Dominik Brunner

Simulation of Elastic Scattering with a Coupled FMBE-FE Approach

In this paper scattering problems with elastic obstacles that are hit by an incident acoustic wave are discussed. Underwater acoustics mainly differs from air acoustics in the fact that a strong coupling scheme between the structural part and the acoustic domain is necessary. Such a scheme is discussed, using the fast multilevel multipole boundary element method (FMBEM) to model the exterior acoustic fluid. The structural part is modeled with the finite element method (FEM). To obtain a high flexibility, an interface to a commercial FE package is established. For a high efficiency, an iterative solver with preconditioning is applied. The numerical results are compared with an analytical solution for a model problem.

Vibroacoustic Simulation of Partly Immersed Bodies by a Coupled Fast BE‐FE Approach

Simulation of vibroacoustic behavior of submerged bodies necessitates dealing with fluid‐structure coupled problems. In case of a high density of the fluid, the feedback of the acoustic pressure onto the structure cannot be neglected and a fully coupled system must be investigated. In this work, the finite element method (FEM) is used for the structural part. The commercial finite element package ANSYS is applied for setting up the mass and stiffness matrices. The boundary element method (BEM) is well suited for simulating the sound propagation in the unbounded exterior acoustic fluid domain. Here, the fast multipole method (FMM) is applied to overcome the known bottleneck of classical BE‐methods. In the case of partly immersed bodies, Dirichlet boundary conditions on the fluid surface additionally have to be incorporated. This is done by applying a halfspace formulation. The extension of the FMM to this scenario is discussed. Iterative preconditioned solvers are employed and the numerical efficiency is d...

Coupling a Fast Boundary Element Method with a Finite Element Formulation for Fluid–Structure Interaction

Fluid–structure interaction plays a crucial role for simulating vibro–acoustic, multi–field problems. The paper starts with the fundamentals of the boundary element method for acoustics, including the Burton–Miller formulation for the solution of exterior problems. The fast multilevel–multipole algorithm is applied together with a preconditioned iterative solver yielding a quasi–linear numerical complexity. The structural part is modelled by the finite element method. Various coupling schemes are discussed depending on the influence of the feedback of the fluid onto the structure. In a first example, an expansion chamber, which is exposed to structural vibrations caused by interior pressure fluctuations, is presented. A weak coupling scheme is used for simulating the surface radiated sound. In a second example, the vibro–acoustic behavior of a totally submerged submarine–like structure is investigated. Two strong coupling formulations are compared for their numerical efficiency. The examples show, that the presented coupling algorithms are well–suited for simulating large–scale industrial applications.

FE‐Model Reduction for FE‐BE Coupling with Large Fluid‐Structure Interfaces

For the finite element method model, reduction techniques exist to represent the dynamic behavior of component substructures. Depending on the type of reduction method, the reduction basis contains constraint or attachment modes, which are computed for all structural degrees of freedom on an interface. The interface can either be defined by adjacent substructures or by coupling interfaces to other physical domains, as it is the case for FE‐BE coupled systems. A large interface thus leads to an increased size of the reduced order model and limits standard model reduction techniques to applications with small interfaces. In this work, interface reduction methods are investigated. Here, the size of the reduced order model is decreased by reducing the number of retained interface modes, while marginally increasing the reduction error. A direct reduction method based on strain‐‐energy considerations is presented. Additionally, an iterative reduction scheme is proposed which only adds a basis vector to the redu...

Simulative and experimental investigations on pressure-induced structural vibrations of a rear muffler

The periodically blown out exhaust gas of a combustion engine may excite structural vibrations of the exhaust system. In addition to the noise of the orifice, these vibrations contribute to the overall noise radiation of the exhaust system. In this work, the excitation of structural vibrations of a rear muffler via the acoustic path is investigated both in experiments and simulations. In both cases transfer functions from the acoustic pressure at the inlet to the structural deflection on the surface of the rear muffler are determined and compared to each other. For the simulation an FE-FE (finite element) coupling is applied to account for the fluid-structure interaction. To efficiently predict the fluid-structure coupled behavior, a model reduction technique for the finite element method based on the Craig-Bampton method and the Rubin method is presented. In a last step, the sound radiation is evaluated by solving the exterior acoustic problem with the fast multipole boundary element method. For this purpose, the results of the FE computation are used as boundary datum.