Showing papers by "Naval Surface Warfare Center published in 2004"
TL;DR: In this article, a compositional approach was proposed to improve the oxidation resistance of ZrB2-SiC and other non-oxide materials to at least 1600°C by compositional modifications which promote immiscibility in the glass component of the scale.
Abstract: Hypersonic flight involves extremely high velocities and gas temperatures with the attendant necessity for thermal protection systems (TPS). New high temperature materials are needed for these TPS systems. A systematic investigation of the thermodynamics of potential materials revealed that low oxidation rate materials, which form pure scales of SiO2, Al2O3, Cr2O3, or BeO, cannot be utilized at temperatures of 1800°C (and above) due to disruptively high vapor pressures which arise at the interface of the base material and the scale. Vapor pressure considerations provide significant insight into the relatively good oxidation resistance of ZrB2- and HfB2-based materials at 2000°C and above. These materials form multi-oxide scales composed of a refractory crystalline oxide (skeleton) and a glass component, and this compositional approach is recommended for further development. The oxidation resistance of ZrB2-SiC and other non-oxide materials is improved, to at least 1600°C, by compositional modifications which promote immiscibility in the glass component of the scale. Other candidate materials forming high temperature oxides, such as rare earth compounds, are largely unexplored for high temperature applications and may be attractive candidates for hypersonic TPS materials.
829 citations
TL;DR: A force model for needle insertion and experimental procedures for acquiring data from ex vivo tissue to populate that model are presented and the effects of needle diameter and tip type on insertion force are characterized.
Abstract: The modeling of forces during needle insertion into soft tissue is important for accurate surgical simulation, preoperative planning, and intelligent robotic assistance for percutaneous therapies. We present a force model for needle insertion and experimental procedures for acquiring data from ex vivo tissue to populate that model. Data were collected from bovine livers using a one-degree-of-freedom robot equipped with a load cell and needle attachment. computed tomography imaging was used to segment the needle insertion process into phases identifying different relative velocities between the needle and tissue. The data were measured and modeled in three parts: 1) capsule stiffness, a nonlinear spring model; 2) friction, a modified Karnopp model; and 3) cutting, a constant for a given tissue. In addition, we characterized the effects of needle diameter and tip type on insertion force using a silicone rubber phantom. In comparison to triangular and diamond tips, a bevel tip causes more needle bending and is more easily affected by tissue density variations. Forces for larger diameter needles are higher due to increased cutting and friction forces.
777 citations
TL;DR: Large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species differed substantially from those of amorphous Se(0) formed by chemical oxidation of H2Se and of black, vitreous Se(*) formed chemically by reduction of selenite with ascorbate.
Abstract: Certain anaerobic bacteria respire toxic selenium oxyanions and in doing so produce extracellular accumulations of elemental selenium [Se(0)]. We examined three physiologically and phylogenetically diverse species of selenate- and selenite-respiring bacteria, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter shriftii, for the occurrence of this phenomenon. When grown with selenium oxyanions as the electron acceptor, all of these organisms formed extracellular granules consisting of stable, uniform nanospheres (diameter, approximately 300 nm) of Se(0) having monoclinic crystalline structures. Intracellular packets of Se(0) were also noted. The number of intracellular Se(0) packets could be reduced by first growing cells with nitrate as the electron acceptor and then adding selenite ions to washed suspensions of the nitrate-grown cells. This resulted in the formation of primarily extracellular Se nanospheres. After harvesting and cleansing of cellular debris, we observed large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species. The spectral properties in turn differed substantially from those of amorphous Se(0) formed by chemical oxidation of H(2)Se and of black, vitreous Se(0) formed chemically by reduction of selenite with ascorbate. The microbial synthesis of Se(0) nanospheres results in unique, complex, compacted nanostructural arrangements of Se atoms. These arrangements probably reflect a diversity of enzymes involved in the dissimilatory reduction that are subtly different in different microbes. Remarkably, these conditions cannot be achieved by current methods of chemical synthesis.
421 citations
TL;DR: In this article, an empirical model of the surface pressure spectrum beneath a two-dimensional, zero-pressure-gradient boundary layer is presented that is based on the experimental surface pressure spectra measured by seven research groups.
