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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${}_1$, $sf_1$, fid${}_1$
.
pmeth${}_n$, direc${}_n$, cid${}_n$, $sf_n$, fid${}_n$

Parameter definition

Variable
Description
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
fid${}_1$
ID of optional activation function
default: not used
.
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 (csysid${}_{tr}$), 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.

Reaction forces, torques and external work are written to the ASCII file prescribed.out. Resulting torques on rigid bodies are expressed in the local rotational coordinate system (csysid${}_{rot}$). If a rotational coordinate system has not been defined, then the torques are presented with respect to the center-of-gravity.

The command can be used to clamp $\gamma SPH$ particles.

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${}_{tr}$=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]