Applied Research Laboratory Research Articles

Acoustical Oceanography and Underwater Acoustics; their role in the Pennsylvania State University Graduate Program in Acoustics

The Pennsylvania State University Graduate Program in Acoustics has a long and successful history in Acoustics Education. A brief history together with the current status of the program will be discussed. An important aspect of the program has been the strong role of the Applied Research Laboratory, both in support of the program as well as for the graduate students enrolled. Presentation includes details of course content, variability to fit student career goals and program structure, including resident and distance education opportunities. The future of the program at Penn State will also be addressed.

Bill Carey as a scientist, motivator, sponsor, and colleague

Bill Carey's long association with the Applied Research Laboratories at the University of Texas at Austin (ARL:UT), gave us the pleasure and good fortune to be associated with him in a wide range of pursuits, over many years. His insight and fortitude as a scientist and motivator led a number of us into productive scientific research that we may not have otherwise undertaken. As a sponsor at the Defense Advanced Research Projects Agency (DARPA), he posed visceral questions with unique viewpoints, sometimes in forceful terms, which led us to undertake difficult and productive projects. Some of these projects are linked to the series of shallow water sea trials called the Area Characterization Tests, which proposed and tested hypotheses, while collecting invaluable data to delineate the acoustics of significant scenarios in littoral ocean environments. We were privileged to participate in these experiments as well as analyze and model the results. As a colleague, while at other institutions, Bill provided the motivation and encouragement for us to undertake many projects, including a seismo-acoustic experiment with the SACLANT Undersea Research Center, which demonstrated the dispersive beam-forming concept for geophone arrays on the sea floor and for the detection and study of Sholte type interface waves. We pay tribute to Bill Carey in this talk by illustrating some of the discoveries made in a number of at-sea experiments and the theoretical and modeling work they spawned. [Work supported by ARL:UT Austin.]

Near- and far-field beam forming using a linear array in deep and shallow water

Underwater sources are typically characterized in terms of a source level based on measurements made in the free-field. Measurements made in a harbor environment, where multiple reflections, high background noise and short propagation paths are typical, violates these conditions. The subject of this paper is estimation of source location and source level from such measurements. Data from a test conducted at the US Navy Acoustic Research Detachment in Bayview, Idaho during the summers of 2010 and 2011 are analyzed. A line array of omnidirectional hydrophones was deployed from a barge in both deep and shallow water using calibrated acoustic sources to evaluate the effectiveness of post-processing techniques, as well as line array beamforming, in minimizing reflected path contributions and improving signal-to-noise ratio. A method of estimating the location of the sources while taking into account a real, non-linear array based on these measurements is presented. [Work supported by the Applied Research Laboratory under an Eric Walker Scholarship.]

Predicting range-frequency interference patterns from broadband sources in a range-dependent, continental shelf environment

The 2007 CALOPS dataset contains horizontal line array received signals from numerous surface vessels transiting an area off the coast of southeast Florida. Parabolic equation propagation models using measured bathymetric, sound velocity profile, and sediment parameter data suggest that substantial mode coupling should be occurring for several down-slope propagation scenarios in the dataset. However, received acoustical data for these scenarios, in the form of range-frequency interference patterns, are best described by adiabatic propagation. This discrepancy has implications that affect waveguide invariant parameter estimation, which is necessary for invariant-based passive ranging. The causes of the incongruous model output will be discussed, as well as their effects on estimating waveguide invariant distributions for these scenarios. [This research was supported by the Applied Research Laboratory, at the Pennsylvania State University through the Eric Walker Graduate Assistantship Program.]

Processing methods for coprime arrays in complex shallow water environments

Utilizing the concept of the coarray, coprime arrays can be used to generate fully populated cross-correlation matrices with a greatly reduced number of sensors by imaging sensors to fill in gaps in the physical array. Developed under free space far-field assumptions, such image sensors may not give accurate results in complicated propagation environments, such as shallow water. Taking shallow water acoustic models under consideration, it will be shown that image sensors can still be used, but to a more limited extent based on spatial variability. Performance of a coprime array with limited image sensors and full image sensors will be compared with that of a fully populated array. [This research was supported by the Applied Research Laboratory, at the Pennsylvania State University through the Eric Walker Graduate Assistantship Program.]

