記述言語：英語   掲載種別：研究論文（学術雑誌）  

The characteristic of two-phase immiscible flow in porous media is controlled by different kinds of force, such as interface surface tension (capillary force) and fluid viscosity (viscous force). Based on those two forces, three typical displacement patterns in porous media are divided, named as capillary fingering, viscous fingering and stable displacement. However, the impact of inertial force in displacement pattern, which generate due to the flow direction or velocity change of fluid, is always neglected. This research used direct numerical simulation (DNS) to study the two-phase immiscible pattern with a wide range of capillary number (Ca) and ratio of Reynolds number (Re). The Ca is a dimensionless value which represents the ratio of viscous force and capillary force. While Re represents the ratio of inertial force and viscous force. The impact of forces on displacement patterns were determined based on the quantitative analyses of the saturation distribution as functions of Ca and Re. The result shows that inertial effects have minimal influence on flow conditions at low capillary numbers. However, at high capillary numbers, capillary forces become less significant, and inertial effects strongly influence flow conditions. These findings contribute the different insight of fluid displacement patterns, controlled by balance of inertial, capillary and viscous forces, has a noticeable influence on recovery or storage efficiency in subsurface process.

DOI： 10.26855/jamc.2024.12.006

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

In fluid dynamics, the generation and bursting of surface bubble liquid films in surfactant-laden environments involve complex phenomena, one of which is marginal pinching at the film's foot—a crucial yet inadequately understood aspect due to experimental limitations. Considering its profound impact on liquid film drainage and lifetime, we utilize high-resolution numerical simulations incorporating a weakly compressible scheme and adaptive mesh refinement to dissect the marginal pinching dynamics with unprecedented detail. Our approach elucidates the pinching dynamics and tracks the evolution of film thickness during the critical late-stage drainage process. By leveraging detailed geometric data from pinched regions, we significantly refine existing drainage models, enhancing their predictive accuracy regarding rupture thickness and film lifetime across various viscosities, surfactant concentrations, and bubble sizes. This refined model demonstrates robust alignment with our simulation results. Furthermore, we establish a quantifiable relationship between the prefactor governing reverse flow induced by the Marangoni effect and surfactant concentration. The methodologies and findings of this study provide foundational knowledge that paves the way for optimized industrial processes and an enhanced understanding of natural phenomena.

DOI： 10.1063/5.0235150

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jcp.2024.113292

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Haines jumps and meniscus reconfiguration are commonly observed in immiscible two-phase flows through porous media. The experiment found that the fluid-fluid interface moves rapidly during these two phenomena. This leads to hydraulic change and entropy production events, which have important implications for relative permeability of two-phase flow in porous media. However, owing to the energy-transfer process remains to be elucidated, their impact on transport of heat and mass in porous media has not yet been well predicted. By analyzing the exchange process between surface energy, kinetic energy, and viscous dissipation, this study provides a better understanding of meniscus dynamics and whether these effects are significant on a larger scale. In this study, Direct Numerical Simulation (DNS) combined with level-set method was used to simulate the process of Haines jumps and meniscus reconfiguration. A governing equation combined with density-scale continuum surface force (CSF) model was derived for energy conservation, and simulations were performed considering high-density and high-viscosity ratios. The rate of surface-energy change was evaluated using CSF model. A capillary tube was designed to verify the rate of surface-energy change in simulation. Comparison of simulation and theoretical data indicates that the density-scale CSF model can satisfactorily evaluate the rate of change in surface energy. Besides, to compare energy transfer process in Haines jumps and meniscus reconfiguration, two simulation cases were designed: (I) Haines jump and meniscus reconfiguration occur individually, and (II) Haines jump and meniscus reconfiguration occur simultaneously. We investigated the energy exchange process and compared the effects of the inertial force and viscous dissipation between cases I and II. Based on the simulation results, the interface releases surface free energy to the system during the Haines jumps and meniscus reconfiguration. In the case of only Haines jumps, a portion of the released surface energy is absorbed by another fluid-fluid interface, thus reducing the surface-energy release rate in the system. This energy can be dissipated promptly, resulting in a rapid viscous-dissipation growth; but the kinetic-energy change is negligible. However, when meniscus reconfiguration occurs, released surface energy is difficult to reabsorb and cannot dissipate quickly. Thus, a significant amount of released energy is converted into kinetic energy, which is subsequently damped by the fluid. This significant kinetic-energy oscillation generates a large inertial force and spreads over a wider sphere of influence in the porous media. Energy transfer process shows a more detailed fundamental understanding of mass transfer in porous media, such as flow perturbations, entropy production and permeability in porous media, and it helps a rigorous process for upscaling models used for thermodynamic, heat and mass transfer in porous media.

