Study on ship's stability loss in surf-riding based on CFD
Based on Computational Fluid Dynamics, ship's righting arms of different heeling angles were calculated to study ship's stability loss in following sea. First, based on the wave-generation method of defining inlet boundary conditions, the numerical wave tank was constructed for ship's movement in surf-riding. Second, one slender ship's flow filed in calm water was numerically simulated, and the righting arms of different heeling angles were calculated. Third, the slender ship was set to navigate in surf-riding with wave crest at the midship section, and the flow field was simulated to get the righting arms of different heeling angles. The simulation results indicate that the righting arm in calm water show good agreement with experiment data; the stability loss is more serious when the wave amplitude is bigger; and ship wave's effect cannot be neglected in calculating ship's stability loss in surf-riding when ship speed is high.
Ship capsizing analysis using advanced hydrodynamic modelling
A ship's stability is fundamental to the safety of its crew, its cargo, and the environment. Several ocean-going vessels are lost due to instability each year, particularly in high seas. To prevent such losses, a better understanding of ship stability is necessary. In this paper we analyse the stability of ships using advanced mathematical models and methods. All the rigid-body motions of a ship, as well as memory effects in the fluid, are accounted for. The analysis shows that a ship's dynamics depend strongly on the nonlinearities of the ship–fluid system. In our analysis of a particular ship, we notice a sequence of bifurcations when wave heights increase, and we believe that this is an explanation for capsizing. Critical wave heights for capsize were identified. In quartering seas, the required wave height was much lower compared with following seas. A path-following method to determine the stability limits in a systematic manner is being developed.
China's experience on population control: The elusive model
Abstract After the Cultural Revolution China initiated a very intensive family planning programme. Although statistical data are not available, there is enough information to conclude that the custom of postponing marriage and planning births is gaining momentum. The new socio-economic environment is much more conducive to the acceptance of family planning by the young adults than was the case in previous campaigns. Contraceptives, abortions and sterilizations are free of charge and readily available through the extensive public health system. Most important to the success of the programme are the unique methods of motivation which involve virtually all segments of the society.