We consider the Tramp Ship Routing and Scheduling Problem (TSRSP) in which we plan routes for a fleet of tramp shipping vessels operating on a combined contract and spot market. Earlier research has been fragmented due to variations in the side constraints studied. Hence we present the first unified model that can handle speed optimization, chartering costs, bunker planning, and hull cleaning. The model is solved by column generation, where the columns represent the possible routes of a vessel, while the master problem keeps track of the binding constraints. The pricing problem is solved efficiently using a time–space graph and several dominance rules. Real-life instances with up to 40 vessels, 35 geographic regions, and four months planning horizon can be solved to optimality in less than half an hour. The optimized routes increase earnings by 7% compared to historical schedules. Furthermore, policy-makers can use the model as a simulation of a rational agent behavior.
This paper summarises the work conducted within the 1st FOWT (Floating Offshore Wind Turbine) Comparative Study organised by the EPSRC (UK) ‘Extreme loading on FOWTs under complex environmental conditions’ and ‘Collaborative computational project on wave structure interaction (CCP-WSI)’ projects. The hydrodynamic response of a FOWT support structure is simulated with a range of numerical models based on potential theory, Morison equation, Navier-Stokes solvers and hybrid methods coupling different flow solvers. A series of load cases including the static equilibrium tests, free decay tests, operational and extreme focused wave cases are considered for the UMaine VolturnUS-S semi-submersible platform, and the results from 17 contributions are analysed and compared with each other and against the experimental data from a 1:70 scale model test performed in the COAST Laboratory Ocean Basin at the University of Plymouth. It is shown that most numerical models can predict similar results for the heave response, but significant discrepancies exist in the prediction of the surge and pitch responses as well as the mooring line loads. For the extreme focused wave case, while both Navier–Stokes and potential flow base models tend to produce larger errors in terms of the root mean squared error than the operational focused wave case, the Navier-Stokes based models generally perform better. Given the fact that variations in the solutions (sometimes large) also present in the results based the same or similar numerical models, e.g., OpenFOAM, the study highlights uncertainties in setting up a numerical model for complex wave structure interaction simulations such as those involving a FOWT and therefore the importance of proper code validation and verification studies.
The integration of offshore wind assets with green hydrogen production and storage units can offer a much-needed solution for intermittency and curtailment issues of the offshore energy industry. To gain confidence that such novel integrated assets will be fit for purpose, the present study presents a comprehensive risk assessment followed by an action plan to mitigate the identified risks to help facilitate their technology qualification. The new methodology introduced here involves all the life-cycle phases of an offshore green hydrogen production system. Following, prevailing failure modes, their effects, and their causes are identified through an extensive review of relevant literature. Subsequently, risk prioritization is performed by ranking the criticality scores obtained from a multidisciplinary group of experts to the questionnaire designed to reveal the chosen subsystems' technology readiness, degree of change, concern in manufacturing and operation, and potential consequences regarding occupational health, safety, environment, economic and regulatory.
Danish seine is an active fishing gear targeting demersal species, such as European plaice (Pleuronectes platessa, hencefort referred as plaice), a commercially important fish species in the North Sea, Skagerrak, Kattegat, and Baltic Sea. Danish seining is a relevant fishery in relation to exemption from the European Union landing obligation. Trials were conducted from a commercial fishing vessel during the summer with high air temperatures and sea salinity and marked salinity and temperature gradients (pycnocline). Video equipment was used to observe fish entering the seine. Captured fish were individually tagged and housed in livewells for ten days to observe short-term survival. Reflex impairments and external injuries were assessed after capture and at the end of the observation periods using reflex action mortality predictor (RAMP) and catch-damage index (CDI) methodologies. We found that plaice entered the seine late in the towing process and that 87 % of the assessed fish survived, after 10 days of observation. There was a significant difference in short-term survival curves for fish that had been subjected to more than 30 min of on-deck during the catch-sorting process relative to those that had remained on deck for 30 min or less. The association between the time on deck and RAMP scores after capture was also significant. External injuries were primarily minor bruises, fin fraying, and net marks and changed little from after capturing to the end of the observation period.
