Increase In Velocity Ratio Research Articles

An efficient pseudoelastic pure P‐mode wave equation and the implementation of the free surface boundary condition

AbstractBased on the elastic wave equation, a pseudoelastic pure P‐mode wave equation has been recently derived by projecting the wavefield along the wavefront normal direction. This pseudoelastic pure P‐mode wave equation offers an accurate simulation of P‐wave fields with accurate elastic phase and amplitude characteristics. Moreover, considering no S‐waves are involved, it is computationally more efficient than the elastic wave equation, making it an excellent choice as a forward simulation engine for P‐wave exploration. Here, we propose a new pseudoelastic pure P‐mode wave equation and apply the stress image method to it to implement the free surface boundary condition. The new pseudoelastic wave equation offers significantly improved computational efficiency compared to the previous pseudoelastic wave equation. Additionally, the wavefields simulated by this new pseudoelastic wave equation exhibit clear physical interpretations. We evaluate the accuracy of the new wave equation in simulating elastic P‐waves by employing a model with high‐velocity contrasts. We find that this new equation, which purely admits P‐waves, though having exact amplitude and phase behaviour as the elastic waves for transmission components, the amplitudes slightly suffer in the scattering scenario. The difference in amplitude between the elastic and our pseudoelastic increases as the contrast in velocity at the interface (interlayer velocity ratio) increases, especially the S‐wave velocities. This has negative implications on scattering from the free surface boundary condition or the sea bottom interface, especially if the shear wave velocity below the surface or the sea bottom is high. However, in cases where, like for land data in the Middle East, the transition to a free surface is smoother, the accuracy of the pseudoelastic equation is high. In all cases, regardless of the interlayer velocity ratio, the accuracy of the pseudoelastic wave equation in simulating the elastic case, for scattered waves, exceeds that of the acoustic wave equation in phase and amplitude.

Investigation on effects of water-shale interaction on acoustic characteristics of organic-rich shale in Ordos Basin, China

The water-shale interaction affect the shale structure, leading to wellbore instability and increasing drilling costs. The extent of structural changes within the shale can be determined non-destructively by analyzing its acoustic characteristics. Experiments were conducted to investigate the acoustic properties of shale from the Yanchang Formation in the Ordos Basin before and after exposure to brines of varying types, soaking times, and salinities. The study investigated the effects of brine type, soaking time, and salinity on shale’s acoustic properties, including changes in acoustic wave propagation speed, P/S wave velocity ratio, and both time-domain and frequency-domain amplitudes. The results indicate that although the type of brine has a limited impact on the water-shale interaction, KCl exhibits a significant inhibitory effect. However, the soaking time and the brine salinity have a significant impact on the acoustic properties of shale. As the soaking time increases, the decrease in wave velocity increases, the P/S wave velocity ratio increases, and the decrease in time-domain amplitude increases. The amplitude of the main frequency in the frequency domain signal also decreases with the increase of reaction time, which is consistent with the analysis results of the time domain signal. As the salinity of brine increases, the decrease in wave velocity decreases, the P/S wave velocity ratio decreases, and the decrease in time-domain amplitude decreases. The amplitude of the main frequency in the frequency domain signal also decreases with the increase of brine salinity, which is consistent with the analysis results of the time domain signal. This work establishes the relationship between water-shale interaction and acoustic characteristics, which can quantitatively evaluate the degree of interaction between water and shale without damaging shale. Furthermore, this research provides new insights and guidance for predicting drilling collapse cycles and optimizing drilling fluid compositions.

Engineering applications development through OHAM in heat and mass transfer during stagnant flow of second-grade nanomaterial

This paper investigates the stagnation point flow of a second-grade nanomaterial, considering nanofluid effects via thermophoresis and Brownian motion. The study addresses convective heat and mass transfer conditions within the flow induced by a stretching cylinder. The transformed systems are solved using the optimal homotopy solutions (OHAM) method, revealing the impact of various parameters on the quantities of interest. The results indicate that an increase in curvature, viscoelasticity, velocity ratio and injection parameters leads to an enhancement in velocity, while the opposite trend is observed due to suction. The viscoelasticity and curvature parameters also increase skin friction. Additionally, thermophoresis enhances the temperature and concentration fields, while Brownian motion reduces mass diffusion.

