Meshes (MDPA)

Generate, inspect and validate Kratos .mdpa meshes. All of this is pure Python — no Kratos needed — except deep validation. See the MDPA format guide for the file format itself.

To change a mesh (nodes, entities, parts, transforms, boundary conditions) see Mesh editing; for other shapes and file formats see Geometry & mesh formats.

Only mdpa_create_structured_mesh is limited to line/rectangle/box grids — mdpa_inspect/mdpa_validate/mdpa_get_nodes work on any valid .mdpa file, including externally-authored unstructured meshes with curved boundaries (e.g. the NACA airfoil example's real ~21k-node GiD mesh) that this server has no way to generate itself.

mdpa_create_structured_mesh

Generate a structured mesh with named boundary submodelparts and write it as .mdpa.

Parameter	Type	Description
path	string	output file (.mdpa appended if missing)
kind	string	line, rectangle or box
size	number[]	[L] / [W, H] / [Lx, Ly, Lz]
divisions	int[]	[n] / [nx, ny] / [nx, ny, nz]
element_name	string?	Kratos element type (defaults below)
condition_name	string?	boundary condition type (defaults below)
triangles	bool	split rectangle quads into triangles

Defaults: rectangle → SmallDisplacementElement2D4N + LineLoadCondition2D2N; box → SmallDisplacementElement3D8N + SurfaceLoadCondition3D4N; line → TrussLinearElement2D2N, no conditions.

Boundary submodelparts (each with nodes and conditions, ready for both Dirichlet fixes and surface loads):

• line: start, end — rectangle: left, right, bottom, top — box: xmin, xmax, ymin, ymax, zmin, zmax
• plus domain with every node and element (target materials here).

// mdpa_create_structured_mesh("/case/mesh.mdpa", "rectangle", [1.0, 0.2], [20, 4])
{
  "written_to": "/case/mesh.mdpa",
  "num_nodes": 105, "num_elements": 80, "num_conditions": 48,
  "sub_model_parts": { "domain": {"nodes": 105, "...": 0}, "left": {"nodes": 5, "conditions": 4}, "...": {} }
}

Thermal / fluid meshes

Use generic simplex elements — element_name: "Element2D3N", triangles: true, and condition_name: "ThermalFace2D2N" (thermal); the solvers replace them with the physical element at import time.

mesh_remesh

Needs Kratos with KratosMeshingApplication built with MMG (the pip wheel bundles it: kratos_install(applications=["MeshingApplication"])). Adaptively remesh a .mdpa with MMG and write a new one; the input is never modified. The adaptive remeshing tutorial walks through verified numbers.

Parameter	Type	Description
input_mdpa, output_mdpa	string	source mesh and the file to write (.mdpa appended; must differ). An existing output is only replaced with overwrite: true
strategy	string	levelset (default), hessian or uniform
region	object?	levelset: {"type": "sphere", "center": [x, y], "radius": r} or {"type": "box", "min": [...], "max": [...]}; optional "mode": inside (default — the whole region gets min_size) or surface (only a layer around its boundary)
distance_expression	string?	levelset alternative to region: a signed distance in x, y, z
field_variable, field_expression	string?	hessian: the Kratos scalar variable (e.g. TEMPERATURE) and the analytic field assigned to it on every node before remeshing
field_results, field_series, field_time, field_step	string?, string?, number?, int?	hessian alternative to field_expression: drive the metric from a solved field. field_results is a job's result-index.json (record picked by field_time, exact, or field_step; default the last) or one ASCII .vtk/.vtu file with field_variable as point data on exactly this mesh's nodes (matched by coordinates; Kratos binary VTK is not readable — use file_format: "ascii"). Give one of field_expression / field_results
min_size, max_size	number?	element size bounds. Defaults: max_size = mean input element size, min_size = max_size / 4. uniform takes one target size in min_size
transition_distance	number?	levelset: distance over which the size grows from min_size to max_size (default 3 * max_size)
interpolation_error	number?	hessian: target P1 interpolation error (default 0.04); smaller means finer
passes	int	repeat remeshing on the previous result, 1–6 (default 1). A metric computed on a mesh too coarse for the feature under-resolves it
preserve_sub_model_parts	string[]?	parts checked for lost conditions and moved bounding box (default: every part with conditions)
freeze_sub_model_parts	string[]?	parts whose nodes MMG may not touch (fix_contour_model_parts)
check_fields	object[]?	[{"variable": "TEMPERATURE", "expression": "x + 2*y"}]: assigned before remeshing, compared with the exact expression on the new nodes
applications	string[]?	applications to import before reading (default: StructuralMechanics, ConvectionDiffusion, FluidDynamics — element names must be registered)

