Upstream End Research Articles

Global dynamics of a two-species competition model in advective homogeneous environments

We investigate a two-species competition model in advective homogeneous environments. We assume that the two species are identical except their diffusion rates and advection rates. It is worth noting that the Neumann boundary condition is assumed at upstream end, meanwhile, there is always a net loss of individuals incurred by water flow or both water flow and diffusive movements at downstream end. Our results show that when the downstream loss is large (incurred by both water flow and diffusive movements), the species adopting both slower diffusion and advection can be favorable or unfavorable depending on the gap between two diffusion rates. When the downstream loss is small (incurred by water flow alone), the species adopting a combination of faster diffusion and weak advection will persist while the movement of faster diffusion and advection can be favorable or unfavorable for species to survive depending on the gap between two advection rates.

End boundary effects on wakes dynamics of inclined circular cylinders

We perform direct numerical simulations to characterize the three-dimensional wake dynamics of long inclined circular cylinders with inhomogeneous end boundary conditions. Three Reynolds numbers, Re=100, 200 and 300, corresponding to the regimes of laminar flow, mode A* wake, and mode B wake, respectively, are considered to reveal the roles of the intrinsic secondary instabilities and the extrinsic end boundary effects in shaping the three-dimensional flows. At Re=100, the end boundary effects are felt over the entire cylinder span by inducing oblique vortex shedding, which is associated with stronger spanwise flow in the wake than a parallel shedding. The Strouhal number of the oblique shedding is related to that of the parallel shedding of straight cylinder by the cosine law, considering the combined inclination angle and oblique angle. At Re=200, the intrinsic secondary instability results in large-scale vortex dislocation, precluding the propagation of the end boundary effects towards further span. Nevertheless, for the inclined cases, oblique shedding is still observed within limited span from the upstream end boundary. The oblique vortices feature intact and straight vortex cores, and are related to the two-dimensional flow at Re=200 (that are void of vortex dislocations) from the viewpoint of cosine law. Further along the span, the oblique vortices destabilizes with the formation of small-scale vortices, and the flow transitions to the typical mode A* wake. At Re=300, the highly three-dimensional flow near the end boundary creates disturbances that travel along the cylinder span, creating vortex dislocations for cases with low inclination angles. For high inclination angle, oblique vortex shedding is again observed over the cylinder span, and is not disrupted by vortex dislocations of either intrinsic or extrinsic causes. The present study offers renewed insights into the three-dimensional wake dynamics of inclined cylinders, and lays the foundation for the designs of long flexible engineering structures and related flow control techniques.

Experiments and Fluent–Engineering Discrete Element Method-Based Numerical Analysis of Block Motion in Underwater Rock-Plug Blasting

Underwater rock-plug blasting is a special blasting technique for excavating underwater inlets. In the process of rock-plug blasting excavation, the blasting-block movement from the difference in water pressure inside and outside the tunnel is one of the key factors for successful construction. Laboratory underwater rock-plug blasting experiments were conducted using small explosive charges, and a high-speed camera was adopted to observe and study block motion. Then, numerical simulations were conducted for the model experiment based on the Fluent and Engineering Discrete Element Method (EDEM) coupling program developed using the user-defined function (UDF) interface to reveal the mechanism underpinning the penetration of underwater rock-plug blasting. The results showed that the process of block motion in underwater rock-plug blasting can be divided into two stages. In the first stage, broken blocks move to two sides along the axis of the rock plug under the blast load. A blasting crater is formed on the downstream end face of the rock plug under the effects of the free face, while the upstream end face is loosened, or blocks are ejected under the influence of the water pressure. In the second stage, blocks flow to the broken-rock pit under the effects of water scouring and gravity, and, finally, the rock plug is penetrated. The larger the head of water and the opening angle of the rock plug are, the better the penetration effect for the rock plug is. The Fluent–EDEM coupling algorithm was in good agreement with the experimental results in terms of the rock-plug blasting effect and the velocity curve of the blocks, indicating that the coupling method had a favorable effect in simulating the interaction of blocks and water during underwater rock-plug blasting. The findings are expected to promote the application and popularization of the rock-plug blasting technique and can provide a reference for rock-plug blasting in water-intake and water-diversion projects.

