REGULARITY OF WEAK SOLUTIONS TO MAGNETO-MICROPOLAR FLUID EQUATIONS

In this article, we study the regularity of weak solutions and the blow-up criteria for smooth solutions to the magneto-micropolar fluid equations in R3. We obtain the classical blow-up criteria for smooth solutions （u,w, b）, i.e., u ∈ Lq（0, T; LP（R3） for 2/q＋3/P≤ 1with 3〈P≤∞,u∈C（[0,T）;L3（R3））or△u∈Lq（0,T,LP）for 3/2〈P≤∞ satisfying 2/q＋3/P≤ 2. Moreover, our results indicate that the regularity of weak solutions is dominated by the velocity u of the fluid. In the end-point case p = ∞, the blow-up criteriacan be extended to more general spaces △u E L1 （0, T; B0∞,∞（R3）.

A disc-type magneto-rheologic fluid damper

A disc-type magneto-rheological fluid damper operating in shear mode is proposed in this paper,which is based on the special characteristics of the magneto-rheological (MR) fluid with rapid, reversible and dramatic change in its rheological properties by the application of an external magnetic field. The magneticfield of the disc-type MR fluid damper is analysed by the finite element method ; the controllability of the disctype MR fluid damper on the dynamic behaviour of a rotor system ; and the effectiveness of the disc-type MR fluid damper in controlling the vibration of a rotor system, are studied in a flexible rotor system with an over-hung disc. It is shown that the magnetic flux density of the disc-type MR fluid damper in the working areas can significantly change with the applied current in the coil ; and that the dynamic behavior of the disc-type MR fluid damper can be varied by the application of an external magnetic field produced by a low voltage electromagnetic coil. The disc-type MR fluid damper can significantly change the dynamic characteristics of a rotor system, provided that the location of the disk-type MR fluid damper is carefully chosen. The disc-type MR fluid damper is a new actuator with good dynamic characteristics for rotating machinery.

Tunable magneto optic modulation based on magnetically responsive nanostructured magnetic fluid

Magnetic fluid is a kind of functional composite material with nanosized structure and unique optical properties. The tunable magneto-optic modulation of magnetic fluid under external magnetic field, achieved by adjusting the polarization direction of incident light, is investigated theoretically and experimentally in this work. The corresponding modulation depth and response time are obtained. The accompanying mechanisms are clarified by using the theory of dichroism of magtietic fluid and the aggregation/disintegration processes of magnetic particles within magnetic fluid when the external magnetic field turns on/off.

Study of Rayleigh-Bénard Magneto Convection in a Micropolar Fluid with Maxwell-Cattaneo Law

The effects of result from the substitution of the classical Fourier law by the non-classical Maxwell-Cattaneo law on the Rayleigh-Bénard Magneto-convection in an electrically conducting micropolar fluid is studied using the Galerkin technique. The eigenvalue is obtained for free-free, rigid-free and rigid-rigid velocity boundary combinations with isothermal or adiabatic temperature on the spin-vanishing boundaries. The influences of various micropolar fluid parameters are analyzed on the onset of convection. The classical approach predicts an infinite speed for the propagation of heat. The present non-classical theory involves a wave type heat transport (SECOND SOUND) and does not suffer from the physically unacceptable drawback of infinite heat propagation speed. It is found that the results are noteworthy at short times and the critical eigenvalues are less than the classical ones.

Magneto and Electro-Optic Intensity Modulator Based on Liquid Crystal and Magnetic Fluid Filled Photonic Crystal Fiber

We propose a novel light intensity modulator based on magnetic fluid and liquid crystal（LC） filled photonic crystal fibers（PCFs）. The influences of electric and magnetic fields on the transmission intensity are theoretically and experimentally analyzed and investigated. Both the electric and magnetic fields can manipulate the molecular arrangement of LC to array a certain angle without changing the refractive index of the LC. Therefore, light loss in the PCF varies with the electric and magnetic fields whereas the peak wavelengths remain constant. The experimental results show that the transmission intensity decreases with the increase of the electric and magnetic fields. The cut-off electric field is 0.899 V/um at 20 Hz and the cut-off magnetic field is 195 m T. This simple and compacted optical modulator will have a great prospect in sensing applications.

接闪阳极参数对雷电弧材料损伤数值分析的影响

接闪材料遭受雷电直击损伤的数值分析中尚不清楚阴极-放电电弧-阳极结构下材料参数对损伤分析的影响。为此,该文以飞机常用金属和复合蒙皮材料为研究对象,基于热等离子体电弧的磁流体动力学理论,建立雷电电弧的电-磁-热-力多场分析及其与材料的耦合模型,研究不同材料参数对雷电弧材料损伤数值分析的影响。结果表明,接闪阳极材料的电导率和热导率变化会改变电弧-材料界面的电流和能量分布及其耦合过程,影响各过程对材料致损的贡献。接闪材料表面的洛伦兹力、磁感应强度和电流密度随着电导率和热导率变化0.1~20倍时,其峰值最大可分别改变622.2%、172.5%和63.5%,峰值位置最大可分别变化-54.8%、59.4%和-53.1%。该文可为接闪材料的雷击损伤数值分析和耐受能力改进提供参考。

具有无穷磁雷诺数的三维磁微极流体方程的整体适定性

主要研究了具有无穷磁雷诺数的三维磁微极流体方程在T^(3)上的Cauchy问题的整体适定性,证明了当初始磁场很接近于背景磁场并且也满足丢番图条件时,该Cauchy问题是整体适定的.

