!VELOCITY

Definition of velocity boundary conditions

Parameter

TYPE = INITIAL (Initial velocity boundary conditions)
= TRANSIT (Time history velocity boundary conditions
specified in !AMPLITUDE;Default)
AMP  = Time function name (specified in !AMPLITUDE)
Provides the relationship between time t and factor f(t) in !AMPLITUDE.
The time multiplied by factor f(t) to the following value
becomes the restrained value of that time
(when not specified: time and factor relationship becomes f(t) = 1.0).
ROT_CENTER = Node ID or node group name of the center of the rotational
velocity constraint. When specified, the !VELOCITY is recognized as a
rotational (angular) velocity constraint.

** 2nd line or later **

(2nd line) NODE_ID, DOF_idS, DOF_idE, Value

Parameter Name	Attributions	Contents
NODE_ID	I/C	Node ID or node group name
DOF_idS	I	Start No. of restricted degree of freedom
DOF_idE	I	End No. of restricted degree of freedom
Value	R	Restricted value (Default: 0)

Example of Use

!VELOCITY, TYPE=TRANSIT, AMP=AMP1
1, 1, 1, 0.0
ALL, 3, 3
* Restricted value is 0.0
!VELOCITY, TYPE=INITIAL
1, 3, 3, 1.0
2, 3, 3, 1.0
3, 3, 3, 1.0

Note: The velocity boundary conditions are different than the displacement boundary conditions, and the multiple degrees of freedom can not be defined collectively. Therefore, the same number must be used for DOF_idS and DOF_idE. When the TYPE is INITIAL, AMP becomes invalid.

Rotational velocity constraint (ROT_CENTER)

When ROT_CENTER is specified, an angular velocity about a center of rotation can be given as a velocity boundary condition, analogous to ROT_CENTER of !BOUNDARY (rotational displacement). Valid only in dynamic analysis.

Each data line Value gives a component (DOF 1-3) of the angular velocity vector \(\boldsymbol{\omega}=(\omega_x,\omega_y,\omega_z)\) [rad/s]. Each node is assigned the tangential velocity \(\boldsymbol{v}=\boldsymbol{\omega}\times(\boldsymbol{x}-\boldsymbol{x}_c)\), where \(\boldsymbol{x}_c\) is the center. With AMP, \(\boldsymbol{\omega}(t)=\boldsymbol{\omega}_0 f(t)\).

!VELOCITY, TYPE=TRANSIT, AMP=AMP1, ROT_CENTER=CENTER
  RIM, 1, 1, 0.0        ! omega_x
  RIM, 2, 2, 0.0        ! omega_y
  RIM, 3, 3, 6.283185   ! omega_z [rad/s]

When ROT_CENTER is specified:

• The node group given to ROT_CENTER must consist of a single node.
• Unlike the rotational displacement constraint (!BOUNDARY, ROT_CENTER), which is a finite rotation by the Rodrigues formula, the rotational velocity constraint is a tangential velocity from the cross product of the angular velocity vector.