From FreeCAD Documentation
- After adding an Elmer solver as described here, select it in the tree view.
- Either use the toolbar button or the menu Solve → Flux equation.
- Now either add a heat equation (toolbar button or menu Solve → Heat equation) or an electrostatic equation (toolbar button or menu Solve → Electrostatic equation). This is important because the flux equation needs the boundary conditions set for these equations.
- When using the electrostatic equation, change the property DataFlux Coefficient to None. and the property DataFlux Variable to Potential.
- Change the equation's solver settings or the general solver settings if necessary.