bluuebunny/crossref_metadata_2025 huggingface dataset:
Computing Resonant Frequencies and Coupled Mode-Shapes of Structural-Acoustic Systems Using the Finite Element Method
Authors: Botelho Rui M.
Published: June 2009

This paper examines numerical techniques to compute the resonant frequencies and coupled mode-shapes of general structural-acoustic systems using the finite element method. This information is useful in quantifying the key frequencies and vibration patterns of elastic structures coupled to bounded or unbounded acoustic fluid volumes. This paper reviews and evaluates three finite element solution techniques that deal with the computational difficulties encountered in structural-acoustic eigen-analysis. One of the difficulties stems from the fluid-structure coupling in the finite element equations, which depending on the variable used to discretize the acoustic fluid, either introduces non-symmetric area coupling terms in the mass and stiffness matrices or adds symmetric area coupling terms in the damping matrix. The other difficulty is related to the application of a radiation boundary condition in those structural-acoustic problems involving unbounded acoustic domains. The radiation boundary condition introduces damping terms in the finite element equations that lead to a complex eigen-analysis to determine the resonant frequencies and coupled mode-shapes. The finite element techniques evaluated in this paper consist of subspace projection employing an augmented-symmetric form of the fluid-structure equations as well as new extensions of component mode synthesis (CMS). Basic examples of simplified structural-acoustic systems are used to compare the solution accuracy between the three finite element techniques. Examples consist of simplified one-dimensional (1-D) and two-dimensional (2-D) elastic structures coupled to closed and open acoustic spaces.
Active Sound Transmission Control of an Experimental Double-Panel Partition Using Decoupled Analog Feedback Control
Authors: Sagers Jason , Blotter Jonathan D. , Leishman Timothy W.
Published: June 2009

This paper addresses the construction, measurement, and analysis of a double-panel active partition (DPAP) and its accompanying analog feedback controllers. The DPAP was constructed by attaching an aluminum cone loudspeaker at each end of a short segment of a circular duct. Two analog feedback controllers were designed and built using the measured frequency response function of each panel. Two independent (decoupled) feedback controllers were then used to minimize the vibration amplitude of each panel in the presence of an acoustic disturbance. A normal-incidence transmission loss measurement system was used to assess the performance of the DPAP and of a single panel passive partition. Error signal attenuations show that it is both feasible and effective to simultaneously control both panels with decoupled feedback controllers, and that simultaneously controlling both panels of the DPAP has a distinct advantage over controlling a single panel. The reduction in vibration amplitude across the surface of the transmitting panel was confirmed with scanning laser vibrometer measurements. Transmission loss results were obtained for two passive and three active configurations. The average normal incidence transmission loss over the active measurement bandwidth (50–1,000 Hz) for the active double-panel was 60 dB. This is an average of 39 dB more transmission loss than a passive single panel partition.
Beamforming in Reflecting Environments: An Experiment in a Reverberation Chamber
Authors: Dougherty Robert P. , Fonseca William D’Andrea , Gerges Samir N. Y.
Published: June 2009

Beamforming in reverberant environments is important to locate and quantify noise sources in turbofan engine nacelles, automobile interiors, factories, and architectural settings. In order to validate and explore the limits of this approach, a beamforming experiment was conducted in a reverberation chamber using a 32 channel planar phased array and a B&K sound power source. In the reference configuration, the source was located 2 m from the 1.1 m diameter array, and neither was close to the chamber walls. A less-demanding case was constructed by adding some foam absorber to the room to reduce reverberation. A difficult case resulted when the source was placed 5 m from the array, about 1 m from a corner of the chamber. Conventional frequency-domain beamforming with diagonal deletion was applied. The sound source was accurately located at the 2 m distance, with and without the added absorber. In the 5 m case, the sound source could be located at only a few frequencies and only when the processing bandwidth was increased from 48.8 Hz to 781 Hz. Processing individual eigenvectors of the CSM separated the direct and reflected source in 5 m case. The error in the deduced broadband sound power was 0.72 dB in the baseline case, 1.47 dB with the added absorber, and 5.41 dB with the speaker in the corner. Application of CLEAN-SC did not improve the accuracy of the corner results. Use of a Green’s function that attempts to account for reflections was ineffective. It is concluded that beamforming in highly reverberant environment with the free space Green’s function is practical, provided the array is designed and positioned correctly for the environment and source location.
Ray-Based Acoustic Localization of Discreet Sound Sources in a Highly Reverberant Environment
Authors: Chang Natasha A. , Dowling David R.
Published: June 2009