A comprehensive water tunnel test of a horizontal axis marine hydrokinetic turbine for model validation and verification

As interest in waterpower technologies has increased over the last few years, there has been a growing need for a public database of measured data for these devices. This would provide a basic understanding of the technology and means to validate analytic and numerical models. Through collaboration between Sandia National Laboratories, Penn State University Applied Research Laboratory, and University of California, Davis, a new marine hydrokinetic turbine rotor was designed, fabricated at 1:8.7-scale, and experimentally tested to provide an open platform and dataset for further study and development. The water tunnel test of this three-bladed, horizontal-axis rotor recorded power production, blade loading, near-wake characterization, cavitation effects, and noise generation. Additionally, preliminary comparisons are mode from unsteady CFD for the flow fields measured.

The Penn state lunar lion: A university mission to explore the moon

The Penn State Lunar Lion Team plans to send a robotic explorer to the surface of the Moon and, by applying 30 years of technological advancements, win the Google Lunar X Prize. The Google Lunar X Prize aims to showcase the ability of the growing private space industry by having teams pursue the goal of becoming the first private entity to land a spacecraft on another body in the solar system. Through the Team's pursuit of this Prize, Penn State will establish itself as a leader in space exploration. The Lunar Lion Team will win this Prize through the collaboration of faculty and students from multiple disciplines, and the engineering and technical staff at the Penn State Applied Research Lab, as well as strategic collaborations with industry partners. The diversity of technical disciplines required to build a system that can land on the Moon can be found at Penn State. This multidisciplinary project will be not only a means for bringing together personnel from around the University, but also a way to attract faculty and students to these fields. The baseline concept for the Lunar Lion will strictly follow the requirements of the Grand Prize and the Grand Prize only, leading to the simplest possible system for the mission. By achieving the Grand Prize, Penn State will have accomplished what once took the large-scale effort of NASA's early robotic lunar landers or the USSR's space program. While the Bonus Prizes are noteworthy, ensuring their accomplishment will add development and operational risk to the flight system that could jeopardize the Team's ability to win the Grand Prize. The Team will build the simplest spacecraft, with the fewest number of systems and components. This philosophy will shorten the development timeline and result in a robust flight system that is of minimum cost. Wherever possible, the Team will use commercially available products to satisfy the needs of the system. The work of the Team will be efficient systems integration, careful operational planning, and focused mission execution, all with the Grand Prize in mind. By focusing on innovation rather than invention, Penn State will lead the field of competitors and land the next spacecraft on the Moon.

Coprime arrays in the context of compressive sensing

Arising naturally from the formalism of coarrays, coprime arrays offer a means of achieving sparsity along an array while maintaining certain measures of performance. This configuration offers benefits over traditional configurations for large aperture towed arrays in the ocean environment, but shallow water propagation complicates the wide sense stationarity assumption that is essential to proper application of coarray concepts. Compressive sensing techniques allow for the reconstruction of generalized signals which are sparse on some known basis. Existing literature has shown the connection between compressive sensing and random arrays, drawing direct parallels between the results and methods that arose independently in both fields. Compressive sensing may offer an alternative understanding of coprime arrays, which is independent of wide sense stationarity, and thus applicable to shallow water environments. Coprime arrays will be considered in the context of compressive sensing. It will be discussed if the measurement matrices that arise from this array geometry might possess properties necessary for compressive sensing reconstruction to function, such as the Restricted Isometry Property. [This research was supported by the Applied Research Laboratory, at the Pennsylvania State University through the Eric Walker Graduate Assistantship Program.]

Pneumatic infrasound source: Expanded model development and tests

A model experiment discussed in a companion paper is expanded through the engineering development of a larger scale system to provide concept evaluation of portable infrasound generation, for calibration and tests of receiver array stations. This system utilizes an industrial compressor producing 350 cubic feet per minute of air at pressures up to 150 pounds per square inch, which is stored in two 500 gallon tanks. Air streams from each tank are released through two synchronized, rotating, 2 in. diameter ball valves, producing modulated pulse jets into the atmosphere, which then create infrasonic tone bursts. Measurements on the propagation and frequency response of infrasound so produced are compared and modeled with a view toward assessment of practical utility. [Work supported by Applied Research Laboratories, University of Texas at Austin.]

