7.4. Kinematic Boundary Conditions

The various kinematic boundary conditions available in Sierra/SM are described in this section. The kinematic boundary conditions are nested inside the region scope.

Kinematic constraints can potentially be in conflict with other constraints. Refer to Appendix D for information on how conflicting constraints are handled.

7.4.1. Fixed Displacement

BEGIN FIXED DISPLACEMENT
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # direction commands
  COMPONENT = <string>X|Y|Z | COMPONENTS = <string>X/Y/Z |
    DIRECTION = <string>dirName
  #
  # additional commands
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [FIXED DISPLACEMENT]

The FIXED DISPLACEMENT command block fixes displacement components (X, Y, Z, or some combination thereof, or some other direction) for a set of nodes to be zero. This command block contains two groups of commands—node set and component. Each of these command groups is basically independent of the other. In addition to the command lines in the two command groups, there are two additional command lines: ACTIVE PERIODS and INACTIVE PERIODS. These are used to activate or deactivate this kinematic boundary condition for certain time periods.

For rigid bodies, any kinematic boundary condition is applied directly to the rigid body reference node. The kinematics for the nodes attached to the rigid body are applied via the rigid body constraint conditions. Since rigid bodies are defined using element blocks, only the BLOCK or RIGID BODY commands may be used to specify fixed displacement conditions on rigid bodies.

Warning

Note the fixed displacement command sets the displacement of a node to ZERO. To instead keep the current nodal displacement, a zero velocity boundary condition should be used.

Following are descriptions of the different command groups.

7.4.1.1. Node Set Commands

The node set commands portion of the FIXED DISPLACEMENT command block specifies the nodes associated with the boundary condition. This portion of the command block can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.1.2. Specification Commands

There are two component specification commands available in the FIXED DISPLACEMENT command block:

COMPONENT = X|Y|Z | COMPONENTS = X/Y/Z |
   DIRECTION = <string>dirName

A single displacement component may be set with the COMPONENT command line. A single direction of constraint can be set with the DIRECTION command. Multiple components can be constrained simultaneously with the COMPONENTS. One and only one COMPONENT, DIRECTION, or COMPONENTS command must be specified in the block. The COMPONENTS command can constraint multiple components simultaneously, for example

COMPONENTS = X Y

7.4.1.3. Additional Commands

The ACTIVE PERIODS and INACTIVE PERIODS command lines can optionally appear in the FIXED DISPLACEMENT command block:

ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

These command lines determine when the boundary condition is active. See Section 2.6 for more information about these optional command lines.

Warning

If FIXED DISPLACEMENT becomes active the displacement is returned to zero. If the intention is to maintain the current displacement when activated PRESCRIBED VELOCITY with a value of zero should be used.

7.4.2. Prescribed Displacement

BEGIN PRESCRIBED DISPLACEMENT
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # specification commands
  DIRECTION = <string>defined_direction |
    COMPONENT = <string>X|Y|Z |  COMPONENTS = <string>X/Y/Z |
    CYLINDRICAL AXIS = <string>defined_axis |
    RADIAL AXIS = <string>defined_axis
  FUNCTION = <string>function_name
  #
  # user subroutine commands
  NODE SET SUBROUTINE = <string>subroutine_name
  SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
  SUBROUTINE REAL PARAMETER: <string>param_name
    = <real>param_value
  SUBROUTINE INTEGER PARAMETER: <string>param_name
    = <integer>param_value
  SUBROUTINE STRING PARAMETER: <string>param_name
    = <string>param_value
  #
  # external database commands
  READ VARIABLE = <string>var_name
  COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
  TIME = <real>time|FIRST|LAST
  #
  # additional commands
  SCALE FACTOR = <real>scale_factor(1.0)
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [PRESCRIBED DISPLACEMENT]

The PRESCRIBED DISPLACEMENT command block prescribes a displacement field for a given set of nodes. The displacement field associates a vector giving the magnitude and direction of the displacement with each node in the set of nodes. The displacement field may vary over time and space. If the displacement field has only a time-varying magnitude and uses one of four methods for setting direction, the specification commands in the above command block can be used to specify the displacement field. If the displacement field is more complex, a user subroutine specifies the displacement field. The displacement field can also be read from an external mesh database. In a given boundary condition command block, commands from only one of the command groups (specification commands, user subroutine commands, or external database commands) may be used.

For rigid bodies, any kinematic boundary condition is applied directly to the rigid body reference node. The kinematics for the mesh nodes attached to the rigid body are applied via the rigid body constraint conditions. Since rigid bodies are defined using element blocks, only the BLOCK or RIGID BODY command lines may be used to specify prescribed displacement conditions on rigid bodies.

The PRESCRIBED DISPLACEMENT command block contains four groups of commands—node set, function, user subroutine, and external database. Each of these command groups is basically independent of the others. In addition to the command lines in the four command groups, there are three additional command lines: SCALE FACTOR, ACTIVE PERIODS, and INACTIVE PERIODS. The SCALE FACTOR command line can be used in conjunction with the specification commands the user subroutine commands, or the external database command. The ACTIVE PERIODS and INACTIVE PERIODS command lines are used to activate or deactivate this kinematic boundary condition for certain time periods. Following are descriptions of the different command groups and the SCALE FACTOR and ACTIVE PERIODS command lines.

7.4.2.1. Node Set Commands

The node set commands portion of the PRESCRIBED DISPLACEMENT command block defines a set of nodes associated with the prescribed displacement field and can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, ASSEMBLY, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.2.2. Specification Commands

If the specification commands are used, the displacement vector at any given time is the same for all nodes in the node set associated with the particular PRESCRIBED DISPLACEMENT command block.

Following are the command lines used to specify the prescribed displacement with a direction and a function:

DIRECTION = <string>defined_direction |
  COMPONENT = <string>X|Y|Z |
  CYLINDRICAL AXIS = <string>defined_axis |
  RADIAL AXIS = <string>defined_axis
FUNCTION = <string>function_name

The displacement can be specified along an arbitrary user-defined direction, along a component direction (X, Y, or Z), along the azimuthal direction in a cylindrical coordinate system (defined in reference to an axis), or along a radial direction (defined in reference to an axis). Only one of these options is allowed per command block. The displacement is prescribed only in the specified direction. A prescribed displacement boundary condition does not influence the motion in directions orthogonal to the prescribed direction.

The DIRECTION command line is used to prescribe displacement in an arbitrary user-defined direction. The name in the string defined_direction is a reference to a direction, which is defined using the DEFINE DIRECTION command block within the SIERRA scope.
The COMPONENT command line specifies that the prescribed displacement vector lies along one of the component directions. The COMPONENT command line is a shortcut to an internally defined direction vector; for example, component x corresponds to using direction vector (1, 0, 0).
The CYLINDRICAL AXIS command line specifies that the prescribed displacement is to be applied in the azimuthal direction of a cylindrical coordinate system. The string defined_axis refers to the name of the axis of the cylindrical coordinate system, and which is defined via a DEFINE AXIS command block in the SIERRA scope. The displacement is prescribed as a rotation in radians about the axis. Nodes with this type of boundary condition are free to move in the radial and height directions in the cylindrical coordinate system. Restraints can be placed on the node set in those directions if desired by applying separate kinematic boundary conditions that contain RADIAL AXIS or DIRECTION commands that refer to the same axis. Note that this type of boundary condition is not a rotational boundary condition; it only affects translational degrees of freedom.

