Steady Momentum Research Articles

Open channel flow within and above a layered vegetation: Experiments and first-order closure modeling

Flow within vegetation characterized by non-uniform roughness density is drawing significant research attention given its relevance to a plethora of applications in eco-hydraulics including river restoration, and flow in wetland and marshes. The focus here is on flume experiments and modeling of the mean longitudinal velocity profile in a two layered cylindrical vegetation system. Layer 1 represents the region close to the channel bottom where the flow experiences maximum drag due to the densely placed vegetation, while layer 2 represents the flow region above the short vegetation characterized by a smaller vegetation density. Considering the aforementioned arrangements, a new analytical model based on Reynolds-averaged closure principles is proposed to describe the vertical distribution of mean streamwise velocity in an open channel with two different vegetation densities. In the proposed model, the one-dimensional steady and planar-homogeneous momentum equation is used where the turbulent eddy viscosity is assumed to be linearly related to the local mean velocity. The proposed analytical model has been calibrated using experiments reported here in which vegetation is represented by using circular plastic cylinders of two different heights. The proposed model is further tested against published experiments with similar arrangements. In total, 22 different experimental conditions with distinct densities, rigidity, and flow depths have been analyzed. The Root Mean Square Error (RMSE) of the velocity comparisons is found to be less than 0.0342 m/s, which is acceptable.

Recent advances in diagnostic upper endoscopy.

BACKGROUNDEsophageo-gastro-duodenoscopy (EGD) is an important procedure used for detection and diagnosis of esophago-gastric lesions. There exists no consensus on the technique of examination.AIMTo identify recent advances in diagnostic EGDs to improve diagnostic yield.METHODSWe queried the PubMed database for relevant articles published between January 2001 and August 2019 as well as hand searched references from recently published endoscopy guidelines. Keywords used included free text and MeSH terms addressing quality indicators and technological innovations in EGDs. Factors affecting diagnostic yield and EGD quality were identified and divided into the follow segments: Pre endoscopy preparation, sedation, examination schema, examination time, routine biopsy, image enhanced endoscopy and future developments.RESULTSWe identified 120 relevant abstracts of which we utilized 67 of these studies in our review. Adequate pre-endoscopy preparation with simethicone and pronase increases gastric visibility. Proper sedation, especially with propofol, increases patient satisfaction after procedure and may improve detection of superficial gastrointestinal lesions. There is a movement towards mandatory picture documentation during EGD as well as dedicating sufficient time for examination improves diagnostic yield. The use of image enhanced endoscopy and magnifying endoscopy improves detection of squamous cell carcinoma and gastric neoplasm. The magnifying endoscopy simple diagnostic algorithm is useful for diagnosis of early gastric cancer.CONCLUSIONThere is a steady momentum in the past decade towards improving diagnostic yield, quality and reporting in EGDs. Other interesting innovations, such as Raman spectroscopy, endocytoscopy and artificial intelligence may have widespread endoscopic applications in the near future.

The detailed dynamics of the June–August Hadley Cell

AbstractThe seminal theory for the Hadley Cells has demonstrated that their existence is necessary for the reduction of tropical temperature gradients to a value such that the implied zonal winds are realisable. At the heart of the theory is the notion of angular momentum conservation in the upper branch of the Hadley Cells. Eddy mixing associated with extratropical systems is invoked to give continuity at the edge of the Hadley Cell and to reduce the subtropical jet by a factor of three or more to those observed. In this article a detailed view is presented of the dynamics of the June–August Hadley Cell, as given by ERA data for the period 1981–2010, with an emphasis on the dynamics of the upper branch. The steady and transient northward fluxes of angular momentum have a very similar structure, both having a maximum on the Equator and a reversal in sign near 12°S, with the transient flux merging into that associated with eddies on the winter subtropical jet. In the northward absolute vorticity flux, the Coriolis torque is balanced by both the steady and transient fluxes. The overturning circulations that average to give the Hadley Cell are confined to specific longitudinal regions, as are the steady and transient momentum fluxes. In these regions, both intraseasonal and synoptic variations are important. The dominant contributor to the Hadley Cell is from the Indian Ocean and west Pacific regions, and the maxima in OLR variability and meridional wind in these regions have a characteristic structure associated with the Westward‐moving Mixed Rossby–Gravity wave. Much of the upper tropospheric motion into the winter hemisphere occurs in filaments of air from the summer equatorial region. These filaments can reach the winter subtropical jet, leading to the strengthening of it and of the eddies on it, implying strong tropical–extratropical interaction.

