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INITIAL_VELOCITY

Initial conditions

*INITIAL_VELOCITY
"Optional title"
entype, enid, $v_{x0}$, $v_{y0}$, $v_{z0}$, $\omega_x$, $\omega_y$, $\omega_z$
$x_0$, $y_0$, $z_0$, $\delta v_x$, $\delta v_y$, $\delta v_z$, csysid, overwrite

Parameter definition

Variable
Description
entype
Entity type
options: N, NS, P, PS, ALL, G, DP, SPH, CFD
enid
Entity identification number
$v_{x0}$
Initial velocity in x-direction
quantity: Velocity
options: constant, fcn
default: 0
$v_{y0}$
Initial velocity in y-direction
quantity: Velocity
options: constant, fcn
default: 0
$v_{z0}$
Initial velocity in z-direction
quantity: Velocity
options: constant, fcn
default: 0
$\omega_x$, $\omega_y$, $\omega_z$
Initial angular velocity vector
quantity: Frequency
default: (0,0,0)
$x_0$, $y_0$, $z_0$
Center of rotation
quantity: Length
default: (0,0,0)
$\delta v_x$, $\delta v_y$, $\delta v_z$
Gradient of velocity field
quantity: Strain rate
default: (0,0,0)
csysid
Optional local coordinate system ID
default: not used
overwrite
Overwrite or add to to exisiting velocity field
options:
0 $\rightarrow$ add to exisiting velocity field
1 $\rightarrow$ replace existing velocity field

Description

This command defines initial velocities for finite element nodes, discrete particles, surface SPH nodes, or for CFD cells. When entype is set to DP, SPH, or CFD, enid refers to a subdomain ID (see PARTICLE_SOIL, PARTICLE_SPH, CFD_HE, CFD_GAS).

An initial velocity term of a node or a particle at coordinate $(x,y,z)$ is defined as:

$\left\{ \begin{array}{c} v_x \\ v_y \\ v_z \end{array} \right\} = \left\{ \begin{array}{c} v_{x0} \\ v_{y0} \\ v_{z0} \end{array} \right\} + \left\{ \begin{array}{c} x-x_0 \\ y-y_0 \\ z-z_0 \end{array} \right\} \times \left\{ \begin{array}{c} \omega_x \\ \omega_y \\ \omega_z \end{array} \right\} + \left\{ \begin{array}{c} \delta v_x (x-x_0) \\ \delta v_y (y-y_0) \\ \delta v_z (z-z_0) \end{array} \right\}$

Example

Initial velocity

The command below initializes the spin of rigid body with part id 333. The axis of rotation is defined from the spin vector (10,20,0) and the point (1,2,3).

*INITIAL_VELOCITY P, 333, 0.0, 0.0, 0.0, 10.0, 20.0, 0.0 1.0, 2.0, 3.0
Initial velocity field using fcn

Complete command file of a rubber sheet that has been assigned a linear velocity field.

*UNIT_SYSTEM SI *TIME 0.01 *COMPONENT_BOX 1, 1, 10, 5, 1 -0.1, 0, 0, 0.1, 0.1, 0.001 *CHANGE_P-ORDER ALL, 0, 3 *MAT_MOONEY_RIVLIN 1, 2000.0, 1.0e9 2.0e5, 2.0e5 *PART "rubber sheet" 1, 1 *INITIAL_VELOCITY P, 1, fcn(22) *FUNCTION 22 100*x *END
Linear variation of velocity in x-direction
Linear variation of velocity in x-direction