Multiscale Modeling For CVI Process

This thesis takes the numerical simulation to the CVI(Chemical Vapor Infiltration) process as the main subject,which is the production procedure of the Silicon Carbide Composite Ceramic Materials reinforced by carbon fibers.In the process. first put the porous carbon fibre preform into the reactor.Under the condition of high temperature and pressure,let the agent gases get through the reactor.When the agent gases reach the surface the prefbrm,chemical reaction will happen and SiC solid will be generated.The reaction will last until the pores of the preform are almost occluded.Because of the long time of the process.and the complexity of the preform structure,if we use global numerical simulation with traditional numerical methods,the time cost will go to the extreme.So we need to use multiscale modeling which solve the complicated problem with its effective macro model.The main point of the multiscale modeling deals the preform with a two phase material model which contains two different scale pores and then set up different pore models on each phase.Combining the reaction diffusion equation,we can deduce the effective homogenization equation.With porosity evolution equation together,a closed system can be set up.Via the homogenization theory and asymptotic expansion, we can see the new model simulate the CVI process better and avoid the defect of the classical model.In the meanwhile,this thesis gives out specific algorithm and example as well as the model under the frame work of HMM(Heterogeneous Multiscale Method).To our revised model,we give out the convergence analysis by FEM theory to make sure the correctness.In another aspect,this thesis researches on how to describe the pore structure in detail during the chemical reaction.This part mainly uses the Level-set Method. To get the normal velocity off the level set function,we need to solve the micro reaction diffusion equation with a surface Dirac source term which we will sort to IIM(Immerse Interface Method).What's more,we couple the micro model with HMM frame so that the computation cost will be saved.However,for the time reason,the thesis does not give out the numerical experiment.