Efficient simulation for analysis and optimization of a wave energy converter in non-linear random sea states

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Obtaining energy from a random source is a fundamental problem in the field of renewable energy. In addition to the possibility of obtaining solar or wind energy, there is also the possibility of obtaining energy from ocean waves. Thereby, mechanical systems are positioned on the sea surface and electrical generators convert the motions of the systems into electrical energy. Since wave energy has a notably high power density compared to wind and solar energy, it is a promising resource for renewable energy. However, in order to harvest as much energy as possible from wave energy converters (WECs), the mechanical system has to be designed in such a way that a large dynamic motion is achieved. On real oceans, sea waves occur randomly. Furthermore, measurements have shown that a linear wave theory is not suitable to fully represent the behavior of a real sea. Therefore, the WEC must be designed in such a way that large system dynamics are to achieved in nonlinear random sea states. However, the current toolboxes for calculating fluid-structure interaction require a large computational effort to simulate interaction between floating bodies and fluids, and thus the motion of the floating bodies in nonlinear random waves. The aim of the proposed project is to create and validate an efficient simulation model that not only accounts for the mechanical part of the WEC, but also for the nonlinear random fluid-structure interaction between the floating body and the water. The created simulation model is used to analyze the dynamics of the WEC and the amount of energy gained by a WEC in nonlinear random sea states. The results are compared to the corresponding results in a linear random sea state. These comparisons are intended to demonstrate the necessity of using nonlinear random sea states. The used WEC is a mechanical system consisting of a floating cylindrical body and a generator, which has been examined in preliminary studies in linear sea state. The generator harvests energy from the motion of the cylinder. The behavior of the system is analyzed in simulations and validated in experiments. For experimental studies, the institute possesses a wave flume, in which random and nonlinear waves can be generated. In order to achieve high motion of the cylinder for a wide range of water waves, the simulation model is used to optimize several system parameters of the WEC (such as the radius and mass of the cylinder). In addition, control strategies are used to increase the amount of harvested energy. In this way, the dynamics of the WEC is optimized to extract a large amount of energy from random and nonlinear waves (as they occur in real sea states).