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Available decision-support tools rarely account for the welfare of technicians in maintenance scheduling for offshore wind farms. This creates uncertainties, especially since current operational limits might make a wind farm accessible but the vibrations from transits might be unacceptable to technicians. We explore technician exposure to vibration in transit based on the levels of discomfort and the likelihood of seasickness occurring on crew transfer vessels (CTVs). Vessel motion monitoring systems deployed on CTVs operating in the North Sea and sea-state data are used in a machine learning (ML) process to model the welfare of technicians based on operational limits applied to modelled proxy variables including composite weighted RMS acceleration (aWRMS) and motion sickness incidence (MSI). The model results revealed poor to moderate performance in predicting the proxies based on selected model evaluation criteria, raising the possibility of more data and relevant variables being needed to improve model performance. Therefore, this research presents a framework for an ML approach towards accounting for the wellbeing of technicians in sailing decisions once the highlighted limitations can be addressed.

This article proposes a framework for the integration of tactical and operational optimisation models for maintenance scheduling and routing at offshore windfarms. A tactical model is formulated to find the optimal schedule for preventive maintenance over a medium-term planning horizon (one month). The schedule is produced assuming a weather forecast for the entire planning horizon, which in practice will be uncertain. However, for each day, an operational maintenance routing model is solved to obtain optimal vessel routes with a one-day planning horizon, assuming an updated weather forecast for that day. In the operational routing model, the turbines scheduled for preventive maintenance are provided by the tactical scheduling model, whereas the turbines requiring corrective maintenance are provided by information about failures and alarms updated on a daily basis. In the case that the solution generated by the routing model contains turbines that cannot be maintained, the monthly maintenance activities are rescheduled by solving the tactical scheduling model considering the delayed activities. As the routing problem is too time consuming to solve exactly, we propose efficient matheuristic solution methods incorporating Variable Neighbourhood Search and an exact method. Computational experiments have been carried out to assess the performance of the tactical-operational framework. [ABSTRACT FROM AUTHOR]

IntroductionCoastal and continental shelf ecosystems are among the most productive, yet exploited, ecosystems. The Grande Vasière (GV) covers most part of the French Northern part of the Bay of Biscay, a crucial fishing ground for metropolitan France. It is the place of numerous uses, especially fishing, and will soon shelter sand extraction activities and offshore windfarms. All these activities may compete for space and resources and put pressure on habitats, biodiversity and subsequent ecosystem services (ES). Current management strategies integrate these activities and biodiversity conservation schemes but no ES.MethodsTo fill that gap, we quantified and mapped nine indicators of ecosystem processes (EP), used as proxies of four ES (i.e. sea food provisioning, biological control, regulation of environmental conditions and life cycle maintenance). Due to the complexity of ES, we investigated several EP by ES. Then we identified hotspots and coldspots of supply and spatial overlap among EP and other uses (conservation, fishing, offshore windfarms and sand extraction).ResultsEP mapping suggests a higher capacity of supply of the chosen ES in the Northern part of the GV. We found a strong spatial heterogeneity among the EP related to the same ES, underlining a point of vigilance when designing management measures to sustain ES supply. Northern EP hotspots overlap with high amounts of bottom trawl fishing effort. Higher levels of commercial species diversity and sole spawning grounds in the South overlap with higher amounts of gillnet fishing effort. Areas of sand extraction prospection and offshore windfarms under construction should not overlap with hotspots of EP, at the exception of the sole spawning ground and the commercial species diversity hotspots. Finally, we highlight an overlap of more than 20% of four EP hotspots with Natura 2000 areas, while the Marine Natural Park in the South covers more EP coldspots (i.e. hake nursery, encounter rate, trophic links diversity) than hotspots.DiscussionIncorporating such a multifunctional spatial approach with hotspots and coldspots opens new perspective for marine spatial planning, pointing out the potential strengths and weaknesses of areas currently defined or prioritized for future uses like conservation, sand extraction or emerging activities like offshore windfarms.

In this article, current research findings of local scour at offshore windfarm monopile foundations are presented. The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized, including the current-only condition, wave-only condition, combined wave-current condition, and complex dynamic condition. Furthermore, this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific conditions. The weakness of existing researches and future prospects are also discussed. It is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex loadings. The computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.

