GOALI: Multiscale Modeling of Electro- and Magnetorheological Fluids

摘要-0424087电流变和磁流变（ER和MR）流体是颗粒悬浮液，其流变特性分别被电场和磁场显著改变。所施加的领域也改变了悬浮液的微观结构，导致在静态悬浮液中的字段方向取向的颗粒柱的形成，并在剪切悬浮液中的流动方向取向的集中的颗粒条纹的形成。这些结构变化与流变现象密切相关。已知颗粒柱的形成会引起显著的流变学变化。条纹的出现与瞬态流变响应的开始相关，其中剪切应力随着条纹聚结、粗化和致密化而缓慢增加。ER和MR流体正在开发应用，如减震器，离合器和制动器，MR应用最近达到商业化。理解和建模的瞬态结构和流变行为是至关重要的设计，优化和控制的ER和MR流体和设备。粒子级模拟对于理解粒子性质、相互作用和宏观行为之间的关系很有价值。然而，这些方法在计算上是昂贵的，并且因此不适合于对整个设备的行为进行建模。必须开发其他建模策略来补充粒子级模拟并克服其固有的局限性。我们发展了电流变悬浮液结构演化的连续描述，其特征在于随时间和位置变化的颗粒体积分数_（x; t）。粒子通量通过动量平衡与粒子对应力的贡献有关。使用这种双流体的方法，一个预测的模式实验观察到的列形成在静止的悬浮液中，和条纹形成剪切悬浮液-没有计算费用以下的个别粒子的运动。虽然这种连续介质模型可以成功地再现结构演化的某些特征，但对本构行为的假设限制了其预测能力。最值得注意的是，假设一种形式的静电应力适合于各向同性悬浮液排除了估计的场致剪切应力，从而相关的流变瞬变;和忽略非局部极化给小的洞察到长时间的瞬变。所提出的工作的主要目标是联合收割机的两种建模方法的优势，以获得一个多尺度的描述ER/MR流体和设备，克服我们以前的连续建模工作的局限性。我们将采用粒子级模拟（即，Stokesian动力学模拟），以确定用于连续介质模型的颗粒应力和颗粒通量的适当本构行为。采用这种本构行为将使我们能够从连续介质的角度来探讨结构和剪切流变的演变。我们还将扩展一个自洽场模型的电流变流体模型的非局部极化的贡献，在连续模型，以描述长时间的瞬态现象。拟议的工作将产生一个完整的连续描述的流变学和质量传输的ER和MR流体，可用于设计，优化和控制的ER和MR流体和设备。 模拟研究将由克林根贝格、莫里斯和学生进行，并继续与通用汽车公司的乌利茨尼协商。验证实验将在UW和GM进行。通用汽车公司还将提供离合器性能的实验结果，从测量离合器试验台在通用汽车公司。智力的优点和更广泛的影响。提出的工作将特别有利于剪切电流变和磁流变器件的设计，优化和控制提供了一个模型的流变学和质量输运。这些信息是必要的，因为颗粒传输似乎是无处不在的剪切ER和MR流体，并影响表观流变学。更一般地说，所提出的工作将有利于悬浮力学研究，因为我们进一步发展连续介质的方法来描述悬浮液的流动。 这项工作的更广泛的影响包括通过培训本科生和研究生在这项工作的技术建模方面的教育组成部分，以及实验技术。这项工作的结果将通过向评审期刊提交手稿和在科学会议上发表演讲的方式提供给科学界。

ABSTRACT - 0424087Electro- and magnetorheological (ER and MR) fluids are particulate suspensions whose rheological properties are dramatically altered by electric and magnetic fields, respectively. The applied fields also alter the suspension microstructure, causing the formation of particulate columns oriented in the field direction in quiescent suspensions, and the formation of concentrated particulate stripes oriented in the flow direction in sheared suspensions. These structural changes are intimately connected to the rheological phenomena. The formation of particulate columns is known to cause the dramatic rheological changes. The appearance of stripes is associated with the onset of a transient rheological response, where the shear stress slowly increases as the stripes coalesce, coarsen, and densify. ER and MR fluids are being exploited in the development of such applications as shock absorbers, clutches, and brakes, with MR applications recently reaching commercialization. Understanding and modeling the transient structural and rheological behavior is crucial for the design, optimization and control of ER and MR fluids and devices. Particle-level simulations have been valuable for understanding the relationships between particle properties, interactions, and macroscopic behavior. However, these approaches are computationally expensive, and thus ill-suited for modeling the behavior of an entire device. Other modeling strategies must be developed to complement particle-level simulations and overcome their inherent limitations. We have developed a continuum description of the structure evolution in ER suspensions, as characterized by the time and position-dependent particle volume fraction _(x; t). The particle flux is related to the particle contribution to the stress via a momentum balance. Using this two-fluid approach, one predicts the patterns observed experimentally-column formation in quiescent suspensions, and stripe formation in sheared suspensions- without the computational expense of following the motion of individual particles. Although this continuum model can successfully reproduce certain features of structure evolution, assumptions employed for the constitutive behavior limit its predictive power. Most notably, assuming a form for the electrostatic stress appropriate for an isotropic suspension precludes an estimate for the field-induced shear stress and thus the associated rheological transients; and the neglect of nonlocal polarization gives little insight into the long-time transients. The main goal of the proposed work is to combine the strengths of the two modeling approaches to obtain a multiscale description of ER/MR fluids and devices, overcoming the limitations of our prior continuum modeling effort. We will employ particle-level simulations (i.e., Stokesian dynamics simulations) to determine the appropriate constitutive behavior for particle stress and particle flux for use in the continuum model. Employing this constitutive behavior will allow us to probe both the evolution of structure and shear rheology from a continuum perspective. We will also extend a selfconsistent field model of ER fluids to model nonlocal polarization contributions in the continuum model, in order to describe the long-time transient phenomena. The proposed work will yield a complete continuum description of the rheology and mass transport in ER and MR fluids that can be used in the design, optimization and control of ER and MR fluids and devices. Simulation studies will be performed by Klingenberg, Morris, and students, with continuing consultation with Ulicny at General Motors. Experiments for verification will be performed at both UW and GM. GM will also provide experimental results for clutch performance from measurements on a clutch test rig at GM.Intellectual Merit and Broader Impact. The proposed work will specifically benefit the design, optimization and control of sheared ER and MR devices by providing a models for both the rheology and mass transport. Such information is necessary as particle transport appears to be ubiquitous in sheared ER and MR fluids, and impacts the apparent rheology. More generally, the proposed work will benefit suspension mechanics research as we further develop continuum methods for describing the flow of suspensions. The broader impact of this work includes an educational component through the training of undergraduate and graduate students in the technical modeling aspects of this work, as well as the experimental techniques. Results from this work will be available to the scientific community through submission of manuscripts to refereed journals, and presentations at scientific meetings.