Holger Waubke

  • Objective:

    The boundary element method (BEM) is an often used tool for numerically solving acoustic radiation and reflection problems. Most of the time, a formulation in the frequency domain can be used, however, for short impulses  or when the acoustic simulation is coupled with a non-linear behaviour caused by structure deformation, a formulation in the time domain is necessary.

    Method:

    The boundary integral equations and the fundamental solution necessary for the BEM in the time domain are derived by inverse Fourier transformation of the corresponding formulations in the frequency domain. These equations are then discretized using the Galerkin method in the spatial dimensions and the collocation method in the time dimension. The MOT (Marching-On-in-Time) method is used to solve the resulting system of equations. The well known stability problem of the MOT-method is handled by using the Burton-Miller approach in combination with the Galerkin method in the spatial discretization and high order temporal interpolations. It is well known that these measures enhance the stability of MOT.

    Additionally it is planned to enhance the efficiency of the method by using a modified plane wave time decomposition (PWTD) algorithm.

  • Objective:

    Acoustic holography is a mathematical tool for the localization of sources in a coherent sound field.

    Method:

    Using the information of the sound pressure in one plane, the whole three-dimensional sound field is reconstructed. The sound field must be coherent and the half-space in which the sources are situated must be known.

    Application:

    Acoustic holography is used to calculate the sound field in planes parallel to the measured plane. Normally, a plane near the hull of the structure is chosen. Concentrations in the plane are assumed to be the noise source.

  • Objective:

    The beam forming method focuses an arbitrary receiver coil using time delay and amplitude manipulation, and adds to the temporal signal of the microphones or the short time Fourier transform.

    Method:

    64 microphones are collected by a microphone array with arbitrary shape. For compatibility with acoustic holography, equal spacing and a grid with 8 x 8 microphones is used.

    Application:

    Localization of sound sources on high speed trains is a typical application. The method is used to separate locations along the train and especially the height of different sound sources. Typical sound sources on high speed trains are rail-wheel contact sites and aerodynamic areas. The aerodynamic conditions occur at all heights, especially at the pantograph.

  • Objective:

    Upon first investigation, the design of new outward-curved noise barriers has an improved noise-shielding effect if absorbing material is applied. Further investigation shall prove this ability. Numeric simulations and measurements are being processed.

    Method:

    Advanced boundary element methods (BEM) in two dimensions will prove the noise-shielding ability of the sound barrier. Different curvy and straight designs are compared to each other with respect to their shielding effect in the spectrum. Measurements at existing walls are processed and compared. Measurements are conducted without a noise barrier. A simulated softening affect of the noise barrier walls is used to simulate the noise signal behind the new barriers.

    Application:

    Calma Tec has patented the designs and will offer new designs in practice.

    List of Deliverables:

    01. Traffic Noise Recording Plan. 02. Sound Data Storage, Retrieval and Spectrographic Description. 03. Descriptive Noise Statistics. 04. Pricipal Component Analysis. 05. Sound Barrier Mesh Models. 06. Simulation, Transfer Functions & Clustering. 07. Visualization. 08. Psychoacoustic Irrelevance. 09 Modulation Effects. 10. Subjective Preference Tests. 11. Conclusions

  • Objective:

    In certain measurement setups, such as the measurement of gear mechanism behavior undergoing load reversal, the fine structure of the rotation speed function within a single rotation is interesting. In these situations, measurement errors caused by irregular cog intervals or by other failures of cogwheels are disturbing and must be corrected.

    Method:

    From a reference signal, the distribution parameter of the rotation angle for each cog of the cogwheel is assigned as a cogwheel model. This cogwheel model can minimize the measurement failures caused by the cogwheel if its cog is implemented in synch with the measurement signal. If the reference signal and the measurement signal come from different measurements, the synchronicity has to be established first. The calculation of the shift between the two signals is determined by the cog index, which has the maximum correlation of the rotation angle allocation between the reference signal and the measurement signal.

    Application:

    The developed method will be used as a module in the acoustic measurement and analysis system PAK.

  • Objective:

    This project aims to develop an independent modulus for the wavelet analysis that contains a simple program interface and can be used flexibly.

