Flow Velocity Research Articles

The novel and slowest arterial pressure waves: clinical implications in children with congenital heart disease following cardiovascular surgery.

Certain rhythmic arterial pressure waves in humans and animals have been noticed for over one century. We found the novel and slowest arterial pressure waves in children following surgical repair for CHD, and examined their characteristics and clinical implications. We enrolled 212 children with 22 types of CHD within postoperative 48 h. We monitored haemodynamics (blood pressure, cardiac cycle efficiency, dP/dTmax), cerebral (ScO2), and renal (SrO2) oxygen saturation every 6 s. Electroencephalogram was continuously monitored. Mean blood flow velocity (Vm) of the middle cerebral artery was measured at 24 h. We found the waves with a frequency of ∼ 90 s immediately following surgical repair in 46 patients in 12 types of CHD (21.7%), being most prevalent in patients with aortic arch abnormalities (Aorta Group, n = 24, 42.3%) or ventricular septal defect (Ventricular Septal Defect Group, n = 12, 23.5%). In Aorta and Ventricular Septal Defect Groups, the occurrence of the waves was associated with lower blood pressures, dP/dTmax, cardiac cycle efficiency, ScO2, SrO2, Vm, worse electroencephalogram background abnormalities, higher number of electroencephalogram sharp waves, and serum lactate (Ps <0.0001-0.07), and were accompanied with fluctuations of ScO2 and SrO2 in 80.6% and 69.6% of patients, respectively. The waves observed in children following cardiovascular surgery are the slowest ever reported, occurring most frequently in patients with aortic arch abnormalities or ventricular septal defect. While the occurrence of the waves was associated with statistically worse and fluctuated ScO2 and SrO2, worse systemic haemodynamics, and electroencephalogram abnormalities, at present these waves have no known clinical relevance.

MEASUREMENT OF THE VELOCITY OF PULSED PLASMA FLOW AT THE PW-7 INSTALLATION

The paper considers two independent methods for measuring the velocity of the plasma flow generated in the PV-7 pulsed plasma accelerator: a method based on observation and evaluation of the Doppler shift of spectral lines, and a method of high-speed visualization of plasma motion. To record the plasma flow radiation spectrum, a monochromator M833 was used. High-speed video recording was carried out at 640,000 fps using a Phantom VEO710S CMOS camera. The results of measurements of the average flow velocity obtained at a working gas pressure of 2⋅10-2 Torr, capacitance and voltage of the capacitor bank of 400 μF and 4 kV are presented. The results obtained by two independent methods were compared with each other. Argon was used as the working gas in the experiments. It is shown that the value of the plasma flow velocity estimated by the first method is 12.5 m/s, and the value of the plasma flow velocity estimated by the second method is 16.7 m/s. From these data the measured flow velocity values have a small discrepancy. Thus, it has been established that high-speed video recording and Doppler shift methods make it possible to obtain comparable estimates of flow velocity within the measurement errors. Determining the magnitude of the plasma flow velocity is of great practical importance.

Numerical study of the vortex-induced vibrations of a cantilevered pipe with a concentrated mass end using a wake oscillator model

In this paper, a numerical study based on a wake oscillator model has been carried out to determine the vortex-induced vibration (VIV) response characteristics of a flexible cantilevered pipe with a concentrated mass at the free end. First, a coupled model consisting of a cantilevered pipe and a wake oscillator is established, followed by discretization of the model and an iterative solution using the second-order central difference method. The displacement response and frequency response characteristics for different flow velocities and concentrated end masses have been compared. The numerical results reveal that the maximum value of the structural vibration displacement occurs at the bottom; i.e., free boundary end, for the cantilevered pipe with a concentrated mass at the free end. The dominant vibration mode typically shows a stepwise increase for an increase of the maximum flow velocity. As the vibration mode is transmitted from a lower order to a higher one, the vibration displacement of the structural end decreases fast. As the concentrated end mass increases, the dominant vibration mode shows a stepwise decrease, and as the vibration mode is transmitted from a higher order to a lower one, the vibration displacement of the structural end experiences a sharp increase.

