The engine valve cover is known to be major contributor to powertrain noise due to its large surface area and relatively small thickness. Thus, the acoustic analysis of the valve cover has become one of the key steps in the design process. The present paper describes an acoustic infinite element approach to model the sound radiation of the valve cover.
The valve cover bolted to the engine block behaves like a vibrating membrane in an acoustic medium of infinite extent. Typically, the effect of the infinite medium is modeled using either the boundary element method (BEM), or by specifying an equivalent boundary impedance on the terminating surface of an acoustic finite element mesh (NRBC). In this paper, a third method is introduced, wherein the boundary impedances are replaced by acoustic infinite elements. The methodology is presented using two different models. In the first model, a cover with a geometrically simple shape is analyzed. Due to the simplicity of the shape, the acoustic infinite elements may be coupled directly to the cover structural finite element model, without the need for an intermediate acoustic finite element domain. The results from this model are consistent with those obtained earlier for the same model using acoustic finite elements and an impedance condition. However, the use of acoustic infinite elements has proven to be significantly more efficient, both in terms of meshing effort and computational cost.
Next, a fairly complicated cover assembly is modeled using a combination of acoustic finite and infinite elements. Due to the complex features of the cover, a small volume of acoustic finite elements is constructed so as to encompass the cover, and the infinite element mesh is constructed on the terminating surface of this finite element region. The results from this model have been compared with experimental measurements conducted at various engine operating conditions, and satisfactory correlations have been observed.
Moreover, the use of acoustic infinite elements and a simple Python script enables the visualization of acoustic results in the far field. This allows the analyst to mesh the acoustic domain only as much as is required to obtain accurate results, thereby further reducing the cost of the analysis.
On the whole, the use of acoustic infinite elements proves to be an accurate and efficient technique for modeling the sound radiation from realistic structures.