Function Of Velocity Research Articles

Flow past a rotating porous sphere in the existence of a toroidal magnetic field

This model consists of a porous spherical body rotating in an incompressible conducting fluid in the existence of a toroidal magnetic field. The toroidal field is generated by an electric dipole along the axis of symmetry. The model is split into two parts—the clear fluid region and the porous sphere. The clear fluid area is driven by the momentum equation and the permeable sphere region is driven by the Brinkman equation. The study is being done for the scenario where the impact of viscous force is much more than inertia force. The expression is found for fluid velocity and stream function by the superposition method. The results depict the impact of rotational parameters and the Darcy number on separation parameter. It is shown that the separation is low for the highly permeable sphere.

Investigation of time-dependent mechanical loading on the start-stop process of functionally graded rotating disks under thermal conditions

Rotating disks are used in industries, such as aerospace, automotive, and power plants. These disks are under time-dependent mechanical loading when the machine starts or stops working conditions. Thermal stresses caused by temperature changes with this time-dependent mechanical load create dangerous conditions. Therefore, the estimation of the elastic limit angular velocity and acceleration as a criterion for the initiation of plastic deformations has special importance in the start-stop process. An analytical Homotopy perturbation method is used to solve the heat transfer equation and the governing Navier equations in both radial and tangential directions of functionally graded rotating disks with non-uniform thickness. The Tamura-Tomoto-Ozawa model is implemented to calculate the yield stress at a different radius of the disk. The obtained results will be verified with the higher-order finite difference method. The effect of thickness parameter, type of thermal and boundary conditions on the angular velocity and acceleration, and also the starting radius of the plastic deformations are investigated by numerical examples. It is shown that by defining the appropriate temperature gradient on the outer surface of the disk and the parameters in the time-dependent angular velocity function, the level of stresses can be controlled and optimized in all working processes.

Experimental investigation of different sub-regimes in horizontal stratified and intermittent gas-liquid two-phase flow: Flow map and analysis of pressure drop fluctuations

Horizontal stratified and intermittent gas-liquid two-phase flows exhibit several sub-regimes. Identifying these correctly would enable the development of more robust predictive models. This study reports on experimental investigation, based on observations and the collection of time series of pressure drop in a 40 mm ID pipe. Nine different sub-regimes (SS, 2D wave, 3D wave, RW, ED+RW, PS+RW, plug, LAS, HAS) were revealed. An original flow pattern map for this diameter is proposed including transitory regions between the sub-regime. Comparison of experimental observations with existing flow maps has highlighted the effect of pipe diameter on transition of sub-regimes. As reported in literature the sub-regimes, could be identified by direct visualization of the pressure drop time series obtained from differential pressure sensor a swell as using Probability Density Function. Furthermore, statistical analysis of standard deviation as function of gas superficial velocity enabled detection of the transition of various sub-regimes. Finally, a space feature based on standard deviation and mixture Froude number is proposed as an identification tool between the different sub-regimes investigated.

Multi‐objective multiperiod stable environmental economic power dispatch considering probabilistic wind and solar PV generation

