scholarly journals High vertical shear and dissipation in equatorial topographic wakes

2021 ◽  
Author(s):  
Kaushik Srinivasan ◽  
James C. McWilliams ◽  
Arjun Jagannathan
Keyword(s):  
Energy Dissipation ◽  
Evolution Equations ◽  
Energy Dissipation Rate ◽  
Maximum Energy ◽  
Vertical Shear ◽  
Near Wake ◽  
Wake Structure ◽  
Barotropic Flow ◽  
Bottom Boundary Layers ◽  
The Tropics

AbstractSubmesoscale coherent vortices (SCVs) are a ubiquitous feature of topographic wakes in the extratropical oceans. Recent studies demonstrate a mechanism wherein high vorticity bottom boundary layers (BBLs) on the slopes of the topography separate (forming shear layers), undergo instabilities, and subsequently merge in the horizontal and align in the vertical to form vertically coherent, columnar, SCVs (i.e. with low vertical shear). Background rotation is critical to the vertical alignment of unstable vortical filaments into coherent SCVs. In the tropics, however, the weakening of rotation prevents this alignment. Employing an idealized framework of steady barotropic flow past an isolated seamount in a background of constant stratification N and rotation rate f, we examine the wake structure for a range of f values spanning values from the poles to the tropics. We find a systematic increase in the interior vertical shear with decreasing f that manifests as a highly layered wake structure consisting of vertically thin, ‘pancake’ SCVs possessing a high vertical shear. A monotonic increase in the wake energy dissipation rate is concomitantly observed with decreasing f. By examining the evolution equations for the vertical shear and vertical enstrophy, we find that the interior shear generation is an advective process, with the location of peak shear generation approximately colocated with maximum energy dissipation. This leads to the inference that high wake dissipation in tropical tropographic wakes is caused by parameterized shear instabilities induced by interior advective generation of vertical shear in the near wake region.

scholarly journals Numerical Simulation of Stepped Spillways with Front Step Deformation

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Guodong Li ◽  
Haifeng Zhang ◽  
Xingnan Li ◽  
Lihao Guo ◽  
Yanyan Gao ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Energy Dissipation ◽  
Water Flow ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Maximum Energy ◽  
Single Step ◽  
Stepped Spillway ◽  
Flow State ◽  
Front Step

In order to solve the flood discharge problem of both small- and medium-sized warping dams in the Loess Plateau, a stepped spillway scheme, based on an ecological bag, to achieve full-section water flow and energy dissipation has been proposed in this paper. The hydraulic and energy dissipation characteristics of a stepped spillway layout scheme were studied using 3D numerical simulation. As the height of the dams is low and the spillways are short, the research has shown that the traditional single-step layout scheme leads to a low overall energy dissipation rate due to the small amount of energy dissipated in the initial steps. As a result of this, this paper has put forward two kinds of step layout schemes such as the shunt type and the staggered type for the initial steps. Through analysis of the flow state, the pressure distribution, and the total energy dissipation rate, the results have shown that shunt type and staggered type with front step deformation produced an obvious mixing of the water flow, fewer negative pressure areas, and a higher energy dissipation rate. The optimal energy dissipation rate of the staggered type reached 87.75%, and the maximum energy dissipation rate was increased by 27.97%.

scholarly journals The Influence of Whitecapping Waves on the Vertical Structure of Turbulence in a Shallow Estuarine Embayment

2008 ◽  
Vol 38 (7) ◽  
pp. 1563-1580 ◽  
Author(s):  
Nicole L. Jones ◽  
Stephen G. Monismith
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Water Column ◽  
Turbulent Kinetic Energy ◽  
San Francisco ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Breaking Wave ◽  
Bottom Boundary Layers

Abstract The vertical distribution of the turbulent kinetic energy dissipation rate was measured using an array of four acoustic Doppler velocimeters in the shallow embayment of Grizzly Bay, San Francisco Bay, California. Owing to the combination of wind and tide forcing in this shallow system, the surface and bottom boundary layers overlapped. Whitecapping waves were generated for a significant spectral peak steepness greater than 0.05 or above a wind speed of 3 m s−1. Under conditions of whitecapping waves, the turbulent kinetic energy dissipation rate in the upper portion of the water column was greatly enhanced, relative to the predictions of wind stress wall-layer theory. Instead, the dissipation followed a modified deep-water breaking-wave scaling. Near the bed (bottom 10% of the water column), the dissipation measurements were either equal to or less than that predicted by wall-layer theory. Stratification due to concentration gradients in suspended sediment was identified as the likely cause for these periods of production–dissipation imbalance close to the bed. During 50% of the well-mixed conditions experienced in the month-long experiment, whitecapping waves provided the dominant source of turbulent kinetic energy over 90% or more of the water column.

