Large-scale and/or long-span structures, which must be sustained for long service life, are susceptible to strong winds. Their design wind speeds are mostly decided by typhoons in Japan. Global warming typically causing the increase of the sea-surface temperature would affect, probably intensify typhoons approaching Japan. In order to investigate the effects of the increase of the sea-surface temperature on typhoon frequency and intensity, a new typhoon simulation technique was developed incorporating the sea-surface temperature. The new simulation technique predicted future trends due to the increase of the sea-surface temperature that the number of typhoon approaching Japan increased and depression of the central pressure increased. It was also shown that 100-year recurrence wind speeds in 24 regions in Japan increased by 10 - 15% on the average due to future increase of the sea-surface temperature.
Since the wind load is critical for the design of transmission lines, it is important to assess the design wind speed reasonably at construction sites. Wind loads acting on the transmission tower usually vary greatly by direction because of the structural characteristics. However, in the current design method of transmission towers, non-directional basic wind speed is applied in Japan, and therefore in many cases this may result in overestimation. In this paper, a method to estimate directional basic wind speed for the transmission tower design is proposed. The return period of the directional wind speed is estimated keeping the same non-exceeding probability of occurring stresses as the current design method. Then directional basic wind speeds at meteorological stations are determined by comparing with the typhoon simulation results.
The purpose of this research is to construct a database of a non-stratified airflow past a steep simple terrain under an imposition of a uniform flow, and, in addition, is to do the accuracy inspection of the numerical model under development at present. This numerical model is referred to as the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain), and is for the purpose of the prediction of airflow over complex terrain with several m to several km. This paper describes the experimental and numerical study of a non-stratified airflow past a two-dimensional ridge in a uniform flow as the first phase. The Reynolds number, based on the uniform flow and the height of the ridge, is about 104. Airflows around the ridge include the unsteady vortex shedding. Attention is focused on airflow characteristics in a wake region. For this purpose, the velocity components in the streamwise direction were measured with a SFP (Split-Film Probe) in the wind tunnel experiment. In addition, the flow visualization was performed by using the smoke-wire technique. Through comparison of the experimental and numerical results, they showed a good agreement. The accuracy of both of the wind tunnel experiment by the SFP and also numerical simulation by the RIAM-COMPACT were confirmed as the result.