Applied Research Laboratory Research Articles

Energy conversion through thermoacoustics and piezoelectricity

Waste or prime heat can be converted into electricity with thermoacoustic-Stirling engines coupled to piezoelectric alternators. An inline arrangement of engines and alternators allows a vibration balanced, multiphase power generator that is compact, light weight and low cost. The engines convert heat into high amplitude ≈400 Hz oscillations in pressurized helium gas. These pressure oscillations cause a thin steel diaphragm to flex like a drumhead. The diaphragm is supported at its perimeter by a ring of piezoelectric elements. As the diaphragm flexes in either direction, it pulls inward on the piezoelectric elements causing a large amplified ≈800 Hz fluctuating compressive stress in the elements which then convert the stress into electricity with high efficiency. The flexible-diaphragm piezoelectric alternator overcomes the large acoustic impedance mismatch between the helium and piezoelectric elements without exceeding the limited fatigue strength of available materials. So far, a prototype generator has produced 37 W, and is being modified to produce 600 W. Also, a project is underway to recover 7 kW peak electrical power from the exhaust of an over-the-road heavy-duty diesel truck. The generator appears scalable up to megawatt power levels. [Work supported by DOE, ONR, Clean Power Resources, Innovation Works, and Applied Research Laboratory.]

Two techniques for measurement of flow resistance

The accurate measurement of flow resistance has many applications in acoustics. In our laboratory, it is particularly important for the characterization of materials used as regenerators in thermoacoustic refrigerators and for the quantification of leakage paths in complex assemblies. This presentation will describe two techniques for flow resistance measurements made at sufficiently low Reynolds numbers that the resistances measured for unidirectional flow are relevant to acoustic flows. One technique uses a “constant current generator” configuration to characterize stacked stainless steel screens and the other uses an Airpot® graphite piston in a glass cylinder to produce a constant pressure difference and accurate flow rate. Both techniques use air at atmospheric pressure as the test fluid. The constant current technique produces results that are consistent to ±3% for stacks of stainless steel screens that vary in thickness from 10 to 50 screens. The Airpot® technique can produce similar accuracy for flow resistances as large as 1010 Pa-sec/m3. [Work supported by the Applied Research Laboratory and the U.S. Department of Energy.]

Design, Manufacturing, and Testing of an Improved Watertight Door for Surface Ships

Designed in the 1950s to be watertight during flooding and airtight under normal operating conditions, the Navy standard watertight door for surface ships is inexpensive to manufacture but expensive to properly install and maintain. Furthermore, by today's requirements, it is too heavy. The need for a lightweight, affordable, low maintenance watertight door led to a collaborative project involving the Applied Research Laboratory at Penn State University, Naval Surface Warfare Center, Carderock Division, Ship Systems Engineering Station, and Northrop Grumman Corporation Newport News to design, fabricate, and test an improved watertight door for surface ships. The design and manufacturing of this door is entirely new and based on advances in laser cutting and welding technology. Its novel design reduces the number of dogs (latches) and linkages of the Navy standard watertight door, decreasing the weight of the complete door assembly from 290 to 213 lbs. The door is fabricated from corrosion resistant stainless steel, and its opening and closing forces are extremely low, reducing the potential for mechanical and gasket wear. Pending successful completion of certification testing and with technical warrant holder approval, the new door will offer an attractive choice for insertion by Acquisition Program Managers and Fleet Maintenance Managers.

Forensic research methods and means based on automated hardware-software complexes

This paper presents a retrospective review of the methods and hardware-software means for forensic examinations developed during the two decades in the applied research laboratory at the chair of radio engineering devices and systems (RTUS) of the radio engineering department. The research results were reviewed covering studies in four expert directions: analysis of the materials and means of audio- and video-recording; ballistic tests; technical expertise of documents; and vehicle identification number (VIN) expert authentication.

Graduate acoustics at University of Texas at Austin.

