North Sea Environment Research Articles

Value of information from fatigue monitoring of the monopile foundation of an offshore wind turbine

Value of information (VoI) allows quantifying benefits of adopting structural health monitoring (SHM) even before implementation by altering the prior risk of structural failure using the probabilities of damage detection from SHM data. The VoI is the reduction in the expected failure cost when SHM data becomes available. In this study, an optimized time of SHM deployment for fatigue crack growth in an offshore wind turbine (OWT) monopile foundation is achieved by maximising VoI. The prior probabilities of failure are obtained from stochastic analysis of dynamic responses to random wind and waves characteristic of North Sea environment. Short-term stress time histories are statistically processed to determine the probability distribution functions of their extrema and ranges and statistical extrapolation techniques are then implemented to analyse the long-term probability distributions of axial stresses. The long-term stress ranges and numbers of cycles are determined by the rainflow count and used in fatigue reliability analysis. The probability of detecting a fatigue crack by SHM is modelled and used for calculating the OTW failure risk after repair is conducted based on SHM outcome. The optimal deployment time of the fatigue crack monitoring system for the analysed 5-MW OWT is determined as 21 years past erection.

Risk assessment of war wrecks – a comprehensive approach investigating four wrecks containing munitions in the German Bight/North Sea

AbstractShipwrecks and dumped munition continue to be a major hazard, both in the North Sea but also on a global scale. Research within the EU Interreg project North Sea Wrecks (NSW), in cooperation with the German Aerospace Centre, Institute for the Protection of Maritime Infrastructures (DLR), is generating new insights into the status of wrecks, the potential leakage of pollutants from remaining munitions loads and the effects of contamination on exposed marine organisms in the North Sea environment. Further, historical documents are generated from archives to describe ship's history and sinking scenario. These historical findings were compared to models and images of the visual inspections of the wrecks. Further, samples of water, sediment and organisms are being analysed for traces of explosives. Combining the results of these different fields of research allows for a better understanding of the environmental risks deriving from these wrecks. This process is shown below by focusing on the wreck of the German light cruiser SMS MAINZ, which sank in 1914. Data were compared to three additional wrecks situated also within the southern German Bight. Available data about the wrecks were preliminary assessed using a wreck risk model. Finally, wrecks were ranked according to their potential environmental risk.

Temporal trends of mercury levels in fish (dab, Limanda limanda) and sediment from the German Bight (North Sea) in the period 1995–2020

As a toxic and harmful global pollutant, mercury (Hg) enters the marine environment through natural sources, and human activities. It bioaccumulates through the food chain and therefore, Hg is of great importance for environmental monitoring. This study aims to answer the question if Hg contamination in fish and sediment from the German Bight follows temporal trends. Therefore, 496 individual female dab (Limanda limanda) were analyzed. The Hg concentrations in the muscle of dab from the German Bight showed significant increase in function of time with an annual percental change of 1.4%, leading to a 41% increase in Hg contamination level within 25 years of monitoring. At the same time, Hg concentrations in sediment—analyzed in 86 samples—significantly decreased in the nearby North Sea environment. This surprising contradiction is shown in the present study and possible causes are discussed. It could be clearly shown that contamination in sediment and biota can follow completely different time courses and therefore, different environmental matrices should be considered in future monitoring studies. Age of the fish turned out to be a biological factor of particular importance for temporal trend analysis.

Biological site suitability for exposed self-regulating cultivation of blue mussel (Mytilus edulis): A Belgian case study

Several reasons, from stakeholder conflicts to water quality issues, are pushing bivalve cultivation to less accessible, exposed, and offshore waters. Because sheltered areas are absent along the Belgian coastline, the possibility to culture mussels with self-regulated systems in exposed conditions has been explored by various research projects. Farmers consider offshore environments unsuitable on the assumption that spat densities are low, and growth is insufficient for commercialization.This study evaluates the potential for self-regulated mussel cultivation in an exposed North Sea environment based on data collected from several research projects that evaluated the biological and technical feasibility of commercial longline cultivation in Belgium. The cultivation methods were variable, but always relied on wild spat that was grown to market size. No husbandry practices such as seed harvesting, thinning, grading, or socking were performed. This cultivation technique, also called self-regulating cultivation, reduces operational costs when extreme weather and exposed conditions limit handling.A 3D hydro-dynamic larvae dispersal model (LDM) was used to simulate the spatial variability in arrivals and the timing of the arrival peak. In addition, a locally validated metabolic model (DEB) for the blue mussel (M. edulis) was forced with 10 year optimized remote sensing observations (Copernicus, Sentinel-3/OLCI) to predict industry-relevant information such as site suitability, inter-annual growth variability, and cultivation time.This study concludes that exposed mussel cultivation near the Belgian east coast is characterised by fast growth. Mussels grown in this area will reach a marketable size (6 cm) after 12–15 months of cultivation, which is just in time for the peak consumption season (July-August). Moving offshore prolongs the cultivation cycles to 17–25 months, but provides more stable growth conditions with less inter-annual variability. When considering a cultivation period of 12 months, the mussels originating from offshore cultivation are comparable in size to the smaller Dutch “Smitse” and French "Bouchots".

