Three-dimensional mixed convection stagnation-point fow past a vertical surface with second-order slip velocity

This study is concerned with the three-dimensional(3D)stagnation-point for the mixed convection flow past a vertical surface considering the first-order and secondorder velocity slips.To the authors’knowledge,this is the first study presenting this very interesting analysis.Nonlinear partial differential equations for the flow problem are transformed into nonlinear ordinary differential equations(ODEs)by using appropriate similarity transformation.These ODEs with the corresponding boundary conditions are numerically solved by utilizing the bvp4c solver in MATLAB programming language.The effects of the governing parameters on the non-dimensional velocity profiles,temperature profiles,skin friction coefficients,and the local Nusselt number are presented in detail through a series of graphs and tables.Interestingly,it is reported that the reduced skin friction coefficient decreases for the assisting flow situation and increases for the opposing flow situation.The numerical computations of the present work are compared with those from other research available in specific situations,and an excellent consensus is observed.Another exciting feature for this work is the existence of dual solutions.An important remark is that the dual solutions exist for both assisting and opposing flows.A linear stability analysis is performed showing that one solution is stable and the other solution is not stable.We notice that the mixed convection and velocity slip parameters have strong effects on the flow characteristics.These effects are depicted in graphs and discussed in this paper.The obtained results show that the first-order and second-order slip parameters have a considerable effect on the flow,as well as on the heat transfer characteristics.

Re-adhesion control strategy based on the optimal slip velocity seeking method

In the railway industry, re-adhesion control plays an important role in attenuating the slip occurrence due to the low adhesion condition in the wheel-rail inter- action. Braking and traction forces depend on the normal force and adhesion coefficient at the wheel-rail contact area. Due to the restrictions on controlling normal force, the only way to increase the tractive or braking effect is to maximize the adhesion coefficient. Through efficient uti- lization of adhesion, it is also possible to avoid wheel-rail wear and minimize the energy consumption. The adhesion between wheel and rail is a highly nonlinear function of many parameters like environmental conditions, railway vehicle speed and slip velocity. To estimate these unknown parameters accurately is a very hard and competitive challenge. The robust adaptive control strategy presented in this paper is not only able to suppress the wheel slip in time, but also maximize the adhesion utilization perfor- mance after re-adhesion process even if the wheel-rail contact mechanism exhibits significant adhesion uncer- tainties and/or nonlinearities. Using an optimal slip velocity seeking algorithm, the proposed strategy provides a satisfactory slip velocity tracking ability, which was demonstrated able to realize the desired slip velocity without experiencing any instability problem. The control torque of the traction motor was regulated continuously to drive the railway vehicle in the neighborhood of the opti- mal adhesion point and guarantee the best traction capacity after re-adhesion process by making the railway vehicle operate away from the unstable region. The results obtained from the adaptive approach based on the second- order sliding mode observer have been confirmed through theoretical analysis and numerical simulation conducted in MATLAB and Simulink with a full traction model under various wheel-rail conditions.

Effects of nonlinear velocity slip and temperature jump onpseudo-plastic power-law fluid over moving permeable surface in presence of magnetic field

Flow and heat transfer of a pseudo-plastic power-law fluid over a stretching permeable surface with the magnetic effect is investigated. In the boundary conditions,the nonlinear temperature jump and the velocity slip are considered. Semi-similarity equations are obtained and solved by bvp4c with MATLAB. The problem can be considered as an extension of the previous work done by Mahmoud(Mahmoud, M. A. A. Slip velocity effect on a non-Newtonian power-law fluid over a moving permeable surface with heat generation. Mathematical and Computer Modelling, 54, 1228–1237(2011)). Efforts are made to discuss the effects of the power-law number, slip velocity, and temperature jump on the dimensionless velocity and temperature distribution.

Hematocrit and Slip Velocity Influence on Third Grade Blood Flow and Heat Transfer through a Stenosed Artery

A theoretical investigation concerning hematocrit and slip velocity influence on the flow of blood and heat transfer by taking into account the externally applied magnetic field has been carried out. The mathematical models considered in this work treated blood as a non-Newtonian fluid obeying the third grade fluid model. A suitable geometry of the stenosis is taken into account. Galerkin weighted residual and Newton Raphson methods are used to solve the equations that govern the flow of blood and heat transfer. Analytical expression for the velocity profile, temperature profile, volume flow rate, wall shear stress and resistance to flow were obtained. Graphical representation of results shows that the flow velocity, volumetric flow rate and shear stress increase while resistance to flow and heat transfer rate decrease when the slip velocity increases. Also, flow velocity and volume flow rate decrease while shear stress, heat transfer rate, and resistance to flow increase when the hematocrit parameter increases. Finally, increases in magnetic field parameter lead to decrease in flow velocity, flow rate and shear stress but increase the flow resistance.

