Breaching flow slides result in a turbidity current running over and directly interacting with th... more Breaching flow slides result in a turbidity current running over and directly interacting with the eroding, submarine slope surface, thereby promoting further sediment erosion. The investigation and understanding of this current are crucial, as it is the main parameter influencing the failure evolution and fate of sediment during the breaching phenomenon. In contrast to previous numerical studies dealing with this specific type of turbidity currents, we present a 3D numerical model that simulates the flow structure and hydrodynamics of breaching-generated turbidity currents. The turbulent behavior in the model is captured by large eddy simulation (LES). We present a set of numerical simulations that reproduce particular, previously published experimental results. Through these simulations, we show the validity, applicability, and advantage of the proposed numerical model for the investigation of the flow characteristics. The principal characteristics of the turbidity current are rep...
ABSTRACT Floating wood is increasingly recognized as a source of hazard during flood events, beca... more ABSTRACT Floating wood is increasingly recognized as a source of hazard during flood events, because of its potential to clog bridges and hydraulic structures. However, wood entrainment by water is not well understood and only few studies addressing this issue are published. This paper reports on laboratory tests that were performed in a straight flume with fixed bed on logs with different shapes, orientations and densities. The logs oriented parallel to the water flow moved by sliding at undisturbed water depths larger than their buoyant depths, which was due to significant lowering of the water level around the log. Our analyses demonstrate that the entrainment condition cannot be simply defined as a balance between bed friction and drag force. Instead, the flow around the logs should be taken into account, with inclusion of acceleration and streamline curvature. For reliable predictions more experimental data are needed, including the effects of a mobile bed.
Wide crested dike can reduce the kinetic energy of the overtopping wave and make the overtopping ... more Wide crested dike can reduce the kinetic energy of the overtopping wave and make the overtopping wave to flow back to the seaside. If a coastal town were built on or near a dike, the overtopping wave running on the dike crest generates the force which can affect the buildings located in its path. However, quantifying the hydrodynamic load on the building caused by overtopping waves is not straightforward because little empirical formulas are given in literature for this kind of configuration. Therefore, physical scale model research was carried out. The purpose of this research is to come up with a relationship describing the force on a vertical wall exerted by the overtopping wave as a function of wave parameters and geometrical characteristics.
Concepts of a submerged floating tunnel (SFT) for novel sea-crossings have been researched in rec... more Concepts of a submerged floating tunnel (SFT) for novel sea-crossings have been researched in recent years. An SFT tube should be moored afloat by tensioned mooring systems to maintain the tube position under complex hydrodynamic loads. In-line force is amongst the dominant hydrodynamic parameters in the SFT cross-section design and the mooring system reliability evaluation. Selecting a suitable in-line force computation method is crucial to successful and accurate SFT cross-section optimization. The transition SST model is an effective turbulence transition prediction tool in the boundary layer computation subjected to tidal flow at both low and high Reynolds numbers. Two types of parametric Bezier curves applied in airfoil optimization are used to describe the SFT cross-section. We show that an SFT cross-section described by a leading-edge Bezier-PARSEC (BP) curve has better hydrodynamic performance than a trailing-edge BP curve of equal aspect ratio (AR). To avoid large flow sepa...
Confluences are special, complex elements within river systems which have been subject of much re... more Confluences are special, complex elements within river systems which have been subject of much research. However, little attention has been given to the effects of density differences in confluences. The aim of this research is to see when and how density differences are important in confluences with respect to other occurring flow structures. Non-dimensional flow parameters will be linked to certain types of flow. These non-dimensional parameters can then be used to determine to some degree which flow processes can occur. Using numerical simulations of a schematized confluence the effects of density differences were identified. These effects were visible on several aerial photographs of large confluences. For one specific confluence, the Rio Negro – Solimoes confluence near Manaus, Brazil, a separate model was made and run. The numerical simulations show that the denser water flowed under the lighter water. In a cross-section the shape of the interface between the two waters is ver...
