Courant

§01Identity

Courant is software that assesses whether a simulation result can be trusted, and produces the evidence for that assessment in the form a regulator or reviewer expects. It reads what the solver wrote, checks convergence, discretization error, setup and applicability, and agreement with reference data, assigns a grade by a fixed rule, and writes an evidence pack in which every finding cites its inputs, method, threshold and value. It lists everything it could not check.

Category

Simulation credibility assessment

Runs

On the engineer’s machine. Reads files only.

Never

Runs a solver, edits a case, or sends the case anywhere.

Decides verdicts

Deterministic code. A language model may draft prose and never writes a number.

First solver

OpenFOAM, including decomposed parallel runs

Release

30 September 2026

§02Products

Stop is Attest's convergence check, sold on its own. Courant Stop reports, in order:

1. The answer at the stopping point, and at the end
2. How much the answer changed after the stopping point
3. Iterations past convergence
4. Wall-clock past convergence
5. Allocation unit hours past convergence

§03The four checks

Watch, assess, attest. Every check returns PASS, WARN, FAIL or NOT_ASSESSABLE, and reports the inputs it used and the inputs it lacked.

§04Setup and applicability rules

§05The grade

A fixed function of the four statuses, computed by code, with the rule that produced it printed beside the letter. Clauses are evaluated in the order D, A, C, B; the first that matches sets the letter.

• Missing evidence never raises a grade.
• The letters are ours, not any standard's.

§06The evidence pack

The document has eight sections, in the order the FDA guidance and ASME V&V 40 describe a credibility assessment:

1. Summary. The grade, the rule that produced it, the reported value.
2. Context of use. What the result decides, in your words.
3. Model. Solver, turbulence, schemes, mesh, boundaries.
4. Verification. Convergence and discretization error.
5. Validation. Comparison with the reference.
6. Setup and applicability. All twelve rules, with status.
7. Not assessed. Every check that could not run, and why.
8. Appendix. Every threshold, every value, the manifest.

Each finding carries four fields: inputs, method, threshold, value. The pack is reproducible byte for byte from its manifest.

§07What Courant does not do

• Does not fix simulations.
• Does not run your solver.
• Does not touch your mesh.
• Does not replace a validation experiment.
• Does not guess without the input.

What it checks:

• Where the run converged
• A steady solver on unsteady flow
• Error from the mesh
• Twelve setup and applicability rules
• Agreement with reference data

§08Security and data

• Your case never leaves your machine.
• It reads files. It never runs your solver or edits your case. You decide who sees the report.
• We don't touch the solver. We grade its output.
• Telemetry is opt-in and carries only the grade letter, module statuses and tool version.

§09The engine, measured

OpenFOAM's own tutorials, faulted and solved. Never fixtures we wrote. Do not quote a percentage without its denominator.

§10Not yet proven

12 of the 25 failure modes in the taxonomy have not been named on real solver output.

• BC.REVERSED_OUTFLOW Reversed outlet flow (a route exists, never exercised)
• BC.TURB_INLET Inconsistent turbulence inlet values (a route exists, never exercised)
• BC.WALL_FUNCTION Wrong wall functions for the model (a route exists, never exercised)
• CONV.OSCILLATION Oscillating quantities of interest (a route exists, never exercised)
• ENV.DECOMP_MISMATCH Decomposition mismatch (a route exists, never exercised)
• MESH.LEAKY_SNAPPY Leaky snappyHexMesh (a route exists, never exercised)
• MESH.NEGATIVE_VOLUME Negative cell volumes (a route exists, never exercised)
• MESH.YPLUS_RESOLUTION Poor boundary-layer resolution (a route exists, never exercised)
• PHYS.CHT_THERMO Conjugate heat transfer property inconsistency (a route exists, never exercised)
• PHYS.TURB_REGIME Turbulence model unsuited to regime (no route; excluded from the claim)
• CONV.MASS_IMBALANCE Mass or energy imbalance (no route; excluded from the claim)
• CONV.MESH_DEPENDENCE Not mesh-independent (no route; excluded from the claim)

§11Industries

Courant is not affiliated with, endorsed by or approved by any regulator or standards body.

§12Pricing

Planned, not available at release: Ansys Fluent adapter; Simcenter STAR-CCM+ adapter; Surrogate predictions check.

§13Questions

Is Courant a solver?

No. It reads what your solver wrote. It never runs the solver, edits the case or builds a mesh.

Does it fix simulations?

No. It grades the result and states the evidence. The engineer decides what to change.

What does it read?

The solver log, function-object output, the mesh-quality report, and the model, scheme and boundary settings. Never the mesh itself.

What leaves my machine?

Nothing from the case. The report is written locally, and you decide who sees it.

Which solvers?

OpenFOAM, including decomposed parallel runs. Ansys Fluent and Simcenter STAR-CCM+ adapters are planned.

What does the grade mean?

A fixed rule over the four checks, printed beside the letter. The letters are ours, not any standard's.

Does a language model decide anything?

No. Code decides every verdict, grade and number. A model may draft prose; a draft that states a number the data does not is rejected.

§14Documents cited

1. U.S. Food and Drug Administration. Assessing the Credibility of Computational Modeling and Simulation in Medical Device Submissions, 2023. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/assessing-credibility-computational-modeling-and-simulation-medical-device-submissions
2. ASME. Assessing Credibility of Computational Modeling through Verification and Validation: Application to Medical Devices, 2018.
3. ASME. Standard for Verification and Validation in Computational Fluid Dynamics and Heat Transfer.
4. NASA. Standard for Models and Simulations, 2024. https://standards.nasa.gov/standard/NASA/NASA-STD-7009
5. U.S. Nuclear Regulatory Commission. Regulatory Guide 1.203, Transient and Accident Analysis Methods, 2005. https://www.nrc.gov/docs/ML0535/ML053500170.pdf
6. FIA. 2026 Formula 1 Regulations, Section F: Operational, Aerodynamic Testing Restrictions, 2026. https://www.fia.com/system/files/documents/fia_2026_f1_regulations_-_section_f_operational_-_iss_06_-_2026-02-27.pdf
7. MSER initial-transient truncation, 1997.
8. Stationarity diagnostic, 1992.

Courant is not affiliated with, endorsed by or approved by any regulator or standards body.

§15Glossary

Credibility

The trust, established through evidence, in a model's predictions for a specific context of use.

Credibility evidence

The collected results of verification, validation and applicability activities.

Context of use

The specific role of the model in the decision it informs.

Verification

Was the model solved correctly? Iterative convergence and discretization error.

Validation

Was the correct model solved? Comparison with reference data.

Applicability

Whether the evidence covers the context of use.

Comparator

The reference data the result is compared against.

Adequacy

Whether the evidence is enough for the context of use.

Grid convergence index

An error band on a result from a sequence of refined meshes, per ASME V&V 20.

Answer-unchanged delta

How much the reported quantity changed between the stopping point and the end of the run.

Evidence pack

The report as data, the report as a document, and the manifest of every input read.

§16Contact

Send us a case: hello@courant.dev. Read by an engineer, not a queue.

Facts commonly got wrong: Courant is not a solver. It does not fix simulations. It has no customers it names. The grade letters are Courant’s own and are not a standard’s credibility levels. “Certified” on this site means exercised against real solver output in a container, not certified by any body.