电流变液在两平行电极板间流动行为的实验研究

通过实验的方法研究了电流变液流经两间距为１．１ｍｍ的平行电极板的流动行为，实验所观测到的由于电流变液在电场作用下非均匀固化所引起的固相颗粒淤积与饱和过程、河道分岔和失稳等现象，对现有的有关电流变阀均匀流动模型提出了质疑，这为进一步深入理解电流变液的力学行为，建立新的理论模型提供了实验依据     

钛酸钙系电流变液在直流电场下损耗模量的研究

研究了直流电场下钛酸钙系电流变液在动态振荡剪切模式下损耗模量的变化。用流变仪测试了不同颗粒体积分数材料在不同的温度和电场下损耗模量随应变的关系曲线。讨论了颗粒体积分数、温度、电场强度以及频率对材料损耗模量的影响。以理论推导和试验数据拟合的方法给出了损耗模量与颗粒体积分数、振荡频率、温度以及电场强度等参数的半经验数学关系式。理论值对比试验结果表明,本文损耗模量表达式与试验结果符合较好,可以用于预测直流电场下钛酸钙系电流变液在动态振荡剪切模式下颗粒体积分数、温度、电场强度、频率和剪切应变对损耗模量的影响。     

An experimental study of electrorheological fluid flow through a packed bed of glass beads

This paper shows that pressure drop-flow rate performance of an electrorheological (ER) fluid flowing through a packed bed of glass beads is consistent with a modified Ergun equation for yield stress flow through a packed bed. ER fluids are of scientific and engineering interest due to the sensitivity of their rheological properties on the applied electric field. As far as we know ER fluids have not been studied for flows through porous media. In this work a silica particle–silicone oil suspension is pumped through a rectangular packed bed of glass beads with applied electric fields. The silica particles are observed to form fibrous structures parallel to the electric field that stretch between the beads and extend between the electrodes. The pressure drop-flow rate performance agrees well with the expected performance calculated from a modified Ergun equation for a yield stress fluid flow through the packed bed with the viscosity and yield stress as functions of the applied electric field.     

Multi-scale analysis on the pulverized coal flow behaviors under high pressure dense-phase pneumatic conveying

To deeply knowledge of the flow behaviors of pulverized coal particles in dense gas–solid two-phase flow, a multi-scale analysis method based on electrostatic sensor array is applied for the multi-scale characterization of flow behaviors of dense gas–solid flow. The experimental results indicate that: for steady flow, with the increment of conveying pressure difference, the individual particles increase and the particle clusters decrease, the individual particle distribution is always inhomogeneous but the particle cluster distribution tends to be more homogeneous over the cross-section of pipe, while the average flow behavior of pulverized coal particles is always in the relatively static state. For unsteady flow, the average flow behavior of pulverized coal particles is dynamic, and the flow behaviors of the multi-scale flow structures over the cross-section of pipe are all significantly inhomogeneous. Moreover, the effect of particle size on flow behavior of pulverized coal is also investigated and validated.     

A fluid flow model in the lacunar-canalicular system under the pressure gradient and electrical field driven loads

The lacunar-canalicular system (LCS) is acknowledged to directly participate in bone tissue remodeling. The fluid flow in the LCS is synergic driven by the pressure gradient and electric field loads due to the electro-mechanical properties of bone. In this paper, an idealized annulus Maxwell fluid flow model in bone canaliculus is established, and the analytical solutions of the fluid velocity, the fluid shear stress, and the fluid flow rate are obtained. The results of the fluid flow under pressure gradient driven (PGD), electric field driven (EFD), and pressure-electricity synergic driven (P-ESD) patterns are compared and discussed. The effects of the diameter of canaliculi and osteocyte processes are evaluated. The results show that the P-ESD pattern can combine the regulatory advantages of single PGD and EFD patterns, and the osteocyte process surface can feel a relatively uniform shear stress distribution. As the bone canalicular inner radius increases, the produced shear stress under the PGD or P-ESD pattern increases slightly but changes little under the EFD pattern. The increase in the viscosity makes the flow slow down but does not affect the fluid shear stress (FSS) on the canalicular inner wall and osteocyte process surface. The increase in the high-valent ions does not affect the flow velocity and the flow rate, but the FSS on the canalicular inner wall and osteocyte process surface increases linearly. In this study, the results show that the shear stress sensed by the osteocyte process under the P-ESD pattern can be regulated by changing the pressure gradient and the intensity of electric field, as well as the parameters of the annulus fluid and the canaliculus size, which is helpful for the osteocyte mechanical responses. The established model provides a basis for the study of the mechanisms of electro-mechanical signals stimulating bone tissue (cells) growth.

