Selective Withdrawal Research Articles

Ethics of residency programs and fellowships that electively withdraw from the National Resident Matching Program

The National Resident Matching Program, known as “The Match” facilitates the placement of medical graduates into residency and fellowship programs in the United States. Programs may opt out of The Match for various reasons. The selective and intermittent withdrawal of programs from The Match raises ethical concerns surrounding fairness, transparency, beneficence, autonomy, and justice for applicants. We discuss these issues, present the history behind The Match, and offer suggestions to promote fairness.

Effect of two-dam coexistence on thermal regime: A special withdrawal measure in Fengman reservoir, China

The Fengman Reservoir in China employs a distinctive approach termed two-dam coexistence to mitigate the risks associated with aging and hazardous dams. This method involves the partial demolition of the old dam and construction of a new dam downstream, which allows the remaining part of the old dam to act as a retaining wall for selective water withdrawal. Through a comprehensive study, long-term water temperature data were analyzed, along with the characteristics of the two-dam coexistence system, to comprehend its effects on thermal stratification in the main basin near the dams and the withdrawal water temperature (WWT) regime. The results revealed that the metalimnion shifted upwards, strengthening stratification, and the temperature gradient expanded from 0–0.9 °C/m to 0–10.5 °C/m compared to that under the one-dam condition. Vertical mixing was reduced, causing the temperature difference between surface and bottom waters to range from 6.8 to 26.8 °C. This enhanced the stratification stability by 1.8 times compared with the one-dam condition, with some annual variability. Thus, the buoyancy frequency decreased accordingly. Furthermore, two-dam coexistence influenced the WWT, resulting in higher WWT during the warming period (averaging 4.3 °C from May to June) and lower WWT during the freeze-up period (averaging 0.1 °C from January to February) than that of the one-dam condition. The most significant temperature difference between the main basin near the old dam and the one near the new dam occurred at the bottom of the reservoir (ranging from 3.5 to 12.0 °C), confirming that the old dam functioned as a retaining wall, allowing the thermal regime to change. Owing to the two-dam coexistence, the withdrawal layer shifted by 20.0 m from near the intake to close to the demolition elevation. These changes in stable stratification and variations in WWT play crucial roles in reservoir management. This study offers practical insights for treating similar aging and hazardous reservoirs and serves as a reference for optimizing water quality management strategies.

A robust decision-making framework to improve reservoir water quality using optimized selective withdrawal strategies

In arid locations such as Oman, improving the quality of water released from a reservoir can be daunting. This is particularly true for Wadi Dayqah Dam, which struggles to provide sufficient, high-quality water for downstream needs. The study's objective was to establish more reliable operational guidelines, as well as identify vulnerable outlets and release ratios. To do so, a multi-objective optimization algorithm (NSGA-II) was combined with a selective withdrawal approach, using CE-QUAL-W2 and an Artificial Neural Network to simulate water quality in a reservoir. Then, a Robust Decision Making (RDM) approach was utilized to diagnose solutions that maintain acceptable water quality according to users’ requirements. Finally, scenario discovery models (Patient Rule Induction Method (PRIM) and Classification and Regression Tree (CART)) were used to calculate vulnerable outlets and release ratios based on the established threshold. The study adopted an XLRM framework to manage a proposed model under climate change scenarios and specify the effects of involved factors. XLRM stands for eXogenous factors, Levers used by the policy-makers, Relationships between L and X, and Measurement matrix to evaluate scenarios. This study found that a higher-quality reservoir release correlated with more activated outlets and decreased pollutant concentration. Evaluating robust solutions showed that vulnerability increased under scenarios with lower annual rainfall, and water released from low and mid-level outlets was more vulnerable than that from the surface. To enhance operational stability and reduce vulnerability, the suggestions advocate for a strategic approach in releasing varying water ratios from outlets situated at different levels. Specifically, the proposal emphasizes the controlled release of both smaller and larger volumes of water from outlets positioned at lower and higher levels within the dam structure, respectively. This deliberate variation in water release aims to bolster the overall resilience of the operational framework, contributing to a more robust and reliable system.

