Branch Flow Research Articles

Comparison of clinical outcomes between sufficient versus insufficient diagonal branch flow in anterior acute myocardial infarction.

In primary percutaneous coronary intervention (PCI), revascularization to the main branch is considered to be more important than that to the side branch. The purpose of the present study was to compare in-hospital clinical outcomes between sufficient and insufficient diagonal flow in patients with anterior ST-elevation acute myocardial infarction. A total of 229 left anterior descending artery (LAD)-AMI with final Thrombolysis in Myocardial Infarction (TIMI)-3 LAD flow were included, and divided into the sufficient diagonal flow group (TIMI-3 diagonal flow: n = 170) and the insufficient diagonal flow group (TIMI ≤2 diagonal flow: n = 59). The primary endpoint was the incidence of mechanical complication. The secondary endpoints were incidences of in-hospital death, heart failure at discharge, and left ventricular thrombus. There were no significant differences in the primary endpoint (the sufficient diagonal flow group: 1.2%, the insufficient diagonal flow group: 0%, P = 0.403). In-hospital death was more frequently observed in the insufficient diagonal flow group (8.5%) than the sufficient diagonal flow group (2.9%) without reaching statistical significance (P = 0.073). The incidence of heart failure at discharge, and thrombus in left ventricular were not different between the two groups. In conclusion, in-hospital outcomes were not significantly different between the sufficient and insufficient diagonal flow groups. We may not stick to the diagonal flow in LAD-STEMI, as long as the LAD flow is maintained by PCI.

Free and forced morphodynamics of river bifurcations

AbstractWater and sediment distribution by river bifurcations is often highly unbalanced. This may result from a variety of factors, such as migration of bars, channel curvature and backwater effects, which promote an uneven partition of flow and sediment fluxes in the downstream branches, which we call ‘forcings’. Bifurcations also display an intrinsic instability mechanism that leads to unbalanced configurations, as occurs in the idealized case of a geometrically symmetric bifurcation, which we call ‘free’, provided the width‐to‐depth ratio of the incoming flow is large enough. Most frequently, these free and forced mechanisms coexist; however, their controlling roles in bifurcation dynamics have not been investigated so far. In this paper we address this question by proposing a unified free‐forced modelling framework for bifurcation morphodynamics. Upstream channel curvature and different slopes of downstream branches (slope advantage) are specifically investigated as forcing effects typically occurring in bifurcations of alluvial channels. The modelling strategy is based on the widely used two‐cell model of Bolla Pittaluga et al. (Water Resources Research, 2003, 39(3), 1–13), here extended to account for the spatially non‐uniform fluxes entering the bifurcation node. Results reveal that the relative role of free and forced mechanisms depends on the width‐to‐depth ratio falling above or below the resonant threshold that controls the stability of free bifurcations: when the main channel is relatively wide and shallow (super‐resonant regime) the bifurcation invariably evolves towards unbalanced configurations, whatever the combination of curvature and slope advantage values, which instead control the bifurcation response under sub‐resonant conditions. Detection of the resonant aspect ratio as a key threshold also releases the modelling approach from the need for parameter calibration that characterized previous approaches, and allows for interpreting under a unified framework the opposite behaviours shown by gravel‐bed and sand‐bed bifurcations for increasing Shields parameter values. © 2018 John Wiley & Sons, Ltd.

