Showing papers by "Naval Surface Warfare Center published in 1998"

The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis

Abstract: A new method for analysing nonlinear and non-stationary data has been developed. The key part of the method is the empirical mode decomposition method with which any complicated data set can be dec...

Spatiotemporal evolution of ventricular fibrillation

Abstract: Sudden cardiac death is the leading cause of death in the industrialized world, with the majority of such tragedies being due to ventricular fibrillation1. Ventricular fibrillation is a frenzied and irregular disturbance of the heart rhythm that quickly renders the heart incapable of sustaining life. Rotors, electrophysiological structures that emit rotating spiral waves, occur in several systems that all share with the heart the functional properties of excitability and refractoriness. These re-entrant waves, seen in numerical solutions of simplified models of cardiac tissue2, may occur during ventricular tachycardias3,4. It has been difficult to detect such forms of re-entry in fibrillating mammalian ventricles5,6,7,8. Here we show that, in isolated perfused dog hearts, high spatial and temporal resolution mapping of optical transmembrane potentials can easily detect transiently erupting rotors during the early phase of ventricular fibrillation. This activity is characterized by a relatively high spatiotemporal cross-correlation. During this early fibrillatory interval, frequent wavefront collisions and wavebreak generation9 are also dominant features. Interestingly, this spatiotemporal pattern undergoes an evolution to a less highly spatially correlated mechanism that lacks the epicardial manifestations of rotors despite continued myocardial perfusion.

Benchmark for radar allocation and tracking in ECM

Abstract: A benchmark problem for tracking maneuvering targets is presented. The benchmark problem involves beam pointing control of a phased array (i.e., agile beam) radar against highly maneuvering targets in the presence of false alarms (FAs) and electronic counter measurements (ECM). The testbed simulation described includes the effects of target amplitude fluctuations, beamshape, missed detections, FAs, finite resolution, target maneuvers, and track loss. Multiple waveforms are included in the benchmark so that the radar energy can be coordinated with the tracking algorithm. The ECM includes a standoff jammer (SOJ) broadcasting wideband noise and targets attempting range gate pull off (RGPO). The limits on the position and maneuverability of the targets are given along with descriptions of six target trajectories. The "best" tracking algorithm is the one that minimizes a weighted average of the radar energy and radar time, while satisfying a constraint of 4% on the maximum number of lost tracks, The radar model, the ECM techniques, the target scenarios, and performance criteria for the benchmark are presented.

DC link stabilized field oriented control of electric propulsion systems

Abstract: Induction motor based electric propulsion systems can be used in a wide variety of applications including locomotives, hybrid electric vehicles, and ships. Field oriented control of these drives is attractive since it allows the torque to be tightly and nearly instantaneously controlled. However, such systems can be prone to negative impedance instability of the DC link. This paper examines this type of instability and sets forth a readily implemented albeit nonlinear control strategy to mitigate this potential problem.

An efficient and accurate model for the simulation and analysis of synchronous machine/converter systems

Abstract: A new synchronous machine model is presented which is readily implemented in either circuit-based or differential-equation-based simulation programs. This model is well suited for the simulation and analysis of synchronous machine-power converter systems. It is based upon standard representations and no approximations are made in its derivation. However, the numerical implementation is shown to be significantly more efficient. An example is provided which demonstrates a 1700% increase in simulation speed with no observable loss in accuracy. The model includes provisions for an arbitrary number of damper or rotor windings and may be easily modified to represent synchronous or induction machines with an arbitrary number of stator phases.

Analysis of X-ray Absorption Spectra of Some Nickel Oxycompounds Using Theoretical Standards

Abstract: X-ray absorption spectra have been measured for NiO, β-Ni(OH)2, α-Ni(OH)2, LiNiO2, and KNiIO6 samples, which contain nickel with valency in the range 2−4. Information on the local structure and nature of bonding of nickel compounds has been derived using theoretical standards generated with the FEFF code. The Ni K-edge energy was found to shift to higher values by about 1.5 eV per unit change in valency of nickel. The energy of the preedge peak (generally attributed to the transition from the 1s core states to the 3d unoccupied states) shifts to higher values by about 0.6 eV per unit change in valency of nickel. A many body amplitude reduction factor ( ) of 0.77 ± 0.03 for Ni K-edge absorption can be used to scale theoretical spectra to fit the experimental ones in order to accurately determine the coordination numbers for compounds with complex structures. Our results show that chemical effects are very small and can be ignored for reliable structural analysis. Results of local structure for the first, s...