Abstract: An empirical model of the surface pressure spectrum beneath a two-dimensional, zero-pressure-gradient boundary layer is presented that is based on the experimental surface pressure spectra measured by seven research groups. The measurements cover a large range of Reynolds number, 1.4 × 10 3 < Reθ < 2.34 × × 10 4 . The model is a simple function of the ratio of the timescales of the outer to inner boundary layer. It incorporates the effect of Reynolds number through the timescale ratio and compares well to experimental data. It is proposed that the effect of Reynolds number is more aptly described as the effect of the range of relevant scales. Spectral features of the experimental data and the scaling behavior of the surface pressure spectrum are also discussed.
356 citations
TL;DR: In this paper, the authors used finite element models to predict material response in internally heated nozzle tests, and the results of the modeling suggest that HfB2 should survive the high thermal stresses generated during the nozzle test primarily because of its superior thermal conductivity.
Abstract: The thermal conductivity, thermal expansion, Young's Modulus, flexural strength, and brittle-plastic deformation transition temperature were determined for HfB2, HfC0.98, HfC0.67, and HfN0.92 ceramics. The mechanical behavior of αHf(N) solid solutions was also studied. The thermal conductivity of modified HfB2 exceeded that of the other materials by a factor of 5 at room temperature and by a factor of 2.5 at 820°C. The transition temperature of HfC exhibited a strong stoichiometry dependence, decreasing from 2200°C for HfC0.98 to 1100°C for HfC0.67 ceramics. The transition temperature of HfB2 was 1100°C. Pure HfB2 was found to have a strength of 340 MPa in 4 point bending, that was constant from room temperature to 1600°C, while a HfB2 + 10% HfCx had a higher room temperature bend strength of 440 MPa, but that dropped to 200 MPa at 1600°C. The data generated by this effort was inputted into finite element models to predict material response in internally heated nozzle tests. The theoretical model required accurate material properties, realistic thermal boundary conditions, transient heat transfer analysis, and a good understanding of the displacement constraints. The results of the modeling suggest that HfB2 should survive the high thermal stresses generated during the nozzle test primarily because of its superior thermal conductivity. The comparison the theoretical failure calculations to the observed response in actual test conditions show quite good agreement implying that the behavior of the design is well understood.
233 citations
TL;DR: An amplitude modulation (AM) detector is developed to identify single-point defects in rolling element bearings and detect the bearing fault while it is still in an incipient stage of development.
Abstract: The purpose of this research is to identify single-point defects in rolling element bearings. These defects produce characteristic fault frequencies that appear in the machine vibration and tend to modulate the machine's frequencies of mechanical resonance. An amplitude modulation (AM) detector is developed to identify these interactions and detect the bearing fault while it is still in an incipient stage of development (i.e., to detect the instances of AM when the magnitude of the characteristic fault frequency itself is not significant). Use of this detector only requires machine vibration from one sensor and knowledge of the bearing characteristic fault frequencies. Computer simulations as well as machine vibration data from bearings containing outer race faults are used to confirm the proficiency of this proposed technique.
223 citations
TL;DR: In this paper, the Young's modulus was 65 GPa in the loading direction with a Poisson's ratio of 0.45 on the (0,0,1) major face.
207 citations
TL;DR: A modification of the Susceptible–Infected–Susceptible (SIS) epidemiological model is considered as a model of computer virus spread, which includes a reintroduction parameter, which models the rerelease of a computer virus, or the introduction of a new virus.
146 citations
TL;DR: In this article, a research effort funded through the U.S. Defense Advanced Research Projects Agency and Naval Air System Command aimed at enhancing prognostic accuracy through more advanced physics-of-failure modeling and intelligent utilization of relevant diagnostic information.
Abstract: Technology that enables failure prediction of critical machine components (prognostics) has the potential to significantly reduce maintenance costs and increase availability and safety. This article summarizes a research effort funded through the U.S. Defense Advanced Research Projects Agency and Naval Air System Command aimed at enhancing prognostic accuracy through more advanced physics-of-failure modeling and intelligent utilization of relevant diagnostic information. H-60 helicopter gear is used as a case study to introduce both stochastic sub-zone crack initiation and three-dimensional fracture mechanics lifing models along with adaptive model updating techniques for tuning key failure mode variables at a local material/damage site based on fused vibration features. The overall prognostic scheme is aimed at minimizing inherent modeling and operational uncertainties via sensed system measurements that evolve as damage progresses.
131 citations
TL;DR: A review of constitutive models based on the mechanics of dislocation motion is presented, with focus on the models of Zerilli and Armstrong and the critical influence of Armstrong on their development as mentioned in this paper.
