/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
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/DAMP/VREL/damp_ID  
damp_title  
CDAMP_Mx  CDAMP2_Mx  grnd_ID  skew_ID  T_{start}  T_{stop}  
Freq  Rby_ID  Func_ID  Xscale  
CDAMP_My  CDAMP2_My  
CDAMP_Mz  CDAMP2_Mz 
Definition
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) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
CDAMP2_Mx  Mass quadratic damping coefficient used for translational
direction X. (Real) 
$\left[\frac{1}{m}\right]$ 
grnd_ID  Node group
identifier. (Integer) 

skew_ID  Skew
identifier. (Integer) 

T_{start}  Start
time. (Real) 
$\left[\text{s}\right]$ 
T_{stop}  Stop time. Default = 10^{20} (Real) 
$\left[\text{s}\right]$ 
Freq  Damping frequency. 1 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
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) 
$\left[\text{s}\right]$ 
CDAMP_My  Mass damping coefficient
used for translational direction Y. Default = CDAMP_Mx (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
CDAMP_Mz  Mass damping coefficient
used for translational direction Z. Default = CDAMP_Mz (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
CDAMP2_My  Mass quadratic damping coefficient used for translational
direction Y. Default = CDAMP2_Mx (Real) 
$\left[\frac{1}{m}\right]$ 
CDAMP2_Mz  Mass quadratic damping coefficient used for translational
direction Z. Default = CDAMP2_Mx (Real) 
$\left[\frac{1}{m}\right]$ 
Comments
 Rayleigh damping computation
is:$$C=\alpha M$$$${C}_{i}={\alpha}_{i}m$$Where,
 $C$
 Viscosity matrix
 $M$
 Mass matrix
 ${C}_{i}$
 Nodal viscosity with the direction $i=\left\{x,y,z\right\}$
 $m$
 Nodal mass
 If Freq = 0:$${\alpha}_{i}=\frac{CDAMP\_{M}_{i}}{dt}\xb7Func\_ID\left(t\right)$$
 If Freq ≠ 0:$${\alpha}_{i}=4\pi \xb7CDAMP\_{M}_{i}\xb7Freq\xb7Func\_ID\left(t\right)$$
 The damping in the direction
$i=\left\{x,y,z\right\}$
is applied to the node
$\left(j\right)$
belonging to a node group (grnd_ID) as follows:$${F}_{i\left(j\right)}={m}_{\left(j\right)}\xb7Vre{l}_{i\left(j\right)}\xb7\left({\alpha}_{i}+CDAMP2\_{M}_{i}\xb7Vre{l}_{i\left(j\right)}\right)$$
Where, $Vre{l}_{i\left(j\right)}$ 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.