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SUMMARYThe impact of flow on a structure plays a crucial part when considering structural behavior, for example, in aviation. As structural vibrations (also denominated as structural sound) propagate within a structure, sound radiation is a likely consequence. To reduce the emission of noise, the use of poroelastic material is investigated. The approach consists in applying a poroelastic layer on the surface submitted to flow, as such utilizing the damping properties of poroelastic material.To predict flow-induced sound, a computational model has been developed to account for (1) flow-induced sound immission into a structure; (2) sound propagation; and (3) possible resulting sound radiation. Consistent formulation of the interactions between the components-that is, flow, poroelastic material, elastic structure, and acoustic fluid-allows to apply different simulation techniques for each component and thus to exploit each method's advantages. The key aspect of this work is the formulation of the interface conditions to couple flow with poroelastic material. The proposed and implemented coupling conditions are studied. The given example shows a possible application and demonstrates the effectiveness of poroelastic material to reduce flow-induced sound emission.

Inverse scattering acoustics find practical applications in the detection and imaging of objects embedded in continuous media as well as in finding the optimum geometric configuration of an object to produce a given radiation performance. This work introduces a boundary element method (BEM) approach for the solution of acoustic identification and optimization problems via a topological-shape sensitivity method. The devised optimization tool takes advantage of the inherent characteristics of BEM to effectively solve the forward and adjoint acoustic problems arising in the topological derivative formulation and to deal with infinite domains. The objectives for the identification and optimization problems are to achieve a prescribed sound pressure at a given region of the problem domain. The locus giving extreme values for the topological derivative indicates the optimum positions for the placement of sound-hard scatterers in order to minimize the cost function. The proposed implementation has the ability to deal with initially empty design spaces as well as with design spaces containing pre-existent scatterers. The capabilities of the method are demonstrated by solving a number of identification and optimization problems.

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To model flow-induced structural vibrations, an interface to couple fluid flow and poroelastic material in a finite element formulation has been developed. One parameter of this interface condition is the slip rate coefficient, resulting from the socalled Beavers-Joseph-Saffman condition. This condition states that the jump in tangential velocity at a fluid flow -porous interface is proportional to the shear stress. Up to now no a priori determination of this parameter exists, and the known parameter range has been deducted from measurements, i. e., in our case from the results of the pore-resolving simulations.When modeling realistic problems assuming incompressible fluids, vectorial flow velocity and scalar pressure interact with the poroelastic material. As the slip rate coefficient only influences the tangential contributions, its overall influence is not clear. In this work, the sensitivity of the slip rate coefficient regarding the interface's coupling conditions is evaluated.