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Selecting the appropriate model structure for overland flow modelling is an important task in drainage design and floodplain simulation. Comparison of overland flow models based on dimensionality and by applying hydrodynamic principles for same roughness coefficient is a topic to be investigated. The work evaluates the ability of three types of one-dimensional model structures by applying non-linear reservoir routing (MS-I), kinematic wave routing (MS-II and MS-III) and a two-dimensional model structure by applying diffusive wave routing (MS-IV) for 16 events, each on an impervious experimental watershed. These model structures are used for a V catchment, and a comparison study is done using reference hydrographs. The analysis indicated that model structures that conceptualized the flow process as 2D produced better results after time offset bias corrections for hydrographs. If the resultant slope of the overland flow planes largely deviates from the dominant flow direction, then two-dimensional hydrodynamic models (MS-IV) are essential to simulate the overland flow process. Average NSE of 0.99 and 0.96, RSR of 0.11 and 0.15 are obtained for equilibrium and non-equilibrium storm events after bias corrections for MS-IV. However, if the deviation is marginal, then one-dimensional hydrodynamic models (MS-III) are capable of simulating flows with reasonable accuracy.

The investigation of magnetohydrodynamic (MHD) flow has been carried out through a two-dimensional approximation known as the PSM model within the FlowCube platform (Pothérat and Klein, 2014). The platform itself is a cubic vessel featuring alternating positive and negative electrodes that are uniformly located on its bottom. The flow is driven by the Lorentz force, which is induced by injected currents and imposed magnetic fields. The energy spectrum of two-dimensional flow agrees well with our three-dimensional one, confirming the two-dimensionality of MHD turbulence under strong magnetic fields. For quasi-two-dimensional (Q2D) flow in FlowCube, the energy spectrum displays ∼ k −3 and ∼ k 2 slopes, corresponding to direct enstrophy cascade from forcing scale l i to small scale and statistical equilibrium state of large scale (> l i ), where l i is electrodes space in FlowCube. Moreover, a comprehensive study has been conducted on the transition from a laminar state to a turbulent state, revealing various flow states, including periodic, quasi-periodic, and chaotic states. Furthermore, under the same driving force, the periodic network of alternating vortices, which are typical structures in the FlowCube configuration, display different flow states. This observation may correspond to a large-scale intermittency in MHD flows due to the complex interaction between the driving force and dissipation.

Purpose This study aims to investigate the two-dimensional magnetohydrodynamic flow and heat transfer of a fractional Maxwell nanofluid between inclined cylinders with variable thickness. Considering the cylindrical coordinate system, the constitutive relation of the fractional viscoelastic fluid and the fractional dual-phase-lag (DPL) heat conduction model, the boundary layer governing equations are first formulated and derived. Design/methodology/approach The newly developed finite difference scheme combined with the L1 algorithm is used to numerically solve nonlinear fractional differential equations. Furthermore, the effectiveness of the algorithm is verified by a numerical example. Findings Based on numerical analysis, the effects of parameters on velocity and temperature are revealed. Specifically, the velocity decreases with the increase of the fractional derivative parameter α owing to memory characteristics. The temperature increase with the increase of fractional derivative parameter ß due to a decrease in thermal resistance. From a physical perspective, the phase lag of the heat flux vector and temperature gradients τq and τT exhibit opposite trends to the temperature. The ratio τT/τq plays an important role in controlling different heat conduction behaviors. Increasing the inclination angle θ, the types and volume fractions of nanoparticles Φ can increase velocity and temperature, respectively. Originality/value Fractional Maxwell nanofluid flows from a fixed-thickness pipe to an inclined variable-thickness pipe, and the fractional DPL heat conduction model based on materials is considered, which provides a basis for the safe and efficient transportation of high-viscosity and condensable fluids in industrial production.