Efficacy of Longitudinal Training Walls to Mitigate Riverbed Erosion

AbstractThe Waal Branch of the Rhine River has eroded over the last 150 years following channel straightening and narrowing. In 2014–2015 a pilot project replaced existing groynes over an 11 km long reach with three longitudinal training walls (LTWs) to mitigate channel bed erosion, among other purposes. Walls are lower than the river bank and split the flow between a primary and an auxiliary channel, which are hydraulically connected during floods. Water enters the auxiliary channel at three elevations (from bottom to top): via an entrance weir, through inter‐wall notches, and over the wall. Bathymetry and discharge data were collected for 5 years after construction, which is a first indication that longitudinal dams can help mitigate channel bed erosion and analyzed to understand how the walls partition water and sediment and whether erosion is mitigated by LTWs. As the river discharge increases, a larger fraction of flow is diverted from the primary channel into the auxiliary channel. After a flood, sediment is deposited in the primary channel near the upstream end of each wall and localized scour occurs where the auxiliary channel rejoins the primary channel. Between floods, the accumulated sediment disperses and scour pits tend to fill. We observe a net‐accumulation of sediment in the study domain 5 years after construction. Erosion is best mitigated when weir flow is minimized to keep bed material in the primary channel, but weir flow remains important at lower flows for ecological purposes.

Computational pulmonary edema: A microvascular model of alveolar capillary and interstitial flow.

We present a microvascular model of fluid transport in the alveolar septa related to pulmonary edema. It consists of a two-dimensional capillary sheet coursing by several alveoli. The alveolar epithelial membrane runs parallel to the capillary endothelial membrane with an interstitial layer in between, making one long septal tract. A coupled system of equations is derived using lubrication theory for the capillary blood, Darcy flow for the porous media of the interstitium, a passive alveolus, and the Starling equation at both membranes. Case examples include normal physiology, cardiogenic pulmonary edema, noncardiogenic edema Acute Respiratory Distress Syndrome (ARDS) and hypoalbuminemia, and the effects of positive end expiratory pressure. COVID-19 has dramatically increased ARDS in the world population, raising the urgency for such a model to create an analytical framework. Under normal conditions, the fluid exits the alveolus, crosses the interstitium, and enters the capillary. For edema, this crossflow is reversed with the fluid leaving the capillary and entering the alveolus. Because both the interstitial and capillary pressures decrease downstream, the reversal can occur within a single septal tract, with edema upstream and clearance downstream. Overall, the interstitial pressures are found to be significantly more positive than values used in the traditional physiological literature that creates steep gradients near the upstream and downstream end outlets, driving significant flows toward the distant lymphatics. This new physiological flow may provide a possible explanation to the puzzle, noted since 1896, of how pulmonary lymphatics can function so far from the alveoli: the interstitium can be self-clearing.

Impact of floodplain and Stage 0 stream restoration on flood attenuation and floodplain exchange during small frequent storms

AbstractRiver flooding impacts human life and infrastructure, yet provides habitat and ecosystem services. Traditional flood control (e.g., levees, dams) reduces habitat and ecosystem services, and exacerbates flooding elsewhere. Floodplain restoration (i.e., bankfull floodplain reconnection and Stage 0) can also provide flood management, but has not been sufficiently evaluated for small frequent storms. We used 1D unsteady Hydrologic Engineering Center's River Analysis System to simulate small storms in a 5 km‐long, second‐order generic stream from the Chesapeake Bay watershed, and varied % channel restored (starting at the upstream end), restoration location, restoration bank height (distinguishes bankfull from Stage 0 restoration), and floodplain width/Manning's n. Stream restoration decreased (attenuated) peak flow up to 37% and increased floodplain exchange by up to 46%. Floodplain width and % channel restored had the largest impact on flood attenuation. The incremental effects of new restoration projects on flood attenuation were greatest when little prior restoration had occurred. By contrast, incremental effects on floodplain exchange were greatest in the presence of substantial prior restoration, setting up a tradeoff. A similar tradeoff was revealed between attenuation and exchange for project location, but not bank height or floodplain width. In particular, attenuation and exchange were always greater for Stage 0 than for bankfull floodplain restoration. Stage 0 thus may counteract human impacts such as urbanization.

