がたを含む連続体のランダム振動における等価減衰比の実験的評価 : 線形伝達関数のあてはめによる評価

抄録

This paper deals with an equivalent damping ratio of a nonlinearly vibrating beam due to a collision between the beam and a plate. The vibration model is a cantilever beam with a gap. The input force, generated by an electromagnet shaker, is stationary white noise. Acceleration of the spherical top of the cantilever beam is measured and used to experimentally evaluate the transfer function. An analytical transfer function for a vibration model without a gap is obtained and employing the parameters η, ω_e, and ξ_e for expressing the magnitude of the transfer function, dominant angular frequency and equivalent damping ratio for the nonlinear beam system respectively, we compare the equivalent transfer function with those obtained experimentally. The equivalent damping ratios from experiments are constant at about 20% within 0.4 to 0.8 of the collision rate. Reduction of energy by collision is evaluated to produce only 3% to 4% damping under the experimental conditions. If the plates have the characteristic of the nonlinear spring after the collision, it is shown by calculations that the equivalent damping ratios become a large constant value. We think that the equivalent damping ratios ξ_e from experiments are composed of the reduction of energy by collision and characteristic of the nonlinear spring.