Research On Simulation Method And Fracture Properties Of Cracked Cylindrical Shell On Offshore Platform

Offshore platforms are served as the physical supporting structure for developing theocean resource nowadays. Their bearing capacity and security becomes the focus ofexperts from all over the world. In this paper, one of the important ocean components,cylindrical shell, is the research object. And two different methods are developed toanalyze and calculate the bearing capacity of cylindrical shell, providing a solid base forpredicting the overall structure characteristics of offshore platforms effectively.First of all, a series of solutions about the cylindrical shell with crack damage faraway from the edge are introduced based on the semi-membrane theory and Dugdalemodel. By derivation calculation, the matrix relationship between the additionaldisplacement and load is obtained, considering different states of the crack section, andthen the stiffness matrix of crack element is gained, providing an effective crack elementinterface for integrated calculation of the finite element method. With this matrix, manyresults are solved, including the effect of critical CTOD and CTOA of material on thecrack length and the relationship curve between the additional displacement and load ofthe crack section.Then with the similar methods, the stiffness matrixes of cylindrical shell with crackon the connection point with other strong structure are obtained, and a new crack elementcomes true. With the numerical calculation method and program compiling, therelationship between the crack extension length and load, and the relationship betweenadditional displacement and load are calculated and contracted with the results of theshells with crack far away from the edge. The relationship is analyzed afterwards.Besides, based on the large FEM soft ware ANSYS, a simulation method isdeveloped based on the critical CTOD and CTOA parameters. The dealing skill of netsand simulation method of the crack tip opening displacement, extension simulation ofcrack and loading method during the period of crack extension, are introduced. With thismethod, a simple supported cylindrical shell model is given and many results arecalculated, including the stress distribution situation during different period, CTODderivation curve and so on. The above crack elements are integrated with the ordinary cylindrical shell beamelements, to calculate the real engineering situation. In this paper, the initial stiffness ofthe cylindrical shell is solved with different crack length. And the relationship betweeninitial stiffness and crack length is analyzed. Then the initial stiffness and the extensionstiffness, introduced in an experiment, are contrasted and a method, predicting theextension stiffness with the initial stiffness is discussed. Other results including the CTODand displacement are given too and all the results are contrasted with the ANSYS results.The high efficiency and accuracy are very obvious.Finally, the limit of the adopted theory in this paper is discussed and some dealingskills in the large FEM soft ware and compiling methods in the new crack elements areanalyzed again, to find some deficits of the above research and results and propose theresearch to be done in the future.