sfcontrol#

FeSurfaceLoads.sfcontrol(kcsys='', lcomp='', val1='', val2='', val3='', ktaper='', kuse='', karea='', kproj='', kfollow='', **kwargs)#

Defines structural surface-load properties on selected elements and nodes for subsequent loading commands.

Mechanical APDL Command: SFCONTROL

Parameters:
kcsysstr

Specifies how the load direction is determined:

  • 0 (or blank) - Use the coordinate system of an element face. A local coordinate system is projected onto the face, if defined ( VAL1 ) (default).

  • 1 - Use a local coordinate system. A local coordinate system must be defined and is not projected onto the face.

  • 2 - Use a custom (user-defined) vector in the global Cartesian coordinate system.

lcompstr

Load-component definition when KCSYS = 0 or 1. The following table shows how the component (or primary direction) is determined based on the coordinate system:

This command contains some tables and extra information which can be inspected in the original

documentation pointed above.

val1str

When KCSYS = 0:

  • VAL1 - Determines the first tangential axis (x axis). Not valid for the edges of 3D shell or 2D elements.

  • 0 - Aligns the x axis to the first parametric direction \(equation not available\) (default).

  • 1 - Aligns x axis to the second parametric direction \(equation not available\).

  • >10 - ID of the local coordinate system. The local coordinate system is projected to selected face of the element.

  • VAL2 - Not used.

  • VAL3 - Rotation angle of a tangential load (optional). Not valid for the edges of 3D shell or 2D elements. If this value is specified, the tangential load rotates further with respect to the surface normal. The load component ( LCOMP ) becomes the reference axis to rotate.

When KCSYS = 1:

  • VAL1 - ID of the local coordinate system for the load. The axes of the local coordinate system are fixed in the global cartesian coordinate system.

  • VAL2 - Not used.

  • VAL3 - Not used.

When KCSYS = 2:

  • VAL1, VAL2, VAL3 - The X / Y / Z components, respectively, of the direction vector in the global Cartesian coordinate system.

val2str

When KCSYS = 0:

  • VAL1 - Determines the first tangential axis (x axis). Not valid for the edges of 3D shell or 2D elements.

  • 0 - Aligns the x axis to the first parametric direction \(equation not available\) (default).

  • 1 - Aligns x axis to the second parametric direction \(equation not available\).

  • >10 - ID of the local coordinate system. The local coordinate system is projected to selected face of the element.

  • VAL2 - Not used.

  • VAL3 - Rotation angle of a tangential load (optional). Not valid for the edges of 3D shell or 2D elements. If this value is specified, the tangential load rotates further with respect to the surface normal. The load component ( LCOMP ) becomes the reference axis to rotate.

When KCSYS = 1:

  • VAL1 - ID of the local coordinate system for the load. The axes of the local coordinate system are fixed in the global cartesian coordinate system.

  • VAL2 - Not used.

  • VAL3 - Not used.

When KCSYS = 2:

  • VAL1, VAL2, VAL3 - The X / Y / Z components, respectively, of the direction vector in the global Cartesian coordinate system.

val3str

When KCSYS = 0:

  • VAL1 - Determines the first tangential axis (x axis). Not valid for the edges of 3D shell or 2D elements.

  • 0 - Aligns the x axis to the first parametric direction \(equation not available\) (default).

  • 1 - Aligns x axis to the second parametric direction \(equation not available\).

  • >10 - ID of the local coordinate system. The local coordinate system is projected to selected face of the element.

  • VAL2 - Not used.

  • VAL3 - Rotation angle of a tangential load (optional). Not valid for the edges of 3D shell or 2D elements. If this value is specified, the tangential load rotates further with respect to the surface normal. The load component ( LCOMP ) becomes the reference axis to rotate.

When KCSYS = 1:

  • VAL1 - ID of the local coordinate system for the load. The axes of the local coordinate system are fixed in the global cartesian coordinate system.

  • VAL2 - Not used.

  • VAL3 - Not used.

When KCSYS = 2:

  • VAL1, VAL2, VAL3 - The X / Y / Z components, respectively, of the direction vector in the global Cartesian coordinate system.

ktaperstr

Global tapered load behavior (valid for sfe only):

  • 0 - Load does not vary (default).

