Downstream Side Research Articles

On the Optimum Layout of a Drainage Gallery in Concrete Gravity Dams On Isotropic Foundation

ABSTRACT This study investigates the optimum location of drainage galleries of concrete gravity dams under usual, unusual, and extreme loading conditions. The uplift and the stress distributions were computed using the gravity method and the beam theory, whereas the leakage rate into the gallery was determined by the finite-element method. The results show that the presence of a drainage gallery can reduce the uplift by over 60 percent compared to a non-drained case. The suitable gallery location shifts toward the upstream if the drain diameter increases and the spacing decreases. This is consistent with previous research. As the gallery is moved toward the downstream, the crack length decreases; however, this increases the uplift. The most effective solution is found to be placing the gallery 10 percent of the base width away from the heel and at the downstream water level or below and adding post-tension cables on the downstream side. This option also yields lower pumping costs by reducing the pump head.

Determination of Heavy Metals in Waters of Lower River Kuywa

Heavy metals are required by the biological organisms as nutrients but their availability above certain limits leads to adverse conditions such as bone, nerve and internal body organs damage like liver, high blood pressure, acute poisoning and death in animals and human beings and reduction of photosynthesis production, inhibition of seed germination and decreased crop yield in plants. River Kuywa being in a rich inorganic farming of sugarcane and maize area as well as industrial and urban environment, it is exposed to pollution. The objective was to determine the levels of heavy metal concentration using an Atomic absorption spectrometer and the effects of physicochemical parameters to the metal ions concentration which could arise from pollution. Temperature, pH, electrical conductivity and total dissolved solids were found to be (22.9, 23.3 C̊), (7.19, 4.34), (312.43, 318.45 µS) and (201, 204 mg/L) for upstream and downstream side of pollutants entry point respectively. Chromium, Copper and Zinc ions had relatively high concentrations compared to Cadmium ions. Lead ions were below the detection limit. Chromium, Copper and Zinc had (0.2660 ppm, 0.4276 ppm), (0.1306 ppm, 0.085 ppm) and (0.1369 ppm, 0.1395 ppm) while Cadmium had (0.0684 ppm, 0.0513 ppm) for upstream and downstream respectively. All physicochemical parameters were within WHO limits except pH. Chromium and Cadmium concentrations were above WHO limits while Copper and Zinc were below. Chromium had elevated concentration compared to other metals. There should be continuous and close monitoring of Chromium levels by reducing the factors leading to high rate of rock weathering and leaching. The water having Chromium and Cadmium concentrations above recommended limits, it should be treated first for Quality Assurance before it is consumed. Agencies like NEMA and WARMA should increase water quality surveillance operations for surface water.

Mapping Electron Temperature Variations across a Spiral Arm in NGC 1672

Abstract We report one of the first extragalactic observations of electron temperature variations across a spiral arm. Using Multi Unit Spectroscopic Explorer mosaic observations of the nearby galaxy NGC 1672, we measure the [N ii]λ5755 auroral line in a sample of 80 H ii regions in the eastern spiral arm of NGC 1672. We discover systematic temperature variations as a function of distance perpendicular to the spiral arm. The electron temperature is lowest on the spiral arm itself and highest on the downstream side. Photoionization models of different metallicity, pressure, and age of the ionizing source are explored to understand what properties of the interstellar medium drive the observed temperature variations. An azimuthally varying metallicity appears to be the most likely cause of the temperature variations. The electron temperature measurements solidify recent discoveries of azimuthal variations of oxygen abundance based on strong lines, and rule out the possibility that the abundance variations are artifacts of the strong-line calibrations.

Stability of supported geomembrane tube flood barriers of novel design

AbstractGeomembrane tube is an alternative method for the construction of flood barriers, cofferdams and breakwaters for flood risk management. Compared to the traditional method of using sandbags to build flood barriers, geomembrane tubes could be inflated very quickly using water, folded and transported easily after the flood recedes and reused in the future. A method of inserting the L‐shaped block on the downstream side of a geomembrane tube is proposed to prevent the geomembrane tubes from rolling off or slipping along the ground surface. Numerical studies using particle flow code (PFC2D) software are carried out to analyse the behaviour of the geomembrane tube supported by L‐shaped blocks. Parametric studies are also conducted to identify the influences from the key factors and to provide predictive charts for practical usage. It is found that the optimum edge length of the L‐shaped block is 0.12L and the suggested initial pumping pressure is 0.162γL where L is the cross‐sectional perimeter of the geomembrane tube and γ is the unit weight of the filling liquid. The suggested central angle of the segment of the L‐shaped block is π/3. The geomembrane tube designed using the suggested parameters can sustain and external water level of 0.296L.