Velocity Slip and Interfacial Momentum Transfer in the Transient Section of Supersonic Gas-Droplet Two-Phase Flows

Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity slip between gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) x 104 Pa. The relaxation time corresponding to this transient process is in the range of 0.015-0.090ms for the two-phase flow formed inside the LJ and less than 0.5ms outside the LJ. It demonstrates the unique performance of this system for application to fast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulations of the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside the LJ, it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach number decreases. Due to compression by the shock wave at the end of the LJ, the flow pattern becomes two dimensional and viscous outside the LJ. Laser Doppler velocirneter (LDV) measurements of droplet velocities outside the LJ are in reasonably good agreement with the results of the simulation.

Interseismic slip distribution and locking characteristics of the mid-southern segment of the Tanlu fault zone

We employ the block negative dislocation model to invert the distribution of fault coupling and slip rate deficit on the different segments of the Tanlu(Tancheng-Lujiang) fault zone, according to the GPS horizontal velocity field from 1991 to 2007(the first phase) and 2013 to 2018(the second phase). By comparing the deformation characteristics results, we discuss the relationship between the deformation characteristics with the M earthquake in Japan. The results showed that the fault coupling rate of the northern section of Tancheng in the second phase reduced compared with that in the first phase. However, the results of the two phases showed that the northern section of Juxian still has a high coupling rate, a deep blocking depth, and a dextral compressive deficit, which is the enrapture section of the 1668 Tancheng earthquake. At the same time, the area strain results show that the strain rate of the central and eastern regions of the second phase is obviously enhanced compared with that of the first phase. The occurrence of the great earthquake in Japan has played a specific role in alleviating the strain accumulation in the middle and south sections of the Tanlu fault zone. The results of the maximum shear strain show that the shear strain in the middle section of the Tanlu fault zone in the second phase is weaker than that in the first phase, and the maximum shear strain in the southern section is stronger than that in the first phase. The fault coupling coefficient of the south Sihong to Jiashan section is high, and it is also the unruptured section of historical earthquakes. At the same time, small earthquakes in this area are not active and accumulate stress easily, so the future earthquake risk deserves attention.

Variable fluid properties and thermal radiation effects on flow and heat transfer in micropolar fluid film past moving permeable infinite flat plate with slip velocity

This work deals with the influence of thermal radiation on the problem of the mixed convection thin film flow and heat transfer of a micropolar fluid past a moving infinite vertical porous flat plate with a slip velocity. The fluid viscosity and the thermal conductivity are assumed to be the functions of temperature. The equations governing the flow are solved numerically by the Chebyshev spectral method for some representative value of various parameters. In comparison with the previously published work, the excellent agreement is shown. The effects of various parameters on the velocity, the microrotation velocity, and the temperature profiles, as well as the skin-friction coefficient and the Nusselt number, are plotted and discussed.

Effect of Slip Velocity on Blood Flow through a Catheterized Artery

A mathematical model for pulsatile flow of blood in a catheterized artery in presence of an axisymmetric stenosis with a velocity slip at the constricted wall is proposed. The expressions for the flow characteristics, velocity profiles, the flow resistance, the wall shear stress, the effective viscosity are obtained in the present analysis. The effects of slip velocity on the blood flow characteristics are shown graphically and discussed briefly.

Effects of Velocity and Thermal Slip Conditions with Radiation on Heat Transfer Flow of Ferrofluids

To analyze the thermal convection of ferrofluid along a flat plate is the persistence of this study. The two-dimensional laminar, steady, incompressible flow past a flat plate subject to convective surface boundary condition, slip velocity in the presence of radiation has been studied where the magnetic field is applied in the transverse direction to the plate. Two different kinds of magnetic nanoparticles, magnetite Fe3O4 and cobalt ferrite CoFe2O4 are amalgamated within the base fluids water and kerosene. The effects of various physical aspects such as magnetic field, volume fraction, radiation and slip conditions on the flow and heat transfer characteristics are presented graphically and discussed. The effect of various dimensionless parameters on the skin friction coefficient and heat transfer rate are also tabulated. To investigate this particular problem, numerical computations are done using the implicit finite difference method based Keller-Box Method.

Integral Transform Method for a Porous Slider with Magnetic Field and Velocity Slip

Current research is about the injection of a viscous fluid in the presence of a transverse uniform magnetic field to reduce the sliding drag.There is a slip-on both the slider and the ground in the two cases,for example,a long porous slider and a circular porous slider.By utilizing similarity transformation Navier-Stokes equations are converted into coupled equations which are tackled by Integral Transform Method.Solutions are obtained for different values of Reynolds numbers,velocity slip,and magnetic field.We found that surface slip and Reynolds number has a substantial influence on the lift and drag of long and circular sliders,whereas the magnetic effect is also noticeable.

