Research On Key Technologies Of CAE Analysis Automation Based On Boundary Face Method

The Computer Aided Engineering(CAE)analysis has become one of the indispensable means for supporting engineering and industrial product innovation.In CAE analysis,Finite Element Method(FEM)and Boundary Element Method(BEM)are two representation numerical methods.It has long been recognized that the FEM is the most basic CAE analysis technique.The FEM is difficult to realize automatization because of the simplification of CAD model and the defect of the separation of geometric model and analysis model.The BEM based on the Boundary Integral Equation(BIE)has the advantages of reduced dimension and higher accuracy,besides,the interpolation functions and computational element can be discontinuous in the BEM,which provides an idea for the automatization of CAE analysis.Nonetheless,in the traditional BEM,the geometric model is achieved by the discrete mesh model just like the FEM,which could arouse approximation error so that the computational accuracy is reduced.By contrast,the Boundary Face Method(BFM)also based on BIE,which inherited the advantages of BEM and avoid the geometry errors by means of combined the BIE with Computer Graphics(CG).In BFM,CAE analysis is performed on the CAD model directly,which naturally achieved the seamless integration of CAD and CAE.Therefore,on the basis of the BFM,the complete solid CAE analysis software was developed by our groups,which has the characteristics of the structure to be analyzed without geometry repairing and defeaturing,generated meshes adaptively and provides more accurate stress when analysis the complicated structures with small configurations and infinite domain problem.The BFM provides a theoretical basis for CAE analysis automation and a series of studies and trials are made based on it.Firstly,an expanding element interpolation method is proposed,which integrates the continuous and discontinuous element by collocating virtual nodes along the perimeter of the traditional discontinuous element.Therefore,the method reduces the burden of mesh generation greatly and improves the calculation accuracy by two orders.On the other hand,an enhanced quadrilateral adaptive surface mesh generator has been developed and also proposed a mixed quadrilateral and triangle mesh algorithm.At the same time,the unit geometry interface module and CAD reprocessing module promote the automation of CAE analysis to a certain extend.The contributions of the dissertation are listed as followed.(1)A unit geometry interface module is developed to enable the seamless integration of CAD and CAE that can exchange Boundary Representation(B-Rep)data between CAE software and CAD software.Then,the obtained CAD-Brep data is used to build CAE-Brep and defines kinds of parametric curves and surfaces classes by using C++ codes.At the same time,the point inversion and projection algorithm for curves and surfaces and calculation the first and the second derivative are also developed,which can be a geometry calculation tool for subsequent mesh generation and numerical integration.Furthermore,a new sphere named polar sphere which has only one pole is defined to avoid the defect of traditional sphere that the two poles affect the mesh generation and numerical integration seriously.The impact of pole is eliminated through the virtual decomposition of the whole sphere which is divided to two semi-spheres,and then each semi-sphere is defined by the polar sphere.(2)A novel expanding element interpolation method is proposed to unify the continuous and discontinuous element.The expanding element is achieved by collocating virtual nodes along the perimeter of the traditional discontinuous element.With the virtual nodes,the interpolation accuracy increases by two orders compared with the original discontinuous element and the difficulty of mesh generation is effectively reduced.Meanwhile,the BIEs are built up for the inner nodes of the traditional discontinuous elements,only(taking these nodes as source points),while the virtual nodes are used for connecting the shape functions at the source points,thus the size of the final system of linear equations will not increase.In addition,the discrete BIE of 2D potential problem and plane static elasticity problem based on expanding element is deduced.The final numerical results show that the expanding element interpolation method has higher exactness and convergence rate.(3)The Paving method,which can generate quadrilateral surface mesh during 2D parametric space automatically,is studied and improved to take the advantage of the merit that the BFM only need to mesh the surfaces of the problem domain.The Paving method is more efficient by simplifying the algorithmic procedure and using an elaborately redesigned front management tool.The tool is developed by the C++Standard Template Library(STL),which can very efficiently classify front type and supervise the intersection of fronts.Meanwhile,the final mesh quality is enhanced by take advantage of topology clean-up operation and Geometry Element Transformation Method(GETMe).In addition,the Paving is improved and extended to mesh the surface with the random hard point and hard line constraints.Finally,many complex examples show that the improved Paving method is general and efficient.(4)A triangular and quadrilateral hybrid mesh generation method based on binary tree is proposed to enable the development of new algorithm that can take advantage of the mesh nodes can be discontinuous and without geometry repairing and defeaturing in the BFM.The binary tree method is an improved method based on quadtree.Firstly,the mesh is generated by taking into account the Riemannian metric in the 2D parameter space,and then the resulting mesh is mapped back to the 3D physical space without distortion and the mesh nodes are on the actual surface.Secondly,the binary tree is subdivided by using the boundary curve curvature and surface curvature and the subdivision direction is changed from two-way to one-way,subsequently reduces the unnecessary mesh generated.Thirdly,in the balance binary tree process,the area ratio of adjacent leaves cannot exceed default value which can avoid coarse mesh generation;Fourthly,a double-ray method is introduced to judge the attribute of the point;At last,a practical template used to deal with the boundary element is proposed according to the actual situation,which makes the binary tree can apply to mesh the region with complex boundary.The validity of the quadtree method is proved by some examples.(5)A solid modeling module of the actual weld(Software Registered Number:2016SR323544)is developed to solve the problem that the weld modeling module in the UG-NX cannot express the actual weld shape.The module is a CAD reprocessing module in the software of Complete Solid Stress Analysis,which fusions with the CAE analysis software by means of the response menu written by menu script language provided by UG-NX secondary development tool.Kinds of dialog are designed for interaction with UG-NX,which are developed by MFC technology.The user only needs to input a few parameters and locates the weld through the dialog,and then the actual weld shape can be automatically simulated with B-spline.Beside,the mesh generation of some kinds of welds is realized,which create condition for the subsequent CAE analysis.