Simulation Of Vortex-Induced Vibrations Of A Circular Cylinder Near A Plane Boundary With Lattice Boltzmann Method

The main work in this thesis are:simulation of both a stationary cylinder and an oscillating cylinder undergoing steady flow at Re=100near a moving ground and a still ground of different gaps that varies from0.05to2.0; simulation of an elastically supported cylinder undergoing steady flow at Re=200near a still ground of different gaps varies from0.05to2.0while whose natural frequency varies to make reduced velocity vary from2.6to12.4; and the analysis of the parameters gained. The key response parameters are vortex shedding frequencies, fluid force coefficients and vibrating amplitudes of the cylinder.The main conclusions are as follows:As the gap between the cylinder and the ground decreases, vortex shedding gets suppressed especially when the gap-to-diameter ratio is less than0.6; but if the reduced velocity is between10.4and23.6, vortex shedding gets suppressed until the gap ratio gets to a small number at which a single row of vortex appears.The drag and the inline shift are closely related to the reduced velocity:if the boundary layer exists, the drag and inline shift decreases as the gap ratio decreases.As the gap between the cylinder and the ground decreases:the mean lift coefficient increases rapidly; the amplitude of lift coefficient increases first, then decreases and at last stays constant if reduced velocity is between4.5and6.0; if reduced velocity is out of that range, the amplitude of lift coefficient goes a small fluctuate, then stays low between gap ratio=0.4and0.25, and at last increases a lot. The lateral shift amplitude goes with the reduced velocity like the common VIV situation when the gap ratio is larger than0.6. There is a jump of the amplitude when reduced velocity is in the lock-in span. When the gap ratio is smaller, the lock-in span of reduced velocity gets larger and the amplitude value appears at higher reduced velociry.The cylinder undergoes a loop motion in most cases and an abnormal figure "8" in the rest cases.