bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling Secondary-Flow Structure by Leading-Edge Airfoil Fillet and Inlet Swirl to Reduce Aerodynamic Loss and Surface Heat Transfer
Authors: Shih T. I-P. , Lin Y.-L.
Published: January 2003

Computations, based on the ensemble-averaged compressible Navier-Stokes equations closed by the shear-stress transport (SST) turbulence model, were performed to investigate the effects of leading-edge airfoil fillet and inlet-swirl angle on the flow and heat transfer in a turbine-nozzle guide vane. Three fillet configurations were simulated: no fillet (baseline), a fillet whose thickness fades on the airfoil, and a fillet whose thickness fades on the endwall. For both fillets, the maximum height above the endwall is positioned along the stagnation zone/line on the airfoil under the condition of no swirl. For each configuration, three inlet swirls were investigated: no swirl (baseline) and two linearly varying swirl angle from one endwall to the other (+30 to −30 deg and −30 to +30 deg). Results obtained show that both leading-edge fillet and inlet swirl can reduce aerodynamic loss and surface heat transfer. For the conditions of this study, the difference in stagnation pressure from the nozzle’s inlet to its exit were reduced by more than 40% with swirl or with fillet without swirl. Surface heat transfer was reduced by more than 10% on the airfoil and by more than 30% on the endwalls. When there is swirl, leading-edge fillets became less effective in reducing aerodynamic loss and surface heat transfer, because the fillets were not optimized for swirl angles imposed. Since the intensity and size of the cross flow were found to increase instead of decrease by inlet swirl and by the type of fillet geometries investigated, the results of this study indicate that the mechanisms responsible for aerodynamic loss and surface heat transfer are more complex than just the intensity and the magnitude of the secondary flows. This study shows their location and interaction with the main flow to be more important, and this could be exploited for positive results.
Using Gurney Flaps to Control Laminar Separation on Linear Cascade Blades
Authors: Byerley Aaron R. , Sto¨rmer Oliver , Baughn James W. , Simon Terrence W. , Van Treuren Kenneth W. , List Jo¨rg
Published: January 2003

This paper describes an experimental investigation of the use of Gurney flaps to control laminar separation on turbine blades in a linear cascade. Measurements were made at Reynolds numbers (based upon inlet velocity and axial chord) of 28×103,65×103 and 167×103. The freestream turbulence intensity for all three cases was 0.8%. Laminar separation was present on the suction surface of the Langston blade shape for the two lower Reynolds numbers. In an effort to control the laminar separation, Gurney flaps were added to the pressure surface close to the trailing edge. The measurements indicate that the flaps turn and accelerate the flow in the blade passage toward the suction surface of the neighboring blade thereby eliminating the separation bubble. Five different sizes of Gurney flaps, ranging from 0.6 to 2.7% of axial chord, were tested. The laser thermal tuft technique was used to determine the influence of the Gurney flaps on the location and size of the separation bubble. Additionally, measurements of wall static pressure, profile loss, and blade-exit flow angle were made. The blade pressure distribution indicates that the lift generated by the blade is increased. As was expected, the Gurney flap also produced a larger wake. In practice, Gurney flaps might possibly be implemented in a semi-passive manner. They could be deployed for low Reynolds number operation and then retracted at high Reynolds numbers when separation is not present. This work is important because it describes a successful means for eliminating the separation bubble while characterizing both the potential performance improvement and the penalties associated with this semi-passive flow control technique.
Flow and Heat (Mass) Transfer Characteristics in an Impingement/Effusion Cooling System With Crossflow
Authors: Rhee Dong Ho , Choi Jong Hyun , Cho Hyung Hee
Published: January 2003

The present study is conducted to investigate flow and heat/mass transfer characteristics in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of two times of the hole diameter, and initial crossflow passes between the plates. Both the injection and effusion hole diameters are 10 mm, and the Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and six times of the hole diameter, respectively. To investigate the effect of crossflow, the flow rate of crossflow is changed from 0.5 to 2 times of that of the impinging jet, and the results of impingement/effusion cooling with crossflow are compared with those of the crossflow in the channel and of an array of impingement jets and the effusion cooling system. A naphthalene sublimation method is used to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. The flow patterns are calculated numerically using a commercial package. With the initial crossflow, the flow and heat/mass transfer characteristics are changed significantly from the results without the crossflow. Jet flows ejected from the injection plate are deflected by the crossflow, so that the stagnation points of the impinging jets move downstream. The heat/mass transfer rates on the effusion (target) plate decrease as the velocity of crossflow increases, since the crossflow induces the locally low transfer regions formed at the mid-way between the effusion holes. However, the impingement/effusion cooling with crossflow presents higher heat/mass transfer rates than the array jet impingement cooling with the same initial crossflow.
Multiple Equilibria of a Hydrodynamically Coupled Flexible Disk Rotating Inside a Thin Housing
Authors: Warner and G. M. , Renshaw A. A.
Published: January 2003

