Pipeline Sress Aalysis Based On Numerical Simulation Of FPSO Deformation

The general FPSO is composed of many systems,the pipeline system is one of the key systems connecting the main engine,auxiliary engine and related equipments,and the stress analysis of the pipeline is an important embodiment of the safety performance of the ship;FPSO operates in waves all year round,and is subjected to external loads on it by environmental factors such as the gravity of its own cargo,resulting in deformation of the hull.Therefore,combined with the influence of hull deformation,it is more meaningful to analyze the stress of the pipeline.At present,the engineering parameter method(also known as the empirical formula method)is commonly used in the industry to analyze the stress of the pipeline,that is,the coefficient of thermal expansion calculated by superimposing the maximum design temperature superimposed on linear interpolation to simulate the deformation of the hull and then carry out the pipeline stress analysis.This method is easy to calculate,but it has the disadvantages of insufficient accuracy and one-dimensional deformation data.In view of this situation,the finite element is used to calculate the hull deformation,the three-dimensional displacement value after the joint deformation in the finite element model is extracted,and the displacement value is integrated into the Caesar Ⅱ software pipeline model for pipeline stress analysis.This is the pipe stress analysis under the numerical simulation method.Considering the differences between these two methods,the pipeline stress analysis results calculated by these two methods are compared and discussed in engineering,the main contents are as follows:(1)Use Patran finite element software to establish a 1:1 finite element model of the hull,determine the number of cabins for simulation calculation of the hull model according to the length of the pipeline model,and adjust and improve the model;Simulate the wave environment during the working state of the hull,sort out the loading conditions,and establish the typical working conditions that need to be calculated,that is,the full load medium vertical working condition and the ballast medium arch working condition;The middle compartment model of the hull is used to predict the hull deformation,adjust and optimize the hull model,and simplify the calculation of hull deformation analysis;(2)Extract the displacement data of hull nodes after numerical simulation deformation in Patran software.The pipe and the main deck of the hull are linked together through the pipe support,and the 3D coordinate value information of all supports is queried in the pipeline model,and the 3D coordinate value of each bracket is mapped to the nodes in the hull model,and these nodes are marked to extract the 3D displacement value of these nodes.Analyze the deformation trend of the marker node and analyze the cause of this deformation trend;(3)Establish the Caesar Ⅱ pipeline model,correspond the marked node to the bracket in the pipeline,and enter the corresponding deformation displacement value into the pipe support.Caesar Ⅱ software combined with deformation displacement values generates more than 20 working conditions,and the pipe stress results under each working condition are viewed and analyzed;(4)The pipeline stress analysis is carried out by the engineering parameter method,that is,the coefficient of temperature expansion and the coefficient of linear interpolation are superimposed together to simulate the hull deformation,and the pipeline is analyzed from the aspects of primary stress and secondary stress;(5)Finally,the two methods of calculating pipeline stress(pipeline stress analysis calculated by engineering parameter method and pipeline stress analysis calculated by numerical simulation)are compared,and the three aspects of stress profile,nodal displacement and constraint reaction force are compared and analyzed,and the causes of large differences are analyzed(such as the phenomenon of opposite directions of the support constraint reaction force),and finally the similarities and differences and advantages and disadvantages of the two are summarized,and their application in engineering;Through the analysis of the two methods of pipeline,the deformation of pipeline is broadened from one-dimensional linear to three-dimensional spatial,which broadens the application of Caesar Ⅱ in pipeline stress analysis,and can accurately analyze the degree of pipeline affected by hull deformation.By comparing the two methods of pipeline,the following main conclusions are obtained: the engineering parameter method is applied to the scheme estimation of the early design of FPSO pipeline,and the numerical simulation method is used for further pipeline mechanics analysis.