Showing papers by "Naval Surface Warfare Center published in 2002"

Magnetostrictive Properties of Galfenol Alloys Under Compressive Stress

Abstract: Fe–Ga alloys, in which the α-Fe structure is maintained, are rich sources of high strength, low cost magnetostrictive alloys for transducer and vibration reduction applications. Although the magnetostriction of Fe itself is very low, when a relatively small fraction of the Fe atoms are replaced by Ga, the magnetostriction, (3/2)λ100, increases greatly. Until recently, the highest magnetostriction was found with the replacement of Fe by Al (Alfenol). In this paper, we present our measurements of magnetostriction on Fe1−x Gax , 0.13 ≤ x ≤ 0.24, (Galfenol). With the substitution of 19% Ga for Fe in Fe1−x Gax , a 12-fold increase in magnetostriction to ∼ 400 ppm occurs, even though Ga is non-magnetic. In these alloys, the saturation magnetizations remain high, Ms ∼= 1.7 T, and the Curie temperatures are far above room temperature, TC ∼= 700◦C. In most alloys studied, the magnetostrictions and magnetizations are fully saturated in fields less than 24 kA/m, even under compressive stresses >100 MPa. For x = 0.24 (near Fe3Ga), an anomalous increase in magnetostriction with temperature occurs with a peak magnetostriction above room temperature. Small additions of Ni and Mo to the binary Fe–Ga alloys decrease the room temperature value of λ100.

An amplitude modulation detector for fault diagnosis in rolling element bearings

Abstract: As rolling element bearings begin to fail they induce characteristic fault frequencies in the vibration of an electric machine. These characteristic fault frequencies tend to modulate the electric machine's frequencies of natural mechanical resonance. Therefore, an amplitude modulation (AM) detector, similar to the bispectrum, is proposed. This new tool is especially designed to detect instances of AM when the measured magnitude of the characteristic fault frequency itself is not significant (e.g. incipient bearing faults). A normalized version of this detector is also presented to assist in the interpretation of results. Computer simulations as well as actual bearing vibration data are used to confirm the proficiency of this proposed AM detector in identifying bearing faults.

Multilevel voltage-source duty-cycle modulation: analysis and implementation

Abstract: Multilevel converters have become increasingly popular due to high power quality, high-voltage capability, low switching losses, and low electromagnetic compatibility concerns. Considering these advantages, the multilevel converter is a suitable candidate for implementation of future naval ship propulsion systems. This paper focuses on modulation techniques for the multilevel converter. In particular, a novel voltage-source method of multilevel modulation is introduced and compared to existing methods. The proposed method is discrete in nature and can therefore be readily implemented on a digital signal processor. The method is also readily extendable to any number of voltage levels. Results of experimental implementation are demonstrated using a four-level rectifier/inverter system, which incorporates diode-clamped multilevel converters and an 11-level cascaded multilevel H-bridge inverter.

Reduced-parts-count multilevel rectifiers

Abstract: Multilevel power converters have gained much attention in recent years due to their high power quality, low switching losses, and high-voltage capability. These advantages make the multilevel converter a candidate topology for the next generation of naval ship prolusion systems. The primary disadvantage of these systems is the large number of semiconductors involved. This paper presents a reduced-parts-count rectifier which is well suited for naval rectifier applications where bidirectional power flow is not required. The proposed converter is analyzed and experimentally verified on an 18-kW four-level rectifier/inverter system.

Turbulence Ingestion Noise, Part 2: Rotor Aeroacoustic Response to Grid-Generated Turbulence

Abstract: This is the second of two papers that discuss an experimental investigation of the aeroacoustic response characteristics of a 10-bladed rotor to grid-generated turbulence. To characterize empirically the rotor response, both the ingested velocity field and resulting far-field sound were measured. In part 1, an empirical velocity characterization of the grid- generated turbulence field was presented. This characterization culminated in a semi-empirical model of the ingested small-scale turbulence field and a modal decomposition of the circumferentially varying mean velocity field in the rotor inlet plane. This detailed velocity model is now used to investigate the aeroacoustic response of a 10-bladed rotor ingesting the grid-generated turbulence field. In particular, the semi-empirical turbulence model is used, in conjunction with theoretical spectral analysis techniques, to predict the far-field sound generated by the 10-bladed rotor. These predictions are compared to corresponding measured data to assess the fidelity of the spectral analysis methods and the semi-empirical turbulence model

