Search

Offshore renewable energy systems are generally required to operate in exposed offshore locations for long deployment periods at low cost. This requires innovative new mooring system solutions to g...

Combined Autonomous Surface Vehicles (ASV) and remotely operated underwater vehicles (ROV) inspection and intervention systems can contribute to future asset management of offshore renewable energy. This paper presents the design and performance of the winch system which couples the ASV and ROV and deploys/recovers the ROV. The hydrodynamic models and control algorithms are developed and solved with analytical and numerical approaches. The winch performance needs to meet a range of operational profiles, including i) ASV following/not following the ROV ii) winch operating in speed control iii) winch operating in tension control iv) varying ROV distance and depths targets. For a representative ASV/ROV configuration, the work determines the required umbilical length for different ROV targets and suitable winch speeds. The results show that the strategy where the ASV follows the ROV can reduce the umbilical tension, but conditions of compression should be carefully managed. The umbilical tension can also be decreased by tension control and shows to be very effective in larger sea states. This study also models the accidental limit case, where a malfunctioning ROV is recovered. The estimated increase of umbilical tension during the recovery stage of a malfunctioning ROV can thus be incorporated into the design calculations.

Understanding ecosystem dynamics within shallow shelf seas is of great importance to support marine spatial management of natural populations and activities such as fishing and offshore renewable energy production to combat climate change. Given the possibility of future changes, a baseline is needed to predict ecosystems responses to such changes. This study uses Bayesian techniques to find the data-driven estimates of interactions among a set of physical and biological variables and a human pressure within the last 30 years in a well-studied shallow sea (North Sea, UK) with four contrasting regions and their associated ecosystems. A hidden variable is incorporated to model functional ecosystem change, where the underlying interactions dramatically change, following natural or anthropogenic disturbance. Data-driven estimates of interactions were identified, highlighting physical (e.g. bottom temperature, potential energy anomaly) and biological variables (e.g. sandeel larvae, net primary production) to be strong indicators of ecosystem change. There was consistency in the physical and biological variables, identified as good indicators in three of the regions, however the shallower region (with depths

Consenting and environmental impact assessment (EIA) procedures are two of the major non-technical barriers to the further expansion of offshore renewable energy (ORE). Risk-based consenting of offshore renewable energy (RiCORE) is a Horizon 2020 funded project which aims to promote the successful development of ORE in the European Union by developing an environmental risk-based approach to the consenting of ORE projects, where the level of survey requirement is based on the environmental sensitivity of the site, the risk profile of the technology and the scale of the proposed project. The project aims to provide guidance on how to potentially improve consenting processes to ensure cost-efficient delivery of the necessary surveys, clear and transparent reasoning for work undertaken, improving knowledge sharing and reducing the non-technical barriers to the development of the ORE sector. The output from RiCORE includes deliverables over six work packages including four expert workshops conducted with relevant stakeholders (regulators, industry and EIA practitioners). The first workshop considered the practices, methodologies and implementation of pre-consent surveys, post-consent and post-deployment monitoring. The second workshop examined the legal framework in place in the partner Member States (MS) to ensure that the framework developed will be applicable for roll out across these MS and further afield. Two further workshops have involved target stakeholders to develop and refine recommendations and discuss their effective implementation. This communication highlights the main findings and draft recommendations from the RiCORE project to date. For further information and associated deliverable reports visit http://ricore-project.eu.

The production potential of offshore renewable energy meets the objectives of energy and climate policy at international and European level. Under French law, the necessary planning for the development of the offshore renewable energies is carried out within the framework of energy law. This situation, which was not entirely satisfactory in terms of participation and respect for the marine environment, has led to legal developments. In particular, the planning method chosen should be improved through the implementation of MSP. The purpose of this article is to present the planning of offshore renewable energies under French law and to analyze its relevance.

