**fix_all_dof#

Description#

This boundary condition sets all degrees of freedom at the nodes to zero.

Syntax#

The syntax required to impose nodal DOFs is:

**fix_all_dof begin_time end_time [expiring | (ramp_off ramp_time)] \(~\,~\,\) nset_name

begin_time and end_time

specify the start and end times, respectively, for applying the boundary condition.

expiring

to specify that the boundary condition will be removed just after the end_time.

ramp_off

allows to remove the boundary condition after a ramp_time.

nset_name

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

Note

The imposed value is a zero incremental dof value. So if the start time is not zero this will “catch” and fix the nset’s current positions.

Example#

The following example can be found in $Z7PATH/TESTS/Static_test/INP/ramp_fixed_dof.inp. A “peristaltic” motion is applied on a volume element:

  • From time = 0 to time = 1: U1 = U2 = U3 = 0 on y=0. On y=1, The imposed U2 goes from 0 to 1. The command **fix_all_dof y=1 allows to keep U1 = 0, and keep the imposed value of U2.

  • From time = 1 to time = 2: on y=0, Dofs will be gradually and linearly released (ramp_off 1.0). On y=1, U1 = 0 and U2 =1 (**fix_all_dof y=1).

  • From time = 2 to time = 3: U1 = U2 = U3 = 0 on y=0. On y=1, The imposed U2 goes from 1 to 2.

 ***bc
  **fix_all_dof 0. 1. ramp_off 1.0
    y=0
  **fix_all_dof y=1 % this one will fix the current position of y=1
  **fix_all_dof 2.05 3.
    y=0

 **impose_nodal_dof
  x=0    U1 0.0
  z=0    U3 0.0
  y=1    U2 1. tab

***table
 **name tab
  *time  0. 1. 2. 3.
  *value 0. 1. 1. 2.
../../_images/fix_all_dof.gif

Fig. 10 The displacement U2 over time#