FEM ConstraintDisplacement/ro

Descriere

The FEM displacement task panel

Formulas

introduced in 0.21

General

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

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

${\displaystyle \quad d(t)=0.006\cdot t}$

enter this in the Formula field:
Variable "time"; Real MATC "0.006*tx"

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) values
• MATC is a prefix for the Elmer solver indicating that the following code is a formula
• tx is always the name of the variable in MATC formulas, no matter that tx in our case is actually t

Rotations

Elmer only uses the Displacement * fields of the boundary condition. To define rotations, we need a formula.

If for example a face should be rotated according to this condition:

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

then we need to enter for Displacement x
Variable "time, Coordinate" Real MATC "(cos(tx(0)*pi)-1.0)*tx(1)-sin(tx(0)*pi)*tx(2)

and for Displacement y
Variable "time, Coordinate" Real MATC "(cos(tx(0)*pi)-1.0)*tx(2)+sin(tx(0)*pi)*tx(1)

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) refers to the first coordinate x
• pi denotes ${\displaystyle \pi }$ and was added so that after ${\displaystyle t=1{\rm {\,s}}}$ a rotation of 180° is performed

Note