1. Postdoctoral Research Fellow, Waterpower Laboratory, Norwegian Univ. of Science and Technology, NTNU, Alfred Getz vei 4, 7491 Trondheim, Norway.
2. Professor, Waterpower Laboratory, Energy and Process Dept., Faculty of Engineering Science and Technology, Norwegian Univ. of Science and Technology, NTNU, Alfred Getz vei 4, 7491 Trondheim, Norway (corresponding author).