Showing papers by "Naval Surface Warfare Center published in 1991"
TL;DR: In this article, the general salvation equation, log VG0 (or log L) was used to set up a new π2H parameter of solute dipolarity-polarisability, mainly through the extensive data of McReynolds and Patte et al.
264 citations
TL;DR: In this paper, a term-by-term analysis of the solvation equation yields a quantitative measure of the contribution to log K of various solute-stationary phase interactions, and leads to an understanding of how these interactions affect solute retention.
93 citations
TL;DR: For groups of nitramines and nitroaliphatics, taken separately it is shown that sensitivity is related to the strength of all of NNO2 and/or CNO2 bonds in the molecule, taken in conjunction with its overall size as discussed by the authors.
89 citations
TL;DR: In this article, the effedts of pressure on the thermal decomposition kinetics, chemical reactivity, and phase behavior of RDX have been studied by a combination of measurement techniques in conjunction with a high-pressure diamond anvil cell.
72 citations
TL;DR: In this paper, a high-power spark gap switch capable of 100 mu s recovery times can be constructed without gas flow by using high-pressure hydrogen gas and by triggering the main gap in a highly undervolted state.
Abstract: A high-power spark-gap switch capable of 100- mu s recovery times can be constructed without gas flow by using high-pressure hydrogen gas and by triggering the main gap in a highly undervolted state. These techniques have been demonstrated to work at voltages up to 120 kV, peak currents of up to 170 kA, and energy transfers of up to 12.5 kJ. Tests underway to test the concepts at 600 kV and for multiple-pulse bursts are discussed. >
65 citations
TL;DR: In this article, the effect of processing variables on the development of texture in commercially processed tantalum for deep drawing applications was investigated, and it was shown that tantalum processed with a deformation zone parameter less than one, after rolling and recrystallization, had a desirable fiber texture through the plate thickness and also a fine grain size.
Abstract: The effect of processing variables on the development of texture in commercially processed tantalum for deep drawing applications was investigated. Orientation distribution functions (ODFs) showed that tantalum processed with a deformation zone parameter less than one, after rolling and recrystallization, had a desirable {111} fiber texture through the plate thickness and also a fine grain size. For tantalum rolled with a deformation zone parameter greater than one and recrystallized, severe texture gradients formed which influenced the final recrystallized grain size. Orientation distribution function analysis indicated that a strong {001}(110) orientation developed in cross-rolled and recrystallized tantalum. The influence of processing variables on the final recrystallized texture and microstructure is discussed, but the deep drawability of the textured tantalum is not described.
64 citations
TL;DR: In this article, the authors investigated the transition from two-frequency quasiperiodicity to chaotic behavior in a model for a quasiprocessor driven magnetoelastic ribbon.
Abstract: We investigate the transition from two-frequency quasiperiodicity to chaotic behavior in a model for a quasiperiodically driven magnetoelastic ribbon. The model system is a two-frequency parametrically driven Duffing oscillator. As a driving parameter is increased, the route to chaos takes place in four distinct stages. The first stage is a torus-doubling bifurcation. The second stage is a transition from the doubled torus to a strange nonchaotic attractor. The third stage is a transition from the strange nonchaotic attractor to a geometrically similar chaotic attractor. The final stage is a hard transition to a much larger chaotic attractor. This latter transition arises as the result of acrisis, the characterization of which is one of our primary concerns. Numerical evidence is given to indicate that the crisis arises from the collision of the chaotic attractor with the stable manifold of a saddle torus. Intermittent bursting behavior is present after the crisis with the mean time between bursts scaling as a power law in the distance from the critical control parameter; τ ∼ (A-Ac)-α. The critical exponent is computed numerically, yielding the value α=1.03±0.01. Theoretical justification is given for the computed critical exponent. Finally, a Melnikov analysis is performed, yielding an expression for transverse crossings of the stable and unstable manifolds of the crisis-initiating saddle torus.
60 citations
TL;DR: In this paper, the existence of a saddle point of attachment in low-speed flows over a cylinder mounted on a flat plate is studied numerically in order to confirm the existence in the flow before an obstacle, and to analyze the flow characteristics near the saddle point theoretically.