Modeling and numerical analysis of nanoliquid (titanium oxide, graphene oxide) flow viscous fluid with second order velocity slip and entropy generation

The prime objective of the present communication is to examine the entropy-optimized second order velocity slip Darcy–Forchheimer hybrid nanofluid flow of viscous material between two rotating disks.Electrical conducting flow is considered and saturated through Darcy–Forchheimer relation.Both the disks are rotating with different angular frequencies and stretches with different rates.Here graphene oxide and titanium dioxide are considered for hybrid nanoparticles and water as a continuous phase liquid.Joule heating,heat generation/absorption and viscous dissipation effects are incorporated in the mathematical modeling of energy expression.Furthermore,binary chemical reaction with activation energy is considered.The total entropy rate is calculated in the presence of heat transfer irreversibility,fluid friction irreversibility,Joule heating irreversibility,porosity irreversibility and chemical reaction irreversibility through thermodynamics second law.The nonlinear governing equations are first converted into ordinary differential equations through implementation of appropriate similarity transformations and then numerical solutions are calculated through Built-in-Shooting method.Characteristics of sundry flow variables on the entropy generation rate,velocity,concentration,Bejan number,temperature are discussed graphically for both graphene oxide and titanium dioxide hybrid nanoparticles.The engineering interest like skin friction coefficient and Nusselt number are computed numerically and presented through tables.It is noticed from the obtained results that entropy generation rate and Bejan number have similar effects versus diffusion parameter.Also entropy generation rate is more against the higher Brinkman number.

Viscous Slip MHD Flow over a Moving Sheet with an Arbitrary Surface Velocity

The magnetohydrodynamic（MHD） flow induced by a stretching or shrinking sheet under slip conditions is studied.Analytical solutions based on the boundary layer assumption are obtained in a closed form and can be applied to a flow configuration with any arbitrary velocity distributions. Seven typical sheet velocity profiles are employed as illustrating examples. The solutions to the slip MHD flow are derived from the general solution and discussed in detail. Different from self-similar boundary layer flows, the flows studied in this work have solutions in explicit analytical forms. However, the current flows require special mass transfer at the wall, which is determined by the moving velocity of the sheet. The effects of the slip parameter, the mass transfer at the wall, and the magnetic field on the flow are also demonstrated.

Monitoring Longitudinal Vehicular Velocity by Using Driving Wheels Information

In order to enhance the accuracy and overcome the limitation of representing the vehicular velocity with non driving wheel speed signals, which is commonly used in researching on automotive dynamic control systems at present, the dynamic and kinematics models of running vehicles and wheels are established. The concept that expresses vehicle velocity using only the driving wheel speed information with adjustable weight factors is described and an algorithm is proposed. A Matlab program with the algorithm embedded is made to simulate the vehicle’s accelerating under different road conditions, and it’s simulation results coincide well with the experimental results, which demonstrates the validity of the algorithm.

粒子群算法在多种数据联合反演断层三维滑动速率的应用研究

建立多种大地测量数据联合反演的数学模型。利用青藏高原东北缘地区的GPS、水准、重力三种观测数据,结合附有LDW策略的惯性权重的粒子群算法,反演龙首山断裂的三维滑动速率。结果表明:龙首山断裂主要以右旋、逆冲为主,兼具挤压趋势,且具有空间分布不均匀性的特征。相比单一数据的反演结果,多种数据联合反演更具稳定性和规律性。

改进PSO算法在断层滑动参数反演中的研究与应用

利用地面大地测量数据反演断层的滑动速率等动态参数,是大地测量主要研究问题之一。本文首先提出了一种改进的粒子群算法,以此弥补标准粒子群算法可能局部最优解的不足,并通过模拟数据进行试验验证。然后以渭河盆地两条主要断裂为研究对象,利用地面GPS观测数据反演了秦岭北侧大断裂、临潼-长安断裂的三维滑动速率,并分析了两种算法的运行耗时。结果表明:改进的粒子群算法比标准粒子群算法耗时减少,收敛速度更快;本文所提算法反演得到的断层参数更符合真实的断裂条件,具有一定的实际应用价值。

自适应双层无迹卡尔曼滤波的车辆状态估计

针对在车辆行驶状态估计中存在估计不准确、鲁棒性较差以及系统噪声不确定等问题,提出一种将双层无迹卡尔曼滤波(DLUKF)与改进的Sage-Husa算法相结合的自适应双层无迹卡尔曼滤波算法(ADLUKF)作为车辆行驶状态的估计器,再结合三自由度汽车模型对车辆行驶的横摆角速度和质心侧偏角进行估计。通过改进的Sage-Husa滤波器对系统过程噪声和测量噪声进行动态调整,进而减少车辆行驶状态估计的误差。应用Carsim与Matlab/Simulink进行联合仿真以及实车试验数据来验证该估计器的有效性,并与无迹卡尔曼滤波(UKF)算法进行对比。结果表明:与UKF算法相比,该算法有效提高了车辆行驶的横摆角速度和质心侧偏角的估计精度和稳定性。

