Numerical Prediction And Free Running Model Test Of The Maneuverability Of A VLCC In Waves

The maneuverability of ship has very close relation with safety and economy of sailing. Moreover, because of the large breadth, inertia moments and block coefficients etc., there are much more differences between the maneuverability of VLCC and that of common merchant ships. What's more, people begin to pay more and more attentions to the problems about environment pollutions and ecological destructions caused by oil leak. So the deep and detailed research on the maneuverability of VLCC has become a vital research topic. Especially, the maneuverability of VLCC in waves has become one of the problems which have been payed more attention.As there are mainly two popular and important methods of study ship maneuverability, which are numerical simulation and free-running model test which developed by shanghai Jiao Tong University independently , so the paper use those two methods to research the maneuverability of 320KDWT VLCC in calm water and waves respectively.The key point of Numerical simulation of ship maneuverability is the construction of mathematical model. Kijima MMG separate mathematical model is used in this present paper, and rolling is also considered in this model. Using numerical simulation program developed by Fortran programming language, present paper has predicted the maneuverability of 320KDWT VLCC in calm water firstly. The free-running model test is also carried out to verify the results of simulation. In this paper, maneuverability experiments in four different trimming condition of three kinds of different loading which include full load, half load,ballast load has been carried out by free-running model . The tests mainly include turning circle test, zig-zag test, crash stop test, spiral test and so on. The maneuverability is checked by IMO standards. The influences of trimming conditions and loading conditions to VLCC maneuverability have been analyzed in detail in this paper.The theoretical research on Maneuverability of VLCC was also on the base of MMG separate mathematical model, but the wave forces were considered in the maneuvering motion formulations. By change the wave parameters, such as wave heights, frequencies, wave length and wave angle, the VLCC maneuvering performances at different wave steepness and initial wave angles have been predicted by mathematical simulation program, the influences of different wave steepness and initial wave angles to maneuvering performances have been studied. By comparing the maneuvering performances in calm water, the influences of wave force to the maneuverability of VLCC can be easily discovered. Maneuverability experiments of VLCC in waves have also completed in this paper, including turning test, zig-zag test, crashing stop test. Test results have been compared with numerical simulation results. As for the maneuvering performance numerical prediction of vessels in waves, one of the most important problems is how to compute the wave forces. By using general software, first order and send order wave forces at different speeds and different wave angles have been attained, then the wave force data was packed into module and prepared for been called by main program. During the progress of numerically simulating, using the Lagrange interpolation, instantaneous wave force at some a speed and some a wave angle can be acquired, then the instantaneous wave force can be used as the initial condition of next step of calculation. Except for the numerical simulation, free running model test, synchronous wave height gauge system has been developed to study the relative the change of wave height of ships in sailing.Comparing the results of numerical prediction with those of Free-running model test, discover that numerical prediction agree very well with experiments in calm water, which proved that maneuvering performance numerical simulation program could predict the maneuverability of VLCC effectively. Numerical prediction of VLCC maneuverability in waves also agrees well with experiments in regular waves, so the simulation program was also qualified for the maneuverability predictions in waves.Analyzing the numerical simulation and free-running model test in calm water, discovered that load condition and trimming condition both can influence the maneuvering performances of VLCC prominently; studying the numerical simulation and free-running model test in waves, found that wave steepness and initial wave angle could influence the maneuvering performances in waves obviously.