scholarly journals Numerical Modeling of turbidity currents with Ansys CFX and Telemac 3D

2018 ◽  
Vol 40 ◽  
pp. 03014 ◽  
Author(s):  
Magali Jodeau ◽  
Sabine Chamoun ◽  
Jiawei Feng ◽  
Giovanni De Cesare ◽  
Anton J. Schleiss
Keyword(s):  
Numerical Modeling ◽  
Experimental Work ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Reservoir Sedimentation ◽  
Engineering Teams ◽  
Fine Sediments ◽  
First Case ◽  
Ansys Cfx

Turbidity currents may be a relevant lever to manage the accumulation of fine sediments in reservoirs. In this paper, we propose to show how two different numerical codes simulate the propagation of turbidity currents. Telemac 3D and Ansys CFX 17.1 solver were chosen as they are commonly used by many research and engineering teams. The simulations are performed on two configurations. The first case aims at modeling the plunging of a turbidity current. The second model is validated based on an experimental work performed at EPFL. The latter consisted on testing turbidity current venting as a solution to manage reservoir sedimentation. A long and narrow flume was used to simulate the reservoir where a turbidity current was triggered. The advantages and limits of both approaches are discussed in order to supply guidelines for the modeling of turbidity currents in real reservoirs.

scholarly journals Application of the adjoint approach to optimise the initial conditions of a turbidity current

2016 ◽  
Author(s):  
Samuel D. Parkinson ◽  
Simon W. Funke ◽  
Jon Hill ◽  
Matthew D. Piggott ◽  
Peter A. Allison
Keyword(s):  
Initial Conditions ◽  
Current Model ◽  
Deep Ocean ◽  
Turbidity Current ◽  
Significant Advance ◽  
Turbidity Currents ◽  
General Behaviour ◽  
Depositional Processes ◽  
Sediment Deposits ◽  
Adjoint Approach

Abstract. Turbidity currents are one of the main drivers for sediment transport from the continental shelf to the deep ocean. The resulting sediment deposits can reach hundreds of kilometres into the ocean. Computer models that simulate turbidity currents and the resulting sediment deposit can help to understand their general behaviour. However, in order to recreate real-world scenarios, the challenge is to find the turbidity current parameters that reproduce the observations of sediment deposits. This paper demonstrates a solution to the inverse sediment transportation problem: for a known sedimentary deposit, the developed model reconstructs details about the turbidity current that produced these deposits. The reconstruction is constrained here by a shallow water sediment-laden density current model, which is discretised by the finite element method and an adaptive time-stepping scheme. The model is differentiated using the adjoint approach and an efficient gradient-based optimisation method is applied to identify turbidity parameters which minimise the misfit between modelled and observed field sediment deposits. The capabilities of this approach are demonstrated using measurements taken in the Miocene-age Marnoso Arenacea Formation (Italy). We find that whilst the model cannot match the deposit exactly due to limitations in the physical processes simulated, it provides valuable insights into the depositional processes and represents a significant advance in our toolset for interpreting turbidity current deposits.

scholarly journals Modeling of Breaching-Generated Turbidity Currents Using Large Eddy Simulation

2020 ◽  
Vol 8 (9) ◽  
pp. 728
Author(s):  
Said Alhaddad ◽  
Lynyrd de Wit ◽  
Robert Jan Labeur ◽  
Wim Uijttewaal
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Large Eddy Simulation ◽  
Flow Characteristics ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Eddy Simulation ◽  
Failure Evolution ◽  
Large Eddy ◽  
Flow Slides

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 reproduced well, apart from the layer thickness. We also propose a breaching erosion model and validate it using the same series of experimental data. Quite good agreement is observed between the experimental data and the computed erosion rates. The numerical results confirm that breaching-generated turbidity currents are self-accelerating and indicate that they evolve in a self-similar manner.