scholarly journals A Study of the Conditions of Energy Dissipation in Stepped Spillways with Λ-shaped step Using FLOW-3D

2017 ◽  
Vol 3 (10) ◽  
pp. 856 ◽  
Author(s):  
Abbas Mansoori ◽  
Shadi Erfanian ◽  
Farhad Khamchin Moghadam
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Mesh Networks ◽  
Maximum Flow ◽  
Energy Dissipation Rate ◽  
Maximum Energy ◽  
Trial And Error ◽  
Stepped Spillways ◽  
Flow Energy ◽  
Proposed Model

In the present study, energy dissipation was investigated in a specific type of stepped spillways. The purpose was to achieve the highest level of energy dissipation in downstream of the spillway. It was performed by providing a specific type of geometry for step as a great roughness. Here, steps were recognized as great roughness against flow. Their shape and number were designed in such a way that the maximum flow energy can be minimized in this stage, i.e. over steps before reaching to downstream. Accordingly, it can be stated that the highest energy dissipation rate will be obtained in the structure at downstream. Moreover, thereby, heavy costs imposed by designing and constructing stilling basin on project can be minimized. In this study, FLOW-3D was employed to analyse and obtain energy dissipation rate. The best geometry of the steps, through which the maximum energy dissipation can be achieved, was determined by reviewing related literature and inventing the proposed model in FLOW-3D. To evaluate the proposed method, analyses were performed using trial and error in mesh networks sizes as well as the mentioned methods and the results were compared to other studies. In other words, the most optimal state was obtained with Λ-shaped step at angel of 25 degree with respect to energy dissipation rate compare to smooth step.

scholarly journals Experimental investigation of hydraulic characteristics and energy dissipation in a baffle-drop shaft

2020 ◽  
Vol 82 (8) ◽  
pp. 1603-1613
Author(s):  
Qinghua Yang ◽  
Qian Yang
Keyword(s):  
Energy Dissipation ◽  
Dissipation Rate ◽  
Reverse Flow ◽  
Energy Dissipation Rate ◽  
Maximum Energy ◽  
Optimal Size ◽  
Discharge Process ◽  
Drop Shaft ◽  
The Impact ◽  
Inflow Discharge

Abstract The baffle-drop shaft structure is usually applied in deep tunnel drainage systems to transfer shallow storm water to underground tunnels. At present, the definition of the maximum operational capacity of baffle-drop shafts is lack of scientific and reasonable analysis, and the researches on hydraulic and energy dissipation characteristics have been insufficient. In this paper, a 1:25 scale hydraulic model test was conducted to observe the flow phenomena during the discharge process, analyze the relationship between the maximum inflow discharge and the baffle parameters, and calculate the energy dissipation rate of the shaft under different flow conditions. The results demonstrated that three kinds of flow regimes were presented in the discharge process: wall-impact confined flow, critical flow, and free-drop flow. The impact wave majorly brought about the energy dissipation of water on the baffle. The impingement and breakup of the inflow at the bottom of the drop shaft, as well as the reverse flow, resulted in the final energy loss. The time-averaged pressure value of the upper baffle was 1.5–3 times that of the central and lower baffles. The baffle with a design angle could effectively reduce the time-averaged pressure of the water flow acting on the baffle. The energy dissipation rate of the drop shaft decreased with the increase in the inflow discharge, and the energy dissipation rate was found to range from about 63.14% to 96.40%. The optimal size of the baffle-drop shaft with the maximum energy dissipation rate was d/B = 0.485 and θ = 10° (d, B, and θ are the baffle spacing, width, and angle, respectively).

scholarly journals Comment on “Using an ADCP to Estimate Turbulent Kinetic Energy Dissipation Rate in Sheltered Coastal Waters”

2017 ◽  
Vol 34 (6) ◽  
pp. 1387-1390 ◽  
Author(s):  
Ann E. Gargett
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Vertical Velocity ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Vertical Shear ◽  
Length Scale ◽  
Ocean Turbulence ◽  
Large Eddy

AbstractGreene et al. revisit the suggestion that the turbulent kinetic energy dissipation rate could be estimated through a “large-eddy estimate,” employing acoustic measurements of velocity fields associated with the largest energy-containing scales of ocean turbulence. While the large-eddy estimate as originally proposed used vertical velocity and a vertical eddy length scale, Greene et al. chose instead to substitute a horizontal length scale for the latter. This comment argues that combining a horizontal scale for length with a vertical velocity scale produces a large-eddy estimate of the dissipation rate that is accurate only if the energy-containing eddies are isotropic, and that this condition is highly unlikely in naturally occurring ocean turbulence, subject as it is to influences of stratification, vertical shear, and/or the presence of horizontal boundaries. The problem is documented using data from a large-eddy simulation of Langmuir supercells.