Block Copolymer-Templated Nanocomposite Electrodes for Rechargeable Lithium Batteries

Abstract: Department of Chemistry, Northeastern University, Boston, Massachusetts 02115-5000, USAA self-organizing, nanocomposite electrode~SONE! system was developed as a model lithium alloy-based anode for rechargeablelithium batteries. In situ X-ray adsorption spectroscopy, galvanostatic testing, cyclic voltammetry, X-ray diffraction, and trans-mission electron microscopy were used to analyze the electrode, which was fabricated from a polyethylene oxide-based blockcopolymer, single-walled carbon nanotubes, and gold salt. Processing involved a single mixing step without need of a reducingagent. It was found that thermodynamic self-assembly of the block copolymer could provide a template for incorporation of boththe gold salt and nanotubes. Electrochemical testing and subsequent analysis showed that owing to the small particle size and thesurrounding block copolymer matrix, the SONE system could cycle over 600 cycles with rates varying between C/1.8 and 8.8Cwith little evidence of decrepitation or coarsening.© 2002 The Electrochemical Society. @DOI: 10.1149/1.1518482# All rights reserved.Manuscript submitted February 6, 2002; revised manuscript received June 13, 2002. Available electronically October 31, 2002.

Development of a Digital Array Radar (DAR)

Abstract: Twenty-first century littoral and open-sea missions present US Navy (USN) shipboard-radar systems with the challenge of detecting small targets in severe clutter and against multiple sources of interference. In Fiscal Year 2000 (FY00), the Office of Naval Research (ONR) sponsored a program to develop an active array radar that includes a digital beamforming (DBF) architecture. The DBF radar system has the potential for improved time-energy management, improved signal-to-clutter (S/C) ratios, improved reliability and reduced life-cycle costs. This paper summarizes the latest developments of the program during FY00.

Naval combat survivability testbeds for investigation of issues in shipboard power electronics based power and propulsion systems

Abstract: There are numerous issues involved in the design of power electronics based power distribution and propulsion systems. These issues include power density, dynamic stability, efficiency, acoustic and waterborne noise, and electromagnetic compatibility, to name a few. In order to address these issues, as well as to test CAD tools for designing these systems, two reduced scale hardware test beds have been developed. The first of these, the Naval Combat Survivability Generation and Propulsion Testbed, focuses on primary power generation and propulsion. The second of these, the Naval Combat Survivability DC Distribution test bed, focuses on DC power distribution using a zonal architecture.

Turbulence Ingestion Noise, Part 1: Experimental Characterization of Grid-Generated Turbulence

Abstract: Results are presented of an experimental investigation into the aeroacoustic response characteristics of rotor turbulence ingestion. To fully characterize the rotor response, both the ingested velocity field and the resulting far-field sound were measured. The results are presented of a detailed velocity characterization, which was performed upstream of the rotor. The velocity measurements included an evaluation of the streamwise development of turbulence characteristics downstream of the grid, a high-resolution mapping of the spatial distribution of the mean velocity and rms turbulence fluctuations in the rotor inlet plane, and the development of a semi-empirical, functional representation of the three-dimensional wave number spectral density of the ingested turbulence

A metrics-based approach to intrusion detection system evaluation for distributed real-time systems

Abstract: This paper describes a set of metrics that will help administrators of distributed, real-time (clustered) computer facilities to select the best intrusion detection system for their facilities. The metrics herein are the subset of our general metric set that particularly impact real-time and distributed processing issues. We discuss related works in this field, the role of intrusion detection in information assurance, some basic classes of intrusion detection systems, a general architecture of network intrusion detection systems, and the scorecard metrics and their application to real-time and distributed processing systems. Finally we discuss the lessons we learned using a preliminary version of the metric scorecard to test three commercial intrusion detection systems and the opportunities for further work in this area.

