Oscillatory flow of a micropolar fluid generated by the rotary oscillations of two concentric spheres

In this paper we examine the flow of an incompressible micropolar fluid between two concentric spheres, generated by their rotary oscillations about a common diameter. The spheres are assumed to be oscillating with the same amplitude but with different angular speeds. The speeds of oscillation are assumed to be small so that the nonlinear terms in the equations of motion can be neglected under the usual Stokesian assumption. The analytical expressions for velocity and microrotation components are determined in terms of modified Bessel functions of first and second kind. The couples experienced by the inner and outer spheres are calculated and are expressed in terms of two real parameters K and K^′ whose variation is studied numerically. The variations of K and K^′ with respect to micropolarity parameter and frequency parameter are displayed graphically.     

Stability of thermocapillary convection and regimes of a fluid flow acted upon by a standing surface wave

It has been established that, in the case where a standing surface wave acts on a thermocapillary-convection flow in a cylindrical volume, there arises an oscillating-convection zone between the laminar and turbulent regimes of flow. It is shown that the boundary between these regimes is determined by the amplitude δ and the number of periods n of the standing wave and is practically independent of the Marangoni number and the oscillation frequency of this wave. At n = 2, in the range 0.004 < δ < 0.006, the parameters of the fluid cease to oscillate. The mechanisms by which the thermocapillary convection in closed volumes loses its stability are discussed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 5, pp. 108–115, September–October, 2007.     

Nonstationary flow field generated by dielectric barrier discharge

The search for new methods of the flow control is of great importance because the capability of traditional control devices is one of the limits of the aircraft efficiency. A promising method of flow control involves application of electrogasdynamic devices based on the direct transformation of the electric energy to the force acting on the flow. An activator employing the principles of dielectric barrier discharge (DBD) was studied. Nonstationary characteristic of the activator have been studied by measuring the electrodynamic parameters of DBD and the induced velocity fields (particle image velocimetry). Instantaneous and integral parameters of the gas acceleration are determined and the activator efficiency is evaluated.     

Separation of latex spheres using dielectrophoresis and fluid flow

The authors present a method for separation of two latex spheres populations using dielectrophoresis (DEP) and the fluid drag force. Microelectrodes of a suitable layout are used to trap one population of spheres, while the other one is dragged away from the electrodes by the generated fluid flow. The finite difference method is implemented in C++ to calculate the potential distribution by solving Laplace's equation. From the potential distribution, the DEP force on particles is calculated. The drag force on particles due to the liquid motion is calculated from the observed fluid velocity. The experimental results are shown to be in good agreement with the numerical solution.     

Optimal control of thermal fluid flow using automatic differentiation

The aim of this study is to present a method for numerical optimal control of thermal fluid flow using automatic differentiation (AD). For the optimal control, governing equations are required. The optimal controls that have been previously presented by the present authors’ research group are based on the Boussinesq equations. However, because the numerical results of these equations are not satisfactory, the compressible Navier–Stokes equations are employed in this study. The objective is to determine whether or not the temperature at the objective points can be kept constant by imposing boundary conditions and by controlling the temperature at the control points. To measure the difference between the computed and target temperatures, the square sum of these values is used. The objective points are located at the center of the computational domain while the control points are at the bottom of the computational domain. The weighted gradient method that employs AD for efficiently calculating the gradient is used for the minimization. By using numerical computations, we show the validity of the present method.     

Turbulent flow generated in an annulus by a rotating screen

Summary The computational method for treating curved channel flow and flow in annuli driven by rotating screens is extended to cover turbulent flow, by making the viscosity a function of the average perimeter friction viscosity and using appropriate boundary conditions near the rigid walls, which are consistent with the logarithmic law. Although the turbulent flow model is very primitive, it serves to illustrate the big influence of the secondary flow on the obtained values of velocity distribution and friction factor.     

