著者

渡辺 勢也 青木 尊之 長谷川 雄太 河原 淳 橋本 博公

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.33, no.1, pp.55-62, 2019-03-15 (Released:2019-04-08)

参考文献数

21

被引用文献数

1

---

Numerical simulations are powerful tools to study tsunami impacts on building structures. We have developed a CFD code for free-surface flows interacting with floating debris by using Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM). Both methods are suitable for GPU computing and large-scale simulations because they are explicit time-integration schemes. In order to improve the accuracy and the stability of flow computation, the cumulant LBM model has been employed and coupled with the conservative Allen-Cahn equation for the purpose of free-surface capturing. A moving boundary approach based on the interpolated bounce-back scheme is utilized at liquid-solid interfaces. Rigid body dynamics of floating debris is computed by using DEM. A model constructed by multiple small spheres represents complex shapes of debris. We measure the weak scalability on multiple GPUs of the TSUBAME3.0 supercomputer, and the code achieved 83.4% parallel efficiency when scaled 16 to 256 GPUs. As a test case, we demonstrate a tsunami flow with driftwoods using 200×600×3000 lattice nodes and 24 GPUs Tesla P100, and the simulation has completed within 24 hours. The impact force of the driftwoods acting on the wall is about 15 times larger than only water. It shows that effects of driftwoods are important to evaluate the tsunami damage on building structures.

著者

山口 拓真 師岡 愼一

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

pp.2018.004, (Released:2018-05-18)

参考文献数

15

被引用文献数

2

---

The severe accident in Fukushima daiichi nuclear power plant revealed the importance of molten core cooling system without the electric power, then cooling system by natural circulation flow has attracted attention. The heat removal performance of this system depends on the natural circulation flow rate, so it is essential to predict the flow rate accurately for the safety design. The purpose of this study is to develop the evaluation method for the natural circulation, and to examine its accuracy dependence on the channel shape. Experiments were carried out at atmospheric pressure, using room temperature air-water flow. We used seven kinds of channels with various shape and diameter, and measured natural circulation flow rate and pressure drop for each channel. Predictive analysis was conducted by our method based on balance between driving force and pressure drop in the loop channel. The major results are as follows: (1) It is possible to predict the natural circulation flow rate with an error of less than 20 percent for various shaped channels. The average and standard deviation for the ratio between calculated and experimental flow rate is 0.98 and 0.047. (2) Two phase prediction method for pressure drop has maximum 15 % error. To improve the prediction accuracy, it is important to improve the prediction of the void fraction and the two-phase multiplier.

著者

菱田 公一

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.31, no.3, pp.250-256, 2017-09-15 (Released:2017-10-24)

参考文献数

20

---

This paper presents mainly a review of measuring techniques for multiphase flows in the past 30 years and an outlook of future progress on distributed measuring systems. Laser based measuring system had started by point measurement such as a probe, laser Doppler, and Phase Doppler anemometry, and then extended to Particle Imaging techniques to obtain 2D plane information. Recently, high speed digital cameras allowed us to get 3D3C temporal velocity information. The possibility of IoT based distributed sensing system is discussed with an application of multiphase flow analysis for future developments.

著者

川原 顕磨呂 佐田富 道雄 斉藤 栄俊 佐藤 泰生

出版者

THE JAPANESE SOCIETY FOR MULTIPHASE FLOW

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.9, no.1, pp.26-36, 1995

被引用文献数

2

---

To provide data necessary for modeling turbulent mixing between subchannels in a nuclear fuel rod bundle, three experiments were made in series for equilibrium two-phase flows, in which net mass exchange does not occur between subchannels for each phase. The first one was the measurement of turbulent mixing rates of both gas and liquid phases by a tracer technique, using air and water as the working fluids. Three kinds of vertical test channels consisting of two subchannels were used. The data have shown that the turbulent mixing rate of each phase in a two-phase flow is strongly dependent on flow regime. So, to see the relation between turbulent mixing and two-phase flow configuration in the subchannels, the second experiment, flow visualization, was made. It was observed in slug and churn flows that a lateral inter-subchannel liquid flow of a large scale is caused by the successive axial transit of large gas bubbles in each subchannel, and the turbulent mixing for the liquid phase is dominated by this lateral flow. To investigate a driving force of such large scale lateral flow, the third experiment, the measurement of an instantaneous pressure differential between the subchannels, was made. The result showed that there is a close relationship between the liquid phase mixing rate and the magnitude of the pressure differential fluctuation.

著者

梶島 岳夫

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.31, no.2, pp.135-138, 2017-06-15 (Released:2017-07-18)

参考文献数

19

---

The turbulence modulation, that means influences of dispersed particles to the fluid turbulence, is one of the challenging subjects in the multiphase flow research. In recent decades, experimental and numerical researches have been conducted extensively. Especially the direct numerical simulation (DNS) became a powerful means to reveal the multiphase turbulence phenomena. But DNS cannot become a practical tool for multiphase flows in industry or in nature. In this review article, an example of particle-laden flow by the immersed solid method and our recent progress for the application to the two-phase heat transfer are shown. Then, considering the current status, it is pointed out that some moderately-averaged equation, which includes momentum exchange and residual stress terms, is essential for semi-DNS including finite-sized particles (e.g., Kolmogorov scale particle) to deal with large-scale multiphase flow fields.

