SOUND AND VIBRATION/JUNE 2004 This article presents a case study on the radiation, transmission and reduction of noise from a table saw typically used in the construction industry. The National Institute of Occupational Safety and Health... more
SOUND AND VIBRATION/JUNE 2004 This article presents a case study on the radiation, transmission and reduction of noise from a table saw typically used in the construction industry. The National Institute of Occupational Safety and Health (NIOSH) initiated this project through a multi-university student project program. In the construction industry, little attention has been given to control of noise from equipment and power tools. In order to address these issues, the work presented here is focused on reducing noise radiation from a table saw used in the construction industry from an engineering control point of view. The testing methodologies and results presented in this article address both the airborne and structure-borne noise contributors of the table saw. Sound power and sound intensity measurements were used to identify and rank all possible noise sources from the table saw. The use of these testing techniques in conjunction with experimental modal analysis, operational defl...
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A mathematical model to study the longitudinal vibration of an adhesively bonded double-strap joint is presented in this paper. Energy method and Hamilton’s principle are used to derive the governing equations of motion and natural... more
A mathematical model to study the longitudinal vibration of an adhesively bonded double-strap joint is presented in this paper. Energy method and Hamilton’s principle are used to derive the governing equations of motion and natural boundary conditions of the joint system. The adhesive is modeled as a viscoelastic material using complex modulus approach. Both the shear and longitudinal deformation in the adhesive layer are included in the analysis. The equations to predict the system resonance frequencies and loss factors are derived from the system natural and forced boundary conditions for the case of simply supported boundary conditions. A special searching strategy for finding the zeros of a complex determinant has been utilized to obtain the numerical results. The effects of the adhesive shear modulus and structural parameters such as lap ratio, adhesive and strap thickness on the system resonance frequencies and loss factors are also studied.
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Damping measurements on vehicle subsystems are rarely straightforward due to the complexity of the dynamic interaction of system joints, trim, and geometry. Various experimental techniques can be used for damping estimation, such as... more
Damping measurements on vehicle subsystems are rarely straightforward due to the complexity of the dynamic interaction of system joints, trim, and geometry. Various experimental techniques can be used for damping estimation, such as frequency domain modal analysis curve-fitting methods, time domain decay-rate methods, and other methods based on energy and wave propagation. Each method has its own set of advantages and drawbacks. This paper describes an analytical and an experimental comparison between two, widely used loss factor estimation techniques frequently used in Statistical Energy Analysis (SEA). The single subsystem Power Injection Method (PIM) and the Impulse Response Decay Method (IRDM) were compared using analytical models of a variety of simulated simple spring-mass-damper systems. Frequency averaged loss factor values were estimated from both methods for comparison. The parameters of the analytical models were varied to study the effects of the total number of modes, amount of damping, location of modes within frequency bands, and the width of the frequency bands on loss factor estimation. The analytical study showed that both methods give accurate loss factor values as long as one modal resonance is present in each frequency band and as long as the damping values remain realistic for linear systems. These analytical results were confirmed experimentally by measuring the loss factors of simple steel plates, with and without damping treatments applied.
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This article presents the damping effectiveness of free-layer damping materials through standard Oberst bar testing, solid plate excitation (RTC3) testing and prediction through numerical schemes. The main objective is to compare damping... more
This article presents the damping effectiveness of free-layer damping materials through standard Oberst bar testing, solid plate excitation (RTC3) testing and prediction through numerical schemes. The main objective is to compare damping results from various industry test methods to performance in an automotive body structure. Existing literature on laboratory and vehicle testing of free-layer viscoelastic damping materials has received significant attention in recent history. This has created considerable confusion regarding the appropriateness of different test methods to measure material properties for damping materials/treatments used in vehicles. The ability to use the material properties calculated in these tests in vehicle CAE models has not been extensively examined. Existing literature regarding theory and testing for different industry standard damping measurement techniques is discussed. This discussion is followed by the comparison of damping treatments through laboratory testing.
