A practical estimation methodology of the mean added resistance in irregular waves is shown, and the present paper provides statistical analyses of estimates for ships in actual conditions. The study merges telemetry data of more than 200 in-service container vessels with ocean re-analysis data from ERA5. Theoretical estimates relying on spectral calculations of added resistance are made for both long- and short-crested waves and are based on a combination of a parametric expression for the wave spectrum and a semi-empirical formula for the added resistance transfer function. The theoretical estimates are compared to predictions from an indirect calculation of added resistance relying on shaft power measurements and empirical estimates of the remaining resistance components. Overall, the comparison reveals a bias in bow oblique waves and higher sea states of the spectral estimates as well as the large variance of the empirically derived predictions — particularly in beam-to-following waves. One of the study’s main findings, confirming previous studies but based on a much larger dataset than in earlier similar studies, is that added resistance assessment based on in-service data is complex due to significant associated uncertainties.
Wind Propulsion Systems (WPS) for commercial ships are vital to achieving the IMO targets on energy efficiency and GHG emissions. Most WPS will operate in a hybrid mode alongside actual main propulsion units. This will affect the propeller and engine operating conditions and thus, their performance. The present paper discusses a preliminary assessment of commercial ship propellers and engine performance variation as a function of the wind power installed for two propeller plant types (Fixed Pitch Propeller, FPP, and Controllable Pitch Propeller, CPP) at constant speed operational mode. The contribution is based on empirical and analytical methods requiring minimal input data. It aims to provide general trends and contribute basic knowledge on this matter. A cost model is included for a cost-benefit assessment of both propeller types. This leads to advice on which systems to install as a function of WPS installation size.
This paper presents a wave flume investigation of beaching times for buoyant microplastic particles dropped at various distance from the shoreline. The beaching times are used to quantify the cross-shore Lagrangian transport velocities of the microplastic particles. Results show that prior to breaking, there is little dependence on particle characteristics (e.g. their rise velocity), and the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity. In the surf zone the Lagrangian transport velocities of the microplastic particles increase significantly, becoming closer to the wave celerity. Additionally, particle characteristics become important, as particles with low Dean numbers (high rise velocity) have a greater tendency to be captured by surface rollers relative to particles with larger Dean numbers (lower rise velocity). An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles. The expression matches the present experiments well and is valid for both non-breaking and breaking irregular waves. These findings help in understanding the accumulation of microplastics at beaches due to the surf-zone processes, especially for buoyant particles.
As a young researcher—admittedly a long time ago—I was struggling with capturing the connections of the many published articles on logistics management. Apparently, many articles dealt with the same topics, yet they were not the same. There seemed to be different viewpoints on what was a scientific contribution and what kinds of methods were allowed. Why did everyone not agree with these questions? Without an understanding of the different research traditions, it was difficult to compare results, validate them and create a meaningful discussion of the various contributions.
Within the Nordic research community, which consists of economists, engineers and management researchers, there were several answers to these questions. In this community, I learnt about systems from engineers. Then, it became clear that there are various philosophies of science that do not have the same understanding of what a theory is and what appropriate methods are. I was searching the philosophy of science literature for a systems perspective and the research implications of such a perspective. To my surprise, I did not find it here, but luckily, I came across a book about methodologies in business research where the systems approach was one of three approaches. I also learnt that, depending on the methodology, the term theory has a different meaning depending on the philosophy of science it originates from. That made a lot of sense to me. Understanding this better, I published my research on this topic in “Schools in Logistics Research” in 2004 (Gammelgaard, 2004). This rather old article is still my daily research guide.
