Ansys MAPDL coded database (.cdb / .inp)

The coded database is the text archive Ansys MAPDL writes with CDWRITE and reads with CDREAD, and what Ansys Workbench, HyperMesh and other preprocessors export for MAPDL. meshio++ reads its mesh (nodes, elements, element types and components) and writes one MAPDL reads back. It is distinct from the Fluent .msh format, which meshio++ calls ansys. Results live in MAPDL's binary .rst files.

Format name	ansysInp
Extensions	.cdb, .inp
Read / Write	✓ / ✓
Extra dependencies	—

Reading & writing

The native reader views mapped/buffered source lines and command/fixed fields, retaining CRLF handling and owned names/results. Numeric parsing is bounded; integer fields still accept floating spellings before checked conversion. The installed owning card API, writer bytes and parsing behavior are unchanged; see the deck-line comparison and shared-card evidence.

import meshioplusplus

mesh = meshioplusplus.read("model.cdb")
mesh.regions                           # CMBLOCK components
mesh.cell_data["ansys:element"]        # element routine per cell (185, 186 ...)
meshioplusplus.write("out.cdb", mesh)

meshioplusplus.ansysInp.read("model.cdb", lenient=True)  # skip unmappable elements

meshioplusplus convert model.cdb model.vtu

.inp is shared with Abaqus, which is imported first, so meshioplusplus.read("x.inp") reads Abaqus. Pass file_format="ansysInp" to read a MAPDL .inp.

File structure

A .cdb file is a list of MAPDL commands. Four of them open blocks of fixed-width rows, and a Fortran format line after the block header gives the column widths:

ET,1,186                                  -- element type slot 1 is SOLID186
KEYOPT,1,2,0
NBLOCK,6,SOLID,     321,     321
(3i9,6e21.13e3)                           -- 3 integers of 9 columns, then reals of 21
        1        0        0 1.0000000000000E+000 0.0000000000000E+000 ...
N,R5.3,LOC,       -1,
EBLOCK,19,SOLID,      40,      40
(19i10)
         1         1         1         1         0         0         0         0        20         0         1        12 ...
        ...                               -- nodes past the eighth continue on the next line
        -1
CMBLOCK,FIXED,NODE,       2               -- a node component
(8i10)
         1       -40                      -- nodes 1 to 40

• Format lines are parsed as Fortran formats (detail::parse_fortran_format), so each field is cut at its own width: (3i9,6e21.13e3) from MAPDL, (1i7,2i9,6e21.13) from Workbench, (3i8,6e16.9) from HyperMesh, repeat counts and groups included. The same parser serves the LS-DYNA reader.
• ET (by number, ET,1,186, or by name, ET,1,SOLID186), ETBLOCK and KEYOPT (and its abbreviations, such as KEYOP) give each element type slot its routine number and key options.
• NBLOCK rows hold the node number and coordinates. Nodal rotation angles, when a row has them, are dropped with a warning.
• EBLOCK rows (the SOLID layout MAPDL writes) hold the material, type, real constant and section numbers, the node count, the element number and the nodes. A non-solid EBLOCK (which Workbench can write for contact elements) is skipped with a warning.
• CMBLOCK lists a component's node or element numbers, a negative value closing a run opened by the value before it. A block whose header count is too large ends at the next command.
• A ! comment after a command is ignored. Other commands (MP, R, SECTYPE, D, F ...) are skipped.

Cell types

An element becomes a cell by its routine's category, as in the open readers pymapdl-reader and mapdl-archive:

Category	Routines (examples)	meshio++
point	MASS21, 71, 175	vertex
line	LINK180, BEAM189, PIPE289, SURF151/153 ...	line, or line3 when the third node is set
linear line	BEAM188, 214, 216, 217 (the extra nodes orient the beam)	line
shell or plane	SHELL181/281, PLANE182/183, SURF152/154, TARGE170, CONTA174 ...	quad/quad8; triangle/triangle6 when K = L
brick	SOLID45, 185, 186, SOLSH190, 272, 273 ...	hexahedron/hexahedron20, or a degenerate form
tetrahedron	SOLID92, 187, 285 ...	tetra/tetra10

MESH200's shape comes from its KEYOPT(1). Degenerate bricks are resolved by their repeated nodes: a hexahedron when O ≠ P, a wedge when K = L and O = P, a pyramid when M = N = O = P, and a tetrahedron when also K = L. A shell with K = L is a triangle. A shell of five nodes (SURF152's extra orientation node) is linear, and so is an 8-node shell whose last two midside nodes are equal (a contact face written without midsides).

Missing midside nodes are written as node 0, or left off the end of a row (SOLID92 rows sometimes carry nine nodes). meshio++ creates each one at its edge midpoint, shared between the elements on that edge, with one warning. An element whose type has no category, or whose corner node is 0 (a TARGE170 pilot node), is a ReadError naming it; read with lenient=True to skip such elements with a warning.

Data mapping

.cdb	meshio++
element routine, type slot, MAT, REAL, SECNUM	cell_data["ansys:element"], "ansys:type", "ansys:mat", "ansys:real", "ansys:secnum"
CMBLOCK NODE / ELEM component	point / cell region (so also point_sets / cell_sets)

Cells are grouped into one block per meshio++ type, in the order the types first appear.

Writing

The writer emits /PREP7, one ET per element type slot, an NBLOCK in MAPDL's (3i9,6e21.13e3) layout, a SOLID EBLOCK in (19i10), one CMBLOCK per point or cell region (runs of consecutive numbers packed as first, -last) and FINISH. Nodes and elements are numbered from 1 in mesh order. Each type is written in the layout MAPDL expects:

meshio++	written as
hexahedron, wedge, pyramid	SOLID185, the wedge and pyramid as degenerate bricks
hexahedron20, wedge15, pyramid13	SOLID186, likewise
tetra / tetra10	SOLID285 / SOLID187
quad, triangle / quad8, triangle6	SHELL181 / SHELL281, the triangle as a degenerate quad
line / line3 / vertex	BEAM188 / BEAM189 / MASS21

ansys:element and ansys:type are kept when the cell's type fits that routine's layout, so a MAPDL model keeps its element types through a round trip. Otherwise, with a warning, the default above is written. ansys:mat, ansys:real and ansys:secnum are written back, defaulting to 1. Side regions have no component equivalent and are dropped with a warning and a provenance note. Polygons, polyhedra and other types without a MAPDL element are a WriteError. The provenance block is written as ! comments. Both engines write the same bytes.

Notes

• Validation. The test fixtures in tests/python/meshes/ansys/ are decks from mapdl-archive (MIT) that MAPDL, Workbench and HyperMesh wrote. Both engines read them into the cells mapdl-archive builds, compared as sets of node coordinates, and the components mapdl-archive finds. The one difference: mapdl-archive puts three missing triangle midside nodes at the origin, where meshio++ puts them at their edge midpoints. MAPDL itself was not available, so a written deck is checked by reading it back, not by CDREAD.
• AnsysInfo, the C++ side channel that carried components before v16.3.0, is still filled on read and still written, for code that uses it. Regions are the primary route.