Unresolved Rayleigh target detection using monopulse measurements

Abstract: When the returns from two or more targets interfere (i.e., the signals are not resolved in the frequency or time domains) in a monopulse radar system, the direction-of-arrival (DOA) estimate indicated by the monopulse ratio can wander far beyond the angular separation of the targets. Generalized maximum likelihood (GML) detection of the presence of unresolved Rayleigh targets is developed with probability density functions (pdfs) conditioned on the measured amplitude of the target echoes. The Neyman-Pearson detection algorithm uses both the in-phase and quadrature portions of the monopulse ratio and requires no a priori knowledge of the signal-to-noise ratio (SNR) or DOA of either target. Receiver operating characteristic (ROC) curves are given along with simulation results that illustrate the performance and application of the algorithm.

Hydrodynamic effect of a satellite transmitter on a juvenile green turtle (Chelonia mydas)

Abstract: Wind tunnel tests were performed to measure the effect of a satellite transmitter on a juvenile green turtle (Chelonia mydas). A full-scale turtle model was constructed from an 11.5 kg specimen with a 48 cm carapace length, and a transmitter model was constructed from a Telonics ST-6. The turtle model was tested in a wind tunnel with and without the transmitter, which was mounted on the forward, topmost part of the carapace. Drag, lift and pitch moment were measured for several speeds and flow angles, and the data were scaled for application to the marine environment. At small flow angles representative of straight-line swimming, the transmitter increased drag by 27-30 %, reduced lift by less than 10 % and increased the pitch moment by 11-42 %. On the basis of the drag data at zero angle of attack, it is estimated that the backpack will reduce swimming speed by 11 %, assuming that the turtle produces the same thrust with the unit attached. The drag data are also used to estimate the effect of a transmitter on the swimming energetics of an adult green turtle. Design guidelines are included to minimize the adverse forces and moments caused by the transmitter.

Effect of ion energy upon dielectric breakdown of the capacitor response in vertical power MOSFETs

Abstract: The effect of ion energy upon the ion-induced dielectric breakdown response of the capacitor response in vertical power metal-oxide semiconductor field effect transistors (MOSFETs) was investigated. The single event gate rupture response was experimentally determined using mono-energetic ion beams of copper, niobium, and gold. Irradiations were conducted using an ion species tuned to different energies, producing a range of linear energy transfer (LET) values for that ion. Numerous MOSFETs were characterized to identify the onset of ion-induced dielectric breakdown. These data along with previously taken data demonstrated that the ion-induced dielectric breakdown cannot be adequately described in terms of LET, but is better described in terms of atomic number (Z). Based upon these observations, a new semi-empirical expression is presented describing the critical ion-induced breakdown response in terms of Z instead of LET. This expression is shown to be a better single event gate rupture model of the capacitor response.

Evaluation of proposed hardness assurance method for bipolar linear circuits with enhanced low dose rate sensitivity (ELDRS)

Abstract: Data are presented on several low dose rate sensitive bipolar linear circuits to evaluate a proposed hardness assurance method. The circuits include primarily operational amplifiers and voltage comparators with a variety of sensitive components and failure modes. The proposed method, presented in 1997, includes an option between a low dose rate test at 10 mrd(Si)/s and room temperature and a 100/spl deg/C elevated temperature irradiation test at a moderate dose rate. The results of this evaluation demonstrate that a 10 mrd(Si)is test is able (in ail but one case) to bound the worst case response within a factor of 2. For the moderate dose rate, 100/spl deg/C test the worst case response is within a factor of 3 for 8 of 11 circuits, and for some circuits overpredicts the low dose rate response. The irradiation bias used for these tests often represents a more degrading bias condition than would be encountered in a typical space system application.