Численная оценка вероятностного распределения перетоков мощности

Background. Active power flow capacities are used to monitor the compliance with power system stability requirements while configuring and running the system. The grid is modeled mathematically for such design. The projected daily load curve and its associated magnitudes are calculated per rules, i.e. set specifically for specific time intervals. However, actual loads are not constant and can generally be represented by an interval that contains the actual values. Grid parameters are also seasonal, as they are affected by accidents, weather, etc. In other words, a grid model uses a number of assumptions. This paper proposes Monto-Carlo simulation to simulate the parameters of a power system as affected by changing the initial loads at grid nodes as well as the line resistance values per Gaussian distribution. The method can find how these values affect power flows in grid branches as well as determine the margin of static stability. Materials and methods: Monte Carlo Method (method of statistical testing). Results. This methodology has been applied to a base-generator/base-load two-node system as well as to a base-load-generator three-node system; besides, it has been applied to the model of Radkino-Arlansky District, Republic of Bashkortosan’s power system. For these models, the team calculated the active and reactive power flows for each successfully computed operating mode that would not compromise static stability. The obtained values were used to plot distributions and to find the range of their variation. Then the static stability factors were calculated and their dependences on the interval length of initial grid parameters changing were constructed. Conclusions. Changing the range of power flows in the branches of the analyzed grid helped researchers find which of them had the greatest fluctuation range and which nodes would affect the flows the most if altered in capacity. Thus, the capacities of these nodes are subject to more accurate adjustment.

Гибридная трехфазно-однолинейная режимная модель для оценки состояния электроэнергетической системы

The article considers a new formulation of the state estimation problem, i.e., calculating the electric power system operation mode based on remote measurement data. The suggested approach implies the possibility of computing the electric operation mode parameters in a three-phase formulation for the grid parts equipped with three-phase measurement instruments. As regards the grid parts that are not fitted with such instrumentation, but in which single-line measurements are available, or which are characterized by an insignificant imbalance of operation mode parameters, their state is estimated in the single-line formulation. A distinguishing feature of such problem formulation is that the AC power flows in the grid circuit branches are used as the sought variables. The use of this approach essentially simplifies the problem and brings about additional advantages that are especially important for distribution networks. A hybrid three-phase and single-line operation mode analysis model for solving the state estimation problem is proposed and described. Owing to the use of AC power flows in the grid circuit branches as independent variables (a flow model), it becomes possible to use the phase or line form of the described model depending on the available measurement information in the grid part or component and the requirements posed to the problem being solved. The change over from one system of coordinates to another is made without making essential changes in the analysis model itself. The model errors were analyzed on a test network circuit. The analysis results have shown that the proposed model can be used for calculating the electric operation mode if the phase voltages at the interface between the three-phase and single-line grid submodels do not differ from each other by more than 10%.

Successful endovascular management of renal artery aneurysm containing several outflow vessels supplying significant part of the renal parenchyma

Background: Complex renal artery aneurysms (RAAs) represent a therapeutic challenge, especially in those who contain branches of the renal artery. Treating the RAA may compromise renal perfusion, cause ischemia, and significant parenchymal loss. Purpose: The current report describes a rare case of complex RAA with three dependent arterial branches, successfully managed by a flow diverting stent (FDS) which is usually indicated for the treatment of large and giant cerebral aneurysms. Methods: We report a case of a 61-year-old male who presented with a 2.3 cm left RAA which contained the origin of three major arterial branches that provide a significant part of the blood supply to the entire left kidney. Due to the existence of these three branching blood vessels within the aneurysm, a standard stent-graft or an open procedure were not considered as adequate therapeutic alternatives in this case. To overcome this challenge, we have elected to use an FDS which is commonly used in the treatment of cerebral aneurysms. This unique type of stent promotes gradual thrombosis of the aneurysmal sac with the advantage of maintaining flow in regional side branches. Results: At 6 months of follow up, creatinine level was 1.3 mg/dL (baseline was 1.1) and upon follow up CT - the renal parenchyma was well preserved. Conclusions: This case report presents a unique solution for treating complex RAA by using an FDS that is routinely used for the treatment of large and giant cerebral aneurysms. FDS is a valuable treatment option for complex RAAs since it can treat the aneurysm without compromising the branching blood vessels.