Abstract Offshore windfarms have recently emerged as a renewable energy solution. The effects of pile‐driving and long‐term impacts of operational noises on fish chorusing still, however, remain largely unknown. In this study, we investigated the variations of fish chorusing intensity and duration during the construction (2016) and operational phases (2017–2018) of a windfarm at the Eastern Taiwan Strait (ETS). At the ETS, two types of fish choruses (Types 1 and 2) were found to repeat over a diurnal pattern. In the 2 days after the pile driving, Type 1 chorusing showed lower intensity and longer duration, while Type 2 chorusing exhibited higher intensity and no changes in its duration. During the operational phases in 2017 and 2018, both choruses were longer in duration (2–3 h for Type 1; 0.5–1 h for Type 2). The intensity of Type 1 chorus increased by 5–10 dB, but no significant variation was recorded for Type 2. Our findings document, for the first time, different behavioral responses of two chorusing types exposed to pile‐driving and windfarm noise pressure. Fish choruses have been associated with several behavioral functions. Deviation from a regular pattern might affect fish reproductive success, cause migration, augmented predation, or physiological alterations. Because offshore windfarms installations are growing in magnitude and capacity worldwide, this study provides essential insights for policymakers and constitutes an important reference for assessing the effects of noise from pile driving and windfarms on fishes.

Suction caissons are cylindrical-shaped foundation elements closed at the top and open at the bottom which are almost completely embedded with their cylindrical part in the soil. The main advantage of this foundation compared to other commonly used foundation concepts is its fast, ease, and almost noiseless installation, as well as the effortless removal at the end of the lifetime. Suction caissons supporting three- or four-legged jackets have been employed successfully in several recent offshore windfarm projects around the world. The study presented herein investigates the general suitability of suction caissons in the south china sea at three representative sites. The results show that suction caisson foundations are technically feasible. Sizes can be large and may vary between 13 m to 15 m in diameter and 10 m to 13 m in length, which, however, may reduce noticeably when considering load redistribution in the design, typically done in a FEED and detailed design. The main challenges of suction caisson application are the very soft soil conditions and possible liquefaction potential due to large earthquake events. Although technically feasible, the economic viability of suction caissons needs to be investigated on project-specific basis. For that purpose, the authors provide an overview of general aspects which need to be considered in such an evaluation. This study gives realistic case studies for research and industry in offshore wind farm development. [ABSTRACT FROM AUTHOR]

Globally there are concerns over a warming climate and the UK has declared a climate and ecological emergency and has an ambitious programme for the growth of offshore windfarms to contribute to commitments to achieving a legally binding Net Zero for greenhouse gas emissions by 2050. Offshore windfarm consenting is comparatively mature in the UK but evidence gaps to inform impact assessment and uncertainty to inform decision making has led to a precautionary approach that slows the speed of consent decisions. This paper examines the approach to UK offshore windfarm consenting, reviews the precautionary but risk-based approach that environmental decision makers have adopted in light of evidence gaps, and summarises how the collection of empirical data and reviews of evidence collected from operational windfarms has improved scientific knowledge and focussed decision making. A summary is also provided of the enduring legislative safeguards that apply during the lifetime of any consent and recommendations are made on the risk appetite that advisers and decision makers should adopt in view of policy that seeks to accelerate sectoral growth whilst enhancing nature recovery. • The UK has an ambitious programme for the construction of offshore windfarms. • Environmental evidence gaps lead to a precautionary approach that slows consenting. • Consenting should use a risk-based approach and an appropriate risk-appetite. • Empirical data and reviews of evidence are needed to improve scientific knowledge. [ABSTRACT FROM AUTHOR]

Offshore windfarms have recently emerged as a renewable energy solution. The effects of pile‐driving and long‐term impacts of operational noises on fish chorusing still, however, remain largely unknown. In this study, we investigated the variations of fish chorusing intensity and duration during the construction (2016) and operational phases (2017–2018) of a windfarm at the Eastern Taiwan Strait (ETS). At the ETS, two types of fish choruses (Types 1 and 2) were found to repeat over a diurnal pattern. In the 2 days after the pile driving, Type 1 chorusing showed lower intensity and longer duration, while Type 2 chorusing exhibited higher intensity and no changes in its duration. During the operational phases in 2017 and 2018, both choruses were longer in duration (2–3 h for Type 1; 0.5–1 h for Type 2). The intensity of Type 1 chorus increased by 5–10 dB, but no significant variation was recorded for Type 2. Our findings document, for the first time, different behavioral responses of two chorusing types exposed to pile‐driving and windfarm noise pressure. Fish choruses have been associated with several behavioral functions. Deviation from a regular pattern might affect fish reproductive success, cause migration, augmented predation, or physiological alterations. Because offshore windfarms installations are growing in magnitude and capacity worldwide, this study provides essential insights for policymakers and constitutes an important reference for assessing the effects of noise from pile driving and windfarms on fishes. [ABSTRACT FROM AUTHOR]