DOI： 10.1016/j.ijheatmasstransfer.2024.125749

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Investigating Rayleigh–Bénard convection, its onset, and its effect on mass transfer are crucial for understanding the effective dissolution processes between carbon-dioxide (CO2)-saturated and CO2-free brines in CO2 geological storage. However, most previous investigations on the onset of convection and mass transfer properties were conducted by 2D and 3D numerical simulations. Only a few 3D experimental studies of Rayleigh–Bénard convection were reported. In this study, we proposed a non-destructive experimental approach to visualize the three-dimensional (3D) fingering structure of Rayleigh–Bénard convection using a micro-focused X-ray computed tomography (X-ray CT) scanner. The experimental conditions covered the Rayleigh number (Ra) range between 3400 and 23000, which also includes the Ra value of the actual condition of gas reservoir field. Results show that fingers and coalescence dynamics significantly developed upon increasing Ra. At higher Ra, the finger concentration experienced greater dilution due to the combined effects of unsteady finger motion and enhanced dispersion strength. The maximum finger extension velocity is linearly proportional to Ra. The convective mass flux (Sh) correlated with Ra by a power-law relationship. The findings in this study provide a better understanding of the influence of Ra on mass transport properties and can be used as a reference for developing the convective mass transfer model of Rayleigh–Bénard convection in 3D porous media.

DOI： 10.1016/j.advwatres.2024.104666

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2023WR034849

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

<jats:p>In this paper, we discuss the effects of a foam generated by a chemical reaction on viscous fingering (VF) as observed using a Hele–Shaw cell and a microchannel. Sodium bicarbonate solution both with and without surfactant was used as the displacing fluid, and citric acid solution was used as the displaced fluid. We found that the presence of surfactant can significantly increase the coalescence time and decrease the nucleation time; the displacement time was found to change with the injection flow rate. The nature of the VF pattern was found to depend on the interrelationship between these three characteristic times. When the displacement time was significantly larger than the coalescence time, which was, in turn, much larger than the nucleation time, small bubbles were generated at the start of the experiment, but these merged into large bubbles at the end. However, small bubbles were still created and did not coalesce, and the shape of the VF was more stable. When the displacement time was close to the nucleation time but considerably smaller than the coalescence time, many small bubbles were produced without coalescence, inhibiting the flow of the advancing fluid and widening the fingers. The effects of the surfactant and citric acid concentrations were also examined from the viewpoint of the characteristic times in the Hele–Shaw cell. In the microchannel, we discovered that the foam structure produced early in the experiment inhibits the development of preferential flow channels, impedes the formation of an oil film, and enhances the micro-displacement efficiency.</jats:p>

DOI： 10.1063/5.0139528

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/app13031955

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Drying process of porous medium is of interest in engineering applications. However, pore-scale studies of wettability effects on the drying process of three-dimensional (3D) porous media remain limited. X-ray microtomography was used to investigate the wettability effects on the drying process of 3D porous medium from a pore-scale perspective. Results show higher wettability increases capillary pressure, which enhances the rearrangement of liquid from large pores to small pores. We also found that liquid clusters are unlikely to disappear for a long time confirming that higher wettability supports the flow through liquid film. This study also provides new insight that capillary flow by liquid film is associated with branch clusters. These clusters maintain the gas–liquid interfacial area that acts as the evaporation surface. As a result, drying is intensive in a water-wet porous medium with a longer constant rate period in which drying is controlled by external diffusion. In a neutral-wet porous medium, an early drop in drying rate occurs. Thus, drying is mainly a falling rate period limited by vapor diffusion through the newly emerging dried region within the medium.