This paper details the work undertaken at the University of Dundee in the last 5 years to develop understanding of screw piles to allow them to be deployed offshore as an alternative foundation type to driven piles used in jacket structures. This has been prompted by several UK and European funded research initiatives to develop silent foundation techniques to mitigate affects on marine mammals and other animals. Current mitigation systems also have significant associated costs and questionable environmental credentials. Prior to starting this work, it was recognized that development would not progress unless the ability to predict installation requirements did not form an early part of the research investigation. This then led to investigation of methods to reduce installation requirements and development of new design approaches for the required new screw pile geometries. This paper details the progress of these investigations which are still ongoing.

The main aim of theMATES Identification of Priorities and Lines of Actions Report(updated March 2021) is to describe the reference framework used to set up the priorities and Lines of Action within theMATESproject. The report includes a list of the Lines of Action identified during the first year of the project, the prioritisation criteria for the Lines of Action and the instructions for the voting process (which was held in an online workshop on 7 March 2019 with 51 experts). The prioritisation system was defined so that the Lines of Actions, within which the most important training needs and skills gaps fit, are addressed through thePilot Experiences.

The three main objectives of the MATES Baseline Strategy Reportare: Prioritisation of the actionsneeded andselection of those most relevant to the Shipbuilding and Offshore Renewable Energy sectors. First, a prioritisation system had to be established (which would include both priority criteria and the terms of reference for their application) as well as the classification of all the training needs captured in the different foresight scenarios. Cleardefinition of the actionswhich must be put in placeto address the top-rated priorities. Across-linking of the Prioritised Lines of Action with MATES Pilot Experiencesto identify how bestto maximise their strategic alignment and impactand in this way to providefeedback for the Pilot Experiences’ comprehensive planning, execution and assessment. For this purpose, three different sets of information were collected and analysed: The results of thevoting process set up with the experts(which involved an online workshop with over 50 experts and a SurveyMonkey survey). The results from theDelphi questionnaire(which was used to identify and assess theParadigm Shiftersrelevant to each sector; six for Shipbuilding and five Offshore Renewable Energy). Thedraft proposals from the Pilot Experiences. Click herefor more details on the Pilot Experiences.

Environmental impacts from wave energy generators on the local mobile mega- and macrofauna community have been investigated in the Lysekil project by Uppsala University. Offshore renewable energy installations provide hard, artificial substrates, and as such, they could act as artificial reefs. Foundations with manufactured holes served as complex habitats and foundations without served as non-complex. In this long-term study, SCUBA surveys of mobile fauna in the years 2007, 2008 and 2016-2019 were analyzed. The results show a distinct reef effect on the foundations with significant greater species richness, total number of individuals, greater values of the Shannon-Wiener biodiversity index, and greater abundance of specific reef fauna. Complex foundations accommodated a greater abundance of brown crabs than non-complex foundations, other taxa did not show differences between the two foundation types. A successional increase of species richness, numbers of individuals and Shannon-Wiener biodiversity could be revealed from the first to the second survey period. Inter-annual variation was visible throughout all taxa and years.

Offshore renewable energy has been showing remarkable growth and acceptable yields over recent years, the concept of this study centres on the idea of connecting a wind turbine to a tidal turbine, where both energy sources may be utilised at any one location for maximum energy yield. AutoCAD and MATHCAD have been used to simulate the aerodynamics and hydrodynamics of the structure. The power generation and risk analysis were also accounted for. The result of a wave spectral analysis effect on tidal turbines is demonstrated in the study for 6 different cases at different mean crossing period, wave heights, and fatigue life. The power generation of 2 bladed wind/tidal turbine versus 3 bladed was calculated. Although 3 bladed turbines have a marginal higher power generation output, this does not reflect the feasibility of the extra percentages of power on the economics.

