 play an important role in cellular cholesterol esterification and thus modulate intestinal cholesterol absorption and hepatic lipoprotein secretion. ACAT2 is proposed to play a central role in cholesterol absorption from the intestine. ACAT1, on the other hand is widely distributed in tissues, and plays a pivotal role in cholesterol metabolism in macrophages and steroidogenic tissues. It is anticipated that inhibitors of ACAT2 activity could be developed that would decrease cholesterol absorption, whereas specific ACAT1 inhibitors could be used to reduce foam cell formation and prevent atherosclerosis. However, the results of studies have indicated that ACAT1 inhibition is not a good strategy and, in fact, could have detrimental consequence [97]. In contrast, mice lacking ACAT2 exhibited attractive metabolic findings. These include a restricted capacity to absorb cholesterol and protection against diet-induced hypercholesterolemia and gallstone formation [98, 99]. Further, ACAT2 inhibitor reduces cholesterol esters in apolipoprotein B-containing lipoproteins and protects from atherosclerosis in murine models of the disease [100]. A fundamental question remains: would ACAT2 specific inhibition in humans, either pharmacologically or with anti-sense oligonucleotides, prevent or reduce atherosclerosis? "The sole test of the validity of an idea is experiment." Until a potent and specific inhibitor of ACAT2 is tested in humans, the hypothesis remains uncertain [101].

#### **10.2. Future perspectives of cholesterol-lowering products and their potential impact on CVD**

#### *10.2.1. Identification of new molecular targets*

Target identification is an essential first step in drug development. Although cholesterol metabolism has been studied for decades and relatively well understood, the specific molec‐ ular targets that can be used for drug discovery and development are far from well-known. It is believe that with the development and use of modern molecular technology and techniques in nutritional and physiological research, more targets will be indentified and used for future drug development.

#### *10.2.2. Application of gene silencing technology*

Apart from the identification of new targets, several new approaches have been introduced or shown great potential for the development of new cholesterol-lowering products. Of them is gene-silencing technology. One technology that has generated a lot of excitement is RNA interference (RNAi) [102]. For example, clinical trials have been launched using RNA inter‐ ference approaches to reduce PCSK9 expression or specific antibodies targeting and inhibiting PCSK9 interaction with the LDL receptor. They constitute very promising approaches to reducing cholesterol levels and coronary heart disease. Understanding of PCSK9 and its potential as a therapeutic target through which to reduce LDL cholesterol for prevention and treatment of coronary heart disease has been of great interest recently [103]. The administration of chemically modified small interference RNAs (siRNAs) results in silencing of a target mRNA, such as apolipoprotein B (apoB) mRNA in liver and jejunum and decreasing plasma levels of apoB protein. ApoB is a molecule involved in the metabolism of cholesterol; the concentrations of this protein in human blood samples correlate with those of cholesterol. Higher levels of both compounds are associated with an increased risk of coronary heart disease. Intravenous injections of the siRNA-cholesterol conjugates in mice resulted in a lowering of the levels of blood cholesterol comparable to that in mice in which the apoB gene had been deleted. These results demonstrate that siRNA can be delivered systemically to target the liver and suggest that RNAi has the potential to become a new therapeutic for the treatment of metabolic diseases [102].

#### *10.2.3. Development of target-specific inhibitors or enhancers*

For those molecular targets that have several different isoforms, the biggest challenge in the drug development is the specificity. A good example is ACAT inhibitors. To date, it has been demonstrated that there are two sioforms, ACAT1 and ACAT2. ACAT1 is ex‐ pressed universally while ACAT2 is expressed mainly in the liver and small intestine. Both isoforms can esterify cholesterol and other sterols. However, ACAT1 primarily works on the esterification of plant sterols and other sterol products, while ACAT2 main‐ ly converts cholesterol to its esters. Due to their different distribution and activities in the body, a universal inhibitor of both enzymes has been shown to be detrimental and recent humans trials are disappointing [104, 105]. The study of Bell et al. in 2006 breathes life back into the idea of ACAT2-specific inhibition [106]. In atherosclerosis-prone mice, ACAT2 was specifically ihibhied in the liver with antisense oligonucleotides. Biweekly intraperitoneal injections, which reduced ACAT2 expression by a remarkable 80%, de‐ creased diet-induced hypercholesterolemia and sharply reduced cholesterol ester deposi‐ tion in the aorta. The specific inhibition can be achieved from the antisense gene technology or small molecules that inhibit only ACAT2. There is no mature product in this category and lots more work needs to be done.

