Begin with the decision
Model credibility is contextual: a model may be adequate for comparing concepts yet inadequate for certifying a limit. The engineering question, quantity of interest, operating envelope and consequence of error determine the evidence required.
- Define the decision and accountable owner.
- State quantities of interest and acceptance criteria.
- Record intended use and prohibited use.
- Choose fidelity that is proportionate to decision risk.
Separate verification from validation
Verification asks whether the equations and numerical implementation are being solved correctly. Validation asks whether the selected model represents the relevant physical behaviour with sufficient accuracy for its intended use.
- Check code, setup and numerical implementation.
- Demonstrate iterative and discretization convergence.
- Compare with experiments, trusted references or analytical behaviour.
- Treat agreement at one point as insufficient for a broad validity claim.
Quantify what can change the answer
Mesh, time step, material data, turbulence assumptions, contacts, boundary conditions and measurement uncertainty can all change the quantity used for a decision. Sensitivity and uncertainty work should focus on influential inputs.
- Identify epistemic and aleatory uncertainty.
- Rank influential assumptions and parameters.
- Report numerical error separately from model-form uncertainty.
- Retain unresolved uncertainty in the final margin or recommendation.
Deliver a decision record
A useful report connects inputs, assumptions, checks, results and limitations with an explicit engineering action. Attractive visualization supports interpretation but does not replace traceability.
- Version geometry, mesh, solver and material definitions.
- Show convergence and validation evidence near the result.
- Identify extrapolation beyond tested conditions.
- State residual risk, next test and approval authority.
Apply the method to the decision—not as a checklist.
The appropriate evidence depends on intended use, technical risk, operating environment, contractual obligations and the authority responsible for acceptance. This guide is educational and does not replace project-specific analysis, applicable standards or independent review.