Navy Underwater Sound Laboratory Research Articles

Nonlinear acoustics and the Acoustical Society of America

The modern era of nonlinear underwater acoustics had its roots in a remarkable session at the 57th ASA meeting at Providence RI in June, 1960, chaired by Westervelt, of Brown University, who also presented his remarkable new theory of the parametric acoustic array. This conceptual “device” enables highly directive low frequency sound to be created from the nonlinear interaction of two high frequency radiations of high directivity, which was confirmed in a model- tank study paper in this session by Brown Univ. Professor Robert Beyer and student Bellin. JASA has been the major worldwide forum for publications in nonlinear underwater acoustics, ever since, with much of the U.S. work done at the Navy Underwater Sound Laboratory and its successor, the Naval Underwater Systems Center, as well as the Applied Research Laboratories of the University of Texas at Austin. Topics have included parametric arrays, the nonlinear generation of harmonic radiations and transients, acoustic saturation, nonlinear transmitting and receiving sonar and imaging, and many practical applications to underwater sound and acoustical oceanography. Current and/or developing applications include underwater communications, backscattering measurements, penetration of narrow beams into sediments, sub-bottom profiling, and fish school quantification and classification. These and other topics are reviewed and recent implementations are described. [Work supported by ARL:UT Austin.]

Columbia Division of War Research and the work of Ewing, Worzel, and Pekeris

Three University laboratories were established in WWII to conduct underwater acoustics research, in response to widespread attacks on allied shipping by German submarines; the Columbia University Division of War Research, Harvard Underwater Sound Laboratory, and the University of California Division of War Research, and the last two of these are being discussed by other speakers in this session. During the war, outstanding work was done at Columbia by Maurice Ewing, J. Lamar Worzel, and C. L. Pekeris, which has been summarized in the book, Propagation of Sound in the Ocean. Experiments utilizing explosive sources were done at sea in 1943 and 1944, in both shallow and deep water, off the east coast of the United States, with the USS Saluda (IX87) and other vessels, in cooperation with the Naval Ordnance Laboratory, Woods Hole Oceanographic Institution, and the U.S. Navy Underwater Sound Laboratory. Pekeris is noted for his wave theoretic analysis of the shallow water propagation results and is credited with being the first to apply normal mode theory to shallow water waveguides. Ewing and Worzel are noted for their development of some of the first long range ocean acoustics experiments, which continue to this day in similar context and importance. Some highlights of this work are presented to illustrate the beginnings of long range underwater acoustic propagation research in the United States.

The Sound Lab at Fort Trumbull, New London, Connecticut, 1945–1996

The Navy Underwater Sound Laboratory was formed in 1945 when the U.S. Navy merged on-going efforts of Columbia and Harvard Universities to combat the German U-boat threat in the North Atlantic. Prior to that time, the Division of War Research of Columbia, housed in a single building at Fort Trumbull, was sponsored by the National Defense Research Committee (NDRC) while the Harvard Underwater Sound Laboratory was doing similar work in Cambridge, Massachusetts. For the next 50 years, until it was formally closed in 1996, the “Sound Lab” continued to support virtually all aspects of Naval Warfare technology. This talk will attempt to describe the rich scientific culture and technological contributions of the New London Sound Lab.

Contributions to the development of underwater acoustics at the Harvard Underwater Sound Laboratory

The Harvard Underwater Sound Laboratory (HUSL) began in June 1941, six months before Pearl Harbor, and closed on January 31, 1946. HUSL was directed throughout its existence by (then) Assoc. Prof. Frederick V. Hunt, who incidentally coined the acronym sonar. This paper traces several contributions HUSL made to undersea warfare through exploitation of underwater acoustics. Especially significant were developments by HUSL in sonar and underwater ordnance (torpedoes). Both developments were supported by numerous subprojects on a wide range of applications such as reverberation suppression, Doppler enhancement, and torpedo transducer design. Particular attention is paid to work on air-dropped and submarine-launched acoustic homing torpedoes. HUSL’s far-reaching influence continues to be evident in today’s sonar and torpedo systems. Closure of HUSL spawned Penn State’s Ordnance Research Laboratory (now Applied Research Laboratory) and enriched sonar development at the US Navy Underwater Sound Laboratory, New London. Moreover, HUSL personnel returning to the University of Texas soon founded the Defense Research Laboratory (now Applied Research Laboratories) at Texas. We pay particular homage to living HUSL alumnus A. Wilson Nolle, who, along with our recently departed colleague, Reuben Wallace, and 12 other deceased alumni, had come to HUSL from the University of Texas.