Market-Oriented Reforms and China’s Green Economic Development: An Empirical Study Based on Stochastic Frontier Analysis

ABSTRACT The expanding of market-oriented reforms (MORs) over the past 40 years has provided steady momentum for China’s rapid economic growth. Based on the balanced panel data of 28 Chinese provinces from 1985–2015, an empirical analysis using stochastic frontier analysis was conducted to examine the impacts of MORs on the evolution of China’s green economic development. Energy efficiency is used to evaluate the degree of China’s green economic development. Results demonstrated that the average level of provincial energy efficiency was relatively low and the deviation of real energy efficiency from the optimal efficiency frontier was approximately 58%. This indicated China’s energy resources were extensively utilized. Provincial energy efficiency evolved dynamically in line with the degree of marketization. The MORs were the driving force of the improvements in China’s energy efficiency, and provided strong institutional support for China’s future green economy development.

Spatial variability and abundance pattern of Indian squid off Maharashtra coast, India

An analysis was carried out on monthly spatial distribution and unusual congregation of Indian squid (Uroteuthis (Photololigo) duvaucelii) off Maharashtra coast. Decadal, annual and monthly squid landing data were taken from National Marine Living Resources Data Centre (NMLRDC) of ICAR-CMFRI. Onboard fisheries information were collected from multi-day trawlers operating from Mumbai and Ratnagiri. Ocean environment parameters coming from Copernicus Marine Service Information with 1/12 degree horizontal resolution and 50 vertical depth level and OSCAR (Ocean Surface Current Analysis Real-time) near-surface ocean current estimates was derived using quasi-linear and steady flow momentum equations on a 1/3 degree grid with a 5 day resolution. In last decade, contribution of squid to total marine fish landing of Maharashtra rose from 2% to 7.3%. The decadal landing shows two peaks in 2012 and 2017. Indian squid landing in 2017 shows two peak, one during August to October confined to 150 N to 170 N latitude in 15 to 60 m depth off south Maharashtra and second in summer, during March-April months widely scattered in north and south Maharashtra. The unusual abundance of Indian squid during mid-October to mid- November 2017 were attributed to rise in coastal surface and subsurface temperature. Catch per hour of trawl and SST shows strong positive correlation (0.79) during the same period.

Terminal thermocapillary migration of a droplet at small Reynolds numbers and large Marangoni numbers

In this paper, the overall steady-state momentum and energy balances in the thermocapillary migration of a droplet at small Reynolds numbers and large Marangoni numbers are investigated to confirm the quasi-steady state assumption of the system. The droplet is assumed to have a slight axisymmetric deformation from a sphere shape. It is shown that under the quasi-steady state assumption, the total momentum of the thermocapillary droplet migration system at small Reynolds numbers is conservative. The general solution of the steady momentum equations can be determined with its parameters depending on the temperature fields. However, a nonconservative integral thermal flux across the interface for the steady thermocapillary migration of the droplet at small Reynolds numbers and large Marangoni numbers is identified. The nonconservative integral thermal flux indicates that no solutions of the temperature fields exist for the steady energy equations. The terminal thermocapillary migration of the droplet at small Reynolds numbers and large Marangoni numbers cannot reach a steady state and is thus in an unsteady process.

On heat transfer of weakly compressible power-law flows

This paper completes a numerical research on steady momentum and heat transfer in power-law fluids in a channel. Weakly compressible laminar fluids are studied with no slip at the walls and uniform wall temperatures. The full governing equations are solved by continuous finite element method. Three thermal conductivity models are adopted in this paper, that is, constant thermal conductivity model, thermal conductivity varying as a function of temperature gradient, and a modified temperature-gradient-dependent thermal conductivity model. The results are compared with each other and the physical characteristics for values of parameters are also discussed in details. It is shown that the velocity curve from the solution becomes straight at higher power-law index. The effects of Reynolds numbers on the dilatant fluid and the pseudo-plastic look similar to each other and their trends can be easily predicted. Furthermore, for different models, the temperature curves also present pseudo-plastic and dilatant properties.