Known Issue

If a prescribed displacement with the CYLINDRICAL AXIS option is applied to nodes that fall on the axis, it will have no effect. Separate boundary conditions should be applied to those nodes to fix them in the plane normal to the axis.
The RADIAL AXIS command line requires an axis definition that appears in the SIERRA scope. The string defined_axis uses an axis_name that is defined in the SIERRA scope (via a DEFINE AXIS command line). For this option, a radial line is drawn from a node to the radial axis. The prescribed displacement vector lies along this radial line from the node to the radial axis.

The magnitude of the displacement is specified by the FUNCTION command line. This references a function_name (defined in the SIERRA scope using a FUNCTION command block) that specifies the magnitude of the displacement vector as a function of time. The magnitude can be scaled by use of the SCALE FACTOR command line described in Section 7.4.2.5.

7.4.2.3. User Subroutine Commands

If the user subroutine option is used, the displacement vector may vary spatially at any given time for each of the nodes in the node set associated with the particular PRESCRIBED DISPLACEMENT command block. The user subroutine option allows for a more complex description of the displacement field than do the specification commands, but also requires writing a user subroutine to implement this capability. The user subroutine will be used to define a displacement direction and a magnitude for every node to which the boundary condition will be applied. The subroutine will be called by Sierra/SM at the appropriate time to generate the displacement field.

Following are the command lines related to the user subroutine option:

NODE SET SUBROUTINE = <string>subroutine_name
SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
SUBROUTINE REAL PARAMETER: <string>param_name
  = <real>param_value
SUBROUTINE INTEGER PARAMETER: <string>param_name
  = <integer>param_value
SUBROUTINE STRING PARAMETER: <string>param_name
  = <string>param_value

The user subroutine option is invoked by using the NODE SET SUBROUTINE command line. The string subroutine_name is the name of a FORTRAN subroutine that is written by the user.

Following the NODE SET SUBROUTINE command line are other command lines that may be used to implement the user subroutine option. These command lines are described in Section 10.2.2 and consist of SUBROUTINE DEBUGGING OFF, SUBROUTINE DEBUGGING ON, SUBROUTINE REAL PARAMETER, SUBROUTINE INTEGER PARAMETER, and SUBROUTINE STRING PARAMETER. Examples of using these command lines are provided throughout Section 10.

The magnitude set in the user subroutine can be scaled by use of the SCALE FACTOR command line, as described in Section 7.4.2.5.

See Section 7.4.10 and Section 10 for more details on implementing the user subroutine option.

7.4.2.4. External Mesh Database Commands

If the external database option is used, the displacement vector (or specified components of the vector) is read from an external mesh database. The displacements are read from a finite element model defined via the FINITE ELEMENT MODEL command block described in Section 6.1. The finite element model can either be the model used by the region for its mesh definition as specified with the USE FINITE ELEMENT MODEL command (see Section 2.3), or it can be a different (but compatible) model. The following command lines control the use of an external mesh database to prescribe the displacement:

READ VARIABLE = <string>var_name
COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
  MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
TIME = <real>time |FIRST|LAST

Specifying multiple components using external mesh database commands is not currently implemented. To read all components from an external mesh database, please specify three separate prescribed displacement blocks and specify the three different components

See Section 7.3.5 for more details.

7.4.2.5. Additional Commands

These command lines in the PRESCRIBED DISPLACEMENT command block provide additional options for the boundary condition:

SCALE FACTOR = <real>scale_factor(1.0)
ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

The SCALE FACTOR command line is used to apply an additional scaling factor, which is constant in both time and space, to all vector magnitude values of the field defined by the specification commands or the user subroutine. For example, if the magnitude of the displacement in a time history function is given as 1.5 from time 1.0 to time 2.0 and the scale factor is 0.5, then the magnitude of the displacement from time 1.0 to 2.0 is 0.75. The default value for the scale factor is 1.0.

The ACTIVE PERIODS and INACTIVE PERIODS command lines determine when the boundary condition is active. See Section 2.6 for more information about these command lines.

7.4.3. Prescribed Velocity

BEGIN PRESCRIBED VELOCITY
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # specification commands
  DIRECTION = <string>defined_direction |
    COMPONENT = <string>X|Y|Z | COMPONENTS = <string>X/Y/Z |
    CYLINDRICAL AXIS = <string>defined_axis |
    RADIAL AXIS = <string>defined_axis
  FUNCTION = <string>function_name
  #
  # user subroutine commands
  NODE SET SUBROUTINE = <string>subroutine_name
  SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
  SUBROUTINE REAL PARAMETER: <string>param_name
    = <real>param_value
  SUBROUTINE INTEGER PARAMETER: <string>param_name
    = <integer>param_value
  SUBROUTINE STRING PARAMETER: <string>param_name
    = <string>param_value
  #
  # external database commands
  READ VARIABLE = <string>var_name
  COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
    MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
  TIME = <real>time|FIRST|LAST
  #
  # additional commands
  SCALE FACTOR = <real>scale_factor(1.0)
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [PRESCRIBED VELOCITY]

The PRESCRIBED VELOCITY command block prescribes a velocity field for a given set of nodes. The velocity field associates a vector giving the magnitude and direction of the velocity with each node in the node set. The velocity field may vary over time and space. If the velocity field has only a time-varying magnitude and uses one of four methods for setting direction, the specification commands in the above command block can be used to specify the velocity field. If the velocity field is more complex, a user subroutine specifies the velocity field. The velocity field can also be read from an external mesh database. In a given boundary condition command block, commands from only one of the command groups (specification commands, user subroutine commands, or external database commands) may be used.

For rigid bodies, any kinematic boundary condition is applied directly to the rigid body reference node. The kinematics for the mesh nodes attached to the rigid body are applied via the rigid body constraint conditions. Since rigid bodies are defined using element blocks, only the BLOCK and RIGID BODY command lines may be used to specify prescribed velocity conditions on rigid bodies.

The PRESCRIBED VELOCITY command block contains four groups of commands—node set, function, user subroutine, and external database. Each of these command groups is basically independent of the others. In addition to the command lines in the four command groups, there are three additional command lines: SCALE FACTOR, ACTIVE PERIODS, and INACTIVE PERIODS. The SCALE FACTOR command line can be used in conjunction with either the specification commands or the user subroutine commands. The ACTIVE PERIODS and INACTIVE PERIODS command lines are used to activate or deactivate this kinematic boundary condition for certain time periods. Following are descriptions of the different command groups.

7.4.3.1. Node Set Commands

The node set commands portion of the PRESCRIBED VELOCITY command block defines a set of nodes associated with the prescribed velocity field and can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, ASSEMBLY, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.3.2. Specification Commands

If the specification commands are used, the velocity vector at any given time is the same for all nodes in the node set associated with the particular PRESCRIBED VELOCITY command block.

Following are the command lines used to specify the prescribed velocity with a direction and a function:

DIRECTION = <string>defined_direction |
  COMPONENT = <string>X|Y|Z |
  CYLINDRICAL AXIS = <string>defined_axis |
  RADIAL AXIS = <string>defined_axis
FUNCTION = <string>function_name

The velocity can be specified along an arbitrary user-defined direction, along a component direction (X, Y, or Z), along the azimuthal direction in a cylindrical coordinate system (defined in reference to an axis), or along a radial direction (defined in reference to an axis). Only one of these options is allowed per command block. The velocity is prescribed only in the specified direction. A prescribed velocity boundary condition does not influence the motion in directions orthogonal to the prescribed direction.