AbstractThe economic‐environmental power dispatch (EEPD) problem, a widely studied bi‐objective non‐linear optimization challenge in power systems, traditionally focuses on the economic dispatch of thermal generators without considering network security constraints. However, environmental sustainability necessitates reducing emissions and increasing the penetration of renewable energy sources (RES) into the electrical grid. The integration of high levels of RES, such as wind and solar PV, introduces stability issues due to their uncertain and intermittent nature. This article addresses these concerns by formulating and solving the economic environmental and stable power dispatch (EESPD) problem, which includes fixed zonal reserve capacity from conventional thermal generators and uncertain reserves from RES. Uncertainties in RES and load demand are modelled using random variable generation techniques, applying Gaussian, Weibull, and log‐normal probability density functions (PDFs) for load demand, wind velocity, and solar irradiance, respectively. The stochastic EESPD problem extends to multiple periods by replicating the single‐period problem for each interval in the planning horizon, linking periods through intertemporal ramping costs, physical ramp rate, and fixed zonal reserve constraints on dispatch variables. Multi‐objective evolutionary algorithms (MOEAs) have gained prominence for solving complex non‐linear problems involving multi‐objective functions. This article applies the latest MOEAs to tackle the proposed EESPD problem, incorporating stochastic wind and solar PV power sources. Network security constraints, such as transmission line capacities and bus voltage limits, are considered along with constraints on generator capabilities and intertemporal spinning reserves, ramp‐up and ramp‐down constraints for thermal generators. A bidirectional coevolutionary‐based multi‐objective evolutionary algorithm is employed, integrating an advanced constraint‐handling technique to ensure compliance with system constraints. The simulation results show that the proposed formulation achieves a better trade‐off between various conflicting objective functions compared to other state‐of‐the‐art MOEAs.

Left atrial appendage emptying velocity and left ventricular function as predictors of inotropic support in patients undergoing elective off-pump coronary artery bypass grafting

Abstract Background: Patients undergoing elective off-pump coronary artery bypass grafting (CABG) are at risk of hemodynamic instability, ischemia, arrhythmia, and dysfunction. These events need to be managed by pharmacological supports or relieving of mechanical obstruction (octopus) of the heart to maintain the hemodynamic stability. There is a paucity of data on the effect of left ventricular (LV) dysfunction on left atrial appendage (LAA) emptying velocity. We evaluated the relationship between LV function and LAA emptying velocity and requirement of inotropic support perioperatively. Materials and Methods: In this prospective open-label all-comer study, fifty patients undergoing elective off-pump CABG under general anesthesia, we measured LAA emptying velocity by pulsed wave Doppler and evaluated if it could predict the need for inotropes perioperatively. It is a case series of 50 patients without a comparator arm. We measured pulsed wave Doppler across the mitral valve leaflet and early mitral inflow velocity (Evel) and late mitral inflow velocity, tissue Doppler at the lateral annulus of the mitral valve (e’) and also calculated the ratio of Evel and e’. Need for inotrope in the intraoperative and postoperative period was captured perioperatively. Vasoactive-inotropic score (VIS) was calculated for all the patients. Results: The VIS was significant (P < 0.0001, with odds ratio of 131.6 and confidence interval of 95% (0.9–1). However, there was no significant correlation between ejection fraction (EF) and VIS (P = 0.87). In patients with the need of inotropes, LAA emptying velocity was significantly increased in the postgrafting period as compared to the pregrafting period (75.64 cm/s vs. 57.9 cm/s, P < 0.001). Conclusion: The assessment of LAA emptying velocity value was a useful predictor of the need of inotropic support during off-pump surgery, especially during Obtuse marginal and Ramus grafting. This study paves the need of larger case–control studies to validate the findings.

Downburst wind loading on bridge decks through an analytical model

A mathematical model is proposed for estimating the wind loads caused by the passage of a downburst through horizontal structures, such as bridge decks. The model simulates the three-dimensional flow fields of stationary and environmentally-driven downbursts. It is based on radial and vertical shaping functions of the velocity components, following a path developed for aircraft structures. The radial shaping function of the horizontal velocity is defined with attention to reproducing the local increase in velocity observed in the average field measurements. In addition, the coefficients of an existing empirical vertical shaping function of the horizontal velocity are re-calibrated to better fit the available field data. The shaping functions of the vertical components are derived by imposing mass conservation.The model allows for predicting the large angles of attack on the decks during the passage of downbursts with small to medium diameters. The occurrence of such large angles of attack also implies a change in the aerodynamic design procedure of bridge decks, for which wind tunnel tests are commonly conducted only for angles of attack in the range of about ±10°. The aerodynamic coefficients of a NACA profile and a pseudo-rectangular section are used due to the absence in the literature of aerodynamic coefficients of bridge decks for very large angles of attack. Several runs are conducted by varying the downburst properties and the deck height above the ground to provide results useful for the aerodynamic design of bridges. The results confirm the key role played by the vertical component of the velocity in developing the wind loads on the decks during the passage of a downburst. Non-negligible wind loads are obtained, which are not predictable with the existing approaches. The need for conducting dynamic analyses of flexible bridges is also emerging.

