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Measurement of sound intensity techniques has very good application in the source identification of a particular noise character. It has been applied effectively along with modal analysis and FE experimental excitation techniques to find out root cause of a particular noise character in small gasoline engine. A FEM shell model was used to make cylinder block and cylinder head model. FEM simulation was carried out which matched with experimental results. It helped to remove the noise character from engine. The other part of the paper describes the noise reduction of the crankcase cover used for the same motorcycle. It houses crankcase as well as two speed gearbox. The methodology involves very effective combination of experimental harmonic analysis, FE model with the shell element for the 3 piece crankcase cover, and experimental measurements. A particular sequence of this experimental techniques along with computer simulation techniques gives extremely good results.

At low frequencies, the finite element method reliably predicts the dynamic response of structures. At high frequencies where modal density is high, statistical energy analysis (SEA) is a useful tool to determine the global dynamic behavior of the structures. SEA gives only the space frequency band averaged energy for each subsystem. In the mid-frequency range where both short and long waves are present, neither low nor high frequency approximation to the dynamic response is valid. In this frequency range, there is a need to utilize another technique to capture the dynamic response of the structure. In this study, the energy finite element analysis (EFEA) method is evaluated as a possible technique to close the mid-frequency analysis gap related to NVH analyses. EFEA gives spatial variations of energy density and power in each subsystem, and models localized damping treatment and localized power input.

An improvement in a vehicle's front of dash barrier assembly's acoustical performance has in the past been addressed by both adding individual absorbers and increasing the overall weight of the dash sound barrier assembly. Depending upon the target market of the vehicle, adding mass may not be an option for improved acoustical performance. Understanding the value of an increase in vehicle mass and / or cost for a specific level of improved acoustical performance continues to plague both Original Equipment Manufacturer (OEM) Engineers and Purchasing representatives. This paper examines the importance of properly sealing the front of dash pass-through areas and offers recommendations which can improve the overall vehicle acoustical performance without the addition of cost and mass to the vehicle.

Until recently, the positioning of loudspeakers in a car was based on a combination of experience and empirical studies carried out relatively late in the vehicle development cycle when the choice of speaker package space, and hence audio system performance, may have already been severely compromised. This paper describes how a Boundary Element Analysis (BEA) model can be used to establish the best location for low frequency ‘woofer’ loudspeakers at the early stages of an automotive audio system design and for ‘trade off’ studies prior to physical prototypes. The model generates virtual sounds, which can be used in listening studies to assess the quality of the model and to optimize the whole audio system. This paper presents the Computational, Experimental and Auralisation work involved in this project.

A reliable finite element model (FE model) for the suspension of front-engine front-wheel-drive vehicles (FF vehicle) was developed. The model allows analysis which clarifies the role of each suspension component for road noise reduction in the 130- 160 Hz range. To analyze road noise up to 200 Hz, an accurate suspension FE model including tire FE model was developed. All suspension components are modeled in detail by shell or solid element. This saves the validation of model and enables us to use it early in the design stage. To save calculation time, some suspension components in which structure is not a concern are transformed into modal model. To acknowledge each subsystem's role to the entire suspension system a new approach was introduced. In this approach, important internal forces between subsystems are selected. These internal forces have high contribution to transmissibility forces at the body attachment point (body transmissibility force).

A full tracked vehicle model is developed with the objective of providing new capabilities in modeling track and suspension system dynamic response. This capability is essential for predicting the durability of the track as well as the vibration transmission to the interior of the vehicle. In this model, the track is represented as a continuous elastic member with longitudinal (stretching) and transverse track response described using low-order vibration modes. This modeling approach captures dynamic effects with few degrees of freedom relative to established multi-body dynamic formulations. Using this method, a full vehicle model involving relatively few degrees of freedom is assembled for an example military tank. A mixed Eulerian/Lagrangian description is employed wherein the rigid-body elements of the hull and suspension are coupled to component modes of the track spans.