Abstract: A review of constitutive models based on the mechanics of dislocation motion is presented, with focus on the models of Zerilli and Armstrong and the critical influence of Armstrong on their development. The models were intended to be as simple as possible while still reproducing the behavior of real metals. The key feature of these models is their basis in the thermal activation theory propounded by Eyring in the 1930’s. The motion of dislocations is governed by thermal activation over potential barriers produced by obstacles, which may be the crystal lattice itself or other dislocations or defects. Typically, in bcc metals, the dislocation-lattice interaction is predominant, while in fcc metals, the dislocation-dislocation interaction is the most significant. When the dislocation-lattice interaction is predominant, the yield stress is temperature and strain rate sensitive, with essentially athermal strain hardening. When the dislocation-dislocation interaction is predominant, the yield stress is athermal, with a large temperature and rate sensitive strain hardening. In both cases, a significant part of the athermal stress is accounted for by grain size effects, and, in some materials, by the effects of deformation twinning. In addition, some simple strain hardening models are described, starting from a differential equation describing creation and annihilation of mobile dislocations. Finally, an application of thermal activation theory to polymeric materials is described.
106 citations
TL;DR: Structural changes in 1,1-diamino-2,2-dinitroethylene (DADNE, FOX-7) compressed to high pressure in diamond anvil cells were investigated using angle-dispersive x-ray diffraction analysis, Raman spectroscopy, and optical polarizing microscopy.
Abstract: Structural changes in 1,1-diamino-2,2-dinitroethylene (DADNE, FOX-7) compressed to high pressure in diamond anvil cells were investigated using angle-dispersive x-ray diffraction analysis, Raman spectroscopy, and optical polarizing microscopy. The x-ray results show several changes above 1 GPa. When the x-ray data are indexed according to the ambient-pressure structure, DADNE shows anisotropic compression, with higher compression along the b axis than along the a or c axis. An ambient-temperature isothermal equation of state of DADNE was generated from these data. In addition, the experimentally obtained Raman spectra were matched with vibrational normal modes calculated using quantum chemistry calculations. The shifts in vibrational modes indicate changes in H-wagging vibrations with pressure.
TL;DR: The results indicate that the friction disk machine may serve as a valuable tool for investigating the effects of experimental coatings, both antifouling and fouling-release, on microfouled and associated drag penalties.
Abstract: Fouling by biofilms significantly increases frictional drag on ships' hulls. A device, the friction disk machine, designed to measure torque on rotating disks, was used to examine differences among experimental fouling-release coatings in the drag penalty due to accumulated biofilms. Penalties were measured as the percentage change in the frictional resistance coefficient Cf. Drag penalties due to microfouling ranged from 9% to 29%, comparable to previously reported values. An antifouling control coating showed a smaller drag penalty than the fouling-release coatings. There were also significant differences among the fouling-release coatings in drag due to biofilm formation. These results indicate that the friction disk machine may serve as a valuable tool for investigating the effects of experimental coatings, both antifouling and fouling-release, on microfouling and associated drag penalties.
05 Jan 2004
TL;DR: In this paper, an experimental investigation was conducted in a water tunnel to explore the application of Coanda-effect circulation control to low aspect ratio wings for high lift control surfaces (appendages) on underwater naval vehicles.
Abstract: : An experimental investigation was conducted in a water tunnel to explore the application of Coanda-effect circulation control to low aspect ratio wings. The facility was the Large Cavitation Channel in Memphis, TN. The intended application is to high-lift control surfaces (appendages) on underwater naval vehicles. Test results are interpreted in light of both theory and the extensive experience with circulation control (CC) technology at NSWCCD. The semi-span wing test model with a taper ratio of 0.76 was mounted on a load cell; a reflection plane provided for an effective aspect ratio of 2. Dual upper/lower trailing edge tangential jet slots were incorporated for bi-directional force generation. Findings include: finite-span effects on CC augmented lift are consistent with the effects on conventional lift-due-to-angle-of-attack, and cavitation in the Coanda wall jet region does not result in jet detachment or an abrupt lift stall. Wing lift augmentation ratios are up to 36 and meet expectations. Unexpected virtues of a dual-slotted configuration were found that enhance the value of CC to ship and VSTOL aircraft applications. A small flow from the second slot will significantly extend the lift capability beyond that of single slot operation by preventing what is believed to be the adverse effects of excessive turning of the wall jet at high momentum coefficients. Dual slot flow produces a merger of the two wall jets into a free planar jet that enables static thrust vectoring of the jet momentum flux over the full 0-360 degree range. This steerable-jet provides a jet-flap mode of lift development for use at very low vehicle speeds, as an extension of the high efficiency CC mode.