An improved method for incorporating magnetic saturation in the q-d synchronous machine model

Abstract: An improved technique for incorporating saturation into the q-d axis model (Park's model) of a synchronous machine is proposed. By choosing magnetizing flux linkage as a state variable, iterative procedures required by traditional methods are avoided. The saturation function is represented by an arctangent function which has some distinct advantages over polynomial representations and look-up tables. In particular, the parameters of the proposed function all have physical significance and the proposed function is defined over an infinite range of flux linkage. The model is verified for steady-state and transient conditions using a laboratory synchronous machine-rectifier system similar to those commonly used for naval and aerospace power generation.

Helicopter Rotor System Fault Detection Using Physics-Based Model and Neural Networks

Abstract: A comprehensive physics-based model of the helicopter rotor in forward flight is used to analyze the impact of selected faults on rotor system behavior. The rotor model is based on finite elements in space and time. The helicopter rotor model is used to develop a neural network-based damage detection methodology. Simulated data from the rotor system are contaminated with noise and used to train a feedforward neural network using backpropogation learning. Cases considered for training and testing the neural network include both single and multiple faults on the damaged blade. Results show that the neural network can detect and quantify both single and multiple faults on the blade from noise-contaminated simulated vibration and blade response test data. For accurate estimation of type and extent of damages, it is important to train the neural networks with noise-contaminated response data.

Statistical description of monopulse parameters for tracking Rayleigh targets

Abstract: The conditional probability density function (pdf) is developed for each monopulse measurement of a Rayleigh target by conditioning the pdf of the complex monopulse ratio on the measured amplitude of the sum signal. The conditional pdf is used to develop the conditional Cramer-Rao Lower Bound (CRLB) for any unbiased estimator of the direction-of-arrival (DOA). Conditional maximum likelihood (CML) and conditional method of moments (CMM) estimators of the DOA are developed along with estimates of the variances associated with the monopulse ratio and DOA estimate. Using simulation results, the performances of the CML and CMM estimators of the DOA are compared with the performance of standard monopulse ratio and the performances of the variance estimators are also studied.

An investigation of the spatial location of proton-induced traps in SiGe HBTs

Abstract: The effects of 46 MeV proton irradiation induced trap generation and its impact on the electrical characteristics of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) from an advanced ultrahigh vacuum/chemical vapor deposition (UHV/CVD) SiGe BiCMOS technology are examined and discussed for the first time. At proton fluences as high as 10/sup 14/ p/cm/sup 2/ the peak current gain of the devices degraded by less than 8% compared to the pre-irradiated samples. The maximum oscillation frequency and cutoff frequency of the SiGe HBTs showed only minor degradation after 10/sup 14/ p/cm/sup 2/. Calibration of 2-D device simulation (MEDICI) to measured data in both forward and inverse modes of operation was used to infer the spatial location of the proton-induced traps. Traps in the collector-base space charge region appear as generation/recombination (G/R) centers in the inverse emitter-base region and are the result of displacement damage. Traps at the emitter-base spacer oxide interface appear as G/R centers in the forward emitter-base space charge region and are the result of ionization damage. Taken together, these results suggest that UHV/CVD SiGe HBT technology is robust to proton fluences at least as high as 10/sup 13/ p/cm/sup 2/ without radiation hardening.

Optimal Design of Integrated Missile Guidance and Control

Abstract: Tactical ballistic missiles (TBM) target may experience severe spiral maneuvers as they reenter the earth's atmosphere due to a configurational asymmetry To hit these targets, the interceptor must possess extremely fast maneuver response characteristics Before 10 sees to go optimal integrated guidance and control (OIGC) is slightly better than a conventional autopilot From 2 to 10 sees OIGC is much better than a conventional autopilot in closing up trajectories However, with 2 sees to go, OIGC uses up full authority and with the aerodynamic surfaces alone may not catch the tactical ballistic missile target Therefore, there is a need for thrusters In this paper, a blending mechanism of optimal integrated guidance and control (OIGC) and fuzzy logic controlled thruster is developed for a skidto-turn missile to improve the missile interception performance OIGC is an innovative approach to designing guidance and control laws The OIGC approach combines the guidance law and autopilot designs into one framework so that the end-game parameters can be accounted for in the control gains This design augmentation has the merits of optimizing the interactions between the guidance dynamics and control dynamics, leading to a reduced miss distance Fuzzy logic control is used to determine the magnitude and direction of the thrust As a result, the blending control of the OIGC controlled aerodynamic surface and the fuzzy logic controlled thruster is specifically investigated A 6DOF nonlinear missile model is

Identification of man-made regions in unmanned aerial vehicle imagery and videos

Abstract: Details work in our group on the use of low-level features for the identification of man-made regions in unmanned aerial vehicle (UAV) imagery. The feature sets that we have examined include classical statistical features such as the coefficient of variation in a window about a pixel, locally computed fractal dimension, and fractal dimension computed in the presence of wavelet boundaries. We discuss these techniques of feature extraction along with our approach to the classification of the features. Our classification work has focused on the use of a semiparametric probability density estimation technique. In addition, we present classification results for region of interest identification based on a set of test images from an UAV test flight.

