Showing papers by "Naval Surface Warfare Center published in 2005"

Energy Release Characteristics of Impact-Initiated Energetic Materials

Abstract: Impact-initiated energetic materials are a class of energetic materials that are formulated to release energy under highly dynamic loads. Under quasi-static or static loads, however, the materials are intended to be inert and carry a material classification of 4.1 flammable solid. In general, these materials are formed by introducing metal powders into a polymer binder but a number of binderless varieties exist (primarily pressed/sintered intermetallics and thermites). Most of the materials are sufficiently insensitive so as not to produce a self-sustaining reaction; as such, they require the mechanical work of a high-strain-rate plastic deformation process to provide the energy required to drive the reaction. Traditional initiation techniques such as exploding bridge wires or flame initiation are not sufficient to maintain a reaction in this class of materials. This paper presents a brief overview of the energy release characteristics of this class of materials, including a discussion of the material formulations, initiation phenomena, and a discussion of the manner in which the material properties affect the energy release characteristics.

Rubbery Graft Copolymer Electrolytes for Solid-State, Thin-Film Lithium Batteries

Abstract: Graft copolymer electrolytes (GCEs) of poly[(oxyethylene)9 methacrylate]-g-poly(dimethyl siloxane) (POEM-g-PDMS) (70:30) have been synthesized by simple free radical polymerization using a macromonomer route. Differentialscanning calorimetry, transmission electron microscopy, and small angle neutron scattering confirmed the material to be microphase-separated with a domain periodicity of ∼25 nm. Over the temperature range 290 200 cycles) at a discharge rate of 2/3 C and could be cycled (charged and discharged) at subambient temperature (0°C).

A New Deterministic Approach Using Sensitivity Region Measures for Multi-Objective Robust and Feasibilty Robust Design Optimization

Abstract: We present a deterministic non-gradient based approach that uses robustness measures in multi-objective optimization problems where uncontrollable parameter variations cause variation in the objective and constraint values. The approach is applicable for cases that have discontinuous objective and constraint functions with respect to uncontrollable parameters, and can be used for objective or feasibility robust optimization, or both together. In our approach, the known parameter tolerance region maps into sensitivity regions in the objective and constraint spaces. The robustness measures are indices calculated, using an optimizer, from the sizes of the acceptable objective and constraint variation regions and from worst-case estimates of the sensitivity regions'sizes, resulting in an outer-inner structure. Two examples provide comparisons of the new approach with a similar published approach that is applicable only with continuous junctions. Both approaches work well with continuous functions. For discontinuous functions the new approach gives solutions near the nominal Pareto front; the earlier approach does not.

Vented Chamber Calorimetry for Impact-Initiated Energetic Materials

Abstract: Over the past several years, the Naval Surface Warfare Center, Dahlgren Division (NSWC-DD) and its contractors have used vented test chambers to evaluate the performance of impactinitiated energetic materials. These chambers are initially sealed but have a thin steel cover plate through which a test specimen is launched onto a steel anvil on the interior. During this impact process, the test specimen perforates the thin plate and leaves a vent hole through which chamber gases are vented as the reaction takes place on the interior. The test chamber includes a variety of pressure and light measurements to gauge the performance of the test specimen. The quasi-static pressures have been the primary performance metric used to judge the performance of the material; these pressures most directly relate to the material’s ability to damage a target. This paper will derive the fundamental relationships between the peak quasistatic pressure and the total energy deposited into the gas within the chamber, thereby allowing calorimetric measurements using the vented chamber system. Particular attention will be paid to the uncertainties and assumptions associated with this derivation, including assumptions about gas properties, venting from the chamber, and distribution of the energy between kinetic and potential energy in the gas-phase.

Active learning for detection of mine-like objects in side-scan sonar imagery

Abstract: A data-adaptive algorithm is presented for the selection of the basis functions and training data used in classifier design with application to sensing mine-like targets with a side-scan sonar. Automatic detection of mine-like targets using side-scan sonar imagery is complicated by the variability of the target, clutter, and background signatures. Specifically, the strong dependence of the data on environmental conditions vitiates the assumption that one may perform a priori algorithm training using separate side-scan sonar data collected previously. In this paper, a novel active-learning algorithm is developed based on kernel classifiers with the goal of enhancing detection/classification of mines without requiring an a priori training set. It is assumed that divers and/or unmanned underwater vehicles (UUVs) may be used to determine the binary labels (target/clutter) of a small number of signatures from a given side-scan collection. These sets of signatures and associated labels are then used to train a kernel-based algorithm with which the remaining side-scan signatures are classified. Information-theoretic concepts are used to adaptively construct the form of the kernel classifier and to determine which signatures and associated labels would be most informative in the context of algorithm training. Using measured side-looking sonar data, the authors demonstrate that the number of signatures for which labels are required (via diver/UUV) is often small relative to the total number of potential targets in a given image. This procedure designs the detection/classification algorithm on the observed data itself without requiring a priori training data and also allows adaptation as environmental conditions change.

