Wave excitation tests on a fixed sphere with the center at the still water level were carried out with three different physical wave basin setups. The tests were completed as a continued effort of the working group OES Wave Energy Converters Modeling Verification and Validation to increase confidence in numerical models of wave energy converters by generation of accurate benchmarks datasets for numerical model validation. An idealized test case with wave excitation of a fixed sphere to be used with the benchmarks was formulated. The three investigated physical wave basin setups included: 1) a six degree-of-freedom load cell mounted to the top of the sphere, 2) a bending beam force transducer mounted to the top of the sphere, and 3) a system of six pretensioned wires mounted to the top and bottom of the sphere with force transducers attached to each wire. The aim of the present paper is to identify the best representation of the idealized test case. To this end, the three experimental setups are inter-compared in terms of dynamic properties, sensitivity, and disturbances of the water phase from the presence of measurement equipment. Low inter-experiment variability was disclosed, ie, 5-8% depending on wave-nonlinearity, indicating accurate representations of the idealized test case across all setups. Setup 3 was found to be the more accurate representation and further work with this setup to release a public benchmark dataset was planned.
The design of large diameter monopiles (8–10 m) at intermediate to deep waters is largely driven by the fatigue limit state and mainly due to wave loads. The scope of the present paper is to assess the mitigation of wave loads on a monopile by perforation of the shell. The perforation design consists of elliptical holes in the vicinity of the splash zone. Wave loads are estimated for both regular and irregular waves through physical model tests in a wave flume. The test matrix includes waves with Keulegan–Carpenter (KC) numbers in the range 0.25 to 10 and covers both fatigue and ultimate limit states. Load reductions in the order of 6%–20% are found for KC numbers above 1.5. Significantly higher load reductions are found for KC numbers less than 1.5 and thus the potential to reduce fatigue wave loads has been demonstrated.
Accurate prediction of wave transformation is key in the design of coastal and nearshore structures which typically depends on numerical models. Turbulent and rotational effects call for the use of Computational Fluid Dynamics (CFD) solvers of which a large range of formulations including free surface treatments exists. Physical wave flume tests of wave propagation over a submerged bar with various levels of nonlinearity, regularity, and wave-breaking, dedicated to numerical model benchmarking or validation, were carried out in the Ocean and Coastal Engineering Laboratory of Aalborg University. Three fundamentally different CFD models each widespread within their category are benchmarked against the experimental data. The CFD models are based on (i) the Volume of Fluid (VoF) based interFoam solver of OpenFOAM, (ii) the sigma-transformation solver of MIKE 3 Waves Model FM, and (iii) the weakly compressible delta-SPH solver of DualSPHysics. Accuracy of the numerical models is assessed from surface elevation time series, evaluation metrics (averaged errors on surface elevations, amplitudes, phases, and wave set-up), and spectral analyzes to calculate the amplitude and phase contents of primary and higher-order components along the wave flume. Applicability is assessed from computational costs and ease-of-use factors such as the effort to configure the numerical models and achieve convergence. In general, the numerical models have high correlation to the physical tests and are as such suitable to model complex wave transformation with an accuracy sufficient for most coastal engineering applications. The VoF model performs more accurately under the turbulent conditions of breaking waves, increasing its relative accuracy in the prediction of downwave surface elevation. The sigma transformation model has simulation times one to two orders of magnitude lower than those of the VoF and SPH models.
