Research On Reliability Analysis Of LNG Storage Tank Under Earthquakeground Motion

With the progress of science and technology,environmental protection has aroused more and more attention,LNG(Liquid natural gas)is widely used.Therefore,the study of structural safety for LNG storage tank has an obvious social significance.the study about structural security for the liquefied natural gas storage tanks is practical significant.LNG storage tank structural failure under the action of earthquakes would contribute to disastrous consequences.At present,domestic research on structural strength related in large LNG storage tank under seismic wave focus responds analysis to the significant structure using the deterministic method.However,the variation in load and resistance always have strong randomness.In view of it,an uncertain approach to research on problem about structural strength of LNG storage tank under seismic wave.The concept of structural reliability is used to characterize uncertainty of structural strength in this dissertation.Reliability defined as the probability for the structures to fulfill the specified function under the specified time and conditions is a measure which is used to assess the reliability of the structure.This dissertation provides the following researches in order to calculate the large LNG storage tank reliability under seismic action.Contents are as follows:(1)Based on finite element method using transient dynamics method to calculate structural response,and then probability distribution model of structural responses of stress are obtained.Research contains: the theoretical formula of additional quality standard which is used to characterize the liquid-solid coupling effect in the dynamic response is deduced,the natural vibration characteristics of the storage tanks is analyzed.(2)A computation method for the structural reliability of large LNG storage tank under seismic wave are presented based on explicit performance function.A tutorial is given upon this computation method by program compilation in this dissertation,as well as the related result andanalysis.(3)According to the characteristics that the structure response of LNG reservoir tank is complicated by high degree nonlinear,a calculation method to approximate expression the complex relationship between stochastic parameters and system response is given based on Stochastic Response Surface Method in this dissertation.Thus the geometric method is used to solve the structural reliability.The complex relationship is transformed to the function of random variables by Hermite polynomial expansion.Thereby,limit state equation is established which is used to obtain the reliability corresponding to the structural failure criteria.(4)Comparison the reliability calculation method which is based on explicit function of LNG tank structure with the reliability calculation method which is based on implicit function of LNG tank structure,discover that stochastic response surface method has the advantage of high precision and small number of iterations.