Structure of melt-spun Fe-Ga based magnetostrictive alloys

Abstract: Fe/sub 1-x/Ga/sub x/ (x=0.17, 0.21, 0.25 and 0.3) alloys were rapidly quenched by the melt-spinning technique to determine the maximum Ga concentration that retains the disordered bcc (/spl alpha/-Fe) phase at room temperature. The texture of the ribbons as a function of melt-spinning parameters and annealing was also extensively studied. All of the as-spun samples were found to be crystalline. For x=0.17, only the disordered bcc phase was found and for x=0.25 and 0.3, primarily DO/sub 3/ phase was found, while for x=0.21, the phase is bcc at high wheel speed and DO/sub 3/ at low speed. For the free side of the as-spun ribbons, the easy growth axis of /spl alpha/-Fe or of DO/sub 3/ tilts about 10/spl deg/ to 20/spl deg/ from the ribbon normal and is along the ribbon length. This texture does not change significantly with wheel speed. The texture on the wheel side of the ribbon is close to random at high speed but increases with slower speed. For Fe/sub 83/Ga/sub 17/, 900/spl deg/C annealing reduces the tilt angle while 1100/spl deg/C annealing recrystallizes the grains and produces strong out of plane texture but randomizes the directionality in the plane. Annealing with sulfur addition was found to enhance the {100} texture but did not produce the desired along the longitudinal direction of the ribbon. The saturation magnetostriction, /spl lambda//sub s/, of as-spun Fe/sub 79/Ga/sub 21/ and Fe/sub 83/Ga/sub 17/ both having a disordered bcc structure and strong {100} texture was measured as 98 and 130 ppm, respectively, along the ribbon length.

Polyurethane networks with controlled architecture of dangling chains

Abstract: Network formation from A x + B y precursors (A + B → A - B) with functionality and molecular weight distributions is described by the statistical theory of branching processes. Network formation is described in terms of sol and gel fractions, dangling chains, elastically active network chains (EANC), elastically active crosslinks, free chain ends and branch points partitioned between sol and gel. Various definitions of an EANC are considered. The general relations are applied to a special case of A1 + A2 + A3/B2 system. It is show how the size and weight fractions of dangling chains can be varied indepently by varying the functionality or molecular weight distributions. This is demonstrated experimentally analyzing corresponding polyetherurethane networks prepared from mixtures of polyoxypropylene polyols. The width of the main transition region correlates with the fraction of material in dangling chains. The dependence of the equilibrium shear modulus on the concentration of EANC's indicates much weaker intermolecular interactions for networks with many short dangling chains compared with systems having few longer dangling chains.

Quality-Assisted Multi-Objective Multidisciplinary Genetic Algorithms

Abstract: A new method is presented to solve multi-objective multidisciplinary optimization (M-MDO) problems. This M-MDO method is applicable to multi-objective optimization problems that can be decomposed hierarchically into multi-objective subproblems and whose objective functions are either separable or additively separable. In the decomposition, the subproblems may have both common and unique objectives. The method uses a multiobjective genetic algorithm (MOGA) to optimize the multi-objective subproblems; hence, it is referred to as a multi-objective multidisciplinary genetic algorithm (M-MGA). It is shown that for any Pareto point of the original (single-level) problem, M-MGA generates at least one point that is noninferior with respect to that Pareto point. Also a comparison is shown between the computational complexity of M-MGA and a single-level MOGA in terms of number of functions calls. The M-MGA is demonstrated by two engineering examples: the design of a speed reducer and the design of a payload for an undersea autonomous vehicle. In both examples, the generated solutions are similar to solutions generated by solving the examples as single-level problems. M-MGA produces relatively the same solutions from one M-MGA run to another.

Amorphous Al 90 Fe x Ce 10 − x alloys: X-ray absorption analysis of the Al, Fe and Ce local atomic and electronic structures

Abstract: X-ray-absorption fine structure (XAFS) above the Fe K edge, the Ce ${L}_{3}$ edge, and the Al K edge in amorphous ${\mathrm{Al}}_{90}{\mathrm{Fe}}_{x}{\mathrm{Ce}}_{10\ensuremath{-}x}$ $(x=3,$ 5, and 7) alloys have been measured and analyzed. Quantitative analyses of the Fe K-edge and Ce ${L}_{3}$-edge extended XAFS spectra are limited to local structure parameters of the first coordination sphere. Comparison of experimental x-ray-absorption near-edge structure (XANES) spectra with theoretical multiple-scattering (MS) XANES spectra for model compounds, such as crystalline ${\mathrm{FeAl}}_{6}$ and ${\mathrm{CeAl}}_{4},$ allows one to determine the local structure around the aluminum, iron, and Ce sites in ternary amorphous alloys. Using the theoretical MS approach, we show that the Fe and Al K-edge XANES are sensitive to the structure of coordination spheres, which extend up to nearly 4.4 and 3.3 \AA{}, respectively. The Ce ${L}_{3}$-edge XANES, on the other hand, is sensitive to the structure that extends up to 3.15 \AA{}.

