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Technical Paper

Time-domain Transfer Path Analysis for Transient Phenomena Applied to Tip-in/Tip-out (Shock & Jerk)

2012-06-13
2012-01-1545
Tip-in/Tip-out of the accelerator pedal generates transient torque oscillations in the driveline. These oscillations may be amplified by P/T, suspension and body modes and will eventually be sensible at the receiver side in the vehicle, for example at the seat or at the steering-wheel. The forces that are active during this transient excitation are influenced by non-linear effects in both the suspension and the power train mounts. In order to understand the contribution of each of these forces to the total interior target response (e.g. seat rail vibration) a detailed investigation is performed. Traditional force identification methods are not suitable for low-frequent, transient phenomena like tip-in/tip-out. Mount stiffness method can not be used because of non-linear effects in the P/T and suspension mounts. Application of matrix inversion method based on trimmed body vibration transfer functions is not possible due to numerical condition problems.
Technical Paper

Synthesis of Drive-by Noise Based on Numerically Evaluated Source-Receiver Transfer Functions Employing the FMBEM

2011-05-17
2011-01-1610
Prediction of the drive-by noise level in the early design stage of an automotive vehicle is feasible if the source signatures and source-receiver transfer functions may be determined from simulations based on the available CAD/CAE models. This paper reports on the performance of a drive-by noise synthesis procedure in which the transfer functions are numerically evaluated by employing the Fast Multipole Boundary Element Method (FMBEM). The proposed synthesis procedure first computes the steady-state receiver contributions of the sources as appearing from a number of vehicle positions along the drive path. In a second step, these contributions are then combined into a single transient signal from a moving vehicle for each source-receiver pair by means of a travel time correction.
Technical Paper

Structural Modelling of Car Panels Using Holographic Modal Analysis

1999-05-17
1999-01-1849
In order to optimise the vibro-acoustic behaviour of panel-like structures in a more systematic way, accurate structural models are needed. However, at the frequencies of relevance to the vibro-acoustic problem, the mode shapes are very complex, requiring a high spatial resolution in the measurement procedure. The large number of required transducers and their mass loading effects limit the applicability of accelerometer testing. In recent years, optical measuring methods have been proposed. Direct electronic (ESPI) imaging, using strobed continuous laser illumination, or more recently, pulsed laser illumination, have lately created the possibility to bring the holographic testing approach to the level of industrial applicability for modal analysis procedures. The present paper discusses the various critical elements of a holographic ESPI modal testing system.
Technical Paper

Sound Quality Equivalent Modeling for Virtual Car Sound Synthesis

2001-04-30
2001-01-1540
The pressure on development cycles in the automotive industry forces the acoustical engineers to create awareness of sound quality in the early stages of development, perhaps even before a physical prototype is available. Currently, designers have few tools to help them listen to their “virtual” models. For the design of a synthesis platform of in-vehicle binaural sound, the sound should be modeled with almost identical sound quality perception. A concept is presented where the total sound of a vehicle is split in a number of components, each with its own sound characteristics. These characteristics are described in a signal model that allows the analysis of an existing sound into a limited number of signal components: orders-frequency spectra, time envelopes and time recordings.
Technical Paper

On-Line Sound Brush Measurement Technique for 3D Noise Emission Studies

2013-05-13
2013-01-1973
A key issue in noise emission studies of noise producing machinery concerns the identification and analysis of the noise sources and their interaction and radiation into the far field. This paper presents a new acoustic measurement technique for noise source identification in stationary applications. The core of the technology is a handheld measurement instrument combining a position and orientation tracking device with a 3D sound intensity probe. The technique allows an on-line 3D visualization of the sound field while moving the probe freely around the test object. By focusing on the areas of interest, troublesome areas can be identified that require further in-depth analysis. The measurement technique is flexible, interactive and widely applicable in industrial applications. This paper explains the working principle and characteristics of this new technology and positions it to existing methods like traditional sound intensity testing and array techniques.
Technical Paper

Numerical Modeling of Engine Noise Radiation through the use of Acoustic Transfer Vectors - A Case Study

2001-04-30
2001-01-1514
This paper presents the numerical modeling of noise radiated by an engine, using the so-called Acoustic Transfer Vectors and Modal Acoustic Transfer Vectors concept. Acoustic Transfer Vectors are input-output relations between the normal structural velocity of the radiating surface and the sound pressure level at a specific field point and can thus be interpreted as an ensemble of Acoustic Transfer Functions from the surface nodes to a single field point or microphone position. The modal counter part establishes the same acoustic transfer expressed in modal coordinates of the radiating structure. The method is used to evaluate the noise radiated during an engine run-up in the frequency domain. The dynamics of the engine is described using a finite element model loaded with a rpm-dependent excitation. The effectiveness of the method in terms of calculation speed, compared with classical boundary element methods, is illustrated.
Technical Paper

