Cost-effectiveness assessment of CO2 reducing measures in shipping

International shipping is a significant contributor to global greenhouse gas (GHG) emissions, and is under mounting pressure to contribute to overall GHG emission reductions. There is an ongoing debate regarding how much the sector could be expected to reduce emissions and how the reduction could be achieved. This paper details a methodology for assessing the cost-effectiveness of technical and operational measures for reducing CO₂ emissions from shipping, through the development of an evaluation parameter called the Cost of Averting a Tonne of CO₂-eq Heating, CATCH, and decision criterion, against which the evaluation parameter should be evaluated. The methodology is in line with the Intergovernmental Panel on Climate Change (IPCC) and with regulatory work on safety and environmental protection issues at the International Maritime Organization (IMO).

The results of this study suggest that CATCH <50 $/tonne of CO₂-eq should be used as a decision criterion for investment in emission reduction measures for shipping. In total, 13 specific measures for reducing CO₂ emissions have been analysed for two selected case ships to illustrate the methodology. Results from this work shows that several measures are cost effective according to the proposed criterion. The results suggest that cost effective reductions for the fleet may well be in the order of 30% for technical measures, and above 50% when including speed reductions. The results of this study show that the cost effectiveness approach for the regulation of shipping emissions is viable and should be pursued in the ongoing regulatory process.     

Effects of wave directionality and choice of wave spectrum on the extreme response of a deep water jacket

Wave-induced load effects in an idealized deep water jacket are considered. The structure is selected more to examine the worst effects of wave-induced uncertainties than to represent a realistic North Sea installation. The largest natural period is about 5 9 s and the structural response is significantly affected by dynamics. The structural system is linearized and response extremes are predicted by means of a stochastic, dynamic long term response analysis. A realistic modelling of ocean waves for long term response calculations is outlined. Various possibilities concerning the choice of wave spectrum are included and the corresponding effects on the predicted extremes are demonstrated. A sensitivity study is carried out both for the quasi-static response and for the resulting dynamic response. Finally, the effects of accounting for wave directionality are indicated. This includes both the introduction of a varying main wave direction and the modelling of the shortcrestedness for a given sea state.     

Numerical calculations of propeller shaft loads on azimuth propulsors in oblique inflow

This paper evaluates various computational methods used to compute propeller performance, hydrodynamic side force and bending moment applied to an azimuth propulsor propeller shaft in oblique inflow. The two non-viscous models used are the BEM method and the blade element momentum theory (BEMT). RANS calculations are used to compute the loads on the propeller and the nominal wake velocity from the thruster body to be used in the BEMT model. The effect of the ship hull is also considered in the calculation by implementing the measured nominal wake of a ship hull at different propeller azimuthal positions. All the models are compared and validated against the experimental results, and the discussions are presented.