Smooth and Stepped Converging Spillway Modeling Using the SPH Method

Three-dimensional (3D) simulations using the smoothed particle hydrodynamics (SPH) method were performed for smooth and stepped spillways with converging walls, in order to evaluate the influence of the wall deflection and the step macro-roughness on the main non-aerated flow properties. The simulations encompassed a 1V:2H sloping spillway, wall convergence angles of 9.9° and 19.3°, and discharges corresponding to skimming flow regime, in the stepped chute. The overall development of the experimental data on flow depths, velocity profiles, and standing wave widths was generally well predicted by the numerical simulations. However, larger deviations in flow depths and velocities were observed close to the upstream end of the chute and close to the pseudo-bottom of the stepped invert, respectively. The results showed that the height and width of the standing waves were significantly influenced by the wall convergence angle and by the macro-roughness of the invert, increasing with a larger wall deflection, and attenuated on the stepped chute. The numerical velocity and vorticity fields, along with the 3D recirculating vortices on the stepped invert, were in line with recent findings on constant width chutes.

The Crucial Importance of Air Valve Characterization to the Transient Response of Pipeline Systems

Air valves are often crucial components in an air management strategy for pressurized water conveyance systems. However, the reliability of characteristic curves of air valves found in product catalogs is quite variable. This paper evaluates the consistency of a selection of product curves to basic air flow principles. Several recurring issues are identified: catalogs that present identical curves for admission and expulsion (they are, in fact, quite distinct); admission curves that are inconsistent with the isentropic inflow model; inflow (admission) curves actually consistent with the shape of the isentropic outflow model; limited validity curves that encompass only part of the subsonic flow regimen; and unclear or unstated specifications regarding the conditions under which the characterization tests were performed or their results displayed. To examine the significance of these representational issues related to air valve capacity on system behaviour, this paper uses a case study involving the simulated transient response arising from a pump trip at the upstream end of a rising water line having a distinct high point fitted with an air valve. It is found that employing inaccurate air valve characteristics in a transient simulation may potentially result in appreciable or even dangerous simulation errors.

Pressure pattern for fault diagnosis in gas pipelines through graph tools

This paper deals with the detection and localization of damage in gas-filled pipelines by means of an oriented-signals graph. The purpose is to search for transient patterns in a faulty main conduit, when an external acoustic source excites the viscous fluid. The study assumes a linearized model of distributed parameters for the healthy sections of the pipe and two-port lumped models for leaks and blockages. Based on these models, the exact transcendental transfer function of an acoustic source at the upstream end P(0,s) to the pressure P(z0,s) at point z0 is derived and transformed through graph tools in an oriented-signals graph for one and two faults. Thus, one establishes the transient response patterns associated with the faults from the graph paths without numerical parameters. This shown that graph theory is another suitable tool to visualize pressure wave propagation in a damage conduit. To validate the responses for one and two leaks, one compares the features with the analytical solution and the digital simulated pressure.

Inverse Flood Routing Using Simplified Flow Equations

The paper considers the problem of inverse flood routing in reservoir operation strategy. The aim of the work is to investigate the possibility of determining the hydrograph at the upstream end based on the hydrograph required at the downstream end using simplified open channel flow models. To accomplish this, the linear kinematic wave equation, the diffusive wave equation and the linear Muskingum equation are considered. To achieve the hydrograph at the upstream end, an inverse solution of the afore mentioned equations with backward integration in the x direction is carried out. The numerical solution of the kinematic wave equation and the Muskingum equation bases on the finite difference scheme. It is shown that both these equations are able to provide satisfying results because of their exceptional properties related to numerical diffusion. In the paper, an alternative approach to solve the inverse routing using the diffusive wave model is also presented. To this end, it is described by a convolution which involves the instantaneous unit hydrograph (IUH) corresponding to the linear diffusive wave equation. Consequently, instead of a solution of partial or ordinary differential equations, the integral equation with Laguerre polynomials, used for the expansion of the upstream hydrograph, is solved. It was shown that the convolution approach is more reliable comparing to the inverse solution of the simplified models in the form of differential equations.