DOI： 10.1016/j.icheatmasstransfer.2022.106527

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

X-ray micro-tomography was used to comprehensively study the pore-scale drying process and characterize the liquid film region and the invasion front. Our finding reveals that the decrease in saturation is not uniform across the pore size. The capillary rearrangement, which refers to the restructuring of the liquid phase due to the capillary pressure difference, drives the liquid to flow from large pores to small pores. As a result, the decrease in liquid saturation occurs preferentially within the larger pores. A sharp decrease in liquid saturation occurred at the invasion front, where saturation ranged from 1 to around 0.15. The obtained invasion width that characterized the extent of roughness and disorder of the invasion front obeyed the scaling law of the percolation model. Therefore, this region is significantly limited by the interaction between capillary and gravity. However, with more multi-pore connected clusters observed within the porous medium, the critical exponent of the cumulative cluster size distribution obtained from the cluster region deviates from the universal power-law behavior. This result indicates the presence of liquid film within the cluster region, where the viscous force becomes comparable to the capillary force. We also found that the total gas-liquid-specific interfacial area has no effect on the drying rate. This result provides new evidence that the liquid film region is vapor saturated.

DOI： 10.1016/j.ijheatmasstransfer.2022.123299

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

An in-situ dual-surfactant formulation is developed by using a novel cationic surfactant adsorbing the in-situ acid components in crude oil. As a result, various oil deformation patterns are first revealed and applied to control the viscous instabilities for oil recovery application. To this end, four dynamic oil displacement tests are conducted via camera snapshotting or X-ray microtomography in two and three dimensions, without and with porous media, in single to multipore-throat structures as well as through pore-scale and macroscale visualizations. As suggested in the results, displacing the oil phase using a 20 mmol/L cationic surfactant is the most effective method to suppress interfacial instability. The preferential flow path is frequently diverted by the repeated change of oil shape at a low flow rate. By contrast, emulsification plays a key role when the flow rate is high. It depends on which is dominant between the oil deformation and shearing velocity. From a deep insight into the pore spaces, oil deformation patterns are classified into oil spreading, shrinking, splitting, film detachment, and bridge breakup. The most significant oil deformation in the tortuous pore spaces occurs after 10 min of aging. Based on this time, we propose a new injection–alternate–stop scenario to suppress the viscous fingering and maximize the oil recovery efficiency to 80% in a large-scale reservoir.

DOI： 10.1021/acs.iecr.2c01735

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microemulsion flooding has recently gained attention as an effective chemical-based method for enhanced oil recovery (EOR). The high performance of this technique is attributed to the classical mechanism: plugging effect and divergence of preferential flow path. In this study, miscible behavior was identified as a novel mechanism by which oil recovery was controlled by dissolution process instead of capillary forces. To this end, a new type of solvent-based microemulsion phase was prepared by mixing solvent, water, and surfactant as a flooding fluid. A series of experiments with direct water flooding, microemulsion flooding, and water-alternate-emulsion flooding for EOR were carried out for strong water-wet and oil-wet artificial rock sample. X-ray microtomography was used to visualize the oil configurations in three-dimensional pore spaces. An advanced workflow image processing method was developed for the first time to capture the miscible behavior in a pore-scale view. As suggested in the results, microemulsion flooding has a miscible displacement front where the oil phase is gradually solubilized. Therefore, capillary forces can be eliminated because the emulsion-oil interface is invisible but has a compositional gradient, leading to higher oil recovery. Compared with the immiscible waterflooding process, the capillary forces remained dominant, which hinders additional oil recovery. Based on EOR scenarios, we found that emulsion flooding could effectively solubilize larger well-connected oil clusters instead of small separate ganglia or singlets. Therefore, considering the miscible behavior, emulsion flooding can be applied to secondary oil recovery regardless of the reservoirs’ wettability, or to tertiary oil recovery in weakly/strongly oil-wet reservoirs with a well-connected oil phase after waterflooding.