Fault signature modeling and detection of inner race bearing faults

Abstract: This research develops a fault signature model and fault detection scheme for using machine vibration to detect inner race defects. To motivate this research, it is explained and illustrated with experimental results why fault signatures from non-outer race defects (e.g., inner race defects) can be less salient than those from outer race defects. Afterwards, a signal model is presented for the production and propagation of an inner race fault signature; this model is then used to design an inner race fault detection scheme. This scheme examines machine vibration spectra for peaks with phase coupled sidebands occurring at a spacing predicted by the model. The proficiency of this fault detection scheme at detecting inner race bearing faults is then experimentally verified with results from 12 bearings representing varying degrees of fault severity

A Bayesian approach to diagnosis and prognosis using built-in test

Abstract: Accounting for the effects of test uncertainty is a significant problem in test and diagnosis, especially within the context of built-in test. Of interest here, how does one assess the level of uncertainty and then utilize that assessment to improve diagnostics? One approach, based on measurement science, is to treat the probability of a false indication [e.g., built-in-test (BIT) false alarm or missed detection] as the measure of uncertainty. Given the ability to determine such probabilities, a Bayesian approach to diagnosis, and by extension, prognosis suggests itself. In the following, we present a mathematical derivation for false indication and apply it to the specification of Bayesian diagnosis. We draw from measurement science, reliability theory, signal detection theory, and Bayesian decision theory to provide an end-to-end probabilistic treatment of the fault diagnosis and prognosis problem.

Variation among families for characteristics of the adhesive plaque in the barnacle Balanus amphitrite.

Abstract: A quantitative genetics approach was used to examine variation in the characteristics of the adhesive plaque of the barnacle Balanus amphitrite Darwin attached to two silicone substrata. Barnacles settled on silicone polymer films occasionally form thick, soft adhesive plaques, in contrast to the thin, hard plaques characteristic of attachment to other surfaces. The proportion of barnacles producing a thick adhesive plaque was 0.31 for Veridian, a commercially available silicone fouling-release coating, and 0.18 for Silastic T-2, a silicone rubber used for mold-making. For both materials, significant variation among maternal families in the proportion of barnacles producing a thick adhesive plaque was observed, which suggests the presence of genetic variation, or maternal environmental effects, for this plaque characteristic. For the Veridian coating, barnacles expressing the thick adhesive plaque also exhibited significantly reduced tenacity. This represents the first reported case for potential genetic control of intraspecific phenotypic variation in the physical characteristics and tenacity of the adhesive of a fouling invertebrate.

Modeling of Wall Pressure Fluctuations Based on Time Mean Flow Field

Abstract: Time-mean flow fields and turbulent flow characteristics obtained from solving the Reynolds averaged Navier-Stokes equations with a κ-e turbulence model are used to predict the frequency spectrum of wall pressure fluctuations. The vertical turbulent velocity is represented by the turbulent kinetic energy contained in the local flow. An anisotropic distribution of the turbulent kinetic energy is implemented based on an equilibrium turbulent shear flow, which assumes flow with a zero streamwise pressure gradient. The spectral correlation model for predicting the wall pressure fluctuation is obtained through a Green's function formulation and modeling of the streamwise and spanwise wave number spectra

High-power optical microswitch based on direct fiber actuation

Abstract: An optical microswitch is presented for high-power switching applications. The device, capable of switching several watts of optical power, employs large-core multimode fibers to switch output from a laser diode operating at a wavelength of 810 nm. Switching is achieved through the direct deflection of an on-chip fiber using a high force electrothermal actuator. Optical losses in the system are identified, and optical efficiency is predicted and verified with experimental measurements. The switch demonstrated in this work requires an electrical current of 120 mA and has an electrical power consumption of 5280 mW. The optical efficiency is found to be on the order of 88% (0.55–0.60 dB loss) with a maximum power transfer of 1690 mW from a 1930 mW input. Switching time is 40 ms with channel isolation between the on and off states of 55 dB.

