Geometry & mesh interchange
Generate meshes of parametric shapes, convert from and to other mesh formats, and (optionally) mesh arbitrary geometry with gmsh. Pure Python except the gmsh route, which runs in its own subprocess.
mdpa_create_geometry_mesh
Write a mesh of a parametric shape. Every mesh has a domain part plus named boundary parts carrying conditions of condition_name (default LineLoadCondition2D2N in 2D, SurfaceLoadCondition3D4N in 3D), oriented with the domain on their left. Existing files are only replaced with overwrite=true.
kind | params | Parts |
|---|---|---|
annulus | r_inner, r_outer, n_radial, n_theta, angle=360, triangles=false | inner, outer (+ start, end for a sector) |
disc | radius, n_radial, n_theta (triangles) | boundary |
cylinder | radius, height, n_radial, n_theta, n_z, inner_radius? (prisms, or hexahedra when hollow) | lateral, zmin, zmax |
sphere | radius, divisions (radially mapped cube of hexahedra; stretched corner cells) | surface |
polygon | vertices: [[x, y], ...], refinements=0, holes?, target_size?, size_field?, size_sources?, max_elements=200000, smooth_iterations=0 (ear clipping with hole bridging + midpoint subdivision; holes is a list of strictly interior vertex loops; target_size adds subdivision rounds until no edge is longer than it, at most 6 rounds total; the grading parameters are described below) | side_0, side_1, ... plus hole_<k> per hole |
element_name overrides the default SmallDisplacementElement… type. For CAD input or quality-driven meshes use gmsh.
Graded polygon meshes (no gmsh)
size_field is an expression of x and y (the same safe subset as the selectors: arithmetic plus sqrt sin cos tan exp log tanh atan abs min max, e.g. "0.1 + 0.3*sqrt((x-1)**2 + y**2)"). size_sources is a list of {"point": [x, y], "size": 0.05, "growth": 0.4} or {"segment": [[x0, y0], [x1, y1]], "size": …, "growth": …} giving size + growth * distance; growth defaults to 0.3. The smallest of all given sizes wins. After the optional uniform target_size rounds the mesh is refined by conforming longest-edge (Rivara) bisection — no hanging nodes, boundary nodes stay on their original segments, hole slits are handled — until every triangle's longest edge is at most the local size (the smallest of the size at its corners and centroid). max_elements stops runaway sizes with an error; smooth_iterations (0–100), when above 0, first applies Delaunay edge flips and then that many rounds of Laplacian smoothing of the interior nodes, skipping any move that would lower the worst adjacent angle. Boundary nodes never move, so the smallest angle can be limited by the polygon itself (a 2:1 rectangle split by ear clipping keeps its 26.6° corners); check it with mdpa_quality (angle_degrees). Triangle shape is otherwise that of ear clipping plus bisection; use gmsh when quality matters more.
mesh_import / mesh_export
mesh_import(source, output, element_name?, condition_name?, property_id?, file_format?) converts anything meshio reads (gmsh .msh, .vtk/.vtu, MED, Abaqus .inp, Nastran, XDMF, …) into .mdpa: the highest-dimension cells become elements, the next lower dimension conditions, and named physical groups / cell sets become sub model parts (a domain part with everything is added). Linear and quadratic line, triangle, quad, tetra, hexahedron, wedge and pyramid cells are converted (quadratic Kratos ordering matches meshio/VTK), plus the cubic line4, triangle10 and quad16; 15-node wedges and 13-node pyramids cannot be represented by meshio itself and other cubic/higher Lagrange cells are rejected). The default type names are generic (Element2D3N … SurfaceCondition3D4N, with …2D6N / …3D10N / … variants for quadratic cells); set element_name for a specific solver, e.g. SmallDisplacementElement2D3N.
mesh_export(path, output, file_format?, overwrite?, linearize_unsupported?) goes the other way. Elements come first, then conditions; cell data holds kratos:id, kratos:property_id and kratos:entity (0 element / 1 condition), sub model parts become cell sets where the format supports them, scalar nodal data becomes point data (vector nodal data too, when its [d](…) value parses). 15-node wedges cannot be exported through meshio (nor 13-node pyramids): linearize them first (mdpa_convert_cells quadratic_to_linear), pass linearize_unsupported=true to write only their corner nodes (a warnings entry says so) or keep the .mdpa. Cubic triangles/quads/lines only export to formats that have them (gmsh .msh, written in Gmsh format; VTK is refused).
mesh_generate_gmsh
Needs the optional extra: uv sync --extra gmsh (or pip install gmsh; on Linux gmsh also needs libGLU and libXft). gmsh runs in a subprocess (gmsh_worker.py), never inside the server, because it is a large native library.
kind | Inputs | Result |
|---|---|---|
polygon | vertices (counter-clockwise), optional holes (vertex loops), size, quads | parts domain, side_<i>, hole_<k> |
shape | shape = box (shape_params: {size_xyz: [lx, ly, lz], origin}), cylinder ({radius, height}) or sphere ({radius}), size | tetrahedra; parts domain, boundary |
file | cad_file (.step, .brep, .geo, .iges, …), dim, size | its physical groups, else domain / boundary |
size is the target element size, size_min its lower bound. Defaults are Element2D3N / LineCondition2D2N (2D) and Element3D4N / SurfaceCondition3D3N (3D) unless element_name / condition_name are given. Without gmsh the tool answers with an install hint instead of failing.