A New Adaptive Order FEM Approach, FEM AO, for Vibro-acoustic Problems: a Report on its Accuracy and Time Performance in Predicting Acoustic Transfer Functions for an Engine in Engine Bay Mockup

As legislation for automotive pass-by noise is becoming more stringent, the industry looks to further optimize the engine and engine bay to reach the quietest design. It is clear that engineering insight is crucial to achieve quiet solutions as early as possible in in the design process. This explains the interest in using simulations to help making the right design decisions before any prototype is made. Moreover, recently a couple of advances have been made in modeling and solver technologies for predicting engine radiated noise, not only in free condition but also in installed condition, i.e. the engine in the engine bay. For the latter, advanced methods are required to obtain results in a reasonable amount of time, thus allowing for examining multiple sound proofing design layouts. This is challenging because the models for such exterior acoustic application are rather large, as they need to represent the engine bay part of the vehicle or even the full vehicle and cover a broad frequency range up to 4 or 5 kHz (for PBN). This paper will discuss on Finite Element Method (FEM) and Boundary Element Method (BEM) acoustic technologies available to predict exterior Acoustic Transfer Functions (ATFs) for a mockup model of an engine installed in the engine bay. The focus will be on a recently developed FEM method, FEM AO (FEM Adaptive order). In a first series of models, the mockup's panels are assumed to be rigid and the acoustic treatments are represented by frequency dependent surface impedances. In a second step, the flexibility of the mockup's plywood panels is included to assess its influence on the acoustic transfer functions. For a third model, the acoustic treatment is taken into account using a poro-elastic modeling approach, to also quantify the improvements made by capturing the poro-elastic effects.