No abstract

To simulate the dynamic responses of the multibody system with a floating base when the upper parts spread with a certain sequence and relative speed, the homogeneous matrix method is employed to model and simulate a four-body system with a floating base and the motions are analyzed when the upper parts are spread sequentially or synchronously. The rolling, swaying and heaving temporal variations are obtained when the multibody system is under the conditions of the static water along with the wave loads and the mean wind loads or the single pulse wind loads, respectively. The moment variations of each joint under the single pulse wind load are also gained. The numerical results showed that the swaying of the floating base is almost not influenced by the spreading time or form when the upper parts spread sequentially or synchronously, while the rolling and the heaving mainly depend on the spreading time and forms. The swaying and heaving motions are influenced significantly by the mean wind loads. The single pulse wind load also has influences on the dynamic responses. The torque of joint 3 and joint 4 in the single pulse wind environment may be twice that in the windless environment when the system spreads with 60 s duration.

Following general explanations of the working principles of different existing retardation systems to restrain an advancing powerless ship the principles of a new overhead retardation system are presented. A two dimensional simplified model of the activated overhead system is formulated based on Huston's interpretation of the Kane methodology. Reduced Kane equations are used in the actual simulation, once initial conditions and mechanical analysis of constituent elements have been formulated. Having presented the computational process the various velocity, motion and joint constraint force characteristics of the anchor, the ship and the other elements are monitored in the time domain for the duration of the retardation process. Validation of the Kane based method is established utilising the conservation law and the Lagrangian based formulation of the retardation system within the ADAMS software. The results indicate that a peak value of constraint will occur because of the sudden movement of anchor and this peak is affected significantly by initial ship speed. Variation in anchor chain, overall cable length and its horizontal projected length has little influence upon retardation system performance, whilst the changes of sea bed friction, anchor mass, water depth, initial ship velocity and ship mass will make retardation behaviour different.

No abstract