Experimental results are reported and a simple model proposed to explain a phenomenon in which the equilibrium deflection of a flexible disk rotating inside a narrow housing undergoes an abrupt jump when the rotation speed is varied slightly. Discontinuous jumps are observed in a small fraction (25%) of Zip disks rotating between 3000 rpm and 4500 rpm. For those disks exhibiting jumps, the jumps are repeatable for both increases and decreases in rotation speed during a test; no hysteresis is observed. A disk that initially exhibits the jump phenomenon may fail to exhibit jumps several days or weeks later and vice versa. Numerical results for a rotating membrane hydrodynamically coupled to the surrounding flow show that the number of possible equilibria is a sensitive function of the radial flows above and below the disk. In particular, a small change in radial flow from a radially inward flow to a radially outward flow can abruptly change the number of possible equilibria from two to one. The characteristics of this transition are compatible with the experimental observations.
An Alternative Method of Solving Multilayer Bending Problems
Authors: Hsueh C. H. , Lee S. , Chuang T. J.
Published: January 2003

Stress distributions in multilayers subjected to both residual stresses and external bending are analyzed to derive closed-form analytical solutions. There are always three unknowns to be solved and three equilibrium conditions to be satisfied in the present analysis. In contrast, the numbers of unknowns and conditions increase with the number of layers in the system in existing analyses.
Squeeze Film Force Using an Elliptical Velocity Profile
Authors: Usha R. , Vimala P.
Published: January 2003

The squeeze film force in a circular Newtonian squeeze film has been theoretically predicted by using the elliptical velocity profile assumption in the squeeze film by three different approximation methods. As examples, the numerical results for the sinusoidal squeeze motion, constant velocity squeezing state, and constant force squeezing state have been obtained and the results have been found to be in good agreement with those obtained using experimental test coefficients predicted by the spectral analysis techniques for Newtonian circular squeeze film geometry. The validity of applying the energy integral method (EIM) or the successive approximation method (SAM) has been justified and the effectiveness of EIM or SAM in predicting squeeze film force using the elliptical velocity profile assumption in the squeeze film for large-amplitude motion has been demonstrated.
Stabilization Parameters and Smagorinsky Turbulence Model
Authors: Akin J. E. , Tezduyar T. , Ungor M. , Mittal S.
Published: January 2003

For the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin formulations for flow problems, we present in this paper a comparative study of the stabilization parameters defined in different ways. The stabilization parameters are closely related to the local length scales (“element length”), and our comparisons include parameters defined based on the element-level matrices and vectors, some earlier definitions of element lengths, and extensions of these to higher-order elements. We also compare the numerical viscosities generated by these stabilized formulations with the eddy viscosity associated with a Smagorinsky turbulence model that is based on element length scales.
An Extended Finite Element Method for Two-Phase Fluids
Authors: Chessa J. , Belytschko T.
Published: January 2003

An extended finite element method with arbitrary interior discontinuous gradients is applied to two-phase immiscible flow problems. The discontinuity in the derivative of the velocity field is introduced by an enrichment with an extended basis whose gradient is discontinuous across the interface. Therefore, the finite element approximation can capture the discontinuities at the interface without requiring the mesh to conform to the interface, eliminating the need for remeshing. The equations for incompressible flow are solved by a fractional step method where the advection terms are stabilized by a characteristic Galerkin method. The phase interfaces are tracked by level set functions which are discretized by the same finite element mesh and are updated via a stabilized conservation law. The method is demonstrated in several examples.
Optimal Temperature and Current Cycles for Curing of Composites Using Embedded Resistive Heating Elements
Authors: Mawardi A. , Pitchumani R.
Published: January 2003

Curing is an important and time consuming step in the fabrication of thermosetting-matrix composite products. The use of embedded resistive heating elements providing supplemental heating from within the material being cured has been shown in previous studies (Ramakrishnan, Zhu, and Pitchumani, 2000, J. Manuf. Sci. Eng., 122, pp. 124–131; and Zhu and Pitchumani, 2000, Compos. Sci. Technol., 60, 2699–2712.) to offer significant improvements in cure cycle time and cure uniformity, due to the inside-out curing. This paper addresses the problem of determining the temperature and electrical current cycles, as well as the placement configuration of the conductive mats, for time-optimal curing of composites using embedded resistive heating elements. A continuous search simulated annealing optimization technique is utilized coupled with a numerical process simulation model to determine the optimal solutions for selected process constraints. Optimization results are presented over a range of material systems and different numbers of conductive mats to assess the effects of materials reactivity on the optimal number of conductive mats.
Surface Temperature Measurement of Semi-Transparent Ceramics by Long-Wavelength Pyrometry
Authors: Pfefferkorn Frank E. , Incropera Frank P. , Shin Yung C.
Published: January 2003