Accurate prediction of wave transformation is key in the design of coastal and nearshore structures which typically depends on numerical models. Turbulent and rotational effects call for the use of Computational Fluid Dynamics (CFD) solvers of which a large range of formulations including free surface treatments exists. Physical wave flume tests of wave propagation over a submerged bar with various levels of nonlinearity, regularity, and wave-breaking, dedicated to numerical model benchmarking or validation, were carried out in the Ocean and Coastal Engineering Laboratory of Aalborg University. Three fundamentally different CFD models each widespread within their category are benchmarked against the experimental data. The CFD models are based on (i) the Volume of Fluid (VoF) based interFoam solver of OpenFOAM, (ii) the sigma-transformation solver of MIKE 3 Waves Model FM, and (iii) the weakly compressible delta-SPH solver of DualSPHysics. Accuracy of the numerical models is assessed from surface elevation time series, evaluation metrics (averaged errors on surface elevations, amplitudes, phases, and wave set-up), and spectral analyses to calculate the amplitude and phase contents of primary and higher-order components along the wave flume. Applicability is assessed from computational costs and ease-of-use factors such as the effort to configure the numerical models and achieve convergence. In general, the numerical models have high correlation to the physical tests and are as such suitable to model complex wave transformation with an accuracy sufficient for most coastal engineering applications. The VoF model performs more accurately under the turbulent conditions of breaking waves, increasing its relative accuracy in the prediction of downwave surface elevation. The sigma transformation model has simulation times one to two orders of magnitude lower than those of the VoF and SPH models.
Ship-to-ship (STS) bunkering of liquid fuel, e.g., LNG, has emerged as a more practical way to ensure high bunkering volumes and good access without regional restrictions and upgrading of existing infrastructures at the port. Wave resonance in the narrow gap between side-by-side receiving vessel and bunkering vessel happens when the wave frequency is close to the natural frequency of the gap flow. Large wave elevation in the gap and hydrodynamic forces on the
ships are expected, thus reducing the time window of the bunkering operation and even risking the safety of the crew. It is well known that the wave frequency and amplitude can be affected by the presence of current. Correspondingly, the waves and loads on marine structures will be somewhat different from the scenario without current, which will have significant influence on the bunkering operation. However, few previous studies have reported in the literature for wave resonance considering current effect. In the present work, the finite-amplitude fluid resonance inside the gap between two ship cross-sections in side-by-side configuration is studied under combined waves and currents. Both a uniform current and a shear current with constant vorticity are considered. A fully nonlinear numerical wave tank is established based on the commercial CFD package STAR-CCM+. The unsteady Reynolds averaged Navier-Stokes turbulence model is applied to consider viscous dissipation. The volume of fluid method is applied to capture the free surface, and the flow field analytically obtained from the stream function method is specified in the forcing zones at upstream and downstream boundaries, respectively, by the user-defined wave elevation and velocity. The influence of following current on the wave amplitude in the gap and hydrodynamic load on the cross-sections is investigated by comparison with the cases without current. The relation between the wave or force amplitude and the vorticity of the shear is further analysed. The present study may provide useful results about gap resonance and hydrodynamic loads on two approaching marine structures during the bunkering operation in wave-current environment.
The reduction of Greenhouses gasses (GHG) and other air emissions represents a major challenge for ports. The world over, however, ports vary considerably in their efforts to reduce air emissions, and the causes for this variation remain under-researched. This paper examines the drivers for the adoption of air emissions abatement measures in a sample of 93 of the world’s largest ports, covering all continents and mobile emitters. We test five hypotheses with a Linear Probability Model to disentangle the impacts of key port characteristics on the current adoption of abatement measures and identify three key drivers for adoption: Population density, the port landlord business model, and a specialization in servicing container shipping. We also find that ports are more likely to implement specific bundles of measures, in particular combining pricing and new energy sources. Our work has implications for ports, as we suggest that they should coordinate abatement efforts to achieve effectiveness in their work.
Background: Seafarers are at an increased risk of developing cardiovascular diseases (CVDs), potentially due to a stressful working environment and behavioral risk factors. To develop better prevention strategies, it is important to elucidate the extent of this risk. Therefore, we conducted a systematic literature review on CVD in seafarers. Method: We conducted systematic searches in five databases. All studies investigating CVDs among occupational seafarers, published in articles or conference papers, were eligible for inclusion. The identified records were screened and reviewed by two independent researchers, who also evaluated the methodological quality of the included studies. Results: Three thousand nine hundred and seventeen records qualified for screening, and 55 were eligible for inclusion. Most of the studies were observational, including cohort, frequency, incidence or prevalence studies, and review of case records. Around half were assessed at risk of biased findings. Participants in the studies were primarily from North America or the European continent and work onboard transportation vessels. Many studies investigated CVDs as a cause of death, focusing on conditions such as CVD, ischemic heart disease, and myocardial infarction. Frequency of CVD conditions varied but indicate that seafarers face a greater risk compared to the reference populations or control groups. Environmental factors were mainly investigated as risk factors. Conclusion: Our results indicate a higher risk of CVDs among seafarers compared to reference or control groups. However, due to the variable quality of the evidence, well-designed studies are needed to establish the causes of cardiovascular mortality and morbidity in seafarers and to investigate behavioral aspects of cardiovascular risk.