Hamiltonian mechanics of “magnetic” solitons in two‐component Bose–Einstein condensates

AbstractWe consider the motion of a “magnetic” soliton in two‐component condensates along a nonuniform and time‐dependent background in the framework of Hamiltonian mechanics. Our approach is based on generalization of Stokes' remark that soliton's velocity is related to its inverse half‐width by the dispersion law for linear waves continued to the region of complex wave numbers. We obtain expressions for the canonical momentum and the Hamiltonian as functions of soliton's velocity and transform the Hamilton equations to a Newton‐like equation. The theory is illustrated by several examples of concrete soliton's dynamics.

Thermal magnetization transport analysis featuring darcian and multi-physical rheological characteristics in chemically reactive dual convective tangent-hyperbolic nanomaterial confined by vertical cone

The Soret-Dufour characteristics elaborate the phenomena of cross-diffusion where solutal gradients yield heat flux (Dufour aspect) and thermal gradients engender mass flux (Soret effect). Such consideration finds significance in multi-component fluid systems, influencing both heat-mass transportation processes. This study evaluates the porous medium characteristics in convectively heated tangent-hyperbolic nanomaterial driven by a magnetized convected cone. The analysis features Buongiorno nanomaterial model which accounts Brownian motion together with thermophoresis. Thermal transport expression which reports heat transfer characteristics is modeled by considering thermal radiation, convective thermal conditions and heat generation while mass transfer considers the chemical reaction effects. Dimensional expressions are converted into dimensionless forms deploying similarity transformations ensuing in a set of ODEs (ordinary differential expressions) which are computed by deploying bvp4c algorithm. Graphical and tabular behavior of velocity, nanoparticles concentration and temperature fields is inspected corresponding to related variables. This research highlights key findings, revealing a decrease in Nusselt number with increasing heat generation, Dufour parameter and thermophoresis parameter values while opposite trends are verified for radiation parameter values. The velocity function declines for escalating Weissenberg number, magnetic field and permeability parameters but it upsurges with material and buoyancy parameters.

Convective heat transfer and drag coefficients of human body in multiple crowd densities and configurations in semi-outdoor scenarios

This study numerically assessed the impact of human crowd density and outdoor wind conditions (average velocity, its profile, and direction) on the convective heat transfer and drag coefficients (hc and Cd). Five different configurations of standing computer-simulated persons (CSPs) were tested in a semi-outdoor environment. A single isolated CSP, nine CSPs in a block array (with three representative crowd densities), and eighteen randomly allocated CSPs were used. The results indicated a significant impact of crowd density on the overall and local hc values. As the density increases, the body's obstruction against wind increases, resulting in lower heat loss. Newly proposed formulas for hc as a function of the average wind velocity (UAVE.) are (7.56 × UAVE.0.65), (8.02 × UAVE.0.64), and (8.26 × UAVE.0.63) for the high, medium, and low crowd densities, respectively. This reveals an overestimation of hc when an isolated human body is used. The hc values of the upper segments were the most affected by a 22 % reduction in the predicted hc. Moreover, when the crowd density increased, local hc and Cd decreased simultaneously, particularly in the chest, pelvis, and thigh segments. Oblique wind angles (60° and 150°) resulted in the highest hc and Cd values compared to other angles. The chest and pelvis were most affected by shifting the wind direction, indicating the dominance of these segments in concurrently controlling the thermal and drag performances. These results provide valuable insights into the optimization of human thermal and physical comfort models.

