Effect Of Velocity Gradient Research Articles

Interactive effects of temperature and velocity on the feeding behavior of competing native and invasive stream fishes

The integration of invasive species into native communities may result in the destabilization of food webs through predation of native prey and competition with native predators. These negative effects are likely to be exacerbated by climate change, increasing the frequency of heat waves, droughts, and high-flow events. Invasive Round Goby (Neogobius melanostomus) and native White Sucker (Catostomus commersonii) were collected from the wild and acclimated to a range of temperatures expected to capture increases in temperature under climate change. In the laboratory, we measured the effects of temperature (19, 22, 25, and 28°C) and velocity gradients (0, 0.15, 0.3, 0.6 m/s at 22 and 25°C) on the prey consumption and foraging behavior of each species. We found that the prey consumption and number of attacks (lunges at prey) of both species increased with temperature but were consistently higher in Round Goby. Velocity had an interactive effect with temperature for prey consumption and foraging behavior, where generally, velocity tolerance for both species was higher at 22°C than at 25°C. White Sucker tolerance to velocity was higher than Round Goby, suggesting that systems with higher velocities may provide a competitive advantage in high-flow environments. Our results stress the importance of interactive experiments when examining the impact of invasive species on native competitors under shifting climatic conditions.

Influence of mixing conditions on coagulant recovery efficiency and quality

Abstract In this work, the influence of mixing conditions on aluminium recovery from alum sludge and on the recovered coagulant (RC) quality was investigated using acidic treatment. The response surface methodology with a Face Centred Design was used to evaluate the effects of velocity gradient and mixing time on aluminium recovery efficiency, and on the chemical oxygen demand (COD), total suspended solids (TSS) and total phosphorus contents of the RC. No significant effects of both mixing intensity and mixing time on aluminium recovery efficiency were observed; however, these factors significantly affected the quality of the RC in terms of COD, TSS and total phosphorus. The higher velocity gradient increased COD and TSS and the longer mixing time increased phosphorus and TSS in the RC. Operational conditions velocity gradient = 100 s−1 and mixing time = 5 minutes) for aluminium recovery were suggested on economic basis. At these conditions, the RC presented the lowest values of TSS and total phosphorus (100 mg L−1 and 7.0 mg P L−1, respectively), and the following other characteristics: 1,001 mg Al L−1; 384 mg Fe L−1; 1100 mg COD L−1.

The Effect of Spatial Velocity Gradients on Block-Matching Accuracy for Ultrasound Velocimetry

Block matching serves as the foundation for ultrasound velocimetry techniques such as blood speckle tracking and echo-particle image velocimetry. Any spatial velocity gradients (SVGs) inside a block-matching pair will result in tracking error, due to both the finite block size and the ultrasound point-spread-function. We assess, using an in silico sinusoidal flow phantom, the effect of SVG magnitude and beam-to-flow angle on block-matching bias and precision. Secondarily we assess the effect that SVGs have on velocimetry bias when using angled plane-wave compounding. The magnitude and angle of SVGs were varied by adjusting the wavelength and direction of a sinusoidal flow profile. Scatterers displaced by this flow profile were used for simulating ultrasound radio frequency data at discrete time points. After beamforming, the 2-D flow field was estimated using block matching. Two imaging sequences were tested, a single plane-wave and a three-angled plane-wave. Smaller sinusoidal flow wavelengths resulted in increased bias and reduced precision, revealing an inverse relationship between sinusoidal flow wavelength and tracking error, with median errors ranging from 69%-90% for the smallest flow wavelengths (highest SVGs) down to 3%-5% for the largest (lowest SVGs). The SVG angle was also important, in which lateral SVGs (with axially oriented flows) resulted in significant speckle decorrelation and high tracking errors in regions with high SVGs. Conversely, axial SVGs (laterally oriented flow) experienced higher bias in the peak velocity regions of the flow profile. Coherent compounding resulted in higher velocity errors than using a single transmission for lateral SVGs but not for axial SVGs. The highest SVGs that could be measured with ≤10% error was when the sinusoidal flow wavelength was less than 20 times the ultrasound pulse wavelength. The clinical significance is that the high SVGs present in high kinetic energy flows, such as severe carotid stenosis and aortic regurgitation, will limit the ability to accurately quantify the velocities in these flow structures.

