Publications

A technological break through for supporting rotating shafts is the active magnetic bearing (AMB). Active magnetic bearings offer some important advantages over conventional ball, roller or journal bearings such as reduced frictional drag, no physical contact in the bearing, no need for lubricants, compatibility with high vacuum and ultra-clean environments, and ability to control shaft position within the bearing. The disadvantages of the AMB system are the increased cost and complexity, reduced bearing stiffness and the need for a controller. Still, there are certain applications, such as high speed machining, biomedical devices, and gyroscopes, where the additional cost of an AMB system can be justified. The inherent actuator capabilities of the AMB offer the potential for active balancing of spindles and micro-shaping capabilities for machine tools, The work presented in this paper concentrates on an AMB test program that utilizes the actuator capability to dynamically balance a spindle. In this study, an unbalanced AMB spindle system was enhanced with an LMS (Least Mean Squares) algorithm combined with an existing PID (proportional, integral, differential) control. This enhanced controller significantly improved the concentricity of an intentionally unbalanced shaft. The study included dynamic system analysis, test validation, control design and simulation, as well as experimental implementation using a digital LMS controller.

This report summarizes measured performance of residential geothermal heat pumps (GHP`s) that were installed in family housing units at Ft. Hood, Texas and at Selfridge Air National Guard base in Michigan. These units were built as part of a joint Department of Defense/Department of Energy program to evaluate the energy savings potential of GHP`s installed at military facilities. At the Ft. Hood site, the GHP performance was compared to conventional forced air electric air conditioning and natural gas heating. At Selfridge, the homes under test were originally equipped with electric baseboard heat and no air conditioning. Installation of the GHP systems at both sites was straightforward but more problems and costs were incurred at Selfridge because of the need to install ductwork in the homes. The GHP`s at both sites produced impressive energy savings. These savings approached 40% for most of the homes tested. The low cost of energy on these bases relative to the incremental cost of the GHP conversions precludes rapid payback of the GHP`s from energy savings alone. Estimates based on simple payback (no inflation and no interest on capital) indicated payback times from 15 to 20 years at both sites. These payback times may be reduced by considering the additional savings possible due to reduced maintenance costs. Results are summarized in terms of 15 minute, hourly, monthly, and annual performance parameters. The results indicate that all the systems were working properly but several design shortcomings were identified. Recommendations are made for improvements in future installations at both sites.