Flywheel energy storage system for electric start and an all-electric ship

Abstract: This paper reports on the investigation and development of flywheel technology as energy storage for shipboard zonal power systems. The goal was to determine where energy storage devices could improve operation and/or reduce life-cycle maintenance costs. Applications where energy storage can provide benefits include uninterruptible power to essential loads, "dark" start capability, load leveling, system stability and pulse weapons. A flywheel energy storage system (FESS), with 25 kWh of available energy, is presented as an alternative to the current shipboard electrochemical battery system, highlighting the advantages for and challenges presented by shipboard applications. Flywheel technology overcomes some of the shortcomings of today's energy storage systems by having an extremely high cyclic-life, limited temperature sensitivity, no chemical hazards, charge rate equal to discharge, and reduced weight and space. As gas turbine electric starter development enters into fleet evaluation, FESS may provide dark ship start capability more so than any other systems being investigated. This paper discusses the critical technical challenges of the FESS for shipboard systems, and the steps for future development.

Quasi-static Transduction Characterization of Galfenol

Abstract: The objective of this work is to characterize the magnetoelastic transduction properties of single-crystal and textured polycrystalline Fe-Ga alloys (Galfenol) under controlled mechanical, magnetic, and thermal conditions. Polycrystalline samples of interest include a directionally solidified specimen, which possesses a favorable saturation magnetostriction output, and an extruded specimen, whose magnetostriction properties are significantly reduced by annealing. A brief discussion of the thermally controlled transducer used for the magnetic testing is presented first. Thereafter, the single-crystal response to major-loop cyclic magnetic fields under different temperature and stress conditions, as well as its response to minor-loop cyclic magnetic fields and major-loop cyclic stress are examined. Next, the magnetic and magnetostrictive responses to major-loop cyclic magnetic field conditions are compared for the directionally solidified, extruded, and single-crystal specimens. The paper concludes with a m...

Vertical impulse measurements of mines buried in saturated sand

Abstract: The ultimate aim of our overall task, of which the effort described in this paper is a part, is to be able to model the impulsive output of buried charges and the response of targets of interest. It is not practical or cost-effective to determine the response of all targets of interest to buried charges of all sizes by testing them. In order to have confidence in our models, however, they must be validated by a modest number of tests. A critical element in modelling the response of a target is the ability to model the loading function. The load a buried charge applies to a target above it when the charge detonates can be characterized in terms of the vertical impulse. The vertical impulse is a function of the size of the charge, its depth of burial, and the properties of the soil in which it is buried. The primary objective of the effort described in this paper is to determine the load a known charge places on a non-responding target so the data can be used to validate our models. For model validation, a ...

High Reynolds number experimentation in the US Navy's William B Morgan Large Cavitation Channel

Abstract: The William B Morgan Large Cavitation Channel (LCC) is a large variable-pressure closed-loop water tunnel that has been operated by the US Navy in Memphis, TN, USA, since 1991. This facility is well designed for a wide variety of hydrodynamic and hydroacoustic tests. Its overall size and capabilities allow test-model Reynolds numbers to approach, or even achieve, those of full-scale air- or water-borne transportation systems. This paper describes the facility along with some novel implementations of measurement techniques that have been successfully utilized there. In addition, highlights are presented from past test programmes involving (i) cavitation, (ii) near-zero pressure-gradient turbulent boundary layers, (iii) the near-wake flow characteristics of a two-dimensional hydrofoil and (iv) a full-scale research torpedo.

Nonlinear Meissner effect in a high-temperature superconductor

Abstract: The lowest nonlinear correction to the penetration depth, i.e., the nonlinear Meissner effect, is calculated and compared to data from high-quality $\mathrm{YB}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{u}}_{3}{\mathrm{O}}_{7\ensuremath{-}\mathit{\ensuremath{\delta}}}$ (YBCO) films. The calculation is based on the Green-function formulation of superconductivity, and the data consist of the intermodulation power as function of temperature and circulating power. At a low power level, the calculated temperature dependence compares very well with the data, including the divergence as ${T}^{\ensuremath{-}2}$ at very low temperatures. The calculated power dependence of the nonlinear penetration depth follows the data semiquantitatively and is enhanced due to the $d$-wave symmetry of the order parameter. These results support the assertion that the origin of nonlinearity in high-quality YBCO films is intrinsic. The analysis also implies that the nonlinear corrections to the penetration depth depend primarily on the total current carried by the strip and thus are insensitive to the edges. The comparison of the present approach with an alternative approach, based on quasiparticle backflow, is discussed.