Passive ranging in strongly range-dependent environments: Effects of mode coupling on the waveguide invariant

Prior work has shown that the value of the shallow water waveguide invariant changes in range-dependent environments due to non-uniform phase and group speed along the propagation path caused by either a range-dependent bathymetry or sound speed profile. Much of the work on these scenarios has dealt with weak range-dependence and the effects of mode coupling were neglected. In certain situations when mode coupling occurs, energy from higher order, surface-reflected-bottom-reflected modes may be lost to lower order, surface-refracted-bottom-reflected modes. These lower order modes, which do not interact with the surface, are associated with waveguide invariant values that differ greatly from the standard shallow water approximation where the waveguide invariant equals one. This talk will examine a case from the 2007 CALOPS experiment where the adiabatic approximation for modal propagation is no longer valid and mode coupling appears to be important. Acoustical data and analysis will be presented to demonstrate the effect that mode coupling has on the waveguide invariant in strongly range-dependent environments, and methods for incorporating coupled modes into waveguide invariant estimates will be discussed. [This research was supported by the Applied Research Laboratory, at the Pennsylvania State University through the Eric Walker Graduate Assistantship Program.]

Water Tunnel Flow Diagnostics of Wake Structures Downstream of a Model Helicopter Rotor Hub

A scaled model of a notional rotor hub design was tested at one-third- and two-thirds scale Reynolds number with reference to a large helicopter at an advance ratio of 0.2 in the 48” Garfield Thomas Water Tunnel (GTWT) at the Applied Research Laboratory (ARL) at Penn State University. The main objectives of the experiment were to understand the spatial- and temporal content of the unsteady wake downstream of a rotor hub up to a distance corresponding to the empennage of a large helicopter. Measurements included total hub drag and flow diagnostics involving PIV, SPIV and LDV at several locations downstream of the model rotor hub. Computations of the rotor hub flow were also performed by Sikorsky Aircraft and compared with the experimental results. Various flow structures were identified and linked to geometric features of the hub model. The most prominent structures were two-per-revolution (scissors) and four-per-revolution (main hub arms) vortical structures shed by the hub. Both the two-per-revolution and four-per-revolution structures persisted far downstream of the hub, but the rate of dissipation was greater for the four-per-rev structure. This work provides an extensive dataset for enhanced understanding of the fundamental physics underlying rotor hub flows and serves as validation data for future CFD analyses in the rotorcraft community.

The impact of including diffraction when predicting the effect of listener environment on the perceived loudness of outdoor sonic booms

The human impact of sonic booms varies with listening environment. Given the incident sonic boom waveform, the specular field around a realistic geometry has been predicted via a C++ implementation of image source method (ISM) tailored to outdoor applications. This work explores the necessity of including the diffracted field when predicting time series and PLdB, both in and out of shadow zones. The impulsive nature of the excitation, and the sensitivity of the PLdB to temporal details, constrains appropriate diffraction modeling techniques to those capable of time domain accuracy. Uniform Theory of Diffraction (UTD) and Biot Tolstoy Medwin (BTM) approaches are considered. The benefits and challenges of each approach are explored, particularly with regards to scalability and bandwidth. The importance of accurately predicting diffraction in this application is evaluated through comparison with booms recorded around a building corresponding to the simulated geometry. [Work supported by the FAA/NASA/Transport Canada PARTNER Center Excellence and the Applied Research Laboratory. Experimental data courtesy of NASA.]

Membership notes

Reports on the IMS Taipei Section Chapter Highlights of the International Scientific Instrument Technology Workshop (ISITW). The International Scientific Instrument Technology Workshop (ISITW) is an annual two-week training course that is hosted by the Instrument Technology Research Center (ITRC) of the National Applied Research Laboratories (NARL) in Hsinchu, Taiwan with the desire to build an international collaboration platform, as well as the i-ONE International Instrument Technology Innovation Competition.