Dynamic response and acoustic characteristics of composite hydrofoil under cavitation-induced vibration

Nonconstant characteristics of cavitating flow can cause adverse effects, including vibration, noise, and cavitation. With the application of composite materials, the vibration and deformation of hydrofoils are becoming increasingly obvious, and the fluid–solid coupling problem is becoming very important. Herein, the cavitating flow field of National Advisory Committee for Aeronautics 0012 hydrofoil composed of bronze alloy and composite material is numerically investigated. The hydro-elastic response of a hydrofoil is obtained via a fluid–structure coupling method under a tight coupling strategy. The Schnerr–Sauer model is used to describe the cavitation process, and the large eddy simulation method is used to solve the turbulence problem. Additionally, the finite element method is used to determine the structural deformation. A comparison of the numerical calculation results of the fluid–solid acoustic coupling under two operating conditions shows that the composite materials can suppress the sheet cavitation attached to the hydrofoil suction surface and the tip leakage vortex (TLV) cavitation and can decrease the flow field pressure pulsation and increase the lift-to-drag ratio of the hydrofoil. Additionally, the composite material significantly improves the wake field turbulence, reducing the turbulence intensity and integration scale, and nearly eliminates the large-scale vortex. Moreover, the composite material changes the vortex structure evolution at the gap flow field, results in smoother TLV development, and enhances the flow field velocity gradient effect. Finally, the monitoring of the flow noise radiation characteristics shows that the composite material effectively reduces the sound pressure level of the self-noise and far-field radiation noise.

The The Effect of Velocity Gradient and Camp Number on Solids Removal using Bio-Coagulant from Corbula faba Hinds Shells

The TSS and TDS values of water are required to meet the standard. Like coagulation, the pretreatment process in water helps reduce solid content in water. The coagulant destabilizes water pollutants and helps flocs formation with the coagulation process. This paper studies the performance of chitosan bio-coagulant produced from Corbula faba Hinds shells. The velocity gradient and the Camp number of solids removal were also evaluated. The velocity and period of rapid mixing varied from 110 to 150 rpm, and the velocity gradient (G) was 181.2 to 288.5 s-1. The mixing period also ranged from 1 to 5 minutes. The highest TSS and TDS removal resulted in 140 rpm or 260.2 s-1 and 4 minutes of mixing. The residual TSS and TDS decreased with the increase of Camp Number until reaching a point and increased again afterward.

Trajectory of a spherical bubble rising in a fully developed laminar flow

The rising trajectory of bubbles subjected to shear-induced lift force in a vertical channel is of great interest for designing and optimising a variety of electrochemical equipment. In this work, the rising trajectory of a spherical microbubble with a diameter of 0.3-1.0mm in a vertical channel with a fully developed laminar flow is investigated experimentally. Subsequently, the lift and drag forces on the bubble are assessed. Due to the limitation of the existing correlations for lift force coefficient, a new correlation is developed, which can be used to estimate the trajectory of a bubble in a vertical channel. The effect of flow velocity gradient and bubble diameter on the bubble motion is discussed to control bubble rising trajectory. It is concluded that the lift coefficient for a spherical microbubble in vertical channels with a fully developed laminar flow is slightly higher than the reported shear lift coefficient for larger bubbles rising in a high viscous liquid.

