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Vincolo fissaggio

Vincolo piano di rotazione

FEM

Descrizione

The FEM displacement task panel

Utilizzo

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

Vincolo fissaggio

Vincolo piano di rotazione

FEM