Seagrass meadows provide an acoustic refuge for estuarine fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 472:117-127 (2013) - DOI: https://doi.org/10.3354/meps10045 Seagrass meadows provide an acoustic refuge for estuarine fish Christopher J. Wilson1,*, Preston S. Wilson2, Chad A. Greene2, Kenneth H. Dunton1 1Marine Science Institute, The University of Texas at Austin, Port Aransas, Texas 78373-5015, USA 2Mechanical Engineering Department and Applied Research Laboratories, The University of Texas at Austin, Austin, Texas 78712-0292, USA *Email: cjw32485@gmail.com ABSTRACT: It has been widely accepted that fish reside within seagrass meadows because of the visual protection and structure provided by the standing biomass. However, for many larger species of estuarine fish, marine mammals that use echolocation to forage represent a significant threat. We hypothesized that seagrasses may serve as an acoustic refuge to fish from dolphin predators by sufficiently attenuating the high-frequency sounds used in echolocation. To test this hypothesis, we measured the attenuation of a 100 kHz acoustic signal with increasing distance into a seagrass meadow. The transmission loss of low-frequency sound energy relevant to fish calls (300 to 500 Hz) was also investigated to address the hypothesis that marine mammals may use passive acoustic detection to locate fish in vegetated substrates. Our results show that seagrasses attenuate high-frequency sounds during summer months and reduce prey detection thresholds by 58 to 88% relative to bare substrates. Also, based on the low-frequency hearing threshold of bottlenose dolphins, we calculated that dolphins are capable of detecting low-frequency fish calls within vegetation at a distance of roughly 2.3 to 4.2 m, which is within the detection threshold of 2.8 to 9.8 m for dolphins using echolocation. This study demonstrates that acoustically complex features, such as seagrass meadows, can significantly alter bioacoustic signal transmission, possibly providing an important seasonal refuge to fish from marine mammal predators. KEY WORDS: Seagrass meadows · Acoustics · Echolocation Full text in pdf format PreviousNextCite this article as: Wilson CJ, Wilson PS, Greene CA, Dunton KH (2013) Seagrass meadows provide an acoustic refuge for estuarine fish. Mar Ecol Prog Ser 472:117-127. https://doi.org/10.3354/meps10045 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 472. Online publication date: January 09, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Investigation of contact acoustic nonlinearities on metal and composite airframe structures via intensity based health monitoring

Nonlinear structural intensity (NSI) and nonlinear structural surface intensity (NSSI) based damage detection techniques were improved and extended to metal and composite airframe structures. In this study, the measurement of NSI maps at sub-harmonic frequencies was completed to provide enhanced understanding of the energy flow characteristics associated with the damage induced contact acoustic nonlinearity mechanism. Important results include NSI source localization visualization at ultra-subharmonic (nf/2) frequencies, and damage detection results utilizing structural surface intensity in the nonlinear domain. A detection metric relying on modulated wave spectroscopy was developed and implemented using the NSSI feature. The data fusion of the intensity formulation provided a distinct advantage, as both the single interrogation frequency NSSI and its modulated wave extension (NSSI-MW) exhibited considerably higher sensitivities to damage than using single-sensor (strain or acceleration) nonlinear detection metrics. The active intensity based techniques were also extended to composite materials, and results show both NSSI and NSSI-MW can be used to detect damage in the bond line of an integrally stiffened composite plate structure with high sensitivity. Initial damage detection measurements made on an OH-58 tailboom (Penn State Applied Research Laboratory, State College, PA) indicate the techniques can be transitioned to complex airframe structures achieving high detection sensitivities with minimal sensors and actuators.

CLOUD BASED WEB 3D GIS TAIWAN PLATFORM

Abstract. This article presents the status of the web 3D GIS platform, which has been developed in the National Applied Research Laboratories. The purpose is to develop a global earth observation 3D GIS platform for applications to disaster monitoring and assessment in Taiwan. For quick response to preliminary and detailed assessment after a natural disaster occurs, the web 3D GIS platform is useful to access, transfer, integrate, display and analyze the multi-scale huge data following the international OGC standard. The framework of cloud service for data warehousing management and efficiency enhancement using VMWare is illustrated in this article.

