We present a high-order nodal spectral element method for the two-dimensional simulation of nonlinear water waves. The model is based on the mixed Eulerian–Lagrangian (MEL) method. Wave interaction with fixed truncated structures is handled using unstructured meshes consisting of high-order iso-parametric quadrilateral/triangular elements to represent the body surfaces as well as the free surface elevation. A numerical eigenvalue analysis highlights that using a thin top layer of quadrilateral elements circumvents the general instability problem associated with the use of asymmetric mesh topology.We demonstrate how to obtain a robust MEL scheme for highly nonlinear waves using an efficient combination of (i) global L2 projection without quadrature errors, (ii) mild modal filtering and (iii) a combination of local and global re-meshing techniques. Numerical experiments for strongly nonlinear waves are presented. The experiments demonstrate that the spectral element model provides excellent accuracy in prediction of nonlinear and dispersive wave propagation. The model is also shown to accurately capture the interaction between solitary waves and fixed submerged and surface-piercing bodies. The wave motion and the wave-induced loads compare well to experimental and computational results from the literature.
We present an arbitrary-order spectral element method for general-purpose simulation of non-overturning water waves, described by fully nonlinear potential theory. The method can be viewed as a high-order extension of the classical finite element method proposed by Cai et al. (1998)[5], although the numerical implementation differs greatly. Features of the proposed spectral element method include: nodal Lagrange basis functions, a general quadrature-free approach and gradient recovery using global L2projections. The quartic nonlinear terms present in the Zakharov form of the free surface conditions can cause severe aliasing problems and consequently numerical instability for marginally resolved or very steep waves. We show how the scheme can be stabilised through a combination of over-integration of the Galerkin projections and a mild spectral filtering on a per element basis. This effectively removes any aliasing driven instabilities while retaining the high-order accuracy of the numerical scheme. The additional computational cost of the over-integration is found insignificant compared to the cost of solving the Laplace problem. The model is applied to several benchmark cases in two dimensions. The results confirm the high order accuracy of the model (exponential convergence), and demonstrate the potential for accuracy and speedup. The results of numerical experiments are in excellent agreement with both analytical and experimental results for strongly nonlinear and irregular dispersive wave propagation. The benefit of using a high-order – possibly adapted – spatial discretisation for accurate water wave propagation over long times and distances is particularly attractive for marine hydrodynamics applications.
Monitoring methods, such as seabed bottom-towed cameras, sediment grabs, and benthic sledges, have limitations in spatial coverage, cause seabed disturbance, are restricted to soft-bottom substrates, and offer low flexibility for marine seabed monitoring. In this study, we investigate the potential of a non-invasive and simple underwater remotely operated vehicle (ROV) to enhance marine seabed monitoring. A tethered ROV equipped with a GoPro camera was deployed in three areas of Skagerrak at depths from 15-34 m to assess accuracy in species identification and substrate classification identified from still frames. The quality of still frames varied between areas due to turbidity, motion blur, and marine snow, which reduced the number of high-quality frames by approximately 20%. Classification of substrates and taxa identification were possible in the remaining still frames. Two different substrates were detected: sand and stone reef. Stone reefs had a lower occurrence compared to sand. A total of 10 taxa were detected in the two substrate types. The highest abundance was observed in the stone reef substrate compared to the sand substrate. Identification at the species level was limited due to the quality of the still frames, which affected the detectability of morphological traits. This study demonstrates that a widely accessible ROV can be used for marine monitoring. The ROV can be used in different substrates, and still frames provide valuable information on species composition, which can enhance the replicability of monitoring programs.
Led by the UN’s International Maritime Organization (IMO) and the EU, the shipping industry struggles to reduce its greenhouse gas (GHG) emissions to align with the Paris Agreement. Clean Cargo, the leading voluntary buyer–supplier forum for sustainability in the cargo shipping industry, developed some years ago a methodology to calculate and report the GHG emissions from containerships. The recently introduced carbon emission requirements by the IMO and EU have reinforced the members’ interest in a new Clean Cargo reporting mechanism that enables a more effective and efficient monitoring of the decarbonization progress. A better understanding of the user needs accompanied by due consideration to the regulatory environment and the technological advances are key to build this new framework. This paper builds on the case of the Clean Cargo initiative to (1) identify the stakeholders’ expectations and motivations for voluntary disclosure of environmental information, and (2) discuss the governance challenges of voluntary initiatives. A questionnaire was designed and deployed to investigate the current uses of Clean Cargo data and the information sharing among different stakeholders. Voluntary schemes can speed up the decarbonization process by proposing standards accepted by all actors of the global value chain. Clean Cargo members envision reporting on absolute GHG emissions per shipment as the way forward.
Operational cycles for maritime transportation is a new concept to improve the assessment of ships’ energy efficiency and offer benchmarking options among similar ship types and sizes. This work extends previous research to consolidate the methodology, bring more comprehensiveness, and provide a more holistic assessment of these operational cycles. The cycles are designed from noon reports from a fleet of around 300 container ships divided into eight size groups. The comparison between cycles derived from speed and draft with those based on main engine power identifies that the cycles based on speed and draft are more accurate and allow for estimating the Energy Efficiency Operational Index but require more data. The main-engine-power cycles are more effective in benchmarking through the Annual Efficiency Ratio. These cycles reduce the inherent variability of the carbon intensity indicator and present good opportunities as a benchmarking tool for strengthening the regulatory framework of international shipping.