It has been demonstrated by numerous studies that inhibition of cholesterol absorption is associated with much less side-effects than other approaches. It remains challenge but highly promising that a potent inhibitor of cholesterol absorption would sufficiently low‐ er blood cholesterol or keep blood cholesterol levels within the recommended healthy range. To achieve this goal, other approaches have to be take in addition to the specific inhibitor of cholesterol absorption, such as a combination of two or more products, in particular the combinations that work synergistically through one or multiple pathways of cholesterol homeostasis. Recent studies on the combination of the plant alkaloid ber‐ berine and plant sterols/stanols have shown an excellent example of this approach. The researchers have demonstrated consistently that plant sterols or stanols and berberine have a moderate effect to lower blood cholesterol levels in different animal models. However, when plant sterols/stanols were combined with berberine, a significant syner‐ gism was produced. They remarkably improved cholesterol-lowering efficacy by synerg‐ istically inhibiting cholesterol absorption [90,91].


*2.2. Procedure*

The study was initially approved by the institutional Ethics Committee. For the enrolment of the participants, it became necessary in the first stage, to contact through electronic email, di fferent victim support institutions, which were informed of the purposes of the present study. All the contacted institutions agreed to cooperate in this study, and during 5 months of announcements, 25 persons requested details about the study. After explaining the study in detail, 15 of these 25 persons agreed to participate in the study. Of those 15, 13 participants met the eligibility criteria and were thus interviewed. The two excluded subjects had already perpetrated violence on dating partners.

After obtaining the informed consent of the participants, the interviews were conducted in the facilities of the support institution and also in a room of the university where the study was carried out, specifically reserved for that purpose. The interviews had a duration ranging from 45 to 120 min and were carried out by researchers with experience in interviewing victims and with specific training in the scope of DV. Due to the possibility of dealing with potentially disturbing experiences, participants were also warned of the possible psychological consequences of the interview. Where necessary, and in the interest of the participants, further specialized support was also made available. The interviews were recorded using a digital audio and were verbatim transcribed in order to preserve the integrity of the reports, aiming further analysis.


3.1.5. Vegetation Cover: The Presence/Absence Effect of Ponds

This factor is the focal point of this study since by slightly changing this parameter the outcome changes significantly. At this point, two vegetative cover scenarios are presented: the first presents the actual setting of the Claise accounting for the presence of ponds, while the second simulates a scenario where ponds are removed to assess the difference in erosion outcomes with and without their presence. This last step allowed to quantify the impact of ponds on erosion in the Claise basin. In the second scenario, the land occupation group "ponds" was changed to their surrounding class (grasslands).

The large area of ponds, which makes up around 11% of the Claise (Table 3), displays their potential role as modifiers basin processes. Figure 7 presents the two considered vegetation covers as inputs for crossing with the potential soil erosion risk map to yield two different actual soil erosion risk maps. These maps were then compared to evaluate the effect of the presence and absence of ponds and their role on erosion.

**Figure 7.** (**a**) Current Claise vegetation cover and (**b**) alternative vegetation cover and corresponding CORINE classification; 1: fully protected, 2: not fully protected.

Class 0 refers to land cover categories that are not considered in CORINE; these categories are urban areas and water bodies, while classes 1 and 2 refer to the fully protected and not fully protected covers. From Figure 7b, 72.5% of the Claise basin corresponds to the fully protected class, while 27.5% of the study area is occupied by not fully protected cover. To assess the impact of pond presence, the second scenario of replacing ponds by their surrounding dominant cover was performed.

3.1.6. Actual Soil Erosion Maps Under Current and Alternative Scenarios

The two actual soil erosion risks maps were produced by multiplying the respective indices of the potential soil erosion risk map and the two vegetation cover scenarios using the "raster calculator" tool. Figure 8 reveals the outcome under both scenarios.

**Figure 8.** Actual soil erosion risk map of the Claise under (**a**) current vegetation cover and (**b**) the alternative pondless scenario.

The Actual soil erosion map was cross-checked against: Institut National de la Recherche Agronomique (INRA) 2000 erosion maps and the combined GIS sol–INRA–SOeS 2011 maps [80]. These were produced following the Modèle d'Évaluation Spatiale de l'Aléa d'Érosion des Sols (MESALES). The comparison between the INRA maps, and the produced actual soil erosion risk map, is presented in Table 6. By this comparison, it is concluded that there is a good agreement between these maps. In addition, since INRA maps are not completely adequate to be considered at the basin scale [80], the established erosion maps are considered for the no-erosion zones, overcoming, this way, the challenge of coarse representation.

