Theoretical And Experimental Studies On Dynamic Characteristics Of Flexible Spinning Beams

Flexible spinning beam-like structures are widely used in rotating machinary and space structures. Recently, spinning beams become more and more flexible and slender. And the spinning speed also increases rapidly. All of these changes bring new challenges to researchers. The researches on dynamics characteristics of flexible spinning beams synthetically involve several cross subjects: beam theory, rotor dynamics, gyro dynamics, nonlinear dynamics and geometrical nonlinearity. Hence, the studies on dynamics characteristics of flexible spinning beams are considerably important both in theoretical study and engineering application.An important gyroscopic term due to centrifugal forces is missing in many reports in the spinning beam literature. In this thesis, the term due to centrifugal force is considered to belong to gyroscopic effects, and also proved to be indispensable for correct modeling and analysis of spinning beams. The influences of rotary inertia, spinning speed, gyroscopic effects, slenderness, and gravity on dynamic characteristics are investigated in detail using analytical and finite-element methods.Geometrically nonlinear models of spinning beams usually only include von Karman or cubic nonlinearity in the literature. Base on local displacements, Jaumann stress and strain measures, and an exact coordinate transformation, a total Lagrangian geometrically exact nonlinear theory of spinning beams undergoing large deflection vibration is derived. The new geometrically exact theory can account for large displaces and large rotations of spinning beams. By analyzing the deformed geometries of flexible spinning beams under different working conditions using numerical methods, the nonlinear model is verified to be of powerful adaptability. The model is proved to be correct by comparing the numerical and experimental results.A camera-based noncontact measurement theory for dynamic testing of structures that undergo large deflection is derived in this thesis. Static calibration is used to estimate system parameters at first. Then dynamic calibration is performed for refinement of estimated system parameters and establishment of a lens distortion model. Some key issues that are essential for measure accuracy are discussed, such as key devices, experimental set-up and singularity problem. The thesis also makes a preliminary study of using just one camera for accurate dynamic measurement. The small-sized cylindrical makers which are self-designed, combined with the camera-based measurement system, are used to realize the accurate measurement of large deflection vibration of flexible spinning beam. The paper also analyses the evolution mechanism.A experience-based signal compensation method (SCM) is presented to reduce the mode mixing phenomenon. The empirical mode decomposition (EMD), combined with SCM, is proposed to avoid the mode mixing phenomenon. Furthermore, this method could also be used to do noise filtering effectively. Based on the new technique, the conjugate-pair decomposition (CPD) and Hilbert-Huang transform (HHT) are used to investigate the experimental vibration signal in order to obtain time-varying frequencies and amplitudes to reveal nonlinear dynamic characteristics of a spinning beam.In this paper, the research on flexible spinning beams enriches the structure dynamics of spinning beams both theoretically and experimentally, and also provides theoretical basis for design and analysis of spinning structures.