document

A critical assessment of methodologies for operations and safety evaluations of freeway turbulence

van Beinum, A.S. (author), Farah, H. (author), Wegman, F.C.M. (author), Hoogendoorn, S.P. (author)

Turbulence in traffic is a commonly known phenomenon, but the exact characteristics of this phenomenon are not yet clear. It reflects individual changes in speed, headways, and lanes in the traffic stream. The currently used freeway design guidelines prescribe different measures for handling turbulence, such as sufficient ramp spacing, and...

conference paper 2016

document

Stratocumulus transitions in present-day and future climate

Van der Dussen, J.J. (author)

Clouds have a strong net cooling effect on our planet, as they reflect a large part of the incident solar radiation. To be able to make accurate forecasts of the global climate, cloudiness should therefore be correctly represented by climate models. Currently, however there are large differences in the forecasted temperature increase among...

doctoral thesis 2015

document

Efficiency of hanging silt curtains in cross-flow

Radermacher, M. (author), De Wit, L. (author), Uijttewaal, W.S.J. (author), Winterwerp, J.C. (author)

When dredging in sensitive environments, efforts have to be made to limit the free dispersal of suspended fine sediment from the dredging spill. Especially the use of hanging silt curtains as an environmental mitigation measure is widespread. Despite frequent application, their ability to reduce turbidity levels through vertical diversion of...

journal article 2015

document

Modelling Vertical Variation of Turbulent Flow Across a Surf Zone Using SWASH

Zijlema, M. (author)

This paper presents the application of the open source non-hydrostatic wave-flow model SWASH to propagation of irregular waves in a barred surf zone, and the model results are discussed by comparing against an extensive laboratory data set. This study focus not only on wave transformation in the surf zone, but also on the numerical prediction of...

conference paper 2014

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A conceptual framework for shear flow–induced erosion of soft cohesive sediment beds

Winterwerp, J.C. (author), Van Kesteren, W.G.M. (author), Van Prooijen, B.C. (author), Jacobs, W. (author)

This paper proposes a conceptual framework for erosion of cohesive sediment beds. We focus on cohesive beds, distinguishing between floc erosion, surface erosion, and mass erosion. By (our) definition, surface erosion is a drained soil mechanical process, whereas mass erosion occurs under undrained conditions. The eroding shear stress is modeled...

journal article 2012

document

Macrophytes in estuarine gradients: Flow through flexible vegetation

Dijkstra, J.T. (author)

Aquatic plants –or macrophytes- are an important part of coastal, estuarine and freshwater ecosystems worldwide, both from an ecological and an engineering viewpoint. Their meadows provide a wide range of ecosystem services: forming a physical protection of the shoreline, enhancing water quality and harbouring many other organisms. Unfortunately...

doctoral thesis 2012

document

Transport of suspended particles in turbulent open channel flows

Breugem, W.A. (author)

Two experiments are performed in order to investigate suspended sediment transport in a turbulent open channel flow. The first experiment used particle image velocimetry (PIV) to measure the fluid velocity with a high spatial resolution, while particle tracking velocimetry (PTV) was used to measure the velocity of individual sediment particles....

doctoral thesis 2012

document

Modeling the interaction between flow and highly flexible aquatic vegetation

Dijkstra, J.T. (author), Uittenbogaard, R.E. (author)

Aquatic vegetation has an important role in estuaries and rivers by acting as bed stabilizer, filter, food source and nursing area. However, macrophyte populations worldwide are under high anthropogenic pressure. Protection and restoration efforts will benefit from more insight into the interaction between vegetation, currents, waves and...

journal article 2010

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Dynamics of shallow lateral shear layers: Experimental study in a river with a sandy bed

Sukhodolov, A.N. (author), Schnauder, I. (author), Uijttewaal, W.S.J. (author)

Shallow lateral shear layers forming between flows with different velocities, though essential for mixing processes in natural streams, have been examined only in laboratory settings using smooth, fixed?bed channels. This paper reports the results of an experimental study of a shear layer in a straight reach of a natural river where the layer,...

journal article 2010

document

Large-eddy simulation of a curved open-channel flow over topography

Van Balen, W. (author), Uijttewaal, W.S.J. (author), Blanckaert, K. (author)

Large-eddy simulation (LES) is performed of a curved open-channel flow over topography based on the laboratory experiment by Blanckaert [“Topographic steering, flow circulation, velocity redistribution and bed topography in sharp meander bends,” Water Resour. Res., doi:10.1029/2009WR008303 (in press)] . In the experiment, the large-scale bed...

