Among all environmental forces acting on ocean structures and marine vessels, those resulting from wave impacts are likely to yield the highest loads. Being highly nonlinear, transient and complex, a theoretical analy...Among all environmental forces acting on ocean structures and marine vessels, those resulting from wave impacts are likely to yield the highest loads. Being highly nonlinear, transient and complex, a theoretical analysis of their impact would be impossible without numerical simulations. In this paper, a pressure-split two-stage numerical algorithm is proposed based on Volume Of Fluid (VOF) methodology. The algorithm is characterized by introduction of two pressures at each half and full cycle time step, and thus it is a second-order accurate algorithm in time. A simplified second-order Godunov-type solver is used for the continuity equations. The method is applied to simulation of breaking waves in a 2-D water tank, and a qualitative comparison with experimental photo observations is made. Quite consistent results are observed between simulations and experiments. Commercially available software and Boundary Integral Method (BIM) have also been used to simulate the same problem. The results from present code and BIM are in good agreement with respect to breaking location and timing, while the results obtained from the comrnercial software which is only first-order accurate in time has clearly showed a temporal and spatial lag, verifying the need to use a higher order numerical scheme.展开更多
The creation of geometric model of a ship to determine the characteristics of hydrostatic and hydrodynamic, and also for structural design and equipments arrangement are so important in the ship design process. Planni...The creation of geometric model of a ship to determine the characteristics of hydrostatic and hydrodynamic, and also for structural design and equipments arrangement are so important in the ship design process. Planning tunnel high speed craft is one of the crafts in which, achievement to their top speed is more important. These crafts with the use of tunnel have the aero-hydrodynamics properties to diminish the resistance, good sea-keeping behavior, reduce slamming and avoid porpoising. Because of the existence of the tunnel, the hull form generation of these crafts is more complex and difficult. In this paper, it has attempted to provide a method based on geometry creation guidelines and with an entry of the least control and hull form adjustment parameters, to generate automatically the hull form of plarming tunnel craft. At first, the equations of mathematical model are described and subsequent, three different models generated based on present method are compared and analyzed. Obviously, the generated model has more application in the early stages of design.展开更多
Climate change is widely recognized as the major environmental problem facing the globe today. One of the most urgent environmental problems facing shipping industry is the reduction of GHG (greenhouse gas) emission...Climate change is widely recognized as the major environmental problem facing the globe today. One of the most urgent environmental problems facing shipping industry is the reduction of GHG (greenhouse gas) emissions from its operations. Given the growing concern of the international community on "the deep reduction of global GHG emissions", it cannot be expected that the non-regulation of maritime GHG emissions can further continue. This paper investigates the main challenges and threats of the development of two MBMs (market-based measures) for the reduction of GHG emissions from international shipping, i.e., the "global levy scheme on maritime GHG emissions" and the "maritime emission trading scheme". A SWOT (strengths weaknesses opportunities threat) analysis is used, in this survey, to evaluate the environmental effectiveness as well as the easiness of implementation of the two policy options. Moreover, we make apparent their strengths and weaknesses concerning abatement of maritime GHG emissions. Given the fact that the discussion regarding the implementation of some MBMs with maritime GHG-emission reduction potential is still carried out with the exception of EEDI (energy efficiency design index) and SEEMP (ship energy efficiency management plan), this paper's results present special significance, as they could be further analyzed and taken into account during the adoption of any future MBM for the reduction of maritime GHG emissions.展开更多
The mega-size containership viability was analyzed by considering different service networks for different ship sizes:hub-and-spoke and multi-port-calling (MPC) networks for mega-size containerships and conventional s...The mega-size containership viability was analyzed by considering different service networks for different ship sizes:hub-and-spoke and multi-port-calling (MPC) networks for mega-size containerships and conventional ships.A model was proposed,which quantifies the economies of scale in operating large con- tainerships and constructs models for ship routing under different service networks.A sensitivity analysis was conducted to test the effect of feeder costs and the results analyzed to determine optimal containership size with respect to different operational scenarios.Throughout model applications for Asia-Europe and Asia-North America trades,the mega-size containership is competitive in all scenarios for Asia-Europe,while it is viable for Asia-North America only when the feeder costs are low.展开更多
The margins in elite sport are becoming increasingly smaller particularly in timed sporting events forcing the limits of perfor- mance to be pushed further. Although traditionally only the phys- iological and physical...The margins in elite sport are becoming increasingly smaller particularly in timed sporting events forcing the limits of perfor- mance to be pushed further. Although traditionally only the phys- iological and physical attributes of performance were considered, there is growing awareness of a range of factors including but not limited to; the performance culture including the team environ- ment, athlete coach relationship, facilities etc; specific physical attributes and skills for each sports; mental skills such as confi- dence, resilience, motivation etc; technical skills including agility, coordination; tactical skills and finally lifestyle skills including nutrition, well-being, and recovery.展开更多
As one of the vital steps in the 3rd phase of China's lunar exploration program (CLEP), the circumlunar return and reentry spacecraft, developed by China Academy of Space Technology (CAST), is used to demonstrate...As one of the vital steps in the 3rd phase of China's lunar exploration program (CLEP), the circumlunar return and reentry spacecraft, developed by China Academy of Space Technology (CAST), is used to demonstrate the key technologies of by- per-speed return and reentry spacecraft. The system configuration and flight process are presented in this paper, as well as the analysis of mission characteristics, the key technologies and the technical advancement during the R&D progress. The significance of circumlunar return and reentry spacecraft is given at the end.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 50679010 and 50579004.