A wireless active sensing system for impedance-based Structural Health Monitoring

Abstract: Deployment of Structural Health Monitoring (SHM) systems for permanent damage detection is limited by the availability of sensor technology. The development of a single board computer system is the focus for initial efforts in realizing a fully self-contained active sensor system utilizing impedance-based SHM. The active sensing system interrogates a structure utilizing a self-sensing actuator and the low cost impedance method, and all the data processing, storage, and analysis is performed at the sensor location. A wireless transmitter is used to communicate the current status of the structure. Piezoelectric-based power harvesting allows the sensing system to be completely self-contained and autonomous. With this new low cost, field deployable impedance analyzer, reliance on traditional expensive, bulky, and power consuming impedance analyzers is no longer necessary. Experimental validation of the prototype is performed on a representative structure and compared to traditional methods of damage detection. The benefits of this new system are discussed, along with current research and the path forward to a complete stand alone SHM system.

Turbulence Correlation Length-Scale Relationships for the Prediction of Aeroacoustic Response

Abstract: Expressions to describe the correlation length scales of turbulent inflow to an aerodynamic body are derived as functions of the classic integral length scale and anisotropy correction factors. These one-point parameters are significantly easier to determine experimentally than traditional correlation-scale measurement techniques, which involve multiple probes at multiple locations. As such correlation scales are necessary to properly estimate the aeroacoustic response of the body, such a technique could have substantial benefit in a wide variety of applications. The approach is applied to a recent experimental study examining the response of a stator downstream of a propeller that is itself ingesting broadband turbulence. Results suggest that the derived expressions not only accurately represent correlation length scales, but also enable the accurate prediction of the acoustic output of the stator.

Initial evaluation of the new real-time tracking gradiometer designed for small unmanned underwater vehicles

Abstract: The shallow water localization of buried mines places increased emphasis on sensor and sensor platform size and maneuverability. The Office of Naval Research (ONR) has funded a number of projects to develop efficient buried minehunting capabilities. In particular, they are supporting the development of two Unmanned Underwater Vehicles (UUVs) designed specifically for shallow water minehunting. In addition, the ONR has funded the development of two magnetic sensors for use on these UUV's. This paper documents the recent progress that has been made in operating one of these sensors, the uuv-Real-time Tracking Gradiometer (uuv-RTG) underwater and in motion. The new uuv-RTG, with a 165 mm baseline, consists of four, 3-axis fluxgate magnetometers, each located within a 3-axis Helmholtz coil. The coils on the fourth magnetometer are not connected to allow its use as a reference sensor that provides magnetic feedback to the other three sensors. The feedback developed by the reference sensor is used to null the signals caused by motion, allowing the three primary sensors to operate at low noise levels in large magnetic fields. These three magnetometers are then used to develop six gradients, five of which are independent. With the appropriate software algorithms, this system is able to provide useful range and bearing to ferromagnetic targets, as well as their magnetic moment. Initial evaluation of RTG technology underwater was accomplished by installing a field prototype RTG (RTG-fp) with a 305 mm baseline, onboard a towed, low mag sled designed by Florida Atlantic University (FAU) for their Buried Object Scanning Sonar (BOSS II). The RTG-fp operating in unison with the BOSS II system on the BOSS sled, provided limited but useful data regarding its performance and ability to be fused with a sonar, such as the BOSS II. Prior to their planned integration in late 2005, the new generation uuv-RTG and the BOSS III are currently undergoing performance testing on individual AUVs called Bluefin 12s. Operating a magnetic sensor onboard a small AUVs such as the 324 mm diameter Bluefin 12 is especially difficult. This is due, not only to the close proximity of the magnetometers to multiple magnetic interference sources that are integral to the vehicle, but also to magnetic interference generated by other sensors that are present and share the same payload section. An extensive noise mitigation package consisting of three, 3-axis magnetometers and 2 current sensors were installed on the Bluefin 12 to mitigate this problem. The uuv-RTG is currently being magnetically characterized. Once the characterization is completed, it will be integrated with BOSS III on a winged version of the Bluefin 12. Here it will be evaluated both independently and in fusion with the BOSS III.