An acoustic localization method is applied in a reverberant environment to locate the sources of discrete sounds having unknown timing and waveform. In particular, the localization method is applied to study low event rate cavitation in a vortical flow in a water-tunnel test-section with characteristic cross section dimension of 0.3 m. The primary frequency and bandwidth of the acoustic pulses from the small isolated cavitation bubbles are 10 kHz and 200 kHz respectively, and the measured pulse duration is ∼15–20 micro-seconds. The localization method involves using an array of receiving hydrophones to record the cavitation sound pulses. These hydrophone recordings, which include direct-path signal, reflected path signal, and noise, are time windowed and cross-correlated to obtain direct-path arrival-time differences. These arrival time differences are used in conjunction with a simple ray-based acoustic model to estimate the source location in three dimensions via a robust Monte-Carlo routine. The ratio of the primary-frequency wavelength to the water-tunnel cross-section dimension is ∼1/2. Consequently the time-windowing is tight; only 1 to 1.5 center-frequency cycles at the beginning of a signal pulse are readily useful for localization purposes. The remainder of the signal is contaminated by reflections and is not used in the present effort. To check and validate the results of the acoustic method, two-camera high-speed video data was taken synchronously with the acoustic data for 53 cavitation events. The acoustic localization scheme provided an unambiguous location estimate for all 53 cavitation bubbles. The average distance between the optical and acoustic measurement of the bubble location was 18.4 mm, or ∼1/8 of the wavelength of the primary signal frequency.
Noise Source Identification on a Continuous Mining Machine
Authors: Camargo Hugo E. , Smith Adam K. , Kovalchik Peter G. , Matetic Rudy J.
Published: June 2009

Noise Induced Hearing Loss is the most common occupational disease in the U.S. and of paramount importance in the mining industry. According to data for 2006 from the Mine Safety and Health Administration (MSHA), Continuous Miner operators accounted for 30.2% of underground mining equipment operators with noise doses exceeding the Permissible Exposure Limit (PEL). This figure becomes more significant considering that 49% of the 2006 national underground coal production was extracted using continuous mining methods. Thus, there is a clear need to reduce the sound radiated by Continuous Mining Machines. The first step towards efficient noise control of a Continuous Mining Machine requires identification of the various noise sources under controlled operating conditions. To this end, a 42-microphone phased array was used in conjunction with 4 reference microphones to sample the acoustic field of a machine in the Hemi-anechoic chamber of the Pittsburgh Research Laboratory. These data were processed using a frequency-domain beamforming algorithm to obtain acoustic maps of 5 sides of the machine. The focus of the test was on the conveyor noise since previous studies showed that operation of the conveyor is the most important contributor to the sound radiated by the machine. From the acoustic maps, the following potential areas for noise control were identified, and included: chain-tail-roller interaction, chain flight tip-side board interaction, and chain-upper deck interaction.
Using a Dynamometer Along With Road Tests to Measure Vehicle Rolling and Wind Noise
Authors: Wentzel Richard E. , Aubert Allan
Published: June 2009

The consumer today places greater demands upon the vehicle acoustical engineer than in the past. Product quality has always been associated with a quiet ride. Automotive engineers recognize that the predominant sources of vehicle interior noise are wind, tire-road or rolling noise, and the powertrain. This paper suggests a test protocol for measuring wind and rolling noise using a chassis rolls dynamometer and road tests. Automotive engineers are frequently confronted by customer complaints concerning wind noise. Usually, engineers resort to using wind tunnels to address these concerns and to conduct diagnostic studies to remedy wind noise problems. Unfortunately, wind tunnels are expensive to rent and difficult to schedule. As an alternative, the engineer can learn a great deal about the wind noise of a vehicle by using a chassis rolls dynamometer along with road tests [1,2]. If the chassis rolls surface texture closely matches that of the road surface, the tire-road or rolling noise signal in both situations can be assumed to be equivalent. The powertrain noise source can be minimized by shifting the vehicle into neutral and coasting. Wind noise is a source for the road measurements, but not for the chassis rolls. Hence, the wind noise can be calculated by measuring the cab interior noise for both operating conditions, and subtracting the rolling noise measured on the chassis rolls. The two vehicles tested in this study included a pickup truck and a sport utility vehicle. The acoustical data revealed significantly different rolling and wind noise characteristics. The pickup truck had significantly louder rolling noise, and the wind noise was dominated by low frequency sound. The sport utility vehicle was much quieter overall and was significantly quieter for rolling noise than the pickup. The wind noise of the sport utility vehicle also was dominated by high frequency components. Both vehicles showed that rolling and wind noise trends increase linearly with speed. However, the slope of wind noise data for the sport utility vehicle was much steeper than the pickup, which suggested that it was more sensitive to wind noise as speed increased. Exterior noise data from both vehicles showed that the tire-road signal from the road differed significantly from that of the chassis rolls dynamometer. Rolling & wind noises will become even more critical as the motor vehicle industry adopts hybrid electric and, in the future electric fuel cell vehicles, because powertrain noise sources in the vehicle will likely be reduced. The procedure suggested here provides an inexpensive simple approach to assessing rolling and wind noise in the vehicle.
Calculating the Speed of Sound in an Engine Exhaust Stream
Authors: Keske Justin D. , Blough Jason R.
Published: June 2009

