Holger Waubke

  • Randelementemethode im Zeitbereich

    Ziel

    Die Randelemente-Methode (BEM) wird oft zur Simulation von akustischen Abstrahl- und Reflektionsproblemen benutzt. Im Allgemeinen wird eine Formulierung im Frequenzbereich verwendet, wenn jedoch kurze Impulsantworten oder eine Kopplung mit nichtlinearem Strukturverhalten in Interesse sind, ist eine Formulierung im Zeitbereich zielführender.

    Methode:

    Die für die BEM notwendigen Randintegralgleichungen und Fundamentallösungen werden mittels inverser Fourier-Transformation der äquivalenten Formulierungen im Frequenzbereich ermittelt. Diese Gleichungen werden dann mittels Galerkin-Methode im Ortsbereich und Kollokation im Zeitbereich diskretisiert. Die MOT (Marching-On-in-Time) Methode wird verwendet um das durch die Diskretisierung erhaltene lineare Gleichungssystem zu lösen. Die bekannten Stabilitätsprobleme der MOT-Methode werden mittels einer Burton-Miller Formulierung im Ortsbereich und höhere Interpolationsordnung im Zeitbereich behandelt.

    Zusätzlich ist geplant, die Effizienz des Codes mittels eines modifizierten Plane-Wave-Time-Decomposition Algorithmus zur erhöhen.

  • RailVib - Vibrationen von Eisenbahntunnels

    Beschreibung

    Eisenbahntunnel vermeiden direkte akustische Beeinträchtigungen durch den Bahnverkehr. Schwingungen aus Tunneln breiten sich jedoch im Boden aus und führen zu Störungen durch wahrgenommene niedrigfrequente Vibrationen.

    Ziel dieses Projektes ist es, ein mathematisches Modell zu entwickeln und zu implementieren, das eine bewegte schwingende Last berücksichtigt. Außerdem wird der umgebende Boden als anisotropes Material modelliert, das aus beliebig orientierten Schichten besteht.

     

    Methoden

    Die Ausbreitung der Vibrationen im Tunnelinneren werden mittels einer finiten Elemente Methode (FEM) berechnet, in der auch die "Superstruktur" des Tunnels und der Gleisanlagen berücksichtigt werden können. Schwingungen außerhalb des Tunnels, im Erdreich, werden durch die Randelementemethode (boundary element method (BEM)) modelliert. Für ein detailiertes Model des ganzen Systems müssen beide Ansätze miteinander gekoppelt werden.

  • Acoustic Holography

    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.

  • Beam Forming

    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.

  • Calm Tracks & Routes

    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

  • Correction of Failures in Cogwheels

    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.

  • Development of a General C++ Class for Wavelet Analysis

    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.

  • Documentation Wavelet Analysis and Transformations of the Cohen Class

    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

  • LARS

    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.

  • LION - Localisation and Identification of Moving Noise Sources

    Beschreibung

     

    Wir danken dem FWF für die Förderung des Projekts mit der Nummer I 4299-N32

    Schallquellenlokalisierungsverfahren sind weit verbreitet in der Automobil-, Schienenfahrzeug- und Luftfahrtindustrie. Viele verschiedene Methoden stehen für die Analyse von ruhenden Schallquellen zur Verfügung. Geeignete Verfahren für bewegte Schallquellen kämpfen nach wie vor mit den Problemstellungen der Dopplerverschiebung, der vergleichsweise kurzen Messzeiten und Ausbreitungseffekten durch die umgebende Atmosphäre. Das Projekt LION kombiniert die Expertise von vier Arbeitsgruppen aus drei verschiedenen Ländern im Bereich der Schallquellenlokalisierung: Die Beuth Hochschule für Technik Berlin (Beuth), das Fachgebiet Turbomaschinen- und Thermoakustik der TU Berlin (TUB), das Akustische Forschungsinstitut (ARI) der Österreichischen Akademie der Wissenschaften und das Schweizer Forschungslabor für Akustik / Lärmminderung der EMPA. Die genannten Institutionen kooperieren, um die existierenden Methoden zur Analyse von bewegten Schallquellen zu erweitern und zu verbessern. Dabei soll der Dynamikbereich erweitert sowie die räumliche und die Frequenzauflösung erhöht werden. Die neuen Verfahren sollen auf komplexe Probleme wie die Analyse von tonalen Quellen mit starker Richtcharakteristik oder kohärenten, räumlich verteilten Quellen angewandt werden.

