In this paper existing guidelines to predict wave overtopping on rubble mound breakwaters and coastal structures are modified and improved with respect to the influence of the roughness and crest width. Data from recently made model tests and existing data are combined to demonstrate the need for modifying these formulations in EurOtop. A new reduction factor γcw for the crest width is established and is an improvement of the method by Besley. The influence of the roughness of the slope normally also includes an influence of the breaker parameter when it is larger than a certain limit (EurOtop suggest ξm-1.0 > 5). The present study shows that the breaker parameter is not the ideal dimensionless parameter describing the influence of the wave period for breakwaters with steep slopes, as for such structures the front slope has much less influence on the overtopping than the wave steepness. Thus slope angle and wave steepness have been uncoupled to describe the influence of the armor roughness on wave overtopping. The improvement in the overtopping prediction compared to EurOtop is significant, specifically for the new data sets that have data outside the range of the calibration data used for influence of roughness in EurOtop. The proposed improved methods enlarge the range of applicability with respect to crest width and wave steepness.
A two-dimensional (2D) Reynolds-averaged Navier–Stokes (RANS) equations solver with k–ω turbulence closure is developed, employing immersed boundary (IB) technique on Cartesian grids. Generalized wall functions are introduced to enhance computational efficiency for problems with high Reynolds numbers. To address existing challenges in applying wall functions within IB methods, a novel, effective and easy-to-implement strategy is proposed. Another distinguishing feature of this turbulent-flow solver is that it employs the highly accurate immersed-boundary generalized harmonic polynomial cell (IB-GHPC) method to solve the Poisson equation for fluid pressure. The new solver is firstly validated by simulating channel flows on both hydraulically smooth and rough walls, achieving excellent agreement with benchmark experimental and numerical studies for various flow parameters including velocity, turbulent kinetic energy and shear stress. For channel flow simulations, our implementation of generalized wall functions using the proposed strategy results in a remarkable reduction of grid nodes by over 80%. Moreover, the solver is applied to simulate flow around both smooth and rough cylinders, producing promising results for drag, lift, and pressure coefficients. Our analysis demonstrates a robust performance of the developed solver in modeling turbulent flows based on Cartesian grids, offering a substantial improvement in computational efficiency for tackling problems involving large Reynolds numbers.
This paper deals with uncertainty modelling of wave-vessel transfer functions used to calculate or predict wave-induced responses of a ship in a seaway. Although transfer functions, in theory, can be calculated to exactly reflect the behaviour of the ship when exposed to waves, uncertainty in input variables, notably speed, draft and relative wave heading, often compromises results. In this study, uncertainty modelling is applied to improve theoretically calculated
transfer functions, so they better fit the corresponding experimental, full-scale ones. Based on a vast amount of full-scale measurements data, it is shown that uncertainty modelling can be successfully used to improve accuracy (and reliability) of theoretical transfer functions.
The completeness and high predictability of hazardous scenarios by hazard identification methods are issues in risk analyses. A way to the improvement is to carry out both an exhaustive - to the extent possible - post-accident and predictive accident analysis. Currently, Natural Language Processing (NLP) allows quick processing of many accident reports. In combination with graphical tools, it is now even possible to automatically output causal diagrammatic models of accidents and visualize them on a multi-scenario accident diagram. A step forward is the application of NLP to support predictive analysis. Predictive accident analysis focuses on identifying deviations from expected or normal conditions, the subsequent events following these deviations, and their interactions leading to an accident. The expected or normal conditions are typically outlined in specifications and procedures. This paper demonstrates how NLP can assist hazard identification and predictive accident analysis during lifting operations on ships and offshore platforms.
This paper contributes to the understanding of competition and industry evolution by analyzing how submarket dynamics and agency influence the development of the emerging industrial field of Danish offshore wind energy. We argue that industry evolution is sensitive to the balance between integration, overlap and disintegration across submarkets. This balance depends on how strategic intent and behavior influence submarket dynamics, leading to the conclusion that effects of agency and managerial intent should play a more prominent role in studies of industry evolution.
Marine cables are primarily designed to support axial loads. The effect of bending stiffness on the cable response is therefore often neglected in numerical analysis. However, in low-tension applications such as umbilical modeling of ROVs or during slack events, the bending forces may affect the slack regime dynamics of the cable. In this paper, we present the implementation of bending stiffness as a rotation-free, nested local Discontinuous Galerkin (DG) method into an existing Lax–Friedrichs-type solver for cable dynamics based on an hp-adaptive DG method. Numerical verification shows exponential convergence of order P and P + 1 for odd and even polynomial orders, respectively. Validation of a swinging cable shows good comparison with experimental data, and the importance of bending stiffness is demonstrated. Snap load events in a deep water tether are compared with field-test data. The bending forces affect the low-tension response for shorter lengths of tether (200–500 m), which results in an increasing snap load magnitude for increasing bending stiffness. It is shown that the nested LDG method works well for computing bending effects in marine cables.
