FreeDyn

Multi-Body System (MBS) Simulation and Analysis Software

What is FreeDyn?

FreeDyn is a powerful simulation software for modeling and analyzing Multi-Body Systems (MBS). It supports:

• Rigid and flexible body dynamics with arbitrary kinematic structures
• Advanced constraint modeling (joints, contact, etc.)
• Multiple force models (springs, dampers, external forces, etc.)
• HHT time integration solver for implicit integration
• Python/MATLAB/Scilab interfaces for custom analysis
• GUI and command-line tools for pre- and post-processing

Download

Download the latest release as a ZIP archive from GitHub Releases.

Documentation

• Getting Started - Installation and first steps (GUI & Python)
• C API - Canonical C header location and ABI conventions
• Examples - Python code examples and tutorials
• Release Notes - What's new

Quick Start

Option A – GUI (no programming required)

1. Download and extract the release ZIP
2. Run bin\x64_MD\Freedyn_GUI.exe from the extracted folder
3. Open a model file (.fds) and start simulating

No Python or other tools required.

Option B – Python Scripting

For automated simulations, custom analysis, and batch processing:

1. Install the Python bindings from the extracted release directory:

   cd C:\FreeDyn
   pip install .
   

2. Run a model from the command line:

   freedyn-run path/to/model.fds
   

3. Or script it:

   import freedyn as fd
   
   fd.initialize()  # loads freedyn.dll
   with fd.Model("path/to/model.fds") as model:
      model.solve()
      for idx, time, states in model.iterate_time_steps():
         print(idx, time, states["Q"][0, 0])
   

More detail: docs/GETTING_STARTED.md

Features

Simulation Capabilities

• Kinematic and dynamic analysis
• Time-domain simulation with implicit integration
• Automatic constraint handling
• Flexible body dynamics
• Contact models

Analysis Tools

• Jacobian extraction - System matrices at any time point
• Force/motion analysis - Extract forces, accelerations, constraint forces
• Parameter sensitivity - Analytical jacobians w.r.t. parameters
• Custom measures - User-defined outputs

Integration Options

• GUI - Pre- and post-processing with Freedyn_GUI.exe
• Python API - Programmatic simulation and analysis
• MATLAB API - Scripting via freedyn_api.m + Simulink integration
• Scilab API - Scripting via freedyn_api.sce (uses MT variant)
• C interface (CDLL) - Direct DLL linking for other languages (see include/freedyn/freedyn_c_api.h)

Architecture

FreeDyn consists of several components:

• Freedyn_GUI.exe - Graphical pre- and post-processor
• freedyn.dll - Core MBS solver (C-interface Dynamic Link Library)
• Python bindings - High-level API for scripting and analysis (open source)
• CLI tool - Command-line interface (freedyn-run)

Requirements

GUI / Standalone Use

• Windows 7 or later (64-bit)
• Visual C++ Redistributable (included in release)
• Intel MKL runtime (included in release)

Python Bindings (optional)

• Python 3.8+
• numpy, scipy

License

FreeDyn is released under the GNU Lesser General Public License v3.

The Python bindings (source code in this repository) are open source. The binary components (freedyn.dll, Freedyn_GUI.exe, etc.) are distributed as pre-built binaries via GitHub Releases.

See LICENSE for details.

Support & Issues

• GitHub Issues: Report bugs
• Documentation: See docs/ folder
• Examples: See examples/ folder

Release Notes

Latest Release

• Initial public release
• Complete Python bindings refactoring
• High-level API (Model, ModelInfo, analysis functions)
• Command-line tool (freedyn-run)
• Core MBS simulation capabilities
• Matrix/vector extraction functionality
• Comprehensive documentation

Contributing

Contributions to the Python bindings are welcome:

1. Check existing issues
2. Follow the coding guidelines
3. Submit pull requests with clear descriptions

Citation

If you use FreeDyn in your research, please cite:

@software{freedyn2025,
  title = {FreeDyn: Multi-Body System Simulation Software},
  author = {Oberpeilsteiner, Stefan and others},
  year = {2025},
  url = {https://github.com/freedyn-org/freedyn}
}

Author

Stefan Oberpeilsteiner (FreeDyn Development Team)

Repository: https://github.com/freedyn-org/freedyn
Version: See _version.py for current version