Experimental Study of Wave Forces on Vertical Circular Cylinders in Long and Short Crested Sea

The three-dimensional structure of ocean waves is generally ignored in favour of two-dimensional waves, which are easier to handle from a theoretical and computational point of view. For design fixed structures where horizontal in-line and resultant wave forces are important, this is normally on the safe side, as the directional spreading of the wave field Ieads to reduced horizontal velocities and acceleration; in the fluid and hence a reduction of the resultant and in-line wave forces on the structure. The directional spreading of the horizontal velocity field generally causes an increase in the transverse wave forces on the structure, whereas the vertical forces generally are unaffected. In this study the effect from wave directionality on the horizontal wave forces on a slender vertical cylinder in a laboratory environment is investigated. In addition wave forces from regular waves on a slender cylinder in the near-surface-zone are investigated and suggestions for the force coefficients C_d, C_m and C₁ in this region presented. The approximately 100 physical experiments have been condueted using a newly designed 2nd generation smooth circular cylinder with diameter, D = 0.0635 m and instrumented with miniature pressure transducers. The experiments were carried out in the 3-D wave tank in the Hydraulics & Coastal Engineering Laboratory at Aalborg University and in the off-shore basin at the Danish Hydraulic
Institute.