The DIRECTION command line is used to prescribe velocity in an arbitrary user-defined direction. The name in the string defined_direction is a reference to a direction, which is defined using the DEFINE DIRECTION command block within the SIERRA scope.
The COMPONENT command line specifies that the prescribed velocity vector lies along one of the component directions. The COMPONENT command line is a shortcut to an internally defined direction vector; for example, component x corresponds to using direction vector (1, 0, 0).
The CYLINDRICAL AXIS command line specifies that the prescribed velocity is to be applied in the azimuthal direction of a cylindrical coordinate system. The string defined_axis refers to the name of the axis of the cylindrical coordinate system, and which is defined via a DEFINE AXIS command block in the SIERRA scope. The velocity is prescribed as a rotation in radians about the axis. Nodes with this type of boundary condition are free to move in the radial and height directions in the cylindrical coordinate system. Restraints can be placed on the node set in those directions if desired by applying separate kinematic boundary conditions that contain RADIAL AXIS or DIRECTION commands that refer to the same axis. Note that this type of boundary condition is not a rotational boundary condition; it only affects translational degrees of freedom.

Known Issue

If a prescribed velocity with the CYLINDRICAL AXIS option is applied to nodes that fall on the axis, it will have no effect. Separate boundary conditions should be applied to those nodes to fix them in the plane normal to the axis.
The RADIAL AXIS command line requires an axis definition that appears in the SIERRA scope. The string defined_axis uses an axis_name that is defined in the SIERRA scope (via a DEFINE AXIS command line). For this option, a radial line is drawn from a node to the radial axis. The velocity vector lies along this radial line from the node to the radial axis.

The magnitude of the velocity is specified by the FUNCTION command line. This references a function_name (defined in the SIERRA scope using a FUNCTION command block) that specifies the magnitude of the velocity vector as a function of time. The magnitude can be scaled by use of the SCALE FACTOR command line described in Section 7.4.3.5.

7.4.3.3. User Subroutine Commands

If the user subroutine option is used, the velocity vector may vary spatially at any given time for each of the nodes in the node set associated with the particular PRESCRIBED VELOCITY command block. The user subroutine option allows for a more complex description of the velocity field than do the specification commands, but also requires writing a user subroutine to implement this capability. The user subroutine will be used to define a velocity direction and a magnitude for every node to which the boundary condition will be applied. The subroutine will be called by Sierra/SM at the appropriate time to generate the velocity field.

Following are the command lines related to the user subroutine option:

NODE SET SUBROUTINE = <string>subroutine_name
SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
SUBROUTINE REAL PARAMETER: <string>param_name
  = <real>param_value
SUBROUTINE INTEGER PARAMETER: <string>param_name
  = <integer>param_value
SUBROUTINE STRING PARAMETER: <string>param_name
  = <string>param_value

The user subroutine option is invoked by using the NODE SET SUBROUTINE command line. The string subroutine_name is the name of a FORTRAN subroutine that is written by the user.

Following the NODE SET SUBROUTINE command line are other command lines that may be used to implement the user subroutine option. These command lines are described in Section 10.2.2 and consist of SUBROUTINE DEBUGGING OFF, SUBROUTINE DEBUGGING ON, SUBROUTINE REAL PARAMETER, SUBROUTINE INTEGER PARAMETER, and SUBROUTINE STRING PARAMETER. Examples of using these command lines are provided throughout Section 10.

The magnitude set in the user subroutine can be scaled by use of the SCALE FACTOR command line, as described in Section 7.4.3.5.

7.4.3.4. External Mesh Database Commands

If the external database option is used, the velocity vector (or specified components of the vector) is read from an external mesh database. The velocities are read from a finite element model defined via the FINITE ELEMENT MODEL command block described in Section 6.1. The finite element model can either be the model used by the region for its mesh definition as specified with the USE FINITE ELEMENT MODEL command (see Section 2.3), or it can be a different (but compatible) model. The following command lines control the use of an external mesh database to prescribe the velocity:

READ VARIABLE = <string>var_name
COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
  MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
TIME = <real>time|FIRST|LAST

See Section 7.3.5 for more details.

7.4.3.5. Additional Commands

These command lines in the PRESCRIBED VELOCITY command block provide additional options for the boundary condition:

SCALE FACTOR = <real>scale_factor(1.0)
ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

The SCALE FACTOR command line is used to apply an additional scaling factor, which is constant in both time and space, to all vector magnitude values of the field defined by the specification commands or the user subroutine. For example, if the magnitude of the velocity in a time history function is given as 1.5 from time 1.0 to time 2.0 and the scale factor is 0.5, then the magnitude of the velocity from time 1.0 to 2.0 is 0.75. The default value for the scale factor is 1.0.

The ACTIVE PERIODS and INACTIVE PERIODS command lines determine when the boundary condition is active. See Section 2.6 for more information about these command lines.

7.4.4. Prescribed Acceleration

BEGIN PRESCRIBED ACCELERATION
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # specification commands
  DIRECTION = <string>defined_direction |
    COMPONENT = <string>X|Y|Z | COMPONENTS = <string>X/Y/Z |
  FUNCTION = <string>function_name
  #
  # user subroutine commands
  NODE SET SUBROUTINE = <string>subroutine_name
  SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
  SUBROUTINE REAL PARAMETER: <string>param_name
    = <real>param_value
  SUBROUTINE INTEGER PARAMETER: <string>param_name
    = <integer>param_value
  SUBROUTINE STRING PARAMETER: <string>param_name
    = <string>param_value
  #
  # external database commands
  READ VARIABLE = <string>var_name
  COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
    MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
  TIME = <real>time|FIRST|LAST
  #
  # additional commands
  SCALE FACTOR = <real>scale_factor(1.0)
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [PRESCRIBED ACCELERATION]

The PRESCRIBED ACCELERATION command block prescribes an acceleration field for a given set of nodes. The acceleration field associates a vector giving the magnitude and direction of the acceleration with each node in the node set. The acceleration field may vary over time and space. If the acceleration field has only a time-varying component, the specification commands in the above command block can be used to specify the acceleration field. If the acceleration field has both time-varying and spatially varying components, a user subroutine specifies the acceleration field. The acceleration field can also be read from an external mesh database. In a given boundary condition command block, commands from only one of the command groups (specification commands, user subroutine commands, or external database commands) may be used.

For rigid bodies, any kinematic boundary condition is applied directly to the rigid body reference node. The kinematics for the mesh nodes attached to the rigid body are applied via the rigid body constraint conditions. Since rigid bodies are defined using element blocks, only the BLOCK and RIGID BODY commands may be used to specify prescribed acceleration conditions on rigid bodies.

The PRESCRIBED ACCELERATION command block contains four groups of commands: node set, function, user subroutine, and external database. Each of these command groups is independent of the others. In addition to the command lines in the four command groups, there are three additional command lines: SCALE FACTOR, ACTIVE PERIODS, and INACTIVE PERIODS. The SCALE FACTOR command line can be used in conjunction with either the specification commands or the user subroutine commands. The ACTIVE PERIODS and INACTIVE PERIODS command lines are used to activate or deactivate this kinematic boundary condition for certain time periods. Following are descriptions of the different command groups.

