A combined shape and topology optimization algorithm based on isogeometric boundary element method for 3D acoustics is developed in this study. The key treatment involves using adjoint variable method in shape sensitivity analysis with respect to non-uniform rational basis splines control points, and in topology sensitivity analysis with respect to the artificial densities of sound absorption material. OpenMP tool in Fortran code is adopted to improve the efficiency of analysis. To consider the features and efficiencies of the two types of optimization methods, this study adopts a combined iteration scheme for the optimization process to investigate the simultaneous change of geometry shape and distribution of material to achieve better noise control. Numerical examples, such as sound barrier, simple tank, and BeTSSi submarine, are performed to validate the advantage of combined optimization in noise reduction, and to demonstrate the potential of the proposed method for engineering problems.

Combined shape and topology optimization; isogeometric boundary element method; shape sensitivity analysis; topology sensitivity analysis; adjoint variable method; sound absorption material