**impose_nodal_dof_and_release#

Description#

This boundary condition imposes degrees of freedom located at nodes to defined values in time. The DOFs are imposed until a specified time; they are then progressively relaxed to a null flux BC.

Syntax#

The syntax of this boundary condition is:

**impose_nodal_dof_and_release \(~\,~\,\) nset_name  dof_name  t_ini  t_release  value  table_name

nset_name

is the name of a valid node set (nset) where the DOF is imposed.

t_ini

is the time until which the DOF is imposed. At t_ini, the BC automatically switches to impose the equivalent force (nodal reactions) on the given nodes.

t_release

is the time at which the force imposed on constrained nodes is set back to 0. The time interval t_ini t_release is used to progressively shed this force from its current value back to 0.

dof_name

is the name of the DOF to be imposed. This must be one of the defined DOF types given by the problem. DOF names are also listed in the problem.ut reference file.

value

this real value acts as a multiplier on the current applied load table value. If the value is zero, no table will be required. It may also be any valid basic value (see p. for more details).

table_name

a character name for the loading table which describes the DOF evolution in time. A corresponding table must therefore be given elsewhere (see table).

Note

  • This command is equivalent to

    **impose_nodal_dof \(~\,~\,\) nset_name ramp_off delta_t dof_name value  table_name

    where delta_t = t_release - t_ini.

  • If delta_t =0, one can use

    **impose_nodal_dof \(~\,~\,\) nset_name exp dof_name value  table_name

Example#

Supposing that a mesh has been created with two node sets composed of a single node, node 1 and node 2. This example sets the displacement of specified nodes to 0 in the direction \(u_1\) until the current time is 100s. Then, this constraint is released in 0.5 s. Such an example can be used to simulate crack propagation using a node releasing approach.

***bc
 **impose_nodal_dof_and_release node1 U1 100.0 100.5 0.
 **impose_nodal_dof_and_release node2 U1 100.0 100.5 0.