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Section 3.10: Boundary Section Up Section 3.10: Boundary Section Subsection 3.10.2: Fixed Nodal Degrees of Freedom

3.10.1 Prescribed Nodal Degrees of Freedom

Nodal degrees of freedom (dof) can be prescribed using the prescribe boundary condition. This element has two required attributes: the type is set to “prescribe” and the node set to which this boundary condition applies is defined vua node_set. The optional name attribute can be used to give the boundary condition a name. The value is defined via the scale parameter. (If omitted the default value is 1.0). The degree of freedom is defined via the dof parameter. A loadcurve can be associated with the scale parameter. The relative parameter defines wheter the values are absolute or relative to the current displacement.
<bc type="prescribe" node_set="nodeset1">
<dof>x</dof>
<scale lc="1">2.0</scale>
<relative>0</relative>
</bc>

Here, nodeset1 is the name of a node set defined in the Mesh section. See Section 3.6.3↑ for more information on how to define node sets. Node sets can also be defined via surfaces or element sets. To define a node set via a surface, use the following syntax.
node_set="@surface:surface1"

Here, surface1 is a surface defined in the Mesh section. Similarly, defining a node set via an element set is done using @elem_set:.
The dof parameter specifies the particular degree of freedom. The following values are allowed:
x apply displacement in -direction
y apply displacement in -direction
z apply displacement in -direction
sx apply shell back-face displacement in -direction (new shell formulation)
sy apply shell back-face displacement in -direction (new shell formulation)
sz apply shell back-face displacement in -direction (new shell formulation)
u apply shell director component in -direction (old shell formulation)
v apply shell director component in -direction(old shell formulation)
w apply shell director component in -direction(old shell formulation)
p apply prescribed effective fluid pressure (biphasic and multiphasic analyses)
T apply prescribed temperature (heat transfer analysis)
c apply prescribed effective solute concentration (solute analysis)
c[] apply prescribed effective solute concentration on solute (multiphasic analysis)
wx apply prescribed fluid velocity relative to mesh in -direction (fluid and FSI analyses)
wy apply prescribed fluid velocity relative to mesh in -direction (fluid and FSI analyses)
wz apply prescribed fluid velocity relative to mesh in -direction (fluid and FSI analyses)
ef apply prescribed fluid dilatation (fluid analysis)
For solutes, replace “” with the solute id from the global solute table (Section 3.4.2↑); for example, “c2”.
The loadcurve for the scale parameter is specified with the lc attribute. The value of the lc attribute is the ID of the loadcurve that is defined in the LoadData section of the input file.
The optional relative parameter allows users to choose between absolute (default) and relative boundary conditions. Absolute boundary conditions assign the specified value to the desired nodal degree of freedom. Relative boundary conditions are meaningful only in multi-step analyses. When a nodal degree of freedom is specified to be relative at a particular step, the value prescribed for that node is superposed over the value of that degree of freedom at the end of the preceding step.
To define a different displacement value for each node, a mesh_data section needs to be defined.
<Boundary>
<bc type="prescribe" node_set="set1">
<dof>x</dof>
<scale lc="1">2.0</scale>
<relative>0</relative>
</bc>
</Boundary>
<MeshData>
<mesh_data param="fem.bc_prescribed[0]">
<node lid="1">1.0</node>
<node lid="2">2.0</node>
<node lid="3">3.0</node>
</mesh_data>
</MeshData>

Keep in mind that the scale parameter of the prescribed bc will scale the values defined in the mesh data section.
Section 3.10: Boundary Section Up Section 3.10: Boundary Section Subsection 3.10.2: Fixed Nodal Degrees of Freedom