Flow Imbalance Research Articles

Увеличение продолжительности работы установки электроцентробежного насоса для повышения безопасности и сокращения рисков при спускоподъемных операциях

The study analyzes basic complications associated with generating mechanical impurities; numeric modeling to optimize the electrical submersible pump operation has been performed. Modeling the fluid flow in combination with erosion models has been used to determine the key factors facilitating the erosion of the electrical submersible pump action wheel impeller during oil production. In order to obtain a complete view of the flow and erosion properties, modeling has been performed for the entire fluid flow route. Modeling of the flow and the action wheel component erosion has been performed to determine the impact of the flow imbalance as well as to ensure the boundary conditions at the input for the modeling. The modeling results have shown: the rotational flow introduced in the mixing point at the action wheel input significantly impacts the strength properties of the modeled object; the area most exposed to erosion is the area of the action wheel impeller. The values of loss of material have been determined via the time sequence of geometry changes in the compounds in combination with the actual hydraulic operational parameters. The flow trajectories proposed for modeling show that the recirculating flow is the dominant. It is widely adopted that recirculation is one of the main causes of increased erosion in the compounds of the electrical submersible pump as it leads to the high frequency of high-speed impacts by sand particles. In order to reduce the erosion risk, the analysis aiming to identify the impeller geometrical parameters has revealed that the erosion rate in the compound can be reduced by decreasing the inclination of the action wheel impeller. The study has demonstrated that numerical modeling can provide a detailed and precise evaluation of erosion potential in cases associated with the high velocity of fluid flow with particles of mechanical impurities.

Effect of multiscale metro network-wide attributes on peak-hour station passenger and flow balancing

Analyzing the balance of station passenger and passenger flow is essential for understanding jobs-housing balance and built environment in station areas and network-wide range as well as for enhancing the efficiency of urban rail transit operations. Taking the Shanghai rail transit network as a case study, this paper defines the Multiscale Subnetwork (MSSN) based on a specific spatial scope. By extracting the network features and built-environment elements of the stations and the MSSN, this study analyzes the factors affecting the peak-hour station passenger and the imbalance of regional network passenger flow. The research suggests that the small MSSN analysis, within 6-8 km from a station, can provide valuable results from a network-wide perspective, rather than solely focusing on individual station areas or the entire network. The regional attributes of jobs-housing balance and the transportation conditions in the MSSN range have great impact on both station passengers and flow imbalance. This research provides theoretical insights for urban planners and policymakers to formulate effective strategies for urban rail transit networks.

An ultrasound-assisted resin transfer molding to improve the impregnation and dual-scale flow for carbon fiber reinforced resin composites

The imbalance of the dual-scale flow, i.e., microscopic intra-bundles and macroscopic inter-bundles flow, always generates voids in resin transfer molding (RTM) of composites, substantially weakening the mechanical performance. An ultrasound-assisted strategy to improve the impregnation and to balance dual-scale flow is promising to suppress the voids, while, it has still not been explored. Here, an ultrasound-assisted RTM for carbon fiber reinforced resin composites, realized by a self-developed device, is originally proposed. The influences of ultrasound vibration on the carbon fibers, resins, wettability, and impregnation process are systematically explored. Furthermore, the dual-scale flow, affected by the ultrasound vibration, is optimized. It is identified that the ultrasound vibration effectively reduces the viscosity of the resin and increases the roughness and surface activity of the fibers, hence significantly weakening the delayed impregnation in the intra-bundles, and speeding up the impregnation velocity in the inter-bundles. The reduction of the viscosity and the contact angle synergistically lowers the modified capillary number Ca*, hence balancing the dual-scale flow, while the excessively high impregnation velocity in the inter-bundles detrimentally enlarges Ca*, leading to the imbalance of the dual-scale flow. Accordingly, a critical ultrasound energy input (4 min of ultrasound vibration at the power range of 400–600 W) is figured out to achieve an optimal Ca*, providing a promising approach to suppress the flow-induced voids in composites manufacturing by RTM.

