bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Temperature and Residence Time of the Exhausts in the Combustion Chamber of an Incinerator Plant
Authors: Costa M. , Dell’Isola M. , Massarotti N. , Mauro A.
Published: September 2009

The interest for energy recovery from waste incineration has increased over the years, in order to reduce the number of landfills and produce electricity and heat. At the same time, concern for the impact such processes have on the environment has also grown, and to reduce such an impact, new legislation is being enforced in Europe and Italy. In particular, important restrictions are imposed on the temperature of the exhausts in the combustion chamber, which must be kept above certain values for a given period of time, depending on the type of waste that is being incinerated. Such conditions can be rather difficult and certainly very expensive to monitor with acceptable accuracy. For this reason, in practical applications the temperature of the exhausts in the chamber is usually calculated through semi-empirical and approximate models that relate the temperatures in different sections of the chamber. In this work, the authors present a numerical approach for the analysis of such models that can be used to quantify the uncertainty on this type of measurement due to the common approximations used in full scale incineration plants. The analysis is based on the CFD simulation of the thermo-fluid-dynamic field in the combustion chamber of a full scale plant in Italy, whose results have verified based on a comparison with the data collected during an experimental campaign.
Dynamic Modeling of Hydrokinetic Energy Extraction
Authors: Miller Veronica B. , Schaefer Laura A.
Published: September 2009

The world is facing an imminent energy supply crisis. Our well-being is linked to the energy supply, and energy is in high demand in both the developed and the developing world. Therefore, in order to sustain our energy supply, it is necessary to advance renewable technologies. Despite this urgency, however, it is paramount to consider the larger environmental effects associated with using renewable resources. Hydropower, in the past, has been seen as a viable resource to examine given that its basics of mechanical to electrical energy conversion seem to have little effect on the environment. Discrete analysis of dams and in-stream diversion set-ups has shown otherwise though. Modifications to river flows and temperatures (from increased and decreased flows) cause adverse effects to fish and other marine life because it changes their adaptive habitat. Recent research developments have focused on kinetic energy extraction in river flows, which prove to be more sustainable as this type of extraction does not involve a large reservoir or large flow modification. The field of hydrokinetic energy extraction is immature. Little is known about their performance in the river environment, and their risk of impingement, fouling, and suspension of sediments. Basic principles of hydrokinetic energy extraction are presented along with a computational fluid dynamics model of the system. Through examining these principles it is clear that more research is required in hydrokinetic energy extraction with emphasis towards lower environmental and ecological impact.
Dynamic Synthesis/Design and Operation/Control Optimization Under Uncertainty of a PEMFC System
Authors: Kim Kihyung , Wang Meng , von Spakovsky Michael R. , Nelson Douglas J.
Published: September 2009

Proton exchange membrane fuel cells (PEMFCs) are one of the leading candidates in alternative energy conversion devices for transportation, stationary, and portable power generation applications. Such systems with their own fuel conversion unit typically consist of several subsystems: a fuel processing subsystem, a fuel cell stack subsystem, a work recovery-air supply subsystem, and a power electronics subsystem. Since these subsystems have different physical characteristics, their integration into a single system/subsystem level unit make the problems of optimal dynamic system synthesis/design and operation/control highly complex. Thus, dynamic system/subsystem/component modeling and highly effective optimization strategies are required. Furthermore, uncertainties in the results of system synthesis/design and operation/control optimization can be affected by any number of sources of uncertainty such as the load profiles and cost models. These uncertainties can be taken into account by treating the problem probabilistically. The difficulty with doing this, particularly when large-scale dynamic optimization with a large number of degrees of freedom is being used to determine the optimal synthesis/design and operation/control of the system, is that the traditional probabilistic approaches (e.g., Monte Carlo Method) are so computationally intensive that combined with large-scale optimization it renders the problem computationally intractable. This difficulty can be overcome by the use of approximate approaches such as the response sensitivity analysis (RSA) method based on Taylor series expansion. Thus, in this paper, a stochastic modeling and uncertainty analysis methodology for energy system synthesis/design and operation/control which uses the RSA method is proposed and employed for calculating the uncertainties on the system outputs. Their effects on the synthesis/design and operation/control optimization of a 5kWe PEMFC system are assessed by taking the uncertainties into account in the objectives and constraints. It is shown that these uncertainties significantly affect the reliability of being able to meet certain constraints (e.g., that on the CO concentration) during the synthesis/design and operation/control optimization process. These and other results are presented.
Use of State Space in the Dynamic Synthesis/Design and Operation/Control Optimization of a PEMFC System
Authors: Wang Meng , Kim Kihyung , von Spakovsky Michael R. , Nelson Douglas J.
Published: September 2009

An often used approach to the synthesis/design optimization of energy systems is to only use steady state operation and high efficiency (or low total life cycle cost) at full load as the basis for the synthesis/design. Transient and partial load operations are considered secondarily by system and control engineers once the synthesis/design is fixed (i.e. system testing with standard load profiles). This paper considers the system dynamics from the very beginning of the synthesis/design process by developing the system using a set of transient thermodynamic, kinetic, geometric as well as cost models developed and implemented for the components of a 5 kW PEMFC (Proton Exchange Membrane Fuel Cell) system. The system is composed of three subsystems: a stack subsystem (SS), a fuel processing subsystem (FPS), and a work and air recovery subsystem (WRAS). In addition, state space is used in a looped set of optimizations to illustrate the effect of the control system on the synthesis/design optimization and to develop a set of optimal multi-input, multi-output (MIMO) controllers consistent with the optimal synthesis/design of the PEMFC system. It is shown that these MIMO controllers correspond to the ones found in a non-looped optimization in which the gains for the controllers are part of the decision variable set for the overall synthesis/design and operation/control optimization. These last set of results are then compared with the optimizations results found with the traditional approach of using a single load point in order to show the advantage of the dynamic optimization.
A Methodology for Applying Energy Harvesting to Extend Wildlife Tag Lifetime
Authors: MacCurdy Robert , Reissman Timothy , Garcia Ephrahim , Winkler David
Published: September 2009

Wildlife monitoring tags are a widely used technique for studying animals in their natural habitats. At present, these devices are energy limited, based on the mass of the electrochemical battery that can be carried by the animal. Flying animals are particularly restricted, based on a requirement for minimal excess loading. This requirement causes tag lifetimes to be far shorter than would be useful from an ecological perspective, particularly for smaller animals. Energy harvesting is being widely adopted in applications where access to permanent power is limited. If applied to wildlife tags, this approach offers the possibility of extending functional lifetimes indefinitely; however, it presents unique challenges. Practical applications on flying animals are extremely mass limited, subject to environmental stress, and operate at very low frequencies. This paper is meant to address the critical issues in the design task, and makes attempts to place bounds on unknown design parameters, based on literature research where applicable, and on experiment when no data exists. We discuss candidate harvester materials, novel data acquisition tools, and a prototype harvester design.
Three Dimensional Analysis of a PEM Fuel Cell With the Shape of a Fermat Spiral for the Flow Channel Configuration
Authors: Jua´rez-Robles D. , Herna´ndez-Guerrero A. , Damia´n-Ascencio C. E. , Rubio-Arana C.
Published: September 2009

This work presents the analysis of a non-isothermal three-dimensional model in single phase of a PEM fuel cell with an innovative flow field path in the form of the Fermat spiral, i.e. two concentric spirals. The model is used to predict the current density contours and the water content in all of the zones of the fuel cell. The three-dimensional model includes: the gas flow channels with the shape of the new geometry proposed, the current collectors, gas diffusion layers, catalyst layers on both sides of the model, anode and cathode, and a proton exchange membrane in between. The model solves the energy equation, mass conservation, and species transport equations, including the source terms due the electrochemical effects occurring in the cell. The results show a higher average current density than the fuel cells with conventional flow paths, showing also that the current density attained is more uniform from the inlet to the outlet of the flow channels.
Cow Power: The Energy and Air Quality Benefits of Converting Manure to Biogas
Authors: Cue´llar Amanda D. , Webber Michael E.
Published: September 2009

This report consists of a top-level aggregate analysis of the total potential for converting livestock manure into a domestic renewable fuel source (biogas) that could be used to help states meet renewable portfolio standard requirements, reduce greenhouse gas (GHG) emissions, and improve air quality. In the U.S. livestock produces over one billion tons of manure annually. Typical disposal methods for animal manure allow for the emission of ammonia, particulate matter, unpleasant odors, volatile organic compounds (VOCs) and a variety of other air pollutants, which can damage the environment and pose risks to animal and human health. These disposal methods also allow for the uncontrolled emission of methane and nitrous oxide, two potent greenhouse gases (GHGs), with 21 and 310 times the global warming potential of carbon dioxide, respectively. Annually, 51 to 118 million metric tons (MMT) of carbon dioxide equivalent are emitted from livestock manure alone. Because air quality problems are on the rise, and trends show the contribution to GHG emissions from manure increasing from 1990 to 2005, limiting emissions from manure represents a valuable starting point for improving air quality and mitigating global climate change. Through anaerobic digestion, a well-known and time-tested process, animal manure is converted to methane rich biogas and many of the emissions of common manure management practices are avoided. Biogas is useful in a variety of applications such as a coal or natural gas substitute in electricity generation, which is the scenario considered in this analysis. Using values for the amount of biogas that can be produced per animal unit (defined as 1000 pounds of animal) per day and the number of animal units in the U.S., the authors determined that the 95 million animal units in the country could produce nearly 1 quad of renewable energy per year, approximately 1% of the U.S. total energy consumption. Converting the biogas into electricity using standard microturbines could produce 88 ± 20 billion kWh, or 2.4 ± 0.6% of annual electricity consumption in the U.S. Such an approach replaces two relatively dirty energy sources—manure and coal combustion—with a relatively cleaner source, biogas combustion, thereby yielding a net potential GHG emissions reduction of 99 ± 59 million metric tons or 3.9 ± 2.3% of the annual GHG emissions from electricity generation in the U. S. In addition, this approach has the potential to eliminate 0.4 ± 0.09 MMT of sulfur dioxide emissions, 0.1 ± 0.03 MMT of NOx, 0.002 MMT of mercury, and 0.69 ± 0.12 MMT of particulate matter from coal combustion. When natural gas is displaced, biogas use could eliminate 0.083 ± 0.019 of NOx and 0.006 ± 0.001 of SO2 while biogas combustion would emit approximately 0.068 MMT of NOx, 0.007 MMT of carbon monoxide, 0.005 MMT of particulate matter, 0.002 MMT of sulfur dioxide and 0.002 MMT of VOCs.
A New Approach in Approximating Thermodynamics Properties in Compressed Liquid Region
Authors: Karimi Amir , Tan Isa
Published: September 2009

