Development of a Backward-Whirl-Based Damage Detection Technique in Rotor Systems

  • Hanan Al-Hosani

Student thesis: Master's Thesis


Rotary machinery with long life spans has been a required instrument in almost every field, which makes the rotor fault detection investigation increasingly important. Studying the dynamic behavior of cracked rotor systems has gained great interest in literature. The extensive applications of heavy-duty rotor dynamic systems in various industrial and aerospace rotating equipment could lead to catastrophic crack-based damages. Early detection of cracks in a cracked rotor is of significant importance for safety, reliability and durability of large rotating machinery in service. The proposed backward-whirl approach could help in detecting early crack damages in rotor systems, by identifying a unique crack signature based on backward whirling analysis. Few studies theoretically reported the appearance of the crack and the backward whirling relation. In this study, it is numerically and experimentally proven in contrast with most studies available, that the appearance of the crack starts to excite the backward whirling speeds. The experimental work curried in this study is conducted in the cracked-rotor-bearing-disk simulator in two stages for two disk configurations; single and double. Furthermore, the dynamic behavior of the cracked rotor-bearing system at various parameters is examine using the approximated solution of the harmonic balance and the numerical integration of the obtained equations of motion. The time-periodic equation of motion of the cracked system with an open crack model are formulated according to the finite element time-varying stiffness matrix. Moreover, the IV combined effect of the crack and the unbalance angle on the shift of the critical whirl speeds for a cracked rotor-bearing-disk system is investigated. The whirl response during the passage through the forward and backward whirl zones is obtained via numerical simulation for various unbalance angles with respect to the crack opening direction. It is verified that obtained experimental results successfully correlate with the implemented numerical analysis. It is found that the variation (increasing) in the unbalance angle with respect to the crack opening direction significantly shifts the critical whirl amplitudes to the critical backward whirl zone. Consequently, the critical speeds of the cracked rotor are shifted to higher values due to the combination effect of the crack and the varying unbalance force direction. Furthermore, the analysis is extended to study above findings in the neighborhood of the 2/3 of the critical speed, where the inner whirl orbit and the multiple frequency components using the wavelet transform is observed. Indexing Terms: Dynamic systems, rotor dynamics, crack detection, backward whirl, unbalance angle
Date of AwardApr 2017
Original languageAmerican English
SupervisorMohammad Alshudeifat (Supervisor)


  • Dynamic systems
  • rotor dynamics
  • crack detection
  • backward whirl
  • unbalance angle.

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