     

    Methoden

    Die Partner werden die Methoden gemeinsam entwickeln, validieren und Synergieeffekte heben, die sich durch diese Partnerkonstellation ergeben. Beuth plant, die Methode der äquivalenten Schallquellen im Frequenzbereich auf bewegte Quellen im Halbraum zu erweitern und dabei die Einflüsse des Bodens und der Schallausbreitung in der Atmosphäre zu berücksichtigen. ARI steuern die akustische Holografie, die Hauptkomponentenanalyse und die Methode der unabhängigen Komponenten bei und möchten diese zusammen mit ihrer Expertise für vorbeifahrende Züge nutzen, um numerische Randelementeverfahren inklusive der Transformation vom stehenden in das bewegte Bezugssystem zu verbessern. TUB entwickelt Optimierungsmethoden und modellbasierte Ansätze für die Lokalisierung von bewegten Schallquellen und bringt eine umfangreiche Datenbasis an mit einer großen Anzahl von Mikrofonen erfassten Überflugversuchsdaten ins Projekt ein. EMPA fügt seine Expertise zur Schallausbreitungsmodellierung mit atmosphärischer Turbulenz und Bodeneffekten basierend auf zeitvarianten digitalen Filtern hinzu. Sie werden überdies einen synthetischen Testfall zur Validerung der erweiterten und verbesserten Schalllokalisierungsmethoden aufsetzen. Das Projekt ist für eine Laufzeit von drei Jahren geplant. Das Arbeitsprogramm ist in vier Arbeitspakete organisiert: 1) Entwicklung der Algorithmen und Modelle, 2) die Entwicklung einer virtuellen Testumgebung für die Methoden, 3) die Simulation von Szenarien in der virtuellen Testumgebung und 4) die Anwendung der verbesserten und erweiterten Verfahren auf existierende Mikrofonmessungen von Zügen und Flugzeugen.

     

  • MPEG4-Features for Diadem

    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.

  • Multilevel Fast Multipole Method (MLFMM)

    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.

  • New Approaches in Ray-Tracing and Boundary Element Method

    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.

  • Orthobem: Simulation of Vibrations in Tunnels

    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.

  • PAAB

    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.

     

     

  • PASS - Psychoakustische Analyse von schienen-verkehrsinduzierten Schallimmissionen

    Das Projekt PASS, welches in Kooperation mit dem IEW der TU Wien und psiacoustic GmbH durchgeführt wird, beschäftigt sich mit der psychoakustischen Bewertung von Lärm. Aufbauend auf den Ergebnissen des Projektes RELSKG werden dabei hohe und niedrige Lärmschutzwände numerisch simuliert mittels der 2.5 dimensionalen Randelemente Methode (2.5 D). Der Vergleich mit Messungen zeigt, dass die Annahme einer inkohärenten Linienquelle, wie sie mit der 2.5 D Methode möglich ist, für die Reproduktion der Messergebnisse erforderlich ist. Zusätzlich werden Schienenstegdämpfer aus Messdaten psychoakustisch bewertet. Die Bewertung erfolgt in zwei Tests mit 40 Probanden. Der erste Test vergleicht die relative Lästigkeit und der zweite die Schwellen für lästiger bzw. weniger lästig. Es ergab sich, dass Güterzüge bei gleichen A-Pegel als weniger lästig als Personenzüge eingestuft werden und dass bei gleichen A-Pegel der Lärm hinter einer Lärmschutzwand als geringfügig lästiger empfunden wird. Das Projekt starte in 2013 und läuft bis Ende 2014.

  • Principal Component Analysis (PCA) for the Estimation of the Acoustic Far-Field Level

    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.

  • RAARA - Residential Area Augmented Reality Acoustics

    Beschreibung

    Wir danken für die Förderung durch die Forschungsförderungsgesllschaft (FFG), Projektnummer 873588. Lärm bedeutet Ärger. Er wird neben Verkehr und Gewerbe vor allem von Heiz- oder Kühlgeräten emittiert: Luftwärmepumpen, Rückkühlern und Lüftern. Um die Schallimmissionen auf die Bevölkerung im urbanen Gebiet zu minimieren, werden im Projekt Methoden entwickelt, die einen einfachen, intuitiven und zugleich akkuraten Umgang mit Schallemissionen und deren Minderung ermöglichen.

     

    Methoden

    Ziel ist, die Lärmquellen vor deren Installation VOR ORT in realer Umgebung mittels Augmented Reality virtuell zu platzieren und die Schallemissionen visuell farblich darzustellen und hörbar zu machen. Hindernisse oder Schalldämmmaßnahmen, wie Wände, Zäune und Mauern werden automatisiert erkannt oder können virtuell hinzugefügt werden. Um diese Ziele zu erreichen, sind umfassende Methodenentwicklungen zur effizienten akustischen Berechnung erforderlich: frequenzabhängiges und zeitabhängiges Verhalten, Absorption und Reflexion. Dieser einzigartige Ansatz erleichtert die Planung von erneuerbaren Heiz- und Kühlgeräten, erhöht die Akzeptanz und damit den Anteil erneuerbarer Energien und senkt den Lärmpegel in Städten.

     

     

     

     

     

  • RELSKG: Development of a computational method for noise barriers with a complex geometry

    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.

    Wirkung einer T-Wand bei 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)

  • Spectral Transform of Sound Fields (STSF)

    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.