GENERALIZED ASYMMETRIC HYSTERESIS MODEL OF CONTROLLABLE MAGNETORHEOLOGICAL DAMPER FOR VEHICLE SUSPENSION ATTENUATION

A generalized model is synthesized to characterize the asymmetric hysteresisforce-velocity (F-v) properties of the magneto-rheological (MR) fluids damper. The model isrepresented as a function of the command current, excitation frequency, and displacement amplitude,based on the symmetric and asymmetric sigmoid functions. The symmetric hysteresis damping propertiesof the controllable MR-damper and properties of the conventional passive hydraulic damper can alsobe described by the proposed model. The validity of the model is verified by experiments, which showthat the results calculated from the model are consistent with the measured data. In addition, itis shown that the model applies to a wide vibration frequency range. The proposed model haspotential application in vehicle suspension design employing the symmetry MR-damper, and also indeveloping the asymmetry MR-damper especially for the vehicle suspension attenuation.

Magneto-Micropolar流体方程组恰当弱解的存在性

采用类似于Caffarelli-Kohn-Nirenberg和Fanghua Lin等人的方法,证明了Magneto-Micropolar流体方程组恰当弱解的存在性.

Existence of a Hartmann layer in the peristalsis of Sisko fluid

Analytical solutions for the peristaltic flow of a magneto hydrodynamic （MHD） Sisko fluid in a channel, under the effects of strong and weak magnetic fields, are presented. The governing nonlinear problem, for the strong magnetic field, is solved using the matched asymptotic expansion. The solution for the weak magnetic field is obtained using a regular perturbation method. The main observation is the existence of a Hartman boundary layer for the strong magnetic field at the location of the two plates of the channel. The thickness of the Hartmann boundary layer is determined analytically. The effects of a strong magnetic field and the shear thinning parameter of the Sisko fluid on the velocity profile are presented graphically.

Natural convection flow of a couple stress fluid between two vertical parallel plates with Hall and ion-slip effects

The Hall and ion-slip effects on fully developed electrically conducting couple stress fluid flow between vertical parallel plates in the presence of a temperature dependent heat source are investigated. The governing non-linear partial differential equations are transformed into a system of ordinary differential equations using similarity transformations. The resulting equations are then solved using the homotopy analysis method （HAM）. The effects of the magnetic parameter, Hall parameter, ion-slip parameter and couple stress fluid parameter on velocity and temperature are discussed and shown graphically

Melting phenomenon in magneto hydro-dynamics steady flow and heat transfer over a moving surface in the presence of thermal radiation

The Lie group method is applied to present an analysis of the magneto hydro-dynamics（MHD） steady laminar flow and the heat transfer from a warm laminar liquid flow to a melting moving surface in the presence of thermal radiation.By using the Lie group method,we have presented the transformation groups for the problem apart from the scaling group.The application of this method reduces the partial differential equations（PDEs） with their boundary conditions governing the flow and heat transfer to a system of nonlinear ordinary differential equations（ODEs） with appropriate boundary conditions.The resulting nonlinear system of ODEs is solved numerically using the implicit finite difference method（FDM）.The local skin-friction coefficients and the local Nusselt numbers for different physical parameters are presented in a table.

MHD Mixed Convection Flow of a Casson Fluid over an Exponentially Stretching Surface with the Effects of Soret, Dufour, Thermal Radiation and Chemical Reaction

The present study deals with MHD (magneto hydrodynamics) mixed convection flow of a Casson fluid over an exponentially stretching sheet with the effects of Soret and Dufour, thermal radiation, chemical reaction. The governing partial differential equations are converted into ordinary differential equations by using similarity transformations. These equations are then solved numerically by applying finite difference scheme known as the Keller Box method. The effects of various parameters on velocity, temperature and concentration profiles are presented graphically to interpret and the results are discussed.

Non-Newtonian Power-Law Fluid Flow and Heat Transfer over a Non-Linearly Stretching Surface

The problem of magneto-hydrodynamic flow and heat transfer of an electrically conducting non-Newtonian power-law fluid past a non-linearly stretching surface in the presence of a transverse magnetic field is considered. The stretching velocity, the temperature and the transverse magnetic field are assumed to vary in a power-law with the distance from the origin. The flow is induced due to an infinite elastic sheet which is stretched in its own plane. The governing equations are reduced to non-linear ordinary differential equations by means of similarity transformations. These equations are then solved numerically by an implicit finite-difference scheme known as Keller-Box method. The numerical solution is found to be dependent on several governing parameters, including the magnetic field parameter, power-law index, velocity exponent parameter, temperature exponent parameter, Modified Prandtl number and heat source/sink parameter. A systematic study is carried out to illustrate the effects of these parameters on the fluid velocity and the temperature distribution in the boundary layer. The results for the local skin-friction coefficient and the local Nusselt number are tabulated and discussed. The results obtained reveal many interesting behaviors that warrant further study on the equations related to non-Newtonian fluid phenomena.

