Flow Constancy Research Articles

Simulation studies of the granular flow beryllium target for the compact materials irradiation facility

The Compact Materials Irradiation Facility (CMIF) project will provide a high-energy, high-flux neutron source for material irradiation research which will be indispensable for the long-term Accelerator-Driven Advanced Nuclear Energy (ADANE) project in China. CMIF is a Be(d, xn) neutron source driven by a 10 mA @ 50 MeV continuous wave (CW) deuteron beam with a granular flow target. This paper presents numerical studies of a granular beryllium target which adopts inclined granular flow to serve as both the target body and also the heat carrier. First of all, the flow constancy of the chute flow is investigated. Next the relationship between the irradiation conditions and the beam-target parameters is studied. To investigate the heat processing ability of this kind of target, the heat deposition and transfer in the target are simulated numerically. Finally, the heat removal for the backplate and also irradiation damage are investigated.

Validation of the idea of granular flow target: A beam coupling test

The concept of granular flow target was proposed very recently and there are many potential advantages of the target on flow constancy, energy deposition and heat removal, etc. In this work first loop of granular flow target is built and an electron beam coupling experiment is reported, which aims to test the flow constancy, energy deposition and heat removal of the granular materials. The results show a good constancy of the dense granular flow and indicate granular flow as a candidate for energy removal. Moreover, there is a consistence in flow rate and temperature rise between experimental and numerical studies. This work supports the idea of granular target and is valuable for the following ADS facilities and granular flow target design.

Flow alteration signatures of diversion hydropower: An analysis of 32 rivers in southwestern China

AbstractHydrologic changes caused by diversion hydropower are poorly described. Herein, we evaluate hydrologic alteration in 32 ungauged rivers developed for diversion hydropower. We simulated long‐term unregulated discharge records before perturbing flows with the hydropower diversion and comparing periods with and without diversion. We detected statistically significant changes to flow regime metrics across all rivers. Magnitudes across a range of flows consistently decreased following diversion, flow variability decreased substantially, and transitions between flows of different magnitudes became more abrupt. Magnitudes of 7‐day minimum flows were lower by a mean of 41 ± 23% (p < .05 for 19 rivers), annual maximum flows decreased significantly (p < .05) in 22 rivers, and 7‐day maximum flows decreased by a mean of 52 ± 18% (p < .05 for 26 rivers). Temporally dynamic low to moderate flows were replaced by static minimal flows, leading to a mean 184 ± 49% increase in flow constancy. Mean duration of events sustained below the prediversion Q75 increased (p < .05 for 32 rivers) from a mean of 3 days to a mean of 27 days after diversion. Mean hydrograph rise and fall rates doubled and tripled, respectively (p < .05 for 28 rivers). We detected few changes to peak flow timing. Although direction of observed change was consistent among the rivers, magnitudes and significance of response often varied between rivers. A proposed diversion index largely explained response variability among the 32 rivers. Results highlight that hydropower systems without storage reservoirs can profoundly affect river flow regimes when water is diverted from the river.

Environmental flows in the context of unconventional natural gas development in the Marcellus Shale.

Quantitative flow-ecology relationships are needed to evaluate how water withdrawals for unconventional natural gas development may impact aquatic ecosystems. Addressing this need, we studied current patterns of hydrologic alteration in the Marcellus Shale region and related the estimated flow alteration to fish community measures. We then used these empirical flow-ecology relationships to evaluate alternative surface water withdrawals and environmental flow rules. Reduced high-flow magnitude, dampened rates of change, and increased low-flow magnitudes were apparent regionally, but changes in many of the flow metrics likely to be sensitive to withdrawals also showed substantial regional variation. Fish community measures were significantly related to flow alteration, including declines in species richness with diminished annual runoff, winter low-flow, and summer median-flow. In addition, the relative abundance of intolerant taxa decreased with reduced winter high-flow and increased flow constancy, while fluvial specialist species decreased with reduced winter and annual flows. Stream size strongly mediated both the impact of withdrawal scenarios and the protection afforded by environmental flow standards. Under the most intense withdrawal scenario, 75% of reference headwaters and creeks (drainage areas <99km2 ) experienced at least 78% reduction in summer flow, whereas little change was predicted for larger rivers. Moreover, the least intense withdrawal scenario still reduced summer flows by at least 21% for 50% of headwaters and creeks. The observed 90th quantile flow-ecology relationships indicate that such alteration could reduce species richness by 23% or more. Seasonally varying environmental flow standards and high fixed minimum flows protected the most streams from hydrologic alteration, but common minimum flow standards left numerous locations vulnerable to substantial flow alteration. This study clarifies how additional water demands in the region may adversely affect freshwater biological integrity. The results make clear that policies to limit or prevent water withdrawals from smaller streams can reduce the risk of ecosystem impairment.