Helicon Injected Inertial Plasma Electrostatic Rocket

The Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is a space propulsion system developed at the University of Illinois Urbana-Champaign. The HIIPER couples a helicon tube with an inertial electrostatic confinement (IEC) fusion system. Its operating principle involves a helicon ionization stage followed by an electrostatic grid (IEC cathode grid) extraction stage. The helicon setup used in the HIIPER is modified to include a helicon bias grid at the upstream end of the tube. This grid is applied with a positive direct-current voltage to increase the plasma potential and the most probable ion energy of the plasma injected into the IEC fusion chamber. The IEC cathode grid in the HIIPER uses an innovative asymmetric design, graphically depicted through a computational model, that ejects a stream of electrons that accelerate the exhaust ions and simultaneously neutralize the exhaust jet. The model is also used to plot ion trajectories inside the HIIPER to identify any wall collision losses. A separate numerical study was undertaken to show augmentation of plasma kinetic energy on adding a magnetic nozzle as the final propulsion stage of the HIIPER. Experimental results were used to establish a relation between the input parameters and the ion density of the resulting plasma. Langmuir probe measurements were performed at two locations to validate corresponding computational results, indicating ion losses due to ion-wall collisions inside the helicon-IEC coupling. The results in this study add to the proof of concept of the HIIPER and allow for designing an upgrade of the propulsion system. Increasing thrust while maintaining plasma densities between 1017 and 1018 throughout the system is the current aim of HIIPER research. This study summarizes the various performance parameters of the propulsion system, along with a discussion of ongoing research and future scope.

Food loss and waste in maize in Mozambique and its economic impacts: a system dynamics assessment approach

ABSTRACT Food loss and waste are of global concern. In developing countries like Mozambique, it seems to be a major issue at the upstream end of supply chains, which is also regarded as postharvest losses (PHL). In this study, PHL is analysed in the context of maize in Mozambique, which is the most important crop in that country. The analysis focuses on empirically testing a simulation modelling approach for determining the short and mid-run economic impacts of PHL. A system dynamics model is applied. This model acknowledges climate, management, and domestic and regional marketing related factors as major drivers of PHL. A novel result from this study suggests climate related factors as the cause of a systematic amount of PHL at about 70,000 tons per year. However, marketing forces also play an important role to explain the overall PHL, particularly in periods domestic production increases sharply. The impact of potential interventions in the value chain are also tested.

Historical Steps in Establishing Diagnostic Criteria for Grading Stenosis of Brain Supplying Arteries: A Litmus Test for Clinical Usefulness

This publication describes the development of the diagnosis of stenosing diseases of brain-supplying arteries using ultrasound Doppler sonography, based on the personal experience of the author. It starts with the search test of flow alteration at the ophthalmic arteries as evidence of upstream obstruction and ends with the examination of extra- and intracranial arteries using Color Duplex technology. The advantage of ultrasound diagnostics is the good morphological description of the wall changes together with the assessment of hemodynamics. A meaningful assessment of the degree of stenosis requires knowledge of existing collateral circulation. The clinical utility of this method is in constant flux, depending on new therapeutic methods.

Just mobility futures: Challenges for e-mobility transitions from a global perspective

E-mobility has become the dominant answer for many governments in the Global North for reducing carbon emissions in the transport sector. Recently, several contributions discussed the justice implications of such e-mobility transitions. However, these were largely focused on the production and consumption of electric vehicles. Studies on injustices at the upstream end of global e-vehicle commodity chains are largely missing. We therefore suggest studying conflicts around the extraction of resources needed for the electrification of the mobility sector to identify justice demands made by protest actors in the Global South. We bring together the large body of literature on conflicts around mining in the Global South, and the literature on energy and mobility justice. We ask what justice demands are formulated by protest actors in conflicts over the extraction of cobalt, lithium, and copper, and what implications these demands have for the understanding and conceptualization of transitions towards just mobility futures from a global perspective. To answer these questions, we develop an analytical framework based on Fraser’s conceptualization of justice, and the concept of “justice frames”. We conclude with an overview of different justice demands voiced in resource conflicts and their implications for envisioning different types of just mobility futures.