Effects of tributary inflow and sediment input on reservoir turbidity current formation and evolution

2021 ◽  
Author(s):  
Yining Sun ◽  
Ji Li ◽  
Zhixian Cao ◽  
Alistair G.L. Borthwick
Keyword(s):  
Yellow River ◽  
Sediment Concentration ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Front Speed ◽  
Sediment Input ◽  
Formation And Evolution ◽  
Maximum Utilization

<p>For reservoirs built on a hyper-concentrated river, tributary inflow and sediment input may affect the formation and evolution of reservoir turbidity current, and accordingly bed morphology. However, the understanding of tributary effects on reservoir turbidity currents has remained poor. Here a series of laboratory-scale reservoir turbidity currents are investigated using a coupled 2D double layer-averaged shallow water hydro-sediment-morphodynamic model. It is shown that the tributary location may lead to distinctive effects on reservoir turbidity current. Clear-water flow from the tributary may cause the stable plunge point to migrate upstream, and reduce its front speed. Sediment-laden inflow from the tributary may increase the discharge, sediment concentration, and front speed of the turbidity current, and also cause the plunge point to migrate downstream when the tributary is located upstream of the plunge point. In contrast, if the tributary is located downstream of the plunge point, sediment-laden flow from the tributary causes the stable plunge point to migrate upstream, and while the tributary effects on discharge, sediment concentration, and front speed of the turbidity current are minor. A case study is presented as of the Guxian Reservoir (under planning) on the middle Yellow River, China. The present finding highlights the significance of tributary inflow and sediment input in the formation and propagation of reservoir turbidity current and also riverbed deformation. Appropriate account of tributary effects is warranted for long-term maintenance of reservoir capacity and maximum utilization of the reservoir.</p>

Essai d'interpretation du mecanisme des courants de turbidite

1962 ◽  
Vol S7-IV (6) ◽  
pp. 849-856
Author(s):  
Wladimir D. Nesteroff
Keyword(s):  
Fine Sand ◽  
Turbidity Current ◽  
Abyssal Plain ◽  
Upper Ocean ◽  
Turbidity Currents ◽  
Current Pulses ◽  
Coarse To Fine

Abstract When the mechanism of turbidity currents was first proposed, it was thought that ooze deposits, which alternated with coarse to fine sand, were deposited on abyssal plains by pelagic sedimentation between turbidity current pulses. Later it was thought that concentrations of calcareous bioclastic material in the upper part of the ooze pointed to turbidity current deposition of the sand and lower part of the ooze, with only the upper ooze a result of pelagic sedimentation. Because CaCO <sub>3</sub> tests dissolve in sinking, no calcareous tests of upper ocean origin are found below 5500 to 5600 m. However, a study of terrigenous turbidites from abyssal plain samples taken at depths exceeding 5900 m which follow the sand to ooze sequence with foraminiferal concentrations in the upper ooze demonstrate that the beds are turbidite alone. It is hypothesized that any pelagic deposits forming between turbidity currents would be eroded away at the beginning of each pulse and that the fossil concentrations in the upper ooze result from delayed settling of the gas or protoplasm filled tests.

Three-dimensional numerical simulation of the turbidity current on a flume slope

2020 ◽  
Author(s):  
Ruoyin Zhang ◽  
Baosheng Wu ◽  
Y. Joseph Zhang
Keyword(s):  
Sediment Transport ◽  
Open Channel ◽  
Sediment Concentration ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Concentration Profiles ◽  
Time Step ◽  
Densimetric Froude Number ◽  
Plunge Depth ◽  
Inflow Conditions

<p>Density-driven gravity flows frequently occur in nature, due to density difference between inflowing and ambient water. When a sediment-laden flow reaches the backwater zone of a reservoir, with a greater density than the ambient waters, an underflow can occur along steep bottom slopes. The formation and evolution of an underflow depend on various natural conditions. It is necessary and crucial for reservoir management to understand the dynamics and prediction of the turbidity currents. In addition to field investigation and laboratory experiments, numerical models are gaining popularity for solving open-channel flows and sediment transport processes such as turbidity currents in reservoirs.</p><p>SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) is a 3D seamless cross-scale model grounded on unstructured grids for hydrodynamics and ecosystem dynamics. A general set of governing equations are used for the flow and tracer transport, and a new higher-order implicit advection scheme for transport (TVD<sup>2</sup>) is proposed. A mixed triangular-quadrangular horizontal grid and a highly flexible vertical grid system are developed in the model to faithfully represent complex geometry and topography of environmental flows in open channel cases. SCHISM has found a wide range of cross-scale applications worldwide including general circulation, storm surges, sediment transport and so on. However, the feasibility of simulating turbidity currents caused by sediment-laden flows in a reservoir is rarely validated. In this study, SCHISM is applied to a lab experiment to simulate the turbidity currents on a flume slope to examine how the model predicts the hydraulic characteristics of turbidity currents in a reservoir.</p><p>Model results can describe the process of the turbidity current plunging beneath the free surface with the time step of 0.1s. It is relatively uncommon in previous studies to clearly show the evolution of the velocity and sediment concentration profiles in such a short time step. The simulated velocity and sediment concentration profiles of the turbidity currents match well with the measured profiles at the cross section downstream of the plunge point. The calculated depth-averaged velocity, thickness, and depth-averaged concentration of the turbidity current all agree well with the measured values. The correlation coefficient between the measured and calculated values is 0.92, 0.95, and 0.94, respectively. Also, the densimetric Froude number of the stable plunge point is found to be approximately 0.54 in this study, which is between 0.5 and 0.8 based on previous research. The plunge depth is smaller with higher sediment concentration and smaller discharge of the inflow. Besides, the ratio of plunge depth to inlet depth is proportional to the densimetric Froude number of inflow conditions. This finding can be used to predict the depth and location of the plunge point based on the inflow conditions in a reservoir, which has great practical implications in reservoir management. Our results demonstrated that SCHISM is generally applicable to simulate the turbidity currents in small-scale water environments, and has the potential to be adopted in large-scale open water environments.</p>