Numerical Simulation of Fixed-Free End Beam’s Modal Behaviour using Two-Way Coupled Fluid-Structure Interaction Approach

The fluid flow velocity stands as a pivotal parameter with a great influence on the mutual interaction between the fluid domain and structure. This paper focuses on structural deformation, structural velocity, von-Mises stress and frequency response of a fixed-free end beam using two-way coupled fluid-structure interaction within ANSYS Workbench. The parameters such as deformed fluid pressure and velocity were analysed across three diverse flow regimes: laminar, transitional and turbulent – each aligned with distinct fluid velocities. The outcomes show that the total deformation, velocity and von-Mises stress distribution of the fixed-free end beam increase as the inlet fluid velocity increases. As a result, the pressure and velocity distribution in the fluid flow which receiving the resultant or leftover structure deflection also increases as the incoming fluid velocity increases. Furthermore, the analysis probes the frequency response in turbulent flow conditions reveals higher values compared to laminar and transitional flows, albeit within the same natural frequency domain. This observation marks significant vibrational characteristics found in the presence of turbulent flow dynamics.

Nonlinear geometrically exact dynamics of hyperelastic pipes conveying fluid: Comparative study of different hyperelastic models

This work presents a comparative analysis of the nonlinear dynamic responses of fluid-conveying pipes modelled by four different phenomenological hyperelastic constitutive models, namely the Mooney-Rivlin model, the Neo-Hookean model, the Yeoh model, and the Ogden model. Based on the strain energy density functions and the exact geometric relation, the geometrically exact dynamic models corresponding to different hyperelastic contitutive models are established. Then the Galerkin's truncation is adopted to transfer the obtained nonlinear integral-partial differential equations into the nonlinear ordinary differential equations. Subsequently, linear dynamic study and finite difference method are taken to explore the natural frequencies and stabilities and nonlinear dynamic responses of the pipe, respectively. And the fitting coefficients for various models obtained from Treloar's experiment data are utilized in the numerical calculation. It is found the Hopf bifurcation and the limit cycle oscillations in the post-flutter status are influenced by the choice of the hyperelastic models, particularly under large flow velocity. However, hyperelastic constitutive models do not exert a significantly extreme influence on the results, which can be attributed to the relatively small strains even though large deformations occur in the pipe. Mathematically, it is proven that the symmetry observed in the pipe's displacement response stems from the symmetry of its cross-section and the inextensibility assumption of the centerline, with hyperelasticity having no effect on this symmetry.

Revising the Interpretation of Transcranial Doppler Ultrasound Examinations in Pediatric Cerebral Malaria.

Cerebral malaria (CM) is a devastating disease globally. Transcranial Doppler ultrasound (TCD) has identified five different phenotypes of deranged cerebrovascular hemodynamics in children with CM, each associated with different outcomes. For TCD to be used as a point of care neurodiagnostic and neuromonitoring tool in CM patients, proper interpretation of examinations is paramount. Comparison of measured cerebral blood flow velocities (CBFVs) to age-matched normative values is needed to interpret any pediatric TCD study. Until recently, normative values in African children did not exist, so previous work reported the frequency of CM phenotypes by classifying studies compared with normative values of European children. Now that normative TCD values in healthy African children have been established, we performed this retrospective analysis of prospectively collected data to determine phenotype frequency and associated outcomes in children with CM by comparing CBFV values to these contemporary controls.

Numerical analysis of gas-solid flow erosion in different geometries as alternatives to a standard pipe elbow

This study was conducted with the aim of replacing different geometric fittings instead of the standard 90° elbow and trying to change the flow pattern to reduce erosion damage. Among fittings, the elbows are at a more serious risk. Numerical investigation of the present erosion with the novelty of research on non-spherical particles and changes in the impact angle of particles along with fluid flow using eight new proposed fittings, including two miter fittings, three blinded fittings, one reducer elbow fitting, and two spherical elbows fittings in comparison with the standard 90° elbow was controlled. The numerical simulation of the gas-solid two-phase flow of non-spherical particles was studied using the Euler-Lagrange approach. To carry out the study numerical, first, the gas flow was modeled by the Navier-Stokes equations and the turbulent Reynolds stress model, and then the solid particles were injected using Newton's equation. Finally, the erosion was calculated using Grant and Tabakoff model of the restitution of particles of after hitting the wall and the erosion model of Oka. The amount of erosion caused by changes in the flow pattern was investigated to evaluate the performance of the new proposed fittings. Numerical results for the most critical mode (Vin = 27 m/s and DP = 300 μm) showed that the new proposed fittings increase the erosion resistance by 22.5 % to 39.6 % compared to the standard 90° elbow. Also, in this research, the effect of different parameters including flow velocity, particle diameter size, particle input rate, and particle rotation on erosion were investigated.

