### 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
**

**
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*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.