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This paper presents a method for modelling Pass-By Noise from a light weight truck by using Direct and Inverse Boundary Element Techniques. One of the issues in evaluating Pass-By Noise of a vehicle is to assess the internal noise sources. In the present study, it is assumed that the noise is mainly due to sound radiation from the truck engine. Therefore a proper source model of the engine is derived by using an Inverse Boundary Element scheme involving experimental data and a boundary element model of the engine defined as a set of prescribed acceleration surfaces. Once the engine noise model has been derived, the Pass-by Noise is computed by using the standard Variational Boundary Element Method as packaged in I-DEAS Vibro-Acoustics of SDRC which includes RAYON-3D solver of STRACO SA. Finally, computed acoustics pressures at standardized Pass-By Noise locations are compared to experimental results.

A number of objective measures are commonly used for an indication of subjective response to vehicle interior noise, including dBA, Loudness, Speech Interference Levels (SIL). Intelligibility etc.. Additional measures have been developed from a combination of specific orthogonal objective parameters with the aim of further improving the correlation with subjective response. For example, the Composite Rating of Preference (CRP) Index has been found to consistently improve the correlation upon dBA, through the inclusion of a spectral balance, and high frequency component However the ability of any objective parameter or index to provide a good correlation will be limited by any non-linearity present in the subject response, typically occurring through saturation of one or more aspect of the vehicle noise. This is further frustrated through subject inconsistencies and disagreements.

Airport land planning commissions often are faced with determining how much area around an airport is affected by the sound exposure levels (SELs) associated with helicopter operations. This paper presents a study of the effects changing the size and composition of a microphone array has on the computed SEL contour (ground footprint) areas used by such commissions. Descent flight acoustic data measured by a fifteen microphone array were reprocessed for five different combinations of microphones within this array. This resulted in data for six different arrays for which SEL contours were computed. The fifteen microphone array was defined as the “baseline” array since it contained the greatest amount of data. The computations used a newly developed technique, the Acoustic Re-propagation Technique (ART), which uses parts of the NASA noise prediction program ROTONET. After the areas of the SEL contours were calculated the differences between the areas were determined.

In this work, we discuss statistical energy methods for predicting mid-frequency vibration transmission between two spring-coupled substructures with parameter uncertainties. We adopt a parameter-based approach, which allows us to relax certain assumptions associated with a classical Statistical Energy Analysis (SEA) approximation. We consider both a numerical method and an analytical method. The latter is called a Parameter-based Statistical Energy Method (PSEM). An example of two elastic bars coupled by a single spring or multiple springs is examined. The power transmitted from the excited substructure to the other substructure is calculated and compared for the various methods.

The possibility of using a trailer to measure pass-by sound levels of tires has been limited by the tire noise generated by the tow vehicle. In order to verify the viability of the trailer method for passenger car tires, a trailer and tow vehicle were constructed and tested. A reduction goal of 3 dB(A) below the tow vehicle and trailer with the test tire was required for the tow vehicle alone. The noise reduction treatment, designed and developed for this project, successfully reduced the tow vehicle sound level enough to permit the coast-by trailer method to be used for tires as small as P145/80R13.

The development of systems and components for control of exterior noise has traditionally been done through an iterative process of on road testing. Frequently, road testing of vehicle modifications are delayed due to ambient environmental changes that prevent testing. Vehicle dynamometers used for powertrain development often had limited space preventing far field measurements. Recently, several European vehicle manufacturers constructed facilities that provided adequate space for simulation of the road test. This paper describes the first implementation of that technology in the U.S.. The facility is typical of those used world wide, but it is important to recognize some of the challenges to effective utilization of the technique to correlate this measurement to on road certification.

Vold and Leuridan [1] introduced in 1993 an algorithm for high resolution, slew rate independent order tracking based on the concepts of Kalman filters [5, 6]. The algorithm has been highly successful as implemented in a commercial software system in solving data analysis problems previously intractable with other analysis methods. At the same time certain deficiencies have surfaced, prompting the development of an improved formulation. This paper presents for the first time the second generation algorithm and its theoretical foundations. The new algorithm allows for the simultaneous estimation of multiple orders, effectively decoupling close and crossing orders. This is especially important for acoustics applications, where order crossings cause transient beating events. The algorithm now allows for a much wider range of filter shapes, such that signals with sideband modulations are processed with high fidelity.