Comment: Revisiting Lassen cerebral blood flow constancy with hysteresis and 3D.

Roh et al.1 present a unique case of severe, prolonged hypercapnic respiratory failure that triggered refractory global cerebral edema (GCE). This case report is interesting because edema was not abatable by hyperventilation, despite adequate reversal to a normocapnic state, and responded only to aggressive osmotherapy. The authors thank Julie D. Coats, medical illustrator, for her assistance in graphic design.

Fish assemblages respond to altered flow regimes via ecological filtering of life history strategies

Summary1. In riverine ecosystems, streamflow determines the physical template upon which the life history strategies of biota are forged. Human freshwater needs and activities have resulted in widespread alteration of the variability, predictability and timing of streamflow, and anticipating the biotic consequences of anthropogenic streamflow alteration is critical for successful environmental flow management. In this study, we examined relationships between dam characteristics, metrics of flow alteration and fish functional community composition according to life history strategies by coupling stream flow records and fish survey data in paired flow‐regulated and free‐flowing rivers across the conterminous United States.2. Dam operations have generally reduced flow variability and increased flow constancy based on a comparison of pre‐ and post‐dam flow records (respective mean record lengths 26.2 and 43.1 years). In agreement with ecological theory, fish assemblages downstream of dams were characterised by a lower proportion of opportunistic species (a strategy favoured in environmental settings dominated by unpredictable environmental change) and a higher proportion of equilibrium species (a strategy favoured in more stable, predictable environments) compared to free‐flowing, neighbouring locations.3. Multiple linear regression models provided modest support for links between alteration of specific flow attributes and differential life history representation below dams, and they provided strong support for life history associations with dam attributes (age and release type). We also found support for a relationship of both reduced flow variability and dam age with higher representation of non‐native species below dams.4. Our study demonstrated that river regulation by large dams has significant hydrological and biological consequences across the United States. We showed that on ecological time scales (i.e. the order of years to decades), dams are effectively changing the functional composition of communities that have established over millennia. Furthermore, the changes are directional and indicate a filtering by dams for some life histories (equilibrium strategists) and against other life histories (opportunists). Finally, our study highlights that dependence upon long‐term flow records and availability of biotic surveys extracted from national survey efforts limit our ability to guide environmental flow standards particularly in data‐poor regions.

Does river regulation increase the dominance of invasive woody species in riparian landscapes?

ABSTRACTAim A regional analysis was used to explore the influence of river regulation on the dominance of non‐native, invasive shrubs and trees. We addressed the following questions: (1) How do large dams affect hydrological parameters that influence riparian vegetation? (2) How do flow regimes affect the dominance of non‐native woody species? (3) How do changes in flow regimes affect the dominance of non‐native woody species?Location South‐western USA.Methods We sampled the canopy cover of woody species on 179 point bars along seven non‐dammed and thirteen dammed river segments. Wilcoxon rank sum tests were used to determine differences between flow parameters in dammed and non‐dammed rivers. We used correlation analyses and generalized linear model comparisons to examine associations of flow parameters and canopy cover of native (Populus and Salix) and non‐native (Tamarix and Elaeagnus) taxa. An index of flow alteration that was created using principal components analysis was regressed with vegetation cover.Results Tamarix cover was positively related to drainage area, flow constancy, August and May median flow and flow recession rate, but Elaeagnus cover was unrelated to flow variables. River segments with peak flows in late summer or high constancy had the highest Tamarix cover. Populus cover was positively influenced by low maximum temperatures and frequent high pulses. Flow alteration was negatively related to Populus cover and positively related to Tamarix cover. Total non‐native, Elaeagnus and Salix covers were not correlated with flow alteration.Main conclusions Rivers with a large drainage area and low flow variability are inherently more vulnerable to invasions. River regulation does not necessarily increase the cover of non‐native, invasive species. Instead, changes in flow allow proliferation of species that have life‐history traits suited to modified flow regimes. River restoration projects that aim to reinstate natural flow regimes should be designed with knowledge of native and non‐native species' life history strategies.

