Forced Flow Research Articles

Рекомендації з відновлення водопропускальних труб із застосуванням металевих гофрованих конструкцій

Introduction. The reliability and durability of culverts are affected by static and dynamic loads from vehicles and temperature and climatic influences, the destructive force of water flow, abrasive destruction, corrosion of the material, shortcomings in the choice of structures and unsatisfactory design, all of which cause the premature collapse of the structure. Today, culverts made of metal corrugated structures (hereinafter referred to as metal corrugated structures) are widely used. The well-known advantages that justify the choice of such a solution are mainly a short term and a relatively low cost of construction, construction provided that the appropriate technological regime is observed does not cause any particular problems. Therefore, there is a need to develop a recommendation for the restoration of culverts using metal corrugated structures. Problems. It was established that there is a need to restore culverts without stopping the movement of vehicles. Goal. It consists in offering approaches for the restoration of culverts using metal corrugated structures.

Hydrodynamic optimization and performance verification of fairings for round-ended cofferdams using dam-break wave experiments and numerical simulations

Round-ended cofferdams are crucial for large-scale marine projects but are vulnerable to the complex marine environment, including waves, tides, and storms. Enhancing the hydrodynamic performance of these cofferdams is essential for improving safety and efficiency in marine construction. This study introduces a novel fairing design aimed at reducing water flow resistance during the quasi-stable stage of a tsunami. The flow field is analyzed using computational fluid dynamics (CFD) simulations, and an adaptive surrogate model is employed to optimize the parameterized fairing shape. The results demonstrate that the optimized shape significantly suppresses vortex shedding, leading to a 16.59 % reduction in the drag coefficient and a 44.3 % reduction in the lift coefficient under flow conditions. Experimental and numerical simulations of dam-break waves are conducted for two designs, R1 and R0. By comparing their flow field and force characteristics, it is found that R1 effectively separates waves during the impulse stage, reduces wave climb height, and decreases impact loads. In the quasi-stable stage, R1 mitigates the blockage effect, reducing the liquid level difference between the front and back, and thus lowering flow forces. Experimental data further reveals that when the downstream is a dry riverbed, R1′s load reduction is particularly notable, with maximum reductions of 45.62 % in the impulse stage and 28.75 % in the quasi-stable stage. When the riverbed is wet, the maximum load reduction rates are 18.04 % and 8.72 %, respectively. Therefore, R1 not only reduces the resistance of round-end cofferdams under water currents but also under extreme wave forces, providing valuable insights for advancing ocean engineering design.

Minimizing movements for forced anisotropic curvature flow of droplets

We study forced anisotropic curvature flow of droplets on an inhomogeneous horizontal hyperplane. As in Bellettini and Kholmatov [J. Math. Pures Appl. 117 (2018), 1–58], we establish the existence of smooth flow, starting from a regular droplet and satisfying the prescribed anisotropic Young’s law, and also the existence of a 1/2 -Hölder continuous in time minimizing movement solution starting from a set of finite perimeter. Furthermore, we investigate various properties of minimizing movements, including comparison principles, uniform boundedness, and the consistency with the smooth flow.

Vortex shedding and induced forces in unsteady flow

AbstractThis survey paper is concerned with vortex shedding from bodies in unsteady flow due either to time dependent motion of the body in a still fluid or unsteady motion of the fluid about a fixed body. The fluid is treated as incompressible, and the main emphasis is on starting flows and oscillatory flows. Much of the discussion describes 2D flow around sections of long or slender bodies. The first part of the paper covers the inviscid flow scaling of the forces induced by vortex shedding in time dependent flows which drive the shedding. This is followed by application of Wu’s impulse integral of the moment of vorticity to predict the forces induced by vortex shedding from a body in both inviscid and viscous flows. Vortex shedding phenomena involving small amplitude, high-frequency oscillatory flow such as vortex-induced vibration (VIV) and fluid-structure interaction (FSI) are not included in this discussion as in these cases the unsteady flow controls rather than drives the vortex shedding and they are well covered elsewhere.The second part of the paper describes a vortex force mapping (VFM) method derived by considering the Lamb–Gromyko formulation for the pressure contribution which allows the integral of the vorticity field to be restricted to regions which are not far from the body. It is applied to both inviscid and viscous flows. The section finishes with discussion of application of the VFM to the calculation of forces induced on bodies from flow field measurements, such as particle image velocimetry (PIV).