Numerical Simulation of Pollutant Channeling between Adjacent Road Tunnels

With the development of highway tunnels, the increasing number of continuous tunnels has brought forth a growing concern regarding the dispersion of pollutants between tunnel entrances. This study employs numerical simulations with Star CCM+ to analyze factors influencing pollutant dispersion between continuous tunnel entrances, such as inlet and outlet velocities, longitudinal spacing, and lateral wind. Results indicate that maintaining a constant longitudinal size ratio while increasing velocity ratio augments intrusion ratio. Altering longitudinal spacing and equivalent diameter does not affect dispersion with constant velocity and size ratios. The intrusion ratio decreases with increasing longitudinal size ratio at a constant velocity ratio. Increased lateral wind weakens intrusion with constant velocities and longitudinal size ratio. This investigation aims to identify ventilation measures for mitigating pollutant dispersion impact in continuous tunnels.

Theoretical exploration of heat transport in a stagnant power-law fluid flow over a stretching spinning porous disk filled with homogeneous-heterogeneous chemical reactions

The distinction between homogeneous and heterogeneous chemical reactions is crucial because many chemically reactive systems, such as hydrometallurgical processes, cooling towers, biological systems, fog dispersion, catalysis, etc., involve both types of reactions. Thus, this study analyzes the heat transmission (HT) characteristics in an MHD stagnant flow of power-law fluid caused by a spinning disk that is stretched and saturated in a porous medium. The study considers homogeneous-heterogeneous (HH) reactions and nonlinear thermal radiation subject to no-slip and convection boundary conditions. The leading equations are switched into ordinary differential equations (ODEs) employing similarity variables. The study focuses on the dimensionless concentration, velocity, temperature, Nusselt number, and skin friction coefficient, which are discussed in detail in the results and discussion section. The study observes that for power-law fluids with an index value less than 1, the skin friction coefficient decays as the power-law index grows. It also notes that the dimensionless skin friction of power-law fluids decreases as the velocity ratio increases. The dimensionless concentration increases with Schmidt and modified Prandtl numbers for both power-law fluids over a stretching spinning porous disk. The HH reaction parameters decline the concentration of power-law fluids.

Numerical Study of Multiple Momentum Jets in a Vegetated Crossflow

Vertically discharged multiple jets in crossflow is a common form of wastewater discharge. The presence of vegetation in the flow channel complicates the hydraulic characteristics of jets. The realizable k-ε turbulent model is used to simulate the flow, turbulence, and vortex characteristics of multiple jets with different spacing and jet-to-crossflow velocity ratios, to study the flow characteristics and vortex structure of multiple jets in a vegetated channel. The results reveal that vegetation inhibits the development of a counterrotating vortex pair. The jets with a low jet-to-crossflow velocity ratio are concentrated near the flow symmetry profile by the dual constraints of ambient flow and vegetation. The jets gradually spread outward and the counterrotating vortex pair become more obvious when the jet-to-crossflow velocity ratio increases. Vegetation reduces the shading effect of the front jet on the rear jet by accelerating the dissipation of shear layer vortices. The influence of the front jet on the rear jet decreases as the spacing increases.

Self-excited oscillations in variable density counter-current round jets

The paper investigates the global instability phenomenon in variable-density counter-current round jets. The analysis is performed using a large eddy simulation and the computations are carried out employing a high-order numerical code. The configuration of two co-axial nozzles, where suction applied in an annular nozzle is a driving force for the counterflow, is investigated. In order to simulate conditions conducive to the emergence of global instability a wide range of velocity and density ratios is considered. Depending on these parameters two different types of modes are observed, i.e., Mode I — shear layer mode, and Mode II — jet column mode. The former is recognized by a high level of perturbations in the shear layer which vanish away from the shear layer reaching a low level at the jet centerline. The latter is characterized by strong disturbances throughout the entire jet region. The results obtained are in remarkable agreement with the theoretical basis reported in the literature. They reveal that the critical velocity ratio for which global instability emerges decreases along with the density ratio. Additionally, the transition from Mode II to Mode I is found for sufficiently strong suction. In general, the lower the density ratio, the weaker suction is required to induce Mode I. Consistently to the literature, Mode II is characterized by a lower frequency of oscillations compared to Mode I for which an increase in density ratio and/or velocity ratio shifts the peaks of the velocity spectra toward higher frequencies.

