The present paper deals with separation of long-crested regular waves into incident and reflected components. Such methods have been available for several decades for linear waves, but have recently been extended to cover nonlinear waves over horizontal foreshores. The overall goal of the present paper is to extend the separation method for nonlinear regular waves to also cover sloping foreshores. This requires the combination of the existing method with a nonlinear shoaling model. A nonlinear shoaling model was very recently found valid for the shoaling of the primary and bound components in regular waves when the slope angle is positive and mild. In the present paper this shoaling model is utilized and assumed valid also for the de-shoaling of the reflected waves, ie on a negative mild slope angle. However, if the reflected waves are nonlinear the de-shoaling process is much more complicated and will for example cause the release of free waves. Interactions among those free reflected wave components may cause nonlinear interactions not included in the mathematical model. For that reason, the applicability range is limited to mildly nonlinear reflected waves. Using numerical model data with various foreshore slopes, wave nonlinearities and reflection coefficients the reliability of the developed model is examined in detail.
Large volumes of produced water are being discharged globally as byproducts of oil production. Commercial production chemicals are conventionally needed to avoid problems such as bacterial growth, pipe corrosion, and oil/water separation issues. These chemicals will partition between oil and water phases and may affect both treatment processes and the environmental impact when water is discharged to the ocean after treatment. Capillary zone electrophoresis is used to measure partitioning coefficients of oilfield chemicals when these are dissolved in the water phase and in contact with either octanol or crude oil. The technique is fast and, due to simplicity, could have merits as on-site assessment of the partition coefficient for direct assessment of the fate of chemicals. The method was first qualified by estimating partitioning coefficients of aliphatic carboxylic acids and chemicals with a molecular structure similar to those of some production chemicals. Subsequently, the coefficients were determined for two different commercial corrosion inhibitors and a biocide that are used in the oilfield as production chemicals. The results showed that the chemicals predominantly preferred to remain in the water phase after contact with either octanol or crude oil. The partitioning coefficients log(p) spanned between −0.36 and −1.68 in the case of water/octanol contact and between 2.68 and −1.41 in the case of water/crude oil contact. One of the corrosion inhibitors exhibited a significant difference in the partitioning depending on whether the organic phase was octanol or crude oil. The chemical had a preference for the water phase in the case of the former but a preference for the crude oil phase in the case of the latter. The result demonstrates that it makes it challenging to evaluate the use of partitioning coefficients for oilfield applications.
The following report presents the results of the experimental testing of the Exowave wave energy converter (WEC) performed in September 2023 at the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The model tests are performed based on the current design of the WEC35 Exowave floater as part of the project 250 MW bølgekraft I den danske Nordsø før 2030 – fase 1 supported by the Danish Energy Agency under the Energy Technology Development and Demonstration Program (EUDP) contract number 64022-1062.
This paper introduces an interactive method which aims to map out perspectives on the state of ecosystem-based approaches (EbA) in marine spatial planning (MSP). MSP meets a need for organizing the allocation of space to maritime uses. MSP should also control and limit the pressures induced by these activities on marine ecosystems. To evaluate how EbA is actually applied, this research proposes a participatory method to assess the effectiveness of current EbA practices within the MSP process using perceptual maps. The mapping focuses on two dimensions: relevance and implementation of a set of 13 key elements of EbA. The method was tested on a sample of marine planners from ongoing MSP processes in northern European sea basins. The study shows that perceptual maps provide four main benefits: participatory, visualization capacity, qualitative and quantitative applicability, and easy to use. This tool undoubtedly has the potential to illustrate the state of integration of EbA in MSP and highlight the priority issues to develop in future plans, and consequently to provide keys to revise marine plans in a way that better takes into account EbA principles.
Small-scale fishing communities along Cambodia's coast have relied on marine resources as a mainstay of their livelihood for many decades. However, in the past 10 to 15 years, environmental change, increased fishing pressure, illegal, underreported, and unregulated fishing, and sand mining have contributed to a progressive decline in their catch. At the same time, economic opportunities outside the coastal village have acted as a draw and catalyzed migration to secondary cities and to the capital. This study examines out-migration of people from coastal communities to the city of Koh Kong. Using qualitative data collected from three fishing villages, I explore why people leave and why others stay in the village. In the context of city provisioning systems, the study also reveals a shift in climate-related vulnerability for coastal village migrants when they become urban residents. The study highlights the importance of looking not only at city planning, infrastructure challenges, and climate risks but also at the attendant social effects that phenomena such as migration have on people who are increasingly on the move. Such a perspective offers a more people-centred understanding of urban climate resilience in Cambodia, and potentially for other countries across Southeast Asia.