Application of CE-QUAL-W2 model for optimal selective withdrawal of reservoir concerning water quality (case study: Shahr Bijar Dam Reservoir, Iran)

Application of CE-QUAL-W2 model for optimal selective withdrawal of reservoir concerning water quality (case study: Shahr Bijar Dam Reservoir, Iran)

Assessment of Stoplog Gates’ Operational Effectiveness for Improving Discharged-Water Temperatures during the Thermal Stratification Period in a Reservoir

The discharge of low-temperature water from the middle and lower layers of thermally stratified dam reservoirs leads to thermal pollution and adversely affects fish production and reproduction in downstream rivers. Selective water withdrawal using stoplog gates is an effective approach to address this issue. However, comprehensively and effectively evaluating the effects of stratified withdrawal and optimizing the scheduling of stoplog gates to provide better ecological services to downstream habitats pose significant challenges for reservoir managers. In this study, an equivalent elevation method (EEM) was developed based on in situ observation data of water temperature. The EEM calculates the equivalent withdrawal elevation (EWE) in the far dam area corresponding to the discharge-water temperature (DWT), facilitating the evaluation of stoplog-gate effects. EEM was applied to a thermally stratified dam reservoir in southwestern China (Guangzhao reservoir, GZ). The results showed a significant positive correlation (r > 0.7, p < 0.05) between DWT and the vertical-water-temperature structure in the far dam area. The average EWEs for the 5-layer, 4-layer, and 3-layer stoplog gates in GZ were 697.2 m, 690.8 m, and 689.9 m, respectively. Utilizing the EEM findings, a scheduling operation scheme was proposed to improve DWT while reducing the number of stoplog-gate operations, thereby increasing their efficiency and saving the cost of invested labor and time. This method provides a reference for reservoir managers in optimizing stoplog-gate-scheduling strategies to mitigate potential risks to aquatic ecosystems caused by abnormal water temperature.

Optimization of selective withdrawal strategy in a warm monomictic reservoir based on thermal stratification

Selective withdrawal from reservoirs is an effective strategy for balancing economic goals and environmental demands. Multilevel intake operation (MIO) is one of the main options for improving the thermal regime of deep reservoirs. In this study, a combination of measured data and a two-dimensional hydrodynamic model (CE-QUAL-W2) was utilized to analyze the impact of MIO processes on the thermal stability of a reservoir and the improvement effect of the withdrawal water temperature (WWT). The purpose of this study was to identify an optimal selective withdrawal strategy to meet the water temperature needs of fish downstream during their spawning and breeding activities. The results showed that the MIOs raised the withdrawal water intake position (8.3–11.2 m) for the WWT. Meanwhile, MIOs resulted in statistically significant changes in the water temperature structure of the reservoir (p < 0.01). The stratification stability of the water column weakened (6.8 %-34.5 %), and there were interannual differences. The WWT increased by 0.0 °C∼1.9 °C every ten days, and the time to reach the optimum temperature (18 °C) for fish spawning was 7 to 17 days earlier. There was a statistically significant positive correlation between the WWT improvement and the stability index (SI) (R = 0.7817, p < 0.01). The threshold values of the SI (above the water intake) for average WWT improvements of 0.5 and 1.0 °C were 90.3 and 221.9 kg/m2, respectively, and the recommended operating period was from early-April to May. Under MIOs, the weakening stratification and the increasing WWT during the warming period reduced risks to the water quality and ecological health in the reservoir and downstream rivers. This study provides a helpful reference for the implementation of selective withdrawal operations and the optimization of water quality management strategies in similar large, deep reservoirs.

Digitally supported health care; evaluation approaches to a complex intervention embedded in a tria

Abstract Many important health care interventions do not fit the classic RCT paradigm. Drug trials have struggled with issues of non-compliance and selective withdrawal. Surgical researchers have done extensive work on incorporating operator skills and experience into trial settings. Working on innovative models of care delivery related issues arise. As part of an EU funded multi-centre stepped-wedge trial, GERONTE, of nurse-led, digitally supported, health care coordination for older people with cancer and other significant co-morbidity, we have developed and tested an outline of a novel method of evaluation, drawing on realist evaluation. There are three pieces, first the central trial outcome, quality of life, for those in the trial, analysed by intention-to-treat. Second an economic evaluation, based on care pathways, and collecting costs during the control and intervention phases in 16 centres, in 3 countries. Third, a realist evaluation of implementation, with 3 phases in each site, the first of which is underway. 1) Readiness to implement GERONTE, and documenting current practice, and identifying barriers and facilitators for change with clinical staff, technical staff and administrators; 2) Experience of implementation as the intervention is brought in over the course of the study; 3) Experience in keeping GERONTE running after the initial implementation phase. Early results show great site to site variability, in practice and in resources, but common barriers are data handling and sharing. In each phase, guided by ideas from participatory rapid appraisal, we stress the rapid feedback to participants, of their response, and the synthesis of responses to support successful implementation. One aim is to prepare an implementation guide to support future deployments of GERONTE and similar projects, drawing on lessons from all 16 sites, and filling a gap in the literature. GERONTE is funded by the Horizon 2020 research and innovation programme under grant agreement No 945218. Key messages • Innovative health care delivery, such as integrated care, requires complex assessment approaches, designed for the specific innovation. • Site-to-site variability in the implementation of novel care pathways and approaches is the norm, and needs to be considered at design stage.