TRPV4 Antagonist Treatment of Hydrocephalus Causes Cell and Molecular Changes in Multiple Brain Cell Types

Hydrocephalus is defined by cerebrospinal fluid (CSF) accumulation in the brain’s ventricles causing ventriculomegaly, an imbalance in CSF secretion, flow, and/or absorption. Treatments for hydrocephalus include invasive surgical procedures, which commonly fail throughout a patient’s life. Transient receptor potential vanilloid member 4 (TRPV4) is a mechanosensitive cation channel implicated in osmotic regulation. Our laboratory found that a TRPV4 antagonist, RN1734, ameliorates hydrocephalus in a rat model of congenital hydrocephalus. It was hypothesized that treatment slowed production of CSF by targeting choroid plexus (CP), a contiguous layer of tightly regulated epithelial cells, that is responsible for CSF production. However, hydrocephalus pathology can have various effects on the brain. This study focuses on changes occurring in CP epithelial cells (CPe) and glia, which have roles in brain-barrier maintenance and brain fluid/electrolyte regulation. Interestingly, CPe and glia contain many of the same channels and transporters, including TRPV4, that are important in regulating both CSF and brain interstitial fluid. These cells contain aquaporins (AQP), AQP1 in CPe, and AQP4 in glia. AQPs have been implicated in diseases associated with fluid regulation and may interact with TRPV4. We hypothesize that TRPV4 and AQPs are important in hydrocephalus pathology, and that changes may be attenuated with RN1734 treatment. A point mutation in TMEM67 results in hydrocephalus (hydro). Changes in cell morphology, gene transcription, protein expression, localization of TRPV4, AQP1, and AQP4 were observed. Postnatal day 15 (P15) untreated (unt) and RN1734-treated (RN;2mg/ml DMSO; 4mg/kg intraperitoneal injection daily P7-P14) wildtype and mutant ( Tmem67−/−) rats were utilized in this study. CPe and periventricular (PV) glia were visualized using fluorescent immunohistochemistry (IHC) of GFAP and a plasma membrane marker. Cell volume of CPe’s and process morphology of glia were altered in hydro rats. RN returned these changes to relatively normal in CPe, but not glia. Next, we used IHC to examine localization of TRPV4 and the AQPs. Increased immunoreactivity of TRPV4 and AQP1 was observed in CPe of unt and RN Tmem67−/− rats. AQP4 and TRPV4 immunoreactivity increased in the subventricular zone and PV white matter of hydro rats. TRPV4 immunoreactivity, but not AQP4, was normalized with RN. We then utilized RTqPCR to inspect transcriptional changes. The data showed increased AQP1 and decreased TRPV4 mRNA in PV cortex and CP of unt and RN Tmem67−/− rats. Previous data from our laboratory found no change in TRPV4 protein in unt Tmem67−/− CPe, but we were curious about AQP expression. The amount of AQP1 protein was increased in the CP of unt and RN Tmem67−/− rats. In PV cortex, AQP4, but not TRPV4, protein was increased in hydro rats. With RN, AQP4 protein was not normalized. In summary, TRPV4 changes in the Tmem67−/− rats returned to normal with RN, glial morphology and AQP changes did not. This may indicate residual inflammation in the Tmem67−/− rats, which we aim to address in future studies. To further elucidate TRPV4’s role in hydrocephalus pathology, future studies will explore post-translational and membrane localization changes. Overall, investigating cell and molecular changes that occur in hydrocephalus will help find better pharmacological targets for this disease. Funding: United States Department of Defense Congressionally Directed Medical Research Program Award; Hydrocephalus Association. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Nitrogen precooling heat exchanger replacement and control system upgrade in superfluid cryoplant at CMTF

Liquid nitrogen precooling is used in most cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF superfluid cryoplant, where the helium supply directly exchanges heat with liquid nitrogen, freezing of nitrogen occurred inside the heat exchanger due to heat exchanger flow imbalance during a cryoplant trip. Trapped vapor pockets of nitrogen within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold helium gas from cold end during abrupt cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of nitrogen which can damage the heat exchanger.

Asymmetric post earnings announcement drift and order flow imbalance: The impact on stock market returns

We conduct an event study around the earning announcement to examine the asymmetric post earnings announcement drift, and its relationship with the bid-ask bias, order follow imbalance on post earnings announcement period for UK stock market from 2000 2021. The earning drift is significantly asymmetric in the post earnings announcement period, stocks with good news have less drift, and it (at least) partly due to the order flow imbalance during the event period. The earning announcement attracts more sell than buy orders, and an overall negative reaction in the market. The difference between transaction price return and quote price returns shows that the bid-ask bias is also a possible explanation of post earnings announcement drift. Our results are robust across different estimations and robustness tests.

Altered Cortical Information Interaction During Respiratory Events in Children with Obstructive Sleep Apnea-Hypopnea Syndrome.

