/DAMP/VREL

Block Format Keyword Used to define the Rayleigh mass damping relative to the average velocity of the set of nodes or the motion of the local frame.

Format


Field	Contents	SI Unit Example
`damp_ID`	Damping identifier. (Integer, maximum 10 digits)
`damp_title`	Damping title. (Character, maximum 100 characters)
`CDAMP_Mx`	Mass damping coefficient used for translational direction X. (Real)	$[\frac{1}{s}]$
`CDAMP2_Mx`	Mass quadratic damping coefficient used for translational direction X. (Real)	$[\frac{1}{m}]$
`grnd_ID`	Node group identifier. (Integer)
`skew_ID`	Skew identifier. (Integer)
`T`_start	Start time. (Real)	$[s]$
`T`_stop	Stop time. Default = 10²⁰ (Real)	$[s]$
`Freq`	Damping frequency. 1 (Real)	$[\frac{1}{s}]$
`Rby_ID`	Rigid body identifier. (Integer)
`Func_ID`	Function identifier defining damping coefficient scaling factor as a function of time. (Integer)
`Xscale`	Abscissa scaling factor for function `Func_ID`. (Real)	$[s]$
`CDAMP_My`	Mass damping coefficient used for translational direction Y. Default = `CDAMP_Mx` (Real)	$[\frac{1}{s}]$
`CDAMP_Mz`	Mass damping coefficient used for translational direction Z. Default = `CDAMP_Mz` (Real)	$[\frac{1}{s}]$
`CDAMP2_My`	Mass quadratic damping coefficient used for translational direction Y. Default = `CDAMP2_Mx` (Real)	$[\frac{1}{m}]$
`CDAMP2_Mz`	Mass quadratic damping coefficient used for translational direction Z. Default = `CDAMP2_Mx` (Real)	$[\frac{1}{m}]$

Rayleigh damping computation is:
$C = α M$
$C_{i} = α_{i} m$
Where,

$C$

Viscosity matrix

$M$

Mass matrix

$C_{i}$

Nodal viscosity with the direction $i = \{x, y, z\}$

$m$

Nodal mass
- If Freq = 0:
  $α_{i} = \frac{C D A M P_M_{i}}{d t} \cdot F u n c_I D (t)$
- If Freq ≠ 0:
  $α_{i} = 4 π \cdot C D A M P_M_{i} \cdot F r e q \cdot F u n c_I D (t)$
The damping in the direction $i = \{x, y, z\}$ is applied to the node $(j)$ belonging to a node group (grnd_ID) as follows:
$F_{i (j)} = - m_{(j)} \cdot V r e l_{i (j)} \cdot (α_{i} + C D A M P 2_M_{i} \cdot V r e l_{i (j)})$
Where, $V r e l_{i (j)}$ is the relative velocity.
If damping is relative to the motion of a rigid body, force is also applied on the rigid body to keep the global momentum.
The damping is computed according to the average velocity of the node set (if Rby_ID = 0) or relative to the motion of a rigid body (Rby_ID ≠ 0).
If skew_ID is defined, the direction x, y and z are the local coordinate system directions.
It is possible to define multiple /DAMP or /DAMP/VREL keywords in the same input file.
Damping is accumulated. It is not recommended to set the same node in different damping cards.