In making the decision whether to use component-based modeling, its benefits must be balanced against computational costs. Studies evaluating these costs using the Open Modeling Interface (OpenMI) have largely used models with simplified formulations, small spatial and temporal domains, or a limited number of components. We evaluate these costs by applying OpenMI to a relatively complex Stormwater Management Model (SWMM) for the City of Logan, Utah, USA. Configurations of coupled OpenMI components resulting from decomposing the stormwater model by process (i.e., runoff coupled to routing) and then by space (i.e., groups of catchments coupled together) were compared to a reference model executed in the standard SWMM configuration. Simulation times increased linearly with the number of connections between components, and mass balance error was a function of the degree to which a component resolved time series data received. This study also examines and proposes some strategies to address these computational costs. We developed the SWMMOpenMIComponent (a C# SWMM Component), SWMMOpenMINoGlobals (a modified, native C SWMM computational engine code underlying the component), and a modified OpenMI C# project. We forked the OpenMI 2.0 C# project, including the Software Development Kit (SDK), the command line interface, and the OpenMI Configuration Editor found at http://sourceforge.net/p/openmi/code/HEAD/tree/trunk/src/csharp for this study. In addition to implementing minor bug fixes to ensure that the code compiled, we implemented a new graphical user interface for creating connections with chained adapters in accordance with the OpenMI 2.0 specification, a new simulation monitoring dialog, and fixed the project file reading and writing classes to ensure that connections with adapters are read and written properly. Caleb A. Buahin caleb.buahin@aggiemail.usu.edu 2015 PC running Microsoft Windows The C# SWMM Component (SWMMOpenMIComponent) and its underlying modified native C SWMM library (SWMMOpenMINoGlobals) are freely available under the GNU Lesser General Public License (LGPL) license at https://github.com/cbuahin/SWMMOpenMIComponent. The source code for the modified version of the OpenMI C# project can be found at https://github.com/cbuahin/OpenMI under the LGPL license. 
Evaluating the simulation times and mass balance errors of component-based models: An application of OpenMI 2.0 to an urban stormwater system