1. Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513, Eindhoven 5600 MB, The Netherlands e-mail:
2. State Key Laboratory of Hydraulic Engineering, Simulation and Safety, School of Civil Engineering, Tianjin University, Tianjin 300350, China e-mail:
3. Hydromechanics Laboratory, Department of Civil Engineering, Middle East Technical University, Ankara 06800, Turkey e-mail: