2021 Fiscal Year Research-status Report
Development of a particle simulator for realistic clayey particles considering mechanical and electro-chemical forces - demystify microscopic mechanisms inside the 'house of cards' at micrometer scale
| Project/Area Number |
21K04265
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| Research Institution | Japan Agency for Marine-Earth Science and Technology |
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Principal Investigator |
CHEN JIAN 国立研究開発法人海洋研究開発機構, 深海資源生産技術開発プロジェクトチーム, 特任研究員 (20640931)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Keywords | discrete element method / clayey particles / plate-like geometry / unit quaternions |
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| Outline of Annual Research Achievements |
The purpose of this project is to develop a particle simulator for realistic clayey particles. The discrete element method (DEM) is widely recognized as a powerful tool for investigating the complex dynamics of granular materials from particle-scale interactions. Most DEM simulations are built on round particles, which deviate from actual particle shapes in reality. The particle shapes at microscopic scale play an important role in the macroscopic response of the granular assemblies. There are granular particles with platelike geometry where the thickness dimension is negligible. Clayey particles, which are importance in everyday life, are prominent example of plate-like granular particles. Such plate-like geometry has a very large surface to volume ratio which is difficult to model by spheres or cluster of spheres. Though polyhedral DEM is available, the overlap geometry computation would suffer numerical difficulties due to the vanishing of thickness dimension. Thus, it is worthy developing a new plate DEM for granular materials such as clayey particles. As a first step of this research project, we put forward the formulations for the kinematics of plate DEM using unit quaternions for the description of the angular degree of freedom. In addition, the angular motion is solved in a body-fixed rather than a space-fixed reference frame. Based on this formulation for plate-particle kinematics, the simulations have been developed and demonstrated for the rotation of a collection of plate particles under the conservation of angular momentum without external torque.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project is progressing smoothly as planned for the reasons as follows: we have settled with a polygonal geometry in 3D to represent plate-like particle shape, and we have derived a unit-quaternion based kinematics for the rotation of such plate-like particle shape. Further, we have implemented the kinematics of such particles as a prototype DEM program using MATLAB in a computationally efficient way. In the next year, this prototype program will be extended with particle interactions.
To represent the plate-like geometry of typical clay particles, we decided to use polygons in the DEM code with a small extension in the orthogonal direction instead of polyhedra. In comparison with a polyhedron, using an extended polygonal DEM particle can simplify the overlap computation considerably.
The rotation of a plate-like particle requires proper treatment in DEM simulations. Unlike spheres or disks, the rotation of such a particle is nonlinear and the moment of inertial tensor is time-varying. To describe the rotation properly, we have chosen unit quaternions over Euler angles. Using unit quaternions and their time derivatives, we can avoid singularities which are common in angle-based formulations. Further, for this plate-like geometry, an alternative formulation for rotation is derived for a body-fixed reference frame. Using the body-fixed reference frame, only the torque has to be transformed from the space-fixed reference frame, requiring much less computational effort.
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| Strategy for Future Research Activity |
As the next step, the interactions between particles have to be modeled. Based on the study of clayey particles, not only the mechanical forces but also the electro-chemical forces play important roles in their particle dynamics. This is because the surface of the clayey particles are often negatively charged while their edges are positively charged or neutral depends on the properties of the environmental fluid. To model the mechanical forces, we will follow the treatment of DEM particles, using the overlap geometry to determine the magnitude and direction of contact forces. For the non-contact electro-chemical forces, the interactions between the positive and negative electrical charges will be computed. If such electro-static forces are not strong enough to cause flocculation of clayey particles, additional attractive mechanisms for adhesion has to be explored and implemented.
When the kinematics and dynamics are both ready for the simulator, we will move to the validation phase. Consolidation experiment is considered to check whether the difference between virgin compression and recompression can be reproduced and to check how the void spaces vary due to the change of ambient chemical conditions, i.e., pH values and electrolyte concentrations (which affect the charge on particles). Other physical tests will also be conducted to validate the developed simulator.
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| Causes of Carryover |
Due to Covid situation, plans for travelings for conferences and for inviting experts were not carried out.
In the next fiscal year, with the improvement of pandemic situation and vaccination, academic travelings for presentations and for discussions will be conducted more actively with surplus. Also a grade up (like increasing memory) of the planed workstation for simulation is considered.
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Research Products
(6 results)