Drag reduction utilizing a wall-attached ferrofluid film in turbulent channel flow

This study explores the application of a wall-attached ferrofluid film to decrease skin-friction drag in turbulent channel flow. We conduct experiments using water as a working fluid in a turbulent channel flow set-up, where one wall is coated with a ferrofluid layer held in place by external permanent magnets. Depending on the flow conditions, the interface between the two fluids is observed to form unstable travelling waves. While ferrofluid coating has been previously employed in laminar and moderately turbulent flows (Reynolds number $Re&lt;4000$ ) to reduce drag by creating a slip condition at the fluid interface, its effectiveness in fully developed turbulent conditions, particularly when the interface exhibits instability, remains uncertain. Our primary objective is to assess the effectiveness of ferrofluid coating in reducing turbulent drag with particular focus on scenarios when the ferrofluid layer forms unstable waves. To achieve this, we measure flow velocity using two-dimensional particle tracking velocimetry (2D-PTV), and the interface contour between the fluids is determined using an interface tracking algorithm. Our results reveal the significant potential of ferrofluid coating for drag reduction, even in scenarios where the interface between the surrounding fluid and ferrofluid exhibits instability, with observed drag reduction rates up to 95 %. In particular, waves with an amplitude significantly smaller than a viscous length scale positively contribute to drag reduction, while larger waves are detrimental, because of induced turbulent fluctuations. However, for the latter case, slip outcompetes the extra turbulence so that drag is still reduced.

The effects of water flow velocity and odor release frequency on the odor-tracking behavior of swimming crabs (Portunus trituberculatus)

Chemical-guided tracking is vital for critical activities such as foraging and mating in swimming crabs (Portunus trituberculatus), as it facilitates the detection and localization of odor sources. While water flow and odor release patterns are known to influence odor-tracking behavior, the specific mechanisms of their impact remain poorly understood. This study quantified the tracking behaviors of juvenile swimming crabs in response to varying water flow velocities (0.7 cm/s, 1.6 cm/s, and 2.5 cm/s) and odor release frequencies (0.5 Hz, 1.0 Hz, and 1.5 Hz). Results indicate that (1) at a flow velocity of 1.6 cm/s, crabs exhibited a higher proportion of tracking and success. Successful trackers at this flow velocity also demonstrated better tracking performance, including higher net-to-gross displacement ratios (NGDR), reduced gross displacements, shorter exit and track durations, and simpler tracking trajectories. (2) While odor release frequency did not significantly affect the proportion of tracking or success, the successful trackers at a higher frequency (1.5 Hz) had lower NGDR and higher gross displacements compared to those exposed to a lower frequency (0.5 Hz). (3) The successful trackers were not stastistically affected by the interaction between flow velocities and release frequencies. (4) In contrast to successful trackers, unsuccessful ones showed highly variable responses to flow velocity and odor release frequency, with generally inferior tracking performance. These findings provide valuable insights into the olfactory ecology of swimming crabs and can inform the optimized of aquaculture management and formulated feeds production.

Unveiling riverine N2O dynamics along urbanization gradients by integrating hydrological, biogeochemical and microbial processes