The objective of this paper is to demonstrate the use of Stereo Photogrammetry (SP) measuring shi... more The objective of this paper is to demonstrate the use of Stereo Photogrammetry (SP) measuring ship-generated waves and to determine under which conditions they are suitable for surfing. A physical experiment is conducted to gain insight in ship wave behavior under specific conditions. Waves are generated by a hull and are measured using SP. It is concluded that the SP technique holds great potential in laboratory use and ship waves can potentially be used for surfing purposes.
With the intention to reduce the negative effects of ongoing bed erosion, as well as to improve... more With the intention to reduce the negative effects of ongoing bed erosion, as well as to improve several other river functions such as protection against floods, provision of safe and efficient navigation and ecology, a ‘pilot project longitudinal training dams’ was initiated. The training dams have recently been implemented in the Waal between Tiel and Sind Andries. In this project, river groynes have been completely removed and replaced by dams that lie parallel to the river bank. With help of the longitudinal training dams, a two-channel river system is created in which the river is divided into a main and side channel. The dams are placed in a continuous manner with openings in between that are relatively small compared to the dam length. At the beginning and end of the dam an inlet and outlet region is situated, as shown in Fig. 1. The combination of inlet and openings allows for water and sediment to be divided between the main and the side channel. Both i...
Physical model tests were conducted to estimate the overtopping wave force acting on vertical wal... more Physical model tests were conducted to estimate the overtopping wave force acting on vertical walls which represented buildings on top of dikes. The result showed that the force can be related to the mean wave energy density and the dimensionless run-up height thereby accounting for the freeboard as it is present above the still water level.
Abstract Accurate rheological characterisation of sewage waste activated sludge (WAS) is of high ... more Abstract Accurate rheological characterisation of sewage waste activated sludge (WAS) is of high importance for downstream processing related to optimised sludge pumping and mixing, assessment of energy demands and overall process design. However, to elaborate rheological behaviour is often challenging under dynamic operational conditions in practice. In this study, two practical influencing factors were investigated: long-term shearing and temperature. Compared to anaerobic digestate (DGT), concentrated WAS had more complex and stronger thixotropic behaviour. Under the long-term shearing conditions, the sludge thixotropic behaviour was well characterised by two quantified limitation states. Temperature had a striking impact on the rheological properties, which was strongly correlated to solids content and digestion process. The impact discrepancy between the long-term shearing and temperature, implied different mechanisms to shift the equilibrium of hydrodynamic and non-hydrodynamic interactions for structure deformation and recovery. The distinct rheological properties between the two determined states were clearly reflected in pipe flow behaviour, revealing a concrete link between lab-measured sludge rheology and its practical flow performance. The pipe flows were well assessed using the developed Computational Fluid Dynamics model with effective rheological data integration, which is promising for practical design and optimisation of sewage sludge systems.
Breaching flow slides are accompanied by the generation of turbidity currents. Measurements of th... more Breaching flow slides are accompanied by the generation of turbidity currents. Measurements of these currents are critical for understanding the interaction between the turbidity current and the slope surface, as well as for the validation of numerical models. However, there are insufficient data available detailing the velocity distribution or sediment concentration in these currents. This paper presents experimental results of unique large‐scale physical model experiments on breaching flow slides conducted at the water lab of Delft University of Technology, The Netherlands. The model tests were carried out in a tank with a subaqueous sandy slope steeper than the internal friction angle for that sand. We performed a series of novel experiments in which various non‐vertical initial slope angles were tested, providing the first quantitative data for such initial conditions. Measurements of flow thickness, velocities, and sediment concentrations are obtained, providing the spatial and temporal evolution of the turbidity currents and the resulting underwater slope morphology. The experimental results reveal that the breaching‐generated turbidity currents are self‐accelerating, and that they dominate the problem of breaching flow slides. We evaluated the theoretical expression for the erosion velocity in the case of pure beaching ‐ where the turbidity current has no influence on the erosion ‐ and it overestimated the observed erosion. The analysis of the failure evolution showed that the sand erosion rate increases due to the acceleration of the turbidity currents downslope, until a certain threshold, leading to the steepening of the breach face and thus the occurrence of surficial slides.