Future projections of thermal regimes and mixing characteristics in a monomictic reservoir under climate change

Stratified structures are basic physical characteristics of lakes and reservoirs, which play important roles in vertical convection and mixing processes. Global warming is expected to alter the thermal regimes and stratified characteristics of lakes and reservoirs, leading to potential environmental risks and ecological problems. In this study, we used a two-dimensional hydrodynamic model to explore the response characteristics of the thermal regime to climate change in the Xiluodu Reservoir. The study is conducted based on four representative concentration pathways (RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5). The results show that the projected surface water temperature of the reservoir will significantly increase (0.13 °C/10a-0.34 °C/10a) from 2022 to 2099, and the warming rate of the water in the epilimnion and thermocline will be greater than that in the hypolimnion, leading to enhanced vertical stratification in the reservoir. The stratification stability index (SI) will increase by 14.4 % under RCP 8.5 compared to that under RCP 2.6. The main responses of the reservoir to climate change are earlier start date and later end date of stratification, which may increase the duration of hypoxia in the hypolimnion and promote the succession of planktonic algal communities. The withdrawal water temperature in the reservoir will significantly increase under the climate warming scenarios (0.03 °C/10a-0.22 °C/10a). Furthermore, our research results indicate that selective withdrawal is still needed to mitigate the adverse effects of cold water from the reservoir during the fish spawning period under the strongest warming scenario, and can also be an effective adaptive management strategy to regulate thermal stability in the reservoir. This study provides a scientific and theoretical reference for the sustainable management of similar deep monomictic reservoirs under climate change.

Reservoir-derived subsidies provide a potential management opportunity for novel river ecosystems

Aquatic ecosystems world-wide are being irreversibly altered, suggesting that new and innovative management strategies are necessary to improve ecosystem function and sustainability. In river ecosystems degraded by dams environmental flows and selective withdrawal (SWD) infrastructure have been used to improve habitat for native species. Yet, few studies have quantified nutrient and food web export subsidies from upstream reservoirs, despite their potential to subsidize downstream riverine food webs. We sampled nutrient, phytoplankton, and zooplankton concentrations in outflows from the Shasta-Keswick reservoir complex in Northern California over a 12-month period to understand how SWD operation and internal reservoir conditions interact to influence subsidies to the Sacramento River. We found that nutrients, phytoplankton, and zooplankton were continuously exported from Shasta Reservoir to the Sacramento River and that gate operations at Shasta Dam were important in controlling exports. Further, our results indicate that gate operations and water-export depth strongly correlated with zooplankton community exports, whereas internal reservoir conditions (mixing and residence time) controlled concentrations of exported zooplankton biomass and chlorophyll a. These results demonstrate that reservoirs can be an important source of nutrient and food web subsidies and that selective withdrawal infrastructure may provide a valuable management tool to control ecosystem-level productivity downstream of dams.

A Novel Compromise Approach for Risk-Based Selective Water Withdrawal from Reservoirs Considering Qualitative-Quantitative Aspects

A Novel Compromise Approach for Risk-Based Selective Water Withdrawal from Reservoirs Considering Qualitative-Quantitative Aspects

Optimizing selective withdrawal strategies to mitigate hypoxia under water-level reduction in Germany's largest drinking water reservoir

Water-level reduction frequently occurs in deep reservoirs, but its effect on dissolved oxygen concentration is not well understood. In this study we used a well-established water quality model to illustrate effects of water level dynamics on oxygen concentration in Rappbode Reservoir, Germany. We then systematically elucidated the potential of selective withdrawal to control hypoxia under changing water levels. Our results documented a gradual decrease of hypolimnetic oxygen concentration under decreasing water level, and hypoxia occurred when the initial level was lower than 410 m a.s.l (71 m relative to the reservoir bottom). We also suggested that changes of hypoxic region, under increasing hypolimnetic withdrawal discharge, followed a unimodal trajectory with the maximum hypoxic area projected under the discharge between 3 m3/sec and 4 m3/sec. Besides, our results illustrated the extent of hypoxia was most effectively inhibited if the withdrawal strategy was applied at the end of stratification with the outlet elevation at the deepest part of the reservoir. Moreover, hypoxia can be totally avoided under a hybrid elevation withdrawal strategy using surface withdrawal during early and mid stratification, and deep withdrawal at the end of stratification. We further confirmed the decisive role of thermal structure in the formation of hypoxia under water-level reduction and withdrawal strategies. We believe the conclusions from this study can be applied to many deep waters in the temperate zone, and the results should guide stakeholders to mitigate negative impacts of hypoxia on aquatic ecosystems.

