Analyzing On The Method Of Constructing And Simplifying Octahedral Unit Truss Structure

The space deployable structure is a kind of folding and expandable mechanism. It becomes compact after being folded, which saves space and makes storage and transportation easier. When it is unfolded, it has the big-scale work-needed space shape or suface. As the space deployable structure that is unfolded is in the working state,it needs a certain shape-preserving and load-carrying capacity, so lots of space deployable structures which are in the unfolded state show the truss structures. The stability of unit truss structure compares favourably with that of many other truss structures and any desired space shape could be constructed using the unit truss structures,so this type of structure is used widely. This paper will use octahedral truss units to construct a space deployable structure which is on the basis of the unfolded state.The method of constructing the octahedral units truss structure is studied firstly. After various assumptions and using a variety of geometric methods, we can ultimately determine the node coordinates of paraboloid truss structure which consists of nine octahedral units and get the method of constructing octahedral unit paraboloid truss structure. Using this method,we can construct the studied octahedral unit paraboloid truss structure.Secondly,analyze the expansibility and stability of the octahedral unit paraboloid truss structure. Through the comparison of the structural units, the correspondence between the deformation of octahedral unit and the distance of two points is derived, and the peripheral expansion limit of the structure is found using this correspondence. The relationship betwen stress modal number s,displacement modal number m and the geometric stability is given out,and the equilibrium matrix of the structure can be worked out using structure system balance equation, by the size of the modal number we can determine the stability of the paraboloid truss structure.Thirdly, using the ANSYS finite element analysis, analyze the stress of the truss structure under the condition of not applying prestress. The equilibrium matrix of the truss structure is then decomposed by singular value decomposition (SVD) method. Combining the self-stress modal vectors linearly and optimizing them by genetic algorithm (GA), we can get a group of optimal prestress. Analyze the stress of the truss structure under the condition of applying prestress and find out the constant tension bars. We can use the cables instead of those constant tension bars,and the cable-strut structure model is set up. At last we should test the feasibility of what we have done.In the end, using the equilibrium matrix and the judgment method of geometric stability,we can analyze the structural feasibility of removing the bars through the associated matrix transformation. At the same time, we must keep the equilibrium matrix rank invariant and make the rigidity of structure basically unchanged under the action of vertical force. On the premise of trying to ensure the structural stability, the goal of simplifying structure and reducing quality is achieved.Through these studies, the method of constructing the space truss structure by some basic unit is acquired, the determinant of the stability for the space structure is known,and the simplification of the space structure is explored. After that we can lay a foundation for further constructing space developable structure.