Experimental data for the validation of Computational Fluid Dynamics results need an evaluation of the accuracy. Uncertainty assessment applied to the measure of the wave field generated by a combatant model is performed in this experimental work. The application of uncertainty assessment to a parameter changing in space (or in time) with zero averaged value gives some interesting point of discussion, especially about the bias and precision limit characterization and the error normalization. Moreover, in this particular case, it can give indications about some relevant characteristics of the wave field. For example the relatively high precision limit (bad accuracy), in the region close to the model, highlights random fluctuations associated to the free surface turbulence or wave breaking. Finally the individuation of the zones, where the bias and precision limit are the lowest, allows realizing with better accuracy the determination of the wave making resistance by longitudinal cut method.
The total ship resistance is mostly dued to the viscous resistance component and to the wavemaking resistance component. The first one is related to the Reynolds number Re, whereas the second one is related to the Froude number Fn. The viscous drag is aroused by the relative motion between ship and water and is confined into the internal region of the flow. More correctly viscous dissipation phenomena are also present in the far field when wave breaking occurs. A dot-shaped disturbance moving relatively to the fluid in the proximity of the free surface generates a wave system that spreads below in a region bounded by the Kelvin angle [Lighthill, 1980]. Usually the residual resistance, whose main part is the wavemaking resistance, is obtained subtracting the friction drag to the total resistance, approximately determined by empirical formula (e.g. ITTC 57).
