1. Department of Mechanical Engineering, University of Genoa, 16145 Genoa, Italy (e-mail: alessandri@dime.unige.it)
2. Department of Mechanical Engineering, University of Genoa, 16145 Genoa, Italy.
3. Institute of Marine Engineering, National Research Council of Italy, 16149 Genoa, Italy.
4. Boschman Technology BV, 6921 EX Duiven, The Netherlands.