Breaching flow slides result in a turbidity current running over and directly interacting with th... more Breaching flow slides result in a turbidity current running over and directly interacting with the eroding, submarine slope surface, thereby promoting further sediment erosion. The investigation and understanding of this current are crucial, as it is the main parameter influencing the failure evolution and fate of sediment during the breaching phenomenon. In contrast to previous numerical studies dealing with this specific type of turbidity currents, we present a 3D numerical model that simulates the flow structure and hydrodynamics of breaching-generated turbidity currents. The turbulent behavior in the model is captured by large eddy simulation (LES). We present a set of numerical simulations that reproduce particular, previously published experimental results. Through these simulations, we show the validity, applicability, and advantage of the proposed numerical model for the investigation of the flow characteristics. The principal characteristics of the turbidity current are rep...
ABSTRACT Floating wood is increasingly recognized as a source of hazard during flood events, beca... more ABSTRACT Floating wood is increasingly recognized as a source of hazard during flood events, because of its potential to clog bridges and hydraulic structures. However, wood entrainment by water is not well understood and only few studies addressing this issue are published. This paper reports on laboratory tests that were performed in a straight flume with fixed bed on logs with different shapes, orientations and densities. The logs oriented parallel to the water flow moved by sliding at undisturbed water depths larger than their buoyant depths, which was due to significant lowering of the water level around the log. Our analyses demonstrate that the entrainment condition cannot be simply defined as a balance between bed friction and drag force. Instead, the flow around the logs should be taken into account, with inclusion of acceleration and streamline curvature. For reliable predictions more experimental data are needed, including the effects of a mobile bed.
Wide crested dike can reduce the kinetic energy of the overtopping wave and make the overtopping ... more Wide crested dike can reduce the kinetic energy of the overtopping wave and make the overtopping wave to flow back to the seaside. If a coastal town were built on or near a dike, the overtopping wave running on the dike crest generates the force which can affect the buildings located in its path. However, quantifying the hydrodynamic load on the building caused by overtopping waves is not straightforward because little empirical formulas are given in literature for this kind of configuration. Therefore, physical scale model research was carried out. The purpose of this research is to come up with a relationship describing the force on a vertical wall exerted by the overtopping wave as a function of wave parameters and geometrical characteristics.
Concepts of a submerged floating tunnel (SFT) for novel sea-crossings have been researched in rec... more Concepts of a submerged floating tunnel (SFT) for novel sea-crossings have been researched in recent years. An SFT tube should be moored afloat by tensioned mooring systems to maintain the tube position under complex hydrodynamic loads. In-line force is amongst the dominant hydrodynamic parameters in the SFT cross-section design and the mooring system reliability evaluation. Selecting a suitable in-line force computation method is crucial to successful and accurate SFT cross-section optimization. The transition SST model is an effective turbulence transition prediction tool in the boundary layer computation subjected to tidal flow at both low and high Reynolds numbers. Two types of parametric Bezier curves applied in airfoil optimization are used to describe the SFT cross-section. We show that an SFT cross-section described by a leading-edge Bezier-PARSEC (BP) curve has better hydrodynamic performance than a trailing-edge BP curve of equal aspect ratio (AR). To avoid large flow sepa...
Confluences are special, complex elements within river systems which have been subject of much re... more Confluences are special, complex elements within river systems which have been subject of much research. However, little attention has been given to the effects of density differences in confluences. The aim of this research is to see when and how density differences are important in confluences with respect to other occurring flow structures. Non-dimensional flow parameters will be linked to certain types of flow. These non-dimensional parameters can then be used to determine to some degree which flow processes can occur. Using numerical simulations of a schematized confluence the effects of density differences were identified. These effects were visible on several aerial photographs of large confluences. For one specific confluence, the Rio Negro – Solimoes confluence near Manaus, Brazil, a separate model was made and run. The numerical simulations show that the denser water flowed under the lighter water. In a cross-section the shape of the interface between the two waters is ver...
