1. Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
2. Laboratory for Hydraulic Machines (LMH-IMHEF), École Polytechnique Fédérale de Lausanne (EPFL), Avenue de Cour 33bis, CH-1007 Lausanne, Switzerland