Stationary Flow Research Articles

Modelling study on pedestrian evacuation dynamics considering exit selection behaviour under flood disaster

Flood spreading in metro stations is a dangerous hazard that frequently causes casualties and property losses. However, pedestrian evacuation under flood spreading scenarios has not been fully investigated. To fill this gap,we propose an extend Floor-Field model incorporating flood spreading and exit selection behaviour of individuals. In the model, the dynamic flood spreading process on metro platforms is expressed by using a simulation software named Mike21. The optimal exit selected by pedestrians in each step is decided on three factors, that is pedestrian density around the exit, pedestrian distance to the exit, and water depth at the exit. Meanwhile, the movement speed of pedestrain also changes with the water depth at each time step. Based on this, the transition probability to neighbor cell including static field, dynamic field, height field, and water flow field is calculated. This results in a flood evacuation model considering the pedestrian's behaviour when choosing an exit. The effects of flooding, pedestrian density, different exit selection behaviours, water flow field, and inlet flow on evacuation were thoroughly analysed. The analysis demonstrates that the likelihood of flooding significantly impacts the evacuation of pedestrians from the subway station; the more flooding is taken into account, the more influential the impact. In addition, the effect of inlet flow on evacuation is also noteworthy; considering exit selection behaviour can significantly increase the effectiveness of evacuation. The study's findings can be used to develop evacuation plans for flooded metro stations.

VascuFit: Aerobic exercise improves endothelial function independent of cardiovascular risk: A randomized-controlled trial.

Background and aimsEndothelial dysfunction predicts elevated cardiovascular (CV) risk in healthy individuals. Aerobic exercise reduces endothelial dysfunction in part by improving CV risk factors. Yet, this explains less than 50% of the effect and a direct influence of exercise training on the endothelium is discussed as possible contributor. The VascuFit study applied non-linear periodized aerobic exercise (NLPE) training to assess its multilevel effects on endothelial function including potential epigenetic endothelial modifications by circulating micro-ribonucleic acids (endomiRs). MethodsSedentary adults with elevated CV risk between 40-60 years were randomized 2:1 and engaged in an eight-week ergometer-based NLPE training (n=30) or received standard exercise recommendations (n=14). Macro-, microvascular, cellular and molecular adaptations were assessed via brachial-arterial flow-mediated dilation (baFMD), static retinal vessel analysis (SVA), flow cytometry, and endomiRs regulating key pathways of endothelial function. Statistics included ANCOVA, Principal Component Analysis (PCA), and regression analyses. ResultsbaFMD improved by 2.38% (CI:0.70-4.06, p=0.007) independent of CV risk, whereas SVA parameters and circulating endothelial (progenitor) cells did not significantly change in the NLPE group. The mean distance between baseline and follow-up PCA loadings of the endomiR dataset explaining 44.2% of dataset variability was higher in the NLPE-group compared to the control group (2.71±2.02 vs. 1.65±0.93). However, regression analyses showed no evidence of endomiRs explaining the improvement of baFMD. ConclusionsThe improvement of macrovascular endothelial function by aerobic exercise training was independent from CV risk factors. Increased heterogeneity among endomiRs did not explain this effect, but suggests an adaptive response to the exercise stimulus on the epigenetic level.

Instability of isolator shocks to fuel flow rate modulations in a strut-stabilised scramjet combustor

Abstract Reynolds-Averaged Navier–Stokes (RANS) simulations, both steady and unsteady, are used to investigate supersonic, chemically reacting, flow fields inside a strut-stabilised supersonic combustion ramjet (scramjet) engine operating under different fuel flow rates. Fully supersonic, fully subsonic and mixed modes of operations inside the combustor, obtained at different fuel flow rates, are studied numerically through shock wave visualisations and top-wall static-pressure probing. The effect of changing fuel flow rates, imposed both suddenly and gradually, on the behaviour of shock waves and wall pressure profiles are studied in detail. For certain modes of combustion characterised by the presence of oblique shocks at the strut, shockwaves in the combustor respond predictably to an increase or decrease in fuel flow rate attaining the steady state flow fields as predicted by RANS simulations for those fuel flow rates. For certain other modes of combustion, characterised by the presence of shockwaves in the isolator and the absence of oblique shocks at the leading edge of the strut, shockwaves in the flow field appear unstable to fuel flow rate modulations. For such cases, any change in fuel flow rates, sudden or gradual, increase or decrease, causes the isolator shocks to immediately move upstream and eventually out of the isolator. A plausible physics-based explanation of the observed phenomena is presented.