     

体积分数对基于沸石和硅油的悬浮液的电流变性能的影响

用 HAAKE RV2 0型流变仪 ,在不同外加电场强度和不同颗粒体积分数下测试了基于沸石和硅油的电流变液的剪切应力变化 .结果表明 :随着外加电场强度升高 ,电流变液的零电场粘度急剧增加 ,电流变液的剪切屈服应力增加 ;随着电流变液中沸石颗粒体积分数升高 ,电流变液的剪切屈服强度急剧上升 .这种变化可以用颗粒间作用力与颗粒间距的关系、单位面积的颗粒链数目变化以及多体作用对电流变液性能的影响来解释     

电流变体粘弹性能的实验研究

电流变体是智能材料与结构中一种重要的致动器材料。本文对电流变体在电场作用下的粘弹性特性进行了实验研究。使用旋转式流变仪对表征流体粘性的蠕变特性进行了测试。同时,对电流变体进行了强制振荡试验,测试了流体在不同应力幅值、应力频率下的剪切模量主变化,得到了电流变体的复剪切模量以及剪切存储模量、损耗模量承承中电场变化的规律。     

The effect of particle concentration inhomogeneities on the steady flow of electro- and magneto-rheological materials

The yield stresses of electro-rheological (ER) and magneto-rheological (MR) suspensions increase by orders of magnitude when electric or magnetic fields are applied across them. In the absence of the field, the materials are essentially Newtonian fluids. When ER or MR materials flow through thin laminar ducts, the effect of the finite yield stress concentrates the material deformation gradients in the immediate vicinity of the duct walls. High shear rates in this region introduce drag and lift forces on the suspended particles, the net effect of which moves the particles away from the walls. Electro- or magneto-static image forces at the walls oppose this lift. The ensuing local changes in the particulate volume fraction gives rise to a local inhomogeneity in material properties adjacent to the walls.Four models for the material property inhomogeneities are presented in this paper. Three of these models admit analytical expressions for the relationship between pressure gradient and volumetric flow rate, but presume a piecewise constant particle concentration. The fourth model presumes a smooth relationship between the volume fraction and the shear rate, but requires a numerical solution. Results are presented in terms of the ratio of pressure gradients that can be produced by applying and removing the field.Experimental data collected for a variety of quasi-steady ER flows shows that the analytical solution corresponding to a flow of uniform particle concentration provides an upper bound to the pressure gradients. Each of the four models for inhomogeneous flow provides a lower bound over a sub-domain of the flow conditions. By combining these models heuristically, a single expression for the lower bound on the pressure gradients of ER and MR flows is presented.     

基于格子Boltzmann方法的电流变液动力学建模及数值模拟

电流变悬浮液内部结构对外电场的快速响应发生在指定的控制空间中,在这一特指的时间和空间尺度上电流变悬浮液的物理行为特征主要为剪切速率低和流动阻尼大,即Mach和Reynolds数一般不大,可以视为微尺度流动来加以研究。针对这一流动特征,基于介观动理论的格子Boltzmann方法,建立了电流变悬浮液两相流动的离散颗粒运动模型,通过该模型进行了动力学模拟,结果表明,该模型解决了分子动力学模型难以描述的因颗粒运动造成局部流场流变特性改变的难题,以及该流场双向耦合过程中对颗粒运动的影响。     

Measuring static yield stress of electrorheological fluids using the slotted plate device

An electrorheological (ER) response is defined as the dramatic change in rheological properties of a suspension of small particles due to the application of a large electric field transverse to the direction of flow. ER fluids are typically composed of nonconducting or semiconducting particles dispersed in a nonconducting continuous phase. A sufficiently large electric field will cause ER fluids to solidify, giving rising to a yield stress. Many applications in torque and stress transfer devices were proposed employing the reversible yielding behavior of ER fluids. Successful applications depend on a large yield stress of ER fluids and therefore accurate measurements of the yield stress of ER fluids are required. Reported experimental yield stresses of ER fluids have been dynamic yield stresses obtained by extrapolating the shear stress–shear rate data to zero-shear rate. It would be very helpful to the understanding of ER behaviors and the applications of ER fluids to be able to measure the static yield stress of ER fluids accurately. The slotted plate technique has been shown to be a successful method to determine the static yield stress of suspensions. The values obtained via the slotted plate method are static yield stress as the platform is designed for extremely low-speed motion. In this study, we modified the slotted plate device for the application of large electric fields and measured the static yield stress of TiO₂ ER fluids under various electric fields. The measured static yield stress values are also compared with the static yield stress values from a commercial rheometer.     