Sensor technologies for hunting buried sea mines

Abstract: Conventional high frequency sonars may be ineffective in the detection and classification of buried sea mines. Hence new approaches are required to address this problem. Under the magnetic and acoustic detection of mines (MADOM) advanced technology demonstration in 1990, the fusion of low-frequency imaging sonars and magnetic sensors was introduced and successfully demonstrated to provide detection and classification capabilities against buried mines. In February 2002, the Office of Naval Research initiated a project to provide a deliberate capability for hunting buried sea mines. Recent developments in acoustic and electromagnetic sensor technology, signal processing, and data fusion are being pursued. Objectives and approaches for this buried minehunting (BMH) project are described. The new sensor technologies and system concepts that have evolved since MADOM are discussed. Plans to test and demonstrate these technologies and concepts are presented.

Are more models better?: the effect of the model transition matrix on the IMM filter

Abstract: The purpose of this investigation was to determine what approach is best to deal with the question of how to choose the model transition matrix for the interactive multiple model filter. The desire is to determine an approach to choosing the model transition matrix that is "best" in some sense. In the study, many target tracking simulations were run using the interacting multiple models algorithm (IMM) with two models: constant velocity and constant acceleration. During these simulations, the transition matrix used and the target tracks used were varied to allow viewing of behavior of the IMM under different conditions. It is difficult to decide whether changing the probabilities gives better performance, since performance is not measured by one number, but by a balance of competing interests. Using a three-model IMM inputs were used in order to test which values should be on the diagonal and what effect changing the off-diagonal elements would have on the filter's behavior. The results obtained imply that having three models is not necessary except in exceptional cases. This leads one to pose the question: Are more models better?.

Cusp gun TE/sub 21/ second-harmonic Ka-band gyro-TWT amplifier

Abstract: A second-harmonic TE/sub 21/ gyrotron traveling-wave tube (gyro-TWT) amplifier with an axis-encircling electron beam is being constructed at the University of California-Davis that is predicted to double the efficiency of our previous 200-kW 12%-efficient magnetron injection gun (MIG) TE/sub 21//sup (2)/ gyro-TWT. Both devices employ a sliced mode-selective circuit to suppress the odd-order azimuthal modes. The new device will avoid the loss in efficiency that is due to off-axis electrons interacting with the resulting linearly polarized mode. The amplifier is predicted by our large signal code to produce 50 kW in Ka-band with 20% efficiency, 30 dB saturated gain, and 3% bandwidth. The 70-kV 3.5-A axis-encircling electron beam with /spl upsi//sub /spl perp////spl upsi//sub z/ = 1.2 and /spl Delta//spl upsi//sub z///spl upsi//sub z/ = 7% will be produced by a Cusp electron gun delivered by Northrop Grumman. The amplifier has been designed using linear theory to provide a 30% safety margin from absolute instability. Distributed loss is added to the first 30.5 cm of the circuit to ensure the device is stable to harmonic gyro-BWO. The last 11.5 cm of the circuit is standard copper to avoid attenuating the wave at high power levels.

Preparation of Phase Pure Cubic Gallium Nitride, c-GaN, by Ammonothermal Conversion of Gallium Imide, {Ga(NH)3/2}n

Abstract: Gallium imide, {Ga(NH)3/2} n , was sealed in quartz tubes with anhydrous NH3 and NH4X (X=Cl, Br, I) and heated vertically in an autoclave with the hot-zone (bottom) temperature ranging from 300–530°C. With NH4I mineralizer, the imide was converted to primarily the zinc-blende phase of GaN (c-GaN), usually in the form of micron sized or smaller tetrahedra. With NH4Cl mineralizer, hexagonal GaN nanoparticles formed instead, and NH4Br facilitated the conversion of imide to irregular h-GaN nanoparticles at lower temperatures, and larger particles above 500°C. At the higher temperatures, chemical transport took place and GaN crystals grew on the walls at the middle to the top of the tube. Most of the deposited GaN was cubic, usually in a heavily etched triangular prismatic morphology. Several experiments were performed in a Pt lined pressure vessel in order to demonstrate that the synthesis method can be scaled up.