Generalized magnetic gradient contraction based method for detection, localization and discrimination of underwater mines and unexploded ordnance

Abstract: We report significant progress toward full development of a unique magnetic-gradient-tensor-based "scalar triangulation and ranging (STAR)" method for detection, localization and classification (DLC) of magnetic targets. The STAR method converts magnetic tensors to rotationally invariant scalar parameters that are virtually unaffected by the effects of sensing platform motion. Thus, the STAR method is particularly appropriate for magnetic target DLC using highly mobile sensing platforms such as autonomous underwater vehicles (AUV). Prior work has resulted in development of a two-dimensional (2D) magnetic target-homing concept for fully autonomous localization of mines using crawler-type AUVs. However, the simple 2D STAR approach cannot effectively discriminate between magnetic clutter and mine-like target signatures. Improved, 3D simulations demonstrate that the STAR concept can be applied to measurements of the vector positions and dipole signatures of magnetic objects. The new results indicate that an improved STAR system will provide an enhanced capability for discrimination between magnetic clutter and real targets such as magnetic mines and Unexploded Ordnance (UXO). Consequently, further development of the advanced STAR concept will provide high-mobility autonomous sensing platforms (such as AUVs and man-portable systems) with a uniquely effective modality for DLC of magnetic mines and UXO

Analysis of scattering from very large three-dimensional rough surfaces using MLFMM and ray-based analyses

Abstract: Several techniques are considered for the analysis of electromagnetic scattering from rough ocean surfaces. A rigorous Multi-level Fast Multipole Method (MLFMM) is employed, as well as a high-frequency ray-based solution. The MLFMM analysis is implemented in scalable form, allowing consideration of scattering from very large surfaces (in excess of 100/spl lambda//spl times/100/spl lambda/, where A represents the electromagnetic wavelength). Plane-wave incidence is assumed, and a key aspect of the MLFMM study involves investigating techniques for rough-surface truncation. The rough surface is modeled as a target placed in the presence of an infinite half-space background; to minimize edge effects, the surface is smoothly tapered into the planar half space. We also consider the technique of employing a resistive taper on the edges of the rough surface. These two truncation techniques are compared in accuracy, memory requirements (RAM), and in computational time (CPU). The MLFMM results are used to validate an approximate ray-based high-frequency model that allows rapid analysis of large surfaces. The computational results are compared to measured forward-scattering data from scaled laboratory measurements, used to simulate scattering from an ocean surface.

Estimation and verification of radiation induced N/sub ot/ and N/sub it/ energy distribution using combined bipolar and MOS characterization methods in gated bipolar devices

Abstract: Complementary bipolar and MOS characterization techniques, specifically the gate sweep (GS) and sub-threshold sweep (SS), are used to estimate the radiation induced oxide charge (N/sub ot/) and interface trap (N/sub it/) buildup in gated bipolar test devices. The gate sweep and sub-threshold sweep data from recent TID testing of gated lateral PNP devices suggests an asymmetric energy distribution of interface traps after ionizing radiation exposure. Charge pumping (CP) experiments were done on the test devices to estimate the energy distribution of interface traps induced by radiation. The CP results are used in this paper to confirm the analytical findings from the GS and SS techniques and solidify the use of the complementary method as a simple way of determining radiation induced interface trap distribution in gated bipolar devices.

Vibrational Spectroscopic Studies of Alane

Abstract: Alane has been subjected to Raman studies under static compression. The Raman spectra showed four modes, which increased in frequency as pressure was increased from ambient to 6.6 GPa. From the pressure dependence, the pressure coefficient, dνi/dP, for each mode has been estimated and used to evaluate the mode Gruneisen parameter γi for that mode. Independently the thermodynamic Gruneisen parameter γth has also been calculated using the pressure derivative of the isothermal bulk modulus value from the literature. Preliminary infrared spectra were also collected under ambient conditions and are discussed with those reported in the literature for alane polymorphs.

