Apply Centrifugal Force in FreeCAD FEM Analyses

This guide explains how to apply centrifugal loads to rotating components using the FreeCAD Finite Element Method (FEM) workbench. You will learn how to configure the centrifugal force constraint, define the rotation axis, set angular velocity, and run the simulation using the integrated CalculiX solver to evaluate stress distributions caused by rotation.

1. Prepare Your Model and Mesh

  1. Open your 3D model in FreeCAD and switch to the FEM Workbench.
  2. Click Analysis container (the yellow folder icon with a capital 'A') to create a new analysis environment.
  3. Apply a material to your part by clicking Material for solid and selecting an appropriate material (e.g., Steel or Aluminum). Centrifugal force calculation depends heavily on material density (\(\rho\)), so ensure the density parameter is correctly defined.
  4. Select your geometry and generate a solid finite element mesh using either Netgen or Gmsh.

2. Add the Centrifugal Load Constraint

  1. In the model tree, ensure your active analysis container is selected.
  2. In the top toolbar or via the menu (Model > Mechanical boundary conditions and loads), click Centrifugal load. A new constraint object named FemConstraintCentrif will appear in your analysis container, and the task panel will open on the left.

3. Define the Rotation Axis and Center

The solver needs to know the exact axis of rotation to calculate the radial distance (\(r\)) from the axis to each node in the mesh:

  • Rotation Axis: In the task panel, define the vector representing the direction of the rotation axis (e.g., \((0, 0, 1)\) for the Z-axis). You can also click Add and select a cylindrical face or straight edge on your geometry to automatically extract the orientation.
  • Axis Center (Point on Axis): Set the coordinates for a point that the rotation axis passes through (e.g., \((0, 0, 0)\)). If you selected a circular or cylindrical feature, FreeCAD will automatically compute this center point.

4. Set the Angular Velocity

  1. Locate the Rotation speed or Angular velocity field in the task panel.
  2. Enter your desired rotational speed. FreeCAD allows inputs using frequency units such as revolutions per minute (e.g., 3000 rpm) or standard angular velocity (e.g., 314.16 rad/s). FreeCAD automatically converts the value to the unit system expected by CalculiX (\(rad/s\)).
  3. Click OK to close the task panel and save the constraint.

5. Apply Boundary Constraints

Centrifugal force is a body load, but the part still requires structural constraints to prevent unconstrained rigid body translation along the axis of rotation:

  • Apply a Fixed constraint or Displacement constraint to faces where the part is supported (such as a shaft bore, keyway, or mounting holes) to restrain axial movement while permitting or restricting radial expansion as appropriate for your physical setup.

6. Run the Solver and Review Results

  1. Double-click the SolverCalculixCxxtools object in the tree.
  2. Verify that the analysis type is set to Static. Centrifugal forces are steady-state inertial loads and are treated statically when the rotational speed is constant.
  3. Click Write .inp file, followed by Run CalculiX.
  4. Once the calculation finishes, close the solver task panel and double-click the resulting CCX_Results object to visualize the Von Mises stress, displacement, and deformation resulting from the rotation.