The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

A method is presented which enables the computation of the bed-load transport as the product of the saltation height, the particle velocity and the bed-load concentration. The equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity. Experiments with gravel particles (transported as bed load) are selected to calibrate the mathematical model using the lift coefficient as a free parameter. The model is used to compute the saltation heights and lengths for a range of flow conditions. The computational results are used to determine simple relationships for the saltation characteristics. Measured transport rates of the bed load are used to compute the sediment concentration in the bed-load layer. A simple expression specifying the bed-load concentration as a function of the flow and sediment conditions is proposed. A verification analysis using about 600 (alternative) data shows that about 77% of the predicted bed-load-transport rates are within 0.5 and 2 times the observed values.

Sediment transport; Part I, Bed load transport

Development and validation of a three-dimensional morphological model

A method is presented which enables the computation of the suspended load as the depth-integration of the product of the local concentration and flow velocity. The method is based on the computation of the reference concentration from the bed-load transport. Measured concentration profiles have been used for calibration. New relationships are proposed to represent the size gradation of the bed material and the damping of the turbulence by the sediment particles. A verification analysis using about 800 data shows that about 76% of the predicted values are within 0.5 and 2 times the measured values.

Sediment Transport, Part II: Suspended Load Transport

A critical review of the intrinsic nature of vortex-induced vibrations

Simulation of turbulent wave boundary layers on spatially varying bottom roughness

Ship-propeller scour

Shape and dimensions of ripples and dunes

In the summer of 2010 a ferry harbour was opened at the south coast of Iceland connecting the Vestmannaeyjar islands to the mainland. The harbour was constructed on a sandy beach in a dynamic area open to the Atlantic Ocean causing massive longshore sediment transport across the navigational channel to the harbour. Sedimentation in the harbour entrance has turned out to be more than expected causing the harbour to be closed for navigation for large part of the winter time. The volcanic eruption of the Eyjafjalljokull glacier started four months before the opening of the harbour in April 2010. The floods that followed from the river Markarfljot, caused large amount of fine sediments, estimated as 2 million m3 of sand and 20 million m3 of mud, to be drifted down through the delta of the river located only 2 km east of the harbour. In the following years the deposition of fine sediments caused navigation problems in the harbour as the necessary navigation depth could not be obtained without heavy dredging. The last two years however the main settlement of sand has been taking place in a limited area between the two breakwater roundheads. In the winter time, it has turned out to be difficult to dredge in the harbour entrance. This is due to the high ambient wave conditions during the winter time where Hs is larger than 2 m 80% of the time. The limiting wave height for operating dredging vessels in the entrance is less than 2 m. The aim of this study is to assess the possibility of keeping the necessary navigation depth across the harbour entrance by placing a series of static pumps under the seabed in the harbour mouth. Physical model tests were carried out focusing on that problem. First focusing on the effect of a single pump located under the seabed and then on a combined effect of several pumps.

/pdf/behaviour-of-pumping-pits-in-harbour-entrance-on-an-exposed-5ew5bzw36y.pdf

Behaviour of pumping pits in harbour entrance on an exposed sandy coast.

This study investigates particle motions near the bed in an oscillating tunnel with a smooth bed. Trajectories of a heavy particle were recorded in two dimensions (horizontal and vertical) and in time. The wave boundary layer Reynolds number is Re = 520000. Kinematical quantities such as the probability distribution of particle position in the vertical, and the horizontal and vertical particle velocities, among others, are determined. The particle is observed to reach heights of 2.5-3d, similar to that characterizing a typical bedload particle in sediment transport.

/pdf/particle-motions-in-oscillatory-flow-over-a-smooth-bed-55psli634m.pdf

Jørgen Fredsøe

Papers

Simulation of turbulent wave boundary layers on spatially varying bottom roughness

Ship-propeller scour

Shape and dimensions of ripples and dunes

Behaviour of pumping pits in harbour entrance on an exposed sandy coast.

Particle motions in oscillatory flow over a smooth bed