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.

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.

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 super-sonic two-phase (gas-droplet) flow in the transient section inside and outside a Laval jet(L J). The initial velocity slipbetween gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) × 104 Pa. The relaxationtime corresponding to this transient process is in the range of 0.015-0.090 ms for the two-phase flow formed insidethe LJ and less than 0.5 ms outside the LJ. It demonstrates the unique performance of this system for application tofast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulationsof the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside theLJ. it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach numberdecreases. Due to compression by the shock wave at the end of the L J, the flow pattern becomes two dimensionaland viscous outside the LJ. Laser Doppler velocimeter (LDV) measurements of droplet velocities outside the LJ arein reasonably good agreement with the results of the simulation.

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.

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。

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。

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.

Numerical prediction of particle slip velocity in turbulence by CFD-DEM simulation

Turbulent environment improves the flotation recovery of fine particles by promoting the particle–bubble collision rate,which directly depends on the particle slip velocity.However,the existing slip velocity models are not applicable to fine particles in turbulence.The mechanism of turbulence characteristics and particle properties on the slip velocity of fine particles in turbulence was unclear.In this study,a coupled ANSYS FLUENT and EDEM based on computational fluid dynamics(CFD)and discrete element method(DEM)were used to simulate the slip velocity of fine particles in the approximately homogenous isotropic turbulence,which was excited by the grid.The reliability of the used CFD-DEM simulation method was validated against the slip velocity measured by the particle image velocimetry(PIV)experiments.In particular,the effects of the particle shapes,particle densities,and turbulence intensities on the slip velocity have been investigated with this numerical method.Numerical results show that particle shapes have no significant effect on fine particles between 37 and 225μm.The slip velocity of the spherical particles increases with the turbulence intensity and particle density.Based on the simulated data,a model which has a correlation coefficient of 0.95 is built by using nonlinear fitting.

Mixed convectional and chemical reactive flow of nanofluid with slanted MHD on moving permeable stretching/shrinking sheet through nonlinear radiation,energy omission

Hybrid nanofluids are remarkable functioning liquids that are intended to reduce the energy loss while maximizing the heat transmission.In the involvement of suction and nonlinear thermal radiation effects,this study attempted to explore the energy transmission features of the inclined magnetohydrodynamic(MHD)stagnation flow of CNTs-hybrid nanofluid across the nonlinear permeable stretching or shrinking sheet.This work also included some noteworthy features like chemical reactions,variable molecular diffusivity,quadratic convection,viscous dissipation,velocity slip and heat omission assessment.Employing appropriate similarity components,the model equations were modified to ODEs and computed by using the HAM technique.The impact of various relevant flow characteristics on movement,heat and concentration profiles was investigated and plotted on a graph.Considering various model factors,the significance of drag friction,heat and mass transfer rate were also computed in tabular and graphical form.This leads to the conclusion that such factors have a considerable impact on the dynamics of fluid as well as other engineering measurements of interest.Furthermore,viscous forces are dominated by increasing the values ofλ_(p),δ_(m)andδ_(q),and as a result,F(ξ)accelerates while the opposite trend is observed for M andφ.The drag friction is boosted by the augmentation M,λ_(p)andφ,but the rate of heat transfer declined.According to our findings,hybrid nanoliquid effects dominate that of ordinary nanofluid in terms of F(ξ),Θ(ξ)andφ(ξ)profiles.The HAM and the numerical technique(shooting method)were found to be in good agreement.

青藏高原东北隅断层活动及地壳变形模式

精准分析青藏高原东北隅断层活动和地壳变形模式对于理解区域大地震空间分布特征和地震危险性分析具有重要意义.本文在已有GPS速度场的基础上,通过建立由21个GPS连续观测站组成的3条跨断层剖面的加密观测,获得研究区较高空间分辨率的GPS速度场.利用K-中心点和欧拉矢量结合的方法分析GPS速度场的空间聚类特征,发现在陇西块体内部存在显著的差异性变形,进而结合区域已有块体-断层划分模型,给出与最新GPS速度场更为吻合的块体-断层模型.改进模型的最大特点是在陇西块体内部存在一条北北东向的右旋剪切带.利用最新GPS速度场和改进的块体-断层模型,基于负位错理论反演主要块体的运动特征和主要断层的滑动速率,结果显示在改进块体-断层模型中新增的右旋剪切带在分配该地区应变积累特征时扮演着重要的角色,进而计算的六盘山断裂的挤压速率远小于已有的结果,其地震危险性也可能相应地降低.

含沙流下双吸泵磨蚀特性分析

为深入分析含沙流下双吸泵磨蚀特点,采用RNGk-ε模型计算获得叶片正背面的剪切力、泥沙分布及固液滑移速度等参数,进而基于正交试验法对含沙量、沙粒直径和进口流速等对磨蚀的影响进行分析。研究表明,在含沙流下,叶片正、背面沙粒多集中在进口处。固液滑移速度受沙粒直径影响最大,沙粒直径增大,固液滑移速度也随之增大。三种因素中,沙粒直径对双吸泵磨蚀的影响权重最大,含沙量其次,流量的影响相对较少。