Aerodynamic performances and near wake of an Ahmed body under unsteady flow conditions

This paper experimentally characterizes unsteady effects and flow fields around the Ahmed Body, by analyzing global forces and detailed wake effects. The results are compared to those obtained under steady conditions, with varying wind tunnel velocities and different yaw angles between the model and the free stream. Unsteady fields are generated by means of oscillating blades positioned at the inlet of the test section, whose amplitudes and frequencies can be easily controlled. Specifically, low frequencies, around a few Hertz, as those in the typical range generating load oscillations on vehicles, are considered. The results in terms of force coefficients, obtained by a dynamometric balance, and velocity fields, obtained by Particle Image Velocimetry, are processed in order to derive time-average statistics and also phase-average statistics, as related to forcing blade instantaneous positioning. This type of analysis can be performed thanks to the high temporal resolution of measurement systems, around 100 Hz for the force measurements and around 4000 Hz for the velocity measurements. Results in steady conditions well compare with previous results in references, both as functions of wind tunnel velocity and yaw angles. In unsteady conditions, whatever amplitude is considered, time-average drag and lift coefficients and their dependence on yaw angle are consistently lower compared to the steady case. Phase-averaged coefficients in unsteady conditions can oscillate by around 20 % in comparison to time-average values and these fluctuations are strongly dependent on yaw angle and amplitude of oscillations, thus suggesting that they both contribute to instantaneous loads. Present investigations are related to improvements in set-up of control systems in assisted-driving (self-driving) vehicles.

Identification of amplitude-dependent aerodynamic damping from free vibration data using iterative unscented kalman filter

This study presents an innovative approach employing an iterative Unscented Kalman Filter (IUKF) for the identification of amplitude-dependent nonlinear aerodynamic damping using wind tunnel free vibration data. The wind-structure interaction system is represented as a single-degree-of-freedom system, with the amplitude-dependent aerodynamic damping modeled as a polynomial function of structural displacement and velocity. The augmented state variables, encompassing structural vibration frequency and polynomial coefficients for aerodynamic damping, are concurrently estimated from free vibration data using the UKF technique. To enhance the robustness of the identification results against variations in initial conditions, the UKF is applied iteratively by assigning the estimated polynomial coefficients as new initial values for the state variables. Validation of the IUKF-based method is performed through a numerical example featuring a typical bridge deck sectional model, as well as experimental data from two spring-suspended sectional models experiencing vertical vortex-induced vibration (VIV) and torsional post-flutter limit cycle oscillation. The feasibility of identifying amplitude-dependent aerodynamic damping for amplitude range not covered by the displacement signal is examined.

Porosity estimation based on the shear modulus inversion of seismic shear wave

Reliable estimation of subsurface porosity is necessary for hydrocarbon reservoir characterization and fluid identification. Porosity estimations from seismic data can provide the lateral distribution of subsurface porosity, but the results may be highly nonunique because subsurface elastic properties (such as velocity and density) can be affected by porosity and pore fluids. Because shear modulus is insensitive to pore fluid content, it can be effectively used to estimate porosity. We develop a novel porosity estimation method using the reflected SH wave (SH-SH wave), whose propagation characteristics depend mainly on shear modulus and S-wave velocity. We derive a new analytical expression for the SH-SH-wave reflection coefficient, which acts as a function of shear modulus and S-wave velocity in its natural logarithm form. This new approximation has high accuracy, and both coefficients corresponding to shear modulus and S-wave velocity are “model-parameter independent”; thus, there is no need for prior estimation of any model parameter during inversion. Numerical analysis indicates that shear modulus inverted from the SH-SH wave has lower uncertainty, the problem is better conditioned, and the method requires data with fewer incidence angles than algorithms that invert for the shear modulus from the PP wave. Furthermore, the highly correlated rock-physics relationships between porosity and shear modulus facilitate accurate porosity estimation. A field data application indicates that high-resolution porosity of fine structures can be reliably recovered using our method.

