This paper analyzes the nonlinear forces on a moored point-absorbing wave energy converter (WEC) in resonance at prototype scale (1:1) and at model scale (1:16). Three simulation types were used: Reynolds Averaged Navier-Stokes (RANS), Euler and the linear radiation-diffraction method (linear). Results show that when the wave steepness is doubled, the response reduction is: (i) 3% due to the nonlinear mooring response and the Froude-Krylov force; (ii) 1-4% due to viscous forces; and (iii) 18-19% due to induced drag and non-linear added mass and radiation forces. The effect of the induced drag is shown to be largely scale-independent. It is caused by local pressure variations due to vortex generation below the body, which reduces the total pressure force on the hole. Euler simulations are shown to be scale-independent and the scale effects of the WEC are limited by the purely viscous contribution (1-4%) for the two waves studied. We recommend that experimental model scale test campaigns of WECs should be accompanied by RANS simulations, and the analysis complemented by scale-independent Euler simulations to quantify the scale-dependent part of the nonlinear effects.
Although prevention of incidents leading to evacuations at sea is of vital importance, little is known about its causal patterns and demographic determinants. We investigated therefore relationships between age, occupation and nationality and causes of evacuations. The data were obtained from the Telemedical Assistance Service (TMAS) in Denmark between 2004 and 2014 supplemented with data on all seafarers from the Danish Maritime Authority (N = 73,344). These data included information on broad age groups, occupational position and nationality. The outcomes were evacuations from any cause and in four broad categories of causes leading to evacuations. A total of 403 evacuations were reported in the 11-year study period. 27% of the evacuations were due to external causes, 19% due to diseases of the circulatory system, 14% due diseases of the digestive system and 40% from other or undetermined causes. Age-adjusted all-cause evacuation rates varied between 1.4 and 3.4 incidents per 1000 person-years in 2004–2014 for officers and between 3.3 and 20.2 incidents for non-officers. An elevated risk of evacuations was found among both officers and non-officers aged ≥50 years, compared with those aged 30–49 years with odds ratios of 2.73 (95% confidence intervals 1.66, 4.50) and 2.59 (2.03, 3.31), respectively. The odds ratios for non-officers from non-Danish European Union and from non-European Union countries compared with Danish non-officers were 1.51 (1.12, 2.04) and 0.55 (0.42, 0.71), respectively. In conclusion, working as non-officer, older age and non-Danish EU nationality were associated with a higher risk of evacuations irrespective of the cause leading to evacuation.
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.
Autonomous surface vessels comprise complex automated systems with advanced onboard sensors. These help establish situation awareness and perform many of the complex tasks required for safe navigation. However, situations occur that require assistance by a human proxy. If not physically present on board, information digestion and sharing between human and machine become crucial to maintain safe operation. This paper addresses the co-design of on-board systems and a Remote Control Centre (RCC). Using the international regulations on watch-keeping (STCW) as a basis, the paper discuss how an autonomous system is designed to meet the STCW requirements. It is discussed how the autonomous system is made aware of the state of the vessel, its surroundings, on-board defects or navigational challenges and shared with the RCC in a collaborating system perspective.
Autonomous systems strive to obtain salient features that include computer intelligence for obtaining situation awareness, decision support to a human navigator, or for facilitating autonomous decision-making in unmanned vehicles. This paper considers the case of autonomous marine surface vehicles, where high-quality decision support will be instrumental for obtaining a periodically unattended bridge and for approval of unmanned bridge operation with fallback through remote operation. The proposed design focuses on a sovereign-based architecture that facilitates safety, resilience and cyber-security. We address central elements of risk in the development and approval of autonomous systems; we analyze the challenges associated with testing, commissioning and maintenance of a highly complex cyber-physical system, and describe design principles for the sovereign agents architecture.
Marine autonomy research has focused on algorithmic and technical developments, targeting autonomous craft in restricted areas where international rules and regulations are not prioritised. This paper addresses the system engineering aspect of a highly complex system in which the seamless, predictable, and secure interoperability of vendorspecific hardware and software subsystems is a fundamental requirement for designing and implementing cyber-physical systems with artificial intelligence to assist or replace the navigating officer, such as autonomous marine surface vehicles. It addresses international rules in the sector and exhibits a system architecture that can fulfil the criteria for safe behaviour in foreseen occurrences and the capacity to request human aid if the autonomous system cannot manage a problem. The system thinking and engineering provided in this article have been applied to The GreenHopper, a harbour bus currently under construction and intended to undergo certification and enter commercial service.
The present paper deals with overtopping prediction for berm breakwaters in line with the EurOtop methodology. The basis for the paper is the recent advances proposed for EurOtop for conventional breakwaters with respect to the influence of the wave steepness and the crest width. New model tests have been performed to investigate the applicability of these influence factors to berm breakwaters. To cover a white spot in existing data for berm breakwaters, the model tests included wave conditions with very low wave steepness. The results show that the recently developed influence factors for conventional breakwaters also improve predictions for berm breakwaters. Based on this, an additional influence factor for the dimensionless berm width is established. The berm width was in previous studies made dimensionless by the wave height, but the present study indicates that the wavelength is more appropriate.
The current and potential use of the seas and oceans is often called the 'Blue Economy'. Recently, the European Commission launched its Blue Growth Strategy on the opportunities for marine and maritime sustainable growth. The European Commission considers that Blue Growth is a long-term strategy in the marine and maritime sectors with great potential for innovation and economic growth. Holistic spatial planning systems supporting sustainable development have proven themselves in terrestrial planning and are also needed at sea. Due to this reason,
the BONUS BASMATI project is based on the ecosystem services approach to assist in assessing sustainable solutions corresponding to policy goals.
As the world collectively looks to technology to salvage what is left of our world to sustain a habitat that can accommodate our way of life, users are increasingly exposed to technological solutions, rarely developed with an offset in their practice. This also holds for the maritime sector in Denmark, where the way of developing technology is limited to the applicability of technological artifacts and can reduce the potential efficiency gains that technologies can introduce. This paper applies qualitative research to show that there is a disconnect between, on the one hand, funders, technology developers, and decision-makers and, on the other hand, technology users and practitioners in the Danish maritime sector. It argued that if technology is to replace or assist any human practice and solve for example the climate crises, then knowledge of users’ practices must be key to developing the technological solutions.