Linear Static MITC4 Shell Reference Cases

Metadata

feature_id: linear-static-mitc4-shell
source_requirement: docs/linear-static-mitc4-shell/requirements.md
source_io_definition: docs/linear-static-mitc4-shell/io.md
status: approved-for-implementation-planning
owner_agent: reference-model-agent
date: 2026-08-13
comparison_revalidated_on: 2026-08-18
artifact_policy: read-only-existing-files
authoritative_fesa_output: results.h5

1. Purpose and boundary

This document is the lightweight inventory and comparison contract for the sole approved full-integration S4 reference case. Abaqus supplies an external displacement reference; it does not define FESA element equations, integration, stabilization, recovery, or implementation structure. FESA and Abaqus are not required to operate identically.

Reference readiness requires only:

the declared Abaqus .inp file and displacement CSV for each case;
the FESA results.h5 generated from that case's .inp;
deterministic source-instance/node/component matching;
the approved tolerance and decision rule in Section 5.

README, metadata.json, canonical naming, legacy-alias approval, Abaqus version or generation provenance, duplicated unit/coordinate/model/step/frame/material/section descriptions, and a CSV schema-version record are not required. If metadata.json later exists, it is optional read-only context and does not override the declared input, CSV, row mapping, or tolerance.

2. Read-only case inventory

case_id	source label	role	exact path	SHA-256	observed content
`shell-s4`	`S4`	input	`reference/shell/shell.inp`	`4005851E1AB22FD3A16AC17A8D5DA3E051233F69F37419079F3553AD134ECFCF`	`TYPE=S4`; one linear-static case
`shell-s4`	`S4`	required reference	`reference/shell/shell displacements.csv`	`C81D94E0B4A849F87AA0F79C83A79B94D5661AC79E44ED826919AB432C87746B`	49 data rows; U and UR components

The existing reaction and stress CSVs in reference/shell/ are optional inspection evidence only. Existing files under reference/shellR/ are also optional inspection evidence and are not consumed by acceptance comparison. They are not pass/fail inputs. No agent may rename, rewrite, normalize, repair, regenerate, or restore any reference artifact unless a later phase explicitly authorizes that operation.

3. Required CSV mapping

Trim surrounding whitespace from header names, then apply this exact projection:

Abaqus CSV column	normalized identity/value	FESA HDF5 source
`Part Instance Name`	`instance_name`	`/model/nodes.instance_name`
`Node Label`	`source_node_label`	`/model/nodes.source_label`
`U-U1`	`U1`	`/steps/Step-1/frames/0/nodal/displacement[:,0]` (`UX`)
`U-U2`	`U2`	`/steps/Step-1/frames/0/nodal/displacement[:,1]` (`UY`)
`U-U3`	`U3`	`/steps/Step-1/frames/0/nodal/displacement[:,2]` (`UZ`)
`UR-UR1`	`UR1`	`/steps/Step-1/frames/0/nodal/displacement[:,3]` (`URX`)
`UR-UR2`	`UR2`	`/steps/Step-1/frames/0/nodal/displacement[:,4]` (`URY`)
`UR-UR3`	`UR3`	`/steps/Step-1/frames/0/nodal/displacement[:,5]` (`URZ`)

The normalized row key is (case_id,instance_name,source_node_label,component). Stable comparison order is case shell-s4; then FESA instance declaration order; stable source-node order; and component order [U1,U2,U3,UR1,UR2,UR3].

4. Precheck

Before numerical comparison, each case shall satisfy all of the following:

The declared input, displacement CSV, and FESA results.h5 exist.
The six required displacement headers map exactly as Section 3 specifies.
Each required CSV and HDF5 value is finite.
Each normalized row key is unique.
CSV and HDF5 normalized row-key sets are exactly equal.

Missing, extra, duplicate, nonfinite, header-mismatched, or source-identity-mismatched required rows fail reference verification before tolerance evaluation. Values are not zero-clamped and mismatched rows are not omitted, averaged, or synthesized.

5. Tolerance and decision rule

Matched U1/U2/U3 rows form one blocking translation family and matched UR1/UR2/UR3 rows form one warning-only rotation family. For each family:

S = max(abs(abaqus_value_i))
absolute_error_i = abs(fesa_value_i-abaqus_value_i)
near_zero_band = 0.01*S

near-zero row: absolute_error_i <= near_zero_band
other row: absolute_error_i/abs(abaqus_value_i) <= 0.05
relative_rms = sqrt(mean(absolute_error_i^2))/S <= 0.01

The scale uses read-only Abaqus values only. No independent absolute-error gate, zero clamp or row omission is permitted. A zero-scale family passes only when all FESA values are exactly zero; otherwise it reports zero-reference-scale-nonzero-error without NaN/Inf. The U family controls the verdict and the UR family uses the same numeric rule for deterministic warning-only evidence.

Every matched U1/U2/U3 row and the translation family RMS must satisfy the common row/RMS rule. Any U row or family-RMS exceedance fails the feature reference comparison.
UR1/UR2/UR3 uses the same family-scale row/RMS rule. Every row or family-RMS exceedance produces deterministic warning evidence but does not change pass/fail.

The comparison report records every U/UR row decision, family scale, near-zero branch, maximum absolute error, row relative error, scale-relative RMS, worst source row/component, and every UR warning.

6. Coverage and handoff

The S4 case is the complete required reference inventory for this feature:

shell-s4 checks the approved full-integration S4 -> FESA-MITC4 input path against Abaqus U.
S4R -> FESA-MITC4 support is verified by parser, common-kernel, deterministic-assembly and HDF5 source-metadata tests without consuming an Abaqus S4R reference artifact.

They do not prove Abaqus formulation equivalence or general MITC4 accuracy outside the modeled cases. Additional flat/thin/thick/distorted/curved models, mesh studies, drilling sweeps, drilling-energy criteria, NR-O03, and NR-O04 are not required before Implementation Planning or feature completion.

Numerical Review may use this inventory as downstream comparison input, but missing bundle-administration data shall not change a mathematically consistent formulation verdict. The revised Numerical Review passes the formulation and authorizes Implementation Planning; this does not authorize implementation or Harness execution.

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