Sabine Langer

Parallel Computation of 3-D Soil-Structure Interaction in Time Domain with a Coupled FEM/SBFEM Approach

This paper introduces a parallel algorithm for the scaled boundary finite element method (SBFEM). The application code is designed to run on clusters of computers, and it enables the analysis of large-scale soil-structure-interaction problems, where an unbounded domain has to fulfill the radiation condition for wave propagation to infinity. The main focus of the paper is on the mathematical description and numerical implementation of the SBFEM. In particular, we describe in detail the algorithm to compute the acceleration unit impulse response matrices used in the SBFEM as well as the solvers for the Riccati and Lyapunov equations. Finally, two test cases validate the new code, illustrating the numerical accuracy of the results and the parallel performances.

Large scale simulation of wave propagation in soils interacting with structures using FEM and SBFEM

This paper applies a parallel algorithm for a coupled Finite Element/Scaled Boundary Element (FEM/SBFEM)-approach to study soil-structure-interaction problems. The application code is designed to run on clusters of computers, and it enables the analysis of large-scale problems. A crucial point of the approach is that the SBFEM fulfills the radiation condition. Hence, the hybrid numerical approach is well suited for such problems where wave propagation to infinity in an unbounded domain must be considered. The main focus of the paper is to show the applicability of the numerical implementation on large scale problems. First the coupled FEM/SBFEM approach is validated by comparing the numerical results with a semi-analytical solution for a settlement problem. Then the implemented algorithm is applied to study the dynamical behavior of founded wind energy plants under time dependent loading.

Topology Optimization of 3D Elastic Structures Using Boundary Elements

A numerical approach for the topological optimization of 3D linear elastic problems using boundary elements and the topological derivative is presented in this work. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Identification of Material Parameters for the Simulation of Acoustic Absorption of Fouled Sintered Fiber Felts

As a reaction to the increasing noise pollution, caused by the expansion of airports close to residential areas, porous trailing edges are investigated to reduce the aeroacoustic noise produced by flow around the airframe. Besides mechanical and acoustical investigations of porous materials, the fouling behavior of promising materials is an important aspect to estimate the performance in long-term use. For this study, two sintered fiber felts were selected for a long-term fouling experiment where the development of the flow resistivity and accumulation of dirt was observed. Based on 3D structural characterizations obtained from X-ray tomography of the initial materials, acoustic models (Biot and Johnson–Champoux–Allard) in the frame of the transfer matrix method were applied to the sintered fiber felts. Flow resistivity measurements and the measurements of the absorption coefficient in an impedance tube are the basis for a fouling model for sintered fiber felts. The contribution will conclude with recommendations concerning the modeling of pollution processes of porous materials.

MODELING OF FLOW-INDUCED SOUND IN POROELASTIC MATERIALS

The use of poroelastic materials on the surfaces under flows–part of the Collaborative Research SFB 880, “Fundamentals of high-lift for future commercial aircrafts”– is investigated. Besides the positive influence that porous surfaces have on aeroacoustics, a poroelastic layer may also help reduce the impact sound. An approach to model the interface between a flow and a poroelastic material, which tracks the propagation of flow-induced structure-borne sound into the poroelastic medium, is illustrated. Firstly, the overall simulation approach and the selected material model is presented, followed by an explanation of the coupling conditions for the interface between the fluid and the poroelastic material. To illustrate the plausibility of this coupling, flow-induced structure-borne sound entry into an airfoil-like structure, layered with a porous material, is examined. The analysis is carried out on a finite element method-based in-house code. MODELING The Navier-Stokes equations constitute the basic equations of fluid mechanics and state conservation of mass, momentum and energy. The viscosity is taken into account by the Stokes friction approach, which is a generalization of Newton’s first law of motion. Assuming an incompressible fluid, the Navier-Stokes equations simplify to ∂vi ∂xi =0 (1)

An Approach to Use the Structural Intensity for Acoustical Topology Optimization

The aim of vibroacoustic engineering is to find a design of a part which is optimal in strength, weight and acoustics. To find the optimal construction shape in early design stages, topology optimization is the most widely used tool. Based on numerically calculated local mechanical values, the optimization method considered in this contribution decides to delete or add material in the region concerned, based on one value, e.g. stress. The aim is to find the best possible utilization of the material’s mechanical strength, regarding the component weight. This approach works very well for static problems.

Innovationsschübe und die Verantwortung der Lehrenden in den Ingenieurwissenschaften

Die Lehre an der Hochschule misst sich heute insbesondere in den MINT-Fachern (Mathematik – Informatik – Naturwissenschaft – Technik) vornehmlich an der Bildung einer moglichst hohen fachlichen Kompetenz der Studierenden. Die Hochschullehre bereitet die Studierenden darauf vor, auf neue Herausforderungen durch die Erweiterung und Weiterentwicklung bekannter Grundlagen zu reagieren. Allerdings zeigt sich, dass notwendige Innovationsschube erst durch die Beachtung vollig neuer Ideen und Visionen tatsachlich moglich werden. Dies ist insbesondere in den Ingenieurwissenschaften relevant, da Ingenieure einen grosen Anteil an der Entwicklung von Ideen zur Gestaltung unseres zukunftigen Lebens haben.

On the prediction of absorption coefficient of porous materials with Finite Elements

The absorption coefficient gives the relation between incited and reflected sound power on a surface and is a measure for the damping properties of materials. Experimentally it can be investigated by using the impedance tube for perpendicular incitation and the echo chamber in the case of a diffuse sound field as is known. To optimize the sound absorption properties of materials in the pre‐prototype stage, numerical simulation can support the design of materials. A detailed finite element simulation based on Biots Theory for poroelastic‐media is used to predict the absorption coefficient of materials with open‐pored surfaces. Prospects and limits of this strategy are discussed.