Infinite Flow Research Articles

Vortex-Induced Vibration Characteristics of a PTC Cylinder with a Free Surface Effect

The experimental study of vortex induced vibration needs to be carried out in water tunnel, but in previous associated simulation work, the water tunnel was treated as an infinite flow field in the depth direction with the effect of the free surface neglected. In the paper, the dynamic characteristics and physical mechanisms of a passive turbulence control (PTC) cylinder in a flow field with a free surface is studied, and the combined technique of a volume of fluid (VOF) method and vortex-induced vibration (VIV) was realized. In the range of Reynolds number studied in this paper (3.5 × 104 ≤ Re ≤ 7.0 × 104), the dynamic parameters (lift and drag coefficients), vortex structures, VIV response (amplitude and frequency ratios), and energy harvesting characteristics of a PTC cylinder under different flow conditions were obtained. The study found that: (1) the shear layer was made more unstable behind the cylinder by the free surface, which made it quicker to reach periodic stability, and the asymmetry shortened the initial stage of vibration of the oscillator, which made it easier to produce dynamic control of the motion of the oscillator; (2) the presence of the free surface only affected the positive amplitude ratio, but had almost no effect on the negative amplitude ratio; (3) the frequency ratio in the free surface flow was closer to the experimental data; (4) the presence of the free surface did not affect the detached vortex pattern in the flow around the stationary cylinder, but in the VIV, the lower the free surface height Z, the more vortices that were shed from the moving cylinder.

Dual-based methods for solving infinite-horizon nonstationary deterministic dynamic programs

We develop novel dual-ascent and primal-dual methods to solve infinite-horizon nonstationary deterministic dynamic programs. These methods are finitely implementable and converge in value to optimality. Moreover, the dual-ascent method produces a sequence of improving dual solutions that pointwise converge to an optimal dual solution, while the primal-dual algorithm provides a sequence of primal basic feasible solutions with value error bounds from optimality that converge to zero. Our dual-based methods work on a more general class of infinite network flow problems that include the shortest-path formulation of dynamic programs as a special case. To our knowledge, these are the first dual-based methods proposed in the literature to solve infinite-horizon nonstationary deterministic dynamic programs.

Three-dimensional simulation of a new cooling strategy for proton exchange membrane fuel cell stack using a non-isothermal multiphase model

In this study, a new cooling strategy for a proton exchange membrane (PEM) fuel cell stack is investigated using a three-dimensional (3D) multiphase non-isothermal model. The new cooling strategy follows that of the Honda’s Clarity design and further extends to a cooling unit every five cells in stacks. The stack consists of 5 fuel cells sharing the inlet and outlet manifolds for reactant gas flows. Each cell has 7-path serpentine flow fields with a counter-flow configuration arranged for hydrogen and air streams. The coolant flow fields are set at the two sides of the stack and are simplified as the convective heat transfer thermal boundary conditions. This study also compares two thermal boundary conditions, namely limited and infinite coolant flow rates, and their impacts on the distributions of oxygen, liquid water, current density and membrane hydration. The difference of local temperature between these two cooling conditions is as much as 6.9 K in the 5-cell stack, while it is only 1.7 K in a single cell. In addition, the increased vapor concentration at high temperature (and hence water saturation pressure) dilutes the oxygen content in the air flow, reducing local oxygen concentration. The higher temperature in the stack also causes low membrane hydration, and consequently poor cell performance and non-uniform current density distribution, as disclosed by the simulation. The work indicates the new cooling strategy can be optimized by increasing the heat transfer coefficient between the stack and coolant to mitigate local overheating and cell performance reduction.

On the Stokes Paradox in a Micropolar Liquid

Classical problem of an infinite flow past an infinite porous cylinder perpendicular to its axis is considered for the micropolar liquid. It is demonstrated that for a porous body, classical Stokes paradox exists neither in non-polar nor in polar liquid, i.e. non-trivial solutions was found unlike in the case of impermeable infinite obstacle. The solution is presented in finite analytical form, which is ready for exploitation in experiments and engineering applications. The interrelation of liquid and porous medium characteristics and their influence on the flow velocity is studied.

