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Molecular Gas Flow LaboratoryAssociate Professor Shigeru Yonemura
Study of Gas Film Lubrication Appearing at the Micro/NanoscaleIt was reported that the coefficient of friction decreases drastically when a partly polished
diamond-coated surface slides on a rotating metallic disk. In this experiment, the sliding was
noiseless, which indicates that the sliding mechanism is the gas film lubrication, and the
diamond-coated surface is suspended in the air. In this study, we focused on and investigated the
micro/nanoscale gas flow between both surfaces, and clarified the floating mechanism of the
diamond-coated surface by performing numerical simulations and by theoretical consideration.
Results showed that the high gas pressure was generated by microasperities on the surface, and then
gas lubrication was achieved. This result indicates that if the fine structure on the surface is the same
with this simulation, then high gas pressure will be generated in the same way even if the surface
material is not diamond. This pressure generation becomes considerable when spacing between both
surfaces is reduced from microscale to nanoscale, and it disappears at macroscale. This gas
lubrication phenomenon appears only at the micro/nanoscale. Results of this study are expected to
spur development of a new gas lubrication system.
Fig. 1 Computational domain. Fig. 2 Pressure distribution
(u = 10 m/s, l1 = l2 = 11.52 μm, d = 1.44 μm)
Study of self-bias potential in the radio frequency magnetron plasmaRadio frequency (RF) magnetron discharge is widely used in fabrication processes, such as
sputtering, used for semiconductor devices. During sputtering, high-energy ions accelerated by an
electrical field hit the target and sputter atoms from the target. Those sputtered atoms are deposited
on the substrate, thereby producing a thin film. Ions cannot follow the RF electric field. They move
in accordance with the time-averaged electric field. Consequently, they are accelerated by the
potential difference between the time-averaged plasma potential and the self-bias potential appearing
on the target. The sputtering rate depends strongly on the energy of incident ions. Therefore, it is
important to elucidate the characteristics of the self-bias potential. Little is known about the self-bias
potential in RF magnetron discharge, although much knowledge related to self-bias potential in RF
capacitively-coupled plasmas without magnetic fields has been obtained experimentally and
theoretically. This study clarified the discharge structure and characteristics of the self-bias potential
in the RF magnetron discharge.
Study of microplasmaPlasma-enhanced chemical vapor deposition (PECVD) is used to fabricate thin films, which are
necessary to produce electronic devices such as liquid-crystal displays and solar cells. Along with
the recent miniaturization of devices, as seen in μ-TAS or MEMS, microplasma technology is
attracting attention. This study examined the SiH4 microplasma structure, as generated by DC
electrodes arranged on both ends of the glass tube, by performing self-consistent PIC/MC
simulations. Strong interaction was observed between the tube wall and the plasma bulk.
Most electrons were generated near the sheath edge along the tube surface. This structure
differs greatly from that of a traditional plasma reactor. Results show that the electron number
density becomes higher and the discharge starting voltage decreases when the tube radius is reduced
from 1.5 mm to 0.5 mm. We clarified the mechanisms of these phenomena theoretically.
Relevant journal papers
S. Yonemura and K. Nanbu, DC Self-bias Voltages in Radio Frequency Magnetron
Discharges, Thin Solid Films, Vol. 506-507, pp. 517-521 (2006).
L. Tong, S. Yonemura, H. Takana and H. Nishiyama, Effect of Configuration on
Microdischarge Structure in a Narrow Channel, Physics Letters A, Vol. 371, Issues 1-2, pp.
140-144 (2007).
S. Yonemura, M. Yamaguchi, T. Takeno, H. Miki and Toshiyuki Takagi, Effect of Micro Gas
Flow on Low Friction Properties of Diamond Coating with Partly Polished Surface, AIP
Conference Proceedings, Vol. 1084, pp. 1153-1157 (2008).
Related research budget
Grant-in-Aid for Young Scientists (B) (2005–2007), ¥2,500,000.
Grant-in-Aid for Scientific Research (C) (2008–2010), ¥4,550,000.
Grant-in-Aid for Scientific Research (C) (2011–2013), ¥5,330,000.