Abstract: Low-speed flows over a cylinder mounted on a flat plate are studied numerically in order to confirm the existence of a saddle point of attachment in the flow before an obstacle, to analyze the flow characteristics near the saddle point theoretically, and to address the significance of the saddle point of attachment to the construction of external flow structures, the interpretation of experimental surface oil-flow patterns, and the theoretical definition of three-dimensional flow separation. Two numerical codes, one for an incompressible flow and another for a compressible flow, are used for various Mach numbers, Reynolds numbers, grid sizes, and numbers of grid points. It is pointed out that the potential presence of a saddle point of attachment means that a line of 'oil accumulation' from both sides of a skin-friction line emanating outward from a saddle point can be either a line of separation or a line of attachment.
49 citations
TL;DR: In this paper, the influence of initial ingot breakdown on the rolling and recrystallization textures of high-purity tantalum plate was investigated using optical microscopy and X-ray diffraction.
Abstract: The influence of initial ingot breakdown on the rolling and recrystallization textures of high-purity tantalum plate was investigated using optical microscopy and X-ray diffraction The four ingot breakdown processes investigated include two commercial processes and two processes new to tantalum Correlations among the four ingot breakdown processes, the recrystallized grain size, and the final texture were established Of the four breakdown processes investigated, the plate from the completely upset-forged ingot had the strongest {111} and {111} texture components, while the plate from the side-forged ingot recrystallized with a mixed texture Increased upset forging along the ingot centerline strenghened the {111} orientations and weakened the {100} orientations in the annealed plates Recrystallization studies were conducted on the rolled plates to develop an optimum texture with both {111} and {111} texture components in the final recrystallized plate
49 citations
TL;DR: This work investigates experimentally the scaling of the average time between intermittent, noise-induced bursts for a chaotic mechanical system near a crisis, then determines \ensuremath{\gamma} for the low-noise (``deterministic'') system, then add noise and observe that the scaling for £tau is as predicted.
Abstract: We investigate experimentally the scaling of the average time \ensuremath{\tau} between intermittent, noise-induced bursts for a chaotic mechanical system near a crisis. The system studied is a periodically driven (frequency f) magnetoelastic ribbon. Theory predicts that for deterministic crises where \ensuremath{\tau} scales as \ensuremath{\tau}\ensuremath{\sim}\ensuremath{\Vert}f-${\mathit{f}}_{\mathit{c}}$${\mathrm{\ensuremath{\Vert}}}^{\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$ (f${\mathit{f}}_{\mathit{c}}$, f=${\mathit{f}}_{\mathit{c}}$ at crisis), the characteristic time between noise-induced bursts (f\ensuremath{\ge}${\mathit{f}}_{\mathit{c}}$) should scale as \ensuremath{\tau}\ensuremath{\sim}${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$g(\ensuremath{\Vert}f-${\mathit{f}}_{\mathit{c}}$\ensuremath{\Vert}/\ensuremath{\sigma}), where \ensuremath{\sigma} is the noise strength and \ensuremath{\gamma} is the same in both cases. We determine \ensuremath{\gamma} for the low-noise (``deterministic'') system, then add noise and observe that the scaling for \ensuremath{\tau} is as predicted.
43 citations
TL;DR: In this article, mineralogical data, thermodynamic stability diagrams, and simplexity principle for precipitation reactions were used to evaluate corrosion product mineralogy on copper alloy, and the results showed that copper alloy is corrosion resistant.
Abstract: Mineralogical data, thermodynamic stability (Pourbaix) diagrams, and the simplexity principle for precipitation reactions were used to evaluate corrosion product mineralogy on copper alloy...
TL;DR: In this article, the expected zero-crossing rate of random processes that are monotone transformations of Gaussian processes can be obtained by using two different techniques: the first technique involves derivation of the expected ZR for discrete-time processes and extends the result of the continuous-time case by using an appropriate limiting argument.
Abstract: Formulas for the expected zero-crossing rates of random processes that are monotone transformations of Gaussian processes can be obtained by using two different techniques. The first technique involves derivation of the expected zero-crossing rate for discrete-time processes and extends the result of the continuous-time case by using an appropriate limiting argument. The second is a direct method that makes successive use of R. Price's (1958) theorem, the chain rule for derivatives, and S.O. Rice's (1954) formula for the expected zero-crossing rate of a Gaussian process. A constant, which depends on the variance of the transformed process and a second-moment of its derivative, is derived. Multiplying Rice's original expression by this constant yields the zero-crossing formula for the transformed process. The two methods can be used for the general level-crossing problem of random processes that are monotone functions of a Gaussian process. >
TL;DR: In this article, an optical fiber probe was constructed to obtain real-time measurements of fluorescence radiation during twin screw mixing and extrusion of plasticized polybutadiene and calcium carbonate particulate.