Phase fluctuation of cross-spectrum by dividing a vertical linear array for shallow water source depth discrimination

This study proposes a depth-dependent characteristic for discriminating source depth by dividing a vertical linear array (VLA) in shallow water with a typical downward-refracting sound-speed profile. Theoretical analysis of the phase fluctuation of cross-spectrum between the wide-band acoustic field recorded by the upper-half VLA and that recorded by the lower-half VLA was conducted. Results showed that the number of zero crossing points of the phase fluctuation of cross-spectrum had significant separability for the surface and submerged sources. The effects of velocity gradient, SNR, thermocline depth fluctuation, and array aperture on depth separability were investigated using simulation analysis, which is important for the application of depth discrimination method in real marine environments. Furthermore, the effect of array tilt on depth separability was illustrated and improved using a modified sound field summation method. On this basis, the VLA acoustic data collected in the South China Sea were processed to verify the detection ability of the current method on submerged sources.

Variational Formulations and Isogeometric Analysis of Timoshenko–Ehrenfest Microbeam Using a Reformulated Strain Gradient Elasticity Theory

This paper presents a novel non-classical Timoshenko–Ehrenfest beam model based on a reformulated strain gradient elasticity theory. The strain gradient effect, couple stress effect, and velocity gradient effect for vibration are included in the new model by only one material length scale parameter for each. The variational formulation and Hamilton’s principle are applied to derive the governing equations and boundary conditions. Both an analytical solution and an isogeometric analysis approach are proposed for static bending and free vibration of the microbeam. A non-uniform rational B-splines (NURBS) isogeometric analysis with high-order continuity can effectively fulfill the higher derivatives of the displacement variables in the reformulated gradient beam model. Convergence studies and comparisons to the corresponding analytical solutions verify the model’s performance and accuracy. Finally, different boundary conditions, material length scale parameters, and beam thicknesses are investigated in order to certify the applicability of the proposed approach.

EFFECT OF THE DENSITY AND VELOCITY GRADIENTS ON THE KELVIN-HELMHOLTZ INSTABILITY THROUGH POROUS MEDIUM

The combined effect of density and velocity gradients on the Kelvin-Helmholtz instability through porous medium is investigated. The linear growth rate and frequency are obtained analytically. The behavior of both growth rate and frequency with respect to the variables of the problem are analyzed. The results show that the behavior of frequency is independent on both the viscosity and medium permeability, while the porosity of the medium has a destabilizing influence on frequency. The growth rate reduces in the presence of both viscosity and medium permeability, while it enhances in the presence of porosity of the medium.

Dynamics and 2D temperature distribution of plasma obtained by femtosecond laser-induced breakdown

Recently, plasma produced by focusing femtosecond laser in gases has been introduced as an etching tool in materials processing. Proper control of the plasma in this application necessitates the apt understanding of the different morphological features of the plasma. In this contribution we show that, the plasma produced in air goes through several stages of morphological development–from ellipsoidal to spherical to toroidal plasma, whereas in argon, axial compression of an ellipsoidal plasma is observed. To explain this dissimilarity, we have quantified the temperature by emission spectroscopy (Planck analysis with Wien’s approximation). The evolution of temperature shows a triple exponential dependence in time which can be correlated with different stages of morphological changes of the plasma. Open Source Field Operation and Manipulation simulations using experimentally determined temperature values show that—(i) the reverse pressure gradient propagates radially inwards and compresses the plasma in both air and argon and forms a localized high pressure zone at the center that generates a secondary pressure wave in air, but not in argon, and (ii) the baroclinic torque that is generated because of the Richtmyer–Meshkov instability, dominates the rate of vorticity in air, whereas effects of flow compressibility and velocity gradients dominate the vortices in argon. Knowledge of the initial state and the dynamics of the subsequent stages of the plasma formation can be utilized for control and optimization of laser-induced plasma applications.

