Wave flume tests to check a semi-analytical method for calculating solitary wave loads on horizontal cylinders

In this work, the solitary wave loads on a submerged horizontal circular cylinder are studied by comparing new analytical results with ad-hoc experimental data. The proposed analytical solution has been recently proposed by Gurnari and Filianoti (2017) and represents an extension of the formulation developed by Filianoti and Piscopo (2008) to assess the solitary wave loads acting on a submerged breakwater and tested in a wave flume on a small-scale model (Filianoti and Di Risio, 2012). Here we deal with a submerged horizontal cylinder following the concept that a solitary wave is subjected to a slowdown passing over a submerged cylinder. A laboratory investigation was addressed to calibrate the adopted semi-analytical method. The speed of the solitary wave celerity crossing the solid submerged cylinder was measured for several wave amplitudes. In the adopted wave flume at the University of Calabria equipped by a piston-type wavemaker, an horizontal cylinder with diameter D= 0.127 m was posed with its center at a depth of 0.2 m. Twelve transducers measured the instantaneous pressures along the external contour of the body. A battery of wave gauges measured the free surface elevation to evaluate the celerity crossing the equivalent water cylinder. Tests confirmed the existence of the slowing down of the celerity of the wave pressure. In other words, we found that the pressure wave is nearly double the time necessary to cross the cylinder with respect to the time necessary to cover the same distance in the undisturbed field, for solitary waves amplitudes ranging from about 0.08 and 0.19 times the water depth. The slowing down increases the horizontal wave force on the solid body with respect to the Froude-Krylov one. Moreover, it appears that in the adopted experimental range the wave force is essentially inertial if compared to the drag one, enabling us to rely upon a simplified analytical model to obtain an effective estimate of the horizontal force produced by a solitary wave on a cylinder.