Research On Automobile Modeling Design Method Based On A Novel Parametric Surface

As the most representative product of modern design and industrialization,the rapid development of automobile industry is an important reflection of the modernization process of a country or even the world.With the increasingly fierce competition in the automotive industry,the automotive body styling design which directly affects its market performance and brand competitiveness is highly valued by the industry.In the current technical environment,the use of computer-aided geometric design theory for vehicle modeling design and the establishment of mathematical model of vehicle surface is undoubtedly the most efficient technical means.Aiming at the surface design of car modeling,a new type of mathematical model of shape adjustable surface is put forward,and a kind of matching typical body template is constructed in this paper.Besides,combined with surface modeling technology,generative design concept,computational fluid dynamics technology and parameterized design means,a set of parameterized body surface modeling design method is formed.Finally,a CAD software prototype system is built,which effectively integrates body design,modification,analysis,optimization and other processes parameterized together.The main research work is as follows:(1)Combined with the modeling characteristics of common household cars,a set of typical Body CAD templates with certain applicability is summed up.The body assembled by 25 quadrilateral surface patches can be adjusted to describe different body appearance modeling.Based on the template,this paper proposes a fairing and continuous processing method between the surfaces in the car body.By the introduction of segmentation parameters and the concept of transition surface,the interface of each sub-surface is G1 continuous,and the segmentation parameters can be used to adjust the shape of the transition surfaces.(2)In view of the defects of the current mainstream parametric surface,this study combines the construction logic of the first kind of Coons surface and the basis function GE-Bezier surface,and proposes a new m×n-degree parametric surface,named SQ-Coons surface.On the basis of interpolating the edge into four boundary curves,the surface detail modeling of the central part can be adjusted by several shape parameters.At the same time,according to the principle that it is built by superposition of multiple surfaces,the segmentation algorithm and transition surface generation algorithm for SQ-Coons surface are proposed.(3)Combined with the typical automobile CAD template and the geometric characteristics in SQ-Coons surface,a whole set of car body surface modeling design and adjustment method is presented in this paper.This method starts with the plane sketch of the car body by hand,and creates the whole car body surface model by establishing the three-dimensional feature line of the space.In this process,through the adjustment of the boundary curve control points,shape parameters and segmentation parameters,it achieves the purpose of parametric modification of the whole car modeling,and maintains the G1 continuity among the surfaces under the influence of the transition surface.According to the theory of generative design,based on the sample database of 50 different vehicle models built by SQ-Coons surface,a new method of vehicle model generation by extracting its modeling feature parameters is formed,in order to provide a new modeling design idea and further expand the application scope of the new surface and CAD template.(4)On the basis of the above research,an analysis and calculation method of vehicle similarity is proposed.Based on the sample database established by CAD body template and SQ-Coons surface,a method of calculating the difference value and similarity between all modeling parameters of the whole body is constructed by comparing them in the whole sample database.The conclusion can be used for the analysis of brand model expectation or design trend.(5)On the premise of keeping the overall vehicle design unchanged,the segmentation parameters and shape parameters are taken as variables,and model generated by different value combinations are put into the CFD analysis process.According to the simulation results,a set of methods to improve the aerodynamic performance of the whole vehicle through the adjustment of vehicle details is proposed.By introducing the concept of curvature ratio to limit the degree of surface deformation,the corresponding surface details with the lowest aerodynamic drag coefficient can be screened out in a limited combination of parameters.(6)Using the design software Rhinoceros and the parameterized programming platform Grasshopper,the design method built by the body CAD template and SQ-Coons surface are developed and packaged into a set of body modeling design program,in which the control point coordinates,segmentation parameters,shape parameters and other features are integrated,and a set of plug-in program for efficient body surface modeling design is formed。The research results of this paper have important theoretical guidance and practical value for automobile modeling design,and can also be used as reference for other surface product modeling design.