Determining a reasonable distance of collecting irrigation data for real‐time management of furrow irrigation

AbstractOne basis for the real‐time management of furrow irrigation is to estimate the infiltration parameters and Manning roughness, which can represent the furrow condition as early as possible. Closed‐end furrow irrigation experiments were conducted on 45 fields on the Guanzhong Plain in Shaanxi province, China. The infiltration parameters of the Kostiakov equation and Manning roughness were estimated according to multipoint advance trajectory and upstream end water depth at four advance distances (50%, 60%, 70%, and 100% of furrow length; i.e., 0.5 L, 0.6 L, 0.7 L, and 1.0 L, respectively). The estimated infiltration parameter and Manning roughness were then input into WinSRFR to evaluate their effects on furrow irrigation and determine a reasonable distance for collecting multipoint advance trajectory and upstream end water depth. The results indicated that the estimated infiltration parameters and Manning roughness by multipoint advance trajectory and upstream end water depth at 0.6 L or later were highly consistent with the measured values. Except for the upstream end water depth, the mean absolute percentage errors between the simulated advance trajectory, irrigation performance, and applied water volume with measured values were lower than 10% for all furrow irrigation experiments. Therefore, the reasonable distance for collecting irrigation data should not be less than 0.6 L.

Extreme Hydrological Events and Reservoir Methane Emissions

Floating chamber measurements of CH4 emissions from Cotter Reservoir (Canberra, Australia) were performed on five occasions between October 2010 and April 2012. The timing of the measurements spanned the first major flood events that followed drought-breaking rains that ended the Millenium Drought in southeast Australia. The flood events were the largest in 26 years and followed the 3 lowest flow years on record. The floods warmed the hypolimnion of this normally monomictic reservoir by ∼8°C during the first summer and by ∼3°C during the second summer of the study compared to “normal” summer hypolimnion temperatures. In addition, the floods carried large amounts of vegetation and soil that had accumulated in the catchment during previous years. Average CH4 emissions prior to the flooding were low (4.3 mg-CH4 m−2 d−1) and relatively uniform across 8 measurement sites spaced along the long axis of the reservoir. Following the first floods, which occurred during spring and summer 2010–2011, the mean reservoir CH4 emission increased to 99 mg-CH4 m−2 d−1 with emissions at the upstream end of the reservoir approximately 100 times greater than emissions near the dam wall. The following year (2011–2012) average emissions were lower (30 mg-CH4 m−2 d−1) and the longitudinal gradient weakened. A major flood occurred in autumn 2012 and warmed the hypolimnion by ∼3 C, but emissions did not change much in response. We hypothesize that the changes in mean reservoir CH4 emission can be attributed to both thermal enhancement of sediment methanogenesis by a factor of 2–7, and to the supply of fresh organic matter from the catchment by a factor of 3.

Establishment and Persistence of Trees Growing in the Channel of an Intermittent Stream in a Temperate, Karst Environment

AbstractTrees, mostly sycamore (Platanus occidentalis L.), are growing in the channel of the lower 7 km of Sinking Creek in the Appalachian Mountains of Virginia. Sinking Creek is a gravel‐bedded stream that disappears into a subsurface cave network and for its lower 7 km, flows intermittently throughout the year, exposing a dry streambed. We hypothesize that there have been low‐flow periods in the past conducive to tree‐seedling establishment. We describe this system and test our hypothesis through an analysis of hydrologic, dendrochronological, and geomorphic data to better understand the conditions leading to tree establishment and persistence in the stream channel. To our knowledge, this is the first study on trees growing in the channel of an intermittent stream in a temperate environment. Most riparian vegetation studies along intermittent rivers and ephemeral streams focus on dryland areas, where trees have also been observed growing in the channel. Our results show that sycamores are the oldest trees in the channel, that they established during periods of low precipitation, and they are located at the upstream end of bars. In their wake, on bars, other younger trees have established. Analysis of tree roots suggest that scour of the base of some trees occurred during thalweg migration. Additionally, we present a conceptual model of the flow‐tree‐sediment dynamics occurring in Sinking Creek that can be further tested as part of future work. This work highlights the conditions for tree establishment in streams, which is an important threshold for any streams under projected future drying.