Currently it is a common practice to use saturated liquid properties to approximate thermodynamics properties of fluids in the compressed liquid region. In this practice it is assumed that specific volume, internal energy, and entropy of fluids in the compressed liquid region are functions of temperature only and pressure practically has very little or no effect on these properties. Therefore, these properties at a given temperature and pressure are approximated by the saturated liquid properties at the given temperature. In the current literature the approximation formula given for enthalpy in the compressed liquid region is expressed as h(T, p) = hf (T) + vf (T) [p – psat (T)], where the aim of the second term on the right hand side of the equation is to improve the accuracy of the approximation, when pressure is much greater than the saturation pressure. However, in a recent study of thermodynamic properties of water, Kostic has shown that the second term in the equation improves the accuracy of the approximation of the enthalpy only at temperatures below 100 °C. In fact, he has shown that the second term increases the error when the formula is used to approximate the enthalpy of water in the compressed liquid region at intermediate and high temperatures. Kostic’s investigation is expanded in this paper to include substances other than water. The study shows that in many situations pressure has a bigger influence on the internal energy than it does on enthalpy of fluids in the compressed liquids. This paper demonstrates that the current practice of approximating properties of fluids in the compressed liquid region is not accurate at all range of temperatures and pressures. It establishes the range of pressures and temperatures for which the current approximation method could be used with reasonable accuracies. It also proposes a new scheme for the approximation of thermodynamic properties in the compressed liquid region.
Analysis of Gas-Steam Combined Cycle Based on Pressure Energy Recovery of Gas Transportation Pipelines
Authors: Lun Li-Yong , Yang Xian-Liang , Wang Hai-Yan , Wang Yu-Long
Published: September 2009

As the economy developing rapidly, the quota of natural gas in Chinese energy consumption is increasing rapidly. Meanwhile, the natural gas transportation pipelines have been developing quickly and the pressure of the pipelines is also becoming higher and higher. So the pressure energy stored in the pipelines is tremendous. This paper analyzed the gas-steam combined cycle based on the recovery of pressure energy in the gas transportation pipelines. The high pressure natural gas expands in the expander to recover some work to drive the air compressor, and then the lower temperature and lower pressure natural gas from the expander goes to cool the air which is going into the compressor and the exhaust of the turbine successively. Then the lower pressure natural gas recovers the heat of the smoke which is going to exhaust to air. At last the lower pressure natural gas is heated by a certain temperature and supplied to the consumer. This paper makes a qualitative analysis of the benefits brought by the new flow to the combined cycle. Generally speaking, the new cycle will increase the efficiency of the combined cycle and the utilization rate of energy.
Understanding Transport and Reaction Processes in the Solid Oxide Fuel Cell Anode at Sub-50 nm Resolution
Authors: Izzo John R. , Joshi Abhijit S. , Grew Kyle N. , Chiu Wilson K. S.
Published: September 2009

The Solid Oxide Fuel Cell (SOFC) holds great promise for a variety of portable power based applications because of the fuel flexibility and gravimetric power densities that it can maintain. These advantages are a product of the SOFC’s ability to directly use a wide variety of hydrocarbon based fuels that maintain high energy densities and are relatively easy to store. Models can be developed to describe the operation of SOFCs, where the pore structure is described with idealized structures or quantified with parameters. However, there are discrepancies in fundamental descriptions within these models resulting from a lack of a fundamental understanding of the physics of the associated pore scale processes. To continue development efforts, an improved understanding of the role of the anode microstructure at the pore scale and below is required. This paper will review our effort to develop such an understanding through anode structure reconstruction and characterization using non-destructive high resolution x-ray computed tomography (XCT).
Recent Progress at the Idaho National Laboratory in High Temperature Electrolysis for Hydrogen and Syngas Production
Authors: Stoots C. , O’Brien J. , Herring J. , Hartvigsen J.
Published: September 2009