Experimental Study on a Diesel Particulate Filter with Reciprocating Flow.

In this article, a new diesel particulate filter (DPF) system with reciprocating flow is proposed, and an experimental study on the characteristics of the active–passive component regeneration of the DPF system is carried out. Several control parameters such as temperature distribution, pressure difference, and pollution emissions of the DPF system are measured for different reciprocating cycles. The mechanism of reciprocating flow regeneration of the DPF system and the effects of the reciprocating flow cycle on the performance of the DPF system are analyzed. Results show that (1) the DPF system can use a tiny amount of extra fuel to maintain the chemical reaction, which in turn realizes the regeneration of the catalyzed DPF because of its properties of heat recovery and reverse blowing of ash; (2) with the increase in the reciprocating flow cycle, the temperature profile moves toward the downstream side of the DPF system and the fluctuation amplitudes of the components of CO, NO, and NO2 increase; (3) if reasonable temperature distribution is formed in the DPF system for a certain reciprocating cycle, the regeneration efficiency can be obviously improved and the average content of particulate matter emission can be kept at quite a low level.

Modelling bacterial twitching in fluid flows: a CFD-DEM approach

Bacterial habitats are often associated with fluid flow environments. Bacterial twitching is important for initial bacterial colonization and biofilm formation. The existing research about bacteria twitching is largely experimental orientated. There is a lack of models of twitching motility of bacteria in shear flows, which could provide fundamental understanding about how bacterial twitching would be affected by bacteria associated properties such as number of pili and their distribution on the cell body and environmental factors such as flow and surface patterns. In this work, a three-dimensional modelling approach of Computational Fluid Dynamics (CFD) coupled with the Discrete Element Method (DEM) proposed to study bacterial twitching on flat and groove surfaces under shear flow conditions. Rod-shaped bacteria are modelled as groups of spherical particles and Type IV pili attached to bacteria are modelled as dynamic springs which can elongate, retract, attach and detach. The CFD-DEM model of rod-shape bacteria is validated against orbiting of immotile bacteria in shear flows. The effects of fluid flow rate and surface topography on twitching motility are studied. The model can successfully predict upstream twitching motility of rod-shaped bacteria in shear flows. Our model can predict that there would be an optimal range of wall shear stress in which bacterial upstream twitching is most efficient. The results also indicate that when bacteria twitch on groove surfaces, they are likely to accumulate around the downstream side of the groove walls.

Active Floating with Buoyancy of Pseudopodia Versus Passive Floating by Hydrodynamic Drag Force: A Case Study of the Flat-Shaped Spumellarian Radiolarian Dictyocoryne

It has been suggested that the pseudopodia of radiolarians play a role in controlling buoyancy for floating behaviour. To understand the function of pseudopodia in terms of planktonic capability, we performed culture experiments on the flat-shaped radiolarian Dictyocoryne. A glass cell, a stereomicroscope and an X-Y-Z stage were used to observe the behaviour of Dictyocoryne from a lateral view. Under static conditions, Dictyocoryne grounded on the bottom of the glass cell extended pseudopodia from both sides of the flat disc surface. Subsequently, these individuals rose slightly by a length equal to that of the extended pseudopodia but remained attached to the bottom. These results suggest that Dictyocoryne lacks the ability to surface by obtaining buoyancy through the emergence of pseudopodia. Under conditions of convection flow, Dictyocoryne moved in the downstream direction only when pseudopodia were completely extended. When the convection flow moved upward, the individuals moved with the flow to just under the surface. In addition, convection flow changed the direction of a long, thick pseudopodium, called the axoflagellum, to be parallel with the flow. Consequently, the axoflagellum was always oriented towards the downstream side, being the disc face in the axoflagellum side on the upturn. Given that the flat-shaped spumellarians have symbiotic algae inside their cells, their unique planktonic capability leads to the stable efficiency of the algal photosynthesis.