The aim of this work is to validate a BE numerical methodology to calculate how the acoustic properties of seats can affect the acoustic behaviour of the passenger compartment of a vehicle. An analytical model, based on the Delany and Bazley approach, was implemented in order to simulate the acoustic impedance of the foam-fabric system. This model has been validated with absorption coefficient measurements on a certain number of foam-fabric combinations. The calculated impedance was used as input for a BEM analysis of the interior cavity of a trimmed vehicle. The measured impedance of trimming components as floor carpet, door panels and parcel shelf were included into the cavity model. The acoustic field due to a known source with and without seats was calculated, in the frequency range 20-400 Hz: the calculated FRFs are in good agreement with the measured ones.

The problem of NVH CAE model correlation in light of test and product variation has been addressed. An objective metric based on statistical hypothesis testing has been proposed and evaluated. This technique has been shown to work for frequency response functions. The hypothesis test answers the question ‘Are the involved frequency response functions statistically different than those in a reference set?’ This paper demonstrates that vehicles are uniquely identifiable by their frequency response functions. Under certain restrictive assumptions, the average gross error normalized by the ensemble variance is chi-squared distributed. Using a chi-squared test, the probability that a NVH CAE prediction is a member of a reference (test) set can be estimated. Within the context of a reference (test) set, this metric represents the limit to predictability. The metric was applied to examples including two midsize car NVH CAE models.

Vibrations of a cup-shaped rotor in a bushless DC motor are investigated. The 4-phase motor has 12 pole pieces in the stator which is surrounded by a cylindrical, cup-shaped rotor with 14 magnets. The strong, pulsating magnetic forces acting on the rotor result in strong vibrations. Finite Element Analysis is used to analyze the vibrational pattern of the rotor. The impact of small changes in the dimensions of the rotor on its vibrational frequencies is also investigated. Details of FEA modeling will be presented and its predictions will be compared with the experimental data.

The parameters that could influence the vibration and noise levels are always a concern for noise control engineers. The Finite Element Method (FEM) and Boundary Element Method (BEM) will be used to examine ribbed effect, plate thickness (t), material density (ρ), Young's modulus (E) and modal damping (ζ) on noise contributions. A model updating process that compares the calculated results in modal frequencies and mode shapes to the test results (from a modal testing) will increase the accuracy of the FEM model. This improved model will be used for evaluating/validating the noise response of motorcycle transmission top covers.

Several of the authors have recently developed procedures to efficiently evaluate experimentally the relative contributions of various wind noise paths and sources. These procedures are described and, as a case study, results are provided for the noise in the interior of a production automobile subjected to wind tunnel airflow. The present measurements and analysis indicate that for the tested vehicle significant contributions to interior noise are provided by underbody and wheel well flows, radiation from the roof and seal aspiration. A significant tone associated with vortex shedding from the radio antenna was also noted.

The coupling of shear layer instabilities with the acoustic resonances at the interface of two ducts, a main duct and a connecting sidebranch, leads to whistle noise. The present study investigates experimentally the mechanism of such pure tone noise. A generic sidebranch adapter is fabricated to allow for: (1) the ability to mount downstream of the throttle body in the induction system of a production engine; (2) the adjustment of sidebranch length; and (3) the changes in the diameter of the branch duct. Experiments are conducted both in a flow facility and an engine dynamometer facility for the same set of flow rates. The correlation of the whistle noise between these two facilities is examined in terms of frequency and the dimensionless numbers, including Strouhal and Mach.

Grazing flows over open windows or sunroofs may result in “flow buffeting,” i.e. self-sustained flow oscillations at the Helmholtz acoustic resonance frequency of the vehicle. The associated pressure fluctuations may cause passenger fatigue and discomfort. Many solutions have been proposed to solve this problem, including for example leading edge spoilers, trailing edge deflectors, and leading edge flow diffusers. Most of these control devices are “passive” i.e. they do not involve dynamic control systems. Active control methods, which do require dynamic controls, have been implemented with success for different cases of flow instabilities. Previous investigations of the control of flow-excited cavity resonance have used mainly one or more loudspeakers located within the cavity wall. In this study, oscillated spoilers hinged near the leading edge of the cavity orifice were used. Experiments were performed using a cavity installed within the test section wall of a wind tunnel.