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ABSTRACT In this paper, a theoretical analysis to evaluate the stress field in the adhesive layers of tubular bonded joints subjected to torsional loading is presented. The formulation is suitable to study the static behavior of the joint... more
ABSTRACT In this paper, a theoretical analysis to evaluate the stress field in the adhesive layers of tubular bonded joints subjected to torsional loading is presented. The formulation is suitable to study the static behavior of the joint under general loading conditions as well as steady-state behavior under cyclic loading conditions. The adhesive material is modeled using linear viscoelasticity and numerical results for the shear stresses in the adhesives, joint compliance and joint loss factor are presented for various cases that provide some insights and guidelines in the design of the joint.
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In this paper, the results of analytical investigation into the effects of cocuring fiber composite tubes with commercially available damping materials are presented. A comprehensive theory has been developed for studying the vibration of... more
In this paper, the results of analytical investigation into the effects of cocuring fiber composite tubes with commercially available damping materials are presented. A comprehensive theory has been developed for studying the vibration of a composite tube with multiple viscoelastic damping layers. The effects of transverse shear deformation, transverse normal stress and strain, rotary inertia, and higher-order stiffness terms are included in the modeling along with shear correction factors. Resonance frequency and loss factor results as a function of various geometric and physical parameters are presented for composite tubes with single and double damping layers. It is demonstrated through a parametric study that in all these systems, careful selection of damping and pre-preg material is needed to optimize the damping benefits desirable and the stiffness reductions that can be tolerated.
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This paper presents a modeling technique to study the vibroacoustics of multiple-layered viscoelastic laminated beams using the Biot damping model. In this work, a complete simulation procedure for studying the structural acoustics of the... more
This paper presents a modeling technique to study the vibroacoustics of multiple-layered viscoelastic laminated beams using the Biot damping model. In this work, a complete simulation procedure for studying the structural acoustics of the system using a hybrid numerical model is presented. The boundary element method (BEM) was used to model the acoustical cavity, whereas the finite element method (FEM) was the basis for vibration analysis of the multiple-layered beam structure. Through the proposed procedure, the analysis can easily be extended to another complex geometry with arbitrary boundary conditions. The nonlinear behavior of viscoelastic damping materials was represented by the Biot damping model taking into account the effects of frequency, temperature, and different damping materials for individual layers. The curve-fitting procedure used to obtain the Biot constants for different damping materials for each temperature is explained. The results from structural vibration an...
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ABSTRACT This paper is a continuation of previously presented research work involving the dynamic characterization of automotive shock absorbers. The objective was to develop new testing and analysis methodologies for obtaining equivalent... more
ABSTRACT This paper is a continuation of previously presented research work involving the dynamic characterization of automotive shock absorbers. The objective was to develop new testing and analysis methodologies for obtaining equivalent linear stiffness and damping of the shock absorbers for use in CAE- NVH low-to-mid frequency chassis models. It is well known that a hydraulic actuated elastomer test machine is not suitable for testing shocks in the mid-to-high frequency range where the typical road input displacements fall within the noise floor of the hydraulic machine. Hence, initially in this project, an electrodynamic shaker was used for exciting the shock absorbers under displacements less than 0.05 mm up to 500 Hz. Furthermore, instead of the swept sine technique, actual road data were used to excite the shocks. Equivalent linear spring-damper models were developed based on least- squares curve-fitting of the test data. The type of road profile did not influence the stiffness and damping values significantly for the range of amplitudes and frequencies considered. The success of the characterization of shock absorbers on the electrodynamic shaker using non-sinusoidal input has led to the development of a similar methodology to be employed on the hydraulic actuated elastomer test machine.
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The objective of this project was to model and study the interior noise in an Off-Highway Truck cab using Statistical Energy Analysis (SEA). The analysis was performed using two different modeling techniques. In the first method, the... more
The objective of this project was to model and study the interior noise in an Off-Highway Truck cab using Statistical Energy Analysis (SEA). The analysis was performed using two different modeling techniques. In the first method, the structural members of the cab were modeled ...
