Run-up and Wave Forces on an Array of Vertical Circular Cylinders: Experimental Study on the Second-Order Near Trapping

This paper summarizes the results of experimental tests conducted at the Danish Hydraulic Institute (DHI) in the frame of the EU-IHP-ARI project “Wave Forces on an Array of Circular Cylinders: Experimental Investigation on the Higher Order Near Trapping”. The aim of this research project was to study in detail the so-called “near trapping”, specifically the second order near trapping. This phenomenon regards diffraction effects on TLP like structures in waves or, in general, on arrays of vertical cylinders that encircle a portion of free surface. The result of the wave-structure interaction is a rather large amplification of the oscillations of the free surface in the inner domain. These magnifications are particularly large at the fluid-body interface with associated large induced pressures; they show their maximum effect for specific ratios of the diffraction parameter ka and of the column radius a to the distance between the column axis d. Second order near trapping is a double frequency phenomenon that is expected to occur when double frequency component waves exhibit a wavelength comparable to that of linear waves giving first order near trapping. The paper describes the set-up of the experiments, the tests conducted and finally presents the most meaningful results obtained.