Research of scale effect on propeller bearing force of a four-screw ship in oblique flow

To study the scale effect on propeller bearing forces in oblique flow, the propeller bearing forces of a fully appended four-screw ship that refers to a vessel propelled by four propellers are calculated and investigated. The findings reveal that scale effects in wake fields lead to an increase in the axial velocity of the propeller disk in the full-scale ship compared to the model, influenced by boundary layer flow. Moreover, asymmetric differences in the impact of oblique flow on the leeward and windward sides result in varied effects of positive and negative drift angles on the wakefield. The disparity in wake fields between inside and outside disks exacerbates unbalanced load distribution, with time-averaged loads showing an increase with drift angle for both propellers at full scale. Additionally, pronounced scale effects lead to variations in blade loads between model and full scale, with drift angles shifting the locations of single-blade load extremums. Unsteady bearing force components exhibit periodic fluctuations, with larger amplitudes at the blade passage frequency for the model scale propeller compared to the full scale, particularly evident under negative drift angles. The aforementioned findings can provide theoretical guidance for load balancing and vibration reduction of the four-screw ships.

دراسة علمية حول العزم الزاوي وعلاقته بالخصائص الميكانيكية لشفرات التوربينات

The general trend now in all countries of the world and all sectors is to achieve sustainability. One of how this sustainability can be achieved is to develop and improve the properties of raw materials, and in the field of turbine-powered power plants, sustainability must be achieved in light of the global crisis facing the energy sector, in this study, which aims to study the effect of angular torque on Mechanical properties of turbine blades, so that we can develop and improve the properties of those blades Angular torque is very important in turbine blades because it drives the turbine to rotate. Angular torque results from a force acting on a rotating body. In the case of turbine blades, the force of the gas flow produces angular torque. Turbine blades typically consist of thin, curved metal sheets. When gas passes through the blades, it exerts a force on the blades. This force forces the blades to rotate around its axis the greater the angular torque it produces. The greater the angular torque, the faster the turbine rotates. This study provides a mathematical model to calculate the angular torque resulting from turbine blades. The model was used to study the effect of various factors on the angular torque, including the gas flow speed, the shape of the blades, and their mechanical properties. Then, a simulation was run using the ANSYS program to determine the relationship between the angular torque and the mechanical properties of the turbine blades. The results indicated a large deviation of the flexible blades and unstable rotation of the rotating blade systems, due to the coupling effect of rotation and vibration, where the mechanical properties of mass/inertia distributions, damping, and stiffness are related to changes in rotational speed and local deformation in rotor blade systems, thus, the harmonic balance must occur and the mechanical properties of the blades be improved. Keywords: Angular Torque, Mechanical Properties, Raw Materials, Turbine blades, mathematical model, flow speed, ANSYS, rotation and vibration, harmonic balance.

Forces of Filtrate Flow on Podocyte Foot Processes Studied by Three-Dimensional and Two-Dimensional Computational Fluid Dynamics

Forces of Filtrate Flow on Podocyte Foot Processes Studied by Three-Dimensional and Two-Dimensional Computational Fluid Dynamics

Określenie zmian ciśnienia podczas wiercenia otworu z półzanurzalnej platformy wiertniczej