Parametric acoustic array development at the U.S. Navy’s New London, Connecticut laboratory.

A brief history of the development of parametric acoustic sources at the U.S. Navy Underwater Sound Laboratory (USNUSL), and its successor, the Naval Underwater Systems Center is presented. Inspired by Robert Mellen, the Parametric Sonar Group was formed to explore the practical implications of Westervelt’s idea for underwater acoustics. Spanning more than two decades, this research pursued various potential applications exploiting the unique characteristics of parametric sources, including echo‐ranging in reverberant environments, communications involving voice, data, music, and video signals, target‐strength measurements, bottom bathymetry, high‐resolution sub‐bottom profiling, and measurements of scattering and reflection from surfaces. Parametric source design procedures were developed, and guidelines were established for diagnosing and avoiding undesirable effects, such as difference‐frequency instability and spurious nonlinearities, such as direct radiation from the projector, cavitation, and receiver nonlinearity. Theoretical models extended the Westervelt theory to realistic primary fields. For planar projector arrays, parametric source design curves, valid for levels in the primary far field, enabled designers to predict performance without resorting to computer calculations. To obtain source‐levels and beam‐widths within the primary near field, where the secondary signal is generated, a computer program, called CONVOL5 in its present configuration, can be used to obtain more detailed performance predictions.

A brief history of the discovery of the low frequency sound absorption mechanism in seawater and its pH dependence.

In the 1960s tests with a new surface ship sonar indicated that low‐frequency (less than 10 000 Hz) propagation loss was greater than predicted by the existing MgSO4 absorption model. Propagation measurements in the SOFAR channel showed that the anomalous absorption was up to ten times greater than predicted and could be fitted by a 1‐kHz relaxation. This was not without controversy at the time, but interest in this fundamental parameter spurred a major measurement effort by the U.S. Navy Underwater Sound Laboratory and other laboratories in the US, Canada, New Zealand, Europe, and Australia, resulting in at‐sea measurements from Hudson Bay to the Tasman Sea. Yeager and Fisher conducted laboratory t‐jump measurements that identified a boron based low‐frequency relaxation mechanism in seawater. Simmons and Fisher followed with resonant sphere measurements to quantify the resulting acoustic absorption. A compilation of the at‐sea results showed, somewhat surprisingly, a correlation with pH: the lower the pH, the lower the absorption. Mellen quantified the pH dependence by extensive laboratory resonator measurements. These results were confirmed by measurements conducted in China. The possible application of acoustically monitoring ocean pH was first suggested by Browning and Mellen in 1990.

Navy Underwater Sound Laboratory and the cylindrical array

On 1 July 1945, the sonar development program of the Harvard Underwater Sound Laboratory (HUSL) was transferred to the United States Navy Underwater Sound Laboratory at New London, Connecticut (USNUSL). Especial emphasis was placed on the continuation of research and development work on scanning sonar systems at New London. Major developments initiated by HUSL were completed and evaluated; these included an integrated search-attack sonar involving both horizontal and vertical scanning and an electronically scanned cylindrical transducer for submarine applications. USNUSL continued the exploitation of the versatility provided by the cylindrical array in development of the concepts incorporated in modern surface ship sonar systems and extended these concepts to the spherical arrays of modern submarine sonars.

Effects of Partial Shields on Transmission Lines at Low Frequencies

It is often desirable to estimate the degree of shielding achieved between two transmission lines crossing at some specified angle, when one of them is surrounded by a metallic tubing of finite length. A simple analysis that allows a rather accurate estimation of the shielding effectiveness of the tubing at low frequencies where the quasi-static assumption holds is presented. Based upon this quasi-static assumption and the empirical results that the fields generally fall off inversely with the square of the distance from a line and with the aid of Schelkunoff's shielding theory, an equation predicting the shielding effectiveness of the tubing has been derived and confirmed experimentally. Examples are given involving coaxial cables, parallel-wire lines, and copper shields of various lengths crossing at various angles. The discrepancies between calculated and measured values are generally less than 4 dB and in most cases less than 1 dB. The theory has also been applied to cases where the cables approach, but do not cross each other, such as were recently measured sured at the U. S. Navy Underwater Sound Laboratory.[1] Good agreement is obtained in this case also. Other situations involving ferro-magnetic shields and twistedpair lines have also been considered. The restrictions on the applicability of the formula developed have been pointed out explicitly.