著者

深野 徹

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.6, no.1, pp.92-98, 1992-03-15 (Released:2011-02-22)

参考文献数

10

---

今回は流動様相という語句の周辺の用語について述べる。この語句は気液二相流特有の学術用語というより、一般的な意味あいが強いし、この語句のもとに定義されている気液二相流の様相自体もまた、使用している研究者によって必ずしも同じではないように思える。すなわち流動現象の複雑さと、それを観察する研究者のphilosophyによって、同じ語句のもとに違った流動様相を頭に描いている可能性がある。このことは、以下の説明にみられるように定量的に定義されているのではなく、観察者の感性に依っている面が多いことにも示される。したがって本解説にはあいまいな点が多く、かつ著者の独断も多く含まれているので、賢明なる読者諸氏の意見をいただければ幸いである。なお流動様式の名称としてここで述べなかった語句は数多いが、それらについては文献 (5) に詳述されているので、それらを参照していただきたい。

著者

深野 徹

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.6, no.2, pp.189-190, 1992-06-15 (Released:2011-02-22)

参考文献数

1

---

数式・数量やあいまいさの入りようのない明りょうな表現による言葉、で定義されていない場合は、同じ語句であっても使用者によって若干異なった意味あるいは現象を表わしていることがある。前回に述べた流動様式の定義にもその一例が見られた。本稿では同じような現象を対象にしながらも、観点や立場によって表現すなわち語句 (用語) が変わってくることもあり得ることを「沸騰二相流」という語句を介して考えてみたい。

著者

茂渡 悠介 酒井 幹夫 水谷 慎 青木 拓也 斉藤 拓巳

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.24, no.5, pp.681-688, 2011-03-15 (Released:2011-06-15)

参考文献数

11

被引用文献数

3 3

---

Numerical approaches of the solid-liquid flows were not established so far. This is because the modeling of free surface and solid phase was difficult, furthermore the calculation cost might become excessive. In the present study, a new method is developed to simulate the solid-liquid flows involving the free surface. In this method, the solid-liquid flows were computed by combining the Discrete Element Method (DEM) and the Moving Particle Semi-implicit (MPS) method. This is called the DEM-MPS method. In the present study, the validation of the DEM-MPS method was performed in a solid-liquid flow involving free surface in a rotating tank. The angle of repose and solid distribution were compared between the simulations and experiments. The simulation results were in good agreement with those obtained by the experiment.

著者

細田 尚

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.23, no.4, pp.412-419, 2009-12-15 (Released:2010-06-23)

参考文献数

9

---

It is an increasing concern that the depletion of dissolved oxygen (DO) concentration at the bottom layer of the northern-part of Lake Biwa with 100m in maximum depth has been worsen in recent years not only due to eutrophication in water but also the effects of global warming such as the raise of air temperature during winter. Many research have been carried out by various organizations to clarify the mechanism of DO depletion near the lake bottom and to propose the countermeasures. This article firstly describes the seasonal variations of the vertical water temperature and water quality distributions to explain the fundamental features of heat and mass transfer occurring in the northern part of Lake Biwa throughout the year. Since it is well known that the thermal convection during the cooling period is the main mechanism of DO transfer from the surface to the lake bottom, the mixing processes caused by thermal convection are shown using the results of a 3D CFD simulation. Then, the electrolysis of water at the lake bottom for the restoration and DO recovery is introduced as one of the countermeasures proposed by Lake Biwa Environmental Research Institute, Shiga Prefecture. The simulation results of O2 bubble plumes with the dissolution into lake water are also shown under the conditions of laboratory and field experiments.

著者

宮野 直樹 大川 富雄

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.30, no.1, pp.75-86, 2016-03-15 (Released:2016-04-16)

参考文献数

32

---

Experiments were carried out to explore the mechanisms of bubble lift-off from a vertical heated surface in subcooled pool boiling. The experiments were conducted at atmospheric pressure and distilled water was used as the test fluid. A high speed camera was used for observation of bubble behavior. The main experimental parameters were the static contact angle of the heated surface, the liquid subcooling, and the wall heat flux. The time variation of bubble size was measured through image analysis. The growth force acting on the bubble was calculated using the measured time-evolution of the bubble size. The bubble growing on the vertical heated surface started to be extended in the horizontal direction when the sign of the growth force turned from negative to positive. It was hence considered that the growth force is one of the main causes of the bubble lift-off from a vertical heated surface. Furthermore, a correlation was developed for the bubble lift-off diameter considering the distribution of heat transfer rate around the bubble.