Offshore windfarm developments are expanding, requiring assessment and mitigation of impacts on protected species. Typically, assessments of impacts on marine mammals have focused on pile-driving, as intense impulsive noise elicits adverse behavioral responses. However, other construction activities such as jacket and turbine installation also change acoustic habitats through increased vessel activity. To date, the contribution of construction-related vessel activity in shaping marine mammal behavioral responses at windfarm construction sites has been overlooked and no guidelines or mitigation measures have been implemented. We compared broad-scale spatio-temporal variation in harbor porpoise occurrence and foraging activity between baseline periods and different construction phases at two Scottish offshore windfarms. Following a Before-After Control-Impact design, arrays of echolocation click detectors (CPODs) were deployed in 25 km by 25 km impact and reference blocks throughout the 2017–2019 construction. Echolocation clicks and buzzes were used to investigate porpoise occurrence and foraging activity, respectively. In parallel, we characterized broadband noise levels using calibrated noise recorders (SoundTraps and SM2Ms) and vessel activities using AIS data integrated with engineering records. Following an impact gradient design, we then quantified the magnitude of porpoise responses in relation to changes in the acoustic environment and vessel activity. Compared to baseline, an 8–17% decline in porpoise occurrence was observed in the impact block during pile-driving and other construction activities. The probability of detecting porpoises and buzzing activity was positively related to the distance from vessel and construction activities, and negatively related to levels of vessel intensity and background noise. Porpoise displacement was observed at up to 12 km from pile-driving activities and up to 4 km from construction vessels. This evidence of broad-scale behavioral responses of harbor porpoises to these different construction activities highlights the importance of assessing and managing all vessel activities at offshore windfarm sites to minimize potential impacts of anthropogenic noise.

Offshore windfarms (OWFs) offer part of the solution for the energy transition which is urgently needed to mitigate effects of climate change. Marine life has rapidly exploited the new habitat offered by windfarm structures, resulting in increased opportunities for filter- and suspension feeding organisms. In this study, we investigated the effects of organic matter (OM) deposition in the form of fecal pellets expelled by filtering epifauna in OWFs, on mineralization processes in the sediment. OM deposition fluxes produced in a 3D hydrodynamic model of the Southern Bight of the North Sea were used as input in a model of early diagenesis. Two scenarios of OWF development in the Belgian Part of the North Sea (BPNS) and its surrounding waters were calculated and compared to a no-OWF baseline simulation. The first including constructed OWFs as of 2021, the second containing additional planned OWFs by 2026. Our results show increased total mineralization rates within OWFs (27–30%) in correspondence with increased deposition of reactive organic carbon (OC) encapsulated in the OM. This leads to a buildup of OC in the upper sediment layers (increase by ∼10%) and an increase of anoxic mineralization processes. Similarly, denitrification rates within the OWFs increased, depending on the scenario, by 2–3%. Effects were not limited to the OWF itself: clear changes were noticed in sediments outside of the OWFs, which were mostly opposite to the “within-OWF” effects. This contrast generated relatively small changes when averaging values over the full modeling domain, however, certain changes, such as for example the increased storage of OC in sediments, may be of significant value for national / regional carbon management inventories. Our results add to expectations of ecosystem-wide effects of windfarms in the marine environments, which need to be researched further given the rapid rate of expansion of OWFs.