Benthic biodiversity near brine discharge sites in the Port of Rotterdam

The Port of Rotterdam is a heavily man-modified estuarine system, Europe's major seaport and home to a large number of chemical and petrochemical plants, many of which are supplied with distilled water from two demineralized water plants in Botlek and Maasvlakte. In this study, we assessed the ecological conditions near the brine outfalls and at a reference site unimpacted by brine, focusing on the benthic macrofaunal composition. Overall, the analysis of the communities and species revealed a similar macrobenthic composition, although with lower abundance and diversity compared to the nearby North Sea environment. The outfall area of the Botlek demineralized water plant, which is a dead-end entirely marine waterway with no to little currents in contrast to the well flushed brackish environment of the outfall of the Maasvlakte demineralized water plant, was characterized by the lowest abundance of benthic macroinvertebrates, species richness and Shannon diversity index. Higher biodiversity values at the Maasvlakte demineralized water plant compared to the reference site were also associated with the presence of a large biogenic reef of the Pacific oyster Crassostrea gigas with specimens of over 8 years estimated age being observed, however with many dead individuals recorded at the time of surveys. The outfall area of the Botlek demineralized water plant also had the highest disturbance levels according to the results of AZTI's Marine Biotic Index (AMBI) in conjunction with Benthos Ecosystem Quality Index (BEQI). Its community was dominated by the opportunistic native species Capitella capitata and Varicorbula gibba, and species typical for organic matter enrichment such as Alitta succinea (native), Streblospio cf shrubsolii (native) and Theora lubrica (invasive), which correlates well with higher levels of anthropogenic pollution in this area. Generalized linear model (GLM) and distance-based multivariate linear model (DistLM) showed that the distance from the outfalls was an important factor in terms of brine impacts however explaining a small part of the variation observed. Similarity percentage analysis (SIMPER), multivariate analysis, and permutational multivariate analysis (PERMANOVA) showed low similarity between and within study sites, confirming that high levels of heterogeneity exist within the estuarine system in terms of natural conditions and anthropogenic stress.

Mooring system reliability in tropical cyclone and North Sea winter storm environments

The characteristics of waves, winds and currents in a tropical cyclone environment differ significantly from those in a winter storm environment, like the North Sea. This can have a significant effect on the reliability of a mooring system that is designed to satisfy 100 yr conditions with specified Factors of Safety in accordance with ISO19901-7 or API RP 2SK. This paper presents reliability analysis of the mooring system of a permanently connected Floating LNG vessel, placed at two locations: (a) a tropical cyclone environment of the North West Shelf of Australia and (b) a winter storm environment of the North Sea. It is demonstrated that as a result of differences in the long term distribution of environmental parameters (waves, winds) between a North Sea environment and a tropical cyclone environment, the long term distribution of the mooring line response differs significantly in these two locations.This paper shows that a mooring system which is designed in accordance with ISO (or API), in these two environments, will achieve very different reliability levels because of the significant differences in environmental characteristics. In order to achieve the same reliability for the mooring system at these two geographical locations, Factors of Safety for use with 100 yr environmental conditions (Ultimate Limit State) were derived to achieve the same target probability of failure of 10−4/annum. It was found that for the North Sea environment, a factor of 1.5 is required for both the mooring chain and the pile, while for the tropical cyclone environment the required Factor of Safety has to be increased to 2.1. These differences are very significant and design standards need to be revised to reflect these findings.

Environmental benefits of leaving offshore infrastructure in the ocean

The removal of thousands of structures associated with oil and gas development from the world's oceans is well underway, yet the environmental impacts of this decommissioning practice remain unknown. Similar impacts will be associated with the eventual removal of offshore wind turbines. We conducted a global survey of environmental experts to guide best decommissioning practices in the North Sea, a region with a substantial removal burden. In contrast to current regulations, 94.7% of experts (36 out of 38) agreed that a more flexible case‐by‐case approach to decommissioning could benefit the North Sea environment. Partial removal options were considered to deliver better environmental outcomes than complete removal for platforms, but both approaches were equally supported for wind turbines. Key considerations identified for decommissioning were biodiversity enhancement, provision of reef habitat, and protection from bottom trawling, all of which are negatively affected by complete removal. We provide recommendations to guide the revision of offshore decommissioning policy, including a temporary suspension of obligatory removal.

