Although the actual level of marine air pollution is unclear, the contribution of ships to global emissions can be roughly indicated as being in the following ranges: nitrogen oxides (NO x ), 10-20 per cent; carbon dioxide (CO 2 ), 2-4 per cent; sulphur oxides (SO x ), 4-8 per cent. Several studies, which aim to minimize and reduce the maritime environmental pollution by the gas emissions from ships, have shown that there are different methods by which this can be achieved. This paper shows that the use of natural gas as the main fuel on board ships is considered to be the optimum selection for this purpose as regards the environmental and economic issues. A short-voyage ship of high power rating is deemed to be suitable for naturalgas application to obtain the maximum environmental and economic benefits. As a case study, this paper discusses the environmental and the economic benefits of using natural gas as an alternative to diesel oil on board one of the high-speed passenger ships operating in the Red Sea area between Egypt and the Kingdom of Saudi Arabia. The study illustrated that NO x , SO x , particulate matter, and CO 2 emissions were reduced by 72 per cent, 91 per cent, 85 per cent, and 10 per cent respectively. In addition, the cost of both fuel consumption and maintenance operation demonstrated reductions by 39 per cent and 40 per cent respectively.

No abstract

Determining and understanding the performance characteristics of marine propellers by experiments is quite a complex and costly task. Numerical predictions using computational fluid dynamics simulations could be a valuable alternative provided that the laminar-to-turbulent transition flow effects are fundamentally understood with the suitable numerical models developed. Experience suggests that the use of classical turbulent flow models may lead to high discrepancies especially at low rotational speeds where the effects of fluid flow transition from the laminar to the turbulent state may influence the predicted propeller's performance. This article proposes a complete and detailed procedure for the computational fluid dynamics simulation of non-cavitating flow over marine propellers using the ''k-kl-v'' transition-sensitive turbulence model. Results are evaluated by ''ANSYS FLUENT 16'' for the ''INSEAN E779A'' propeller. Comparisons against the fully turbulent standard ''k-e'' model and against experiments show improved agreement in way of flow transition zones at lower rotational speeds, that is, at low Reynolds numbers.

No abstract

No abstract