Numerical tests are performed to investigate wave transformations of nonlinear nonbreaking regular waves with normal incidence to the shore in decreasing and increasing water depth. The wave height transformation (shoaling) of nonlinear waves can, just as for linear waves, be described by conservation of the mechanical energy flux. The numerical tests show that the mechanical energy flux for nonlinear waves on sloping foreshores is well described by stream function wave theory for horizontal foreshore. Thus, this theory can be used to estimate the shoaled wave height. Furthermore, the amplitude and the celerity of the wave components of nonlinear waves on mildly sloping foreshores can also be predicted with the stream function wave theory. The tests also show that waves propagating to deeper water (de-shoaling) on a very gentle foreshore with a slope of cot(β) = 1200 can be described in the same way as shoaling waves. For de-shoaling on steeper foreshores, free waves are released leading to waves that are not of constant form and thus cannot be modelled by the proposed approach.
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.
This paper investigates the influence of a crown wall on wave overtopping on rubble mound breakwaters. Existing data is used to modify the EurOtop overtopping formula updated by Eldrup et al. (2022) to cover the influence of the crown wall. The effect of raising the wall above the armor crest (elevated wall) or lowering the wall below the armor crest (lowered wall) is investigated. A crown wall at the armor crest level is considered as the reference case. By increasing the elevation of either the armor crest or the crown wall, overtopping is reduced and by lowering either of them, overtopping increases. The influence of the crown wall height, elevated or lowered compared to the armor crest, is not considered accurately in the present design guidelines and thus corrections are suggested. For an elevated wall, a modified crest width has been defined, to better describe the presence of the armor crest in front of the wall. For the lowered wall the effective freeboard might be taken as the average of the wall and armor freeboards. The improvement compared to existing methods is significant, especially for breakwaters with a large elevated wall. The proposed modifications to the EurOtop Manual increase the range of applicability with respect to the wall configuration.
This study investigates the critical parameters necessary for evaluating large-scale renewable offshore energy hubs, based on insights from industry experts. Using a Multi-Criteria Decision Analysis methodology, the experts emphasized that, in their view, technical and economic parameters rank higher than environmental and societal considerations when evaluating large-scale renewable offshore projects, including green hydrogen production. Environmental and societal parameters should not be neglected, but they ought to be evaluated outside this assessment framework. This could refer to the environmental impact assessment already in use. These findings provide a foundation for evolving the traditional Triple Bottom Line theory into a Quadruple Bottom Line approach by incorporating technical parameters alongside economic, social, and environmental factors, while addressing the specific challenges of offshore energy hubs. Among all the parameters ranked across the four domains, the top 15 were exclusively techno-economic, with technical and economic scores averaging 4.5 and 4.3 out of 5, respectively. In contrast, societal and environmental scores averaged below 3.0. To ensure the successful deployment of offshore energy hubs, a stepwise approach is recommended to manage complexity, reduce risks, and support scalable solutions. This approach aims to align the needed industrial parameters with the demands of the energy transition.
A new proposed framework to assess sustainability impacts of maritime spatial plans (MSP-SA) utilizes the ecosystem service (ES) concept to address the often-lacking social sustainability of the plans. This study departs from the MSP-SA framework and applies it to the (emerging) sea use of mussel farming. Informed by a literature review and two surveys, it is investigated whether the benefits and impacts of mussel farming can be related to underlying ES and relevant planning questions. The results show that most benefits and impacts of mussel farming can be connected to ES and reveal different user-environment-beneficiary interactions, ranging from conflicts to synergies. The marine planning framework is structured into different planning phases and it is shown that the ES concept can contribute to a normative vision, strategic objectives, and site-specific operational questions. Studying the different user-environment-beneficiary interactions can reveal who benefits and who loses from planning decisions. While the marine planning framework developed in this study is targeted at mussel farming, the approach can be adapted to other uses and planning areas and can contribute to social and equity aspects in MSP by considering the receivers of (dis)benefits.
This paper emphasizes some of the challenges and trends associated with the future development of marine structures. Its main focus is on ways to improve the efficiency of energy-consuming ships, and on design challenges related to energy-producing offshore structures. This paper also discusses the analysis tools that are most needed to enable sustainable designs for future ships and offshore structures. The last section of the paper contains thoughts on the role of universities in education, research, and innovation regarding marine structures. It discusses curriculum requirements for maritime-technology education, basic research activities, and international cooperation.
The main objective of this research is to present an improved and more accurate formula to estimate the reflection coefficient (K R ) for rubble mound breakwaters. Physical model tests were performed for this purpose and existing data was also considered. The evaluation of existing prediction formulas for K R based on the Iribarren number (ξ) shows that the scatter in the experimental results increases with increasing ξ. This is caused by the wavelength having greater influence on the reflection than the wave height and thus the use of the wave steepness is inappropriate. The influence of potentially dimensionless parameters on the wave reflection from literature was analyzed. The major dimensionless parameters were found to be the relative water depth (h/L) and the structure front slope angle (α). Hence, a formula to estimate wave reflection for rubble mound breakwaters based on these two parameters is proposed.
This paper investigates the challenges associated with remote harmonic compensation in offshore wind power plants through long cables and transformers. The interaction between the grid network and the wind power plant network can lead to the amplification of certain harmonics and potentially resonant conditions. Hence, the plant developer is required to maintain the harmonic distortion at the point of common coupling within the planning level limits using harmonic compensation, which is usually done by static filters. In this paper an active damping compensation strategy with a STATCOM using emulation of using emulation of resistance at the harmonic frequencies of concern is analyzed. Finally the results are demonstrated using time domain simulations in PSCAD.
When an offshore wind power plant is connected to the grid, there is a risk of amplification of certain harmonics and appearance resonances at the point of connection due to the interaction between the grid network and the wind power plant network. Hence, the plant developer is obliged to maintain the harmonic distortion at the point of common coupling within the planning level limits using harmonic compensation, which is usually done by passive filters. In this paper a novel active harmonic compensation technique using voltage feedback from a non-local bus has been proposed and analyzed. Its effectiveness has been demonstrated through real time simulations on a test system model.
Due to the presence of long high voltage cable networks, and power transformers for the grid connection, the offshore wind power plants (OWPPs) are susceptible to harmonic distortion and resonances. The grid connection of OWPP should not cause the harmonic distortion beyond the permissible limits at the point of common coupling (PCC). The resonance conditions should be avoided in all cases.
This paper describes the harmonic analysis techniques applied on an OWPP network model. A method is proposed to estimate the harmonic current compensation from a shunt-connected active power filter to mitigate the harmonic voltage distortion at the PCC. Finally, the harmonic distortions in the compensated and the uncompensated systems are compared to demonstrate the effectiveness of the compensation.