While graduate study in acoustics takes place in several colleges and schools at the University of Texas at Austin (UT Austin), including Communication, Fine Arts, Geosciences, and Natural Sciences, this presentation focuses on the acoustics program in Engineering. The core of this program resides in the Departments of Mechanical Engineering (ME) and Electrical and Computer Engineering (ECE). Acoustics faculty in each department supervise graduate students in both departments. One undergraduate and seven graduate acoustics courses are cross-listed between ME and ECE. Instructors for these courses include staff at Applied Research Laboratories at UT Austin, where many of the graduate students in acoustics hold research assistantships. The undergraduate course, offered every fall, begins with basic physical acoustics and proceeds to draw examples from different areas of engineering acoustics. Three of the graduate courses are offered every year, a two-course sequence on physical acoustics and a course on acoustic transducers. The other four graduate courses, offered in alternate years, are on nonlinear acoustics, underwater acoustics, architectural acoustics, and ultrasonics. An acoustics seminar with invited speakers is held most weeks during the academic year, averaging over 10 per semester. The ME and ECE departments both offer a Ph.D. qualifying exam in acoustics.

Acoustics at University of Texas: History and current introductory course in physical acoustics.

As an academic discipline at the University of Texas, acoustics began in the 1930s under C. Paul Boner in Physics and Lloyd A. Jeffress in Psychology. World War II saw Boner and many physics graduate students go to Harvard for “war work,” largely in underwater acoustics. When the war ended, Boner returned and founded the Defense Research Laboratory, later named Applied Research Laboratories. Interest in acoustics grew in Physics during the postwar years but eventually waned in the 1950s and 1960s. Acoustical activity developed in the 1960s in the College of Engineering, chiefly Electrical Engineering and Mechanical Engineering. Today physical and engineering acoustics is a strong interdisciplinary program at Texas, with faculty in several departments in Engineering and still a vestige in Physics. In addition, much work on speech, hearing, and music is done in other parts of the University. Engineering features two basic courses in physical acoustics, Acoustics I and II, and five specialty courses, which are described in an accompanying paper. Here we concentrate on Acoustics I and II, which provide an introduction to propagation, reflection and transmission, refraction, normal modes, horn theory, propagation in stratified fluids, absorption and dispersion, waveguides, directional radiation, diffraction, and arrays.

Classroom noise at the Applied Research Laboratory, Penn State.

Session 3.8: Building Design and Construction for Effective Acoustic Performance Classroom Noise at ARL Penn State by Marshall Long The Applied Research Laboratory at Penn State is a well known center of acoustics education in the United States. When Marshall Long Acoustics was selected to be the acoustical engineer on the new ARL building, we were particularly careful to check every noise source. When we went out on the final inspection, the question arose, “Why is the background noise level NC 42 in a classroom when it should be under 30?” The answer was not so elementary my dear Watson.

Special issue on Bio-inspired Learning and Intelligent Systems for Security (BLISS-07)