The typical approach for generating nonlinear waves in physical models involves employing first- or second-order wave theory, requiring a large water depth at the wavemaker. When the prototype bathymetry shows a gentle slope, a large facility is required. However, practical constraints often make this unfeasible, leading to the use of steep transition slopes to obtain sufficient water depth at the generator. Incorporating a transition slope may generate unwanted free waves beyond the transition point, significantly impacting the wave parameters. The presence of these free waves causes the response of the tested structure to deviate from that found in the prototype. This paper offers guidelines for using transition slopes effectively while avoiding the generation of unwanted free waves after the transition point.
The offshore oilfields in the North Sea area are increasingly employed for projects beyond oil production, like carbon capture and storage (CCS). Still, the fossil fuel production from mature fields is significant. It has raised environmental concerns associated with discharging produced waters (PW) and drilling mud into the sea. These discharges, which may be highly saline and contain production chemicals, vary significantly in metals and particulate content. Due to density and release depth, the plume is assumed to sink towards the seafloor. Also, a single oilfield can input up to 7.5 tons of Ba, 675 kg of Fe, and 619 kg of P into the water column through PW. Therefore, this study investigates the impact of these discharges on seafloor sediments around two Danish oilfields, assesses the mobility of metals within these sediments, and evaluates the environmental status. PW samples were collected at the discharge outlets from the platforms. Sediment cores were taken near the two oil platforms and from control sites. Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and an optimized BCR sequential extraction, we analyzed the composition and distribution of 24 elements in sediment samples. The results revealed significant differences in total extracted concentrations between sediments near the platforms and those from distant locations and stratigraphically older samples, with relevant levels of Br, Ba, and Sn near the platforms (averaged 14, 27, and 0.1 ppb, respectively). Sediment quality indices showed considerable enrichment and geo-accumulation of toxic metals, particularly at one of the platform sites. However, cumulative indices did not display significant pollution anomalies. Therefore, our findings suggest that oil extraction activities may increase the availability of toxic metals in nearby sediments, potentially impacting marine ecosystems.
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.
Despite a list of national and international efforts to harmonise data management procedures, the categorisation of space and time within datasets in marine spatial planning (MSP) has not been addressed so far. This paper proposes a conceptual framework to categorise the spatial and temporal dimensions of data used in MSP and introduces a method to jointly manage non-spatial information and spatial data in the same geographic information system (GIS). The presented categorisation provides easy and intuitive classifications for a more detailed and transparent data description of spatial and temporal data properties, which can be applied both in attribute tables and in metadata. It allows the differentiation of the vertical and the horizontal dimensions, enabling users to focus on operations taking place at specific parts of the marine environment. The categorisation with predefined attribute domains allows space and time based automatic analyses. The inclusion of non-spatial data within GIS repositories ensures the availability of all relevant data in one database minimising the risk of incomplete data. Overall, the framework provides effective steps towards a more coherent data management and subsequently may foster better use of information in MSP processes.
A new motivation for marine restoration has been observed, associated with the dissatisfaction with current marine restoration governance arrangements (MRGAs). An MRGA consists of alliances of public and private actors (coalitions) who, through their common conceptualisation of the problem (discourses), try to influence and design marine restoration activities while considering the rules of decision-making, and the management of limited resources. Emerging MRGAs rise in parallel to existing ones and aim to contribute to the same goals or show another way of reaching those goals. This phenomenon raises questions of legitimacy both for the emerging and the existing arrangement. Building on existing literature, this paper proposes an analytical framework to simultaneously explore input, throughput and output legitimacy as three essential pre-conditions of legitimacy for MRGAs. The framework is tested in three European cases of MRGAs that were part of the European Union MERCES project (http://www.merces-project.eu/). Analysis showed that actors who are influential in achieving restoration goals, and also those who are impacted by restoration actions, should be involved in the MRGAs (input legitimacy); actors within MRGAs should establish and follow procedures for decision-making that are both transparent and clear (throughput legitimacy); and actors within MRGAs need to establish a common understanding of restoration, of the goal to reach and of the related uncertainties (output legitimacy). Awareness of these pre-conditions allows actors internal and external to MRGAs to address aspects that give legitimacy to restoration actions. It also creates a language that allows actors to engage in discussion on legitimacy that goes beyond the mere application of the rule of law.