Abstract: Two prefabricated centrally-clamped cosine beams were proposed as a nonlinear vibration isolator for active and passive vibration isolation of marine equipment. The analytical expression of the beam’s force-displacement relationship was given, and the nonlinear differential equations of active and passive vibration isolation were established, respectively. The harmonic balance method (HBM) was applied to get the approximate analytical solutions of the differential vibration equations, and then the solutions were compared with those numerical ones obtained by the Runge-Kutta method. In order to characterize the vibration isolation capability of the isolator, the expressions of force transmissibility and displacement transmissibility were given. In addition, the effects of different nonlinear stiffness coefficients, excitation amplitudes and damping coefficients on force and displacement transmissibility were studied. The results show that HBM yields the same solution as the numerical method. The proposed nonlinear isolator has excellent performance of low-frequency vibration isolation, and its response and vibration isolation performance are affected by the excitation amplitude and damping coefficient.

Key words: cosine beams; vibration isolator; nonlinear vibration; harmonic balance method (HBM); vibration transmissibility