COMPAS CRA

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Coupled Rigid-Block Analysis (CRA) implementation using COMPAS framework.

developed with ♥ by Gene Ting-Chun Kao

Installation

pip install compas_sandbox

Nothing else is needed on Windows, macOS (Apple Silicon and Intel) or Linux: the wheels bundle a statically linked IPOPT 3.14.19 executable (Eclipse Public License 2.0, MUMPS linear solver, no HSL), built from source by packaging/. See packaging/README.md for how it is built and which licenses apply, and the installation docs for development installs.

Rhino 8

The easiest way is to let the ScriptEditor install everything for you. Start a new Python 3 script with this header and run it — on the first run Rhino installs compas_sandbox and all of its dependencies into its own environment (this takes a couple of minutes, watch the progress in the ScriptEditor console):

#! python3
# venv: compas-sandbox
# r: compas_sandbox

No extra # r: lines are needed for compas, numpy, shapely, etc. — they are dependencies of compas_sandbox and pip installs them automatically. The bundled IPOPT executable works inside Rhino as well, so no conda or manual solver install is needed.

Ready-to-run examples for the ScriptEditor are in scripts/:

  • scripts/rhino_cra_cubes.py — three stacked cubes, baked as wireframe blocks with interface outlines and resultant contact forces.
  • scripts/rhino_cra_arch.py — a parametric masonry arch (span, rise, thickness, number of voussoirs, friction) solved and baked the same way.

Alternatively, install manually into Rhino's Python with the shell that ships with Rhino (Tools > Options > Plugins > Rhino Code > Open Shell, or ~/.rhinocode/py39-rh8/shell/open-shell on macOS):

pip install compas_sandbox

Note that Rhino 8 ships CPython 3.9: compas_sandbox supports it since version 0.6.2, and pip automatically selects dependency versions that still support 3.9 (for example pyomo 6.9.x rather than 6.10+).

Known issue: Windows antivirus and the bundled solver

The wheels bundle an ipopt.exe built from source by CI. Because every release produces a brand-new, unsigned binary with no reputation, some Windows antivirus setups (notably managed/corporate Defender policies) quarantine it after the first run. The symptom is a solve that worked once and then fails with "No IPOPT executable found" — run scripts/rhino_ipopt_check.py to confirm (an empty bin dir means the exe was removed).

What to do:

  • Personal machine: restore the file from the antivirus quarantine and add an exclusion for the install folder (e.g. %USERPROFILE%\.rhinocode for Rhino), then pip install --force-reinstall --only-binary :all: compas_sandbox.
  • Managed machine (no admin rights): ask IT to allowlist the file or folder, or point the solver at any trusted ipopt binary by setting the environment variable COMPAS_SANDBOX_IPOPT to its full path (a conda-forge ipopt works).
  • The binaries carry version metadata identifying what they are, and the release workflow supports Authenticode signing (Azure Trusted Signing) once a certificate is configured, which resolves this properly.

To find out more about CRA, please refer to our paper in the CAD Computer-Aided Design journal: https://doi.org/10.1016/j.cad.2022.103216

Coupled Rigid-Block Analysis: Stability-Aware Design of Complex Discrete-Element Assemblies

image

Abstract

The rigid-block equilibrium (RBE) method uses a penalty formulation to measure structural infeasibility or to guide the design of stable discrete-element assemblies from unstable geometry. However, RBE is a purely force-based formulation, and it incorrectly describes stability when complex interface geometries are involved. To overcome this issue, this paper introduces the coupled rigid-block analysis (CRA) method, a more robust approach building upon RBE’s strengths. The CRA method combines equilibrium and kinematics in a penalty formulation in a nonlinear programming problem. An extensive benchmark campaign is used to show how CRA enables accurate modelling of complex three-dimensional discrete-element assemblies formed by rigid blocks. In addition, an interactive stability-aware design process to guide user design towards structurally-sound assemblies is proposed. Finally, the potential of our method for real-world problems are demonstrated by designing complex and scaffolding-free physical models.

Please cite our work if you use CRA in your research

Paper

@article{kao2022coupled,
    title     = {Coupled Rigid-Block Analysis: Stability-Aware Design of Complex Discrete-Element Assemblies},
    author    = {Kao, Gene Ting-Chun and Iannuzzo, Antonino and Thomaszewski, Bernhard and Coros, Stelian and Van Mele, Tom and Block, Philippe},
    journal   = {Computer-Aided Design},
    volume    = {146},
    pages     = {103216},
    year      = {2022},
    publisher = {Elsevier},
    doi       = {10.1016/j.cad.2022.103216},
    url       = {https://doi.org/10.1016/j.cad.2022.103216}
}

Software implementation

@misc{compas-sandbox,
    title  = {{COMPAS CRA}: Coupled Rigid-Block Analysis ({CRA}) for the {COMPAS} framework},
    author = {Kao, Gene Ting-Chun},
    note   = {https://github.com/BlockResearchGroup/compas\_cra},
    year   = {2020-2022},
    doi    = {10.5281/zenodo.7043135},
    url    = {https://doi.org/10.5281/zenodo.7043135},
}

Read the docs

https://github.com/petrasvestartas/compas_sandbox

Examples to reproduce our paper results

See examples in docs or try them in docs/examples.

Project links

Data verified by PyPI on Aug 23, 2026
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Newer release available (0.7.6)

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Credits

Author: Gene Ting-Chun Kao

GitHub Statistics

Data verified by PyPI on Aug 23, 2026
The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License

MIT License

Requires

Python >=3.9

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