Mesh Coarsening and Other Tools for Effective Fe and Be in Acoustics

The types of F5 and BE methods which can be used for acoustics and uid-structure interaction are reviewed, together with the types of model for which they can be applied, topologies and other features.The nature of the uid-structure coupling is discussed, with its implications for the modelling and analysis procedures.Fine structural FE meshes, with many nodes and elements, are often available, or may be required for non-acoustic reasons.The mesh of the acoustic mode] can often be coarser, in order to give feasible calculation times, but with acceptable accuracy.and a compatible structural model may be used, based on a modal description of structural behaviour.Details such as ribs may not be signi cant in terms of acoustic radiation and may be removed, and other mesh cleaning may be necessary.Procedures to be used in carrying-out the 'mmh coarsening' to produce the simpli ed and coarser acoustic mesh are disaussed and illustrated. INTRODUCTI ONThis paper is concerned with some of the practical issues which can arise in carrying-out vibro-acoustic modelling ( uid-structure interaction) using nite element (FE) and boundary element (BE) methods, and the associated techniques and modelling strategies.The focus is on the data handling which can be required for 'industrial-scale' applicationsthat is to say, applications where the model size re ects the combination of frequency range and structural dimensions which can be found in realistic applications, in the automotive, marine, aerospace and other industries.Firstly, the types of analysis and the assodated BE/FE methods are reviewed, and then some of the practical techniques are described, in particular related to mesh manipulations and coupling.' REMARKS 0N FINITE ELEMENT AND BOUNDARY ELEMENT VlBRO-ACOUSTICS2.1 Physical Phenomena FE and BE acoustics use numerical models in which the wave equation in a continuum is described by the behaviour on a diScrete mesh.The solution can be in the frequency or the time domain (the former being the most used, until now) and is usually assumed to be linear. Frequency RangeThe frequency range which can be modelled accurately is typically dependent on the mesh density, since, to avoid excessive errors in characterising the acoustic wave behaviour (3 sort of spatial aliasing') one needs of the order of six linear elements per wavelength.For a given mesh and a given uid, this provides an upper frequency at which the 'roll-o of accuracy becomes unacceptable.Some other details of the mesh may require modelling with greater re nement, depending on the BE/FE method, which will be remarked later,