PULSE WAVE VELOCITY AND BLOOD PRESSURE VARIABILITY AS PROGNOSTIC INDICATORS IN VERY ELDERLY PATIENTS WITH DECOMPENSATED CHRONIC CONDITIONS

Objective: There is scarce evidence of the prognostic importance of hemodynamic measures, such as blood pressure (BP), BP variability and arterial stiffness in the very elderly population with advanced chronic conditions. We aimed to evaluate the prognostic importance of 24-hour BP, BP variability and arterial stiffness in a cohort of very elderly patients admitted to the hospital due to a decompensated chronic disease. Design and method: We studied 249 patients older than 80 (66% women), admitted due to a chronic disease decompensation (60% congestive heart failure). During admission, 24-hour brachial and central BP, BP and heart rate variabilities, aortic pulse wave velocity and BP variability ratio were determined through non-invasive 24-hour monitoring. The primary outcome was 1-year mortality. Secondary outcome was the composite of 1-year mortality or readmission. Results: Increased arterial stiffness (aortic pulse wave velocity and BP variability ratio) was associated with 1-year mortality. For each standard deviation (SD) increase in aortic pulse wave velocity and BP variability ratio, mortality increased 3.3 times and 31%, respectively, after adjustments for clinical confounders and BP. Increased BP variability (38% increase for each SD change) and reduced heart rate variability (32% increase for each SD change) also predicted 1-year mortality in fully adjusted models. No association was found between 24-hour BP (either brachial or aortic) and 1-year mortality. Conclusions: Increased aortic stiffness and BP and heart rate variabilities predict 1-year mortality in very elderly patients with decompensated chronic conditions. Measurements of such estimates could be useful in the prognostic evaluation of this specific population.

Investigation of Inlet Conditions in The Mixing Process of Nanoparticles and Blood in a T-Shaped Microfluidic Reactor with Small Rectangular Cavities.

During the metastasis of cancer cells, circulating tumor cells (CTCs) are released from the primary tumor, reach the bloodstream, and colonize new organs. A potential reduction of metastasis may be accomplished through the use of nanoparticles in micromixers in order to capture the CTCs that circulates in blood. In the present study, the effective mixing of nanoparticles and the blood that carries the CTCs are investigated. The mixing procedure was studied under various inlet velocity ratios and several T-shaped micromixer geometries with rectangular cavities by using computational fluid dynamics techniques. The Navier-Stokes equations were solved for the blood flow; the discrete motion of particles is evaluated by a Lagrangian method while the diffusion of blood substances is studied by using a scalar transport equation. Results showed that as the velocity ratio between the inlet streams increases, the mixing rate of nanoparticles with the blood flow is increased. Moreover, nanoparticles are uniformly distributed across the mixing channel while their concentration is decreased along the channel. Furthermore, the evolution in time of the blood substances in the mixing channel increases with the increase of the velocity ratio between the two streams. On the other hand, the concentration of both the blood substances and the nanoparticles is decreased in the mixing channel as the velocity ratio increases. Finally, the differences in the dimensions of the rectangular cavities seems to have an insignificant effect both in the evolution in time of the blood substances and the concentration of nanoparticles in the mixing channel.

Large-eddy simulation of a planar offset-jet with heat transfer: The effects of ventilation