The article states that a ship in the open sea is in a complex oscillatory motion due to the aerodynamic force of water flow and hydrodynamic pressure. Among the lateral, keel, horizontal, and vertical vibrations, only the vertical vibration of the vessel primarily affects the technological process of drilling a well. The article determines the magnitude of the hydrodynamic pressure that arises in the wellbore from the oscillation of the semi-submersible drilling platform in the absence of well flushing and a telescopic string, a compensator for vertical movement. When formulating the problem accurately, one should take into account the presence of natural vibrations of both the drilling tool and the semi-submersible drilling platform from which the well is to be drilled. The semi-submersible drilling platform was awarded by Caspian Drilling Company to two subsidiaries of Keppel offshore & Marine Company with Caspian Rigbuilders and Caspian Shipyard Company. This platform, named after Heydar Aliyev, is the first and the only drilling platform in the world with a 1,400-atmosphere system technology. Its carrying capacity is 5,600 tons, and its displacement is 47,500 tons. Vertical vibrations of the semi-submersible platform, caused by hydrometeorological conditions, set in motion the drilling tool associated with the semi-submersible drilling platform, along with the flushing solution that fills the well during drilling without a riser. This leads to a change in the hydrodynamic pressure in the well. Therefore, the change in hydrodynamic pressure in the well must be checked using a special installation that simulates the vibrations of the vessel and drilling tool in a well filled with drilling fluid.

Fixed Airflow Obstruction in Asthma Can Be Identified Early by Low FEF25-75% and is Associated with Environmental Exposure.

This study aimed to identify environmental risk factors associated with asthmatic fixed airflow obstruction (FAO) and assess the relationship between small airway abnormalities defined by forced expiratory flow at 25-75% (FEF25-75%) and FAO. We analyzed data from 312han Chinese patients with stable asthma on standard treatment. Low FEF25-75% was defined as post-bronchodilator FEF25-75% z-score <-0.8435, and FAO as post-bronchodilator FEV1/FVC z-score <-1.645. Exposure levels were retrospectively analyzed in relation to FAO risk in asthmatics. Asthmatics were grouped by low FEF25-75% and FAO, and lung function, environmental exposure, daily symptoms, and exacerbations in the previous year were compared cross-sectionally across groups. In retrospective analyses, pack-years of smoking in male patients (adjusted odd ratio [95% confidence interval] 1.05 [1.03-1.07], P<0.001), biomass exposure for >20 years (2.65 [1.13-6.43], P=0.027), occupational exposure for >10 years (2.01 [1.06-3.86], P=0.035) and occupational exposure for >20 years (2.67 [1.24-5.91], P=0.013) were associated with asthmatic FAO. In cross-sectional analyses, compared with the normal FEF25-75%/ asthmatics without FAO (NON-FAO) group, the low FEF25-75%/ asthmatics with FAO (FAO) group had lower FEV1 z-scores and FEV1/FVC z-scores, more pack-years and years of biomass and occupational exposure, higher Asthma Control Questionnaire-5 and Chronic Obstructive Pulmonary Disease Assessment Test scores, and more frequent exacerbations. The low FEF25-75%/NON-FAO group showed the same trend, but to a lesser extent. Chronic airway inflammation is not the only driver of asthmatic FAO, and management and treatment targeting environmental risk factors (smoking and biomass and occupational exposures) may slow FAO progression in asthmatics. The FEF25-75% determined by the z-score is a reliable marker of small airway abnormalities, and patients with low FEF25-75% are at greater risk for FAO, requiring more frequent follow-up.

