Supported Solvers in FreeCAD FEM Workbench

The FreeCAD Finite Element Method (FEM) workbench allows engineers and designers to perform structural, thermal, and multiphysics simulations directly inside FreeCAD's parametric modeling environment. Because FreeCAD functions primarily as a pre-processor and post-processor, it relies on external, open-source solver backends to calculate simulation results. This guide outlines the solver engines natively supported by the FreeCAD FEM workbench, their primary capabilities, and their ideal use cases.

CalculiX

CalculiX is the default, most mature, and most deeply integrated solver within the FreeCAD FEM workbench. It utilizes an Abaqus-like input file format and is capable of handling both linear and nonlinear analysis. Within FreeCAD, CalculiX can be used for:

  • Linear and Nonlinear Static Stress Analysis: Resolving displacements, strains, and stresses under various boundary conditions and hyperelastic or plastic material behaviors.
  • Modal Analysis: Computing natural frequencies and vibration mode shapes.
  • Pure Thermal and Coupled Thermo-Mechanical Analysis: Simulating steady-state and transient heat transfer alongside thermally induced mechanical stresses.
  • Contact Analysis: Managing face-to-face and surface interactions between multiple bodies.

Elmer

Elmer is an open-source multiphysics simulation solver developed by CSC – IT Center for Science. It is designed to handle coupled physical phenomena across multiple domains. FreeCAD includes dedicated tools for writing Elmer input files and running Elmer simulations. Key capabilities in FreeCAD include:

  • Electrostatics and Magnetodynamics: Simulating electric potentials, fields, and electromagnetic interactions.
  • Heat Equations: Calculating conductive, convective, and radiative heat transfer.
  • Elasticity: Basic mechanical stress modeling.
  • Multiphysics Coupling: Solving complex simultaneous equations where fluid, thermal, and electrical fields interact.

Z88

Z88 (specifically Z88OS) is a compact, robust, and fast finite element solver tailored for mechanical engineering problems. It was developed at the University of Bayreuth. In the FreeCAD FEM workbench, Z88 serves as an alternative to CalculiX for basic mechanical simulations. Its features include:

  • Linear Static Stress Analysis: Calculating stress distribution, deformations, and safety factors for solid bodies.
  • Speed and Low Memory Footprint: Efficient execution on compact or resource-constrained machines for purely linear problems.

Mystran

Mystran is an open-source solver compatible with the historical NASA structural analysis program (NASTRAN). Its integration into FreeCAD provides an open-source pathway for engineering workflows that rely on standard NASTRAN bulk data entry formats. Mystran focuses primarily on:

  • Linear Static Analysis: Computing deflections and stresses under steady mechanical loads.
  • Normal Modes: Calculating structural natural frequencies and corresponding mode shapes.

Workflow and Solver Selection

FreeCAD FEM organizes these solvers into distinct solver objects that can be added to an active Analysis container. Users assign geometry, meshes, materials, and boundary conditions to the container, and the chosen solver module generates the required input deck, runs the external binary, and imports the calculated results back into FreeCAD for visualization and post-processing.