Field experiment on random-wave forces on vertical cylinders. Part II: systematic analysis of hydrodynamic coefficients

The paper shows some results of a small-scale-field experiment on wave forces on a vertical truncated cylinder. The experiment was performed off the city of Reggio Calabria where often there are wind waves with Hs within 1m . We measured wave pressures on the cylinder, and free surface displacements at the point xo,yo where the ideal axis of the cylinder pierces the free surface, and at a point close to xo,yo. We took 500 records of pure wind waves (no swell superimposed on wind waves) with Hs ranging between 0.3m and 1.1m, with three diameters of the cylinder: 0.07m, 0.14m, and 0.22m. Our data enable us to get a picture of the relationship between Cin, Cdg and KE, RE, for KE in (0,20) and RE in ( 2 104 , 5 2 10 ). Cin vs RE for some fixed values of KE is a monotonically increasing function. Cdg vs RE for some fixed values of KE is a decreasing function. This is like what emerges from the data of Sarpkaya, from laboratory experiments with a periodic flow in a conduct. However, our values of Cin and Cdg prove to be somewhat smaller than Sarpkaya's. This difference from the data of Sarpkaya, gets smaller as KE grows. The trend of our data is compatible with the asympotic values of Cin and Cdg suggested by Sarpkaya for large values of RE.