Research On Longitudinal Ultimate Strength Of Trimaran

The trimaran have following features: high speed, high sea keeping ability, good overall performance, and strong vitality. But as they are running at high speed, the endured slamming load is big, and the weight must be strictly limited .In order to reduce the weight while meet the strength requirement, main structures are usually made of aluminum alloy or high-strength steel to decrease the scantling of the structural member. So the trimaran have low strength margin, when sailing at heavy sea condition or high speed, the structure response appears highly nonlinear, and easier to get structural buckling than normal vessel. In this case,it is essential to evaluate the longitudinal ultimate strength .The main contents of this thesis are:(1) Summarize failure mode at longitude compressed buckling of plants and stiffened plant element. Using the analytic calculation,formulas of classification societies rules,and NFEM method to calculate and compare the ultimate strength of the stiffened plate elements in all failure modes. Verify the non-linear FEM method of ABAQUS, and make preparation for calculating the ultimate strength of grillage structure and hull girder.(2)Point out the phenomena of longitudinal multi-span buckling existed in long span hull deck , while SMITH method has its own limitations as it only considers the longi-structure buckling between ring frames. Analyse stress-strain curve of multi-span buckling plated grillage, compare it with stiffened plant element between ring frames. Discuss the applicability of SMITH method, issue the stability calculation method of long-span plated grillage in the condition of multi-span buckling, and suggest the optimize design. At last calculate and estimate the ultimate strength of trimaran main deck in engine room area.(3)Analyse ultimate strength of trimaran with SMITH method, compartment NFEM ,hull NFEM, then compare with the test result. Estimate the ultimate strength of trimaran under longitudinal bending, analyse the characteristic of ultimate strength of trimaran and the effect of the side hull. Finally provide the technical support of trimaran design.The thesis has following creative points:(1)It has analyzed and compared the calculation methods for ultimate strength of stiffened plate element , grillage structure and hull structure in all aspects.(2)Point out stability calculation method of long-span plated grillage and suggest the optimize design. Study the stress-strain curve under multi-span buckling of longitudinal regarding limitations of SMITH method, and apply it into trimaran grillage structure design and estimation of ultimate strength.(3)Use the hull NFEM under multi-bulkhead load to estimate the trimaran ultimate strength. It realize the external load distribution and actual carrying capacity simulate in the same model.Then direct gains the weakness point and ultimate strength.This method overcomes the limitation of SMITH method and compartment NFEM,those methods would divide the load and ultimate strength into two steps and make the calculation and estimation separately.(4)For the first time in China estimate the ultimate strength of trimaran under longitudinal bending, get the effect of side hull towards ultimate strength of hull girder, point out the speciality of trimaran ultimate strength comparing with common vessel, provide the technical support of trimaran design.