Thor Ugelvig Petersen

Backfilling of a Scour Hole around a Pile in Waves and Current

This paper presents the results of an experimental investigation of the backfilling of scour holes around circular piles. Scour holes arounda pile aregenerated either by a current or a wave.Subsequently, the flow climate is changed from current to wave, combined waves and current, or wave to a smaller wave, leading to the backfilling of the scour hole. The investigation has shed light onto the mechanism behind the backfillingprocess.Theresultsshowthatthescourdepthcorrespondingtotheequilibriumstateofbackfillingisthesameasthatcorrespondingto the equilibrium state of scour aroundthepilefor thesame wave (or combined waves and current) climate. The time scale of backfilling hasbeen determinedasafunctionofthreeparameters,namely,(1)theKeulegan-Carpenternumberoftheinitialwaveorcurrent(whichgeneratestheinitial scourhole);(2)thatofthesubsequentwave,whichbackfillsthescourhole;and(3)theShieldsparameterassociatedwiththelatterwave,forlive- bedconditions.Inthecaseofthecombinedwavesandcurrent,thecurrent-to-wave-velocityratioisalsoinvolved.Thetimescaleofthebackfilling process is completely different from that of scour. The time scale of backfilling is much larger than that of scour when the Keulegan-Carpenter numberassociatedwiththebackfillingisKCf ,Oð10Þ(typicalwindfarmapplication),whilethetimescaleofbackfillingcanbesmallerthanthat of scour when KCf ..Oð10Þ. DOI: 10.1061/(ASCE)WW.1943-5460.0000161.

Flow and Edge Scour in Current Adjacent to Stone Covers

AbstractThis paper presents the results of an experimental investigation on edge scour adjacent to a stone cover laid on a sandy bed. The three-dimensional flow over the edge of the stone layer has been investigated by the use of particle image velocimetry. The flow measurements show a significant amount of turbulence in the primary flow near the junction between the stone layer and the sand bed and the formation of complex secondary-flow structures. The results show that the flow and the edge scour process in a steady current are governed by the size of the roughness elements and to some extent the side slope of the berm. The edge scour is caused by the combined action of the primary flow and the secondary flow. The primary flow stirs up the sediment and puts it into suspension, and the secondary flow carries it away from the junction between the stone layer and the sand bed, resulting in a scour hole forming adjacent to the toe of the stone layer. The measured scour depth attained a constant level of ap...

Measuring Sandy Bottom Dynamics by Exploiting Depth from Stereo Video Sequences

In this paper an imaging system for measuring sandy bottom dynamics is proposed. The system exploits stereo sequences and projected laser beams to build the 3D shape of the sandy bottom during time. The reconstruction is used by experts of the field to perform accurate measurements and analysis in the study of the final equilibrium conditions of sea bottoms in the presence of water flows. Results obtained by processing data acquired in hydraulic laboratory confirm the effectiveness of the system which makes simple and fast the understanding of the sandy bottom dynamics and the related equilibrium phenomena.