Special Relationships between the Farfield and the Radiation Impedance

Some new relationships between the sound pressure at certain points in the farfield and the radiation impedance for certain acoustic sources have been derived from the Helmholtz integral formula. Under special conditions these relationships reduce to exact analytical solutions of problems that can otherwise only be solved numerically. For example, for a cylinder of arbitrary cross sectional shape with the ends vibrating uniformly and the sides motionless the farfield pressure in the direction of the cylinder axis is simply related to the radiation impedance. Such relationships provide helpful checkpoints for evaluating the success of some of the elaborate numerical methods which are currently being developed for attacking previously unsolved acoustic radiation problems with large digital computers. In certain cases, they can also provide new methods for determining radiation impedance from farfield calculations or possibly from farfield measurements. [Work supported by U. S. Navy Underwater Sound Laboratory.]

Acoustic Turbulent Water-Flow Tunnel

The acoustic turbulent water-flow tunnel designed and constructed at the U. S. Navy Underwater Sound Laboratory has a clear plastic-pipe test section (312-in. i.d.) through which water is pumped at centerline velocities ranging from 9 48 knots. Noise-reduction techniques have prevented pump and piping noises from entering the test section through either structural or fluid paths. Measurements at centerline velocities between 9 and 48 knots with flush mounted hydrophones at several longitudinal spacings show that the ratio of convection velocity to centerline velocity ranges from 0.86 to 0.61. The curve of maximum space-time correlation in frequency bands versus hydrophone spacing in wavelengths is in good agreement with other published results. Frequency spectra measured from 200–10 000 Hz coincided when nondimensionalized with respect to centerline velocity and boundary-layer thickness. When corrected for hydrophone size, the spectral curve was similar to those reported for turbulent airflow and rising and falling bodies in water.

Scaled Spherical Transducer Array

A scale model of a large truncated spherical transducer array has been designed and fabricated to provide means for obtaining design data in a test tank. Scaled transducer elements are mounted on a scaled supporting structure with a removable dome. Modular amplifiers drive an array aperture in transmission or preamplify in reception. Delay lines used with aperture selection cable harnesses form beams directed along the acoustic axes of the apertures and steered slightly from these axes. Horizontal beam patterns at depression angles of 0°, 15°, and 45° and vertical beam patterns at azimuth angles of 0°, 60°, and 120° may be measured. Transmitting and receiving responses at scaled operating frequencies for all system modes can be determined. In transmitting, measurements of voltage, current, and phase to each transducer element can be used to determine element input power and impedance. Scaling parameters are outlined. Effects of aperture shape, the dome, element acoustic interaction, and manufacturing tolerances are reviewed. Available data are presented. [Work supported by U. S. Navy Underwater Sound Laboratory.]

Sound Transmission through a Periodically Supported Thin Plate

The transmitted and reflected sound fields resulting from a plane sound wave incident upon a periodically supported thin plate have been computed. The supports are taken to lie parallel to the incident wavefronts and to offer an impedance to transverse plate motion that is uniform over their length. A measure of the sound transmission that is of particular interest is the transmission loss, defined as TL=−10 log [intensity of the main transmitted wave/intensity of the incident wave]. In this definition, the main transmitted wave is the component wave in the transmitted sound field that has the same direction as the incident wave. The effect of the supports on TL are presented as a function of acoustic frequency, incidence angle, support spacing, support impedance, and the density of the fluid in which the supported plate is. immersed. In addition, the effect of plate damping on TL is shown to be much larger for supported plates than for free plates. [Work supported by the U. S. Navy Underwater Sound Laboratory.]

