We present a depth-integrated Boussinesq model for the efficient simulation of nonlinear wave–body interaction. The model exploits a ‘unified’ Boussinesq framework, i.e. the fluid under the body is also treated with the depth-integrated approach. The unified Boussinesq approach was initially proposed by Jiang (2001) and recently analyzed by Lannes (2017). The choice of Boussinesq-type equations removes the vertical dimension of the problem, resulting in a wave–body model with adequate precision for weakly nonlinear and dispersive waves expressed in horizontal dimensions only. The framework involves the coupling of two different domains with different flow characteristics. Inside each domain, the continuous spectral/hp element method is used to solve the appropriate flow model since it allows to achieve high-order, possibly exponential, convergence for non-breaking waves. Flux-based conditions for the domain coupling are used, following the recipes provided by the discontinuous Galerkin framework. The main contribution of this work is the inclusion of floating surface-piercing bodies in the conventional depth-integrated Boussinesq framework and the use of a spectral/hp element method for high-order accurate numerical discretization in space. The model is verified using manufactured solutions and validated against published results for wave–body interaction. The model is shown to have excellent accuracy and is relevant for applications of waves interacting with wave energy devices.
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.
There is growing evidence that the ecosystem service (ES) concept can provide valuable input to marine spatial planning (MSP), by highlighting which ecosystem goods and services can be produced from a planning area. ES link the underlying ecosystem processes and functions to the benefits humans can receive from ecosystems (the ecosystem cascade). In this study, we argue that the ecosystem cascade can be used to structure the stock-taking and future scenario analysis in MSP. However, indicators, which are needed for measuring ES, have often been applied in various ways to the different steps of the cascade. Here, we apply a consistent approach to sorting indicators into the cascade. The indicators are presented in an indicator pool that can be used to filter them based on the cascade steps, several quality criteria, and themes. The pool consists of 772 indicators, of which 735 were analyzed. In total, 252 analyzed indicators belong to the provisioning services, 314 indicators to the regulating services and 169 to the cultural services. The indicator pool offers a suitable starting point to select indicators for ES assessments within MSP. Using indicators at the different cascade steps allows the assessment of i) the ecosystem components generating the services and ii) the impacts on ES and their beneficiaries when changes occur in the provision of the services due to planning or management decisions.
This paper presents a literature survey on the fleet size and mix problem in maritime transportation. Fluctuations in the shipping market and frequent mismatches between fleet capacities and demands highlight the relevance of the problem and call for more accurate decision support. After analyzing the available scientific literature on the problem and its variants and extensions, we summarize the state of the art and highlight the main contributions of past research. Furthermore, by identifying important real life aspects of the problem which past research has failed to capture, we uncover the main areas where more research will be needed.
Waiting times for trucks, trains, airplanes and ships in service represent apparent transport system inefficiencies, and measures to reduce these may have the potential to abate transport GHG emissions. In international shipping, transportation researchers have pointed out that reduced waiting time in association with port calls holds such promise. We explore the potential for GHG abatement through port call optimization, focusing on crews and their employers - the shipping companies. Adding new empirical evidence to the transportation literature, we confirm the existence of idle time during port calls, and go beyond this in describing the causes for it. We show how several port stakeholders, including government officials, limit the crews’ and shipping companies’ room for maneuver in relation to port calls. We also show why the process of reducing waiting time in shipping is more complex than that for onshore transport modes, where real-time traffic information guides drivers’ route choices, and reduces congestion and waiting time. Our findings have implications for both policy makers and transportation research.
The use of the seas and oceans is generally regulated by the United Nations through the UN Convention on the Law of the Sea, which defines the rights and responsibilities. However, with the rapidly increasing use of the sea and oceans it is inevitable that conflicts may arise. Accordingly, there has been an increasing international recognition of the need to manage human activities that influence the marine environment and its ecosystems in an integrated, cross-sectoral manner. Recently, Maritime Spatial Planning (MSP) has gained significant attention as a new paradigm aiming at minimizing the conflicts among different sea uses through involving various stakeholders and sectors while aiming for sustainable growth. The aim of this research is to build a conceptual model for a Data Infrastructure to support marine space in a transnational context addressing the challenges related to the increasing use of marine areas and resources. The work was carried out in a close cooperation between several public authorities and research institutes in the Baltic Sea Region.
Marine space is overall under increasing pressures from human activities. Traditionally, the activities taken place in oceans and seas were related to fisheries and transport of goods and people. Today, offshore energy production – oil, gas, and wind, aquaculture, and sea-based tourism are important contributors to the global economy. This creates competition and conflicts between various uses and requires an overall regulation and planning. Maritime activities generate pressures on the marine ecosystems, and in many areas severe impacts can be observed. Maritime spatial planning is seen as an instrument to manage the seas and oceans in a more sustainable way, but information and tools are needed. The current paper describes a tool to assess the cumulative impacts of maritime activities on the marine ecosystems combined with a tool to assess the conflicts and synergies between these activities.
The hybrid combination of hydrogen fuel cells (FCs) and batteries has emerged as a promising solution for efficient and eco-friendly power supply in maritime applications. Yet, ensuring high-quality and cost-effective energy supply presents challenges. Addressing these goals requires effective coordination among multiple FC stacks, batteries, and cold-ironing. Although there has been previous work focusing it, the unique maritime load characteristics, variable cruise plans, and diverse fuel cell system architectures introduce additional complexities and therefore worth to be further studied. Motivated by it, a two-layer energy management system (EMS) is presented in this paper to enhance shipping fuel efficiency. The first layer of the EMS, executed offline, optimizes day-ahead power generation plans based on the vessel's next-day cruises. To further enhance the EMS's effectiveness in dynamic real-time situations, the second layer, conducted online, dynamically adjusts power splitting decisions based on the output from the first layer and instantaneous load information. This dual-layer approach optimally exploits the maritime environment and the fuel cell features. The presented method provides valuable utility in the development of control strategies for hybrid powertrains, thereby enabling the optimization of power generation plans and dynamic adjustment of power splitting decisions in response to load variations. Through comprehensive case studies, the effectiveness of the proposed EMS is evaluated, thereby showcasing its ability to improve system performance, enhance fuel efficiency (potential fuel savings of up to 28%), and support sustainable maritime operations.
For design validation of offshore structures and conceptualisation of wave energy converters, physical model testing performed in wave basin laboratories is often applied. In such cases, knowledge about the wave conditions is of great significance. For validation of the wave condition in such tests, different methods for estimation of the directional wave spectra may be applied. However, different assumptions are imposed in the methods and deviations here from providing uncertainties in the results. The following paper quantifies the influence of nonlinear effects on the accuracy of the estimated directional wave spectra. This is done by analysis of idealised, synthetically generated waves based on second order wave theory and secondly with simplified amplitude dispersion included. The present analyzes show that the uncertainties of the directional wave spectra are proportional to the level of nonlinearity present in the wave field.
Profitable energy saving measures are often not fully implemented in shipping, causing energy efficiency gaps. The paper identifies energy efficiency gaps in ship operations, and explores their causes. Lack of information on energy efficiency, lack of energy training at sea and onshore and lack of time to produce and provide reliable energy efficiency information cause energy efficiency gaps. The paper brings together the energy efficiency and ship management literatures, demonstrating how ship management models influence energy efficiency in ship operations. Achieving energy efficiency in ship operations is particularly challenging under third party ship management. Finally, the paper discusses management implications for shipping companies, which outsource ship management to third parties.