Statics And Dynamics Anlyses And Applications Of Tensegrity Structures On Wave Energy Harvesting

Tensegrity structure is a novel kind of space structures with the rapid development abroad.They have advantages of light-weight,compact structure,high stiffness,easily modeled,geometric nonlinearity,deployablity etc.These characteristics make them widely applied in the field of architectures,aerospaces and robots.Moreover,tensegrity-based parallel mechanism evolved from tensegrity structures,have aroused the scholars’ great attention and become a research hotspot of mechanisms gradually,due to their advantages of light-weight and under-actuated.In this dissertation,the form-finding problems have been investigated.The workspaces,input and output responses,dynamics and applications on the energy harvesting of tensegrity-based parallel mechanisms are researched.The main results have been summarized as follows:1)A novel form-finding method for tensegrity structures is studied.Since conventional FDM(Force Density Method)could not be used to solve the form-finding of large scale and irregular tensegrity structures efficiently,a novel approach is proposed on the basis of FDM and IAFSA(Improved Artificial Fish Swarm Algorithm).Firstly,the equilibrium equations are derived on the basis of FDM.Afterwards,the equations are solved by IAFSA.By employing the position information of current global best artificial fish and the behaviors of swallowing and leaping of the artificial fish,IAFSA has higher search efficiency.Moreover,due to leaping behaviors of the artificial fish,IAFSA has the ability of finding global extremums.A set of appropriate values of force density is found by IAFSA in the force density space to make the rank of the equilibrium matrix satisfy the required conditions.Take expandable octahedron as an example,its form-finding problem is conducted by using IAFSA.The experimental results indicate that the form-finding results of IAFSA are reliable.Compared with conventional artificial fish swarm algorithm,the IAFSA has fast convergent rate.2)The methods for the static and dynamic analyses of tensegrity mechanisms are researched.Firstly,the approachs for computing the geometric workspace of tensegrity-based parallel mechanisms are studied.By numerical examples,the geometric workspaces are simulated and the evolutions of geometric workspace volumes as geometric parameters are analyzed.Based on the analysis of geometric workspace,the concept of equilibrium workspace is proposed.On the basis of the solutions to the inverse kinematics,a model for computing the equilibrium workspace is developed.This model considers the mechanisms’ the constraints including energy constraints,length limitations of kinematic chains,and angle limitations of joints and bars’ interferences.The equilibrium workspaces of tensegrity-based parallel mechanisms are analyzed by numerical simulations.Moreover,the influence on geometric workspaces by mechanisms’ parameters is revealed.Finally,the dynamics of tensegrity-based parallel mechanisms have been researched.On the basis of the principles of virtual work and D’Alambert,the dynamic model of tensegrity-based parallel mechanisms is set up.The virtual work of the rigid bodies and springs is computed.It follows that the dynamic equations of tensegrity-based parallel mechanisms can be derived.The dynamic model is solved by using MATLAB software package.The influence on motion laws by mechanisms’ parameters is obtained.3)The methods of analyzing the input and output responses are proposed.On the basis of energy method,the input and output responses’ model of the symmetrical and asymmetrical tensegrity-based parallel mechanisms is built.The responses of the structures,researched in this dissertation,to the external forces and torques are analyzed.Afterwards,an experimental prototype is made.The input and output responses of the theoretical model are compared with that of the experimental model.The validity of the theoretical model has been verified.4)A 6-DOF wave energy harvesting device is investigated.The dynamic model of the 6-DOF wave energy harvesting device is developed.This model considers not only the coupling between the rigid-body dynamics and fluid dynamics but also the coupling between the 6-DOF movements of the float.On the basis of the Runge-Kutta method,the dynamic model is solved.The translational and rotational movements of the 6-DOF wave energy harvesting device and the efficiency of the energy transforming are analyzed.