This special issue is based on the 2007 ECSIS Symposium on Bio-inspired Learning and Intelligent Systems for Security (BLISS-07) that was held in Edinburgh, Scotland, UK. That successful symposium emphasized reliable, versatile, and intelligent systems employed by a broad range of security applications. The goal was to integrate developers of intelligent systems with those who use them in security applications, including project managers, system integrators, and end users. As here used intelligent systems denote those artificial computational systems that operate in part or fully autonomously and that display behavior that if it were to be observed in animals, would normally become associated with intelligence of one sort or another. Systems with different degrees of autonomy of operation benefit greatly from incorporating aspects and mechanisms that are found in a broad range of biological systems, from survivability and adaptation of the simple living structures to learning, creativity, cognition and various forms of intelligence that are normally associated with humans. These features are often incorporated into algorithms by mimicking the biological processes that provide the inspiration. Such intelligent systems have been applied to a wealth of practical problems, including those in security. Examples of such applications discussed at the symposium include the detection and prevention of cybercrimes and identity theft, internet security, security of financial systems, security of public transportation systems, emergency response systems, combining space-based systems with geographical information systems, etc. A subset of selected papers presented at BLISS-07 have been chosen for this special issue of Journal of Soft Computing. These papers deal with a broad range of applications relevant to security including Voice over Internet Protocol (VOIP), identifying faces, image analysis, determining the source of an unknown airborne contaminant release, encryption for communication, among others. Two additional papers were contributed from a similar special issue being edited by Dr. Daniel Howard. All papers contained herein have relevance for security in either the civilian or defense arenas. We thank the authors who have all taken considerable effort to expound on their work for permanent archival in this journal. We similarly thank the reviewers who have facilitated this process, enhancing the quality of this special issue. We especially thank the editors of Journal of Soft Computing, particularly Brunella Gerla, for patience as we worked to make this special issue a reality. We hope the reader will capture a piece of the excitement and collegiality present in Edinburgh for the BLISS-07 conference as preserved in these papers. S. E. Haupt (&) Applied Research Laboratory, The Pennysylvania State University, State College, PA, USA e-mail: seh19@psu.edu

Spectrum of the sound produced by a jet impinging on the gas–water interface of a supercavity

An analysis is made of the sound generated by the impingement of an air jet on the gas–water interface of a supercavity. The water is in uniform low Mach number motion over the interface. The interface is rippled by the jet, which produces an unsteady surface force on the water that behaves as a dipole or monopole acoustic source, respectively, at high and low frequencies. In a first approximation the very large difference in the gas density and that of water implies that the surface force is similar to that occurring when a jet impinges on a rigid wall. Data from recent measurements by Foley (2009, Ph.D. Dissertation, Department of Mechanical Engineering, Boston University) of the frequency spectrum of the surface force produced by the impact of a turbulent jet on a wall are used to formulate an analytical representation of the spectrum and thence to predict the sound produced in water when the same jet impinges on the cavity interface. The prediction is used to estimate the characteristics of gas jet impingement noise for an experimental supercavitating vehicle in use at the Applied Research Laboratory of Penn State University.

Optimal Continuous-Thrust Trajectories Via Visual Trade Space Exploration

Engineering design problems often contain correlations and trade-offs that may or may not be obvious or well-understood. As design problem complexity increases, decision makers find it more and more difficult to grasp these trade-offs effectively. The rapid growth of computing power now allows the simulation of millions of design alternatives, and the ability to effectively visualize these alternatives and understand the tradeoffs associated with them has never been more important. Trade space visualization tools are designed to aid decision makers by allowing them to effectively explore a design space and grasp the underlying trade-offs and nuances particular to their specific problem. These tools provide great potential in evaluating complex dynamic systems in the aerospace industry, among others. In this article, we apply our trade space visualization software, the Applied Research Lab Trade Space Visualizer, to search for optimal constant-acceleration orbit transfers. This problem is formulated as a multi-objective optimization problem in which it is desirable to explore various competing objectives. We identify a known optimal solution and explore the input space to search for other optimal or near-optimal trajectories. Significantly perturbing the known solution to an example problem has demonstrated that the optimal solution can be converged upon successfully.

A finite element model for acoustic propagation in shallow water waveguides.

A finite element model is developed using a commercial code to calculate the backscattering of acoustic waves in a two-dimensional shallow water waveguide with rough interfaces. Finite elements approach an exact solution to the Helmholtz equation as the discretization density increases. A time series for the backscattering is computed from time harmonic computations using Fourier synthesis. A parametric study of the roughness parameters for the sediment/water interface and the air/water interface will be presented in order to assess the range of validity of approximate methods. [Work sponsored by Internal Research and Development, Applied Research Laboratories.]