Confined seepage analysis of saturated soils using fuzzy fields

Seepage refers to the flow of water through porous materials. This phenomenon has a crucial role in dam, slope, excavation, tunnel, and well design. Performing seepage analysis usually is a challenging task, as one must cope with the uncertainty associated with the parameters such as the hydraulic conductivity in the horizontal and vertical directions that drive this phenomenon. However, at the same time, the data on horizontal and vertical hydraulic conductivities are typically scarce in spatial resolution. In this context, so-called non-traditional approaches for uncertainty quantification (such as intervals and fuzzy variables) offer an interesting alternative to classical probabilistic methods, since they have been shown to be quite effective when limited information on the governing parameters of a phenomenon is available. Therefore, the main contribution of this study is the development of a framework for conducting seepage analysis in saturated soils, where uncertainty associated with hydraulic conductivity is characterized using fuzzy fields. This method to characterize uncertainty extends interval fields towards the domain of fuzzy numbers. In fact, it is illustrated that fuzzy fields are an effective tool for capturing uncertainties with a spatial component, since they allow one to account for available physical measurements. A case study in confined saturated soil shows that with the proposed framework, it is possible to quantify the uncertainty associated with seepage flow, exit gradient, and uplift force effectively.

Simulation analysis and optimization of pilot type electro-hydraulic proportional directional valve based on multi field coupling

The pilot-operated electro-hydraulic proportional directional valve is widely used in complex and precision engineering fields. Its operational stability and reliability determine the overall performance of the hydraulic system. During the working process of the pilot-operated electro-hydraulic proportional directional valve, the spool is deformed due to the influence of pressure and temperature, resulting in problems such as clamping or stagnation. In order to solve this problem, this study uses the fluid-solid-thermal coupling simulation method to analyze the flow field characteristics and thermal deformation of the spool with different structural throttling grooves, and optimizes the U-shaped throttling groove structure. The results indicate that as the valve opening increases, the front section of the throttling groove becomes the primary region where the maximum radial deformation of the spool occurs. In this paper, the steady-state flow force of the valve core is taken as the measurement standard, the constraint range of the structural parameters is determined, and the radial thermal deformation is included in the optimization analysis of the structural size. It’s verified that the optimized flow characteristics are improved by about 32 % compared with that before optimization, and the maximum steady-state flow force after considering thermal deformation is reduced by about 4N compared with that before optimization. This provides an important design basis and reference for the structural design and optimization of the pilot electro-hydraulic proportional directional valve.

Discretization of Thin-Walled Sections with Variable Wall Thickness

At the stage of designing thin-walled aircraft structures, to simplify calculations, their cross sections are idealized. To do this, the section with the skin and the longitudinal elements reinforcing it is replaced (when determining normal stresses) by a discrete one, consisting of concentrated areas at characteristic points. In this case, the equality of the moments of inertia of the initial and discrete sections is preserved. Such idealization is used in the calculation of thin-walled rods for normal and shear stresses (Wagner model). For sections consisting of a system of rectangular strips of constant thickness, discretization allows to set approximate values of normal and shear stresses and accurately find the locations of the singular points of the bending center (in an open contour) and the center of rigidity (in a closed one). The discrete model of a strip consists of three lumped areas: two at the edges and one in the center. The paper proposes to extend the discrete model to sections in which the skin thickness changes according to a linear law. In addition to the rectangular strip, it is possible to use elongated triangles and trapezoids, replaced by three and four concentrated areas, respectively. The possibility of using a discrete model for calculating some thin-walled sections of open and closed contours is considered. The section of an open contour is studied - the problem of transverse bending without torsion of a channel having flanges with a linearly variable thickness. Differences in the flows of tangential forces calculated from the exact and discrete models are shown. The coincidence of the results in determining the position of the bending center according to two models was established. When studying the application of a discrete model to a closed contour, its simplified option is proposed. The problem of transverse bending without torsion and finding the center of rigidity in a section with a contour line in the form of a trapezoid with front and rear walls of constant thickness and upper and lower skins and a similar section with a contour in the form of a rectangle was considered. Differences in the flows of tangential forces calculated by exact and discrete models are established. For a closed section in the form of a rectangle, the decrease in the moment of inertia for torsion due to the redistribution of material in the cross section was studied separately. It has been established that when finding the position of the center of rigidity, the discrepancy between the results of the exact and discrete models in sections with geometric parameters close to real ones was less than 1% for a rectangular contour, and 4% for a trapezoidal contour. The results indicate the possibility of extending the application of the discrete model of thin-walled cross section to the design calculations of thin-walled rods with variable skin thickness, representing practical structures.