Molecular Heat Transfer LaboratoryProfessor Taku Ohara, Senior Assistant Professor (2011.4-)/Assistant Professor (2007.4–2011.3)/
Research Associate (2007.1–2007.4) Gota Kikugawa
Molecular Dynamics Mechanism Governing Thermal Transport Characteristics of Polymer Liquids and Soft Matter
Elucidation of molecular dynamics (MD) mechanisms that govern thermal energy transport in liquids gives an essential answer to the question of why the liquid exhibits this thermal conductivity. It also gives the required feature of molecules that exhibit desired properties, which leads to the design of thermal transport phenomena and the thermal media. In this study, contributions of inter- and intramolecular energy transfer to thermal energy transport in saturated liquid alkanes were evaluated quantitatively based on a newly derived MD expression of heat conduction flux. The results showed that the contribution of intramolecular energy transfer increases as the molecular chain length increases, and is a dominant factor at a molecular weight of several hundreds. These findings suggest that a peculiar anisotropic heat conduction occurs in soft matter formed by self-organization of polymer molecules with a certain orientation. This was demonstrated by a MD simulation of lipid membrane in water. It was found that the cross-membrane thermal conductivity is five times higher than the in-plane one.
Transport Properties at the Interface of Self-Assembled MonolayersSelf-assembled monolayer (SAM) and other organic thin materials are being studied extensively
as novel surface-modification techniques. An essential understanding of heat and mass transportproperties over such interfaces is of critical importance in various applications to nano- and
(a) (b)
Fig. 2 A snapshot of the alkanethiolate SAM and water solvent interface obtained from the molecular dynamics simulation. Figures (a) and (b) represent the methyl-terminated SAM (hydrophobic surface) and hydroxyl-terminated SAM (hydrophilic), respectively.
(a)
(b)
Fig. 1(a) Contribution of intramolecular energy transfer to heat conduction flux as a response to molecular chain length of liquid alkanes. (b) Lipid bilayer membrane formed by self-organization of chain lipid molecules.
biotechnologies. In this study, we performed molecular dynamics simulations of typical SAM interfaces with various solvents in order to investigate heat transfer characteristics in detail. As a result, it was found that the SAM modification enables a decrease of thermal resistance at the organic solvent–gold interface. Moreover, we discussed the effect of an affinity between SAM and solvent on thermal boundary resistance and the microscopic mechanisms of peculiar heat transfer inside the SAM layer, which has a highly ordered molecular orientation.
Mass Transport Characteristics in the Vicinity of Solid-Liquid InterfacesAdsorption and desorption of solute and
solvent molecules to/from a solid-liquid interface, which are influenced by the liquid structure in the interface region and mass transport characteristics, are governing factors in the processes of chemical treatment of nanostructures and dynamic coating. In this study, the processes of surface treatment of SiO2 and alcohol substitution of water are simulated by MD and the free energy distribution for transport of molecular species is measured. Based on these results, mass transport characteristics in liquids in the vicinity of solid surfacesand influences of molecular-scale structure in the liquids are analyzed.
Relevant journal papersD. Torii, T. Ohara and K. Ishida, Molecular scale mechanism of thermal resistance at solid-liquid interfaces (Influence of interaction parameters between solid and liquid molecules), Transactionsof ASME, Journal of Heat Transfer, Vol. 132, 012402 (2010).
T. Nakano, G. Kikugawa and T. Ohara, A molecular dynamics study on heat conduction characteristics in DPPC lipid bilayer, Journal of Chemical Physics, Vol. 133, 154705 (2010).
T. Ohara, Tan C.-Y., D. Torii, G. Kikugawa and N. Kosugi, Heat conduction in chain polymer liquids: Molecular dynamics study on the contributions of inter- and intramolecular energy transfer, Journal of Chemical Physics, Vol. 135, 034507 (2011).
Relevant research budgetsGrant-in-Aid for Scientific Research (C) (2006–2008), ¥3,500,000Grant-in-Aid for Scientific Research (C) (2009–2011), ¥4,680,000, and others
AwardsJSME Young Engineers Awards, Gota Kikugawa (2009.4.7)JSME Medal for Outstanding Paper, Taku Ohara (2009.4.7)JSME Thermal Eng. Division Awards for Outstanding Achievement, Taku Ohara (2011.3.31)Japan Society of Thermophysical Properties Best Paper Awards, Taku Ohara and Gota Kikugawa(2011.11.22)
(a)
(b)
Fig. 3(a) Measurement of free energy by the analysis of IPA molecules immersed at a SiO2(011)-water interface. (b) Substitution of water by IPA in the vicinity of a SiO2 surface.
