Experimental Investigation of Slamming Loads on Vertical Column Exposed to Short and Long Crested Waves

Model test campaigns conducted recent years indicate large wave impact loads on vertical surfaces above the waterline for various types of moored floating structures. These impacts are caused by breaking or near breaking waves in extreme sea states. Due to the large variability of the load, it is challenging to estimate the characteristic slamming loads, defined as the q-annual extreme 3-hour slamming load level of 10-2 for the Ultimate Limit State (ULS) and 10-4 for the Accidental Limit State (ALS). Hence, many tests realizations are necessary to assess extreme loads. It is common practice to assume long crested waves in design against slamming loads. This assumption is regarded as conservative, and there have been indications that the effect of short crested waves on impact loads could be significant. In the present work an experimental investigation was set up to study effect of short crested waves for slamming against a rigid vertical column. Influence of current and other modeling parameters like type of wavemaker (single vs double flap), were also studied. A test model in scale 1:55 of a 31m diameter column at water depth 121m was used. The area of the column facing the incoming wave was instrumented by slamming panels. The setup covers 80 degrees of the cylinder circumference over a height of 24 meters from the still water surface and upwards. In addition to the slamming loads measured on the column, shear force and bending moment at the base of the column and global accelerations for the column were measured. High-speed video recordings were made for slamming events above a given threshold.