A procedure using a long-wavelength pyrometer is developed for the measurement of surface temperatures on materials that are semitransparent at shorter wavelengths, and specific application is made to a dense zirconia ceramic (Mg-PSZ) undergoing laser-assisted machining (LAM). The pyrometer operates in a waveband between 11 and 14 μm, and a detailed description of measurement uncertainties is provided. The largest uncertainties relate to knowledge of the surface emissivity and the large temperature gradients generated by the LAM process. Repeatability of the measurements is demonstrated, and a parametric study of three LAM parameters reveals expected trends.
Analytical and Experimental Study of Combustion and Heat Transfer in Submerged Flame Metal Fiber Burners/Heaters
Authors: Leonardi S. A. , Viskanta R. , Gore J. P.
Published: January 2003

A theoretical model has been developed to predict the thermal performance of inert, direct-fired, woven-metal fiber-matrix porous radiant burner. The local chemical heat release was modeled by a detailed mechanism, and convection heat transfer between the gas and the solid phases in the burner was described by an empirical heat transfer coefficient. The solid matrix was modeled as a gray medium, and the discrete ordinates method was used to solve the radiative transfer equation to calculate the local radiation source/sink in the energy equation for the solid phase. The fully coupled nature of the calculations without external specification of flame location represents a key advance over past efforts towards modeling of porous radiant burners, because for a given mass flow rate the actual heat loss from the flame determines its position and is not a free parameter. The calculated results for the burner surface temperature, the gas exhaust temperature and the radiation efficiency for a single layer Fecralloy burner were compared with experimental data from this laboratory and reasonable agreement was obtained for a range of operating conditions.
Operational Performance of a 5-kW Solar Chemical Reactor for the Co-Production of Zinc and Syngas
Authors: Kra¨upl Stefan , Steinfeld Aldo
Published: January 2003

We report on the improved operational performance and energy conversion efficiency of a 5-kW solar chemical reactor for the combined ZnO-reduction and CH4-reforming SynMet process. The reactor features a pulsed vortex flow of CH4 laden with ZnO particles, which is confined to a cavity-receiver and directly exposed to solar power fluxes exceeding 2000kW/m2. Reactants were continuously fed at ambient temperature, heated by direct irradiation to above 1350°K, and converted to Zn and syngas during mean residence times of 10 seconds. Typical chemical conversion attained was 100% for ZnO and up to 96% for CH4. The thermal efficiency was in the 15–22% range; the exergy efficiency reached up to 7.7% and may be increased by recovering the sensible and latent heat of the products. The SynMet process avoids emissions of greenhouse-gases and other pollutant derived from the traditional fossil-fuel-based production of zinc and syngas, and further converts solar energy into storable and transportable chemical fuels.
Performance Evaluation of the 200-kWth HiTRec-II Open Volumetric Air Receiver
Authors: Hoffschmidt Bernhard , Te´llez Fe´lix M. , Valverde Antonio , Ferna´ndez Jesu´s , Ferna´ndez Valerio
Published: January 2003

The High Temperature Receiver (HitTRec) consists of a modular ceramic absorber, a supporting structure and an air-return system. It has been designed to prevent possible flow instability at 700-800°C average outlet air temperature with atmospheric pressure. The HiTRec-II prototype was developed to solve the structural problems of the first prototype (HiTRec-I). Testing in the Plataforma Solar de Almerı´a (PSA) test bed lasted from November 2000 through May 2001, accumulating 150 test hours under concentrated sun. Results demonstrated the durability of the modified stainless-steel structure. Inlet aperture flux was up to 900kW/m2 and average outlet air temperatures of up to 840°C with peak outlet air temperatures of up to 950°C. Thermal efficiency under steady-state conditions was 76±7% at 700°C, nominal conditions for a PHOEBUS-type volumetric receiver. Other performance characteristics were also evaluated (e.g., Air Return Ratio of 46% and characteristic receiver response time of 70 s).
Parametric Study of a Simplified Ice Storage Model Operating Under Conventional and Optimal Control Strategies*
Authors: Henze Gregor P.
Published: January 2003

A simplified ice storage system model was developed in which the icemaking mode is reflected by a higher power consumption per unit cooling than in chilled-water mode. The performance of four control strategies for ice storage systems is evaluated. The four control strategies investigated are chiller-priority and constant-proportion as conventional, instantaneous controls, while storage-priority and optimal control represent sophisticated controls employing load forecasting. Six parameters were investigated with respect to their influence on the ice storage system performance: Storage losses, utility rate structures, rate periods, penalty for icemaking, storage capacity, and the impact of load forecasting. Optimal control was determined to provide maximal operating cost savings. The storage-priority control yields operating costs only slightly higher than those of optimal control. Chiller-priority control realized savings that were typically on the order of 50% of what is theoretically possible (optimal control). Constant-proportion control proved to be a simple control strategy yielding higher savings than chiller-priority, yet lower than storage-priority control.
An Overset Finite-Element Large-Eddy Simulation Method With Applications to Turbomachinery and Aeroacoustics
Authors: Kato C. , Kaiho M. , Manabe A.
Published: January 2003