DOI： 10.1016/j.petrol.2022.110788

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

When viscosity and density contrast exist in the vertical miscible displacement in porous media between two fluids, the interplay between the viscous force and gravity determines the interface stability. Two stability criteria are derived to determine the interface stability. Hill's and Dumore's stability criteria are used to determine the interface stability of the sharp and diffused interface, respectively. In this study, we visualized the crossover between unstable displacement and stable displacement for a vertical displacement in porous media using microfocused x-ray computed tomography. The experiments were divided into four possible configurations: (1) unconditionally stable (gravitationally stable-viscously stable), (2) unconditionally unstable (gravitationally unstable-viscously unstable), (3) conditionally stable (gravitationally stable-viscously unstable), and (4) conditionally stable (gravitationally unstable, viscously stable). The structure of the displacement interface was visualized for the critical velocity ratio (V/Vc) in the range of 0.5–11.9. In the conditionally stable configurations 3 and 4, a crossover between stable and unstable displacements was observed. We found that Dumore's stability criterion is more appropriate for predicting interface stability than Hill's stability criterion. Viscous fingering occurs in configuration 3 when V/Vc is higher than Dumore's critical velocity, whereas gravity fingering occurs in configuration 4 when V/Vc is lower than Dumore's critical velocity. Similar events in two-dimensional experiments, such as tip-splitting, shielding, and coalescence, were also observed three-dimensionally. The significant changes in the mixing length and sweep efficiency signify the crossover between the stable and unstable displacements.

DOI： 10.1063/5.0090387

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Crude oil often contains long-chain fatty acid components. The fatty acid usually exists as a dissociative anionic surfactant in the oil phase. This study introduced a novel cationic surfactant to absorb the in situ anionic surfactant. Thus, a dual surfactant system was formed, and surfactant aggregates were produced near the water–oil interface. Due to the viscoelastic and fragile aggregates, spontaneous oil deformation and splitting were discovered as a novel mechanism for chemical enhanced oil recovery (EOR). First, we used a water phase doped with stearyltrimethylammonium chloride to displace the heavy oil with palmitic acid in the Hele-Shaw cell. The fingering patterns were observed in the water flooding (WF) and chemical flooding (CF) systems under different flow rates. After that, the experiments were transferred to the wettability-altered micromodel to simulate real oil recovery applications. The Hele-Shaw cell experiments show that viscous fingering was intensive at a low flow rate whereas it was significantly suppressed at a high flow rate in the CF system. The micromodel experiments show that oil recovery is higher in the CF system than in the WF system. The spontaneous cocurrent and counter-current oil blebbing was observed in the dynamic CF process. As the blebbing developed to a certain degree, the oil phase split into tiny droplets that could easily pass through the pore spaces. Additionally, the wettability was also altered from oil-wet to water-wet. As a result, oil recovery was improved significantly. The residual oil was classified into cluster, ganglia, and singlet based on the circularity and Euler number. We found the large clusters dominated in the WF system, whereas the small size of ganglia and singlets were the main forms in the CF system. The new chemical used can be applied for large-scale industrial EOR fields due to its good performance and low cost.

DOI： 10.1021/acs.energyfuels.2c00772

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Hydrodynamic fingering induced by gel formation shares common features with growing biofilms, bacterial colonies, and the instability of a confined chemical garden. Fluid displacement with gel formation is also essential in various engineering applications, including CO2 leakage remediation from storage reservoirs and enhanced oil recovery. We conducted Hele-Shaw cell displacement experiments for a miscible fluid system using skim milk and aqueous citric acid solution. This study aimed to investigate the effects of gel film formation on the fingering instability of a miscible fluid system and develop a mathematical model of the sequential growth of gel film formation at the fingertip. We found that the gel film formation thickens with time, resulting in instability at the interface. A distinctive fingering pattern, resembling tentacles, appears where miscibility is suppressed, and the growth of the finger is localized at the fingertip. The finger width remains constant with increasing flow rate, whereas the number of fingers increases linearly before the fingers merge. The gap width significantly limits the finger width. Finally, a mathematical model of sequential film thickness growth for a bubble-like fingertip structure was developed. This model is based upon the interplay between the diffusion of citric acid through the existing gel film formation and elongation of the fingertip. The model provides an understanding of the fundamental mechanism of the growth of the bubble-like fingertip.