Several industrial and engineering applications employ ventilated offset-jets such as flow separation control devices, upper surface blowing used in short take-off and landing aircraft, drying processes, and fuel injection systems. The design and efficient operation of these devices relies on controlling the turbulence levels, heat transfer rates, and the locations of flow reattachment points. Therefore, an understanding of the flow and thermal characteristics of ventilated offset-jets helps in the design and operation of these devices. The present study aims to address this by performing large-eddy simulations (LES) of a planar turbulent offset-jet for different velocities of the ventilated-jet. To understand and quantify the effects of ventilation on the offset-jet, a range of velocity-ratios of 0, 0.1, 0.14, and 0.18 are considered for a primary offset-jet Reynolds number of 14,000. First, a grid-sensitivity study is performed to establish the convergence of the solver and the LES index of quality of resolution is obtained to ascertain the quality of the mesh. Thereafter, the mean and second-order statistics of the streamwise component of velocity are compared with reference data from the literature to validate the numerical solver. The effects of ventilation on the offset-jet are studied using the decay of streamwise velocity, jet-spread, the evolution of pressure coefficient, friction coefficient, the mean Nusselt number, and the unsteady characteristics. As the velocity-ratio increases, the suction pressure in the initial region of the domain decreases, which causes the jet to spread away from the bottom wall. Further the peak magnitudes of the mean Nusselt number and coefficient of pressure decrease exponentially with an increase in the velocity-ratio. The peak magnitude of the mean Nusselt number for the unventilated-jet case – the offset-jet without the ventilated-jet – is the largest and its value for the ventilated-jet cases decreases as the velocity-ratio is increased. It is concluded that in the initial region, the ventilated-jet has a profound effect on the offset-jet flow and as the flow develops into a wall-jet the effects of ventilation vanish.

Effect of varying velocity ratio and separation distance on thin lip coaxial jet

Purpose In comparison to a nozzle with a larger/finite separation distance (Thanigaiarasu et al., 2019), a thin-lip nozzle (Srinivasarao et al., 2017) minimizes drag. Coaxial nozzles with thin lips are an appropriate tool for studying high subsonic jets because it does not create a dominant re-circulation zone. This study aims to analyze the characteristic of separation distances, between primary and secondary nozzles, within the range of 0.7–3.2 mm which can be considered a thin lip. Design/methodology/approach A separation distance of 0.7 (Papamoschou, 2004), 1.7 and 2.65 mm (Lovaraju and Rathakrishnan, 2011) is considered for the present study. The main nozzle exit Mach number is maintained at a subsonic condition of Mach 0.6, and the co-flowing nozzle exit Mach number is varied from 0% (secondary jet stopped/single jet) to 100% (Mach 0.6) in steps of 20% with respect to the main nozzle exit Mach number. A comparison was made between these velocity ratios for all three lip thicknesses in the present study. Design mesh and analysis were done by using Gambit 2.6.4 and Fluent 6.12. Velocity contours and turbulence contours were studied for qualitative analysis. Findings When lip thickness increases from 0.7 to 2.65 mm, the potential core length (PCL) of the primary jet decreases marginally. Additionally, the PCL of the primary jet elongates significantly as the velocity ratio increases. The primary shear layer is dominant at 20% co-flow (20 PCF), less dominant at 60% co-flow (60 PCF) and almost disappeared at 100% co-flow (100 PCF). Concurrently, the secondary shear layer almost disappeared in 20 PCF, dominant in 60 PCF and more dominant in 100 PCF. Different zones such as initial merging, intermediate and fully merged zones are quantitatively and qualitatively analyzed. Practical implications Co-flow nozzle is used in turbofan engine exhaust. The scaled-down model of a turbofan engine has been analyzed. Core length is directly proportional to the jet noise. The PCL signifies the jet noise reduction in a high-speed jet. For a low-velocity ratio, the potential core is reduced and hence can reduce the jet noise. At the same time, as the velocity ratio increases, the mass flow rate of the coaxial increases. The increase in the mass flow increases the thrust of the engine. The aircraft engine designer should analyze the requirement of the aircraft and choose the optimal velocity ratio coaxial nozzle for the engine exhaust (Papamoschou, 2004). Originality/value There have been many research studies carried out previously at various lip thickness such as 0.4 (Georgiadis, 2003), 0.7 (Papamoschou, 2004), 1.5 (Srinivasarao et al., 2014a), 1.7 (Sharma et al., 2008), 2 (Naren, Thanigaiarasu and Rathakrishnan, 2016), 2.65 (Lovaraju and Rathakrishnan, 2011), 3 (Inturiet al., 2022) and 3.2 mm (Perumal et al., 2020). However, there is no proper study to vary the lip thickness in this range from 0.7 to 3.2 mm to understand the flow behavior of a co-flowing jet.

