/DAMP
Block Format Keyword This keyword can be used to define the Rayleigh mass and stiffness damping coefficients applied to a set of nodes. The damping can be applied to any nodal DOF either in local or global coordinate system.
Format 1 (short format)
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/DAMP/damp_ID  
damp_title  
α  $\beta $  grnd_ID  skew_ID  T_{start}  T_{stop} 
Format 2 (full format)
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/DAMP/damp_ID  
damp_title  
α_{x}  $\beta $ _{x}  grnd_ID  Skew_ID  T_{start}  T_{stop}  
α_{y}  $\beta $ _{y}  
α_{z}  $\beta $ _{z}  
α_{xx}  $\beta $ _{xx}  
α_{yy}  $\beta $ _{yy}  
α_{zz}  $\beta $ _{zz} 
Definition
Field  Contents  SI Unit Example 

damp_ID  Damping
identifier. (Integer, maximum 10 digits) 

damp_title  Damping
title. (Character, maximum 100 characters) 

α  Mass damping coefficient
used for all DOF. 5 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
$\beta $  Stiffness damping
coefficient used for all DOF. 5
(Real) 
$\left[\text{s}\right]$ 
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^{30} (Real) 
$\left[\text{s}\right]$ 
α_{x}  Mass damping coefficient
for translational degree of freedom (DOF) in x direction. 6 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
α_{y}  Mass damping coefficient
for translational DOF in y direction. 6 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
α_{z}  Mass damping coefficient
for translational DOF in z direction. 6 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
α_{xx}  Mass damping coefficient
for rotational DOF in xx direction. 6 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
α_{yy}  Mass damping coefficient
for rotational DOF in yy direction. 6 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
α_{zz}  Mass damping coefficient
for rotational DOF in zz direction. 6 (Real) 
$\left[\frac{\text{1}}{\text{s}}\right]$ 
$\beta $ _{x}  Stiffness damping
coefficient for translational DOF in x direction. 6 (Real) 
$\left[\text{s}\right]$ 
$\beta $ _{y}  Stiffness damping
coefficient for translational DOF in y direction. 6 (Real) 
$\left[\text{s}\right]$ 
$\beta $ _{z}  Stiffness damping
coefficient for translational DOF in z direction. 6 (Real) 
$\left[\text{s}\right]$ 
$\beta $ _{xx}  Stiffness damping
coefficient for rotational DOF in xx direction. 6 (Real) 
$\left[\text{s}\right]$ 
$\beta $ _{yy}  Stiffness damping
coefficient for rotational DOF in yy direction. 6 (Real) 
$\left[\text{s}\right]$ 
$\beta $ _{zz}  Stiffness damping
coefficient for rotational DOF in zz direction.
6 (Real) 
$\left[\text{s}\right]$ 
Comments
 Rayleigh damping computation
is:
(1) $$C=\alpha M+\beta K$$(2) $${C}_{i}=\alpha {m}_{i}+\beta {k}_{i}$$(3) $${C}_{crit}=\sqrt{4{m}_{i}{k}_{i}}$$Where, C
 Viscosity matrix
 M
 Mass matrix
 K
 Stiffness matrix
 α and $\beta $
 Coefficients
 ${C}_{i}$
 Nodal viscosity
 ${m}_{i}$
 Nodal mass
 ${k}_{i}$
 Nodal stiffness
 ${C}_{crit}$
 Critical damping
 The damping is applied to the nodes
belonging to a node group (grnd_ID).
The specification of grnd_ID is compulsory.
 It is possible to define multiple /DAMP keywords in the same input file.
 If there are several /DAMP keywords, each applied to different node groups, then these node groups should not have common nodes.
 Two formats of this keyword are available. In the Format 1 (short format), only three lines are prescribed. In this case α_{x}, α_{y}, α_{z}, α_{xx}, α_{yy}, α_{zz}, $\beta $ _{y}, $\beta $ _{z}, $\beta $ _{xx}, $\beta $ _{yy} and $\beta $ _{zz} are not provided, and the values of α and $\beta $ are used as damping coefficients for all degrees of freedom (DOFs). In the Format 2 (full format), six lines are provided and all damping coefficients should be prescribed directly.
 The coefficients in Format 2 are used to define nonisotropic damping, when the full keyword format is used, in a global reference system or in a local one if skew_ID is specified.
 Stiffness damping is a unit of time and for any DOF cannot be greater than the current time step. If stiffness damping becomes greater than the current time step, the time step value is used as the stiffness damping, instead.
 The damping parameters can be modified with the Engine option /DAMP. In this case the values of α and $\beta $ will substitute the corresponding values of α_{x}, α_{y}, α_{z}, α_{xx}, α_{yy}, α_{zz}, $\beta $ _{y}, $\beta $ _{z}, $\beta $ _{xx}, $\beta $ _{yy} and $\beta $ _{zz} are not provided, and the values of α and $\beta $ .