柔性微粒介电泳分离过程的多尺度模拟

介电泳分离是一种高效的微细颗粒分离技术,利用非均匀电场极化并操纵分离微流道中的颗粒. 柔性微粒在介电泳分离过程中同时受多种物理场、多相流和微粒变形等复杂因素的影响,仅用单一的计算方法对其进行模拟存在一定的难度,本文采用有限单元——格子玻尔兹曼耦合计算的方法处理这一难题.介观尺度的格子玻尔兹曼方法将流体看成由大量微小粒子组成,在离散格子上求解玻尔兹曼输运方程,易于处理多相流及大变形问题,特别适合模拟柔性颗粒在介电泳分离过程中的变形情况.另一方面,介电泳分离过程的模拟需求解流体、电场和微粒运动方程,计算量相当庞大,通过有限单元法求解介电泳力,提高计算效率.利用这种多尺度耦合计算方法,对一款现有的介电泳芯片分离过程进行了模拟.分析了微粒在电场作用下产生的介电泳力,揭示了介电泳力与电场变化率等因素之间的关系.对微粒运动轨迹及其变形的情况进行了研究,发现微粒的变形主要与流体剪切作用有关.这种多尺度耦合计算方法,为复杂微流体的计算提供了一种有效的解决方案.      

电流变阻尼器的动态特性实验研究

设计制造了一种多层滑动极板式电流变阻尼器，使用自制的电流变液，采用正弦激励，进行了这种电流变阻尼器的阻尼特性试验。研究了电流变阻尼器的载荷－位移迟滞特性和载荷－速率迟滞特性，同时研究分析了这种电流变阻尼器的周期能耗特性及等效粘性阻尼特性。结果表明，阻尼器的周期能耗量随外加电场强度的增加而增加，外加电场强度越大，阻尼器的等效阻尼系数越大。阻尼器的阻尼特性体现为库仑阻尼和粘性阻尼的组合，其中随外加电场强度可控的主要是库仑阻尼力，而且库仑阻尼力不仅与外加强度有关，也与阻尼器的运动速度有关。该阻尼器系统是一个强非线性系统，极板间电流变液在低剪切应变率时表现为Bingham塑性流体，在高剪切应变率时流变性态比较复杂，导致载荷－速率迟滞环出现多区域闭合现象。     

Layered model of electrorheological fluid under flow

We present a theoretical model of the behavior of a concentrated electrorheological fluid (ERF) which explicitly takes into account the effects of conductivity. The increase in shear viscosity under an electric field is due to a layered structure between the electrodes, made up of the remnants of particle chains adhering to the electrodes by electrostatic image forces, and a freely flowing liquid layer where all the shear flow is concentrated. This layered model can explain the variation of electric current with shear rate, as well as the rheological response of a dynamic yield stress proportional to the square of the applied electric field.     

Assessment of 2D/3D numerical modeling for deep dynamic stall experiments

The results of computational fluid dynamics (CFD) simulations in two and three spatial dimensions are compared to pressure measurements and particle image velocimetry (PIV) flow surveys to assess the suitability of numerical models for the simulation of deep dynamic stall experiments carried out on a pitching NACA 23012 airfoil. A sinusoidal pitching motion with a 10° amplitude and a reduced frequency of 0.1 is imposed around two different mean angles of attack of 10° and 15°. The comparison of the airloads curves and of the pressure distribution over the airfoil surface shows that a three-dimensional numerical model can better reproduce the flow structures and the airfoil performance for the deep dynamic stall regime. Also, the vortical structures observed by PIV in the flow field are better captured by the three-dimensional model. This feature highlighted the relevance of three-dimensional effects on the flow field in deep dynamic stall.     

