Composite Flywheel Technology Documented

The recently issued book, Composite Materials: Testing and Design, published by ASTM International, and edited by C.E. Bakis, contains two papers authored or co-authored by staff members from the Center for Electromechanics. One summarizes the application of the hydroburst test technique to characterize the hoop properties of composite rings and to use that characterization to predict the performance of full-scale composite flywheels. R. Thompson, T. Pak, and B. Rech, all Center staff members wrote this paper. The other examines the usefulness of the time and temperature dependence of the mechanical properties of the epoxy matrix to bound the relaxation time of the relaxation of the radial pre-stress in a flywheel rotor. The radial pre-stress is an important design and operational parameter for composite flywheel operation. Staff members at NASA Glenn Research Center in collaboration prepared this paper with R. Thompson of the Center.

For further information, contact Richard Thompson.

Power for Future Electric Ships

The electric ship program, sponsored by the Office of Naval Research at the University of Texas at Austin, is developing information to be used to improve power train technology in future electric ships. The initial focus was to establish a reasonable baseline system volume and mass for future comparisons, guide the selection of high payoff technologies for further development, understand the technical constraints on design, and understand the influence of subsystem design choices on the full system. One approach to establishing the baseline would have been to select a system that is in service. This approach is problematic as any system in service lags the state-of-the art by many years and there is a continuing issue with proprietary information. To overcome these constraints, the UT staff designed a system using advanced, but currently available, technology. J. Beno, et al., describe the resulting baseline system in the report “Baseline Prime Power System Used by the University of Texas at Austin”.

For further information, please contact Bob Hebner.

Modeling Transient Magnetic Fields

Dr. Kent Davey has conducted a comparison of modified Green’s functions and of impedance matrix approaches to solve transient eddy current problems. The analysis showed, for the conditions considered, either approach could be used successfully. The modified Green’s function approach is somewhat more robust as the impedance matrix approach requires taking derivatives of the impedances, a source of additional error. This work was presented in the paper “Working Transient Eddy Current Problems with Velocity using Modified Green’s Functions and Impedance Matrices,” which Dr. Davey presented at the Compumag conference, in July 2003.

For further information, contact Kent 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.

Developments in Energy Storage

In a paper titled, “Integrated Composite Arbor and Flywheel Rim Technology Development,” R. Thompson described progress toward a novel flywheel geometry that shows promise for doubling the energy density of composite flywheels. The system uses an arbor to couple the flywheel to a shaft. The key technical challenge that was met was to design and fabricate an arbor having the mechanical properties to match the growth of the flywheels as the speed increases while maintaining sufficient stiffness for good rotor dynamics. Preliminary spin testing has been completed to validate both the design code and the manufacturing processes. The paper was presented at the Aerospace Flywheel Workshop 2003 in August 2003.

For further information, please contact Richard Thompson.

Windage Losses in High Speed Generators and Flywheels

Increasing the rotational speed makes it possible to store more energy and make more power in a rotating machine that is smaller and lighter. A loss mechanism that becomes more important as the speed is raised is the loss due to air resistance. The general approach to limiting this loss is to operate the generator or flywheel in vacuum. As long as the mean free path of a molecule is short compared to pertinent dimensions of the flow field, i.e. continuum flow, the Navier-Stokes equations can be used to calculate losses. New work measures and predicts behavior near the transition between continuum flow and slip flow, where the flow dimensions are near the mean free path. This investigation developed appropriate theoretical approaches to predict the losses in this regime. The theoretical work was validated by a set of experiments on composite rotors. The experimental approach was described in the paper, “Measurement of Windage Losses and Temperature Distribution for a High Speed Composite Rotor in a Stator Assembly at Low Air Pressures,” by J. Hahne, M. Werst, C. Penney, H-P Liu, J. O’Rarden, and D. Bogard. The theoretical approach used and the extent of its validation is given in a second paper, “Prediction of Windage Losses of and Enclosed High Speed Composite Rotor in Low Air Pressure Environments,” by H-P Liu, M. Werst, J. Hahne, and D. Bogard. Both papers were presented at the ASME Summer Heat Transfer Conference, July 2003.

For further information, please contact Mike Werst.

Efficient Approach to Modeling Nonlinear Transient Eddy Currents

Traditional approaches to modeling transient events use a time stepping procedure. When velocity effects are not involved an alternative approach, which accounts for nonlinear effects and is based on developing the system transfer function using time harmonic solutions, provides efficient computation of the transient response without the accumulation of stepping errors. This approach can be used for a multitude of source excitations. The computational approach is described in a paper “Working Nonlinear Transient Eddy Current Problems with Time Harmonic Solutions,” which Dr. Davey presented at the Compumag conference, in July 2003.

For further information, contact Kent Davey.