Showing papers by "Naval Surface Warfare Center published in 1997"

The effect of pulsed electric fields on biological cells: experiments and applications

Abstract: The effect of pulsed electric fields with amplitudes in the range of 100 V/cm-100 kV/cm on bacteria and aquatic nuisance species has been explored. The pulse duration was so short that heating of the biological matter could be neglected. The electrical energy required for lysing of bacteria, or stunning of aquatic species, decreases when the pulse duration is reduced. For lysing of Eschericia coli, this tendency has been proven to hold for pulsewidths as short as 60 ns. For macroorganisms, however, it was found that for pulsewidths of less than 5 /spl mu/s, the tendency is reversed: the energy required to affect the macroorganisms increases again. This minimum in energy, or maximum in efficiency, respectively, can be understood by taking the time required for electrical charging of the cell membrane into account. Applications of the pulsed electric field technique (PEFT) are in biofouling prevention, debacterialization of liquids, and in the field of medicine. A series of field tests on biofouling prevention in a cooling system with untreated water as coolant has demonstrated the economic feasibility of the electro-technology.

Fire resistant aluminosilicate composites

Abstract: The fire response of a potassium aluminosilicate (Geopolymer) matrix carbon fiber composite was measured and the results compared to organic matrix composites being used for transportation, militar y, and infrastructure applications . At irradiance levels of 50 kW/m 2 typi- cal of the heat flux in a well developed fire, glass- or carbon-reinforced polyeste r, vinylester, epoxy, bismaleimde, cyanate ester, polyimide, phenolic, and engineering thermoplastic laminates ignited readily and released appreciable heat and smoke, while carbon-fiber reinforced Geopolymer com- posites did not ignite, burn, or release any smoke even after extended heat flux exposure . The Geopolymer matrix carbon fiber composite retains sixty-seven percent of its original flexural strength after a simulated large fire exposure.

Automated detection and classification of sea mines in sonar imagery

Abstract: An advanced capability for automated detection and classification of sea mines in sonar imagery has been developed. The advanced mine detection and classification (AMDAC) algorithm consists of an improved detection density algorithm, a classification feature extractor that uses a stepwise feature selection strategy, a k-nearest neighbor attractor-based neural network (KNN) classifier, and an optimal discriminatory filter classifier. The detection stage uses a nonlinear matched filter to identify mine-size regions in the sonar image that closely match a mine's signature. For each detected mine-like region, the feature extractor calculates a large set of candidate classification features. A stepwise feature selection process then determines the subset features that optimizes probability of detection and probability of classification for each of the classifiers while minimizing false alarms.

Phthalonitrile‐glass fabric composites

Abstract: Phthalonitrile polymers, under development at the Naval Research Laboratory, offer promise as high temperature, high performance composite matrix materials. A fully cured resin shows outstanding thermal stability with no evidence of a glass transition temperature or T g up to 450°C, good mechanical properties, and is easily processed into void-free components. Phthalonitrile/glass fabric composite panels have been successfully fabricated by conventional consolidation of prepregged glass and by a more recently developed simplified process, resin infusion molding. Both processes can be used to produce panels with comparable mechanical properties. More important, flammability performance of these composites, evaluated in terms of specific optical density, combustion gases, heat release, and ignitability, excels over other state-of-the-art polymer/glass composites. This finding is significant given that overcoming flammability obstacles has been the main limiting factor for use of composites in marine applications.

Spectroscopic Determination of Impact Sensitivities of Explosives.

Abstract: A simple theory is developed which predicts impact sensitivities in crystalline explosives from vibrational spectra measured at room temperature. The theory uses Raman spectra of energetic materials to construct vibrational energy level diagrams, which are then used as input for a model designed to calculate the rate of energy transfer from phonon and near-phonon vibrational energy levels to higher energy vibrational levels. Energy transfer rates are determined using Fermi's Golden Rule and results from simple theories of near-resonant energy transfer. The application of the theory and model, using Raman spectra of seven different neat explosive samples, gives results in good agreement with results of drop weight impact tests.

