Comparison of CEM Methods for fast Simulation of Rotating Wind Turbines

Comparison of CEM Methods for fast Simulation of Rotating Wind Turbines

Weinmann, Frank (Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR)
Wald, Stefan O. (Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR)
Knott, Peter (Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR)

2018-12-06

This paper highlights the application and performance of Computational Electromagnetics (CEM) approaches to the simulation of EM effects caused by rotating wind turbines, and compares the benefits and drawbacks of the different methods. In most of the relevant cases, a wind turbine is an electrically very large target, which is too large for EM computation using full-wave methods. Consequently, only high-frequency methods remain, such as Geometrical Optics (GO) and Physical Optics (PO). A common implementation of a GO/PO approach is Shooting-and-Bouncing-Rays (SBR) for estimating surface currents and PO for integration of the currents over the lit surface. However, this method has some drawbacks when phase accuracy is required, e.g., for further post-processing of the simulation data to obtain ISAR images. A fast alternative to the SBR part is the direct calculation of the incident field strength using GO. In the basic form of the algorithm, reflections on a flat ground are included but other multi-path reflections are neglected. This approach allows for an extremely fast calculation of field strengths for a large number of time steps, while the phases are accurate for post-processing. Higher-order reflections can also be implemented, but significantly slow down the computations.

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