Research Activities
- Publication List [Research Activity Database]
Recent Studies
1. Direct numerical simulations (DNS) of microswimmers
Dispersed systems of microscale swimmers (microswimmers), such as microorganisms, are of interest not only in science as a typical application of nonequilibrium statistical mechanics, but also in engineering, for example, as a drug delivery system or as an active viscoelastic fluid. It is known that globally organised collective motion can occur in a microswimmer dispersion system without a coordination mechanism to align the direction of motion of individual swimmers. Such collective motion is a consequence of complex hydrodynamic interactions between swimmers and cannot be easily predicted from the motion of individual particles. We have developed an original numerical method that can simulate the motion of microswimmers and the surrounding fluid as a coupled particle-fluid problem in a consistent, efficient and accurate manner. For the simulation of microswimmers, a spherical particle model called the squammer model is widely used in existing studies, which we have also used. Microswimmers can be broadly classified into three swimming modes, the Pusher type, the Puller type and the Neutral type, which lies between the two, based on the characteristics of the flow field created in the surrounding area during swimming. The squammer model can freely simulate these swimming forms by changing the values of the model parameters described below. In this laboratory, direct numerical simulations of microswimmers are carried out, in which the specific collective motion of microswimmers between parallel plates, the motion of microswimmers in complex fluids and rotational motion (rotlet) are explicitly taken into account.
2. Direct numerical simulations (DNS) of colloidal dispersions
We have developed a unique mesoscale method for simulating colloidal dispersions. Our program has been released as a colloid simulator KAPSEL, which enables us to perform successful DNS simulations for neutral and charged colloidal dispersions. We have applied this method to analyze the dynamics of self-propelled particles for a schematic model of micro-organisms.
3. Development of multiscale simulation method to predict polymeric liquid flows and its applications to industrial polymer processing
To manufacture more sophisticated polymeric products, it is needed to predict and control flow behaviors of polymeric liquids in industrial processes. In general, it is difficult to do this for polymeric chains with a molecular weight distribution and with various types of polymer architecture, because a microscopic state of polymer chains such as an orientation and entanglements of constituent polymer chains does strongly influence on the macroscopic flow behavior. To deal with macro-scopic flow behaviors and micro-scopic state of polymer chains simultaneously, it has been desired strongly to establish a multiscale simulation (MSS) method that enables to bridge between the two different spatial scales. For this purpose, we are addressing to develop the MSS method and to apply it to various industrial polymer processing. (See Fig.1: application of the MSS method to a polymer melt spinning process).
Fig. 1. Configuration of polymer chains at four points (a)-(d) on a thread of a polymer melt spinning process. Red: longer polymer chain, Black: shorter polymer chain.
4. Physical modeling of biological tissues
Inspired by recent studies on the model of crawling and dividing cells [Coburn et al., Phys. Biol. 10, 046002 (2013); Basan et al., PNAS 110, 2452 (2013).], we developed a unique particle-based minimal model for crawling and dividing cells on substrate (see Fig. 2). It mimics a real mechanics of migrating/dividing cells with the mechanisms of the contact inhibition of locomotion (CIL) and the contact inhibition (CI) of cell division in a straightforward way. The present model has been applied to simulate the dynamics of growing colony composed of active cells. Some basic properties seen in real growing colonies have been successfully reproduced. The true mechanism behind such complex biological systems will be discussed in physical context.
