Abstract
Basic design principle of reducing radiation noise from engine covers was developed. A thin air-film placed between inner and outer cover shells can give damping to the engine cover at its resonant frequencies. The air-film motion along the shells is much greater than the lateral motion of the shells. The damping can be best utilized by adjusting the combination of the resonant frequencies and the mode shapes of the inner and outer shells. The effect was analyzed with FEM and shaker test. Further, a prototype was built and was proved its performance in engine test bench.
