1. Hitachi Research Laboratory, Hitachi, Ltd.
832-2 Horiguchi, Hitachinaka-shi, Ibaraki 312-0034, Japan e-mail:
2. Shikoku Electric Power Co., Inc., 2-5 Marunouchi, Takamatsu-shi, Kagawa 760-8573, Japan
3. Basic Engineering/Hydraulic Laboratory, Hitachi Mitsubishi Hydro Co., 3-2-1 Saiwai, Hitachi-shi, Ibaraki 317-0073, Japan
4. Basic Engineering/Hydraulic Laboratory, Hitachi Mitsubishi Hydro Co., 3-2-1 Saiwai, Hitachi-shi, Ibaraki 317-0073, Japan e-mail: