We present computations of cavitating flow over a NACA0015 hydrofoil. The simulations are performed by a finite volume compressible Euler model with dynamic mesh adaptation. The adaptive mesh refinement (AMR) is driven by a generic, simple and efficient error estimator based on the jump in value between cell faces for a given variable. It is shown that AMR based on vapour fraction provide unsatisfactory results both for (quasi-) steady and unsteady cavitation, as the major flow features are not captured. Instead, adaptivity driven by the Q-value proved successful even for resolving the cavity interface.
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.
Even though that there has been increasing focus on the energy-efficient operation of vessels and that the knowledge of cost-effective improvements is widespread in the industry, energy-efficient operation is only a minor topic on board many working vessels. A significant reduction in fuel can be achieved through changes in the operational practices, but to establish a successful system for best practices within energy-management the installation of a decision support system is essential. This article presents a decision support system for working vessels to determine best practice for the reduction of fuel consumption. Requirements for the system are defined through interviews with crew and observations on board vessels. Case studies are used for illustrating the usefulness. The use of generators onboard is analyzed using the software. It is found that the generators are not running optimally, but the crew can use the software to re-organize and find the most fuel-efficient loading range for the generators on board.
Current modeling practices for social-ecological systems (SES) are often qualitative and use causal loop diagrams (CLDs), as these models promote an evaluation of the systems loops and variable connectivity. Our literature review demonstrated that quality assurance of these models often lacks a consistent validation procedure. Therefore, a guide to improving the validation of qualitative models is presented. The presumed utility protocol is a multi-dimensional protocol with 26 criteria, organized into four dimensions, designed to assess specific parts of the modeling process and provide recommendations for improvement. This protocol was applied to three demonstration cases, located in the Arctic Northeast Atlantic Ocean, Macaronesia, and the Tuscan archipelago. The “Specific Model Tests” dimension, which focuses on the structure of the model, revealed positive evaluations of its structure, boundaries, and capacity to be scaled up. "Guidelines and Processes", which focuses on the meaning and representativeness of the process, showed positive results regarding purpose, usefulness, presentation, and meaningfulness. "Policy Insights and Spillovers", a dimension focused on the policy recommendations, revealed a high number of "not apply", indicating that several criteria are too advanced for the status of the models tested. The "Administrative, Review, and Overview" dimension, which focused on the managerial overview, showed the models needed improvement in the documentation and replicability, while time and cost constraints were positively evaluated. The presumed utility protocol has shown to be a useful tool providing quantitative and qualitative evaluations for an intermediate evaluation of the model-building process, helping to substantiate confidence, with recommendations for improvements and applications elsewhere.
The purpose of this paper is to investigate a multiple ship routing and speed optimization problem under time, cost and environmental objectives. A branch and price algorithm as well as a constraint programming model are developed that consider (a) fuel consumption as a function of payload, (b) fuel price as an explicit input, (c) freight rate as an input, and (d) in-transit cargo inventory costs. The alternative objective functions are minimum total trip duration, minimum total cost and minimum emissions. Computational experience with the algorithm is reported on a variety of scenarios.
Nowadays, sea traveling is increasing due to its practicality and low-cost. Ferry boats play a significant role in the marine tourism industry to transfer passengers and tourists. Nevertheless, traditional ferry ships consume massive amounts of fossil fuels to generate the required energy for their motors and demanded loads. Also, by consuming fossil fuels, ferries spatter the atmosphere with CO2 emissions and detrimental particles. In order to address these issues, ferry-building industries try to utilize renewable energy sources (RESs) and energy storage systems (ESSs), instead of fossil fuels, to provide the required power in the ferry boats. In general, full-electric ferry (FEF) boats are a new concept to reduce the cost of fossil fuels and air emissions. Hence, FEF can be regarded as a kind of dc stand-alone microgrid with constant power loads (CPLs). This article proposes a new structure of a FEF ship based on RESs and ESSs. In order to solve the negative impedance induced instabilities in dc power electronic based RESs, a new intelligent single input interval type-2 fuzzy logic controller based on sliding mode control is proposed for the dc-dc converters feeding CLPs. The main feature of the suggested technique is that it is mode-free and regulates the plant without requiring the knowledge of converter dynamics. Finally, we conduct a dSPACE-based real-time experiment to examine the effectiveness of the proposed energy management system for FEF vessels.
While systematic literature reviews (SLRs) have contributed substantially to developing knowledge in fields such as medicine, they have made limited contributions to developing knowledge in the supply chain management domain. This is due to the ontological and epistemological idiosyncrasies of research in supply chain management, which need to be accounted for when retrieving, selecting, and synthesizing studies in an SLR. Therefore, we propose a new paradigm for SLRs in the supply chain domain that is based on both best practice and the unique attributes of doing supply chain management research. This approach involves exploring existing studies with attention to theoretical boundaries, units of analysis, sources of data, study contexts, definitions and the operationalization of constructs, as well as research methods, with the goal of refining or revising existing theory. This new paradigm will push supply chain management research to the frontier of current methodological standards and build a foundation for improving the contribution of future SLRs in the supply chain and adjacent management disciplines.
This article seeks to provide a sociological understanding both of the logistics service field and of the impact the COVID-19 pandemic has had on this field. To address this issue, we analyze the case of logistics services used by the shipping industry to manage maritime safety, namely statutory and classification services. These services verify the compliance of shipping vessels with private and public safety norms. We develop the Bourdieusian concept of nomos, according to three dimensions: A normative framework, a legitimate vision, and structural divisions. The findings highlight a complex set of industrial and regulatory norms which give rise to complementary and sometimes overlapping obligations. Nomos materializes as some actors, typically IACS member societies, benefit from an uncontested legitimacy to deliver such services, whereas other actors are excluded for a variety of reasons.
Current practice for maritime search and rescue (MSAR) adheres to predetermined full-coverage patterns for finding targets. These do not account for key success factors for MSAR missions such as the dynamic location of targets, updates on situational awareness during mission execution, and search vehicle kinematics. Consequently, current practice cannot incorporate realistic MSAR operational conditions into path-finding, increasing the likelihood of mission failure. To address this issue, a novel, flexible path-finding framework is proposed for generating a path while dynamically updating the probability of a target based on the path's trajectories. The solution approach implements the A* algorithm, which can accommodate the dynamics of a vehicle and guarantees the optimality of the final path with respect to the target objective function. Experiments show that a more than 50% improvement in the time needed to guarantee a certain probability of finding a target is exhibited compared to the parallel sweep coverage path-finding approach.
Stricter regulations imposed on emissions are motivating the scientific community to consider studying alternative fuels to achieve low emission, high efficient dual-fuel (DF) marine engines. In this context, three dimensional computational fluid dynamic (CFD) simulations are performed to study the combustion and emission formation under two-stroke, dual-fuel marine engine-like conditions. The DF engine configuration consists of a pilot diesel fuel and a high-pressure, direct injection (HPDI) of natural gas (NG). The simulation results are validated under both high load (high charge density) and low load (low charge density) operating conditions. Detailed analysis of the flame development and emission formation are performed. The interaction between the pilot diesel jets and the methane flame jets is studied. Based on the results, the further methane jets penetration in the low load case leads to better air–fuel mixing and a higher combustion intensity than that in the high load. Effects of the pilot fuel injection timing on combustion and emission formation and the governing mechanisms are also investigated in detail. Results indicate that the intense combustion of the accumulated methane expands the methane flame towards the piston when the pilot injection timing is retarded. The NO formation is lower in the high load case with higher charge density due to the lower combustion intensity. Also, retarding the pilot injection timing decreases the NO formation.