**Table 6.** Verification of the established erosion map.

As can be seen from Table 6, a total of 134 validation points were chosen. These were divided into 86, 37, and 11 low-erosion, moderate-erosion, and high-erosion zones validation points, respectively. A large part of the moderate-erosion class was misinterpreted as the low-erosion class. This discrepancy is due to the fact that the no-erosion zones do not exist in the INRA maps, but are instead classified as low-erosion zones. Therefore, the error margin in the moderate-erosion class from Table 6 is justified by the finer scale representation of the produced maps, compared to the INRA maps. The overall

accuracy was determined to be 75%, while the computed Cohen's kappa coefficient [81] was found to be 0.7; this indicates a substantial agreement between the INRA maps, and the produced actual soil erosion risk map. The kappa coefficient was used since it tests inter-rater reliability; i.e., the coefficient represents the extent to which the generated data are correct representations of the measured data. In the case of this study, the generated data is the actual soil erosion risk map, while the measured data consists of the validation points obtained from the INRA maps.

From Figure 8, three main results can be drawn:

(1) The role of vegetation cover in changing erosion risks is solidified. This is particularly reflected by the setting of the Claise basin due to the agricultural and grass cover. By comparing the actual soil erosion risk map with the potential soil erosion risk map and statistics, a shift of erosion risk classes is observed. As mentioned in Section 3.1.4, considering the potential soil erosion risks, and ignoring the vegetation cover, low, moderate and high-risk areas take over 3%, 96.5% and 0.5% of the total basin area, accordingly. When the vegetation cover layer was taken into account the resulting actual soil erosion risk shifted to 65.66%, 21.68% and 0.18%, for low, moderate and high-risk areas. These observations solidify that vegetative cover is the most influential aspect for erosion assessment. In further detail regarding the vegetation cover layer, areas corresponding to agricultural classes are seen to have higher erosion risks than areas with different land cover types. This is in agreement with Verheijen et al. (2009) [82] observations that despite the considerable effect of soil type, topography and climatic conditions, the major influencer of soil erosion is the vegetative cover, especially cultivated areas.

(2) The remainder 12.48% of the actual soil erosion risk map is the no-erosion zone. As seen in Figure 7a, most of the no-erosion zone corresponds to the concentration area of ponds, while the remainder 1.48% represents the Claise River. The ponded area represents 88.23 km2 of the Claise under no risk of erosion, making these ponds a counter-erosion zone.

(3) At a graphical scale, a complete shift from low to moderate risks, in the greatest part of the basin, is observed. Table 7 presents the statistical difference between the actual soil erosion risks with current vegetation cover and those of the pondless scenario. From Table 7, the effective role of ponds as an erosion counter-measure is revealed.

**Table 7.** Actual soil erosion risk (ASE) for the Claise basin under current and simulated vegetation cover.

Additionally, the impact of ponds on erosion at the scale of the basin is revealed. Not only did the no-erosion and low-erosion classes decrease by 11.36% and 65.14%, in the absence of ponds scenario, but also the moderate and high-erosion risks increased by 55.12% and 21.38%, respectively. These changes are due to several reasons:

(1) The most evident reason is that ponds effectively and directly nullify splash erosion in the areas they occupy.

(2) Their widespread, yet dense, positioning throughout the basin, counteracts runoff erosion in a twofold way: first, by intercepting eroded soils by overland flow, retaining this way, the transported material and preventing them from reaching the streams, and second, by slowing surface runoff and thus, abating its erosive force. Despite the fact that the low-slope topography does not particularly favor runoff erosion, let alone high velocities of overland flow, this obviously has some effect, especially in cases of intense rainfall events.

(3) Their dense aggregation in the basin attributes them the role of cascade check dams, containing sediments.

(4) Their large density and chain sequence where the retention effect is greatly amplified (factor of 2179 ponds) [38].

(5) The highly erodible setting of the basin resulting from a challenging pedology.


On the Design and Manufacture of Wind Turbine Blades

*Mohamed Mahran Kasem*

### **Abstract**

Wind turbines become extremely important worldwide along with the need for clear energy sources. The concept of wind turbines is based on using the wind energy to produce lift that turns into toque, which rotates the wind turbine blades and subsequently produces electric power using a proper generator. However, the wide use of wind turbines and their design and manufacturing process are a challenge. Therefore, much research has been conducted to improve and develop new methods for the design and manufacturing of wind turbines. In this chapter, the author discusses some techniques for wind turbine design and manufacturing, including airfoil appropriate selection, design optimization methods, and manufacturing techniques. One of the manufacturing techniques that are found to be superior is the use of chordwise and spanwise stiffeners to increase the stiffness of the skin of carbon fiber wind turbine blades. Those stiffeners are not bonded externally to the skin; otherwise, they are layers of carbon fibers that are buried inside the skin of the wind turbine blades.