Инфографика как тип публицистического текста: позиция автора

Purpose. Revealing the basic ways of creation of publicistic image and defining the means of expression of author’s position in this popular type of media text after the analysis of publications on the web-site “TASS. Infographic”. Results. Publicism as the most demanded type of art in native mass media and developing during three centuries faces now the challenges of the 21st century. Abilities of publicistic perception of reality based upon the dialectic interaction of a fact and an image, a standard and expression, an active dialogue between an author and an addressee which leads to co-creativity, preserved and developed traditions in contemporary media. Evolution of digital and multimedia technologies, informational globalization on all the levels of mass communication, content visualization – all those demanded a search for new formats and genres from the authors of journalistic works. The transformation touched both communication channels and text formation principles with the problem of author being especially acute; his “death” was announced by post-modernists and he seems to have no place in the infinite flow of news generated with the help of new technologies. Remaining a high unit of communication, publicistic text changes under the influence of various tendencies: development of news journalism and personification of media text; visualization and digitalization; convergence and diversification. Infographic became the most convincing and effective response to the challenges of the new age. The main research methods are textual, discursive and cognitive analysis as well as case-method. Conclusion. As the result of the analysis the following conclusion has been drawn: infographic as a convenient format of “package” of a large informational volume is developing towards publicism; the author’s role enhanced in this kind of multimedia text is supported by such tendencies as “visual turn” and personification of journalistic text.

Exact solution of non-Newtonian fluid motion between side walls

Abstract In this paper non-Newtonian flow (Brinkman) type fluid over an infinite plate between side walls is being investigated. The flow is generated by oscillating shear stress of the bottom plate and the solutions are obtained by using Fourier integral transformation. The obtained results are presented in steady and transient states for both sine and cosine-shaped shear stresses. The general solutions are reduced to some special cases corresponding, namely to the Brinkman type fluid over an infinite plate and flow of a Newtonian viscous fluid. Graphical illustrations are carried out to have in depth analysis of the involved physical parameters.

Analysis of Runoff Aggregation Structures with Different Flow Direction Methods under the Framework of Power Law Distribution

The main purpose of this study is to evaluate the performances of different flow direction methods (FDM) in affecting the runoff aggregation structures within a watershed under the framework of power law distribution. To this end, SFD (single flow direction method), MFD (multiple flow direction method) and IFD (Infinite flow direction method) were applied for determination of flow direction for water particles in Susu river basin, and consequently assessed with respect to the variation of flow accumulation. The results indicate that different patterns of flow accumulation were observed from each flow direction method. Effect of flow dispersion on DEM is strongest with ascending order of SFD, IFD, MFD. However, contribution of individual pixels into outlet follows descending order of SFD, IFD, MFD. Notably MFD and IFD tend to make additional hydrologic abstraction from rainfall excess due to the flow dispersion within the flow paths generated on DEM. This study also investigated the size distribution of flow accumulation which is equivalent to the drainage area generated from the selected FDM. They were fitted to the power law distribution and flow accumulation was recognized as a scale invariance factor based on the parameter estimation for power law distribution by maximum likelihood. It was also noticed that FDM affects the parameter estimation of power distribution where highest exponent was estimated for MFD following by IFD and SFD.

A Heuristic for extractive agent flow rate in extractive distillation

Distillation is the most widely used separation process for liquids separation in the industry. Even when the volatilities of the mixture are not favorable, then enhanced distillation is used. Extractive distillation is the enhanced distillation most widely used that consists in introducing a large flow rate of a third compound called extractive agent with a high boiling point that it is collected at the column bottoms and recovered in another column and reused again. Some heuristics are available for distillation column design, e.g. the optimum reflux is around 1.2 to 1.35 times the minimum reflux (or 1.1-1.2 times for refrigerated systems). Unfortunately, there is not a similar heuristic to determine the optimum extractive agent flow rate. Based on a literature review of rigorous simulations of extractive distillation processes, a heuristic is proposed that indicates that the optimum extractive distillation flow rate is which provides a Distillation Sequence Efficiency at 78 % of its maximum value. The maximum value is calculated assuming infinite flow rate of extractive agent. The Distillation Sequence Efficiency is a shortcut method available for distillation columns sequencing.