Efforts to meet climate change targets are resulting in rapid and global expansion of offshore windfarms. In many regions, development areas are also used by protected marine mammals, requiring the assessment and mitigation of any risk of injury during construction and operation. For small cetaceans such as the harbour porpoise, there is particular concern over the risk of injury from impulsive noise should individuals remain within near-field injury zones during the installation of pile driven turbine foundations. Currently, this risk is assessed by comparing predicted noise levels at the start of piling with baseline estimates of animal density, which are, in turn, based on data collected at least one year earlier. However, vessel-based preparation work immediately prior to piling may displace animals, thus reducing any risk of injury when pile-driving begins. We investigated the effects of pre-piling activities on local soundscapes and harbour porpoise occurrence during the construction of two deep-water offshore windfarms in NE Scotland. Arrays of echolocation click detectors deployed at a sub-set of turbine sites were used to assess porpoise occurrence within a 5 km buffer during a 48-h period prior to the initiation of piling. In parallel, we characterised local vessel activity using AIS data and underwater broadband noise levels. We then used daily engineering records to characterise variation in construction activities and explore how porpoise occurrence varied during the 48 h prior to piling. On average, vessels arrived onsite 11–15 h before the start of pile-driving activities at both windfarms. In both installation campaigns, harbour porpoise acoustic detection gradually declined by up to 33% during the 48 h prior to piling. This decrease in detections was associated with increased levels of vessel and pre-piling installation activities, and increased local underwater broadband noise levels. These results provide strong evidence of porpoise displacement prior to active mitigation activities, highlighting the need to account for disturbance from multiple sources when optimising mitigation measures aimed at reducing impacts of windfarm construction on protected marine mammal populations. • Activities prior to piling may deter marine mammals reducing the number of animals within the predicted injury zone • Harbour porpoise occurrence gradually decreased several hours prior to piling • Harbour porpoise displacement was associated with increased levels of vessel activity and broadband noise • Accounting for animal displacement before piling may help optimise mitigation measures aimed at reducing cumulative impacts [ABSTRACT FROM AUTHOR]

This paper presents the design and control of an advanced unidirectional DC/DC modular multilevel converter (MMC) that facilitate the integration of off-shore windfarms with the high-voltage direct current (HVDC) transmission system. The proposed converter deploys a single-phase MMC inverter coupled with series-connected rectifier modules through multiple medium frequency transformers. Unlike the conventional dq control method, which involves multiple transformations, this paper also proposes a simple control strategy that directly acts on the AC output of the MMC, under the stationary reference frame.

This paper presents the design and control of an advanced unidirectional DC/DC modular multilevel converter (MMC) that facilitate the integration of off-shore windfarms with the high-voltage direct current (HVDC) transmission system. The proposed converter deploys a single-phase MMC inverter coupled with series-connected rectifier modules through multiple medium frequency transformers. Unlike the conventional dq control method, which involves multiple transformations, this paper also proposes a simple control strategy that directly acts on the AC output of the MMC, under the stationary reference frame. [ABSTRACT FROM AUTHOR]

Highlights • Underwater noise is becoming recognised as a significant pollutant globally. • Noise abatement measures (reducing noise emitted at source) are still scarce. • Significant noise-emitting industries include shipping, offshore wind, oil and gas. • Viable policy options for noise abatement are available. • Noise abatement can reduce cumulative pressure on aquatic ecosystems. Abstract Underwater noise pollution is becoming globally recognised as a significant threat to aquatic ecosystems and the resources they provide. The effects of noise pollution extend from blue whales to zooplankton, impacting threatened species and affecting key industries including fisheries and ecotourism. In response, policymakers in some jurisdictions have made substantive high-level commitments to address noise pollution, however the implementation of noise reduction measures (noise abatement) remains limited. To support the development of effective noise management policies, this paper explores the economic and policy context to noise abatement in three major noise-generating industries: shipping, offshore windfarm construction, and seismic surveying for oil and gas. In each case, tractable policy options are identified which make considered use of command-and-control and incentive-based measures in light of the available noise abatement methods. Drawing on instructive examples from terrestrial noise management and other sectors, it is concluded that such measures offer the most promising long-term solution to deliver existing and future policy commitments to manage cumulative levels of underwater noise pollution. [ABSTRACT FROM AUTHOR]

