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In large rotor-bearing systems, the rolling element bearings act as a considerable source of subcritical vibration excitation. Simulation of such rotor bearing systems contains major sources of uncertainty contributing to the excitation, namely the roundness profile of the bearing inner ring and the clearance of the bearing. In the present study, a simulation approach was prepared to investigate carefully the effect of varying roundness profile and clearance on the subcritical vibration excitation. The FEM-based rotor-bearing system simulation model included a detailed description of the bearings and asymmetricity of the rotor. The simulation results were compared to measured responses for validation. The results suggest that the simulation model was able to capture the response of the rotor within a reasonable accuracy compared to the measured responses. The bearing clearance was observed to have a major effect on the subcritical resonance response amplitudes. In addition, the simulation model confirmed that the resonances of the 3rd and 4th harmonic vibration components in addition to the well-known 2nd harmonic resonance (half-critical resonance) can be significantly high and should thus be taken into account already in the design phase of large subcritical rotors.

Bearing performance significantly affects the dynamic behaviors and estimated working life of a rotating system. A common bearing type is the ball bearing, which has been under investigation in numerous published studies.The complexity of the ball bearing models described in the literature varies.Naturally, model complexity is related to computational burden. In particular, the inclusion of centrifugal forces and gyroscopic moments significantly increases the system degrees of freedom and lengthens solution time. On the other hand, for low or moderate rotating speeds, these effects can be ne-

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Design of High Speed (HS) electric machines is an iterative process that requires a multidisciplinary design team to accomplish the required performance. In this study, a design space method (DSM) is developed to streamline conceptual designing of a high-speed and high-power electric machine. The method uses analytical equations and a rotordynamic model to determine geometrical dimensions based on the application requirements. These dimensions create a feasible baseline design for the particular application. However, considering the dimensions as design variables and using the baseline design as a starting point, a multidimensional combination and interaction of the design variables and the correlated output for the particular topology of motor and performance range can be further studied for design exploration and optimization purposes. The study includes a test case where the baseline dimensions are determined and compared to an existing machine from literature, and then further explored to identify the sensitivity of different outputs with respect to different design variables. The method enables rapid design iterations, rotordynamics and rotor mass optimization. The baseline design can be also used as a starting point for the detailed design.

High-speed solid-rotor induction machines (HSIMs) are popular within high-speed (HS) applications because of their high rotor structural integrity and their fairly well-established manufacturing process guaranteeing high quality series products. Designing a new HS electric machine requires a multidisciplinary team to accomplish the machine performance desired. In case of a HS machine design, the components and applied materials often reach their physical limits at the rated operating condition. Therefore, the design process is highly iterative and, thus, a systematic approach has a high potential to reduce the time of the design phase significantly. In this article, a systematic design process is proposed for a modular, multimegawatt (MMW) HSIM with three radial active magnetic bearings. The process includes a traditional multidisciplinary design flow with extra critical aspects of MMW HS machines: manufacturability, bearing system, housing, and operating unit. In addition, the manufactured machine is reported. The proposed systematic design process is described, including several multidisciplinary critical design aspects of HS machinery.