Effects of the rotation number on flow and heat transfer in contra-rotating disk cavity with superposed flow

The turbulent fluid flow and convective heat transfer in counter-rotating disk cavity with central axial air inflow and radial air outflow are numerically studied based on the finite volume method. Efforts are focused upon the influence of the rotation number Rt on the flow structure, cooling performance, sealing effect, and surface tangential friction characteristics in the cavity. The stagnation point where the radial outward flow along the upstream disk driven by the rotation force meets the radial outward flow along downstream disk driven by the combination of rotation force and inflow inertial force moves from upstream disk wall to the shroud with increasing Rt. At the Rt far smaller than 1, the fluids in the core region between two disks rotate with the upstream disk like a rigid body, and the tangential velocity of the rotating core decreases with the increase of the disk cavity radius, which is different from the Batchelor-type flow. At the Rt larger than 1, the fluids on the upstream disk side rotate like the Batchelor-type flow, while the sandwich rotation disappears in the fluid on the downstream disk side. The temperature on the upstream disk wall increases and then decreases with increasing values of Rt, and the critical value of Rt for the change of temperature variation is assessed to be at about Rt = 0.69. The temperature and radial temperature gradient of the downstream disk wall decrease with increasing Rt. With increasing Rt by increasing the disk rotation rate, the pressures near the downstream disk decrease, while the frictional moments on rotating disks increase. Due to the effect of flow structure, the frictional moment on the upstream disk is smaller than that on the downstream disk.

Performance evaluation of tunnel type sediment excluder efficiency by machine learning

ABSTRACT A tunnel type sediment excluder is a preventive fluidic device constructed on the bed of the river in front of head regulator to mitigate the sediment in the off-taking canal. The water approaching the head regulator is separated into two parts by the roof slab of the tunnels. The top part having relatively clearer water enters into the offtake canal, while the bottom layer which carries most of sediment flows through the tunnels and is discharged from the undersluices to downstream side. Very crude methods for design of sediment excluder are in vogue to date which are based on past experiences and physical model study. So, a rational approach of machine learning methods; multivariate adaptive regression splines (MARS), group method of data handling (GMDH) and M5P has been utilized for estimating the removal efficiency of sediment excluder (E). These machine learning methods have also been compared with the conventional models given by earlier researchers. Sensitivity study indicated that extraction ratio (R) was the most influencing parameter, which is followed by size of silt (S). Parametric study further suggests that with increase of R, E is getting enhanced.

Structure and hydrogen permeability of V–15Ni alloy

The structure of the V–15Ni at.% alloy before and after hydrogen permeability tests was investigated by means of XRD and SEM with EDS analysis. We have found that decomposition of supersaturated V-based solid solution with variable Ni content occurred during testing. The volume fraction of the solid solution decreased and the fraction of V3Ni phase increased during permeability testing, thus bringing the alloy to nearly equilibrium. The membrane without Pd coating showed satisfactory hydrogen fluxes with a significant impact of the surface dissociation rate of hydrogen. The shape of hydrogen permeation curves at the downstream side of the membrane at various temperatures was unusual. We attribute it to the high concentration of dissolved hydrogen in the metal lattice and its effect on the hydrogen diffusivity and solubility. In addition, the multiphase structure with non-uniform distribution of nickel both between the phases and within the BCC solid solution (and, consequently, different hydrogen concentrations) may cause dilatation or compressing effect on neighbouring micro-volumes of the alloy.

Construction of Roller Compacted Concrete Dams in Hot Arid Regions.

Roller compacted concrete (RCC) dams are attractive to many water and energy corporations around the world due to their ease in construction and low construction cost. The hydration of cement and the climatic changes on the convective boundaries are the two main heat sources for the temperature rise in the roller compacted concrete dams. Thus, changing the RCC placement schedule according to climate conditions might eliminate the problem of thermal cracks. In this research, the RCC dam method was applied in an arid region; the Bisha state in Saudi Arabia was chosen as a case study. We found that RCC dam technology can be applied safely with an alternative solution, like selecting a suitable placement schedule and reducing the placing temperature of facing at upstream and downstream sides to overcome the risk of thermal cracks.

