FEM ConstraintSelfWeight: Difference between revisions

From FreeCAD Documentation
(added acceleration change)
(Fixed value in <=V0.21 as a separate paragraph. That way it can easily be deleted later.)
Line 23: Line 23:


<!--T:12-->
<!--T:12-->
Defines a gravity acceleration of 9,81 m/s^2 (or {{Version|0.22}}: another user-defined value) acting on the whole model in the prescribed direction.
Defines a gravity acceleration acting on the whole model in the prescribed direction.

{{VersionMinus|0.21}}: The magnitude of the acceleration has a fixed value of 9.81 m/s^2.


==Usage== <!--T:3-->
==Usage== <!--T:3-->

Revision as of 09:48, 24 January 2024

FEM ConstraintSelfWeight

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

Description

Defines a gravity acceleration acting on the whole model in the prescribed direction.

version 0.21 and below: The magnitude of the acceleration has a fixed value of 9.81 m/s^2.

Usage

  1. There are several ways to invoke the command:
    • Press the Gravity load button.
    • Select the Model → Mechanical boundary conditions and loads → Gravity load option from the menu.
  2. You can modify the direction of gravity load by changing its vector coordinates in the property bar of the newly created ConstraintSelfWeight object. introduced in version 0.22: Acceleration magnitude can also be changed using another property of this object.

Scripting

New object:

import ObjectsFem
ObjectsFem.makeConstraintSelfWeight(name)

Add object to the analysis named Analysis:

App.ActiveDocument.Analysis.Member = App.ActiveDocument.Analysis.Member + [(object)]

Example:

import ObjectsFem
selfweight_obj = ObjectsFem.makeConstraintSelfWeight("MySelfWeightObject")
App.ActiveDocument.Analysis.Member = App.ActiveDocument.Analysis.Member + [selfweight_obj]

Solver CalculiX

Limitations

  • version 0.21 and below: You need to modify the .inp file to edit gravity acceleration.
  • Self-weight is applied to the element set Eall which includes the whole model.

Editing CalculiX input file

The acceleration constant can be manually edited after generating the CalculiX input file.

Example of lines in the .inp file:

*DLOAD
Eall,GRAV,9810,0.0,0.0,-1.0

where 9810 is a gravity acceleration magnitude in [mm/s^2], and 0,0,-1 is the direction vector. The value can be set as a multiple of standard gravity acceleration to simulate loading of e.g. 4g.

Solver Z88

  • Currently, not implemented in the Z88 solver.