EXPERIMENTS ON DENSITY AND TURBIDITY CURRENTS: I. MOTION OF THE HEAD

1966 ◽  
Vol 3 (4) ◽  
pp. 523-546 ◽  
Author(s):  
Gerard V. Middleton
Keyword(s):  
Turbidity Current ◽  
Turbidity Currents ◽  
Density Current ◽  
Density Currents ◽  
Salt Solutions ◽  
Overlying Water ◽  
Numerical Coefficient ◽  
Series Of Experiments ◽  
The Difference ◽  
Clay Suspensions

Two series of experiments were performed in a lucite flume 5 meters long, 50 cm deep, and 15.4 cm wide. In the first series saline density currents were formed by pumping salt solutions at constant discharge into the tilted flume. In the second series, the flume was horizontal and turbidity currents were formed by the releasing of suspensions of plastic beads from a box at one end.In both series of experiments a characteristic head was formed at the front of the flow. It was found that the motion of the head in the turbidity current experiments was closely described by laws developed by Keulegan (1958) for saline surges, and it is concluded that certain aspects of the motion of turbidity current heads can be investigated indirectly by means of experiments on density currents formed from clay suspensions or salt solutions.The salt-solution experiments were designed to investigate the effect of bottom slope on the motion of density current heads. It was found that the velocity of density (and by inference, turbidity) current heads on slopes up to 4% is adequately expressed by Keulegan's formula[Formula: see text]where v is the velocity of the head, Δρ is the difference between the density of the current (ρ) and that of the overlying water, d2 is the thickness of the head, and g is the acceleration due to gravity. The numerical coefficient is approximately constant, but may increase slightly with increase in slope. The form of the equation differs greatly from that of the Chézy equation which has previously been used for the analysis of the movement of turbidity currents.Observations were also made regarding the shape of the head and the motion within and in front of the head.

3-D Simulation of Conservative and Non-Conservative Density Current

2006 ◽  
Author(s):  
S. Hormozi ◽  
B. Firoozabadi ◽  
H. Ghasvari Jahromi ◽  
S. M. H. Moosavi Hekmati
Keyword(s):  
Flow Structure ◽  
Environmental Flows ◽  
Three Dimensional ◽  
Turbidity Currents ◽  
Density Current ◽  
Density Currents ◽  
Straight Channel ◽  
Suspended Material ◽  
Series Of Experiments ◽  
Good Agreement

Flows generated by density differences are called gravity or density currents which are generic features of many environmental flows. These currents are classified as the conservative and non-conservative flows whether the buoyancy flux is conserved or changed respectively. In this paper, a low Reynolds k-ε turbulence model is used to simulate three dimensional density and turbidity currents. Also, a series of experiments were conducted in a straight channel to study the characteristics of the non-conservative density current. In experiments, Kaolin was used as the suspended material. Comparisons are made between conservative and non-conservative's height, concentration and velocity profiles of the current and their variations along the transverse intersections. Outcomes indicate that the presence of the particles influences the flow structure sensibly. The results are compared with the experiments and showed a good agreement.

scholarly journals Effects of morphology in controlling propagation of density currents in a reservoir using uncalibrated three-dimensional hydrodynamic modeling

2020 ◽  
Author(s):  
Behnam Zamani ◽  
Manfred Koch ◽  
Ben R. Hodges
Keyword(s):  
Hydrodynamic Model ◽  
Large Scale ◽  
Three Dimensional ◽  
Density Current ◽  
Density Currents ◽  
Large Reservoir ◽  
Bottom Water Temperature ◽  
The Difference ◽  
Basin Morphology ◽  
Southwest Iran

In this study, effects of basin morphology are shown to affect density current hydrodynamics of a large reservoir using a three-dimensional (3D) hydrodynamic model that is validated (but not calibrated) with in situ observational data. The AEM3D hydrodynamic model was applied for 5-month simulations during winter and spring flooding for the Maroon reservoir in southwest Iran, where available observations indicated that large-scale density currents had previously occurred. The model results were validated with near-bottom water temperature measurements that were previously collected at five locations in the reservoir. The Maroon reservoir consists of upper and lower basins that are connected by a deep and narrow canyon. Analyses of simulations show that the canyon strongly affects density current propagation and the resulting differing limnological characteristics of the two basins. The evolution of the Wedderburn Number, Lake Number, and Schmidt stability number are shown to be different in the two basins, and the difference is attributable to the morphological separation by the canyon. Investigation of the background potential energy (BPE) changes along the length of the canyon indicated that a density front passes through the upper section of the canyon but is smoothed into simple filling of the lower basin. The separable dynamics of the basins has implications for the complexity of models needed for representing both water quality and sedimentation.