7.4.4.1. Node Set Commands

The node set commands portion of the PRESCRIBED ACCELERATION command block defines a set of nodes associated with the prescribed acceleration field and can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, ASSEMBLY, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.4.2. Specification Commands

If the specification commands are used, the acceleration vector at any given time is the same for all nodes in the node set associated with the particular PRESCRIBED ACCELERATION command block. The direction of the acceleration vector is constant for all time; the magnitude of the acceleration vector may vary with time, however.

Following are the command lines used to specify the prescribed acceleration with a direction and a function:

DIRECTION = <string>defined_direction |
  COMPONENT = <string>X|Y|Z
FUNCTION = <string>function_name

The acceleration can be specified along an arbitrary user-defined direction or along a component direction (X, Y, or Z). Only one of these options is allowed per command block. The acceleration is prescribed only in the specified direction. A prescribed acceleration boundary condition does not influence the motion in directions orthogonal to the prescribed direction.

The DIRECTION command line is used to prescribe acceleration in an arbitrary user-defined direction. The name in the string defined_direction is a reference to a direction, which is defined using the DEFINE DIRECTION command block within the SIERRA scope.
The COMPONENT command line specifies that the prescribed acceleration vector lies along one of the component directions. The COMPONENT command line is a shortcut to an internally defined direction vector; for example, component x corresponds to using direction vector (1, 0, 0).

The magnitude of the acceleration is specified by the FUNCTION command line. This references a function_name (defined in the SIERRA scope using a FUNCTION command block) that specifies the magnitude of the acceleration vector as a function of time. The magnitude can be scaled by use of the SCALE FACTOR command line described in Section 7.4.4.5.

7.4.4.3. User Subroutine Commands

If the user subroutine option is used, the acceleration vector may vary spatially at any given time for each of the nodes in the node set associated with the particular PRESCRIBED ACCELERATION command block. The user subroutine option allows for a more complex description of the acceleration field than do the specification commands, but also requires writing a user subroutine to implement this capability. The user subroutine will be used to define an acceleration direction and a magnitude for every node to which the boundary condition will be applied. The subroutine will be called by Sierra/SM at the appropriate time to generate the acceleration field.

Following are the command lines related to the user subroutine option:

NODE SET SUBROUTINE = <string>subroutine_name
SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
SUBROUTINE REAL PARAMETER: <string>param_name
  = <real>param_value
SUBROUTINE INTEGER PARAMETER: <string>param_name
  = <integer>param_value
SUBROUTINE STRING PARAMETER: <string>param_name
  = <string>param_value

The user subroutine option is invoked by using the NODE SET SUBROUTINE command line. The string subroutine_name is the name of a FORTRAN subroutine that is written by the user.

Following the NODE SET SUBROUTINE command line are other command lines that may be used to implement the user subroutine option. These command lines are described in Section 10.2.2 and consist of SUBROUTINE DEBUGGING OFF, SUBROUTINE DEBUGGING ON, SUBROUTINE REAL PARAMETER, SUBROUTINE INTEGER PARAMETER, and SUBROUTINE STRING PARAMETER. Examples of using these command lines are provided throughout Section 10.

The magnitude set in the user subroutine can be scaled by use of the SCALE FACTOR command line, as described in Section 7.4.4.5.

See Section 7.4.10 and Section 10 for more details on implementing the user subroutine option.

7.4.4.4. External Mesh Database Commands

If the external database option is used, the acceleration vector (or specified components of the vector) is read from an external mesh database. The accelerations are read from a finite element model defined via the FINITE ELEMENT MODEL command block described in Section 6.1. The finite element model can either be the model used by the region for its mesh definition as specified with the USE FINITE ELEMENT MODEL command (see Section 2.3), or it can be a different (but compatible) model. The following command lines control the use of an external mesh database to prescribe the acceleration:

READ VARIABLE = <string>var_name
COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
  MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
TIME = <real>time|FIRST|LAST

See Section 7.3.5 for more details.

7.4.4.5. Additional Commands

These command lines in the PRESCRIBED ACCELERATION command block provide additional options for the boundary condition:

SCALE FACTOR = <real>scale_factor(1.0)
ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

The SCALE FACTOR command line is used to apply an additional scaling factor, which is constant in both time and space, to all vector magnitude values of the field defined by the specification commands or the user subroutine. For example, if the magnitude of the acceleration in a time history function is given as 1.5 from time 1.0 to time 2.0 and the scale factor is 0.5, then the magnitude of the acceleration from time 1.0 to 2.0 is 0.75. The default value for the scale factor is 1.0.

The ACTIVE PERIODS and INACTIVE PERIODS command lines determine when the boundary condition is active. See Section 2.6 for more information about these command lines.

7.4.5. Periodic Boundary Conditions

BEGIN PERIODIC
  SIDE B  = <string>side_b_node_set
  SIDE A = <string>side_a_node_or_face_set
  COMPONENT = <string>X/Y/Z
  PRESCRIBED QUANTITY = DISPLACEMENT|FORCE|VELOCITY
  SEARCH TOLERANCE = <real>tol
  FUNCTION = <string>func_name
  SCALE FACTOR = <real>func_scale
  POINT ON AXIS = <string>point_name
  REFERENCE AXIS = <string>direction_name
  THETA = <real>theta
END [PERIODIC]

The PERIODIC boundary condition command is used to define a set of periodic boundary constraints between two surfaces.

The side_b_node_set is the name of the side B node set for the constraints. The side_a_node_or_face_set is the name of either the side A node set or side A surface for the constraint. If a side A node set is used the side A node set and side B node set must have the same number of nodes. Additionally the side A node set and side B node set must be related by a simple translation. When two node sets are specified, a periodic constraint is defined between each pair of coincident (after applying the translation) nodes in the two node sets.

When a node set and a surface are specified the constraints will be defined between the side B nodes and the faces of the side A surface. When using surfaces to specify periodic boundary conditions, the number of nodes must be the same on the side A and side B sides. The side B node set and side A face set must still be related to one another by a simple translation.

COMPONENT specifies which directional component should enforce the prescribed quantity. This quantity can be DISPLACEMENT, VELOCITY, or FORCE as defined by the PRESCRIBED QUANTITY command. Note, all degrees of freedom on the node are considered periodic. Only the COMPONENT will have the PRESCRIBED QUANTITY enforced, the other degrees of freedom will be effectively linked with zero offset unless overridden by another periodic boundary condition.

Warning

At this time the COPY VARIABLE command can only be used with nodal variables. Neither the COPY VARIABLE command nor the READ VARIABLE command is compatible with global variables.

Warning

Multi-component periodic BCs are not currently supported with FETI/Full Tangent Preconditioner. Please break-up each component of your periodic BCs into separate periodic BC command blocks.

Note that neither of the COMPONENT or PRESCRIBED QUANTITY command are needed when dealing with rotational symmetry.

The FUNCTION and SCALE FACTOR commands are used to define a relative difference in the prescribed quantity on the side B and side A sets. This function can be used to define an isotropic expansion or contraction of a periodic boundary. For the common default use case the function is set to zero zero meaning the prescribed quantities on the two sets are the same.

The SEARCH TOLERANCE command specifies a search tolerance used for matching up nodes and faces between the side A and side B sets. The search tolerance is necessary to account for slightly varying mesh topologies between the side A and side B sets. The search tolerance should be something small, generally some small fraction of the characteristic face length of facets on the surfaces.

