Showing papers by "Jørgen Fredsøe published in 1989"

Turbulent oscillatory boundary layers at high Reynolds numbers

Abstract: This study deals with turbulent oscillatory boundary-layer flows over both smooth and rough beds. The free-stream flow is a purely oscillating flow with sinusoidal velocity variation. Mean and turbulence properties were measured mainly in two directions, namely in the streamwise direction and in the direction perpendicular to the bed. Some measurements were made also in the transverse direction. The measurements were carried out up to Re = 6 × 106 over a mirror-shine smooth bed and over rough beds with various values of the parameter a/ks covering the range from approximately 400 to 3700, a being the amplitude of the oscillatory free-stream flow and ks the Nikuradse's equivalent sand roughness. For smooth-bed boundary-layer flows, the effect of Re is discussed in greater detail. It is demonstrated that the boundary-layer properties change markedly with Re. For rough-bed boundary-layer flows, the effect of the parameter a/ks is examined, at large values (O(103)) in combination with large Re.

Response of Marine Pipelines in Scour Trenches

Abstract: This paper reviews the results of a model test study with the aim of determining the hydroelastic vibrations of a marine pipeline placed in the vicinity of a scoured trench and exposed to regular and irregular waves. The so‐called carriage technique was used in the study. The experiments were conducted for two values of Keulegan‐Carpenter number, namely KC=10, and KC=40. The range of reduced velocity is from 3 to 8. The range of Reynolds number of the tests is R=2-7×104. The pipe's surface‐roughness parameter is k/D=4×10-3. The model pipe has two degrees of freedom. Pipe displacements and forces have been measured. The position of the pipe relative to the trench appears to be quite significant in the vibratory response of the pipe. It turns out that the presence of the scour trench protects the pipe against the vibrations. The experiments also show that the amplitudes of vibrations are generally larger for irregular waves than for regular waves.

Engineering Models for Coastal Sediment Transport

Abstract: During the last ten years Danish Hydraulic Institute (DHI) has together with the Institute of Hydrodynamics and Hydraulic Engineering (ISVA) of the Technical University of Denmark been working on the development of engineering models for sediment transport and morphology in the coastal zone. The models are centered around the model 'STP' which describes the transport of non-cohesive sediment under waves and current. The STP model is discussed, along with wave and current effects, and the longshore sediment transport model LITLONG.