| Trawling Sonar System. |
05 AUG 1996 |
15 pages |
| Authors:
G. C. Carter; DEPARTMENT OF THE NAVY WASHINGTON DC
|
 | Disclosed is a sonar system comprising a platform, axially extendable supports projecting from the platform, a flexible cable array deployed from the platform means through said support means, and an acoustic detector connected to the flexible cable. By increasing the physical aperture of the sonar system, performance is enhanced. |
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| New Approaches for Modeling of Liquid Jet Atomization Processes |
01 AUG 96 |
99 pages |
| Authors:
Stephen D. Heister; PURDUE UNIV LAFAYETTE IN SCHOOL OF AERONAUTICS AND ASTRONAUTICS
|
| This report summarizes atomization simulations performed to investigate the role of this process in liquid rocket engine combustion instabilities. The research involves the development and application of a series of nonlinear free-surface models based on boundary element methods (BEMs). Models have been developed to study the effects of unsteady injection, transverse acoustic wave interactions (such as those experienced in the F-1 engine), longitudinal acoustic wave interactions, and the dynamics of ... |
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| Modeling of Liquid Jet Atomization Processes |
01 AUG 96 |
99 pages |
| Authors:
Stephen D. Heister; PURDUE UNIV LAFAYETTE IN SCHOOL OF AERONAUTICS AND ASTRONAUTICS
|
| This report summarizes atomization simulations performed to investigate the role of this process in liquid rocket engine combustion instabilities. The research involves the development and application of a series of nonlinear free surface models based on boundary element methods (B EMs). Models have been developed to study the effects of unsteady injection, transverse acoustic wave interactions (such as those experienced in the F-1 engine), longitudinal acoustic wave interactions, and the ... |
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| Receptivity in Boundary-Layer Transition to Turbulence |
AUG 96 |
244 pages |
| Authors:
William S. Saric; ARIZONA STATE UNIV TEMPE DEPT OF MECHANICAL AND AEROSPACE ENGINEERING
|
| Experiments are conducted in the Arizona State University Unsteady Wind Tunnel to investigate acoustic receptivity in the leading-edge region of a Blasius boundary layer. The experiment utilizes two different flat-plate models. One model has a leading edge with a special geometry that limits the receptivity mechanism to the leading edge. The second model is a tapered elliptical-leading- edge flat plate with a junction. A Blasius basic state isolates the instability ... |
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| Efficient Calculation of Directivity Indices for Certain Three- Dimensional Arrays |
26 JUL 96 |
44 pages |
| Authors:
Albert H. Nuttall; Benjamin A. Cray; NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV RI
|
| Array directivity is defined as the ratio of the output signal-to- noise ratio of an array to the input signal-to-noise ratio at an omni- directional element in an isotropic noise field. Calculation of directivity is obtained by integrating the magnitude-squared response of the array over all angles of incidence. In spherical coordinates, these arrival angles are denoted by an azimuthal angle, theat, and a polar angle, phi. Hence, calculation of ... |
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| Finite Difference Modelling of Scattering by Objects in the Seabed |
JUL 96 |
45 pages |
| Authors:
J. A. Fawcett; J. L. Grimbergen; SACLANT UNDERSEA RESEARCH CENTRE LA SPEZIA (ITALY)
|
| In this report we describe the theory and some implementation issues of a finite difference code used at SACLANT Centre. In particular, we consider the modelling of attenuation and the excitation of a remote incident field by using Huygen's sources. A series of comparisons of finite difference results with analytical results is performed. The report concludes with a series of computations of scattering of a generalized plane wave from a ... |
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| Development of Methods for Improved Breast Imaging Using Ultrasound |
JUL 96 |
86 pages |
| Authors:
John M. Reid; DREXEL UNIV PHILADELPHIA PA
|
| A novel framework was introduced for the deconvolution of B-scan images. A model for the rf image was developed first, and then imaging distortions were reconstructed using higher-order statistics of the measured image lines. Based on the estimated distortions deconvolution of the corresponding image was performed, which for the case of images of tissue mimicking phantom as well as human tissue images, led to significant resolution improvement. In the past, ... |
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| The Barents Sea Polar Front in Summer |
15 JUN 96 |
|
| Authors:
A. R. Parsons; Robert H. Bourke; Robin D. Muench; Ching-Sang Chiu; James F. Lynch; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF OCEANOGRAPHY