TL;DR: In this article, the presence of microstructural bands in AL-6XN stainless steel plate has been examined, which consist of a high density of second-phase particles, and range in thickness up to 300 µm, and are continuous over lengths up to 50 mm.
Abstract: The presence of microstructural bands in AL-6XN stainless steel plate has been examined. The bands, which consist of a high density of second-phase particles, are located near the midthickness of the plate, range in thickness up to 300 µm, and are continuous over lengths up to 50 mm. Chemical analyses of the microstructural bands indicate elevated levels of chromium and molybdenum, while orientation imaging microscopy identified primarily sigma-phase particles within the bands; a small volume fraction of chi phase was also found. Tensile specimens oriented in the short transverse direction of the plate show low ductility and exhibit a large variation in failure strains, depending on the continuity of the bands as well as the presence of large precipitate particles within the bands. When oriented in either the longitudinal or the long transverse direction of the plate, circumferentially notched tensile specimens exhibit comparatively high ductility, although at high stress triaxialities, the material was susceptible to specimen splitting parallel to the tensile axis due to cracking along microstructural bands.
TL;DR: In this paper, a laser forward-transfer and micromachining process was developed to fabricate and optimize mesoscale electrochemical power sources, such as primary Zn-Ag2O and secondary Li-ion microbatteries.
Abstract: A laser forward-transfer and micromachining process has been developed to fabricate and optimize mesoscale electrochemical power sources, such as primary Zn–Ag2O and secondary Li-ion microbatteries. The laser direct-write technique allows for adding, removing and processing the various material systems required for the fabrication of micropower sources on many types of substrates under ambient conditions. In this work, we demonstrate planar zinc–silver oxide alkaline cell configurations with 1.5–1.55 V open-circuit potentials. The 10 mm2 samples show a flat discharge behavior under constant-current loads and capacities of ∼100 μA h cm-2. Stacked Li-ion cells with 3.80-V open-circuit potentials have also been fabricated and continue to operate after 50 charge/discharge cycles. The 9 mm2 samples exhibit capacities of 110 μA h cm-2.
TL;DR: In this article, the total current was divided between the inside, upper/lower, and outside surface based on the results of a current distribution calculation and the diffusion of the magnetic field into each surface was modeled in order to determine the current distribution and the resistive heating.
Abstract: This work presents a model that can be implemented to quickly estimate the resistive heating and the resulting transient temperature response. Quantifying the energy deposited in the rails and implementing an effective thermal management system will be key elements of an effective design for a large-scale electromagnetic launcher. The total current was divided between the inside, upper/lower, and outside surface based on the results of a current distribution calculation. The diffusion of the magnetic field into each surface was modeled in order to determine the current distribution and the resistive heating. Cooling between shots was taken into account by solving the one dimensional transient heat diffusion equation within each surface. Repeating these calculations for a number of discrete segments down the length of the rail enabled the prediction of the total resistive rail heating and the temperature profile along the length of the rail. Experimental tests were conducted that verify the presence of localized heating in the corners of a U-shaped conductor made of 7075 Aluminum. Taking into account the localized resistive heating near the surface of the conductor will become increasingly important with large-scale guns.
TL;DR: In this paper, a range of bore and rail geometries and their effects on key railgun system parameters such as parasitic mass, inductance gradient, linear current density, required pulse forming network (PFN) size, and barrel mass were explored.
Abstract: A large-scale railgun is being considered by the U.S. navy as a future long range (>200 nm) naval weapon system. The notional concept includes a 15 kg projectile with a 2.5 km/sec muzzle velocity. The choice of bore and rail geometry for such a weapon can influence key aspects of the total system design. This study explored a range of bore and rail geometries and looked at their effects on key railgun system parameters such as parasitic mass, inductance gradient, linear current density, required pulse forming network (PFN) size, and barrel mass. Preliminary solid modeling and structural analysis of the integrated launch package was performed in order to quantify parasitic mass. Inductance gradient calculations were based on a current density distribution analysis. A PFN/Launcher numerical simulation model was then used to determine linear current density and PFN size. Finally, barrel mass was estimated by structural analysis based on calculated rail repulsive forces. Trends and sensitivities of the different parameters to changes in the bore and rail geometries are presented and conclusions are given.
