Vibration characteristics analysis for rotating bolted joined cylindrical shells considering the discontinuous variable-stiffness connection

The non-uniform connection stiffness in the influence zone of bolts has been rarely considered in previous studies. This paper proposes a unified discontinuous variable-stiffness model to simulate the actual connection situation of bolts by improving the artificial spring technology. Further, a new dynamic model of rotating bolted joined cylindrical shells is established based on the Lagrange equation and solved by the efficient state space approach. The influences of centrifugal and Coriolis force are introduced into the model. According to Sanders' shell theory, the natural frequencies and mode shapes are obtained by utilizing orthogonal polynomials as mode functions. Besides, the mode test of the bolted joined cylindrical shell is conducted. Based on the test results and proposed model, the connection stiffness of bolts is identified by the particle swarm optimization algorithm. The established model is validated by comparing with the results of mode test, FEA, and literature. Furthermore, the comprehensive influences of the rotating speed, connection stiffness, and number of bolts on the mode shapes and natural frequencies are investigated. The irregular mode shape at the frequency veering is found. The mechanism and crucial rule of complex frequency veering and corresponding mode shape transfer caused by the coupling between multiple modes are revealed.