ASA 126th Meeting Denver 1993 October 4-8

4pEA12. Sensitivity of axial vibration reactions to design asymmetries in a Stirling cycle cryocooler dual-opposed compressor assembly.

Fred W. Hausle

Phys. Analysis Dept., Mail Stop WE-4, Ball Aerosp. Syst. Group, P.O. Box 1062, Boulder, CO 80306

Stringent constraints are placed upon allowable vibration reactions from cryocoolers used for space-borne optical sensors. Stirling cycle cryocoolers typically use dual-opposed compressors to virtually cancel the net axial reaction produced by the steady-state driven oscillations of paired pistons by virtue of symmetry. Under steady-state operation, harmonics of the drive frequency occur due to the nonlinear characteristics of both the working gas and the mechanical piston support spring stiffnesses. Asymmetries in the system design due to fabrication tolerances may result in intolerable net reactions primarily at the harmonics of the drive frequency. The axial dynamics of a simple two-degree-of-freedom compressor model are examined using a finite-difference time-step Runga--Kutta algorithm. The sensitivity of the axial reaction harmonics to asymmetric characteristics between the paired compressors such as gas volume, support spring stiffness and piston mass is examined. A Fourier decomposition of the limit cycle is conducted to observe the frequency content of the vibration reactions. Comparison is made with results of an application of perturbation methods. Cryocooler design parameter asymmetry tolerances based upon specified limits on peak vibration reaction responses are obtained.