We investigate piston-mode fluid resonance within the narrow gap formed by two identical fixed barges in a side-by-side configuration, utilizing a two-dimensional fully nonlinear numerical wave tank. The focus is on examining the effects of uniform and shear currents. Under ‘wave+uniform-current’ conditions, a certain current speed is identified, beyond which the gap resonance reduces dramatically and monotonically with the current speed. This reduction is attributed to a stronger increase in damping compared to wave excitation, qualitatively explained by a linearized massless damping lid model. Furthermore, we study the effects of waves propagating on shear currents, maintaining an identical ambient current speed at the gap depth. Complementary to previous studies on this topic, our study reveals that the velocity profile of the studied shear current has an insignificant effect on the resonant gap amplitudes. The ambient current velocity at the gap depth is a more important key parameter to consider when assessing wave-induced gap responses, leading to a non-negligible increase in the resonant gap response. Consequently, disregarding the influence of currents in engineering practices is not a conservative approach.
A recently signed memorandum of understanding (MoU) between Ethiopia and Somaliland to develop the Port of Berbera and establish a naval base has sparked tensions and fears of conflict with Somalia. The MoU grants Ethiopia commercial access to Somaliland ports and a 20-kilometer lease for a naval base in exchange for Ethiopia's recognition of Somaliland's independence, drawing strong criticism from Somalia, which considers Somaliland part of its territory.
The article, ‘Logistics, Politics and Berbera in the Eye of an International Storm’ examines how the pursuit of economic development through logistics infrastructure can exacerbate political tensions and reignite historical conflicts. The Berbera corridor, envisioned as a pathway to peace, stability, and prosperity through economic interdependence, now underscores the potential for violent conflict inherent in modern logistics and infrastructure development. The case furthermore brings out the complex interplay of local, regional, and international interests at play in the Horn of Africa. Thus, the port's upgrade, intended to attract foreign investment and transform the area into a major trade hub, has intensified competition among Somaliland's clan lineages, inflamed historical tensions between Somalia and Ethiopia, and challenged the security and logistic interests of regional and global powers in the Red Sea and Western Indian Ocean.
The article is part of a special issue of Politique Africaine about the current armed conflicts in the Horn of Africa.
The success of the Seychelles Coast Guard shows how regional states, however tiny, can play an outsized role not only in countering piracy but also in maritime security in general. By taking quick and sharp action against malicious actors, small states can make a major contribution to regional maritime security. To stop the ominous return of piracy and address other maritime crimes like illegal fishing, smuggling, and pollution crimes across the world’s oceans, the contributions of small states will be crucial. Drawing on the Seychelles example, small states should overcome the sea blindness that pervades in many governments, recognize the sustainable development benefits from the blue economy, and understand security at sea as a political priority, while making efficient use of external security assistance.
The literature on climate change in the maritime transport industry has grown rapidly in the last few years. Yet as the research agenda has progressed, scientific debates have become more isolated and fragmented, making it difficult to translate new findings into broader policy debates. This article draws on problematization methodology to help organize the scientific debate on maritime emissions and to identify analytical gaps and challenges. We argue that scholars investigate shipping's emission problem from four distinct analytical perspectives— (1) international laws and regulations, (2) markets and economics, (3) engineering and technology, and (4) authority and legitimacy. Each of these perspectives problematizes maritime emissions in specific ways, leading to different policies and strategies to address the problem. We call for better integrating these four literatures and highlight three crosscutting areas and problems for future research. First, developing institutions that facilitate market and engineering solutions; second, integrating climate mitigation and adaptation research; and third, focusing on justice concerns to ensure an equitable green transition in the maritime industry.
This chapter examines the role of industry self-regulation in relation to international maritime law. While multilateral intergovernmental agreements are important to encouraging regulatory harmonisation, private actors have an essential role in industry, both in developing norms and in making rules and standards effective to ensure safe and secure shipping on clean oceans. Nonetheless, private actors are often overlooked and yet to be placed in the context of international maritime law and especially the United Nations Convention of Law of the Sea (UNCLOS). This chapter does so by analysing industry self-regulation in relation to UNCLOS, flag states and the International Maritime Organization (IMO) respectively.
