Quasi-probabilistic fatigue damage evaluation for piping systems under random frequency control in inverter-driven air conditioners

Conventional compressors operate at a fixed motor frequency, simplifying resonance and fatigue evaluations. However, inverter-driven compressors vary their frequency between 10 and 150 Hz, complicating resonance analysis and fatigue prediction. Random vibration fatigue (RVF) has been widely applied to evaluate fatigue under stochastic loads, yet it has limitations for outdoor unit piping systems. It neglects phase information in power spectral density (PSD) transformations and assumes fully random excitation, conflicting with the quasi-deterministic nature of inverter-induced forces. To address these issues, this study proposes a quasi-probabilistic fatigue evaluation method in the frequency domain. The approach integrates deterministic excitations with random vibrational loads to accurately capture resonance effects, predict fatigue damage, and identify critical frequency ranges. Using Abaqus/CAE for modal and finite element analysis, the proposed method enhances reliability and efficiency in fatigue assessment, offering a tailored solution for inverter-driven air conditioning systems.