Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with speci...Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with special focus on the low frequency(LF) fatigue damage. Several influential factors, including water depth, wave spectral parameters, and riser system, are considered. Numerical simulation of a semi-submersible platform with the mooring/riser system is executed under different conditions, and the fatigue damage of mooring lines is assessed by using the time domain analysis method as a benchmark. The effects of these factors on the mooring line tension and the fatigue damage are investigated and discussed in detail. Research results indicate that the LF fatigue damage only accounts for a very small portion of the total damage, although the LF components dominate the global motion response and the mooring line tension of the semi-submersible platform. However, it is demonstrated that the LF fatigue damage is clearly affected by the influential factors. The increase in water depth and spectral peak periods, and the existence of risers can weaken the contribution of the LF components to the mooring line fatigue damage, while the fatigue damage due to the LF components increases with the increase of significant wave height.展开更多
This study examines oblique wave motion over multiple submerged porous bars in front of a vertical wall.Based on linear potential theory,an analytical solution for the present problem is developed using matched eigenf...This study examines oblique wave motion over multiple submerged porous bars in front of a vertical wall.Based on linear potential theory,an analytical solution for the present problem is developed using matched eigenfunction expansions.A complex dispersion relation is adopted to describe the wave elevation and energy dissipation over submerged porous bars.In the analytical solution,no limitations on the bar number,bar size,and spacing between adjacent bars are set.The convergence of the analytical solution is satisfactory,and the correctness of the analytical solution is confirmed by an independently developed multi-domain BEM(boundary element method) solution.Numerical examples are presented to examine the reflection and transmission coefficients of porous bars,C_R and C_T,respectively,for engineering applications.The calculation results show that when the sum of widths for all the porous bars is fixed,increasing the bar number can significantly improve the sheltering function of the bars.Increasing the bar height can cause more wave energy dissipation and lower C_R and C_T.The spacing between adjacent bars and the spacing between the last bar and the vertical wall are the key parameters affecting C_R and C_T.The proposed analytical method may be used to analyze the hydrodynamic performance of submerged porous bars in preliminary engineering designs.展开更多
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 pro...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.展开更多
基金financial support by the National Basic Research Program of China (Grant No. 2011CB013704)the major program of the National Natural Science Foundation of China (Grant No. 51490675)+1 种基金the Shandong Provincial Science & Technology Development Project (Grant No. 2013GHY11503)the Taishan Scholars Program of Shandong Province
文摘Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with special focus on the low frequency(LF) fatigue damage. Several influential factors, including water depth, wave spectral parameters, and riser system, are considered. Numerical simulation of a semi-submersible platform with the mooring/riser system is executed under different conditions, and the fatigue damage of mooring lines is assessed by using the time domain analysis method as a benchmark. The effects of these factors on the mooring line tension and the fatigue damage are investigated and discussed in detail. Research results indicate that the LF fatigue damage only accounts for a very small portion of the total damage, although the LF components dominate the global motion response and the mooring line tension of the semi-submersible platform. However, it is demonstrated that the LF fatigue damage is clearly affected by the influential factors. The increase in water depth and spectral peak periods, and the existence of risers can weaken the contribution of the LF components to the mooring line fatigue damage, while the fatigue damage due to the LF components increases with the increase of significant wave height.
基金supported by the National Natural Science Foundation of China(Nos.51490675,51322903 and 51279224.)
文摘This study examines oblique wave motion over multiple submerged porous bars in front of a vertical wall.Based on linear potential theory,an analytical solution for the present problem is developed using matched eigenfunction expansions.A complex dispersion relation is adopted to describe the wave elevation and energy dissipation over submerged porous bars.In the analytical solution,no limitations on the bar number,bar size,and spacing between adjacent bars are set.The convergence of the analytical solution is satisfactory,and the correctness of the analytical solution is confirmed by an independently developed multi-domain BEM(boundary element method) solution.Numerical examples are presented to examine the reflection and transmission coefficients of porous bars,C_R and C_T,respectively,for engineering applications.The calculation results show that when the sum of widths for all the porous bars is fixed,increasing the bar number can significantly improve the sheltering function of the bars.Increasing the bar height can cause more wave energy dissipation and lower C_R and C_T.The spacing between adjacent bars and the spacing between the last bar and the vertical wall are the key parameters affecting C_R and C_T.The proposed analytical method may be used to analyze the hydrodynamic performance of submerged porous bars in preliminary engineering designs.
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)+1 种基金the Taishan Scholars Program of Shandong Provincethe Fundamental Research Funds for the Central Universities(No.841713035)
文摘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.