We demonstrate the use of general Polynomial Chaos (gPC) in determining the reliability of a mooring system designed for an offshore renewable energy (ORE) device. General Polynomial Chaos is used to forward propagate uncertainties in two design variables, and to obtain the probability density function of the Most Probable Maximum tension in the most loaded line. Then, the probability of failure is estimated using the First Order Reliability Method. For this case study, we obtain a probability of failure of 3.4×10 -6 for the mooring system, around 10 times lower than required by DNV-OS-E301. The most interesting result, however, is that by applying gPC, we can build a probability density function for the tension running only 36 simulations using the deterministic numerical model, instead of hundreds or thousands as would be required by using a Monte-Carlo method. This reduces the computational effort required for probabilistic design and analysis of floating structures, enabling the shift from conservative Partial Safety Factor based design, to Reliability and Risk based design.

TheMATES State of the Art Reportwas developed as a summary of the analysis of the 390 publications and 150 projects. The main findings were presented to theMATESnetwork of experts during two rounds of regional workshops in five European countries. The report describes the current situation and future prospects of the shipbuilding and offshore renewable energy sectors, as well as the challenges expected in the coming years. It establishes a vision of the different drivers of that will affect the transformation and evolution of the sectors, and finally a perspective on the socio-demographic situation. This deliverable includes a list of the most relevant documents forMATESavailable as aDigital Repository.

Improving the reliability of marine renewable energy devices such as wave and tidal energy convertors is an important task, primarily to minimize the perceived risks and reduce the associated cost for operation and maintenance. Marine systems involve a wide range of uncertainties, due to the complexity of failure mechanism of the marine components, scarcity of data, human interactions and randomness of the sea environment. The fundamental element of a probabilistic risk analysis necessarily needs to rely on operational information and observation data to quantify the performance of the system. However, in reality it is difficult to ascertain observation of the precursor data according to the number of component failures that have occurred, mainly as a result of imprecision in the failure criterion, record keeping, or experimental and physical modelling of the process. Traditional reliability estimation approaches such as Fault Tree, Event Tree and Reliability Block Diagram analysis offer simplified, rarely realistic models of this complex reliability problem. The main reason is that they all rely on accurate prior information as a perquisite for performing reliability assessment. In this paper, a hierarchical Bayesian framework is developed for modelling marine renewable component failures encountered the uncertainty. The proposed approach is capable to incorporate the conditions, which lack reliable observation data (e.g. unknown/uncertain failure rate of a component). The hierarchical Bayesian framework provides a platform for the propagation of uncertainties through the reliability assessment of the system, via Markov Chain Monte Carlo (MCMC) sampling. The advantages of using MCMC sampling has proliferated Bayesian inference for conducting risk and reliability assessment of engineering system. It is able to use hyper-priors to represent prior parameters as a subjective observations for probability estimation of the failure events and enable an updating process for quantitative reasoning of interdependence between parameters. The developed framework will be an assistive tool for a better monitoring of the operation in terms of evaluating performance of marine renewable system under the risk of failure. The paper illustrates the approach using a tidal energy convertor as a case study for estimating components failure rates and representing the uncertainties of system reliability. The paper will be of interest to reliability practitioners and researchers, as well as tidal energy technology and project developers, seeking a more accurate reliability estimation framework.

Subsea power cables are critical assets within the distribution and transmission infrastructure of electrical networks. Over the past two decades, the size of investments in subsea power cable installation projects has been growing significantly. However, the analysis of historical failure data shows that the present state-of-the-art monitoring technologies do not detect about 70% of the failure modes in subsea power cables. This paper presents a modeling methodology for predicting damage along the length of subsea cables due to environmental conditions (e.g., seabed roughness and tidal flows) which result in the loss of the protective layers on the cable due to corrosion and abrasion (accounting for over 40% of subsea cable failures). For a defined cable layout on different seabed conditions and tidal current inputs, the model calculates the cable movement by taking into account the scouring effect and then it predicts the rate at which the material is lost due to corrosion and abrasion. Our approach integrates accelerated aging data using a Taber test which provides abrasion wear coefficients for the cable materials. The models have been embedded into a software tool that predicts the life expectancy of the cable and demonstrated for narrow conditions, where the tidal flow is unidirectional and perpendicular to the power cable. The paper also provides discussion on how the developed models can be used with other condition monitoring data sets in a prognostics framework.

