FESADev/docs/ABAQUS_INPUT_SUBSET.md

Abaqus Input Subset

Purpose

This document defines the Abaqus .inp subset supported by FESA Phase 1.

FESA aims for strict, explicit compatibility with a small subset rather than partial silent interpretation of the full Abaqus language.

Source Basis

• Abaqus input files use keyword lines, data lines, and comment lines; keyword and parameter names are case-insensitive, comma-separated, and may use continuation lines: https://abaqus-docs.mit.edu/2017/English/SIMACAEMODRefMap/simamod-c-inputsyntax.htm
• Abaqus sets are a central reference mechanism for nodes and elements: https://abaqus-docs.mit.edu/2017/English/SIMACAEMODRefMap/simamod-c-inputsyntax.htm
• Abaqus shell library documents S4 as a 4-node general-purpose shell and S4R as a reduced-integration shell with hourglass control: https://abaqus-docs.mit.edu/2017/English/SIMACAEELMRefMap/simaelm-r-shellgeneral.htm
• Abaqus *BOUNDARY direct data lines use node or node set, first DOF, optional last DOF, and optional magnitude: https://abaqus-docs.mit.edu/2017/English/SIMACAEKEYRefMap/simakey-r-boundary.htm
• Abaqus *CLOAD data lines use node or node set, DOF, and reference load magnitude: https://abaqus-docs.mit.edu/2017/English/SIMACAEKEYRefMap/simakey-r-cload.htm

Phase 1 Supported Keywords

Keyword	Status	FESA Object	Notes
*Node	Supported	Node	3D coordinates only
*Element	Supported	Element	TYPE=S4 maps to MITC4
*Nset	Supported	NodeSet	Explicit list and GENERATE should be supported
*Elset	Supported	ElementSet	Explicit list and GENERATE should be supported
*Material	Supported	Material	NAME required
*Elastic	Supported	LinearElasticMaterial	Isotropic E, nu only
*Shell Section	Supported	ShellProperty	Homogeneous shell section only
*Boundary	Supported	FixBoundaryCondition	Direct zero-valued constraints
*Cload	Supported	NodalLoad	Concentrated forces/moments
*Step	Supported	StepDefinition	Static linear Phase 1 step
*Static	Accepted inside *Step	LinearStaticAnalysis	Optional for Phase 1
*End Step	Supported	Step delimiter	Required for explicit step closure

Unsupported keywords must produce a clear diagnostic unless explicitly listed as ignorable metadata.

General Parser Rules

FESA parser rules:

• Keyword names and parameter names are case-insensitive.
• Keyword lines start with *.
• Comment lines start with ** and are ignored.
• Data fields are comma-separated.
• Empty trailing fields may be ignored.
• Numeric data may use decimal or scientific notation.
• D exponents should be accepted and normalized as E exponents.
• Keyword continuation with a trailing comma should be supported for keyword lines.
• Data continuation should be supported only where this document explicitly allows it.
• Abbreviated Abaqus keywords are not supported in Phase 1. Require exact keyword names after case normalization.
• Include files through INPUT= are not supported in Phase 1.
• Part/Assembly/Instance syntax is not supported in Phase 1 unless added by ADR.

Labels and Names

Rules:

• Set and material labels are stored case-insensitively by default.
• Preserve the original spelling for diagnostics and result metadata.
• Labels must start with a letter unless quoted.
• Quoted labels may be accepted, but Phase 1 should warn if quoting is required for disambiguation.
• Labels beginning and ending with double underscores are reserved and should be rejected.

*Node

Supported form:

*Node
node_id, x, y, z

Rules:

• node_id is signed 64-bit integer.
• Coordinates are double.
• 2D node definitions are not supported for MITC4.
• Duplicate node ids are an error.
• Node ids need not be contiguous.

*Element

Supported form:

*Element, type=S4, elset=EALL
element_id, n1, n2, n3, n4

Rules:

• TYPE=S4 maps directly to FESA MITC4.
• TYPE=S4R is not supported in Phase 1. It is reserved for future support.
• Element and node ids are signed 64-bit integers.
• Four node connectivity entries are required.
• Duplicate element ids are an error.
• Missing nodes are an error.
• If ELSET is given, the element is added to that element set.
• Element node ordering follows Abaqus shell ordering and determines the positive normal by right-hand rule.

