This paper presents the methods developed and key findings of the IWEC project performed by Ocean Harvesting Technologies AB (OHT). It aimed to reduce the levelized cost of energy (LCoE) of OHT’s wave energy converter InfinityWEC, by analysing how different key parameters impact cost and annual output using a model of a 100-MW array installation. Component-level cost functions were developed and mapped to key parameters and constraints of the system. A large number of system configurations were then evaluated with a numerically efficient 3 degree-of-freedom (DoF) nonlinear radiationdiffraction model in WEC-Sim along with OHT’s sea statetuned polynomial reactive control (PRC). The most promising configurations were identified and investigated in more detail. The configuration with the best LCoE were finally identified and analysed further, including estimation of the effect of changing the PRC to model predictive control, which resulted in 17-34% higher annual output and 12-23% lower LCoE. The final LCoE was found to be 93-162 EUR MWh at 100 MW installed capacity. An important finding from the study is that using simplified metrics such as CAPEX/ton was found to be irrelevant. Numerical wave tank testing, high-fidelity computational fluid dynamics (CFD), were used to tune the viscous drag of the 3 DoF WEC-Sim model. Applying verification and validation (V&V) techniques the CFD simulations showed a relatively large numerical uncertainty, but the average power and the motion responses were found to be sufficiently accurate.
This paper aims to determine what the proper role of the judiciary should be in developing climate change policy. It does so in light of the sometimes contentious relationship between ‘activist’ or ‘progressive’ judges and the doctrine of separation of powers. This relationship has a long history by which much of human rights law has been shaped. The paper analyses the court judgments in the cases of Urgenda v Kingdom of the Netherlands, Juliana v United States, and Friends of the Irish Environment v Ireland in order to identify how different legal systems view this relationship. The paper also considers the upcoming climate case in the Supreme Court of Norway. In particular, the question is asked whether the separation of powers in Europe and the United States is a doctrine mandating systems of power balance rather than of strict separation.
Drawing on the argumentation from the Urgenda judgment, the paper concludes that the protection and development of human rights should be the main concern in climate change litigation. The judiciary should accordingly take an important role in climate change policy-making in order for the state to comply with its duty to instigate emission limits.
Two different media platforms played a key role in keeping Tema Port in Ghana afloat during the period immediately leading up to and during the three-week COVID-19 pandemic-related lockdown in late March–April of 2020. The one media platform, Eye on Port, is a weekly broadcast television show by the port’s authorities, which caters primarily to external commercial stakeholders of the port. The other platform is a closed WhatsApp forum used by stakeholders working at the operational level of the port. Both platforms served specific needs among their users, who had been restricted in their mobility but had to keep the port operational. Combining ‘scalable sociality’ with the concept of polymedia, we identify how the two media functioned to meet the different informational and conversational needs of their respective users. We argue that either medium alone could not fulfil the communicative needs necessary to keep the port operational during the early stage of the COVID-19 pandemic.
The 0.1% sulphur limit within Sulphur Emission Control Areas (SECA) has made compulsory the use of either pricier ultra-low sulphur fuel, or the installation of abatement technologies that require significant capital investments. Due to the unexpectedly low fuel prices, Ro-Ro operators have been able to cope with the new sulphur limits, but recent research has shown that if fuel prices increase some Ro-Ro services may face the risk of closure. This paper proposes three key performance indicators (KPIs) to enable the asssessment of the impact of SECAs on Ro-Ro shipping. The KPIs are used on a set of case studies for services of a leading European Ro-Ro operator, and allow benchmarking of a series of operational and policy measures that aim to reverse the negative impacts of SECAs. The operational measures consider speed reduction, new sailing frequency, fleet reconfiguration, as well as investments in abatement technologies. Policy measures include the options of either subsidizing shippers or ship operators, or alternatively introducing new taxes on landbased options. The KPIs can be useful to ship operators seeking to improve the resilience of their network, as well as to regulatory bodies designing new environmental policies and understanding any negative implications these may have on ship operators.