The paper presents a cost benefit analysis of using polymer mooring components in the mooring system design of the Maine Aqua Ventus I (MAV1) floating offshore wind turbine (FOWT) project. Polymer components in mooring lines can offer new mooring system responses, which can be tailored to the needs of challenging mooring systems. For FOWT deployments these can deliver mooring system responsiveness at the thrust loads of the turbine, despite the high background mooring loads. MAV1 will deploy two 6MW floating offshore wind turbines off the coast of Maine and this paper compares the existing mooring system design against a polymer mooring component solution, undertaking dynamic analysis of the mooring systems across multiple sea states (including ultimate limit states, fatigue limit states and accidental limit states). The Aqua Ventus platform is modelled in Orcaflex, with multiple mooring system designs containing different polymer component responses modelled and contrasted. Results are analyzed and load analysis data used to undertake a cost benefit analysis. Cost reductions are shown across the mooring system (anchors, lines, connectors), as well as the platform and tower structures. Fatigue analysis is undertaken using a Rainflow analysis of the sea states to be experienced by the platform over its life, for both the existing and the polymer mooring configurations. Polymer mooring components which can be used throughout the renewable energy and offshore industries to manage mooring loads, and are capable of mooring any sized platform, in any challenging conditions. While the specific components modelled in this work are targeted at FOWT or tidal platforms with novel stress-strain response curves designed to suit the high background thrust load conditions, other component responses are available to deliver design load and fatigue reductions on existing catenary or TLP moored platforms. Components can be easily retrofitted into existing mooring lines or deployed in new lines. Using polymer mooring components can dramatically reduce the peak loads experienced by the platform. Previous work has looked at an OC4 FOWT model in hypothetic conditions, whereas the current paper presents new work related to a real US FOWT deployment. The paper demonstrates that >50% reductions in design loads are possible. Cyclic loads are also substantially reduced, resulting in >60% reduction in wave induced fatigue in extreme sea states. This results in operational and maintenance cost savings. The patented mooring components have been developed initially for aquaculture and wave energy applications and have now been scaled to the MN loads required by the FOWT and offshore industries. Components are certified to relevant standards and delivered to projects globally.

The paper will present the design of a floating platform incorporating the following systems: Conventional Wind Turbine Long and Short Period Wave Energy Capture Ocean Thermal Energy Conversion (OTEC) Open Flow Current Turbines Energy Storage The focus will be integration of the systems from a structural standpoint; effects on the cost of each system and the resulting LCOE and overnight cost; and the nameplate and peak power for given conditions. Energy mechanisms in the marine environment are the wind, waves, water currents, and seawater temperature differences. An assessment and rating of the energy resource potential of a given development site is used to inform the renewable energy technology system selection process. Offshore Renewable Energy (ORE) technologies can be summarized into the following groups: Offshore Wind Turbines are the prevalent ORE technology exploiting the present market, similar to onshore wind turbines, but mounted upon a fixed or floating offshore platform. Ocean Thermal Energy Conversion (OTEC) uses the temperature differential between surface water and seabed water to drive heat engines. Marine Hydro-Kinetic (MHK) devices convert energy from waves or fluid flow. Wave Energy Converters (WEC) are oscillating/reciprocal/pressure driven systems operating at or near the ocean surface or bottom mounted in shallow waters. Flow Energy Converters (FEC) are used in areas where velocity and direction of water flow is relatively constant or highly predictable if intermittent (tidal). Unlike an onshore wind energy site, offshore wind energy systems (especially floating ones) are surrounded by these other energy sources; the integrated renewable energy facility design process addresses selecting systems that will complement each other while capturing the energy resident in the operating environment, as well as leveraging the wind turbine supporting structure and infrastructure to reduce the costs of the WEC, FEC and OTEC systems. The amount of CAPEX spent on non-power generating equipment can be optimized by leveraging the floating system structure cost to host various ORE technologies. Between 50% and 70% of the overnight cost of a typical MHK or OTEC facility will consist of equipment and activities that do not generate power. This is one of the key differences with offshore wind which has an overnight capital cost overhead of roughly 30%. By combining multiple technologies into a single platform, it is possible to reduce the MHK overhead costs to 18 to 36%, with little or no effect on the offshore wind overhead costs. The resulting design is novel in configuration which takes the form of a Multi-source Articulated Spar Leg (MASL) platform and can reduce the Levelized Cost of Energy (LCOE – the economic measure used to compare energy systems) by at least 25%; can be fabricated and pre-commissioned in port; is fully configurable to the local conditions; is more stable than the current floating wind designs in use; and can be scaled up to carry any sized wind turbine. Both cost savings and an increase in revenue can be realized using integrated ORE facilities given the higher average availability factor offered by blended ORE systems and reduction of individual system OPEX relative to stand-alone ORE systems, and example of which is shown in Illustration of Results A single MASL platform prototype is expected to produce power as cost effectively as the only commercial floating wind farm consisting of 5 spar-type platforms that comprise the Hywind Project. Using published information, the internal rate of return (IRR) of Hywind is between 8% and 10%. The estimated return for the MASL prototype is 8.7%. Both based on a realized electricity price of $0.25/kWh and design life of 25 years.

