README.md

Finite Element models 4 Nonlinear Intrinsic Aeroelastics in JAX [FENIAX]

FENIAX is an aeroelastic toolbox written in Python using JAX. It acts as a post-processor of commercial software such as MSC Nastran.

Some of the key features of the software are:

• Arbitrary FE models built for linear aeroelastic analysis are enhanced with geometric nonlinear effects, flight dynamics and linearized state-space solutions about nonlinear equilibrium.
• Leveraging on the numerical library JAX and optimised algorithms, a high performance is achieved that leads to simulation times comparable to the linear counterparts on conventional platforms.
• The software runs on modern hardware architectures such as GPUs in a addition to standard CPUs.
• Algorithm differentiation (AD) of the aeroelastic response is available via JAX primitives.
• Concurrent simulations for multiple load cases have been developed.

Installation

• Currently the code has been tested and is developed in Linux and MacOS.
• A minimum installation into the current environment is possible by navigating to the main directory and

pip install .

• However developer mode is recommended and also installing the full set of packages which include testing and visualisation capabilities:

pip install -e .[all]

• see pyproject.toml file for the options available. Python 3.10+ is required.

• To install with GPU support install jax first:

pip install -U "jax[cuda12]"
pip install -e ".[all]"

Python environment

Although it is not necessary, it is recommended that the software is installed in its own environment. Options that have been tested out follow.

• Conda:

Although it is not necessary, If conda is being used as package manager, one can make a specific environment as,

conda create -n feniax python=3.11
conda activate feniax

If pytest has been installed, check everything is OK by running the tests:

pytest

• Thus a typical installation would comprise of these 4 steps:

conda create -n feniax.python=3.11
conda activate feniax
pip install -e .[all]
pytest

• pyenv: Navigate to the root directory and run the following:

  pyenv install 3.11.10
  pyenv virtualenv 3.11.10 feniax
  pyenv local feniax
  pip install -e .[all]
  pytest

By setting pyenv local to feniax, every time one moves to feniax directory the environment is automatically activated

Documentation

Available at https://acea15.github.io/FENIAX/

Examples

The most relevant examples in the code base are shown here, these and more can be found in the folder /examples They are also part of a large test suite that is integrated into the development using CI/CD.

!!! tip Navigate to the code of the various examples, including the simulation input settings and postprocessing of the simulation --exactly as it was used for the articles backing the software. See examples

Nonlinear structural static results

!!! success - Validated with MSC Nastran nonlinear solution (sol 400) - AD differentiation of the response verified against finite-differences

Notebook

!!! note Take a liner FE model of arbitrary complexity from your favourite FE solver, and turn it into a fully geometrically nonlinear model. You just need a condensation step into the main load paths and the resulting linear stiffness and mass matrices.

Wing free dynamics

!!! success - Validated with MSC Nastran nonlinear solution (sol 400) - Runs over x100 faster than Nastran - AD differentiation of the response verified against finite-differences

Notebook

Free flying structure

This example first appeared in the work of Juan Carlos Simo (see Bio) , a pioneer in the field of computational structural mechanics and the

Notebook

2D dynamics

3D dynamics

Concurrent aeroelastic simulations on ultra-high aspect ratio aircraft

!!! success - Nonlinear aeroelastic response in our solvers takes similar times or less to the linear Nastran solution!! - Concurrent simulations for various loading settings achieve unparalleled computational times. - CPU VS GPU benchmarks available.

Wing-tip static loading

• Extremely large deformations
• Validation of concurrent solution
• 300 modes in the solution, 8 different loading scenarios running in parallel each with 11 substeps, 24 seconds in total on A100 GPU

Aeroelastic equilibrium for varying AoA

• Nonlinear effects: follower aerodynamic forces, geometric stiffening, wing shortening.
• Steady manoeuvre varying flow conditions and AoA for a total 256 cases in 14 seconds.

Dynamic loads at large scale: gust envelopes

• 512 different gust cases run on A100 GPU NVIDIA in 38 seconds!
• Rigid body modes included, rigid/elastic nonlinear couplings accounted for.
• Load envelopes available from the simulation.