Unsteady flow rate in transient, incompressible pipe flow

AbstractKnowledge regarding current flow rates through pipes and other components is crucial for most hydraulic systems. The hydraulic power can be computed in combination with the pressure, which may be used in many applications, such as predictive maintenance. Most flow rate sensors used in the field of fluid power operate invasively. Therefore, the measurement process itself alters the flow rate. Furthermore, most sensors operate accurately for stationary flow but produce inaccurate measurements for transient flow. A well‐known method of determining the flow rate is to measure the pressure difference between two points along a pipeline and calculate the flow rate based on the law of Hagen and Poiseuille. However, since the relation mentioned above only applies to laminar, steady, and incompressible flow, its usefulness for transient flows is limited. This paper derives a system equation based on the fundamental laws of fluid mechanics, which describe transient, incompressible pipe flow. As a result, the fundamental equations are solved in the Laplace domain and subsequently transformed back into the time domain. The four‐pole theorem relates the pressure difference and the volumetric flow rate. The analytical solution consists of a convolution integral containing a weighting function and the pressure difference. Compared to a simulation, the novel equation displays high accuracy for transient and stationary incompressible pipe flow. This equation paves the way for a soft sensor, which allows the noninvasive measurement of arbitrary volumetric flow rates within pipes.

Experimental study of solid-liquid two-phase flow field in a centrifugal pump volute under multiple working conditions

In order to study the variation law of the solid-liquid two-phase flow field in the volute of centrifugal pump and the distribution law of the solid particles in the volute, based on PIV technology, the dynamic and static interference flow field of the volute under different flow conditions (30 m3/h, 40 m3/h, 50 m3/h, 60 m3/h, 70 m3/h) and different solid phase volume fractions (1 %, 1.5 %, 2 %) is studied. It is found that with the increase of the solid phase volume fraction, the head and efficiency of the centrifugal pump gradually decrease, and the addition of the solid phase has little effect on the pump head when the solid phase volume fraction is small under the condition of the large flow. The high turbulent kinetic energy area in the volute is mainly concentrated near the outer wall of the volute and the area where the tongue is located. Under the same solid phase volume fraction, the turbulent kinetic energy in the volute increases with the increase of the flow rate. The turbulent kinetic energy in the volute decreases with the increase of the solid phase volume fraction. The absolute velocity component of the flow field in the volute is significantly affected by the flow condition.

Experimental Evaluation of Gas-Dynamic Conditions of Heat Exchange of Stationary Air Flows in Vertical Conical Diffuser

Conical diffusers are widely used in technical devices (gasifiers, turbines, combustion chambers) and technological processes (ejectors, mixers, renewable energy). The perfection of flow gas dynamics in a conical diffuser affects the intensity of heat and mass transfer processes, the quality of mixing/separation of working media and the flow characteristics of technical devices. These parameters largely determine the efficiency and productivity of the final product. This article presents an analysis of experimental data on the gas-dynamic characteristics of stationary air flows in a vertical, conical, flat diffuser under different initial boundary conditions. An experimental setup was created, measuring instruments were selected, and an automated data collection system was developed. Basic data on the gas dynamics of air flows were obtained using the thermal anemometry method. Experimental data on instantaneous values of air flow velocity in a diffuser for initial velocities from 0.4 m/s to 2.22 m/s are presented. These data were the basis for calculating and obtaining velocity fields and turbulence intensity fields of the air flow in a vertical diffuser. It is shown that the value of the initial flow velocity at the diffuser inlet has a significant effect on the gas-dynamic characteristics. In addition, a spectral analysis of the change in air flow velocity both by height and along the diffuser axis was performed. The obtained data may be useful for refining engineering calculations, verifying mathematical models, searching for technical solutions and deepening knowledge about the features of gas dynamics of air flows in vertical diffusers.

