- This paper contains an overview of the primitive variable finite element models of viscous, incompressible fluids in three-dimensional enclosures, with emphasis on penalty finite element models. The mixed and penalty finite element models are described and their computational aspects are discussed. Methods for the solution of large systems of equations associated with the finite element analysis of three-dimensional problems are also discussed. Numerical results are included to illustrate the applicability of the penalty finite element model and solution methods described here. 1993.