FEM ConstraintDisplacement

Description
Creates a FEM constraint for a prescribed displacement of a selected object for a specified degree of freedom.

Usage

 * 1) Either press the button   or select the menu.
 * 2) In the 3D view select the object the constraint should be applied to, which can be a vertex (corner), edge, or face.
 * 3) Press the  button.
 * 4) Uncheck Unspecified to activate the necessary fields for edition.
 * 5) Set the values or  specify a formula for the displacements.

General
For the solver Elmer it is possible to  define the displacement as formula. In this case the solver sets the displacement according to the give formula variable.

Take for example the case that we want to perform a transient analysis. For every time step the displacement $$d$$ should be increased by 6 mm:

$$\quad d(t)=0.006\cdot t $$

enter this to the Formula field:

This code has the following syntax:
 * the prefix Variable specifies that the displacement is not a constant but a variable
 * the variable is the current time
 * the displacement values are returned as Real (floating point value)
 * MATC is the prefix for the Elmer solver that the following code is a formula
 * tx is always the name of the variable in MATC formulas, no matter that tx is in our case actually t

Rotations
Elmer only uses the Displacement * fields of the constraint. To define rotations, one needs a formula.

For example a face should be rotated according to this condition:

$$\quad \begin{align} d_{x}(t)= & \left(\cos(\phi)-1\right)x-\sin(\phi)y\\ d_{y}(t)= & \left(\cos(\phi)-1\right)y+\sin(\phi)x \end{align} $$

then we need to enter for Displacement x

and for then we need to enter for Displacement y

This code has the following syntax:
 * we have 4 variables, the time and all possible coordinates (x, y z)
 * tx is a vector, tx(0) refers to the first variable, the time while tx(1) is the first coordinate x
 * pi denotes $$\pi$$ and was added to set that after $$t=1\rm\, s$$ a rotation of 180° is performed