热力膨胀阀流动噪声试验研究

为了获得热力膨胀阀的瞬态噪声特性,采用试验方法对不同温包充注、不同阀内结构的膨胀阀的啸叫噪声进行研究。获得了系统开机过程中热力膨胀阀啸叫噪声与温包充注、阀内结构的关系。结果表明:采用交叉充注,低蒸干压力充注,在阀内安装碟形弹簧有利于降低膨胀阀啸叫噪声。     

Real-time assessment of fog-related crashes using airport weather data: A feasibility analysis

The effect of reduction of visibility on crash occurrence has recently been a major concern. Although visibility detection systems can help to mitigate the increased hazard of limited-visibility, such systems are not widely implemented and many locations with no systems are experiencing considerable number of fatal crashes due to reduction in visibility caused by fog and inclement weather. On the other hand, airports’ weather stations continuously monitor all climate parameters in real-time, and the gathered data may be utilized to mitigate the increased risk for the adjacent roadways. This study aims to examine the viability of using airport weather information in real-time road crash risk assessment in locations with recurrent fog problems. Bayesian logistic regression was utilized to link six years (2005–2010) of historical crash data to real-time weather information collected from eight airports in the State of Florida, roadway characteristics and aggregate traffic parameters. The results from this research indicate that real-time weather data collected from adjacent airports are good predictors to assess increased risk on highways.     

Starting flow generated by the impulsive start of a floating wedge

The initial stage of the plane unsteady flow caused by the impulsive vertical motion of a wedge initially floating on an otherwise flat free surface is investigated with the help of a combination of numerical and asymptotic methods. The liquid is assumed ideal and incompressible and its flow potential. Compressible effects give a negligible contribution to the flow close to the entering body at the stage considered in the present paper. The vertical velocity of the body is constant after the impulsive start. The flow domain is divided into an outer region, where the first-order solution is given by the pressure-impulse theory, and inner regions close to the intersection points between the free surface and the moving body. The relative displacement of the body plays the role of a small parameter. The inner solution is matched with the outer one. The outer solution is given in quadratures but the inner solution, which is shown to be nonlinear and self-similar, can be found only numerically. With the aim of deriving the inner solution, the inner region is divided into three parts. In the far-field zone the solution is given in terms of its asymptotic behavior while, in the jet region, attached to the wedge, the flow is described by a second-order shallow-water approximation. In the intermediate region a boundary-element method is used, which is suitably coupled with the solutions in both the jet and the far-field regions through an iterative pseudo-time stepping procedure. The procedure is dependent on the deadrise angle of the wedge. If the angle is equal or smaller than π/4, eigensolutions appear in the far-field asymptotics and their amplitudes are recovered together with the solution. The approach is applied to different values of the wedge deadrise angle. The obtained results can be used to improve the prediction of the hydrodynamic loads acting on floating bodies, the velocity of which changes rapidly.     

Probing fluid flow using the force measurement capability of optical trapping

Interest in microfluidics is rapidly expanding and the use of microchips as miniature chemical reactors is increasingly common. Microfluidic channels are now complex and combine several functions on a single chip. Fluid flow details are important but relatively few experimental methods are available to probe the flow in confined geometry. We use optical trapping of a small dielectric particle to probe the fluid flow. A highly focused laser beam attracts particles suspended in a liquid to its focal point. A particle can be trapped and then repositioned. From the displacement of the trapped particle away from its equilibrium position one estimates the external force acting on the particle. The stiffness (spring constant) of the optical trap is low thus making it a sensitive force measuring device. Rather than using the optical trap to position and release a particle for independent velocimetry measurement, we map the fluid flow by measuring the hydrodynamic force acting on a trapped particle. The flow rate of a dilute aqueous electrolyte flowing through a plastic microchannel (W × H × L = 5 mm × 0.4 mm × 50 mm) was mapped using a small silica particle (1 μm diameter). The fluid velocity profile obtained experimentally is in very good agreement with the theoretical prediction. Our flow mapping approach is time efficient, reliable and can be used in low-opacity suspensions flowing in microchannels of various geometries.     