Abstract: An optical fiber probe has been constructed in order to obtain real-time measurements of fluorescence radiation during twin screw mixing and extrusion of plasticized polybutadiene and calcium carbonate particulate. The probe consists of an optical fiber bundle which was inserted along the axis of a half-inch sensor bolt, and it was used to transmit optical excitation energy to the processed material and to detect the subsequent fluorescence. The source of fluorescence radiation was a fluorescent dye which was doped into the processed ingredients at very low concentrations. Although most of our measurements were taken with the probe positioned close to the exit die, the sensor bolt can be placed in any instrumentation port along the extruder line. Experiments were carried out to measure residence time distribution, quality-of-mix, and mix concentrations as a function of processing conditions. Product mix changes in response to variations in material feed rates and screw RPM were also observed. Values of residence time were obtained by measuring the transit times for the dye to travel from an upstream injection port to the measurement probe, a distance of 63 cm. Flow instabilities, such as mat formation of the solids, were observed by noting the abrupt changes and discontinuities in the fluorescence signal.
TL;DR: In this article, the scaling of the average time τ between intermittent bursts for a chaotic system that undergoes a homoclinic tangency crisis, which causes a sudden expansion in the attractor was investigated.
TL;DR: In this article, the backscattering or sonar crosssection (SCS) of a submerged elastic spherical shell was obtained and analyzed by exact Fourier synthesis, and the individual resonances associated with each pole (i.e., eigenfrequencies) can be obtained and studied one at a time, provided we use long illuminating pulses, since these excite transients at their carrier frequencies that ring and decay.
TL;DR: In this article, a series of polyurethanes of varying soft-segment molecular weight were fitted to the modified Havriliak-Negami equation and the fitting parameters related to molecular structure.
Abstract: Dynamic mechanical measurements of complex shear modulus versus frequency and temperature were made on a series of polyurethanes of varying soft-segment molecular weight. The time-temperature shifted data (master curves) mapped out the soft-segment glass transition. Shift factor curves were fitted to the Williams-Landel-Ferry (WLF) equation to obtain shift constants. The fractional free volume and coefficient of thermal expansion at the glass transition, determined from the shift constants, decrease as the molecular weight increases. Master curves were fitted to the modified Havriliak-Negami equation and the fitting parameters related to molecular structure. The limiting low-frequency modulus is dependent on the soft-segment molecular weight and percent crystallinity, but the limiting high-frequency modulus is about the same for all these polymers. The average relaxation time decreases with increasing soft-segment molecular weight and is correlated with glass transition temperature.
11 Dec 1991
TL;DR: In this article, the use of a kinematic constraint as a pseudomeasurement in the tracking of constant speed, maneuvering targets is considered and a novel formulation of the constraint equation is presented and the rationale for this formulation is discussed.
Abstract: The use of a kinematic constraint as a pseudomeasurement in the tracking of constant speed, maneuvering targets is considered. A novel formulation of the constraint equation is presented and the rationale for this formulation is discussed. The filter using the kinematic constraint as a pseudomeasurement is shown to be unbiased, and sufficient conditions for stochastic stability of the filter are given. Simulation results indicate that the use of the novel formulation of the kinematic constraint improves the tracking of constant speed, maneuvering targets. >
10 Mar 1991
TL;DR: In this article, an interacting multiple model (IMM) filter with constant velocity and exponentially-correlated acceleration (ECA) models is proposed for tracking maneuvering targets, where an IMM filter is implemented separately in each Cartesian coordinate to allow for different model probabilities in each coordinate.
Abstract: An interacting multiple model (IMM) filter with constant velocity and exponentially-correlated acceleration (ECA) models is proposed for tracking maneuvering targets. An IMM filter is implemented separately in each Cartesian coordinate to allow for different model probabilities in each coordinate. For each coordinate, one of two ECA models is designed to track an increasing acceleration while the other ECA model is designed to track a decreasing acceleration. The IMM filter is designed so that the ECA model with increasing acceleration provides transition from the constant velocity model to the ECA model with decreasing acceleration. The ECA model with decreasing acceleration provides transition to the constant velocity model. Simulated tracking results are given for a constant speed target performing a 'S' trajectory maneuver. >
10 Mar 1991
TL;DR: In this paper, the alpha-beta filter is used to quantify the filter's performance against different measurement models representing a target's trajectory, and closed form expressions for smoothed position and velocity outputs for various measurement models are derived.