Obstructive sleep apnea-hypopnea syndrome (OSAHS) significantly impairs children's growth and cognition. This study aims to elucidate the pathophysiological mechanisms underlying OSAHS in children, with a particular focus on the alterations in cortical information interaction during respiratory events. We analyzed sleep electroencephalography before, during, and after events, utilizing Symbolic Transfer Entropy (STE) for brain network construction and information flow assessment. The results showed a significant increase in STE after events in specific frequency bands during N2 and rapid eye movement (REM) stages, along with increased STE during N3 stage events. Moreover, a noteworthy rise in the information flow imbalance within and between hemispheres was found after events, displaying unique patterns in central sleep apnea and hypopnea. Importantly, some of these alterations were correlated with symptom severity. These findings highlight significant changes in brain region coordination and communication during respiratory events, offering novel insights into OSAHS pathophysiology in children.

Investigation of microstructural and mechanical properties of weld lines in injection‐molded short glass fiber‐reinforced polyamide 6

AbstractThis research investigates the impact of weld lines on the mechanical properties and fracture behavior of injection‐molded unfilled and glass fiber‐reinforced polyamide 6 (PA6). The study aims to predict the weld line strength by analyzing the composite's microstructure at the weld line and investigating the influence of injection molding parameters. While weld lines had minimal effects in unfilled PA6 thanks to the matrix's high healing capability, composite samples showed reduced mechanical properties due to unfavorable fiber orientation at the weld line. Fracture surfaces revealed a bell‐shaped structure linked to the ‘underflow’ process caused by flow imbalances during injection molding. This phenomenon impacts fiber orientation at the weld line, affecting mechanical properties. The ‘underflow’ is simulated using Autodesk Moldflow®, predicting enhanced fiber alignment along the flow direction. Regarding processing parameters, both melt and mold temperatures showed negligible impacts, while enhanced mechanical properties were observed at elevated packing pressures. The analysis of fracture surfaces showed intensified “underflow” with increased packing pressure. A relationship is established between weld line strength and fiber orientation at the weld line, potentially serving as a predictive tool for estimating weld line strength.Highlights Weld lines in unfilled PA6:Negligible impact on the mechanical properties. In the PA6 composite: significant drop due to unfavorable fiber orientation. Fracture behavior of the composite: Bell‐shaped weld line linked to “underflow.” Melt and mold temperature: minor effect; packing pressure enhances properties. Correlation established between the weld line strength and fiber orientation.

Research on passenger flow prediction of tourist attractions by integrating differential evolution and GWO optimization

Abstract With the rapid development of tourism, the rapid growth in the number of tourists caused by the imbalance of the passenger flow carrying capacity of tourist attractions, tourist crowding, overloading, and other problems caused by the frequent occurrence of safety accidents, to the tourist attractions has caused a huge negative impact. For this reason, this paper constructs a model for predicting passenger flows at tourist attractions based on the GWO algorithm. Optimizing the model involves using a differential evolutionary algorithm following a feature study with the Gray Wolf Optimization (GWO) algorithm. Then, for the problems that are prone to occur in the fusion of the GWO algorithm and DE algorithm for solving nonlinear systems of equations, a combined GWO-DE-SVM model is proposed to realize the accurate prediction of tourist attractions’ passenger flow. On this basis, the prediction effect of the GWO-DE-SVM combination model is examined. The loss values of the model in the training set and test set of this paper are around 0.034 and 0.029, respectively, with the lowest average error of 2.524% among all the models. The passenger flow and the total tourism revenue of W tourist attraction in the coming year are successfully predicted in the practical application, which is estimated to be 681 million and 106.88 million yuan, respectively. Million and 106.88 million yuan are the respective amounts. And two peaks of tourist attractions in W were predicted in May and October. This study provides a scientific basis for the management of scenic spots to prevent tourist crowding.

A ONE-WAY COUPLED APPROACH FOR MULTISCALE CHARACTERIZATION OF FILLING OF DUAL-SCALE FIBROUS REINFORCEMENTS CONSIDERING AIR COMPRESSIBILITY AND DISSOLUTION IN LUMPED FASHION