Identifying the mixed and forced convection flow with transverse magnetic field

AbstractOptimal control of the steady, laminar, magnetohydrodynamics (MHD) mixed convection flow of an electrically conducting fluid is considered under the effect of the transverse magnetic field in a square duct. The viscous and Joule dissipations are included and the flow is driven by a constant pressure gradient. The triple nonlinear set of momentum, induction, and energy equations are solved in dimensionless form by using the mixed finite element method (FEM) with the implementation of Newton's method for nonlinearity with the discretize‐then‐linearize approach. Accordingly, FEM solutions are obtained for various values of the problem parameters to ensure the efficiency of the underlying scheme. This study aims to investigate the problem of controlling the steady flow by using the physically significant parameters of the problem as control variables in the case of a mixed convection flow. In this respect, classification of the type of convection, forced or free, is achieved by controlling the Grashof number (Gr). Besides, single and pairwise controls with Hartmann number (M), Prandtl number (Pr), and magnetic Reynolds number (Rm) are also used to regain the prescribed fluid behaviors and required magnetic field. Control simulations are conducted with the sequential‐least‐squares‐programming (SLSQP) algorithm in the optimization.

Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis.

The inherent instability of laser welding, particularly keyhole instability, poses significant challenges in industrial applications, leading to defects such as porosities that compromise weld quality. Various forces act on the keyhole and molten pool during laser welding, influencing process stability. These forces are categorized into those promoting keyhole opening and penetration (e.g., recoil pressure) and those promoting keyhole collapse (e.g., surface tension, Darcy's damping forces), increasing instability and defect likelihood. This paper provides a comprehensive instability analysis to uncover key factors affecting keyhole and process instability, presenting future avenues for improving laser welding stability. Using a novel numerical method for simulating laser spot welding on aluminum with COMSOL Multiphysics 5.6, we investigated the effect of laser pulse shaping on keyhole and process instability. Our analysis focused on keyhole morphology, fluid flow behaviour, and force analysis. The results indicated that the curvature effect, Marangoni effect, and Darcy's damping force are primary contributors to instability, with the curvature effect and Darcy's damping force being the most dominant. Additionally, erratic and high-velocity magnitudes induce intense fluid flow behaviour, exacerbating keyhole instability. Moreover, single/quadruple peak triangular and variant rectangular ramp-down pulse shapes produced the least instability, while multi-pulse rectangular shapes exhibited intense instability. It was found that combining triangular/rectangular pulse shapes can reduce force and keyhole instability by smoothing spontaneous force spikes, resulting in a more stabilized welding process. Controlling fluid flow and abrupt force changes with appropriate pulse shaping is key to defect-free welded products.

Accumulation of Cerebrospinal Fluid, Ventricular Enlargement, and Cerebral Folate Metabolic Errors Unify a Diverse Group of Neuropsychiatric Conditions Affecting Adult Neocortical Functions.

Cerebrospinal fluid (CSF) is a fluid critical to brain development, function, and health. It is actively secreted by the choroid plexus, and it emanates from brain tissue due to osmolar exchange and the constant contribution of brain metabolism and astroglial fluid output to interstitial fluid into the ventricles of the brain. CSF acts as a growth medium for the developing cerebral cortex and a source of nutrients and signalling throughout life. Together with perivascular glymphatic and interstitial fluid movement through the brain and into CSF, it also acts to remove toxins and maintain metabolic balance. In this study, we focused on cerebral folate status, measuring CSF concentrations of folate receptor alpha (FOLR1); aldehyde dehydrogenase 1L1, also known as 10-formyl tetrahydrofolate dehydrogenase (ALDH1L1 and FDH); and total folate. These demonstrate the transport of folate from blood across the blood-CSF barrier and into CSF (FOLR1 + folate), and the transport of folate through the primary FDH pathway from CSF into brain FDH + ve astrocytes. Based on our hypothesis that CSF flow, drainage issues, or osmotic forces, resulting in fluid accumulation, would have an associated cerebral folate imbalance, we investigated folate status in CSF from neurological conditions that have a severity association with enlarged ventricles. We found that all the conditions we examined had a folate imbalance, but these folate imbalances were not all the same. Given that folate is essential for key cellular processes, including DNA/RNA synthesis, methylation, nitric oxide, and neurotransmitter synthesis, we conclude that ageing or some form of trauma in life can lead to CSF accumulation and ventricular enlargement and result in a specific folate imbalance/deficiency associated with the specific neurological condition. We believe that addressing cerebral folate imbalance may therefore alleviate many of the underlying deficits and symptoms in these conditions.