Linear/quadratic programming-based optimal power flow using linear power flow and absolute loss approximations

This paper presents novel methods to approximate the nonlinear AC optimal power flow (OPF) into tractable linear/quadratic programming (LP/QP) based OPF problems that can be used for power system planning and operation. We consider a linear power flow and branch flow approximation and derive a power loss approximation in the form of absolute value functions that are suitable to cover a broader operating range. The key ideas are (1) to capture power losses and power flows in the full decision variable domain, (2) to combine these approximations to recast the nonlinear constraints of the OPF problem into linear ones, and (3) to solve the approximate OPF problem with off-the-shelf solvers in a non-iterative fashion. In this way, the problem complexity can be reduced significantly. In detail, we present four OPF approximation methods, in which we relax the absolute power loss functions as linear constraints. In a comprehensive case study the usefulness of our OPF methods is analyzed and compared with an existing OPF relaxation and approximation method. As a result, the errors on voltage magnitudes and angles are reasonable, while obtaining near-optimal results for typical scenarios. We find that our methods reduce significantly the computational complexity compared to the nonlinear AC-OPF making them a good choice for power system planning purposes.

Joint optimization of day-ahead and uncertain near real-time operation of microgrids

Due to the feature of a distribution-free model of uncertainties, robust optimization has become an attractive and efficient way to the energy management systems. In microgrids, regardless of the real-time conditions, this approach is used only to model the day-ahead energy management in the presence of renewables uncertainties. However, energy management can be done more efficiently by joint optimization of day-ahead and near real time conditions. In this case, in addition to the renewable uncertainty, the uncertainty of the real time market price is added to the problem. Furthermore, in the existing joint optimization models, which are mostly formulated with stochastic methods, the operational constraints such as exact power flow equations are discarded. This paper proposes a two-stage full robust model for joint optimization of day-head and uncertain real-time operation of microgrids considering exact modeling of the operational constraints. According to the forecasted value of renewable generations, the day-ahead problem is formulated as a MILP at the first stage. The uncertain real-time operation is formulated in the second stage by completely robust modeling of the uncertainties. In order to maintain the convex structure of the real-time problem, nonlinear constraints of the power flow equations are formulated based on the second-order cone relaxation of the branch flow equations, which is necessary for solving the problem using the cutting plan methods in a polynomial time. For solving the two-stage model, the dual Bender's decomposition algorithm is used. The proposed model is implemented on the modified IEEE 33 bus network, and the results including sensitivity analysis on the price and renewable budgets are presented. In addition, the efficiency and effectiveness of the proposed model are shown by comparing the results with two other methods in joint optimization and traditional robust day-ahead management method to determine the effect of considering real-time operation. At the end, the effect of the network structure and operational limitations on the results has been studied.

The Impact of the NAO on the Delayed Break-Up Date of Lake Ice over the Southern Tibetan Plateau

ABSTRACTThe changing characteristics of lake ice phenology over the Tibetan Plateau (TP) are investigated using historical satellite retrieved datasets during 2002–15 in this study. The results indicate that the freezing process mainly starts in December, and the ice melting process generally occurs in April for most lakes. However, the changes in lake ice phenology have varied depending on the location in recent years, with delayed break-up dates and prolonged ice durations in the southern TP, but no consistent changes have occurred in the lakes in the northern TP. Further analysis presents a close connection between the variation in the lake ice break-up date/ice duration over the southern TP and the winter North Atlantic Oscillation (NAO). The positive NAO generally excites an anomalous wave activity that propagates southward from the North Atlantic to North Africa and, in turn, strengthens the African–Asian jet stream at its entrance. Because of the blocking effect of the TP, the enhanced westerly jet can be divided into two branches and the south branch flow can deepen the India–Myanmar trough, which further strengthens the anomalous cyclonic circulation and water vapor transport. Therefore, the increased water vapor transport from the northern Indian Ocean to the southern region of the TP can increase the snowfall over this region. The increased snow cover over the lake acts as an insulating layer and lowers the lake surface temperature in the following spring by means of snow–ice feedback activity, resulting in a delayed ice break-up date and the increased ice duration of the lakes over the southern TP in recent years.

Piecewise Linearization of Quadratic Branch Flow Limits by Irregular Polygon

This letter addresses the issue of linearization of quadratic thermal limits of transmission lines for linear optimal power flow formulation. A new irregular polygon based linearization is proposed. The approach is purely based on geometrical concepts and does not introduce any optimization problem. Comparison of the number of constraints is given with different errors for different branch capabilities and systems. Test case analysis is also presented to validate the irregular polygon linearization strategy with optimal value and computational time results.

