Block Format Keyword
/DAMP - Rayleigh Damping
Description
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)
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(2)
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(3)
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(4)
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(5)
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(6)
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(7)
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(8)
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(9)
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(10)
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/DAMP/damp_ID
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damp_title
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grnd_ID
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skew_ID
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Tstart
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Tstop
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Format 2 (full format)
(1)
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(2)
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(3)
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(4)
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(5)
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(6)
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(7)
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(8)
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(9)
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(10)
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/DAMP/damp_ID
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damp_title
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grnd_ID
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skew_ID
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Tstart
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Tstop
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Field
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Contents
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SI Unit Example
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damp_ID
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Damping identifier
(Integer, maximum 10 digits)
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damp_title
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Damping title
(Character, maximum 100 characters)
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Mass damping coefficient used for all DOF (Comment 5).
(Real)
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Stiffness damping coefficient used for all DOF (Comment 5).
(Real)
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grnd_ID
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Node group identifier
(Integer)
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skew_ID
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Skew identifier
(Integer)
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Tstart
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Start time
(Real)
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Tstop
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Stop time
Default = 1030 (Real)
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Mass damping coefficient for translational degree of freedom (DOF) in x direction (Comment 6)
(Real)
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Mass damping coefficient for translational DOF in y direction (Comment 6)
(Real)
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Mass damping coefficient for translational DOF in z direction (Comment 6)
(Real)
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Mass damping coefficient for rotational DOF in xx direction (Comment 6)
(Real)
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Mass damping coefficient for rotational DOF in yy direction (Comment 6)
(Real)
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Mass damping coefficient for rotational DOF in zz direction (Comment 6)
(Real)
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Stiffness damping coefficient for translational DOF in x direction (Comment 6)
(Real)
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Stiffness damping coefficient for translational DOF in y direction (Comment 6)
(Real)
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Stiffness damping coefficient for translational DOF in z direction (Comment 6)
(Real)
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Stiffness damping coefficient for rotational DOF in xx direction (Comment 6)
(Real)
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Stiffness damping coefficient for rotational DOF in yy direction (Comment 6)
(Real)
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Stiffness damping coefficient for rotational DOF in zz direction (Comment 6)
(Real)
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| 1. | Rayleigh damping computation is as follows: |
[C] = [M] + [K]
Where,
[C] is the viscosity matrix
[M] is the mass matrix
[K] is the stiffness matrix
and are coefficients
Ci is the nodal viscosity
mi is the nodal mass
ki is the nodal stiffness
Ccrit is the critical damping
| 2. | The damping is applied to the nodes belonging to a node group (grnd_ID). |
The specification of grnd_ID is compulsory.
| 3. | It is possible to define multiple /DAMP keywords in the same input file. |
| 4. | If there are several /DAMP keywords, each applied to different node groups, then these node groups should not have common nodes. |
| 5. | Two formats of this keyword are available. In the Format 1 (short format), only three lines are prescribed. In this case  ,  ,  ,  ,  ,  ,  ,  ,  ,  and  are not provided, and the values of 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. |
| 6. | 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. |
| 7. | 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. |
| 8. | The damping parameters can be modified with the Engine option /DAMP. In this case the values of and will substitute the corresponding values of  and  . |
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See Also:
Example 16.1 - Dummy Positioning
Rayleigh damping in Theory Manual
Skew and Frame (/SKEW & /FRAME)