Relaxed hydrodynamic theory of electrically driven nonequilibrium steady states

The capability of hydrodynamics to accurately describe slow and long-wavelength fluctuations around nonequilibrium steady states (NESS), characterized by a stationary flow of energy or matter in the presence of a driving force, remains an open question. In this study, we explicitly construct a hydrodynamic description of electrically driven nonequilibrium charged steady states in the limit in which the relaxation of the first nonhydrodynamic excitation is parametrically slow. Our approach involves introducing gapped modes and extending the effective description into a relaxed hydrodynamic theory (RHT). Leveraging the gauge-gravity duality as a tool for controlled computations within nonequilibrium systems, we establish an ultraviolet complete model for these NESS that confirms the validity of our RHT. In summary, our findings provide a concrete realization of the validity of hydrodynamics beyond thermal equilibrium, offering valuable insights into the dynamics of nonequilibrium systems. Published by the American Physical Society 2024

Design optimization of floating offshore wind farms using a steady state movement and flow model

Abstract In this study, we demonstrate how to carry out the design optimization of floating offshore wind farms by considering the impacts brought by the movements of the floating wind turbines. A steady state movement and flow model is applied in the modelling process. This model is developed by building a turbine surrogate model for estimating the steady state movement and power production of floating wind turbines and incorporating it in an open-source static wind farm simulator, PyWake. Using this modelling methodology, layout optimization problems of floating offshore wind farms are solved by using algorithms like Random Search to maximize the energy yield while satisfying certain constraints. Case studies are carried out for two wind farms with met-ocean conditions from a real planned site in Scottland to show the potential of layout optimization for floating wind farms.

Langevin dynamics for a heavy particle immersed within a flow of light particles

A micro-hydrodynamics model based on elastic collisions of light point solvent particles with a heavy solute particle is investigated in the setting where the light particles have velocity distribution corresponding to a background flow. Considering a range of stationary background flows and distributions for the solvent particle velocities, the macroscopic Langevin-type description of the behaviour of the heavy particle is derived in the form of a generalized Ornstein–Uhlenbeck process. At leading order, the drift term in this process depends upon both the geometric structure of the background flow and the size of the heavy particle, while both drift and diffusion terms scale with moments of the light particle velocity distribution. Computational methods for simulating the micro-hydrodynamics model are then designed to confirm the theoretical results. To enable long-time calculations, simulations are performed in a frame co-moving with the heavy particle. Efficient methods for sampling the position and velocity distributions of incoming solvent particles at the boundaries of the co-moving frame are derived for a range of distributions of solvent particles. The simulations show good agreement with the theoretical results.

A Simulation Study on the Effect of Supersonic Ultrasonic Acoustic Streaming on Solidification Dendrite Growth Behavior During Laser Cladding Based on Boundary Coupling

Laser cladding has unique technical advantages, such as precise heat input control, excellent coating properties, and local selective cladding for complex shape parts, which is a vital branch of surface engineering. During the laser cladding process, the parts are subjected to extreme thermal gradients, leading to the formation of micro-defects such as cracks, pores, and segregation. These defects compromise the serviceability of the components. Ultrasonic vibration can produce thermal, mechanical, cavitation, and acoustic flow effects in the melt pool, which can comprehensively affect the formation and evolution for the microstructure of the melt pool and reduce the microscopic defects of the cladding layer. In this paper, the coupling model of temperature and flow field for the laser cladding of 45 steel 316L was established. The transient evolution laws of temperature and flow field under ultrasonic vibration were revealed from a macroscopic point of view. Based on the phase field method, a numerical model of dendrite growth during laser cladding solidification under ultrasonic vibration was established. The mechanism of the effect of ultrasonic vibration on the solidification dendrite growth during laser cladding was revealed on a mesoscopic scale. Based on the microstructure evolution model of the paste region in the scanning direction of the cladding pool, the effects of a static flow field and acoustic flow on dendrite growth were investigated. The results show that the melt flow changes the heat and mass transfer behaviors at the solidification interface, concurrently changing the dendrites’ growth morphology. The acoustic streaming effect increases the flow velocity of the melt pool, which increases the tilt angle of the dendrites to the flow-on side and promotes the growth of secondary dendrite arms on the flow-on side. It improves the solute distribution in the melt pool and reduces elemental segregation.