Elastodynamic behavior of mechanical cloaks designed by direct lattice transformations

Steering waves in elastic solids is more demanding than steering waves in electromagnetism or acoustics. As a result, designing material distributions which are the counterpart of optical invisibility cloaks in elasticity poses a major challenge. Waves of all polarizations should be guided around an obstacle to emerge on the downstream side as though no obstacle were there. Recently, we have introduced the direct-lattice-transformation approach. This simple and explicit construction procedure led to extremely good cloaking results in the static case. Here, we transfer this approach to the dynamic case, i.e., to elastic waves or phonons. We demonstrate broadband reduction of scattering, with best suppressions exceeding a factor of five when using cubic coordinate transformations instead of linear ones. To reliably and quantitatively test these cloaks efficiency, we use an effective-medium approach.

Studies of vortex characteristics and gas-dynamic fields in Ar-H2 inductively coupled plasma

Numerical simulation of a technical RF inductively coupled torch of Ar-H2 plasma were made with five turns and under a variation of H2 mole fraction from 0 to 20%. The coupled power and generator frequency varied in the range from 4 to 16 kW and from 1 to 10 MHz, respectively. The gas dynamic fields were compared with experimental and numerical results. The presence of frontal and stern vortices on the upstream and downstream sides of discharge zone was analysed. The differences in the vortex flow patterns and gas-dynamic fields under different H2 mole fractions, coupled powers and generator frequencies were compared. Special attention was paid to investigate the transition conditions of the frontal vortex from Benard to toroidal, as well as the conditions to sweep away the stern vortex. Two different methods have been applied to penetrate the frontal vortex. The critical flow rates of central and outer gases have been determined under different H2 mole fractions, coupled powers and generator frequencies. The choice about the injection probe position to penetrate the frontal vortex in Ar-H2 plasma with different gas compositions has been discussed. The dependences of the vortex intensity on the generator frequency and H2 mole fraction under different coupled powers have been established.

Molecular bow shock in the 3 kpc Norma Arm

AbstractA molecular bow shock (MBS) at G24.4+00+112 (l ∼ 24${^{\circ}_{.}}$4, b ∼ 0°, vLSR ∼ 112 km s−1) is studied using the 12CO(J = 1–0)-line survey obtained with the Nobeyama 45 m telescope at 20″ (0.71 pc) resolution. The terminal velocity uniquely locates the object at the tangent point of the 3 kpc expanding arm (Norma arm) with the distance of 7.3 kpc. The bow ridge extends over ∼160 pc (1${^{\circ}_{.}}$3) perpendicularly to the galactic plane, and is concave to a ring of H ii-regions centered on G24.6+00 at the same distance. The edge on the down-stream (higher longitude) side of the MBS is extremely sharp, and is associated with several elephant trunks in gear-to-gear contact with the H ii regions. On the up-stream (lower longitude) side of MBS, a broad H i bow is associated at the same velocity. The coherently ordered structure of H i, CO, and H ii gases indicates H i-to-H2transition at the galactic shock followed by efficient star formation due to dual compression, where the molecular gas is shock-compressed from the up-stream side by galactic shock and from the down-stream side by H ii expansion. We propose a scenario of galactic sequential star formation along the spiral arms. We also discuss related ISM phenomena such as the hydraulic jump, bow shock, and Rayleigh–Taylor instability occurring around the MBS.

Heat release rate and thermal fume behavior estimation of fuel cell vehicles in tunnel fires

This study proposes a heat release rate (HRR) estimation method for a carrier loaded with fuel cell vehicles (FCVs) trapped in a tunnel fire. The carrier is divided into several parts, and the HRR is estimated by adding the HRRs of all system parts (carrier and FCVs). The HRR of one FCV was compared with that of a gasoline vehicle. The thermal fume behavior in longitudinally inclined tunnel fires was also investigated. Even a modest inclination hastened the thermal fume propagation of the FCV fires. Of relevance to the prevention of tunnel fire disasters, the thermal fume behavior differed between FCV and gasoline fires. For safety assessment of tunnel fires, the thermal fume behaviors of an FCV fire and gasoline vehicle fire in a tunnel were investigated by the proposed method. In the case of no longitudinal inclination, the thermal fume of the FCV fire arrived earlier than that of the gasoline vehicle fire (by 1 min at x = 200 m and over 4 min at x = 250 m) because of the emitted hydrogen gas. At 2% longitudinal inclination, the thermal fume of the FCV fire propagated to the downstream side 4 min before that of the gasoline vehicle fire. At 4% longitudinal inclination, the thermal fume propagated 50 m downstream of the initial fire after 10 min. Therefore, after the hydrogen emission, the thermal fume of the FCV fire traveled faster than that of the gasoline vehicle fire. The proposed HRR estimation method can contribute to the risk analysis of various types of tunnel fires.