Expressions use x, y, z, pi, e, + - * / % ** (constant exponent, |n| ≤ 16) and sqrt sin cos tan exp log tanh atan abs min max; anything else is rejected before anything runs. Elements must be linear simplices (triangles or tetrahedra, not mixed): quads, hexes, quadratic cells and mixed meshes are refused before anything runs, naming the offending element. The result reports mesh_kind — planar2d, volume3d or surface3d (triangles spanning z) — and checks the matching MMG variant (MmgProcess2D, 3D, 3DSurfaces); the 3D kinds come with a warnings entry because they are not yet verified against reference numbers. The element and condition types of the input are kept.

// mesh_remesh("/case/plate.mdpa", "/case/adapted.mdpa", strategy="hessian",
//             field_variable="TEMPERATURE", field_expression="tanh(30*(x-0.5))",
//             min_size=0.005, max_size=0.25, passes=3)   (excerpt)
{
  "written_to": "/case/adapted.mdpa",
  "passes": [{"pass": 1, "nodes": 162, "elements": 286},
             {"pass": 2, "nodes": 269, "elements": 496},
             {"pass": 3, "nodes": 385, "elements": 724}],
  "before": {"num_elements": 200, "element_size": {"min": 0.114, "mean": 0.114, "max": 0.114}},
  "after":  {"num_elements": 724, "element_size": {"min": 0.0208, "mean": 0.0503, "max": 0.158}},
  "change": {"nodes": 264, "elements": 524, "conditions": 4, "element_count_ratio": 3.62},
  "preserved": {"left": {"ok": true, "before": {"nodes": 11, "conditions": 10}, "after": {"nodes": 7, "conditions": 6}}},
  "transfer": {},
  "issues": []
}

preserved.<part>.ok is false (with problems) when a part loses its conditions or nodes, vanishes, or its node bounding box moves. MMG keeps straight boundaries and corners exact but is free to coarsen or refine the boundary discretization (above, left goes from 11 to 7 nodes where the field is smooth) — freeze_sub_model_parts forbids that. transfer.<variable> gives max_abs_error, mean_abs_error and value_range of the interpolated field. For a solved field (field_results) there is no exact expression, so it reports {"source": "field", "value_range_before", "value_range_after"} instead — MMG's interpolation can overshoot a sharp front, so compare the two ranges.

A field read from results (and any scalar Begin NodalData blocks of the input mesh) is transferred to the new nodes and written to the output .mdpa as Begin NodalData; fields_written lists the variable names, and the field is carried from one pass to the next. Analytic field_expression / check_fields values are not written. Vector NodalData blocks are read through the same parser as the mesh editor (kept verbatim, fixed flags preserved).

Errors ({"error": ...}): missing/identical/existing files, invalid input mesh, bad arguments, MMG not available (meshing_support explains what the build lacks).

mdpa_inspect

Report the contents of an .mdpa file: counts by entity type, bounding box, property ids and the full submodelpart tree with per-part entity counts.

Parameter	Type	Description
path	string	mesh file

mdpa_validate

Lint a mesh: dangling node/element/condition references, empty submodelparts, parse errors.

Parameter	Type	Description
path	string	mesh file
deep	bool	also round-trip through the real Kratos ModelPartIO (needs Kratos; catches unregistered element names, malformed blocks)

Returns: {valid, issues: [...], kratos_read?: {...}}.

mdpa_get_nodes

Return node ids and coordinates — useful for choosing probe points or checking where a boundary region actually is.

Parameter	Type	Description
path	string	mesh file
sub_model_part	string?	dotted path, e.g. right or outer.inner
node_ids	int[]?	explicit selection
limit	int	max nodes returned (default 100; truncated flags overflow)