FEM Core

NGSolve/Netgen finite-element model-building core — pure Python, no PySide6 or Qt dependency. Runs headlessly (no display required).

Features

• 🧱 Layered FEM pipeline — mesh → function space → weak-form assembly, each stage a swappable service
• 🧩 Typed, serializable models — FemModel, FemFormulation, BoundaryCondition, ... with to_dict()/from_dict()
• 🌊 Physics formulations — linear elasticity, (complex) Helmholtz, Reissner-Mindlin plates, Naghdi shells, and CUSTOM symbolic weak forms
• 🎯 Domain facades — AcousticModel, PlateModel, ShellModel builders in physics vocabulary
• 🧮 Studies — static, modal and frequency-sweep analyses through one StudyManager
• 📐 Stress — stresses, membrane forces, moments and shear forces as CoefficientFunctions
• 🗂️ Geometry import — STEP/IGES/BREP with deterministic, geometry-sorted region indices
• 💾 Results and projects — HDF5 result files and shared FemProject documents, with the fem-core-run / fem-core-view CLIs
• 🔒 Safe expressions — boundary and custom-form expressions parsed by a restricted AST walker, never eval()
• 🧪 Dependency-injectable services — every service behind a Protocol, so tests can mock NGSolve/Netgen
• 📊 Visualization — VTK post-processing (.vtu, .png, interactive) via the companion package fem-post

Scope

fem-core builds the mesh, function space and forms, and solves them with static, modal or frequency-sweep studies. Transient (time-stepping) analysis is out of scope for now.

Installation

pip install fem-core            # from PyPI
pip install "fem-core[viz]"     # plus fem-post (VTK post-processing)
pip install "fem-core[pardiso]" # plus MKL, for the PARDISO solver (x86-64 Linux/Windows)

For development, from the repo root:

uv sync
source .venv/bin/activate

Quick Start

from netgen.occ import Box, OCCGeometry, Pnt

from fem_core.enums import BoundaryConditionType, FemDimension, FormulationType, FunctionSpaceType, StudyType
from fem_core.managers.fem_model_manager import FemModelManager
from fem_core.managers.study_manager import StudyManager
from fem_core.models.boundary_condition import BoundaryCondition
from fem_core.models.fem_formulation import FemFormulation
from fem_core.models.fem_model import FemModel
from fem_core.models.formulation_parameters import LinearElasticityParameters
from fem_core.models.function_space_config import FunctionSpaceConfig
from fem_core.models.mesh_config import MeshConfig
from fem_core.models.study import Study
from fem_core.models.study_parameters import ModalStudyParameters, StaticStudyParameters

geo = OCCGeometry(Box(Pnt(0, 0, 0), Pnt(100, 20, 10)))

model = FemModel(
    name="Bracket",
    dimension=FemDimension.DIM_3D,
    formulation=FemFormulation(
        formulation_type=FormulationType.LINEAR_ELASTICITY,
        parameters=LinearElasticityParameters(E=210e9, nu=0.3, body_force_y=-9.81),
    ),
    function_space=FunctionSpaceConfig(space_type=FunctionSpaceType.VECTOR_H1, order=2),
    mesh_config=MeshConfig(maxh=5.0),
    boundary_conditions=[BoundaryCondition(bc_type=BoundaryConditionType.DIRICHLET, region="fixed_face")],
)

manager = FemModelManager()
managed = manager.build_model(model, geo=geo.shape)  # mesh -> function space -> forms

studies = StudyManager(manager)
static = studies.create_study(managed.model_id, Study(parameters=StaticStudyParameters()))
studies.run_study(static.study_id)
static.result.gridfunction

modal = studies.create_study(
    managed.model_id, Study(study_type=StudyType.MODAL, parameters=ModalStudyParameters(num_modes=6))
)
studies.run_study(modal.study_id)
modal.result.eigenvalues  # omega^2, ascending

Facades build the same FemModel from domain vocabulary:

from fem_core.facades.acoustic_model import AcousticModel

fem_model = (
    AcousticModel(name="Cabin Acoustics", speed_of_sound=343.0, density=1.225, frequency=250.0)
    .add_sound_hard_wall("rigid_walls")
    .add_impedance_boundary("absorber_panel", impedance=415.0 + 50.0j)
    .to_fem_model()
)

Saved projects and results can be solved or viewed from the command line:

fem-core-run beam.cadw
fem-core-view beam.results.h5 --study Modes --png modes.png

Documentation

• User Guide — studies, undo/redo, result storage, projects, geometry import, 2D/shell/plate models, stress, subdomains, visualization
• Architecture — layers, services, managers, facades and key design decisions
• Development — testing and releasing
• fem-post — VTK post-processing
• Examples and validations

License

MIT — see LICENSE.