Characterization of microstructures using contour tree connectivity for fluid flow analysis

Quantifying the connectivity of material microstructures is important for a wide range of applications from filters to biomaterials. Currently, the most used measure of connectivity is the Euler number, which is a topological invariant. Topology alone, however, is not sufficient for most practical purposes. In this study, we use our recently introduced connectivity measure, called the contour tree connectivity (CTC), to study microstructures for flow analysis. CTC is a new structural connectivity measure that is based on contour trees and algebraic graph theory. To test CTC, we generated a dataset composed of 120 samples and six different types of artificial microstructures. We compared CTC against the Euler parameter (EP), the parameter for connected pairs, the nominal opening dimension (d_nom) and the permeabilities estimated using direct pore scale modelling. The results show that d_nom is highly correlated with permeability (R² = 0.91), but cannot separate the structural differences. The groups are best classified with feature combinations that include CTC. CTC provides new information with a different connectivity interpretation that can be used to analyse and design materials with complex microstructures.     

Quantitative analysis of cerebrospinal fluid flow in complex regions by using phase contrast magnetic resonance imaging

To develop a method for segmenting cerebrospinal fluid (CSF) regions with complex, inhomogeneous pulsatile patterns in phase contrast magnetic resonance imaging (PC‐MRI) sequences. Our approach used various temporal features of flow behavior as input attributes in an unsupervised k‐means classification algorithm. CSF flow parameters for the cervical subarachnoid spaces and the pontine cistern were calculated in 26 healthy volunteers. Background and aliasing corrections were applied automatically. The algorithm's reproducibility was determined by calculating two parameters (area and stroke volume) while varying the initially selected seed point. The influence of background correction on these parameters was also assessed. The method was highly reproducible, with coefficients of variation of 3 and 4% for the cervical stroke volume and area, respectively. In an analysis of variance, background correction did not have a statistically significant effect on either the stroke volume (p = 0.32) or the CSF net mean flow (p = 0.69) at the C2C3 level. The method presented here enables rapid, reproducible, quantitative analysis of CSF flow in complex regions such as the C2C3 subarachnoid spaces and the pontine cistern. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 290–297, 2011;     

分层流体中水平运动潜体产生的内波分析

从线性化的Euler方程和连续方程出发，采用线性自由面条件，通过傅里叶变换法研究水平运动点源在分层流体中产生的内波．利用源汇分布法分析运动潜体产生的lee渡，采用稳定相法计算远场速度．计算结果表明，高模态内渡的渡域角小于低模态内波的渡域角，内渡的渡域角小于Kelvin波的渡域角；随航速增大lee波主要表现为散波．     

Real-time adaptive clutter rejection filtering in color flow imaging using power method iterations

We propose a new algorithm for real-time, adaptive-clutter-rejection filtering in ultrasound color flow imaging (CFI) and related techniques. The algorithm is based on regression filtering using eigenvectors of the signal correlation matrix as a basis for representing clutter, a method that previously has been considered too computationally demanding for real-time processing in general CFI applications. The data acquisition and processing scheme introduced allows for a more localized sampling of the clutter statistics and, therefore, an improved clutter attenuation for lower filter orders. By using the iterative power method technique, the dominant eigenvalues and corresponding eigenvectors of the correlation matrix can be estimated efficiently, rendering real-time operation feasible on desktop computers. A new adaptive filter order algorithm is proposed that successfully estimates the proper dimension of the clutter basis, previously one of the major drawbacks of this clutter-rejection technique. The filter algorithm performance and computational demands has been compared to that of conventional clutter filters. Examples have been included which confirms that, by adapting the clutter-rejection filter to estimates of the clutter-signal statistics, improved attenuation of the clutter signal can be achieved in normal as well as more excessive cases of tissue movement and acceleration.     

A numerical model for the jet flow generated by water impact

In this paper a numerical model is developed aimed at describing the jet flow caused by water impact. The study, carried out in the framework of a potential-flow assumption, exploits the shallowness of the jet region to significantly simplify the local representation of the velocity field. This numerical model is incorporated into a fully nonlinear boundary-element solver that describes the flow generated by the water entry of two-dimensional bodies. Attention is focused on the evaluation of the capability of the model to provide accurate free-surface shape and pressure distribution along the wetted part of the body contour, with particular regard to the jet region. After a careful verification, the proposed model is validated through comparisons with the similarity solution of the wedge impact with constant entry velocity. This similarity solution is derived with the help of an iterative procedure which solves the governing boundary-value problem written in self-similar variables.     