A sensitivity analysis on thermal and pumping power for the flow of nanofluid inside a wavy channel

In this study, a sensitivity analysis is performed by means of surface methodology in order to manage thermal and pumping power for nanofluid flow inside a wavy channel. The governing equations such as 2D steady continuity, momentum, and energy equations have been solved using a finite volume approach. The computational simulations are performed for different Reynolds number (300≤Re≤600), solid volume fractions of nanoparticles (0.01≤φ≤0.05) and channel aspect ratio. The average Nusselt number and the pressure drop ratio are also calculated by numerical experimentation. It was found that the mixing of fluid in wavy channel improves, consequently, the temperature gradient near the wall increases by increasing the amplitude of the wavy wall. The maximum enhancement in Nusselt number with increase in aspect ratio (λ=0.1→0.3) is in the vicinity of 56% for Re=600 and φ=1%, while it is in the vicinity of 24% due to increase in the solid volume fraction (φ=1%→5%)for Re=600 and λ=0.1. Moreover, the non-dimensional pressure drop is more sensitive to the channel aspect ratio rather than the Reynolds number and solid volume fraction. Besides, the sensitivities of average Nusselt number to the Reynolds number and channel aspect ratio increase with increase in the channel aspect ratio.

Bibliometric Analysis of PPP and PFI Literature: Overview of 25 Years of Research

AbstractAcademics have been devoting a growing attention to different matters involving public-private partnerships (PPPs), and, as the use of PPPs for delivering infrastructure evolves worldwide, so does the number and type of papers addressing this procurement model. The objective of this paper is to undertake a comprehensive literature review of papers relating to PPPs and private finance initiatives (PFIs), using a bibliometric analysis. More than 600 papers published between 1990 and 2014 were examined. None of the previously existing studies analyzed such a large sample of papers. The research found that PPP studies appear to have a steady momentum toward growth. Engineering journals (and engineering as a research area) have been particularly active in this field. Authors based in Europe and Asia had written almost two-thirds of the papers, with transportation and health sectors at the top of sector-based papers. Most of the existing work is focused on aspects of contract design, risk sharing, and a...

27aSC-11 AdS/CFT対応を用いた非平衡定常状態の記述と運動量化学ポテンシャル

27aSC-11 AdS/CFT対応を用いた非平衡定常状態の記述と運動量化学ポテンシャル

Dual solutions of MHD stagnation point flow and heat transfer over a stretching/shrinking sheet with generalized slip condition

An analysis was made to study the steady momentum and heat transfer characteristics of a viscous electrically conducting fluid near a stagnation point due to a stretching/shrinking sheet in the presence of a transverse magnetic field and generalized slip condition. Two flow problems corresponding to the planar and axisymmetric stretching/shrinking sheet were considered. By means of similarity transformations, the obtained resultant nonlinear ordinary differential equations were solved numerically using a shooting method for dual solutions of velocity and temperature profiles. Some important physical features of the flow and heat transfer in terms of the fluid velocity, the temperature distribution, the skin friction coefficient and the local Nusselt number for various values of the controlling governing parameters like velocity slip parameter, critical shear rate, magnetic field, ratio of stretching/shrinking rate to external flow rate and Prandtl number were analyzed and discussed. An increase of the critical shear rate decreases the fluid velocity whereas the local Nusselt number increases. The comparison of the present numerical results with the existing literature in a limiting case is given and found to be in an excellent agreement.

Implementation of a dynamic equation constraint based on the steady state momentum equations within the WRF hybrid ensemble‐3DVar data assimilation system and test with radar T‐TREC wind assimilation for tropical Cyclone Chanthu (2010)

AbstractProper dynamic equation constraints in data assimilation (DA) systems can help improve balance of analyzed atmospheric state. The formulation of ensemble‐variational DA algorithms allows for easy incorporation of such constraints, but their impacts within such DA systems have been little studied. A dynamic constraint based on the steady momentum equations is incorporated into the WRF (Weather Research and Forecasting) hybrid ensemble‐three‐dimensional variational (3DVar) (En3DVar) DA system as a weak constraint. The constraint aims at improving the coupling and balance among wind and thermodynamic state variables, especially when few state variables are directly observed. The scheme is applied to the assimilation of radar T‐TREC (Typhoon‐Tracking Radar Echo by Correlation) winds at a convection‐allowing resolution, for landfalling typhoon, Chanthu (2010), when it was within the range of a coastal radar. Parallel experiments using the 3DVar and En3DVar with and without the dynamic constraint are run to examine the impact of the constraint. The flow‐dependent ensemble covariance used in En3DVar helps to update unobserved pressure and temperature fields in a dynamically more consistent way compared to the static covariance; the added dynamic constraint produces more accurate pressure within the typhoon. The pressure field improved by the dynamic constraint also leads to better temperature and moisture analyses within the variational minimization through flow‐dependent cross covariance. En3DVar analysis with the dynamic constraint produces the best intensity forecast for the typhoon, in terms of the minimum sea level pressure and maximum surface wind speed. Additional sensitivity experiments examine the impact of the weight of the dynamic constraint.