EXPERIMENTS ON DENSITY AND TURBIDITY CURRENTS: II. UNIFORM FLOW OF DENSITY CURRENTS

1966 ◽  
Vol 3 (5) ◽  
pp. 627-637 ◽  
Author(s):  
Gerard V. Middleton
Keyword(s):  
Reynolds Number ◽  
Average Velocity ◽  
Large Scale ◽  
Quantitative Estimation ◽  
Uniform Flow ◽  
Turbidity Currents ◽  
Density Current ◽  
Density Currents ◽  
Review Of The Literature ◽  
Fluid Interface

The basic theory for the average velocity of uniform flow of a density current is now well established. The resistance at the bottom may be estimated from reasonable assumptions regarding the roughness of the bottom and the size of the current. The principal problem remaining is quantitative estimation of the resistance of the upper (fluid) interface. A review of the literature suggests that this resistance increases with increase in Froude number and decreases with increase in Reynolds number, and the writer's experiments support this hypothesis.As many turbidity currents are large scale and flow over low slopes of relatively small roughness it seems probable that both the bottom resistance and the resistance at the upper interface are small.

Comparison of 2-D Turbulent Particle Laden Density Current and Wall Jets

2006 ◽  
Author(s):  
S. Hormozi ◽  
B. Firoozabadi ◽  
H. Ghasvari Jahromi ◽  
H. Afshin
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Suspended Solids ◽  
Turbidity Currents ◽  
Density Current ◽  
Wall Jet ◽  
Density Currents ◽  
Ambient Water ◽  
Wall Jets ◽  
Good Agreement

Dense underflows are continuous currents, which move down the slope due to the fact that, their density are heavier than ambient water. In turbidity currents the density differences arises from suspended solids. Vicinity of the wall make density currents and wall jets similar in some sense but Variation of density cause this flows more complex than wall jets. An improved form of ‘near-wall’ k-ε turbulence model is chosen which preserve all characteristics of both density and wall jet currents and a compression is made between them. Then the outcomes from low Reynolds number k-ε model is compared with v2–f model which show similarity. Also results show good agreement with experimental data.

scholarly journals Direct numerical simulations of particle-laden density currents with adaptive, discontinuous finite elements

2014 ◽  
Vol 7 (3) ◽  
pp. 3219-3264 ◽  
Author(s):  
S. D. Parkinson ◽  
J. Hill ◽  
M. D. Piggott ◽  
P. A. Allison
Keyword(s):  
High Resolution ◽  
Numerical Simulations ◽  
Turbidity Current ◽  
Direct Numerical Simulations ◽  
Three Dimensions ◽  
Turbidity Currents ◽  
Normal Velocity ◽  
Density Currents ◽  
Conservation Of Energy ◽  
Computationally Expensive

Abstract. High resolution direct numerical simulations (DNS) are an important tool for the detailed analysis of turbidity current dynamics. Models that resolve the vertical structure and turbulence of the flow are typically based upon the Navier–Stokes equations. Two-dimensional simulations are known to produce unrealistic cohesive vortices that are not representative of the real three-dimensional physics. The effect of this phenomena is particularly apparent in the later stages of flow propagation. The ideal solution to this problem is to run the simulation in three dimensions but this is computationally expensive. This paper presents a novel finite-element (FE) DNS turbidity current model that has been built within Fluidity, an open source, general purpose, computational fluid dynamics code. The model is validated through re-creation of a lock release density current at a Grashof number of 5 × 106 in two, and three-dimensions. Validation of the model considers the flow energy budget, sedimentation rate, head speed, wall normal velocity profiles and the final deposit. Conservation of energy in particular is found to be a good metric for measuring mesh performance in capturing the range of dynamics. FE models scale well over many thousands of processors and do not impose restrictions on domain shape, but they are computationally expensive. Use of discontinuous discretisations and adaptive unstructured meshing technologies, which reduce the required element count by approximately two orders of magnitude, results in high resolution DNS models of turbidity currents at a fraction of the cost of traditional FE models. The benefits of this technique will enable simulation of turbidity currents in complex and large domains where DNS modelling was previously unachievable.

scholarly journals Experimental observation of saline underflows and turbidity currents, flowing over rough beds