TL;DR: The methodology, which is dubbed Integrated Sensing and Processing Decision Trees (ISPDT), optimizes adaptive sequential sensing for scenarios in which sensor and/or throughput constraints dictate that only a small subset of all measurable attributes can be measured at any one time.
Abstract: We introduce a methodology for adaptive sequential sensing and processing in a classification setting. Our objective for sensor optimization is the back-end performance metric-in this case, misclassification rate. Our methodology, which we dub Integrated Sensing and Processing Decision Trees (ISPDT), optimizes adaptive sequential sensing for scenarios in which sensor and/or throughput constraints dictate that only a small subset of all measurable attributes can be measured at any one time. Our decision trees optimize misclassification rate by invoking a local dimensionality reduction-based partitioning metric in the early stages, focusing on classification only in the leaves of the tree. We present the ISPDT methodology and illustrative theoretical, simulation, and experimental results.
TL;DR: In this paper, measurements of the intermodulation distortion as a function of temperature from 1.7 to Tc in Y Ba2Cu3O7−δ are presented.
Abstract: Measurements of the intermodulation distortion (IMD) as a function of temperature from 1.7 K to Tc in Y Ba2Cu3O7−δ are presented. Films of the highest quality show an increase in IMD as the temperature decreases for temperatures below approximately 30 K. Films of lower quality do not show the increase in the temperature range measured. The increase is in qualitative agreement with that predicted by the nonlinear Meissner effect in d-wave superconductors. The temperature dependence of the measurements is compared with a new calculation of the nonlinear penetration depth.
TL;DR: In this paper, the authors measured the 14N NQR line widths in powdered samples of the nitramine explosives hexahydro-1,3,5-trinitro-s-triazine (RDX), octahydroid-1.4,6,8,10,12-hexanitro-2,4, 6,8.8, 10,12, 12hexanitrirophenitro, 2.5, 6.1, 8.6, 10.12, 11.12-hexa
Abstract: A number of factors associated with crystal quality contribute to the nuclear quadrupole resonance (NQR) line width. Imperfections such as dislocations, voids, strain and impurities can be electrical sources that distort the electric field gradient at nearby quadrupolar nuclei and broaden the observed NQR line. We measured the14N NQR line widths in powdered samples of the nitramine explosives hexahydro-1,3,5-trinitro-s-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane and show correlations with sample purity, particle size distribution and density. Cast plastic-bonded explosives containing either RDX or HMX were also studied and their line widths compared with those of the powdered samples.
16 Aug 2004
TL;DR: In this paper, a Global Positioning System (GPS) guided spinning projectile known as the Autonomous Naval Support Round (ANSR) is proposed for development by the US Navy that utilizes the GPS and a gyro-less inertial measurement unit (AO IMU) for guidance and navigation purposes.
Abstract: This paper describes the system design and a preliminary performance assessment of a Global Positioning System (GPS) guided spinning projectile known as the Autonomous Naval Support Round (ANSR). The ANSR is a rolling 5 inch gun launched rocket assisted guided projectile being considered for development by the US Navy that utilizes the GPS and a gyro -less “accelerometer only” inertial measurement unit (AO IMU) for guidance and navigation purposes. The ANSR guidance, navigation and control (GNC) concept (initia lly proposed by NSWC Dahlgren) is based on being able to exploit commercial off the shelf components (COTS) for lower cost, while providing a projectile with an extended range capability. The proposed GNC concept for ANSR is based on using GPS measurement s to provide the onboard guidance system with position and velocity states and using a Forward Integrated Terminal States (FITS) guidance policy to guide the projectile to stationary ground based targets. A traditional Inertial Navigation System (INS) is n ot used. This is in contrast to previous assessment studies which assume an integrated GPS/INS system in a tightly coupled configuration. The ANSR functions with an open loop autopilot that generates deflection commands for a single pair of canards. The pe rformance analysis for this paper is done using a six degree of freedom simulation, and the primary metric used for the terminal navigation performance is the circular error probable (CEP).
TL;DR: The metal borides are obtained in good chemical and ceramic yield upon pyrolysis, and the polymeric precursors obtained through the reaction of borazine with the metal Borohydride exhibit viscosities amenable to use as preceramic binders in powder processing as discussed by the authors.