Monitoring of caesium-137 in surface seawater and seafood in both the Irish and North Seas: trends and observations

The objective of this paper is to compile selected caesium-137 concentrations in seafood and seawater (the key OSPAR indicators) from the data submitted by the United Kingdom to the OSPAR Commission. The impact upon the surrounding environment of the Irish Sea and North Sea has been determined from trends of caesium-137 concentration data over time, from the start of the OSPAR evaluation period to the present date. Generally, caesium-137 concentrations, in each of the key OSPAR indicators (by sample type and site locations), have declined in both the Irish and North Sea environments over the long time period.

북해설치 FPSO의 플레어 슬래밍 하중에 대응한 선수 설계

This paper is about the bow structure design of the ship-typed and turret moored FPSO which is subjected to the bow-flare slamming load in harsh North Sea environments. Quad 204 FPSO project involves the redevelopment of the existing Schiehallion FPSO which is damaged by impact wave loads. Normally all offshore systems including FPSO are designed to withstand the 100 year storm I.e. the storm that happens once every hundred years at the location where the system is installed. Several incidents have revealed that impact loading is important issue for moored floating production systems. In this paper, the design impact loads are estimated considering the ship owner’s specification, measured data from model tests, requirements of the classification society rules and results of numerical simulation analyses. The impact pressure by numerical analysis is 1.8 times greater than required value by CSR adopted by IACS. Based on the selected design load, plastic design formulae allowing the local material yielding are applied for the initial scantling of the bow structure. To verify the structural integrity, FE analyses are carried out considering the local area subjected to the impact wave loads. Their results such as structural arrangement, design loads and scantlings are shown and discussed. It is found that plastic design formulae in adopting Initial design phase give sufficiently conservative results in terms of structural strength.

Evolution of Multistage-Fracture Completions in a North Sea Environment

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 170641, “The Evolution, Optimization, and Experience of Multistage- Fracturing Completions in a North Sea Environment,” by T.R. Koløy, K. Brække, T. Sørheim, and P. Lønning, Trican, prepared for the 2014 SPE Annual Technical Conference and Exhibition, Amsterdam, 27–29 October. The paper has not been peer reviewed. This paper reviews two newly developed novel completion systems that significantly reduce time spent performing multistage stimulation in environments where cost and consequence of failure are high. Both coiled-tubing and wireline-manipulated sliding-sleeve/valve systems and balldrop-actuated systems have been developed and deployed, depending on the various completion and stimulation challenges faced. Since their first installation in 2009, these systems have been proven and refined in multiple wells for two major operators. Background For many of the fields requiring stimulation in the North Sea, cemented plug-and- perforation (plug-and-perf) completions have been used historically. It is a flexible solution in terms of the various types of stimulation designs that can be accommodated. However, because of the large number of perforating runs required, the bridge-plug setting, the retrieving or milling involved, and the clean out runs required, it is also a very time-consuming option. The turnaround times per stage have been widely documented and often range from 3 to 7 days. Prototype Development, Testing, and Qualification. Sliding sleeves have been used for flow-control purposes in oil and gas wells for decades. Although sliding sleeves are simple in design, many users have questioned their reliability, and they did not see much use for fracturing operations until the mid-2000s, when ball-drop-actuated sliding sleeves entered the market. The preferred method for stimulating a reservoir with a cemented liner—stage by stage—has been with plug-and-perf methods. Plug-and-perf provides a proven method of initial stimulation, compartment for compartment, but provides no solution for efficient production management over the life of the well.

Host-specific microbial communities in three sympatric North Sea sponges.

The establishment of next-generation technology sequencing has deepened our knowledge of marine sponge-associated microbiota with the identification of at least 32 phyla of Bacteria and Archaea from a large number of sponge species. In this study, we assessed the diversity of the microbial communities hosted by three sympatric sponges living in a semi-enclosed North Sea environment using pyrosequencing of bacterial and archaeal 16S ribosomal RNA gene fragments. The three sponges harbor species-specific communities each dominated by a different class of Proteobacteria. An α-proteobacterial Rhodobacter-like phylotype was confirmed as the predominant symbiont of Halichondria panicea. The microbial communities of Haliclona xena and H. oculata are described for the first time in this study and are dominated by Gammaproteobacteria and Betaproteobacteria, respectively. Several common phylotypes belonging to Chlamydiae, TM6, Actinobacteria, and Betaproteobacteria were detected in all sponge samples. A number of phylotypes of the phylum Chlamydiae were present at an unprecedentedly high relative abundance of up to 14.4 ± 1.4% of the total reads, which suggests an important ecological role in North Sea sponges. These Chlamydiae-affiliated operational taxonomic units may represent novel lineages at least at the genus level as they are only 86-92% similar to known sequences.