  • 1 - Load varies with respect to the current element locations. The magnitude changes with respect to the element deformation.

  • 2 - Load varies with respect to the initial element locations. The load magnitude for each element remains constant throughout the solution..

For more information, see Global Tapered Load Behavior ( KTAPER).

kusestr

Load direction with respect to the surface normal of the selected face:

  • 0 - Use the load as calculated (default).

  • 1 - Use a positive load only (negative set to zero, valid for LCOMP = 0 and KCSYS = 0).

  • 2 - Use a negative load only (positive set to zero, valid for LCOMP = 0 and KCSYS = 0).

  • 3 - Applied load is not used if the surface normal is oriented in the same general direction as the user-defined vector. Valid for KCSYS = 2 only.

kareastr

Loaded area during large deformation:

  • 0 - Use the current (deformed) area (default).

  • 1 - Use the initial area.

kprojstr

Vector-oriented load ( KCSYS = 2) behavior:

  • 0 - Apply the load on the full area and include the tangential component (default).

  • 1 - Apply the load on the projected area and include the tangential component.

  • 2 - Apply the load on the projected area and exclude the tangential component.

kfollowstr

Controls follower-load behavior. Valid when KCSYS = 1 or 2, or when KCSYS = 0 and VAL1 > 10.

  • 0 - The load maintains a fixed direction (default).

  • 1 -The load follows the element deformation.

For more information, see Follower Load Behavior.

Notes

sfcontrol defines the properties of structural distributed loads for all subsequent sf or sfe loading commands. ( sfa and sfl are not supported.)

The command does not support analyses in which remeshing occurs, such as nonlinear mesh adaptivity and 2D to 3D analysis.

To update a load property or properties, reissue sfcontrol with the new option(s) before issuing further sf or sfe commands.

This command contains some tables and extra information which can be inspected in the original documentation pointed above.

To list the current set of control data, issue sfcontrol,STAT.

To reset all input values to defaults, issue sfcontrol,NONE.

When KCSYS = 0, the positive normal load acts in the negative surface normal (- z ) direction. The positive tangential loads act in the positive coordinate direction. A user-defined coordinate system ( VAL1 ) is ignored if the load is applied on an edge of a plane element ( PLANE182, PLANE183, SHELL208, SHELL209, PLANE222, and PLANE223 ).

When KCSYS = 1, the loading direction follows the positive direction of the local coordinate system. The ID of a local coordinate system ( VAL1 ) is required.

The following figure shows how the coordinate directions are determined on a face of a solid or shell element with different KCSYS and VAL1 input:

Coordinate System for Load Application on the Faces of 3D Solid and Shell Elements This command contains some tables and extra information which can be inspected in the original documentation pointed above.

  • where:

  • z, x 1, y 1 : normal and tangential directions (default surface coordinate system)

  • z, x 2, y 2 : normal and user-defined tangential directions (user-defined surface coordinate system)

  • x 3, y 3, z 3 : x, y, and z directions defined by the local coordinate system when KCSYS = 1

When KCSYS = 0:

  • The parametric direction determines the default coordinate system on a face. By default, the first parametric direction ( \(equation not available\) ) becomes the first tangential direction (x direction). If VAL1 = 1, the second parametric direction ( \(equation not available\) ) is selected as the x direction.

  • For the projected local coordinate system ( VAL1 > 10), the direction of the first tangential axes (x 2 ) is determined by the projection of the local coordinate system onto the face. The projected tangential axes may rotate if the direction of the face normal (z) changes in the space during solution. If the direction of the face normal (z) is fixed (for in-plane rotation, for example), the tangential axes do not follow element deformation. To enable your coordinate system to always follow the element deformation, specify the follower option ( KFOLLOW ).

  • Coordinate System vs. Load Direction

  • For the loads defined in the default coordinate system ( KCSYS = 0), the tangential direction of a load is restricted because it is aligned to the direction of the axis ( LCOMP ). The load direction can be arbitrary by adding additional rotation to the load ( VAL3 ). The following figure shows how the load direction is determined on the face of an element. If VAL3 > 0, LCOMP becomes the reference axis to define the rotation.

Load Direction in the Default Coordinate System This command contains some tables and extra information which can be inspected in the original documentation pointed above.