Vortex–wave interaction arrays: a sustaining mechanism for the log layer?

Vortex–wave interaction theory is used to describe new kinds of localised and distributed exact coherent structures. Starting with a localised vortex–wave interaction state driven by a single inviscid wave, regular arrays of interacting vortex–wave states are investigated. In the first instance the arrays described are operational in an infinite uniform shear flow; we refer to them as ‘uniform shear vortex–wave arrays’. The basic form of the interaction remains identical to the canonical one found by Hall & Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666) and subsequently used to describe exact coherent structures by Hall & Sherwin (J. Fluid Mech., vol. 661, 2010, pp. 178–205). Thus in each cell of a vortex–wave array a roll stress jump is induced across the critical layer of an inviscid wave riding on the streak part of the flow. The theory is extended to arbitrary shear flows using a nonlinear Wentzel–Kramers–Brillouin–Jeffreys or ray theory approach with the wave–roll–streak field operating on a shorter length scale than the mean flow. The evolution equation governing the slow dynamics of the interaction turns out to be a modified form of the well-known mean equation for a turbulent flow, and its particular form can be interpreted as a ‘closure’ between the small and large scales of the flow. If the array structure is taken to be universal, in the sense that it applies to arbitrary shear flows, then the array takes on a form which supports a logarithmic mean velocity profile trapped between what can be identified with the ‘wake region’ and a ‘buffer layer’ well known in the context of wall-bounded turbulent flows. The many similarities between the distributed structures described and wall-bounded turbulence suggest that vortex–wave arrays might be involved in the self-sustaining process supporting the log layer. The modification of the mean profile within each cell of the array leads to ‘staircase’-like streamwise velocity profiles similar to those observed experimentally in turbulent flows. The wave field supporting the ‘staircase’ is concentrated in critical layers which can be associated with the shear layer structures that have been attributed by experimentalists to be the mechanism supporting the uniform-momentum zones of the staircase.

Quantitative comparison of 2D and 3D shock control bumps for drag reduction on transonic wings

In this paper, the design spaces of the 2D and 3D shock control bumps on an infinite unswept natural laminar flow wing are investigated by adopting an optimization enhanced parametric study method. The design space spanned by the design variables are explored through a series of design optimization and their landscapes around the optima are revealed. The effects of the bump spacing, bump length, and Mach number are investigated respectively around the optima. The maximum cross-sectional area, bump incident angle, and aspect ratio are found to be important design parameters. The associated flow physics is discussed in relation to these parameters. The comparative performance of the 2D and 3D bumps are explained in the context of the transonic area rule. Two types of flow separation are identified by varying the bump aspect ratio at off-design conditions. It is concluded that the 2D and 3D shock control bumps can have nearly the same performances at optimal designs with similar cross-sectional areas. Some practical design principles and guidelines are suggested.

Analytical solution of two-dimensional advection–dispersion equation with spatio-temporal coefficients for point sources in an infinite medium using Green’s function method

In the present study analytical solutions of a two-dimensional advection–dispersion equation (ADE) with spatially and temporally dependent longitudinal and lateral components of the dispersion coefficient and velocity are obtained using Green’s Function Method (GFM). These solutions describe solute transport in infinite horizontal groundwater flow, assimilating the spatio-temporal dependence of transport properties, dependence of dispersion coefficient on velocity, and the particulate heterogeneity of the aquifer. The solution is obtained in the general form of temporal dependence and the source term, from which solutions for instantaneous and continuous point sources are derived. The spatial dependence of groundwater velocity is considered non-homogeneous linear, whereas the dispersion coefficient is considered proportional to the square of spatial dependence of velocity. An asymptotically increasing temporal function is considered to illustrate the proposed solutions. The solutions are validated with the existing solutions derived from the proposed solutions in three special cases. The effect of spatially/temporally dependent heterogeneity on the solute transport is also demonstrated. To use the GFM, the ADE with spatio-temporally dependent coefficients is reduced to a dispersion equation with constant coefficients in terms of new position variables introduced through properly developed coordinate transformation equations. Also, a new time variable is introduced through a known transformation.

