# Momentum Transport Force

This scheme is only used with the ALE formulation (Arbitrary Lagrangian Eulerian) and in the CFD version of Radioss. The force is calculated using the relation:

- $w$
- Grid velocity
- $\nu $
- Material velocity
- $V$
- Element volume
- $\eta $
- Upwind coefficient (user-defined, default = 1 for full upwind)

When a Lagrangian formulation is used, the values of ${w}_{j}$ and ${\nu}_{j}$ are equal. Thus, Equation 1 is equal to zero.

## Upwinding Technique

An upwinding technique is introduced to add numerical diffusion to the scheme; otherwise it is generally under diffusive and thus unstable. The upwind coefficient used in Equation 1 is calculated by:

Development of a less diffusive flux calculation is currently under investigation.

This option is activated with the flag `INTEG` (only in the CFD version).