    Method:

    The implementation was in C++ in the form of a wavelet analysis class and a signal queue. Features:

    • The Input/Output data format can be chosen at run time. The Input and the Output are separately configurable.
    • There are several possibilities for choosing the array and distribution of the frequency bin. The frequency bin vector can also be transferred.
    • Seven wavelets are implemented.
    • A down-sampling method can be used for the acceleration (factor: 1.2 convert frequency bins are chosen automatically).
    • Because of the disjunction in signal queue and analysis, an asynchrony Input/Output is possible.
    • Compiling an optimized numerical library can be achieved. Currently, the application of the "Intel® Signal Processing Library" (SPL) or of the "Intel® Integrated Performance Primitives" (IPP) is possible.
    • The signal queue class can be used independently of the analysis class. It also implements the down-sampling function.

    Application:

    The developed classes are used as a modulus in the acoustic measurement and analysis system PAK. The analysis class was also integrated as a signal processing atom WLLIB in STx.

  • Objective:

    The usual transformation in acoustics is the Fourier-Transformation. A fast and simple implementation is the windowed Fast Fourier Transformation. A disadvantage of the FFT is that all frequencies are equally spaced in the time frequency plane. A logarithmic spacing that allows keeps the relative resolution in the frequency plane constant is the Wavelet Transformation. This gives the possibility of a higher temporal resolution in the high frequency plane. Several types are implemented in STX and PAK.

    Method:

    A higher temporal resolution is possible, if quadratic transformations defined in the Cohen Class are used. The Windowed Pseudo Wigner Ville Distribution and a discrete version of the Choi-Williams Distribution are implemented in STX and PAK. Disadvantages of these transformations are the cross products that are reduced by smoothing in the different transformations of the Cohen class.

    Application:

    A handbook is written for or the practical use of the difficult transformations. The Handbook documents the possibilities and the limits of the transformations

  • Introduction                                                                                                                                                   

    Rumble strips are (typically periodic) grooves place at the side of the road. When a vehicle passes over a rumble strip the noise and vibration in the car should alert the driver of the imminent danger of running off the road. Thus, rumble strips have been shown to have a positive effect on traffic safety. Unfortunately, the use of rumble strips in the close vicinity of populated areas is problematic due to the increased noise burden.

    Aims

    The aim of the project LARS (LärmArme RumpelStreifen or low noise rumble strips) was to find rumble strip designs that cause less noise in the environment without significantly affecting the alerting effect inside the vehicle. For this purpose, a number of conventional designs as well as three alternative concepts were investigated: conical grooves to guide the noise under the car, pseudo-random groove spacing to reduce tonality and thus annoyance, as well as sinusoidal depth profiles which should produce mostly vibration and only little noise and which are already used in practice.

    Methods

    Two test tracks were established covering a range of different milling patterns in order to measure the effects of rumble strips for a car and a commercial vehicle running over them. Acoustic measurements using microphones and a head-and-torso-simulator were done inside the vehicle as well as in the surroundings of the track. Furthermore, the vibration of the steering wheel and the driver seat were measured. Using the acoustics measurements, synthetic rumble strip noises were produced, in order to get a wider range of possible rumble strip designs than by pure measurements.

    Perception tests with 16 listeners were performed where the annoyance of the immissions as well as the urgency and reaction times for the sounds generated in the interior were determined also using the synthetic stimuli.

    LARS was funded by the FFG (project 840515) and the ASFINAG. The project was done in cooperation with the Research Center of Railway Engineering, Traffic Economics and Ropeways, Institute of Transportation, Vienna University of Technology, and ABF Strassensanierungs GmbH.

  • Objective:

    In Cooperation with National Instruments an implementation of MPEG4 features in the software package DIADEM is planned.

    Method:

    The application of MPEG4 features to noise is proven. Now the implementation of MPEG4 features into DIADEM is planned. In preparation of the project additional features were implemented into STX. The implementation into DIADEM is projected in the future.

    Application:

    DIADEM is a database that allows for a rapid search of measurement recordings. New search indexes can be generated based on the MPEG4 features of the recordings.

  • Objective:

    The Multilevel Fast Multipole Method, when used in combination with the Boundary Element Method (BEM), is a tool to significantly speed up the simulation of large objects almost without loss in accuracy.

