Framework for reconstructing wave loads on a floating cylinder using monitored data of structural motion and wave elevation

Abstract

This study develops a framework for reconstructing the wave loads on a floating cylinder by utilising the monitored data of wave elevation and structural motions, which involve surge, sway, roll, and pitch motions. The proposed method can be applied to perform wave load monitoring and data collection for offshore structures in a stochastic wave field. The derivation of the wave load reconstruction based on the potential flow theory is presented in detail. The linear reconstruction method (as the basis of the proposed method) is first established to simplify the reconstruction process. A nonlinear reconstruction method considering the second-order wave effects is introduced to improve the reconstruction accuracy for nonlinear wave loads. The concept of wave load reconstruction on a complex structure is also addressed. A case analysis is performed on a floating circular cylinder under three conditions. When the structural motions are pure translational motions or pure rotational motions, the wave loads on the cylinder can be reconstructed accurately with the transfer functions ατ,n and βτ,n. When the structural motions consist of both translational and rotational motions, the transfer functions are dependent on the structural motion pattern. Singularity points with a specific motion pattern are present, whereby the reconstruction would fail. In the cases where diffraction and radiation waves occur simultaneously, the two types of waves need to be decoupled from the monitored wave elevation, and the wave loads caused by the diffraction and radiation waves are reconstructed separately.