54 / 2021-10-14 15:30:01

Nonlinear stiffness topology optimization for the bend stiffener of flexible riser

Bend stiffener; Structural nonlinearity; Topology optimization; Specified ocean load direction; Rotational symmetry assumption; Parallel computation

A bend stiffener is of significant importance to improve the safety of the flexible riser used in deep water. In conventional design, a rotational symmetry assumption is commonly employed to deal with the complex ocean load environment. However, for a specified ocean area, the load direction only varies within a certain range. Thus, the rotational symmetry design will inevitably lead to the redundant or insufficient local performance for the bend stiffener. In the present study, a topology optimization considering the material and geometry nonlinearity is developed to maximize the structural bending stiffness. The Dirichlet boundary condition is adopted to simulate the ocean load, and reaction force at the loading end is employed to quantify the structural bending stiffness. The Heaviside projection, Helmholtz-PDE filter and fictitious strain energy method are introduced to eliminate the numerical instabilities. Moreover, to improve the efficiency of the structural nonlinear analysis and optimization, a parallel computational framework based on PETSc library is developed. In the numerical examples, considering the constant amount of the available material, comparisons between three different designs, i.e., the conventional homogenous reference design, the 2D topology optimization considering the rotational symmetry, and the 3D topology optimization without rotational symmetry are performed. The optimized results show that the designs obtained by topology optimization can significantly improve the structural bending stiffness. The 2D design with rotational symmetry gives a good but mediocre load bearing capability for any load direction, and the 3D design without rotational symmetry assumption exhibits the better stiffness performance under the specified variation scale of the ocean load.