Solitary wave-induced forces on horizontal circular cylinders: Laboratory experiments and SPH simulations

This work deals with an experimental and numerical study on the horizontal and vertical hydrodynamic forces induced by solitary waves on submerged horizontal circular cylinders. Laboratory tests were performed in the wave flume of the University of Calabria. A battery of pressure transducers was mounted along the external contour of a cylinder placed at half water depth, while four wave gauges were located close to the cylinder and an ultrasonic sensor behind the paddle to measure its displacement. From the numerical viewpoint, a diffusive weakly-compressible SPH model was adopted. To prevent spurious flows near the cylindrical contour, a packing algorithm has been applied to initialize the SPH fluid particles. The acoustic components occurring in the numerical pressure field were filtered through the application of Wavelet Transform. Experimental and numerical analyses were performed in the inertia-dominated regime where these force components are more relevant than the drag and lift ones. The deviation from the fully inertia regime was highlighted in the simulations by the occurrence of a couple of asymmetric vortices behind the cylinder. The good agreement between experimental and SPH forces and kinematics at the cylinder has allowed the numerical calibration of the hydrodynamic coefficients in the Morison and transverse semi-empirical equations by different time-domain methods. For engineering purposes, we propose simple empirical formulas based on the knowledge of wave amplitude to calculate the hydrodynamic coefficients.