This review paper examines the possible pathways and possible technologies available that will help the shipping sector achieve the International Maritime Organization’s (IMO) deep decarbonization targets by 2050. There has been increased interest from important stakeholders regarding deep decarbonization, evidenced by market surveys conducted by Shell and Deloitte. However, deep decarbonization will require financial incentives and policies at an international and regional level given the maritime sector’s ~3% contribution to green house gas (GHG) emissions. The review paper, based on research articles and grey literature, discusses technoeconomic problems and/or benefits for technologies that will help the shipping sector achieve the IMO’s targets. The review presents a discussion on the recent literature regarding alternative fuels (nuclear, hydrogen, ammonia, methanol), renewable energy sources (biofuels, wind, solar), the maturity of technologies (fuel cells, internal combustion engines) as well as technical and operational strategies to reduce fuel consumption for new and existing ships (slow steaming, cleaning and coating, waste heat recovery, hull and propeller design). The IMO’s 2050 targets will be achieved via radical technology shift together with the aid of social pressure, financial incentives, regulatory and legislative reforms at the local, regional and international level.
This paper evaluates the effect of forcing to sustain turbulence on the transfer function of the fluid with particles suspended in a homogeneous and isotropic flow. As mentioned by Lucci et al. [“Modulation of isotropic turbulence by particles of Taylor length-scale size,” J. Fluid Mech.650, 5–55 (2010)10.1017/S0022112009994022], there are three limitations of forcing particle-laden homogeneous and isotropic turbulence: (a) large fluctuations on the temporal evolution of the kinetic energy are created when forcing is active at low wavenumbers, (b) the redistribution of energy is affected when forcing is performed over all wavenumbers, and (c) the nonlinear transfer function of the fluid due to the triadic interactions is affected when forcing is active over a wavenumber range. These limitations make the interpretation of the effects of particles on the energy spectrum of the fluid difficult. A new forcing scheme in physical space has been designed which avoids these limitations in wavenumber space, so the spectral effects of particles can be evaluated. The performance of this forcing scheme is tested using Direct Numerical Simulations. It is shown that the nonlinear transfer function of the fluid with the current forcing scheme is only affected at the wavenumbers it is acting, consistent with the theory. Even so, the spatial coherence and phase spectra between the two-way coupling and the fluid computed from the simulations show that the new forcing scheme is only moderately correlated even for the forced wavenumbers, with correlation coefficient typically about 10%.
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