DOI： 10.3390/app12105043

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Academic Press Inc.  

DOI： 10.1016/j.jcp.2021.110605

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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DOI： 10.3811/jjmf.2021.004

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jiec.2021.03.046

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0044756

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   出版者・発行元：一般社団法人 日本トライボロジー学会  

Simulation of gas-liquid two-phase flows include multi-scale and multi-physics problems. We have developed a weakly compressible computational scheme for incompressible flows with a purely explicit time integration and successfully implemented on GPU (Graphics Processing Unit) providing very high computational performance. AMR (Adaptive Mesh Refinement) method is available for the scheme and high-resolution meshes are assigned dynamically near the region of the gas-liquid interface. The AMR method greatly enhances the computational efficiency and makes it possible to compute the dynamics of thin liquid film such as a soap bubble which is a typical multi-scale problem. At the surface, viscoelasticity becomes more important and transportation of surfactant should be taken into consideration. It has been confirmed that the Marangoni effect stabilizes and avoids breaking-up a thin film covering a bubble on the water surface against the gravity in the simulation.

DOI： 10.18914/tribologist.65.11_678

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その他リンク： https://ndlsearch.ndl.go.jp/books/R000000004-I030778045

記述言語：日本語   掲載種別：学位論文（博士）  

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記述言語：日本語   出版者・発行元：[電気化学会] 技術・教育研究会  

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

A weakly compressible scheme for gas–liquid two-phase flows with low Mach number is proposed for a fully-explicit time integration. The scheme is based on the fractional-step method with the Euler equation solver and time integration for viscous, surface tension and gravity terms. For the efficient solution of the Euler equation, we introduce the directional-splitting method and the method of characteristics which is applicable to semi-Lagrangian methods. A reduction of the speed of sound is also taken into consideration to enlarge the time step intervals. The primitive flow variables are time-integrated on the node-center configuration. To capture the gas–liquid interface, the conservative phase-field equation is solved by using the multi-moment method. It is computed as a conservative form for the volume-averaged value defined at the cell center, in which the flow velocities are given on the node. We discard the exact momentum conservation, however the total mass of gas and liquid is conserved by introducing a phase-field variable. Several benchmark problems are examined and the results of the explicit scheme are in good agreement with the experimental and computational references.

DOI： 10.1016/j.jcp.2018.10.019

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担当区分：筆頭著者   記述言語：日本語   出版者・発行元：日本混相流学会  

<p>A weakly compressible scheme for low-Mach number gas-liquid two-phase flows have been developed for a full-explicit time integration to avoid solving Poisson equation for large-scale two-phase flow simulations. To describe the gas-liquid interface the conservative Allen-Cahn equation, which is one of the phase-field models, is introduced and combined with the continuum equation. The accuracy of numerical results of two-phase flow strongly depends on the mesh resolution near the interface. The AMR(Adaptive Mesh Refinement) method greatly reduces the computational cost to assign high-resolution mesh to the region around the moving interface. We have developed a GPU-code of the tree-based AMR. We choose the node-centered configuration and the interpolation can be closed within a leaf in refining the leaf. We successfully have carried out two-phase flow simulations including very thin liquid film efficiently.</p>

DOI： 10.3811/jjmf.2019.008

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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担当区分：筆頭著者   記述言語：日本語   出版者・発行元：一般社団法人 日本計算工学会  

