3. Uncertainties

It is generally not expected that the numerical simulation of a mechanical problem involving a real structure will produce "exact" results. This is partly because the problem is far too complex for that, and partly because the formulation of the real problem is often only partial: it is impossible to know precisely the properties of the materials at every point, the boundary conditions, the imperfections, and so on. Uncertainties are therefore inherent in the modeling process, and even more so in the transition to a numerical model (or approximate solution). A numerical result on its own provides poor information for the client. Confidence in a model's output must be weighed against the level of uncertainty necessarily associated with it. ASN defines uncertainty as the range of variation in the result of a measurement or calculation, which characterizes the possible values and which is...