A numerical method for the prediction of an unsteady fluid flow in a complex geometry that involves moving boundary interfaces is presented in this paper. The method is also applicable to the prediction of the far-field sound that results from an unsteady fluid flow. The flow field is computed by large-eddy simulation (LES), while surface-pressure fluctuations obtained by the LES are used to predict the far-field sound. To deal with a moving boundary interface in the flow field, a form of the finite element method in which overset grids are applied from multiple dynamic frames of reference has been developed. The method is implemented as a parallel program by applying a domain-decomposition programming model. The validity of the proposed method is shown through two numerical examples: prediction of the internal flows of a hydraulic pump stage and prediction of the far-field sound that results from unsteady flow around an insulator mounted on a high-speed train.
Investigation of a Solar-Thermal Bio-mimetic Metal Hydride Actuator
Authors: Lloyd George M. , Kim Kwang J. , Razani A. , Shahinpoor Mohsen
Published: January 2003

Metal hydrides have been investigated for use in a number of solar thermal energy applications, such as heat regenerators or hydrogen storage technology, but rarely for thermal actuators. Preliminary experimental results from a prototype solar thermal metal hydride actuator, using copper-encapsulated porous metal hydride compacts of LaNi5, indicate that this thermal-mechanical system can produce high specific forces (over 100 (N/g)), with response times on the order of seconds. These operational characteristics, along with features such as being bio-mimetic, compact, operationally safe, lubricationless, noiseless, soft actuating, and environmentally benign, result in an actuator that is ideal for many industrial, space, defense, and biomedical applications. In this paper, we report recent work directed toward predicting and characterizing the performance bounds of the actuator, specifically concentrating on elements which might comprise an actuator driven by concentrated solar radiation. A complete solution of the 1-D governing heat and mass transfer equations with an ideally selective reactor surface are used to predict bounds on performance in terms of volume flow rates and realistic actuation times. The advantages and disadvantages of the design are discussed from this perspective. The preliminary data show a great potential for these metal hydride actuators to be used for solar thermo-mechanical applications.
Analyzing Two Federal Building-Integrated Photovoltaics Projects Using ENERGY-10 Simulations
Authors: Walker Andy , Balcomb Doug , Kiss Gregory , Weaver Norm , Becker Melinda Humphry
Published: January 2003

A new version of the ENERGY-10 computer program simulates the performance of photovoltaic (PV) systems and evaluates a wide range of opportunities to improve energy efficiency in buildings. This paper describes two test cases in which the beta release of ENERGY-10 version 1.4 was used to evaluate energy efficiency and building-integrated photovoltaics (BIPV) for two federal building projects: an office and laboratory building at the Smithsonian Astrophysical Laboratory (SAO) in Hilo, Hawaii, and housing for visiting scientists at the Smithsonian Environmental Research Center in Edgewater, Maryland. The capabilities of the software, the design assistance provided by ENERGY-10, and a synopsis of results are given. Estimates of annual energy delivery by the five PV arrays of the SAO are compared to F-Chart to help inform a validation of ENERGY-10. Results indicate that, by simulating both the building electrical load and simultaneous PV performance for each hour of the year, ENERGY-10 facilitates a highly accurate, integrated analysis useful early in the design process. The simulation is especially useful in calculating the effect of PV on the building peak load, and associated demand cost savings.
Advanced Thermal Storage Fluids for Solar Parabolic Trough Systems
Authors: Moens Luc , Blake Daniel M. , Rudnicki Daniel L. , Hale Mary Jane
Published: January 2003

It has been established that the development of a storage option and increasing the operating temperature for parabolic trough electric systems can significantly reduce the levelized electricity cost compared to the current state of the art. Both improvements require a new heat transfer fluid that must have a very low vapor pressure at the hot operating temperature and combined with a high thermal stability, higher than 450°C. Further, the piping layout of trough plants dictates that the fluid not be allowed to freeze, which dictates the use of extensive insulation and heat tracing unless the fluid has a freezing point near 0°C. At present, it seems likely that this “ideal” fluid will have to be found among organic rather than inorganic salts. We are, therefore, investigating the chemical and thermal properties of “room temperature ionic liquids” that hold much promise as a new class of heat transfer or storage fluids.
Three-Dimensional Green’s Functions in an Anisotropic Half-Space With General Boundary Conditions
Authors: Pan E.
Published: January 2003

