Frequently Asked Question

Evidence and uncertainty

Verification asks whether the equations and computational implementation are solved correctly. Validation asks whether the model represents physical reality for the intended use. Uncertainty should distinguish numerical error, input uncertainty, model-form uncertainty, measurement uncertainty, and operating variation. A single residual or a single comparison does not establish credibility.

The root-sum-square form is appropriate only when contributors are on compatible bases and reasonably independent. Otherwise, correlation or conservative bounds are required.

Worked example

If numerical, input, and measurement uncertainties are 2%, 3%, and 4%, the independent estimate is √(2²+3²+4²) = 5.39%. This is an uncertainty estimate, not validation by itself. The comparison must also use the same quantity, regime, boundary condition, and reference plane.

Check: report discrepancies, data quality, confidence basis, and the decision consequence of the remaining uncertainty.

Engineering check

For Heat-Transfer Verification Example, report the governing output together with the reference condition, mesh or model assumptions, boundary data, convergence evidence, and sensitivity to the dominant input. Check a conservation balance or limiting case before comparing the result with a requirement. If the output changes materially under a reasonable refinement or input variation, the conclusion should be treated as conditional rather than final.

Engineering note

For Heat-Transfer Verification Example, state the intended use, input range, dominant mechanism, units, boundary conditions, acceptance criterion, and evidence owner. Use an independent balance, limiting case, repeat measurement, or sensitivity check to challenge the result. Document the configuration and uncertainty so another engineer can reproduce the reasoning and determine whether the result remains valid after a design, material, boundary, or process change.