**impose_nodal_dof

Description

This boundary condition imposes degrees of freedom located at nodes to defined values in time. The condition is general and therefore applies to all types of DOF for all types of problem.

Syntax

The syntax required to impose nodal DOFs is:

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

nset_name

This is the name of a valid node set (nset) which gives all the nodes where the DOF is to be imposed.

dof_name

The character name of the DOF to be imposed. This must be one of the defined DOF types given by the problem, and as indexed in the appendix. 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.

table_name

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

Example

Supposing that a mesh has been created with a node set composed of a single node, node 1. This example displaces that node a fixed amount in the directions \(u_1\) and \(u_2\). The \(u_1\) magnitude will be \(1.2\) times the table value specified by table3 while \(u_2\) will be only \(0.2\) times that value. Using the same table assures synchronization between the loadings.

***bc
 **impose_nodal_dof node1 U1 1.2 table3
 **impose_nodal_dof node1 U2 0.2 table3

Note that a structure will normally have more displacement conditions than the fixing of a single node. Other conditions such as pressure and force are also likely.

The same command may be used to specify the temperature in a thermal problem.

**impose_nodal_dof node1 TP 200.0 tab1

Note

Some variants exist, which allow the value to vary in space:

**impose_nodal_dof nset_name  dof_name function function(x,y,z);   table_name nset_name  dof_name file binary_file   table_name nset_name  dof_name ascii_file ascii_file   table_name

The function variant allows the DOF value to depend on nodal coordinates. The function may also depend on time; this is however discouraged, because in that case incremental values are not properly computed. The time dependency should rather be specified through the table.

Both file variants read the value of each DOF from a file; thus the file should contain as many entries as nodes in the nset, values being ordered as in the nset. Note that the binary form expects entries as “floats” (not “doubles”).