# /ALE/SOLVER/FINT

Engine Keyword This option defines the numerical method for internal force integration. This is relevant only for brick element and the ALE legacy solver (momentum equation solved with FEM).

## Format

/ALE/SOLVER/FINT/Iform

## Definitions

Field Contents SI Unit Example
Iform Integration method (internal force for brick elements) flag.
= 0
Set to 3.
= 1
Volume integration of the stress tensor using a shape function.
= 2
Surface integration for the hydrostatic stress tensor only.
= 3 (Default)
Surface integration for the stress tensor.

(Real)

1. Momentum equation has local form:
(1)
$\frac{\partial \rho u}{\partial t}+div\left(\rho uu\right)=div\left(\sigma \right)+\rho g$
Iform is a flag defining the numerical method to compute $div\left(\sigma \right)$ when integrated over the cell with legacy solver (nodal velocities).
Iform=1
${F}_{\mathrm{int}}={\int }_{\Omega }^{}div\left(\sigma \right)dV$
Was the default method up to Radioss version 2019.
Iform=2
${F}_{\mathrm{int}}=\text{-}{\int }_{\partial \Omega }^{}pdS+{\int }_{\Omega }^{}div\left(\sigma \right)dV$
The integration method used with obsolete card /CAA (Obsolete)
Iform=3
${F}_{\mathrm{int}}={\int }_{\partial \Omega }^{}\left(\text{-}pI+{\sigma }_{dev}\right)dS$
The integration method used as of Radioss version 2020.
For volume integration, shape functions are used to compute at node, N:(2)
${F}_{\mathrm{int}}^{iN}={\sigma }_{ik}{\frac{\partial {\Phi }_{N}}{\partial {x}_{k}}|}_{0}|\Omega |$

Where, $i=1,3$

The value ${\frac{\partial {\Phi }_{N}}{\partial {x}_{k}}|}_{0}$ is taken at the integration point. It is assumed that:(3)

This assumption is exact for parallelepipedic shape only, which is why the new default value method is set to surface integration (Iform=3).