Variation in Zero Plane Displacement and Roughness Length for Momentum Revisited

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Hydrodynamic Porosity: A New Perspective on Flow through Porous Media, Part II

In this work, we build upon our previous finding that hydrodynamic porosity is an exponential function of pore-scale flow velocity (or interstitial Reynolds number). We previously discovered this relationship for media with a square cavity geometry—a highly idealized case of the dead-ended pore spaces in a porous medium. Thus, we demonstrate the applicability of this relationship to media with other cavity geometries. We do so by applying our previous analysis to rectangular and non-rectangular cavity geometries (i.e., circular, and triangular). We also study periodic flow geometries to determine the effect of upstream cavities on those downstream. We show that not only does our exponential relationship hold for media with a variety of cavity geometries, but it does so almost perfectly with a coefficient of determination (R2) of approximately one for each new set of simulation data. Given this high fit quality, it is evident that the exponential relationship we previously discovered is applicable to most, if not all, unwashed media.

Influence of the Presence of Different Signatures on the Heat Transfer Profile of Laminar Flow Inside a Microchannel

Abstract The process of transferring heat and mass involves a high-pressure decline. Hence microchannels are utilized in extremely efficient heat and mass transfer processes, such as in the systems of the lungs and kidneys. Due to their high surface-to-volume ratio and compact volume, microchannels have demonstrated superior thermal performance. In this work, micro-fins of different topologies and arrangements were used inside microchannels for modulating heat transfer from the surface of the fins, in the presence of flowing media. The influx of media was simulated in sinusoidal form, reproducing simplified form of physiological circulatory blood flow. The study was conducted in numerical domain, while heat transfer and mass transfer equations were solved using pardiso solver. Temperature modulation at the fin surfaces was conducted to examine the transient profile of heat transfer, as function of both variable fluid velocity as well as variable feeding heat sources. In case of different input boundary conditions, the effect of heat distributions on fluid flow with respect to spatial distribution of micro-fins within a microchannel was evaluated. Results revealed the difference in heat transfer profiles in microchannels in presence of different sets of fin configurations. It was found that rectangular fins have the highest heat transfer in fluid at all its spatial configurations; while semi-ellipsoidal-shaped fins had shown the least heat transfer profile at same surface area. At the same time, it was also observed that the rate of heat dissipation was faster and limited in semi-ellipsoidal-shaped fins configuration; while the heat transfer rate was found symmetrical and low in presence of rectangular fins. Hence, this article emphasizes the modulation of temperature and velocity variations within the working fluid by emphasizing the thermo-fluid coupling effects in microchannels.

Experimental study of particle impact on cohesive granular packing.

We investigate experimentally the impact process of sand particles onto a cohesive granular packing made of similar particles. We use a sand-oil mixture with varying liquid content to tune the cohesive strength of the packing. The outcome of the impact is analyzed in terms of the production of ejected particles from the packing. We quantify this production as a function of the impact velocity of the particles for increasing cohesion strength. We identified three different regimes depending on the cohesion number Co, defined as the ratio of the interparticle cohesive force to the particle weight. For small cohesion (i.e., Co⪅1), the ejection process is not modified by the cohesion. For intermediate cohesion (i.e., 1⪅Co⪅20), the ejection process becomes less efficient: the number of ejected particles per impact for a given impact velocity is decreased but the critical impact velocity to trigger the ejection process remains unchanged. Finally, for strong cohesion (i.e., Co⪆20), we observed a progressive increase of the critical impact velocity. These experimental results confirm spectacularly the outcomes of recent numerical simulations on the collision process of a particle onto a cohesive packing and open avenues to model the aeolian transport of moist sand.