*Nset and *Elset

Supported explicit form:

*Nset, nset=FIXED
1, 2, 3, 4

Supported generated form:

*Elset, elset=EALL, generate
1, 100, 1

Rules:

• Explicit lists may span repeated data lines.
• GENERATE means start, end, increment.
• The increment must be positive.
• Set references to other sets are not required in Phase 1.
• UNSORTED is not required in Phase 1.
• Duplicates should be deduplicated while preserving a deterministic order for diagnostics.
• Missing referenced ids should be reported when the set is consumed by a property, load, or boundary condition.

*Material and *Elastic

Supported form:

*Material, name=STEEL
*Elastic
E, nu

Rules:

• Only isotropic linear elasticity is supported in Phase 1.
• Temperature dependence, field-variable dependence, orthotropic elasticity, plasticity, density, and damping are unsupported.
• E must be positive.
• nu must be in a physically meaningful isotropic range. For Phase 1, reject nu <= -1.0 or nu >= 0.5.

*Shell Section

Supported form:

*Shell Section, elset=EALL, material=STEEL
thickness

Rules:

• ELSET and MATERIAL are required.
• Homogeneous single-layer shell sections only.
• Thickness is double and must be positive.
• Offsets, composite layups, section integration controls, orientations, temperature-dependent sections, and transverse shear stiffness overrides are unsupported in Phase 1.
• Thermal-stress coupling is a future feature and must not be inferred from Phase 1 section data.

*Boundary

Supported direct form:

*Boundary
node_or_nset, first_dof, last_dof, magnitude

Rules:

• node_or_nset may be a node id or node set label.
• DOFs are 1..6.
• If last_dof is omitted, constrain only first_dof.
• Phase 1 supports zero-valued constraints. Omitted magnitude means zero.
• Nonzero prescribed displacement/rotation is not a Phase 1 requirement.
• Type-format boundary labels such as PINNED, XSYMM, or ENCASTRE are not supported unless later documented.
• Constrained DOFs are eliminated by DofManager.

*Cload

Supported form:

*Cload
node_or_nset, dof, magnitude

Rules:

• node_or_nset may be a node id or node set label.
• DOFs are 1..6.
• Translational DOFs define concentrated forces.
• Rotational DOFs define concentrated moments.
• FOLLOWER, AMPLITUDE, OP=NEW, file-based loads, buoyancy/drag/inertia loads, and cyclic symmetry loads are unsupported in Phase 1.

*Step, *Static, and *End Step

Supported form:

*Step, name=Step-1
*Static
*Cload
...
*Boundary
...
*End Step

Rules:

• Phase 1 supports linear static steps.
• NLGEOM is ignored only if explicitly false or absent. NLGEOM=YES must be rejected until nonlinear analysis is implemented.
• Multiple steps may be parsed into Domain, but Phase 1 execution may initially support one active static step if documented in implementation steps.
• Step activation should feed AnalysisModel.

Diagnostics

Required parser diagnostics:

• Unknown keyword.
• Unsupported keyword parameter.
• Missing required parameter.
• Duplicate node, element, material, property, or set definition.
• Missing node in element connectivity.
• Missing set used by shell section, boundary, or load.
• Unsupported element type such as S4R.
• Unsupported material or shell section mode.
• Invalid DOF number.
• Invalid generated set range.

Diagnostic messages should include file path, line number, keyword, and offending token.

Explicit Non-Goals

• Abaqus Part, Assembly, Instance, and instance-qualified labels.
• *Include.
• S4R, S4R5, S8R, triangular shells, solid elements, beam elements.
• Pressure loads.
• RBE2/RBE3.
• Nonzero prescribed displacements.
• Amplitudes.
• Local coordinate transforms.
• Composite shell sections.
• Thermal-stress input.
• Mesh quality diagnostics.