気液二相流の数値シミュレーションは, 未だに数値流体力学的課題の多いテーマである. 近年のコンピュータの著しい性能向上に伴って, 流体方程式と界面追跡の方程式を直接解くことによる解析がなされてきている. しかし, 格子を増やすと新たな水滴や気泡が生じるなど, 解の収束性に至る十分な格子解像度で計算することは非常に困難である. 一般に気液二相流は界面近傍が激しく運動し複雑な挙動を示すため, 界面挙動を精度よく捉えるためには多くの格子が必要である. 界面近傍をより高解像度で効率的に計算するために, 細かい格子が必要となる領域に格子を集めることのできるAdaptive Mesh Refinement (AMR) 法を気液界面に適用することが考えられる. 総格子点数を大幅に削減することができ, 界面近傍をより高解像度で計算することが可能となる. 直交格子上で界面を追跡する手法として, レベルセット法, VOF法が広く用いられてきた. しかし, 激しい流れでは液体よりVOF値は小さいが気体より大きな値を持つ領域が気体中を浮遊する問題などが生じてしまう. 近年, 新たなアプローチとして保存形フェーズフィールド法が提案されており, 本研究では界面捕獲手法として良い結果が報告されている保存形Allen-Cahn方程式を用いる. マルチモーメント法である保存形IDO法を用いて保存形Allen-Cahn方程式を解くことにより, 格子点上に変数を配置しながら気相と液相の質量保存性を担保する. 保存形マルチモーメント法では格子点上の値に加えて線積分値や面積分値といったモーメントが時間積分される変数として定義されている. レベル差補間の際にはコンパクトな領域で精度の高い補間関数を構築可能であり, AMR法に適した手法であると言える. また, 界面が時間とともに動く場合には保存形Allen-Cahn方程式の時間微分項に流束の微分項が加わる. フェーズフィールド変数に対する連続方程式と保存形Allen-Cahn方程式に分離して解くことにより, 連続方程式に対してはCIP-CSLR1法を, 保存形Allen-Cahn方程式には保存形IDO法を用いることができる. 分離した式はいずれも方向分離法で各々の方向に対する1次元の式を繰り返し解くことができ, 連続方程式の解法に精度の高いセミ・ラグランジアン法が適用可能である. AMR法適用に際しても1次元方向のみの補間を考えれば良くAMR法の実装が容易な手法となっている. <br>本論文では流束項付き保存形Allen-Cahn方程式をマルチモーメント法の解法を高精度で解くために, 木構造に基づいたAMR法により界面の時間的・空間的に追従する動的な適合格子細分化法を導入した. フェーズフィール変数が急激に変化する領域に細かい格子を動的に配置する. ベンチマーク問題としてSingle Vortex問題をレベル0から5までの格子細分化を行って計算し, 最も細かい格子解像度で均一格子を用いた場合と比較して平均で1/12.3に格子点数を削減することができ, 9.26倍に計算を高速化することができた. 界面形状も計算領域全体を均一に細かい格子で計算した場合と同じ精度が出ていることを確認した. マルチモーメント法を用いることによりコンパクトで高精度な補間関数を構築可能であるため, 界面が大変形するような問題に対しても高い精度で計算できる. 本論文の成果は, 気液界面に適合した動的な格子細分化による気液二相流計算に適用可能である.

DOI： 10.11421/jsces.2018.20180005

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記述言語：日本語   出版者・発行元：東京 : 日本計算工学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語   出版者・発行元：日本計算工学会  

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記述言語：日本語  

identifier:oai:t2r2.star.titech.ac.jp:50588402

CiNii Research

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記述言語：日本語   出版者・発行元：日本計算工学会  

CiNii Books

CiNii Research

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J-GLOBAL

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記述言語：日本語   出版者・発行元：日本計算工学会  

CiNii Research

J-GLOBAL

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記述言語：日本語   出版者・発行元：日本流体力学会  

コレクション : 国立国会図書館デジタルコレクション > 電子書籍・電子雑誌 > 学術機関 > 学協会

CiNii Books

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

<p>A fully explicit gas-liquid two-phase flow solver without solving Poisson equation based on weakly compressible assumption with interface-adapted AMR method is proposed to achieve high resolution simulation. Solving independent hyperbolic pressure evolution equation derived from isothermal Navier-Stokes equation allows us to achieve a fully explicit time integration. We have developed a GPU-code of the tree-based AMR method, which can greatly reduce the computational cost to assign high-resolution mesh to the region around the moving interfaces. The memory pool data structure having extra allocated space is prepared to prevent frequent memory allocation and deallocation to enhance the computational performance. The results of benchmarks have good agreements with that of incompressible solver and experiments. The soap bubble simulation using the finest mesh width (= 0.07825mm) on single GPU are demonstrated and the thin liquid film can be reproduced by achieving high-resolution two-phase flow simulation with explicit scheme and AMR method.</p>

