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Transmission loss (TL) is a good performance measure of mufflers since it represents the muffler's inherent capability of sound attenuation. There are several existing numerical methods, which have been widely used to calculate the TL from numerical simulation results, such as the four-pole and three-point methods. In this paper, a new approach is proposed to evaluate the transmission loss based on the reciprocal work identity. The proposed method does not assume plane wave propagation in the inlet and outlet ducts, and more importantly, does not explicitly apply the anechoic termination impedance at the outlet. As a result, it has the potential of extending TL computation above the plane wave cut-off frequency.

Carbon nanomaterials such as vertically aligned carbon nanotubes arrays are emerging new materials that have demonstrated superior mechanical, thermal, and electrical properties. The carbon nanomaterials have the huge potential for a wide range of vehicular applications, including lightweight and multifunctional composites, high-efficiency batteries and ultracapacitors, durable thermal coatings, etc. In order to design the carbon nanomaterials for various applications, it is very important to develop effective computational methods to model such materials and structures. The present work presents a structural mechanics approach to effectively model the mechanical behavior of vertically aligned carbon nanotube arrays. The carbon nanotube may be viewed as a geometrical space frame structure with primary bonds between any two neighboring atoms and thus can be modeled using three-dimensional beam elements.

In many industries, muffler and silencer design is primarily accomplished via trial and error. Prototypes are developed and tested, or numerical simulation (finite or boundary element analysis) is used to assess the performance. While these approaches reliably determine the transmission loss, designers often do not understand why their changes improve or degrade the muffler performance. Analyses are time consuming and models cannot be changed without some effort. The intent of the current work is to demonstrate how plane wave muffler models can be used in industry. It is first demonstrated that plane wave models can reliably determine the transmission loss for complicated mufflers below the cutoff frequency. Some tips for developing dependable plane wave models are summarized. Moreover, it is shown that plane wave models used correctly help designers develop intuition and a better understanding of the effect of their design changes.

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.

Partial enclosures are commonly utilized to reduce the radiated noise from equipment. Often, enclosure openings are fitted with silencers or louvers to further reduce the noise emitted. In the past, the boundary element method (BEM) has been applied to predict the insertion loss of the airborne path with good agreement with measurement. However, an alteration at the opening requires a new model and additional computational time. In this paper, a transfer function method is proposed to reduce the time required to assess the effect of modifications to an enclosure. The proposed method requires that the impedance at openings be known. Additionally, transfer functions relating the sound pressure at one opening to the volume velocity at other openings must be measured or determined using simulation. It is assumed that openings are much smaller than an acoustic wavelength. The sound power from each opening is determined from the specific acoustic impedance and sound pressure at the opening.

Partial enclosures are a very common way to reduce noise emissions from machinery. However, partial enclosures exhibit complex acoustic behavior that is difficult to predict. The boundary element method (BEM) was used to model the airborne path of a partial enclosure. Simulation results were compared to measurement with good agreement. Special attention is given to the determination of negative insertion loss. It is demonstrated that the enclosure insertion loss will be negative at the Helmholtz frequencies for the enclosure.

This paper examines the feasibility of using the boundary element method (BEM) and the Rayleigh integral to assess the sound radiation from engine components such as oil pans. Two oil pans, one cast aluminum and the other stamped steel, are used in the study. All numerical results are compared to running engine data obtained for each of these oil pans on a Cummins engine. Measured running-engine surface velocity data are used as input to the BEM calculations. The BEM models of the oil pains are baffled in various ways to determine the feasibility of analyzing the sound radiated from the oil pan in isolation of the engine. Two baffling conditions are considered: an infinite baffle in which the edge of the oil pan are attached to an infinite, flat surface; and a closed baffle in which the edge of the oil pan is sealed with a rigid structure. It is shown that either of these methods gives satisfactory results when compared to experiment.