Benchmarking the energy efficiency of ships is not a straightforward task, mainly due to the diversity of operations. Although driving cycles have been used for decades in evaluating the performance of road vehicles, these do not exist in formal policy-making for maritime transport. This work builds on a previously proposed methodology. It uses noon reports of 327 vessels for 2019 to construct operational cycles for seven size classes of container ships using the main engine power as the main parameter. Concerning the main engine emissions, the resulting cycles reduce variation in the carbon intensity indicator values by more than 30% while maintaining an average accuracy of 97.7% in absolute emissions. These figures show that the concept can improve operational carbon intensity indicators in terms of robustness and their technical counterparts in optimizing ship design. The paper also proposes further work required for benchmarking applications in policy-making.
The International Maritime Organization employs technical and operational indicators to assess ship energy efficiency. Weather conditions significantly impact ship fuel consumption during voyages, necessitating the consideration of this influence in energy efficiency calculations. This study aims to design models for estimating the impact of weather components on fuel consumption and develop correction factors to cope with the weather effect on the fuel consumption of container ships for different sea states. Using model-based machine learning, the study analyzes noon reports and hindcasted weather data from two sister container ships. It quantifies weather-induced fuel consumption across various sea states, ranging from 2% to 20%, with an average of 7%–13% depending on the model used. Correction factors specific to each sea state are derived, and different approaches for their integration into energy efficiency indicators are proposed. This study advocates tailored weather correction factors for energy efficiency metrics tied to specific sea states, emphasizing the need for standardized weather impact assessments. Prior to any formal policy application, future work is needed to address the limitations of the present study and extend this approach to various ship types and sizes and different geographical regions.
Monopiles are often the preferred foundation concept for an offshore wind turbine. The interaction between extreme waves and the large diameter monopile will in some cases result in a vertical jet of water uprush on the monopile (i.e., wave run-up) which subsequently may lead to large slamming loads on monopile appurtenances like the external working platform.
Extreme wave run-up interaction with an external working platform is often an area of concern during the design phase of an offshore wind project as an overly conservative assessment of the run-up loads may lead to unneeded costs in material and an increased project carbon footprint. An insufficient assessment of the run-up loads may lead to structural failure of the appurtenances and subsequent costly maintenance and repair works, further exacerbated by possibly difficult access to the damaged platform.
The practical process in the assessment of wave run-up on monopiles and associated loads on appurtenances can be a challenge to the designer due to lack of guidance on this topic in governing standards. The designer may then have to rely on several sources of available literature and must assess and include the effect of associated uncertainties like: Adjustment to site specific environmental conditions, unclear or unconcise terminology in the literature, lack of model test results representing the actual geometry and limited knowledge of spatial and temporal run-up load distribution on the appurtenances.
The aim of the present paper is to describe a complete methodology for assessment of wave run-up on monopiles and associated loads on appurtenances. The methodology, which will serve as a practical guide, is based on a collection of existing methods with new analysis to consider the pressure distribution on modern asymmetric grated platforms. This was based on experiences gained and challenges encountered during a detail design project of a monopile foundation for an offshore wind turbine in extreme environmental conditions. The sensitivity of the run-up assessment related to the design input (water depth, wave height and period, associated water level and current conditions) is discussed by considering a matrix with various environmental input combinations representing extreme environmental conditions.
The maritime sector contributes significantly to climate change, given thenumber of global emissions that this represents. Emissions inventorying isone of the measurement system approaches considered in terminals to mitigate harmful emissions. The concept of sustainability has gained attentionwhere economic, social, and environmental dimensions need to be balanced.Assessing all three sustainability dimensions is important. Both the environment and the society, e.g., human health and safety, are impacted by terminal operations. Reducing their negative impact can compromise the economicgrowth of the terminal. This is challenging the maritime sector, and althoughsome authors define methods to evaluate sustainability in terminals, nostandard guideline is available in the literature. The lack of a common reference guideline makes comparison of sustainability actions in terminals difficult.This paper presents a sustainability assessment framework based on theanalysis of the state of the art in literature contributing to sustainable development of terminals and supporting decision-makers.
As Arctic sea ice recedes due to global warming, ship traffic is increasing, posing global climate risks, particularly from black carbon emissions. Emitted by ships burning heavy fuel oil, black carbon accelerates ice melt and contributes to climate change. Despite this urgency regulatory progress on the topic has been slow. The International Maritime Organization has debated Arctic black carbon emissions for over a decade with little advancement. Notably, regulatory efforts on the topic so far have been driven mainly by non-state actors rather than states. However, their regulatory influence is hindered by a critical barrier: a lack of transparency. This article analyses the crucial role of transparency in international law-making, specifically for non-state actors, using Arctic black carbon regulation as a case study. Drawing on semi-structured interviews, the article identifies transparency challenges and suggests recommendations to overcome them, thereby strengthening the role of non-state actors within the regulation.