Structural Strength Analysis And Optimization Design Of Truss Spar Platforms

With the exploration and development of oil and gas resources in the deep sea, the deep-sea platform has developed rapidly. Spar platform has been widely applied for its favorable stability, more effective load, satisfying safety and economy. The second generation spar, truss spar, has become one of the most competitive and potential type of platforms, since its motion cycles of various degrees of freedom are far away from the concentrated band of ocean wave under the actions of the mooring system, control of the main floating body and the heave plate, resulting in good stability.As a large and complex structure, truss spar suffers complex load combinations of wave, wind, current, mooring and gravity under the rough environment in deep sea, so it is very important to make structural strength analysis of spar and evaluate the strength and stability of the whole spar. In this paper, the integral model of truss spar is developed by APDL (ANSYS Parameter Design Language) based on ANSYS software, and the parameterized modeling platform for truss spar using visual basic is developed. Then the finite element analysis of the spar structure is performed based on the refined truss spar model corresponding to the designed platform under the load combination of wind, current, mooring and wave obtained by DNV specification and AQWA-WAVE software, respectively. The structural responses of the spar are completed under the sea states of different return periods, and evaluated according to the DNV specifications. The major structural members of truss spar are made of steel, which covers a large proportion of the total cost. Satisfying the requirements of the structural strength and stability, it is significant to reduce the structural weight and increase the effective load of spar. The spar is optimized to minimize the weight of the hard tank by combining the approximate model and genetic algorithm for the complex and large-scale optimum problem.