A floating substructure for wind turbines is modeled using the object-oriented modeling language Modelica in a coupled simulation environment. The equation-based modeling facilitates the implementation for engineers due to declarative model descriptions and acausal formulations. Predefined components from the Modelica Standard Library are used to represent several parts of a wind turbine. Especially the MultiBody library combined with the graphical editing feature is a powerful method to model the rigid body motions of a floating structure as shown herein. This paper illustrates how the resulting nonlinear differential-algebraic equation system can be implemented and solved in a convenient way. Different solvers can be easily tested to detect the solver with the best performance, without changing the code of the model. The developed model of the floating substructure has been verified with results of the Offshore Code Comparison Collaboration (OC3)-project and the resul ts show good agreement

A vital part in development of physical models, i.e., mathematical models of physical system behavior, is testing whether the simulation results match the developer's expectations and physical laws. Creation and automatic execution of tests need to be easy to be accepted by the user. Currently, testing is mostly performed manually by regression testing and investigation of result plots. Furthermore, comparisons between different tools can be cumbersome due to different output formats. In this paper, the test framework MoUnit is introduced for automatic testing of Modelica models through unit testing. MoUnit allows comparison of Modelica simulation results with reference data, where both reference data and simulation results can originate from different simulation tools and/or Modelica compilers. The presented test framework MoUnit brings the widespread approach of unit testing from software development into practice also for physical modeling. The testing strategy that is used within the Modelica IDE OneModelica from which the requirements for MoUnit arose, is introduced using an example of linear water wave models. The implementation and features of MoUnit are described and its flexibility is exhibited through two test cases. It is outlined, how MoUnit is integrated into OneModelica and how the tests can be automated within continuous build environments.

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To predict the characteristic impact pressure due to breaking waves on platform columns corresponding to an annual exceedence probability of 10−4 model test data with the Sleipner A gravity based structure (GBS) are subjected to a stochastic analysis. The analysis is based on the environmental contour line approach. In addition, the procedure recommended by Det Norske Veritas (DNV) for calculating shock pressures due to breaking waves is used for comparison. Time histories of pressure and wave elevation for the most severe measured impacts show that the measured pressures are induced by breaking waves. However, a difference between the resulting characteristic impact pressures based on the two approaches can be observed: The stochastic analysis results in much higher pressures than the approach recommended by DNV. These findings are supported by the analysis of data that were collected during model tests with the Gjo̸a semi-submersible and the Snorre A tension leg platform (TLP), where the difference between the results was rather large as well. For the semi-submersible and the TLP, one reason for the difference is bias in the fitment of the stochastic model. Furthermore, dynamic amplification effects in the force sensors have to be considered. However, this bias is less significant for the GBS and dynamic amplification effects are not present since different force sensors were used. For all three model tests, an important source for the different impact pressures is the size of the force sensor area, which varies between 2.25m2 and 10.89m2. Large areas may smoothen the pressure whereas small areas are overrating the impact. Further model testing is required to clarify this effect. If the difference is still present, the recommendation of DNV has to be altered to ensure a reliable prediction of the characteristic impact loads.