UBoundary

*UBoundary [, <type>]
<node set name>, <degree of freedom>, <value>

This command is used to prescribe user-defined boundary conditions on nodes or node sets. If this command is used, numgeo expects the user defined subroutine to be accessible (see here). Therefore, the user has to implement the desired relation for the boundary condition using the predefined user_boundary_conditions interface, create the corresponding shared object user_boundary_conditions.so and place the object in the current working directory. For the compilation of the subroutine, a shell script is provided. It is possible to describe multiple degrees of freedom using one user file, since the name of the degree of freedom is passed into the subroutine, see here.

• <type>

  The optional keyword <type> can be used to define time derivatives in the subroutine rather than the actual value of the boundary conditions. For instance, if type=velocity is defined, the integrated value (e.g. displacement) is automatically calculated after the call of the subroutine, such that it is not required to define the integrated value (e.g. displacement) within the subroutine. By default, the type is none.

  Type	Description	Section
  none	prescribe degree of freedom (dof)	Section 1
  type=velocity	first time derivative of the prescribed dof	Section 2
  type=acceleration	second time derivative of the prescribed dof	Section 3

• <node set name> = name of the node set to which the boundary condition is applied

• <degree of freedom> = the degree of freedom to be constrained. The following degrees of freedom can be modified:

  Degrees of freedom	Description
  u1	Displacement in x1-direction
  u2	Displacement in x2-direction
  u3	Displacement in x3-direction
  r1	Rotation in x1-direction (only beam elements)
  r2	Rotation in x2-direction (only beam elements)
  r3	Rotation in x3-direction (only beam elements)
  pw	Pore-water pressure
  pa	Pore-air pressure
  w1	Water displacement in x1-direction
  w2	Water displacement in x2-direction
  w3	Water displacement in x3-direction

• <value> = set this parameter equal to the value to be prescribed to the boundary condition. Notice that this value is interpreted as a reference value, which is multiplied with the value defined in the user subroutine. It is recommended to set this value to 1.0 and define the desired value directly in the user subroutine.

• Good to know

  ---

  • Boundary conditions can only be applied to degrees of freedom that are actually defined for the chosen element type. For example, in single-phase solid elements of type u-solid, you can prescribe a boundary condition for the horizontal displacement u1, but attempting to prescribe a boundary condition for pw would raise an error, since pw is not an active degree of freedom for these elements.

  • Boundary conditions defined using this command can vary in time but are active at all nodes of the assigned node set.

  The theory behind the implementations