Noise Contribution Analysis at Suspension Interfaces Using Different Force Identification Techniques

2011-05-17
2011-01-1600
Road-tire induced vibrations are in many vehicles determining the interior noise levels in (semi-) constant speed driving. The understanding of the noise contributions of different connections of the suspension systems to the vehicle is essential in improvement of the isolation capabilities of the suspension- and body-structure. To identify these noise contributions, both the forces acting at the suspension-to-body connections points and the vibro-acoustic transfers from the connection points to the interior microphones are required. In this paper different approaches to identify the forces are compared for their applicability to road noise analysis. First step for the force identification is the full vehicle operational measurement in which target responses (interior noise) and indicator responses (accelerations or other) are measured.
Technical Paper

Modeling the Sound Source of an Intake and Predicting the Intake Sound Pressure Level for a Motorcycle

2003-09-15
2003-32-0058
In order to accurately estimate the intake sound pressure level, it is important to improve the accuracy of the air cleaner simulation model and precisely estimate the sound source of the intake. It has been confirmed that the modeling accuracy of an air cleaner can be improved by considering the vibro-acoustic coupling. Meanwhile, the sound source of the intake depends not only on the engine specifications, but on the intake system and even the exhaust system design. In this reported example, since it is difficult to estimate the sound source of the intake only by calculation, due to the aforementioned reasons, actual measurements were carried out to define the sound source. The method is such that the sound source is modeled by acoustic impedance and volume velocity in the engine, and the acoustic impedance is measured using an impedance tube. Then, the sound pressure at the intake opening is measured.
Technical Paper

Measuring a Geometry by Photogrammetry: Evaluation of the Approach in View of Experimental Modal Analysis on Automotive Structures

2001-04-30
2001-01-1473
The very first step when starting an experimental modal analysis project is the definition of the geometry used for visualization of the resulting mode shapes. This geometry includes measurement points with a label and corresponding coordinates, and usually also connections and surfaces to allow a good visualization of the measured mode. This step, even if it sounds straightforward, can be quite time consuming and is often done in a rather approximate way. Photogrammetry is a technique that extracts 2D or 3D information through the process of analyzing and interpreting photographs. It is widely used for the creation of topographic maps or city maps, and more and more for quick modeling of civil engineering structures or accident reconstruction. The purpose of this paper is to evaluate the use of this technique in the context of modal testing of automotive structures.
Technical Paper

Investigation of Gravel Noise Mechanisms and Impact Noise Transfer

2007-05-15
2007-01-2274
Impact noise, inside a car, due to tire-launched gravel on the road can lead to loss of quality perception. Gravel noise is mainly caused by small-sized particles which are too small to be seen on the road by the driver. The investigation focuses on the identification of the mechanisms of excitation and transfer. The spatial distribution of the particles flying from a tire is determined, as well as the probable impact locations on the vehicle body-panels. Finally the relative noise contributions of the body-panels are estimated by adding the panel-to-ear transfer functions. This form of Transfer-Path-Analysis allows vehicle optimization and target setting on the level of the tires, exterior panel treatment and isolation.
Technical Paper

Inverse Numerical Acoustics of a Truck Engine

2003-05-05
2003-01-1692
Source identification applied to a truck engine and using inverse numerical acoustics is presented. The approach is based on acoustic transfer vectors (ATV) and truncated singular value decomposition (SVD). Acoustic transfer vectors are arrays of transfer functions between surface normal velocity and acoustic pressure at response points. They can be computed using boundary element methods (indirect, direct or multi-domain direct formulations) or finite element methods (in physical or modal coordinates). Regularization techniques such as the so-called L-curve approach are used to identify the optimum SVD truncation. To increase the reliability of the source identification, the approach can use velocity measurements on the boundary surface as well as the standard nearfield pressure measurements. It also allows for linear or spline interpolation of the acoustic transfer vectors in the frequency domain, to increase computational speed.
Technical Paper

Identification, Quantification and Reduction of Structural- Borne Road Noise in a Mid-Size Passenger Car