Present order tracking methods for solving noise and vibration problems are reviewed, both FFT and re-sampling based order tracking methods. The time variant discrete Fourier transform (TVDFT) is developed as an alternative order tracking method. This method contains many advantages which the current order tracking methods do not possess. This method has the advantage of being very computationally efficient as well as the ability to minimize leakage errors. The basic TVDFT method may also be extended to a more complex method through the use of an orthogonality compensation matrix (OCM) which can separate closely spaced orders as well as separate the contributions of crossing orders. The basic TVDFT is a combination of the FFT and the re-sampling based methods. This method can be formulated in several different manners, one of which will give results matching the re-sampling based methods very closely.

Governing equations have been derived to model the space- and frequency-averaged behavior of structural acoustic systems. These equations were derived using assumptions similar to the approximations made in SEA. The equations can be used to develop continuous models of 1-D, 2-D, and 3-D subsystems. The equations have been formulated into a finite element approximation referred to as the Energy Finite Element Method (EFEM). In this paper the theory for coupling plate-like structural systems to acoustical systems is derived and implemented into the EFEM. The results of a verification study using a plate mounted on a rectangular acoustical enclosure are shown for two cases, a mechanically driven plate and an acoustically driven enclosure.

This study analyzes methods of comparing SEA model results with experimental results for key traits. These qualitative traits provide the basis for correlation of model results with experimental results through the development of a comparison index. This paper formulates a comparison index and illustrates the application to SEA models. A customized data structure was designed around the comparison index to store all necessary aspects of the modeling, experiment and comparison results. This data structure was then implemented using relational database software. These new tools; the comparison index and the SEA database, will create a common language and a forum for SEA model results that will aid and stimulate dialog in the SEA modeling community and in tern, advance the science of SEA modeling.

Wavelet transform analysis is capable of revealing aspects of data that other techniques miss such aspects are trends, and discontinuities in higher derivates. This method can often compress or de-noise a signal without any appreciable degradation and it provides accurate information on the localization of energy content in time and frequency [1]. The Wavelet transform method has been applied to the analysis of combustion noise and piston slap in order to identify the effects on the engine structure vibration. The experimental results showed that combustion noise and piston slap were successfully detected from the acceleration signals picked up by external transducers in the outer wall of an in-line, 6 cylinder diesel engine.

As the drive to make automobiles more noise and vibration free continues, it has become necessary to analyze transient events as well as periodic and random phenomena. Averaging of transient events requires a repeatable event as well as an available trigger event. Knowing the exact event time, the data can be post-processed by re-sampling the time scale to capture the recorded event at the proper instant in time to allow averaging. Accurately obtaining the event time is difficult given the sampling restrictions of current data acquisition hardware. This paper discusses the ideal hardware needed to perform this type of analysis, and provides analytical examples showing the transient averaging improvements using time scale re-sampling. These improvements are applied to noise source identification of a single transient event using an arrayed microphone technique. With this technique, the averaging is performed using time delays between potential sources and microphones in the array.

A simple set-up for quick and purely electrical QC testing of knock sensors is described in this paper. The main goal is to measure the “impedance” frequency response function of the sensors. The advantages of the test procedure described in this paper are as follows: Simple “pseudo” one channel measurement, from the operator's point of view. Electrical testing, i.e. no need for shakers, power amplifiers, elaborate fixtures etc.. Pulse excitation, thus very fast - in the order of 100ms for one measurement test. No averaging needed. Standard frequency response function display is used, i.e. no complex postprocessing needed. The only requirement is a small junction box with the necessary transformer and some electronics. The power supply for the junction box is the analyzer. The testing method can be extended to other types of transducers such as accelerometers.

A new vibration signal processing technique is applied to a four-cylinder spark ignition engine for characterization of its transient motion during crank-on/idling/engine-off. This technique utilizes the directional Wigner distributions(dWDs) of the transient complex-valued vibration signals measured from the engine block. In order to avoid the aliasing problem and the interference terms between the forward(positive) and backward(negative) frequency components, the transformations of complex-valued signals to the forward and backward pass analytic signals were developed for calculation of the two types of dWDs: the auto-dWD essentially tracks the shape and directivity of the instantaneous planar motion, whereas the phase of the cross-dWD indicates its inclination angle.

