Numerical results of simplified dynamic analyses on large imperfect space structures

Abstract

Large space structures, with eigenfrequencies in the order of 10 −3–10 −4 Hz undergo dynamic excitations which can be periodic (e.g. at the orbiting frequency) or shock-like, as sudden load application (crossing the Earth's shadow), and e.g. control system thruster pulses. The calculated dynamic response can essentially deviate from that obtained by linear analyses. Indeed the overall eigenfrequency of a truss-like structure can decrease by some orders of magnitude due to the inevitable imperfection of the struts, and a strong non-linearity occurs for larger vibration amplitudes. Slenderness ratios < 50 are relatively insensitive to initial crookedness, they lead, however, to complicated and expensive structures due to the great number of nodal points. With increasing length and slenderness ratios, the imperfection sensitivity grows and the eigenfrequency of the struts themselves decreases. In this paper an attempt is made to evaluate the fundamental influences by simple analytical and numerical invesigations and to find some indications towards the design of an improved conception.