Calculation method of wind-wave joint forces exerted on offshore structures considering coherence

There is stronger coherence between environment elements of random wind and wave, it affects fluctuating wind speed and wave form in wind-wave joint propagation process to further affect wind-wave joint forces and structural responses of offshore structures. Here, to correctly calculate random wind-wave joint forces exerted on structures, based on the established wind-wave coherence function describing random wind-wave joint propagation coherence, the cross-correlation spectrum between fluctuating wind speed exerted on ocean structures and incident random wave surfaces was calculated and obtained. The structural random wind-wave joint power spectral matrix was established including wind speed self-spectrum, wind speed cross-spectrum, wave spectrum and wind-wave cross-spectrum. Based on Cholesky matrix decomposition for the joint power spectral matrix, the harmonic synthesis method was used to generate fluctuating wind speed time histories exerted on structures under wind-wave interaction, and then the wind resistance coefficient of structure upper parts was combined, fluctuating wind force time histories exerted on structure were generated. Based on Cholesky matrix decomposition for the joint power spectral matrix, the structural random wave action hydrodynamic transfer function was introduced into the harmonic synthesis calculation formula to generate structural random wave action force time histories under wind-wave interaction. Synchronous time histories of structural random wind-wave joint action forces were established by jointly arranging the generated random wind time histories and the generated random wave time histories. Taking calculation of wind-wave joint forces exerted on an upright cylinder as an example, the application analysis of the above algorithm was performed. © 2024 Chinese Vibration Engineering Society. All rights reserved.