The filling characterization of dual-scale fibrous reinforcements is challenging due to the presence of subdomains with dissimilar permeabilities, existence of wicking effects, and combination of air compressibility and dissolution phenomena. These factors cause flow imbalances inside the representative unitary cell (RUC), which lead to void formation and influence the behavior of macroscopic field variables, affecting the parts manufacturing by liquid composite molding (LCM). Here, the filling characterization of woven fabrics used in LCM is done using one-way coupled simulations. Once RUC geometry is characterized by scanning-electron microscopy (SEM), and stereomicroscopy, standard thickness test, and resin viscosity are measured, the multiphase finite volume method-volume of fluid (FVM-VOF) model of ANSYS Fluent is used for the three-dimensional filling of the RUC, incorporating an experimentally calibrated air entrapment parameter (λ) to consider air compressibility and dissolution; then, a lumped function for the coupling term with macroscopic equations is obtained in terms of volume-averaged variables. This function is used in the equivalent Darcy macroscopic model, which is solved using a dual-reciprocity boundary element method (DR-BEM) algorithm. By considering a single value of λ during the simulation, neglecting wicking effects, and normalizing physical variables, unified injection pressure-independent results for the local tows saturation and normalized pressure fields at mesoscopic scale were obtained, as well as for global tows saturation and normalized pressure and fluid front profiles at macroscopic scale, thus simplifying the filling characterization of reinforcements. Numerical results are coherent with unidirectional injection experiments at both scales.

Poststroke Mania During the COVID-19 Pandemic.

The pandemic of coronavirus infection 2019 (COVID-19) is stressing people's daily lives and making them more susceptible to various mental illnesses. Depression and suicide attempt as well as, strangely enough, manic patients are on the rise. The main complication of COVID-19 infection is ischemic stroke. Multiple lacunar infarcts in the white matter of the right middle cerebral artery region induce an imbalance of blood flow in the left and right cerebral cortex and risk causing mania. The increase in mania during the COVID-19 must be considered not only a primary increase due to stress but also poststroke mania secondary to COVID-19 infection.

External wealth of nations and systemic risk

External imbalances played a pivotal role leading to the global financial crisis and were an important cause of turmoil. While current account (flow) imbalances narrowed in the aftermath of the crisis, the net international investment position (NIIP) (stock) imbalances persisted. This study explores the implications of countries’ net foreign positions on systemic risk. Using a sample of 470 banks located in 49 advanced economies, emerging countries, and developing economies over 2000–2020, we find robust empirical evidence that banks can reduce their systemic risk exposure when the countries in which they are incorporated improve their NIIPs and maintain creditor status vis-à-vis the rest of the world. However, only the equity component of the NIIP is responsible for this outcome, whereas debt flows are not significant. Similarly, we find that the mitigating effect of an external balance sheet on systemic risk is derived from valuation gains rather than from the incremental net acquisition of assets or liabilities represented by the current account. Our findings are particularly relevant for policymakers seeking to improve banks’ resilience to adverse shocks and maintain financial stability.

Coronary Computed Tomographic Angiography With Fractional Flow Reserve in Patients With Type 2 Myocardial Infarction

BackgroundType 2 myocardial infarction (T2MI) related to a supply/demand imbalance of coronary blood flow is common and associated with poor prognosis. Coronary artery disease (CAD) may predispose some individuals to T2MI and contribute to its high rate of recurrent cardiovascular events. Little is known about the presence and extent of CAD in this population. ObjectivesThe goal of this study was to evaluate the presence and characteristics of CAD among patients with T2MI. MethodsIn this prospective study, consecutive eligible individuals with Fourth Universal Definition of Myocardial Infarction criteria for T2MI were enrolled. Participants underwent coronary computed tomography angiography (CTA), fractional flow reserve derived with coronary CTA (FFRCT), and plaque volume analyses. ResultsAmong 50 participants, 25 (50%) were female, and the mean age was 68.0 ± 11.4 years. Atherosclerotic risk factors were common. Coronary CTA revealed coronary plaque in 46 participants (92%). A moderate or greater stenosis (≥50%) was identified in 42% of participants, and obstructive disease (≥50% left main stenosis or ≥70% stenosis in any other epicardial coronary artery) was present in 26%. Prevalence of obstructive CAD did not differ according to T2MI cause (P = 0.54). A hemodynamically significant focal stenosis identified by FFRCT was present in 13 participants (26%). Among participants with a stenosis ≥50% (n = 21), FFRCT excluded lesion-specific hemodynamically significant stenosis in 8 cases (38%). ConclusionsAmong individuals with adjudicated T2MI, CAD was prevalent, but the majority of patients had nonobstructive CAD. Mediators of ischemia are likely multifactorial in this population. (Defining the Prevalence and Characteristics of Coronary Artery Disease Among Patients with Type 2 Myocardial Infarction using CT-FFR [DEFINE TYPE 2 MI]; NCT04864119)