Partial gravity flammability of cast PMMA rods in concurrent axial stagnation flow

Testing was performed in a partial gravity centrifuge drop vehicle in the Zero Gravity Research Facility with cast PMMA rods in concurrent axial buoyant stagnation flow to determine flammability limits as a function of partial gravity level. The partial gravity levels studied varied from 0.04 g to a simulated 1g for ambient oxygen concentrations from 13.2 % to 15.2 % O2 by volume at an average 57.6 kPa (8.4 PSIA) ambient pressure, which is very close to the anticipated Lunar habitat pressure. The PMMA flammability boundary as a function of oxygen concentration and gravity level has been determined at five gravity levels. Coriolis effects appear to be minimal in the stagnation region where the flame is stabilized while the tips of the flame do show some bending at the higher gravity levels. Lunar gravity levels are near the minimum in the oxygen - gravity level flammability boundary. This suggests that fire is a significant safety risk for future exploration missions to the Moon since materials are screened in normal gravity to evaluate their safe use in space. If normal gravity screening is not conservative, a material derating method will need to be applied to ensure the material is not flammable on the Moon. Since the blowoff boundary appears to be linear with forced flow velocity, it may be possible to conduct elevated forced flow blowoff testing that could then be extrapolated down to effective Lunar gravity levels to provide an oxygen delta between 1g and Lunar flammability limits to derate the material.

Energy Recovery from Hexavalent Chromium Reduction for In Situ Electrocatalytic Hydrogen Peroxide Production.

Recovering chemical energy embedded in pollutants is significant in achieving carbon-neutral industrial wastewater treatment. Considering that industrial wastewater is usually treated in a decentralized manner, in situ utilization of chemical energy to achieve waste-to-treasure should be given priority. Herein, the chemical energy released by the electroreduction of Cr(VI) was used to enhance on-site H2O2 generation in a stacked flow-through electrochemical system. The driving force of water flow efficiently coupled O2 evolution with 2-e O2 reduction to facilitate H2O2 generation by transporting anode-produced O2 to the cathode. Meanwhile, the chemical energy released by Cr(VI) promoted O2 evolution and impeded H2 evolution by regulating the electrode potentials, accounting for the enhanced H2O2 generation. The system could completely reduce 10-100 ppm of Cr(VI), reaching the maximum H2O2 concentration of 2.41 mM. In particular, the H2O2 concentrations in the Cr(VI)-containing electrolyte were 10.6-88.1% higher than those in the Cr(VI) free electrolyte at 1.8-2.5 V. A 24-day continuous experiment demonstrated the high efficiency and stability of the system, achieving a 100% reduction efficiency for 100 ppm of Cr(VI) and producing ∼1.5 mM H2O2 at 1.8 V. This study presents a feasible strategy for Cr(VI) detoxification and synchronous on-site H2O2 generation, providing a new perspective for innovative Cr(VI) wastewater treatment toward resource utilization.

