EQUIVALENT CONTINUUM FINITE ELEMENT MODELLING OF PLATE-LIKE SPACE LATTICE STRUCTURES (OPTIMAL, VIBRATIONS, CONTROL)
Abstract
A variety of research projects are being pursued involving the dynamics and control of large plate-like space platforms made up of repetitive lattice-type truss structures. A method involving finite element modelling of an equivalent continuum formulation based on matching the strain energy and kinetic energy is developed for truss type lattices with pinned joints. The method is shown to give modal results consistent with those obtained using detailed finite element modelling of the pin jointed space lattice structure, even for structures with fairly small numbers of repetitions of an identical unit cell. Feedback controllers designed using reduced system models derived from these modal results using Modal Cost Analysis are shown to perform as well as controllers designed using the detailed analysis results. The efficiency of this method for coupled structure, control system design is demonstrated with a parametric study. Lattice plate finite elements are used to examine the effect of variation of several fundamental structural parameters on the natural frequencies and mode shapes of the structure. Feedback control systems are designed and the resulting system performance evaluated by examining the steady state regulation cost of the structure as a function of the structural design parameters. A micropolar plate continuum model of large plate-like repetitive space lattice structures with rigid joints is derived. A plate finite element is derived based on this continuum model with micropolar rotations and transverse shear deformations included as nodal degrees of freedom (d.o.f.'s). The natural frequencies and mode shapes are calculated using this element for a free floating hexahedral plate-like space lattice structure. These natural frequencies and mode shapes are compared to those calculated using a detailed finite element model (with every structural member modelled by a beam-column element) for several sets of frame member cross sectional properties. The static deflections of a centrally loaded and corner supported rectangular plate-like space lattice structure are also obtained and compared using these two types of structural models.
Degree
Ph.D.
Subject Area
Aerospace materials
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