Scour around tripod/tripile foundations used in offshore wind turbines: use of a finite array of cylinders as tripod piles

Abstract

Scour around pier foundations for coastal structures is an inevitable process when these structures are mounted on an erodible bed. Recent findings have indicated that a group of permeable piles offers certain advantages as a supporting structure in marine structures. In line with this vision, in this study we present an experimental investigation of the characteristics of clear water scour at solid cylinder and porous arrays arranged in the form of a tripod. Based on an experimental perspective, the study is motivated by the influence of different solid volume fractions of cylindrical arrays on the scour depth, width, volume, and area. To accomplish this, experiments are conducted using a uniform sand bed, two different tripod configurations, and three different distances for the sides of the tripod forms. The channel in which the experiments were conducted is 26 m long, 1 m wide and 0.85 m deep. The experimental observations indicated that in favorable hydrodynamic form (FHD) layouts, the local scour depth, width, and volume resulting from the isolated upstream cylinder were consistently less than those induced by the downstream side-by-side cylinders. The highest levels of local scour values were seen near the adjacent pairs of cylinders positioned in the downstream direction, in all FHD configurations. Additionally, it has been shown that how many sediment mounds that develop behind the tripod is directly dictated by the number of tripod piles positioned downstream. It was also seen that the formation of local scour holes for each individual pile of the tripod remains autonomous.