Morphology And Control Of Tensegrity Structures

Based on previous researches, this thesis has carried out an intensive research and investigation towards the general scientific problems and critical technique challenges in tensegrity structures. Analytic and numerical means including energy analysis, stochastic search algorithms, finite element method, nonlinear force method, optimal control algorithms and so on have been used in our researches.The form-finding of tensegrities has been classified into two general problems: 'force finding' and 'shape finding'. Corresponding mathematic models for these two form-finding problems are proposed and stochastic search algorithms are used to solve them. The proposed models and algorithms provide an effective way for form-finding and design of nonregular tensegrity structures. Meanwhile, we have discovered the multi-stable behavior of tensegrities with the above method. The energies and conditions for the transformation between different stable states of the six-strut diamond tensegrity and the icosahedron type Z tensegrity are investigated. The multi-table behavior of tensegrites has a potential application in actuators and force amplifiers.Analytic formulations for the pre- and post-buckling response of a simple tensegrity are presented. And a numerical procedure for analysis of complex tensegrites with buckling struts is proposed. The stress stiffening behavior before the buckling of struts and the stress softening behavior after the buckling of struts have been revealed, which provides a mechanical basis for the stress stiffening and softening properties exhibited by the actin network of cells. Viscoelastic analysis of tensegrity structures is achieved by the finite element method. A multi-modular tensegrity model for a stress fiber is proposed, and it has successfully predicted many viscoelastic properties observed in living stress fibers and isolated stress fibers. These practices have extended the application of tensegrity structures from traditional architectural/structural engineering to biomechanics.A single-objective optimal control procedure based on force method and simulated annealing algorithm is developed. The nonlinear optimal control of tensegrity structures is solved by the above procedure. Meanwhile, to find the correlation between the control efficiency and the control effort, a Pareto genetic algorithm for multi-objective control of tensegrity structures is proposed. With this multi-objective genetic algorithm, the trade off between the control efficiency and the control effort can be determined, which will help the designer selecting actuators and adjustment according to practical requirements.The dynamic equation for tensegrity systems considering the electromechanical coupling between piezoelectric actuators and structural members is derived. Linear quadratic regulator and instantaneous optimal control are used to implement the linear vibration control and nonlinear vibration control of tensegrity systems respectively. The feasibility and the control efficiency of these two algorithms in the vibration control of tensegrity systems are compared and discussed. Influence of the number and the layout of actuators to the control effect is investigated. The obtained results give a good guidance and reference for the practical application of active control systems based on tensegrities.This study has advanced the development of morphology of tensegrity structures, and has promoted the application of tensegrity structures into interdisciplinary field. It also has provided a basis for the further researches on tensegrity structures and tensile structures. Moreover, some guidelines and instructions for project design and construction control of tensile structures are given throughout the thesis.