This paper derives, for the first time, the complete set of three-dimensional Green’s functions (displacements, stresses, and derivatives of displacements and stresses with respect to the source point), or the generalized Mindlin solutions, in an anisotropic half-space z>0 with general boundary conditions on the flat surface z=0. Applying the Mindlin’s superposition method, the half-space Green’s function is obtained as a sum of the generalized Kelvin solution (Green’s function in an anisotropic infinite space) and a Mindlin’s complementary solution. While the generalized Kelvin solution is in an explicit form, the Mindlin’s complementary part is expressed in terms of a simple line-integral over [0,π]. By introducing a new matrix K, which is a suitable combination of the eigenmatrices A and B, Green’s functions corresponding to different boundary conditions are concisely expressed in a unified form, including the existing traction-free and rigid boundaries as special cases. The corresponding generalized Boussinesq solutions are investigated in details. In particular, it is proved that under the general boundary conditions studied in this paper, the generalized Boussinesq solution is still well-defined. A physical explanation for this solution is also offered in terms of the equivalent concept of the Green’s functions due to a point force and an infinitesimal dislocation loop. Finally, a new numerical example for the Green’s functions in an orthotropic half-space with different boundary conditions is presented to illustrate the effect of different boundary conditions, as well as material anisotropy, on the half-space Green’s functions.
Nonlinear scattering of acoustic waves by natural and artificially generated subsurface bubble layers in sea
Authors: Ostrovsky Lev A. , Sutin Alexander M. , Soustova Irina A. , Matveyev Alexander L. , Potapov Andrey I. , Kluzek Zigmund
Published: January 2003

The paper describes nonlinear effects due to a biharmonic acoustic signal scattering from air bubbles in the sea. The results of field experiments in a shallow sea are presented. Two waves radiated at frequencies 30 and 31–37 kHz generated backscattered signals at sum and difference frequencies in a bubble layer. A motorboat propeller was used to generate bubbles with different concentrations at different times, up to the return to the natural subsurface layer. Theoretical consideration is given for these effects. The experimental data are in a reasonably good agreement with theoretical predictions.
Anechoic chamber qualification: Traverse method, inverse square law analysis method, and nature of test signal
Authors: Cunefare Kenneth A. , Biesel Van B. , Tran John , Rye Ryan , Graf Aaron , Holdhusen Mark , Albanese Anne-Marie
Published: January 2003

Qualification of anechoic chambers is intended to demonstrate that the chamber supports the intended free-field environment within some permissible tolerance bounds. Key qualification issues include the method used to obtain traverse data, the analysis method for the data, and the use of pure tone or broadband noise as the chamber excitation signal. This paper evaluates the relative merits of continuous versus discrete traverses, of fixed versus optimal reference analysis of the traverse data, and of the use of pure tone versus broadband signals. The current practice of using widely space discrete sampling along a traverse is shown to inadequately sample the complexity of the sound field extant with pure tone traverses, but is suitable for broadband traverses. Continuous traverses, with spatial resolution on the order of 15% of the wavelength at the frequency of interest, are shown to be necessary to fully resolve the spatial complexity of pure tone qualifications. The use of an optimal reference method for computing the deviations from inverse square law is shown to significantly improve the apparent performance of the chamber for pure tone qualifications. Finally, the use of broadband noise as the test signal, as compared to pure tone traverses over the same span, is demonstrated to be a marginal indicator of chamber performance.
Acoustic and perceptual evaluation of Mandarin tone productions before and after perceptual training
Authors: Wang Yue , Jongman Allard , Sereno Joan A.
Published: January 2003

Training American listeners to perceive Mandarin tones has been shown to be effective, with trainees’ identification improving by 21%. Improvement also generalized to new stimuli and new talkers, and was retained when tested six months after training [Y. Wang et al., J. Acoust. Soc. Am. 106, 3649–3658 (1999)]. The present study investigates whether the tone contrasts gained perceptually transferred to production. Before their perception pretest and after their post-test, the trainees were recorded producing a list of Mandarin words. Their productions were first judged by native Mandarin listeners in an identification task. Identification of trainees’ post-test tone productions improved by 18% relative to their pretest productions, indicating significant tone production improvement after perceptual training. Acoustic analyses of the pre- and post-training productions further reveal the nature of the improvement, showing that post-training tone contours approximate native norms to a greater degree than pretraining tone contours. Furthermore, pitch height and pitch contour are not mastered in parallel, with the former being more resistant to improvement than the latter. These results are discussed in terms of the relationship between non-native tone perception and production as well as learning at the suprasegmental level.
Cochlear toughening, protection, and potentiation of noise-induced trauma by non-Gaussian noise
Authors: Hamernik Roger P. , Qiu Wei , Davis Bob
Published: January 2003

An interrupted noise exposure of sufficient intensity, presented on a daily repeating cycle, produces a threshold shift (TS) following the first day of exposure. TSs measured on subsequent days of the exposure sequence have been shown to decrease relative to the initial TS. This reduction of TS, despite the continuing daily exposure regime, has been called a cochlear toughening effect and the exposures referred to as toughening exposures. Four groups of chinchillas were exposed to one of four different noises presented on an interrupted (6 h/day for 20 days) or noninterrupted (24 h/day for 5 days) schedule. The exposures had equivalent total energy, an overall level of 100 dB(A) SPL, and approximately the same flat, broadband long-term spectrum. The noises differed primarily in their temporal structures; two were Gaussian and two were non-Gausssian, nonstationary. Brainstem auditory evoked potentials were used to estimate hearing thresholds and surface preparation histology was used to determine sensory cell loss. The experimental results presented here show that: (1) Exposures to interrupted high-level, non-Gaussian signals produce a toughening effect comparable to that produced by an equivalent interrupted Gaussian noise. (2) Toughening, whether produced by Gaussian or non-Gaussian noise, results in reduced trauma compared to the equivalent uninterrupted noise, and (3) that both continuous and interrupted non-Gaussian exposures produce more trauma than do energy and spectrally equivalent Gaussian noises. Over the course of the 20-day exposure, the pattern of TS following each day’s exposure could exhibit a variety of configurations. These results do not support the equal energy hypothesis as a unifying principal for estimating the potential of a noise exposure to produce hearing loss.
Understanding speech in modulated interference: Cochlear implant users and normal-hearing listeners
Authors: Nelson Peggy B. , Jin Su-Hyun , Carney Arlene Earley , Nelson David A.
Published: January 2003