This paper presents the most recent results of experiments conducted at the Idaho National Laboratory (INL) studying electrolysis of steam and coelectrolysis of steam / carbon dioxide in solid-oxide electrolysis stacks. Single button cell tests as well as multi-cell stack testing have been conducted. Multi-cell stack testing used 10 × 10 cm cells (8 × 8 cm active area) supplied by Ceramatec, Inc (Salt Lake City, Utah, USA) and ranged from 10 cell short stacks to 240 cell modules. Tests were conducted either in a bench-scale test apparatus or in a newly developed 5 kW Integrated Laboratory Scale (ILS) test facility. Gas composition, operating voltage, and operating temperature were varied during testing. The tests were heavily instrumented, and outlet gas compositions were monitored with a gas chromatograph. The ILS facility is currently being expanded to 15 kW testing capacity (H2 production rate based upon lower heating value).
Revising the Power Generation Systems Curriculum: The 1000 MW Solution
Authors: Manno Vincent P.
Published: September 2009

Student interest in electric power generation is increasing as national and worldwide attention to energy grows. While a power plant or thermal design course was a staple of pre-1980s mechanical engineering education, such courses fell out of favor as the bio-info-nano revolution refocused academic programs. The relevant textbook literature also stagnated. There is now an opportunity to reinvent the curriculum for mechanical engineering courses focused on 21st Century electric power generation. This paper addresses developing appropriate content for and teaching of such courses. The overarching goal is for a broad spectrum of students to develop a working knowledge of the scientific and technical similarities, differences, and challenges associated with various electric power production technologies including engineering, design, analysis, economics, and appropriate consideration of sustainability and societal impact. A unifying motivational exercise advocated is to estimate and catalogue the resources, sizes, performance characteristics, and impact streams for generating 1000 MW(e) using each technology studied.
On Thermodynamics of Advanced Adsorption Cooling Devices
Authors: Saha Bidyut B. , Chakraborty Anutosh , El-Sharkawy Ibrahim I. , Koyama Shigeru , Ng Kim Choon , Srinivasan Kandadai
Published: September 2009

This article presents a thermodynamic framework for the estimation of the minimum driving heat source temperature of an advanced adsorption cooling device from the rigor of Boltzmann distribution function and the condensation approximation of adsorptive molecules on adsorbent porous surface. The calculated resuls are validated with our own experimentally measured data. From this thermodynamic analysis, an interesting and useful finding has been established that it is possible to develop an adsorption cooling device that operates with a driving heat source temperature as low as 40 °C along with a coolant of temperature 30 °C. We have also presented here the thermodynamic modeling and experimental investigation of an advanced adsorption chiller for understanding its working principles.
A Low Order Control-Oriented Model of Liquid Water Transport in PEM Fuel Cell
Authors: Esposito Angelo , Pianese Cesare , Guezennec Yann G.
Published: September 2009

In this work, an accurate and computationally fast model for liquid water transport within a proton exchange membrane fuel cell (PEMFC) electrode is developed by lumping the space-dependence of the relevant variables. Capillarity is considered as the main transport mechanism within the gas diffusion layer (GDL). The novelty of the model lies in the simulation of the water transport at the interface between gas diffusion layer and gas flow channel (GFC). This is achieved with a phenomenological description of the process that allows its simulation with relative simplicity. Moreover, a detailed two-dimensional visualization of such interface is achieved via geometric simulation of water droplets formation, growth, coalescence and detachment on the surface of the GDL. The accomplishment of reduced computational time and good accuracy makes the model suitable for control strategy implementation to ensure PEM fuel cells operation within optimal electrode water content. Furthermore, the model is useful for optimization analysis oriented to both PEMFC design and balance of plant.
The Use of Vegetable Oil as Fuel for Distributed Power Generation in Developing Countries
Authors: Reding T. , Akbari P. , Frank A. , Rodriguez S. , Zambito J. , Bosco S. , Basinger M.
Published: September 2009

This study reports an ongoing effort to investigate the degradation rate of a low-speed Listeroid diesel engine running on filtered waste vegetable oil (WVO). It aims to measure the performance, wear rate, and emissions of the engine over the course of a 1,000 hour longevity test. In a consecutive arrangement, exhaust gas is used to heat the oil, reducing its viscosity close to that of diesel for the duration of the residence time in the fuel line. This reduces engine power loss, pumping losses, head losses, carbonization and coking, which ultimately increases longevity. When completed, the technical methods developed, data collected, lessons learned, and hardware used will all be incorporated into a manufacturable, stand-alone, cost-efficient, field conversion kit for the Listeroid engine. The results of this study will be beneficial in actualizing the widespread and practical use of WVO and straight vegetable oil (SVO) fuels in developing countries.
Optimized Modeling of Gas Turbine Power Augmentation Using Steam Injection and Inlet Cooling
Authors: Hashemi Ehsan , Dolatabadi Ebrahim , Pezeshkpour Pegah
Published: September 2009