In recent years much progress has been made getting Offshore Renewable Energy (ORE), wind, wave and current/flow harnessed for use in electrical supply. This paper is aimed at giving the newcomer to ORE, both wind and Marine Hydro Kinetic (MHK) devices, an awareness and understanding of the basics. This includes what is needed to garner energy from natural offshore resources, what some of the issues/challenges are, and what some of the currently proposed solutions are and where they are in their maturity. Also included is a resource and reference list where further information may be obtained. This is not a definitive dialogue of everything that is happening in the ORE arena, but more an overview, orientation and guideline for the early entrant. This paper is focused on the physical and technical issues and does not endeavor to get into details regarding the financial and economics questions and details. The economic and financial element of this emerging industry is a very complex issue with many variables and deserves its own focus.

In recent years, caisson foundations are being increasingly used as alternative foundations for supporting offshore renewable energy structures. In general, caisson foundations for offshore wind turbines (OWTs) are subjected to combined loadings including lateral, vertical and overturning moments. To guarantee the normal operation of OWTs and reduce uncertainty in the design of OWT foundations, the response to horizontal loading must be accurately estimated. This paper presents a closed-form model to estimate the lateral bearing capacity of caisson foundations for OWTs. To understand the behaviour of caisson foundations under lateral loading, and to derive the necessary parameters and relationships to build the closed-form model, a series of laboratory tests (both 1g and centrifuge) as well as numerical simulations were conducted. Field and laboratory data from the published literature were used to validate the proposed model. The proposed solution has shown to provide a better estimate of the lateral bearing capacity of caissons compared to existing models. The model is capable of predicting the lateral bearing capacity of caissons with aspect ratios less than or equal to 1.0 in both sandy and silty soils. Additionally, the method takes into account the effect of vertical loading on the lateral bearing capacity.

The paper presents a new selection technique of wave spectra for the numerical simulation of offshore renewable energy (ORE) devices in the form of representative directional spectra, which conserves information about the distribution of wave energy along with frequency and direction classes. As a test case, an assessment of wave power resource for the Condor Submarine Mount (Azores Archipelago) is provided. The wave climate for this location was studied using the numerical model WAVEWATCH III for the period 2008–2018. Modelling results were compared with observations from four wave-buoys from the CLIMAAT project distributed around the Azores archipelago. Results indicated an annual averaged wave energy flux of 40.2 kW/m, with winter months providing more than eight times the energy that was observed during summer. The resultant nine representative spectra were used to further understand the wave climate in the region, including its seasonal variability. Compared to the traditional approach that employs simple H m 0 − T e combinations, this spectral strategy describes better the energy variability while allowing for more accurate numerical simulations of ORE devices.