Investigation of the liquid carryovers in the branching T-junction, based on historical data

High liquid content is obtained in the T-junction side arm, which affects the operational performance of downstream equipment installed in offshore petroleum industries. Diameter ratio, velocity ratio, and side arm angle of T-junction play dynamic role to control phase redistribution. The effect of these parameters on liquid take-offs is unclear from literature, without any agreement among researchers. Literature only provides empirical correlations valid for one specific application for which the correlations were developed. There is a dire need of correlations with high accuracies to conclude the effect of a certain variable on liquid carryovers based on available data. Objectives of this study are to collect data from multiple research publications, develop easy to use correlations, and to study parameters response surfaces. Plot digitization and Design Expert software are utilized for data collection and statistical analysis, respectively. Results depicted that phase separation improves by reducing diameter ratio to 0.33 and upward inclined side arm. Furthermore, liquid carryovers escalate by increasing velocity ratio and decrease at higher velocity ratios. This research study is first attempt in last few decades which is based on collection of data from different experimentation facilities and eliminating confusions among researchers about effect of parameters on phase separation.

Particle dispersion in turbulent mixing layer at supercritical pressure

The heterogeneous structures of particles are generated due to the significant temperature changes when cold particles-dilute jet injects into a supercritical water fluidized bed, which is unfavorable for the reaction of coal particles. We expect to promote the particle dispersion by entrainment mechanism of large-scale vortical structures. The Eulerian-Lagrangian point-source method is used to numerically investigate the dynamics of dilute particles in mixing layer sustained by supercritical water with different temperatures. The effects of density ratio and velocity ratio between two streams are analyzed. In addition to the smaller particle numbers at high-density side, the particle clustering in the vortex core regions is found due to the inhibition of vortical structures by increasing density ratio. With increasing velocity ratio, however, the enhanced vortex stretching promotes the entrainment of particles. As a result, the increase in particle number density at high-density side is up to 26% compared with the constant-property flow. • Study on variable-density effect on dynamics of particle-laden mixing layer. • Enhancement of vortical structure by increasing velocity ratio between two streams. • Particle acceleration decrease with increasing density ratio between two streams. • Improvement of particle dispersion due to the entrainment of vortical structures.

Ignition studies of hydrogen-air mixtures over hot wire

Hot surface ignition of combustible gas mixtures poses a safety threat in many engineering applications. Gaseous mixtures ignite when hot surface temperature reaches the ignition threshold. In the present work, two-dimensional numerical simulations with detailed reaction mechanism are performed to simulate the flow of stoichiometric hydrogen-air mixture over a stationary hot wire. The effect of heating rates, wire diameters, mixture inlet velocities, and mixture equivalence ratios on the ignition threshold is investigated. In all the cases investigated, ignition is found to occur at the rear stagnation point, and wire heating rate did not influence the ignition phenomenon significantly. With an increase in mixture inlet velocity and mixture equivalence ratio, the ignition threshold increases, whereas the threshold has been found to decrease with increasing wire diameters. The role of the local equivalence ratios at the ignition point and reaction rates prior to the ignition process has been studied to help better understand the ignition phenomenon under different conditions.

A novel pre-dilution, swirling jet diffuser to enhance effluent mixing: Hydrodynamics and dilution performance

Diffusers are widely-used to quickly dilute effluents in receiving water bodies. This study proposed a novel diffuser that pre-mixes effluent with ambient water before discharging and that uses the swirling jet to further enhance near-field dilution. The nozzle of the diffuser was examined in two ambient flow conditions: co-flow and counter-flow that are commonly-met in the environment such as oceans due to tidal effect. Physical experiments were first conducted in co-flow on its dilution performance and hydrodynamics, using heated water as the effluent. A 3-D CFD model was developed and calibrated the co-flow scenarios, and then used to investigate the diffuser in counter-flow. The results showed that the nozzle can effectively reduce the maximum temperature rise of the effluent by about 50 % before discharging. The swirling jet from the outlet has a larger shear area, half-width and entrainment rate, enabling the effluent to be rapidly diluted to a minimum of around 10 times at x/D = 6 in co-flow, whereas the dilution for conventional nozzles is about 1 because of the potential core. The flow amplification ratio (α) decreases gradually with increasing velocity ratio in co-flow but increases with increasing velocity ratio in counter-flow. The counter-flow reduces the water drawn into the device; however, the pre-dilution effect at the outlet remains stable. The near-field dilution in counter-flow was significantly enhanced than that in co-flow. Environmental regulations at outfalls and mixing zones can be more easily met using this novel diffuser.

