J.R. Kitzmiller

An application guide for compulsators

Focus toward advanced mobile tactical configurations for railgun power supplies has resulted in the evolution of five compulsator generations in the past 15 years. Unfortunately, the rapid maturation of the technology has tended to dilute the relative importance and application base of previous generations. Technical variance between generations has been significant, including air-core or iron-core, rotating armature or field, single- or multiphase, solid rotor or shell, and externally excited or self-excited. It is useful, therefore, to review and classify the important distinctions between the generations of machines, thus allowing proper selection of the one best suited for a given application. This paper provides an overview of the evolution of compulsators developed at The University of Texas at Austin Center for Electromechanics. Features of past and present configurations are discussed, such as machine topology, method of excitation, basic switching methods, discharge pulse shapes, and potential energy and power densities. A list of potential applications is generated for all disciplines within the armed forces. This information is used to create an application guide that can be used to select appropriate compulsator options for the mission given. An extensive list of references is also provided.

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.

Discarding armature and barrel optimization for a cannon caliber electromagnetic launcher system

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. >

Design and testing of a rapid fire, lightweight, ultra stiff railgun for a cannon caliber electromagnetic launcher system

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. >

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.

Compulsator rotordynamics and suspension design

High speed compulsator rotors utilizing high strength composite bandings pose unique problems from a rotor-dynamic standpoint. This article describes the basic design approach for rotordynamics used at The University of Texas at Austin Center for Electromechanics at (UT-CEM). As an example, the CCEML compulsator rotor-dynamic design is presented. The key considerations are seen to be: (1) mass and stiffness properties of the fully assembled rotor, (2) selection of rotor support bearings, (3) bearing supporting structure, (4) proper placement of rotor critical speeds, (5) adequate attenuation of rotor response at all speeds, and (6) bearing load capacity to react large discharge forces. Due to large mechanical and thermal shocks which occur during discharge, a primary design goal is to maximize tolerance to rotating imbalance. Another primary design goal is avoidance of destructive whirling instabilities which can occur with high speed rotors possessing large amounts of damping within the rotating assembly.

Ultra-stiff, low mass, electromagnetic gun design

High performance in an electromagnetic (EM) gun implies high velocity with minimal transition from a solid to plasma armature. Factors that affect gun performance include armature integrity, bore straightness, and bore stiffness. Experiences firing solid armature at the Center for Electromechanics at The University of Texas at Austin since 1987 have shown that the lack of one or more of these three ingredients will result in less than desirable performance. This work presents a simple, ultra-stiff and low mass EM gun design that provides five to six times the rail-to-rail structural stiffness than a conventional bolted, composite sidewall-type EM gun construction. This translates into minimal bore deflection which lessens the amount the armature must distort to maintain a low voltage contact with the rails. The EM gun design incorporates a passive preloading mechanism that maintains a compressive stress state in the bore components without the use of hydraulics. Bore preload is provided that exceeds the maximum rail-to-rail EM loads and is reacted by a composite structure that also provides longitudinal barrel stiffness. Manufacturing techniques are presented that would allow the design to be built on a small or large scale using standard manufacturing tolerances and demonstrated assembly processes. Material selection and impact on the ability to actively cool a railgun is also presented.

Rotordynamics design and test results for a model scale compulsator rotor

The model scale compulsator is a high speed (12000 rpm), high energy rotating machine. The rotor is a highly optimized pulsed power electrical machine consisting of electrical windings, slip rings, and highly pre-stressed composite bandings. This paper describes the design of this machine from the standpoint of rotordynamics. The rotor is supported on oil-lubricated hybrid ceramic duplex ball bearings, which in turn are supported on compliant squeeze film dampers. Test results are presented for both mechanical checkout runs and full energy discharge experiments. Also described is experience gained from low speed balancing on a commercial balancing machine, followed by high speed in situ balancing.