Performance of cork-based thermal protection material P50 exposed to air plasma

Cork P50 thermal protection material was characterized under the Earth atmospheric entry conditions in the framework of the in-flight experiment QARMAN. A total of 25 P50 samples were exposed to air plasma ranging the chamber static pressure values of 1500, 4100, 6180, and 20,000 Pa and heat fluxes between 280 and 3250 kW/m^2. The sample radius was also varied between 11 and 25 mm radius to investigate the effects of the stagnation line velocity gradient. The experimental results on heat flux, pressure, surface and in-depth temperatures, surface emissivity, swelling and recession rates, and computed boundary layer profiles as well as the mass blowing rates are presented. A material characterization data suite is also provided including thermogravimetric analysis, specific heat, and thermal conductivity. Overall, a wide range of experimental data of Cork P50 material in Earth atmospheric entry conditions is made available to modelers and engineers for improved material response models and heat shield design consolidation.

Examining the Effects of Fluid Velocity Gradients on 4D Digital Holographic PIV/PTV Measurements

4D digital holographic PIV/PTV (4D-DHPIV/PTV) methods have demonstrated theoretical viability due to their relative ease of setup and high spatial resolution (Soria (2018)). This study investigates how velocity gradients related to different flow regimes and their magnitudes affect 3-component–3-dimensional (3C-3D) digital holographic PIV measurement uncertainty. The error introduced by velocity gradients within the interrogation volume is studied by simulating particles in a velocity field, with a given constant velocity gradient superimposed on a uniform flow from which a time-series of hologram pairs are generated and the 3C-3D velocity fields and their errors are determined using 4D-DHPIV/PTV Sun et al. (2020). Hologram pairs are simulated by modelling the propagation and particlediffraction of coherent laser light using the angular spectrum method (Goodman (1996)). The hologram reconstruction then involves direct reconstruction, followed by deconvolution, a particle position refinement and a hologram subtraction step (Sun et al. (2020)). The particle positions obtained from 4D-DHPIV/PTV are then used to resolve particle displacement measurements using 3D cross-correlation digital analysis with a 3D Gaussian fit to sub-pixel resolution (Soria (2006)). The effects of velocity gradients on the displacement uncertainty and bias error have been investigated by undertaking Monte Carlo simulations under a range of velocity gradient environments. Specifically, 5 common velocity gradients have been studied, which included pure strain, pure vorticity and x, y and z-directional shear. The results indicate that the novel 4D-DHPIV/PTV has poorer accuracy and precision in the z-propagation axis, resulting in larger minimum uncertainties and bias errors. The errors in the z axis are also significantly less affected by velocity gradients in the z direction when compared to the effects of x and y directional velocity gradients on x and y errors respectively. Furthermore, the rate of cross-correlation maximum and SNR decrease are approximately 1.36 times slower due to velocity gradients in the z axis than other axes.

Two-and-three-dimensional analysis of Joule and viscous heating effects on MHD nanofluid forced convection in microchannels

This paper aims to study viscous heating, Joule heating and their simultaneous impacts on Al2O3-water nanofluid laminar flow and thermal characteristics in the presence of a magnetic field inside microchannels. The flow field and heat transfer are modeled two- and three-dimensionally by employing the finite volume method. To investigate the influence of viscosity variation with temperature on viscous heating, a temperature-dependent viscosity correlation specifically presented for Al2O3-water is employed. Predicted results indicate that viscosity changes due to temperature changes are negligible and although viscous heating can be reasonably ignored in the absence of the magnetic field, it must be taken into account when the magnetic field is applied. At the Hartmann number of 20, near microchannel walls, the velocity gradient rises up to 165% where the viscous dissipation significantly increases the temperature. In addition, when the magnetic field is applied, the 2D model underestimates the temperature compared to the 3D model where the effects of maximum velocity and velocity gradient on the energy equation and heat dissipation exist. The temperature profiles demonstrate that at the Hartmann number of 20, the effects of Joule heating or viscous heating increase the maximum dimensionless temperature by a factor of about 2.5 and by the rise of the Hartmann number, the dimensionless temperature increases and the effects of Joule and viscous heating become more significant. All in all, it is concluded that the heat generated by viscous and Joule heating can remarkably decrease the cooling performance of microchannels in the presence of magnetic fields.