As penetration of renewable energy sources increases, the proportion of synchronous generators with rotating masses directly coupled to the grid decreases. In the case of wind generation, the kinetic energy stored in the machine rotor is not available to perform the natural task of frequency support for the AC power system. New active control methods must therefore be developed to synthetically recouple this inertia characteristic to the grid. European offshore windpower is growing and the average distance to shore is increasing. Voltage Source Converter based HVDC (VSC-HVDC) is a promising method for transporting this power to the onshore AC grid over long distances. The fast power transfer capability of VSC-HVDC offers the opportunity for new control strategies to provide frequency support to the AC grid. The authors propose a method for using a VSC-HVDC transmission link to follow and amplify the traditional primary frequency response behavior of a small synchronous generator connected at the point of common coupling (PCC). In terms of frequency support, the onshore grid will then see the HVDC connected offshore windfarm (OWF) and small synchronous generator together as one large synchronous generator with rotor inertia directly coupled to the grid (i.e. synthetic inertia). The method will therefore enable the OWF to provide frequency support services equivalent to that of a traditional power plant at the same rating. Electromagnetic transient simulation is used to investigate the proposed active control strategy. Fiber-optic technology is considered as a method of remote communication between the OWF and the small synchronous generator (SSG). A second communication-less method is also considered which utilizes a cascaded droop frequency to DC voltage control at the Grid Side VSC (GS-VSC) and then DC voltage to frequency at the Windfarm Side VSC (WF-VSC). Simulation results are used to justify the proposed method. [ABSTRACT FROM AUTHOR]

Current maintenance planning strategies in the operations and maintenance of offshore wind farms rarely account for the comfort of technicians during transits. This creates uncertainties as transit from the vessel to structure might be unacceptable to technicians. Here, we model the welfare of technicians using the discomfort from the motions (three-dimensional accelerations) felt on crew transfer vessels (CTVs) during transits from port to wind farm. To explore technician exposure to vibration, acceleration data from vessel motion monitoring systems deployed on CTVs operating in the North Sea was synchronised with sea-state data from an operational ocean model. Processes of dimensionality reduction and machine learning (ML) were used to model the comfort of technicians from operational limits applied to models predicting Composite Weighted RMS Acceleration. Trained models were shown to provide estimations for the comfort variable with an R2 value of 0.67 and an RMSE of 0.06 ms−2. The comfort-based decision-making model is shown to be able to predict sail or not sail decisions for maintenance transits. The proposed model will have applications in maintenance planning for offshore wind farms, able to account for the comfort of technicians once identified limitations have been addressed to improve model predictions. • Comfort assessment for offshore Wind Farm Technicians was modelled. • Dimensionality reduction and machine learning(ML) processes were used. • Data from vessel motion monitoring systems and sea-state were synchronised. • Model predicted sail or not sail comfort variable for Wind Farm Technicians. • Proposed model can be useful in maintenance planning for offshore wind farms once the highlighted limitations are addressed. [ABSTRACT FROM AUTHOR]

The installation of marine renewable energy devices (MREDs, wind turbines and converters of wave, tidal and ocean thermal energy) has increased quickly in the last decade. There is a lack of knowledge concerning the effects of MREDs on benthic invertebrates that live in contact with the seabed. The European common cuttlefish (Sepia officinalis) is the most abundant cephalopod in the Northeast Atlantic and one of the three most valuable resources for English Channel fisheries. A project to build an offshore wind farm in the French bay of Saint-Brieuc, near the English Channel, raised concern about the possible acoustic impact on local cuttlefish communities. In this study, consisting of six exposure experiments, three types of noise were considered: 3 levels of pile-driving and 3 levels of drilling. The objectives were to assess possible associated changes in hatching and larva survival, and behavioural and ultrastructural effects on sensory organs of all life stages of S. officinalis populations. After exposure, damage was observed in the statocyst sensory epithelia (hair cell extrusion) in adults compared to controls, and no anti-predator reaction was observed. The exposed larvae showed a decreased survival rate with an increasing received sound level when they were exposed to maximum pile-driving and drilling sound levels (170 dB re 1 μPa2 and 167 dB re 1 μPa2, respectively). However, sound pressure levels's lower than 163 dB re 1 μPa2 were not found to elicit severe damage. Simulating a scenario of immobile organisms, eggs were exposed to a combination of both pile driving and drilling as they would be exposed to all operations without a chance to escape. In this scenario a decrease of hatching success was observed with increasing received sound levels. • Noise from Windmill operations affects Sepia officinalis at short ranges. • Effects of pile-driving and drilling on hatching, larvae and adults can be monitored. • Mitigation measures may be implemented by establishing threshold noise levels. • Technological developments allow limiting negative effects of human-made noise. [ABSTRACT FROM AUTHOR]