Implicit only The commands POINT ON AXIS, REFERENCE AXIS, and THETA are used to define axisymmetric periodic wedge conditions. point_name gives the name of a point defined by a domain level DEFINE POINT command. direction_name gives the name of a point defined by a domain level DEFINE DIRECTION command. Taken together these two commands define the axis of rotation for the wedge body. THETA defines the angle, in degrees, covered by the wedge. By way of the thumb rule, THETA should always be positive when sweeping from side A to side B, in a positive rotation.

Warning

The axisymmetric periodic boundary condition capability is still in development and has only been evaluated for implicit, serial analysis.

Examples:

SIDE B              = nodeset_11
SIDE A              = nodeset_12
COMPONENT           = xz
PRESCRIBED QUANTITY = displacement
SEARCH TOLERANCE    = 0.001
FUNCTION            = function_1
SCALE FACTOR        = 0.0

The above commands will create a periodic boundary condition between nodeset_11 and nodeset_12. The translational offset between nodeset_11 and nodeset_12 will be automatically determined. After the translation is applied, the coincident nodes in these node sets will match. For each node pair a constraint will be created to ensure the \(x\)- and \(z\)-displacements of the two nodes in the pair are equal.

Warning

Periodic boundary conditions should generally not be combined with other kinematic boundary conditions (such as fixed displacement). The periodic boundary conditions define a full set of kinematic constraints and additional constraints may conflict with the periodic constraints in unexpected ways.

7.4.6. Fixed Rotation

BEGIN FIXED ROTATION
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # specification commands
  COMPONENT = <string>X/Y/Z | COMPONENTS = <string>X/Y/Z |
    DIRECTION = <string>dir_name
  #
  # additional commands
  ACTIVE PERIODS = <string list>periods_names
  INACTIVE PERIODS = <string list>periods_names
END [FIXED ROTATION]

The FIXED ROTATION command is only applied to nodes that have rotational degrees of freedom such as shell element nodes and rigid body reference nodes. In the case of rigid bodies, the boundary condition must be specified on the block that defines the rigid body using the BLOCK or RIGID BODY line command.

The FIXED ROTATION command block fixes rotation about direction components (X, Y, Z, or some combination thereof) for a set of nodes to zero. This command block contains two groups of commands—node set and component. Each of these command groups is basically independent of the other. In addition to the command lines in the two command groups, there are additional command lines: ACTIVE PERIODS and INACTIVE PERIODS. These command lines are used to activate or deactivate this kinematic boundary condition for certain time periods.

Warning

Note the fixed rotation command sets the rotation of a node to ZERO. To instead keep the current nodal displacement, a zero rotational velocity boundary condition should be used.

Following are descriptions of the different command groups.

7.4.6.1. Node Set Commands

The node set commands portion of the command block specifies the nodes associated with the boundary condition. This portion of the command block can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, ASSEMBLY, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.6.2. Specification Commands

There are two component specification commands available in the FIXED ROTATION command block:

COMPONENT = X|Y|Z | COMPONENTS = X/Y/Z |
   DIRECTION = <string>dirName

A single rotation component may be set with the COMPONENT command line. A single direction of constraint can be set with the DIRECTION command. Multiple components can be constrained simultaneously with the COMPONENTS. One and only one COMPONENT, DIRECTION, or COMPONENTS command must be specified in the block. The COMPONENTS command can constraint multiple components simultaneously, for example

COMPONENTS = X Y

7.4.6.3. Additional Commands

The ACTIVE PERIODS and INACTIVE PERIODS command lines can optionally appear in the FIXED ROTATION command block:

ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

This command line determines when the boundary condition is active. See Section 2.6 for more information about this optional command line.

7.4.7. Prescribed Rotation

BEGIN PRESCRIBED ROTATION
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # specification commands
  DIRECTION = <string>defined_direction
  COMPONENT = X|Y|Z
  FUNCTION = <string>function_name
  #
  # user subroutine commands
  NODE SET SUBROUTINE = <string>subroutine_name
  SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
  SUBROUTINE REAL PARAMETER: <string>param_name
    = <real>param_value
  SUBROUTINE INTEGER PARAMETER: <string>param_name
    = <integer>param_value
  SUBROUTINE STRING PARAMETER: <string>param_name
    = <string>param_value
  #
  # external database commands
  READ VARIABLE = <string>var_name
  COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
    MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
  TIME = <real>time|FIRST|LAST
  #
  # additional commands
  SCALE FACTOR = <real>scale_factor(1.0)
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [PRESCRIBED ROTATION]

Warning

The BEGIN PRESCRIBED ROTATION command is only applied to nodes that have rotational degrees of freedom such as shell element nodes and rigid body reference nodes. Displacements consistent with rotation about a fixed axis for nodes that do not have rotational degrees of freedom, are imposed using the CYLINDRICAL AXIS command line in the PRESCRIBED DISPLACEMENT command block described in Section 7.4.2.

Warning

The behavior of the BEGIN PRESCRIBED ROTATION command differs for implicit and explicit analyses. For implicit analyses, the BEGIN PRESCRIBED ROTATION command fully prescribes all rotational degrees of freedom. Consequently, a prescribed rotation in a given direction restricts rotation in the remaining two orthogonal directions. If multiple prescribed rotation boundary conditions are applied to a node, only the last one specified in the input is enforced. In explicit analyses, the BEGIN PRESCRIBED ROTATION command block prescribes rotational degree of freedom in only the specified direction. The node is free to rotate in the directions orthogonal to that direction. Multiple prescribed rotation boundary conditions can be applied to constrain rotations in those other directions if desired.

For nodal rotational degrees of freedom, the rotations applied using the BEGIN PRESCRIBED ROTATION command are the three components of the rotational degree of freedom itself. For rigid bodies, the rotations must be the nonlinear components that result in the desired quaternion on the rigid body reference node. For rigid bodies, the boundary condition is applied to the reference node and therefore must be specified on the block that defines the rigid body using the BLOCK or RIGID BODY line command.

The PRESCRIBED ROTATION command block prescribes the rotation about an axis for a given set of nodes. The rotation field associates a vector giving the magnitude and direction of the rotation with each node in the node set. The rotation field may vary over time and space. If the rotation field has only a time-varying component, the specification commands in the above command block can be used to specify the rotation field. If the rotation field has both time-varying and spatially varying components, a user subroutine is used to specify the rotation field. The rotation field can also be read from an external mesh database. In a given boundary condition command block, commands from only one of the command groups (specification commands, user subroutine commands, or external database commands) may be used.

The PRESCRIBED ROTATION command block contains four groups of commands—node set, function, user subroutine, and external database. Each of these command groups is basically independent of the others. In addition to the command lines in the four command groups, there are three additional command lines: SCALE FACTOR, ACTIVE PERIODS, and INACTIVE PERIODS. The SCALE FACTOR command line can be used in conjunction with either the specification commands or the user subroutine commands. The ACTIVE PERIODS and INACTIVE PERIODS command lines are used to activate or deactivate this kinematic boundary condition for certain time periods. Following are descriptions of the different command groups.

7.4.7.1. Node Set Commands

The node set commands portion of the PRESCRIBED ROTATION command block defines a set of nodes associated with the prescribed rotation field and can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, ASSEMBLY, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.7.2. Specification Commands

If the specification commands are used, the rotation vector at any given time is the same for all nodes in the node set associated with the particular PRESCRIBED ROTATION command block. The direction of the rotation vector is constant for all time; the magnitude of the rotation vector may vary with time, however.