Human-disturbed rivers are globally significant sources of atmospheric nitrous oxide (N2O). Yet, the underlying mechanisms of urbanization impact on riverine N2O dynamics are not well understood. This study unveiled the effects of urbanization on N2O dynamics by integrating hydrological, biogeochemical and microbial processes in a river with various urbanization intensities. Riverine NO3− concentration enhanced with increasing urban land percentage, primarily because of the increased proportional contribution of sewage & manure source. The 15N site preference and relevant isotopic evidences revealed that the proportion of denitrification derived N2O increased from 60% to 76%, with the urban land percentage increasing from < 5% to > 22%, which was caused by decreases in flow velocity and dissolved oxygen saturation, increases in NO3− concentration and N2O-denitrifying genes. The non-negligible contribution of nitrification to N2O production (∼ 40%) in lower-urbanized river stretches may be attributed to aerobic conditions and lower impermeable riparian zone facilitating the occurrence of in-river nitrification and the access of in-soil nitrification to river. Urbanization-mediated decreases in flow velocity and dissolved oxygen and increases in nitrogen availability and denitrification process resulted in an increase in N2O concentration and flux, with N2O concentration approximately four times higher in higher-urbanized river reaches (50.7 ± 26.3 nmol/L) than in lower-urbanized river reaches (14.4 ± 2.5 nmol/L). In addition, increased proportional contribution of sewage & manure source also provides the possibility for exogenous N2O inputs with urban expansion. These findings contribute to deepening our understanding of how urbanization drives N2O dynamics in river systems.

Phase-contrast Magnetic Resonance Angiography of Foot at Ultra-high field 5 T System: Visualization of Distal Small Vessels and Enhancement by Warm Water Immersion

Ultra-high field strength MR system has been proved to offer improved visualization of the distal intracranial vessels and branches, but its effectiveness on peripheral vasculatures was not investigated. We aim to assess the visualization of lower-extremity vessels using three-dimensional phase contrast MR angiography (3D PC-MRA) at 5T field-strength through the feet with warm water immersion (WWI). Participants were prospectively recruited and underwent 3T, 5T 3D PC-MRA on feet with and without WWI (water temperature between 40 to 45 ℃ for a duration of 10minutes). Patients with suspected lower-extremity vessel diseases underwent CTA for lesion identification. Signal-to-noise ratio (SNR), subjective scoring, quantitative vessel segmentation and flow velocity were performed to assess vessel visualization before and after WWI. Friedman's test was conducted to determine statistical significance. Out of thirty participants (mean age, 46.2±5.9; males, 20; lower-extremity vessel disease, 10), 900 vessel segments were available for evaluation. 5T images showed significantly higher scores of image quality and foot vessel visualization than 3T (all P <.05). WWI further improved the visualizing scores (percentage of score 3: 40.2% vs 66.2%, P =.008), SNR (44.27 vs 67.78, P <.001), total branch count (151.92 ± 29.17 vs 225.63 ± 16.76; P <.001), and the flow velocity (0.72 ± 0.03 vs 0.48 ± 0.11cm/s; P <.001). 3D PC-MRA at 5T effectively visualizes foot vessels in patients with lower-extremity disease. Furthermore, WWI can significantly enhance the depiction of distal and small vessels.

Electro-osmotic flow instability of viscoelastic fluids in a nanochannel

The study of the complex rheological properties of viscoelastic fluids in nanochannels will facilitate the application of nanofluidics in biomedical and other fields. However, the flow of viscoelastic fluids in nanochannels has significant instabilities, and numerical simulation failures are prone to occur at high Weissenberg numbers (Wi). In this study, the simplified Phan-Thien-Tanner viscoelastic fluid model is solved using the log-conformation tensor approach, and the effects of rheological parameters of the viscoelastic fluid, such as the Weissenberg number (Wi), extensibility parameter (ε), and viscosity ratio (β), on the flow characteristics and flow instability within the nanochannel are investigated. The results indicate that the variation of rheological parameters of viscoelastic fluids has a significant effect on the flow state and flow instability of fluids in nanochannels. When the rheological parameters are in a specific range, the flow velocity and outlet current in the nanochannel exhibit relatively regular periodic fluctuations. As the flow transitions from an up-and-down moving single-vortex state to a symmetric double-vortex state, the average velocity of the central axis in the nanochannel is increased by about 15%. Furthermore, when Wi increases from 150 to 400, the length and height of the vortex increase by 50% and 100%, respectively.

Effect of Gasket Wear Rate on Hydraulic Performance and Internal Flow of Multistage Centrifugal Pump with Floating Impellers

Abstract The sealing gaskets of multistage centrifugal pumps are prone to wear during operation. This study investigates the influence of gasket wear rate on hydraulic performance and internal flow field through numerical simulations. As the wear rate of the gasket increases, both the efficiency and head coefficient of the pump gradually decrease. When the gasket is completely worn out, the efficiency decreases by 5.6% and the head coefficient decreases by 9.5% compared to the unworn gasket condition. Analysis of the internal flow field reveals that the front side chamber is most significantly affected by gasket wear. As the gasket wears, the flow velocity within the front side chamber increases gradually, and the high-entropy production zone expands, thereby affecting the hydraulic performance of the pump. The findings of this study provide practical engineering insights for enhancing the operational performance of multistage centrifugal pumps.

