The study concerns the vortex-flow regimes around a cylinder exposed to an oscillatory flow and undergoing vibrations in the cross-flow direction. The flow of vortices was visualized, using the aluminum-powder technique. The study focuses on the lock-in regions. The tests have been carried out for the values of the Keulegan-Carpenter number KC = 10 and 20, and for a range of reduced velocities. The identified vortex-flow regimes were compared with the fixed cylinder case. The changes to the vortex-flow patterns were discussed with regard to their influence on the lift force. To complement the results of the experimental study, an attempt has been made to simulate the flow numerically, using the discrete vortex model. The numerical results agree with the experiments.

A numerical model that simulates the sediment transport due to plunging breaking waves has been developed. A plunging breaker is simulated by superimposing a jet on a nonbreaking wave. The hydrodynamics are described by applying a discrete vortex model based on the mixed Eulerian-Lagrangian description of the cloud-in-cell method. Rotation is introduced in the flow where the jet impinges on the surface and in the boundary layer along the bottom. A combined diffusion-convection procedure provides a Lagrangian description of the suspended sediment. The pickup and initial suspension event in the boundary layer is simulated by a diffusion process, while the transport in the outer flow domain is simulated by convection, using the flow field provided by the hydrodynamic module. The bed-load transport is calculated by a conventional formula that relates the transport rate to the Shields parameter. A simulation over a complex bottom topography is compared to the full-scale laboratory experiments performed by Dette and Uliczka in 1986. The calculated and measured time-averaged concentration profiles show good agreement both with respect to the overall concentration levels and the cross-shore distribution.

Oscillatory flow over wave ripples is described by use of a discrete vortex model using the ''cloud in cell'' concept. The distribution of suspended sediment over the ripple bed is simulated by a Lagrangian model, following the track of individual sediment particles. A boundary-layer model is used to determine the strength and the motion of the vortices very close to the ripple, surface. The development of the boundary layer is described by the integrated momentum equation, assuming the boundary layer to be turbulent with a logarithmic velocity profile. In the boundary layer, turbulent diffusion is used to describe the distribution of suspended sediment. Outside the boundary layer along the ripple surface, advection with the velocity field resolved by the discrete vortex model determines the suspended-sediment distribution. The simulated sediment concentrations are compared to measurements from the literature. The agreement between the time averaged simulated concentration profiles and the measurements from an oscillating water tunnel is satisfactory.

Numerical simulations are presented for the flow and the dynamics of noncohesive sediment over 2D ripples in waves and current. For this purpose, a model based on a discrete vortex approach using the cloud-in-cell concept has been applied. The hydrodynamic model drives a Lagrangian model for the suspended sediment. The characteristic vorticity structures prevailing in the vicinity of ripples are accurately replicated and sediment suspension mechanisms are successfully described. Thus, the sediment transport resulting from asymmetrical waves and combined waves and current can be predicted. Especially, the wave-related component of the transport opposes the maximum free stream velocity and contributes significantly to the total transport. In the present work, the effect of the wave-induced drift is not included.

Abstract This paper deals with the scour below pipelines exposed to a current. In a typical field situation, the scour pattern along a pipeline is not uniform; the scour holes are interrupted with the reaches where the pipeline is partially or totally buried. This paper focuses on the longitudinal extent of the individual scour holes. A simplified picture of the process is given to describe the longitudinal dimension of a scour hole. The sagging of the pipeline is an essential element of the process. The effect of sagging on the final scour depth is investigated, using a two-dimensional laboratory model. A simple equation to calculate the length of individual scour holes (the span length) is developed. The practical application of the equation is demonstrated by an example.

The paper presents a series of experiments carried out with a cylinder suspended by springs and placed very close to a plane wall. The cylinder is exposed to a steady current. The range of gap ratios between zero and one has been studied in detail. Different combinations of spring stiffness and mass of cylinder is applied in the range of reduced velocity between 2 and 10. The proximity of the wall is shown to have important influence on the behavior of the pipe. Some of these trends are explained by a mathematical model including the effect of lift force close to the wall.