|
 | In August 1992 a combined physical oceanography and acoustic tomography experiment was conducted to describe the Barents Sea Polar Front (BSPF) and investigate its impact on the regional oceanography. The study area was an 80 X 70 km grid east of Bear Island where the front exhibits topographic trapping along the northern slope of the Bear Island Trough. Conductivity- temperature-depth, current meter, and acoustic Doppler current profiler (ADCP) data, combined ... |
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| Thermoacoustic Pin Stacks |
15 JUN 96 |
14 pages |
| Authors:
Robert M. Keolian; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| This technical report describes progress building and testing a 'pin stack' during the period 01 June 1995 through 31 May 1996. The pin stack produced 18% higher acoustic pressures, reached onset at a 40% lower mean pressure, and was about 25% more efficient than a conventional rolled stack in a thermoacoustic prime mover. A publications, presentations, and honors report is also included. |
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| Geometrical Aspects of Scattering and Physical Effects of Sound |
15 JUN 96 |
16 pages |
| Authors:
Philip L. Marston; WASHINGTON STATE UNIV PULLMAN DEPT OF PHYSICS
|
| Research is reported in the following areas: 1 Transient and high- frequency enhancements of the scattering of sound by elastic objects in water are measured and analyzed. (The impulse response of a thick cylindrical shell in water was measured as a function of aspect angle. The measurements show the frequency locus of a backscattering enhancement extending to near end-on incidence in agreement with predictions for an antisymmetric leaky Lamb wave. ... |
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| Transient Phenomena in Thermoacoustic Prime Movers |
JUN 96 |
72 pages |
| Authors:
Ching-Kai Meng; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| The purpose of this thesis is to investigate the evolution of the acoustic pressure waveform and temperature change across the heat exchangers as functions of time in a thermoacoustic prime mover. Measurements are reported for both nitrogen and helium gas under different mean pressures and initial temperature differences. Aspects of this thesis included the design and construction of the prime mover and implementation of a computer controlled data acquisition system. ... |
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| Effects of Shallow Water Bottom Interface Roughness and Volume Fluctuations on Broadband Pulse Resolution |
JUN 96 |
68 pages |
| Authors:
Mei-Chun Yuan; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| Typical acoustic propagation in shallow water environments is dominated by bottom-interacting paths. The effects of rough bottom interfaces and sediment volume fluctuations are investigated using model simulations. A numerical study of low-frequency (approx. 2OO Hz) broadband pulse propagation is presented and several characterizations of bottom factors are examined. In particular, the variations of the interface rms roughness and a volume fluctuation strength constant on the time resolution of the broadband ... |
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| Quantitative Evaluation of the Limitations of the Radiation Boundary Elements in the Finite Element Code ATILA |
JUN 96 |
65 pages |
| Authors:
Panagiotis A. Sinanoglou; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| A quantitative evaluation of the limitations of the radiation boundary elements in the finite element code ATILA has been performed. Five three dimensional models were employed, each representing a rigid spherical solid surrounded by water. Monopolar, dipolar and quadrupolar incident spherical waves were introduced and the corresponding scattered waves were computed using the ATILA code and an exact analytical solution. The dimensionless parameters that characterize the problem are ka, kL, ... |
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| Observations and Characterizations of Non-Linear Internal Waves on the Mid-Atlantic Bight Continental Shelf |
JUN 96 |
64 pages |
| Authors:
Donald W. Taube; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| During the summer of 1995, an intensive, joint field study called Shallow Water Acoustics in a Random Medium (SWARM 95) was conducted by the Naval Research Laboratories (NRL), Woods Hole Oceanographic Institution (WHOI), University of Delaware (UD), Applied Physics Laboratory of Johns Hopkins University (APL/JHU) and Naval Postgraduate School (NPS), among others, in the Mid-Atlantic Bight continental shelf region off the coast of New Jersey. Environmental and acoustic sensors were ... |
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| An Experimental Comparison of a Pin Stack to a Conventional Stack in a Thermoacoustic Prime Mover |
JUN 96 |
69 pages |
| Authors:
Rodney J. Gibson; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| This thesis is an experimental comparison of a pin stack to a conventional stack in a thermoacoustic prime mover. A thermoacoustic prime mover is a type of natural heat engine which converts a temperature gradient across a stack into acoustic energy. A pin stack uses wires which are arranged in a hexagonal array instead of the parallel or rolled plates of a conventional stack. The pin stack was constructed by ... |
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| A Double-Sum Technique for Performing a Fourier Transformation on an Integrand Composed of Aliased Factors |
31 MAY 96 |
19 pages |
| Authors:
G. Maidanik; K. J. Becker; NAVAL SURFACE WARFARE CENTER DAHLGREN DIV SILVER SPRING MD
|
| Structural acoustics often utilizes Fourier transformation to either reveal a phenomenon that is more directly recognized in one domain than in its Fourier conjugate domain or to employ complementarity in order to decipher a phenomenon. In this paper, a novel computational technique is introduced. This technique advantageously performs this transformation in situations in which specific spatial scales govern aliased factors in the integrand of a Fourier transformation. The technique can ... |
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| Underwater Sensing Device for Ocean Floor Contact |
10 MAY 1996 |
16 pages |
| Authors:
Colin J. Lazauski; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| An underwater sensing device for measuring or sensing an underwater condition proximate the floor of an ocean, lake or similar body of water. The sensing device includes an underwater sensing device mounting member and an underwater sensing device sensor, such as a hydrophone, mounted on the mounting member. The mounting member has known acoustic properties including a thickness and a largest dimension, each of which is a function of an ... |
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| Experiments in Axisymmetric Supersonic Jets |
MAY 96 |
236 pages |
| Authors:
Cyrille D. Moore; CALIFORNIA INST OF TECH PASADENA GRADUATE AERONAUTICAL LABS
|
| An experimental study of the effects of Mach number and density ratio on the development of axisymmetric jets is described. Values of the ratio of jet to-ambient-density from 0.23 to 5.5 were obtained by using different pairs of helium, nitrogen and argon gases. Jet exit Mach numbers were 1.41, 2.0, and 3.0. These discharge into gases at rest (velocity ratio = 0), providing density ratios from 0.23 to 5.5. To ... |
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| Actively Controlled Afterburner for Compact Waste Incinerator |
MAY 1996 |
11 pages |
| Authors:
T. P. Parr; K. J. Wilson; R. A. Smith; K. C. Schadow; NAVAL AIR WARFARE CENTER WEAPONS DIV CHINA LAKE CA
|
| Active control of fluid dynamics has been used to enhance mixing in incinerator afterburner experiments and increase the DRE for a waste surrogate. Experiments were conducted in a 50 kW scale burner in two configurations: one with direct modulation of the fuel and waste (GB), and another with indirect modulation of starved air pyrolysis surrogate (AB). The open loop active control system is based on the concept of combustion in ... |
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| Influence of Surface Roughness on Guided Waves in Plates |
30 APR 96 |
66 pages |
| Authors:
Dale E. Chimenti; Oleg I. Lobkis; IOWA STATE UNIV AMES CENTER FOR NONDESTRUCTIVE EVALUATION
|
| This report covers fundamental research performed on the effect of surface roughness on ultrasonic guided waves in plates. The effort reported here consists both of experiments and calculations. The measurements exploit guided waves generated in either immersion or with contact coupling. Samples have included aluminum prepared by indenting or sandblasting. The sandblasted specimens have been independently profiled to determine rms roughness. A simple model calculation is also described which, using ... |
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| Effect of Coulomb Collisions, Landau Damping and Particle Trapping on Linear and Nonlinear Ion Aooustic Waves |
30 APR 96 |
36 pages |
| Authors:
Chung Chan; NORTHEASTERN UNIV BOSTON MA DEPT OF ELECTRICAL ENGINEERING
|
| The general propagator expansion method is used for the study of the collision effects and the Fokker-Planck kinetic equation is employed for several collisional processes. In drift-free plasma, the studies show that the plasma may become unstable if e-i collision growth can overcome Landau damping and other collision damping. The contamination can affect ion acoustic waves significantly and a small amount of light ion contamination can cause much higher damping. ... |
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| Impedance Measurements of Loctite Silicone Rubber and Structural Damping Results of Mold-Ex Silicone MX-111 |
26 APR 96 |
53 pages |
| Authors:
Andrew J. Hull; Rolf G. Kasper; NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV RI
|
| On 5 December 1995, the Naval Undersea Warfare Center (NUWC) detachment in New London, Connecticut, and the Loctite Corporation in Rocky Hill, Connecticut, signed a Cooperative Research and Development Agreement (CRADA). The CRADA required that the NUWC detachment perform a number of acoustic impedance tests in their New London calibrated air tube facility. Loctite provided specimens of standard silicone rubber and silicone rubber embedded with iron powder and glass microbeads, ... |
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| Acoustic Thermometry of Ocean Climate (ATOC): Pioneer Seamount Source Installation |
APR 96 |
85 pages |
| Authors:
Bruce M. Howe; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
|
| The ATOC acoustic source was installed on Pioneer Seamount during October and November 1995. Three vessels were used for this work. On 5 October, M/V McGaw laid 3 nmi of cable at Pillar Point, California. The cable is terminated at the Pillar Point Air Force Station. On 14 October, a survey of the proposed source site on Pioneer Seamount was conducted using the U.S. Navy's Deep Submergence Vehicle Sea Cliff ... |
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| Liquid Viscosity and Density Measurement with Flexural-Plate-Wave Sensors |
APR 1996 |
10 pages |
| Authors:
Stuart W. Wenzel; Ben J. Costello; Richard M. White; BERKELEY MICROINSTRUMENTS INC RICHMONDCA
|
| Micromachined flexural plate wave (FPW) sensors can detect subtle variations in the density and viscosity of liquids. Liquid density causes a mass-loading effect that lowers the sensor operating frequency. In viscous liquids, the attenuation coefficient of the acoustic wave is proportional to the square-root of the viscosity. We discuss recent results that explore the density-sensing precision and the viscosity-sensing range of FPW sensors. A micromachined FPW sensor (wavelength 100 micrometers, ... |
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| Acoustic Thermometry of Ocean Climate (ATOC): Pioneer Seamount Source Installation |
APR 96 |
84 pages |
| Authors:
Bruce M. Howe; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
|
| The ATOC acoustic source was installed on Pioneer Seamount during October and November 1995. Three vessels were used for this work. On 5 October, M/V McGaw laid 3 nmi of cable at Pillar Point, California. The cable is terminated at the Pillar Point Air Force Station. On 14 October, a survey of the proposed source site on Pioneer Seamount was conducted using the U.S. Navy's Deep Submergence Vehicle Sea Cliff ... |
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| Acoustic Characterization of Soil |
28 MAR 1996 |
91 pages |
| Authors:
William D. O'Brien Jr.; Robert G. Darmondy; David C. Munson Jr; ILLINOIS UNIV AT URBANA-CAMPAIGN BECKMAN INST FOR ADVANCED SCIENCES AND TECHNOLOGY
|
| Detection and classification of buried cultural artifacts in ground soil are principal goals for the production, detection and processing of acoustic signals. Time domain, frequency domain, and combined time-frequency domain approaches to transmit and process acoustic signals all depend critically on the acoustic transduction device to transmit high-amplitude acoustic pressure waves and to receive low-amplitude acoustic pressure waves over a large band of frequencies. |
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| Ultra-Broadband Hydrophone. |
22 MAR 1996 |
14 pages |
| Authors:
Roger L. Woodall; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| The present invent ion relates to an ultra-broadband hydrophone which has two major electronic components and one mechanical component. The first electronic component comprises a flux gate magnetometer for sensing changes in an ambient magnetic field and for creating an electrical signal representative of the ambient magnetic field. The second electronic component comprises an electrical circuit for demodulating the electrical signal and a low pass filter for smoothing the demodulated ... |
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| Transducer Design Experiments for Ground-Penetrating Acoustic Systems |
19 MAR 1996 |
17 pages |
| Authors:
E. G. Eckert; J. W. Maresca Jr; VISTA RESEARCH INC MOUNTAIN VIEW CA
|
| The transmission of impulsive acoustic signals into a homogeneous soil medium was investigated. Measurements performed using a piezoelectric driver and a hydrophone as the acoustic sources demonstrate that both types of transmitters (positioned at the air soil interface) are capable of producing acoustic waves in soil. The relative strength of the acoustic signals produced by each source was found to be approximately equal. The angular ... |
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| Observations of T-Phase Arrivals at Pt Sur and Wake Island |
15 MAR 96 |
17 pages |
| Authors:
Catherine DE Groot-Hedlin; SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA
|
| We have assembled a large suite of T-phase observations recorded on hydrophones located at Point Sur and Wake Island, in an attempt to understand how acoustic energy from underwater earthquakes is coupled to the sound channel and bow the sound propagates from source to receiver. The events cover a wide range of locations in the North Pacific. We find that T-phases observable at Point Sur are generated only in a ... |
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| Flow Measurements in a Tidal Channel Using an Acoustic Current Profiler |
15 MAR 96 |
63 pages |
| Authors:
Youyu Lu; Rolf G. Lueck; VICTORIA UNIV (BRITISH COLUMBIA) CENTRE FOR EARTH AND OCEAN RESEARCH
|
| An acoustic Doppler current profiler (ADCP) was applied to measure the three-dimensional flow field in a tidal channel along the coast of Vancouver Island, British Columbia. The ADCP was rigidly mounted to the bottom in the center of the channel, and rapidly sampled the velocity profiles along its inclined beams. The data were directly read by a computer on shore. This method of deployment allows for an explicit estimate of ... |
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| Reflected-Afterflow Virtual-Source (RAVS) Model Response Compared to Exact Calculations for Elastic Cylinders Attacked by Planar Waves |
MAR 96 |
60 pages |
| Authors:
George V. Waldo Jr; NAVAL SURFACE WARFARE CENTER CARDEROCK DIV BETHESDA MD
|
| A recently developed theoretical approximation, the Reflected Afterflow Virtual Source (RAVS) model, is applied to the case of a planar shock wave attacking an elastic cylindrical shell. To do this, an equation of motion for a structural surface is presented. Also, equations for the pressure that develops when an acoustic wave interacts with a curved and compliant surface are presented. These equations were derived using the RAVS model. An expression ... |
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| Oceanology International '96', Conference Proceedings, Volume 1, Held in Brighton, United Kingdom, on 5-8 March 1996. Environmental Factors Affecting the Acoustic Resonant Frequency Due to Internal Solitons |
MAR 96 |
10 pages |
| Authors:
Michael K. Broadhead; Robert L. Field; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS SHALLOW WATER COASTAL ACOUSTICS SECTION
|
| Nonlinear shallow water internal waves can enhance the bottom interaction of underwater sound. For a lossy ocean bottom, this has the effect of an overall level change (in addition to fluctuations) in the transmission loss at preferred ('resonant') frequencies. The mechanism for this effect is acoustic mode coupling due to the depression of higher sound speed water into lower speed water (at the pycnocline). It is also possible for this ... |
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| Robot Evidence Grids |
MAR 96 |
|
| Authors:
Martin C. Martin; Hans P. Moravec; CARNEGIE-MELLON UNIV PITTSBURGH PA ROBOTICS INST
|
| The evidence grid representation was formulated at the CMU Mobile Robot Laboratory in 1983 to turn wide angle range measurements from cheap robot- mounted sonar sensors into detailed spatial maps. It accumulates diffuse evidence about the of a grid of small volumes of nearby space from individual sensor readings into increasingly confident and detailed maps of a robot's surroundings. It worked surprisingly well in the first implementation for sonar navigation ... |
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| A Towed Acoustic Doppler Current Profiler System |
FEB 96 |
15 pages |
| Authors:
Nancy A. Bray; SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA
|
| This grant covered the cost of acquiring a complete towed ADCP/CTD system, assembling it and doing preliminary tests. The system has subsequently been used very successfully as part of the ONR-funded program 'A Towed Acoustic Doppler Current Profiler System,' to collect upper ocean profiles of current in the data scarce eastern Indonesian Archipelago. A cruise report is appended. The system was designed particularly for use on foreign research vessels not ... |
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| Method and Apparatus for Separating Suspended Particles from a Flowing Fluid. |
FEB 1996 |
26 pages |
| Authors:
Stuart C. Dickinson; Robert Kuklinski; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| Apparatus and methods for filtering particulate matter from a fluid traveling proximate a surface containing a port. First and second ultrasonic wave generators produce superposed ultrasonic waves to define a composite wave pattern in a region of the fluid body upstream of the port. Nodes and antinodes in the composite wave region define regions at which the particulate matter accumulates. The accumulating particulate matter is displaced out of the fluid ... |
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| Method and Apparatus for Separating Particulate Matter from a Fluid. |
FEB 1996 |
29 pages |
