/DAMP/INTER

Block Format Keyword The card is intended to apply Rayleigh damping to the nodes inside of specified contact to increase its stability and reduce results scattering due to small variations of initial or boundary conditions.

Format 1 (short format)

(1)	(2)	(3)	(5)	(6)	(7)	(9)
/DAMP/INTER/`damp_ID`
`damp_title`
`Nb_dt`	`Iselect`
$α$		$β$	`grnd_ID`	`skew_ID`	`T`_start	`T`_stop

Format 2 (full format)

(1)	(2)	(3)	(5)	(6)	(7)	(9)
/DAMP/INTER/`damp_ID`
`damp_title`
`Nb_dt`	`Iselect`
$α$ _xx		$β$ _xx	`grnd_ID`	`Skew_ID`	`T`_start	`T`_stop
$α$ _yy		$β$ _yy
$α$ _zz		$β$ _zz

Definition

Field	Contents	SI Unit Example
`damp_ID`	Damping identifier. (Integer, maximum 10 digits)
`damp_title`	Damping title. (Character, maximum 100 characters)
`Nb_dt`	Number of time steps. 4 Default = 20 (Integer)
`Iselect`	Extended node selection flag. 8 = 0 (Default) Damping applied only to nodes in contact. = 1 Damping applied to nodes in contact and neighboring nodes. (Integer)
$α$	Mass damping coefficient. $α$ is used for all DOF. (Real)	$[\frac{1}{s}]$
$β$	Stiffness damping coefficient. $β$ is used for all DOF. (Real)	$[s]$
`grnd_ID`	Node group identifier. (Integer)
`Skew_ID`	Skew identifier. (Integer)
`T`_start	Start time. (Real)	$[s]$
`T`_stop	Stop time. Default = 10³⁰ (Real)	$[s]$
$α$ _xx	Mass damping coefficient for rotational DOF (in xx direction). 6 (Real)	$[\frac{1}{s}]$
$α$ _yy	Mass damping coefficient for rotational DOF (in `yy` direction). 6 (Real)	$[\frac{1}{s}]$
$α$ _zz	Mass damping coefficient for rotational DOF (in `zz` direction). 6 (Real)	$[\frac{1}{s}]$
$β$ _xx	Stiffness damping coefficient for rotational DOF (in `xx` direction). 6 (Real)	$[s]$
$β$ _yy	Stiffness damping coefficient for rotational DOF (in `yy` direction). 6 (Real)	$[s]$
$β$ _zz	Stiffness damping coefficient for rotational DOF (in `zz` direction). 6 (Real)	$[s]$

Comments

The damping parameters can be modified with the Engine option /DAMP.
Rayleigh damping is applied only on rotational DOF and is computed as:(1)
$C = α I + β K$
(2)
$C_{i} = α m_{i} + β k_{r i}$
(3)
$C_{c r i t} = \sqrt{4 m_{i} k_{i}}$

Where,

$C$

Viscosity matrix

$I$

Intertia matrix

$K$

Rotational stiffness matrix

$α$ and $β$

Coefficients

$C_{i}$

Nodal viscosity

$i_{n i}$

Nodal inertia

$k_{r i}$

Rotational nodal stiffness

$C_{c r i t}$

Critical damping
The damping is applied to all the nodes of the prescribed node group (grnd_ID) that are subjected to contact forces. The specification of grnd_ID is compulsory.
The damping is active for nodes that are no longer in contact during Nb_dt cycles.
The same node cannot be referred by more than one /DAMP/INTER card.
The coefficients in Format 2 are used to define non-isotropic damping in global reference system or in a local one if skew_ID is specified.
/DAMP/INTER is only compatible with contacts TYPE7, TYPE10 and TYPE11.
With Iselect=1, the damping is applied to all the nodes having one shell element in common with nodes in contact to increase the effect of contact damping.