Takuro Michibata, RIAM Research Institute for Applied Mechanics, Kasuga, Japan, Kentaroh Suzuki, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan, Miho Sekiguchi, Tokyo University of Marine Science and Technology, Tokyo, Japan and Toshihiko Takemura, Kyushu University, Research Institute for Applied Mechanics, Fukuoka, Japan