When KCSYS = 1:

  • The positive direction of the x 3, y 3, and z 3 axes follow the direction of the local coordinate system without adjustment. Therefore, they do not follow element deformation.

When KCSYS = 2:

  • The loading direction follows the positive direction of the orientation vector, defined via VAL1, VAL2, and VAL3. The direction is calculated as \(equation not available\), where \(equation not available\), \(equation not available\), and \(equation not available\) are unit vectors in the global Cartesian coordinate system. The loading direction is fixed and does not follow the deformation of a face of a selected element.

  • You can adjust the load magnitude ( KUSE and KPROJ ).

  • Use the follower option ( KFOLLOW ) to specify whether the load has a fixed direction ( KCSYS = 1 or 2), or projects the local coordinate system to the element face to follow element deformation ( KCSYS = 0 and VAL1 > 10).

The following figure shows the default direction of the normal (z) and tangential (x) components on an edge of a 3D shell element ( SHELL181 or SHELL281 ).

Default Coordinate System of Surface Load on the Edge of a 3D Shell Element If a local coordinate system is defined and KCSYS = 0 for the edge of the 3D shell element, the tangential directions are adjusted in the plane of the edge.

Projected Coordinate System of Surface Load on the Edge of a 3D Shell Element The following figure shows the positive direction of the loads on the edge of a plane element when KCSYS = 0. The positive direction of the tangential load is defined by the definition of the faces (J-I, K-J, L-K, I-L).

Positive Tangential Load on the Edge of a Plane Element If KCSYS = 1 or 2, the load direction does not change and KUSE = 1 or 2 is ignored.

If KCSYS = 1 or 2, or KTAPER > 0, you cannot specify a gradient (slope) for surface loads ( sfgrad ) or a varying surface load ( sffun ).

This command is also valid in the PREP7 processor.

If KTAPER = 1, the magnitude of the load is determined by the current location of a point:

\[equation not available\]

  • where:

  • \(equation not available\) : Values on sfe ( VAL1 ~ VAL4 )

  • \(equation not available\) : Global Cartesian coordinates at the current location of the point.

If KTAPER = 2, the magnitude of the load is determined by the initial location of a point:

\[equation not available\]

  • where:

  • \(equation not available\) : Values on sfe ( VAL1 ~ VAL4 )

  • \(equation not available\) : Global Cartesian coordinates at the initial location of the point.

KTAPER is not valid for use with sf.

The follower option ( KFOLLOW ) determines whether the load maintains a fixed direction (default) or follows element deformation. The option applies to surface loads defined by a fixed direction ( KCSYS = 1 or 2) or by a projected user-defined coordinate system ( KCSYS = 0 and VAL1 > 10).

When KCSYS = 0 and VAL1 > 10:

The selected local coordinate system is projected onto the face at the initial state, then the projected tangential component ( LCOMP ) is attached to the orthonormal basis ( e 1, e 2, e 3 ) of the face. The orthonormal basis may or may not be coincident to the \(equation not available\) coordinate system. During solution, the basis is updated at the current time step and the load direction is updated with respect to the basis.

Follower Load Behavior in the Projected Coordinate System When KCSYS = 1 or 2:

The global direction vector is attached to the orthonormal basis of selected face at the initial state. When KCSYS = 1, the direction of selected axis is considered as the direction vector and attached to the basis. During solution, the basis is updated at current time step and the load direction is updated with respect to the basis.

Follower Load Behavior for a User-Defined Orientation Follower loads on the edges of 3D shell and 2D elements:

The load is attached to the basis defined on the edge ( e t, e ne, e nf [tangential, edge-normal, and face-normal vector, respectively]). For 2D solid elements, the face-normal orientation ( e nf ) is that of the global Z axis. For 2D shell elements, the edge-normal ( e ne ) is that of the global Z axis.

Follower Load Behavior on the Edges of 3D Shell and 2D Elements If it is necessary to use the follower option after the first load step or at the restart analysis, define the load direction with respect to the current geometry (that is, the current basis of an element face). The follower option for the local coordinate system ( KCSYS = 1) is not allowed after the first load step or at the restart analysis.

Load-stiffness effects are included in the supported elements for the real part of all loads at the current configuration. All other load properties are included in the load vector of the elements.

You can specify an unsymmetric matrix ( nropt,UNSYM) for the load-stiffness effects if needed.