Thermogravimetry and X-Ray Absorption Spectroscopy Study of Heated V 2 O 5 ⋅ n H 2 O Aerogels and Ambigels

Abstract: We have used thermogravimetry and X-ray absorption spectroscopy to examine the water content, oxidation state, and local structure of V for V 2 O 5 nH 2 O aerogels and ambigels in the pristine state and after heating under vacuum (100 μTorr) at 114 and 220°C for 25 h On the basis of thermogravimetric analysis, the composition of the aerogels and ambigels consists of about 2 and I mol of H 2 O per mole of V 2 O 5 in the pristine state and after heating at 114°C, respectively Thermogravimetric analysis reveals the absence of loosely bound H 2 O in the network of the aerogels and ambigels heated at 220°C Analyses of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra reveal that the oxidation state of V for aerogels and ambigels in the pristine state (V 2 O 5 20H 2 O) as well as those heated at 114°C (V 2 O 5 10H 2 O) is similar to that of V in V 2 O 5 ; that is to say +5 (pentavalent V) Heat-treating the aerogels and ambigels at 114°C does not lead to a measurable change in the oxidation state of V The local structure of V under these conditions is similar to that of V in orthorhombic V 2 O 5 except for a higher degree of local symmetry within the structure of the VO 5 square pyramid Analyses of XANES and EXAFS spectra of aerogels and ambigels heated at 220°C, on the other baud, reveal the presence of both tetravalent and pentavalent V The fractions of tetravalent V are estimated to be 029 ± 008 and 026 ± 008 for the aerogels and ambigels, respectively The mixed valency can be in the form of a single phase with a solid solution of tetravalent and pentavalent V sites or a two-phase system with one phase containing tetravalent V and the other phase containing pentavalent V

Improving the model development process: expanding our horizons in verification, validation, and accreditation research and practice

Abstract: Many different types of modeling and simulation (M&S) applications, consisting of a combination of software, hardware, and humanware, are used in dozens of disciplines under diverse objectives including acquisition, analysis, education, entertainment, research, and training. Certification of sufficient accuracy of an M&S application by conducting verification, validation, and accreditation (VV&A) requires multifaceted knowledge and experience, and poses substantial technical and managerial challenges for researchers, practitioners, and managers. The challenges can only be met by using a very broad spectrum of approaches and expanding our horizons in VV&A. This paper presents 13 strategic directions to meet those challenges. The strategic directions provide guidelines for successful VV&A research and practice.

The global positioning system geodesy odyssey

Abstract: Fundamental to GPS operation and application are the computational developments that have led to accurate user positioning. This paper reviews some of these developments from a historical perspective. The developmental odyssey begins with the events leading to initial GPS operation. Early developments in satellite geodesy, which led to the development of the GPS constellation, are briefly reviewed. A chronology of the incremental improvements in satellite orbit determination is presented. Contributions basic to GPS operation and accuracy, including coordinate frame definition and software development for user absolute and differential/kinematic positioning, are reviewed. Applications are also discussed, including surveying and mapping, geodynamics, and spaceborne geodesy, which have motivated the most stringent accuracy requirements for GPS. The paper ends with a discussion of expected future geodetic capabilities and then a summary of the impact of GPS geodesy contributions on the user community.

The effect of fluid loading on radiation efficiency

Abstract: The metric “radiation efficiency,” used to estimate a panel’s radiated acoustic power from a measure of its normal velocity, is typically derived under the condition of very light fluid loading. This paper shows that efficiencies calculated in this manner can significantly overestimate the radiated power when the condition of light fluid loading is not met, as can be the case for steel plates in water. It is also shown that, when fluid loading is not light, a baffled semi-infinite plate is not a good model for an interior support. Numerical results are presented for radiation efficiencies calculated for steel plates in water, and are compared to those calculated under the assumption of vanishing fluid loading.

Evaluation of Pressure Side Film Cooling With Flow and Thermal Field Measurements—Part I: Showerhead Effects

Abstract: The goal of this study was to determine how showerhead blowing on a turbine vane leading edge affects of the performance of film cooling jets farther downstream. An emphasis was placed on measurements above the surface, i.e. flow visualization, thermal field, and velocity field measurements. The film cooling performance on the pressure side of a simulated turbine vane, with and without showerhead blowing, was examined. Results presented in this paper are for low mainstream turbulence; high mainstream turbulence effects are presented in the companion paper. At the location of the pressure side row of holes, the showerhead coolant extended a distance of about 3d from the surface (d is the coolant hole diameter). The pressure side was found to be subjected to high turbulence levels caused by the showerhead injection. Results indicate a greater dispersion of the pressure side coolant jets with showerhead flow due to the elevated turbulence levels.Copyright © 2002 by ASME