Gas turbines are major equipment in power generation; they are also used as compressor drivers especially in offshore industries and pipeline compressors. Nowadays, rapidly increasing global demand for energy has a major role in selecting efficient equipment. Gas turbine power augmentation is an effective solution for increasing installed GT power. Several methods have been developed for this purpose, but the basic principles of all methods include lowering the inlet air temperature, increasing the inlet mass flow rate, or combination of both mentioned methods. Using these methods such as steam injection, inlet chillers, inlet fogging, injection in combustor, etc., an increasing in turbine output power will be obtained, but the required power of driven compressor changes, so a precise evaluation of overall GT performance, considering its main parts all together and its operating conditions are essential in determining the appropriate method of power augmentation. In this paper first the performance characteristics of the compressor, combustion chamber and power turbine are explained, and then overall performance and efficiency of GT package are discussed. Effect of each power augmentation method is also considered in the following sections. Real data from testing of installed gas turbines and a computer code are executed to validate the proposed technologies. It is concluded that the use of an inlet cooling system together with a steam injection facility improves the efficiency, enhances the output power and makes the GT run at lower pressure ratios at maximum efficiency point.
Thermodynamic Considerations for Thermal Water Splitting Processes and High Temperature Electrolysis
Authors: O’Brien J. E.
Published: September 2009

A general thermodynamic analysis of hydrogen production based on thermal water splitting processes is presented. Results of the analysis show that the overall efficiency of any thermal water splitting process operating between two temperature limits is proportional to the Carnot efficiency. Implications of thermodynamic efficiency limits and the impacts of loss mechanisms and operating conditions are discussed as they pertain specifically to hydrogen production based on high-temperature electrolysis. Overall system performance predictions are also presented for high-temperature electrolysis plants powered by three different advanced nuclear reactor types, over their respective operating temperature ranges.
The Production of Syngas via High Temperature Electrolysis and Biomass Gasification
Authors: McKellar M. G. , Hawkes G. L. , O’Brien J. E.
Published: September 2009

A process model of syngas production using high temperature electrolysis and biomass gasification is presented. Process heat from the biomass gasifier is used to improve the hydrogen production efficiency of the steam electrolysis process. Hydrogen from electrolysis allows a high utilization of the biomass carbon for syngas production. Based on the gasifier temperature, 94% to 95% of the carbon in the biomass becomes carbon monoxide in the syngas (carbon dioxide and hydrogen). Assuming the thermal efficiency of the power cycle for electricity generation is 50%, (as expected from GEN IV nuclear reactors), the syngas production efficiency ranges from 70% to 73% as the gasifier temperature decreases from 1900 K to 1500 K.
Bootstrap Statistical Method to Attain the Average Nusselt Number Correlation for Milli Channels and Micro Channels Heat Sink Using Aluminum Oxide (Al2O3)/Water Nanofluid
Authors: Valencia Guillermo E. , Aldana Jose D. , Ramos Miguel A. , Bula Antonio J.
Published: September 2009

The Bootstrap Statistical method is applied for estimating the accuracy of the convective heat transfer non linear correlation of AL2O3 nanofluid working as cooling fluid. The flow experiment considers laminar and turbulent regimen through an array of aluminum microchannels and millichannels heat sink, taking into account the Volume Fractions, Reynolds, Peclet and Prandtl numbers. The β’s parameters are estimated with nonlinear least square approach. StatGraphics® was used, considering the Gauss-Newton algorithm with Levenberg-Marquardt modifications for global convergence. Correlation for Nusselt number is presented and suggestions for future experimentation are presented in order to improve the accuracy of the regression.
An Object-Oriented Online Tool for Solving Generalized Chemical Equilibrium Problems
Authors: Paolini Christopher P. , Bhattacharjee Subrata
Published: September 2009

Analysis of chemical equilibria is a topic covered in both undergraduate and graduate courses such as physical chemistry, chemical thermodynamics, and engineering thermodynamics. Manual calculation of problems that require a student to solve for species concentrations, partial pressures, or mole fractions usually involve the method of equilibrium constants. Exercises in homework assignments or in-class examinations are frequently limited to reactions that involve no more than four gas phase species as the resulting arithmetic required to solve for the unknown quantity becomes too cumbersome and prone to error. Students who invest the requisite time in manually solving complex equilibrium problems in homework assignments need a tool to verify their answer. A Java web application (“applet”) has been developed to assist engineering students who encounter general multiphase equilibrium problems involving many species. In addition to students, educators and professional researchers will benefit from a user friendly and free to use software package that can numerically compute equilibrium distributions for arbitrary reactions. The applet we present in this work can be used to analyze complex reactions involving twenty or more species and one such reaction, the combustion of isooctane and air, is presented as an example.
Exergy and the Hubbert Peak: Assessment of the Scarcity of Minerals on Earth
Authors: Valero Antonio , Valero Alicia , Torres Cesar
Published: September 2009

