FEM ConstraintDisplacement: Difference between revisions

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{{docnav|[[FEM_ConstraintFixed|Constraint fixed]]|[[FEM_ConstraintPlaneRotation|Constraint plane rotation]]|[[FEM_Module|FEM_Module]]}}
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{{Docnav
|[[FEM_ConstraintFixed|Constraint fixed]]
|[[FEM_ConstraintContact|Constraint contact]]
|[[FEM_Workbench|FEM]]
|IconL=FEM_ConstraintFixed.svg
|IconR=FEM_ConstraintContact.svg
|IconC=Workbench_FEM.svg
}}


<!--T:1-->
<!--T:1-->
{{GuiCommand
{{GuiCommand|Name=FEM ConstraintDisplacement|MenuLocation=Model → Mechanical Constraints → Constraint displacement||Workbenches=[[Fem Workbench|FEM]]|Shortcut=|SeeAlso=[[FEM_tutorial|FEM tutorial]]}}
|Name=FEM ConstraintDisplacement
|MenuLocation=Model → Mechanical boundary conditions and loads → Displacement boundary condition
|Workbenches=[[FEM_Workbench|FEM]]
|Shortcut=
|SeeAlso=[[FEM_tutorial|FEM tutorial]]
}}


==Description== <!--T:2-->
==Description== <!--T:2-->


<!--T:6-->
<!--T:6-->
Creates a FEM constraint for a prescribed displacement of a selected object for a specified degree of freedom.
Creates a FEM boundary condition for a prescribed displacement of a selected object for specified degrees of freedom.


==How to use== <!--T:3-->
==Usage== <!--T:3-->


<!--T:7-->
<!--T:7-->
# Press the {{Button|[[Image:FEM_ConstraintDisplacement.svg|16px]] [[FEM_ConstraintDisplacement|Displacement boundary condition]]}} button or select the menu {{MenuCommand|Model → Mechanical boundary conditions and loads → [[Image:FEM_ConstraintDisplacement.svg|16px]] Displacement boundary condition}}.
#Click on [[Image:FEM ConstraintDisplacement.png|32px]] or choose {{KEY|Model}} → '''Mechanical Constraints''' → {{KEY|[[Image:FEM ConstraintDisplacement.png|32px]] Constraint displacement}} from the top menu.
#Select in the 3D-view the object the constraint should be applied to, which can be
# In the [[3D_view|3D view]] select the object the boundary condition should be applied to, which can be a vertex (corner), edge, or face.
# Press the {{Button|Add}} button.
## vertices (corners)
# Uncheck ''Unspecified'' to activate the necessary fields for editing.
## edges
# Set the values or ({{Version|0.21}}) specify a formula for the displacements.
## faces
#Choose a degree of freedom to fix or prescribe a displacement to.


==Limitations== <!--T:4-->
==Formulas== <!--T:13-->

<!--T:14-->
{{Version|0.21}}

===General=== <!--T:15-->

<!--T:16-->
For the [[Image:FEM_SolverElmer.svg|32px]] [[FEM_SolverElmer|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.

<!--T:17-->
Take for example the case that we want to perform a [[FEM_SolverElmer_SolverSettings#Timestepping_(transient_analyses)|transient analysis]]. For every time step the displacement <math>d</math> should be increased by 6 mm:

<!--T:18-->
<math>\quad
d(t)=0.006\cdot t
</math>

<!--T:19-->
enter this in the ''Formula'' field:</br>
{{incode| Variable "time"; Real MATC "0.006*tx"}}

<!--T:20-->
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=== <!--T:21-->

<!--T:22-->
Elmer only uses the '''Displacement *''' fields of the boundary condition. To define rotations, we need a formula.

<!--T:23-->
If for example a face should be rotated according to this condition:

<!--T:24-->
<math>\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}
</math>

<!--T:25-->
then we need to enter for '''Displacement x'''</br>
{{incode| Variable "time, Coordinate"
Real MATC "(cos(tx(0)*pi)-1.0)*tx(1)-sin(tx(0)*pi)*tx(2)}}

<!--T:26-->
and for '''Displacement y'''</br>
{{incode| Variable "time, Coordinate"
Real MATC "(cos(tx(0)*pi)-1.0)*tx(2)+sin(tx(0)*pi)*tx(1)}}

<!--T:27-->
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 <math>\pi</math> and was added so that after <math>t=1\rm\, s</math> a rotation of 180° is performed


==Notes== <!--T:5-->
==Notes== <!--T:5-->


<!--T:8-->
<!--T:8-->
For the [[Image:FEM_SolverCalculixCxxtools.svg|32px]] [[FEM_SolverCalculixCxxtools|solver CalculiX]]:
#The constraint uses the *BOUNDARY card in CalculiX. Fixing a degree of freedom is explained at http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node164.html and prescribing a displacement for a degree of freedom is explained at http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node165.html
* This tool uses the *BOUNDARY card.
* Fixing a degree of freedom is explained at http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node164.html
* Prescribing a displacement for a degree of freedom is explained at http://web.mit.edu/calculix_v2.7/CalculiX/ccx_2.7/doc/ccx/node165.html



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{{Docnav
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|[[FEM_ConstraintContact|Constraint contact]]
|[[FEM_Workbench|FEM]]
|IconL=FEM_ConstraintFixed.svg
|IconR=FEM_ConstraintContact.svg
|IconC=Workbench_FEM.svg
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Latest revision as of 14:17, 16 November 2023

FEM ConstraintDisplacement

Menu location
Model → Mechanical boundary conditions and loads → Displacement boundary condition
Workbenches
FEM
Default shortcut
None
Introduced in version
-
See also
FEM tutorial

Description

Creates a FEM boundary condition for a prescribed displacement of a selected object for specified degrees of freedom.

Usage

  1. Press the Displacement boundary condition button or select the menu Model → Mechanical boundary conditions and loads → Displacement boundary condition.
  2. In the 3D view select the object the boundary condition should be applied to, which can be a vertex (corner), edge, or face.
  3. Press the Add button.
  4. Uncheck Unspecified to activate the necessary fields for editing.
  5. Set the values or (introduced in version 0.21) specify a formula for the displacements.

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

Notes

For the solver CalculiX: