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    Experiment-Based Design of Stirling Cryocooler Compressor Using Response-Controlled Testing
    (Mdpi, 2025) Gucyilmaz Cetin, Suna; Karaagacli, Taylan; Ertas, Ahmet H.
    Flexure-based Stirling cryocooler compressors are a critical technology in providing cryogenic temperatures in various advanced engineering fields, such as aerospace, defense, and medical imaging. The most challenging problem in the design of this type of compressor is achieving a precise alignment that preserves small gaps between the components moving relative to each other and avoids severe friction and wear. This paper introduces a novel experimental procedure for designing Stirling cryocooler compressors, leveraging a recently developed nonlinear experimental modal analysis method known as response-controlled stepped-sine testing (RCT). The alignment in a compressor prototype was significantly improved in light of a series of RCT with base excitation. The enhanced compressor design was subsequently validated though a series of constant-current tests, which confirmed the elimination of the sticking/locking phenomenon observed in the initial design. Furthermore, an indirect harmonic force surface (HFS)-based approach proposed for weakly nonlinear systems was extended to identify the high and nonlinear damping (up to a 65% hysteretic modal damping ratio) observed in the enhanced compressor design due to excessive friction. As another contribution, it was shown that the extrapolation of the HFS gives accurate results in the prediction of the nonlinear modal parameters at response levels where no experimental data are available. In light of these findings, it was concluded that the enhanced design needs further design modifications to further decrease the friction and wear between the moving parts. Overall, this study provides valuable insights for designing cryocooler compressors, with implications for aerospace and medical applications.