Decision support system for selective withdrawal in water supply reservoirs: an approach based on thermal stratification

Abstract We consider the problem of determining water withdrawal depth in water supply reservoirs with multilevel intakes in an effective and systematic manner. In the traditional way, operators decide which intake port to use based on their own experience and water samples taken from various depths. Our goal is to provide assistance to operators in the decision-making process and establish a systematic approach for determining the appropriate water withdrawal level in a stratified reservoir. To achieve this, we propose an algorithmic approach as a decision support system for estimating the water withdrawal level. We validate our approach using long-term data collected from a water supply reservoir and compare the results with those of the operator's decisions. The results reveal that when the depth tolerance is set to 10 m, the approach and operator's decisions match at an 80% rate. However, when the depth tolerance is increased to 15 m, the matching percentage improves to over 90%.

ДЕТЕРМИНИРОВАННЫЙ КОНЕЧНЫЙ АВТОМАТ ПОИСКА КОНТЕЙНЕРОВ В ШТАБЕЛЕ

This paper considers the prospects of digitalization in the warehouse cargo handlingsystem, as well as the&#x0D; impact of modern IT technologies on the logistics of a sea container terminal. The technological process of&#x0D; container transshipment in the operational areas of the terminal and formation of auxiliary stacks for further&#x0D; transfer of cargo between different transport means, their temporary storage and transformation (from containerized&#x0D; form to general cargo and back), as well as the implementation of secondary operations (checking,&#x0D; weighing, etc.) are the object of research. From an operational point of view, the formation of an auxiliary stack&#x0D; is a time-taking technological operation, as it requires the selective search and withdrawal from the general&#x0D; stack of a certain number of containers that make up the logistic flow of cargo moved to the relevant operational&#x0D; zone. The method of research is automatic programming of the simulated technological process. In this case,&#x0D; the simulation object is described by a finite automaton which is then converted into code. The main purpose&#x0D; of the automaton is to implement the control function. In the context of this research work, the control actions&#x0D; are aimed at the reloader and program the sequence of its actions to find the target containers in the stack. A&#x0D; mathematical model of the search and withdrawal of the target containers from the stack in the terminal storage&#x0D; area by means of a computerized control system, as well as a transition graph of the finite automaton with&#x0D; control rules (codes) are the results of this research. The application of above mathematical facility to modeling&#x0D; of technological processes makes it possible to present a unified logic of management of the prestacking process&#x0D; in operational areas of the terminal

Can selective withdrawal control algal blooms in reservoirs? The underlying hydrodynamic mechanism

Selective withdrawal is considered an effective and convenient method to mitigate thermal pollution and environmental problems in reservoirs and downstream rivers. However, the potential effects of selective withdrawal on harmful algal blooms in reservoirs remain uncertain, threatening sustainable reservoir management. This study developed and calibrated a three-dimensional (3D) hydro-ecological model for the Zipingpu reservoir to numerically investigate how selective withdrawal scenarios (including surface, middle, and bottom withdrawal) affect algal growth and hydrodynamic environments. The surface withdrawal scenario could inhibit algal growth efficiently, causing Chlorophyll a (Chl a) concentration below 10 μg L−1 consistently. The Chl a concentration decreased from 27.0 μg L−1 for bottom withdrawal and 21.2 μg L−1 for middle withdrawal to 3.3 μg L−1 for surface withdrawal in the bloom period. The nutrient, light, and temperature limitations among the three withdrawal scenarios showed slight differences and were not the main reason for the bloom differences. Compared with the bottom and middle withdrawal scenarios, the surface withdrawal scenario weakened stratification and decreased surface water temperature, suggesting inhibitory effects on algal blooms. The bottom and middle withdrawal scenarios significantly reduced surface flow velocity and made the flow direction against the water intake, indicating a favorable hydrodynamic environment for algal growth. The surface withdrawal scenario reduced hydraulic residence time, thereby restraining algal growth and accumulation in the reservoir. Implementing surface withdrawal might be an efficient and promising method to prevent algal blooms in reservoirs. These results not only highlight the potential of selective withdrawal for algal bloom control but also reveal that accelerating surface flow velocity is the key mechanism.

