APPLICATION OF SUBPLEX OPTIMIZATION TO SOLUTE-TRANSPORT PROBLEM

Determining parameters,such as interphase exchange rate and dispersivity,in multiphase solute transport problem has always been an interesting issue.These parameters are usually not available because they are too difficult or too expensive to measure although they are necessary as input data or parameters for numerical modeling.To overcome this problem,inverse techniques have been developed.Recently,the subplex optimization approach,which considers reflection,expansion,contraction,and shrinkage as basic components in seeking the minimization point and which uses the subspace concept in search space,has been incorporated into our coupled multiphase fluid－ flow and solute－ transport simulator.In the application of the finite element model to multiphase infiltration and solute transport problem,physical variables,which are easy to observe(such as solute concentrations),are used as constraints in minimizing the differences between computed output and measured data.Therefore,modeling results provide optimized parameter estimates in addition to comparison with field data.Our numerical－ simulation example on interphase－ exchange coefficient as well as water and gas dispersivities shows optimized parameters approaching the same values specified in the forward simulation used to generate the synthetic constrained data.This provides an implication of possible application to the fields of earch sciences,including geotectonics and metallogeny.