2015 ◽  
Vol 42 (11) ◽  
pp. 834-844 ◽  
Author(s):  
Peyman Varjavand ◽  
Mehdi Ghomeshi ◽  
Ali Hosseinzadeh Dalir ◽  
Davood Farsadizadeh ◽  
Alireza Docheshmeh Gorgij
Keyword(s):  
Cross Sections ◽  
Turbidity Currents ◽  
Density Current ◽  
Normal Velocity ◽  
Density Currents ◽  
Transport Mechanisms ◽  
Maximum Value ◽  
Bed Roughness ◽  
Rough Beds ◽  
Peak Value

Density currents are formed when gravity acts upon a density difference between two different fluids, and the driving force is the buoyancy force. These currents are the most important transport mechanisms and deposition of noncohesive sediments in narrow and deep reservoirs. In this research, 126 experiments were performed to investigate the effects of artificial bed roughness on saline and sediment-laden density currents. Conic and cylindrical shapes of roughness were used with three different heights. Velocity and concentration profiles were measured in 4 and 3 cross-sections, respectively. Presence of roughness causes increasing density current body thickness, decreasing maximum value of velocity and increasing distance of peak value of velocity point from the bed in the normal velocity profile. Coefficient of entrainment in the rough beds was more than in smooth beds and increased for greater roughness heights. A special behavior, referred to as “lifting phenomenon”, was present in some of the tests and which had an effect on the velocity profiles.

Non-steady variations of SOD and phosphate release rate due to changes in the quality of the overlying water

2000 ◽  
Vol 42 (3-4) ◽  
pp. 265-272 ◽  
Author(s):  
T. Inoue ◽  
Y. Nakamura ◽  
Y. Adachi
Keyword(s):  
Release Rate ◽  
Oxygen Demand ◽  
Phosphate Concentration ◽  
Sediment Oxygen Demand ◽  
Biochemical Reactions ◽  
Overlying Water ◽  
Phosphate Release ◽  
Do Concentration ◽  
The Difference

A dynamic model, which predicts non-steady variations in the sediment oxygen demand (SOD) and phosphate release rate, has been designed. This theoretical model consists of three diffusion equations with biochemical reactions for dissolved oxygen (DO), phosphate and ferrous iron. According to this model, step changes in the DO concentration and flow velocity produce drastic changes in the SOD and phosphate release rate within 10 minutes. The vigorous response of the SOD and phosphate release rate is caused by the difference in the time scale of diffusion in the water boundary layer and that of the biochemical reactions in the sediment. Secondly, a negative phosphate transfer from water to sediment can even occur under aerobic conditions. This is caused by the decrease in phosphate concentration in the aerobic layer due to adsorption.

Polyamine-mediated regulation of mouse ornithine decarboxylase is posttranslational

1989 ◽  
Vol 9 (12) ◽  
pp. 5484-5490
Author(s):  
T van Daalen Wetters ◽  
M Macrae ◽  
M Brabant ◽  
A Sittler ◽  
P Coffino
Keyword(s):  
Ornithine Decarboxylase ◽  
Translational Regulation ◽  
Feedback Inhibition ◽  
Chimeric Protein ◽  
Sequence Information ◽  
Pulse Label ◽  
Protein Coding ◽  
Coding Sequence ◽  
Series Of Experiments ◽  
The Difference

The activity of ornithine decarboxylase (ODC) is negatively regulated by intracellular polyamines, which thereby mediate a form of feedback inhibition of the initial enzyme in the pathway of their synthesis. This phenomenon has been believed to result, at least in part, from translational regulation. To investigate this further, we performed four series of experiments. First, we found that a chimeric protein encoded by an mRNA containing the ODC 5' leader sequence did not exhibit polyamine-dependent regulation. Second, we showed that transcripts containing the protein-coding sequence of ODC, but no other ODC-derived sequence information, exhibited regulation. Third, we found that the association of ODC mRNA with ribosomes was not altered when intracellular polyamine levels were modulated under conditions previously deemed to cause translational regulation. Last, we carried out experiments to measure the incorporation of [35S]methionine into ODC in polyamine-starved and polyamine-replete cells. Differential incorporation diminished progressively as pulse-label times were shortened; at the shortest labeling time used (4 min), the difference in favor of ODC in polyamine-starved cells was less than twofold. These findings suggest that it is necessary to reevaluate the question of whether polyamines cause alterations of translation of ODC mRNA.

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.

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