This paper proposes the use of a traction boundary element method (TBEM) to evaluate 3D wave propagation in unbounded elastic media containing cracks whose geometry does not change along one direction. The proposed formulation is developed in the frequency domain and handles the thin-body difficulty presented by the classical boundary element method (BEM). The empty crack may have any geometry and orientation and may even exhibit null thickness. Implementing this model yields hypersingular integrals, which are evaluated here analytically, thereby surmounting one of the drawbacks of this formulation. The TBEM formulation enables the crack to be modelled as a single line, allowing the computation of displacement jumps in the opposing sides of the crack. Furthermore, if this formulation is combined with the classical BEM formulation the displacements in the opposing sides of the crack can be computed by modelling the crack as a closed empty thin body.

An important challenge for acoustic engineers in room acoustics design is related to the acoustic performance of multi-purpose auditoriums, which are typically designed to suit several performance requirements. With this intent, the analysis of several scenarios is usually performed individually, and then an acceptable solution, that may be adapted to several situations, is selected. One way of providing a more appropriate acoustic performance for each function of the auditorium is using variable sound absorption techniques to control reverberation and other relevant acoustic phenomena associated to sound perception. In this paper, the acoustic behavior of a perforated system that may be suitable for achieving a variable acoustic solution for room acoustic design is addressed. In the design of a cost-effective solution, the surface appearance is kept unchanged, while variable acoustic behavior is achieved either by closing the holes in the back face of the perforated panel or by placing a porous material in varying positions inside the backing cavity, thus accomplishing different acoustic requirements within a multipurpose auditorium. An analytical approach, based on the transfer matrix method is employed for preliminary acoustic sound absorption assessment provided by the system and to develop optimized solutions. Diffuse sound absorption is then computed and used to simulate, by the ray-tracing method, the acoustic behavior of a multipurpose auditorium to demonstrate efficient acoustic performance for different types of use.

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