Addition of a series spring to a lumped element model of a novel thermoacoustic refrigerator

A lumped element model is introduced for an “in-line” traveling-wave thermoacoustic refrigerator, based on a recent patent by Backhaus and Keolian [US Pat. No. 7,908,856 (22 Mar 2011)]. This model couples three electro-mechanical motors to the acoustical domain using a flexure sealed piston. Results of this lumped-element model were found to be in good agreement with a DELTAEC model. Since large displacements result in flexure fatigue, the addition of a series spring between the motor and piston was evaluated to reduce flexure seal displacement while matching the optimum load impedance. The assignment of the correct dynamic mass of the series spring when both the motor and flexure ends of the spring are moving has not been addressed previously in the literature. To determine the two effective masses required at each end of the spring, the spring is discretized into a large number of elements and is converted into a simplified circuit model to assign values to lumped-element components. These values depend upon an initial knowledge of both end velocity magnitudes and phases. This enables an iterative solution for the effective spring masses since velocities need to be known for effective masses to be determined and vice versa. [Work supported by the Applied Research Laboratory and the U.S. Department of Energy.]

From a "Dead Albatross" to Lincoln Labs: Applied Research and the Making of a Normal Cold War University

Large, military-funded, applied research laboratories became a common and controversial feature of Cold War academe. This paper examines the origins and first twelve years of Lincoln Labs at the Massachusetts Institute of Technology, with two primary purposes. First, it extends our understanding of who encouraged the rise of large laboratories in the Cold War academy, when controversy over these changes arose, and why. Second, it ties academic efforts to privilege theoretical over applied forms of education and research, to academic concerns about competing with industry for military funding. By defining a "normal" MIT in terms of fundamental research and education, administrators sought to negotiate the rapidly changing institutional environments for Cold War science and engineering.

Attenuating underwater pile driving noise at a remote receiving location using an encapsulated bubble curtain

Noise generated underwater by pile driving can reach dangerous levels at significant distances from the source, and thereby potentially disturb both marine life and human activities. In this presentation, we describe a method of shielding a specific underwater region remote from the source using a curtain of encapsulated bubbles. The sizes of these encapsulated bubbles are chosen so that their resonance frequencies are near the peak frequency of the noise generated by the pile driving, thus maximizing each encapsulated bubble's ability to mitigate the incoming noise through resonance phenomena. The method of using encapsulated bubbles has been previously described by the authors [J. Acoust. Soc. Am. 127:2015 (2010); J. Acoust. Soc. Am. 128:2279 (2010); J. Acoust. Soc. Am. 129:2462 (2011)], but in this work a region around the receiver, not the source, was treated with encapsulated bubbles, and the noise was due to pile driving activity rather than tonal. Results show that significant noise reduction can be attained using this encapsulated bubble curtain, in which a single layer yielded about 10 dB of SPL reduction. [Work supported by Applied Research Laboratories Internal Research and Development]

Application of Near Real-Time and Multiscale Three Dimensional Earth Observation Platforms in Disaster Prevention

Taiwan frequently experiences natural disasters such as typhoons, floods, landslides, debris flows, and earthquakes. Therefore, the instant acquisition of high-definition images and topographic or spatial data of affected areas as disasters occur is crucial for disaster response teams and making emergency aid decisions. The National Applied Research Laboratories has implemented the project “development of near real-time, high-resolution, global earth observation 3D platform for applications to environmental monitoring and disaster mitigation.” This developmental project integrates earth observation techniques, data warehousing, high-performance visualization displays, grids, and disaster prevention technology to establish a near real-time high-resolution three-dimensional (3D) disaster prevention earth observation application platform for Taiwan. The main functions of this platform include (1) integration of observation information, such as Formosat-2 satellite remote sensing, aerial photography, and 3D photography of disaster sites, to provide multidimensional information of the conditions at the affected sites; (2) disaster prevention application technologies, such as large-sized high-resolution 3D projection system, medium-sized active stereo projection systems, and small-sized personal computers with multiscale 3D display systems; (3) a 3D geographical information network platform that integrates data warehousing and cloud services, complies with the Open Geospatial Consortium (OGC) international standard for image data exchange and release processes, and includes image overlaying and added-value analysis of disasters; and (4) near real-time and automated simulation of image processing procedures, which accelerates orthophoto processing once raw data are received from satellites and provides appropriate images for disaster prevention decision-making within 3 to 6 h. This study uses the 88 Flood event of Typhoon Morakot in 2009, Typhoon Fanapi in 2011, and the 311 Earthquake of Japan in 2011 as examples to dissert the applications, functions and features of this platform for supporting disaster response and disaster recovery decision-making.