Many competing noises in real environments are modulated or fluctuating in level. Listeners with normal hearing are able to take advantage of temporal gaps in fluctuating maskers. Listeners with sensorineural hearing loss show less benefit from modulated maskers. Cochlear implant users may be more adversely affected by modulated maskers because of their limited spectral resolution and by their reliance on envelope-based signal-processing strategies of implant processors. The current study evaluated cochlear implant users’ ability to understand sentences in the presence of modulated speech-shaped noise. Normal-hearing listeners served as a comparison group. Listeners repeated IEEE sentences in quiet, steady noise, and modulated noise maskers. Maskers were presented at varying signal-to-noise ratios (SNRs) at six modulation rates varying from 1 to 32 Hz. Results suggested that normal-hearing listeners obtain significant release from masking from modulated maskers, especially at 8-Hz masker modulation frequency. In contrast, cochlear implant users experience very little release from masking from modulated maskers. The data suggest, in fact, that they may show negative effects of modulated maskers at syllabic modulation rates (2–4 Hz). Similar patterns of results were obtained from implant listeners using three different devices with different speech-processor strategies. The lack of release from masking occurs in implant listeners independent of their device characteristics, and may be attributable to the nature of implant processing strategies and/or the lack of spectral detail in processed stimuli.
Simulation of ultrasonic focus aberration and correction through human tissue
Authors: Tabei Makoto , Mast T. Douglas , Waag Robert C.
Published: January 2003

Ultrasonic focusing in two dimensions has been investigated by calculating the propagation of ultrasonic pulses through cross-sectional models of human abdominal wall and breast. Propagation calculations used a full-wave k-space method that accounts for spatial variations in density, sound speed, and frequency-dependent absorption and includes perfectly matched layer absorbing boundary conditions. To obtain a distorted receive wavefront, propagation from a point source through the tissue path was computed. Receive focusing used an angular spectrum method. Transmit focusing was accomplished by propagating a pressure wavefront from a virtual array through the tissue path. As well as uncompensated focusing, focusing that employed time-shift compensation and time-shift compensation after backpropagation was investigated in both transmit and receive and time reversal was investigated for transmit focusing in addition. The results indicate, consistent with measurements, that breast causes greater focus degradation than abdominal wall. The investigated compensation methods corrected the receive focus better than the transmit focus. Time-shift compensation after backpropagation improved the focus from that obtained using time-shift compensation alone but the improvement was less in transmit focusing than in receive focusing. Transmit focusing by time reversal resulted in lower sidelobes but larger mainlobes than the other investigated transmit focus compensation methods.
Complex reflection phase gradient as an inversion parameter for the prediction of shallow water propagation and the characterization of sea-bottoms
Authors: Joseph Phillip
Published: January 2003

In this paper a quantity is proposed, referred to as the complex reflection phase gradient, whose use in a matched field inversion procedure allows for the rapid extraction of first order geo-acoustic information about the sea-bottom. It is based on the observation that at low grazing angles the reflection phase and bottom loss for a wide range of sea-bottom types commonly exhibits an approximate linear relationship to the vertical component of the acoustic wave number at the seabed. The real part of this quantity specifies the rate at which the reflection phase varies with vertical acoustic wave number while the imaginary part quantifies the rate of change of bottom loss. Despite being defined with just two real parameters it is shown that it provides an accurate prediction of the sound field for a wide range of bottom types. In addition, its measurement permits an estimate to be made for the input impedance to the seabed in the zero grazing angle limit and, in the case of a homogeneous elastic half-space of known density, the compressional and shear wave speed. The main advantage of the two-parameter seabottom representation is that each parameter is readily inverted from comparatively few acoustic pressure measurements. The usefulness of the technique is illustrated by the results from computer simulated acoustic pressure measurements made at just eleven sensors in a simple shallow water channel, and results from a 10 cm deep laboratory channel at frequencies between 10 kHz and 75 kHz.
The contribution of bubbles to high-frequency sea surface backscatter: A 24-h time series of field measurements
Authors: Dahl Peter H.
Published: January 2003

