Reduction of Engine Sound Radiation through Optimization of Added Ribs

With stricter pass-by norms, reducing engine noise radiation is becoming more important. Adding ribs to improve stiffness is one efficient approach to achieve this goal. This paper performs the optimization of ribs which are added on the surface of an inline six-cylinder engine block. The ribs are placed orthogonally. For the optimization, optimization variables are set up to update the dimensions of the ribs in each iteration. The limits of the size changes are defined by the optimization constraints. The overall sound power radiated from the engine block surface between 500Hz and 1450Hz is chosen as the optimization objective. In each iteration, the radiated sound power is obtained by numerical analysis of a fully coupled structural-acoustic model, while the FEM (finite element method) is adopted for calculating the structural response and BEM (boundary element method) is used to compute the noise radiation from the engine block surface. To achieve the optimized design, Genetic Algorithm (GA) is taken as the optimization algorithm in the process. It is found that the optimization process successfully converges and gives the optimized design. The overall radiated sound power from the optimized design is lower than the initial rib design and bare engine block with no added ribs. The overall sound power value can be reduced by more than 3dB. It is also observed that adding ribs might have negative effect for noise reduction, which further demonstrates the necessity and value of optimization for the ribs.