Microbubbles can grow from nuclei and collapse violently under acoustic pressure. This phenomenon is called acoustic cavitation. The gas in the microbubbles is adiabatically compressed in the violent collapse, and its temperature can reach thousands of degrees. This is regarded as the primary mechanism of sonoluminescence and sonochemical reactions. Research undergoing on the use of acoustic cavitation for inducing therapeutic effects with ultrasound is described in this paper.

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Flow behavior of large particle-water two-phase slug flow was observed in a vertical pipe of 30.3mm inside diameter. Large particles with 12.9 and 17.8 mm in mean diameter and density about 2300kg/m³ were used as solid phase. Velocities of solid slug composed of several particles and of solid particles in liquid slug were estimated by proposed correlations of their restricted settling velocities in a pipe. Departure phenomenon of a solid particle from solid slug were also discussed.

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In this report an experimental study of double diffusive natural convection is performed for a sucrose solution between vertical parallel plates which is heated from one side and cooled from opposite side with an initial condition of a vertically linear concentration gradient. An optical fiber sensor with a thermocouple is used to obtain the vertical distributions of concentration and temperature. The number of multi-layered convection cells changing with the elapsed time from the start of cooling and heating can be counted and the thickness of cells are measured precisely. It is shown that the evolution of layering is a typical example of self-organization in non equilibrium systems. The relationship between the lifetime which is the elapsed time required to become to a vertically uniform concentration and Rayleigh number is obtained. The observation by shadowgraph is also conducted as an auxiliary method.

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This paper presents a finite element method for an incompressible two-fluid model. The solution algorithm is based on the fractional step method, which is frequently used in the finite element calculation for singlephase flows. The calculating domain is divided into quadrilateral elements with four nodes. The Galerkin method is applied to derive the finite element equations. Air-water two-phase flows around a square cylinder are calculated by the finite element method. The calculation demonstrates the close relation between the volumetric fraction of the gas-phase and the vortices shed from the cylinder, which is favorably compared with the existing data. It is also confirmed that the present method allows the calculation with less CPU time than the SMAC finite element method proposed in my previous paper.

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河川流域の地形は侵食・堆積現象を通じて絶えず変動している。これが急激に起こる場合にはときには大災害を引き起こし、緩やかな場合にもそれに伴う河床変動によって治水上の問題が引き起こされる。このような地形の変動は、すべて流砂の不平衡によってもたらされている。ここに、流砂研究が河川工学の中心課題の一つであるゆえんがある。流砂現象は固液混相流の代表的なものの一つであるが、それを統一的に扱う支配方程式が確立されていると云える段階にはない。本講座では、紙面を通じて識者の議論の種を蒔くことを目的として、1. 土石流の力学、2. 掃流状集合流動、3. 掃流砂の流れと土石流の力学の相似性、および4. 固液混相流の支配方程式の課題等について解説したい。

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カオス (決定論的カオス) とは何かについては、専門家の間でも必ずしも統一された見解があるわけではない。
通俗的には、カオス的な系は「決定論的な関係式によって記述される運動であるにも拘わらず、一見不規則に見える複雑な非周期的運動を行う力学系」であり、「初期値の僅かな違いが、長時間後の系の挙動に大きな差異をもたらす」とされている。しかし、実験データから、対象系がカオス的であるかどうかを判定しなければならない場合、カオスに関する上記の説明はあまり役立たない。本稿では、カオスとそれに関連する諸概念を、数学的に厳密な観点からではなく、実験を通じてカオスと接する工学者の立場から解説する。

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The development of a foaming applicator that produces a formed in-place foaming gasket using the pure fluid mechanics system is in progress. This system uses the laminar flow shear function in a pipe to make uniformed small foam via pumping high viscosity liquid-gas two-phase flow under high pressure. The principle, the characteristic, and present state of our foaming applicator are briefly described in this report.

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