Energy dissipation rate in a baffled vessel with pitched blade turbine impeller

1991 ◽  
Vol 56 (9) ◽  
pp. 1856-1867 ◽  
Author(s):  
Zdzisław Jaworski ◽  
Ivan Fořt
Keyword(s):  
Energy Dissipation ◽  
Cross Sections ◽  
Mechanical Energy ◽  
Vessel Diameter ◽  
Energy Dissipation Rate ◽  
Mean Velocity ◽  
Agitated Vessel ◽  
Radial Profiles ◽  
Pitched Blade Turbine ◽  
Turbine Impeller

Mechanical energy dissipation was investigated in a cylindrical, flat bottomed vessel with four radial baffles and the pitched blade turbine impeller of varied size. This study was based upon the experimental data on the hydrodynamics of the turbulent flow of water in an agitated vessel. They were gained by means of the three-holes Pitot tube technique for three impeller-to-vessel diameter ratio d/D = 1/3, 1/4 and 1/5. The experimental results obtained for two levels below and two levels above the impeller were used in the present study. Radial profiles of the mean velocity components, static and total pressures were presented for one of the levels. Local contribution to the axial transport of the agitated charge and energy was presented. Using the assumption of the axial symmetry of the flow field the volumetric flow rates were determined for the four horizontal cross-sections. Regions of positive and negative values of the total pressure of the liquid were indicated. Energy dissipation rates in various regions of the agitated vessel were estimated in the range from 0.2 to 6.0 of the average value for the whole vessel. Hydraulic impeller efficiency amounting to about 68% was obtained. The mechanical energy transferred by the impellers is dissipated in the following ways: 54% in the space below the impeller, 32% in the impeller region, 14% in the remaining part of the agitated liquid.

scholarly journals Experimental and Numerical Analysis of the Mechanical Properties of a Pretreated Shape Memory Alloy Wire in a Self-Centering Steel Brace

Processes ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 80
Author(s):  
Bo Zhang ◽  
Sizhi Zeng ◽  
Fenghua Tang ◽  
Shujun Hu ◽  
Qiang Zhou ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Energy Dissipation ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Loading Rate ◽  
Effective Elastic Modulus ◽  
Maximum Energy ◽  
Numerical Results ◽  
Energy Dissipation Capacity

As a stimulus-sensitive material, the difference in composition, fabrication process, and influencing factors will have a great effect on the mechanical properties of a superelastic Ni-Ti shape memory alloy (SMA) wire, so the seismic performance of the self-centering steel brace with SMA wires may not be accurately obtained. In this paper, the cyclic tensile tests of a kind of SMA wire with a 1 mm diameter and special element composition were tested under multi-working conditions, which were pretreated by first tensioning to the 0.06 strain amplitude for 40 cycles, so the mechanical properties of the pretreated SMA wires can be simulated in detail. The accuracy of the numerical results with the improved model of Graesser’s theory was verified by a comparison to the experimental results. The experimental results show that the number of cycles has no significant effect on the mechanical properties of SMA wires after a certain number of cyclic tensile training. With the loading rate increasing, the pinch effect of the hysteresis curves will be enlarged, while the effective elastic modulus and slope of the transformation stresses in the process of loading and unloading are also increased, and the maximum energy dissipation capacity of the SMA wires appears at a loading rate of 0.675 mm/s. Moreover, with the initial strain increasing, the slope of the transformation stresses in the process of loading is increased, while the effective elastic modulus and slope of the transformation stresses in the process of unloading are decreased, and the maximum energy dissipation capacity appears at the initial strain of 0.0075. In addition, a good agreement between the test and numerical results is obtained by comparing with the hysteresis curves and energy dissipation values, so the numerical model is useful to predict the stress–strain relations at different stages. The test and numerical results will also provide a basis for the design of corresponding self-centering steel dampers.

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