Research And Impletation Of Car Body Surface Modeling Based On Implicit Parameterization

Lightweight is a hot topic in the automotive industry.The optimal design of car body structure is the main mean in addition to the use of new materials.It's more likely to achieve a certain substantial modification in the stage of conceptual design because the design constraints are less.Stiffness,strength,fatigue and other properties of the body structure are evaluation indexes.The calculation of these indicators needs to use CAE analysis.Parametric model is necessary.As a model parameterization method,implicit parameterization uses beam and junction features and the map relationship between beam and surface to model the car body.Compared with the traditional parametric technology,implicit parameterization has advantages such as larger model modification and more stable model.This thesis studied the key technology of implicit parameterization and related algorithms are given.The main work of this thesis is as follows.1.The modeling algorithm of beam was studied.A NURBS-based beam modeling method was introduced.The central guide line of the beam and cross section were constructed by NURBS local interpolation.The center guide line was used to position the cross section.The beam surface was generated using lofting method.The parametric modification of the beam was achieved by modifying the center guide line,the cross section and its position on the center guide line.2.The modeling algorithm of junction was studied.A NURBS-based junction modeling method was introduced.The corresponding relationship between the curves of the beam ends was studied.The bridging surface was generated with the lofting method.The four sides hole was filled using Coons surface.The junction was used to achieve a smooth transition between beams.3.The normal and directional projection algorithm between beam and surface was studied.The end section of the beam was extracted and projected onto the specified surface.The end section and the projection section were used to produce a projected surface.The projection relationship was used to fill the gap between the beam and the target surface.4.The meshing algorithm was studied.The triangular mesh was generated using an AFT method.The quadrilateral mesh was generated using a mapping method.The mesh was used for FEA.5.A front bumper model was built using the algorithms introduced in this thesis.The model was compared with the reference CAD model and showed a good result.Compared with the traditional modeling method,implicit parametric modeling has the advantages of easy modification of the model and large amplitude of modification.