Investigation of flow behaviors in a fluidized bed reactor with binary mixture of Geldart-A and B particles

Flow dynamics in bubbling and turbulent fluidized beds containing both Geldart-A and B particles were investigated in this research. The numerical model was validated against experimental data, with a 6.16% average deviation. Results show that binary mixture segregation is enhanced as superficial gas velocity decreases. A larger flotsam packing ratio promotes homogeneous flotsam distribution; Second, bed density decreases with increasing bed height or superficial gas velocity. As the flotsam packing ratio decreases from 81.10 to 10.70%, bed density reaches the maximum at 41.50%, indicating the most severe volume contraction; Third, when the flotsam packing ratio decreases, the local mixing index's variances between upper and lower sections in dense phase first increases, then decreases, with stronger radial fluctuation detected; Fourth, as superficial gas velocity or flotsam packing ratio increases, the full mixing height ratio improves; Finally, multivariate correlations for dense phase bed expansion are established, yielding a 3.94% average error. • A modified EMMS drag model was adopted to examine flow features in a bidisperse fluidized bed. • The quantified impacts of superficial gas velocity and packing state on flow are obtained. • Multivariate correlations for dense phase bed expansion were fitted with high accuracy.

Midgestation cardiovascular phenotype in women who develop gestational diabetes and hypertensive disorders of pregnancy: comparative study.

Women with gestational diabetes mellitus (GDM) and/or hypertensive disorders of pregnancy (HDP) are at increased long-term cardiovascular risk. Mild cardiac functional alterations have been detected in women with GDM or HDP in midgestation, prior to clinical onset of the disease, but these functional alterations have not been found to be useful as screening tools. In contrast, increased impedance to peripheral blood flow, measured by echocardiography or ophthalmic artery Doppler, has been shown to provide incremental value to maternal characteristics for the prediction of pre-eclampsia. However, it is unknown whether similar changes can be detected in women at risk of GDM. In this study, we performed detailed cardiovascular phenotyping in a large, unselected population of women in midgestation to identify similarities and differences in cardiovascular adaptation in women who are at risk of GDM and/or HDP. This was a prospective observational study in women attending for a routine hospital visit at 19 + 1 to 23 + 3 weeks' gestation. This visit included assessment of flow velocity waveforms from the maternal ophthalmic arteries, echocardiography for assessment of maternal cardiovascular function and measurement of uterine artery pulsatility index and serum placental growth factor (PlGF) for assessment of placental perfusion and function. The measured indices were converted to either multiples of the median (MoM) values or deviation from the median (delta) after adjusting for maternal characteristics and elements of medical history. Biomarker delta or MoM values in the GDM and HDP groups were compared with those in the unaffected group using 95% CI and t-tests. The study population of 5214 pregnancies contained 4429 (84.9%) that were unaffected by GDM or HDP, 509 (9.8%) complicated by GDM without HDP, 41 (0.8%) with GDM and HDP, and 235 (4.5%) with HDP without GDM. In HDP cases, with or without GDM, there was evidence of impaired placentation, with a decrease in PlGF, and increased impedance to flow in the peripheral circulation, suggested by an increase in ophthalmic artery peak systolic velocity (PSV) ratio, peripheral vascular resistance assessed on echocardiography and mean arterial pressure. In the GDM group without HDP, there was no evidence of altered placental perfusion or function and ophthalmic artery PSV ratio was not significantly different from that in the unaffected group; peripheral vascular resistance and mean arterial pressure were increased but to a lesser degree than in the HDP group. In the HDP group, there was an increase in global longitudinal systolic strain and slight increase in isovolumic relaxation time, while in the GDM group, there was an increase in mitral valve E/e', myocardial performance index and global longitudinal systolic strain. In midgestation, women who subsequently develop HDP or GDM have a mild subclinical reduction in left ventricular function. In HDP cases, with or without GDM, there is evidence of impaired placentation and all biomarkers of impedance to peripheral blood flow are consistently increased. In contrast, in the GDM group without HDP, biomarkers of placental function are normal and those of impedance to peripheral blood flow are either marginally increased or not significantly different from those in normal pregnancies. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Rotating convective MHD flow over a vertical moving plate in the presence of heat source, radiation, chemical reaction and Hall effects