Following are the command lines used to specify the prescribed rotation with a direction and a function:

DIRECTION = <string>defined_direction
COMPONENT = X|Y|Z
FUNCTION = <string>function_name

The DIRECTION or COMPONENT command line are used to prescribe the direction of rotation. The name in the string defined_direction is a reference to a direction, which is defined using the DEFINE DIRECTION command block within the SIERRA scope. The rotation is prescribed only in the specified direction. A prescribed rotation boundary condition does not influence the rotation in directions orthogonal to the prescribed direction.

The magnitude of the rotation is specified by the FUNCTION command line. This references a function_name (defined in the SIERRA scope in a FUNCTION command block) that specifies the magnitude of the rotation vector as a function of time. The magnitude can be scaled by use of the SCALE FACTOR command line described in Section 7.4.7.5.

The magnitude of the rotation, as specified by the product of the function and the scale factor, has units of radians per second.

7.4.7.3. User Subroutine Commands

If the user subroutine option is used, the rotation vector may vary spatially at any given time for each of the nodes in the node set associated with the particular PRESCRIBED ROTATION command block. The user subroutine option allows for a more complex description of the rotation field than do the specification commands, but also requires writing a user subroutine to implement this capability. The user subroutine will be used to define a rotation direction and a magnitude for every node to which the boundary condition will be applied. The subroutine will be called by Sierra/SM at the appropriate time to generate the rotation field.

Following are the command lines related to the user subroutine option:

NODE SET SUBROUTINE = <string>subroutine_name
SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
SUBROUTINE REAL PARAMETER: <string>param_name
  = <real>param_value
SUBROUTINE INTEGER PARAMETER: <string>param_name
  = <integer>param_value
SUBROUTINE STRING PARAMETER: <string>param_name
  = <string>param_value

The user subroutine option is invoked by using the NODE SET SUBROUTINE command line. The string subroutine_name is the name of a FORTRAN subroutine that is written by the user.

Following the NODE SET SUBROUTINE command line are other command lines that may be used to implement the user subroutine option. These command lines are described in Section 10.2.2 and consist of SUBROUTINE DEBUGGING OFF, SUBROUTINE DEBUGGING ON, SUBROUTINE REAL PARAMETER, SUBROUTINE INTEGER PARAMETER, and SUBROUTINE STRING PARAMETER. Examples of using these command lines are provided throughout Section 10.

The magnitude set in the user subroutine can be scaled by use of the SCALE FACTOR command line, as described in Section 7.4.7.5.

See Section 7.4.10 and Section 10 for more details on implementing the user subroutine option.

7.4.7.4. External Mesh Database Commands

If the external database option is used, the rotation vector (or specified components of the vector) is read from an external mesh database. The rotations are read from a finite element model defined via the FINITE ELEMENT MODEL command block described in Section 6.1. The finite element model can either be the model used by the region for its mesh definition as specified with the USE FINITE ELEMENT MODEL command (see Section 2.3), or it can be a different (but compatible) model. The following command lines control the use of an external mesh database to prescribe the rotation:

READ VARIABLE = <string>var_name
COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
  MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
TIME = <real>time|FIRST|LAST

See Section 7.3.5 for more details.

7.4.7.5. Additional Commands

These command lines in the PRESCRIBED ROTATION command block provide additional options for the boundary condition:

SCALE FACTOR = <real>scale_factor(1.0)
ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

The SCALE FACTOR command line is used to apply an additional scaling factor, which is constant in both time and space, to all vector magnitude values of the field defined by the specification commands or the user subroutine. For example, if the magnitude of the rotation in a time history function is given as 1.5 from time 1.0 to time 2.0 and the scale factor is 0.5, then the magnitude of the rotation from time 1.0 to 2.0 is 0.75. The default value for the scale factor is 1.0.

The ACTIVE PERIODS and INACTIVE PERIODS command lines determine when the boundary condition is active. See Section 2.6 for more information about these command lines.

7.4.8. Prescribed Rotational Velocity

BEGIN PRESCRIBED ROTATIONAL VELOCITY
  #
  # node set commands
  NODE SET|NODESET = <string list>nodelist_names
  SURFACE|SIDESET|SIDE SET = <string list>surface_names
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  INCLUDE ALL BLOCKS
  REMOVE NODE SET = <string list>nodelist_names
  REMOVE SURFACE = <string list>surface_names
  REMOVE BLOCK = <string list>block_names
  #
  # specification commands
  DIRECTION = <string>defined_direction |
   COMPONENT = <string>X|Y|Z
  FUNCTION = <string>function_name
  #
  # user subroutine commands
  NODE SET SUBROUTINE = <string>subroutine_name
  SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
  SUBROUTINE REAL PARAMETER: <string>param_name
    = <real>param_value
  SUBROUTINE INTEGER PARAMETER: <string>param_name
    = <integer>param_value
  SUBROUTINE STRING PARAMETER: <string>param_name
    = <string>param_value
  #
  # external database commands
  READ VARIABLE = <string>variable_name
  COPY VARIABLE = <string>variable_name [FROM MODEL
    <string>model_name]
  TIME = <real>time|FIRST|LAST
  #
  # additional commands
  SCALE FACTOR = <real>scale_factor(1.0)
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [PRESCRIBED ROTATIONAL VELOCITY]

Warning

The PRESCRIBED ROTATIONAL VELOCITY command is only applied to nodes that have rotational degrees of freedom such as shell element nodes and rigid body reference nodes. Velocities consistent with rotation about a fixed axis for nodes that do not have rotational degrees of freedom, are imposed with the CYLINDRICAL AXIS command line in the PRESCRIBED VELOCITY command block described in Section 7.4.3.

Warning

The behavior of the BEGIN PRESCRIBED ROTATIONAL VELOCITY command differs for implicit and explicit analyses. For implicit analyses, the BEGIN PRESCRIBED ROTATIONAL VELOCITY command fully prescribes all rotational degrees of freedom. Consequently, a prescribed rotational velocity in a given direction restricts rotation in the remaining two orthogonal directions. If multiple prescribed rotational velocity boundary conditions are applied to a node, only the last one specified in the input is enforced. In explicit analyses, the BEGIN PRESCRIBED ROTATIONAL VELOCITY command block prescribes rotational degree of freedom in only the specified direction. The node is free to rotate in the directions orthogonal to that direction. Multiple prescribed rotational velocity boundary conditions can be applied to constrain rotations in those other directions if desired.

The PRESCRIBED ROTATIONAL VELOCITY command block prescribes the rotational velocity about an axis for a given set of nodes. The rotational velocity field associates a vector giving the magnitude and direction of the rotational velocity with each node in the node set. The rotational velocity field may vary over time and space. If the rotational velocity field has only a time-varying component, the specification commands in the above command block can be used to specify the rotational velocity field. If the rotational velocity field has both time-varying and spatially varying components, a user subroutine is used to specify the rotational velocity field. The rotational velocity field can also be read from an external mesh database. In a given boundary condition command block, commands from only one of the command groups (specification commands, user subroutine commands, or external database commands) may be used.

For rigid bodies, the user must specify the rotational velocity components such that they define the desired quaternion on the rigid body reference node. For rigid bodies, the boundary condition is applied to the reference node and therefore must be specified on the block that defines the rigid body using the BLOCK or RIGID BODY line command.