To consider the acoustic quality in car design, a scientific methodology is developed in order to give an objective notation. To obtain a good correlation between the subjective and objective judgments, the first point is the choice of recording points that represent the signature of each sound sources that the human ear detects in space. Then, the information about the sound quality is extracted from signals with the computation of different appropriate parameters like “shock balance” and “roughness”. From these metrics, a notation system similar to a neural network gives a single note. At last, the processing of parameter is different for engine in stationary or run-up conditions.

In the design of Recreational Vehicle generators, a particular challenge arises from marketing and engineering teams' desire to ensure that their products meet “best in class” sound quality characteristics. Furthermore, it is desirable to know these characteristics in measurable engineering terms in the product design stage, preferably before prototypes are built and tested. Using a combination of product engineering knowledge and sound manipulation techniques, this paper shows how several generator sounds were produced. These new hybrid real/ synthetic sounds along with actual competitive generator sounds were then used for consumer jury tests to determine their preferences. The sounds include a target “best in class” sound based on mechanical design criteria. Since published A-weighted sound levels can be a useful marketing tool, in one study a few different sounds were presented to juries at varying levels of loudness.

Product sound quality is becoming increasingly critical in recent years. To help improve customer satisfaction and product quality, Delphi Automotive Systems has taken a proactive approach to address sound quality issues. The first step is to identify customers' expectations. This paper describes a sensory approach to develop sound quality criterion for a power product. To identify critical sound quality characteristics, a large number of sound samples were recorded. Jury (focus group) evaluation was conducted to identify the acceptance level and preference of each sample. Then, critical objective measures, and the criterion level of each measure, were identified via correlation analysis with subjective responses. This article presents a practitioner's point of view on how to apply sensory engineering method to engineering practice.

In the assessment of vehicle noise quality, sound characteristics caused by modulation play an important role because they contribute significantly to the perceived annoyance. The sensations can be roughness, rumble or fluctuation strength depending mainly on the modulation frequency range. The proposed generalized model for modulation parameters was developed as part of a research program with the aim of establishing an onboard analysis system for vehicle interior noise quality based on objective sound parameters. The model can be adjusted by model parameters to calculate versions of roughness, thereby accentuating different psychoacoustical assumptions. The model was successfully tested as reported in [1].

A finite element-based acoustic-structure interaction analysis tool has been developed to determine the noise transmission loss characteristics of door seal systems. This tool has been applied to determine the effects of the individual parameters, such as seal material density, seal constitutive model, separation distance between seal layers, external cavity shape, and seal prestress field, on noise transmission characteristics. Our findings indicate that the external and internal cavity shapes, seal material density, and deformed seal geometry are the key factors affecting the noise transmission through seal system. Increasing seal material density decreases the resonance frequencies and increases the overall sound transmission loss. Changing the separation distance between seal layers changes the sound transmission characteristics without changing the compression load deflection behavior of the seal system.

In an effort to better understand the effectiveness and durability of P.F.P.E.(k) fluids in solving automotive squeak and vibration problems, a test method has been developed that permits an accelerated, quantitative assessment of their impact on a variety of commonly used automotive materials. This paper describes the apparatus and method developed to conduct this testing, as well as presenting data generated to date as the impact of key fluid properties and parameters on various combinations of materials are explored. This information should allow automotive engineers to solve these problems with a much greater degree of precision and confidence.

An experimental analysis is performed on structure-borne sound in the low-frequency range under 50 Hz by applying an acoustic excitation test to a fully trimmed vehicle. This analysis makes use of the structural-acoustic reciprocity technique in which the vibration distribution of the car body is measured while the vehicle is being acoustically excited by a loudspeaker placed at the position of a passenger's ear. This paper explains why the concept of reciprocity should be applied to the study of low-frequency structure-borne sound, and discusses the causes of road noise, a typical problem in structure-borne sound associated with passenger cars.