Research And Implementation Of Geometric Configuration Of Space Grid Structures

Various types of shapes and grid modes of space grid structures bring on lots of difficulties in structural modeling and design. Thus, based on the proposed concept of geometric configuration of space grid structures, this dissertation researches on the modeling and optimization technique, and focuses on the realization process of structures. In this work, three primary modeling techniques are investigated, i.e. generation design, mechanics-based modeling technique and reverse modeling method. Moreover, the extension of grid meshing modes and the optimization of grid system are also discussed.The types of surface shapes and grid modes are firstly analyzed. A number of key technical issues on geometric configuration are then concluded. A state-of-the-art review on modeling and meshing techniques of space grid structures is given and some involved problems are also expounded.The surfaces of space grid structures generally include regular and free-form surfaces, which are respectively expressed by analytic function and B-splines as well as quasi-uniform B-splines. With the combination of numerical method, the prediction technology of clamping boundary is discussed according to the trend. Basic geometric parameters and surface curvature are described. The re-interpolation reflection meshing method is proposed to avoid the uneven grids caused by the distortion curvature.Generation design technique realizes the computer aided design of geometric configuration. Firstly, the characteristic parameters of surfaces used as data points which distribute in rectangular topological relationship can be generated. Then B-splines interpolation is implemented to reconstruct or reshape surface. Especially, how to generate parameters of clubs-shaped and petal-shaped pattern is discussed. Numerical examples prove that the generation design can satisfy the accuracy and improve the efficiency.Mechanics-based modeling techniques are comprised of the theory of geometric and mechanics. One modeling technique is energy modeling method. A complete energy model and physical meanings of parameters are presented. The uniform control equation is given, and with the introduction of quasi-uniform B-spline elements, the simply and clamped supported constraints problems are simplified. Another modeling technique is based on self-equilibrium membrane. The prediction technology of clamping boundary and quasi-uniform B-splines are introduced to express surface, and suppositional stiffness of point is deduced. With the combination of Laplace-Young's equation and dynamic relaxation method, the optimal surface inherited is shaped according to the change of average curvature. Numerical examples present that it is convenient to get minimal surface, seek for similar surfaces and mesh more grids by using above techniques.Reverse modeling method is derived from the principle of reverse engineering. Firstly, it scans the physical model to get cloud data by 3-dimensional laser scanning system. Secondly, the cloud data are handled by reverse software to get scan-lines data. Thirdly, the scan-lines data are shaped by improved skinning surface technique and meshed to CAD model. Finally, the CAD model can be fabricated by paper through the board-lofting technique. Several examples and experiments prove that the reverse modeling method is feasible.In dissertation, some grid quality criteria are given. Several practical grid modes are extended. The improved energy method is applied to smooth grid system, and disciplinarian with punished factor and grid quality criteria is concluded. One optimization algorithm of grid system is proposed, where the grid system characteristics, grid quality and tolerance of elements length, etc. are weighted to perform objective function.According to the theory and algorithm aforementioned, a computer aided design program named geometric configuration, GCCAD for short, is developed. GCCAD has friendly pre- and post- processing functions, and graphical interfaces. It provides operating platform and improve the efficiency and convenience of design work.The conclusions and problems that should be studied further are summarized at the end of dissertation.