Two-step transfer function calculation method and asymmetrical piecewise-linear vibration isolator under gravity

Piecewise-linear isolators are widely used in spacecraft for satisfying ever more stringent vibration requirements of high precision payloads. This paper focuses on ground tests of such isolators, with special consideration of gravitational asymmetry and mount flexibility. With asymmetrical equivalent isolator parameters derived with the extended equivalent linearization method, a two-step transfer function calculation method is proposed for enhancing the computation efficiency in dealing with studies where huge amount of computations are required, such as design parameter studies. The asymmetrical effect due to the gravity is presented by the movement of dynamic equilibrium positions as well as the softening and hardening characteristics of frequency responses. The effects and differences of the rigid mount and flexible mount, which respectively correspond to the shake table test and the whole spacecraft structure ground test, are studied with various design parameters. Numerical results show that the preload is an important factor in determining such effects and differences.