A pair of conical vortices formed on a flat roof of a low-rise building, when an approaching flow attacks to the building with an oblique angle, randomly exchanges their strength to each other. The phenomenon is called as the 'Switching of conical vortices'.
When a splitter plate was set on the roof to prevent the direct interference between conical vortices on the roof, the switching phenomenon still appeared clearly, while a splitter plate set in the wake of the model eliminated the occurrence of the switching of conical vortices on the roof. These findings considerably justify the idea that the switching of conical vortices on a roof, which were connected to vortices in the wake of the model, can be drawn from the interference between vortices in the wake.
Performance of the uneven dual-screen windbreak (UDSW) to protect agricultural products from the strong wind was tested when the typhoon 0310 attacked Okinawa. The test area surrounded by the UDSW is located on a plateau near a cliff. Wind speed was measured by ultrasonic anemometers at 6m high from the ground outside of the test area and 3m and 6m high inside. The relations between the distance from the cliff edge and the average wind speed were indicated a quadratic function of the distance in the range of 400m from the edge. These calculated data by a quadratic function were compared with the measured data. The wind speed at 28m leeward from the UDSW was reduced by 25% at a height of 6m, and that at 90m leeward was reduced by 17%. The wind speed ratio at a height of 3m to 6m was increased with distance from the UDSW about 0.83 to 0.92.
In current design practice, the responses of buildings and structures to fluctuating wind loads are usually separated into the background and resonant components, based on the assumption that these two components are not correlated with each other. The present paper proposes a new model for estimating the wind-induced responses of tall buildings, in which the background and resonant components and their cross-term are strictly defined and included. Therefore, the new model is more exact than the conventional ones. Comparisons are made for the along-wind and across-wind responses of tall buildings between this model and the conventional ones, based on a parametric investigation. The results show that the conventional models give results similar to those obtained from the new model for the along-wind responses, but generally underestimate the across-wind responses. Finally, some conclusions and useful suggestions are presented.