The actual speed of sound in the exhaust medium of an engine plays an extensive role in the noise attenuation characteristics of the engine’s muffler system. For 2-stroke engine applications, the speed of sound in the exhaust gas also greatly affects how the expansion chamber is tuned to maintain maximum power output. The combustion process in an engine creates exhaust gases that differ from the composition of atmospheric air. This difference in chemical composition and humidity content yield a different density and ratio of specific heats. These ultimately yield different sound speeds in the exhaust gases compared to atmospheric air. This paper performs a full chemical analysis of the combustion process in an internal combustion gasoline engine to yield the chemical composition of the of the exhaust gases. An algorithm is written to calculate the speed of sound in the exhaust stream. The inputs of the algorithm include measurements of temperature, pressure, and relative humidity of the ambient intake air, specification of the gasoline/ethanol fuel blend, and a direct measurement of the exhaust gas temperature. Comparisons are made between sound speed approximation calculations based on air to calculations obtained by the algorithm.
Near Field Aeroacoustic Experimental Investigation in Low Speed Axial Fans
Authors: Bianchi Stefano , Corsini Alessandro , Rispoli Franco , Sheard Anthony G.
Published: June 2009

This paper describes a technique for the investigation of noise sources correlated to tip clearance flows in a low-speed axial fan. A detailed experimental acoustic study is carried out examining the chord-wise evolution of a rotor flow field in the proximity of the blade tip in a low-solidity impeller. The experiment is performed by keeping the rotor “frozen” inside an anechoic chamber. The Mach number, Reynolds number, and blade incidence angle are set in the static frame of reference, reproducing the flow field in the rotating frame. The ‘frozen’ fan rotor is mounted in an anechoic chamber. The near-field pressure perturbations are measured using a chord-traversed microphone. Near-field pressure data is then compared with theoretical predictions, experimental data, and numerical simulations. In this way the validity of the developed experimental scheme is assessed. The purpose of the present program of work is to identify the change in near-field noise as a result of the chord-wise turbulent structures that are located close to the blade surface at the tip. The objective is to study the evolution of turbulent flow structure paths along the chord, and thus to provide insights into their acoustic significance. The present program of work is facilitated by the existence of a detailed pre-existing experimental database on the fan studied.
Model Calculations of Wind Noise Measured in a Flat Surface Under Turbulent Flow
Authors: Yu Jiao , Raspet Richard , Webster Jeremy , Dillion Kevin
Published: June 2009

It has been proposed that microphones mounted flush on the ground surface should measure reduced wind noise levels since the microphone does not disturb the flow and the wind velocity at the ground is small. However, there are pressure fluctuations induced on the ground by the interaction of the turbulent fluctuations above the ground with the average wind velocity gradient. Model calculations of the pressure spectrum under different wind velocity profiles have been developed based on the theoretical work of Kraichnan.1 Kraichnan calculated the turbulence-shear contribution to pressure fluctuations under boundary layer turbulence with an exponentially varying flow velocity profile. The calculations presented here incorporate measured outdoor spectra of the turbulence and different models of the velocity profile to investigate pressure fluctuation measurements outdoors at the ground surface. The predicted power spectral densities of the pressure are compared to each other and to measurements. The ultimate purpose of this research is to develop means to minimize wind noise interference in acoustic measurements. [Research supported by the U.S. Army TACOM-ARDEC at Picatinny Arsenal, NJ.]
An Investigation of the Characteristics of a Bayesian Military Impulse Noise Classifier
Authors: Bucci Brian , Vipperman Jeffrey
Published: June 2009

In extension of previous methods to identify military impulse noise in the civilian environmental noise monitoring setting by means of a set of computed scalar metrics input to artificial neural network structures, Bayesian methods are investigated to classify the same dataset. Four interesting cases are identified and analyzed: A) Maximum accuracy achieve on training data, B) Maximum overall accuracy on blind testing data, C) Maximum accuracy on testing data with zero false positive detections, D) Maximum accuracy on testing data with zero false negative rejections. The first case is used to illustrative example and the later three represent actual monitoring modes. All of the cases are compared and contrasted to illuminate respective strengths and weaknesses. Overall accuracies of up to 99.8% are observed with no false negative rejections and accuracies of up to 98.4% are also achieved with no false positive detections.
A Revisit of the Coupling Loss Factors in Determining Power Flows in Structures
Authors: Xu Hongan , Li Wen L.
Published: June 2009