STRUCTURAL AND FUNCTIONAL PARAMETERS OF THE ENDOMETRIUM AND OVARIAN TISSUE IN PATIENTS WITH IMPAIRED REPRODUCTIVE POTENTIAL AND OBESITY

According to the WHO, every second woman has a problem with excess weight, while about 23% of women indicate a pathological body mass index, and excess weight (the so-called “pre-obesity”) is noted in 25% of women.
 The aim of the research was to evaluate the structural and functional parameters of the endometrium and ovarian tissue and to optimize the diagnostic algorithm and monitoring of the endometrium in women with obesity and impaired reproductive function.
 Materials and methods. 110 patients of reproductive age with impaired reproductive health underwent a comprehensive clinical and laboratory examination within the framework of this research. The main group included 64 patients with overweight and class 1 obesity, and the comparison group consisted of 46 women with a normal body mass index. The proposed diagnostic algorithm included a sonographic study of the structural parameters of the endometrium and ovaries, as well as an assessment of the features of the blood supply to the pelvic organs and statistical processing of the results.
 Research results and their discussion. The presented results allow us to note a significant percentage of comorbidity of somatic and gynecological pathology in overweight and obese patients. Pregnancy is accompanied by a higher percentage of early reproductive losses (14.0%), preterm birth (10.9%), preeclampsia (42.2%), placental dysfunction (46.4%) and low birth weight (17.2%). The main clinical forms of endometrial pathology in the main group were polyposis (32.8%), endometrial hyperplasia (23.4%) and dyschronosis of morphological changes of the endometrium (28.1%). The combination of endometrial hyperplasia with/or uterine leiomyoma, adenomyosis, benign ovarian tumors and retention formations was noted in 53.6% of observations in both groups; in 46.4% of women the isolated form was noted. The morphological characteristics of endometrial polyposis allowed us to note the dominance of glandular-fibrous polyps (45.2%) and in the case of a combination with myoma or ovarian retention cysts - glandular forms (32.3%). The most frequent sonographic marker of dysfunction of the endometrial potential (inconsistency of the ultrasound image of the endometrium with the phase of the menstrual cycle) was revealed in more than half of the cases (62.5%). Sonographic evaluation of the structural parameters of the endometrium and ovarian tissue showed an increase in the anterior-posterior size of the uterus and the thickness of the endometrium by 2.8 times, the volume of the ovary – by 2.0 times. It should be noted that the patients of the main group had a greater proportion of cysts and endometriomas. According to dopplerometry data, significantly lower parameters of the vascular resistance index were confirmed in the ovarian arteries and in the arteries of the stroma; in almost half of the observations, varicose veins of the parametrium were noted.
 Conclusions. Changes in steroidogenesis against the background of lipid metabolism disorders are accompanied by an increase in the volume of the endometrium and ovarian tissue, growing proportion of cystic formations in the appendages, an increase in the hemodynamic imbalance of blood flow in pelvic organs, which requires optimization of the monitoring program at the stage of preconception preparation and elimination of risk factors for placental dysfunction.

Deep order flow imbalance: Extracting alpha at multiple horizons from the limit order book

AbstractWe employ deep learning in forecasting high‐frequency returns at multiple horizons for 115 stocks traded on Nasdaq using order book information at the most granular level. While raw order book states can be used as input to the forecasting models, we achieve state‐of‐the‐art predictive accuracy by training simpler “off‐the‐shelf” artificial neural networks on stationary inputs derived from the order book. Specifically, models trained on order flow significantly outperform most models trained directly on order books. Using cross‐sectional regressions, we link the forecasting performance of a long short‐term memory network to stock characteristics at the market microstructure level, suggesting that “information‐rich” stocks can be predicted more accurately. Finally, we demonstrate that the effective horizon of stock specific forecasts is approximately two average price changes.

