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Showing papers by "Jørgen Fredsøe published in 2008"


Journal ArticleDOI
TL;DR: In this article, the results of an experimental investigation on wave boundary layers over a bed with large roughness, simulating stone/rock/armour block cover on the sea bottom, were summarized.

81 citations


Journal ArticleDOI
TL;DR: In this paper, the shape, dimensions and growth rate of an accumulating sandy spit are investigated by a theoretical and experimental study, and the idealised case of a spit growing without change of form under a constant wave forcing is considered.

55 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied suction removal of sediment in steady currents and found that the onset of suction is governed by three parameters: (1) the sediment mobility number (based on the sediment size); (2) the ratio of sediment size to stone size, d∕D ; and (3) the Keulegan-Carpenter (KC) number, based on the armor block/stone size.
Abstract: When a stone/armor layer on a sand bed is exposed to flow, the sand underneath will be agitated by the flow turbulence. When the flow velocity reaches a critical value, the sand will be sucked (winnowed out) from between the armor blocks. In a previous investigation, we studied suction removal of sediment in steady currents. The present study is an extension of our previous investigation to waves. The critical condition for the onset of suction is determined. It is found that the onset of suction is governed by three parameters: (1) the sediment mobility number (based on the sediment size); (2) the ratio of sediment size to stone size, d∕D ; and (3) the Keulegan-Carpenter (KC) number, based on the armor block/stone size. The variation of the critical mobility number for suction as a function of d∕D and KC is determined for the ranges of the parameters 0.001

18 citations




01 Jan 2008
TL;DR: In this article, the boundary layer flow remains laminar for Re numbers smaller than Re=5x10 and the bed shear stress reverses during the deceleration stage of the freestream flow.
Abstract: This paper summarizes the results of an experimental investigation of turbulent solitary wave boundary layers. The wave induced flow has been simulated by a solitary motion in an oscillating tunnel. The experiments show that the boundary layer flow remains laminar for Re numbers smaller than Re=5x10. The experiments further show that the bed shear stress reverses during the deceleration stage of the freestream flow. In a narrow sub-range of Re number (2x10 ≤ Re < 5x10) in the laminar regime, the boundary layer flow experiences a regular array of vortices near the bed over a short period of time during the deceleration stage. The transition-to-turbulence at Re=5x10 is associated with the emergence of turbulent spots, revealed by single/multiple, or, sometimes, quite dense spikes in the bed shear stress variations. Flow resistance in terms of wave friction coefficient including the phase information has also been worked out for both the acceleration and deceleration stages of the free-stream flow of the wave.

11 citations