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Different input excitation approaches to measure the dynamic stiffness and damping properties of two automotive elastomer mounts were investigated in this research. The traditional methods of dynamic characterization of elastomers are... more
Different input excitation approaches to measure the dynamic stiffness and damping properties of two automotive elastomer mounts were investigated in this research. The traditional methods of dynamic characterization of elastomers are based largely on sinusoidal input excitation where discrete frequency sine wave signals at specified amplitudes are used to excite an elastomer sample in a step-sine sweep fashion. This method is straight-forward in its signal processing and can easily be performed with a wide variety of available test equipment. However, many questions remain unanswered with respect to the behaviour of an elastomer during broadband frequency excitation. This paper examines how various other types of excitation affect the dynamic characterization results. These excitation inputs include continuous sine sweep (chirp), shaped random, and acquired road profile data. Use of the broadband data types is expected to provide a more accurate representation of conditions seen in...
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Acoustic cones are often the primary absorption treatment choice in the construction of anechoic chambers. The estimation of sound absorption coefficient of three-dimensional treatments, such as cones, is usually accomplished by the... more
Acoustic cones are often the primary absorption treatment choice in the construction of anechoic chambers. The estimation of sound absorption coefficient of three-dimensional treatments, such as cones, is usually accomplished by the reverberation time method. This method requires isolated, large, heavily constructed reverberation chambers which may not be available due to space and cost constraints. Impedance tubes are an alternative to reverberation chamber measurements for estimating sound absorption coefficients. However, due to the two-dimensional nature of samples used in the impedance tubes, sound absorption of three-dimensional objects is difficult to estimate. Absorption coefficient of the material is a function of not only surface area but also material thickness. This paper proposes a technique to estimate the sound absorption of a three-dimensional treatment using the absorption coefficient data from impedance tube tests. This extrapolation of impedance-tube-measured absorption coefficient to actual sound absorption of cones can be used to evaluate the effectiveness of absorptive acoustic room treatments without the need of testing the actual treatment prototypes.
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During operation, heavy construction equipment can generate high levels of noise, which can adversely affect the health and job performance of operators. This study examined the noise transmitted into the operator's cabin of a crawler... more
During operation, heavy construction equipment can generate high levels of noise, which can adversely affect the health and job performance of operators. This study examined the noise transmitted into the operator's cabin of a crawler excavator during operation. The sources of the noise generated by the excavator and the air-borne and structure-borne transmission paths into the cabin of the excavator were identified and characterized. Order tracking, which utilizes tachometer measurements to relate the occurrence of an event to a multiple of engine rotational speed, was used to identify noise and vibration components related to excitation from the excavator's engine and hydraulic systems. The results of the analysis showed 1st order engine rotational imbalance, 3rd order engine combustion, and 9th and 18th order hydraulic pressure fluctuations were the primary components of noise and vibration generated by the excavator. An ultrasonic leak detector was used to identify small sound leaks into the cabin. Finally, passive noise control treatments were designed to attenuate and dissipate the acoustic energy transmitted into the excavator cabin. These cabin noise control treatments included covering the floor with an acoustic barrier, adding damping to the windows, lining the ceiling and walls with absorptive foam, and sealing leaks found along window, door, and panel edges. Experimental results showed that the noise control treatments reduced the overall A-weighted sound pressure level in the cabin by up to 3 dB.
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Squeeze film damping effects naturally occur if structures are subjected to loading situations such that a very thin film of fluid is trapped within structural joints, interfaces, etc. An accurate estimate of squeeze film effects is... more
Squeeze film damping effects naturally occur if structures are subjected to loading situations such that a very thin film of fluid is trapped within structural joints, interfaces, etc. An accurate estimate of squeeze film effects is important to predict the performance of dynamic structures. This paper presents a finite element solution to the coupled fluid–structure problem of squeeze film dampers. The squeeze film is governed by the linearized isothermal Reynolds equation, which is known from lubrication theory. The structure which is modeled using Reissner–Mindlin plate theory is discretized by four-noded two-dimensional shear deformable isoparametric plate elements. The coupled finite element formulation is derived and an alternative solution to obtain damped eigenvalues and eigenvectors is presented. The coupling between fluid and structure is handled by considering the pressure forces and structural surface velocities on the boundaries. The effects of the driving parameters on...