The two-load method is commonly used to determine the transmission loss of a muffler or silencer. Several practical measurement considerations are examined in this paper. First of all, conical adapters are sometimes used to transition between impedance tubes and the muffler. It is demonstrated that the effect of adding the adapter can be quite significant at low frequencies especially if the adapter is short in length. The effect of changing the length of the adapter was examined via measurement and plane wave theory. Secondly, the effect of selecting the reference microphone was examined experimentally. It was found that measurements are improved by selecting a downstream reference. Finally, the effect of using different frequency response function estimation algorithms (H1, H2 and Hv) was compared sans flow. This had little effect on the measurement.

A mathematical model is presented to help understand sheet metal deformation during forming. The particular purpose of this model is to predict the forming limit diagram (FLD). The present model is an extension of a previous analysis by Jones and Gillis (JG) in which the deformation is idealized into three phases: (I) homogeneous deformation up to maximum load; (II) deformation localization under constant load; (III) local necking with a precipitous drop in load. In phase III the neck geometry is described by a Bridgman type neck. The present model extends the JG theory which was applied to the right hand side of the FLD only. The main difference in treating the two different sides of the FLD lies in the assumptions regarding the width direction deformations. For biaxial stretching, the right hand side, the minor strain rate is assumed to be homogeneous throughout the process.

Properly characterizing input forces is an important part of simulating structure-borne noise problems. The purpose of this work was to apply a known force reconstruction technique to an earthmoving machinery cab to obtain input functions for modeling purposes. The technique was performed on a cab under controlled laboratory conditions to gain confidence in the method prior to use on actual machines. Forces were measured directly using force transducers and compared to results from the force reconstruction technique. The measured forces and vibrations were used as input power to an SEA model with favorable results.

Lack of a precise control over paint droplets released from current coating sprayers has motivated this study to develop an atomizer capable of generating a uniform flow of mono-dispersed droplets. In the current study, a numerical investigation based on CFD incorporating volume of fluid (VOF) multiphase model has been developed to capture the interface between air and paint phases for a typical atomizer equipped with piezoelectric actuator. Effects of inlet flow rate and actuator frequency on ejected droplets' characteristics, droplet diameter and their successive spacing are studied in detail. It will be shown that for a determined flow rate of paint, there is an optimum actuator frequency in which droplet size is minimum. Besides, there exists a direct relationship between the inlet paint velocity and obtained optimal actuator frequency.

This paper documents a finite element approach to predict the attenuation of muffler and silencer systems that incorporate diesel particulate filters (DPF). Two finite element models were developed. The first is a micro FEM model, where a subset of channels is modeled and transmission matrices are determined in a manner consistent with prior published work by Allam and Åbom. Flow effects are considered at the inlet and outlet to the DPF as well as viscous effects in the channels themselves. The results are then used in a macro FEM model of the exhaust system where the transmission relationship from the micro-model is used to simulate the DPF. The modeling approach was validated experimentally on an example in which the plane wave cutoff frequency was exceeded in the chambers upstream and downstream to the DPF.

Helmholtz resonators are normally an afterthought in the design of mufflers to target a very specific low frequency, usually the fundamental firing frequency of the engine. Due to space limitations in a complex muffler design, a resonator may have to be built by punching a few small holes on a thin-walled tube to create a neck passage into a small, enclosed volume outside the tube. The short neck passage created by punching a few small holes on a thin-walled tube can pose a great challenge in numerical modeling, especially when the boundary element method (BEM) is used. In this paper, a few different BEM modeling approaches are compared to one another and to the finite element method (FEM). These include the multi-domain BEM implemented in a substructure BEM framework, modeling both sides of the thin-walled tube and the details of each small hole using the Helmholtz integral equation and the hypersingular integral equation, and modeling just the mid surface of the thin-walled tube.

Insertion loss in one-third or octave bands is widely used in industry to assess the performance of large silencers and mufflers. However, there is no standard procedure for determining the transmission loss in one-third or octave bands using measured data or simulation. In this paper, assuming that the source is broadband, three different approaches to convert the narrowband transmission loss data into one-third and octave bands are investigated. Each method is described in detail. To validate the three different approaches, narrowband transmission loss data of a simple expansion chamber and a large bar silencer is converted into one-third and octave bands, and results obtained from the three approaches are demonstrated to agree well with one another.

