題目 1：Lattice-Boltzmann lattice-spring simulations of flexibility and inertial effects on deformation and cruising reversal of self-propelled flexible swimming bodies

題目2：A model of studies of the effect of bending of microvilli of Leukocyte on its adhesion

報告人：Prof. Dewei Qi（Western Michigan University）

時間：2017年6月9日下午2:30

地點：明故宮校區C12-619

主辦單位：國際合作交流處、科協、航空宇航學院

Abstract 1：

    A lattice-Boltzmann lattice-spring method is employed to simulate cruise dynamic behaviors of self-propelled flexible swimming bodies at finite Reynolds numbers in a three-dimensional space. In simulations, the leading edge of the swimmer plunges in the vertical direction and generates a thrust force, which drives the swimmer to move in the horizontal direction freely. To investigate the effect of rigidity and inertia on cruising speed, power coefficient, propulsive efficiency, and deformation are computed while the rigid and inertia are varied at different levels. It is demonstrated that at a given Reynolds number, the cruising forward speed increases as the rigidity decreases from a high level. The forward speed increases continuously and arrives at a maximum as the rigidity reduces to an intermediate level. However, the forward cruise speed decreases when the rigidity continuously decreases. When the rigidity further reduces to a level lower than a critical value, the cruise reverses its direction and the swimmer moves backward. In this study, it is revealed that a snake-shaped two-curved swimming body due to large deformation induces two vortices and their “sucking” effect is responsible for the backward cruise while the reaction force of sweeping motion of one-curved swimming body causes the forward cruise. It is also found that the forward cruise may become backward as the inertia exceeds a critical level, suggesting that the inertia has a significant impact on the cruising direction reversal. It is revealed that two swimmers in a tandem configuration have one equilibrium separating distance, associated with the reverse Karman vortex street, which is independent of initial distances.

Abstract2：

    In 1992, Hammer and Apte presented a numerical approach, Adhesive Dynamics (AD), for simulation of leukocyte adhesion. This method uses the stochastic Monte Carlo Method and introduces the formation and dissociation kinetic rates measured by experiments to simulate the formation and rupture of a bond between the receptor and the ligand (e.g. PSGL-1 and P-selectin). Late, Jadhav et al. first demonstrated the deformation of leukocytes in the adhesion process in a three-dimensional simulation. However, the property of bending of the microvilli, fingerlike projections on the surface of leukocytes, was not considered in any simulation studies at that time. The existing leukocyte models, however, still neglect the bending of microvilli and the hydrodynamic forces on bending. In this study, we present an advanced leukocyte model which uses the lattice spring model (LSM) to simulate the bending of the microvilli. The model is developed through a combination of the lattice Boltzmann method (LBM), coarse-grained deformable cell model, immersed boundary method (IBM), lattice spring model, and Monte Carlo Adhesive Dynamics. The influences of the hydrodynamic force and elastic bending of microvilli on the deformation, contact area, number of adhesion bonds, and adhesion bond force of leukocytes during a rolling process are investigated and discussed.

Biography：

    DeweiQi is a Professor in the Department of Chemical and Paper Engineering, Western Michigan University. He received her Ph.D. degree in Physics from Universityof Waterloo, Canada,in 1991.After graduation, he worked in Pulp and Paper Research Institute of Canada, Georgia Institute of Technology, Institute for Computer Applications in Science & Engineering NASA, National Institute of Aerospace and Air Force Base. In 1995, he joined Western Michigan University, and was promoted to Full Professor in 2008.Professor Qi has published over 80 scientific articles,and provided 10 invited oral presentations in international conferences. Now he is the member of TAPPI, APS, AICHE and AIAA.