Abstract: The response characteristics of the alpha-beta filter are used to quantify the filter's performance against different measurement models representing a target's trajectory. The transfer functions for an alpha-beta filter are used to derive closed form (solutions) expressions for smoothed position and velocity outputs for various measurement models. The filter's response to constant velocity targets is found to be the input plus a sinusoidal transient. Constant acceleration measurement models, in addition, yield a steady state bias that is a function of the filter parameters alpha and beta . Finally, the filter's response to a sinusoidal input is determined. >
16 Jun 1991
TL;DR: The Pulsed Power Technology Branch at NAVSWC is investigating high-power switch technologies and has found that using hydrogen gas, with its high thermal diffusivity, allows an order-of-magnitude improvement in the recovery time (and therefore, repetition rate) of an unblown spark gap switch.
Abstract: The Pulsed Power Technology Branch at NAVSWC is investigating high-power switch technologies. In- house efforts have concentrated on spark-gap switches because of their high-voltage and high-current capabilities in single-shot devices and because of their simplicity and low cost. We have found that using hydrogen gas, with its high thermal diffusivity, allows an order-of-magnitude improvement in the recovery time (and, therefore, repetition rate) of an unblown spark-gap switch. Recovery of the switch can be made even faster by triggering the switch well below its self-break voltage, allowing voltage to be reapplied while the gas is still hot. Tests have shown that recovery times (to the operating voltage) can be reduced an order-of-magnitude when the gap is undervolted by approximately 50%. Recent tests have demonstrated 100-microsecond recovery of an undervolted hydrogen spark gap at voltages up to 120 kV, peak currents up to 170 kA, and energies up to 12 kJ. Plans are underway to test the switch to 500 kV.
01 Dec 1991
TL;DR: In this article, the authors highlight the efforts of the Naval Surface Warfare Center to develop a fiber optic pressure transducer, which was used to monitor the pressure in the sonar dome of a surface ship.
Abstract: This paper highlights the efforts of the Naval Surface Warfare Center to develop a fiber optic pressure transducer. The initial application for this fiber optic sensor is to monitor the pressure in the sonar dome of a surface ship. This required a 0 - 100 pounds per square inch (gage) sensor. This sensor, developed by Luxtron, Incorporated, under a Small Business Innovative Research contract, utilizes a vibrating quartz crystal as the transduction mechanism. Changes in the resonant frequency of the quartz crystal as a result of force applied to the crystal is monitored using a simple fiber optic link. This paper discusses the principal of operation and design of the sensor, advantages and disadvantages of this type of sensor, development results to date, and future development plans.
Portions of this paper have been presented previously in a paper entitled “Fiberoptic pressure sensor based on vibrating quartz crystal technology” presented at the International Congress on Optical Science and Engineering, The Hague, Netherlands, March, 1990.
TL;DR: In this paper, the general scattering interaction of electromagnetic (EM) pulses of arbitrary shape and duration with a spherical target is studied, where the target is assumed penetrable and can be either totally dielectric, or perfectly conducting but covered with a thin outer masking coating of a dielectoric material.
Abstract: We study the general scattering interaction of electromagnetic (EM) pulses of arbitrary shape and duration with a spherical target The target is assumed penetrable and we model it either as totally dielectric, or as perfectly conducting but covered with a thin outer masking coating of a dielectric material We obtain the radar cross-sections (RCS) of such targets and analyze the many resonance features that are present within their resonance region The dielectric composition makes the resonance features become very prominent and it relates them to the eigenfrequencies in ways analogous to those of the Singularity Expansion Method (SEM), originally developed for perfectly conducting scatterers Transient echoes from these targets are linked to poles and residues in the complex-frequency plane The individual resonances associated with each pole (ie, eigenfrequencies) can be studied one at a time, provided we use long illuminating pulses since these excite transients at their carrier frequencies that ri
16 Jun 1991
TL;DR: In this paper, the authors describe the recent power scaling of the Bulk Optically Controlled Semiconductor Switch (BOSS), which can operate at multi-megawatt power levels.
