FEM: Vincolo di dislocamento

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This page is a translated version of the page FEM ConstraintDisplacement and the translation is 16% complete.

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Vincolo fissaggio

Vincolo piano di rotazione

FEM

Posizione nel menu
Vincolo di dislocamento
Modello → Vincoli meccanici → Vincolo dislocamento
Ambiente
FEM
Avvio veloce
Nessuno
Introdotto nella versione
-
Vedere anche
Tutorial di FEM

Descrizione

Crea un vincolo FEM per un determinato dislocamento di un oggetto selezionato per un dato grado di libertà.

Utilizzo

Cliccare su o scegliere Modello → Vincoli meccanici → Vincolo dislocamento dal menu principale.
Selezionare nella vista 3D l'oggetto a cui deve essere applicato il vincolo, che può essere
1. vertice (angolo)
2. bordo
3. faccia
Scegliere un grado di libertà e prescrivere uno spostamento.

Formulas

introduced in version 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 $d$ should be increased by 6 mm:

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

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:

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

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 $\pi$ and was added so that after $t=1{\rm {\,s}}$ a rotation of 180° is performed