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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
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.