A conceptual basis for surveying fouling communities at exposed and protected sites at sea: Feasible designs with exchangeable test bodies for in-situ biofouling collection

The enhanced inertia load caused by biofouling on device components, such as the foundations of wind turbines or other structures at sea, modifies the hydrodynamic properties, and increases the stress to structures, predominantly in upper water layers with high impact from wave dynamics. This compromises the stability, functioning, operation as well as the durability of these devices especially in exposed environments. A main challenge is the quantification of the impact of hydrodynamic forces on irregular bodies being overgrown by soft- and hard-bodied biofouling organisms. Therefore, test bodies from the upper 1–5 m water depth and thus exposed to the strongest wave actions close to the surface shall be overgrown by biofouling and used in measurement trials in a wave and current flume. These measurements shall shed light on the varying roughness and its influence on the load bearing capacity of foundation piles. Consequently, the main aims of the present work were the development of two independent test stations as holding devices for artificial test bodies for the collection of biofouling organisms during field studies: a carrying unit floating at the surface in an exposed area (System A) and a sampling device with access from a land-based facility (System B). Both systems are relatively easy to access, exhibit straightforward handling, and are reasonable cost-effective. A Test Body Support Unit (TBSU, System A) was designed and mounted on a spare buoy to carry the test bodies (cylinders), which serve as substrate for the fouling. The system was sufficiently robust to withstand several periods of rough sea conditions over the first two years. This system can only be accessed by vessels. System B (MareLift) provided the robustness and functionality needed for areas exhibiting harsh conditions but can be operated from land. The here used test bodies (steel panels) exhibited a sound basis for the monitoring of succession processes in the biofouling development. System B offered the possibility to analyse two habitats (intertidal and subtidal) and revealed clear differences in the composition and development of their fouling communities. Overall, both systems provide advantages in obtaining standardized biofouling samples compared to previous approaches. Such test stations play an important role in the risk management of marine sectors as they could help characterising biofouling communities over different geographical areas. System A and B provide a sound basis for biofouling research but potentially also for other potential research approaches in exposed areas as they provide space for future developments

Dynamic output feedback H ∞ design in finite-frequency domain for constrained linear systems

This paper deals with the design problem of H∞ control for linear systems in finite-frequency (FF) domain. Accordingly, the H∞ norm from the exogenous disturbance to the controlled output is reduced in a given frequency range with utilizing the generalized Kalman–Yakubovic–Popov (gKYP) lemma. As some of the states are hard or impossible to measure in many applications, a dynamic output feedback controller is proposed. In order to meet practical requirements that express the limitations of the physical system and the actuator, these time-domain hard constraints are taken into account in the controller design. An algorithm terminating in finitely many steps is given to determine the dynamic output feedback with suboptimal FF H∞ norm bound. The algorithm consists of solving a series of linear matrix inequalities (LMIs). Finally, two case studies are given to demonstrate the effectiveness and advantageous of the proposed method

Uncertainty and Imprecision in Safety Assessment of Offshore Structures.

Ph.DDOCTOR OF PHILOSOPH

Decommissioning the UKCS: increasing flexibility of approach through proportionate regulation and evidence based practice.

The purpose of this research is to investigate how industry and government can strategically align to improve efficiency and gain environmental benefit from the challenge of decommissioning redundant offshore oil and gas infrastructure, through an alternative evidence-based practice and proportionate regulatory approach. Despite nearly thirty years of periodic decommissioning activity, the regulatory drivers and programme design dynamics continue to be politically driven and not evidence based (Penner, 2001, Bellamy and Wilkinson, 2001 and Pulsipher and Daniel, 2000). Projects are not deliverable as originally agreed in the approved programmes ( BEIS close out reports) and do not maximise the potential benefits to the marine environment of the North Sea ( Jorgensen 2013, Van Der Stap et al, Macreadie et al 2011, Love et al, 2003, and Soldal et al, 2002). Much of the knowledge and experience gained over the past thirty years has not been recorded or archived in any form that would benefit future programmes, and approved decommissioning programmes continue to be audited historically rather than in real time. All stakeholders have a genuine interest and an opportunity to benefit from a regulatory approach that is both evidence-based and proportionate by design. An adopted mixed-methods approach - combining quantitative, qualitative and case study approaches - was used to investigate the current regulatory framework and the resulting decommissioning methods that are employed to achieve compliance. The development and impact of the current decommissioning framework was investigated from both the published literature and the research participants' perspectives. The emerging recommendations for change are based on evidence from this research. This research adds to the body of knowledge on three fronts: theoretical, methodological and practical. Gaps between theoretical compliance demands and deliverability are identified, several evidence-based recommendations are made and an alternative, more flexible framework is proposed. The audit methodology and audit template are significant contributions to practice. The research concludes with key recommendations. The primary recommendation is that the United Kingdom government should implement a fundamental review of the current regulatory framework for offshore decommissioning and consider the evidence base for proposing changes to OSPAR Decision 98/3. The supporting recommendations are: that the derogation limit of 10,000 tonnes should be removed and each project should be assessed on an individual case basis; the UK should initiate the introduction of a "rigs to reefs" programme on the UKCS through a broad stakeholder consultation; the current baseline of a clear seabed, one-size-fits-all approach is not sustainable and a more flexible, proportionate approach should be adopted; specific changes are proposed to the current regulatory framework to increase its proportionality; the audit process needs to be strengthened and focus on invasive audits to increase stakeholder confidence; guidelines provided to industry need to be revised; and the regulator in partnership with industry should develop a decommissioning knowledge bank at the heart of a knowledge transfer system. Taken together, the research and the resulting recommendations have generated a conceptual framework combining strategic, evidence-based decommissioning options with proportionate regulatory practices. This provides both policy makers and industry with a developmental envelope for an alternative framework for future decommissioning in the UK and further afield

