Research On Structural Strength Assessment Method Of Self-elevating Platform Based On Non-linear Loads

A Jack-up platform is an important tool for offshore development of oil and gas, and thestrength assessment method under the nonlinear environment loads is a key problem in shipand ocean engineering structure design,and it has become a research focus in this field. Inorder to consider the nonlinear environment loads and the structure dynamic effect in thegeneral quasi-static way, some study has been done in this paper.Wind, wave and current are the main ambient excitation loads for a jack-up platform inworking status. The calculation method of steady and dynamic wind load is discussed in thispaper. Some research on the interference aerodynamics of the jack-up major structuralmember has been done through wind tunnel model test and CFD numerical simulation, andthe value obtained from the rules is modified based on the gained results. Further the dynamicwind load is numerically simulated using Daveport spectrum. The nonlinear wave loads andcurrent loads are calculated based on the Airy wave and Stokes wave theory. According to theliner wave theory, the PM spectrum is utilized to simulate numerically the random wave.Consequently, the calculation method of environment loads considering the combined effectof wind, wave and current is obtained.On the basis of quasi-static means, transient response analysis method is applied to studythe dynamic response of the jack-up platform in the regular, irregular wave and the jointaction of wind and wave condition in this paper and a strength assessment method with theinclusion of the jack-up dynamic effect revision is presented. The Webull distribution and thethree-dimensional potential theory are used to forecast the jack-up platform random responseextreme when it is in in-place and transit condition.Based on the fatigue spectrum analysis of the jack up platform, dynamic analysis isapplied to modify the stress response transit function, and then the fatigue accumulativedamage results with the inclusion of dynamic effect is gained. Rain-flow counting method isapplied to statistic fatigue accumulative damage results considering nonlinear loads anddynamic effects in time domain. In order to study the effect of dynamic wind loads on theresults of fatigue accumulative damage, time domain fatigue analysis in the combination ofthe wind and wave is studied, Then It summarized some probably ways which can be appliedto the engineering calculation.