Structural energy transfer to the jacket foundation of an offshore wind-wave coupling device based on absolute transmissibility function

Abstract

During the long-term operation of an offshore fixed wind-wave coupling device, the structure is subjected to excitation due to the operation of the wave energy device, harmonic excitation due to the impeller rotation, and environmental excitation. In this study, the whale optimization algorithm (WOA) modified by a random mutation strategy was used to optimize the variational mode decomposition (VMD) parameters and eliminate the effect of environmental noise. Then, the normalization transfer path analysis (N-TPA) method based on the absolute transmissibility function (ATF) was used to analyze the transfer path from each vibration source to the target point. The energy transfer among the structures of the wind-wave coupling device was studied; accordingly, the contribution of the subsystems was intuitively displayed to determine the pile with the highest energy when subjected to external loads. Compared to the traditional transfer path analysis (TPA) method based on the transmissibility function (TF), the method developed in this study can overcome the ocean noise problem through the improved WOA-VMD method and yield more accurate transfer path analysis results. To verify the effectiveness of the method developed in this study, numerical research, simulation, and physical model experiments were conducted using the 5-DOF system theoretical model, finite element model, and physical model. The contributions of the subsystems to the operational state of the structure were analyzed. The results demonstrated that the proposed method could be used to evaluate the stability of each structural element such that appropriate measures can be taken. This provides a reference for the development and stable operation of fixed wind-wave coupling devices.