A high-performance W-band uniplanar subharmonic mixer

Abstract: A uniplanar subharmonic mixer has been implemented in coplanar waveguide (CPW) technology. The circuit is designed to operate at RF frequencies of 92-96 GHz, IF frequencies of 2-4 GHz, and LO frequencies of 45-46 GHz. Total circuit size excluding probe pads and transitions is less than 0.8 mm /spl times/1.5 mm. The measured minimum single-sideband (SSB) conversion loss is 7.0 dB at an RF of 94 GHz, and represents state-of-the-art performance for a planar W-band subharmonic mixer. The mixer is broad-band with a SSB conversion loss of less than 10 dB over the 83-97-GHz measurement band. The measured LO-RF isolation is better than -40 dB for LO frequencies of 45-46 GHz. The double-sideband (DSB) noise temperature measured using the Y-factor method is 725 K at an LO frequency of 45.5 GHz and an IF frequency of 1.4 GHz. The measured data agrees well with the predicted performance using harmonic-balance analysis (HBA). Potential applications are millimeter-wave receivers for smart munition seekers and automotive-collision-avoidance radars.

Detailed Investigation of the Three-Dimensional Separation About a 6:1 Prolate Spheroid

Abstract: The flow in the crossflow separation region of a 6:1 prolate spheroid at 10- and 20-deg angle of attack, Re L = 4.20 x 10 6 , was investigated using a novel, miniature, three-dimensional, fiber-optic laser Doppler velocimeter (LDV). The probe was used to measure three simultaneous, orthogonal velocity components from within the model, and these measurements were simultaneous with wall-pressure measurements made just below the LDV probe volume. The LDV measurements extend from approximately y + = 7 out to beyond the boundary-layer edge. The design and operation of this LDV probe is summarized.

A proposed hardness assurance test methodology for bipolar linear circuits and devices in a space ionizing radiation environment

Abstract: A hardness assurance test approach has been developed for bipolar linear circuits and devices in space. It consists of an initial test for dose rate sensitivity and a characterization test method to develop the conditions for a lot acceptance test at high dose rate. For parts with adequate design margin and/or well behaved parts a generic elevated temperature irradiation test is proposed.

Experimental Results on a Mach 14 Waverider with Blunt Leading Edges

Abstract: The results of wind-tunnel tests of a Mach 14 waverider were analyzed to assess its overall performance. The waverider was optimized using a e gure of merit that included viscosity, volume, and lift-to-drag considerations. The e nal design included a 0.25-in. leading-edge radius. The general performance of the tested waverider was analyzed and compared to the theoretical design from which it was derived. The theoretical design was generated from a conical e owe eld, where the vehicle’ s ine nitely sharp leading edges were everywhere-attached to the conical shock. Since the tested waverider featured blunt leading edges, it was important to assess the performance losses associated with e ow spillage; these losses were found to be relatively small. However, the increased drag due to the blunt leading edges contributed greatly to reducing the aerodynamic performance of the tested waverider. Also, it was found that the aerodynamic coefe cient data were insensitive to changes in Mach number and Reynolds number, indicating excellent off-design performance for the ranges of values tested.

Application of the positive alpha-stable distribution

Abstract: Many physical phenomena are non-Gaussian and if the observed data have frequently occurring extreme values, then the phenomena may be modeled as a random process with an alpha-stable distribution When positive and negative outcomes are equally likely, then the process would be symmetric alpha-stable (S/spl alpha/S); however when only positive outcomes are possible, then the process would be positive alpha-stable (P/spl alpha/S) Phenomena related to energy or power are examples This paper presents the characteristics and potential applications for the P/spl alpha/S distribution For this distribution all negative-order moments exist, and ratios of these moments are used to estimate alpha Application areas that are examined include: seismic activity, ocean wave variability, and radar sea clutter modulation The correlation properties of these data are examined

Homopolar motor with high temperature superconductor field windings

Abstract: A superconducting field winding, assembled with discrete coils wound with bismuth 2223 high temperature superconducting (HTS) wire, has been successfully operated in an electric homopolar motor designed and built by the Naval Surface Warfare Center. The motor's field winding is composed of two HTS coils fabricated by American Superconductor Corporation and two HTS coils fabricated by Intermagnetics General Corporation. These field winding coils were produced for the Navy under contracts with the Naval Research Center. At a HTS field winding operating temperature of 4.2 K, the motor produced 125 kW (167 hp) of output power. At a temperature of 28 K the motor power developed was 91 kW (122 hp). In comparison to other motor types, a homopolar motor provides an ideal operating environment for a superconducting magnet. The design, construction, and operating characteristics of this machine are described. Information describing the HTS field winding and its superconducting capabilities is presented along with that for the laboratory test facility used to measure the performance of the machine. Motor measured performance results and those predicted by computer simulation are compared and presented. An assessment of the state of the engineering development of HTS superconductors for magnet applications and recommendations for future development are made.