A study on heat flux predictions for re-entry flight analysis

The analysis of the risk from re-entry objects has become an important topic. Concerning the uncertainties and different flow regimes, the object-oriented tools have been developed and used for various re-entry mission scenarios because of the simplified computation process and low calculation burden, which allow a probabilistic analysis. In this study, the heat flux correlations that are used in the object-oriented tools are investigated and compared to better understand the heat flux predictions with respect to re-entry survivability. Often these tools calculate the continuum stagnation-point heat flux using the correlation formulae of Lees and Fay–Riddell, which usually assume local thermo-chemical equilibrium with a fully-catalytic wall condition in the shock layer. Based on this observation, heat flux measurements were conducted in a hypersonic wind tunnel, and validated with the theory of Fay–Riddell considering the equivalent velocity gradient. For the comparison, in total, 11 different heat flux correlations were examined. It is shown that, based on the formula of Fay–Riddell, the differences in the final integrated heat flux were less than 16% which led to a large discrepancy in the survivability estimations for the cases of small spheres made of aluminum. This shows the importance of considering the heat flux correlation as well as the velocity gradient effect for such re-entry analysis.

On the effect of biogas bubbles in anaerobic digester mixing

A mixing strategy capable of handling a suitable agitation within digester tanks is a necessity in order to assure continuous contact of substrates and degraders inside bioreactors. As mixing is an energy demanding process, the energy needed for a proper mixing contributes to overall efficiency of digesters. In the current study, the aim is to assess the incorporation of biogas bubble creation into the mixing of anaerobic digesters of wastewater treatment plants (WWTP) tanks with and without an external vertical mixer, in order to analyze the possibility of considering bubble creation as an imperative factor in the mixing scenario. Computational fluid dynamics (CFD) prepares the opportunity to simulate the creation biogas bubbles within a stirred tank of anaerobic digester, in a combination of an Eulerian and Lagrangian platform. The amount of dead volume, average velocity, velocity gradient and bubble particle trajectories are analyzed and discussed.Our key findings are as follows: biogas bubble creation contributes to the reduction of dead volume inside the digester tank, once there is no external rotating mixing, or once the amount of mixer rotation speed is low. However, either in low or in high mixer rotation speed the biogas bubble creation does not have a considerable effect of velocity gradient.

Bending, Buckling and Vibration Analysis of Complete Microstructure-Dependent Functionally Graded Material Microbeams

A new functionally graded non-classical Timoshenko microbeam model is developed by using a variational formulation. The new model incorporates strain gradient, couple stress (rotation gradient) and velocity gradient effects and explains a power-law variation of two-phase materials through the thickness direction. The new model contains three additional material constants to account for the relative three gradient effects. The static bending, buckling and free vibration problems of the newly developed functionally graded material (FGM) beam are then analytically solved. Numerical results show that the differences between the prediction results of the current model and the classic model are significant when FGM beam thickness is very small, but they are diminishing as the thickness increases.

Isogeometric analysis of size-dependent Bernoulli–Euler beam based on a reformulated strain gradient elasticity theory

In this paper, we present an efficient and accurate numerical approach for static bending and free vibration analyses of microstructure-dependent Bernoulli-Euler beams. The current approach includes strain gradient, couple stress (rotation gradient) and velocity gradient effects simultaneously through a reformulated strain gradient elasticity, which applies only one material parameter for each gradient effect. Based on the Hamilton’s principle and an Isogeometric Analysis (IGA) approach, the governing equations are derived and solved, respectively, which effectively fulfills the higher continuity requirements in the present microstructure-dependent Bernoulli-Euler beam formulation. The static bending and free vibration analyses of simply supported microstructure-dependent beams are studied by directly applying the current approach and compared with the corresponding analytical solutions. The physical mesh convergence and numerical results prove the high performance and accuracy of the present numerical approach. In addition, the cantilever and clamped microbeams are also carried out to show the applicability of the present approach.

