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Review ListA Statistical Model to Eliminate the Effects of Speed and Load on the Vibration Signal Generated by Defective Bearing Under Variable Operational Conditions
Samavatian, Mohammad | 2025
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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 58791 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Behzad, Mahdi; Mehdigholi, Hamid; Rohani Bastami, Abbas
- Abstract:
- Bearing failure is the most important causes of shutdown in rotating machines. Most existing fault diagnosis methods are only applicable under constant operating conditions, whereas modern machines often operate under variable loads and speeds. Changes in these operating conditions alter the statistical characteristics of vibration signals, which can lead to false alarms in bearing fault detection. The aim of this research is to propose a statistical indicator for vibration signals that is independent of variations in operating conditions and can more accurately track the progression of bearing faults while reducing false alarm rates.First, the physical mechanisms of bearing degradation were investigated, and the geometries of typical defects were identified and modeled. These geometries were then used in both simulation and experimental tests. The sensitivity of bearing vibration to load, speed, and defect size was analyzed using experimental data obtained under both artificially induced and naturally developed defects. Using time-window segmentation and nonlinear regression, polynomial surfaces were fitted to describe the dependence of vibration levels on operating conditions, and the coefficients of these surfaces were introduced as new statistical indicators.To validate the proposed indicator, a theoretical model based on the dynamic contact interactions between rolling elements and raceways was developed to generate a database of simulated vibration signals under various loads and speeds. The root mean square (RMS) values of acceleration were fitted by third-order polynomial surfaces with respect to load and speed. Nonlinear regression analysis showed that the obtained coefficients were independent of load and speed variations, confirming their potential as condition-independent indicators. An experimental test rig was then designed and built to reproduce the natural degradation process of bearings under variable operating conditions. The experimental results were compared with the model outputs and demonstrated that the proposed indicator consistently varies only with fault growth, remaining unaffected by changes in load and speed. This characteristic enables the proposed indicator to be used in industrial environments with variable operating conditions, without requiring prior knowledge of bearing history or lifetime data
- Keywords:
- Fault Diagnosis ; Bearing ; Vibrational Analysis ; Statistical Analysis ; Variable Working Conditions
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