Use of curvilinear SAR for three-dimensional target feature extraction

Abstract: The use of curvilinear synthetic aperture radar (CLSAR) is considered for three-dimensional feature extraction of small targets consisting of a small number of distinct point scatterers. CLSAR does not suffer from the ambiguities suffered by interferometric SAR. As CLSAR is a relatively new technology, a self-contained detailed derivation of the data model is presented. The Cramer-Rao bounds of the parameter estimates are also derived. Use of the RELAX algorithm for 3-D target feature extraction with CLSAR for different curvilinear apertures is also described.

Maintenance of chaos in a computational model of a thermal pulse combustor.

Abstract: The dynamics of a thermal pulse combustor model are examined It is found that, as a parameter related to the fuel flow rate is varied, the combustor will undergo a transition from periodic pulsing to chaotic pulsing to a chaotic transient leading to flameout Results from the numerical model are compared to those obtained from a laboratory-scale thermal pulse combustor Finally the technique of maintenance (or anticontrol) of chaos is successfully applied to the model, with the result that the operation of the combustor can be continued well into the flameout regime

Nonlinear missile autopilot design using time-scale separation

Abstract: Time-Scale separation helps improve the robustness of feedback linearized autopilots by simplifying the feedback linearization maps, and by permitting the design of low-order controllers. This paper presents the development of three distinct timescale separation schemes for the design of feedback linearized missile autopilots. A six degrees-of-freedom missile model is used in this work. The performance of these autopilots are compared with the design that does not use time-scale separation. Simulation results illustrating controller tracking performance and robustness are presented.

Control and synchronization of chaos in high dimensional systems: Review of some recent results

Abstract: Controlling chaos and synchronization of chaos have evolved for a number of years as essentially two separate areas of research. Only recently it has been realized that both subjects share a common root in control theory. In addition, as limitations of low dimensional chaotic systems in modeling real world phenomena become increasingly apparent, investigations into the control and synchronization of high dimensional chaotic systems are beginning to attract more interest. We review some recent advances in control and synchronization of chaos in high dimensional systems. Efforts will be made to stress the common origins of the two subjects.

IMMPDA solution to benchmark for radar resource allocation and tracking in the presence of ECM

Abstract: In this paper we present a framework for controlling a phased array radar for tracking highly maneuvering targets in the presence of false alarms and electronic countermeasures (ECM). Algorithms are presented for track formation and maintenance; adaptive selection of target revisit interval, waveform, and detection threshold; and neutralizing techniques for ECM, namely, against a standoff jammer and range gate pull off. This tracker/radar-resource-allocator provides a complete solution to the benchmark problem for target tracking and radar control, which considers six trajectories of highly maneuvering targets, with lateral accelerations up to 7g and longitudinal accelerations up to 2g. Simulation results show an average sampling interval of about 2s while maintaining a track loss less than the maximum allowed 4%.

High-frequency/low-frequency synthetic aperture sonar

Abstract: The HF/LF SAS is a high resolution SAS developed by COASTSYSTA and Northrop Grumman for the shallow water (SW) and very shallow water (VSW) regimes This sonar suite has recently been delivered to COASTSYSTA and it is currently undergoing field testing This article describes this sonar and the type of resolution and acoustical images which are expected from this sonar The application of this sonar to the SW and VSW regimes required the development of a novel method of motion compensation A description of this method and the type of accuracy's expected from this technique are presented Finally, a look at future broad band system and their predicted performance is presented© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Simple interpretation of time-domain electromagnetic sounding using similarities between wave and diffusion propagation

Abstract: By using similarities between EM sounding in dielectric and conductive media, it is shown that one can transform between solutions in one type of propagation to the other. The method is based on the similarities of the Laplace transform between diffusive and nondiffusive cases. In the diffusive case, the equation involves the Laplace variable s in the first power, while for the nondiffusive cases, similar equations occur with s2. Three alternative implementations are developed, and their use is demonstrated. The first implementation is based on substituting s2 for the Laplace transform variable s using forward and inverse numerical Laplace transforms. The second implementation is based on expanding the diffusive time response on an exponential time base and replacing it with its image function in the wave case, namely, a sinusoidal function. The third implementation is based on direct transformation in the time domain using exponential time interval sampling. The performance of the techniques on synthetic...

Magnetic dipole localization with a gradiometer: obtaining unique solutions

Abstract: The five independent equations describing the field gradient tensor at a point for a static magnetic dipole source can be inverted to give the bearing vector to the source and the source moment vector divided by the fourth power of the range. The equations have four solutions, two of which are related in a non-trivial way, and two more that are obtained by reflections through the field point. The symmetry of the four solutions in the principal-axis frame of the gradient tensor can be used to express the solutions directly in terms of one another in an arbitrary frame without executing the inversion. This relationship has been exploited to construct explicit proofs that a unique solution for magnetic moment vector and relative position between source and field point can be obtained if either the magnetic field vector, or the rate of change of the gradient tensor and the relative motion of source and field point is known.