Dispatching Stochastic Heterogeneous Resources Accounting for Grid and Battery Losses

We compute an optimal day-ahead dispatch plan for distribution networks with stochastic resources and batteries, while accounting for grid and battery losses. We formulate and solve a scenario-based AC Optimal Power Flow (OPF), which is by construction non-convex. We explain why the existing relaxation methods do not apply and we propose a novel iterative scheme, corrected DistFlow (CoDistFlow), to solve the scenario-based AC OPF problem in radial networks. It uses a modified branch flow model for radial networks with angle relaxation that accounts for line shunt capacitances. At each step, it solves a convex problem based on a modified DistFlow OPF with correction terms for line losses and node voltages. Then, it updates the correction terms using the results of a full load flow. We prove that under a mild condition, a fixed point of CoDistFlow provides an exact solution to the full AC power flow equations. We propose treating battery losses similarly to grid losses by using a single-port electrical equivalent instead of battery efficiencies. We evaluate the performance of the proposed scheme in a simple and real electrical networks. We conclude that grid and battery losses affect the feasibility of the day-ahead dispatch plan and show how CoDistFlow can handle them correctly.

Optimization model and application for the recondensation process of boil-off gas in a liquefied natural gas receiving terminal

In a liquefied natural gas (LNG) receiving terminal, the recirculation flow rate and the branch flow rate entering the tank are important operating parameters that affect the amount of produced boil-off gas (BOG) in the system. However, the operating variables are generally kept unchanged when the flow rate of the external transportation LNG changes, resulting in additional power consumption and poor flexibility. Therefore, a total power consumption optimization model of the recondensation process was constructed for the varied flow rates of the external transportation. The total power consumption of the recondensation process was regarded as the objective function, and the recirculation flow rate and the branch flow rate were regarded as independent variables. Operating strategies for varied flow rates of the external transportation can be proposed using the model. The application of the research results at the Rudong LNG receiving terminal in Jiangsu, China indicated that the optimized operating strategy resulted in 2.93% annual energy reduction compared with the previous strategy, of which the energy reducing rate from June to October was 9.55%.

Charging Coordination of Plug-In Electric Vehicle for Congestion Management in Distribution System

Abstract In modern electricity market, high penetration of Plug-In Electric Vehicle (PEV) creates a huge burden on distribution system operator (DSO). This high penetration creates a gap between demand-supply which further leads to the congestion in distribution lines. Power flow in a grid connected PEV is bidirectional i. e. it can work either in Grid to Vehicle (G2V) or Vehicle to grid (V2G) mode depending upon the grid constraints and owners demand. This paper proposes a charging coordination strategy of PEVs to alleviate congestion in distribution lines. Firstly, Active Power Flow Sensitivity Factors (PFSFs) are calculated to predict the branch flows or congestion status due to the uncoordinated charging of PEVs. Secondly, a coordination strategy of PEVs charging-discharging is made using different heuristic based algorithms in order to mitigate congestion in radial distribution system. The result of proposed work also shows the reduction in total active power loss while maintaining the electricity grid constraints. The present work is simulated and analyzed on IEEE 10 bus radial distribution system integrated with residential systems. Several case studies are analyzed to demonstrate the heftiness of the proposed work.

An experimental investigation into the particle classification capability of a novel cyclone separator

Cyclone separators are widely used for dedusting of particle-laden flows in many branches of industry. A new cyclone containing several collectors was designed in modular structure to investigate the capability of particle classification of the cyclone during particle separation process. The particulate air was supplied into the cyclone in a test bench operated in suction mode under ambient temperature and atmospheric pressure conditions. The flow rate and pressure drop were measured, and the particles accumulated in the dust collectors were weighed and analyzed for each test. The changes in the overall collection efficiency and pressure drop with the flow rate were obtained. In order to determine the classification characteristics of the cyclone, the experiments were repeated in different configurations obtained by changing the locations and number of the collectors. The mean particle diameter and particle size distribution of the dust collected in each collector were acquired. Analysis of the results shows that the designed cyclone is capable of classification incoming particles into 2, 3 or 4 classes in the cyclone according to particle size. Classification performance of the configurations and influences of flow rate on this performance were also investigated. A distinct and satisfactory classification was obtained in the configuration with three collectors.