scholarly journals Field-scale numerical modeling of breaching as a mechanism for generating continuous turbidity currents

Geosphere ◽  
2011 ◽  
Vol 7 (5) ◽  
pp. 1063-1076 ◽  
Author(s):  
Esther Eke ◽  
Enrica Viparelli ◽  
Gary Parker
Keyword(s):  
Numerical Modeling ◽  
Turbidity Currents ◽  
Field Scale

scholarly journals Slow build-up of turbidity currents triggered by a moderate earthquake in the Sea of Marmara

2021 ◽  
Author(s):  
Pierre Henry ◽  
Sinan Özeren ◽  
Nurettin Yakupoğlu ◽  
Ziyadin Çakir ◽  
Emmanuel de Saint-Léger ◽  
...  
Keyword(s):  
Sediment Resuspension ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Central Basin ◽  
Sea Of Marmara ◽  
Sedimentary Records ◽  
Strong Current ◽  
Moderate Earthquake ◽  
Basin Floor ◽  
Hydrodynamic Processes

Abstract. Earthquake-induced submarine slope destabilization is known to cause debris flows and turbidity currents, but the hydrodynamic processes associated with these events remain poorly understood. Records are scarce and this notably limits our ability to interpret marine paleoseismological sedimentary records. An instrumented frame comprising a pressure recorder and a Doppler recording current meter deployed at the seafloor in the Sea of Marmara Central Basin recorded consequences of a MW = 5.8 earthquake occurring Sept 26, 2019 and of a Mw = 4.7 foreshock two days before. The smaller event caused sediment resuspension but no strong current. The larger event triggered a complex response involving a mud flow and turbidity currents with variable velocities and orientations, which may result from multiple slope failures. A long delay of 10 hours is observed between the earthquake and the passing of the strongest turbidity current. The distance travelled by the sediment particles during the event is estimated to several kilometres, which could account for a local deposit on a sediment fan at the outlet of a canyon, but not for the covering of the whole basin floor. We show that after a moderate earthquake, delayed turbidity current initiation may occur, possibly by ignition of a cloud of resuspended sediment. Some caution is thus required when tying seismoturbidites with earthquakes of historical importance. However, the horizontal extent of the deposits should remain indicative of the size of the earthquake.

scholarly journals TURBIDITY - SEDIMENTATION IN CLOSED-END CHANNELS

1986 ◽  
Vol 1 (20) ◽  
pp. 98
Author(s):  
Chung-Po Lin ◽  
Jonathon W. Lott ◽  
Ashish J. Mehta
Keyword(s):  
Exponential Type ◽  
Settling Velocity ◽  
Gravity Currents ◽  
Turbidity Current ◽  
Main Channel ◽  
Turbidity Currents ◽  
Test Results ◽  
Fine Grained ◽  
Gate Opening ◽  
Sediment Settling

In order to investigate the mechanism by which turbidity currents cause sedimentation in closed-end channels such as pier slips or residential canals, a laboratory investigation using fine-grained sediments was carried out. Two similar flume systems were used, each consisting of a main channel carrying sediment-laden flow and an orthogonally placed closed-end channel with a gate at the entrance. Characteristics of the turbidity current and sediment deposition in the closed-end channel were investigated following gate opening. Behavioral similarities between turbidity current and non-settling gravity currents were observed. Several properties, e.g. suspension concentration, showed exponential-type decay with distance. The ratio of sediment settling velocity to the densimetric velocity was found to be a useful parameter for comparing different test results. A relationship for estimating the sediment influx through the entrance is presented.

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