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A method of curve fitting to process the data obtained from damping measurements of free decaying vibration is presented and compared with the logarithmic decrement method. In order to determine the accuracy of the two methods and the... more
A method of curve fitting to process the data obtained from damping measurements of free decaying vibration is presented and compared with the logarithmic decrement method. In order to determine the accuracy of the two methods and the factors that influence the estimation error, a computer simulation is described, and the results have been estimated under different conditions of damping and noise. It is shown that the curve‐fitting method is more accurate than the logarithmic decrement method for most conditions, and that, for values of damping and signal‐to‐noise most frequently encountered in practice, the optimum number of data points, for which the best estimate is obtained, is about 20. The method has been applied in the measurement of damping of a graphite epoxy tube specimen.
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Acoustic cones are often the primary absorption treatment choice for constructing anechoic chambers. Reverberation chamber estimation of room absorption will most accurately represent the actual effect of three-dimensional treatments,... more
Acoustic cones are often the primary absorption treatment choice for constructing anechoic chambers. Reverberation chamber estimation of room absorption will most accurately represent the actual effect of three-dimensional treatments, such as cones. However, for low frequencies, large reverberation chambers are often required, which may not be available due to space and cost constraints. Impedance tubes measurements are more accurate than
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... Michigan Technological University 1400 Townsend Drive Houghton, MI 49931 April 15, 2005 Ashish Jangale – Project Manager Jason Dreyer –Report Author Jagdish Dholaria Kurt Korpela Paul Lefief Amanda Otis Kyle Stewart Chad Walber Page... more
... Michigan Technological University 1400 Townsend Drive Houghton, MI 49931 April 15, 2005 Ashish Jangale – Project Manager Jason Dreyer –Report Author Jagdish Dholaria Kurt Korpela Paul Lefief Amanda Otis Kyle Stewart Chad Walber Page 2. ...
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Recent advances in the understanding of dynamic properties of viscoelastic materials have resulted in many innovative means to enhance the inherent damping in structural systems. Damping is now recognized as a design parameter in all... more
Recent advances in the understanding of dynamic properties of viscoelastic materials have resulted in many innovative means to enhance the inherent damping in structural systems. Damping is now recognized as a design parameter in all stages of analysis and design of structures subjected to dynamic loading. The purpose of this paper is to describe the status of knowledge concerning the application of viscoelastic materials for passive vibration and noise control of structures subjected to dynamic loading. First, the presentation will focus on various mathematical modeling techniques and measurement methods as applied to damping in general, and viscoelastic damping in particular. The advantages and limitations associated with each model/method will be described in the context of recent experimental study of the damping of graphite epoxy composite materials and joints. Then, current research on the prediction of modal parameters (resonance frequencies, loss factors, and mode shapes) of bonded composite struc...
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An analytical method for the solution of squeeze film damping based on Green's function to the nonlinear Reynolds equation considering an elastic plate is presented. This allows calculating the stiffness and damping forces rapidly for... more
An analytical method for the solution of squeeze film damping based on Green's function to the nonlinear Reynolds equation considering an elastic plate is presented. This allows calculating the stiffness and damping forces rapidly for various boundary conditions. The elastic plate velocity is applied to the nonlinear Reynolds equation as a forcing term. The nonlinear Reynolds equation is divided into multiple linear nonhomogeneous Helmholtz equations, which then can be solvable using the presented approach. Approximate mode shapes of a rectangular elastic plate are used, enabling the calculation of the damping ratio and frequency shift for the linear case, as well as the complex resistant pressure, for both linear and nonlinear cases.