6. Validation Domain

The validation domain is the high-dimensional region spanned by all validation points, the specific input conditions at which simulation outputs have been compared with experiments to quantify accuracy.

Within that envelope analysts do not simply interpolate test data; they recompute the model at any interior point but assume the local error resembles that at neighbouring validation points, recognising that model-form accuracy varies as underlying assumptions (e.g., laminar vs. turbulent flow, small-strain vs. large-strain mechanics) become more or less valid across the space.

To make that variability explicit, they often build response-surface or surrogate maps of model-form uncertainty that blend numerical-solution error, input variability and measurement noise into a spatial “error surface” accompanying every prediction.

Experimental uncertainty is integral to this map: large test scatter can inflate total validation uncertainty and may mask or mimic simulation deficiencies at certain points.

The ASME VVUQ standards emphasise that once calculations move beyond the mapped domain they become extrapolations, and extra uncertainty (or fresh experiments) must be added before the results are trusted .

Clearly documenting the bounds of the validation domain and the associated uncertainty landscape therefore gives decision-makers an evidence-based way to set safety margins, judge risk tolerance, or commission additional testing before committing to high-stakes designs.