300 Bibliographic Section

model will adequately represent the distributed duct dy- namics.

The design and analysis of suspensions for vehicles of finite length using pitch-heave models and multiple cushion-duct systems is considered. Analytical models relate vehicle front and rear accelerations to the pitch and heave natural frequencies, which are functions of vehicle and suspension geometry and mass distribution. The performance of suspensions subjected to stochastic guideway irreg&&ty and aerodynamic loading input dis- turbances is evaluated. The cushion-guideway contact problem is approached by representing the plenum as an equivalent stiffness and damping. Procedures arepresented for the design of ,secondary suspensions, tlnite length vehicles, and primary suspension stiffness using minimum compressor power.

Electromagnetic Suspensions for Ground Transportation, Marc Steven Weinberg, Draper Laboratory, 555 Tech Square, Cambridge Mail Station 53, Cambridge, MA. (Dissertation at the Department of Mechanical Engineer- ing, Massachusetts Institute of Technology, Cambridge, MA 02139).

A detailed model of an electromagnetic suspension operating in the heave mode is developed. The model is experimentally verified for zero forward speed.

The heave models study force-current-gap rela-

tionships, leakage fluxes, eddy currents induced by ver- tical motion, the effects of magnet length, and feedback control. The performance of the model is determined for stochastic road inputs. Compared to models which ne- glected leakage flux, magnetic fhuc leakage reduces the magnet’s maximum lift and increases the required vol- tage. Increasing the magnet’s length filters road ir- regularities so that high frequency inputs to the system are reduced. For most practical systems, the eddy cur- reuts induced by vertical motion have negligible effects on system dynamics. Current control with feedback of the average relative displacement and absolute velocity is identified as a rational control strategy.

The heave model was veritied in experiments where a 13 lb. vehicle which was geometrically and dynamically scaled. to represent full I size systems was levitated beneath a ferromagnetic shaker programmed to simulate road ‘inputs.

Preliminary investigations of models with heave and pitch degrees of freedom and lateral guidance are con- ducted.

The heave model is used to generate guidelines and sample designs for full sire systems. For full size suspen- sions, air gaps of 0.4 to 0.6 inches are feasible. For a system with simplesecondary suspension and magnets which weigh 10 to 15% of the vehicle’s total weight, ride comfort and other constraints are satisfied at 300 mph. with track roughness similar to that of welded steel rails and are satisfied at 100 mph. with track roughness com- parable to that of aircraft runways.