Evolution of the Freshwater Coastal Current at the Southern Tip of Greenland

AbstractShipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern Greenland as it encounters Cape Farewell. The velocity structure reveals that the coastal current maintains its identity as it flows around the cape and bifurcates such that most of the flow is diverted to the outer west Greenland shelf, while a small portion remains on the inner shelf. Taking into account this inner branch, the volume transport of the coastal current is conserved, but the freshwater transport decreases on the west side of Cape Farewell. A significant amount of freshwater appears to be transported off the shelf where the outer branch flows adjacent to the shelfbreak circulation. It is argued that the offshore transposition of the coastal current is caused by the flow following the isobaths as they bend offshore because of the widening of the shelf on the west side of Cape Farewell. An analysis of the potential vorticity shows that the subsequent seaward flux of freshwater can be enhanced by instabilities of the current. This set of circumstances provides a pathway for the freshest water originating from the Arctic, as well as runoff from the Greenland ice sheet, to be fluxed into the interior Labrador Sea where it could influence convection in the basin.

Robust Coordinated Optimization of Active and Reactive Power in Active Distribution Systems

Active power dispatch and reactive power optimization problems are usually handled separately in active distribution systems, aiming at minimizing the total generation cost or transmission losses. However, the separate optimization cannot achieve a global optimum scheme in distribution system operations. Moreover, the significant relationship between the active power and reactive power may pose great challenges to distribution system operations due to the uncertain nature of load demands and intermittent renewable energy resources. In this paper, using the branch flow model-based relaxed optimal power flow, we formulate a robust coordinated optimization problem for active and reactive powers as a mixed integer second-order cone (SOC) programming problem. Furthermore, in order to address the uncertainties, a two-stage robust optimization model is proposed to coordinate the on load tap changer ratios, reactive power compensators, and charge–discharge power of energy storage system to find a robust optimal solution. Then the column-and-constraint generation algorithm is applied to solve the proposed robust two-stage optimization model. In the relaxed optimal power flow, a stricter cut is added to speed up the computation process of the SOC relaxation in order to guarantee the exactness for representative cases, such as those with high penetration of distributed energy resources. Numerical results based on the 33-bus and 69-bus systems verify the effectiveness of the proposed method.

Deep‐learning based fault diagnosis using computer‐visualised power flow

Changes in system topology, such as branch breaking and the loss of a generator or load, may profoundly influence the operation security of the power system. This study introduces a novel deep-learning based fault diagnosis method using power flow to diagnose topology changes in the power system. Power flow samples with different system states and topologies are first computed numerically; then, they are transformed into computer-visualised images. Using massive power-flow image samples, a convolutional neural network that aims to identify the system state is trained. A feature-map restriction technique is used to restructure the network. To enhance the robustness of the network, the random noise of branch flow is considered in the sample generation process. The results show that the proposed deep-learning based method may diagnose system faults effectively.

Combining diverse driving forces for smoke control in complex urban traffic link tunnels (UTLTs) using one-dimensional flow modelling

Urban traffic link tunnels (UTLTs) could become increasingly more complex because they incorporate both looped main tunnels and multiple branch tunnels. In such a complex tunnel structure, smoke control in the event of fire becomes more difficult than that in conventional simple tunnels due to the enhanced flow interactions among various branches. Moreover, there are still no specific smoke control guidelines for such complex tunnels. Furthermore, the use of a single smoke control method could be inapplicable or even unaffordable in UTLTs because the complicity of the configuration and the interaction between the flow of different branches. In this paper, hybrid ventilation modes which combine diverse flow driving forces are proposed for smoke control in UTLTs. The hybrid modes could exploit the advantages of each of the constitutive modes. Three-dimensional numerical simulations are performed to show the benefits of combining diverse driving forces. Then, a one-dimensional flow modelling approach was employed to investigate the efficiency of three hybrid modes. The results demonstrate that proper matching of various driving forces is crucial for effective application of the hybrid modes. This paper provides a new route for UTLT smoke control and also demonstrates the advantages of one-dimensional flow modelling in such designs.