SLIGA Based underwater weapon safety and arming system

Abstract: The Naval Surface Warfare Center, Indian Head Division (NSWCIHD) is applying microelectromechanical system (MEMS) technology to underwater weapon Safety and Arming (S&A) system development. MEMS technology provides an opportunity to develop a miniaturized S&A system that is more sophisticated with improved safety and reliability at a lower cost compared to current systems. An S&A system prevents premature initiation of the weapon while reliably ensuring initiation at the appropriate time. An S&A system uses multiple sensors and devices. In comparison with other weapon S&A systems, a critical aspect of underwater weapon S&A systems is the mechanical interlock system utilizing actuators and mechanical sensors. This paper describes the design, development and fabrication of S&A SLIGA device prototypes and of a SLIGA based S&A system. NSWCIHD worked with members of the HI-MEMS Alliance during design, development and fabrication. Advancements achieved by the HI-MEMS Alliance and SLIGA S&A design issues are discussed.

Ballistic Impact Resistance of SMA and Spectra Hybrid Graphite Composites

Abstract: The effect of adding small amounts of high strain hybrid components on the impact resistance of graphite epoxy composites subjected to projectiles traveling at ballistic velocities (greater than 900 ft/sec) has been studied. The hybrid components tested include superelastic shape memory alloy (SMA) and a high performance extended chain polyethylene (ECPE) known as Spectram. In all cases, the embedded SMA fibers were pulled through the graphite without straining to their full potential. It is believed that this is due to high strain rate effects coupled with a strain mismatch between the tough SMA and the brittle epoxy resin. However, a significant increase in energy absorption was found by adding ECPE and ECPE/SMA layers to the backface of the composite.

Performance Deterioration Modeling in Aircraft Gas Turbine Engines

Abstract: Steady-state performance models can be used to evaluate a new engine`s baseline performance. As a gas turbine accumulates operating time in the field, its performance deteriorates due to fouling, erosion, and wear. This paper presents the development of a model for predicting the performance deterioration of aircraft gas turbines. The model accounts for rotating component deterioration based on the aircraft mission profiles and environmental conditions and the engine`s physical and design characteristics. The methodology uses data correlations combined with a stage stacking technique for the compressor and a tip rub model, along with data correlations for the turbine to determine the amount of performance deterioration. The performance deterioration model interfaces with the manufacturer`s baseline engine simulation model in order to create a deteriorated performance model for that engine.

On optimal synchronous and asynchronous track fusion

Abstract: In practice, multisensor systems use dissimilar sensors that may have different data rates. Such sensors may also have inherent delays due to multitasking as well as communication delays between the sensor platform and a remote central processing site. Track fusion algorithms are presented that are valid for asynchronous sensors (the sensors have different data rates and different delays) as well as synchronous sensors (all of the sensors take measurements at the same time and the same rate with no delays). The asynchronous track fusion problem is formulated and solved first. Then the synchronous track fusion problem is obtained as a special case of the asynchronous one. Finally, using simulated target tracks, the performance of the asynchronous track fusion (ASTF) algorithm is analyzed and compared to an existing track fusion algorithm. Different sensor data rates and communication delays are used in the simulations. It is found that the ASTF algorithm outperforms its counterpart and is able to handle relatively large communication delays. The results presented set the foundation for deriving optimal track fusion algorithms when taking into account realistic constraints such as sensors with different data rates and different communication and/or processing delays. The results can also be used as a benchmark to evaluate existing suboptimal track fusion algorithms.

