Yoshiharu Iwatani

Simultaneous measurements of wind speed profiles at two sites using Doppler sodars

In the wind-resistant design of buildings and structures, it is very important to accurately assess the design wind speed at a particular site, considering the variation in wind speed with terrain roughness. The authors attempt to find a reasonable method for estimating design wind speed for given terrain roughness, through simultaneous wind observations at altitudes up to 420 m at sites with different roughnesses using two sets of Doppler sodars. In this paper, the characteristics of the mean wind speed profiles evaluated for each distinguished wind speed in each wind direction were presented. The longitudinal mean wind speed profiles in the same storms were also compared for two pairs of sites to study the variation in longitudinal mean wind speed as it is affected by inland terrain roughness.

Stability dependence of the drag and bulk transfer coefficients over a coastal sea surface

Bulk transfer coefficients were evaluated from eddy correlation flux measurements on a fixed pier during onshore winds. The mean values are CD = 1.69 × 10-3, CH = 2.58 × 10-3 and CE = 1.51 × 10-3. The drag coefficient, CD, gradually increases with wind speed but CH and CE are independent of wind speed. According to theory and empirical formulas based on experimental results over flat grassland, the transfer coefficients should gradually increase with increasing instability. This is confirmed experimentally in the stable region in our case. However, the drag coefficient appears to decrease with increasing instability, which is against the theoretical result. A stability dependence is not clearly observed for CH or CE.

Simultaneous wind measurements over two sites using Doppler sodars

Abstract In wind-resistant design of buildings and structures, it is very important to accurately assess the design wind speed at a particular site, considering the variation in wind speed with terrain roughness. In this study, the authors attempt to find a reasonable method for estimating design wind speed for a given terrain roughness, through simultaneous observations of atmospheric boundary layer wind speeds over two sites with different roughnesses using Doppler sodars. The mean wind speed profiles at the two sites during the same storms were compared to study the variation in mean wind speed as this is affected by inland terrain roughness.

Turbulence of vertical velocities at the coast of reclaimed land

Abstract This paper deals with turbulence properties measured on a 50 m tower on the coast of reclaimed land during strong winds. Special emphasis is placed on the correlation of vertical velocities. Space-time correlations, coherences and phases between various heights are obtained and the resulting estimates are compared with previous observed results. The relationships between these estimates and height are approximated by algebraic expressions. A discussion is given of the characteristic patterns of wind flow observed in the lee of a small hill.