A Constrained Two-dimensional Quadrilateral Mesh Generation Algorithm For Ship

Currently, the most common ship design process of the interface platform between CAD and CAE systems is finishing the project and detailed design firstly based on the parallel design of AutoCAD and Patran and then reconstructing the 3D models on the professional ship design software Tribon according to the pre-design results.. The process plays a vsignificant role in the overall ship design. But the constructed models of different systems are relatively independent of each other, which wastes resources, and can hardly guarantee the data consistency in the product life cycle. This has been the bottleneck of cutting the product design cycle and improving the market competitiveness.Establishing the target structure finite element model is the first step of the ship structure finite element analysis. Quick generation technique of ship structure finite element model is immature at present. First, because of the complexity of ship structure, most finite element modeling was carried out by hand, namely, getting the position of the ship structure coordinates from the two-dimensional drawings completed in the ship structure preliminary design stage; putting them into the finite element software Patran, and Ansys, etc; setting up node and unit, and endowing the units with properties. The modeling process iscumbersome, inefficient and error-prone, greatly reducing the efficiency of ship structure finite element analysis. Second, meshing is a key factor restricting the development of the finite element modeling technique. The speed and quality of the grid will directly affect the efficiency and calculation accuracy of finite element analysis. It takes long to correctly mesh a complex geometric area and the mesh form must be adapted to the nature of the problem under analysis. In consideration of safety and calculation accuracy, the shape of the grid cell in two-dimensional domains is required to be quadrilateral especially in important fields such as ship and aviation,. Generation of quadrilateral mesh is more complicated than and not as mature as that of triangular mesh, leaving meshing technology higher request. Third, the method of establishing finite element model through the interface language or macros often independently defines ship structure, which does not take the actual connection and dependencies between different parts into account, leading to many problems such as independent structure grid.This paper assimilated the advantages of the Q-Morph and paving quadrilateral generation algorithm, based on which a modified quadrilateral generation algorithm was put forward. The new algorithm was verified by C++ and a quadrilateral mesh generation software was developed. Finally, to propel the optimization method of the generated mesh, reduce the number of poor quality unit, and improve the quality of the grid, specific work was done as following:1) Put forward an improved quadrilateral generation method, which effectively combines the advantages of the two algorithms, such as sensitivity to boundary, and higher mesh quality of paving method algorithm, and the adaptability of the Q-Morph algorithm.(1) Improve the frontier classification method of the Q-Morph algorithm to enhance the regularity of the quadrilateral units.(2) Modify the regulation of quadrilateral mesh shape determination of the Q-Morph algorithm combining the sensitivity to boundary of paving algorithm to improve the quadrilateral unit quality.2) Establish the grid optimization system. Chose different grid optimization algorithm according to the characteristics of different grid conversion stages. And meliorate the most widely used Laplace optimization algorithm.Aiming at the shortage of compressed triangle mesh in Laplace optimization algorithm, the algorithm was weighted, ensuring the uniformity of the grid size.3) This paper will study the constraint characteristics of the boat deck structure. In view of unit coordination problems at the constraints in the model, the optimization order of quadrilateral transformation of Q-Morph algorithm was adjusted, guaranteeing the coordination of quadrilateral element at all kinds of constraints.