Multiple-arc cylinder under flow: Vortex-induced vibration and energy harvesting

The shape of a cylindrical cross-section affects the vibrational performance. The vortex-induced vibration (VIV) phenomena of multiple-arc cylinders were numerically investigated to assess their impact on hydrodynamic energy harvesting and potential vibration suppression across a flow velocity range of 0.2 m/s to 1.4 m/s (1.767×104<Re<1.237×105). The study involves five types of multiple-arc cylinders: 4-arc, 8-arc, 16-arc, 24-arc, and circular cylinders. The accuracy of the numerical method was validated through comparison with experimental data. Specifically, increasing the number of arcs generally enhances overall energy conversion efficiency. Then, the VIV response and energy conversion results of the 24-arc cylinder are similar to those of the circular cylinder with maximum efficiency. Notably, the 4-arc cylinder achieves a global maximum amplitude of 0.074 m (A*=0.83) and a power output of 4.4 W with the new P+T mode, making it the most effective configuration for flow velocities between 0.7 and 0.9 m/s. For vibration suppression of multiple-arc cylinders, the appropriate arc structure effectively reduces amplitudes. The small vortices generated by the arc structures disrupt the separation of normal vortices from the boundary layer, leading to approximately a 50% reduction in amplitude responses for 8-arc and 16-arc cylinders.

Study on the influence of sediment erosion of Francis turbine runner under different water heads

Abstract The average measured sediment concentration of the river section where Wanjiazhai Hydropower Station is located over the years is 5.7kg/m 3, The maximum measured sediment concentration reaches 37.6kg/m 3, The erosion of the flow components of hydraulic turbines caused by sand containing water flow is becoming increasingly severe, coupled with the frequent impact of load changes during peak shaving operation, the problems exposed during the operation of hydraulic turbines are becoming more prominent, which affects the stable operation of the units. This article uses numerical simulation and experimental testing to study the sediment wear characteristics and hydraulic performance of the water turbine at Wanjiazhai Hydropower Station. Research has revealed the effects of working head on impeller wear. The increase in working head will exacerbate the impact wear on the main channel wall of the unit. The surface of water turbine blades is the main wear area, and the high-speed impact of particles causes an increase in the wall wear rate. The probability of particles coming into contact with the wall at the outlet increases, resulting in rapid wear at this point. The increase in head will intensify the wear intensity of the unit surface, and the flow velocity in the gap indicates that the local high-speed jet in the gap is the main cause of gap wear. Therefore, in order to ensure the efficient anti-wear performance of the water turbine, multiple factors need to be comprehensively considered to cope with sediment wear of the water turbine, including regular cleaning, optimized structural design, use of wear-resistant materials, replacement of worn parts, and optimization of operating parameters. These measures help to reduce the damage of sediment wear to water turbines and extend their service life.

Developing a virtual physical system for vortex-induced vibration studies of a bluff body

A virtual physical system (VPS) for VIV studies of a bluff body is developed to replace the actual physical systems. It can arbitrarily and accurately control and edit the physical parameters, including mass, damping ratio and spring stiffness, specifically for the mass-spring-damper system. The recursive Duhamel integral method (DIM) with unconditional stability was used for the VPS control system, addressing real-time noise filtering problem and simplifying the system as a single input and single output (SISO) one. Delay compensation and inertial force elimination methods were investigated and proposed to overcome the crucial unwanted damping effects. An experimental facility for VIV model tests by VPS was manufactured, and the bluff body model with a measurement system was specially designed to accurately sense the hydrodynamic force during VPS operation. Systematic verification experiments for parameter editing and control of an actual physical target system were conducted, showing that the VPS can reproduce the equivalent spring-damper-mass system in high fidelity with an accuracy error of less than 5%. VIV model tests for a bluff body at Reynolds numbers (Re= UD/υ, where U is the flow velocity, D represents the diameter of cylinder model, and υ is the kinematic viscosity coefficient) of 5.7E4 and 2.3E5 were performed using the VPS experimental facility, presenting well-repeated VIV responses at low Re and unexpected VIV response with a large amplitude of 2.4 D at high Re, which can cause severe fatigue damage for relevant structures. The present VPS will provide promising and powerful experimental tools for VIV studies of a bluff body to reveal the related sensitive parameter effects.

