Title

Dynamic and thermal analyses of flexible structures in orbit

Date of Completion

January 2006

Keywords

Applied Mechanics|Engineering, Aerospace

Degree

Ph.D.

Abstract

Due to the launch cost and functional requirements, space structures, such as satellite antenna, deployable structures, solar sails, the space station, and solar panels, are necessarily built lightweight, large, and very flexible. These space structures undergo large orbital rigid body motions as well as large structural deformations caused by gravitational force and other disturbances, such as shuttle jet impingement loading, deployment factor, thermal effects, and debris impact. It is of utmost importance to study thoroughly the dynamic behavior of flexible structures in orbit under various external forces. ^ In this study, first a finite element methodology program based on the absolute nodal coordinate formulation is developed to determine the coupled structural and orbital response of the flexible structure under gravitational and external loading, i.e., gravitational force, impact force, and jet impingement, and thermal loading. It is found from the simulation results that pitch and structural response of the flexible structures are greatly impacted by the initial and loading conditions, such as orbit eccentricity, initial misalignment, etc. ^ The absolute nodal coordinate formulation may lead to inaccurate results due to the fact that the orbit radius is used for element coordinate, which is much greater than the amplitude of the pitch (attitude) motion and deformations of the orbiting structures. Therefore, to improve the accuracy of structural response in the simulation, a floating (moving) frame that is attached with the orbiting structure's center of mass and that moves parallel to the inertia frame fixed at the Earth's center is introduced to separate the attitude motion and structural deformation from the orbit radius. The finite element formulation is developed in this parallel reference frame system for two and three dimensional beam structures. It is then used to study dynamic response of flexible structures in two and three dimensional orbits. In some cases the structure is subjected to both the Earth's gravitational force and jet impingement loading and in other only the gravitational force. Numerical examples showed that the parallel reference frame formulation gives more accurate results than the absolute nodal coordinate formulation when they are both used to study the orbital structure dynamics. A simplified beam model is presented for investigation of flexible beam structure in three dimensional orbits to greatly reduce the computational time. ^ The parallel reference frame formulation is also applied to investigate coupled thermal-structural response of orbiting beam structure. It is seen that the flexible structure is experiencing rapid temperature changes when it enters and exits the earth shadow in a short period of time. A non-uniform temperature distribution across the cross section is developed due to the temperature change. The flexible beam structure is bent due to the uneven temperature distribution.^