DOI： 10.1299/jsmecmd.2019.32.173

CiNii Research

J-GLOBAL

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J-GLOBAL

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記述言語：日本語   出版者・発行元：日本計算工学会  

CiNii Research

J-GLOBAL

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記述言語：日本語   出版者・発行元：日本混相流学会  

<p>Incompressible flows have much lower flow speeds to compare with the sound speed and called low Mach number flows. So far, we have simulated incompressible flows by using semi-implicit solvers, in which we iteratively compute the linear equation derived from the pressure Poisson equation. In the case of incompressible gas-liquid two-phase flows, the sparse matrix would be very stiff with non-zero elements changing largely from the gas density to the liquid density at the interface. Even if we use a sophisticated Krylov sub-space iteration solver with the multi-grid preconditioner, the convergence becomes poor for large-scale problems. We have developed a weakly compressible gas-liquid two-phase solver based on fully-explicit time integration of compressible Navier-Stokes equation. For several benchmark problems, the results of the weakly compressible solver are in good agreement with those of the semi-implicit incompressible solver. Since the weakly compressible solver uses a local stencil access, it is possible to implement AMR (Adaptive Mesh Refinement) method with less programming cost. Fine meshes are assigned near the gas-liquid interface and we efficiently compute a liquid film generated by a spoon and a growing soap bubble with the AMR two-phase flow solver.</p>

DOI： 10.3811/jjmf.2018.T011

CiNii Books

CiNii Research

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

<p>A weakly compressible scheme for low-Mach number gas-liquid two-phase flows have been developed for a fullexplicit time integration to avoid solving Poisson equation. We introduce the fractional splitting method and directional splitting method to solve Euler equation which an efficient semi-Lagrangian scheme is applicable to. To describe the gas-liquid interface the conservative Allen-Cahn equation, which is one of the phase-field models, combined with the continuum equation is introduces. The accuracy of numerical results of two-phase flow strongly depends on the mesh resolution near the interface. The AMR (Adaptive Mesh Refinement) method greatly reduces the computational cost, since it is possible to assign high-resolution mesh to the region around the moving interface. We have developed a code to solve the equation in a manner of the tree-based AMR. Fractional step method and the directional splitting method helps to reduce the implementation difficulties of AMR method. We successfully carried out some violent two-phase flow simulation and flow including very thin liquid film by using the method which is combined weakly compressible scheme with AMR method.</p>

DOI： 10.1299/jsmecmd.2018.31.222

CiNii Research

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

<p>In distributed implementations of stencil AMR applications, the inter-node communication time often represents a major performance bottleneck. Thus minimizing communication is an objective as important as maintaining a good load balance. We propose a new domain partitioning method for block-based AMR applications based on the multi-phase-field (MPF) model. The MPF model for polycrystalline growth minimizes the interfacial energy and forms a convex shape for each crystal grain. In our method, each phase of the MPF model represents a computational sub-domain. We show that the MPF partitioning can successfully keep the load balance and reduce the communication cost.</p>

DOI： 10.1299/jsmecmd.2018.31.213

J-GLOBAL

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J-GLOBAL

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記述言語：日本語   出版者・発行元：日本計算工学会  

CiNii Research

J-GLOBAL

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmecmd.2017.30.034

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmecmd.2017.30.070

J-GLOBAL

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmecmd.2016.29.089

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開催年月日： 2018年

記述言語：日本語  

<p>A weakly compressible scheme for low-Mach number gas-liquid two-phase flows have been developed for a fullexplicit time integration to avoid solving Poisson equation. We introduce the fractional splitting method and directional splitting method to solve Euler equation which an efficient semi-Lagrangian scheme is applicable to. To describe the gas-liquid interface the conservative Allen-Cahn equation, which is one of the phase-field models, combined with the continuum equation is introduces. The accuracy of numerical results of two-phase flow strongly depends on the mesh resolution near the interface. The AMR (Adaptive Mesh Refinement) method greatly reduces the computational cost, since it is possible to assign high-resolution mesh to the region around the moving interface. We have developed a code to solve the equation in a manner of the tree-based AMR. Fractional step method and the directional splitting method helps to reduce the implementation difficulties of AMR method. We successfully carried out some violent two-phase flow simulation and flow including very thin liquid film by using the method which is combined weakly compressible scheme with AMR method.</p>