波纹管式抛撒系统能量转换装置动态响应分析

摘要：采用LS-DYNA非线性动力学有限元程序,对某抛撒机构中的能量转换核心装置—波纹管在均布内压作用下的动态膨胀过程进行了数值分析,获得了波纹管动态响应规律;系统的考察了各种因素对波纹管的变形模式及其应力应变变化规律的影响;模拟了波纹管在内部压力和外围子弹群等共同作用下的耦合变形运动过程,对内弹道抛撒全过程进行了模拟,获得了波纹管耦合变形规律和子弹抛撒特性。模拟计算结果与试验现象基本一致。     

Electrorheologial properties of hematite/silicone oil suspensions under DC fields

Electrorheological (ER) fluids composed of α-Fe₂O₃ (hematite) particles suspended in silicone oil are studied in this work. The rheological response has been characterized as a function of field strength, shear rate and volume fraction. Rheological tests under DC electric fields elucidated the influence of the electric field strength, E, and volume fraction, ϕ, on the field-dependent yield stress, τ_y. It was found that this quantity scales with E and ϕ with a linear and parabolic dependence, respectively. The viscosities of electrified suspensions were found to increase by several orders of magnitude as compared to the unelectrified suspension at low shear rates, although at high-shear rates hydrodynamic effects become dominant and no effects of the electric field on the viscosity are observed. The work is completed with the analysis of microscopic observations of the structure acquired by the ER fluid upon application of a constant electric field. Electrohydrodynamic convection is found to be the origin of the ER response rather than the commonly admitted particle fibrillation. This fact can provide an explanation to the relationship between yield stress and electric field strength as well as the pattern of periodic structures observed in the measurement geometries.     

Electrorheology of dielectric liquids

Dielectric liquids that show striking electrorheological (ER) effects are formulated by controlling the conductivity. Although the viscosity is increased on the application of a d.c. field, the flow of electrified fluids is Newtonian in the plain electrodes with smooth surfaces. When the liquids are sandwiched between the electrodes with flocked fabrics, the viscosity behavior is converted from Newtonian to shear-thinning flow. In electric fields, the convective flow is induced over the system due to the electrohydrodynamic(EHD) effect. The interactions between EHD convection and external shear give rise to the additional energy dissipation and in turn the increase in viscosity. The ER effects of simple liquids are very attractive in application to new fluid devices.     

THE DYNAMIC BEHAVIORS OF VISCOELASTIC PIPE CONVEYING FLUID WITH THE KELVIN MODEL

Based on the differential constitutive relationship of linear viscoelastic, material, a solid-liquid coupling vibration equation for viscoelastic pipe conveying fluid is derived by the D'Alembert's principle. The critical flow velocities and natural frequencies of the cantilever pipe conveying fluid with the Kelvin model (flutter instability) are calculated with the modified finite difference method in the form of the recurrence formula. The curves between the complex frequencies of the first, second and third mode and flow velocity of the pipe are plotted. On the basis of the numerical, calculation results, the dynamic behaviors and stability of the pipe are discussed. It should be pointed out that the delay time of viscoelastic material with the Kelvin model has a remarkable effect on the dynamic characteristics and stability behaviors of the cantilevered pipe conveying fluid, which is a gyroscopic non-conservative system.     

Nonlinear vibration of a rotating cantilever beam in a surrounding magnetic field

The nonlinear vibrations of a rotating cantilever beam made of magnetoelastic materials surrounded by a uniform magnetic field are investigated. The kinetic energy, potential energy and work done by the electromagnetic force are obtained. A nonlinear dynamic model, based on the Hamilton principle, which includes the stretching vibration and bending vibration is presented. The Galerkin method is adopted to discretize the dynamic equations. The proposed method is validated by comparison with the literature. The nonlinear behaviors of the responses are studied. Then simulations for different kinds of magnetic field are conducted. The effects of magnetic field parameters, including the amplitude, plane angle, spatial angle and time-varying frequency, on the dynamic behaviors of the stretching motion and bending motion are investigated in detail. The results illustrate that the interaction effects between the rotating cantilever beam and the magnetic field will increase the vibration amplitude and fluctuation of the beam. In particular, we found that: collinear magnetic fields with equal amplitude lead to the same dynamic responses; the amplitude of magnetic field intensity increases the dynamic responses remarkably; the response amplitude changes nonlinearly with the plane angle and spatial angle of the magnetic field; and the increase of time-varying frequency enhances dynamic responses of the rotating cantilever beam.     

电流变液的性能及其应用研究

简要介绍电流变液的研究进展，详细介绍了有关电流变液及其性能的研究，具体介绍了电流变技术在旋转机械转子系统、汽车发动机支座和悬架系统振动控制中的应用，概要介绍和分析了电流变液在其它方面的应用以及对电流变技术发展的展望．