Two-Dimensional Analysis Of Flow Field And Associated Scour Parameters At Downstream Of Weir With And Without Sloping Apron

The downstream scour of the control structure is a more common and very complex issue in river engineering. Flow structure in the vicinity of the control structure is entirely different from other parts of the river. Ansys Fluent Multiphase Eulerian model combined with hybrid Dense Discrete Phase Model (DDPM) provides much accurate and precise view of flow structure. This model provides a better understanding of flow structure, and it is associated scour development at upstream and downstream. Model simulation is performed on the trapezoidal weir and trapezoidal weir with sloping apron platforms to compare the flow structure, and it is associated scour. The erosion is computed by Mc Laury erosion model, and particle tracking is done using DDPM through a Lagrangian approach stimulate the movement of particles within the flow domain, velocity and other properties. This research focused on delivering much better anticipation about all flow features and sediment particle tracking captured in a closer manner. In this analysis with the trapezoidal weir, the velocity reached around 0.835 ms -1. However, as in the case of trapezoidal weir with sloping apron, the maximum velocity goes approximately 0.505 ms-1 which are nearly equal to inlet velocity. From the analysis, the sloping apron proves to be significant in protecting the downstream side of the control structure

Towards understanding potential atmospheric contributions to abrupt climate changes: characterizing changes to the North Atlantic eddy-driven jet over the last deglaciation

Abstract. Abrupt climate shifts of large amplitudes were common features of the Earth's climate as it transitioned into and out of the last full glacial state approximately 20 000 years ago, but their causes are not yet established. Midlatitude atmospheric dynamics may have played an important role in these climate variations through their effects on heat and precipitation distributions, sea ice extent, and wind-driven ocean circulation patterns. This study characterizes deglacial winter wind changes over the North Atlantic (NAtl) in a suite of transient deglacial simulations using the PlaSim Earth system model (run at T42 resolution) and the TraCE-21ka (T31) simulation. Though driven with yearly updates in surface elevation, we detect multiple instances of NAtl jet transitions in the PlaSim simulations that occur within 10 simulation years and a sensitivity of the jet to background climate conditions. Thus, we suggest that changes to the NAtl jet may play an important role in abrupt glacial climate changes. We identify two types of simulated wind changes over the last deglaciation. Firstly, the latitude of the NAtl eddy-driven jet shifts northward over the deglaciation in a sequence of distinct steps. Secondly, the variability in the NAtl jet gradually shifts from a Last Glacial Maximum (LGM) state with a strongly preferred jet latitude and a restricted latitudinal range to one with no single preferred latitude and a range that is at least 11∘ broader. These changes can significantly affect ocean circulation. Changes to the position of the NAtl jet alter the location of the wind forcing driving oceanic surface gyres and the limits of sea ice extent, whereas a shift to a more variable jet reduces the effectiveness of the wind forcing at driving surface ocean transports. The processes controlling these two types of changes differ on the upstream and downstream ends of the NAtl eddy-driven jet. On the upstream side over eastern North America, the elevated ice sheet margin acts as a barrier to the winds in both the PlaSim simulations and the TraCE-21ka experiment. This constrains both the position and the latitudinal variability in the jet at LGM, so the jet shifts in sync with ice sheet margin changes. In contrast, the downstream side over the eastern NAtl is more sensitive to the thermal state of the background climate. Our results suggest that the presence of an elevated ice sheet margin in the south-eastern sector of the North American ice complex strongly constrains the deglacial position of the jet over eastern North America and the western North Atlantic as well as its variability.

Wall-mounted flexible plates in a two-dimensional channel trigger early flow instabilities.

