Probabilistic Analysis and Fatigue Damage Assessment of Offshore Mooring System due to Non-Gaussian Bimodal Tension Processes  

作　　者：CHANG Anteng LI Huajun WANG Shuqing DU Junfeng 

机构地区：[1]College of Engineering,Ocean University of China,Qingdao 266100,P.R.China [2]Shandong Provincial Key Laboratory of Ocean Engineering,Ocean University of China,Qingdao 266100,P.R.China

出　　处：《Journal of Ocean University of China》2017年第4期585-601,共17页中国海洋大学学报（英文版）

基　　金：the financial support of the Major Program of the National Natural Science Foundation of China(No.51490675);the National Science Fund for Distinguished Young Scholars(No.51625902);the Taishan Scholars Program of Shandong Province;the Fundamental Research Funds for the Central Universities(No.841713035)

摘　　要：Both wave-frequency(WF) and low-frequency(LF) components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system.This paper conducts a comprehensive investigation of applicable probability density functions(PDFs) of mooring tension amplitudes used to assess mooring-line fatigue damage via the spectral method.Short-term statistical characteristics of mooring-line tension responses are firstly investigated,in which the discrepancy arising from Gaussian approximation is revealed by comparing kurtosis and skewness coefficients.Several distribution functions based on present analytical spectral methods are selected to express the statistical distribution of the mooring-line tension amplitudes.Results indicate that the Gamma-type distribution and a linear combination of Dirlik and Tovo-Benasciutti formulas are suitable for separate WF and LF mooring tension components.A novel parametric method based on nonlinear transformations and stochastic optimization is then proposed to increase the effectiveness of mooring-line fatigue assessment due to non-Gaussian bimodal tension responses.Using time domain simulation as a benchmark,its accuracy is further validated using a numerical case study of a moored semi-submersible platform.Both wave-frequency （WF） and low-frequency （LF） components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system. This paper conducts a comprehensive investigation of applicable probability density func- tions （PDFs） of mooring tension amplitudes used to assess mooring-line fatigue damage via the spectral method. Short-term statisti- cal characteristics of mooring-line tension responses are firstly investigated, in which the discrepancy arising from Gaussian approximation is revealed by comparing kurtosis and skewness coefficients. Several distribution functions based on present analytical spectral methods are selected to express the statistical distribution of the mooring-line tension amplitudes. Results indicate that the Gamma-type distribution and a linear combination of Dirlik and Tovo-Benasciutti formulas are suitable for separate WF and LF mooring tension components. A novel parametric method based on nonlinear transformations and stochastic optimization is then proposed to increase the effectiveness of mooring-line fatigue assessment due to non-Gaussian bimodal tension responses. Using time domain simulation as a benchmark, its accuracy is further validated using a numerical case study of a moored semi-submersible platform.

关 键 词：fatigue damage non-Gaussian bimodal process rainflow counting cycle distribution offshore mooring system 

分 类 号：P75[天文地球—海洋科学]