FEM: Constrângere de Deplasare

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FEM ConstraintDisplacement

poziția meniului
Model → Mechanical Constraints → Constraint displacement
Ateliere
FEM
scurtătură
nici unul
Prezentat în versiune
-
A se vedea, de asemenea,
FEM tutorial

Descriere

Creează o constrângere MEF pentru a o deplasare prescrisă a unui obiect selectat pentru un număr specificat de grade de libertate.

Cum se folosește

  1. Click pe sau alegeți ModelMechanical Constraints Constraint displacement din meniul de sus.
  2. Selectați în vizualizarea 3D obiectul la care trebuie aplicată constrângerea, care poate fi
    1. vertices (corners)
    2. edges
    3. faces
  3. Alegeți un grad de libertate pentru a stabili sau a prescrie o deplasare la.

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 should be increased by 6 mm:

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:

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 and was added so that after a rotation of 180° is performed

Note

  1. constrângerea utilizează tabelul *BOUNDARY în CalculiX. Fixarea unui grad de libertate este explicată la http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node164.html și se precizează o deplasare pentru un anumit grad de libertate http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node165.html