The use of Kalman filter methods for high-performance order tracking of noise and vibration signals was introduced in 1993. Based on experience with that original formulation, further work has produced significant enhancements which greatly extend the ability of these methods to deal with several practical issues of concern in vehicle testing. This paper reports on advances in the areas of: RPM estimation accuracy, even for fast-changing events such as gear shifts; Higher order Kalman filters, with improved shapes for extracting modulated orders; Decoupling of close and even crossing orders by use of multiple RPM references; Significant speed improvement over the original algorithm. Besides obtaining the magnitude and phase of selected orders as a function of time or RPM, the harmonic content may be extracted as time-histories, with no phase or leakage distortion.

Road induced interior noise, vibration and harshness (NVH) of a vehicle are greatly influenced by the design of the vehicle chassis and body systems. The strategy of improving vehicle NVH performance is to reduce vehicle body sensitivities to suspension force inputs and to increase the isolation of the chassis system to road irregularities. The effectiveness of the isolation is evaluated by the magnitude of transmitted forces at all suspension-body attachments. Currently, no technique is available to directly measure the forces over a broad frequency range. Many efforts have been made to develop force estimation methods, such as Noise Path Analysis (NPA) techniques. NPA techniques have been used to estimate the transmitted forces for steady-state road and powertrain excitations. This paper presents an ongoing effort to extend the NPA techniques to transient excitations, such as impacts caused by tar strips and pot holes.

In a structure, the noise source does not always coincide with the origin of excitation. Vibrational energy is transmitted in the structure and noise is radiated from the surface. For noise and vibration control in beam or shell structures, it is important to clearly identify the excitation sources and vibrational energy transmission characteristics. In this paper, measurement of transient vibrational power flow in a car door excited by impact using the envelope vibration Intensity technique is described. Vibrational power flow caused by flexural vibration in the car door panel is measured with the three channel method. The vibrational power flow is expressed with vibration intensity vectors at each measuring point. Instantaneous distributions of measured vibration intensity vectors in the car door panel are shown in this paper. Temporal and spatial variations of the vibrational power flow are discussed.

A noise source identification technique for the analysis of thermal systems is presented. The proposed method uses transient spectral sound data to assist in determining the source of sound radiation by tracking the variation of the frequency of tones during transient thermal loading (i.e., thermal system warm-up). By considering the temperature dependence of the modulus of elasticity (Young's modulus) it can be shown that structure related tones will decrease in frequency during warm-up. Tones due to propagation of sound in many fluids (i.e., gases and water) will increase in frequency during warm-up due to the temperature dependence of the speed of sound. The analysis method is demonstrated by identifying the source of several noise tones for a pulse combustion furnace.

In this paper, the measured mode shape of a squealing drum brake is presented. The squealing noise is the result of a self-excited vibration that can occur on most types of brakes. In the literature, there are several suggestions for the mechanisms behind the squeal instabilities. Therefore, there is a need for measurements to verify the models. The vibration signals are measured with accelerometers mounted on a drum brake of a heavy duty vehicle. The mode shape is measured in operation, i.e. while the vehicle is running on a test ground. The result from the measurements is the mode shape of a squealing drum brake. The radial and tangential vibration of the drum and the shoes are measured and the accelerometers are distributed both axially and tangentially. The measured shape is a complex mode containing a wave. This wave moves in the same direction as the rotation of the drum. As the drum rotates during the measurement, a Doppler effect influences the measured frequency.

Subjective assessment of shift feel for automatic transmissions is facilitated by simulation on the Ford Vehicle Vibration Simulator, allowing application of advanced psycho-physical methods. Large accelerations present in data in addition to the shift event may generate displacements too large to simulate. Isolation of the shift signal in time and frequency poses unique challenges due to the very low frequencies (VLF) involved. A method involving filtering, windowing, and filtering again solves this problem. The isolation of the 1-2 shift from a wide-open-throttle runup is illustrated. The method is applicable in general to separating VLF signals in time and frequency.