Nanoscale Interfacial Flow LaboratoryAssociate Professor Takashi Tokumasu
Development of Next Generation Fuel Cell System by Large-scale Molecular Dynamics Simulations
We analyze the transport phenomena of reactant materials in a polymer electrolyte fuel cell (PEFC) using large scale molecular dynamics simulations with a supercomputer to develop materials or systems in which the reactant materials can transport efficiently. Proton, oxygen and water, as the reactant materials, must be transferred to electrode catalysts efficiently to improve the PEFC efficiency. These materials, however, transfer through flow fields of which the size is of the order of nanometer or micrometer. Therefore the flow characteristics cannot be obtained throughconventional continuum theory. In this study, we simulate the nanoscale transport phenomena in fuel cells by molecular dynamics and obtain the key factor to ascertain the characteristics of these transport phenomena to construct the design concept of a new system or material that has a structure suitable for the transport property of these reactant materials. The research is collaborative withvarious companies or research institutes. We play our role in helping Japan to establish the technology of this field earliest in the world.
0.04 0.06 0.08 0.10 0.12 0.14
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Initial Translational Energy
DissociationProbability[-]
: Pt-Fix: T=0 K: T=300 K
Dissociation phenomena of H2 on Pt catalystOxygen permeability of ionomerin Catalyst Layer
Phase diagram of water in a nano pore of MPL(collaborative research)
Transport properties of nanoscale water droplet in MPL
Proton diffusivity in PEM
Relativeenergy(kcal/mol)
q (Å)
0 1 2 3 4 50
3
6
9
12
15
MSD of H3O+
Time [ps]
MSD[?
2]
Fig. 1. Large-scale molecular dynamics simulations of transport phenomena of materials
through the parts of PEFC.
Development of Simulation Method Considering the Quantum Effect of MoleculesMolecules have quantum effects to a greater or lesser degree. In many cases, the effects
strongly influence flow fields. Regarding the transport phenomena of proton, which determines the
efficiency of fuel cells, for instance, the Grotthus mechanism, in which dissociation and
recombination occurs between a proton and water
molecule, determines the transport ability. Regarding the
thermodynamic properties of liquid hydrogen, the
uncertainty of position of molecule becomes remarkable
because of the light mass of hydrogen atom, and the
phenomenon affects the pressure of liquid hydrogen.
This study was conducted to reproduce real flow
properties by molecular dynamics simulations and to
analyze the influence of the quantum effect on the flow
properties by including quantum effects of molecules in
molecular dynamics simulations.
Relevant journal papers
T. Tokumasu, D. Ito, The Dynamic Effects of Dissociation Probability of H2-Pt(111) System by
Embedded Atom Method, Journal of Applied Physics, Vol. 109, 063509 (2011).
T. Tokumasu, I. Ogawa, M. Koyama, T. Ishimoto, A. Miyamoto, A DFT Study of Bond
Dissociation Trends of Perfluorosulfonic Acid Membrane, Journal of Electrochemical Society,
Vol. 158, B175-B179 (2011).
T. Tokumasu, M.-H. Meurisse, N. Fillot, P. Vergne, A Molecular Dynamics Study of a
Nanoscale Liquid Bridge under Shear, Tribology International, accepted (2012).
Related research budgets
Grant-in-Aid for Scientific Research (B) (2012–2014), ¥19,282,000
New Energy and Industrial Technology Development Organization (NEDO), Strategic
Development of PEFC Technologies for Practical Application, ¥70,161,000
Awards
Japan Electrochemistry Poster Award, Takashi Tokumasu et al. (2008, 3, 30)
Fig. 2. Schematic diagram of liquid
hydrogen by centroid molecular
dynamics simulation.
Biological Nanoscale Reactive Flow LaboratoryProfessor Takehiko Sato
Activation and Inactivation Mechanisms of Cell Viability by Plasma Flow at Atmospheric Pressure
We aim at clarifying the effects of chemical species generated by a plasma flow on cell
viability for the fundamental study and the application of plasma medicine. We have clarified that
hydrogen peroxide among stable chemical species generated by the plasma flow is the main factor
for inactivation of cell viability by analyzing cell survival ratio, morphological observation (Fig. 1),
reactive oxygen species generation in the cells, effects of catalase on cell survival ratio and
comprehensive gene analysis (Fig. 2).