Load resistance factor design (LRFD) calibration of load factors for extreme storm loading in Malaysian waters

Petronas Carigali Sdn Bhd (PCSB) performs its operations in three regions in Malaysian waters. Currently, fixed offshore structures are designed in accordance with ISO 19902, which is meant to provide guidance for the design of fixed offshore structures internationally, but the load factors in ISO 19902 are often derived from studies performed in the Gulf of Mexico and the North Sea environments. One such load factor is the 1.35 for environmental loading that has been prescribed within ISO 19902. Site specific metocean studies in Malaysian waters reveal environmental conditions that are more benign than the Gulf of Mexico and the North Sea. This study presents the results of a component-based approach and investigates the suitability of the 1.35 load factor for environmental loading in Malaysian Waters to achieve the same target reliability for a similar structure designed consistent with the provisions of the API RP 2A-WSD. First-order reliability methods (FORM) have been undertaken using a database of tubular components with representative geometries, bending-to-axial stress ratios, dead-to-live load ratios and environmental to gravity load ratios. The analysis results show that if the target were to be based on the weighted average probabilities inherent in the API RP 2A-WSD 21st Edition, an environmental action factor of 1.245 (Region A), 1.295 (Region B) and 1.255 (Region C) with the ISO provisions will on average achieve similar reliability.

Tutorial: the seismic response to strong vertical velocity change

Conventional seismic data processing, whether pre-stack data conditioning or migration, is designed with the theory of P-wave reflected energy in mind for travel paths involving only a single reflection. Hence, any energy propagating with other modes or travel paths is not dealt with appropriately during conventional processing. It is primarily for this reason that we spend so much time pre-conditioning seismic data to meet the assumptions of the subsequent processes such as migration. Here I consider a typical North Sea environment where there are both strong vertical compaction gradients and high velocity contrasts in the layered Chalk Formation. I assess the behaviour of refracted and mode-converted seismic arrivals when subjected to conventional processing in order to explain how they give rise to anomalous events that contaminate migrated common reflection point gathers and images.

Platforms for Change: High-Voltage DC Converters and Cable Technologies for Offshore Renewable Integration and DC Grid Expansions

HVdc and cable technologies exist today that permit offshore integration and planning of point-to-point dc links that can be expanded into HVdc grids. Several VSC HVdc links are now in operation offshore in the harsh North Sea environment. Following the rapid increase in power transmission capacity and loss reduction, several new projects in the gigawatt range are in the construction phase. The benefits of larger intercontinental grids are being demonstrated in several ongoing studies. The first MT HVdc networks can therefore be seen as initial building blocks on the way to a larger offshore grid.

Predicting the occurrence of sand banks in the North Sea

Sand banks have a wavelength between 1 and 10 km, and they are up to several tens of meters high. Also, sand banks may have an impact on large-scale human activities that take place in the North Sea like sand mining, shipping, offshore wind farms, etc. Therefore, it is important to know where sand banks occur and what their natural behavior is. Here, we use an idealized model to predict the occurrence of sand banks in the North Sea. The aim of the paper is to research to what extent the model is able to predict the occurrence of sand banks in the North Sea. We apply a sensitivity analysis to optimize the model results for a North Sea environment. The results show that the model correctly predicts whether or not sand banks occur for two thirds of the North Sea area.

Operability of fast podded RoPax vessels in rough seas

Methods are described for the evaluation of the seakeeping performance of a fast RoPax vessel driven by podded propulsors in the North Sea environment. The evaluation procedure is based on the responses of the vessel in regular waves, the wave conditions encountered, and the limiting values associated with the vessel's mission. The seakeeping performance is represented by the average attainable speed (AAS), which is defined as the ratio of the average speed of the vessel on a specified route to the calm water speed. Both the natural (due to the added wave resistance) and the voluntary (due to the excessive ship responses) speed losses are taken into account. The annual average speed of the fast RoPax design in the North Sea is evaluated and compared with that of a similar size conventional RoPax vessel. The results indicate that, despite its 20 per cent smaller displacement, the fast RoPax design, in general, has better seakeeping performance characteristics than that of the conventional design. The effect of podded propulsors on the average annual speed is also investigated and it is found that the presence of podded propulsors can have favourable effects on the seakeeping performance characteristics, particularly on the vertical plane responses.