Abstract: This paper describes the recent power scaling of the Bulk Optically Controlled Semiconductor Switch (BOSS). The processes of persistent photoconductivity followed by photo-quenching have been demonstrated in copper-compensated, silicon-doped, semi-insulating GaAs (GaAs:Cu:Si). These processes allow a switch to be developed which can be closed by the application of one laser pulse and opened by the application of a second laser pulse of longer wavelength. The high-power switching results indicate that the BOSS device will operate at multi-megawatt power levels. The results of our power scaling effort have suggested improvements to the basic BOSS design that will allow us to achieve reliable operation at high power levels.
TL;DR: In this article, the role of crystal defects in forming hot spots during shock loading of large, optical quality, pure single crystals of ammonium perchlorate (AP) was investigated.
Abstract: The purpose of this work is to perform a microscopic-scale study of the role that crystal defects have in forming hot spots during shock loading of large, optical quality, pure single crystals of ammonium perchlorate (AP). The crystals were immersed in mineral oil at various distances from a detonator that provided the shock. The small explosive donor permitted recovery of the crystals for quantitative chemical analysis of decomposition and microindentation hardness testing. Hardness testing was also performed on an unshocked crystal to determine 1) the slip systems associated with primary and secondary deformation in accommodating the indenter and 2) the crack propagation directions at the surface as well as into the crystal. High-speed photographs of the shock-loaded crystals showed slip and cracking systems identified by hardness testing. Some of the systems were luminous. In addition, when a crystal with a large indentation was shocked near its reaction threshold, significant light appeared in the vicinity of the identation following shock passage. As such, preferred chemical reactivity in AP has been associated with its deformation systems and the presence of large strain centers.
TL;DR: In this article, a number of substituted dinitrobenxofurazan oxides and nitrobenzobis (oxadiozoles) by thermolysis of azido precursors is described.
01 Jun 1991
TL;DR: In this paper, the dynamics of unconfined, spatially developing shear layers is studied through the numerical solutions of the time-dependent Euler equations using a second-order Godunov scheme.
Abstract: The dynamics of unconfined, spatially developing shear layers is studied through the numerical solutions of the time-dependent Euler equations using a second-order Godunov scheme. The effects of density and velocity variations between the two streams of the shear layer are studied and color graphics are used to show more clearly the entrainment process of the surrounding streams. The calculations demonstrate that the evolution of the mean flow is dominated by two-dimensional, inviscid effects. The r.m.s. fluctuating velocity and density profiles are in good agreement with the measurements of Oster and Wygnanskiand of Konrad, except for the peak value of the v′ profile.
TL;DR: In this paper, a simple scheme for generating a uniform, steady-state, large-volume plasma is presented, where weakly magnetized plasma is created by direct ionization of the background gas by low-energy electrons generated from thermionic filaments.
Abstract: A simple scheme for generating a uniform, steady-state, large-volume plasma is presented. The weakly magnetized plasma is created by direct ionization of the background gas by low-energy electrons generated from thermionic filaments. An annular arrangement of the filaments ensures a uniform plasma density in the radial direction as predicted by theory. Experiments have been performed to characterize the plasma generated in such a configuration. In order to explain the experimental observation, a bulk plasma theory based on plasma transport by means of cross-field diffusion is developed. As assumed in the theoretical model, the experimental measurements indicate a uniform plasma density along the axis. Both the theory and experiment indicate that the plasma density is a function of the square of the external magnetic field. The theory also predicts the plasma density to be proportional to the neutral density to the two-thirds power, in agreement with the experimental data. The experimental data agree well with theoretical prediction for a broad range of system parameters. >
01 Oct 1991-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The Naval Surface Warfare Center developed a process for the in situ preparation of 80% porous mullite whisker felt which consists of randomly oriented whiskers mutually intergrown, forming a rigid structure as mentioned in this paper.
Abstract: The Naval Surface Warfare Center has developed a process for the in situ preparation of 80% porous mullite whisker felt which consists of randomly oriented whiskers mutually intergrown, forming a rigid structure. The felt can be used as pre-forms for the preparation of metal and ceramic matrix composites. The patented process involves mixing and shaping the powdered precursors followed by firing to form in situ the mullite whisker felt. The powders can be shaped by any conventional process. An advantage of the process is the elimination of health hazards associated with loose respirable whiskers. The low dimensional changes of the final felt compared with the green shapes are a valuable feature for the preparation of near-net shape composite preforms. Methods for infiltration of the felt with cast aluminum alloy A356 and properties of the composites will be discussed.
07 Jan 1991