Sterilization and Chemical Transport Mechanisms by Plasma Flow at Atmospheric Pressure
To reduce infection risks posed by new strains of influenza, by nosocomial infection, and so on,
we aim at developing a plasma sterilization device and clarifying the sterilization mechanism. We
have clarified the radical transport in the plasma flow (Fig. 3) by the fluid engineering point and
damage such as potassium leakage and deformation of the E. coli to elucidate sterilization
mechanisms.
Fig. 1. Morphological observation of HeLa cells for the untreated case (a) and the plasma treated case (b).
Fig. 3 Visualization of the plasma flow (a) and emission distribution of the excited N2.
Fig.4 SEM images of E. coli for the untreated case (a) and plasma-treated case (b).
Fig. 2. Scatter plot of the gene expression intensities obtained by the comprehensive gene analysis for the plasma-treated and H2O2-added cases.
Thermal flow Field Analysis of a Gas–Liquid Plasma Flow and Functional Enhancement of Water
To apply medical applications and environmental treatment, we have clarified the thermal flow
field of an atmospheric plasma flow on water because a gas–liquid system is a typical case in many
applications. The gas flow (Fig. 5) and water flow were induced by the plasma. The flow is the main
factor of the chemical transport. We also obtained that oxygen–reduction potential (ORP) decreased
to -150 mV, which is high reduction property by plasma in water.
Fig. 5. Induced gas flow between the electrode and water surface in the air by the plasma flow.
Relevant journal papers
T. Sato, T. Miyahara, A. Doi, S. Ochiai, T. Urayama, T. Nakatani, Sterilization Mechanism for
Escherichia coli by Plasma Flow at Atmospheric Pressure, Applied Physics Letters, Vol. 89,
073902 (2006).
T. Sato, S. Ochiai, T. Urayama, Generation and Transport Mechanisms of Chemical Species by
a Post-Discharge Flow for Inactivation of Bacteria, New Journal of Physics, Vol. 11, 115018
(2009).
T. Sato, M. Yokoyama, K. Johkura, A key inactivation factor of HeLa cell viability by a plasma
flow, Journal of Physics D: Applied Physics, Vol. 44, 372001 (2011).
Related research budgets
Grant-in-Aid for Scientific Research (A) (2009–2011), ¥36,200,000
Grant-in-Aid for Scientific Research (B) (2007–2008), ¥15,600,000
Awards
JSME, Environmental Engineering Division, Research Achievement Award, Professor Takehiko
Sato (2011.6.30)
Patent No. 4902842, “Plasma Generation Method and Plasma Generation Device”, Takehiko Sato
et al. (registered on Jan. 13, 2012)
Complex Flow Systems LaboratoryAssistant Professor Yuka Iga
Professor (–2012.3) Toshiaki Ikohagi
Numerical Analysis of High-speed Droplet ImpactThe soundness of high-speed gas–liquid two-phase fluid systems is sometimes threatened by
flow phenomena. For instance, in a high-pressure vapor flow in a secondary condenser pipe installed at nuclear reactors, erosion of the pipe wall results from high-speed liquid droplets impacting on the wall. In this study, three-dimensional two-phase fluid / solid coupling numerical simulation areperformed for the liquid droplet impact. By introducing a new estimation index which is the elastic impact region, a power index of the relation between erosion volume and the droplet diameter or the impact speed is indicated. The power index of the relation agrees with the existing experimental equitation of erosion prediction. Additionally, the attenuating effect of a thin liquid film on a wall isindicated numerically, in which the maximum pressure and maximum equivalent stress decrease exponentially with increasing liquid film depth.
This study is linked directly to countermeasures against aging degradation of atomic power plants. The results are expected to contribute to the development of fluid system safety evaluation.
(a) Flat solid surface (b) Thin water film surface (c) Wedged surfaceFig. 1. Aspects of pressure-wave and stress-wave propagation in high-speed droplet impact on solid
surfaces of several types.
Development of Numerical Prediction Method of Cavitation ErosionIn high-speed liquid flow, erosion sometimes results from a cavitation bubble collapse.
Development of A numerical prediction method is anticipated. In this study, coupling numerical calculation is performed for homogeneous cavitating flow simulation around a hydrofoil, tracking simulation of spherical bubble in the cavitating flow, and simulation of a non-spherical bubble collapse near a wall, with consideration of the number density distribution of bubbles in an actual flow field. Then, the erosion rate can be predicted quantitatively using numerical simulation. Results show that the predicted erosion rate agrees well with the experimentally obtained value.