| Authors:
Stuart C. Dickinson; Robert Kuklinski; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| A method and apparatus for filtering particulate matter entrained in a fluid entering a port from a reservoir. First and second ultrasonic wave generators produce ultrasonic waves to define a composite wave pattern. The patterns produce nodes and antinodes in a region through which fluid entering a port passes. The particulate matter in the portion of the fluid passing through the region accumulates along the nodes and antinodes. The accumulating ... |
|
| Proceedings of Air Force Office of Scientific Research and Phillips Laboratory Workshop on Sprites and Blue Jets Held in Phillips Laboratory, Geophysics Directorate, Hanscom AFB, MA on 18-19 October 1995. |
30 JAN 1996 |
410 pages |
| Authors:
L. S. Jeong; PHILLIPS LAB HANSCOM AFB MA
|
| This report contains the viewgraphs presented at the AFOSR-PL workshop on Sprites and Blue Jets held at the Phillips Laboratory, Geophysics Directorate, Hanscom AFB, MA, 18-19 October 1995. (MM) |
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| An Investigation of the Sources and Characteristics of the Noise Component in SeaMarc II Echo Signals |
28 JAN 96 |
4 pages |
| Authors:
Stanley Zisk; HAWAII UNIV HONOLULU SCHOOL OF OCEAN AND EARTH SCIENCE AND TECHNOLOGY
|
| As is well known, the SeaMarc II towfish system was lost at sea during a scientific survey cruise in the Southern Ocean near the beginning of this project. Work was immediately begun on the design and construction of a replacement mapping system to be called HAWAII MR1. The signal processing for this system was designed based on the crude and incomplete information obtained earlier from one short series of noise ... |
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| Perturbation Problems in Fluid Dynamics |
26 JAN 96 |
18 pages |
| Authors:
Lu Ting; NEW YORK UNIV NY COURANT INST OF MATHEMATICAL SCIENCES
|
| Perturbation methods and numerical methods were employed to study four problem areas in fluid dynamics. The areas and the progress were: (1) Viscous vortical flows - We showed how to combine the asymptotic theory and experiments to study slender vortex filaments and how to specify the numerical parameters needed for the vortex element method to predict correctly the motion of slender filament(s) in space. We presented formulas relating a rotational ... |
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| Analysis of Naturally Occurring Slip-Stick Data in Arctic Ice Floes |
96 |
43 pages |
| Authors:
Peter Michaux; INSTITUTE OF OCEAN SCIENCES SIDNEY (BRITISH COLUMBIA)
|
| Naturally occurring slip-stick data was recorded from a closing lead in the arctic in 1994. A portion of that data is analysed here with the idea of a slip-stick stress release model in mind. |
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| New Computational Analytical Methods for Scattering and Propagation in Random Media |
31 DEC 95 |
11 pages |
| Authors:
Charles L. Rino; Hoc D. Ngo; VISTA RESEARCH INC MOUNTAIN VIEW CA
|
| Scattering in inhomogeneous environments with irregular boundaries has ramifications for a number of practical problems of interest to the U. S. Army and other government agencies. Subdividing the problem into smaller and thereby more easily managed units has been successfully exploited. Under this grant new methods were developed that are particularly well suited to highly directed propagation. Propagation at low grazing angles relative to the boundary affords further simplification when ... |
|
| Progress Report for The Catholic University of America Grant N0OO14-94- 1-02O1 |
31 DEC 95 |
4 pages |
| Authors:
M. J. Beran; CATHOLIC UNIV OF AMERICA WASHINGTON DC DEPT OF ELECTRICAL ENGINEERING
|
| The calculations for considering linear sound-speed profiles in channels have been generalized to treat piece-wise linear sound-speed profiles. Calculation of the scattering coefficients for the linear profile was begun. The case of a channel with a complex bottom impedance condition was also under investigation. As a result of the fact that the eigenvalues are now complex, a diffusion-like term has been added to the governing coherence equations. We began studies ... |
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| Bubble Pressure Generating System |
21 DEC 1995 |
12 pages |
| Authors:
Joseph A. Clark; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| A pressure generating system uses a shock wave chamber filled with a liquid pressurized to a static pressure different from ambient atmospheric pressure. Once a preferred location is established in the chamber, a pulsed compressional acoustic shock wave introduced into the liquid is reflected from a free surface of the liquid as a dilatation wave focused on a point at which a bubble forms and expands about an object. The ... |
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| Recovery Factors in Zero-Mean Internal Oscillatory Flows |