This paper demonstrates how thermodynamics and in particular the exergy analysis can help to assess the degradation degree of resources, which constitutes essential information for achieving sustainable development. It presents a mathematical model for the application of the Hubbert peak to the production of fuel and non-fuel mineral resources in terms of its exergy content. The model is applied as a case study to the main minerals produced in Australia. The results show that the peak year of production of most minerals in that country has already arrived. Moreover, in year 2050, the peak of all mineral commodities analyzed will have been reached, and about 64% of Australian mineral reserves will be depleted.
A k-space method for acoustic propagation using coupled first-order equations in three dimensions
Authors: Tillett Jason C. , Daoud Mohammad I. , Lacefield James C. , Waag Robert C.
Published: September 2009

A previously described two-dimensional k-space method for large-scale calculation of acoustic wave propagation in tissues is extended to three dimensions. The three-dimensional method contains all of the two-dimensional method features that allow accurate and stable calculation of propagation. These features are spectral calculation of spatial derivatives, temporal correction that produces exact propagation in a homogeneous medium, staggered spatial and temporal grids, and a perfectly matched boundary layer. Spectral evaluation of spatial derivatives is accomplished using a fast Fourier transform in three dimensions. This computational bottleneck requires all-to-all communication; execution time in a parallel implementation is therefore sensitive to node interconnect latency and bandwidth. Accuracy of the three-dimensional method is evaluated through comparisons with exact solutions for media having spherical inhomogeneities. Large-scale calculations in three dimensions were performed by distributing the nearly 50 variables per voxel that are used to implement the method over a cluster of computers. Two computer clusters used to evaluate method accuracy are compared. Comparisons of k-space calculations with exact methods including absorption highlight the need to model accurately the medium dispersion relationships, especially in large-scale media. Accurately modeled media allow the k-space method to calculate acoustic propagation in tissues over hundreds of wavelengths.
Perception of complete and incomplete formant transitions in vowels
Authors: Divenyi Pierre
Published: September 2009

In everyday speech, formant transitions rarely reach the canonical frequencies of a target vowel. The perceptual system often compensates for such production undershoots, called vowel reduction (VR), by a perceptual overshoot of the final transition frequencies. The present investigation explored the perceptual parameters and existence region of VR. In a series of experiments a 100-ms steady-state vowel V1 was followed by a formant transition toward a target vowel V2. By manipulating both its duration and velocity, in most stimuli the transition was truncated and only seldom reached the target. After being presented with the vowel V2 before each block of trials, listeners were asked to rate their confidence that the transition actually reached the V2 target. Transitions along six trajectories connecting the three cardinal vowels /a/, /i/, and /u/ in both directions as well as the transition /ie/ (halfway along the trajectory /ia/) were examined in experiments in which either the duration of the transition was fixed and its velocity was varied or vice-versa. Results confirmed the existence of perceptual overshoot and showed that, at the point a transition short of reaching the vowel V2 was just perceived as if it had reached the target, transition duration and transition velocity were inversely related. The amount of overshoot was found to be larger for larger V1-V2 distances and shorter trajectory durations. The overshoot could be reliably predicted by a linear model based on three parameters—the extent of V1-V2 distance, transition velocity, and transition acceleration. These findings suggest that the perceptual dynamics of speech relies on mechanisms that estimate the rate of change in the resonant characteristics of the vocal tract.
Investigation of acoustically coupled enclosures using a diffusion-equation model
Authors: Xiang Ning , Jing Yun , Bockman Alexander C.
Published: September 2009

Recent application of coupled-room systems in performing arts spaces has prompted active research on sound fields in these complex geometries. This paper applies a diffusion-equation model to the study of acoustics in coupled-rooms. Acoustical measurements are conducted on a scale-model of two coupled-rooms. Using the diffusion model and the experimental results the current work conducts in-depth investigations on sound pressure level distributions, providing further evidence supporting the valid application of the diffusion-equation model. Analysis of the results within the Bayesian framework allows for quantification of the double-slope characteristics of sound-energy decays obtained from the diffusion-equation numerical modeling and the experimental measurements. In particular, Bayesian decay analysis confirms sound-energy flux modeling predictions that time-dependent sound-energy flows in coupled-room systems experience feedback in the form of energy flow-direction change across the aperture connecting the two rooms in cases where the dependent room is more reverberant than the source room.
Comparison of cochlear delay estimates using otoacoustic emissions and auditory brainstem responses
Authors: Harte James M. , Pigasse Gilles , Dau Torsten
Published: September 2009