Mooring systems for floating wave energy converters often rely on floaters to allow for minimum restraints of the body motion in heavy. However, the inclusion of floaters also introduce possible slack-taut scenarios induced by the dynamic response of the floater in relation to the fair-lead point of the mooring. This can increase the occurrence of snap loads. The present study outlines the work to include floaters and sinks into a high-order discontinuous Galerkin model for mooring cable dynamics. Numerical simulations of a mooring leg adapted from the Waves4Power full-scale device are performed, and the results from varying the floater geometry are analyzed.
For this case the floater influence on the occurrence of snap loads was clearly evident. There is a strong correlation between floater pitch response and cable slack in the upper mooring cable. For a floater with constant buoyancy, increasing the floater height and thereby increasing the pitch inertia of the floater is shown to decrease the range of frequencies where cable slack occurs. It is illustrated that for some cases, changing floater geometry can avoid slack altogether. A careful design of the floater geometry can thus make a large difference for the dynamic load factor of the mooring system.
Existing active absorption systems do not take into account the spurious waves caused by the segmentation of the wavemaker. Thus, the theoretical estimated performance curves for oblique waves are only valid for infinitely narrow segments. In the present paper, it is demonstrated that by ignoring the spurious waves, an unstable system might be designed for box‐mode paddles (piecewise constant segmentation). For vertical hinged pistons (piecewise linear segmentation), the results are the opposite, as the stability of the system is improved at high frequencies when a finite paddle width is considered. It is also shown that finite discretization leads to a directional influence in the system, even for a pseudo‐3D active absorption system. This effect is more pronounced for vertical hinged systems compared to box‐mode paddles.
This paper describes the challenges of the maritime supply chain compared to land transport and discusses the new digital initiatives to simplify the processes and enable a better plan for the entire supply chain. First, the background is outlined with an example of the extensive admin processes in maritime transport compared to road transport, followed by a case example presenting the processes of a booking. The case study concludes that the lack of integration is costly in terms of both admin resources, as well as lost capacity on some ships and missing capacity on others. Finally, the evolution of new digital initiatives are discussed, both in general and in terms of competing “alliances” as seen in the airline industry. The paper concludes that the information exchange in the maritime industry has moved drastically in the last 3 years and that one initiative, TradeLens, seems to have gained a position as maritime standard despite a problematic start with many competing initiatives.
Background: Fishing is a risky occupation as injuries and fatalities in fishing vessels are quite common. This paper investigates the pattern of injuries aboard fishing vessels in Denmark to get a better understanding of areas where further action is needed to reduce the number of injuries and fatalities in Danish fishing vessels. Materials and methods: Data for this study, extracted from the Danish Fishermen’s Occupational Health Service’s database (in the period 1998–2012) and the Danish Maritime Authority’s accident report from 2013 to 2016, include 1840 injuries in Danish fisheries. Result: The results showed decreased injuries in the study period from 45 injuries and deaths per 1000 fishermen reported to the authorities to 12 injuries and deaths per 1000 fishermen in 2016: 2.1% (n = 39) of all reported injuries in the study period resulted in the death of a fisherman and the remaining injuries resulted in sick leave of more than one day; 52.5% (n = 600) of reported injuries involved fishermen who have less than one year’s experience of employment; 29% (n = 407) of injuries took place between 12:00 and 16:00, and the second largest number of injuries, 23.3% (n = 324), took place between 8:00 and 12:00. The incident rate of slip/fall injuries has decreased from 10.06 per 1000 fishermen in 1998 to 3.84 in 2016. The incidence rate of injuries caused by crushing also decreased, from 9.32 accidents per 1000 fishermen in 1998 to 2.56 in 2016. Most of the injuries, 74.5% (n = 1307), happened on the deck of the vessel. Sprain/strain was among the most common injuries (34.2%; n = 538) followed by fracture (24.8%; n = 391). Conclusion: This study indicated that the number of injuries had been gradually decreasing in Danish commercial fishing vessels in the period from 1998 to 2016. The rate of injuries had been declining due to several initiatives such as the establishment of The Danish Fishermen’s Occupational Health Services, training, safety campaigns, technological improvement and structural changes in fisheries management. However, there are still places for improvement.