Use of Toroidal Wavefunctions for the Free-Flooding Ring Transducer

The problem of acoustic radiation from a thin torus has been solved by use of the toroidal wavefunctions derived by V. H. Weston. When a suitable normal velocity on the surface of the torus is chosen, this problem provides an adequate model for calculating the far field of free-flooding ring transducers. Although such transducers are commonly used as underwater sound sources, their development has long suffered from the lack of such a theoretical model. Calculations of the radiation pattern, directivity index, and radiation resistance are in good agreement with published measurements for single transducers and coaxial arrays. However, the nearfield quantities given by this model, such as radiation mass loading, are not adequate for ring transducers and will require more realistic models. Such models can also be based on the toroidal wavefunctions, but will involve more numerical work than the thin torus model. [Work supported by U. S. Navy Underwater Sound Laboratory.]

Flow Excitation of Cylindrical Shells and Associated Coincidence Effects

The purpose of this analysis to predict the vibration level of a pipe conducting a turbulently flowing fluid. First, recent data on the correlation function describing the random pressures in the turbulent boundary layer are reviewed. The Strouhal-number dependence displayed by the cross-spectral density (in both the downstream and transverse direction), is equivalent to a complex vectorial wavenumber proportional to ω/V, where ω is the circular frequency and V is the convection velocity. The components in the transverse and downstream directions are, respectively, imaginary and complex. Starting from the formal solution for the response of an elastic structure to random excitation, published by Powell, the vibration level of the pipe wall is computed, use being made of the correlation function obtained from narrow-band measurements performed at the U.S. Navy Underwater Sound Laboratory. The average spectrum level that would be obtained from vibration measurements made with finite-bandwidth filters is then computed. The maximum frequency at which individual resonance peaks can be observed is expressed in terms of the filter bandwidth. Amplification of the pipe-wall response by coincidence effects in pipes conducting high-speed air or steam flow is examined. Spatial coincidence occurs when the longitudinal wavenumber of a shell mode matches the real component ω/V of the pressure cross-spectral-density wavenumber. Because of the exponential dependence of the cross-spectral density on the transverse Strouhal number, enhancement by coincidence is limited to modes whose circumferential wavelength exceeds approximately one-third of their axial wavelength.

Narrow-Band Investigations of the Longitudinal Space-Time Correlation Function in Turbulent Airflow

The longitudinal space-time correlation function of the fluctuating pressures at the wall in turbulent airflow has been investigated, using the U.S. Navy Underwater Sound Laboratory's 3.5-in. turbulent-pipe-flow facility. Data were obtained for various Reynolds numbers and transducer separations, and were analyzed by using filters of constant 30-cps bandwidth. These measurements of the longitudinal space-time correlation function are compared with a mathematical model that takes into account the effect of finite filter bandwidths.

INTELLIGENCE IN THE FLEET

Naval Engineers JournalVolume 75, Issue 1 p. 65-70 INTELLIGENCE IN THE FLEET CAPTAIN RICHARD L. CORKRAN Jr., USN, CAPTAIN RICHARD L. CORKRAN Jr., USN Captain Richard L. Corkran, Jr., USN, graduated from U. S. Naval Academy, 1941 (Class 1942). After a tour of duty at the Naval Training Station, Norfolk, Virginia, became Gunnery Officer of USS LUNGA POINT (CVE 94) followed by a tour in USS SIBONEY (CVE 112) holding the same billet. In June 1948 completed the Navy course in Electronic Engineering at MIT. Received B. S. E. E. Degree. Then followed tours of duty at the Surface Antisubmarine Development Detachment, Key West, Florida, U. S. Navy Underwater Sound Laboratory, New London, Connecticut, Norfolk Naval Shipyard, Norfolk, Virginia, and Staff, Commander-in-Chief, U. S. Atlantic Fleet. Currently on duty in the Bureau of Ships as assistant Branch Head, Electronics-Electrical Design Branch, Ship Design Division.Search for more papers by this authorMERWYN C. BLY, MERWYN C. BLY Merwyn C. Bly, Virginia Military Institute and New York University. 2nd Lt Pilot World War I. Texas Power & Light Company and then various until August 1941, when called to form the Intelligence & Countermeasures Unit, Bureau of Ships. Holder of Distinguished Civilian Service Medal for contributions in World War II. Five U. S. electronic patents. Author of “A Guide to Cathode Ray Patterns” Jno. W. Wiley and Sons. Registered Engineer District of Columbia. Presently Section Head Electronic Warfare (BUSHIPS).Search for more papers by this author CAPTAIN RICHARD L. CORKRAN Jr., USN, CAPTAIN RICHARD L. CORKRAN Jr., USN Captain Richard L. Corkran, Jr., USN, graduated from U. S. Naval Academy, 1941 (Class 1942). After a tour of duty at the Naval Training Station, Norfolk, Virginia, became Gunnery Officer of USS LUNGA POINT (CVE 94) followed by a tour in USS SIBONEY (CVE 112) holding the same billet. In June 1948 completed the Navy course in Electronic Engineering at MIT. Received B. S. E. E. Degree. Then followed tours of duty at the Surface Antisubmarine Development Detachment, Key West, Florida, U. S. Navy Underwater Sound Laboratory, New London, Connecticut, Norfolk Naval Shipyard, Norfolk, Virginia, and Staff, Commander-in-Chief, U. S. Atlantic Fleet. Currently on duty in the Bureau of Ships as assistant Branch Head, Electronics-Electrical Design Branch, Ship Design Division.Search for more papers by this authorMERWYN C. BLY, MERWYN C. BLY Merwyn C. Bly, Virginia Military Institute and New York University. 2nd Lt Pilot World War I. Texas Power & Light Company and then various until August 1941, when called to form the Intelligence & Countermeasures Unit, Bureau of Ships. Holder of Distinguished Civilian Service Medal for contributions in World War II. Five U. S. electronic patents. Author of “A Guide to Cathode Ray Patterns” Jno. W. Wiley and Sons. Registered Engineer District of Columbia. Presently Section Head Electronic Warfare (BUSHIPS).Search for more papers by this author First published: February 1963 https://doi.org/10.1111/j.1559-3584.1963.tb04661.x AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume75, Issue1February 1963Pages 65-70 RelatedInformation

