Otto von Estorff

Computational Model to Investigate the Sound Radiation from Rolling Tires5

Abstract Tire/road noise is one of the most urgent problems in traffic noise abatement. Therefore, to facilitate the design process of low noise tire/road systems, the development of appropriate computational tools, accounting for the most relevant effects of the noise generation and radiation, seems essential. However, until now no physically based and validated models exist that can be used to determine the sound radiation of rolling vehicle tires within the relevant frequency range and with reasonable accuracy. The numerical model presented here is based on a simulation process that may be split into several analysis steps: computation of the nonlinear stationary rolling process, analysis of the tire dynamics caused by the road roughness, and computation of the sound radiation. This contribution is concerned with the latter part of the analysis procedure. For the sound radiation analysis, the vibrations on the tire surface are extracted from a preceding structural analysis and used as boundary conditio...

Efficient acoustic calculations by the BEM and frequency interpolated transfer functions

Abstract Following the demand for more economic and faster algorithms in computational acoustics, a new procedure is developed, which allows the calculation of frequency dependent acoustic transfer functions in a very efficient way. It is based on an indirect boundary element method which is combined with a special source simulation technique. The combination allows a rather accurate and systematic approximation of acoustical results in major parts of the considered frequency range. This leads to a significant reduction of the computer time needed to calculate complete frequency spectra. Two basic examples are shown which demonstrate how the new approach can be used. The procedure turns out to be computationally very powerful and it seems to be a very promising step towards a more efficient calculation of complex sound radiation problems.

The significance of parameter uncertainties for the prediction of offshore pile driving noise

Due to the construction of offshore wind farms and its potential effect on marine wildlife, the numerical prediction of pile driving noise over long ranges has recently gained importance. In this contribution, a coupled finite element/wavenumber integration model for noise prediction is presented and validated by measurements. The ocean environment, especially the sea bottom, can only be characterized with limited accuracy in terms of input parameters for the numerical model at hand. Therefore the effect of these parameter uncertainties on the prediction of sound pressure levels (SPLs) in the water column is investigated by a probabilistic approach. In fact, a variation of the bottom material parameters by means of Monte-Carlo simulations shows significant effects on the predicted SPLs. A sensitivity analysis of the model with respect to the single quantities is performed, as well as a global variation. Based on the latter, the probability distribution of the SPLs at an exemplary receiver position is evaluated and compared to measurements. The aim of this procedure is to develop a model to reliably predict an interval for the SPLs, by quantifying the degree of uncertainty of the SPLs with the MC simulations.

Efficient Infinite Elements based on Jacobi Polynomials

In this contribution an optimized version of the so–called mapped wave envelope elements, also known as Astley–Leis elements, is presented and its practical usability is assessed. The elements are based on Jacobi polynomials in the direction of radiation, which leads to a low conditioning of the resulting system matrices and to a superior performance in conjunction with iterative solvers. This is shown for practically relevant simulations in the frequency as well as in the time domain.

COMPILE—A Generic Benchmark Case for Predictions of Marine Pile-Driving Noise

The prediction of underwater noise emissions from impact pile driving during near-shore and offshore construction activities and its potential effect on the marine environment has been a major field of research for several years. A number of different modeling approaches have been suggested recently to predict the radiated sound pressure at different distances and depths from a driven pile. As there are no closed-form analytical solutions for this complex class of problems and for a lack of publicly available measurement data, the need for a benchmark case arises to compare the different approaches. Such a benchmark case was set up by the Institute of Modelling and Computation, Hamburg University of Technology (Hamburg, Germany) and the Organisation for Applied Scientific Research (TNO, The Hague, The Netherlands). Research groups from all over the world, who are involved in modeling sound emissions from offshore pile driving, were invited to contribute to the first so-called COMPILE (a portmanteau combining computation, comparison, and pile) workshop in Hamburg in June 2014. In this paper, the benchmark case is presented, alongside an overview of the seven models and the associated results contributed by the research groups from six different countries. The modeling results from the workshop are discussed, exhibiting a remarkable consistency in the provided levels out to several tens of kilometers. Additionally, possible future benchmark case extensions are proposed.