Air pollution exposure, chemical compositions, and risk of expiratory airflow limitation in youth in Northeast China

BackgroundExpiratory airflow limitation (EAL) is closely associated with respiratory health in youth and adulthood. Owing to limited evidence, we aim to estimate the association between air pollutants, both individually and in combination, along with their chemical compositions, and the risk of EAL in youth based on data obtained from Northeast China Biobank. MethodsPulmonary function was evaluated using a medical-grade pulmonary function analyzer, with EAL defined as a forced expiratory flow in 1 s/ forced vital capacity ratio of < 0.8. Land use regression models were used to predict exposure to six air pollutants. Air pollution score (APS) for each participant was constructed as combined exposure. The chemical composition of particulate matter with an aerodynamic diameter of ≤ 2.5 µm (PM2.5) was determined using a validated machine-learning algorithm. Logistic regression models were employed to estimate effect sizes, and odds ratio (OR) and 95 % confidence intervals (CI) were calculated. ResultsIn total, 905 EAL cases were identified among the 4301 participants, with a prevalence of 21.04 %. Each inter-quartile range increase in APS was associated with a 25 % higher risk of EAL (OR = 1.25, 95 % CI: 1.12, 1.39). Among the pollutants analyzed, PM2.5 exposure had the strongest association with the risk of EAL (OR = 1.33, 95 % CI: 1.18, 1.52). Out of the five chemical components, sulfate (SO2-4) (OR = 1.39, 95 % CI: 1.24, 1.57) and ammonium (NH+4) (OR = 1.39, 95 % CI: 1.23, 1.57) exhibited the strongest associations with the risk of EAL. ConclusionsOverall, combined effects of air pollution increased the risk of EAL in youth, with SO2-4 and NH+4 emerging as the predominant contributing chemical components in Northeast China.

Microfluidic measurement of the size and shape of lipid-anchored proteins

The surface of a cell is crowded with membrane proteins. The size, shape, density, and mobility of extracellular surface proteins mediate cell surface accessibility to external molecules, viral particles, and other cells. However, predicting these qualities is not always straightforward, even when protein structures are known. We previously developed an experimental method for measuring flow-driven lateral transport of neutravidin bound to biotinylated lipids in supported lipid bilayers. Here, we use this method to detect hydrodynamic force applied to a series of lipid-anchored proteins with increasing size. We find that the measured force reflects both protein size and shape, making it possible to distinguish these features of intact, folded proteins in their undisturbed orientation and proximity to the lipid membrane. In addition, our results demonstrate that individual proteins are transported large distances by flow forces on the order of femtoNewtons, similar in magnitude to the shear forces resulting from blood circulation or from the swimming motion of microorganisms. Similar protein transport across living cells by hydrodynamic force may contribute to biological flow sensing.

Predicting the skin friction’s evolution in a forced turbulent channel flow

The present paper reports on the ability of neural networks (NN) and linear stochastic estimation (LSE) tools to predict the evolution of skin friction in a minimal turbulent channel (Reτ=165) after applying an actuation near the wall that is localized in space and time. Two different NN architectures are compared, namely multilayer perceptrons (MLP) and convolutional neural networks (CNN). The paper describes the effect that the predictive horizon and the type/size/number of wall-based sensors have on the performance of each estimator. The performance of MLPs and LSEs is very similar, and becomes independent of the sensor’s size when they are smaller than 60 wall units. For sufficiently small sensors, the CNN outperforms MLPs and LSEs, suggesting that CNNs are able incorporate some of the non-linearities of the near-wall cycle in their prediction of the skin friction evolution after the actuation. Indeed, the CNN is the only architecture able to achieve reasonable predictive capabilities using pressure sensors only. The predictive horizon has a strong effect on the predictive capacity of both NN and LSE, with a Pearson correlation coefficient that varies from 0.95 for short times (i.e., of the order of the actuation time) to less than 0.4 for times of the order of an eddy turn-over time. The analysis of the weights and filters in the LSE and NNs show that all estimators are targeting wall-signatures consistent with streaks, which is interpreted as the streak being the most causal feature in the near-wall cycle for the present forcing.