/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 | grnd_ID | skew_ID | Tstart | Tstop |
Format 2 (full format)
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) |
---|---|---|---|---|---|---|---|---|---|
/DAMP/damp_ID | |||||||||
damp_title | |||||||||
αx | x | grnd_ID | Skew_ID | Tstart | Tstop | ||||
αy | y | ||||||||
αz | z | ||||||||
αxx | xx | ||||||||
αyy | yy | ||||||||
αzz | zz |
Definitions
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) |
|
Stiffness damping
coefficient used for all DOF. 5
(Real) |
||
grnd_ID | Node group
identifier. (Integer) |
|
Skew_ID | Skew
identifier. (Integer) |
|
Tstart | Start
time. (Real) |
|
Tstop | Stop time. Default = 1030 (Real) |
|
αx | Mass damping coefficient
for translational degree of freedom (DOF) in x direction. 6 (Real) |
|
αy | Mass damping coefficient
for translational DOF in y direction. 6 (Real) |
|
αz | Mass damping coefficient
for translational DOF in z direction. 6 (Real) |
|
αxx | Mass damping coefficient
for rotational DOF in xx direction. 6 (Real) |
|
αyy | Mass damping coefficient
for rotational DOF in yy direction. 6 (Real) |
|
αzz | Mass damping coefficient
for rotational DOF in zz direction. 6 (Real) |
|
x | Stiffness damping
coefficient for translational DOF in x direction. 6 (Real) |
|
y | Stiffness damping
coefficient for translational DOF in y direction. 6 (Real) |
|
z | Stiffness damping
coefficient for translational DOF in z direction. 6 (Real) |
|
xx | Stiffness damping
coefficient for rotational DOF in xx direction. 6 (Real) |
|
yy | Stiffness damping
coefficient for rotational DOF in yy direction. 6 (Real) |
|
zz | Stiffness damping
coefficient for rotational DOF in zz direction.
6 (Real) |
Comments
- Rayleigh damping computation
is:
(1) (2) (3) Where,- C
- Viscosity matrix
- M
- Mass matrix
- K
- Stiffness matrix
- α and
- Coefficients
- Nodal viscosity
- Nodal mass
- Nodal stiffness
- 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 αx, αy, αz, αxx, αyy, αzz, y, z, xx, yy and zz are not provided, and the values of α and 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 non-isotropic 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 will substitute the corresponding values of αx, αy, αz, αxx, αyy, αzz, y, z, xx, yy and zz are not provided, and the values of α and .