The two-source method was used to measure the bulk properties (complex characteristic impedance and complex wavenumber) of sound-absorbing materials, and results were compared to those obtained with the more commonly used two-cavity method. The results indicated that the two-source method is superior to the two-cavity method for materials having low absorption. Several applications using bulk properties are then presented. These include: (1) predicting the absorptive properties of an arbitrary thickness absorbing material or (2) layered material and (3) using bulk properties for a multi-domain boundary element analysis.

The two-load method is used to measure the transmission loss of thin panels in two different sized impedance tubes (3.49 cm and 10.16 cm). Samples were initially tested with a clamped boundary condition. This was followed by tests with an elastomer inserted between the tube and tested sample to adjust the boundary condition at the periphery. In all tests performed, the influence of the sample holding method could not be removed from the test. The measured transmission loss was compared to finite element simulation with good agreement for both impedance tubes. Additionally, the effect of a compliant boundary condition along the periphery of the sample was also validated via simulation.

Intake, exhaust, and heating / air conditioning systems in automobiles consist of various common duct elements. Noise arises primarily due to the source and is attenuated using common elements like expansion chambers and resonators. This attenuation is straightforward to predict using plane wave simulation and more advanced numerical methods. However, flow noise is often an unexpected important noise source. Predictions require computer intensive analyses. To better understand the aeroacoustic sources in duct systems, a flow rig has been developed at the University of Kentucky. The flow rig consists of a blower, a silencer to attenuate blower noise, external noise sources, and then the test duct. The flow rig can be equipped with an anechoic termination to measure transmission loss or may be used to measure insertion loss directly. In the latter case, the sound power is measured from the pipe outlet inside of a hemi-anechoic chamber.

Piezoelectric materials are smart materials that can undergo mechanical deformation when electrically or thermally activated. An electric voltage is generated on the surfaces when a piezoelectric material is subjected to a mechanical stress. This is referred to as the ‘direct effect’ and finds application as sensors. The external geometric form of this material changes when it is subjected to an applied voltage, known as ‘converse effect’ and has been employed in the actuator technology. Such piezoelectric actuators generate enormous forces and make highly precise movements that are extremely rapid, usually in the micrometer range. The current work is focused towards the realization and hence application of the actuator technology based on piezoelectric actuation. Finite element simulations are performed on different types of piezoelectric actuations to understand the working principle of various actuators.

Typical automotive muffler designs contain complex internal components such as extended inlet/outlet tubes, thin baffles with eccentric holes, internal connecting tubes, perforated tubes, perforated baffles, flow plugs and sound-absorbing materials. An accurate performance prediction for highly complicated muffler designs would greatly reduce the effort in fabricating and testing of multiple design iterations for engineers. This paper discusses the use of a component-based computer simulation tool for design and analysis of exhaust mufflers. A comprehensive computer program based on the Direct Mixed-Body Boundary Element Method was developed to predict the transmission loss characteristics of muffler systems. The transmission loss is calculated by an improved four-pole method that does not require solving the boundary element matrix twice at each frequency, and hence, it is a significantly faster approach when compared to the conventional four-pole method.

Micro-perforated (MPP) panels are acoustic absorbers that are non-combustible, acoustically tunable, lightweight, and environmentally friendly. In most cases, they are spaced from a wall, and that spacing determines the frequency range where the absorber performs well. The absorption is maximized when the particle velocity in the perforations is high. Accordingly, the absorber performs best when positioned approximately a quarter acoustic wavelength from the wall, and larger cavity depths improve the low frequency absorption. At multiples of one half acoustic wavelength, the absorption is minimal. Additionally, the absorption is minimal at low frequencies due to the limited cavity depth behind the MPP. By partitioning the backing cavity, the cavity depth can be strategically increased and varied. This will improve the absorption at low frequencies and can provide absorption over a wide frequency range.