Stronger Composites

The use of light-weight, high-strength, carbon-composite materials in motors, generators, and energy storage devices has become common as a means to maximize energy density. A key contributor to the strength of composite structures is the fiber volume, which is the fraction of the composite volume that is due to carbon fibers. Heretofore, accurate determinations of fiber volumes were destructive. A newly published paper, “Non-destructive Evaluation of Carbon Fiber Composite Reinforcement Content,” by D. Dorsey, R. Hebner, and W. Charlton, in the September issue of the Journal of Composite Materials, documents a new non-destructive approach to the measurement of fiber volume. This approach uses a nuclear analytical technique known as prompt gamma activation analysis using cold neutrons to measure the fiber volume by measuring the carbon content in the composite. The approach is accurate and, with automation, shows promise to be able to determine the variation of fiber volume in complex structures.

For further information, please contact R. Hebner.

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Testing Magnetic Bearings for Mobile Applications

Magnetic bearings used on flywheels in transportation systems must react appropriately to levels of shock and vibration that are not usually present in other flywheel applications. Tests at the University of Texas at Austin have been conducted that provide information about safe design of such systems. The work was summarized in the paper, “Spin Commissioning and Drop Tests of a 130 kW-hr Composite Flywheel,” by M. Caprio, B. Murphy, and J. Herbst that was presented at the Ninth International Symposium on Magnetic Bearings in August. A key technical finding is that steps must be taken to manage forward whirl if a high-speed rotor suddenly impacts on a backup bearing. High-speed flywheels are typically levitated on magnetic bearings to minimize loss. High-speed mechanical bearings (backup bearings), of slightly larger radius than the magnetic bearings, are used to provide a way to safely coast to a stop if a magnetic bearing fails. This work shows an approach to eliminate the potentially serious forward whirl, i.e. the precession of the rotor around the outside of the mechanical bearing in the same direction as the flywheel is spinning around its axis, that can occur if a spinning rotor engages the backup bearing.

For further information, please contact B. Murphy.

Power System Dynamic Reconfiguration

The emergence of an all-electric ship opens the opportunity for innovative approaches to power system control. K. Davey and R. Hebner have published the results of a novel approach in the paper, “Reconfiguration of Shipboard Power Systems,” IASME Transactions, Vol. 1, pp. 241-246, 2004. The approach represents the system using equivalent pi sections over trunk lines. In a compressed system, i.e. 16 million switch positions, optimum configurations of the power system can be determined rapidly. As loads or sources change, the system can automatically reconfigure to produce the most efficient power network available for the specific conditions.

For further information, please contact K. Davey.

A Monte Carlo Approach to Solving Electric and Magnetic Field Problems

Although Monte Carlo methods have been well established for decades, they are rarely used for the calculation of electric and magnetic fields. A key reason for the limited use is the fact that the conventional finite element and boundary element methods of solution are fairly well matched to today’s computing systems. The growth of parallel processing may open the door to alternative interesting solution approaches. To demonstrate the applicability of this approach, Dr. Kent Davey generalizes the Monte Carlo approach to all classes of field theory problems by examining in detail three classes of problems: Laplacian, Poisson, and Helmholtz. The work is described in the paper, “Working Field Theory Problems with Random Walks,” which Dr. Davey presented at the Compumag conference, in July 2003.

For further information, please contact Kent Davey.

Designing Magnetic Bearings

Magnetic bearings are used to levitate flywheels so they can spin at high speeds without mechanical contact. The design of a bearing set to control a flywheel weighing 5100 lbs and spinning at 15,000 revolutions per minute was described in the paper, “Permanent Magnet Bias, Homopolar Magnetic Bearings for a 130 kW-hr Composite Flywheel,” by B. Murphy, H. Ouroua, M. Caprio, and J. Herbst. The paper was presented at the Ninth International Symposium on Magnetic Bearings in August. Among the interesting results presented include the connection among the hysteresis in the lamination material used in the bearings, torque on the rotor, and losses in the operation as well as the division of the vertical thrusts between elastomeric mechanical mounts and a magnetic thrust bearing.

For further information, please contact B. Murphy.

Longer Lasting Roads

Twelve years ago, the Texas Department of Transportation developed an electromechanical prototype machine with properties unsurpassed by any other in the world, to test the life of pavement. Unfortunately, wear and ad hoc repairs have compromised the reliability of this unique test device. R. Thompson of the Center for Electromechanics and M. Mosley and R. Longoria of the Department of Mechanical Engineering teamed to assess the feasibility of returning this accelerated tester to world-leading performance levels. Their assessment identified a number of straightforward electrical and mechanical modifications that are expected to yield unprecedented levels of performance. The report of their findings has been provided to the Texas Department of Transportation.

For further information, please contact R.Thompson.

Measuring Power System Faults

In an electric power system, faults must be detected and isolated rapidly to prevent larger system failures. New research, presented in the paper “Fault Analysis on a Naval Power Grid using Equivalent Impedances,” by Kent Davey, IASME Transactions, Vol.1, pp. 247-252, 2004, shows digital sampling can be an effective way to detect faults. This work shows that three samples, taken in less than a quarter of a cycle, are sufficient to detect a fault, even in the presence of noise. A key to robust detection is in the rapid calculation of phase between the voltage and current based on the sampled data.

For further information, please contact K. Davey.

An Electromagnetic Gun Power Supply as a Component of an Electric Ship Power System

An electromagnetic gun provides a new component that must be integrated into the power system of an electric ship.  An interesting topology for the power supply is a set of pulsed alternators with sufficient energy stored in the kinetic energy of the rotors to power the shot.  In this configuration, when no shot is required, the machine topology is analogous to that of a flywheel battery used to provide ride-through capability and improve power quality in land-based power systems.  The paper, “An Electromagnetic Gun Power Supply as a Component of an Electric Ship Power System,” by R. Hebner, J. Pappas, J. Kitzmiller, K. Davey, J. Herbst, A. Ouroua, and J. Beno and presented at the ASNE High Powered Weapons Systems for Electric Ships in December 2004, expands upon earlier published work showing worst case perturbation to the power system, in this approach, and the use of the pulsed alternators as high-energy active filters to improve power system performance.

For further information, please contact Robert Hebner.