Regulatory processes interacting to maintain hepatic blood flow constancy: Vascular compliance, hepatic arterial buffer response, hepatorenal reflex, liver regeneration, escape from vasoconstriction

Constancy of hepatic blood flow (HBF) is crucial for several homeostatic roles. The present conceptual review focuses on interrelated mechanisms that act to maintain a constant HBF per liver mass. The liver cannot directly control portal blood flow (PF); therefore, these mechanisms largely operate to compensate for PF changes. A reduction in PF leads to reduced intrahepatic distending pressure, resulting in the highly compliant hepatic vasculature passively expelling up to 50% of its blood volume, thus adding to venous return, cardiac output and HBF. Also activated immediately upon reduction of PF are the hepatic arterial buffer response and an HBF-dependent hepatorenal reflex. Adenosine is secreted at a constant rate into the small fluid space of Mall which surrounds the terminal branches of the hepatic arterioles, portal venules and sensory nerves. The concentration of adenosine is regulated by washout into the portal venules. Reduced PFreduces the washout and the accumulated adenosine causes dilation of the hepatic artery, thus buffering the PF change. Adenosine also activates hepatic sensory nerves to cause reflex renal fluid retention, thus increasing circulating blood volume and maintaining cardiac output and PF. If these mechanisms are not able to maintain total HBF, the hemodynamic imbalance results in hepatocyte proliferation, or apoptosis, by a shear stress/nitric oxide-dependent mechanism, to adjust total liver mass to match the blood supply. These mechanisms are specific to this unique vascular bed and provide an excellent example of multiple integrative regulation of a major homeostatic organ.

Large‐Scale Factors Associated with Sicklefin Chub Distribution in the Missouri and Lower Yellowstone Rivers

AbstractThe conservation and management of imperiled fishes requires information on the factors influencing their distribution. The sicklefin chub Macrhybopsis meeki is an imperiled, small‐bodied, riverine fish largely restricted to the main‐stem Missouri, lower Yellowstone, and middle Mississippi rivers. We tested the association of sicklefin chub presence/absence with physical habitat, temperature, turbidity, flow, and piscivore abundance between July and October 1996– 1997 at a riverscape spatial scale encompassing about 48–192‐km‐long segments over nearly 2,000 km of the Missouri and lower Yellowstone rivers. Four of the 64 variables examined were significantly associated with sicklefin chub presence/absence: distance to upstream impoundment, flow constancy (a measure of flow variability), mean turbidity, and percent of total annual flow occurring in August. The frequency of occurrence of sicklefin chub was highest when study segments were over 301 km downstream from an impoundment, flow constancy was 0.56 or lower (indicating variable flow), mean summer–early autumn turbidity was 80 nephelometric turbidity units or greater, and less than 10% of total annual flow occurred in August. Two complimentary models were developed from these results: a univariate model containing only a distance‐to‐upstream‐impoundment term, and a multiple model that included mean turbidity and August flow. Models were evaluated for accuracy with an independent data set from 1998. The univariate model was a more accurate predictor of sicklefin chub presence/absence in 1998, with correct predictions in 79% of the 14 segments sampled, compared with 69% for the multiple model. These results demonstrate, at a riverscape spatial scale, the importance of maintaining or restoring long, free‐flowing reaches containing a natural range of variability in seasonal low flows and turbidity to conserve a small‐bodied, obligate‐riverine fish.

Classification of reaches in the Missouri and lower Yellowstone Rivers based on flow characteristics

AbstractSeveral aspects of flow have been shown to be important determinants of biological community structure and function in streams, yet direct application of this approach to large rivers has been limited. Using a multivariate approach, we grouped flow gauges into hydrologically similar units in the Missouri and lower Yellowstone Rivers and developed a model based on flow variability parameters that could be used to test hypotheses about the role of flow in determining aquatic community structure. This model could also be used for future comparisons as the hydrological regime changes. A suite of hydrological parameters for the recent, post‐impoundment period (1 October 1966–30 September 1996) for each of 15 gauges along the Missouri and lower Yellowstone Rivers were initially used. Preliminary graphical exploration identified five variables for use in further multivariate analyses. Six hydrologically distinct units composed of gauges exhibiting similar flow characteristics were then identified using cluster analysis. Discriminant analyses identified the three most influential variables as flow per unit drainage area, coefficient of variation of mean annual flow, and flow constancy. One surprising result was the relative similarity of flow regimes between the two uppermost and three lowermost gauges, despite large differences in magnitude of flow and separation by roughly 3000 km. Our results synthesize, simplify and interpret the complex changes in flow occurring along the Missouri and lower Yellowstone Rivers, and provide an objective grouping for future tests of how these changes may affect biological communities. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Robust Gauge Control for Hot Finishing Mills

A new gauge control system for hot finishing mills has been developed to distribute the mill motor power of each stand. The new system has the following features : (a) Interstand exit gauge is calculated based on the law of mass flow constancy using the exit thickness gauge. (b) The design strategy of the new system are to cope with a detection time delay, and to simplify the controller to easily tune during actual implementation. (c) The H∞, controller with two degrees of freedom is designed to obtain high responses of the reference and disturbance. The performance of the controller is evaluated by numerical simulation. The effectiveness of the new system has been shown by application in an actual plant.

