CEM Publications

Permanent URI for this collectionhttps://hdl.handle.net/2152/29970


Recent Submissions

Now showing 1 - 20 of 380
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    Higher frequency performance of stress-grading systems for HV large rotating machines
    (Conference on Electrical Insulation and Dielectric Phenomena, 2006) Hebner, R.
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    Electromagnetic and Structural Analyses of Electric Gun and Integrated Launch Package Systems
    (IEEE, 1995-01) Yun, H.D.; Price, J.H.
    The authors describe electromagnetic and structural analyses of electric gun and integrated launch packages. Models presented were developed for the Sabot Launched Electric Gun Kinetic Energy projectile (SLEKE) program and the Cannon Caliber Electromagnetic Launcher (CCEML) program. Analyses were three-dimensional, transient and coupled with thermal calculations including dynamic material properties. In the SLEKE analysis section, the authors focus on the electromagnetic and structural performance of integrated launch packages. SLEKE analyses have been validated by the successful launch of test articles at maximum design levels. CCEML launch package and barrel performance has been studied in detail which benefits from experience gained in the SLEKE program. CCEML analyses presented focus on augmented launcher performance.
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    Discarding Armature and Barrel Optimization for a Cannon Caliber Electromagnetic Launcher System
    (IEEE, 1995-01) Price, J.H.; Yun, H.D.; Cook, K.G.; Kajs, J.P.; Liu, H-P.; Werst, M.D.; Kitzmiller, J.R.
    The authors detail the optimization and baseline design of the discarding metal armature and electromagnetic railgun developed for the US Army Armament Research Development and Engineering Center and US Marine Corps sponsored Cannon Caliber Electromagnetic Launcher program. The primary goals of this program have been to defeat specified targets at 1500 and 3000 m range utilizing an electromagnetic launcher system weighing less than 5000 lb. An optimization algorithm was developed to integrate the armor-penetrating subprojectile with a discarding armature/sabot forming an integrated launch package. This algorithm coupled integrated launch package electromagnetic and structural design requirements to launcher design parameters including rail resistance per unit length and inductance per unit length as a function of launcher rail geometric and structural configurations. Pulsed power supply size and mass requirements were subsequently estimated from launcher performance predictions.
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    Design and Testing of Integrated Metal Armature Sabots for Launch of Armor Penetrating Projectiles from Electric Guns
    (IEEE, 1995-01) Price, J.H.; Yun, H.D.
    Electromagnetic railguns have now demonstrated their potential as an efficient vehicle for the launching of long rod armor penetrating projectiles capable of defeating heavily armored mobile targets. Mid-body-drive, integrated metal sabot/armatures have been developed for launch of tactically configured armor penetrating subprojectiles from an electric gun. The authors discuss the development of five generations of large caliber metal armature and sabot designs for launch of armor-penetrating projectiles and present data on their performance during testing. Sub-scale armature tests performed to establish armature material design limits are also presented. These developments have led to a better understanding of the interdependent nature of launch package and electromagnetic gun design and illustrate that the design of each must be coupled in order to maximize overall launch system performance.
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    Status of the 9 MJ Range Gun System
    (IEEE, 1995-01) Herbst, J.D.; Rech, B.; Thelen, R.F.; Thompson, R.C.
    The 9 MJ Range Gun system under construction at the Center for Electromechanics at The University of Texas at Austin is designed as a self-contained, field portable electromagnetic launch system to accelerate a salvo of three projectiles to a muzzle energy of 9 MJ at velocities ranging from 2.5 to 4.0 km/s. The Range Gun system will consist of a self-excited air-core compulsator, a 90 mm bore railgun launcher, prime power and auxiliary systems, solid state switches for field rectification and gun discharge, and the controls and data acquisition required to operate the system. The compulsator is designed to deliver 3.2 MA current pulses to the railgun launcher at a peak power rating of 10 GW. This paper describes some of the innovations incorporated into the design of the 9 MJ Range Gun system compulsator and presents the status of the fabrication and testing efforts. Initial performance of the 90 mm railgun during testing at the Electric Armaments Research Center will also be presented.
