Some atmospheric phenomena, i.e., gust front, morning glory and pressure dip, and their soliton models are reviewed. Atmospheric solitons of internal gravity wave type based on the weakly nonlinear theory are now classified into two categories : i) Algebraic solitons of the Benjamin-Davis-Ono equation, for which the waves are confined to the lower few kilometers of the troposphere, are used for models of gust front and morning glory. ii) KdV solitons of the Korteweg-de Vries equation, for which the waves occupy the entire troposphere, are used for models of pressure dip. Although the observations support the soliton models for these atmospheric phenomena qualitatively, developments of soliton theory for the treatment of upper layer in algebraic soliton model with non-zero scorer parameter and the upper boundary condition in KdV soliton model with the critical level are desired to discuss them quantitatively.

抄録全体を表示

When a train enters a tunnel, a pressure wave is generated and it travels between both portals of the tunnel. The pressure change in a tunnel is closely related to the problems of aural discomfort to passengers, the strength of car body structure, and so on. When the pressure wave travelling in a tunnel arrives at the tunnel exit, a pressure pulse we name “micro-pressure wave” is radiated from the tunnel exit, raising a new environmental problem. The micro-pressure wave depends on the shape of the pressure wave arriving at the tunnel exit; it is nearly proportional to the pressure gradient of its wave-front. This article deals first with an analysis of the pressure change in a tunnel, next with the radiation of the micro-pressure wave and an analysis of the distortion of the wave-front of the pressure wave as it travels in a tunnel.

抄録全体を表示

Wind waves are familiar but extremely complicated stochastic phenomena that are controlled by strongly nonlinear processes of turbulence and wave breaking. A long history of studies on wind waves has much advanced our ability to forecast their evolution for practical or engineering purposes. There still remain a number of fundamental problems to be solved, however, as regards their generation, growth, and decay. This short article briefly presents a few topics on wind waves among the studies carried out in our institute : (1) wind-wave effects on the roughness of the sea surface, (2) new schemes for computing nonlinear energy transfer among wind waves, (3) interaction of swells (long waves) and wind waves (short waves), and (4) nonlinear properties of wind waves and higer-order spectra.

抄録全体を表示

This paper describes the aerodynamic properties and their generation mechanism of various wind-induced vibration of bridge structures, based on the recent investigations. For vortex-induced vibration, two different kinds of vortices, which are related to the instability of one/two shear layer (s) respectively, play major role. Furthermore, the intermittent Karman vortex shedding can excite the inclined circular cylinder at much higher reduced velocity than the reciprocal of Strouhal number, so called “high speed vortex-induced vibration”. Galloping instability is caused by the unsteady flow for bluff section and the quasi-steady flow for slender section, corresponding to “low speed galloping” and “high speed galloping”, respectively. On the other hand, it is shown that the torsional flutter instability is fundamentally identical to the coupled flutter instability from the point of flow pattern / unsteady pressure distribution characteristics around the body based on non-dimensional chordwise coordinate which is normalized by the body height. Finally the aerodynamic stabilization of these wind-induced vibration is briefly discussed.

抄録全体を表示

Shock wave phenomena, propagation and reflection, are reviewed. One dimensional propagation of exploding and imploding shock waves based on similarity methods is reviewed and in addition, decay exponents of shock waves analyzed by the shock dynamics theory of Witham are discussed for comparison. The oblique reflection of shock waves on a wall is also reviewed for both steady and quasi-steady flows. Results of numerical simulation for various types of shock reflection are discussed. Recent advances on reflection phenomena are also covered.

抄録全体を表示

都市キャノピーにおける垂直乱流構造および組織的な乱流運動を明らかにするために, 札幌市郊外の住宅地 (平均高さh=7m) において1991年から1992年にわたって野外観測を行った.観測高さは, それぞれ5.4m, 10.3m, 18m, 35mおよび45mである.その結果, 変動風速の標準偏差σ_uの垂直分布はキャノピー上でブロードなピークを持ち, 一方, σ_vおよびσ_wはほぼ均一な分布となっていることが分かった.レイノルズ応力の垂直分布は, キャノピー高さの1.5倍付近で弱いピークを示し, それ以上の高度ではゆっくりと減少する.また, レイノルズ応力の高い値を持っ層は, 高速流体魂の下層への流入 (sweep) および低速流体魂の上層へ噴出 (ejection) する2つの特徴的な乱流運動によって形成されていることが, 4象限解析により明らかにされた.更に, アンサンブル平均法によりramp現象に伴う流れ場と温度場の構造が示され, 組織運動が起こした上昇流および下降流はキャノピー内外における熱の垂直輸送に重要な役割を担っていることが明らかとなった.

抄録全体を表示

電磁場が支配的な平行平板間を流れる弱電離気体を取り扱う.平行平板壁は冷電極で, その電極間に外部から電磁場がかかり電流が流れている場合, 弱電離気体の流れと電磁場が荷電粒子の分布と振舞い, さらにシースの形成にどのような影響を及ぼすかをシース領域に限って解析した.その結果, シース領域の厚さ, イオンの密度分布, 電圧-イオン密度の関係などを得た.

抄録全体を表示