using abaqus in sintering

hi, i am currently working on using abaqus software for solving sintering problems . i just want to know how i can introduce new parameters into abaqus so that by giving some eqns for those i can solve the values of final porosity, shrinkage etc that are not pre-determined in the abaqus . i want to know the porosity distribution  and shrinkage rate in a particular given problem as outputs . please help me out . thnq