Coupling loss factor is one of the most important parameters used in the statistical energy analysis (SEA). It regulates the energy flows between two subsystems. Theoretically, the coupling loss factors are usually calculated from the wave transmission coefficients derived using two semi-infinite systems. While the final system equation in the SEA is based on the powerful energy conservation principle, in the process the coupling loss factors are assumed to be unaffected by the configuration changes. In other words, the coupling loss factors which are experimentally or analytically determined under some ideal conditions are considered to be unchanged by the more complicated coupling conditions under a system configuration. The validity of this treatment needs to be carefully studied because there is a belief that the SEA method can be readily extended to lower frequencies so long as the coupling loss factors can be somehow satisfactorily determined. In this study, wave transmission coefficients are obtained by calculating the energy flows for a three-beam system coupled together in T-shape. Separately, the wave transmission coefficients are estimated by using energy flows calculated for each possible pairing of two beams. By comparing the results from these two different approaches, some insightful information has been obtained regarding the characteristics of the coupling loss factors in determining power flows in structures.
Mode-Based Frequency Response Analysis With Frequency-Dependent Material Properties
Authors: Bajer Andrzej
Published: June 2009

A new algorithm for mode-based frequency response analysis, which takes into account frequency-dependent material properties, is proposed. First, the projection subspace is determined by computing the eigenmodes of the system. If the AMLS-type eigensolver is used and the frequency-dependent material is confined to a limited area (often less than 1% of the whole model), eigenmodes are computed only in the region with the frequency-dependent material. Next, during the frequency response analysis portions (corresponding to the frequency-dependent material) of the stiffness, viscous damping, and structural damping operators are computed and projected onto the modal subspace. The original contribution of this paper is the algorithm, which augments the projected operators (stiffness, viscous damping, or structural damping) by the contributions from the area with the frequency-dependent material properties without the need to recompute the operator over the whole domain. This algorithm was successfully implemented in a commercial finite element code, Abaqus 6.8. The results for a vehicle body-in-prime model show good agreement with a direct-solution frequency response analysis. In the addition, the cost of the proposed algorithm is a fraction of the directsolution analysis.
Trailing Edge Noise From Blunt and Sharp Edge Geometries
Authors: Shannon Daniel W. , Morris Scott C. , Blake William K.
Published: June 2009

The objective of this study was to experimentally investigate the broadband trailing edge noise generated by a sharp trailing edge geometry and an asymmetric blunt edge. The flow field in the vicinity of the sharp trailing edge was found to be equivalent to that of a flat plate turbulent boundary layer. The interaction of the two boundary layers with the edge was responsible for broadband noise generation. The blunt trailing edge geometry exhibited additional complexity, with turbulent boundary layer separation and sound generated by vortex shedding. The measurement program included hot-wire anemometry, unsteady surface pressure, and radiated sound utilizing two microphone arrays. The boundary layer parameters and wall pressure spectra were used to compute the radiated sound from existing scattering theory. These calculations agreed very well with the array data, with differences typically within 2dB over the frequency range considered valid for the theory.
Design of Acoustic Cloak by Transmission Line Approach
Authors: Zhang Shu , Fang Nicholas
Published: June 2009

This paper proposed an approach to construct the acoustic cloak by a network of subwavelength Helmholtz resonators. Based on transmission line model to describe the acoustic wave propagation inside such effective anisotropic medium, we derived the acoustic parameters such as effective density and compressibility. Our simulation demonstrates the propagation of acoustic waves can be bent and excluded from an object inside the cloak with no perturbation of exterior field, which may have great potential application in ultrasound noise control.
A New Road-Side Array-Based Method for Characterization of Truck Noise During Passby
Authors: Blake William K. , Donovan Paul
Published: June 2009

This paper describes the development of a new method for measuring pass-by sound from trucks and other vehicles using 2-dimensional arrays. The approach provides 2-dimensional quantitative maps “images” of the cross-range and elevation distribution in the vehicle side view. The method is an application and extension of an array technology that was originally used for the characterization of static aeroacoustic sources in wind tunnels. The focus of this work is on identifying and rank-ordering the important contributing sources of passby noise. This development includes two phases: developmental testing at a test track site, and road-side testing at two California State highway sites. The acquisition post-processing allows the “observer” to track the vehicle cross-range in order to create a time sequence of source maps that may be interpreted as both level relationships and directivity patterns. The processing applies both range and approximate Doppler adjustments to spectra as a function of time during pass-by or, equivalently, to vehicle position relative to the array’s center. An image demodulation scheme is shown to clarify the images. The initial phase of this work occurred at a test track using known “cooperative” truck sources. This experience permitted the verification of the method and the definition of a final measurement approach that was viable at a highway site. Subjects were all trucks that varied in model, vehicle speed, tread, and the presence of a trailer. The array beamformer’s ability to localize and the measurement system’s ability to track were validated using both stationary and moving sources. Following validation at the test track site, the instrumentation was transferred to two California highway sites. There, acoustic calibration was used to align the array with the road track and to provide a spatial reference for mapping the “images”. Both light and heavy vehicles at these sites were “uncooperative” with arrivals and speeds randomly determined by traffic flow. This work was funded by the California Department of Transportation.
Study of Coupled Acoustic Wave Propagation in a Circular Metal Pipe for the Correlation Method
Authors: Kim Ho-Wuk , Lee Sang-Kwon , Kim Min-Soo
Published: June 2009

