Dynamic finite element modeling and analysis of a hermetic reciprocating compressor
Dynamic finite element modeling and analysis of a refrigeration compressor was investigated as part of a noise emission study. Natural frequencies and normal mode shapes were calculated for the major structural components of the compressor. The components were later combined to form a model of the compressor assembly which was subsequently solved for its dynamic properties. Model development included coordination with test data for verification and revision to improve model prediction accuracy.
Considerable efforts were made to accurately represent the hermetic shell which presents several inherent modeling difficulties due to its geometry and other characteristics which result from a deep drawn manufacturing process. The importance of physical simplifications such as geometry representation, thickness variation, attachments, the welded seam, and residual stresses were established. In addition, theoretical limitations of the finite element method were addressed as a cause for analysis-test discrepancies. Housing models developed were found to agree within 12% of experimental natural frequencies up to 1100 Hz.
Compatibility of analytical normal modes with resonant dwell experimental deflection shapes was considered. Analytical forced vibration response showed situations when the deflected shapes can be a superposition of modes rather than the pure mode shape. Analytical simulation of the test setup improved the agreement of analysis and test data.
Additional components modeled include the internal compressor mechanism and its supports. Analysis showed that interactions with the internal components, particularly resonances within the suspension springs, are important for a valid representation of the compressor assembly. Resonances within the internal suspension components more than double or nearly triple the number of resonance frequencies in the compressor assembly.