Optimization of the power performance for three hybrid Darrieus-Savonius rotors based on the Taguchi method

Abstract The hybrid vertical-axis wind turbine is a unique design that overcomes the efficiency limitations of Savonius rotors and the start-up challenges of Darrieus rotors. This study uses the Taguchi optimization method to enhance the performance of a cluster of three hybrid Darrieus-Savonius vertical-axis wind turbines. The optimized parameters include distances between adjacent turbine centers, configuration angles, rotational directions, and the pitch angle. The study is the first to investigate the effect of varying the pitch angle of Darrieus airfoil blades on hybrid design performance. The optimal configuration of the three hybrid VAWTs and the isolated rotor is analyzed through flow velocity, pressure, and turbulence kinetic energy contours. The results show that the pitch angles have the greatest effect on the rated power coefficient among other studied influencing parameters. The optimal cluster configuration’s performance improvement is due to the favorable velocity gradient around the blades. Compared to the isolated rotor, the power coefficient enhancement for the optimal case is 46.545% at the rated tip speed ratio of 3.08. The hybrid rotor in the cluster can achieve almost the same power as the isolated rotor up to a tip speed ratio of 4.1 instead of 2.86 for the isolated rotor. However, the decrease in overall efficiency for some cluster configurations is due to wake flow intensity and trapping between the rotors, which causes a stagnation zone.

Drag Force on Submerged Flexible Vegetation in an Open‐Channel Flow

AbstractThe movement of submerged flexible vegetation leads to an increase in resistance to the stream flow. In this study, a formula that can directly calculate the drag force on a highly flexible submerged vegetation, called Ceratophyllum, by using the vegetation swaying characteristics and the flow field information in a steady‐uniform open‐channel flow is derived. The drag force on submerged flexible vegetation is characterized by the time‐averaged flow velocity, turbulence intensity, and the additional force arising from the vegetation swaying. Based on the results of the numerical models in the previous studies (Wang et al., 2022a, 2022b, https://doi.org/10.1017/jfm.2022.598, https://doi.org/10.1017/jfm.2022.899), the drag coefficient is determined. It is revealed that the drag coefficient is influenced by a combination of factors, including the flow conditions, and the distribution and movement characteristics of vegetation. The drag coefficient decreases with an increase in velocity and is approximately linearly related to the cubic power of the bulk flow velocity. In the case of an inter‐plant spacing of 0.5 times the initial plant height, the drag coefficient ranges from 10.72 to 2.11, as the Reynolds number varies from 20,000 to 50,000. Besides, the vegetation distribution density and the relative submergence influence the drag coefficient. In this context, the drag coefficient decreases linearly with an increase in the inter‐plant spacing. For the Reynolds number equaling 50,000, the drag coefficient ranges from 2.11 to 2.02, when the inter‐plant spacing varies from 0.5 to 2 times the plant height, and from 2.47 to 1.79, when the flow depth varies from 1.5 to 3 times the plant height.

Evaluation of the presence and severity of spontaneous splenorenal or gastrorenal shunts via four-dimensional flow magnetic resonance imaging: a preliminary study.