Diurnal variation characteristics of thermal structure in a deep reservoir and the effects of selective withdrawal

Thermal structure significantly impacts the reservoir ecology and environment. The diurnal temperature variation (DTV) influences the photosynthesis and respiration of phytoplankton in day and night, and meanwhile changes the vertical density convection and current. Selective withdrawal is practical to control the withdrawal elevation and outflow temperature, and can also influence the thermal structure of reservoir area. Previous research mainly focusses on the long-term change pattern of thermal structure in reservoir, while the diurnal thermal dynamics is less studied, and the effects of selective withdrawal on the DTV is still unknow. Hence, this paper aims to illustrate the diurnal variation characteristics of thermal structure in reservoir, and moreover to reveal the corresponding effects of selective withdrawal. Taking the Sanbanxi Reservoir as study case, a hydrodynamic–temperature numerical model with hourly simulating resolution was built and validated using measured temperature profile during August 2015 to August 2016, based on the CE-QUAL-W2. The effects of selective withdrawal schemes, including different withdrawal elevation and withdrawal types, were illuminated. The discrete Fourier transform (DFT), energy spectrum and statistical analysis were used. This paper showed the following: (1) In the reservoir area, there were three main regions with significant DTV, i.e., the surface layer, the 10-m water layer and the 60-m water layer (withdrawal layer). For the baseline (existing intake), the average DTVs were 0.657, 0.497 and 0.174 °C, respectively, at the surface layer, the 10-m-depth layer and the 60-m-depth layer. (2) From the upstream to the downstream channels of reservoir, the DTV kept unchanged at the surface layer, and increased at the 10-m-depth layer and 60-m-depth layer. (3) A higher withdrawal elevation and the internal weir schemes (stoplog gate/temperature-control curtain) could increase the epilimnetic DTV and energy density, and were suggested to mitigate the hypoxia and nutrient enrichment, compared with a lower withdrawal elevation and the multi-level intake scheme. The results could provide technical support for the ecological management of reservoir and engineering design of the selective withdrawal.

Thermal response of a deep monomictic reservoir to selective withdrawal of the upstream reservoir

Selective withdrawal is an effective strategy to alleviate the adverse impact of reservoir construction on the downstream thermal regime. However, most studies mainly focus on the water temperature improvement effect of a single reservoir, while few studies focus on the impact of selective withdrawal of upstream cascade reservoirs on downstream reservoirs. This study combined measured data and a two-dimensional hydrodynamic model (CE-QUAL-W2) to analyze the response of the downstream reservoir to selective withdrawal of the upstream reservoir in the operation mode of cascade reservoirs. The purpose of this study was to optimize reservoir operation to minimize the impact of cold water and satisfy the water temperature requirements of downstream fish spawning and breeding. The results indicated that the proposed index of the response to selective withdrawal (IRSW) could reflect the response of the downstream reservoir to selective withdrawal of the upstream reservoir. There existed a statistically significant positive correlation between the improvement in the withdrawal water temperature (WWT) in the Xiangjiaba Reservoir and the IRSW value (R = 0.9257, P < 0.05). The impact of the Xiangjiaba Reservoir on the incoming water temperature during the selective withdrawal period of the upstream reservoir imposed a negative superposition effect, and the selective withdrawal effect of the upstream reservoir could be maintained at 87.0%. The negative superimposition effect could be alleviated via independent operation of the upper water intake and maintenance of a low water level, and the IRSW could be increased by 6.6% and 10.4%, respectively, compared to that under the designed scenario, which could even approach the equilibrium effect (100%) and could be helpful to improve the WWT. This study provided a helpful reference for the evaluation of selective withdrawal and reservoir management in similar cascade reservoirs.