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    Fabrication and Testing of a 30 mm and 90 mm Laminated, High L’ Railgun Designed and Built at CEM-UT
    (IEEE, 1995-01) Hahne, J.J.; Upshaw, J.L.; Herbst, J.D.; Price, J.H.
    With the emphasis on moving railgun technology from a laboratory based setting out into the field, a new lighter weight and stiff railgun structure was designed at the Center for Electromechanics at The University of Texas at Austin (CEM-UT). This innovative design takes advantage of stainless steel laminations with a composite overwrap to provide radial and longitudinal support for the rail/insulator package. The goal of this design effort was to build a 90 mm bore gun with a 9 MJ muzzle energy and provide comparable stiffness to the hydraulically prestressed 90 mm railgun at CEM-UT. The fabrication phase involved building a 90 mm/spl times/7 m long railgun in conjunction with a 30 mm/spl times/3 m subscale version for performance testing up to full design loads. The 30 mm subscale launcher has been successfully tested at CEM-UT up to its full current rating of 1.0 MA. This paper discusses the problems encountered during the final assembly of the 90 mm skid gun and how these difficulties were overcome. The paper also discusses the successful testing to full load of a 30 mm one-third scale version of the 90 mm gun. The paper concludes with a brief discussion on an additional 30 mm laminated gun which was redesigned based on experience with the previous laminated gun assemblies.
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    Railgun Instrumentation
    (IEEE, 1995-01) Hotz, T.J.; Davis, D.G.
    In recent years, the railgun focus has switched to developing tactical weapons with launch velocities of 2 to 3 km/s. The projectile focus for tactical weapons has switched from plasma to solid armatures because of their high efficiency. Since few measurements have been made on the state of the solid armature during an electromagnetic launch, new diagnostics need to be developed to substantiate theoretical models. This paper presents several recent developments in the area of railgun instrumentation that attempt to directly or indirectly measure physical quantities that relate to the function of a solid armature during a launch.
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    Power Electronics and Controls for Air Core Compulsator
    (IEEE, 1995-01) Wehrlen, D.J.; Lee, R.A.; Thelen, R.F.
    The Center for Electromechanics at the University of Texas (GEM-UT) has been engaged in a large scale effort to develop the power electronics and control systems required to demonstrate a multi-megawatt, full control, SCR based rectifier/inverter and high power SCR closing switch. The ultimate objective of this development effort is to provide high efficiency switching for self-excitation of air core single phase rotating machines and to control the delivery of energy to the final loads. The self-excitation process is initiated by a seed current capacitor followed by active rectification of the compulsator AC output into the field coil. Upon reaching full open circuit voltage, the main closing switch is used to initiate current into the rail gun load. After termination of the gun current pulse, stored field coil energy is returned to the rotor via source commutated, full wave inversion. This paper presents the theory of operation for the complete rectification and inversion cycle, SCR selection criteria, overall design strategy and all available test data. The test results include the testing of individual devices, multiple series/parallel modules, and full system testing if available.
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    Fabrication of a Compact Storage Inductor for Railguns
    (IEEE, 1984-03) Spann, M.L.; Pratap, S.B.; Gully, J.H.; Weldon, W.F.; Woodson, H.H.
    A liquid nitrogen-cooled, coaxial, energy storage inductor has been designed and built to be used in conjunction with a compact homopolar generator to form a high-energy-density power supply for use with electro-magnetic accelerators. The low-resistance, lightweight aluminum inductor stores 3.1 MJ at a peak current of 1.0 MA. Minimizing weight rather than size was emphasized in the design, resulting in a 1.23-m (48.5-in.) diameter by 0.91 m (36 in.) long inductor weighing 14.7 kN (3,300 lb). A coaxial design was chosen to eliminate high external magnetic fields without the necessity for shielding. External magnetic fields are undesirable because of effects on nearby components and the possibility of detection. Also, attention has been given to minimizing the partial flux linkages or internal inductance of the coil, thereby maximizing the overall transfer efficiency into a railgun. Details of the design, fabrication, and predicted performance will be presented.
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    Shaft Signals of salient-Pole Synchronous Machines for Eccentricity and Shorted Field Coil Detections
    (IEEE, 1994-01) Hsu, J.S.; Stein, J.
