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.

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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.

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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.

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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.

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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.

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To investigate turbulence characteristics and organized motion within and above the urban canopy, field observations were conducted in July 1991 and Nov. 1992 in Sapporo, Japan. The measurement heights were 5.4m, 10.3m, 18m, 35m and 45m aboveground; the canopy height was 7m. The profiles of σ_u, peaked slightly above the canopy, while σ_v, and σ_w had nearly uniform profiles. Vertical profiles of Reynolds stress peaked slightly at 1.5 times the canopy height and decreased slowly with height thereafter. A four-quadrant analysis showed that sweep and ejection motions caused the higher layer of Reynolds stress, during which high-velocity fluid from above moves downward toward the surface and low-velocity fluid from below moves upward. An ensemble-averaging technique was used to isolate typical features of the flow and temperature fields. A time-height cross section of velocity vectors and temperature contours showed details of the flow structures associated with temperature ramps. It has been noted that the organized motions play important roles in the transport of heat near the urban canopy, where the sweep motion causes negative temperature fluctuation and the ejection motions causes positive temperature fluctuation.

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The effect of E×B on the flow field of a slightly ionized gas between parallel coldconducting plane walls is investigated theoretically. The gas flows in the direction parallel to conducting walls. A subject of investigation is limited in the sheath region where Ohm's law and Poisson's equation are used. When the magnetic field increases, the thickness of sheath region decreases and then capturing voltage of ion decreases. When gas speed increases, the sheath thickness does not change and the decrease of ion number density is relatively small compared with that without magnetic field.

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