Scepticism over stated preference surveys conducted online revolves around the concerns over 'professional respondents' who might rush through the questionnaire without sufficiently considering the information provided. To gain insight on the validity of this phenomenon and test the effect of response time on choice randomness, this study makes use of a recently conducted choice experiment survey on ecological and amenity effects of an offshore windfarm in the UK. The positive relationship between self-rated and inferred attribute attendance and response time is taken as evidence for a link between response time and cognitive effort. Subsequently, the generalised multinomial logit model is employed to test the effect of response time on scale, which indicates the weight of the deterministic relative to the error component in the random utility model. Results show that longer response time increases scale, i.e. decreases choice randomness. This positive scale effect of response time is further found to be non-linear and wear off at some point beyond which extreme response time decreases scale. While response time does not systematically affect welfare estimates, higher response time increases the precision of such estimates. These effects persist when self-reported choice certainty is controlled for. Implications of the results for online stated preference surveys and further research are discussed. [ABSTRACT FROM AUTHOR]

The concept of eco-maintenance aims to prolong the lifetime of the system to maintain while minimizing environmental losses due to maintenance. This concept is developed for renewable energy production system (Reps) like wind turbines or photovoltaic panel. REPS generate clean and inexhaustible energy. However the production of this energy is unpredictable because it depends on the weather. Moreover failures that occur on the means of production make the operation less interesting. However the implementation of technical resources (fault detection sensor, vehicles and transfer system for technicians, tools and spare parts) improves the performance of the production system. In this paper a model for REPS with an application on wind energy production system (offshore wind farm + maintenance systems) was developed and simulations have been performed. Hence we show the importance to design and optimize the maintenance the REPS for reducing cost and environmental issues. [ABSTRACT FROM AUTHOR]

Integrated marine planning, which must take into consideration environmental and social impacts, is being introduced widely in Europe, the USA, Australia and elsewhere. Installation of offshore windfarms creates impacts both on local marine ecosystems and the view of the seascape and is one of multiple activities in the marine area that must be addressed by marine planning. The impacts on people's values (and hence welfare) of changes in ecology and amenity that could arise from the installation of a windfarm in the Irish Sea were assessed using a discrete choice experiment administered through an online survey. The ecological changes investigated were: increased species diversity resulting from artificial reef effects, and the effect of electromagnetic fields from subsea cables on marine life; whilst the amenity change was the visibility of offshore turbines from land. Respondents expressed preferences for ecological improvements but had less clear preferences regarding the height and visibility of the turbines. In particular distance decay effects were observed with respondents further away from the coast being less concerned about visual impact created by offshore turbines. Understanding ecological and amenity impacts and how they are valued by people can support the decisions made within marine planning and licensing. [ABSTRACT FROM AUTHOR]

Mitigation measures to disperse marine mammals prior to pile-driving include acoustic deterrent devices and piling soft starts, but their efficacy remains uncertain. We developed a self-contained portable hydrophone cluster to detect small cetacean movements from the distributions of bearings to detections. Using an array of clusters within 10 km of foundation pile installations, we tested the hypothesis that harbour porpoises ( Phocoena phocoena ) respond to mitigation measures at offshore windfarm sites by moving away. During baseline periods, porpoise movements were evenly distributed in all directions. By contrast, animals showed significant directional movement away from sound sources during acoustic deterrent device use and piling soft starts. We demonstrate that porpoises respond to measures aimed to mitigate the most severe impacts of construction at offshore windfarms by swimming directly away from these sound sources. Portable directional hydrophone clusters now provide opportunities to characterize responses to disturbance sources across a broad suite of habitats and contexts.