On self-noise at the nose of a supercavitating vehicle

The cavity of a supercavitating vehicle in water is maintained by the steady injection of gas from sources within the vehicle and cavity. An analysis is made in this paper to estimate the spectrum of the acoustic ‘self-noise’ produced at the nose of the vehicle by the unsteady impingement of the gas on the cavity interface. For the purposes of calculation it is assumed that the supercavity is circular cylindrical and is formed to the rear of a hemispherical cavitator. This arrangement closely approximates a supercavity being investigated experimentally at the Penn State Applied Research Laboratory. A ‘transfer function’ is derived for this configuration that relates the self-noise pressure at the nose to the pressure distribution on the cavity wall attributable to the impinging gas. It is applicable also to any geometrically similar supercavity maintained by gas injection, provided that the distribution on the interface of the surface pressure spectrum of fluctuations produced by the impinging gas is known. Numerical results are given using experimental data for the cavity wall surface pressure produced by a narrow, impinging air jet and when the nose is acoustically hard, but the method is easily modified to deal with more general impedance conditions on the cavitator.

Taiwan's second remote sensing satellite

FORMOSAT-2 is Taiwan's first remote sensing satellite (RSS). It was launched on 20 May 2004 with five-year mission life and a very unique mission orbit at 891 km altitude. This orbit gives FORMOSAT-2 the daily revisit feature and the capability of imaging the Arctic and Antarctic regions due to the high enough altitude. For more than three years, FORMOSAT-2 has performed outstanding jobs and its global effectiveness is evidenced in many fields such as public education in Taiwan, Earth science and ecological niche research, preservation of the world heritages, contribution to the International Charter: space and major disasters, observation of suspected North Korea and Iranian nuclear facilities, and scientific observation of the atmospheric transient luminous events (TLEs). In order to continue the provision of earth observation images from space, the National Space Organization (NSPO) of Taiwan started to work on the second RSS from 2005. This second RSS will also be Taiwan's first indigenous satellite. Both the bus platform and remote sensing instrument (RSI) shall be designed and manufactured by NSPO and the Instrument Technology Research Center (ITRC) under the supervision of the National Applied Research Laboratories (NARL). Its onboard computer (OBC) shall use Taiwan's indigenous LEON-3 central processing unit (CPU). In order to achieve cost effective design, the commercial off the shelf (COTS) components shall be widely used. NSPO shall impose the up-screening/qualification and validation/verification processes to ensure their normal functions for proper operations in the severe space environments.

Development of Solid Oxide Fuel Cell Power Systems for Underwater Applications

The development of fuel cell based propulsion technologies is an area of great interest for undersea applications. Under an Office of Naval Research (ONR) supported STTR project, FuelCell Energy (FCE), Barber Nichols, Inc. (BNI), and the Applied Research Laboratory (ARL) at Penn State University are working together to develop a hybrid fuel cell system for torpedo propulsion. The current project addresses the development of high power density systems which increase the duration and/or range of operation as compared to existing systems.

Modeling real porous tube infrasonic arrays

Measured values of acoustic resistance in porous hoses have been implemented into a previously developed porous tube model for infrasonic arrays [J. Acoust. Soc. Am. 122, 2960 (2007)]. Garden soaker hoses are commonly used in porous infrasonic arrays, and a simple method for the measurement the acoustic resistance of a segment of soaker hose will be presented. This experimentally determined resistance value can be implemented into the porous tube model for an improved array response prediction. It is anticipated that this analysis will give rise to improved phase and magnitude predictions for this type of array. Applications include design optimization of porous tube arrays, and infrasonic propagation through porous ducts. [Research funded by the Applied Research Laboratory Educational and Foundational Fund.]

