• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >Direct simulation of flexible particle suspensions using lattice-Boltzmann equation with external boundary force.
【24h】

Direct simulation of flexible particle suspensions using lattice-Boltzmann equation with external boundary force.

机译：使用带有外部边界力的晶格-玻尔兹曼方程直接模拟柔性颗粒悬浮液。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Determination of the relation between the bulk or rheological properties of a particle suspension and its microscopic structure is an old and important problem in physical science. In general, the rheology of particle suspension is quite complex, and the problem becomes even more complicated if the suspending particle is deformable. Despite these difficulties, a large number of theoretical and experimental investigations have been devoted to the analysis and prediction of the rheological behavior of particle suspensions. However, among these studies there are very few investigations that focus on the role of particle deformability.;A novel method for full coupling of the fluid-solid phases with sub-grid accuracy for the solid phase is developed. In this method, the flow is computed on a fixed regular 'lattice' using the lattice Boltzmann method (LBM), where each solid particle, or fiber, is mapped onto a Lagrangian frame moving continuously through the domain. The motion and orientation of the particle are obtained from Newtonian dynamics equations. The deformable particle is modeled by the lattice-spring model (LSM). The fiber deformation is calculated by an efficient flexible fiber model. The no-slip boundary condition at the fluid-solid interface is based on the external boundary force (EBF) method. This method is validated by comparing with known experimental and theoretical results.;The fiber simulation results show that the rheological properties of flexible fiber suspension are highly dependent on the microstructural characteristics of the suspension. It is shown that fiber stiffness (bending ratio BR) has strong impact on the suspension rheology in the range BR 3. The relative viscosity of the fiber suspension under shear increases significantly as BR decreases. Direct numerical simulation of flexible fiber suspension allows computation of the primary normal stress difference as a function of BR. These results show that the primary normal stress difference has a minimum value at BR ∼ 1. The primary normal stress differences for slightly deformable fibers reaches a minimum and increases significantly as BR decreases below 1. The results are explained based on the Batchelor's relation for non-Brownian suspensions. The influence of fiber stiffness on the fiber orientation distribution and orbit constant is the major contributor to the variation in rheological properties. A least-squares curve-fitting relation for the relative viscosity is obtained for flexible fiber suspension. This relation can be used to predict the relative viscosity of flexible fiber suspension based on the result of rigid fiber suspension.;The unique capability of the LBM-EBF method for sub-grid resolution and multiscale analysis of particle suspension is applied to the challenging problem of platelet motion in blood flow. By computing the stress distribution over the platelet, the "blood damage index" is computed and compared with experiments in channels with various geometries [43]. In platelet simulation, the effect of 3D channel geometry on the platelet activation and aggregation is modeled by using LBM-EBF method. Comparison of our simulations with Fallon's experiments [43] shows a similar pattern, and shows that Dumont's BDI model [40] is more appropriate for blood damage investigation. It has been shown that channels with sharp transition geometry will have larger recirculation areas with high BDI values. By investigating the effect of hinge area geometry on BDI value, we intend to use this multiscale computational method to optimize the design of Bileaflet mechanical heart valves.;Both fiber simulations and platelet simulations have shown that the novel LBM-EBF method is more efficient and stable compare to the conventional numerical methods. The new EBF method is a two-way coupling method with sub-grid accuracy which makes the platelet simulations possible. The LBM-EBF is the only method to date, to the best of author's knowledge, that can simulate suspensions with large number of deformable particles under complex flow conditions. It is hoped that future researchers may benefit from this new method and the algorithms developed here.
机译：确定颗粒悬浮液的体积或流变性质与其微观结构之间的关系是物理科学中一个古老而重要的问题。通常，颗粒悬浮液的流变性非常复杂，并且如果悬浮颗粒是可变形的，则问题甚至变得更加复杂。尽管存在这些困难，但是大量的理论和实验研究已经致力于颗粒悬浮液的流变行为的分析和预测。然而，在这些研究中，很少有研究集中在颗粒变形性的作用上。研究了一种新的方法，以固相亚网格精度完全耦合流固相。在这种方法中，使用晶格玻尔兹曼方法（LBM）在固定的规则“晶格”上计算流量，其中每个固体粒子或纤维被映射到连续移动通过该域的拉格朗日框架上。粒子的运动和方向是从牛顿动力学方程获得的。通过晶格弹簧模型（LSM）对可变形粒子进行建模。纤维变形通过有效的柔性纤维模型计算。流体-固体界面的防滑边界条件是基于外部边界力（EBF）方法的。通过与已知的实验和理论结果进行比较，验证了该方法的有效性。纤维模拟结果表明，柔性纤维悬浮液的流变性能高度依赖于悬浮液的微观结构特征。结果表明，在BR <3的范围内，纤维刚度（弯曲比BR）对悬浮液的流变性有很大影响。随着BR的降低，纤维悬浮液的相对粘度在剪切作用下显着增加。柔性纤维悬架的直接数值模拟允许计算作为BR的函数的主要法向应力差。这些结果表明，主法向应力差在BR〜1处具有最小值。轻微变形的纤维的主法向应力差达到最小值，并且随着BR降低到1以下而显着增加。基于非勒索的Batchelor关系对结果进行解释-布朗悬架。纤维刚度对纤维取向分布和轨道常数的影响是流变性质变化的主要因素。对于柔性纤维悬浮液，获得相对粘度的最小二乘曲线拟合关系。该关系可用于基于刚性纤维悬浮液的结果来预测柔性纤维悬浮液的相对粘度。； LBM-EBF方法用于子网格分辨率和颗粒悬浮液多尺度分析的独特功能被应用于具有挑战性的问题血流中血小板运动的变化。通过计算血小板上的应力分布，可以计算出“血液损伤指数”，并与各种几何形状的通道中的实验进行比较[43]。在血小板模拟中，使用LBM-EBF方法来模拟3D通道几何形状对血小板激活和聚集的影响。我们的模拟与Fallon的实验[43]的比较显示出相似的模式，并且表明Dumont的BDI模型[40]更适合于血液损伤研究。已经表明，具有尖锐过渡几何形状的通道将具有较大的再循环区域，并具有较高的BDI值。通过研究铰链区域几何形状对BDI值的影响，我们打算使用这种多尺度计算方法来优化Bileaflet机械心脏瓣膜的设计。纤维模拟和血小板模拟均表明，新颖的LBM-EBF方法效率更高，并且与常规数值方法相比，稳定性更高。新的EBF方法是具有子网格精度的双向耦合方法，这使得血小板模拟成为可能。据作者所知，LBM-EBF是迄今为止唯一的一种可以在复杂的流动条件下模拟具有大量可变形颗粒的悬浮液的方法。希望将来的研究人员可以从这种新方法和此处开发的算法中受益。

著录项

  • 作者

    Wu, Jingshu.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 146 p.
  • 总页数 146
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号