This thesis investigates how the ecosystem-based principles of resilience and adaptive management can be best implemented under the appropriate assessment of the Habitats Directive to reconcile the increasing demand for offshore renewable energy (ORE) and biodiversity conservation. Particular heed is given to the question of how the implementation of the Habitats Directive can be coupled with the development of nascent ORE technologies and the potential impacts these innovations may have on marine Natura 2000 species and their habitats. More specifically, the research challenges the strict interpretation of the precautionary principle which has been crystallised by the EU judiciary under the regime of Article 6(3) of the Habitats Directive. The jurisprudential interpretation of the Habitats Directive needs to evolve in order to better reflect the ecological and infrastructural challenges associated with deploying innovative renewable energy technologies in dynamic and complex offshore environments. In this vein, the thesis suggests a novel approach to interpretation of the Habitats Directive to help accommodate these legal challenges. In so doing, it reinforces the interface between law and ecological science and considers the utility of embracing the principles of adaptive management as a better methodology to enhance the outcomes of the appropriate assessment and reconcile the interests for offshore renewables and protection of Natura 2000 sites. The aim of this research is solution-based: it seeks to improve the implementation of the assessment requirements of the Habitats Directive before they truly become an ‘obstacle course’ for offshore renewable energy developers.

The purpose of this paper is to highlight the most demanding aspects of grid interconnection of marine energy installations while at the same time providing an updated overview and comparative analysis of the connection requirements of eight European Grid Codes. Therefore, the major issues related to marine energy installations will be summarized as well as the requirements of this type of generation. Besides, the extent to which current Grid Codes include marine energy technologies will be analysed jointly with the need of harmonization of different Grid Codes into a generalised European grid code. Apart from this, several future trends of marine energy technology and its interconnection will be provided for the final discussion.

A number of sites around the UK are being considered for development of tidal stream energy, one of which is Ramsey Sound off the coast of Pembrokeshire, South Wales. The Sound was used to test the prototype of the Delta Stream by Tidal Energy Ltd. After initial testing, a 10 MW tidal array was proposed at St David's Head. To investigate any possible environmental impacts of the array due to energy extraction, a case study of the Pembrokeshire coast was performed using a high-resolution depth averaged hydrodynamic model, Telemac2D, to investigate changes to hydrodynamics and morphodynamics. Results show that the proposed array of nine tidal energy converters will cause alterations to eddy propagation leading to changes in the velocity field up to 24 km from the tidal array. Changes in morphodynamics are predicted through alterations to the bed shear stress. Changes to the mean and maximum bed shear stress, over a 30-day period, are found to be more localised and extend 12 km from the array. These changes indicate that the proposed tidal array will lead to localised sediment accumulation and will act as a barrier to sediment transport, with potential consequences for the benthic ecology of the region.

Lowering Operation and Maintenance (O&M) expenses is pivotal in order to increase the penetration of offshore renewables in the generation of electricity. The combined use of Monte Carlo simulation and optimization algorithms has been explored to support the assets management and propose improved solutions in an efficient and automated way. However, due to the lack of operational experience and historical data, validation of these models, intended in the commonly known sense of comparison against observed data is often not possible. This generates concern about their ability to fully grasp and interpret the complex dynamics of an offshore renewable energy system. This paper presents a method to effectively calibrate, verify and benchmark computational tools for O&M strategies and asset management of an offshore wind farm, as an alternative to validation in absence of real data. A case study is used to test the quality of the results and compare them against those provided by similar tools built for the same purpose. The evaluation functions for an optimization of the O&M strategies are then benchmarked against these outputs in order to ensure that the solutions are consistent within the overall characterization and optimization framework. The requirements for acceptability of the models performance, as well as guidelines for analogous verifications using similar models, are derived. Hence, this work provides a basis to benchmark future models and increase confidence and credibility in computational tools for the O&M planning of offshore renewables.