Kinetic theory for a mobile impurity in a degenerate Tonks-Girardeau gas.

A kinetic theory describing the motion of an impurity particle in a degenerate Tonks-Girardeau gas is presented. The theory is based on the one-dimensional Boltzmann equation. An iterative procedure for solving this equation is proposed, leading to the exact solution in a number of special cases and to an approximate solution with the explicitly specified precision in a general case. Previously we reported that the impurity reaches a nonthermal steady state, characterized by an impurity momentum p(∞) depending on its initial momentum p(0) [E. Burovski, V. Cheianov, O. Gamayun, and O. Lychkovskiy, Phys. Rev. A 89, 041601(R) (2014)]. In the present paper the detailed derivation of p(∞)(p(0)) is provided. We also study the motion of an impurity under the action of a constant force F. It is demonstrated that if the impurity is heavier than the host particles, m(i)>m(h), damped oscillations of the impurity momentum develop, while in the opposite case, m(i)<m(h), oscillations are absent. The steady-state momentum as a function of the applied force is determined. In the limit of weak force it is found to be force independent for a light impurity and proportional to √[F] for a heavy impurity.

Computational Analysis of Two Phase Flow Distribution in a Horizonatal Pipe

In this paper, a two phase flow distribution in a horizontal pipe is numerically analyzed by solving one dimensional steady state momentum equation for predicting the pressure drop (∆P), quality of steam at outlet of the pipe (X), void fraction (α). The heat absorbed by the pipe (Q) and the mass flow rate (W) of water are varied over a wide range to investigate the above parameters. The locations of the two phase mixture are discussed. Pressure drop along the pipe is inconsistent for different flow rate so, the stable and unstable steady state solution is also carried out using Linear Stability analysis. The present numerical results are compared with the reported data from the literature and found that they are in good agreement. This study is used to calculate the pressure, temperature, hold up and quality within the horizontal pipe.

Intrinsic variability of the Antarctic Circumpolar Current system: low- and high-frequency fluctuations of the Argentine Basin flow

Abstract. In this paper, the variability of the Antarctic Circumpolar Current system produced by purely intrinsic nonlinear oceanic mechanisms is studied through a sigma-coordinate ocean model, implemented in a large portion of the Southern Ocean at an eddy-permitting resolution under steady surface heat and momentum fluxes. The mean transport through the Drake Passage and the structure of the main Antarctic Circumpolar Current fronts are well reproduced by the model. Intrinsic variability is found to be particularly intense in the Subantarctic Front and in the Argentine Basin, on which further analysis is focused. The low-frequency variability at interannual timescales is related to bimodal behavior of the Zapiola Anticyclone, with transitions between a strong and collapsed anticyclonic circulation in substantial agreement with altimeter observations. Variability on smaller timescales shows clear evidence of topographic Rossby-wave propagation along the eastern and southern flanks of the Zapiola Rise and of mesoscale eddies, also in agreement with altimeter observations. The analysis of the relationship between the low- and high-frequency variability suggests possible mechanisms of mutual interaction.

Bingham plastic fluid flow model in tape casting of ceramics using two doctor blades – analytical approach

One of the most common processes used in manufacturing of multilayer ceramic packages, multilayer capacitors and large scale integration circuits is tape casting. In this process, the wet tape thickness is one of the single most determining parameters affecting the final properties of the product, and it is therefore of great interest to be able to control it. One way to control the tape thickness is to use a two doctor blade configuration in the tape casting machine. In this case, it becomes important to fix the height of the slurry in front of both doctor blades according to the desired tape thickness and casting speed (belt velocity). In the present work, the flow in both doctor blade regions of a slurry is described with a steady state momentum equation in combination with a Bingham plastic constitutive equation, and this is integrated to a closed form analytical solution for both reservoirs based on the desired wet tape thickness and casting speed. The developed model is used to investigate the impact of different material parameters and machine designs on the required slurry height. The solution is compared with experimental findings from the literature, and good agreement is found.