Measurements of acoustic sea surface backscattering, wind speed, and surface wave spectra were made continually over a 24-h period in an experiment conducted in 26 m of water near the Dry Tortugus collection of islands off south Florida in February 1995. The backscattering measurements were made at a frequency of 30 kHz and a sea surface grazing angle of 20°; a time series of the decibel equivalent of this variable, called SS20, was studied in terms of its dependence on environmental variables. On occasion reliable estimates of scattering in the grazing range 15°–27° were also obtained during the 24 hours. The scattering data exhibited evidence, in terms of scattering level and grazing angle dependence, of scattering from near-surface bubbles rather than scattering from the rough air–sea interface. The scattering data were compared with a model for σb, the apparent backscattering cross section per unit area due to bubble scattering, that is driven by a parameter, βI, equal to the depth-integrated extinction cross section per unit volume. Using an empirical model for βI based on data from a 1977 experiment conducted in pelagic waters, model predictions agreed reasonably well with the 1995 measurements presented here. Additional model–data comparisons were made using four measurements from a 1992 experiment conducted in pelagic waters. Finally, the 24-h time series of acoustic scattering exhibited a hysteresis effect, wherein for a given wind speed, there was a tendency for the scattering level to be higher if prior winds had been falling. A better understanding of this effect is essential to reduce uncertainty in model predictions.
Reed vibration in lingual organ pipes without the resonators
Authors: Miklós András , Angster Judit , Pitsch Stephan , Rossing Thomas D.
Published: January 2003

Vibrations of plucked and blown reeds of lingual organ pipes without the resonators have been investigated. Three rather surprising phenomena are observed: the frequency of the reed plucked by hand is shifted upwards for large-amplitude plucking, the blown frequency is significantly higher than the plucked one, and peaks halfway between the harmonics of the fundamental frequency appear in the spectrum of the reed velocity. The dependence of the plucked frequency on the length of the reed reveals that the vibrating length at small vibrations is 3 mm shorter than the apparent free length. The frequency shift for large-amplitude plucking is explained by the periodic change of the vibrating length during the oscillation. Reed vibrations of the blown pipe can be described by a physical model based on the assumption of air flow between the reed and the shallot. Aerodynamic effects may generate and sustain the oscillation of the reed without acoustic feedback. The appearance of subharmonics is explained by taking into account the periodic modulation of the stress in the reed material by the sound field. Therefore, a parametric instability appears in the differential equation of vibration, leading to the appearance of subharmonics.
The importance of cochlear processing for the formation of auditory brainstem and frequency following responses
Authors: Dau Torsten
Published: January 2003

A model for the generation of auditory brainstem responses (ABR) and frequency following responses (FFRs) is presented. The model is based on the concept introduced by Goldstein and Kiang [J. Acoust. Soc. Am. 30, 107–114 (1958)] that evoked potentials recorded at remote electrodes can theoretically be given by convolution of an elementary unit waveform (unitary response) with the instantaneous discharge rate function for the corresponding unit. In the present study, the nonlinear computational auditory-nerve model recently developed by Heinz et al. [ARLO 2(3), 91–96 (2001)] was used to calculate the instantaneous discharge rate ri(t) for fibers i in the frequency range from 0.1 and 10 kHz. The summed activity across frequency was convolved with a unitary response which is assumed to reflect contributions from different cell populations within the auditory brainstem, recorded at a given pair of electrodes on the scalp. Predicted potential patterns are compared with experimental data for a number of stimulus and level conditions. Clicks, chirps as defined in Dau et al. [J. Acoust. Soc. Am. 107, 1530–1540 (2000)], long-duration stimuli comprising the chirp, as well as tones and slowly varying tonal sweeps were considered. The results demonstrate the importance of considering the effects of the basilar-membrane traveling wave and auditory-nerve processing for the formation of ABR and FFR. Specifically, the results support the hypothesis that the FFR to low-frequency tones represents synchronized activity mainly stemming from mid- and high-frequency units at more basal sites, and not from units tuned to frequencies around the signal frequency.
Surface response of a viscoelastic medium to subsurface acoustic sources with application to medical diagnosis
Authors: Royston Thomas J. , Yazicioglu Yigit , Loth Francis
Published: January 2003

The response at the surface of an isotropic viscoelastic medium to buried fundamental acoustic sources is studied theoretically, computationally and experimentally. Finite and infinitesimal monopole and dipole sources within the low audible frequency range (40–400 Hz) are considered. Analytical and numerical integral solutions that account for compression, shear and surface wave response to the buried sources are formulated and compared with numerical finite element simulations and experimental studies on finite dimension phantom models. It is found that at low audible frequencies, compression and shear wave propagation from point sources can both be significant, with shear wave effects becoming less significant as frequency increases. Additionally, it is shown that simple closed-form analytical approximations based on an infinite medium model agree well with numerically obtained “exact” half-space solutions for the frequency range and material of interest in this study. The focus here is on developing a better understanding of how biological soft tissue affects the transmission of vibro-acoustic energy from biological acoustic sources below the skin surface, whose typical spectral content is in the low audible frequency range. Examples include sound radiated from pulmonary, gastro-intestinal and cardiovascular system functions, such as breath sounds, bowel sounds and vascular bruits, respectively.
Accuracy and variability of acoustic measures of voicing onset
Authors: Francis Alexander L. , Ciocca Valter , Ching Yu Jojo Man
Published: January 2003