疏水材料微尺度凹坑流滑移速度特性研究

凹坑构型是疏水材料中常见且重要的结构形式,认识和揭示此类凹坑结构的滑移速度特性对于疏水材料的设计具有指导意义。本文采用离散统一气体动理论,在Kn=0.01~0.5范围内,对低速二维凹坑流动进行数值模拟,模拟结果表明,在不同Kn值下,滑移速度规律呈现显著差异:随着凹坑尺寸减小(Kn> 0.3),凹坑区的滑移速度小于平滑壁面的滑移速度;而随着凹坑尺寸增大(Kn <0.2),凹坑区的滑移速度大于平滑壁面的滑移速度;在凹坑两端,统计平均滑移速度会出现跳跃,随着Kn数增加,这种跳跃现象越来越强。上述演化特征表明,在设计疏水微结构时,Kn不能大于0.3。

水热条件下蛇纹石矿物的摩擦特性

蛇纹石矿物大量存在于俯冲带中,其独特的物理化学性质会对俯冲带动力学产生显著影响。开展蛇纹石矿物的摩擦实验研究有助于理解俯冲带中含蛇纹石断层的摩擦滑动稳定性及解释俯冲带断层的复杂错动行为。目前,实验室对于蛇纹石矿物的研究已取得了很多成果。文中基于前人的研究工作,对以下2个方面进行了综述:1)蛇纹石矿物的稳定赋存状态及蛇纹石矿物之间的相互转换关系;2)控制蛇纹石矿物摩擦强度及滑动稳定性的因素,主要包括温度、孔隙流体及有效正应力的大小。研究表明,温度的升高可显著增大纤蛇纹石和利蛇纹石的摩擦强度。但对于叶蛇纹石而言,在较低的流体压力条件下,其摩擦强度表现出温度强化特征,而在较高的流体压力条件下却表现出温度弱化特征。蛇纹石矿物的摩擦强度均表现出显著的压力依赖性,其中纤蛇纹石的摩擦强度表现出更高的压力敏感性。在俯冲带地幔楔条件下叶蛇纹石可大量赋存。前人研究发现叶蛇纹石在较低的流体压力条件下随着温度升高会发生脱水反应,进而表现出不稳定的速度弱化现象;而在高压流体条件下,叶蛇纹石在低剪切变形速率下会表现出速度弱化现象,叶蛇纹石的摩擦滑动稳定性随剪切滑移速率的变化能够更好地解释俯冲带慢滑移现象。

基于GNSS的红河断裂中段现今变形特征

采用红河断裂带中段加密布设的GNSS连续站观测资料以及前人发布的速度场结果,获取红河断裂带中段及邻区现今地壳运动速度场。根据川滇地区活动断裂分布建立研究区三维有限元模型,以红河断裂带中段及邻区GNSS速度场为约束,获得红河断裂带中段不同段落的现今滑动速率和区域应变率场。结果表明,红河断裂带弥渡-元江段右旋走滑速率为1.2±0.6 mm/a,挤压速率为0.6±0.5 mm/a;红河断裂带元江-元阳段右旋走滑速率为1.8±0.7 mm/a,挤压速率为1.5±0.6 mm/a。应变率结果显示,红河断裂带中段及邻区以剪切变形为主,最大剪应变率高值区位于小江断裂带附近,最大幅度约为62×10^(-9)/a,红河断裂剪切变形相对较弱;面应变率显示,红河断裂元江-元阳段挤压变形较为显著,挤压应变率值约为10×10^(-9)/a,该段落处于强闭锁状态,未来地震危险性值得关注。

Influence of Brownian Motion, Thermophoresis and Magnetic Effects on a Fluid Containing Nanoparticles Flowing over a Stretchable Cylinder

The influence of Brownian motion and thermophoresis on a fluid containing nanoparticles flowing over a stretchable cylinder is examined.The classical Navier-Stokes equations are considered in a porous frame.In addition,the Lorentz force is taken into account.The controlling coupled nonlinear partial differential equations are transformed into a system of first order ordinary differential equations by means of a similarity transformation.The resulting system of equations is solved by employing a shooting approach properly implemented in MATLAB.The evolution of the boundary layer and the growing velocity is shown graphically together with the related profiles of concentration and temperature.The magnetic field has a different influence(in terms of trends)on velocity and concentration.