Deposition of atmospheric trace elements into the north sea: Coastal, ship, platform measurements and model predictions

The atmospheric input of up to 16 trace and other elements into the North Sea is further assessed from aerosol concentrations measured at a coastal station in Belgium, on ships during two cruises, and on a platform, in the years 1992–1994. The Slinn and Slinn model is used to calculate the dry deposition from the measured aerosol concentrations. The total (dry and wet) deposition into the North Sea environment is estimated to be (in tonnes per year): 560 for V, 1300 for Cr, 650 for Ni, 690 for Cu, 3500 for Zn and 1970 for Pb. The “giant” particles dominate the fluxes. The atmospheric contribution to the total input into the North Sea, including riverine inputs and direct discharges, are estimated to be 28% for Cu, 29% for Zn and 57% for Pb. The inputs estimated from the experimental data are compared with results from a model applied for the same area and period. The experimental and model results agree within 56%, which is considered as “satisfactory” in view of both the experimental and the model uncertainties.

The role of adsorption in sediment-water exchange of phosphate in North Sea continental margin sediments

The effect of adsorption on the sediment-water exchange of PO, was investj gated in sediments from four different types of sedimentary environments in the southern and eastern North Sea in August 1991 and February 1992. Nonlinear adsorption isotherms for oxidized sediment from eight stations indicate that North Sea sediments differ widely in their capacity to adsorb PO,. A good correlation between the value of the adsorption coefficient and NH,oxalate-extractable Fe was observed. A combination of the adsorption data with Porewater PO, profiles, solid phase results, and measured and calculated rates of sediment-water exchange of PO, for 15 stations in both August and February indicates that adsorption plays an important role in controlling sediment-water exchange of PO, during at least a part of the year in three of the four North Sea environments. At most stations, PO, adsorption constrains the flux of PO, to the overlying water. At one station in the depositional environment of the Skagcrrak, however, desorption is responsible for the maintenance of a flux of PO, to the overlying water. A one-dimensional reactiondiffusion model, describing Porewater PO, and solid phase P profiles, was de*deloped and applied to results for two stations. The model results show that both enhanced retention and enhanced release of PO, can be adequately described when simultaneous equilibrium and first-order kinetic reversible adsorptive reactions are assumed.

EDXRS study of aerosol composition variations in air masses crossing the North Sea

AbstractX‐ray emission techniques for bulk and individual particle analysis (EDXRF, EPXMA, micro‐PIXE) were combined and applied in atmospheric research on the North Sea area as part of a field‐study on air‐sea exchange processes of particulate matter. The atmospheric loading for a number of elements was determined by EDXRF, yielding bulk concentrations for Mg, Al, Si, S, Cl, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Br and Sr. From these EDXRF data, deposition rates were derived and, based on a classical multivariate statistical approach, different aerosol sources were identified. Complementary to this work, EPXMA combined with automated image analysis was applied to individual size‐segregated aerosol particles to determine their inorganic composition, physical size and shape. Also, the first results of micro‐PIXE analyses on individual North Sea aerosol particles, particularly their large‐size fraction, are discussed and compared with the corresponding EPXMA results. In summary, such a joint approach with the use of different x‐ray emission techniques contributed to the resolution of the mixed structure of the lower North Sea troposphere and to the determination of the atmospheric supply of material to the North Sea environment.

Determination of 206/207Pb isotope ratios by ICP-MS in particulate matter from the north sea environment

The determination of lead isotope ratios can be used for source and pathway characterization of lead in the environment. The suitability of inductively coupled mass spectrometry (ICP-MS) was evaluated for the measurement of 206/207Pb isotope ratios in several marine compartments as marine aerosols from different source regions and suspended particulate matter from the North Sea. Two different ICP-MS systems were used to carry out these investigations. First optimization studies have been performed to yield a sufficient precision (RSD <0.5%) in combination with a reasonable measuring time. This study has been carried out using the standard reference material NBS 981 with certified lead isotope ratios. Furthermore, it could be shown for marine environmental samples, that a precision of less than 0.5% RSD is attainable for counting rates of above approximately 50000 cps. As the following measurements of lead isotope ratios in marine aerosols from main source regions surrounding the North Sea demonstrated, this precision is sufficient to determine significant differences due to the origin of atmospheric lead. The analysis of aerosol samples revealed isotope ratios varying from as low as 1.10, which is close to that ratio for leaded gasoline in Europe to near background (modern lead) values of 1.20. The lead isotope ratios for the investigated suspended particulate matter ranges between 1.13 and 1.18. These values can be related to the solid discharge, the urban density and anthropogenic activity of the drainage basin.