Siamese neural networks for damage detection and diagnosis of jacket-type offshore wind turbine platforms

Offshore wind energy is increasingly being realized at deeper ocean depths where jacket foundations are now the greatest choice for dealing with the hostile environment. The structural stability of these undersea constructions is critical. This paper states a methodology to detect and classify damage in a jacket-type support structure for offshore wind turbines. Because of the existence of unknown external disturbances (wind and waves), standard structural health monitoring technologies, such as guided waves, cannot be used directly in this application. Therefore, using vibration-response-only accelerometer measurements, a methodology based on two in-cascade Siamese convolutional neural networks is proposed. The first Siamese network detects the damage (discerns whether the structure is healthy or damaged). Then, in case damage is detected, a second Siamese network determines the damage diagnosis (classifies the type of damage). The main results and claims of the proposed methodology are the following ones: (i) It is solely dependent on accelerometer sensor output vibration data, (ii) it detects damage and classifies the type of damage, (iii) it operates in all wind turbine regions of operation, (iv) it requires less data to train since it is built on Siamese convolutional neural networks, which can learn from very little data compared to standard machine/deep learning algorithms, (v) it is validated in a scaled-down experimental laboratory setup, and (vi) its feasibility is demonstrated as all computed metrics (accuracy, precision, recall, and F1 score) for the obtained results remain above 96%.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantPostprint (published version

Offshore Wind Power Reef Effects and Reef Fauna Roles

The German Bight is dominated by sandy and muddy sediments whilst rocky terrain is rare. The only rocky intertidal is present on the island of Helgoland. However, thousands of ship wrecks are distributed in the German Bight. Such wrecks have only recently become part of investigations into species settlement and the underwater ecosystem. During the next 30 years 5000 wind power foundations are planned to be built in the German Bight as part of the German renewable energy program. Twelve foundations are completed and 197 in progress. The knowledge of the impact such constructions have on the German Bight underwater ecosystem is poor. Prognoses are the only form of estimation. The present study was conducted at the research platform FINO 1 and different ship wrecks which are located in the German Bight. Consistent with FINO1 it is expected that 4,300 kg biofouling will inhabit the wind power foundations. This means that the foundations can be interpreted as hotspots with 35 times more macrozoobenthos biomass than there was prior to the construction. The 5,000 wind power foundations mean an increased biomass of 0.8% for the entire German Bight. In addition, at least half of this biomasses will be produced at the foundations and leave the foundations on a yearly basis. What impact the increased production and high biomass concentration will have on the energy flow in the North Sea remains unknown. Other scenarios are more obvious. Changes include the increased food supply for species, such as crabs, fish and seals as well as the proliferation of the mussel Mytilus edulis. The number of Mytilus edulis inhabiting all wind power foundations will be the same as half of the amount of mussels currently living in German Wadden Sea. The mussel shell litter fall may lead to changing sediments and additional reefs. The mussels will also add to the significant increase of the filtration of sea water with the possible result of clearer waters. The mussels are seen as the main contributor to changes taking place in the German Bight following the introduction of wind power foundations. The increased number of mussels as well as the effects such increasing numbers of Mytilus edulis on the ecosystem will be titled Mytilusation. The introduction of wind power foundations into the German Bight will also mean an increase in rocky shallow waters and intertidal zones in the German Bight. The result will be a proliferation and the development of exotic species, such as the pacific oyster (Crassostrea gigas) which relies on low water depths. Whilst wind power foundations will be colonized by a similar range of species, they will be inhabited by a smaller number than ship wrecks. 2.0 Million brown crabs (Cancer pagurus) which will inhabit the wind power foundations will be added to the already existing number of 2.3 Million living at the 1,300 ship wrecks. Ship wrecks also provide an ideal environment for the endangered European lobster (Homarus gammarus). No lobsters were sighted at the already existing wind power foundations and it is yet to be seen whether the foundations will add to the spread of this species. Behaviour observations of the striped bristletooth surgeonfish (Ctenochaetus striatus) in the Indo-Pacific Coral Reefs revealed that he swept 18% of the sediment. Reef Sweeping as well as the bioerosion entail two major ecological functions of that fish. Ctenochaetus striatus therefore plays a major role in the preservation of coral reefs. Ongoing studies will show how certain species, such as the edible crab, which inhabit the new wind power foundations, influence the faunal community and surrounding areas. As with the striped bristletooth surgeonfish it is recommended to use behavioural investigations as fauna quantifications and community analyses do not provide satisfying results regarding the relationship between the various species and their environment. As part of the present study, techniques and materials were developed to activate or minimise certain functions of the wind power foundations, i.e., to increase or decrease the development of species at such foundations. Individual techniques are described in detail. Whether to activate wind power foundations or to make them passive, whether the reef effects are positive, negative or neither depends on the interpretation of the individual. The qualitative data reveals that the thousands of future wind power foundations will indeed transform the German North Sea ecosystem. The on-going scientific research is necessary to analyse the extent of such changes and to lead the pathway of renewable energy into the right direction