The stability of the numerical algorithm depends on the size of the time step used for time
integration . For brick elements,
Radioss
uses the following equation to calculate the size of the time step:
(1)
$$h\le k\frac{l}{c\left(\alpha +\sqrt{{\alpha}^{2}+1}\right)}$$
This is the same form as the Courant condition for damped materials. The characteristic
length of a particular element is computed using:
(2)
$$l=\frac{Element\text{\hspace{0.17em}}Volume}{Largest\text{\hspace{0.17em}}Side\text{\hspace{0.17em}}Surface}$$
For a 6sided brick, this length is equal to the smallest distance between two opposite
faces.
The terms inside the parentheses in the denominator are specific values for the damping of
the material:

$\alpha =\frac{2v}{\rho cl}$

$\nu $
effective kinematic viscosity

$c=\sqrt{\frac{1\partial p}{\rho \partial \rho}}$
for fluid materials

$c=\sqrt{\frac{K}{\rho}+\frac{4}{3}\frac{\mu}{\rho}}=\sqrt{\frac{\lambda +2\mu}{\rho}}$
for a solid elastic material
 $K$
is the bulk modulus

$\lambda $
,
$\mu $
are Lame moduli
The scaling factor $k=0.90$
, is used to prevent strange
results that may occur when the time step is equal to the Courant condition. This value can
be altered by the user.