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# Abaqus Input Subset
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## Purpose
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This document defines the Abaqus `.inp` subset supported by FESA Phase 1.
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FESA aims for strict, explicit compatibility with a small subset rather than partial silent interpretation of the full Abaqus language.
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## Source Basis
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- 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
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- Abaqus sets are a central reference mechanism for nodes and elements: https://abaqus-docs.mit.edu/2017/English/SIMACAEMODRefMap/simamod-c-inputsyntax.htm
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- 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
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- 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
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- 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
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## Phase 1 Supported Keywords
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| Keyword | Status | FESA Object | Notes |
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|---|---|---|---|
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| `*Node` | Supported | `Node` | 3D coordinates only |
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| `*Element` | Supported | `Element` | `TYPE=S4` maps to `MITC4` |
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| `*Nset` | Supported | `NodeSet` | Explicit list and `GENERATE` should be supported |
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| `*Elset` | Supported | `ElementSet` | Explicit list and `GENERATE` should be supported |
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| `*Material` | Supported | `Material` | `NAME` required |
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| `*Elastic` | Supported | `LinearElasticMaterial` | Isotropic `E, nu` only |
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| `*Shell Section` | Supported | `ShellProperty` | Homogeneous shell section only |
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| `*Boundary` | Supported | `FixBoundaryCondition` | Direct zero-valued constraints |
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| `*Cload` | Supported | `NodalLoad` | Concentrated forces/moments |
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| `*Step` | Supported | `StepDefinition` | Static linear Phase 1 step |
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| `*Static` | Accepted inside `*Step` | `LinearStaticAnalysis` | Optional for Phase 1 |
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| `*End Step` | Supported | Step delimiter | Required for explicit step closure |
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Unsupported keywords must produce a clear diagnostic unless explicitly listed as ignorable metadata.
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## General Parser Rules
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FESA parser rules:
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- Keyword names and parameter names are case-insensitive.
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- Keyword lines start with `*`.
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- Comment lines start with `**` and are ignored.
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- Data fields are comma-separated.
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- Empty trailing fields may be ignored.
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- Numeric data may use decimal or scientific notation.
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- `D` exponents should be accepted and normalized as `E` exponents.
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- Keyword continuation with a trailing comma should be supported for keyword lines.
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- Data continuation should be supported only where this document explicitly allows it.
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- Abbreviated Abaqus keywords are not supported in Phase 1. Require exact keyword names after case normalization.
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- Include files through `INPUT=` are not supported in Phase 1.
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- Part/Assembly/Instance syntax is not supported in Phase 1 unless added by ADR.
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## Labels and Names
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Rules:
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- Set and material labels are stored case-insensitively by default.
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- Preserve the original spelling for diagnostics and result metadata.
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- Labels must start with a letter unless quoted.
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- Quoted labels may be accepted, but Phase 1 should warn if quoting is required for disambiguation.
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- Labels beginning and ending with double underscores are reserved and should be rejected.
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## `*Node`
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Supported form:
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```text
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*Node
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node_id, x, y, z
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```
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Rules:
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- `node_id` is signed 64-bit integer.
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- Coordinates are `double`.
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- 2D node definitions are not supported for MITC4.
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- Duplicate node ids are an error.
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- Node ids need not be contiguous.
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## `*Element`
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Supported form:
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```text
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*Element, type=S4, elset=EALL
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element_id, n1, n2, n3, n4
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```
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Rules:
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- `TYPE=S4` maps directly to FESA `MITC4`.
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- `TYPE=S4R` is not supported in Phase 1. It is reserved for future support.
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- Element and node ids are signed 64-bit integers.
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- Four node connectivity entries are required.
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- Duplicate element ids are an error.
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- Missing nodes are an error.
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- If `ELSET` is given, the element is added to that element set.
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- Element node ordering follows Abaqus shell ordering and determines the positive normal by right-hand rule.
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## `*Nset` and `*Elset`
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Supported explicit form:
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```text
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*Nset, nset=FIXED
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1, 2, 3, 4
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```
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Supported generated form:
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```text
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*Elset, elset=EALL, generate
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1, 100, 1
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```
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Rules:
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- Explicit lists may span repeated data lines.
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- `GENERATE` means `start, end, increment`.
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- The increment must be positive.
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- Set references to other sets are not required in Phase 1.
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- `UNSORTED` is not required in Phase 1.
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- Duplicates should be deduplicated while preserving a deterministic order for diagnostics.
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- Missing referenced ids should be reported when the set is consumed by a property, load, or boundary condition.
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## `*Material` and `*Elastic`
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Supported form:
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```text
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*Material, name=STEEL
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*Elastic
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E, nu
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```
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Rules:
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- Only isotropic linear elasticity is supported in Phase 1.
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- Temperature dependence, field-variable dependence, orthotropic elasticity, plasticity, density, and damping are unsupported.
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- `E` must be positive.
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- `nu` must be in a physically meaningful isotropic range. For Phase 1, reject `nu <= -1.0` or `nu >= 0.5`.
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## `*Shell Section`
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Supported form:
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```text
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*Shell Section, elset=EALL, material=STEEL
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thickness
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```
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Rules:
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- `ELSET` and `MATERIAL` are required.
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- Homogeneous single-layer shell sections only.
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- Thickness is `double` and must be positive.
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- Offsets, composite layups, section integration controls, orientations, temperature-dependent sections, and transverse shear stiffness overrides are unsupported in Phase 1.
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- Thermal-stress coupling is a future feature and must not be inferred from Phase 1 section data.
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## `*Boundary`
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Supported direct form:
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```text
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*Boundary
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node_or_nset, first_dof, last_dof, magnitude
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```
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Rules:
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- `node_or_nset` may be a node id or node set label.
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- DOFs are `1..6`.
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- If `last_dof` is omitted, constrain only `first_dof`.
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- Phase 1 supports zero-valued constraints. Omitted magnitude means zero.
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- Nonzero prescribed displacement/rotation is not a Phase 1 requirement.
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- Type-format boundary labels such as `PINNED`, `XSYMM`, or `ENCASTRE` are not supported unless later documented.
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- Constrained DOFs are eliminated by `DofManager`.
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## `*Cload`
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Supported form:
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```text
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*Cload
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node_or_nset, dof, magnitude
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```
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Rules:
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- `node_or_nset` may be a node id or node set label.
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- DOFs are `1..6`.
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- Translational DOFs define concentrated forces.
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- Rotational DOFs define concentrated moments.
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- `FOLLOWER`, `AMPLITUDE`, `OP=NEW`, file-based loads, buoyancy/drag/inertia loads, and cyclic symmetry loads are unsupported in Phase 1.
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## `*Step`, `*Static`, and `*End Step`
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Supported form:
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```text
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*Step, name=Step-1
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*Static
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*Cload
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...
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*Boundary
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...
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*End Step
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```
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Rules:
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- Phase 1 supports linear static steps.
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- `NLGEOM` is ignored only if explicitly false or absent. `NLGEOM=YES` must be rejected until nonlinear analysis is implemented.
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- Multiple steps may be parsed into `Domain`, but Phase 1 execution may initially support one active static step if documented in implementation steps.
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- Step activation should feed `AnalysisModel`.
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## Diagnostics
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Required parser diagnostics:
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- Unknown keyword.
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- Unsupported keyword parameter.
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- Missing required parameter.
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- Duplicate node, element, material, property, or set definition.
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- Missing node in element connectivity.
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- Missing set used by shell section, boundary, or load.
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- Unsupported element type such as `S4R`.
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- Unsupported material or shell section mode.
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- Invalid DOF number.
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- Invalid generated set range.
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Diagnostic messages should include file path, line number, keyword, and offending token.
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## Explicit Non-Goals
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- Abaqus `Part`, `Assembly`, `Instance`, and instance-qualified labels.
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- `*Include`.
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- `S4R`, `S4R5`, `S8R`, triangular shells, solid elements, beam elements.
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- Pressure loads.
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- RBE2/RBE3.
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- Nonzero prescribed displacements.
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- Amplitudes.
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- Local coordinate transforms.
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- Composite shell sections.
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- Thermal-stress input.
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- Mesh quality diagnostics.
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