We contribute to the identification of marine biodiversity status and changes in the coastal area of Southeast Greenland through consultation with holders of local and Indigenous knowledge (LEK/IK). Through in-depth interviews with coastal fishermen and hunters in the Ammassalik area, we explore a range of changes to known and new species in relation to ecosystem dynamics. Key observations include diminishing presence of polar cod (Boreogadus saida), new abundance of known fish species (Gadus morhua, Salvelinus alpinus, Reinhardtius hippoglossoides, Cyclopterus lumpus), inflow of new/rare species of whales, fish, and shellfish (Oncorhynchus gorbuscha, Lamna nasus, Paralithodes camtschaticus, Physeter macrocephalus, Globicephala melas, Megaptera novaeangliae, Phocoena phocoena), and increasing absence in the fjords of some local seal species (Cystophora cristata and Pusa hispida). Observed changes in local abundances are understood with reference to the physical changes in temperature, ocean currents, glacier melt, and snowfall. Changed dynamics in prey-predator relationships are observed to mediate the local presence of target species. Other environmental changes include an influx of new food items in food chains and increased seaweed growth. Our study confirms the relevance and timeliness of systematically incorporating local and Indigenous knowledge to enhance the understanding of coastal marine dynamics in the context of climate change and the geographical 'opening' of the East Greenlandic region.
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.
This paper highlights the urgent need to accelerate research and action on ocean carbon sinks through human intervention, known as Global Ocean Negative Carbon Emissions (Global-ONCE) Programme, as a vital strategy in global efforts to mitigate climate change. Achieving 'net zero' by 2050 cannot rely on emission reductions alone, emphasising the necessity of complementary approaches. Global-ONCE's mission extends beyond scientific exploration. It embodies a profound commitment to protecting and restoring blue carbon ecosystems, as well as implementing ocean-based solutions that are sustainable, equitable, and inclusive. Early Career Ocean Professionals (ECOPs) are at the heart of these efforts, and their innovative approaches, technical expertise, and passion make them indispensable leaders in advancing ONCE initiatives. ECOPs bridge the gap between science and society, playing a relevant role in integrating cutting-edge research, technological advancements, and community-driven action to address climate threats. By bringing together diverse perspectives and leveraging their interdisciplinary expertise, ECOPs ensure ONCE strategies are grounded in scientific rigour and practical feasibility. Through advocacy, education, and collaboration, ECOPs not only spearhead research and innovation but also inspire collective action to safeguard our oceans. This paper amplifies the critical role of ECOPs as agents of change and calls for a unified global commitment to harness the ocean's potential for a climate-resilient future.
An analytical framework is presented to describe the attenuation of regular and irregular waves propagating over floating seaweed farms. Kelp blades suspended on longlines are modelled, as a first approximation, as rigid bars rotating around their upper ends. Assuming small-amplitude blade motions under low to moderate sea conditions, the frequency-dependent transfer function of the rotations can be obtained, with quadratic drag loads linearized. Subsequently, the hydrodynamic problem with regular waves propagating over suspended seaweed canopies is formulated using the continuity equation and linearized momentum equations with additional source terms in the vegetation region. Analytical solutions are obtained for attenuated regular waves with their heights decaying exponentially as they propagate over the canopy. These solutions are utilized as the basis for predicting wave attenuation of irregular waves while stochastic linearization of the quadratic drag loads is employed. In contrast to energy-conservation-based models, which assume the velocity profile follows linear wave theory, the present solution can predict the reduced velocity inside the canopy. The analytical solutions are validated against experimental data and verified against a numerical flow solver. The model is capable of resolving the wave attenuation, along with velocity profiles and phase lag. Drag and inertial force exhibit cancellation effects on wave decay and both affect phase lag.
Our recent experimental investigations of flexible side-by-side blades under both steady and unsteady flows have observed flutter in both scenarios. Flutter significantly impacts blade kinematics and the hydrodynamic drag experienced by the blades. Our numerical approach [1], utilizing the reactive force model, successfully reproduces flutter phenomena. In contrast, the traditional Morison’s equation fails to trigger flutter. In the static regime where flutter does not occur, the bulk drag coefficients calibrated from experiments in steady and unsteady flows can be unified through an effective Cauchy number, allowing for the use of analytical models developed for steady flows in unsteady flows. In the flutter regime, using the bulk drag coefficient from steady flows underestimates the drag load in oscillatory flow.
Simulation-based analysis estimating both the energy requirement of the entire carbon capture process and the purity of the recovered CO 2 is scarce. The purity of the captured CO 2 is crucial as it must meet a specification before transportation, preventing phase change and damage to the transportation system. This study conducted 31,104 simulations of a monoethanolamine carbon capture plant treating measured flue gas from an existing cement production plant. After capture, the CO 2 is treated through a deoxygenation unit followed by a compression train to fulfill specific quality specifications. Based on the sensitivity analysis, the energy consumption of the post-treatment process decreased with increased purity downstream. Despite this, the total energy consumption was not affected. Moreover, after the two-step purification the CO 2 stream was able to successfully fulfill the specification for NO x, O 2, NH 3, Ar, CO, SO 2. However, failing to meet the H 2O concentration requirements of both considered specifications and the N 2 concentration specified for ship transport. Thus, increasing the post-treatment energy cost or standard adjustments is required for future applications.