**Keywords:** wind turbine blades, blade manufacturing, blade design methods

## **1. Introduction**

The design of wind turbine blades has two objectives: (1) to determine the blade geometry that can produce an optimum power and (2) to determine the optimum structure required to create the wind turbine blade. The objective of the former is to obtain the wind turbine blade geometry that maximizes the power generated at different tip speed ratios. **Figure 1** illustrates the variation of the power coefficient *Cp* with the tip speed ratio ð Þ*λ* for two different blade designs. Design 1 has the maximum *Cp* but with large drop with small and high *λ*. Design 2 has smaller *Cp*, but performs better over the range of *λ*. Therefore, design 2 seems to be better than design 1; however, it has smaller maximum power coefficient *Cp*.

The aerodynamic design also includes the selection of optimum chord and twist distribution for the wind turbine blade. The objective of the latter is to create a wind turbine blade structure that satisfies the aerodynamic requirements. A typical blade cross section is shown in **Figure 2**. A blade structure is usually constructed from external skin and internal spar.

This chapter summarizes the key steps required to perform an appropriate aerodynamic and structural designs for wind turbine blades. This includes the design

**Figure 1.** *Variation of power coefficient with tip speed ratio for two different blade designs [1].*

#### **Figure 2.**

*Typical cross section of a wind turbine blade [2].*

process, unsteady aerodynamic analysis, design optimization, and structural design of the blade.

## **2. Design of wind turbine blades**

A major objective of wind turbine design is to maximize the output power and improve its performance. This objective can be accomplished by maximizing the aerodynamic lift and minimizing the drag. The process of designing a wind turbine blade starts by the airfoil selection in addition to selecting the appropriate wind turbine geometries according to the required performance. **Figure 3** shows the main variables in a typical wind turbine blade. **Figure 4** shows the relation between the wind turbine power and diameter.

#### **2.1 Airfoil selection**

Wind turbine blades are usually constructed with high taper ratio and twisting angle. Small wind turbines usually have one airfoil type, whereas large-scale wind turbines need different airfoils along the blade radius. An airfoil should be selected with maximum lift-to-drag ratio and minimum pitching moment coefficient. Most optimization models concentrate on improving wind turbine blade performance by enhancing the taper ratio, aerodynamic twist, and geometric twist of the blade;

*On the Design and Manufacture of Wind Turbine Blades DOI: http://dx.doi.org/10.5772/intechopen.104490*

**Figure 3.** *Wind turbine blade variables [3].*

**Figure 4.**

*Relation between wind turbine power and diameter.*

however, some optimization models improve the wind turbine performance by changing the airfoil shape. The latter can be conducted either by considering different airfoil shapes in the optimization problem or by defining control points over the airfoil and change its shape during the optimization process (**Figure 5**).

Sometimes, special types of airfoils are required for the wind turbine based on its characteristics. For instance, low-speed wind turbines require special types of airfoils to generate the torque required to rotate the blades [5]. In most cases, it is required to

**Figure 5.** *The control point motion [4].*

**Figure 6.** *Comparison between different airfoils at Re = 3 104 .*

compare between different airfoil types and select the best airfoil to be integrated with a certain wind turbine. The airfoils are evaluated based on their *Cl Cd* ratio. The maximum is *Cl Cd* ; the airfoil can produce more lift and smaller drag.

There are several airfoils' families suitable for wind turbine blades, such as the NACA family and the S series. **Figure 6** shows a comparison between nine airfoils from different series at Reynold's number 3 104. The performance of each airfoil is different in relative to the angle of attack.

Large wind turbines are usually constructed from more than one airfoil. It could have two or three different airfoils along its radial position. In this case, a linear or higher order chord variation can be assumed between the airfoils.


**1. Introduction**

Multi-target Direction of Arrival (DOA) estimation is an essential issue in array processing and has a wide range of applications in source location, radar, sonar, and wireless communications [1,2]. Sparse representation and compressive sensing methods are used for DOA estimation of coprime array [3–6], while these methods are only applied in the case where the sources are stationary. In addition, difficulties also arise from the uncertainties of the source dynamics: the source may be moving or static. Thus, it is significant to extend the static DOA estimation algorithm to the dynamic DOA tracking algorithm.