3D MHD analysis of prototypical manifold for liquid metal blankets

The water-cooled lead lithium (WCLL) and the dual-cooled lead lithium (DCLL) are two of the breeding blanket (BB) concepts that the EUROfusion consortium is pursuing in the framework of the development of the fusion reactor industrial demonstrator DEMO. Both involve the use of a liquid metal (LM) as working fluid, the lead-lithium eutectic alloy (PbLi), due to its excellent thermal properties and the possibility to serve as both the blanket coolant and tritium breeder and carrier. Unfortunately, due to the high electrical conductivity of LMs, their motion is influenced by the magnetic field used in the reactor to confine the plasma, generating a complex phenomenology which is studied by magnetohydrodynamics (MHD). In this work, a representative prototypical manifold of a BB bottom feeder is investigated for different configurations with the custom phiFoam solver, capable of simulating unsteady, incompressible and isothermal MHD flow. The aim of this study is to investigate which configuration minimizes the flow imbalance in the manifold for the WCLL or in the poloidal breeding zone channels for the DCLL. The distribution of the flow rate among the channels is strongly influenced by the position of the feeding pipe (FP) and by the development of the MHD internal layer near the expansion, which generates important jets close to the lower plate and the upper one, where the channels are attached. The channel aligned with the FP is the one carrying most of the flow, from 55% to 82%, while in the more distant one the flow is almost stagnant, carrying from 17% to 6% of the total flow rate. The total pressure loss is also estimated and its functional dependence on the manifold configuration is discussed.

A Collaborative Method on Reversible Lane Clearance and Signal Coordination Control in Associated Intersection

To improve traffic efficiency and utilization of road resources and alleviate traffic congestion caused by imbalance of bidirectional traffic flow, in view of the conversion conditions of reversible lane function, the operating characteristics of associated intersections under dynamic reversible lanes are analysed in terms of capacity, and a reversible lane control model is constructed based on short-term traffic flow prediction. On this basis, the reversible lane segment clearing time and upstream and downstream signal control strategies under different states are studied. The collaborative control model of reversible lane clearing time and signal timing of associated intersections is established to obtain the optimal time for reversible lane function switching. Finally, using Chaoyang Road, Beijing, as an example, the effectiveness of the proposed model is verified by the simulation indexes of average vehicle delay and reversible lane clearing time. The results show that the optimized clearing efficiency exceeds 15% and the optimized average vehicle delay is reduced by more than 10%. Combined with the future traffic state, the traffic capacity and saturation flow are greatly improved, and the intelligent reversible lane control is better achieved.

Distributed primal-dual method on unbalanced digraphs with row stochasticity

This study investigates distributed convex optimisation that accounts for the inequality constraints over unbalanced directed graphs. In distributed optimisation, agents exchange information on a network to obtain an optimal solution when they only know their own cost function. We propose a distributed primal-dual subgradient method based on a row stochastic weight matrix that is associated with a communication network. In the proposed method, the normalised left eigenvector of the weight matrix is estimated by a consensus algorithm. Then, the subgradient of the Lagrange function is scaled by the estimated values of the left eigenvector to compensate for the imbalance of the information flow in the network. We show that the pair of estimations for the primal and dual problems converge to an optimal primal-dual solution. We also show the relation between the convergence rate of the proposed algorithm and the step-size rule. A numerical example confirms the validity of the proposed method.

Modal decomposition of flow instabilities in a straight turbine diffuser around the best efficiency point

Hydraulic turbines sometimes exhibit a sharp efficiency drop around the best efficiency point. The drop is known to originate from large flow separations in their draft tubes, limiting their ability to recover part of the residual kinetic energy exiting the runner. While the conditions leading to the onset of these separations are not yet understood, the potentially unstable vorticity distribution at the runner exit led to the hypothesis that those separations are the result of an interaction between the flow at the center of the draft tube and the boundary layer at the walls. To study this hypothesis, the turbulent flow inside the draft tube of a bulb turbine was measured with time-resolved particle-image velocimetry (TR-PIV). In this work, coherent structures are identified from spectral proper orthogonal decomposition (SPOD) of the velocity fields to correlate changes in their topology with the efficiency drop. Special attention is given to the periodic vortical motions in the runner's wake, whose shape and energy content are found to be linked to the flow rate. Three-dimensional reconstructions of the underlying structure reveal a shift in its topology that correlates with the efficiency drop and separations at the wall. In addition, comparisons of the SPOD coefficients with the runner position show that the phase angle between the structure and the runner remains the same for each operating condition, suggesting a link with a rotating flow imbalance in the runner blade channels.

Do IOC Orders Improve the Market Quality? Evidence from the KOSPI 200 Futures Market

This study investigates the effect of IOC (immediate-or-cancel) orders on market quality, such as time to execution, volatility, quote spread, and market depth, in the KOSPI 200 index futures market. Analysis of the order flow imbalance indicates that IOC orders, accounting for 50% of trades in the futures market, leads more price impact than non-IOC,. Additionally, the IOC orders, mostly submitted by foreign investors, and simultaneously by multiple traders in the form of herding, incur negative impact on the market quality in the aspect of market volatility, quote spread, and market depth. However, IOC orders have the positive effect of reducing the time to execution.