/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

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/DAMP/VREL/damp_ID
damp_title
CDAMP_Mx CDAMP2_Mx grnd_ID skew_ID Tstart Tstop
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)

[ 1 s ]
CDAMP2_Mx Mass quadratic damping coefficient used for translational direction X.

(Real)

1 m
grnd_ID Node group identifier.

(Integer)

skew_ID Skew identifier.

(Integer)

Tstart Start time.

(Real)

[ s ]
Tstop Stop time.

Default = 1020 (Real)

[ s ]
Freq Damping frequency. 1

(Real)

[ 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)

[ 1 s ]
CDAMP_Mz Mass damping coefficient used for translational direction Z.

Default = CDAMP_Mz (Real)

[ 1 s ]
CDAMP2_My Mass quadratic damping coefficient used for translational direction Y.

Default = CDAMP2_Mx (Real)

1 m
CDAMP2_Mz Mass quadratic damping coefficient used for translational direction Z.

Default = CDAMP2_Mx (Real)

1 m

Comments

  1. Rayleigh damping computation is:
    C = α M MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaGqadabaaaaaaa aapeGaa83qaiabg2da9iabeg7aHjaa=1eaaaa@3A4C@
    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   =   C D A M P _ M i d t   · F u n c _ I D t
    • If Freq0:
      α i   =   4 π   ·   C D A M P _ M i   · F r e q · F u n c _ I D t
  2. 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 ) · V r e l i ( j )   ·   α i   +   C D A M P 2 _ M i   · 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.

  3. 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_ID0).
  4. If skew_ID is defined, the direction x, y and z are the local coordinate system directions.
  5. 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.