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Transfer path analysis is commonly used to determine input forces indirectly utilizing measured responses and transfer functions. Though it is recommended that the source should be detached from the vibrating structure when measuring transfer functions, engineers and technicians frequently have a difficult time in doing so in practice. Recently, a substitute for inverse force determination via transfer path analysis has been suggested. The indirectly determined forces are termed blocked forces and are usable so long as the source and machine are not detached from one another. Blocked forces have the added advantage of being valid even if the machine structure is modified. In this research, a typical automotive engine cover is considered as a receiver structure and is bolted to a plastic source plate excited by an electromagnetic shaker.

An advanced computational method is presented for calculating the sound radiated by vibrating engine of arbitrary shape. The method is based on the numerical evaluation of the Helmholtz Integral Equation. In particular an isoparametric element formulation is introduced in which both the surface geometry and the acoustic variables on the surface of the vibrating body are represented by second order shape functions within the local coordinate system. The formulation includes the case where the surface may have a non-unique normal (e.g. at edges or corners). A general result for the surface and field velocity potential is derived. Test cases involving spherical geometry are given for a pulsating sphere and for an oscillating sphere in which the analytical solutions are known. Examples for bodies with edges and corners are shown for the problems of radiation from a circular cylinder and from a pulsating cube.

This paper explores the use of inverse numerical acoustics to reconstruct the surface vibration of a noise source. Inverse numerical acoustics is mainly used for source identification. This approach uses the measured sound pressure at a set of field points and the Helmholtz integral equation to reconstruct the normal surface velocity. The number of sound pressure measurements is considerably less than the number of surface vibration nodes. A brief guideline on choosing the number and location of the field points to provide an acceptable reproduction of the surface vibration is presented. The effect of adding a few measured velocities to improve the accuracy will also be discussed. Other practical considerations such as the shape of the field point mesh and effect of experimental errors on reconstruction accuracy will be presented. Examples will include a diesel engine and a transmission housing.

This paper documents an inverse visible element Rayleigh integral (VERI) approach. The VERI is a fast though approximate method for predicting sound radiation that can be used in the place of the boundary element method. This paper extends the method by applying it to the inverse problem where the VERI is used to generate the acoustic transfer matrix relating the velocity on the surface to measurement points. Given measured pressures, the inverse VERI can be used to reconstruct the vibration of a radiating surface. Results from an engine cover and diesel engine indicate that the method can be used to reliably quantify the sound power and also approximate directivity.

One of the more useful metrics to characterize the high frequency performance of an isolator is insertion loss. Insertion loss is defined as the difference in transmitted vibration in decibels between the non-isolated and isolated cases. Insertion loss takes into account the compliance on the source and receiver sides. Accordingly, it has some advantages over transmissibility especially at higher frequencies. In the current work, the transfer matrix of a spring isolator is determined using finite element simulation. A static analysis is performed first to preload the isolator so that stress stiffening is accounted for. This is followed by modal and forced response analyses to identify the transfer matrix of the isolator. In this paper, the insertion loss of spring isolators is examined as a function of several geometric parameters including the spring diameter, wire diameter, and number of active coils.

Numerical acoustics has traditionally been relegated to a prediction only role. However, recent work has shown that numerical acoustics techniques can be used to diagnose noise problems. The starting point for these techniques is the acoustic transfer vector (ATV). First of all, ATV's can be used to conduct contribution analyses which can assess which parts of a machine are the predominant noise sources. As an example, the sound power contribution and radiation efficiency from parts of a running diesel engine are presented in this paper. Additionally, ATV's can be used to reliably reconstruct the vibration on a machine surface. This procedure, commonly called inverse numerical acoustics (INA), utilizes measured sound pressures along with ATV's to reconstruct the surface velocity. The procedure is demonstrated on an engine cover for which the reconstructed vibration had excellent agreement with experimental results.

This paper presents an analysis of axle weight data collected during the performance testing of the Broken Bridge dynamic electronic highway scale. Test results are analyzed by comparing the in-motion axle weights as measured by the Broken Bridge scale with the corresponding static values for an instrumented two-axle test vehicle and for a sample of trucks diverted from an Interstate highway. Analysis of the two-axle test truck data shows that the actual loads applied to the highway surface by the wheels of a moving vehicle vary above and below the static equivalents in a manner that is typical for a specific location and range of speeds. For a random selection of different types of trucks, the variation of dynamic from static axle weight is further affected by axle position (front, second, third, and so forth) and spacing.