1. Research Engineer, Fluid Dynamics Sector, Central Research Institute of Electric Power Industry, Chiba 270-1194, Japan (corresponding author).
2. Senior Research Engineer, Fluid Dynamics Sector, Central Research Institute of Electric Power Industry, Chiba 270-1194, Japan.
3. Research Associate, Fluid Dynamics Sector, Central Research Institute of Electric Power Industry, Chiba 270-1194, Japan.
4. Professor, Disaster Prevention Research Institute, Kyoto Univ., Kyoto 612-8235, Japan.