The objective of this paper is to demonstrate the use of Stereo Photogrammetry (SP) measuring shi... more The objective of this paper is to demonstrate the use of Stereo Photogrammetry (SP) measuring ship-generated waves and to determine under which conditions they are suitable for surfing. A physical experiment is conducted to gain insight in ship wave behavior under specific conditions. Waves are generated by a hull and are measured using SP. It is concluded that the SP technique holds great potential in laboratory use and ship waves can potentially be used for surfing purposes.
With the intention to reduce the negative effects of ongoing bed erosion, as well as to improve... more With the intention to reduce the negative effects of ongoing bed erosion, as well as to improve several other river functions such as protection against floods, provision of safe and efficient navigation and ecology, a ‘pilot project longitudinal training dams’ was initiated. The training dams have recently been implemented in the Waal between Tiel and Sind Andries. In this project, river groynes have been completely removed and replaced by dams that lie parallel to the river bank. With help of the longitudinal training dams, a two-channel river system is created in which the river is divided into a main and side channel. The dams are placed in a continuous manner with openings in between that are relatively small compared to the dam length. At the beginning and end of the dam an inlet and outlet region is situated, as shown in Fig. 1. The combination of inlet and openings allows for water and sediment to be divided between the main and the side channel. Both i...
Physical model tests were conducted to estimate the overtopping wave force acting on vertical wal... more Physical model tests were conducted to estimate the overtopping wave force acting on vertical walls which represented buildings on top of dikes. The result showed that the force can be related to the mean wave energy density and the dimensionless run-up height thereby accounting for the freeboard as it is present above the still water level.
Abstract Accurate rheological characterisation of sewage waste activated sludge (WAS) is of high ... more Abstract Accurate rheological characterisation of sewage waste activated sludge (WAS) is of high importance for downstream processing related to optimised sludge pumping and mixing, assessment of energy demands and overall process design. However, to elaborate rheological behaviour is often challenging under dynamic operational conditions in practice. In this study, two practical influencing factors were investigated: long-term shearing and temperature. Compared to anaerobic digestate (DGT), concentrated WAS had more complex and stronger thixotropic behaviour. Under the long-term shearing conditions, the sludge thixotropic behaviour was well characterised by two quantified limitation states. Temperature had a striking impact on the rheological properties, which was strongly correlated to solids content and digestion process. The impact discrepancy between the long-term shearing and temperature, implied different mechanisms to shift the equilibrium of hydrodynamic and non-hydrodynamic interactions for structure deformation and recovery. The distinct rheological properties between the two determined states were clearly reflected in pipe flow behaviour, revealing a concrete link between lab-measured sludge rheology and its practical flow performance. The pipe flows were well assessed using the developed Computational Fluid Dynamics model with effective rheological data integration, which is promising for practical design and optimisation of sewage sludge systems.
Breaching flow slides are accompanied by the generation of turbidity currents. Measurements of th... more Breaching flow slides are accompanied by the generation of turbidity currents. Measurements of these currents are critical for understanding the interaction between the turbidity current and the slope surface, as well as for the validation of numerical models. However, there are insufficient data available detailing the velocity distribution or sediment concentration in these currents. This paper presents experimental results of unique large‐scale physical model experiments on breaching flow slides conducted at the water lab of Delft University of Technology, The Netherlands. The model tests were carried out in a tank with a subaqueous sandy slope steeper than the internal friction angle for that sand. We performed a series of novel experiments in which various non‐vertical initial slope angles were tested, providing the first quantitative data for such initial conditions. Measurements of flow thickness, velocities, and sediment concentrations are obtained, providing the spatial and temporal evolution of the turbidity currents and the resulting underwater slope morphology. The experimental results reveal that the breaching‐generated turbidity currents are self‐accelerating, and that they dominate the problem of breaching flow slides. We evaluated the theoretical expression for the erosion velocity in the case of pure beaching ‐ where the turbidity current has no influence on the erosion ‐ and it overestimated the observed erosion. The analysis of the failure evolution showed that the sand erosion rate increases due to the acceleration of the turbidity currents downslope, until a certain threshold, leading to the steepening of the breach face and thus the occurrence of surficial slides.
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