A series of regular wave studies have been performed on a vertical surface-piercing test cylinder, consisting of an articulated column, 0.06 m diameter, with a swivel joint at its base and orthogonally disposed support links at its tip. A feature of this column was that it contained a number (8) of sleeve elements instrumented to measure the in-line force acting on the 0.01m long sleeves each separated by non-instrumented segments 0.015m in length. The instrumented length of force sleeves was located within the intended splash zone of the incident waves, for which the Still Water depth was 1.035m. The transverse support links were chosen to be either rigid or from two sets of springs, thereby introducing significant compliancy in the transverse direction of the test column. Tip restraint forces in both the in-line and transverse directions were measured by force transducers located on support brackets at the far end of each link. Morison force models were used to fit Cm and Cd values to the in-line force characteristics of the segments and of the column as a whole (from the in-line tip restraint) for a number of regular wave inputs for these three conditions of transverse tip compliancy. Results indicated that the influence of transverse motion upon the in-line force characteristics of the test column was rather "mild" considering the variability encountered in the wave-by-wave force analysis for the largely "troublesome" KC range of waves for these tests (5 < KC <20).
The complexity and difficulty of accurate prediction of cylinder forces in gravity wave flows is due to the intrinsic link between transverse forces and displacements, the vortex shedding process and in-line wave force effects. The "effects" of vortex shedding, such as the generated in-line and transverse oscillations, actually alter the vortex shedding process itself.