Development of Technology for Predicting Resonant Speed and Damping Ratio by using Open-Loop Characteristics

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In a rotating system, when the rotational speed matches the natural frequency of the rotating shaft, a resonance occurs in which the vibration amplitude of the rotating shaft reaches its maximum, and the rotational speed at this time is called the resonant speed. Generally, operation that actually passes the resonant speed is often avoided because the outstanding vibration generated at the resonant speed may damage the components that make up the rotating system. If the rotational speed is increased to pass through the resonant speed, the resonant speed is self-explanatory. Therefore if the resonant speed can be determined without actually passing through it, it is possible to efficiently take measures to operate the rotating system with low vibration. This paper describes a method for predicting the resonant speed from vibration data in the measurable speed range without increasing the rotation speed to the resonant speed. The resonant speed is predicted by obtaining the slope and intercept of the open-loop characteristic gain calculated from the vibration data and equivalent mass, expressing the open characteristic gain as a linear function, and extrapolating the open characteristic gain in the unmeasured rotation speed range. The proposed technique was applied to a one-degree-of-freedom model, a two-degree-of-freedom model, and a rotor model which is modeled by the finite element method, and it was shown that the resonant speed could be predicted with a very small error for all models.