The PRESCRIBED ROTATIONAL VELOCITY command block contains four groups of commands—node set, function, user subroutine, and external database. Each of these command groups is basically independent of the others. In addition to the command lines in the four command groups, there are three additional command lines: SCALE FACTOR, ACTIVE PERIODS, and INACTIVE PERIODS. The SCALE FACTOR command line can be used in conjunction with either the specification commands or the user subroutine commands. The ACTIVE PERIODS and INACTIVE PERIODS command lines are used to activate or deactivate this kinematic boundary condition for certain time periods. Following are descriptions of the different command groups.

7.4.8.1. Node Set Commands

The node set commands portion of the PRESCRIBED ROTATIONAL VELOCITY command block defines a set of nodes associated with the prescribed rotational velocity field and can include some combination of the following command lines:

NODE SET|NODESET = <string list>nodelist_names
SURFACE|SIDESET|SIDE SET = <string list>surface_names
BLOCK = <string list>block_names
ASSEMBLY = <string list>assembly_names
RIGID BODY = <string list>rigid_body_names
INCLUDE ALL BLOCKS
REMOVE NODE SET = <string list>nodelist_names
REMOVE SURFACE = <string list>surface_names
REMOVE BLOCK = <string list>block_names

These command lines, taken collectively, constitute a set of Boolean operators for constructing a set of nodes. See Section 7.1.1 for more information about the use of these command lines for creating a set of nodes used by the boundary condition. There must be at least one NODE SET|NODESET, SURFACE, BLOCK, ASSEMBLY, RIGID BODY, or INCLUDE ALL BLOCKS command line in the command block. Assemblies may contain blocks, surfaces, nodesets, or assemblies of these.

7.4.8.2. Specification Commands

If the specification commands are used, the rotational velocity vector at any given time is the same for all nodes in the node set associated with the particular PRESCRIBED ROTATIONAL VELOCITY command block. The direction of the rotational velocity vector is constant for all time; the magnitude of the rotational velocity vector may vary with time, however.

Following are the command lines used to specify the prescribed rotational velocity with a direction and a function:

DIRECTION = <string>defined_direction |
  COMPONENT = <string>X|Y|Z
FUNCTION = <string>function_name

The rotational velocity can be specified either along an arbitrary user-defined direction or along a component direction (X, Y, or Z), but not both. The rotational velocity is prescribed only in the specified direction. A prescribed rotational velocity boundary condition does not influence the rotational velocity in directions orthogonal to the prescribed direction.

The DIRECTION command line is used to prescribe rotational velocity in an arbitrary user-defined direction. The name in the string defined_direction is a reference to a direction, which is defined using the DEFINE DIRECTION command block within the SIERRA scope.
The COMPONENT command line specifies that the prescribed rotational velocity vector lies along one of the component directions. The COMPONENT command line is a shortcut to an internally defined direction vector; for example, component x corresponds to using direction vector (1, 0, 0).

The magnitude of the rotational velocity is specified by the FUNCTION command line. This references a function_name (defined in the SIERRA scope in a FUNCTION command block) that specifies the magnitude of the rotational velocity vector as a function of time. The magnitude can be scaled by use of the SCALE FACTOR command line described in Section 7.4.8.5.

The magnitude of the rotational velocity, as specified by the product of the function and the scale factor, has units of radians per second.

7.4.8.3. User Subroutine Commands

If the user subroutine option is used, the rotational velocity vector may vary spatially at any given time for each of the nodes in the node set associated with the particular PRESCRIBED ROTATIONAL VELOCITY command block. The user subroutine option allows for a more complex description of the rotational velocity field than do the specification commands, but also requires writing a user subroutine to implement this capability. The user subroutine will be used to define a rotational velocity direction and a magnitude for every node to which the boundary condition will be applied. The subroutine will be called by Sierra/SM at the appropriate time to generate the rotational velocity field.

Following are the command lines related to the user subroutine option:

NODE SET SUBROUTINE = <string>subroutine_name
SUBROUTINE DEBUGGING OFF | SUBROUTINE DEBUGGING ON
SUBROUTINE REAL PARAMETER: <string>param_name
  = <real>param_value
SUBROUTINE INTEGER PARAMETER: <string>param_name
  = <integer>param_value
SUBROUTINE STRING PARAMETER: <string>param_name
  = <string>param_value

The user subroutine option is invoked by using the NODE SET SUBROUTINE command line. The string subroutine_name is the name of a FORTRAN subroutine that is written by the user.

Following the NODE SET SUBROUTINE command line are other command lines that may be used to implement the user subroutine option. These command lines are described in Section 10.2.2 and consist of SUBROUTINE DEBUGGING OFF, SUBROUTINE DEBUGGING ON, SUBROUTINE REAL PARAMETER, SUBROUTINE INTEGER PARAMETER, and SUBROUTINE STRING PARAMETER. Examples of using these command lines are provided throughout Section 10.

The magnitude set in the user subroutine can be scaled by use of the SCALE FACTOR command line, as described in Section 7.4.8.5.

See Section 7.4.10 and Section 10 for more details on implementing the user subroutine option.

7.4.8.4. External Mesh Database Commands

If the external database option is used, the rotational velocity vector (or specified components of the vector) is read from an external mesh database. The rotational velocities are read from a finite element model defined via the FINITE ELEMENT MODEL command block described in Section 6.1. The finite element model can either be the model used by the region for its mesh definition as specified with the USE FINITE ELEMENT MODEL command (see Section 2.3), or it can be a different (but compatible) model. The following command lines control the use of an external mesh database to prescribe the rotational velocity:

READ VARIABLE = <string>var_name
COPY VARIABLE = <string>var_name [FROM MODEL <string>model_name]
  MAP_BY_PROXIMITY|MAP_BY_ID(MAP_BY_PROXIMITY)
TIME = <real>time|FIRST|LAST

See Section 7.3.5 for more details.

7.4.8.5. Additional Commands

These command lines in the PRESCRIBED ROTATIONAL VELOCITY command block provide additional options for the boundary condition:

SCALE FACTOR = <real>scale_factor(1.0)
ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

The SCALE FACTOR command line is used to apply an additional scaling factor, which is constant in both time and space, to all vector magnitude values of the field defined by the specification commands or the user subroutine. For example, if the magnitude of the rotational velocity in a time history function is given as 1.5 from time 1.0 to time 2.0 and the scale factor is 0.5, then the magnitude of the rotational velocity from time 1.0 to 2.0 is 0.75. The default value for the scale factor is 1.0.

The ACTIVE PERIODS and INACTIVE PERIODS command lines determine when the boundary condition is active. See Section 2.6 for more information about these command lines.

7.4.9. Reference Axis Rotation

BEGIN REFERENCE AXIS ROTATION
  #
  # block commands
  BLOCK = <string list>block_names
  ASSEMBLY = <string list>assembly_names
  RIGID BODY = <string list>rigid_body_names
  #
  # specification commands
  REFERENCE AXIS X FUNCTION = <string>function_name
  REFERENCE AXIS Y FUNCTION = <string>function_name
  REFERENCE AXIS Z FUNCTION = <string>function_name
  #
  # rotation commands
  ROTATION = <string>function_name
  ROTATIONAL VELOCITY = <string>function_name
  #
  # torque command
  TORQUE = <string>function_name
  #
  # additional commands
  SCALE FACTOR = <real>scale_factor(1.0)
  ACTIVE PERIODS = <string list>period_names
  INACTIVE PERIODS = <string list>period_names
END [REFERENCE AXIS ROTATION]

The REFERENCE AXIS ROTATION command block is intended to control the rotation of a rigid body. The three REFERENCE AXIS line commands are required and together define a time-varying reference axis or vector. The rigid body will rotate to follow the vector. Depending on other line commands in the block, the rigid body will have either zero or one free rotational degree of freedom. If one degree of freedom is present, it is the rotation about the time-varying reference vector.

