NONLINEAR VIBRATION RESPONSE OF A CYLINDRICAL WATER STORAGE TANK CAUSED BY COUPLING EFFECT BETWEEN BEAM-TYPE VIBRATION AND OVAL-TYPE VIBRATION:PART 1-VIBRATION EXPERIMENT

摘要

In this study, a vibration experiment with a reduced scale model of a large-size cylindrical water storage tank has been performed in order to investigate the nonlinear vibration responses of the cylindrical tank when the beam-type vibration and the oval-type vibration are coupled. In the vibration experiment, a sinusoidal sweep test was performed by using a shaking table on the reduced scale model of the cylindrical water storage tank filled with water to the 95% level. The test was conducted by varying the input acceleration from smaller to larger input in several steps to identify the vibration modes and evaluate the vibration behaviors of the beam-type vibration and the oval-type vibration. As a result, the resonance curves showed that the resonance frequency shifted to the lower frequency region and the response magnification factor became smaller when the input acceleration level became higher. When the magnitude of the input acceleration increased furthermore, the resonance curves were changed to be duller from the sharp peak and the resonance points became unclear. The measured displacements and strains of the sidewall of the model tank showed that the oval-type vibration was excited in the vicinity of the beam-type resonance frequency and that the amplitude of the oval-type vibration increased too significant to be ignored when larger input was applied. It was verified that the oval-type vibration with a subharmonic resonance of order one-half was excited when larger input was applied. This phenomenon was not observed when small input was applied. This shows that the vibration behaviors caused by coupling effect between beam-type vibration and oval-type vibration depend on the magnitude of input excitation. From these results, it can be assumed that the oval-type vibration is closely related to the nonlinear vibration response phenomena of a cylindrical water storage tank.