Numerical Simulation of Two- and Three-Dimensional Circulation Control Problems

Abstract: The flows about 2-D and 3-D bluff trailing edge circulation control (CC) airfoils are computed using steady Reynolds Averaged Navier-Stokes (RANS) methods. The 2-D foil is the NCCR 1510-7067 elliptical CC airfoil with circular and logarithmic spiral trailing edge geometries. The free stream Reynolds number, based on chord, is 5.45 × 10 5 , with a free stream Mach number of 0.12. For the circular trailing edge the slot height, blowing rate and angle of attack are varied, while for the logarithmic spiral only the blowing rate is varied. The 3-D foil is a semi-span wing with an elliptical cross section. It is run with a chord-based Reynolds number of 2 × 10 6 and two blowing rates. The 2-D flows are computed using the compressible, segregated solver, Fluent. 2-D results show that the full-Reynolds stress turbulence model (FRSM) predicts the correct jet detachment behavior for the circular trailing edge although the integrated lift forces are consistently underpredicted. The coanda jet detachment point for the logarithmic spiral trailing edge is predicted correctly for a lower blowing rate, but as blowing rate increases, the jet does not detach until it has wrapped around to the pressure side. We show additional 2-D results using mesh refinement via grid adaption and isotropic eddy viscosity turbulence models. The 3-D simulations use the incompressible segregated Fluent solver applying the k −ω SST turbulence model. Results show a slight attachment of the the coanda jet on the pressure side, but the results are generally encouraging.

In Situ X-Ray Absorption Study of Cycled Ambigel V2O5 ∙ nH2O ( n ≈ 0.5 ) Composite Cathodes

Abstract: We examined the oxidation state and local structure of hydrated ambigel V 2 O 5 .0.5H 2 O composite cathodes cycled in a nonaqueous electrolyte lithium cell. Changes in the oxidation state and local structure were monitored by X-ray absorption spectroscopy under in situ conditions. The cathodes had initial discharge capacities in the range 440-480 mAh/g, which correspond to an intercalation of 3.1-3.4 Li per V 2 O 5 .0.5H 2 O. Analyses of X-ray absorption near-edge structure data reveal that the average oxidation state of vanadium for discharged cathodes increased with cycling in the range of 1-17 cycles and then remained unchanged with further cycling. The oxidation state for charged cathodes remained relatively unchanged with cycling in the range of 1-40 cycles. The lack of strong contributions from higher coordination spheres in the Fourier transforms of extended X-ray absorption fine structure spectra of charged and discharged cathodes indicate that the amorphous nature of the material is retained during cycling. However, a significant increase in the amplitude of the V-O contribution is observed with prolonged cycling for both discharged and charged cathodes, which is likely due to the formation of irreversible phases with increased local symmetry for the V-O coordination geometry. The observed results for the ambigel material cycled in the range of 1-16 cycles are consistent with results previously observed for an aerogel material.

Instrument response measurements of ion mobility spectrometers in situ: maintaining optimal system performance of fielded systems

Abstract: Ion Mobility Spectroscopy (IMS) is the most widespread detection technique in use by the military for the detection of chemical warfare agents, explosives, and other threat agents. Moreover, its role in homeland security and force protection has expanded due, in part, to its good sensitivity, low power, lightweight, and reasonable cost. With the increased use of IMS systems as continuous monitors, it becomes necessary to develop tools and methodologies to ensure optimal performance over a wide range of conditions and extended periods of time. Namely, instrument calibration is needed to ensure proper sensitivity and to correct for matrix or environmental effects. We have developed methodologies to deal with the semi-quantitative nature of IMS and allow us to generate response curves that allow a gauge of instrument performance and maintenance requirements. This instrumentation communicates to the IMS systems via a software interface that was developed in-house. The software measures system response, logs information to a database, and generates the response curves. This paper will discuss the instrumentation, software, data collected, and initial results from fielded systems.

Distributed control of hybrid motor drives

Abstract: The hybrid inverter fed motor drive with two cascaded multilevel inverters is an attractive option for high performance high power applications such as naval ship propulsion systems due to a number of unique features. There is a natural split between a higher-voltage lower-frequency "bulk" inverter and a lower-voltage higher-frequency "conditioning" inverter in the cascaded system which matches the availability of semiconductor devices. Furthermore, the bulk inverter may be a commercial-off-the-shelf (COTS) motor drive meaning that only the conditioning inverter needs to be custom made. However, a drive involving a COTS bulk inverter would require a distributed conditioning inverter control which works completely independent of the bulk inverter control. In this paper, a set of distributed control methods are developed for the hybrid inverter drive with cascaded bulk and conditioning inverters, requiring only single dc source. Moreover, a solution to the practical problem of instant synchronization between the two inverters is presented. Laboratory measurements on a 3.7-kW induction motor drive validate the proposed control. Various practical considerations (such as low m-index performance and capacitor precharging options) are discussed and their solutions provided

Corrosion Characterization of Iron-Based High-Performance Amorphous-Metal Thermal-Spray Coatings

Abstract: New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS N06022) in some very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. One of these compositions, SAM1651, is discussed in detail to illustrate the promise of this general class of materials.