Fig. 2. Time evolution of the aspect of collapse and rebound of single bubble near a wall.
Cavitation Instabilities in Liquid Propellant Rocket TurbopumpIn a liquid-propellant rocket turbopump, cavitation instabilities sometimes occur, which
threaten the soundness. That suppression process increases the cost of the liquid rocket launch. The turbopump is ultra-high-speed and high-pressure fluid machinery. Clarification of the cavitation instabilities is not so easy to investigate solely through experimentation. In this laboratory, through collaboration between experiments performed at the JAXA Kakuda Space Center and supercomputing in IFS, the cavitation instabilities are investigated. In supercomputing, a three-blade inducer in the turbopump inlet is simulated using a three-blade cyclic cascade. The occurrence mechanism of a rotating cavitation, the propagation mechanism of pulsation in cavitation surge, and influence of acceleration during the launch on the cavitation instabilities were clarified and a control technique of the instabilities by tandem cascade was developed.
Fig. 3. Super-synchronous rotating cavitation arising in three-blade cyclic flat-plate cascade.
Relevant journal papers H. Sasaki, Y. Iga, T. Ikohagi, Study of Droplet Impingement Phenomena by Fluid/Solid Coupled
Simulation, Proc. Joint International Conference on Supercomputing in Nuclear Applications and Monte Carlo 2010/SNA+MC2010, Tokyo JAPAN (2010), No. 10189.
N. Ochiai, Y. Iga, M. Nohmi, T. Ikohagi, Numerical Analysis of Nonspherical Bubble Collapse Behavior and Induced Impulsive Pressure during First and Second Collapses near the Wall Boundary, Journal of Fluid Science and Technology, Vol. 6, 860-874 (2011).
Y. Iga, Y. Yoshida, Mechanism of Propagation Direction of Rotating Cavitations in a Cascade, Journal of Propulsion and Power, Vol. 27, 675-683 (2011).
Related research budgetsIntelligent Cosmos Research Institute, ”Structural Improvement of the stronger measures for aging degradation of atomic power plants” (2006–2010), ¥49,329,000Ebara Corporation, “Technique of cavitation analysis with considering of application to prediction of performance and erosion in fluid machineries” (2009–2011), ¥1,985,000
AwardsJSME Encouraging Prize (Research), Yuka IGA (2006. 4. 7)
JSME Fluid Ergineering Division Prize, Toshiaki Ikohagi(2008.10)
Advanced Computational Fluid Dynamics LaboratoryProfessor Yuji Hattori, Assistant Professor Wakana Nakano
Professor (–2009.3) Osamu Inoue, Assistant Professor (–2006.9) Nozomu Hatakeyama
Development of High-Precision Numerical Methods for Simulation of Flow in Complex and/or Deforming Geometries
Increasing needs are being expressed for highly accurate simulation of flows in complex
geometry and flows which involve moving and/or deforming bodies. We are developing numerical
methods for these flows by application of the volume penalization (VP) method, which is one of the
immersed boundary methods. First, by basic studies of a simple one-dimensional problem, we have
developed a new method for improving the accuracy of the VP method. Next, the method is applied
to simulate the formation of a vortex pair by piston motion and the evolution of localized
disturbances in the elliptic flow. Finally, the accuracy of the VP method for compressible flow is
investigated. The aeroacoustic sound generated from the flow past a square cylinder is simulated by
VP method and the sound is captured with sufficient precision, showing that the method is useful for
direct numerical simulation of aeroacoustic sound in complex and/or deforming geometries.
Fig. 1. Formation of a vortex pair simulated by VP method. Fig. 2. Sound generation simulated by VP method.
Statistical Properties of TurbulenceThe statistical properties of turbulence are not only a long-standing problem of physics but also
the key to establishing reliable turbulence models required for simulation of high-Reynolds number
flows encountered in engineering. We are studying the statistical properties of turbulence mainly by
direct numerical simulations. The dynamics of high-enstrophy regions in the three-dimensional
incompressible turbulence including advection/deformation, creation/extinction and merging/fission
is studied by DNS and interactive three-dimensional visualization. For two-dimensional
compressible turbulence, the scaling of the density spectrum is shown to depend on the initial
condition for entropy; when entropy is non-uniform sheet structures are found to emerge in the
density field.