Determination of Static Flow Characteristics of A Prototypical Differential Valve Using Computational Fluid Dynamics

Abstract The paper describes the numerical calculations of a conceptual air brake valve of a trailer equipped with a differential section, which is intended to shorten response time and braking distance. The static flow characteristics have been determined using computational fluid dynamics (CFD). Mixed (global and local) computational meshes were used in the paper to determine the static flow characteristics of the valve sections. The use of the local mesh was relevant for valve openings smaller than 0.5mm. Using CFD, it was possible to determine the static flow characteristics of the main, auxiliary feed and the differential sections, which were linear, degressive and progressive depending on the section. The analyzes, which have not yet been described in the literature, showed a significant difference in the MFR of the additional and main feed tracts, which reached 52.29%.The results are applicable to the configuration of the braking system. Further research will include performing dynamic simulations using dedicated software and building a test rig to validate the CFD calculation results.

Evaluation of the effect of viscosity on blood flow using viscosity models

The study of blood hemodynamics and rheological properties, particularly blood viscosity, is essential for understanding and treating certain cardiovascular conditions. Blood is a non-Newtonian fluid, meaning its viscosity varies with shear rate, a behavior driven by the aggregation and deformation of red blood cells (RBCs). Accurate modeling of blood viscosity is therefore critical for simulating blood flow in both physiological and pathological states. In this work, various viscosity models were assessed to identify the most suitable that represents the blood’s behavior in relation to shear rate. Although the Newtonian model is simple, it fails to capture the non-Newtonian characteristics of blood, particularly at varying shear rates. In comparison, the Power Law, Walburn-Schneck, and Carreau-Yasuda models offer more detailed and complex approaches to modeling blood viscosity. The Effect of blood viscosity on the overall blood flow was evaluated based on the four viscosity models. The work was carried out in a MATLAB Simulation Environment. The Volumetric blood flow rate was evaluated from the Poiseuille’s equation using three viscosity models whose values were defined by shear rates ranging from (217.5 – 226.5)s−1 . The percentage change in the blood volume resulting from changes in the viscosity was examined for each model. The two viscosity models (Power and Carreau models) concurrently reported equal percentage change of blood flux variation with the corresponding variation of the viscosity due to change in shear rate. This shows that any of the two models can be used to study the variation of blood flow to the viscosity with respect to cardiovascular complications.

Flow field analysis of self-sustained flutter of a wide-slotted bridge deck

This study delves into the flutter mechanism of a 5,000 m bridge with a wide-slotted deck, finding that the motion is self-sustained and not violently destructive. The system damping ratio is not fixed, and only one stable orbit exists. High-resolution PIV experiments at an experimental wind speed of 10.5 m/s measured the static and dynamic flow fields on the windward and leeward decks. The static results showed leading-edge separation on the windward deck within the reference range, while separation on the leeward deck was difficult to observe. Dynamic testing identified instantaneous vortices around the windward/leeward deck at each phase, with no signs of vortices in the wind speed vectors at all phases after phase-averaging, indicating that the vortex drift hypothesis is not valid. The analysis of the streamline pattern revealed periodic variations in leading-edge separation size and reattachment length on the windward deck during the vibration process, while the leeward deck showed consistently inconspicuous changes. Further examination uncovered a peculiar behavior in the horizontal wind speed profile on the leeward deck during the vibration process, attributed to dynamic changes in the height difference between the windward and leeward decks during flutter. The study suggests that the unusual wind speed profile on the leeward deck is caused by the dynamic changes in height difference between the windward and leeward decks during the flutter process, resulting in additional wind loading. These findings shed light on the complex dynamics of bridge flutter and have implications for the design and maintenance of long-span bridges.