Developing a Multi-Regional Physical Supply Use Table framework to improve the accuracy and reliability of energy analysis

Physical Supply Use Tables overcome some of the main limitations of the commonly used Energy Extended Input Output Analysis by describing the Energy Conversion Chain in energy terms only. In this paper, we build on recent advances in the field to construct a Multi-Regional Physical Supply Use Table framework. We use data from the International Energy Agency and have developed open source R packages, thereby enabling easy adoption of the present work. The new framework enables analysts to take into consideration the trade in energy products and to track energy flows across regions. In addition, we expand the existing Physical Supply Use Table framework to provide the mathematical structure with symmetry, by adding a resource extraction matrix at the upstream end of the Energy Conversion Chain, thereby enabling reverse Input–Output calculations.Then, we demonstrate two important applications of the new multi-regional framework. First, we show how the framework can be used for energy security analysis, how the primary energy supply can be broken down by region of origin, and how the exposure to overseas suppliers can be quantified by energy product, and final demand sector. Second, we show how energy-related greenhouse gas emissions can be accounted for and disaggregated in terms of energy use by the energy industry, downstream energy use by final demand sectors, and methane leakages and flaring. The framework, which consistently binds energy products supplied to the economy to the Energy Conversion Chain, may be helpful for numerous subfields of energy analysis and modelling.

Hydromechanical assessment of a complex landslide through geophysics and numerical modeling: Toward an upgrade for the Villerville landslide (Normandy, France)

The Pays d'Auge (Normandy, France) is impacted by large deep-seated landslides along its coastline. The largest of these landslides, the “Cirque des Graves”, has been studied since the 1980s because of significant stakes in the active zone. To characterize the hydromechanical functioning of the central part of the cirque, which is the most active part and includes the majority of the issues at stake, we performed new investigations that complement prior studies. Through the joint use of high-resolution geophysics (seismic refraction and ERT) coupled with geotechnical knowledge, a geometric model was highlighted on a large profile. Then, the mechanical behavior and slope stability were assessed by finite-difference numerical modeling (FDM) with FLAC2D®. To calibrate the model, a back-analysis was first realized on an eastern profile, for which the geometry and slip surfaces were identified by field surveys. The agreement of the model results on the eastern profile constrained by inclinometry enables a transposition of the geomechanical parameters on the central profile to assess its functioning and to locate the areas subject to mechanical weaknesses. A translational movement was revealed at the upstream end of the landslide, as well as nested roto-translational envelopes in the downstream two-thirds of the landslide. These results allowed robust assumptions with regard to the location of the slip surfaces and the zones undergoing stress-strain. The influence of groundwater was also assessed and discussed with respect to the overall slope stability. This study demonstrates the pros and cons of conventional finite difference modeling, as well as of back-analysis by parametric transposition. The benefits of the joint use of geophysical methods and numerical modeling were also highlighted and discussed.

Impact of inclined double-cutoff walls under hydraulic structures on uplift forces, seepage discharge and exit hydraulic gradient

In hydraulic structures design, using cutoff walls is essential to reduce and control the resultant uplift force (U), seepage discharge (Q), and exit hydraulic gradient (i). This research investigates the effectiveness of inclined double cutoff walls under hydraulic structures, considering the influence of depths, locations, and inclination angles of the upstream and downstream cutoff walls by using Finite Element Method (FEM). The results confirmed that installing a deeper cutoff wall on the downstream reduces the exit gradient even further. In the case of the cutoff walls located in the upstream and downstream ends, the exit gradient will be less than when the cutoff walls are installed at a closer distance. Increasing the inclination angle of downstream cutoff wall has a major impact on exit gradient reduction. Embedment of cutoff walls in the upstream and downstream ends with right angles and equal depths reduces the seepage discharge more than other cases.