Fig. 3. Vortical structures in 3D turbulence. Fig. 4. Sheet structures in compressible turbulence.
Vortex DynamicsIt is important to understand vortex dynamics when investigating and understanding flow
phenomena. The fundamental properties and the dynamics of various vortical structures are studied.The curvature instability, which appears when vortex tubes are curved, is studied for vortex rings and helical vortices; the effects of curvature, torsion, rotation and axial flow as well as their combined effects are clarified using theoretical analysis. Evolution of localized disturbances in the elliptical flow is studied using DNS. The process starting from an infinitesimal disturbance andleading to turbulence is clarified in detail. The results suggest an effective method for destabilizingvortices.
Fig. 5. Growth rates of curvature instability. Fig. 6. Localized disturbance in the elliptical flow.
Relevant journal papers Y. Hattori, Y. Fukumoto, Short-Wavelength Stability Analysis of a Helical Vortex Tube, Physics
of Fluids, Vol. 21, 014104 (2009). Y. Hattori, Y. Fukumoto, Short-wave Stability of a Helical Vortex Tube: The Effect of Torsion
on the Curvature, Theoretical and Computational Fluid Design, Vol. 24, 363-368 (2010). Y. Hattori, K. Hijiya, Short-wavelength stability analysis of Hill's vortex with/without swirl,
Physics of Fluids, Vol. 22, 074104 (2010).
Related research budgetsGrant-in-Aid for Scientific Research (B) (2007–2008), ¥8,970,000Grant-in-Aid for Scientific Research (C) (2008–2011), ¥3,000,000
Injection well
CO2 leakage path(Fracture)
805010851
0.50.1
0.001
Porous layer filled with reaction grout
Large-Scale Environmental Fluid Dynamics LaboratoryProfessor Takatoshi Ito, Assistant Professor Hiroyuki Shimizu
In-situ Reaction Method to Remedy Leakage from Geological CO2 Storage Reservoirs In order to remedy leakage from a CO2
storage reservoir through pre-existing and/or
induced fractures, we have proposed a new
concept to use an aqueous solution. When the
solution encounters dissolved CO2, precipitation
will occur due to chemical reaction. As a result,
the permeability will be reduced by filling the
pores and fractures in the rocks with the
precipitates. We verified this idea through
laboratory experiments and numerical
simulations.
Estimation of Pressure and Flow Distribution in Fractured Geothermal Reservoirs at Few km Deep Using Microseismic Signals
Geothermal energy development depends
upon how well water flow is understood. In
response to such requirement, we have
developed a method to use a microseismic (MS)
signal as a measure of pressure at its hypocenter,
where the MS are caused by fluid injection. By
compiling the estimated local pressure in a
manner, we can estimate pressure propagation
during fluid injection. From the estimated
pressure propagation, we can estimate
distributions of flow-pathways and hydraulic
conductivity along them.
Fig. 1. Formation of impermeable barrier to
stop leakage through a fracture.
Fig. 2. Estimated pressure distribution
(Australian test site, 4 km depth)
1cm SH
SH
Sh
Sh
Casing pipeSlit
Study of Hydraulically-induced Fracture Behavior in Unconsolidated Sands for Methane Hydrate (MH) Development
For production of gas from MH, the MH
should be dissociated within the layers for the
resultant gas to be collected through wells and
production systems. The dissociation will be
driven by decreasing pressure of the layers.
Hydraulic fracturing may contribute to enhance
gas production. However, the technique of
hydraulic fracturing was originally developed
assuming cohesive rocks but not incohesive
ones such as unconsolidated sediments below
seafloor in which MH is contained. Thus we
have carried out laboratory fracturing tests and
as a result we have found a significant difference
between the fracture behaviors in incohesive and
cohesive rocks.
Relevant journal papers
H. Shimizu, M. Murata, T. Ishida, The Distinct Element Analysis for hydraulic fracturing in
hard Rock considering fluid viscosity and particle size distribution, International Journal of
Rock Mechanics and Mining Sciences, Vol. 48, 712-727 (2011).
T. Ito, K. Yamamoto, S. Nagakubo, Effect of anisotropic confining stresses on
hydraulically-induced fracture, Proceedings of the 45th US Rock Mechanics / Geomechanics
Symposium, San Francisco, ARMA 11-247 (2011).