Different attempts have been made to directly measure frequency specific basilar membrane (BM) delays in animals, e.g., laser velocimetry of BM vibrations and auditory nerve fiber recordings. The present study uses otoacoustic emissions (OAEs) and auditory brainstem responses (ABRs) to estimate BM delay non-invasively in normal-hearing humans. Tone bursts at nine frequencies from 0.5to8kHz served as stimuli, with care taken to quantify possible bias due to the use of tone bursts with different rise times. BM delays are estimated from the ABR latency estimates by subtracting the neural and synaptic delays. This allows a comparison between individual OAE and BM delays over a large frequency range in the same subjects, and offers support to the theory that OAEs are reflected from a tonotopic place and carried back to the cochlear base via a reverse traveling wave.
Temporal and vertical scales of acoustic fluctuations for 75-Hz, broadband transmissions to 87-km range in the eastern North Pacific Ocean
Authors: Colosi John A. , Xu Jinshan , Worcester Peter F. , Dzieciuch Matthew A. , Howe Bruce M. , Mercer James A.
Published: September 2009

Observations of scattering of low-frequency sound in the ocean have focused largely on effects at long ranges, involving multiple scattering events. Fluctuations due to one and two scattering events are analyzed here, using 75-Hz broadband signals transmitted in the eastern North Pacific Ocean. The experimental geometry gives two purely refracted arrivals. The temporal and vertical scales of phase and intensity fluctuations for these two ray paths are compared with predictions based on the weak fluctuation theory of Munk and Zachariasen, which assumes internal-wave-induced sound-speed perturbations [J. Acoust. Soc. Am. 59, 818–838 (1976)]. The comparisons show that weak fluctuation theory describes the frequency and vertical-wave-number spectra of phase and intensity for the two paths reasonably well. The comparisons also show that a resonance condition exists between the local acoustic ray and the internal-wave field, as predicted by Munk and Zachariasen, such that only internal waves whose crests are parallel to the local ray path contribute to acoustic scattering. This effect leads to filtering of the acoustic spectra relative to the internal-wave spectra, such that steep rays do not acquire scattering contributions due to low-frequency internal waves.
Rapid thickness measurements using guided waves from a scanning laser source
Authors: Hayashi Takahiro , Murase Morimasa , Salim Muhammad Nor
Published: September 2009

Guided waves have been effectively used for rapid inspections of plates and pipes. However, the guided-wave technique is not generally used for measuring the remaining thickness in a plate and a pipe due to the difficulties in guided-wave motion. Instead, time-consuming and costly direct contact thickness measurements are still used in practice. This study describes a thickness measurement technique using the A0 mode of a Lamb wave generated by a laser source. A finite element analysis of Lamb wave revealed that this mode propagates with small reflections and mode conversions at a rounded shallow defect and has larger amplitude at thinner regions. Using these characteristics, it is experimentally demonstrated that the distributions of plate thickness were obtained from the amplitude of A0 mode generated by a scanning laser source and received by an angle-beam transducer. The resulting distribution images were obtained at extremely high speed compared to the conventional thickness measurements.
Cross-language categorization of French and German vowels by naïve American listeners
Authors: Strange Winifred , Levy Erika S. , Law Franzo F.
Published: September 2009

American English (AE) speakers’ perceptual assimilation of 14 North German (NG) and 9 Parisian French (PF) vowels was examined in two studies using citation-form disyllables (study 1) and sentences with vowels surrounded by labial and alveolar consonants in multisyllabic nonsense words (study 2). Listeners categorized multiple tokens of each NG and PF vowel as most similar to selected AE vowels and rated their category “goodness” on a nine-point Likert scale. Front, rounded vowels were assimilated primarily to back AE vowels, despite their acoustic similarity to front AE vowels. In study 1, they were considered poorer exemplars of AE vowels than were NG and PF back, rounded vowels; in study 2, front and back, rounded vowels were perceived as similar to each other. Assimilation of some front, unrounded and back, rounded NG and PF vowels varied with language, speaking style, and consonantal context. Differences in perceived similarity often could not be predicted from context-specific cross-language spectral similarities. Results suggest that listeners can access context-specific, phonetic details when listening to citation-form materials, but assimilate non-native vowels on the basis of context-independent phonological equivalence categories when processing continuous speech. Results are interpreted within the Automatic Selective Perception model of speech perception.
Spectral modulation detection and vowel and consonant identifications in cochlear implant listeners
Authors: Saoji Aniket A. , Litvak Leonid , Spahr Anthony J. , Eddins David A.
Published: September 2009

Speech understanding by cochlear implant listeners may be limited by their ability to perceive complex spectral envelopes. Here, spectral envelope perception was characterized by spectral modulation transfer functions in which modulation detection thresholds became poorer with increasing spectral modulation frequency (SMF). Thresholds at low SMFs, less likely to be influenced by spectral resolution, were correlated with vowel and consonant identifications [Litvak, L. M. et al. (2008). J. Acoust. Soc. Am. 122, 982–991] for the same listeners; while thresholds at higher SMFs, more likely to be affected by spectral resolution, were not. Results indicate that the perception of broadly spaced spectral features is important for speech perception.
Influence of the bubble-bubble interaction on destruction of encapsulated microbubbles under ultrasound
Authors: Yasui Kyuichi , Lee Judy , Tuziuti Toru , Towata Atsuya , Kozuka Teruyuki , Iida Yasuo
Published: September 2009