Today's power utilities are evolving towards a more environment-friendly form. Particularly, in undersea power transmission, offshore renewable energy integration and urban power transmission, HVDC cable systems play a significant role. As an essential part of the cable systems, cable joints are often the weakest and the most critical point. Hence, the safe operation of cable joints under different operational stages is one of the key issues to make the cable systems reliable. In this paper, the development of HVDC cable joints has been reviewed. The design aspects, including geometry, insulation materials and interfaces are briefly discussed.

This paper compares and contrasts key aspects of the Offshore Renewable Energy (ORE) and offshore Oil and Gas (O&G) industries. The objective is to illuminate where synergies exist in the context of technical standards as well as government regulations, policies and practices. The thesis of the work will propose a clear and harmonized approach for utilization of existing proven oil and gas standards, rules, and regulations as a key enabler for the efforts of developers of offshore renewable energy standards. Using process mapping and gap analysis the paper will identify where the standards of oil and gas and ORE overlap. The ORE sector is taking root and producing commercial power in many regions accustomed to hydrocarbon based energy production. The tools, techniques, talents, and disciplines of engineering required to support the offshore renewable energy industry have much in common with those of the O&G industry. Notwithstanding, new systems of international standards are being developed specific to offshore renewable energy and not taking full advantage of the legacy of existing standards already in place and proven by the offshore oil and gas industry. The results of the analysis are presented in the following manner: Process map showing each of the ORE modalities (i.e. MHK, Fixed Offshore Wind, Floating Offshore Wind, and OTEC), highlighting the overlap with O&G activities.Planned and existing IEC and other ORE specific standards are listed for each modalityHighlight coverage of common oil and gas standards and align to each modality of ORE.A proposal to fully leverage the existing standards for use in ORE projects and to unify the ORE standards is presented.The review of Regulations is limited to US waters, and the fractured nature of the US ORE Regulatory environment is addressed and suggested improvements made. Existing comparisons of the two industries’ codes and standards are limited to one or two ORE modalities, and this paper is meant to act as the first step in seeing ORE Standards as a unified system.

Residual stresses are often inevitably introduced into the material during the fabrication processes, such as welding, and are known to have significant effects on the subsequent fatigue crack growth behavior of welded structures. In this paper, the importance of welding sequence on residual stress distribution in engineering components has been reviewed. In addition, the findings available in the literature have been used to provide an accurate interpretation of the fatigue crack growth data on specimens extracted from the welded plates employed in offshore wind monopile structures. The results have been discussed in terms of the role of welding sequence in damage inspection and structural integrity assessment of offshore renewable energy structures.

Unexploded ordnance presents an on-going challenge for offshore renewable energy project developers and as some have found to their cost, getting it wrong can be very expensive. With new guidelines on UXO management set to be published, best practice means a better understanding of the risks.

This paper defines a methodology to compare different offshore renewable energy (ORE) mooring configurations in terms of the risk of entanglement they present to marine megafauna. Currently, the entanglement of large marine animals is not explicitly considered in environmental impact studies. Recommendations need to be developed, assessing the risk of entanglement of ORE mooring configurations at the beginning of their design process. Physical parameters of the mooring system affecting the relative risk of entanglement have been identified as tension characteristics, swept volume ratio and mooring line curvature. These have been investigated further through six different mooring configurations: catenary with chains only, catenary with chains and nylon ropes, catenary with chains and polyester ropes, taut, catenary with accessory buoys, taut with accessory buoys. Results indicate that the taut configuration has the lowest relative risk of entanglement, while the highest relative risk occurs with catenary moorings with chains and nylon ropes or with catenary moorings with accessory buoys. However, the absolute risk of entanglement is found to be low, regardless of the mooring configuration. This methodology can also be applied to other mooring configurations, arrays or power cables.

Large marine renewable energy projects such as wind and wave farms located offshore will generally require an offshore platform for power equipment to act as a collection node for the generator cables operating at medium (generating) voltage, the step-up transmission transformers and the necessary switchgear. The platform may not have to be continuously manned for operation of the renewable farm, but temporary manning will be required for maintenance purposes.