Dynamics of Vehicle-Deck Interactions

Doktorsavhandling, 2006

The work presented in this thesis concerns the modelling and analysis of vehicle-ship deck interactions. The physical modelling of vehicles is discussed together with the modelling of supporting structures/ship decks, and the interactions between vehicles and supporting structures. The relevant research and some engineering applications are studied, for example, the dynamic structural behaviour of vehicle-ship deck systems, vehicle vibrations, damping effects of vehicles on structural systems, dynamic interactions between tyres and deck surfaces, and vehicle securing on decks during ship motions. From the study on the dynamic structural behaviour of vehicle-deck systems, it was found that the spring-damping system of vehicle suspensions and tyre can interfere in the dynamic transmission of the vehicle mass into deck structures. It was observed that the vehicle cargoes can work as mass dampers to reduce at least one mode shape response. The dynamic interactions were also dependent on the parking positions of vehicles on decks and the excitation frequencies from decks’ supports. The characteristics of the structural vibrations in both a forced and a free vibration phase were described. It was also found that the typical operations of vehicles on decks will not cause the resonance of the deck structures. Modal testing of unloaded and vehicle-loaded lightweight deck systems and the tyre-deck friction under dynamic loading were carried out. From the tyre-deck friction experiments, carried out at different excitation frequencies, it was found that the friction coefficient is mainly dependent on the types of deck surface paints used as well as the normal force caused by the wheel load. However, the variations of the friction coefficient are not sensitive to the changes of deck excitation frequencies (below 20 Hz). Based on the experimental results, numerical studies were carried out to investigate the interactions between a full vehicle model and decks under ship motions. It was concluded that vehicle securing on decks is highly influenced by the ships’ roll and pitch motions, pitch period, orientations, positions of vehicles parked on decks, and wave height. Finally, suggestions for the layout of deck structures as well as vehicle securing without lashings are proposed.