Ultimate Strength Analysis of FPSO Hull Girder Under Longitudinal Bending

Abstract

Ship and offshore structures have become the key for the development of the offshore world. Production and processing equipment can be placed on a platform, ship and/or barge structure called FPSO (floating, production, storage, and offloading units). The FPSO’s hull works like a beam and deforms in the vertical plane. In this case, weight and bouyancy are not normally distributed and wave loading. The most important aspect of FPSO structure is the materials and structural strength used in the design. The critical condition of FPSO is when the structure is under the operation so that the structure needs to be analysed for the design requirement. In the present study, the ultimate strength of FPSO hull girder under longitudinal bending moment is analysed using numerical approach. The nonlinear finite element analysis is adopted to handle the calculation. For the simple case, the one-frame space and the fully cross section of FPSO are modeled. The quadrilateral shell element of the nonlinear method is used for meshing. By performing the boundary condition with the Multi Point Constraint (MPC) is applied where the neutral axis located. The vertical bending moment is also placed at this point (MPC) and it is connected to the all nodes at both sides of the cross sections. The ultimate strength of FPSO is calculated only for intact in hogging and sagging conditions. The ultimate strength analysis is represented in terms of the moment-curvature relationship for hogging and sagging. The result obtained the nonlinear finite element analysis is compared with Smith’s method including their collapse behavior. It is found that the comparison result of the ultimate strength is about 8.9% and 10.1% in hogging and sagging condition, respectively. It is shown that the nonlinear finite element analysis is in good aggrement with the analytical solution performed by Smith’s method.