In the present study, large eddy simulation is used to investigate combustion recession for the Engine Combustion Network Spray A flame at two ambient temperatures (850 K and 800 K) and two injection pressures (100 MPa and 50 MPa). The present numerical results are able to capture different combustion recession phenomena after the end-of-injection (AEOI). With an injection pressure of 100 MPa, the model predicts a ‘‘separated’’ combustion recession at the ambient temperature of 850 K and no combustion recession at the ambient temperature of 800 K, in which both predictions correspond to the measurements. The combustion recession is mainly controlled by the auto-ignition process at the ambient temperature of 850 K. At the ambient temperature of 800 K, the local temperature within the fuel-rich region is not high enough to promote the hightemperature ignition process. As time progresses, the mixture within the fuel-rich region rapidly transitions to become an overly fuel-lean mixture, which further hinders high-temperature ignition to occur. Nonetheless, it is shown that lowering the injection pressure to 50 MPa causes the combustion recession to occur at the
ambient temperature of 800 K. This is likely attributed to the low injection case having a lower air entrainment rate AEOI, which causes the mixtures upstream of the lift-off position to transition slower from fuel-rich to fuel-lean mixtures.
This paper explores the ways in which maritime labor, maritime risk, and seafarers’ survival are embedded in the financial logics and practices of the global shipping industry. By employing the notion of “existential arbitrage,” the ethnography moves through the pursuit of global profit to the value of labor as a commodity, human and financial risk, and ultimately the value of human lives, all of which are arbitraged. Arbitrage is a profit strategy that is based on a belief in the equalizing power of the market yet is predicated on and creates difference among commodities in order to create opportunities to generate profit. Existential arbitrage brings anthropological studies of security and conflict and trade and finance together. By taking the interdependence of these subfields seriously and showing how the relationship between them manifests itself in practice, the notion of existential arbitrage uncovers a brutal financial trading strategy that requires and forces the oscillation between notions of valuable life and the valuation of labor commodities in a competitive global market.
This article reviews and examines the most significant climate-change-related impacts and adaptation from the perspective of stakeholders in Greenlandic fisheries. The study was constructed as a comprehensive, multi-site, bottom-up case study around Greenlandic fisheries (south-north/offshore-inshore), where interviews and workshops with Greenlandic fishermen and stakeholders have communicated their observations of fishery changes associated with changes in the marine environment within the last decade. Key observations include: changes in sea ice cover; increased abundance of known species in North Greenland; fish species relocation and periodic absences in coastal systems; a northward movement of the shrimp fishery; new and unprecedented bycatch issues; and new fisheries. Stakeholder knowledge acknowledges the capacity of both offshore and coastal fisheries to adapt to changing seasonality and distribution. Factory capacity and decision-making as well as bycatch legislation have been identified as the most critical bottlenecks for (re)diversifying fisheries and increasing the value of the locally available resources.
The design of wave energy converters should rely on numerical models that are able to estimate accurately the dynamics and loads in extreme wave conditions. A high-fidelity CFD model of a 1:30 scale point-absorber is developed and validated on experimental data. This work constitutes beyond the state-of-the-art validation study as the system is subjected to 50-year return period waves. Additionally, a new methodology that addresses the well-known challenge in CFD codes of mesh deformation is successfully applied and validated. The CFD model is evaluated in different conditions: wave-only, free decay, and wave–structure interaction. The results show that the extreme waves and the experimental setup of the wave energy converter are simulated within an accuracy of 2%. The developed high-fidelity model is able to capture the motion of the system and the force in the mooring line under extreme waves with satisfactory accuracy. The deviation between the numerical and corresponding experimental RAOs is lower than 7% for waves with smaller steepness. In higher waves, the deviation increases up to 10% due to the inevitable wave reflections and complex dynamics. The pitch motion presents a larger deviation, however, the pitch is of secondary importance for a point-absorber wave energy converter.
Normal flow past flat plates at high Reynolds numbers appears in various engineering contexts. To accurately model such flows for slender plates in Computational Fluid Dynamics requires scale-resolving rather than scale-modelling methods. The present paper uses Detached-Eddy Simulation to investigate the influence of plate corner curvature on global flow quantities such as the time-averaged drag coefficient. The effect of corner curvature is mapped and collated with the literature. Solution verification is carried out to quantify the numerical uncertainty. The time-averaged drag coefficient increases significantly between semi-cylindrically rounded (〈𝐶〉=2.28) and sharp-cornered (〈𝐶〉=2.42) plates.