Mesh generation method of complex automobile trim

With the development of computer technology and the increasing maturity of finite element analysis algorithm, finite element analysis technology has shown its more and more important position in modern automobile development. The basic flow of finite element analysis technology is: pre-processing, analysis and calculation and result post-processing. Among them, pretreatment often takes up most of the time of the whole process. In addition, a reasonable and effective finite element model often plays a decisive role in the analysis progress and results. In order to obtain more accurate calculation results, physique is used in the analysis of many complex structures. Based on the finite element preprocessing function of HyperMesh and combined with engineering examples, this paper analyzes and summarizes the method of generating hexahedron or pentahedron from complex automobile trim structure

2 generation method of hexahedron or pentahedron physique in HyperMesh

HyperMesh software mainly provides generation tools of hexahedron and pentahedron physique such as drag, spin, line drag, element offset, linear solid and solid map. These tools are basically only for simple structures, and the geometry is required to be mappable. Mappable requires two opposites, a starting face and a target face, as well as a path connecting the starting face and the target face, which can be a line, face or vector. Therefore, the basic idea of generating hexahedral physique in HyperMesh is to divide the complex structure into multiple regions. These regions can directly generate physique in HyperMesh. It should be noted that the lattice correspondence between transition regions

3 example of body generation of automobile trim structure

here, through the air outlet baffle on the automobile instrument panel as the object, through the six face body generation process, this paper summarizes the six face body generation process and the matters needing attention

3.1 understanding the geometric relationship of structure

for a structure, we should first have a comprehensive understanding of it, and then see each feature clearly and decide which are important features and which are secondary and negligible features. In the actual engineering project, we should also consider how to decompose a complex structure so that it can be completed by different people to shorten the construction period

as shown in Figure 1, the air outlet baffle structure can be divided into three parts: A. small air door; b. Gale door; c. Shaft. The structure of small damper is similar to that of large damper, which is composed of upper and lower layers of foam and middle plastic layer, as shown in Figure 2. The rotating shaft can be divided into two partially symmetrical structures, as shown in Figure 3

Figure 1 air outlet baffle

Figure 2 air outlet structure decomposition

Figure 3 rotating shaft structure decomposition

3.2 structure decomposition into feature blocks that can use the physique generation tool to generate physique

in this step, further feature decomposition of the structure should be carried out so that each feature body can be directly generated by the physique generation tool in HyperMesh software. When decomposing the structure, we should use the symmetry or mapping of features, and pay attention to the connection and interface of features. For each feature body, it is necessary to consider whether it can be generated with different lattice generation tools. There should be certain requirements for the initial lattice of the generated physique, mainly considering whether the form of the lattice will affect the generation of adjacent feature bodies, as well as the size and quality of the lattice

for the damper structure, the upper and lower foam layers are mappable feature bodies that can directly generate hexahedrons. For the middle polyurethane material, which belongs to a new high molecular material plastic layer, it is found that through the up-down mapping of features, it can be decomposed into simple cuboids, as shown in Figure 4

Figure 4 cross section of the plastic layer of the damper

it can be seen from Figure 3 that there are some symmetrical pattern features on the left and right sides of the rotating shaft. For the pattern feature body, only one group needs to be generated, and the rest can be generated by mapping. A set of pattern features can be divided into several individuals with mapping features, as shown in Fig. 5. A feature that can be divided into several adjacent rings

Fig. 5 rotating shaft pattern feature body

3.3 determines the generation order of each feature block

before specific lattice, the generation order of feature blocks should be determined. The general principle is to start from the most complex features and generate from inside to outside. Small features should be considered when generating the lattice of large feature bodies. For the damper, the middle plastic layer shall be generated first, and then the upper and lower surface grids shall be used to generate a relatively simple foam layer. For the rotating shaft, the pattern feature in the middle is formed, and then extended to the ring feature at both ends, as shown in Figure 6

3.4 detail treatment during grid division

first of all, proper geometric cleaning should be considered to remove small holes and small fillets, but sometimes the retention of fillets is more conducive to the generation of grids and ensure reliable quality

or temporary monopoly

consider the starting surface and target surface, and do not have a lattice with wide difference in geometry and size, which is prone to distortion

the initial surface lattice generated, such as single edge notched beam 34 point zigzag method, tensile method and indentation, should ensure the quality and size of the lattice, and consider whether it is conducive to the generation of subsequent feature bodies. Extract the lattice from the existing physique

after the physique of each feature is generated, check whether it is continuous with the existing physique. There shall be no free surface inside the lattice, and check whether it fits with the geometry. The generated physical quality should not be too poor, and check whether the grid form can be adjusted to generate the initial grid required for the remaining feature bodies

4 Conclusion

from the above six sided physique generation process, it can be seen that a careful and perfect plan is the starting point and key to generate physique. When starting the generation of the first lattice, you should actually foresee the generation of the last lattice. Although the ultimate goal is physique, it takes much more time to generate lattice than physique. The lattice actually determines whether the physique can be generated, and determines the quality of the physique. When you meet an object you don't know what to do, constant trying is the best way. (end)