AN EFFICIENT SMOOTHED POINT INTERPOLATION METHOD FOR DYNAMIC ANALYSES

In this work, a new procedure to compute the mass matrix in the smoothed point interpolation method is discussed. Therefore, the smoothed subdomains are employed to evaluate the mass matrix, which have already been computed for the construction of the stiffness matrix, rendering a more efficient methodology. The procedure is discussed, taking into account the edge-based, cell-based, and node-based smoothed point interpolation methods, as well as different T-schemes for the construction of the support domain of the approximating shape function, which is here formulated based on the radial point interpolation method. Numerical results of different dynamic analyses are presented, illustrating the potentialities of the proposed methodology.

DIRECT COUPLING OF EFGM-FEM AND EFGM-BEM FOR DYNAMIC SOIL-STRUCTURE INTERACTIONS

A direct approach of coupling the element-free Galerkin method (EFGM) to both the finite element method (FEM) and the boundary element method (BEM) is applied to study dynamic soil-structure interactions. The structure and the soil body are assumed to be two-dimensional systems and discretized by EFG nodes, while the boundary of the soil region is modeled either by FEM or BEM to impose the boundary conditions in an easy way. Essential parameters in the EFG domain are chosen in a way where stable and reliable results at a relatively low cost are obtained. The accuracy and efficiency of the two new methodologies are compared to those of the conventional mesh-based approaches.

On the numerical investigation of sound transmission through double-walled structures with membrane-type acoustic metamaterials

Acoustic metamaterials appear to be of great help in the design of reliable and effective noise reduction measures in the low frequency range. The current contribution is concerned with the modeling of a low-frequency noise shield, based on a double wall arrangement, which includes membrane-type acoustic metamaterials (MAMs), considered as the most promising approach when it comes especially to the tonal noise at frequencies below 300 Hz. MAMs consist of small-sized membranes loaded with a mass. Due to their robustness and relatively simple production, MAMs have been proven to decrease the sound transmission in frequency ranges, for which poro-elastic materials have a rather negligible effect. A simulation model of a double wall panel, whose acoustic cavity is furnished with layers of metamaterials, has been developed and the sound transmission loss (STL) through the structure was calculated, using the finite element method. In order to validate the modelling approach, the STL estimation from the finite element analysis was compared to experimental measurements. The achieved results indicate a noise-decreasing possibility in tunable narrow bands as well as a broadband noise reduction for frequencies less than 300 Hz without significantly adding to the panel mass.

Empirical estimation of peak pressure level from sound exposure level. Part II: Offshore impact pile driving noise

Numerical models of underwater sound propagation predict the energy of impulsive signals and its decay with range with a better accuracy than the peak pressure. A semi-empirical formula is suggested to predict the peak pressure of man-made impulsive signals based on numerical predictions of their energy. The approach discussed by Galindo-Romero, Lippert, and Gavrilov [J. Acoust. Soc. Am. 138, in press (2015)] for airgun signals is modified to predict the peak pressure from offshore pile driving, which accounts for impact and pile parameters. It is shown that using the modified empirical formula provides more accurate predictions of the peak pressure than direct numerical simulations of the signal waveform.

Coupled Numerical Methods in Engineering Analysis

1 Structural Engineering Department, Federal University of Juiz de Fora, Juiz de Fora, MG 36036-330, Brazil 2 Institute of Modeling and Computation, Hamburg University of Technology, 21073 Hamburg, Germany 3 Department of Mechanics, Slovak Academy of Sciences, 845 03 Bratislava, Slovakia 4 CICC—Research Center in Construction Sciences, Department of Civil Engineering, University of Coimbra, 3030-788 Coimbra, Portugal