基于电弧磁流体仿真的DC 1500V两极塑壳断路器气道优化设计

该文开发了用于DC 1500V光伏和储能系统的新一代两极直流塑壳断路器样机。通过DC 1500V/15 kA,时间常数10 ms的短路分断实验发现,电弧电压快速升至350 V是提升断路器限流和分断性能的关键。为了加快初始燃弧阶段电弧运动速度使弧压快速上升,建立了断路器触头区域的二维局部电弧磁流体仿真模型,通过分析灭弧室温度、压力分布和气流速度变化曲线,明确了初始样机中电弧运动停滞的机理,并以此为依据提出了参差栅片排布和添加导流锥的气道优化设计方案。使用优化后的样机进行分断实验,比较优化前后的电压变化曲线和电弧运动高速摄像,验证了优化方案的有效性,对于DC 1500V两极直流塑壳的设计开发具有很强的实践指导意义。

海水磁流体中的磁声波传播

海水可以被看成是磁流体并能传播磁声波,运用建立的海洋磁流体力学模型,从理论上通过声波密度扰动驱动下的离子密度群聚现象,以及磁场脉冲驱动下的离子密度群聚现象的分析,得到磁声波的微观特征,即在地磁场的作用下,声波传播的粒子密度极大值前后会形成离子密度漂移电流,海水的盐离子将群聚到中性粒子密度极大值区,而当在海水中激励一个磁脉冲时,盐离子将产生磁场梯度漂移运动,使得盐离子向磁脉冲极大值区域群聚。在此基础上,探讨海水中无人潜航器激励磁声波的传播特征,提出通过高灵敏磁感应搜索线圈探测磁声波传播时产生的磁场扰动,从而实现一种有效的高灵敏非声探测潜航器的方法。

二维不可压缩磁-微极流初边值问题的全局解

利用T-弱连续算子方法与经典的Galerkin技术,讨论二维有界光滑区域上一类不可压缩磁-微极流方程组的初边值问题,得到了该问题全局弱解的存在性与唯一性定理,并进一步提高了弱解的正则性.

形状记忆合金与磁流变液交替传动性能研究

针对磁流变液在高温下传动性能下降等缺点,提出一种形状记忆合金与磁流变液交替的传动方法。基于形状记忆合金的热力学效应,推导了弹簧挤压力与温度的关系式,并通过实验验证了方程的正确性;对传动装置的磁场进行有限元分析,得出了工作间隙沿径向的磁场分布;基于形状记忆合金弹簧热驱动特性,建立了摩擦转矩与挤压力、结构尺寸等参数的关系。结果表明,形状记忆合金弹簧产生的挤压力随温度升高而增加;温度低于40℃时,主要由磁流变液传递转矩,转矩可达9.14 N·m;温度在40℃~60℃之间时,磁流变液与形状记忆合金共同传递转矩,转矩可达13.24 N·m;温度高于60℃时,主要由形状记忆合金传递转矩,转矩可达9.40 N·m。随着温度升高,形状记忆合金能代替磁流变液传递转矩,装置能感知温度变化,实现交替传动。

三维非均匀不可压磁微极流体的衰减估计

研究非均匀不可压磁微极流体方程组在全空间R^(3)上的最优衰减率.首先,利用能量估计法给出方程组解的高阶导数的能量不等式.其次,在s∈(0,1/2]和s∈(1/2,3/2)的范围内,分别得到在负Sobolev空间中方程组解的估计.最后通过转化得到常微分方程进而求得不可压磁微极流体方程组解的高阶导数的最优衰减率.

磁流变液的屈服应力与温度效应

通常磁流变液的屈服应力大约比电流变液大一个数量级，磁流变液由于其具有较强的屈服应力而受到广泛的重视。我们用多畴的软磁材料同连续相一起充分混合获得的磁流变液，在３×１０５Ａ／ｍ的场强下静态屈服应力达到６０ｋＰａ以上，而其零场时的粘度仅为１５ｍＰａ．ｓ。本文报道了我们研制的拖板式磁流变仪的性能。同时，我们比较了几种磁流变液在零场下的沉淀性、以及外加磁场、屈服应力、温度、永磁材料、表面处理剂、添加剂和磁流变效应的关系。我们发现，磁流变效应主要由固相材料决定；表面处理剂可以改善固液界面的性质，并增强磁流变效应；不同的载液需不同的添加剂与其匹配；磁流变液的屈服应力对温度具有很好的稳定性。