1996-02-01
960195
This paper presents the measurement & analysis procedures and the results of a complete road noise identification and reduction project on a midsize passenger car. Operational interior noise signals and structural accelerations are measured for several test conditions. The operating data are decomposed into sets of mathematically independent phenomena by Principal Component Analysis. Operating Deflection Shape Analysis and Transfer Path Analysis are applied to each of these independent phenomena. Critical transfer paths are thus identified and quantified. The interior sound level is amplified when the frequency content of the transmitted energy coincides with structural resonances or standing waves of the interior car cavity. The vehicle is dynamically characterized by Experimental Structural Modal Analysis and by Acoustic Modal Analysis.
Technical Paper

Identification of the Best Modal Parameters and Strategies for FE Model Updating

2001-04-30
2001-01-1439
The use of numerical models as basis to assemble or modify all kind of new structures is increasing over the last years. This has as benefit that it reduces the number of expensive, physical prototypes. These numerical models however must be verified and validated against measured data. Updating is generally needed to guarantee accurate correspondence with reality. This paper focuses on an exhaust. It describes the different steps of the complete process from the acquisition till the updating. On the measurement side, some typical acquisition measures and an efficient approach to handle (slightly) inconsistent data sets is explained. On the numerical side, it is investigated how to achieve the final updated exhaust with physical relevant characteristics.
Technical Paper

Extraction of Static Car Body Stiffness from Dynamic Measurements

2010-04-12
2010-01-0228
This paper describes a practical approach to extract the global static stiffness of a body in white (BIW) from dynamic measurements in free-free conditions. Based on a limited set of measured frequency response functions (FRF), the torsional and bending stiffness values are calculated using an FRF based substructuring approach in combination with inverse force identification. A second approach consists of a modal approach whereby the static car body stiffness is deduced from a full free-free modal identification including residual stiffness estimation at the clamping and load positions. As an extra important result this approach allows for evaluating the modal contribution of the flexible car body modes to the global static stiffness values. The methods have been extensively investigated using finite element modeling data and verified on a series of body in white measurements.
Journal Article

Effect of Local Mesh Refinement on Inverse Numerical Acoustics

2010-06-09
2010-01-1413
Inverse numerical acoustics is a method which reconstructs the source surface normal velocity from the sound measured in the near-field around the source. This is of particular interest when the source is rotating or moving, too light or too hot to be instrumented by accelerometers. The use of laser vibrometers is often of no remedy due to the complex shape of the source. The Inverse Numerical Acoustics technique is based on the inversion of transfer relations (Acoustic Transfer Vectors) using truncated Singular Value Decomposition (SVD). Most of the time the system is underdetermined which results in a non unique solution. The solution obtained by the truncated SVD is the minimal solution in the RMS sense. This paper is investigating the impact of non homogeneities in the mesh density (local mesh refinement) on the retrieved solution for underdetermined systems. It will be shown that if transfer quantities are inverted as such, big elements get a higher weight in the inversion.
Technical Paper

Application of a FRF Based Model Updating Technique for the Validation of Finite Element Models of Components of the Automotive Industry

1995-05-01
951246
This paper presents two applications of the RADSER model updating technique (ref. 1). The RADSER technique updates finite element model parameters by solution of a linearised set of equations that optimise the Reduced Analytical Dynamic Stiffness matrix based on Experimental Receptances. The first application deals with the identification of the dynamice characteristics of rubber mounts. The second application validates a coarse finite element model of a subframe of a Volvo 480.
Technical Paper

Application of Energy Flow Analysis Focused on Path Visualization into Vehicle Design

2010-10-17
2010-36-0505
The development of new design tools to predict the vibro-acoustic behavior within the vehicle development process is of essential importance to achieve better products in an ever shorter timeframe. In this paper, an energy flow post-processing tool for structural dynamic analysis is presented. The method is based on the conversion of conventional finite element (FE) results into energy quantities corresponding with each of the vehicle subcomponents. Based on the global dynamic system behavior and local subcomponent descriptions, one can efficiently evaluate the energy distribution and analyze the vibro-acoustic behavior in complex structures. By using energy as a response variable, instead of conventional design variables as pressure or velocity, one can obtain important information regarding the understanding of the vibro-acoustic behavior of the system.
Technical Paper

Advances in Industrial Modal Analysis

2001-03-05
2001-01-3832
One of the scientific fields where, for already more than 20 years, system identification plays a crucial role is this of structural dynamics and vibro-acoustic system optimization. The experimental approach is based on the “Modal Analysis” concept. The present paper reviews the test procedure and system identification principles of this approach. The main focus though is on the real problems with which engineers, performing modal analysis on complex structures on a daily basis, are currently confronted. The added value of several new testing approaches (laser methods, smart transducers…) and identification algorithms (spatial domain, subspace, maximum likelihood,..) for solving these problems is shown. The discussed elements are illustrated with a number of industrial case studies.
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