A selection of the results of a research project developed in the frame of the cooperation between University of Trieste and INSEAN, aimed at the investigation of the local nonlinear features of diffraction wave loads on single vertical cylinders in regular waves, is presented. The study has been conducted by means of theoretical and experimental methods allowing a huge amount of information on the behaviour of the pressure at the wall and on the wave pattern around the cylinder when the nondimensional parameters ka and H/D are varied between 0.2 and 1.4 and between 1/15 and 1/50 respectively. The validation of the fully nonlinear numerical procedure developed at INSEAN is carried out, according to the recommendations of several international bodies (ASME, ITTC, AIAA), on the basis of the highly accurate experimental data obtained at University of Trieste during the tests. The adopted method for the validation is based on the comparison between the numerical results and the local quantities involved in the fluid-structure interaction, namely near-field free surface elevation and pressure at the cylinder surface. Preliminary results here presented look promising, the direction to better results being highlighted by the local discrepancies.