Real-time ultrasound process tomography for two-phase flow imaging using a reduced number of transducers

In this paper a novel ultrasound tomography imaging system is presented. It employs a relatively small number of transducers that produce fan-shaped beam profile to effectively insonify the cross-section. The impact on the image quality due to the reduction of the number of transducers is discussed, and different approaches such as multiple receiver data acquisition and nonlinear thresholding are explored. A prototype of a tomographic imaging system with only 36 transducers has been constructed, and processing rates of up to 100 frames per second have been achieved using a parallel processing technique. Good image reconstructions based on simulations and real objects also are provided to confirm the principles of the theoretical analysis.     

Numerical solution of laminar flow generated in an annulus by rotating screens

Summary The governing equation and the appropriate boundary condition describing stationary laminar flow in a curved channel and in an annulus with one (upper) and two (upper and lower) rotating screens, were solved numerically by finite-difference method. In the curved channel multiple solutions were obtained in accordance with the predictions of previous theoretical and experimental investigations. In contrast to that, no multiple solutions were found for the flow in an annulus, neither with two nor with one rotating screen. The numerically computed axial velocity distributions in annulus were compared to the corresponding experimental profiles measured in a turbulent flow of a homogeneous fluid created in annulus by one or two rotating screens. The qualitative agreement between the results was unexpectedly good.     

The flow of a fluid film entrained by a supersonic flow of gas

We have conducted an experimental study into the flow of a high-viscosity fluid directed through an orifice of small diameter onto the surface of a body contained within a supersonic flow of air.Notation M Mach number for the outlet cross section of the nozzle - Re_D Reynolds number calculated from the parameters of the unperturbed flow at the outlet section of the nozzle and from the diameter of model rounding - P₀ total pressure in the pressure chamber of the wind tunnel, Pa - T₀ deceleration temperature - sweepback angle of leading edge of plate (between the normal to the direction of the unperturbed flow and the generatrix of the leading edge), deg - d orifice diameter, mm - angle between direction of unperturbed flow and radius vector of orifice, deg - frictional stress at boundary separating fluid and gas, Pa - Q volumetric fluid flow rate, cm³/sec - kinematic viscosity of fluid, cSt - q /q_g ratio of the velocity head of the fluid at the outlet from the orifice to the local velocity head of the gas - thickness of fluid film, mm - b width of fluid film, mm - angle between tangents to the side boundaries of the fluid film, deg - s coordinate calculated from the center of the orifice along the midline of the film or along the axis of wedge symmetry, mm - z coordinate calculated along the normal to the axis, mm Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 2, pp. 181–186, August, 1990.     

Micropatterned fluid lipid bilayer arrays created using a continuous flow microspotter

We have developed a new method for creating micropatterned lipid bilayer arrays (MLBAs) using a 3D microfluidic system. An array of fluid lipid membranes was patterned onto a glass substrate using a Continuous Flow Microspotter. Fluorescence microscopy experiments were used to verify the formation of a bilayer structure on the glass substrate. Fluorescence recovery after photobleaching experiments demonstrated the bilayers' fluidity was maintained while being individually corralled on the substrate. The reproducibility of bilayer formation within an array was demonstrated by the linear response of membrane fluorescence versus mol % rhodamine functionalized lipids incorporated into the vesicles prior to fusion to the surface. The highly customizable nature of the MLBAs was demonstrated utilizing three different fluorescently labeled lipids to generate a multiple component lipid array. Finally, the cholera toxin B/ganglioside GM 1, antidinitrophenyl (DNP) antibody/DNP, and NeutrAvidin/biotin protein-ligand systems were used to model multiple protein-ligand binding on the MLBAs. The multicomponent patterned bilayers were functionalized with GM 1, DNP, and biotin lipids, and binding curves was generated by recording surface fluorescence versus increasing concentration of membrane bound ligands.