The rotation of the rigid body described by the axis functions over any time step is determined using the reference axis position at the beginning and the end of the time step. If a reference axis is desired to represent movement of a principal axis of the rigid body, its position at the start of rotation must coincide with the position of that principal axis. A constant function can only be used to represent a spin around a principal axis if the principal axis and the reference axis are the same. To represent spin about a principal axis that is moving or is stationary but in a different position than the principal axis, the time history for the axis functions must define the reference axis in the same position as the principal axis at the beginning of the rotation.

At most, one of the ROTATION, ROTATIONAL VELOCITY, or TORQUE line commands may be present. If the ROTATION or ROTATIONAL VELOCITY command line is present, the rigid body will be fully prescribed for rotation. The ACTIVE PERIODS and INACTIVE PERIODS command lines are used to activate or deactivate this kinematic boundary condition for certain time periods.

Use of the REFERENCE AXIS ROTATION command block will cause extra global variables to be written to the results file. These variables describe the reaction force, rotational reaction moment, rotational displacement, and rotational velocity associated with the boundary condition and in the local coordinate system described by the boundary condition. The names of the variables are:

REACTR_<NAME>
REACTS_<NAME>
REACTT_<NAME>

RREACTR_<NAME>
RREACTS_<NAME>
RREACTT_<NAME>

ROTDS_<NAME>

ROTVR_<NAME>
ROTVS_<NAME>
ROTVT_<NAME>

The variables beginning with REACT give the reaction forces in the boundary condition’s local coordinate system. Those beginning with RREACT give the reaction moments.

Only the S component is given for the rotational displacement. This is because that the other coordinate directions are poorly defined, and therefore, rotational displacements in those directions provide no value.

The variables beginning with ROTV give the rotational velocity in the local coordinate system.

For each global variable, <NAME> is the name of the rigid body controlled by this boundary condition.

7.4.9.1. Block Command

The block command portion of the REFERENCE AXIS ROTATION command block defines a block associated with the prescribed rotation field and must include the following command line:

BLOCK = <string list>block_names

or

ASSEMBLY = <string list>assembly_names

where the assemblies must only contain element blocks.

If the element block in the BLOCK command has been defined as a rigid body, the rotation is applied to the rigid body reference node.

Alternatively, the command line:

RIGID BODY = <string list>rigid_body_names

may be used to specify the rotation on the reference node of the specified rigid body.

See Section 7.1.1 for more information about the use of this command line.

7.4.9.2. Specification Commands

The three specification commands are required and together define a time-varying vector that gives the orientation of a reference axis for rotation. The magnitude of the vector is ignored.

Following are the command lines used to specify the reference axis rotation with a direction:

REFERENCE AXIS X FUNCTION = <string>function_name
REFERENCE AXIS Y FUNCTION = <string>function_name
REFERENCE AXIS Z FUNCTION = <string>function_name

At a given time, the function referred to by the REFERENCE AXIS X FUNCTION line command gives the x component of a vector defining the reference axis. The pattern holds for the \(y\) and \(z\) components as well. Since the magnitude of the resulting axis or vector is not used, the three functions do not need to describe a unit vector in time.

7.4.9.3. Rotation Commands

It is possible to prescribe the complete rotation of a rigid body through the use of the ROTATION or ROTATIONAL VELOCITY line commands. Without these line commands, the rigid body is free to rotate about the reference axis.

Following are the command lines to prescribe the rotation about the reference axis:

ROTATION = <string>function_name
ROTATIONAL VELOCITY = <string>function_name

The function referred to by the ROTATION line command gives the magnitude of rotation in radians about the reference axis as a function of time. This function should not be changed across a restarted analysis.

The function referred to by the ROTATIONAL VELOCITY line command gives the rotational velocity in radians per second about the reference axis as a function of time. This function should not be changed across a restarted analysis.

7.4.9.4. Torque Command

A user may specify a moment about the reference axis through the use of the TORQUE line command.

TORQUE = <string>function_name

The function referred to by the TORQUE line command gives the torque or moment about the reference axis as a function of time.

7.4.9.5. Additional Commands

The SCALE FACTOR, ACTIVE PERIODS, and INACTIVE PERIODS command lines can optionally appear in the REFERENCE AXIS ROTATION command block:

SCALE FACTOR = <real>scale_factor(1.0)
ACTIVE PERIODS = <string list>period_names
INACTIVE PERIODS = <string list>period_names

The SCALE FACTOR command line applies the specified value as a scale factor to the rotation, rotational velocity, or torque functions.

The final two command lines can activate or deactivate the reference axis rotation for certain time periods. See Section 2.6 for more information about these command lines.

7.4.10. Subroutine Usage for Kinematic Boundary Conditions

The prescribed kinematic boundary conditions may be defined by a user subroutine. All these conditions use a node set subroutine. See Section 10 for an in-depth discussion of user subroutines. The kinematic boundary conditions will be applied to nodes. The subroutine will have to return six output values per node and one output flag per node. The usage of the output values depends on the returned flag value for a node, as follows:

If the flag value is negative, no constraint will be applied to the node.
If the flag value is equal to zero, the constraint will be absolute. All components of the boundary condition will be specified. For example, suppose the user has specified a subroutine to be called from a prescribed displacement subroutine. The prescribed displacements are to be passed through an array output_values. For a given node inode, the output_values array would have the following values:

output_values(1,inode) = displacement in x at inode
output_values(2,inode) = displacement in y at inode
output_values(3,inode) = displacement in z at inode
output_values(4,inode) = not used
output_values(5,inode) = not used
output_values(6,inode) = not used

If the flag value is equal to one, the constraint will be a specified amount in a given direction. For example, suppose the user has specified a subroutine to be called from a prescribed displacement subroutine. The prescribed displacements are to be passed through an array output_values. For a given node inode, the output_values array would have the following values:

output_values(1,inode) = magnitude of displacement
output_values(2,inode) = not used
output_values(3,inode) = not used
output_values(4,inode) = x component of direction vector
output_values(5,inode) = y component of direction vector
output_values(6,inode) = z component of direction vector

The direction in which the constraint will act is given by output_values 4 through 6 for inode. The magnitude of the displacement in the specified direction is given by output_values 1 at inode. To compute the constraint, Sierra/SM first normalizes the direction vector. Next, Sierra/SM multiplies the normalized direction vector by the magnitude of the displacement and applies the resultant constraint vector.

Displacements or velocities orthogonal to the prescribed direction will not be constrained. (This is true regardless of whether one uses a user subroutine for the prescribed kinematic boundary conditions.) Take the case of a prescribed displacement condition. The displacement orthogonal to a prescribed direction of motion depends on the internal and external forces orthogonal to the prescribed direction. Displacement orthogonal to the prescribed direction may or may not be zero.