The circular cylinder pipe is extensively used for the supplement of the gas. The leakage of this gas induces the catastrophic problem when it leases into open area in the city without any monitoring. A correlation method has been mostly used for the detection of the leakage. It is needed a good coherence and an efficient energy transmission to the external sensors for the reliable estimation of the correlation. This paper investigated theoretically the propagation of the acoustic wave of the circular cylinder pipe containing the gas in a pipe for the development of the leakage monitoring system. The acoustic wave is propagated through the waveguide of the circular pipe with the characteristics acoustically coupled by the gas contained in a cylinder and the shell. However, as a special case, the acoustic waves in a metal pipe containing gas are corresponded closely to the uncoupled in-vacuo shell waves and to the rigid-wall duct fluid waves. In this case, the dominant acoustic energy can be estimated at the frequencies in which coincidence between the shell modes and the acoustic modes occurs. In the paper, the characteristics of the dominant waves are theoretically investigated and analyzed experimenttally with a long steel pipe. The measured data is clearly analyzed by the continuous wavelet transform and by spectral density analysis.
Adaptive IIR Filter Using Variable Step Size for Active Noise Control Inside a Short Duct
Authors: Kim Ho-Wuk , Lee Sang-Kwon
Published: June 2009

FIR filter for a adaptive filter algorithm, is mostly used for an active noise control system. However, FIR filter needs to have more large size of the filter length than it of IIR filter. Therefore, the control system using FIR adaptive filter has slow calculation time. In the active noise control system of the short duct, the reference signal can be affected by the output signal, so IIR filter for ARMA system can be more suitable for the active noise control of the short duct than FIR filter for MA system. In this paper, the recursive LMS filter, which is adaptive IIR filter, is applicated for the active noise control inside the short duct. For faster convergence and more accurate control, a variable step size algorithm is introduced for this recursive LMS filter (R-VSSLMS filter). Using this algorithm and considering the secondary path, the filtered-u R-VSSLMS is conducted successfully on the real experiment in the short duct. The performance of the active control using the filtered-u R-VSSLMS filter, is compared with the performance of the active control using a filtered-x LMS filter.
Characterization of High Frequency Radiation From Panels Subject to Broadband Excitation
Authors: Bliss Donald , Franzoni Linda , Michalis Krista
Published: June 2009

In the high frequency limit, a vibrating panel subject to spatially-random temporally-broadband forcing is shown to have broadband power and directivity properties that can be expressed in simple analytical terms by a limited set of parameters. A lightly-loaded fixed-fixed membrane with a distribution of broadband uncorrelated drive points is analyzed. The theory is developed using classical modal methods and asymptotic modal analysis, assuming small damping. The power and directivity of the radiated pressure field are characterized in terms of structural wave Mach number, damping ratio, and dimensionless frequency. The relatively simple directivity pattern that emerges can be shown to arise from edge radiation. From the point of view of edge radiation, assuming a lightly damped reverberant structure, the same radiation formula and directivity pattern can be derived in a much simpler manner. Broadband radiation from structures with subsonic and supersonic flexural wave speeds is discussed and characterized in terms of a simple interpretation of the surface wavenumber spatial transform. The results show that the physical idea of interpreting edge radiation in terms of uncancelled volumetric sources is not correct, and the effect of higher order edge singularities is in fact very significant. The approach implies a relationship between radiation and structural power flow that is potentially useful in energy-intensity based prediction methods, and can be generalized to more complex structures with application to vehicle interior noise prediction.
Sound Attenuation and Prediction of Porous Media Properties in Hybrid Ducts Utilizing Spatially Periodic Area Changes
Authors: Burton Lisa J. , Bliss Donald B. , Franzoni Linda P.
Published: June 2009

A theory based on cross-sectional averaging is developed to analyze quasi-one-dimensional acoustic propagation in hybrid ducts with two propagation media in the cross-section. Specifically, ducts lined with a thick layer of porous material are considered. The porous material makes the duct wavenumber complex, changing the phase speed and introducing attenuation. To lowest order, the wavenumber depends only on the ratio of cross-sectional areas and the properties of the constituent media, and surprisingly not on the material configuration in the cross-section. High frequency accuracy can be improved by using a small correction that includes shape coefficients that depend on the cross-sectional configurations. If the propagation wavenumber is measured experimentally in a hybrid duct, the complex effective sound speed and density, fundamental porous material properties, can be extracted relatively easily. Experimentally, open cell foam samples line the sides of a tube closed at one end, and the complex wavenumber is determined from standing wave measurements. The cross-sectional averaging theory is then used to determine the acoustic properties of the open-cell foam. Results are compared for various lining configurations to assess the accuracy of the method. Another application of this work is the theoretical and experimental study of the propagation of quasi one-dimensional acoustic waves through a duct with spatially periodic area changes. This configuration exhibits stop-band and pass-band behavior, with substantially reduced sound transmission in stop bands, but little effect in pass bands. The regions of the duct with larger cross-sectional area are partially filled with an annular region of porous material to provide pass-band attenuation, leaving a constant area passage for airflow. Predictions and measurements for hybrid ducts with periodic area changes are presented. A muffler designed to place engine harmonics in targeted stop-bands is described.
Magnetic Noise in Induction Motors
Authors: Curiac Radu S. , Singhal Sumit
Published: June 2009

