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.

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The flow around a vertical circular pile exposed to a steady current is studied numerically and experimentally. The numerical model is a three-dimensional model. The model validation was achieved against new experimental data (which include two-component laser-Doppler anemometry (LDA) flow measurements and the hot-film bed shear stress measurements, and reported in the present paper) and the data of others, and a $k$–$\omega $ turbulence model was used for closure. The model does not have a free-surface facility and therefore is applicable only to cases where the Froude number is small ($\hbox{\it Fr}\,{<}\,O(0.2)$). The flow model was used to study the horseshoe vortex and lee-wake vortex flow processes around the pile. The influence on the horseshoe vortex of three parameters, namely the boundary-layer thickness, the Reynolds number and the bed roughness, was investigated. In the latter investigation, the steady solution of the model was chosen. A study of the influence of the unsteady solution on the previously mentioned flow processes was also carried out. The ranges of the parameters covered in the numerical simulations are: The boundary-layer-thickness-to-pile-diameter ratio is varied from 2$\,{\times}\, 10^{-2}$ to 10$^{2}$, the pile Reynolds number from 10$^{2}$ to $2\,{\times}\, 10^{6},$ and the pile diameter-to-roughness ratio from 2 to about 10$^{3}.$ The amplification of the bed shear stress around the pile (including the areas under the horseshoe vortex and the lee-wake region) was obtained for various values of the previously mentioned parameters. The steady-state flow model was coupled with a morphologic model to calculate scour around a vertical circular pile exposed to a steady current in the case of non-cohesive sediment. The morphologic model includes (i) a two-dimensional bed load sediment-transport description, and (ii) a description of surface-layer sand slides for bed slopes exceeding the angle of repose. The results show that the present numerical simulation captures all the main features of the scour process. The equilibrium scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole. Some discrepancy (up to 30%) was observed, however, for the downstream scour hole. The calculations show that the amplification of the bed shear stress around the pile in the equilibrium state of the scour process is reduced considerably with respect to that experienced at the initial stage where the bed is plane.

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British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.Cover: Flow around a marine pipeline placed over a trench during a half wave period, calculated by use of the discrete vortex method. HYDRODYNAMICS AROUND CYLINDRICAL STRUCTURES (Revised Edition) PrefaceFlow around a circular cylinder is a classical topic within hydrodynamics. Since the rapid expansion of the offshore industry in the sixties, the knowledge of this kind of flow has also attracted considerable attention from many mechanical and civil engineers working in the offshore field.The purpose of the present book is• To give a detailed, updated description of the flow pattern around cylindrical structures (including pipelines) in the presence of waves and/or current.• To describe the impact (lift and drag forces) of the flow on the structure.• And finally to describe the possible vibration patterns for cylindrical structures. This part will also describe the flow around a vibrating cylinder and the resulting forces.The scope does not deviate very much from the book by Sarpkaya and Isaacson (1980) entitled "Mechanics of Wave Forces on Offshore Structures". However, while Sarpkaya and Isaacson devoted around 50% of the book to the drag-dominated regime and around 50% to diffraction, the present book concentrates mainly on the drag-dominated regime. A small chapter on diffraction is included for the sake of completeness. The reason for our concentration on the drag-dominated regime (large ifC-numbers) is that it is in this field the most progress and development have taken place during the last almost 20 years since Sarpkaya and Isaacson's book. In the drag-dominated regime, flow separation, vortex shedding, and turbulence have a large impact on the resulting forces. Good understanding of this impact has been gained by detailed experimental investigations, and much has been achieved, also in the way of the numerical modelling, especially during the last 5-10 years, when the computer capacity has exploded.In the book the theoretical and the experimental development is described. In order also to make the book usable as a text book, some classical flow solutions are included in the book, mainly as examples.