Coastal areas of India have a big potential for establishing renewable energy projects, which are generally regarded as green energy sources. However, such projects' construction work may cause a negative environmental impact on the surrounding waters. Aquaculture projects based on seaweed and fisheries, commonly referred to as integrated multitrophic aquaculture (IMTA), can help to mitigate these impacts. Although the purpose of any IMTA is to recirculate the waste products from cultivated species and not to mitigate the environmental impacts of energy projects, IMTA may serve as a complementary activity to compensate for the environmental impacts of marine energy projects. In return, marine energy projects can provide a few facilities to IMTA projects in their areas. IMTA projects are already practised in some parts of the world; however, rare examples are available with marine energy projects. This study aims to put an idea of potential IMTA projects in the areas of the proposed first offshore wind farm in India. This study also recommends the possible utilisation of the potential tidal energy plant in the estuary as a nursery for a few species in IMTA on the western coast of India. In addition, the current study discussed some major challenges, such as seasonal variations, ecological risks, selection of IMTA components, legal, economic and regulatory and social acceptance. Overcoming these challenges can promote further development of IMTA projects in Indian coastal waters. • Linking integrated multi-tropic aquaculture to ecological engineering. • Need of IMTA for Indian coastal ecosystems restoration. • IMTA can be potential complementary activity to marine energy projects. • Marine windfarm and tidal energy can help for IMTA implemetation. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation of the backfilling of scour holes around circular piles. Scour holes around a pile are generated either by a current or a wave. Subsequently, the flow climate is changed from current to wave, combined waves and current, or wave to a smaller wave, leading to the backfilling of the scour hole. The investigation has shed light onto the mechanism behind the backfilling process. The results show that the scour depth corresponding to the equilibrium state of backfilling is the same as that corresponding to the equilibrium state of scour around the pile for the same wave (or combined waves and current) climate. The time scale of backfilling has been determined as a function of three parameters, namely, (1) the Keulegan-Carpenter number of the initial wave or current (which generates the initial scour hole); (2) that of the subsequent wave, which backfills the scour hole; and (3) the Shields parameter associated with the latter wave, for live-bed conditions. In the case of the combined waves and current, the current-to-wave-velocity ratio is also involved. The time scale of the backfilling process is completely different from that of scour. The time scale of backfilling is much larger than that of scour when the Keulegan-Carpenter number associated with the backfilling is (typical wind farm application), while the time scale of backfilling can be smaller than that of scour when . [ABSTRACT FROM AUTHOR]

Abstract: Theupper ocean responseinthe presenceofawindfarmis studied numerically,takinginto accounttheeffect of surface gravitywaves. Thefarm geometryisa simplified rigid rectangle with characteristic sizeof L aligned with the wind direction. Assuminga typicalwind deficit behindthefarm,an analytical2D U-shapedwake profileis appliedtodrive the upper ocean circulation. The shallow-water equations are modified to includefarm characteristic length, wind-wave and wave-current momentum transfer to study the circulation in the rectangular ocean basin. Solutions of this modified expressionasafunctionoftheRossby deformation radius confirmthattheupper ocean responseinthe vicinityofafarm is strongly related to the wave effects. For the numerical study, the Regional Ocean Modelling System (ROMS) and a wave-modified finite volume technique are used that the wave-modified finite volume technique shows a reasonable agreement withROMS simulation results. Numerical results for both linear and non-linearwave simulations show the existenceof horizontal shear stress gradients relatedtothe fluid motion,wave-induced stressandfarm characteristic size. The wind and wave forcing by including wind stress, Stokes drift and wave-induced stress creates symmetrical, range dependent dipoles in the upper ocean. The dipoles are sensitive to wind stress, wave forcing and L, and have tendency to become asymmetric with time. The near-surface Ekman current is affected significantly, and strong upwelling and downwelling occur.Thelinear numericalsolverresults,however,showthatthepycnoclinedepthasa responseofupper ocean to thefarm becomes weaker after almost one day. Including non-linear term, horizontal diffusion, and bottom friction leadstoa decreaseinthe strengthof eddies. But,the amplitudeof disturbancesintheleeofthefarm becomes weaker after almost three days. [Copyright &y& Elsevier]

The article discusses a research study on the effects of the offshore construction at Horns Rev II wind farm in the Danish North Sea to the marine porpoises Phocoena phocoena in the area. Investigated were the temporal and spatial behavioural responses of Phocoena phocoena to the noise of construction through passive acoustic monitoring devices (T-PODs) that were placed in gradient sampling design. Findings indicated decreased porpoise activity by 100% after 1 hour of pile driving on the site and porpoises staying at lower than normal levels from 24 to 72 hours as far as 2.6 kilometers from the site. Additional findings include reduction of porpoise activity within the 5-month period of construction.

In certain weather conditions, intense power fluctuations have been observed in the Horns Rev offshore windfarm (160 MW) located in the North Sea. This Note presents the results showing a correlation between wind direction and power fluctuations in this large offshore windfarm. [ABSTRACT FROM AUTHOR]