Four-dimensional phase-contrast magnetic resonance imaging (4D flow MRI) is a relatively new type of MRI acquisition technique that provides a unique and comprehensive set of information within a single acquisition, including hemodynamic and anatomical information. This study was designed to noninvasively evaluate the correlation between the presence and severity of spontaneous splenorenal shunt (SRS) or gastrorenal shunt (GRS) and 4D flow MRI-derived parameters. This retrospective case-control study enrolled 70 patients who were diagnosed with hepatocirrhosis portal hypertension and admitted to the Second Affiliated Hospital of Chongqing Medical University. Patients were divided into three groups according to the diameter of the SRS and GRS. 4D flow MRI-derived parameters, including the turbulent kinetic energy, total volume (TV), flow velocity, blood flow volume (BFV), maximum flow (MF), wall shear stress, and relative pressure, were obtained for eight cut planes: proximal to the splenomesenteric confluence and liver hilum of the portal vein (PV1/PV2); the left/right branch of the bifurcation of the PV (LPV/RPV), at the mesosplenic confluence of the splenic vein (SV1), at the splenic hilum of the SV (SV2); at the proximal to the splenomesenteric confluence of the superior mesenteric vein (SMV1), and 5 cm from the splenomesenteric confluence of the SMV (SMV2). Comparisons among the three groups were based on one-way analysis of variance (ANOVA). Logistic regression was used to identify the risk factors for small SRS/GRS (S-SRS/GRS) and for large SRS/GRS (L-SRS/GRS). Receiver operating characteristic curves were used to evaluate the diagnostic performance of the independent risk factors for SRS and GRS. The associations between the clinical data and the 4D flow MRI-derived parameters of GRS and SRS were assessed via Spearman correlation coefficient analysis. The presence of SRS or GRS was correlated with TVLPV (r=-0.302; P=0.035), TVPV1 (r=-0.385; P=0.001), TVPV2 (r=-0.301; P=0.013), BFVPV1 (r=-0.360; P=0.010), BFVSMV2 (r=0.371; P=0.008), MFPV1 (r=-0.341; P=0.004), and MFPV2 (r=-0.291; P=0.017). Meanwhile, the severity of the SRS or GRS was correlated with alanine aminotransferase level (r=-0.535; P<0.001), BFVLPV (r=-0.560; P=0.008), aspartate aminotransferase level (r=-0.321; P=0.038), and model for end-stage liver disease score (r=0.323; P=0.039). TVPV1, TVPV2, BFVPV1, BFVPV2, and MFSMV2 were found to be independent risk factors for L-SRS/GRS, with intermediate diagnostic efficacy, with the area under the curve (AUC)TV PV1=0.706 [95% confidence interval (CI): 0.519-0.853; sensitivity, 61.54%; specificity, 80.77%; P=0.018], AUCBFV PV1 =0.694 (95% CI: 0.507-0.844; sensitivity, 95.00%; specificity, 63.16%; P=0.035), AUCTV PV2 =0.729 (95% CI: 0.544-0.870; sensitivity, 77.78%; specificity, 66.67%; P=0.016), AUCBFV PV2 =0.718 (95% CI: 0.531-0.862; sensitivity, 60.00%; specificity, 82.35%; P=0.017), and AUCMF SMV2 =0.788 (95% CI: 0.608-0.912; sensitivity, 44.00%; specificity, 84.46%; P=0.005), respectively. As the TV of PV1 and PV2 and the BFV of PV1 and PV2 decreased, the risk of L-SRS/GRS increased. As the MF of SMV2 increased, the risk of the presence of L-SRS/GRS increased. 4D flow MRI-derived parameters correlated with the presence and severity of SRS or GRS. Meanwhile, the independent risk factors for the presence of L-SRS/GRS were the TV of LPV, PV1, and PV2; the BFV of PV1 and SMV2; and the MF of PV1 and PV2.

Topology transition description of horseshoe vortex system in juncture flows with velocity characteristic lines

Particle image velocimetry and numerical simulation results of juncture flows were analyzed to parametrically investigate topology transition. The vortex system evolutions from non-vortex to multi-vortex with variations in obstacle bluntness, obstacle width, flow velocity and boundary layer thickness are discussed from the perspective of velocity characteristic lines. The velocity characteristic lines of u=0, v=0, and ∇2v=0 are adopted to describe the vortex system evolution. The motions of the characteristic lines with juncture flow parameters are described in detail, and the corresponding reflections of the vortex system patterns are illustrated. A panoramic picture of the development of velocity characteristic lines corresponding to the HSV topology transition from a non-vortex to a multi-vortex system with variations in the juncture flow parameter is established. Two methods for determining the attachment/separation pattern of the most upstream singularity are proposed. One method is based on the number of intersections of the u=0 and v=0 velocity characteristic curve lines, and the other is based on the relative positions of the most upstream feet of the u=0 and v=0 loop curves with both feet attached to the wall.