Study On Morphogenesis Technique For Free-form Reticulated Shell Structure Based On Genetic Algorithm

Free-form surface structure is gradually becoming the major target in the study of the structure morphology, as a kind of fresh and artistic structure. Free-form reticulated shell structure is a new trend in the development of contemporary space structure, which is necessary to carry on more researches in the field.Based on genetic algorithm, the paper conduct research about the structural morphopoiesis with free-form reticulated shell structure. It discusses the basic principle of genetic algorithm and some of the advanced approach in genetic algorithm, and puts forward ideas on the creation of free-form reticulated shell structure based on genetic algorithm: First of all, consulting Loop subdivision method, reasonable free-form surface is established and consummated to behave as the basic structure in the reticulated shell. Secondly, the basic structure is optimized using genetic algorithm in topology and size. the analogous simulated annealing algorithms is applied to the result after optimization. Eventually, the shape optimization is completed by the means of strain energy sensitivity to move nodes in the final optimized results.For the topology optimization, the stable triangular units are encoded. The binary system ‘0 or 1’ is adopted to represent existence or not. For the sizing optimization, a table containing a set of bars with different cross sections is established, where the code of each bar represents the matching section number according to the integral encoding. For the shape optimization, nodes are moved by adopting sensitivity of strain energy method. Not only the z-coordinate but also the x-coordinate, y-coordinate and z-coordinate can be changed at the same time. Combining the genetic algorithm with a variety of optimization method, the paper makes optimization to free-form reticulated shell structures. The combination makes up the weaknesses of genetic algorithm for its poor ability in local Search, meanwhile improves the solution efficiency.In the process of optimization, the method to deal with the key question, the gravity and distributed load is put forward. The key question including: the way to handle with the necessary bearing node and loading point; the way to insure no isolated bars, in order to avoid structural stiffness matrix singular. The way to deal with the distributed load is dividing the planar projection of the structure into a number of identical grid, then multiplying by the distributed load, finally the product applying to the grid centre, and is assigned to the closest nodes.The paper proposes the method to handle the structure, which is not match constraint conditions. The penalty function is accepted to the constraints, when member strength, slenderness ratio, stability of bending bars, and the overall displacement is beyond the limit.In the paper, we choose the minimizing quality and minimizing the product of the structure mass with external forces as the two optimization objectives. Strengths and weaknesses are explained by the models. A series of good models after optimization design are established, which illustrate the feasibility and practicality of the proposed morphopoiesis method in the paper.