Influence of the bubble-bubble interaction on the pulsation of encapsulated microbubbles has been studied by numerical simulations under the condition of the experiment reported by Chang et al. [IEEE Trans. Ultrason Ferroelectr. Freq. Control 48, 161 (2001)]. It has been shown that the natural (resonance) frequency of a microbubble decreases considerably as the microbubble concentration increases to relatively high concentrations. At some concentration, the natural frequency may coincide with the driving frequency. Microbubble pulsation becomes milder as the microbubble concentration increases except at around the resonance condition due to the stronger bubble-bubble interaction. This may be one of the reasons why the threshold of acoustic pressure for destruction of an encapsulated microbubble increases as the microbubble concentration increases. A theoretical model for destruction has been proposed.
Nearfield acoustic holography using a laser vibrometer and a light membrane
Authors: Leclère Quentin , Laulagnet Bernard
Published: September 2009

This paper deals with a measurement technique for planar nearfield acoustic holography (NAH) applications. The idea is to use a light tensionless membrane as a normal acoustic velocity sensor, whose response is measured by using a laser vibrometer. The main technical difficulty is that the used membrane must be optically reflective but acoustically transparent. The latter condition cannot be fully satisfied because of the membrane mass, which has to be minimized to reduce acoustic reflections. A mass correction operator is proposed in this work, based on a two-dimensional discrete Fourier transform of the membrane velocity field. An academic planar NAH experiment is finally reported, illustrating qualitatively and quantitatively the feasibility of the method and the pertinence of the mass correction operator.
A procedure for the assessment of low frequency noise complaints
Authors: Moorhouse Andy T. , Waddington David C. , Adams Mags D.
Published: September 2009

The development and application of a procedure for the assessment of low frequency noise (LFN) complaints are described. The development of the assessment method included laboratory tests addressing low frequency hearing threshold and the effect on acceptability of fluctuation, and field measurements complemented with interview-based questionnaires. Environmental health departments then conducted a series of six trials with genuine “live” LFN complaints to test the workability and usefulness of the procedure. The procedure includes guidance notes and a pro-forma report with step-by-step instructions. It does not provide a prescriptive indicator of nuisance but rather gives a systematic procedure to help environmental health practitioners to form their own opinion. Examples of field measurements and application of the procedure are presented. The procedure and examples are likely to be of particular interest to environmental health practitioners involved in the assessment of LFN complaints.
Angular scattering of sound from solid particles in turbulent suspension
Authors: Moore Stephanie A. , Hay Alex E.
Published: September 2009

Sound scattering by solid particles suspended in a turbulent jet is investigated. Measurements of the scattered amplitude were made in a bistatic geometry at frequencies between 1.5 and 4.0MHz, and at scattering angles from 95° to 165° relative to the forward direction. Two types of particle were used: nearly spherical lead-glass beads and aspherical natural sand grains. For each particle type, experiments were carried out using ∼200 and ∼500μm median diameter grain sizes, corresponding to 0.7≲ka≲4. The sphericity of the sand grains, defined as the ratio of projected perimeter size to projected area size, was 1.08. The lead-glass bead results are consistent with an elastic sphere model. A rigid movable sphere model provides the best fit to the sand data, and the best-fit diameter is within 4% of the equivalent volume size. However, the scattering pattern for sand is systematically smoother than predicted: that is, the undulations in the angular scattering pattern predicted by spherical scatterer theory are present, but muted. This observed departure from spherical scatterer theory is attributed to disruption of the interference among creeping waves by the irregular surfaces of natural sand grains.
A normal mode projection technique for array response synthesis in range-dependent environments
Authors: Heaney Kevin D.
Published: September 2009

A method is presented to examine the problem of simulating the beam time series response for an array of arbitrary shape in a range-dependent environment using a combination of parabolic equation (PE) forward modeling and local normal mode analysis. The procedure involves computing the acoustic pressure field as a function of depth, using the PE, at the nominal center location of the array. The field is then decomposed into local complex normal mode amplitudes. These mode amplitudes are used to compute the field response on each array element, via range-independent normal mode theory. Conventional plane-wave beamforming is then applied. It is shown that a single matrix computation can be used to map the field as a function of depth to the beam response as a function of angle. The method is applied to two broadband range-independent examples to demonstrate its accuracy. It is then applied to a shallow-water range-dependent experiment from off the Florida coast and a deep-water range-dependent experiment from sound scattering off a seamount in the open ocean. For both range-dependent examples, the model simulation results reproduce the qualitative features observed in the data.
Determining material damping type by comparing modal frequency estimators
Authors: Anthony D. K. , Simón F. , Juan Jesús
Published: September 2009

The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods.