NONLINEAR STIFFNESS TOPOLOGY OPTIMIZATION FOR THE BEND STIFFENER OF FLEXIBLE RISER

The bend stiffener, as the key over-bending protection accessory, is of significant importance to improve the safety of the flexible riser used in deep water. At present, the size optimization method is mainly used in the structural design of the bend stiffener. However, compared with the topology optimization, the design freedom provided by this method is limited, and it lacks capacities in sufficiently improving the mechanical performance and finding the novel configurations of the bend stiffener. In the present study, under Dirichlet boundary conditions, a topology optimization method considering the material and geometric nonlinearity is developed to maximize the structural stiffness of the bend stiffener. The Helmholtz-PDE filter and Heaviside projection are introduced to eliminate the numerical issues caused by the checkerboard pattern and the gray element phenomenon, respectively. The symmetry operator is employed to enhance the load bearing capability under the reciprocating ocean wave load and improve the manufacturability of the bend stiffener. Making use of the adjoint method, a sensitivity analysis is performed to enable a gradient-based algorithm for solving the optimization problems. Simultaneously, a parallel computational framework based on PETSc library is also utilized to improve the efficiency of the structural analysis and optimization. In the numerical examples, with the constant material volume fraction, 2D and 3D optimizations for the bend stiffener are performed to improve the stiffness of the bend stiffener, respectively. Based on that, the load carrying capacity of the two optimization results under different load directions are compared. The numerical examples show that, compared to the 2D optimized result, the 3D optimization can significantly improve the stiffness of the bend stiffener in most loading directions. The present 3D nonlinear topology optimization method provides the new theorical model and implementation technology for the high-performance bend stiffener with the severe water environment in the deep ocean.