    Relationships between shaft signal and eccentricities of salient-pole synchronous machine are Studied. The magnitude and the thickness of shaft-signal loci Reflect steady and dynamic eccentricities. Harmonic components of shaft signals étroitement relates to shorted field coils. Threshold records can be used for exchange of information in eccentricities and shorted field coils. Extensive experimental work with the theoretical predictions Chartered
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    Comparison of the Nature of Torque Production in Reluctance and Induction Motors
    (IEEE, 1990-06) Hsu, J. S.; Liou, S. P.; Woodson, H. H.
    The nature of torque production is different in reluctance and inductance motors. One significant difference occurs in a reluctance motor that has nonsalient stator punching and a salient motor. When the flux per pole is small in such a motor, the torque can still be high, as long as the rate of energy change with respect to the rotor angular displacement at the rotor pole fronts and pole ends is high. A theoretical foundation to improve the torque capability of reluctance motors is provided. Effects of saturation and stray-load loss are also studied. Experimental results show agreement with theoretical conclusions
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    Design and Testing of a Rapid Fire, Lightweight, Ultra Stiff Railgun for a Cannon Caliber Electromagnetic Launcher System
    (IEEE, 1995-01) Werst, M. D.; Cook, K. G.; Kitzmiller, J. R.; Liu, H-P.; Price, J. H.; Yun, H. D.
    The goal of the Cannon Caliber Program is to drive 185 g integrated launch packages to 1850 m/s. Three, five-round salvos with a firing rate of 5 Hz are intended to defeat specified targets at a range of up to 3 km. After an extensive alternative study, the design team consisting of United Defence FMC/BMY, the Center for Electromechanics at The University of Texas at Austin (CEM-UT) and Kaman Electromagnetics Corporation (KEC) has chosen to use an air-core, compensated pulsed alternator (compulsator) to power a rapid fire railgun to accomplish this task. A railgun launcher has been designed to fulfil the rapid fire requirements of the system just described. The design incorporates a directional preloading feature and ceramic sidewalls which combined make the railgun structurally stiff and lightweight. This publication focuses on the design, development and initial testing of the railgun launcher.
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    Effects of Eccentricities on Shaft Signals Studied Through Windingless Rotors
    (IEEE, 1994-09) Hsu, J.S.; Stein, J.
    Shaft signals of electric rotating machines offer potentials for defect detection. The signals are affected by many factors. This study specifically focuses on how eccentricities affect shaft signals through theoretical predictions and tests conducted on windingless rotors. Windingless rotors imply currentless rotors. For symmetrical synchronous machines running at steady synchronous speeds, the induced rotor currents are zero, while harmonics are neglected. One advantage in experiments for this study is that air gaps can be shimmed accurately at standstill without end brackets; certain tests can be conducted at standstill without facing unmanageable locked-rotor currents for the test machines. Shaft signals decrease when the rotor of a machine closely situates at the center of stator bore. Shaft signals increase under greater eccentricities when stator and rotor axes are parallel. Tilted rotors reduce shaft signals. Even when there are no rotor windings, inherent positional characteristics exists. This characteristic produces cyclic shaft-signal components that are related to rotor revolutions
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    Monitoring of Defects in Induction Motors Through Air-Gap Torque Observation
    (IEEE, 1995-09) Hsu, J.S.;
    This paper suggests a method to monitor defects such as cracked rotor bars and the shorted stator coils in induction motors. Air-gap torque can be calculated while the motor is running. No special down time for measurement is required. Data of the air-gap torque for a motor should be periodically kept for comparison purposes. Since more data than just a line current are taken, this method offers other potential possibilities that cannot be handled by examining only a line current. The theoretical foundation for this proposed method is presented. Experiments conducted on a 5-hp motor show the validity and potential of this approach. Further studies are planned to extend the proposed method in detail and to monitor defects developed in other types of rotating machines
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    Shaft Signals Corresponding to Cracked Rotor Bars of Induction Machines
    (0000-00-00) Hsu, J.S.; Gully, J.H.
    Ratings of induction machines range from tens of thousands horsepowers to fractional horsepowers. Unexpected downtime of large Induction motors, such as those used in power plants, can be very costly. Cracked rotor bars of induction machines may overheat rotors, lower outputs, and cause non-retrievable damages.