T. Ito, T. Shono, K. Sekine, K. Yamamoto, A new laboratory test for shear fracture formation
and its permeability measurement, Proceedings of the 12th ISRM International Congress on
Rock Mechanics, Beijing, Vol.1, No.1, pp.645-648 (2011).
Relevant research budgets
Grant-in-Aid for Scientific Research (B), Takatoshi Ito(2009~2011),¥14,950,000
Research fund of JOGMEC, Takatoshi Ito(2010~2011),¥4,250,000
Awards
JCRM Medal for Outstanding Paper, Hiroyuki Shimizu (2011.6.9)
Fig. 3. Fracture induced by laboratory test.
It is branched unlike cohesive rock.
Theoretical Fluid Dynamics LaboratoryConcurrent Professor Michio Tokuyama, Assistant Professor Yayoi Terada
Slow Dynamics near the Glass Transition-Lateral diffusion of magnetic colloidal chains and monolayer colloids –
Liquid becomes glass through the supercooled liquid state if it is cooled with avoidance of
crystallization. Recently, novel glasses such as colloidal glasses, bulk metallic glasses, and so on
have been developed. Their unique properties receive considerable attention. However, the
mechanism of glass transition remains unclear. In our laboratory, we study the dynamics near the
glass transition by performing computer simulations.
Magnetic colloidal chains confined with thin films and monolayer magnetic colloids are good
examples of glass formers. When dilute suspensions of magnetic colloidal particles are confined in
thin films and a strong external field is applied perpendicular to the films, magnetic colloidal
particles dispersed in a solvent form colloidal chains parallel to the field and the lateral diffusion of
the chains can be observed. These diffusive motions of the colloidal chains and monolayer colloids
slow and ultimately become a glass state when the external magnetic field is increased.
Universalities in the dynamics of chains and monolayer colloids in fluid phase are explored based on
the mean-field theory recently proposed by Tokuyama. The long-time self-diffusion coefficient of a
chain is shown to obey a singular function of a control parameter proportional to the square of the
applied field strength, even though the size polydispersity of colloids is changed in Fig. 1.
Slow Dynamics of Hard-sphere Fluids and Hard-disk Fluid near the Glass TransitionThe glass transition can be observed on two-dimensional and three-dimensional systems. The
long-time diffusion process of hard spheres is compared with that of hard disks by performing
extensive molecular simulations with changing of the volume fraction. The long-time self-diffusion
coefficient of both hard disks and hard spheres is described by the singular function proposed
theoretically by Tokuyama. The characteristic times of the β relaxation process and the α relaxation
process of hard disks are also found to be similar to those of hard spheres when the particles had the
same long-time self-diffusion coefficient. The spatial dimension changes the value of the glass
transition point and peak height of the non-Gaussian parameter which are related to the geometric
packing characteristics of hard disks and hard spheres.
Relevant journal papers
Y. Terada, M. Tokuyama, Universalities in the dynamics of suspensions of magnetic colloidal
chains confined in thin films, Journal of the Physical Society of Japan, Vol. 78, 084803 (2009).
Y. Terada, M. Tokuyama, Lateral diffusion of magnetic colloidal chains confined in thin films
and monolayer colloids, Journal of the Physical Society of Japan, Vol. 79, 034802 (2010).
Y. Terada, M. Tokuyama, Spatial Dimensionality Dependence of Long-Time Diffusion on Two-
and Three-Dimensional Systems near Glass Transition, Intermetallics, Vol. 18, 1834-1836
(2010).
Related research budgets
Grant-in-Aid for Scientific Research (C) (2011–2013), ¥5,300,000
Awards
Best Poster Award for the 12th International Conference on Magnetic Fluids, Yayoi Terada
(2010.8.5)
Fig. 1. Snapshot of magnetic colloidal
monolayer and control parameter
dependence of long-time self-diffusion
coefficients of colloidal chains.
Fig. 2. Long-time self-diffusion coefficient
dependence of characteristic times of hard spheres
and hard disks: ◇ , mean free time (tf); □ ○,characteristic times related with β-relaxation (tγ, tβ);
△▽, characteristic times related with α relaxation
(tα, tα2); ◊ , characteristic time with long time
self-diffusion process (tDSL). Open symbols, hard
spheres; filled symbols, hard disks.