The representative dynamic DOA tracking algorithms include the subspace tracking algorithm and the particle filter (PF) algorithm. The subspace tracking algorithm includes Projection Approximation Subspace Tracking (PAST) [7] and the Projection Approximation Subspace Tracking with Deflation (PASTD) [8]. In essence, these algorithms transform the determination of the eigensubspace into solving an unconstrained optimization problem, and combine the recursive least squares (RLS) theory to achieve effective tracking of the eigensubspace of time-varying sources. However, the RLS method is very sensitive to impulse noise, and the PAST algorithm's subspace tracking performance will degrade sharply in the impulse noise environment [9–11]. In an army of acoustic applications, such as underwater and room acoustic signal processing, the noise environment is non-Gaussian and is impulsive in nature [12,13]. Under investigation, it was found that α stable distribution (0 < α ≤ 2) is a suitable noise model to describe this type of noise [14]. In recent years, DOA estimation technology in impulse noise environment has developed rapidly [15–17]. The PF algorithm based on Bayesian recursive estimation can solve the target tracking problem by utilizing a priori DOA and current measurement information [18]. In [19], the author considers the particle filtering method to estimate the single target DOA by using the spatial spectral function based on FLOM matrix as the likelihood function in the impulse noise environment. However, those algorithms needs to know the number of targets in advance and cannot deal with the estimation problem of the time-varying sources DOA.

In practical applications, such as submarine tracking and sonar positioning, the number of the sources are dynamic. Mahler introduced the concept of random finite set (RFS) in [20]. A tutorial on Bernoulli filters is introduced in [21]. A track-before-detect (TBD) Bernoulli filter based on RFS is proposed for DOA tracking in single dynamic system in [22], but it cannot solve the DOA tracking in multiple target dynamic system. The Multi-target Multi-Bernoulli (MeMBer) filtering [23] is a filter developed under the RFS framework. The advantage is that it operates on the dimensions of a single target space, thus avoiding the computational complexity and data association problems of the joint filter. Choppala P B et al. studied the Bayesian multi-target tracking problem based on phased array sensor, and proposed the MUSIC spatial spectral as a pseudo-likelihood in the Multi-Bernoulli filter in [24]. However, the shortcoming of this algorithm is that impulse noise is not considered, and Gaussian noise model is not appropriate in practical applications.

Based on the above analysis, a particle filter algorithm of DOA tracking for Unscented Transform MeMBer (UT-MeMBer) in an impulse noise environment is proposed. UT is used to construct a new important density function, which makes the estimation accuracy higher when the particle degenerates. Since particles close to the real state are more likely to output a larger spatial spectral response, the magnitude of the spatial spectral response is used as a feature of pseudo-likelihood. Based on the FLOM matrix, this paper uses FLOM matrix to substitute the covariance matrix to obtain the corresponding MUSIC spatial spectrum as the particle likelihood function. Further exponential weighting can increase the weight of the particles, making resampling more efficient. The main advantage of the tracking algorithm is that the number and state of the target can be accurately tracked when the number and state of the sources are unknown in impulse noise environment.

The rest of the paper is organized as follows. In Section 2, the problem of the DOA tracking in impulsive noise environment is described. In Section 3, we outline the Multi-Bernoulli's Bayesian theory of DOA tracking. An improved algorithm for likelihood functions is introduced in Section 4. The UT-MeMBer DOA particle filter tracking algorithm is given in Section 5. We then show our simulation results in Section 6 and conclusion in Section 7.


*3.2. Effect of Flue Gas Temperature on the Evaporation Performance*

Figure 7 shows the turbulence kinetic energy under different flue gas temperatures. By increasing the flue gas temperature, the turbulence kinetic energy in the mixing zone of the flue gas and the droplets changes slightly, which indicates the slight difference in the mixing intensity between flue gas and droplets. Figure 8 displays temperature under different flue gas flow rates. Higher flue gas temperature corresponds to higher temperature and more heat in the mixing zone of flue gas and droplets, which is advantageous to evaporate the droplets.

**Figure 6.** Effect of flue gas flow rate on evaporation performance.

**Figure 7.** Turbulence kinetic energy under different flue gas temperatures (m2/s2).

**Figure 8.** Temperature under different flue gas temperatures (K).

Figure 9 shows the effect of flue gas temperature on the droplet evaporation performance in the spray drying tower. It can be seen that increasing the flue gas temperature is beneficial for reducing the droplet residence time in the spray drying tower and improving droplet evaporation performance. This is because the higher flue gas temperature increases the temperature difference between the flue gas and the droplets, enhancing the diffusion and thermophoretic force effects. As a result, heat and mass transfer become more vital, and the droplet evaporation speed is accelerated and reduces the complete evaporation distance.