Newtonian, power law, and infinite shear flow characteristics of concentrated slurries using percolation theory concepts

There is a strong interest today in concentrated particulate-filled dispersion and slurries in both polymeric and Newtonian fluids. This paper reviews and extends theoretical approaches using percolation theory concepts to characterize the rheological behavior of fluids filled with particulate solids. First, a previously proposed limiting, zero shear viscosity model based on percolation theory concepts is reviewed. This model has been primarily tested with rigid fillers in a Newtonian carrier and polymeric fluids. Second, all Newtonian fluid-based slurries that have a high concentration of filler become pseudoplastic, shear-thinning slurries at some threshold shear rate. A new theory is reviewed and new data are evaluated that correlate the power law constant, n, to cluster formation of the fillers suspended in the fluids in shear flow. Slurry systems reported here cover a size range from 58 nm to 200 μm. Third, this cluster percolation-based rheological analysis is then extended to a newly proposed model for the calculation of the ratio of infinite shear, η∞, to the zero shear viscosity, η0. Using literature data, it is demonstrated that measurements of the viscosity ratio, η∞/η0, correlate with the power law through the use of an energy dissipation-based model for Bingham rheological fluids.

A Simplex Method for Uncapacitated Pure-supply Infinite Network Flow Problems

We provide a simplex algorithm for a structured class of uncapacitated countably infinite network flow problems. Previous efforts required explicit capacities on arcs with uniformity properties tha...

One-loop perturbative coupling of A and A★ through the chiral overlap operator

Recently, Grabowska and Kaplan constructed a four-dimensional lattice formulation of chiral gauge theories on the basis of the chiral overlap operator. At least in the tree-level approximation, the left-handed fermion is coupled only to the original gauge field A, while the right-handed one is coupled only to the gauge field A*, a deformation of A by the gradient flow with infinite flow time. In this paper, we study the fermion one-loop effective action in their formulation. We show that the continuum limit of this effective action contains local interaction terms between A and A*, even if the anomaly cancellation condition is met. These non-vanishing terms would lead an undesired perturbative spectrum in the formulation.

Experimental and numerical investigation on bubble dynamics near a free surface and a circular opening of plate

Dynamics behavior for a submerged oscillating bubble is closely related to the physical properties of boundaries adjacent to the bubble. For an incomplete boundary, such as a ship structure broken by the shock wave from underwater explosion attack, the bubble load formed after the shock wave may cause secondary damage to it, and the jet characteristics generated during the bubble collapse are worth exploring. Based on the incompressible potential flow method, a boundary integral method with axisymmetric code is employed to investigate the jet features of the bubble under the combined action of a free surface above and a fixed plate with a centric circular opening below. For the numerical divergence caused by the expanding bubble infinitely approaching the rim of the circular opening, the bubble walls above and below the opening are, respectively, fused with the rigid wall, and the initial infinite flow field surrounding the bubble is then divided into two independent basins that are both required to be solved. Several experiments of a spark-generated bubble oscillating near a free surface and a rigid plate with a circular opening are conducted and the numerical results are validated. Following that, two typical cases with a dominant jet, respectively, directing upward and downward are analysed in detail, and some new phenomena are discovered. Additionally, another particular case that the upward and downward jet collides in the vicinity of the opening centroid is also presented. Finally, the initial bubble-free surface distance effects upon the bubble movement and the jet developments are analysed and discussed.

Confirmation of OH as good thermometric species for gas temperature determination in an atmospheric pressure argon plasma jet

We have proved that the temperatures determined from OH rotational spectra accurately describe the actual gas temperatures in an atmospheric pressure argon plasma jet, expanding in a hot ambient atmosphere. For this, we have operated the radiofrequency jet discharge inside a heated oven at various decreasing forwarded powers and increasing gas flow rates. We compared the rotational temperature values with the temperature of the oven. When extrapolated to zero power or infinite gas flow, the data describing the dependence of the rotational temperatures upon power and mass flow rate indicate the correct oven temperature. We demonstrate that the population of the rotational levels of the OH molecule is in equilibrium with the translational motion of the argon atoms in the plasma jet, from room temperature (RT) to 500 °C.