Numerical solution of nanofluids mixing processes in T-mixer equipped titled gate

AbstractIn this study, a numerical simulation technique is employed to predicate the temperature distribution and velocity profile data of cold and hot nanofluids within a T-mixer was studied. The mixing of nanofluid flow with Al2O3 nanoparticles of 50 nm flows at Φ = 0.4 vol.% in a T-shaped mixer. The present numerical problem has been solved using the COMSOL Multiphysics version 5.4. Six angle of inclination was studied (θ = 15, 30, 45, 60, 75, and 90°) of the gate and evaluated its effects on the temperatures and velocity contour in the T-junction. The study's findings indicated that the presence of a gate in a stationary, non-rotating flow regime has a noteworthy impact on the stationary vortex flow. Also, the mixing occurs more quickly at angles of 45 or 60°. Mixing at a 30° or 90° angle took longer.

Power flow analysis and volt/var control strategy of the active distribution network based on data-driven method

In order to solve the problems of low power flow calculation accuracy and voltage overcrossing of the distribution network caused by large-scale distributed power supply, a data-driven power flow analysis and volt/var optimization control strategy for distribution network are proposed in this paper. Firstly, a data-driven power flow analysis model for the distribution network is proposed, and the nonlinear mapping relationship between the distribution network state and power flow results is described from the data-driven perspective. Secondly, the paper analyzes the influence of photovoltaic power supply on the voltage of the distribution network, and establishes the volt/var optimization model based on photovoltaic power supply. Then, on the basis of data-driven power flow analysis of the distribution network, the distribution network reactive voltage optimization strategy based on data-driven power flow analysis is proposed to ensure the safe and stable operation of distribution network voltage, reduce the operating network loss of distribution network, and realize the distribution network reactive voltage optimization is not affected by factors such as distribution network line parameters. Finally, IEEE 33 node power distribution system is used to verify the effectiveness of the proposed strategy.

Numerical Simulation of the Diffusion of Electroactive Molecule in Biosimilar Hydrogel Media

Based on experimental data of cyclic voltammetry, the values of the diffusion coefficients for toluidine blue in alginate hydrogel, gelatine hydrogel and alginate-gelatine hydrogels were obtained. Using the experimental values of the coefficients in a numerical model, the values of the recovery of flows have been calculated showing them consistent with what was the experimental. It is proposed to use the period in time during which the value of the flow force reaches the value of steady state flow force as an indicator of the diffusion properties of the hydrogel medium. The findings of this study can be used for the development of methods for the evaluation of the diffusion properties of hydrogel media: bioinks and tissue-engineered structures.

Microexpression Recognition Method Based on ADP-DSTN Feature Fusion and Convolutional Block Attention Module

Microexpressions are subtle facial movements that occur within an extremely brief time frame, often revealing suppressed emotions. These expressions hold significant importance across various fields, including security monitoring and human–computer interaction. However, the accuracy of microexpression recognition is severely constrained by the inherent characteristics of these expressions. To address the issue of low detection accuracy regarding the subtle features present in microexpressions’ facial action units, this paper proposes a microexpression action unit detection algorithm, Attention-embedded Dual Path and Shallow Three-stream Networks (ADP-DSTN), that incorporates an attention-embedded dual path and a shallow three-stream network. First, an attention mechanism was embedded after each Bottleneck layer in the foundational Dual Path Networks to extract static features representing subtle texture variations that have significant weights in the action units. Subsequently, a shallow three-stream 3D convolutional neural network was employed to extract optical flow features that were particularly sensitive to temporal and discriminative characteristics specific to microexpression action units. Finally, the acquired static facial feature vectors and optical flow feature vectors were concatenated to form a fused feature vector that encompassed more effective information for recognition. Each facial action unit was then trained individually to address the issue of weak correlations among the facial action units, thereby facilitating the classification of microexpression emotions. The experimental results demonstrated that the proposed method achieved great performance across several microexpression datasets. The unweighted average recall (UAR) values were 80.71%, 89.55%, 44.64%, 80.59%, and 88.32% for the SAMM, CASME II, CAS(ME)3, SMIC, and MEGC2019 datasets, respectively. The unweighted F1 scores (UF1) were 79.32%, 88.30%, 43.03%, 81.12%, and 88.95%, respectively. Furthermore, when compared to the benchmark model, our proposed model achieved better performance with lower computational complexity, characterized by a Floating Point Operations (FLOPs) value of 1087.350 M and a total of 6.356 × 106 model parameters.