Life depends on healthy oceans that provide ecosystem services (ES) to humans, including provisioning, regulating, supporting, and cultural ES (Kovalenko et al., 2023). However, biodiversity, habitats, and the delivery of marine ES and resources are increasingly threatened by growing human activities in the oceans (Worm et al., 2006). Blue-growth activities, such as shipping and energy, eutrophication, and climate change represent major pressures that affect marine ecosystems (Halpern et al., 2008; Ehlers, 2016). Over the past two decades, increasing scientific attention has focused on the need to preserve and restore healthy marine waters and their role in adapting to climate change (Santos et al., 2020). This challenge calls for holistic approaches that advance our knowledge. Within the contributions to this Research Topic (see Figure 1), three themes are central to driving further research to expand our understanding in this interdisciplinary field.
Hybrid testing, often referred to as hardware-in-the-loop, is when some parts of a complete system are modeled virtually and some parts are modeled experimentally, with information flowing back-and-forth between the virtual and experimental parts. Hybrid testing speeds up prototyping and testing. In this paper we outline the hybrid set-up for testing the performance of a hydraulic pump which is used as part of the power take-off system of the Wavepiston multi-body floating oscillating wave surge converter (OWSC). The motion of the OWSC is modeled in Orcaflex and the hydraulic system is simulated using Simscape. Due to the long stroke-length of the telescopic pump, a test rig handling only 1/3 of the stroke-length was constructed. The co-simulation, and linking to the test rig, is done using the Model.CONNECTTM and Testbed.CONNECTTM framework by AVL. The results obtained can be used for improving the numerical representation of the pump and validating models for the wear of the seals inside the pump.
We numerically simulate the hydrodynamic response of a floating offshore wind turbine (FOWT) using computational fluid dynamics. The FOWT under consideration is a slack-moored 1:70 scale model of the UMaine VolturnUS-S semi-submersible platform. The test cases under consideration are (i) static equilibrium load cases, (ii) free decay tests, and (iii) two focused wave cases of different wave steepness. The FOWT is modeled using a two-phase Navier-Stokes solver inside the OpenFOAM-v2006 framework. The catenary mooring is computed by dynamically solving the equations of motion for an elastic cable using the MoodyCore solver. The results are shown to be in good agreement with measurements.
Floating breakwaters (FBs) are frequently used to protect marinas, fisheries, or other bodies of water subject to wave attacks of moderate intensity. New forms of FBs are frequently introduced and investigated in the literature as a consequence of technological advancements. In particular, a new possibility is offered by High-Density Polyethylene (HDPE) by extruding pipes of large diameters (e.g., 2.5 m in diameter) and with virtually no limit in length (hundreds of meters). By connecting two or three such pipes in a vertical layout, a novel low-cost floating breakwater with deep draft is devised. This note investigates numerically and experimentally the efficiency of this type of multi-cylindrical FBs in evaluating different geometries and aims at finding design guidelines. Due to the extraordinary length of the breakwater, the investigation is carried out in two dimensions. The 2D numerical model is based on the solution of the rigid body motion in the frequency domain, where the hydrodynamic forces are evaluated (thanks to a linear potential flow model), and the mooring forces do not include dynamic effects nor drag on the lines. The numerical predictions are compared to the results of a 1:10 scale experimental investigation. An atypical shape of the wave transmission (𝑘𝑡) curve is found, with a very low minimum in correspondence with the heave resonance frequency. The results essentially point out the influence of the position of the gravity center, the stiffness, and the mutual distance among cylinders on 𝑘𝑡.
Cod stocks in the Danish inland waters and the Baltic Sea have collapsed today. Fishing vessels have therefore been required to install video cameras that film the catch for control purposes. The use of artificial intelligence for automated documentation of the catch is therefore a promising solution for control as well as research and management purposes that can contribute to rebuilding cod stocks and ensuring sustainable fishing in the future.