Shape optimization of engine structures for low noise
This thesis describes how the overall noise of an engine design can be predicted using the finite element method together with a time integration technique for the prediction of the dynamic response. A novel method is presented which incorporates the A-weighting and radiation efficiency in the force such that the overall noise level can be predicted directly in the time domain. This method of noise prediction has been used, in conjunction with an automatic procedure for changing the surface boundary profile of an engine crankcase, to assess the overall noise level of a large number of possible shapes. A simple optimization algorithm has also been written to vary the block shape to produce the best design for low noise within practical constraints. Application of the above methods on a simple engine model have provided an experimental noise reduction of 5dB. It is shown that the weight of the engine is very little affected by quite substantial changes in crankcase shape.