Abstract: Polymeric precursors to zirconium and hafnium diboride are described. Initial studies concentrated on carbothermal/borothermal reduction of metal alkoxides; however, improved results were obtained from oxide free-precursors prepared from the metal borohydride and borazine. The metal borides are obtained in good chemical and ceramic yield upon pyrolysis, and the polymeric precursors obtained through the reaction of borazine with the metal borohydride exhibit viscosities amenable to use as preceramic binders in powder processing.
09 Nov 2004
TL;DR: In this article, an algorithm for the detection and localization of magnetic targets is described, which uses overlapping segments of magnetic gradient data (which contain more information than more common single-channel magnetometer data) collected from a moving platform to estimate the positions and moments of stationary dipole targets.
Abstract: An algorithm for the detection and localization of magnetic targets is described. The algorithm uses overlapping segments of magnetic gradient data (which contain more information than more common single-channel magnetometer data), collected from a moving platform, to estimate the positions and moments of stationary dipole targets. Effects of platform motion are removed prior to localization. This motion compensation can be performed with attitude information from inertial measurements, if available. Subtracting a least-square fit to measurements from a vector magnetometer that is used as a reference can also perform the compensation. This general reference-subtraction method can be used to remove other forms of noise. In particular, it can be used to remove interference from active noise sources during operation on UUVs. The dipole parameters are estimated with a combination of linear (to find the moments) and nonlinear (to find the positions) least-squares fits. Multiple targets are handled with an iterative scheme, with new targets being successively added until there is no improvement in the fit. The implementation of this algorithm runs in real time, with only a short lag for processing.
TL;DR: Present are the experimental setup with calibration methodology, measurement conditions, and selected radio-frequency forward-scattering (HH polarization) results for the 5/spl deg/ LDA for sea state 0, 3, and 5 sea conditions.
Abstract: A series of low-angle radar measurements were conducted over a large wave pool capable of producing a wide range of scaled sea conditions. The X-band (8-12 GHz) measurements were performed for 1/spl deg/, 3/spl deg/, and 5/spl deg/ look down angles (LDAs) for the HH and VV polarizations. The roughened water simulated a one-dimensional 1/10th-scale Pierson-Moskowitz surface at sea states 0, 3, and 5. The wave profiles were detailed using both ultrasonic point detectors and a laser sheeting technique capable of measuring a cross section of the sea. The compiled data represent the first forward-scattering measurement 1) preformed under a variety of controlled conditions for low grazing angles and 2) with detail profiling of the wave structure syncronized with the radar. Presented are the experimental setup with calibration methodology, measurement conditions, and selected radio-frequency forward-scattering (HH polarization) results for the 5/spl deg/ LDA for sea state 0, 3, and 5 sea conditions.
TL;DR: In this article, a new styrenic monomer, 4-vinylphenoxyphthalonitrile, was synthesized by nucleophilic aromatic substitution of 4vylphenolate onto 4-nitrophthalonitriles.
05 Jan 2004
TL;DR: The design methodology of the proposed microchip is discussed and a smaller scale prototype of the analog emulator that is currently being developed on printed circuit boards (PCBs) is described.
Abstract: This paper is concerned with the development of a fast, programmable, and reconfigurable power system emulator using an analog/mixed-signal VLSI microchip. The proposed microchip is capable of emulating behaviors of large power system networks under various conditions with faster than real-time computation time that is independent of the size of the power system network. The proposed model focuses on static security analysis, where the main objective is to access the existing operating state of the system. If the state is found to be secure, contingency analysis is performed to evaluate system vulnerability and time necessary to obtain such results. This time is compared to traditional computational techniques to evaluate static security of a power system. This paper discusses the design methodology of the proposed microchip and describes a smaller scale prototype of the analog emulator that is currently being developed on printed circuit boards (PCBs).
TL;DR: In this article, the axial flow within the core of a concentrated line vortex is investigated using molecular tagging velocimetry (MTV) and its spatial/temporal characteristics are quantified using the MTV technique.