Significance: Evaluation of vessel patency and blood flow direction is important in various medical situations, including diagnosis and monitoring of ischemic diseases, and image-guided vascular surgeries. While optical coherence tomography angiography (OCTA) is the most widely used functional extension of optical coherence tomography that visualizes three-dimensional vasculature, inability to provide information of blood flow direction is one of its limitations. Aim: We demonstrate two-dimensional (2D) transverse blood flow direction imaging in en face OCTA. Approach: A series of triangular beam scans for the fast axis was implemented in the horizontal direction for the first volume scan and in the vertical direction for the following volume scan, and the inter A-line OCTA was performed for the blood flow direction imaging while the stepwise pattern was used for each slow axis scan. The decorrelation differences between the forward and the backward inter A-line OCTA were calculated for the horizontal and the vertical fast axis scans, and the ratio of the horizontal and the vertical decorrelation differences was utilized to show the 2D transverse flow direction information. Results: OCTA flow direction imaging was verified using flow phantoms with various flow orientations and speeds, and we identified the flow speed range relative to the scan speed for reliable flow direction measurement. We demonstrated the visualization of 2D transverse blood flow orientations in mouse brain vascular networks in vivo. Conclusions: The proposed OCTA imaging technique that provides information of 2D transverse flow direction can be utilized in various clinical applications and preclinical studies.

The enantiomeric ratio of chiral compounds is known as a useful tool to estimate wine quality as well as observe an influence of wine-producing technology. The incorporation of flow-modulated comprehensive two-dimensional gas chromatography in this type of analysis provides a possibility to improve the quality of results due to the enhancement of separation capacity and resolution. In this study, flow-modulated comprehensive two-dimensional gas chromatography was incorporated in enantioselective analysis to determine the influence of winemaking technology on specific features of botrytized wines. The samples included Tokaj essences (high-sugar wines), Tokaj botrytized wines and varietal wines (Furmint, Muscat Lunel, Lipovina) and wines maturated on grape peels. The obtained data was processed with hierarchic cluster analysis to reveal variations in composition and assess classification ability for botrytized wines. A significant difference between the samples was observed for the enantiomeric distribution of ethyl lactate and presence of monoterpene alcohols. The varietal wines were successfully separated from the other types, which showed more similar results and could be divided with additional parameters. We observed a correlation between the botrytized wines and the varietal wines fermented with grape skins. As to the essences produced from juice of botrytized grapes, the results were quite similar to those of the botrytized wines, even though monoterpenes were not detected in the extracts.

Many applications in river research and management rely upon two‐dimensional (2D) numerical models to characterize flow fields, assess habitat conditions, and evaluate channel stability. Predictions from such models are potentially highly uncertain due to the uncertainty associated with the topographic data provided as input. This study used a spatial stochastic simulation strategy to examine the effects of topographic uncertainty on flow modeling. Many, equally likely bed elevation realizations for a simple meander bend were generated and propagated through a typical 2D model to produce distributions of water‐surface elevation, depth, velocity, and boundary shear stress at each node of the model's computational grid. Ensemble summary statistics were used to characterize the uncertainty associated with these predictions and to examine the spatial structure of this uncertainty in relation to channel morphology. Simulations conditioned to different data configurations indicated that model predictions became increasingly uncertain as the spacing between surveyed cross sections increased. Model sensitivity to topographic uncertainty was greater for base flow conditions than for a higher, subbankfull flow (75% of bankfull discharge). The degree of sensitivity also varied spatially throughout the bend, with the greatest uncertainty occurring over the point bar where the flow field was influenced by topographic steering effects. Uncertain topography can therefore introduce significant uncertainty to analyses of habitat suitability and bed mobility based on flow model output. In the presence of such uncertainty, the results of these studies are most appropriately represented in probabilistic terms using distributions of model predictions derived from a series of topographic realizations.