Investigation of heat and mass transport along a single fissure in a rock mass, by means of numerical modeling methods

A mathematical model is presented for the coupled process of solute and heat transport by the flow of water along a single fissure, with an accounting for the thermal loads induced in the surrounding rock mass. The Barton-Bandis model has been used in describing the fissure behavior. Computer codes have been developed for the conditions of constancy of water flow rate and constancy of pressure drop along the fissure, and these codes have been used in conducting numerical experiments. Analysis of the results has shown that the selected model gives a physical description of the processes of heat and mass transport along a fissure, the warmup of the surrounding mass, and the behavior of the fissure aperture; hence we can rely on successful use of this procedural "tool."

Effects of hydropower-induced flow perturbations on mayfly (Ephemeroptera) richness and abundance in north Swedish river rapids

Mayfly species richness and abundance were investigated at 52 Swedish river rapids. These were either unregulated, or regulated with or without reduced discharge. Sites impacted by regulation had lower mayfly richness and abundances than unregulated reference sites. The relative importance of reduced discharge, daily fluctuations in flow, flow constancy, and the distance to nearest rapid (as a measure of isolation) was evaluated in multiple regression analyses. These indicated negative effects of diel fluctuations on both abundance and richness, whereas flow constancy was favourable for richness. Neither the distance to nearest rapid nor reduced flow were significantly related to mayfly richness and abundance. In total, 26 mayfly species were recorded. Only Baetis rhodani was found at all sites, but another five species were present at more than 40 sites. The strongest effects were found for species within the Heptageniidae. Nineteen of 20 mayfly species present in both the regulated (with unreduced flow) and unregulated reference rapids were on average more common in the unregulated ones. Mayfly assemblage structure was primarily influenced by regional factors and nutrient status, although daily fluctuations in flow together with rapids dimensions also had a significant influence. No rare species appears to be threatened by hydropower regulation though it is conceivable that depressed abundances in regulated rivers indirectly influence predators and periphyton.

A photometric flow measurements method for characterisation of HPLC pumps

The measurement of flow constancy and pulsation amplitudes of HPLC pump based on the photoconversion of malachite green leucocyanide is described. The irradiation time and hence the degree of conversion of the leucocyanide is correlated to flow fluctuations of piston driven HPLC pumps. It is possible to measure the amplitude of pulsations and determine the constancy of the flow rate. Most of the pumps show a flow stability better than ±1% measured as relative standard deviation of the flow rate under HPLC conditions (pressure drop 100 bar at 1 ml/min flow rate). The most expensive pump of those tested showed less than ±0.5% flow instability, however, this result was achieved by installation of a large-volume pulsation damper. The method described also allows flow rate measurements under FIA conditions where there is little or no pressure drop at the pump outlet.

Experimental investigation of a hybrid wind tunnel model

New developments in power electronics (such as the linear motor) may be of great advantage for future economic aerodynamic testing. After a comprehensive review of economical aspects of present wind tunnel technologies, the experimental verification of the hybrid wind tunnel concept will be presented. A scale law is derived to extrapolate the experimental results of the model-HWT to a facility size for simulating full scale Re-numbers. Finally, methods will be discussed by which the flow constancy during the running time may be improved.

The effect of stream regulation on the physico‐chemical properties of the palmiet river, South Africa

AbstractThe effect of regulation, by multiple impoundment, on ‘discontinuity’ (recovery) ‘distances’ (sensu Ward and Stanford, 1983) for various physico‐chemical attributes of the Palmiet River (a short, steep gradient, cool temperate, acid, low‐nutrient system) was investigated. Physico‐chemical features were measured monthly, from February 1986 to August 1987, at 11 sites along the river, but concentrating on two zones: one below an upper‐reach impoundment, Nuweberg Dam, and one below a middle‐reach impoundment, Arieskraal Dam. Median total suspended solids, nitrates, nitrites and ammonium all increased below both dams with varying levels of ‘recovery’. Median spot temperatures, pH and alkalinity increased below Nuweberg, but decreased below Arieskraal Dam, whereas the converse was true for soluble reactive phosphate. Nuweberg had no effect on conductivity and total dissolved solids, while Arieskraal caused a slight decrease. The river remained well oxygenated down its length.Distinct seasonal variations were recorded for: flow rate, with flow reversal below Nuweberg and flow constancy below Arieskraal; temperature, with seasonal shifts and dampening of annual temperature range below both dams; alkalinity, with seasonal shifts below Arieskraal, and nitrites and nitrates, but not for any other attributes. At least partial recovery was noted in all cases, but in some instances, recovery was incomplete to the estuary. The implications of such alterations, for invertebrates, in terms of reduction in habitat diversity as well as for food supply must be considerable and studies are currently under way to determine community structure and diversity.