Controlling blooms of Planktothrix rubescens by optimized metalimnetic water withdrawal: a modelling study on adaptive reservoir operation

BackgroundAggregations of cyanobacteria in lakes and reservoirs are commonly associated with surface blooms, but may also occur in the metalimnion as subsurface or deep chlorophyll maxima. Metalimnetic cyanobacteria blooms are of great concern when potentially toxic species, such as Planktothrix rubescens, are involved. Metalimnetic blooms of P. rubescens have apparently increased in frequency and severity in recent years, so there is a strong need to identify reservoir management options to control it. We hypothesized that P. rubescens blooms in reservoirs can be suppressed using selective withdrawal to maximize its export from the reservoir. We also expect that altering the light climate can affect the dynamics of this species. We tested our hypothesis in Rappbode Reservoir (the largest drinking water reservoir in Germany) by establishing a series of withdrawal and light scenarios based on a calibrated water quality model (CE-QUAL-W2).ResultsThe novel withdrawal strategy, in which water is withdrawn from a certain depth below the surface within the metalimnion instead of at a fixed elevation relative to the dam wall, significantly reduced P. rubescens biomass in the reservoir. According to the simulation results, we defined an optimal withdrawal volume to control P. rubescens blooms in the reservoir as approximately 10 million m3 (10% of the reservoir volume) during its bloom phase. The results also illustrated that P. rubescens growth can be most effectively suppressed if the metalimnetic withdrawal is applied in the early stage of its rapid growth, i.e., before the bloom occurs. In addition, our study showed that P. rubescens biomass gradually decreased with increasing light extinction and nearly disappeared when the extinction coefficient exceeded 0.55 m−1.ConclusionsOur study indicates the rise in P. rubescens biomass can be effectively offset by selective withdrawal as well as by reducing light intensity beneath the water surface. Considering the widespread occurrence of P. rubescens in stratified lakes and reservoirs worldwide, we believe the results will be helpful for scientists and managers working on other water bodies to minimize the negative impacts of this harmful cyanobacteria. Our model may serve as a transferable tool to explore local dynamics in other standing waters.

Influence of a soluble surfactant on the transition to tip streaming

We analyze experimentally the influence of a soluble surfactant on the onset of the tip streaming produced by hydrodynamic focusing. For this purpose, we consider the viscous entrainment mode of the selective withdrawal configuration for very different outer liquid viscosities. The minimum capillary number above which viscous entrainment can be produced is determined as a function of the surfactant concentration. We analyze the influence of the surfactant monolayer on the shape and velocity of the emitted liquid jet. The results show the importance of the monolayer dynamics for sufficiently small values of the outer liquid viscosity.

Experimental Analysis of Temperature-Control Curtain Regulating Outflow Temperature in a Thermal-Stratified Reservoir.

The construction of reservoir dams has changed the environment and natural properties of the river course, and deep-water reservoirs present an obvious phenomenon of thermal stratification. Low-temperature outflow water in spring and summer will have a negative impact on the downstream ecological environment. Therefore, it is necessary to take selective withdrawal measures to regulate low-temperature outflow water. The temperature-control curtain project has the advantages of low cost, convenient construction and wide application. Based on the topographic data, a laboratory test model for regulating outflow temperature by a temperature-control curtain is established. A high-power electric heating system is adopted to form a nonlinear thermal stratification. The accuracy of the test data is verified by the prototype observed water temperature. The main parameters affecting the outflow temperature are investigated, including thermal stratification, flow height above the temperature-control curtain, water level, and discharge flow. The results show the following: firstly, the outflow temperature mainly depends on the thermal stratification, decreases with the increase of water level, and increases with the increase of discharge flow; secondly, the effect of a temperature-control curtain on improving the outflow temperature is directly related to the thermal stratification in different months, and the improvement effect is better in spring and summer; finally, the improvement effect increases with the decrease of flow height above the temperature-control curtain, increases with the increase of water level, and decreases with the increase of discharge flow.

Predicting transition from selective withdrawal to entrainment in two-fluid stratified systems.

Selective withdrawal is a desired phenomenon in transferring oil from large caverns in the U.S. Strategic Petroleum Reserve (SPR), because entrainment of oil at the time during withdrawal poses a risk of contaminating the environment. Motivated to understand selective withdrawal in an SPR-like orientation, we performed experiments in order to investigate the critical submergence depth as a function of critical flow rate. For the experiments, a tube was positioned through a liquid-liquid interface that draws the lower liquid upward, avoiding entrainment of the upper fluid. Analysis of the normal stress balance across the interface produced a Weber number, utilizing dynamic pressure scaling, that predicted the transition to entrainment. Additionally, an inviscid flow analysis was performed assuming an ellipsoidal control volume surface that produced a linear relationship between the Weber number and the scaled critical submergence depth. This analytical model was validated using the experimental data, resulting in a robust model for predicting transition from selective withdrawal to entrainment.