Noise in large high voltage induction motors (500Hp–18000Hp) may be airborne or magnetic in nature. Usually, large high voltage induction motors are custom built and tailored to meet customer’s demand. Since every motor is unique in its design, it is imperative to predict accurately the magnetic noise generation during design phase, this way avoiding expensive rework cost and not loosing the customer confidence. Stator – rotor mechanical design, along with careful electrical coil design, can significantly cut down magnetic noise in an induction motor. This paper discusses the various causes and control of magnetic noise in large induction motors. Theoretical noise predictions in large induction motors, along with measured experimental noise data, are presented.
An Efficient Sandwich Plate Element for Predicting the Vibro-Acoustic Response of Laminated Steel Panels
Authors: Amichi Kamel , Atalla Noureddine , Ruokolainen Robert
Published: June 2009

A New finite element sandwich plate is presented. It is based on discrete displacement approach and allows for both symmetrical and unsymmetrical configurations. The validity and accuracy of the presented element is assessed through comparisons with both tests and classical FE modeling. The tests consist of various configurations of sandwich panels in a coupled plate-cavity system. A parametric study, using the developed element, is finally presented to highlights the effects of skin and core properties on the vibration and radiation of such structures under both airborne and structure-borne excitations.
Wind Noise Reduction for Outdoor Measurement Microphones With Windscreens
Authors: Zheng Z. C. , Xu Ying
Published: June 2009

In this study, effects of windscreen material property on wind noise reduction are investigated at different frequencies of incoming wind turbulence. The properties of porous materials used for the windscreen are represented by flow resistivity. Computational techniques are developed to study the detailed flow around the windscreen as well as flow inside the windscreen that uses a porous material as the medium. The coupled simulation shows that for low-frequency turbulence, the windscreens with low flow resistivity are more effective in noise reduction. Contrarily, for high-frequency turbulence, the windscreens with high flow resistivity are more effective.
Active Noise Control of a Cooling Fan in a Short Duct
Authors: Kinney Charles E. , Villalta Alberto , de Callafon Raymond A.
Published: June 2009

In this paper we develop a data based model, design a high performance robust controller, and apply the controller in real-time to reduce narrowband acoustic noise from a cooling fan. A custom, portable enclosure houses the cooling fan. One end of the enclosure is fitted with four speakers and four microphones, inside of a short duct, connected to a data acquisition system and a personal computer. Passive materials mounted at the other end of the enclosure reduce backside noise. The frequency of the narrrowband noise is assumed unknown and therefore a control design that can be updated in realtime is needed. The control design that is presented uses a nominal model and a nominal controller. The nominal controller is enhanced by using closed loop signals and taking into account the modeling error. The end result is a data-based method for updating a nominal controller to improve performance.
A Method for Noise Reduction in Hydraulic Lines
Authors: Wang James , Paidoussis Michael , Mongeau Luc
Published: June 2009

Sound transmission in hydraulic lines is of great importance in many engineering applications. Sound produced from hydraulic pumps may be radiated to the environment, and transmitted between components through flexible hoses, often modelled as shell-type structures. Noise in hydraulic lines filled with flowing fluid is generated through complex fluid-structure interactions. In this project, a conceptual muffler configuration consisting of a set of alternating shell segments was investigated. By varying parameters such as material properties and the hose dimensions, both fluid and structural waves in the hose are attenuated through the creation of stop bands at the operating frequency. In this paper, thick- and thin-shell theories were investigated. It was found that, for low frequencies or long wavelengths, consistent results were obtained from both theories. The transfer matrix method was used in conjunction with Floquet theory in the analysis of the periodic shell system. Preliminary results showed that numerous stop bands appear and substantial attenuation can be achieved. The first two natural frequencies of a shell with and without fluid loading were computed. Their values agree with similar results from other researchers. Finally, several parameters were varied to study their effects on the natural frequencies. These results will be used later in the design of the shell attenuator.
Reconstruction of Normal Surface Velocities of a Simply-Supported Baffled Plate Using Helmholtz Equation Least Square Method
Authors: Lu Huancai , Wu Sean F.
Published: June 2009