Abstract: The characteristics of the axial flow within the core of a concentrated line vortex are investigated using molecular tagging velocimetry (MTV). A well-defined array of isolated vortices of alternating sign is generated in the wake of a NACA-0012 airfoil pitching sinusoidally at small amplitude and high reduced frequencies. The circulation and peak vorticity of the vortices are varied by the choice of oscillation frequency. Interaction of these two-dimensional vortices with the walls of the test section generates an axial flow within the vortex cores. The magnitude of the axial flow and its spatial/temporal characteristics are quantified using the MTV technique. Results show that the peak axial flow speeds can be very high, of the order maximum swirl speed of the vortices. The maximum axial speed ratio (maximum axial speed normalized by maximum swirl speed) is found to vary in the range 0.6–1.0 for the parameters investigated here. Initially, the axial flow is spatially confined in isolated structures corresponding to the core of vortices. As the vortex convects downstream, however, the spatial structure of axial flow changes from isolated regions to a continuous region for the highest reduced frequency investigated here. This change in structure is correlated with a significant decrease in the peak axial flow speed.
16 Aug 2004
TL;DR: The present work is motivated by the need to implement nonlinear control system designs synthesized using computer-aided design techniques, and three different discrete-time control system design techniques have been investigated.
Abstract: : Design methods for discrete-time linear control systems have reached an advanced level of maturity. However, the direct design of nonlinear discrete-time control systems remains to be fully developed. Although textbooks are available on nonlinear control system design literature on discrete-time nonlinear control system design is rather sparse. From an applications point-of-view, discrete-time designs are important because most controllers are implemented using digital computers. Design techniques of interest in this paper are those that permit the synthesis of discrete-time controllers for continuous-time nonlinear dynamic systems. The present work is motivated by the need to implement nonlinear control system designs synthesized using computer-aided design techniques6, 7 onboard missiles. Three different discrete-time control system design techniques have been investigated in the present research. All of them are discrete-time analogs of continuous-time nonlinear system design techniques discussed in the literature. The first approach is the discrete-time version of the state-dependent Riccati equation (SDRE) technique discussed in References 8 and 9. The second design technique is a discrete-time version of the recursive backstepping10 methodology, and employs discretized system dynamics. The third technique is the discrete-time version of the feedback linearization design approach. In this last technique, the system dynamics is first transformed into a linear, time-invariant form through the definition of state variable feedback. The transformed model is then converted into discrete-time form by defining sample-holds at the input and the outputs. The discretized is linear model is then used for control system design. All three techniques have been employed for the design of missile flight control systems. Section II will present each of the design techniques in detail.
TL;DR: In this article, the authors investigated the thermal decomposition of 3-nitro-2-4-dihydro-3H-1,2,4-triazol-5-one (NTO) in the temperature interval from 200 °C to 260 C using a glass Bourdon gauge.
Abstract: The kinetics of thermal decomposition of 3-nitro-2,4-dihydro-3H-1,2,4-triazol-5-one (NTO) in the temperature interval from 200 °C to 260 °C was investigated using a glass Bourdon gauge. The overall decomposition reaction includes two distinct stages: the fast first-order decomposition and the subsequent autocatalytic reaction. The importance of the first stage increases with increasing decomposition temperature and decreasing loading density of the Bourdon gauge (m/V). A period of preliminary heating, at a lower temperature, strongly influences the autocatalytic stage when the decomposition is carried out at a higher temperature. In the temperature domain 200–220 °C, the Arrhenius constants of the decomposition reaction are found to be close to the values usually observed for nitrocompounds: E=173 kJ/mol and log10k≈12.5 (s−1). It is shown that a simple model of NTO decomposition based on an autocatalytic reaction of the m-th order can describe the course of the decomposition at high temperature but the m number appears to be excessively high, up to 4. A new model of the decomposition is developed, including an initial monomolecular reaction, decomposition of the crystalline substance, and an autocatalytic reaction of NTO dissolved in liquid decomposition products. This model gives the common order of autocatalysis, m=1.
TL;DR: In this paper, the effect of ionizing radiation on gated lateral bipolar junction transistors (BJTs) was investigated and the primary mechanism for this effect was identified as the change in the charge state of interface traps in the oxide over the base.
Abstract: Ionizing radiation experiments on gated lateral bipolar junction transistors (BJTs) show a broadening in the peak base current profile after irradiation. The primary mechanism for this effect is identified as the change in the charge state of interface traps in the oxide over the base. Simulations and theoretical analysis not only describe the mechanism in detail, but also suggest possible solutions for extracting information from the shape of the profile. The effects of the interface-trap energy distribution are investigated, showing that traps between flatband and threshold contribute to the width of the base-current peak.