A mathematical model of pressure and velocity fields resulting from the inflow of hydrocarbons to a well of finite radius from partially penetrated reservoir beds has been presented. It is assumed that two-dimensional flow initiated by an assigned depression in an imperfectly penetrated stratum is axisymmetric. A mathematical formulation of the problem in cylindrical geometry on the pressure field in an isolated isotropic homogeneous stratum whose boundaries do not coincide with the boundary points of a perforation interval has been given. A finite-diff erence model has been described on whose basis a program was made up for calculation of pressure and velocity fields in the stratum and computational experiments were consducted which allowed identifying new regularities of flow of practical importance that arise in actual oil and gas reservoirs. Space–time dependences of the pressure field in an oil and gas stratum and of the radial components and modulus of filtration velocity of hydrocarbons have been shown, which illustrate the distinctive features of two-dimensional flow with imperfect penetration of the stratum and basic differences from the well-studied case of plane radial onedimensional flow to the well of finite radius. Based on an analysis of the contour lines, new physical regularities of the flow have been identified that are associated with incomplete perforation of the thickness of the reservoir bed. By the numerical experiments, it has been established that in axisymmetric flow in the stratum, vertical flows inevitably arise which vanish at exit from the stratum into the well. It has been confirmed that in homogeneous incompletely penetrated reservoirs, intralayer crossflows arise in the near wellbore zone, and the radial component of filtration velocity in two-dimensional axisymmetric flow in the imperfectly homogeneous isotropic stratum depends on the vertical coordinate. This means that the inflow to the well is not uniformly distributed over the stratum thickness, and the modulus of the horizontal velocity component in all the curves peaks on the boundaries of the perforation interval. In the case of two-dimensional flow at the center of the perforation interval equally distant from the upper and lower boundaries of the oil and gas stratum, a minimum specific inflow is observed.

Assuming that the streamlines are given by keeping constant one of the two orthogonal curvilinear coordinates in the Euclidean two-dimensional space, while considering a steady, two-dimensional, isentropic flow of an ideal gas through a convergent-divergent nozzle, and thus parallel to the curvilinear upper and lower walls of the nozzle, the theory of differential geometry together with the balance equations of physics was used to study the existence (or non-existence !) of real-valued, differentiable and integrable mass-density solutions to the problem, by means of analytical solutions, and corresponding to an expansion or compression of the gas along the streamlines. Thus, by initially assuming that the partial mass-density derivatives with respect to both curvilinear coordinates satisfy the integrability condition of Schwarz, the resulting system of four scalar partial differential equations led to an analytically derived quadratic equation for the determination of the ideal-gas mass density, based on generalised orthogonal curvilinear coordinates: Finally, the four orthogonal curvilinear coordinate systems, defined by the Killing two-tensors for the Euclidean two-dimensional space, were used, in order to examine whether these coordinate systems could satisfy the already mentioned generalised curvilinear-geometry equation as a quadratic equation, and the related requirements with regard to the partial mass-density derivatives, or not. Only real and nonzero, positive values for the mass density were considered, based on curvilinear streamlines of nonzero curvature.

This work numerically investigates the effects of combined rotational and transverse oscillations of a square cylinder on the flow field and force coefficients. The primary non-dimensional parameters that were varied are frequency ratio fR (0.5, 0.8), Re (50-200), phase difference (ϕ) between the motions and rotational amplitude (θ0) with the influence of the last three parameters being discussed in detail. The amplitude of transverse oscillations is fixed at 0.2D, where D is the cylinder width. The study has been validated using the mean drag coefficient for stationary and transversely oscillating square cylinders from literature. Output data was obtained in the form of force coefficient (Cd), vorticity and pressure contours. The governing equations for the 2dimensional model were solved from an inertial frame of reference (overset meshing) using finite volume method. The interplay between the convective field and prescribed motion has been used to explain many of the results obtained. The relative dominance of cylinder motion over the flow stream was determined using Discrete Fast Fourier Transform. The influence of Re on Cd disappears when the motions are completely out of phase (ϕ = π). In general, the Cd for low Re flows exhibited low sensitivity to change in other parameters. Direct correlation has been observed between frontal area, vortex patterns and drag coefficient

Numerical simulation of fluids plays an essential role in modeling many physical phenomena, such as weather, climate, aerodynamics, and plasma physics. Fluids are well described by the Navier–Stokes equations, but solving these equations at scale remains daunting, limited by the computational cost of resolving the smallest spatiotemporal features. This leads to unfavorable tradeoffs between accuracy and tractability. Here we use end-to-end deep learning to improve approximations inside computational fluid dynamics for modeling two-dimensional turbulent flows. For both direct numerical simulation of turbulence and large-eddy simulation, our results are as accurate as baseline solvers with 8 to 10× finer resolution in each spatial dimension, resulting in 40- to 80-fold computational speedups. Our method remains stable during long simulations and generalizes to forcing functions and Reynolds numbers outside of the flows where it is trained, in contrast to black-box machine-learning approaches. Our approach exemplifies how scientific computing can leverage machine learning and hardware accelerators to improve simulations without sacrificing accuracy or generalization.