1. Dept. of Hydromechanics, Univ. of Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart, Germany (corresponding author).
2. Dept. of Engineering of Oil and Gas Pipelines, Gubkin Russian State Univ. of Oil and Gas, Leninsky Ave. 65, 119991 Moscow, Russia.
3. Professor, Dept. of Hydromechanics, Univ. of Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart, Germany.