The Research On The Ultimate Strength Assessment Method Of Ship Plates With Non-uniform Corrosion Based On The Lorentz Curve

Ships are typical thin-walled composite structures,and it is of great significance to evaluate the ultimate bearing capacity of structures for the safety evaluation of ships.The service environment of ships and offshore platforms is complex,and the thickness reduction caused by corrosion damage will reduce the ultimate bearing capacity of the structure.Many scholars usually use uniform thinning to calculate the residual strength of corroded plates,ignoring the influence of nonuniformity of corroded plates on ultimate strength,which leads to great errors in the evaluation results.In this paper,Lorentz curve and related nonuniformity coefficient are introduced to quantify the nonuniformity of corroded surface,aiming at establishing an engineering and accurate method for evaluating the ultimate strength of corroded hull plates.The main contents of this paper include:(1)According to the hull thickness test data,the statistical characteristics of corrosion amount are obtained.The data of hull thickness measurement(70 reports of platform thickness measurement)are sorted and screened,and a three-level database of corrosion is established,and the distribution law of corrosion amount of main deck and ballast water tank of jack-up platform in the same years is obtained.(2)According to the statistical information of corrosion,the nonlinear corrosion model of the structure is established.The fitting ability and application scope of existing corrosion models are compared and analyzed,and the corresponding corrosion models are established according to the variation law of average and standard deviation of corrosion quantity of main deck and ballast water tank with years.(3)Lorentz curve and the corresponding nonuniformity coefficient are used to quantify the nonuniformity of corroded plates.On the basis of determining the Lorentz curve type describing the nonuniformity of corrosion data,the variation of nonuniformity of corrosion data in different years is calculated.(4)The random corrosion plate meeting the measured corrosion law was established,and the physical significance of each non-uniformity coefficient was explored.According to the measured non-linear time-varying corrosion model,the probability characteristics of random field corrosion surface are defined,and the non-uniform corrosion plates under different corrosion years are obtained.The relevant non-uniform coefficients are calculated,and the physical meaning of each coefficient is compared and analyzed.The appropriate non-uniform parameters are selected to quantify the degree of non-uniform corrosion morphology.(5)Establish the ultimate strength evaluation method of non-uniform corrosion plate.Through the nonlinear finite element analysis of a large number of randomly corroded plates,the influence of corrosion unevenness on the reduction of ultimate strength is explored,and the evaluation formula of ultimate strength of corroded plates is established,which is compared with the evaluation methods in previous studies.In this paper,based on the hull thickness measurement data,the main deck and side shell are selected as the research objects.The distribution law of corrosion amount in the same age is analyzed.The variation law of corrosion amount mean value and standard deviation with age is studied,and the corrosion model is established.The Lorentz curve is introduced to evaluate the non-uniformity degree of the corrosion plate,and the physical meaning of the non-uniformity coefficient of the random corrosion plate is analyzed,Finally,the ultimate strength evaluation method considering the non-uniformity of corrosion plate is established.