M.D. Werst

Compulsator research at The University of Texas at Austin-an overview

An overview of compulsator research is presented, including a brief history of the device, electromagnetic and mechanical design considerations, status of machines currently in operation and under development, and future technology. The compulsator appears to have great potential as a power supply for a variety of fields including fusion, industrial applications, directed energy weapons, low-frequency sound sources, and electromagnetic launch (EML) technology. Several machines have been built and tested, successfully demonstrating the principle of operation and showing that a compact rotating machine, operating at high efficiency, can provide a series of appropriate high current pulses without the necessity of complicated conditioning and switching networks. >

Predicted versus actual performance of the model scale compulsator system

Performance testing of the model-scale CPA was completed at the University of Texas Center for Electromechanics. A major part of the project was the development of design and simulation codes that would accurately represent the performance of pulsed alternators. This paper discusses the components of the system and its operational sequence. Details of the performance simulation model are presented along with test data. The test result is compared to the predicted data.

Laboratory testing of the pulse power system for the cannon caliber electromagnetic gun system (CCEMG)

The team of (prime contractor) United Defense LP (UDLP) and The University of Texas at Austin Center for Electromechanics (UT-CEM) has completed a significant portion of the testing phase of a trailer mounted compulsator driven 35 mm (round bore equivalent) rapid fire railgun system. The objective of the program is to develop a compact, lightweight pulse power test bed capable of launching 3, 5 round salvos of 185-g integrated launch packages to 1.85 km/s at a firing rate of 5 Hz. Per contractual requirements, the pulse power system is also size compatible with the Amphibious Assault Vehicle (AAV). The pulse power system is developed around a second generation air-core, 4-pole rotating armature, self-excited, compulsator design. The 40 MJ at 12,000 rpm composite rotor stores all 15 shots inertially and is capable of 2.5 GW performance into the 2.21 m long series augmented railgun. This paper describes the CCEMG pulse power supply configuration and highlights important features of the commissioning test plan. The paper then presents test results from mechanical runs, stand alone compulsator (CPA) rectifier tests, short circuit tests, and single shot live fire tests. Finally, CPA performance is compared with predictions for the single shot tests presented.

Testing of a rapid-fire compensated pulsed alternator system

A compensated pulsed alternator (compulsator) has been designed and fabricated to drive a rapid-fire railgun system. Initial testing of the compulsator resulted in the failure of the compensation shield at full speed. An ambitious rebuild effort was undertaken, allowing testing to begin in August 1987. Since then, several rapid-fire shots have been performed, firing two 3 m guns at a 60-Hz repetition rate. A 65-g solid armature projectile was accelerated to 1.8 km/s during the initial tests with the compulsator operating at half-speed and reduced excitation. These preliminary results suggest a high probability that the compulsator rapid-fire system will meet and exceed the design goals. >

Continued testing of the cannon caliber electromagnetic gun system (CCEMG)

The cannon caliber electromagnetic gun system is based upon a compulsator driven 30 mm rapid fire railgun system. The objective of the program was to develop a compact, lightweight test bed capable of launching three, five round salvoes of 185 g integrated launch packages to 1.85 km/s at a firing rate of 5 Hz. Per contractual requirements, the pulse power system is also size compatible with the amphibious assault vehicle. The pulse power system was developed around a fourth generation air-core, 4-pole rotating armature, self-excited, compulsator design. Although the contract for this effort has expired, the system continues to be used in part to demonstrate compulsator driven railgun technology. This system has performed seven single shots using identical control settings for each shot, which is the first such experience using a compulsator driven railgun system. This paper describes the experimental set-up for the demonstrations and compares the generator, converter, gun switch, and launcher performances for each shot.

Testing of the cannon caliber rapid fire railgun

A rapid fire launcher has been designed, built, and tested in single-shot mode for the Cannon Caliber Electromagnetic Gun (CCEMG) System. The 2.25-m long railgun has a rectangular cross-section (30 mm round bore equivalent) and has a series, two-turn augmented rail configuration. The gun is designed for rapid fire operation; three, five round salvos of 185 g integrated launch packages (ILPs) accelerated to 1,850 m/s with a minimum time between salvos of 2.5 s. Launch packages will be autoloaded at a repetition rate of 5 Hz via a hydraulic mechanism capable of up to 3,000 lb insertion forces. The railgun support structure and flexible buswork permit the railgun to recoil approximately 2 cm to mitigate the electromagnetic repulsion loads. Multiple 830 kA pulses provided from the CCEMG compulsator power supply require the gun to be liquid cooled for thermal management. Diagnostics for the single-shot tests include B-dots, flux rulers, voltage, and current measuring sensors. Other launcher diagnostics include rail conductor temperatures, coolant temperatures, and railgun preload mechanism (flatjacks) dynamic pressures. This paper presents the test results and general gun performance observations for single-shot, compulsator powered experiments.

