Improved Simulation of Wave Loads on Offshore Structures in Integral Design Load Case Simulations

摘要

Several wind turbine simulation packages use reduced models for computationally efficient load case simulations of offshore wind turbines. These models capture the global wind turbine behaviour, where the support structure behaviour is expressed using a limited number of eigenmode amplitudes involving the lower frequencies. However, the disregarded higher eigenmodes are significant for the detailed behaviour of support structure members and contribute significantly to the fatigue damage and maximum stresses under extreme loads. To get detailed member load information, fully integrated simulations can be performed at the expense of the computational efficiency gained by using reduced models. Alternatively, load case simulations may be performed sequentially. This involves water flow load evaluation at a stage where the tower motion is not yet known. This paper presents a new sequential approach in which the sensitivities of the water flow loads with respect to support structure motion are conveyed to the dynamic simulation stage, and in which the parts of the water flow loads that are disregarded in the reduced model space are recovered in the retrieval run, allowing evaluation of the contribution of these forces to the fatigue damage and maximum stresses. Application of the new approach confirms that these contributions are significant. Furthermore, the new method is reasonably efficient, requiring about 80% extra calculation time compared to the traditional method.