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.
In a premixed dual-fuel (DF) methane-diesel engine, the ignition of the lean premixed methane/air mixture starts with the assistance of a pilot diesel injection. Auto-ignition of pilot fuel is important as it triggers the subsequent combustion processes. A delay in the auto-ignition process may lead to misfiring, incomplete combustion, and thus higher greenhouse emissions due to methane slip. Hence, a better understanding of the auto-ignition process for the pilot fuel can help to improve the overall engine performance, combustion efficiency, and to lower exhaust emission levels. In the present study, large eddy simulation (LES) is used to investigate the auto-ignition process of micro-pilot diesel in premixed DF combustion in a constant volume combustion chamber (CVCC). The entire DF combustion processes including methane gas injection, methane/air mixing, pilot diesel injection, and ignition are simulated. The numerical model is validated against experimental data. The present numerical model is able to capture the ignition delay time (IDT) within a maximum relative difference of 7% to the measurements. A higher relative difference of 38% is obtained when methane gas injection and mixing are omitted in the simulation and the methane/air is assumed homogeneous. This demonstrates the importance of inhomogeneity pockets. To study the effects of temperature and methane inhomogeneities separately, different idealized inhomogeneities in temperature and methane distribution are considered inside the CVCC. The inhomogeneity in the temperature is observed to have a more profound influence on the IDT than the methane inhomogeneity. The inhomogeneity pockets of temperature advance the first-stage ignition and, subsequently, the second-stage ignition. A sensitivity analysis on the effect of inhomogeneity wavelength reveals that the larger wavelengths enhance the combustion due to the presence of pilot diesel jets in the desirable regions for a longer time duration.
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.
Slugging flow in the offshore oil & gas production attracts a lot of attention due to its limitation of production rate, periodic overload on processing facilities, and even direct cause of emergency shutdown. This work aims at two correlated objectives: (i) Preventing slugging flow; and meanwhile, (ii) maximizing the production rate at the riser of an offshore production platform, by manipulating a topside choke valve through a learning switching model-free PID controller. The results show good steady-state performance, although a long settling time due to the unknown reference for no slugging flow.
The maritime industry is one of the greenest modes of transportation, taking care of almost 90% of the global trade. The maritime container business revolves around liner shipping, which consists of container vessels sailing on fixed itineraries. For the last 20 years, there has been an increasing number of publications regarding how to design such fixed routes (services), to ensure a high level of service while minimizing operational costs and environmental impact. The liner shipping network design problem can briefly be described as follows: Given a set of demands (defined by origin, destination, time limit) and a set of vessels with variable capacity, the task is to design a set of weekly services, assign vessels to the services, and flow the demand through the resulting network such that it arrives within the stated time constraints. The objective is to maximize revenue of transported demand subtracting the operational costs. We present an in-depth literature overview of existing models and solution methods for liner shipping network design, and discuss the four main families of solution methods: integrated mixed integer programming models; two-stage algorithms designing services in the first step and flowing containers in the second step; two-stage algorithms first flowing containers and then designing services; and finally algorithms for selecting a subset of proposed candidate services. We end the presentation by comparing the performance of leading algorithms using the public LINER-LIB instances. The paper is concluded by discussing future trends in liner shipping, indicating directions for future research.
Container shipping drives the global economy and is an eco-friendly mode of transportation. A key objective is to maximize the utilization of vessels, which is challenging due to the NP-hardness of stowage planning. This article surveys the literature on the Container Stowage Planning Problem (CSPP). We introduce a classification scheme to analyze single-port and multi-port CSPPs, as well as the hierarchical decomposition of CSPPs into the master and slot planning problem. Our survey shows that the area has a relatively small number of publications and that it is hard to evaluate the industrial applicability of many of the proposed solution methods due to the oversimplification of problem formulations. To address this issue, we propose a research agenda with directions for future work, including establishing a representative problem definition and providing new benchmark instances where needed.