Hidden corrosion monitoring via phase shift evaluation of Lamb wave modes

Lamb wave inspection is a promising candidate for real-time monitoring of hidden corrosion in thin-walled metallic structures. The time-of-flight (ToF) which represents the variation of group velocity due to thickness reduction is commonly used, but its sensitivity is limited at the early stage of corrosion. To address this issue, the phase shift as a function of the phase velocity is defined and evaluated for corrosion detection in this paper. Specifically, the analytic cross-correlation method is applied, which estimates the group delay and the phase shift between two Lamb wave responses before and after the existence of corrosion simultaneously. The simulated examples show that the phase shift performs an obvious improvement on corrosion sensitivity compared to the ToF, and its value increases nearly linearly as the corrosion gets deeper. Ultimately, an experimental example is also introduced, where an active sensor network is deployed and a probabilistic imaging algorithm is introduced. The imaging results demonstrate that the proposed method could successfully identify and accurately localize the hidden corrosion.

What is the physical origin of the gradient flow structure of variational fracture models?

We investigate a physical characterization of the gradient flow structure of variational fracture models for brittle materials: a Griffith-type fracture model and an irreversible fracture phase field model. We derive the Griffith-type fracture model by assuming that the fracture energy in Griffith's theory is an increasing function of the crack tip velocity. Such a velocity dependence of the fracture energy is typically observed in polymers. We also prove an energy dissipation identity of the Griffith-type fracture model, in other words, its gradient flow structure. On the other hand, the irreversible fracture phase field model is derived as a unidirectional gradient flow of a regularized total energy. We have considered the time relaxation parameter a mathematical approximation parameter, which we should choose as small as possible. In this research, however, we reveal the physical origin of the gradient flow structure of the fracture phase field model (F-PFM) and show that the small time relaxation parameter is characterized as the rate of velocity dependence of the fracture energy. It is verified by comparing the energy dissipation properties of those two models and by analysing a travelling wave solution of the irreversible F-PFM. This article is part of the theme issue 'Non-smooth variational problems with applications in mechanics'.

Combination of ultrafiltration, activated carbon and disinfection as tertiary treatment of urban wastewater for reuse in agriculture

In the present study, three ceramic ultrafiltration (UF) membranes UF1 (20 nm), UF2 (50 nm) and UF3 (100 nm) were optimized using the Box-Behnken design (BBD) of response surface methodology (RSM) to determine the most adaptable membrane for reuse. The effectiveness of membranes was based on the retention capacity of chemical oxygen demand (COD), biochemical oxygen demand at 5 days (BOD5) and total suspended solids (TSS) as a function of transmembrane pressure (TMP), circulation velocity (CV) and volume concentration factor (VCF). In addition, the study investigated membrane fouling based on the variation in permeate flux under different operational conditions. Among the tested membranes, UF1 demonstrated superior retention efficiency compared to UF2 and UF3. Using granular activated carbon (GAC) and powdered activated carbon (PAC) with UF1 significantly improved water quality. Moreover, the combination of UF1 separately with GAC and PAC reduced amoxicillin residues by 60 % and 69 %, respectively. Furthermore, the UF1 membrane alone showed significant removal of bacterial loads, exceeding 90 % removal of total coliforms, fecal coliforms and Escherichia coli, as well as complete (100 %) elimination of helminth eggs. The treatment process ended with disinfection by sodium hypochlorite (NaOCl), providing total (100 %) elimination of all remaining bacteria in the water.

Applicability of a Spinning Disk Apparatus for the Investigation of Particulate Fouling

AbstractThe applicability of a fluidically heated spinning disk apparatus (SDA) was tested for investigating the influence of the tangential velocity on the deposition of particulate material systems, in particular on latex particles. First, the SDA was characterized for particle fouling investigations with micro glass beads as a model system, then, a first series of tests was carried out with a real material system, a vinyl acetate/Versa 10 copolymer. Experiments were performed for a duration of 1 h and a tangential velocity up to 0.3 m s−1. The fouling process was characterized by the local fouling layer thickness and the calculated local mass‐based fouling resistance. A decrease in fouling resistance along the radius of the rotating disk as a function of the tangential velocity was observed.