The normal surface velocities of highly a non-spherical object are reconstructed based on the measurement of field acoustic pressures using Helmholtz equation least-squares (HELS) method. The objectives of this study are to numerically examine the feasibility and accuracy of reconstruction and the impacts of various parameters involved in reconstruction of vibro-acoustic responses using HELS. The vibrating object is a simply-supported and baffled thin plate. The reasons for selecting this object are that plate is the most challenging source geometry for HELS method, and it represents a class of structures that cannot be exactly described by the spherical Hankel functions and spherical harmonics, which are primarily embedded in the HELS formulation, yet the analytic solutions to vibro-acoustic responses of a baffled plate are readily available so the accuracy of reconstruction can be checked in detail. The Rayleigh integral is used to generate the input field acoustic pressures for reconstruction. The Euler’s equation is employed to establish the system model of reconstruction of vector velocities. Regularization associated with the truncated singular value decomposition is utilized to compromise the resultant accuracy and stability of the vector velocity reconstruction. The reconstructed normal surface velocities are validated against the benchmark values, and the out-of-plane vibration patterns at several natural frequencies are compared with the natural modes of a simply-supported plate. The impacts of various parameters such as the measurement points, measurement distance, the location of origin of coordinate system, microphone spacing, and ratio of measurement aperture size to the area of source surface of reconstruction on the resultant accuracy of reconstruction are examined.
Understanding Roughness Noise: Progress in Analytical Modeling and Testing, Part 2—Comparison of Calculations to Data
Authors: Martinez R. , Uhlman J. S. , Ting C. M. , Paul B. S. , Anderson J. M. , Goody M. C. , Stewart D. O.
Published: June 2009

This Part-2 paper applies Part 1’s theory of sheared rapid distortions to compute broadband noise from flow over large roughness elements, and compares those calculations to recent wind-tunnel measurements. The calculations suggest that shear effects are subdominant in the sound-production process. Post-processing of computed results brings out key features of the theory’s non-equilibrium distorting turbulence. A follow-up analysis makes possible the physical interpretation of the measured acoustic spectral densities in terms of the kinematics of the spatially non-uniform carrier flow.
Fluorescence-Based Assay for Phenotypic Characterization of Human Cytomegalovirus Polymerase Mutations Regarding Drug Susceptibility and Viral Replicative Fitness
Authors: Chevillotte Meike , Schubert Axel , Mertens Thomas , von Einem Jens
Published: June 2009

One essential prerequisite for genotypic drug susceptibility testing of human cytomegalovirus (HCMV) is the phenotypic characterization of mutations identified in the viral protein kinase gene UL97 and the viral DNA polymerase gene UL54 regarding their quantitative impact on drug susceptibility. We developed a new method for phenotypic characterization of UL54 mutations with regard to polymerase activity, viral replication, and drug susceptibility. To determine the most suitable viral indicator gene, enhanced green fluorescence protein was C-terminally fused to the HCMV early-late protein UL83 (pp65) or the late proteins UL32 (pp150) and UL99 (pp28), resulting in reporter viruses vTB65g, vTB150g, and vTB28g. vTB65g proved to be superior to the other constructs due to its favorable signal-to-noise ratio and was therefore used to establish the optimum conditions for our assay. The UL54 E756K and D413E mutations were introduced into vTB65g by markerless bacterial artificial chromosome mutagenesis, resulting in virus strains vE756Kg and vD413Eg. The drug susceptibility phenotypes of vE756Kg and vD413Eg were comparable to those previously reported. Furthermore, we found a reduced replicative fitness of vE756Kg by measuring fluorescence intensity as well as by conventional virus growth kinetics. Decreased fluorescence signals of vE756Kg- and vD413Eg-infected cells at late times of infection suggested a reduced polymerase activity, which was confirmed by real-time PCR quantification of the newly synthesized viral DNAs. This new fluorescence-based assay is a highly reproducible method for the phenotypic characterization of mutations potentially influencing drug susceptibility, viral replicative fitness, and polymerase activity of HCMV after marker transfer.
Prevalence and Characterization of Heterogeneous Vancomycin-Intermediate
Staphylococcus aureus
Isolates from 14 Cities in China
Authors: Sun Wenjia , Chen Hongbin , Liu Yudong , Zhao Chunjiang , Nichols Wright W. , Chen Minjun , Zhang Jianzhong , Ma Yue , Wang Hui
Published: June 2009