One-loop perturbative coupling of A and A☆ through the chiral overlap operator

We study the one-loop effective action defined by the chiral overlap operator in the four-dimensional lattice formulation of chiral gauge theories by Grabowska and Kaplan. In the tree-level continuum limit, the left-handed component of the fermion is coupled only to the original gauge field~$A$, while the right-handed one is coupled only to~$A_\star$, which is given by the gradient flow of~$A$ with infinite flow time. In this paper, we show that the continuum limit of the one-loop effective action contains local interaction terms between $A$ and~$A_\star$, which do not generally vanish even if the gauge representation of the fermion is anomaly free. We argue that the presence of such interaction terms can be regarded as undesired gauge symmetry-breaking effects in the formulation.

State-space linear stability analysis of platoons of cooperative vehicles

ABSTRACTPlatoons of vehicles relying on inter-vehicle communication and control mechanisms have a great potential, e.g. to reduce fuel consumption and increase capacity. Linear stability analysis can be performed to investigate the propagation of perturbations in such cooperative platoons. Existing work, however, does not consider the stability analysis of the linearised global cooperative platoon system. Our car-following model framework is based on the cooperative relation introduced by Wilson, R. E. [2008. “Mechanisms for Spatio-Temporal Pattern Formation in Highway Traffic Models.” Philosophical Transactions of the Royal Society A (2008) 366, 2017–2032]. We present the state-space representation of the linearised dynamical system. We prove analytically, and illustrate in simulations, that a platoon of vehicles is always linearly-stable provided that the rational relations [Wilson, R. E., and J. A. Ward. 2011. “Car-Following Models: Fifty Years of Linear Stability Analysis: A Mathematical Perspective.” Transportation Planning and Technology 13, 2167–2176] hold and the coefficients of cooperation are non-negative. We present a brief analysis of controllability, considering heterogeneity in the control inputs. Finally, we show that for a closed platoon, the conditions for linear stability are the same as the conditions for stability of a one-dimensional infinite traffic flow.

Orchestrating Bulk Data Transfers across Geo-Distributed Datacenters

As it has become the norm for cloud providers to host multiple datacenters around the globe, significant demands exist for inter-datacenter data transfers in large volumes, e.g., migration of big data. A challenge arises on how to schedule the bulk data transfers at different urgency levels, in order to fully utilize the available inter-datacenter bandwidth. The Software Defined Networking (SDN) paradigm has emerged recently which decouples the control plane from the data paths, enabling potential global optimization of data routing in a network. This paper aims to design a dynamic, highly efficient bulk data transfer service in a geo-distributed datacenter system, and engineer its design and solution algorithms closely within an SDN architecture. We model data transfer demands as delay tolerant migration requests with different finishing deadlines. Thanks to the flexibility provided by SDN, we enable dynamic, optimal routing of distinct chunks within each bulk data transfer (instead of treating each transfer as an infinite flow), which can be temporarily stored at intermediate datacenters to mitigate bandwidth contention with more urgent transfers. An optimal chunk routing optimization model is formulated to solve for the best chunk transfer schedules over time. To derive the optimal schedules in an online fashion, three algorithms are discussed, namely a bandwidth-reserving algorithm, a dynamically-adjusting algorithm, and a future-demand-friendly algorithm, targeting at different levels of optimality and scalability. We build an SDN system based on the Beacon platform and OpenFlow APIs, and carefully engineer our bulk data transfer algorithms in the system. Extensive real-world experiments are carried out to compare the three algorithms as well as those from the existing literature, in terms of routing optimality, computational delay and overhead.

A Nonlocal Zero‐Equation Turbulence Model and a Deficit‐Power Law of the Wall with a Dynamical Critical Phenomenon

AbstractThis article supports a deficit power law for ‘wall’ turbulent shear flows. For infinite Reynolds number flow the model predicts a power, which is a quadratic irrationality in good agreement with experiments (relative error less than one percent). (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)