The Effects of a Small Reservoir on the Seasonality and Stability of Physicochemical Parameters and Macrobenthic Community Structure in a Rocky Mountain Stream

Physicochemical and biotic characteristics of a headwater stream community above an impoundment on the Sante Fe River, New Mexico, were compared to those in its tailwaters. There was less seasonality in abiotic factors, particularly in discharge and temperature below the impoundment. The streambed below the reservoir was more heterogenous and more stable than that above. Macroinvertebrate density was almost five times greater below the reservoir as a result of enhanced temperature and flow constancy, greater substrate stability and the abundance of aquatic macrophytes at this site. Species richness was also greater below the impoundment and was directly related to its habitat heterogeneity. Reduced discharge and more constant temperatures in conjunction with extremely high macroinvertebrate densities resulted in reduced diversity below the impoundment. Evenness was also reduced. An analysis of seasonal evenness variances and a study of the seasonal abundance patterns of individual taxa indicated that the more constant physicochemical conditions below the reservoir probably decreased biotic interactions and reduced the community stability at this site.

Aquatic Macroinverterbrates of the Piceance Basin, Colorado: Community Response along Spatial and Temporal Gradients of Environmental Conditions

A long-term study of the aquatic biotopes of the Piceance Basin has enabled ana- lyses of macroinvertebrate communities along spatial (downstream) and temporal (year-to-year) gradients of environmental conditions. Cluster analysis indicates four distinct aquatic habitat types: spring sources, springbrooks, and the middle and lower reaches of Piceance Creek. Spatial differences in temperature and flow constancy influence habitat stability with respect to substrate, degree-day distribution, ice conditions, and the distribution and abundance of aquatic macro- phytes. Despite great differences in thermal patterns, total annual degree-days were ca. 3000 in all four habitat types. The principal energy source for macroinvertebrates is autochthonous detritus. Trophic structure shifts from shredders-collectors-scrapers in the headwaters to collectors- predators in lower reaches. Year-to-year variations in discharge altered the density and composi- tion of macroinvertebrates, and were reflected in the thermal regimes at mainstream locations. Data suggest that groundwater discharge from upper reaches is important in maintaining the structural and functional integrity of aquatic systems in the Piceance Basin. Because of the seasonal distribution of precipitation and runoff, headwater streams in arid regions are highly dependent on groundwater discharge for permanent flow (Davis, 1974). Stream segments receiving proportionately large inputs of groundwater exhibit relatively constant thermal, chemical and, flow regimes. With progressive distance downstream these conditions are modified by climatic fluctuations, thus forming an environmental gra- dient that influences the distribution and abundance of aquatic organisms (Deacon and Minckley, 1974). Superimposed upon this spatial gradient is a temporal gradient engendered by year-to-year variations in precipitation which, in arid regions, is most directly reflected by differences in annual dis- charge.

Design of an ion-selective electrode analytical system for monitoring copper in electrochemical reactors

A flow-through cell using ion-selective electrodes has been designed for continuous on-line monitoring of electrochemical reactors. A full range of design considerations is discussed and the characteristics of the cell investigated. Optimal operating conditions are found, of which solution flow rate and constancy of temperature are particularly important. The cell was also designed to have a rapid response time and minimal ‘dead’ volume so as to give continuous measurements of gradually changing metal ion concentrations. Performance has been evaluated using laboratory-simulated conditions and pilot-plant operation of the Ecocell, a rotating-cylinder electrode reactor for the electrowinning of copper from dilute solutions (10–1000 ppm).

Properties of devices for setting or regulating gas flow, including a new flow regulator

With the help of the gas dynamic equations, the properties of four methods used for keeping gas rates constant are derived. Only the flow regulator with a pre-switched pressure regulator and an adiabatically operating aperture with measurable and settable prepressure satisfy the highest requirements of flow constancy. This is the only method that can be calibrated and which allows the connected systems to be observed for leaks.