BEM Methods For acoustic and vibroacoustic problems in LSDYNA

The present work concerns the new capability of LS-DYNA in solving acoustic and vibroacoustic problems in time domain and frequency domain, using the following LSDYNA Cards: *MAT_ACOUSTIC *FREQUENCY_DOMAIN_ACOUSTIC_BEM *FREQUENCY_DOMAIN_ACOUSTIC_FEM *FREQUENCY_DOMAIN_SSD In vibroacoustic problems, which are assumed to be weak acoustic-structure interactions, the transient structural response is computed first. By applying the FFT, it is transformed into a frequency response. The obtained result is taken as boundary condition for the acoustic part of the vibro acoustic problem. Consequently, the radiated noise at any point into space can be calculated. The new developed LS-DYNA keyword is based on boundary element method (BEM) in which only the surface of the acoustic domain needs to be discretized. Besides BEM that solves the Helmholtz equation as a linear system, the new card allows, also, to use two other approximate Rayleigh and Kirchhoff methods. Both methods do not require a system of equations to be assembled and solved. Consequently, they are faster than BEM. Rayleigh method assumes that the radiating structure is a plane surface clamped into an infinite rigid plane. In Kirchhoff method, BEM is coupled to FEM used for acoustics in LS-DYNA by prescribing non reflecting boundary condition. In this case, at least one fluid layer needs to be merged to the vibrating structure.