Dislocation Mechanics Based analysis of Material Dynamics Behavior : Enhanced Ductility, Deformation Twinning, Shock Deformation, Shear Instability, Dynamic Recovery

Abstract: Further developments are described for the dislocation mechanics based constitutive equation analysis previously used to describe the separate dynamic stress-strain behavior of fcc and bcc metal polycrystals. An enhanced hardening and ductility in copper and certain tantalum materials at higher strain rates in split Hopkinson pressure bar tests and in shock loading are attributed to enhanced dislocation generation rather than to dislocation drag. Added material strengthening is accounted for also by deformation twinning in ARMCO iron and titanium and in shocked copper and tantalum. The separate equations are applied to calculate the critical strain for shear banding in copper, iron, and the titanium alloy, Ti-6Al-4V. In the two latter cases, the results are very sensitive to the details of the strain-hardening behavior and the need is demonstrated for a dynamic recovery factor to account for the onset of shear banding. Consideration is given also to the possibility that shear band behavior requires explanation on a more fundamental Hall-Petch dislocation pile-up basis.

Absorption and transport of hydrogen during gas metal arc welding of low alloy steel

Abstract: Although hydrogen induced cracking remains a major problem in the welding of steels, the present methods of managing hydrogen in the weldment are mostly empirical in nature. In recent years, numerical modelling of heat transfer and fluid flow has provided detailed insight into the physical processes in welding. However, very little effort has been made in the past to use these transport phenomena based calculations to understand the dissolution of hydrogen in the weld metal and its subsequent transport in the liquid and solid regions. The aim of the present work was to address this important need. Heat transfer, fluid flow, and hydrogen transport calculations in transient, three-dimensional form are used to predict the spatial distribution of hydrogen concentration in the weld metal during gas metal arc welding of mild steels for different welding conditions. The enhanced hydrogen solubility in the weld metal above that predicted by Sieverts law was determined from a model for the partitioning of ...

HTS coils for the Navy's superconducting homopolar motor/generator

Abstract: We report here on the development of HTS coils at Intermagnetics for the Navy's homopolar motor/generator program. Two coil sizes were used. A series of small test coils (14.0 cm i.d./spl times/15.0 cm o.d./spl times/1.4 cm long) were employed to evaluate various conductor winding, insulation and epoxy impregnation issues. Based upon the results of these test coils, the larger coil modules (19.37 cm i.d./spl times/24.35 cm o.d./spl times/2.54 cm long) for the homopolar motor/generator were fabricated. Several coils each of three types of react-and-wind coils were produced, one type with monocore BSCCO-2223, one type with multifilamentary BSCCO-2223 and the other type with surface coated BSCCO-2212. Test results are presented as well as discussions on various coil technology issues.

A fast algorithm for computing minimum cross-entropy positive time-frequency distributions

Abstract: An algorithm for obtaining nonnegative, joint time-frequency distributions Q(t, f) satisfying the univariate marginals |s(t)|/sup 2/ and |S(f)|/sup 2/ is presented and applied. The advantage of the algorithm is that large time series records can be processed without the need for large random access memory (RAM) and central processing unit (CPU) time. This algorithm is based on the Loughlin et al. (1992) method for synthesizing positive distributions using the principle of minimum cross-entropy. The nonnegative distributions with the correct marginals that are obtained using this approach are density functions as proposed by Cohen and Zaparovanny (1980) and Cohen and Posch (1985). Three examples are presented: the first is a nonlinear frequency modulation (FM) sweep signal (simulated data); the second and third are of physical systems (real data). The second example is the signal for the acoustic scattering response of an elastic cylindrical shell structure. The third example is of an acoustic transient signal from an underwater vehicle. Example one contains 7500 data points, example two contains 256 data points, and example three contains in excess of 30000 data points. The RAM requirements using the original Loughlin et al. algorithm for a 7500 data point signal is 240 mega bytes and for a 30000 data point signal is 3.5 billion bytes. The new algorithm reduces the 240 mega byte requirement to 1 mega byte and the 3.5 billion byte requirement to 4 million bytes. Furthermore, the fast algorithm runs 240 times faster for the 7500 data point signal and 3000 times faster for the 30000 data point signal as compared with the original Loughlin et al. algorithm.