Safety Assessment For The Structure Of Underwater Single Anchor Leg Yoke System

With the increasing requirement of energy,countries around the world pay more attention on the exploitation of marine resources,so people are concerned about the structural safety of ocean engineering.Single Anchor Leg(SAL)Yoke System is the newly developed technology in recent years,which has been used in China' s Bohai Sea oil field.China has some capacity and experience in manufacturing,installation and service of maritime use,but the technology of key equipment is still under research or with a blank status.To guarantee the safe operation of Single Point Mooring(SPM)structures and Floating Production Storage and Offloading(FPSO),it is of great significance to do safety assessment for SPM structure."Hai Yang Shi You 112" FPSO is as the study object in this paper.According to the wind,wave,current and ice loads of SAL Yoke System(SYS)during the service conditions,the response is obtained,and the hydrodynamic performance was calculated based on three-dimensional frequency domain potential flow theory,which may benefit the accuracy of structural safety assessment for FPSO motion response and mooring loads.According to the overall model of the SPM structures built by the finite element software ANSYS,the structural stress concentration is analyzed under the extreme conditions force three typical cases.This paper also analyzes the vibration characteristics of each stage and the power frequency response characteristics on SPM structure by doing modal analysis and harmonic response analysis,and discusses the impact of structural vibration on the safe operation for SPM.Yoke Link in SYS is the main structure which connects the SPM and FPSO.Considering the fatigue fracture problems on the connection,fatigue performance analysis is executed.Based on the S-N curve and Miner linear cumulative damage theory,some analysis on the connections in Yoke Link are calculated by using the alternating loads from Yoke Link,which is to discuss the key factors that affect the structural fatigue damage.Aiming at the occurred problems of SYS during service and the failure accidents happened in recent years,this paper expands local research and analysis to assesses the performance of SYS,and takes the real-time gesture,strain response information and vibration response information of FPSO and SPM.It also analyzes and assess the impact on the SPM structure and staff from vibration acceleration response.