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開催年月日： 2018年

記述言語：日本語  

気液二相流の数値シミュレーションは, 未だに数値流体力学的課題の多いテーマである. 近年のコンピュータの著しい性能向上に伴って, 流体方程式と界面追跡の方程式を直接解くことによる解析がなされてきている. しかし, 格子を増やすと新たな水滴や気泡が生じるなど, 解の収束性に至る十分な格子解像度で計算することは非常に困難である. 一般に気液二相流は界面近傍が激しく運動し複雑な挙動を示すため, 界面挙動を精度よく捉えるためには多くの格子が必要である. 界面近傍をより高解像度で効率的に計算するために, 細かい格子が必要となる領域に格子を集めることのできるAdaptive Mesh Refinement (AMR) 法を気液界面に適用することが考えられる. 総格子点数を大幅に削減することができ, 界面近傍をより高解像度で計算することが可能となる. 直交格子上で界面を追跡する手法として, レベルセット法, VOF法が広く用いられてきた. しかし, 激しい流れでは液体よりVOF値は小さいが気体より大きな値を持つ領域が気体中を浮遊する問題などが生じてしまう. 近年, 新たなアプローチとして保存形フェーズフィールド法が提案されており, 本研究では界面捕獲手法として良い結果が報告されている保存形Allen-Cahn方程式を用いる. マルチモーメント法である保存形IDO法を用いて保存形Allen-Cahn方程式を解くことにより, 格子点上に変数を配置しながら気相と液相の質量保存性を担保する. 保存形マルチモーメント法では格子点上の値に加えて線積分値や面積分値といったモーメントが時間積分される変数として定義されている. レベル差補間の際にはコンパクトな領域で精度の高い補間関数を構築可能であり, AMR法に適した手法であると言える. また, 界面が時間とともに動く場合には保存形Allen-Cahn方程式の時間微分項に流束の微分項が加わる. フェーズフィールド変数に対する連続方程式と保存形Allen-Cahn方程式に分離して解くことにより, 連続方程式に対してはCIP-CSLR1法を, 保存形Allen-Cahn方程式には保存形IDO法を用いることができる. 分離した式はいずれも方向分離法で各々の方向に対する1次元の式を繰り返し解くことができ, 連続方程式の解法に精度の高いセミ・ラグランジアン法が適用可能である. AMR法適用に際しても1次元方向のみの補間を考えれば良くAMR法の実装が容易な手法となっている. <br>本論文では流束項付き保存形Allen-Cahn方程式をマルチモーメント法の解法を高精度で解くために, 木構造に基づいたAMR法により界面の時間的・空間的に追従する動的な適合格子細分化法を導入した. フェーズフィール変数が急激に変化する領域に細かい格子を動的に配置する. ベンチマーク問題としてSingle Vortex問題をレベル0から5までの格子細分化を行って計算し, 最も細かい格子解像度で均一格子を用いた場合と比較して平均で1/12.3に格子点数を削減することができ, 9.26倍に計算を高速化することができた. 界面形状も計算領域全体を均一に細かい格子で計算した場合と同じ精度が出ていることを確認した. マルチモーメント法を用いることによりコンパクトで高精度な補間関数を構築可能であるため, 界面が大変形するような問題に対しても高い精度で計算できる. 本論文の成果は, 気液界面に適合した動的な格子細分化による気液二相流計算に適用可能である.

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開催年月日： 2018年

記述言語：日本語  

<p>In distributed implementations of stencil AMR applications, the inter-node communication time often represents a major performance bottleneck. Thus minimizing communication is an objective as important as maintaining a good load balance. We propose a new domain partitioning method for block-based AMR applications based on the multi-phase-field (MPF) model. The MPF model for polycrystalline growth minimizes the interfacial energy and forms a convex shape for each crystal grain. In our method, each phase of the MPF model represents a computational sub-domain. We show that the MPF partitioning can successfully keep the load balance and reduce the communication cost.</p>

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開催年月日： 2017年5月

記述言語：日本語  

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開催年月日： 2016年

記述言語：日本語  

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