Command manual

Command list

BC_MOTION

Boundary conditions
*BC_MOTION
"Optional title"
coid
entype, enid, bc${}_{tr}$, bc${}_{rot}$, csysid${}_{tr}$, csysid${}_{rot}$, $t_{beg}$, $t_{end}$
pmeth${}_1$, direc${}_1$, cid${}_1$, $sf_1$
.
pmeth${}_n$, direc${}_n$, cid${}_n$, $sf_n$, fid${}_n$

Parameter definition

VariableDescription
coid Command ID (optional)
entype Entity type
options: N, NS, P, PS, ALL, G, GS
enid Entity identification number
bc${}_{tr}$ Translational constraints
options: 0, X, Y, Z, XY, YZ, ZX, XYZ
bc${}_{rot}$ Rotational constraint
options: 0, X, Y, Z, XY, YZ, ZX, XYZ
csysid${}_{tr}$ Coordinate system ID for translational constraints
csysid${}_{rot}$ Coordinate system ID for rotational constraints (0 for rotation around COG)
$t_{beg}$ Activation time
$t_{end}$ Termination time
pmeth${}_1$ Method used to prescribe motion (acceleration/velocity or displacement)
options: A, V, D
direc${}_1$ Direction of prescribed motion
options: X, Y, Z, RX, RY, RZ
cid${}_1$ ID of a CURVE or FUNCTION defining prescribed motion
$sf_1$ Scale factor for curve ordinate values
default: 1
pmeth${}_n$ Method used to prescribe motion (acceleration/velocity or displacement)
options: A, V, D
direc${}_n$ Direction of prescribed motion
options: X, Y, Z, RX, RY, RZ
cid${}_n$ ID of a CURVE or FUNCTION defining prescribed motion
$sf_n$ Scale factor for curve ordinate values
default: 1
fid${}_n$ ID of optional activation function
default: not used

Description

Definition of kinematic boundary conditions. When referring to a local cylindrical coordinate system (csys${}{\mathrm{tr}}$), X corresponds to the radial direction, Y to the tangential direction and Z to the axial direction.

The optional activation function is used to define more complex switches than a simple activation/deactivation time. fid${}_n$ refers to the ID of a FUNCTION. The prescribed motion (or rotation) is active if the specified FUNCTION returns a value > 0.

Example

Constraining rigid body with part

The following commands constrain the rigid body with part ID 333 in translation (all directions) and in rotation around the global x- and y-axes. A prescribed spin (100 rad/s) is defined around the z-axis. The title will show up in the ASCII file prescribed.out and helps the user distiguish between different *BC_MOTION definitions in the input deck.

*BC_MOTION
"this is a title"
P, 333, XYZ, XY
V, RZ, 123
*CURVE
123
0.0, 100.0
1.0, 100.0
Constraints applied in cylindrical coordinate system

Constraints can be applied in a cylindrical coordinate system. The example below constrains the tangential motion of a node set. The polar coordinate system has its center at (%xc, %yc, %zc) and its axial direction is (%xn, %yn, %zn). The tangential motion of the nodes in the set is constrained by setting bc${}_{\mathrm{tr}}$=Z.

*PARAMETER
%xc = 1.0
%yc = 2.0
%zc = 3.0
%xn = cos(30)
%yn = sin(30)
%zn = 0.0
*BC_MOTION
"constrain tangential motion"
NS, 1, Z, 0, 123
*COORDINATE_SYSTEM_FIXED
123, [%xc], [%yc], [%zc]
[%xn], [%yn], [%zn]