OCEAN NOISE BUDGETS

1University of Rhode Island, Department of Ocean Engineering and Graduate School of Oceanography, Narragansett Bay Campus, Narragansett, RI 02882, USA. miller@uri.edu 2University of Washington, Applied Physics Laboratory, 1013 NE 40th Street, Seattle, WA 98105-6698, USA. nystuen@apl.washington.edu 3Pennsylvania State University, Applied Research Laboratory, State College, PA 16804-0030, USA. dlb25@psu.edu

Simulation-based response analysis of porous and non-porous infrasonic arrays

A numerical simulation for porous and non-porous infrasonic arrays has been developed to aid in the analysis of the response of these systems. For design flexibility, the simulation makes use of differential T-elements, which may be used as building blocks to assemble pipes and junctions of various shapes and sizes. The simulation adds to the capabilities of a previously developed model [Alcoverro and Le Pichon, J. Acoust. Soc. Am. 117, 1717 (2005)], by including variable tube porosity, a calculation of wall-losses based on a thermo-viscous function, a calculation of the change in response as the azimuth and elevation of the incoming wave are varied, and a calculation of the wave shape as it propagates through the array in the time domain. [Research funded by the Applied Research Laboratory Educational and Foundational Fund.]

Comparison of measurement and theory for the acoustic pressure field in an infrasonic calibrator through the isentropic-to-isothermal transition

In a previous paper [T. M. Marston and T. B. Gabrielson, J. Acoust. Soc. Am. 119, 3378 (2006)], a simple total-immersion calibrator for infrasonic microphones was described. This calibrator has been improved and so has the correspondence with theory. The Rott equations for thermoviscous acoustics have been incorporated in a stepwise solution for the acoustic field. These equations account for the transition between boundary-layer flow in which the main field is almost isentropic, and the very-low-frequency approach to isothermal pressure oscillations. The entire microphone body is placed in the calibrator so that the pressure-equalization leak functions normally. The calibrator operates from 0.02 Hz to 20 Hz and includes a DC-coupled piezoresistive differential pressure sensor for comparison calibration; however, the model, which incorporates the geometry of the calibrator pipe, the temperature, and the piston stroke, permits response estimation without dependence on the reference sensor. [Research funded by the Applied Research Laboratory Educational and Foundational Fund.]

Directivity and spectral characteristics of aircraft noise during landing operations

Recordings of aircraft landing operations have been analyzed to obtain directivity and spectral characteristics of the noise emitted during these operations. The recordings were made with a widely spaced microphone array positioned near and parallel to the 19R runway at Washington‐Dulles International Airport. In addition, the landings were recorded with a video camera to obtain positional data of the aircraft. Given an aircraft’s position and velocity along the runway, the signal at each microphone is corrected for retarded time, spherical spreading, and Doppler shift. The corrected signals are combined to establish a directivity pattern, and third‐octave analysis is performed to obtain spectral characteristics. The results of this analysis are intended to be used as input to airport noise modeling software such as the Integrated Noise Model (INM), which currently models landing noise using forward‐thrust input data. The current analysis should provide more realistic directivity and spectra for the reverse‐thrust condition. [Work supported by the Federal Aviation Administration and the Applied Research Laboratory Exploratory and Foundational Research Program.]

Network-Centric Systems for Military Operations in Urban Terrain: The Role of UAVs

Military systems are the motivational driver for much of the technology development conducted at applied research laboratories around the world. As the needs of the world's militaries change, so does the focus of this research and development. In this paper, we discuss how the fundamental characteristics of military operations in urban terrain (MOUT) impose requirements and constraints on sensing and reconnaissance. We highlight the importance of a new class of small unmanned aerial vehicles (UAVs) for network-centric military urban operations. We review some of the UAVs that have been developed in recent years, and that are under development, with particular attention to their endurance, portability, performance, payload, and communication capabilities. Selected university testbeds are also briefly noted. Over the last few years there has been considerable research focused on how these small UAVs, both individually and collectively, can operate autonomously in urban environments and help capture and communicate needed information. We discuss some of this research; specific topics covered include guidance and control for autonomous operation, multi-UAV coordination and route optimization, and ad-hoc networking with UAV nodes. A new concept of operations is described that relies on coordination and control of a heterogeneous suite of small UAVs for surveillance and reconnaissance operations in urban terrain