Microstructure-dependent Band Gaps for Elastic Wave Propagation in a Periodic Microbeam Structure

A new model for producing band gaps for flexural elastic wave propagation in a periodic microbeam structure is developed using an extended transfer matrix method and a non-classical Bernoulli–Euler beam model that incorporates the strain gradient, couple stress and velocity gradient effects. The band gaps predicted by the new model depend on the three microstructure-dependent material parameters of each constituent material, the beam thickness, the unit cell length and the volume fraction. A parametric study is conducted to quantitatively illustrate these factors. The numerical results reveal that the first band gap frequency range increases with the increases of the three microstructure-dependent material parameters, respectively. In addition, the band gap size predicted by the current model is always larger than that predicted by the classical model, and the difference is large for very thin beams. Furthermore, both the unit cell length and volume fraction have significant effects on the band gap.

Физико-математическая модель рабочего процесса вихревой трубы

Based on the physical model of the Ranque effect, proposed earlier, a simplified mathematical model of the working process of a vortex tube is compiled taking into account the exchange of work and heat during the interaction of peripheral and axial gas flows. The effect of viscosity and angular velocity gradient on the transfer of kinetic energy from the axis to the periphery is shown. The difference in thermodynamic temperatures when heat is supplied from the periphery to the axis is taken into account, which leads to a decrease in the cooling efficiency of the axial gas flow. Energy exchange is based on the assumption that the peripheral gas layers are compressed by the axial flow. The axial flow work is determined by the pressure difference between the valve and the outlet of the diaphragm

Synthesis and evaluation of cationic flocculant P(DAC-PAPTAC-AM) for flocculation of coal chemical wastewater

In this study, a high-efficiency cationic flocculant, P(DAC-MAPTAC-AM), was successfully prepared using UV-induced polymerization technology. The monomer Acrylamide (AM): Acryloxyethyl Trimethyl ammonium chloride (DAC): methacrylamido propyl trimethyl ammonium chloride (MAPTAC) ratio, monomer concentration, photoinitiator concentration, urea content, and cationic monomer DAC:MAPTAC ratio, light time, and power of high-pressure mercury lamp were studied. The characteristic groups, characteristic diffraction peaks, and characteristic proton peaks of P(DAC-MAPTAC-AM) were confirmed by fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), 1H nuclear magnetic resonance spectrometer (1H NMR), and scanning electron microscopy (SEM). The effects of dosage, pH value, and velocity gradient (G) value on the removal efficiencies of turbidity, COD, ammonia nitrogen, and total phenol by poly aluminum ferric chloride (PAFC), P(DAC-MAPTAC-AM), and PAFC/P(DAC-MAPTAC-AM) in the flocculation treatment of coal chemical wastewater were investigated. Results showed that the optimal conditions for the flocculation of coal chemical wastewater using P(DAC-MAPTAC-AM) alone are as follows: dosage of 8–12 mg/L, G value of 100–250 s − 1, and pH value of 4–8. The optimal dosage of PAFC is 90–150 mg/L with a pH of 2–12. The optimal dosage for PAFC/P(DAC-MAPTAC-AM) is as follows: PAFC dosage of 90–150 mg/L, P(DAC-MAPTAC-AM) dosage of 8–12 mg/L, and pH range of 2–6. When P(DAC-MAPTAC-AM) was used alone, the optimal removal efficiencies of turbidity, COD, ammonia nitrogen, and total phenol were 81.0%, 35.0%, 75.0%, and 80.3%, respectively. PAFC has good tolerance to wastewater pH and good pH buffering. Thus, the flocculation treatment of coal chemical wastewater using the PAFC/P(DAC-MAPTAC-AM) compound also exhibits excellent resistance and buffering capacity.