    Method:

    The Fast Multipole Method subdivides the Boundary Element mesh into different clusters. If two clusters are sufficiently far away from each other (i.e. they are in each other's far field), all calculations that would have to be made for every pair of nodes can be reduced to the midpoints of the clusters with almost no loss of accuracy. For clusters not in the far field, the traditional BEM has to be applied. The Multilevel Fast Multipole Method introduces different levels of clustering (clusters made out of smaller clusters) to additionally enhance computation speed.

    Application:

    The MLFFM is used for the simulation of head related transfer functions. The diagram above compares the result of a classical BEM with the MLFMM.

  • Objective:

    An important difficulty of ray-tracing and boundary element method is the fine grid, which is needed in the high frequency region.

    Method:

    By means of new alternating shape functions e.g. wavelets at the boundary it could be possible to define a grid on the boundary that is independent from the wave number.

  • Objective:

    Methods to predict the propagation of vibrations in soil are relatively undeveloped. Reasons for this include the complexity of the wave propagation in soil and the insufficient knowledge of material parameters. During this project a method was developed to simulate the propagation of vibrations that are caused by a load at the base of a tunnel.

    Method:

    When dealing with the model of a tunnel in a semi-infinite domain like soil, the boundary element method (BEM) seems to be an appropriate tool. Unfortunately it cannot be applied directly to layered orthotropic media, because of the lack of a closed form of the Greens function, which is essential for BEM. But by transforming the whole system into the Fourier domain with respect to space and time, it is possible to numerically construct an approximation for this function on a predefined grid. With this approximation the boundary integral equation, that describes the propagation of waves caused by a vibrating load at the base of a tunnel can be solved.

    Application:

    Models that can help to predict the propagation of vibrations inside soil layers are of great interest in earthquake sciences or when constructing railway lines and tunnels.

  • Introduction

    Railway vehicles passing through tight curves can produce a high pitched noise called curve squeal. Curve squeal is a very salient type of noise located in the high frequency range that can range between a tonal narrow band and a wide band noise. The reason for the tonal noise is lateral creepage on the top of the rail, which excites wheel vibration at frequencies corresponding to their modes. Wide band noise, however, is caused by wheel flanges touching the rail.

    Aims

    The project PAAB aims at investigating the effect on the perceived annoyance of such noises using in a perception test. Using the resulting perceptual characterization of curve squeal should aid in more adequately considering this type of noise in noise mapping.

    Methods

    Based on previous conventional large-scale emission measurements as well as new measurements at immission distances using a head-and-torso-simulator representative samples for curve squeal will be derived and used in a perception test. This will also be aided by using synthetic well defined curve squeal noise.

    PAAB is funded by the FFG (project 860523) and the Austrian Federal Railways (ÖBB). The project is done in cooperation with the Research Center of Railway Engineering, Traffic Economics and Ropeways, Institute of Transportation, Vienna University of Technololgy (project leader), Kirisits Engineering Consultants, and psiacoustic Umweltforschung und Engineering GmbH.

     

     

  • The project PASS, which is processed in cooperation with the IEW of the TU Vienna and psiacoustic GmbH, deals with the psychoacoustic evaluation of noise. The project is a continuation of the project RELSKG and deals with high and low noise barriers that are simulated with the 2.5 D boundary element method (BEM) assuming incoherent line sources. The comparison of the 2.5 D BEM with measurements resulted in a good agreement. Additionally measurements with rail dampers were taken into account in the psychoacoustic tests. The evaluation was done in two tests with 40 test persons. The first test determines the relative annoyance and the second the just noticeable difference in annoyance. The results ware that freight trains at the same A-level are less annoying than passenger trains and that at the same A-level the noise behind a noise barrier is a little bit more annoying than without a measure. The project started in 2013 and lasts until the end of 2014.

  • Objective:

    If measurements are possible only at the hull of a machine, a tool is needed to separate the dominating near-field components from the far-field components. This, in turn, allows the far-field levels to be estimated. The separation is often not possible using spectral methods, because both components have nearly the same frequency. Using a limited number of microphones, a modal separation is also impossible. Instead of a modal analysis, a principal component analysis is applied.