A high level of mixing by passive means is a desirable feature in microchannels for various applications, and use of flexible obstacles (or plates) is one of the prime choices in that regard. To gain further insight, we carry out two-dimensional numerical simulations for flow past one or two flexible plates anchored to a channel's opposite walls using a fluid-structure interaction framework. For the inlet flow Reynolds number vs the Strouhal number plane, we observe a sudden flow change from a laminar to a time-periodic vortex shedding state when flexible plates are present in the channel. We found the critical Reynolds number to be Re_{cr}≈370 when a single plate is anchored on the channel wall and Re_{cr}≈290 or even lower when two plates are anchored. With an increase in the inlet flow Reynolds number (up to 3200), we found that vortices detach regularly at the plates' tips, which causes the flow to meander in the channel. In a two-plate anchored configuration, primary vortices generated at the first plate are constrained by the second plate and result in an energetic secondary vortex generation in the downstream side. The overall flow features and the energy dissipation in the channel are mainly controlled by the separation gap between the plates. At high-inlet-flow Reynolds numbers (≥1600), the probability density function (F) of the kinetic energy dissipation in a flexible plate configuration shows a stretched exponential shape in the form F(Z)∼1/sqrt[Z]e^{-pZ^{q}}, where Z is the normalized kinetic energy dissipation and the constants p=0.89 and q=0.86. The observed increase in energy dissipation comes at the cost of an increase in pressure loss in the channel, and we found that the loss is inversely related to the plates' separation gap. From our simulations, we found that if high mixing levels are desired, then two flexible plates anchored to the channel walls is a better choice than a channel flow without obstacles or flow past a single plate. The two-plate configuration with zero separation gap between the plates is best suited to achieve a high mixing level.

Randomness in flow turbulence around a bridge pier in a sand mined channel

Mining activities have the potential to cause excess scour and affect the streambed stability around bridge piers present in the vicinity. Randomness characteristics of turbulence around the pier in a mining infested channel can be helpful in better understanding of this phenomenon. In this study, the effect of a mining pit on the randomness in turbulent flow around the pier has been explored on the basis of Kolmogorov complexity (KC) measure and its derivative, i.e. KC spectrum. Conventionally, turbulent stresses are supposed to govern the sediment transport characteristics, hence the Reynolds shear stresses (RSS) and bursting events are also analyzed. Results of two cases have been comparatively studied; for the first case, only an oblong pier is embedded in the channel while in the second case, a rectangular mining pit is excavated upstream of the pier. Quadrant analysis of the Reynolds shear stress revealed that strong ejection events in the upstream side and inward interaction events in the downstream side of the pier cause excess momentum transport in presence of a mining pit. Streamwise and vertical turbulence intensities also increase by 20% and 33% respectively in the down-flow zone in front of the pier. KC value of turbulence around the pier, especially in the down-flow zone and separation zone is found to be 10% and 12% higher due to pit excavation. Comparing the KC spectra for both cases suggests that dredging of a pit in the channel increases the degree of randomness of higher velocity scales around the bridge pier. These alterations in turbulent stresses and randomness characteristics can be helpful in explaining the streambed scour and undermining of bridge piers due to mining activities.

Derivatives on the downstream side of a moving, curved shock

Novel relations are developed for the tangential and normal derivatives of the pressure, density, and velocity components just downstream of a regular point on a curved shock wave. The perfect gas flow is three dimensional with a nonuniform freestream and the flow may be unsteady. The analysis starts with data in a fixed, laboratory-frame Cartesian coordinate system. By means of an orthogonal transformation, a coordinate system is introduced via a solid-body translation and two solid-body rotations. This Cartesian system is shock based and limits the analysis to a selected shock point at a given instant of time when the flow is unsteady. The analysis is a local one in that Taylor series expansions are utilized for the configuration of the shock and the upstream gradients of the velocity, pressure, and density. The coefficients in the last three expansions must satisfy Euler equation constraints. These expansions are performed in both Cartesian systems, with occasional preference given to the laboratory-frame expansions where there are known data. The derivatives are in terms of a third coordinate system that is shock based and utilizes the flow plane at the selected shock point. Exact, explicit results are provided for the tangential and normal derivatives in as simple a form as possible. In the Taylor series expansion version for the tangential derivatives, the relative importance of various factors can be assessed. These are the upstream velocity, pressure, and density gradients, curvatures, and shock-shape terms not associated with curvatures. A different type of discussion is provided for the more involved normal derivatives.