The prevalence of heterogeneous vancomycin-intermediate
Staphylococcus aureus
(hVISA) among 1,012 vancomycin-susceptible methicillin (meticillin)-resistant
S. aureus
isolates collected from 14 cities in China from 2005 to 2007 was 13 to 16%, as determined by a combination of (i) measurement by the modified population analysis profile-area under the curve method (PAP-AUC) and (ii) estimation from the measured sensitivity and specificity of a screening method. Two hundred isolates from blood were chosen as a subset for measurement of the sensitivities and the specificities of several previously described screening methods by using the results of PAP-AUC as the reference. During this testing, one isolate was found to be a vancomycin-intermediate
S. aureus
(VISA) strain so was not used in the evaluation of the screening tests. Of the other 199 isolates, 26 (13.1%) were hVISA, as assessed by PAP-AUC. A screening cascade of culturing the isolates on brain heart infusion agar containing teicoplanin (5 mg/liter) and then subjecting the positive isolates to a macro-Etest method was applied to the 812 non-blood isolates, yielding 149 positive results. From these results and by adjusting for sensitivity (0.423) and specificity (0.861), the prevalence was estimated to be 15.7%. The precision of that estimate was assessed by reapplying the screening cascade to 120 randomly selected isolates from the 812 non-blood isolates and simultaneously determining their heterogeneous vancomycin-intermediate susceptibility status by PAP-AUC. Because PAP-AUC is impractical for use with large numbers of isolates, the screening-based estimation method is useful as a first approximation of the prevalence of hVISA. Of the 27 VISA or hVISA isolates from blood, 22.2% and 74.1% were staphylococcal chromosome cassette
mec
types II and III, respectively, while 77.8% and 22.2% were
agr
type 1 and
agr
type 2, respectively; the MIC ranges were 0.5 to 4 mg/liter for vancomycin and 0.25 to 1 mg/liter for daptomycin.
Mosaic Penicillin-Binding Protein 2 in
Neisseria gonorrhoeae
Isolates Collected in 2008 in San Francisco, California
Authors: Pandori Mark , Barry Pennan M. , Wu Abel , Ren Alyssa , Whittington William L. H. , Liska Sally , Klausner Jeffrey D.
Published: June 2009

Using a real-time PCR assay specific for a mosaic
penA
allele that has been associated with oral cephalosporin resistance in Asia, 54 available
Neisseria gonorrhoeae
isolates collected in San Francisco, CA, from January to October 2008 were analyzed. Five isolates tested positive for the mosaic
penA
gene by real-time PCR. DNA sequencing revealed two mosaic
penA
alleles (SF-A and SF-B). Isolates with SF-A and SF-B alleles possessed elevated MICs for the oral cephalosporins cefpodoxime and cefixime.
In Vitro Susceptibilities of
Leishmania donovani
Promastigote and Amastigote Stages to Antileishmanial Reference Drugs: Practical Relevance of Stage-Specific Differences
Authors: Vermeersch Marieke , da Luz Raquel Inocêncio , Toté Kim , Timmermans Jean-Pierre , Cos Paul , Maes Louis
Published: June 2009

The in vitro susceptibilities of the reference strain
Leishmania donovani
MHOM/ET/67/L82 to sodium stibogluconate, amphotericin B, miltefosine, and the experimental compound PX-6518 were determined for extracellular log-phase promastigotes, established axenic amastigotes, fresh spleen-derived amastigotes, and intracellular amastigotes in primary mouse peritoneal macrophages. Susceptibility to amphotericin B did not differ across the various axenic models (50% inhibitory concentrations [IC
50
], 0.6 to 0.7 μM), and amphotericin B showed slightly higher potency against intracellular amastigotes (IC
50
, 0.1 to 0.4 μM). A similar trend was observed for miltefosine, with comparable efficacies against the extracellular (IC
50
, 0.4 to 3.8 μM) and intracellular (IC
50
, 0.9 to 4.3 μM) stages. Sodium stibogluconate, used either as Pentostam or as a crystalline substance, was inactive against all axenic stages (IC
50
, >64 μg Sb
V
/ml) but showed good efficacy against intracellular amastigotes (IC
50
, 22 to 28 μg Sb
V
/ml); the crystalline substance was about two to three times more potent (IC
50
, 9 to 11 μg Sb
V
/ml). The activity profile of PX-6518 was comparable to that of sodium stibogluconate, but at a much higher potency (IC
50
, 0.1 μg/ml). In conclusion, the differential susceptibility determines which in vitro models are appropriate for either drug screening or resistance monitoring of clinical field isolates. Despite the more complex and labor-intensive protocol, the current results support the intracellular amastigote model as the gold standard for in vitro
Leishmania
drug discovery research and for evaluation of the resistance of field strains, since it also includes host cell-mediated effects. Axenic systems can be recommended only for compounds for which no cellular mechanisms are involved, for example, amphotericin B and miltefosine.
A Novel Tryptophanyl-tRNA Synthetase Gene Confers High-Level Resistance to Indolmycin
Authors: Vecchione James J. , Sello Jason K.
Published: June 2009

Indolmycin, a potential antibacterial drug, competitively inhibits bacterial tryptophanyl-tRNA synthetases. An effort to identify indolmycin resistance genes led to the discovery of a gene encoding an indolmycin-resistant isoform of tryptophanyl-tRNA synthetase. Overexpression of this gene in an indolmycin-sensitive strain increased the indolmycin MIC 60-fold. Its transcription and distribution in various bacterial genera were assessed. The level of resistance conferred by this gene was compared to that of a known indolmycin resistance gene and to those of genes with resistance-conferring point mutations.