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    High Magnetic Field Generation Using Single Turn Coils
    (IEEE, 1994-07) Werst, M.D.; Ingram, S.K.; Wehrlen, D.J.; Weldon, W.F.
    This study presents a new observation that links shaft signals to cracked rotor bars. Theoretical foundation for this observation is derived. Experimental results clearly confirm the theory that under loaded conditions, double-slip-frequency shaft signals can be detected while there are cracked rotor bars in induction machines. The new method suggested in this study is simple and reliable. No disassembling is required
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    Commissioning of a High Speed Composite Rotor with Hydrostatic Dampers and Ceramic Rolling Element Bearings
    (American Society of Mechanical Engineers, 1993-09) Headifen, R.N.; Fuller, R.L.; Kitzmiller, J.R.
    A high speed (25,000 rpm) rotating machine with a 300 lb rotor was designed and manufactured. To accommodate the high shaft speed, 2.6 million DN, rolling element bearings were used with ceramic balls and inner races. In order to control the magnitude of the vibration, damping was incorporated into the system using nonrotating hydrostatic dampers. The journal for the dampers was a cylindrical cartridge that had the rolling element bearings clamped inside of it. Extensive analysis was performed on this system. A computer program was written that could model the orbit path of the lumped mass shaft in the damper over the full speed range. A second program was also written that calculated the damper nonlinear stiffness and damping coefficients, and incorporated them in with a one-dimensional beam, finite element rotordynamics model of the system. Analysis results are presented along with experimental run data from the machine. Balancing problems encountered during commissioning have limited the results to 16,500 rpm to date. The last of which is currently being remedied.
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    Preliminary Design of a 1 Gigajoule Homopolar Generator
    (IEEE, 1993-01) Headifen, G.R.; Pappas, J.A.; Weldon, J.M.; Wright, J.C.; Price, J.H.; Gully, J.H.; Brunson, G.
    A high-energy, high-voltage homopolar generator (HPG) has been designed. The HPG will have composite flywheels to maximize energy storage density and a multipass armature to achieve high output voltage. The HPG is designed to discharge a constant 895 kA into a 460 V load for several seconds and recharge in less than a minute. The designed energy density is in excess of 15 J/g. Output current control will be achieved by increasing the field coil current proportionally to the decrease in rotational speed
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    Experimental Testing of Thick Wall Graphite Composite Rings
    (0000-00-00) Headifen, R. N.;
    Test results are presented from pressurizing thick walled graphite hoop wound composite rings to very high internal radial pressure. Hydraulic pressures exceeding 40,000 psi were obtained. The testing was performed on rings wound whh two different resins, a cyanate ester and a Bismaleimide (BMI) resin. To prevent axial delaminations at these high pressures, a thin bidirectional cloth G 11 lining was used inside the rings. The rings were monitored with strain gages and acoustic probes as the pressure was applied. Flaw-free cyanate ester rings survived the testing, indicating that the nominal transverse (radial) compressive strength of hoop-wound rings is higher than 40,000 psi.
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    A New High Current Laboratory and Pulsed Homopolar Generator Power Supply at The University of Texas
    (IEEE, 1984-03) Floyd, J.E.; Aanstoos, T.A.
    The University of Texas at Austin is constructing a spacious facility for research in pulse power technology at the Balcones Research Center, located in north Austin. The arrangement and capacity of the facility are intended to support high-current experiments. The laboratory power supply being designed consists of six homopolar generators, each capable of delivering ten megajoules of energy. The output bus is configured such that various series, parallel, and series-parallel circuits of homopolar generators are possible. Both resistive and inductive loads can be driven from the power supplies. Research programs will be supported with a wide range of physical facilities, including materials handling, machine shop, data acquisition and analysis, engineering and operating personnel, chemical analysis and metallurgical laboratories, and an information center. These facilities will be available to the U. S. technical community through several types of arrangements with The University through the Center for Electromechanics. Each of the six homopolar generators is designed to deliver 1 MA at 100 V, with a maximum repetition rate of a discharge every five minutes. In addition to EM launch research and applications, other intended uses of the power supply include welding of large cross-sections of metal (up to 650 cm2or 100 in.2of steel), generation of high magnetic fields in low-impedance magnets, and testing of high-current opening switches. Status of major elements of the project is reported.