Does sheath size matter: benchtop comparison of flow and pressure across variety of continuous flow endoscopes.

Laser enucleation utilizes purpose-built endoscopes for laser stabilization and continuous flow. No evaluation has been done with respect to flow or intravesical pressure with these scopes. We sought to evaluate the effect different endoscopes and sheath sizes on irrigation outflow and intravesical pressure. Using a benchtop model using a silicone bladder model, five outer/inner sheath combinations were assessed: Storz 28/26Fr, Storz 26/26Fr, Wolf 26/24Fr, Wolf 26/22Fr, and Wolf 24/22Fr. A urodynamics pressure transducer was inserted alongside the scope for bladder pressure measurement and outflow from scope to drain was measured using uroflowmetry device. Four 1-minute trials were recorded for each sheath and the steady state flow and pressure was recorded. The Storz 28F outer sheath and 26F inner sheath had the highest outflow (12.4 ± 0.5 mL/s, p < 0.01). The Wolf 24F outer and 22F inner had the lowest outflow (7.0 ± 0.0 mL/s, p < 0.01). The steady state bladder pressure was the lowest in the Storz 28/26 (1.5 ± 1.7cm H2O, p < 0.01)) and the greatest in the Storz 26/26 (24.2 ± 1.9cm H2O, p < 0.01). The Storz 28/26 combination had best outflow rate and lowest intravesical pressures in our benchtop study. Flow rates generally decreased with smaller sheath sizes and steady state bladder pressures increased as the difference between the outflow and inflow sheath size narrowed. These findings provide initial parameters that could guide sheath selection in future to optimize visualization and success of voiding trials.

Stationary regimes and parametrization of ekman friction in the Karman model of flow induced by external vortical body force

The detailed study of stationary regimes of Karman axisimmetric flow induced by external vortical body force is done. It is extracted two stationary regimes – with small (Batchelor regime) and with substantial (Stewartson regime) secondary circulation. The diagram of regimes existence is plotted in the space of flow parameters – Rossby and small Ekman numbers. For the flow decaying to the stationary flow in the Batchelor regime a theoretical model is proposed with which it was possible to derive a parametrization of linear friction coefficient, Ekman pumping velocity, stationary pressure from mean flow characterictics (vorticity and divergence). In the Stewartson regime a parameterization of the stationary flow is proposed and also numerically studied a decay rate. It is shown a good agreement between theoretical and numerical model results.

Novel dopamine-derived carbon modified fe-based metal–organic framework enhanced aptasensor rendering ultrasensitive electrochemical detection of oxytetracycline

In the present work, an aptasensor with dual binding sites based on Au NPs modified with self-polymerized polydopamine (PDA) and Fe-MOF is successfully constructed. In terms of standard electron transfer, the cyclic voltammetry (CV) analysis showcases a rate constant (ks) of 96.0 s−1, signifying an exceptional electron transfer rate of oxytetracycline at the sensor interface of Apt/Au@PDA@NH2-MIL-101(Fe)/GCE. Further deepening the investigation into electrochemical kinetics using chronoamperometry (CA), we investigated the electrocatalytic parameters (Kcat) of Au@PDA@NH2-MIL-101(Fe) in relation to oxytetracycline. The results divulged an impressive average Kcat value of 3.06 × 105 M−1 S-1. This evidence robustly suggests the superior electrocatalytic activity of Au@PDA@NH2-MIL-101(Fe) when it comes to oxytetracycline oxidation. A custom-designed portable rapid detection platform was developed, achieving detection limits of 6.88 nM under static water flow conditions and 5.56 nM under dynamic conditions. Remarkably, the self-polymerization of PDA on Au NPs not only refines their size but also boosts their interaction with biomolecules, thereby promising excellent biocompatibility. Moreover, the abundance of –COOH groups and unsaturated Fe3+ sites on the NH2-MIL-101(Fe) surface furnishes a considerable number of grafting sites for the aptamer. More importantly, the redox interplay between Au@PDA and NH2-MIL-101(Fe) accelerates electron movement, thus amplifying the electrochemical signal and the detection sensitivity for oxytetracycline.