文摘Among all environmental forces acting on ocean structures and marine vessels, those resulting from wave impacts are likely to yield the highest loads. Being highly nonlinear, transient and complex, a theoretical analysis of their impact would be impossible without numerical simulations. In this paper, a pressure-split two-stage numerical algorithm is proposed based on Volume Of Fluid (VOF) methodology. The algorithm is characterized by introduction of two pressures at each half and full cycle time step, and thus it is a second-order accurate algorithm in time. A simplified second-order Godunov-type solver is used for the continuity equations. The method is applied to simulation of breaking waves in a 2-D water tank, and a qualitative comparison with experimental photo observations is made. Quite consistent results are observed between simulations and experiments. Commercially available software and Boundary Integral Method (BIM) have also been used to simulate the same problem. The results from present code and BIM are in good agreement with respect to breaking location and timing, while the results obtained from the comrnercial software which is only first-order accurate in time has clearly showed a temporal and spatial lag, verifying the need to use a higher order numerical scheme.
文摘The creation of geometric model of a ship to determine the characteristics of hydrostatic and hydrodynamic, and also for structural design and equipments arrangement are so important in the ship design process. Planning tunnel high speed craft is one of the crafts in which, achievement to their top speed is more important. These crafts with the use of tunnel have the aero-hydrodynamics properties to diminish the resistance, good sea-keeping behavior, reduce slamming and avoid porpoising. Because of the existence of the tunnel, the hull form generation of these crafts is more complex and difficult. In this paper, it has attempted to provide a method based on geometry creation guidelines and with an entry of the least control and hull form adjustment parameters, to generate automatically the hull form of plarming tunnel craft. At first, the equations of mathematical model are described and subsequent, three different models generated based on present method are compared and analyzed. Obviously, the generated model has more application in the early stages of design.
文摘Climate change is widely recognized as the major environmental problem facing the globe today. One of the most urgent environmental problems facing shipping industry is the reduction of GHG (greenhouse gas) emissions from its operations. Given the growing concern of the international community on "the deep reduction of global GHG emissions", it cannot be expected that the non-regulation of maritime GHG emissions can further continue. This paper investigates the main challenges and threats of the development of two MBMs (market-based measures) for the reduction of GHG emissions from international shipping, i.e., the "global levy scheme on maritime GHG emissions" and the "maritime emission trading scheme". A SWOT (strengths weaknesses opportunities threat) analysis is used, in this survey, to evaluate the environmental effectiveness as well as the easiness of implementation of the two policy options. Moreover, we make apparent their strengths and weaknesses concerning abatement of maritime GHG emissions. Given the fact that the discussion regarding the implementation of some MBMs with maritime GHG-emission reduction potential is still carried out with the exception of EEDI (energy efficiency design index) and SEEMP (ship energy efficiency management plan), this paper's results present special significance, as they could be further analyzed and taken into account during the adoption of any future MBM for the reduction of maritime GHG emissions.
文摘The mega-size containership viability was analyzed by considering different service networks for different ship sizes:hub-and-spoke and multi-port-calling (MPC) networks for mega-size containerships and conventional ships.A model was proposed,which quantifies the economies of scale in operating large con- tainerships and constructs models for ship routing under different service networks.A sensitivity analysis was conducted to test the effect of feeder costs and the results analyzed to determine optimal containership size with respect to different operational scenarios.Throughout model applications for Asia-Europe and Asia-North America trades,the mega-size containership is competitive in all scenarios for Asia-Europe,while it is viable for Asia-North America only when the feeder costs are low.
文摘The margins in elite sport are becoming increasingly smaller particularly in timed sporting events forcing the limits of perfor- mance to be pushed further. Although traditionally only the phys- iological and physical attributes of performance were considered, there is growing awareness of a range of factors including but not limited to; the performance culture including the team environ- ment, athlete coach relationship, facilities etc; specific physical attributes and skills for each sports; mental skills such as confi- dence, resilience, motivation etc; technical skills including agility, coordination; tactical skills and finally lifestyle skills including nutrition, well-being, and recovery.
基金The Major Special Projects on National MediumLong-term Science and Technology Development Planning
文摘As one of the vital steps in the 3rd phase of China's lunar exploration program (CLEP), the circumlunar return and reentry spacecraft, developed by China Academy of Space Technology (CAST), is used to demonstrate the key technologies of by- per-speed return and reentry spacecraft. The system configuration and flight process are presented in this paper, as well as the analysis of mission characteristics, the key technologies and the technical advancement during the R&D progress. The significance of circumlunar return and reentry spacecraft is given at the end.