Modeling of Anodic Current Transients Resulting from Oxide Rupture of Plastically Strained β + α Titanium

Abstract: The film rupture behavior on dynamically strained Ti-15 Mo-3 Nb-3 Al exposed to 0.6 M NaCl has been examined by rapid data acquisition of anodic current transients. The anodic current transients resulted from dislocation intersection of the passive film, followed by film rupture, bare surface dissolution, and repassivation. The transient morphology during dynamic straining differs from that generated via conventional depassivation techniques (i.e., manual scratch and fractured thin film depassivation) which incorporate an electrode that does not experience active plastic straining following depassivation. During conventional depassivation testing, current transients increase relatively rapidly and decay with an approximately linear slope on the log i-log t plot. In contrast, the transients acquired during dynamic straining are characterized by a relatively slow current increase and a nonlinear current decay on the log i-log t plot. This nonlinear decay is not attributable to ohmic or capacitive effects. Film rupture results from surface intersection of a superdislocation comprised of individual dislocations which are spatially and temporally separated. Current transient modeling of superdislocation intersection agrees qualitatively with that observed experimentally. It is concluded that the repassivation behavior determined by conventional depassivation techniques may not be relevant for modeling of environmentally assisted cracking of dynamically strained electrodesmore » in some cases.« less

Signal processing of the echo signatures returned by submerged shells insonified by dolphin "clicks:" Active classification

Abstract: A large set of dolphin-emitted acoustic pulses (“echolocation clicks”) have been examined, which were reflected from various elastic shells that were suspended, underwater, 4.5 m in front of the animal in a large test site in Kaneohe Bay, Hawaii. A carefully instrumented analog-to-digital system continuously captured the emitted clicks and also the returned, backscattered echoes (A/D conversion at 500 kHz). Using standard conditioning techniques and food reinforces, the dolphin is taught to push an underwater paddle when the “correct” target—the one he has been trained to identify—is presented to him. He communicates his consistently correct identifying choices in this manner. Many echoes returned by three types of cylindrical shells in both the time and frequency domains as well as in the joint time-frequency (t-f) domain, by means of Wigner-type distributions have been examined. It will be shown exactly how specific features observable in these displays are directly related to the physical characteristics of the shells. This processing takes advantage of certain fundamental resonance principles to show which echo features contain information about the size, shape, wall thickness, and material composition of both the shell and its filler substance. In the same fashion that these resonance features give the identifying characteristics of each shell, it is believed they may also give them to the dolphin. These echo features may allow him to extract the target properties by inspection without any need for computations. It is claimed that this may be the fundamental physical explanation of the dolphin’s amazing target ID feats, upon which they base their recognition choices. This claim may be substantiated by the detailed analysis of many typical echoes returned by various shells, when they are interrogated by several dolphins. Thus far, this analysis of many echoes from many shells has only been carried out for a single dolphin.

Comparison of Four Filtering Options for a Radar Tracking Problem

Abstract: : Four different filtering options are considered for the problem of tracking an exoatmospheric ballistic target with no maneuvers The four filters are an alpha-beta filter, an augmented alpha-beta filter, a decoupled Kalman filter, and a fully-coupled extended Kalman filter These filters are listed in the order of increasing computational complexity All of the filters can track the target with some degree of accuracy While the pure alpha-beta filter appreciably lags the other filters in performance for this problem, its augmented version is very competitive with the extended Kalman filter under benign conditions Perhaps the most surprising result is that under all conditions examined, the decoupled (linear) Kalman filter, which is at least an order of magnitude less computationally complex, performs nearly identical to the coupled, extended Kalman filter Four different filtering options are considered for the problem of tracking an exoatmospheric ballistic target with no maneuvers The four filters are an alpha-beta filter, an augmented alpha-beta filter, a decoupled Kalman filter, and a fully-coupled extended Kalman filter These filters are listed in the order of increasing computational complexity All of the filters can track the target with some degree of accuracy While the pure alpha-beta filter appreciably lags the other filters in performance for this problem, its augmented version is very competitive with the extended Kalman filter under benign conditions Perhaps the most surprising result is that under all conditions examined, the decoupled (linear) Kalman filter, which is at least an order of magnitude less computationally complex, performs nearly identical to the coupled, extended Kalman filter