Scattering Cross Section of Arrays of Rigid Pressure-Release and Resonant Elements

The scattering cross section of orderly arrays of identical elements is discussed. Emphasis is placed on spherical scattering elements which are small in terms of wavelengths. In this range, pressure-release elements exhibit a relatively large, frequency-independent, omnidirectional scattering cross section which makes it necessary to consider cross coupling between elements, i.e., to account for the contributions to the wave incident on one element by the waves scattered by other elements. Cross-coupling need not be taken into account in an array of rigid elements because of their much smaller scattering cross section, which stands as (ka)4: 1 to the cross section of a pressure-release element. The two scatterers differ further in that the scattered field of the rigid element comprises a dipole component comparable in magnitude to the omnidirectional component. Finally, the effect of resonances of spherical scatterers is explored. If the resonance occurs at small ka, and in the absence of structural damping, a resonant mode raises the scattering cross section to a value proportional to (ka)−2. In practice, radiation damping is the limiting factor for the breathing mode only. In this case, it can be so large as to exclude resonant amplification. The directivity pattern of 20 equidistant spherical elements arranged in a spherical surface array was computed for pressure-release and rigid scatterers. In contrast to the single spherical scatterer, arrays are markedly directive, and become more so as the radius of the scattering elements is decreased. (This work was supported by BuShips under direction of U. S. Navy Underwater Sound Laboratory.)

Underwater Acoustical Measuring Facilities at the U.S. Navy Underwater Sound Laboratory

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Underwater Acoustical Measuring Facilities at the U. S. Navy Underwater Sound Laboratory

During the war the Underwater Sound Laboratory at New London carried on much of its acoustical test work on a sound barge located at the laboratory pier in the Thames River. Relatively shallow water and the high noise level resulting from rough water, passing ships, and manufacturing establishments located on the water front reduced the usefulness of this barge. A second sound barge was therefore installed on a small inland pond not far from the laboratory. It is intended to use this barge to satisfy the exacting demands of long-term tests of scanning sonar transducers and systems and to serve as a center for developmental research in measuring techniques. The barge is located at the end of a 300-foot pontoon pier in 48 feet of pure and practically noise-free water. It has a four-foot by twenty-foot well with one movable hoist column and one training hoist column. The electronic gear on the new barge is capable of measurements over a frequency range from two to 150 kc. Among the types of measurements made are: (1) frequency responses, receiving, and projecting; (2) directional patterns (polar or rectangular); (3) reciprocity calibrations; (4) admittance measurements; and (5) phase measurements. For frequency responses, a Leeds and Northrup “Speedomax” recorder is used. For directional patterns, the recorder is linked to a polar turntable by a mechanical linkage.