The CEM-UT rapid-fire compulsator railgun system-recent performance and development milestones

Twenty-seven compulsator-powered railgun experiments have been performed, including a 1.0 MJ discharge at 3510 r/min. In this test, a 724 kA current pulse accelerated an 80 g, aluminum armature to 2.05 km/s, thus exceeding the projectile velocity goal at 73%-rated machine speed. Furthermore, operation with a single gun barrel has been achieved using a parallel path, solid-state closing switch to deliver 132 kA to the railgun injector. The latest data are presented from the rapid-fire compulsator railgun facility. Included is a discussion of the energy transfer, power output, and system efficiency during a 1.0 MJ discharge. Also shown are the injector current, voltage, and di/dt curves for this test which were used in the design of the solid-state closing switch. Results of railgun experiments using the solid-state switch are analyzed. >

Combustion Emissions Modeling and Testing of Neat Biodiesel Fuels

This paper presents emissions modeling and testing of a four-stroke single cylinder diesel engine using pure soybean, cottonseed, and algae biodiesel fuels. A system level engine simulation tool developed by Gamma Technologies, GTPower, has been used to perform predictive engine combustion simulations using direct-injection jet modeling technique. Various physical and thermodynamic properties of the biodiesel fuels in both liquid and vapor states are required by the GT-Power combustion simulations. However, many of these fuel properties either do not exist or are not available in published literatures. The properties of the individual fatty esters, that comprise a biofuel, determine the overall fuel properties of the biofuel. In this study, fatty acid profiles of the soybean, cottonseed, and algae methylester biodiesel fuels have been identified and used for fuel property calculations. The predicted thermo-physical properties of biodiesels were then provided as fuel property inputs in the biodiesel combustion simulations. Using the calculated biodiesel fuel properties and an assumed fuel injector sac pressure profile, engine emissions of the conventional diesel and biodiesel fuels have been predicted from combustion simulations to investigate emission impacts of the biodiesel fuels. Soybean biodiesel engine emissions, which include NOx, HC, CO and CO 2 , measured at various engine speeds and loads in actual combustion emissions tests performed in this study were also compared to those predicted by the combustion simulations.

Splits of windage losses in integrated transient rotor and stator thermal analysis of a high-speed alternator during multiple discharges

For a high speed electrical alternator, the rotor outer banding and stator inner liner are typically made of high strength graphite epoxy composites due to their high strength and stiffness. Machine structural integrity at high rotating speeds degrades significantly as the composite resins lose their strength at high temperatures. The magnitude of the frictional windage losses generated in the air gaps and the splits of the windage losses between the rotor and stator become crucial to the machine design since these windage losses greatly influence the rotor outer and stator inner surface temperatures. Splits of windage losses generated by an enclosed high speed composite rotor in low air pressure environments were investigated by The University of Texas at Austin Center for Electromechanics and described in a companion paper. The windage splits are dictated by the air temperature gradients at the rotor outer and stator inner surfaces. Unique heating, cooling, and component material properties of a typical highspeed alternator during repetitive-discharge events make its transient air-gap windage splits very much different from those of the test setup. This paper describes transient windage splits in integrated rotor and stator thermal analyses of a high-speed alternator designed for multiple discharges. The transient windage splits in the air-gap airflow were obtained through multiple iterations on windage losses, air-gap air temperatures, and rotor and stator surface temperatures.

Prediction of Windage losses of an Enclosed High Speed Composite Rotor in Low Air Pressure Environments

The frictional windage losses associated with non-ventilated airflows in the air gaps between the rotor and stator of a high speed rotating machine can greatly influence the rotor outer and stator inner surface temperatures. The characteristics of the radial and axial air-gap flows have been of general interest in many engineering applications. A rotating air gap flow is very complex, and in general, can be categorized as a continuum flow, slip flow, and free molecule flow, depending on the ratio of its mean free path to the air gap dimension. For a continuum flow between concentric rotating cylinders, secondary flow of rows of circumferential Taylor vortices in the air gap due to centrifugal flow instability of a curved flow at relatively high rotating speeds will typically be formed. As the air pressure in the air gap drops significantly, rarefied gas flow, departure from continuum flow, occurs when the mean free path becomes relatively large compared to the air gap dimension. This paper has developed and summarized an analytical approach to predict high speed windage losses (rotor tip velocities up to 900 m/s) at low rotor cavity air pressures (0.1 torr to 10 torr). The predicted transient windage losses at various air pressures and high rotor speeds are compared with measured windage losses generated in continuum and slip flow regimes. The agreements between the predicted and measured windage losses are relatively well.Copyright