Maritime security is one of the latest buzzwords of international relations. Major actors have started to include maritime security in their mandate or reframed their work in such terms. Maritime security is a term that draws attention to new challenges and rallies support for tackling these. Yet, no international consensus over the definition of maritime security has emerged. Buzzwords allow for the international coordination of actions, in the absence of consensus. These, however, also face the constant risk that disagreements and political conflict are camouflaged. Since there are little prospects of defining maritime security once and for all, frameworks by which one can identify commonalities and disagreements are needed. This article proposes three of such frameworks. Maritime security can first be understood in a matrix of its relation to other concepts, such as marine safety, seapower, blue economy and resilience. Second, the securitization framework allows to study how maritime threats are made and which divergent political claims these entail in order to uncover political interests and divergent ideologies. Third, security practice theory enables the study of what actors actually do when they claim to enhance maritime security. Together these frameworks allow for the mapping of maritime security.
The problem of marine litter represents a significant global challenge and illustrates the harmful consequences of an economic model that is based on disposability. The seafood sector is not only among the culprits, but is also among the most affected by this threat to the marine environment. Earlier research has pointed to fishing gear take-back schemes as a measure to mitigate the problem, and policymakers have embraced the idea. The Norwegian scheme for beverage containers has been hailed as a benchmark for the application of Extended Producer Responsibility. Through the lens of business ecosystems, we draw parallels between the existing take-back scheme for beverage containers and the latent system for fishing gear to answer the question: “What would it take to establish a take-back scheme for fishing gear?” We elaborate upon four factors that are well established for beverage container take-back schemes, but lacking or unclear in the case of fishing gear: (i) politico-institutional support, (ii) the system's value proposition, (iii) the system integrator, and (iv) operational factors (i.e., a network of collection points and procedures, and material variety and complexity). Our findings highlight that when innovations are not based on the usual market mechanisms, unconventional conceptualizations of value itself and how value is mapped and distributed are required. Meaningful engagement of the private sector depends upon either explicit articulation of value capture or policy instruments to enforce responsibility; both are currently either unclear or lacking in the context of fishing gear.
In 2020, the Danish Ministry of Environment and Food launched a new state-led ecolabelling scheme for fish originating from small-scale, 'low-environmental-impact' fisheries; "Nature-friendly". The label was introduced to a domestic market where the vast majority of the fish landed by Danish vessels was already certified by the global leader in certification of (wild caught) fish products, the Marine Stewardship Council (MSC). MSC's high market penetration created a situation where especially small-scale fishermen felt that MSC certification had developed into a market norm without providing fishermen the benefits of demonstrating extraordinarily sustainable practices and thereby gaining competitive advantages. Rather, MSC's market penetration was perceived as undermining efforts to brand and market fish originating from small-scale fisheries as particularly sustainable. This article explores the processes that led up to the NaturSkånsom labeling scheme by applying a 'power in planning and policy framework' as an analytical lens. Through the NaturSkånsom process, the article investigates what happens when an ecolabel becomes a market norm, how small-scale fisheries actors who feel disadvantaged by such a development and environmental organizations form alliances, mobilize support and multiple resources to strengthen their positions in the political settings. The examination of this case highlights how stakeholders traditionally thought of as less resourceful can gain political influence. The article offers a glimpse into a possible, emerging future where those who perceive themselves as the most sustainable producers may increasingly view large and dominating ecolabels simultaneously as obstacles and forces for positive change.