    Method:

    The narrow-band Fourier transform method is used, and a separate analysis is conducted for each frequency. The cross-power matrix spanning all microphone positions is used. The components are then calculated using the PCA. As long as the modes at the microphone positions have different relative values, PCA can be used to separate them. In an initial test, the far field is observed and the transfer function for every component from the near field to the far field is estimated. These transfer functions are assumed to be constant in time. They are used for the estimation of the overall far-field level.

    Application:

    Observation of the far-field level of machines.

  • Objective:

    Standard noise mapping software use geometrical approaches to determine insertion loss for a noise barrier. These methods are not well suited for evaluating complex geometries e.g. curved noise barriers or noise barriers with multiple refracting edges. Here, we aim at deriving frequency and source- as well as receiver-position dependent adjustments using the boundary element method. Further, the effect of absorbing layers will be investigated as a function of the geometry. Results will be incorporated into a standard noise mapping software.

    Method:

    The cross-sections of different geometries are first parameterized and discretized and then evaluated using two-dimensional boundary element simulations. The BEM code was developed at our institute. Different parameter sets are evaluated in order to derive the adjustments for the specific geometries compared to a straight noise barrier. To make the simulations more realistic, a grassland impedance model is used instead of a fully reflecting half plane. Simulations will also be evaluated using measurements from actual noise barriers.

    Noise reduction of a T-type barrier at 800 Hz

    Project partners:

    • TAS Schreiner (measurements)
    • Soundplan (implementation in sound mapping software)

    Funding:

    This project is funded from the VIF2011 call of the FFG (BMVIT, ASFINAG, ÖBB)

  • Objective:

    The Spatial Transform of Sound Fields (STSF) is an extension of the acoustic holography that enables the handling of incoherent sound sources.

    Method:

    The Karhunen Loeve Expansion or Principal Component Analysis (PCA) method is used to separate the random field recorded at different microphone positions into coherent components. Again, acoustic holography is used to transform every component from the measurement plane into a plane in arbitrary depth. If needed, the total incoherent sound field in the chosen depth can be reconstructed.

    Application:

    Localization of incoherent sound sources near the hull of the structure.

  • Objective:

    In the past a FWF project dealing with the basics of Stochastic Transformation Methods was executed at the ARI. Explicitly the Karhunen Loeve Expansion and the Transformation of a polynomial Chaos were applied in the wave number domain. The procedure is based on the assumption of Gaussian distributed variables. This assumption shall be generalized to arbitrary random variables.

    Method:

    The assumption of a wave number domain limits the model to a horizontally layered half space. This limitation shall be overcome by Wavelets kernels in the transformation instead of Fourier kernels. The aim is the possibility to calculated one sided statistical distributions for the physical parameters and arbitrary boundaries with the new method.

  • Objective:

    One of the biggest problems encountered when building numerical models for layers is the lack of exact deterministic material parameters. Therefore, stochastic models should be use. However, these models have the general drawback of overusing computer resources. This project developed a stochastic model with the ability to use a shear modulus in conjunction with a special iteration scheme allowing efficient implementation.

    Method:

    With the Karhunen Loeve Expansion (KLE), it is possible to split the stochastic shear modulus, and therefore the whole system, into a deterministic and a stochastic part. These parts can then be transformed into a linear system of equations using finite elements and Chaos Polynomial Decomposition. Combining the KLE and the Fourier Transformation in combination with Plancherel's theorem enables decoupling of the deterministic part into smaller subsystems. An iteration scheme was developed which narrows the application of "costly" routines to only these smaller deterministic subsystems, instead of the whole higher dimensional (up to a dimension of 10,000) system matrix.

    Application:

    As concerns about vibrations produced by machinery and traffic have increased in past years, models that can predict vibrations in soil became more important. However, since material parameters for soil layers cannot be measured exactly in practice, it is reasonable to use stochastic models.

  • Objective:

    Beside the Fast Multipole Method wavelet based approaches are of increasing interest for the fast calculation of large matrices.

    Method:

    The first part of the project is the implementation of the wavelet method for the compression of the data. Next step is the investigation whether wavelet and FMM approaches can be used together and whether an additional speed up is possible.

    Application:

    The aim of the project is the development of an algorithm that allows for a fast calculation of large matrices. The final aim is the possibilities to handle large acoustic problems numerically.