Full-f gyrokinetic simulation over a confinement time

A long time ion temperature gradient driven turbulence simulation over a confinement time is performed using the full-f gyrokinetic Eulerian code GT5D. The convergence of steady temperature and rotation profiles is examined, and it is shown that the profile relaxation can be significantly accelerated when the simulation is initialized with linearly unstable temperature profiles. In the steady state, the temperature profile and the ion heat diffusivity are self-consistently determined by the power balance condition, while the intrinsic rotation profile is sustained by complicated momentum transport processes without momentum input. The steady turbulent momentum transport is characterized by bursty non-diffusive fluxes, and the resulting turbulent residual stress is consistent with the profile shear stress theory [Y. Camenen et al., “Consequences of profile shearing on toroidal momentum transport,” Nucl. Fusion 51, 073039 (2011)] in which the residual stress depends not only on the profile shear and the radial electric field shear but also on the radial electric field itself. Based on the toroidal angular momentum conservation, it is found that in the steady null momentum transport state, the turbulent residual stress is cancelled by the neoclassical counterpart, which is greatly enhanced in the presence of turbulent fluctuations.

A numerical study on convection around a square cylinder using Al2O3-H2O nanofluid

In this paper, a numerical simulation has been performed to study the fluid flow and heat transfer around a square cylinder utilizing Al2O3-H2O nanofluid over low Reynolds numbers. Here, both Reynolds and Peclet numbers are varied within the range of 1 to 40and the volume fraction of nanoparticles (?) is varied within the range of 0&lt;?&lt;0.05. Two-dimensional and steady mass continuity, momentum and energy equations have been discretized using Finite Volume Method (FVM). SIMPLE algorithm has been applied for solving the pressure linked equations. The effect of volume fraction of nanoparticles on fluid flow and heat transfer were investigated numerically. It was found that at a given Reynolds number, the Nusselt number, drag coefficient, recirculation length, and pressure coefficient increases by increasing the volume fraction of nanoparticles.

P1/P0+ elements for incompressible flows with discontinuous material properties

We present a 3-noded triangle and a 4-noded tetrahedra with a continuous linear velocity and a discontinuous linear pressure field formed by the sum of an unknown constant pressure field and a prescribed linear field that satisfies the steady state momentum equations for a constant body force. The elements are termed P1/P0+ as the “effective” pressure field is linear, although the unknown pressure field is piecewise constant within each element. The elements have an excellent behavior for incompressible viscous flow problems with discontinuous material properties formulated in either Eulerian or Lagrangian descriptions. The necessary numerical stabilization for dealing with the inf–sup condition imposed by the incompressibility constraint and high convective effects (in Eulerian flows) is introduced via the Finite Calculus (FIC) approach. For the sake of clarity, the element derivation is presented first for the simpler Stokes equations written in the standard Eulerian frame. The extension of the formulation to the Navier–Stokes equations written in the Eulerian and Lagrangian frameworks is straightforward and is presented in the second part of the paper.The efficiency and accuracy of the new P1/P0+ triangle is verified by solving a set of incompressible multifluid flow problems using a Lagrangian approach and a classical Eulerian description. The excellent performance of the new triangular element in terms of mass conservation and general accuracy for analysis of fluids with discontinuous material properties is highlighted.

Numerical modeling for stratified gas–liquid flow and heat transfer in pipeline

A numerical three-dimensional non-isothermal hydrodynamic and thermal modeling based on the unidirectional flow analysis of stratified flow in the circular cross section pipe is developed and tested by experimental data. The model could solve the steady axial momentum equation and heat transfer equation with a low Reynolds number k∼ε model of turbulence for the eddy viscosity. Due to irregular geometry of stratified pipe flow, the equations of the problem are based on a bipolar coordinate system. Grid refinement near the interface and pipe wall is respectively used for an accurate solution near the boundaries. The model is capable of determining pressure drop and liquid height. In addition, wall and interface shear stress, flow field and temperature field for both phases could be predicted successfully. The predicted data of pressure drop, liquid holdup and velocity profile by the model fit well with some available experiment data and one-dimensional model. And the energy equation is solved, and temperature distribution is gained over the flow and compared well with experimental results. In conclusion, the model could have a practical application for estimation of hydrodynamics and thermodynamics in a pipeline.