The steady MHD rotating flow and heat mass transfer over a semi-infinite vertical plate moving with a constant velocity in the presence of a heat source, thermal radiation, first-order chemical reaction and Hall effect are studied. The methodology proposed to predict the velocity, temperature and concentration evolutions is based on similarity transformation and finite difference method. The simulation has been carried out for different pertinent parameters of problem. The main results are that the velocity fields are considerably affected by the velocity ratio and coriolis parameters. Except the axial w-velocity that increases only near the plate with the velocity ratio parameter, all the velocities decrease as the velocity ratio and Coriolis parameters increase, whereas the temperature and the concentration profiles increase. Also, the fluid velocity and temperature increase when the heat source and radiation parameters increase but the concentration decreases.

Influence of asymmetric rolling on the microstructure, texture evolution and mechanical properties of Al–Mg–Si alloy

The influence of asymmetric rolling on the microstructure, texture and mechanical properties of Al–Mg–Si alloy was investigated comprehensively through finite element simulation (FEM), microstructure and texture characterization, and tensile testing. Cold rolling was applied by imposing different velocity ratios (from 1 to 1.75) between the upper and lower rolls. The results show that asymmetric rolling has some effects on the shear strain, microstructure, texture and mechanical properties. The shear strain always exhibits a non-uniform distribution throughout the sheet thickness, and it is closely related to the velocity ratio; improving the velocity ratio could result in a larger shear strain in the surface contacting the roll with a higher velocity. As the velocity ratio increases, the cold rolled alloy sheet contains an increasing number of fine equiaxed grains, and the solution-treated recrystallization grain structure gradually becomes fine. Unlike symmetric rolling, asymmetric rolling can result in the development of TD-rotated β fiber, and the rotation angle is largely dependent on the velocity ratio. Although no ideal shear texture E {111}<110> and F{111}<112> orientations were developed, the shear texture H{001}<110> orientation appears by applying a sufficient velocity ratio. After solution treatment, the velocity ratio has no influence on the texture component, but improving the velocity ratio can reduce the texture volume fraction. Asymmetric rolling plays a positive role in improving mechanical property. As the velocity ratio increases, there are increases in the strength, elongation and plastic strain ratio R, and a decrease in the planar anisotropy ΔR, which is likely attributable to the weak texture.

Pulsatile CFD Numerical Simulation to investigate the effect of various degree and position of stenosis on carotid artery hemodynamics

This study is intended to investigate the effect of various degree and position (pre-bifurcation and post-bifurcation) of stenosis on carotid artery hemodynamics trough realistic CFD numerical simulations with appropriate turbulence model. The blood rheological properties were assumed as incompressible and Newtonian fluid. A 3 dimensional model of a non-stenotic carotid artery model was used this investigation. Several turbulence model were tested. The non-stenotic artery geometry was altered as 30% and 70%pre-bifurcation stenosis model, 30% and 70% post-bifurcation stenosis model. Pulsatile simulations were conducted for the non-stenotic and each stenotic artery models. The SST k-ω with Low-Reynolds number was found to be more appropriate for the simulation. As the degree of pre-bifurcation stenosis increases from 30% to 70%, the ICA maximum velocity increases from 12% to 65%. Also, the ECA maximum velocity increases from 5% to 45%. Besides, the ICA velocity ratio decreases by 22% but the ECA velocity ratioincreases by 101%. As the degree of post-bifurcation stenosis increases, the ICA maximum velocity takes a longer time to decrease after the peak systole velocity and the ECA maximum velocity becomes higher than a non-stenotic artery throughout the cardiac cycle. A mild stenosis at post-bifurcation does not show much effect on the carotid artery hemodynamics. However, even a mild stenosis at pre-bifurcation resulted in fluctuating maximum velocity at both ICA and ECA, especially during the diastole of the cardiac cycle