Five commonly used methods for determining the onset of voicing of syllable-initial stop consonants were compared. The speech and glottal activity of 16 native speakers of Cantonese with normal voice quality were investigated during the production of consonant vowel (CV) syllables in Cantonese. Syllables consisted of the initial consonants /ph/, /th/, /kh/, /p/, /t/, and /k/ followed by the vowel /a/. All syllables had a high level tone, and were all real words in Cantonese. Measurements of voicing onset were made based on the onset of periodicity in the acoustic waveform, and on spectrographic measures of the onset of a voicing bar (f0), the onset of the first formant (F1), second formant (F2), and third formant (F3). These measurements were then compared against the onset of glottal opening as determined by electroglottography. Both accuracy and variability of each measure were calculated. Results suggest that the presence of aspiration in a syllable decreased the accuracy and increased the variability of spectrogram-based measurements, but did not strongly affect measurements made from the acoustic waveform. Overall, the acoustic waveform provided the most accurate estimate of voicing onset; measurements made from the amplitude waveform were also the least variable of the five measures. These results can be explained as a consequence of differences in spectral tilt of the voicing source in breathy versus modal phonation.
The balanced electromagnetic separation transducer: A new bone conduction transducer
Authors: Håkansson Bo E. V.
Published: January 2003

Conventional bone conduction transducers, which are relatively large, suffer from poor performance at low frequencies. A new type of electro-dynamic transducer, the balanced electromagnetic separation transducer (BEST), was developed to improve the performance of the conventional transducers. By using a balanced suspension principle, the quadratic distortion forces, as well as the static forces between the vibrating parts, are principally counterbalanced. Both the distortion and the size of the transducer can therefore be considerably reduced. Moreover, the static and dynamic magnetic fluxes are separated, except in the air gap regions, giving a more efficient transducer. For example, in comparison with a conventional B71 transducer, a prototype of the BEST has: Lower total harmonic distortion (THD), by 20–25 dB, and improved sensitivity by 10–20 dB for 100 to 1000 Hz and by 2–10 dB for 1 to 10 kHz. From a clinical point of view, the BEST offers a chance to measure bone thresholds, at 250 and 500 Hz, which are reliable at hearing levels not possible before. For example, at 250 Hz the BEST has 23 dB higher sensitivity than the B71; the THD is improved from 61% (B71) to 3.3% (BEST) at 40 dB HL (ISO 389-3, 1994).
Simulations of tonotopically mapped speech processors for cochlear implant electrodes varying in insertion depth
Authors: Faulkner Andrew , Rosen Stuart , Stanton Deborah
Published: January 2003

It has been claimed that speech recognition with a cochlear implant is dependent on the frequency alignment of analysis bands in the speech processor with characteristic frequencies (CFs) at electrode locations. However, the most apical electrode location can often have a CF of 1 kHz or more. The use of filters aligned in frequency to relatively basal electrode arrays leads to the loss of lower frequency speech information. This study simulates a frequency-aligned speech processor and common array insertion depths to assess this significance of this loss. Noise-excited vocoders simulated processors driving eight electrodes 2 mm apart. Analysis filters always had center frequencies matching the CFs of the simulated stimulation sites. The simulated insertion depth of the most apical electrode was varied in 2-mm steps between 25 mm (CF 502 Hz) and 17 mm (CF 1851 Hz) from the cochlear base. Identification of consonants, vowels, and words in sentences all showed a significant decline between each of the three more basal simulated electrode configurations. Thus, if implant processors used analysis filters frequency-aligned to electrode CFs, patients whose most apical electrode is 19 mm (CF 1.3 kHz) or less from the cochlear base would suffer a significant loss of speech information.
Monitoring audiometry for occupational hearing loss: A case for eliminating 500 Hz
Authors: Stephenson Mark
Published: January 2003

Audiometric monitoring is an important element in hearing conservation programs. Nearly every existing hearing conservation standard dictate that hearing thresholds should be measured at specific frequencies, and that 500 Hz be among those frequencies tested. Actual and estimated noise-induced permanent threshold shifts were evaluated as a function of exposure duration and exposure level. The results demonstrate 500 Hz to be of little value in assessing noise-induced hearing loss for typical industrial noise exposures of up to 40 years, at least for time-weighted average exposures of up to 100 dBA. Furthermore, few hearing conservation programs currently require audiometric monitoring to be performed in an environment that meets ANSI standards for maximum permissible background noise levels. This is particularly likely to compromise hearing testing at 500 Hz. As a result, this paper argues against the need for testing at 500 Hz, and recommends it be eliminated as a required test frequency in audiometric monitoring for noise-induced occupational hearing loss.