journal article 2010

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Curved open-channel flows - a numerical study

Van Balen, W. (author)

The flow of water through a river bend can be characterized as a turbulent open-channel flow that is dominated by streamline curvature. In order to adequately manage the planimetry of meandering rivers and the according safety aspects, the features of the flow and the associated turbulence have to be understood well. This thesis presents results...

doctoral thesis 2010

document

Stone stability under decelerating open-channel flow

Hoan, N.T. (author), Booij, R. (author), Hofland, B. (author), Stive, M.J.F. (author), Verhagen, H.J. (author)

The current research is aimed at finding a proper relation between flow forces acting on the bed and the bed response. To this end, experiments were carried out in which both the bed response (quantified by a dimensionless entrainment rate) and the flow field (velocity and turbulence intensity distributions) are measured. The three available...

conference paper 2007

document

Stone stability under non-uniform flow

Hoan, N.T. (author), Booij, R. (author), Hofland, B. (author), Stive, M.J.F. (author), Verhagen, H.J. (author)

The current research is aimed at finding a dimensionless stability parameter for non-uniform flow in which the effect of turbulence is incorporated. To this end, experiments were carried out in which both the bed response (quantified by a dimensionless entrainment rate) and the flow field (velocity and turbulence intensity distributions) are...

conference paper 2007

document

Modelling hydrodynamics in Eelgrass (Zostera Marina)

Dijkstra, J.T. (author), Uittenbogaard, R.E. (author), Stive, M.J.F. (author)

In many areas around the world, there is a large interest in the protection and restoration of aquatic vegetation, like eelgrass (Zostera marina), but little is known about the interaction of such vegetation with its environment. To improve this knowledge, a model has been developed that simulates this interaction between highly flexible...

conference paper 2006

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Rock and roll: Turbulence-induced damage to granular bed protections

Hofland, B. (author)

Layers of stone or rock are often applied around hydraulic structures to protect the sand bed from scouring. Determining the size of the rocks is complicated by the fact that the flow over a bed protection usually is non-uniform. This thesis describes two experimental series in which the stability of a single stone under non-uniform flows is...

doctoral thesis 2005

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Energy transfers and spectral eddy viscosity in large-eddy simulations of homogeneous isotropic turbulence: Comparison of dynamic Smagorinsky and multiscale models over a range of discretizations

Hughes, T.J.R. (author), Wells, G.N. (author), Wray, A.A. (author)

Energy transfers within large-eddy simulation (LES) and direct numerical simulation (DNS) grids are studied. The spectral eddy viscosity for conventional dynamic Smagorinsky and variational multiscale LES methods are compared with DNS results. Both models underestimate the DNS results for a very coarse LES, but the dynamic Smagorinsky model is...

journal article 2004

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Sensitivity of the scale partition for variational multiscale large-eddy simulation of channel flow

Holmen, J. (author), Hughes, T.J.R. (author), Oberai, A.A. (author), Wells, G.N. (author)

The variational multiscale method has been shown to perform well for large-eddy simulation (LES) of turbulent flows. The method relies upon a partition of the resolved velocity field into large- and small-scale components. The subgrid model then acts only on the small scales of motion, unlike conventional LES models which act on all scales of...

journal article 2004

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A linear approach for the evolution of coherent structures in shallow mixing layers

Van Prooijen, B.C. (author), Uijttewaal, W.S.J. (author)

The development of large coherent structures in a shallow mixing layer is analyzed. The results are validated with experimental data obtained from particle tracking velocimetry. The mean flow field is modeled using the self-similarity of the velocity profiles. The characteristic features of the down-stream development of a shallow mixing layer...

journal article 2002

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Entraining Flow of a Concentrated Benthic Suspension: Computations with the Prandtl Mixing-Length Model

Kranenburg, C. (author)

The Prandtl mixing-length model of turbulent exchange of mass and momentum is applied to calculate the entrainment of overlying water into a layer of suspended fine sediment at a horizontal bed. In the field the flow and turbulence in such a concentrated benthic suspension (CBS) are driven by a streamwise pressure gradient resulting from the...

report 1999

document

A pilot study to test a method to enhance the turbulence of a water flow in a laboratory flume

Suastika, I.K. (author)

In this report we present some results of a laboratory pilot study which has been conducted to test a method to artificially enhance the turbulence of a water flow in a laboratory flume. The purpose of this test is to provide data which will be used to verify whether the method is suitable for the study of the dissipative effects of turbulence...

report 1998