DEC 95 |
76 pages |
| Authors:
Nicole L. Tait; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| High speed oscillatory flows, like high speed mean flows, are capable of inducing time-averaged heat transfer effects. This research involves the analytical solution of a model problem of zero-mean internal oscillatory flow, which arises from a high-intensity resonant standing acoustic wave set up across the ends of two parallel plates. The compressible form of the Navier-Stokes equations are solved, along with the equations of continuity, energy, and state, using perturbation ... |
|
| Method and Apparatus for Segmenting a Speech Waveform. |
07 NOV 1995 |
58 pages |
| Authors:
George S. Kang; Lawrence J. Fransen; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| A system that synchronously segments a speech waveform using pitch period and a center of the pitch waveform. The pitch waveform center is determined by finding a local minimum of a centroid histogram waveform of the low-pass filtered speech waveform for one pitch period. The speech waveform can then be represented by one or more of such pitch waveforms or segments during speech compression, reconstruction or synthesis. The pitch waveform ... |
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| Geoacoustic Study of Delaware Atlantic Coast from Cape Henlopen to Fenwick Island |
NOV 95 |
354 pages |
| Authors:
Richard G. McGee; ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS HYDRAULICS LAB
|
| A comprehensive geoacoustic study has been performed for a 3-mile- wide area offshore of the Delaware coast between Cape Henlopen and Fenwick Island for the purpose of defining the limits of available granular materials. The work was performed in support of the U.S. Army Engineer District, Philadelphia's, feasibility study for shore protection solutions for the Atlantic coast of Delaware. Specifically, the objective of this investigation was to quantify the bottom ... |
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| Theoretical Topics in Wave Propagation in a Random Medium |
31 OCT 1995 |
25 pages |
| Authors:
George Lamb; ARIZONA UNIV TUCSON DEPT OF MATHEMATICS
|
| Three aspects of wave propagation in a random medium are considered. The first is the scattering of a plane compressional wave by a spherical inhomogeneity of specified radius. This result is then averaged over a Rayleigh distribution of sphere radii. As a second topic, the scattering by a medium in which an elastic parameter varies randomly is considered. When the randomness is assumed to be described ... |
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| An Experimental Investigation of Nonlinear Behaviour of Beams and Plates Excited to High Levels of Dynamic Response |
31 OCT 95 |
470 pages |
| Authors:
Howard F. Wolfe; Cynthia A. Shroyer; Dansen L. Brown; Larry W. Simmons; WRIGHT LAB WRIGHT-PATTERSON AFB OH
|
| Dynamic tests were conducted utilizing clamped aluminium and composite beams and plates excited by shakers and acoustic progressive wave tubes. The total strains and the components, bending and axial and the displacements were measured with increasing levels of excitation. Bistable behaviour is observed with sinusoidal excitation for both the beams and plates. The beams randomly excited exhibit a slight frequency shift and peak broadening, which can be attributed to an ... |
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| Backscatter Analysis from a Smooth Sand Surface: Diffusion Approximation |
26 OCT 95 |
46 pages |
| Authors:
Nicholas P. Chotiros; Adrienne M. Mautner; Julia Laughlin; TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
|
| The development of a model of backscatter from a smooth underwater sediment surface is described. The model includes two components: the propagation of acoustic energy through the water/sediment interface which is governed by wave theory, and randomization of acoustic energy within the interior of the sediment which is approximated by the diffusion equation. With respect to the wave theory, Biot's poroelastic wave propagation theory is used. The model gives predictions ... |
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| New Multiple Scatter Model of the Ocean Sediment |
15 SEP 95 |
66 pages |
| Authors:
Dennis J. Yelton; Morris Stern; Nicholas P. Chotiros; TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
|
| The reflection and scattering properties of an in homogeneous poroelastic medium were studied via numerical simulation. The inhomogeneous medium was modeled as an ensemble average of randomly layered poroelastic material. Each layer represented a granular material of a particular grain size. The thickness of each layer was related to the associated grain size and porosity by a conservation of mass relationship. Lateral variations in grain size were approximated by performing ... |
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Reports by Keyword(s)
ACOUSTIC WAVES