Synthesis and characterization of 5-substituted 1,3-diazacyclohexane derivatives

Abstract: Three synthetic routes to 5-substituted 1,3-diazacyclohexane derivatives 1 are reported. The first method involves treatment of 1,3-diaminopropan-2-ol 2 with paraformaldehyde to yield 5-hydroxy-1,3-diazacyclohexane 3. A second method is based on the condensation of 2-bromo-2-nitro-1,3-propanediol with tert-butylamine and formaldehyde to yield 1,3-di-tert-butyl-5-bromo-5-nitro-1,3-diazacyclohexane 22. The third method relies on the cycloalkylation of methylenebisacetamide with 3-chloro-2-chloromethyl-2-propene to provide 5-exomethylene-1,3-diacetyl-1,3-diazacyclohexane 28. Functional group manipulations of 3, 22, and 28 provide a number of novel 1,3-diazacyclohexanes functionalized at the 5-position.

Evaporative Compressor Cooling for NOx Suppression and Enhanced Engine Performance for Naval Gas Turbine Propulsion Plants

Abstract: Water, in the liquid or vapor phase, injected at various locations into the gas turbine cycle has frequently been employed to improve engine performance while simultaneously reducing NOx emissions. Commercial steam injected gas turbines have been designed to inject small amounts of steam (less than 15% of air flow), generated in a heat recovery boiler, into or downstream of the combustor. Recently, it has been proposed to inject larger amounts of water (as high as 50% of air flow) and operate combustors near stoichiometric conditions. All these methods increase turbine mass flow rate without increasing air flow rate and consequently increase specific power. The increase in specific power for naval applications means smaller intake and exhaust stacks and therefore less impact on topside space.The present paper presents a new concept, in naval propulsion plants, to decrease NOx production and increase specific power with a water fog (droplet spray) injected (WFI) directly into the inlet of the engine compressor. The simulated performance of a simple-cycle gas turbine engine using WFI is reported. The paper describes the computer model developed to predict compressor performance resulting from the evaporation of water passing through the stages of an axial flow compressor. The resulting effects are similar to those of an intercooled compressor, without the complications due to the addition of piping, heat exchangers, and the requirement for a dual spool compressor. The effects of evaporative cooling on compressor characteristics are presented. These results include compressor maps modified for various water flow rates as well as estimates of the reductions in compression work and compressor discharge temperature.These modified compressor performance characteristics are used in the engine simulation to predict how a WFI engine would perform under various water injection flow rates. Estimates of increased output power and decreased air flow rates are presented.Copyright © 1998 by ASME

Investigations to extend the lower frequency limit of reverberation chambers

Abstract: As the use of reverberation chambers for electromagnetic effects testing increases there is a growing interest in lowering the minimum useable frequency in a specific chamber. This paper describes a series of measurements to investigate the field uniformity of reverberation chambers in the frequency region below which they have been considered useable. The measurements are part of a continuing program to characterize the overall field uniformity of reverberation chambers as a function of frequency. Measurements were taken using the large reverberation chamber (10.82 m/spl times/5.18 m/spl times/3.96 m) at the Naval Surface Warfare Center, Dahlgren Division at frequencies from 80 MHz to 200 MHz. The commonly accepted guideline yields a lowest useable frequency of 110 MHz for the large chamber. Measurements were also obtained using a small reverberation chamber (1.8 m/spl times/1.2 m/spl times/0.8 m) over 100 MHz frequency bands starting at 300, 400 and 730 MHz. The predicted lowest frequency for the small chamber is 556 MHz. The results suggest that the commonly accepted guideline for defining the lowest useable frequency needs to be revised. A performance based criterion using measured uniformity data appears to have merit for defining the lowest useable frequency for typical operations. The results also suggest that useful testing can be conducted at frequencies below the minimum useable frequency as defined by the commonly accepted guidelines.

Stochastic resonance in mammalian neuronal networks.

Abstract: We present stochastic resonance observed in the dynamics of neuronal networks from mammalian brain. Both sinusoidal signals and random noise were superimposed into an applied electric field. As the amplitude of the noise component was increased, an optimization (increase then decrease) in the signal-to-noise ratio of the network response to the sinusoidal signal was observed. The relationship between the measures used to characterize the dynamics is discussed. Finally, a computational model of these neuronal networks that includes the neuronal interactions with the electric field is presented to illustrate the physics behind the essential features of the experiment.