著者

山下 邦博

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.9, no.2, pp.105-115, 1995-06-15 (Released:2011-02-22)

参考文献数

10

被引用文献数

1 1

---

In order to elucidate the physical processes of the formation of fire whirl, a series of laboratory experiments on three dimentional temperature profile of crib fire plume in cross wind were performed. From the experimental result, it became evident that a fire in cross wind produces a pair of vortex-like circulation in the downstream side of fire plume. In rare occasions, fire whirls were observed in the series of experiment of multiple fires at the central or leeward part of multiple fires under weak wind.

著者

林 公祐 高田 尚樹 冨山 明男

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.20, no.3, pp.244-251, 2006-09-15 (Released:2007-02-09)

参考文献数

17

被引用文献数

2 4

---

An accurate method for evaluating surface tension force was proposed. The method utilizes a solution of the Cahn-Hilliard equation for the color function of the Continuum Surface Force model. Curvature vectors on three surfaces of revolution, i.e., sphere, distorted spheroid and spherical-cap were accurately evaluated by the method. Interface tracking simulations of a flow around a neutrally buoyant fluid sphere and of a drop rising through a stagnant liquid demonstrated that the proposed method could significantly reduce pseudo parasitic currents caused by numerical errors in surface tension force.

著者

田中 敏嗣

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.8, no.1, pp.41-47, 1994-03-15 (Released:2011-02-22)

参考文献数

5

被引用文献数

1

---

もう既に聞き飽きた感もあるが、計算機環境の発達によりさまざまな現象が数値シミュレーションにより取り扱われるようになった。混相流のような複雑な流れに対しても、流動を数値シミュレーションにより再現する試みが果敢になされている。最近では、ワークステーションの大幅な能力向上に代表される計算機のダウンサイジングにより、このような数値シミュレーションがより身近なものとなりつつあるのではないだろうか。混相流は時間的および空間的にさまざまなスケールの現象を含んでいるが、計算機の演算能力と記憶容量の増大は、よりミクロな視点に基づくモデルに立脚した数値シミュレーションを可能にする。固気二相流の分野では現在、固体粒子群の運動を個々の粒子レベルでモデル化するラグランジュ型の数値計算が盛んに行われている。この場合に気体の流れの計算には一般的な流体の数値解法が適用できるので、混相流としての特殊性は気流中の粒子群の運動をいかに解くかということと、気流に対する粒子の作用にある。本講座は数回にわたって連載を行うシリーズの中の第1回目であり、本シリーズでは固気二相流をラグランジュ型の数値シミュレーションで取り扱う際に問題となる粒子間衝突の有力な計算法として期待されるDSMC (Direct Simulation Monte-Carlo) 法と、その固気二相流への応用について述べる。DSMC法は希薄気体の流れの数値シミュレーション法としてBird [1] によって1976年に発表されたものであり、現在盛んに応用が行われている。DSMC法では、分子間の衝突判定に確率論的方法を用いることにより、実在する分子数に比べて少数の分子を追跡して、分子群の運動が求められる。この方法を粒子運動の計算に用いれば計算で扱う粒子数を軽減する他に衝突の判断も簡略化できるので、分散系粒子流動の数値シミュレーションを高濃度あるいは規模の大きな流れに拡張するために有望な方法である。さらに、DSMC法の考え方は固気二相流中の粒子運動のみならず、分散系混相流中の分散相の衝突的相互作用を考える場合にも参考になるものと考えられる。まず本報では、どのような場合に粒子間衝突の影響が問題となるかを示し、具体的な計算結果によって粒子間衝突の影響を紹介する。その後、DSMC法を理解するために必要な分子気体力学の基礎概念の解説を行う。

著者

堀田 亮年

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.24, no.4, pp.390-397, 2010-12-15 (Released:2011-02-09)

参考文献数

6

---

As an engineer who has devoted himself in the nuclear industry for almost three decades, the author gave a personal view on educating two-phase flow and developing human resources. An expected role of universities in on-going discussions of collaboration among industry-government-academia is introduced. Reformation of two-phase flow education is discussed from two extreme viewpoints, the basic structure of physics and the practical system analysis.

著者

田中 嘉宏

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.28, no.1, pp.19-31, 2014-03-15 (Released:2014-05-20)

参考文献数

14

---

In an extrusion process of rubber materials, there are a liquid-liquid phase and a gas-liquid phase. It is difficult to solve viscoelastic flow with high Weissenberg number. In this paper, interface between rubbers is solved by using the commercial software. The difficulty in the numerical simulation is specified. The solution to this problem is proposed. The proposed method is applied to the numerical solution of flow problems for a viscoelastic fluid in arbitrary computation domains. The proposed method is enabled to solve the viscoelastic flow with high Weissenberg number in comparison with the conventional method.

著者

一色 尚次

出版者

日本混相流学会

雑誌

混相流 (ISSN:09142843)

巻号頁・発行日

vol.1, no.2, pp.125-137, 1987-12-15 (Released:2011-02-22)

参考文献数

5