Question

In the interest of the simple formulation of viscous flows, which case does not involve time derivative terms?

(a) Static case

(b) Transient case

(c) Unsteady case

(d) Non-periodic

The question was asked by my school principal while I was bunking the class.

This interesting question is from Penalty in section Flows of Viscous Incompressible Fluids of Finite Element Method

Answer 1

Right answer is (a) Static case

Easy explanation: The equations governing flows of viscous incompressible fluids can be viewed as equivalent to minimizing a quadratic functional with a constraint. In the penalty method, in the interest of simplicity, for the static case, the constraint condition does not involve time derivative terms. Then, we add time derivative terms to study transient problems.