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Rods fastened rotor system are widely used in heavy-duty gas turbines. The contact nonlinearity and discontinuity induced by bolted rotor structures, make it difficult to design a scaled rotor system accurately. Thus, a dynamic scaling design strategy for discontinuous bolted rotor systems is proposed in this paper. An improved continuous modeling method considering rods deformation based on equivalent material layer (EML) is introduced to reflect the weakening effect of the rotor stiffness with bolted structure, and the parameter mapping relationships between the continuous and the discontinuous structure are constructed. The scaling factors of each element of the rotor system are derived by the similarity theory. Through this approach, a discontinuous rotor system can be scaled, demonstrating a high level of consistency with the prototype in terms of natural frequencies, critical speeds as well as frequency response. In addition, modal experiments under different preloads and dynamic acceleration experiment are carried out to verify of the proposed modeling method for discontinuous rotor structures. The testing and simulation results prove that the introduced equivalent material layer reflects the contact effect of prototype accurately. Compared with the experimental results, the maximum deviation of the first two natural frequencies is 4.06%, and the maximum deviation of the critical speeds is 1.36%, demonstrating the potential of small size, low-cost scaled models for predicting the complex dynamic characteristics of the prototype rotor system. Overall, the proposed scaling design strategy provides practical guidance for the design and manufacture of the discontinuous scaled rotor systems, which has broad application in testing, fault prediction and dynamic design of prototypes. [ABSTRACT FROM AUTHOR]

Abstract: This article investigates the role of bearing preloads on the modal characteristics of a shaft-bearing assembly with a double row angular contact ball bearing. First, an analytical model is developed to comparatively evaluate the effects of axial bearing preloads on the vibratory responses of alternate double row configurations. The analytical model includes bearings via a five dimensional stiffness matrix. Changes in the resonant amplitudes with respect to the bearing preloads are examined for preload-independent and preload-dependent viscous damping models. The bearing preloads significantly affect the vibration characteristics of the shaft-bearing assembly due to major changes in both diagonal and off-diagonal elements of the stiffness matrix, and such effects depend on the bearing configuration. Second, a new experiment consisting of a vehicle wheel bearing assembly with a double row angular contact ball bearing in a back-to-back arrangement is designed. The bearing is subjected to axial or radial preloads in a controlled manner. Experiments with two preloading mechanisms show that the nature and extent of the bearing preloads considerably affect the natural frequencies and resonant amplitudes, thus influencing the vibration behavior of the bearing assembly. Finally, the new bearing stiffness model is validated using measurements from the modal experiment. Suggestions for further work are briefly discussed. [Copyright &y& Elsevier]