Non-symmetric branching of fluid flows in 3D vessels

Nonsymmetric branching flow through a three-dimensional (3D) vessel is considered at medium-to-high flow rates. The branching is from one mother vessel to two or more daughter vessels downstream, with laminar steady or unsteady conditions assumed. The inherent 3D nonsymmetry is due to the branching shapes themselves, or the differences in the end pressures in the daughter vessels, or the incident velocity profiles in the mother. Computations based on lattice-Boltzmann methodology are described first. A subsequent analysis focuses on small 3D disturbances and increased Reynolds numbers. This reduces the 3D problem to a two-dimensional one at the outer wall in all pressure-driven cases. As well as having broader implications for feeding into a network of vessels, the findings enable predictions of how much swirling motion in the cross-plane is generated in a daughter vessel downstream of a 3D branch junction, and the significant alterations provoked locally in the shear stresses and pressures at the walls. Nonuniform incident wall-shear and unsteady effects are examined. A universal asymptotic form is found for the flux change into each daughter vessel in a 3D branching of arbitrary cross-section with a thin divider.

Usefulness of intraoperative Indocyanine green video angiography to select the recipient artery for bypass surgery in arteriosclerotic occlusion of the middle cerebral artery: a technical case report

BackgroundIn superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass surgery, indocyanine green video angiography (ICG-VA) is usually used to verify bypass patency. Less-commonly reported is the ability to use this technique to evaluate candidate recipient vessels based on either collateral flow or identification of the distal branch of interest.Case presentationAn 82-year-old man presented with progressive cerebral infarction due to infarction of the M2 inferior trunk of the right middle cerebral artery. He underwent superficial temporal artery-middle cerebral artery bypass to prevent further ischemia 1 week after the initial stroke. In the surgery, M4 cortical arteries fed by the inferior trunk could not be identified as recipient arteries. Intraoperative ICG-VA showed delayed luminescence of some M4 arteries. Because the M4 arteries fed by the inferior trunk showed delayed retrograde flows from the anterior cerebral artery on preoperative digital subtraction angiography, the M4 arteries with delayed luminescence on ICG-VA were considered to be M4 arteries fed by the inferior trunk and selected as the recipient arteries.ConclusionsICG-VA shows differences in flow speed as delayed luminescence. This finding may be useful for detecting target vessels.

Numerical Simulation of the Flow Structure in the Inlet Flow Duct Section of the Valve of Steam Turbine

The objective of this scientific paper was to numerically simulate gas dynamic processes in the inlet flow duct section of the valve with the unidirectional lateral input of the actuating medium to the valve box and determine the influence the geometric parameters of a valve have on the energy losses of actuating medium. To simulate gas dynamic processes we used the mathematical model constructed by the solution of Reynolds-averaged Navier-Stokes equation system using the turbulence model κ-ω SST and the numerical solution method based on the reference volume. The influence that the shift of the inlet branch to the side of drifting away from the upper edge of the valve seat has on the energy loss level in the section from the valve box inlet to the valve seat diffusion portion inlet was investigated for different inlet branch flow section and valve box area –to –the seat throat area ratios. The research showed that an increase in the area of the flow section of inlet branch results in reduced energy losses of actuating medium in the valve. An optimal size of the valve box is defined by the relation of the sizes of the inlet branch and the seat throat. Shift of the inlet branch to the side of drifting away from the upper seat edge results in reduced energy losses in an appropriate range of the ratios of geometric valve parameters. The numerical investigation data showed that the range of geometric relations that provide a low level of energy losses has been established.