Multiple Model Adaptive Inverse Scheme For Nonlinear Heat Transfer And Its Application Research

The estimation of internal characteristics or thermal boundary conditions of heat transfer system based on some observable information is typically called the inverse heat transfer problem(IHTP).IHTPs exist widely in scientific research and many technical fields.In recent years,the inverse heat transfer problem and its application research are very active.For the inverse problem of linear and non-time-varying heat transfer,some relatively mature research methods have been established.On the other hand,many heat transfer problems in the field of practical engineering have obvious characteristics such as time-varying uncertainty and nonlinearity.In this case,the existing research methods of IHTP can provide insufficient theoretical support,and the in-depth study of this problem has obvious scientific significance and practical value.In view of the main problems existing in IHTP research,this thesis proposes the application of multi-model adaptive idea to study the inverse problem of nonlinear heat transfer process.The main research contents include the following five aspects:(1)Based on the idea of multi-model adaptive,the temperature prediction model of nonlinear heat transfer system is established.According to the nonlinear characteristic parameters,the heat transfer system is divided into several linearized subspaces,and the temperature prediction sub-model corresponding to each subspace is established based on the step response function.Further,according to the instantaneous matching degree between each linear sub-model and the actual heat transfer system,the global prediction model of the nonlinear heat transfer system is obtained by weighting and synthesizing the prediction sub-models,which lays a foundation for the establishment of multiple model adaptive inverse scheme for nonlinear heat transfer process.(2)A multiple model adaptive inverse(MMAI)scheme is proposed for the inverse problem of thermal boundary conditions in nonlinear heat transfer system.Based on the global prediction model and temperature measurement information of the nonlinear heat transfer system,the estimation of instantaneous thermal boundary conditions is realized by rolling optimization.The MMAI scheme is used to estimate the heat source intensity of heat transfer system with moving heat source and the boundary heat fluxes of heat transfer system with temperature-dependent thermo-physical properties.The results are compared with the adaptive sequential function specification method and the dynamic matrix control scheme,which proves the effectiveness of the MMAI scheme in solving the inverse problem of nonlinear heat transfer.(3)A multiple model adaptive inverse scheme based on boundary condition transfer(BCT-MMAI)is established for the inverse problem of time-varying convective heat transfer coefficient.In this scheme,the estimation of unknown time-varying convective heat transfer coefficient is transferred to the estimation of known boundary condition,which solves the problem that it is impossible to judge the instantaneous matching degree between the linear sub-model and the actual heat transfer system when the time-varying convective heat transfer coefficient is estimated by the general MMAI scheme.Firstly,according to the given discrete points of characteristic variable(convective heat transfer coefficient),the nonlinear heat transfer system is divided into several linear subspaces,and the temperature prediction sub-model corresponding to each linear subspace is established.Secondly,according to the predicted and measured temperatures at the measurement points,the estimated results of known boundary condition are obtained by rolling optimization.Further,the discrete values of characteristic quantity are comprehensively weighted based on the deviation information of the known boundary condition estimated results,and the identification results of time-varying convective heat transfer coefficient are indirectly generated.(4)Estimation of the moving thermal boundary condition and reconstruction of the transient temperature distribution during the drilling process of workpiece are studied by using the aforementioned MMAI scheme.Effects of the number of sub-models,aperture size and the number of future time steps on the inversion results of thermal boundary condition are investigated through numerical simulation experiments.Further,based on the experimental measured temperature data,the moving boundary heat flux of workpiece is estimated by using the MMAI scheme.On this basis,the transient temperature field of workpiece is reconstructed.Finally,the reliability of inversion results is verified by using the temperature measurement information.(5)By using the aforementioned BCT-MMAI scheme,the simultaneous estimation of multiple time-varying thermal boundary conditions of membrane water wall such as the local radiant heat flux on the fire side,fluid temperature inside the tube and the convective heat transfer coefficient is studied.The estimation of convective heat transfer coefficient is transferred to the estimation of adiabatic boundary condition on the back side of water wall.Based on the MMAI scheme,the inversion results of local radiant heat flux on the fire side and fluid temperature in the tube are obtained directly,and the convective heat transfer coefficient in the tube is indirectly generated by weighting and synthesizing the discrete values of characteristic quantity.The above results provide a promising solution for online monitoring of water wall temperature.