Construction Of Offshore Wind Farms Research Articles

Going digital: challenges in monitoring marine megafauna when comparing results from visual and digital aerial surveys

Since the first plans to develop offshore wind farms (OWFs), concerns have been raised about the impacts on marine megafauna. Today, it is required to assess these impacts over the whole lifecycle of the OWF. Before construction, initial assessments are often conducted by visual surveys, but subsequent monitoring over the lifecycle of the OWF has to be digital due to safety requirements, leading to challenges in data comparability. The aim of this study was to attempt to establish generalizable intercalibration factors for this transition between visual and digital monitoring methods. To this end, intercalibration surveys were conducted at five different sites and at different times of the year within a site, using both visual monitoring at low-altitude and digital monitoring at both low and high altitudes. We tested the potential for intercalibration of the results based on the ratio of abundance estimated from data collected by the different methods. We explored factors such as the species under study and site-specific conditions that may influence intercalibration. We computed more than 100 intercalibration factors and found that, on average, abundance estimates from digital methods were higher than those from visual methods and that flight altitude for digital monitoring did not significantly influence abundance estimates. Aside from divergent abundance estimates depending on monitoring method, the findings also revealed significant heterogeneity, only one-third of which was explained by contextual factors such as taxonomy or the sea conditions. This outcome presents a pessimistic outlook on the prospect for the intercalibration of results between an initial assessment carried out with visual observations and subsequent monitoring with digital methods after OWF construction and until decommissioning. The high heterogeneity prevents seamless transferability of intercalibration factors and highlights the importance of local context.

Impulsive pile driving sound does not induce hearing loss in the longfin squid (Doryteuthis pealeii)a).

Offshore windfarms are a key means to produce clean energy as we seek to limit climate change effects. Impulsive pile driving used for their construction in shallow water environments is among the most intense anthropogenic sound sources. There is an increasing understanding that an array of marine invertebrates detects acoustic cues, yet little is known about how pile driving sound could impact their sound detection abilities. We experimentally quantified potential changes in sound sensitivity for an abundant, commercially and ecologically important squid species (Doryteuthis pealeii) exposed to actual in situ pile driving. The pile was 0.3-m diameter and 10-m long; hammer energy reached 16 kJ per strike. Sound detection thresholds were determined using auditory evoked potentials in animals with no exposure, after one 15-min or five repeated 15-min long pile driving sound sequences, corresponding to cumulative sound exposure levels of 110 and 131 dB re (1 μm s-2)2 s for acceleration and 187 and 214 dB re (1 μPa)2 s for pressure. We found no statistical evidence of temporary threshold shifts in any squid exposed to pile driving sound sequences. These results, combined with companion behavioral studies, suggest that squid may be robust to the sound impacts during offshore windfarm construction.

Pile driving noise impacts behavioral patterns of important East Asian juvenile marine fishes

The surge in renewable energy demand, particularly from offshore wind farm (OWF), raises concerns about underwater noise pollution during their construction. Despite extensive studies on underwater noise impacts in European and Western countries, local species targeted investigations are crucial for global application. We assessed how pile driving noise during OWF construction affected the behavior of three juvenile Korean fishes (Lateolabrax japonicus, Acanthopagrus schlegelii, and Platichthys stellatus) prevalent in East Asian seas. Pile driving noise playback induced rapid changes in L. japonicus and A. schlegelii swimming speed and group cohesion, with 40 % remaining un-habituated after 5 min. Notably, L. japonicus showed clear avoidance of the noise source, while P. stellatus behavior remained unchanged at all. Our findings confirm that even relatively low-intensity impulsive noise can alter fish behavior, potentially due to species-specific characteristics. Accumulated data will inform the development of strategies for smart OWF establishment, advancing sustainable energy practices.

Research on the ice-resistance performance of conical wind turbine foundation in brash ice fields

Due to the significantly higher wind energy density in high-latitude sea areas compared to other regions, the construction of offshore wind farms is shifting towards these areas. However, in high-latitude sea areas, large amounts of sea ice float on the surface during winter, making ice loads a critical factor affecting the structural safety of wind turbines. For monopile flexible wind turbines, installing an ice-breaking cone near the waterline is an effective measure to withstand the threat of sea ice. To clarify the ice resistance performance of conical wind turbine foundations in brash ice zones, this study proposes a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM). This method is used to calculate the ice load results for a cylindrical riser, and the results were found to be in good agreement with the ice load experiment results from China University of Petroleum's wave flume (CUPWF). This validation confirms the rationality of the method. Taking a 5 MW monopile wind turbine installed with an ice-breaking cone as the research object, the time history of dynamic ice loads and the displacement response of ice-induced vibration during the interaction between the wind turbine and brash ice are simulated. Considering the water level variations caused by tides, the differences in ice resistance performance between the upright cone and the inverted cone of the ice-breaking cone are analyzed. Finally, the impact of changes in cone angle on the ice resistance performance of the wind turbine foundation is determined. The results indicate that under the impact of brash ice, the upright cone of the ice-breaking cone has a higher ice resistance capacity compared to the inverted cone. With changes in cone angle, the trends of ice loads in the horizontal and vertical directions vary oppositely. However, the overall ice resistance capacity of the wind turbine foundation decreases as the cone angle increases. This study can provide a reference for the rational design of conical wind turbines in cold regions.

Offshore windfarm construction elevates metabolic rate and increases predation vulnerability of a key marine invertebrate

A global increase in offshore windfarm development is critical to our renewable energy future. Yet, widespread construction plans have generated substantial concern for impacts to co-occurring organisms and the communities they form. Pile driving construction, prominent in offshore windfarm development, produces among the highest amplitude sounds in the ocean creating widespread concern for a diverse array of taxa. However, studies addressing ecologically key species are generally lacking and most research is disparate, failing to integrate across response types (e.g., behavior, physiology, and ecological interactions), particularly in situ. The lack of integrative field studies presents major challenges to understand or mitigate actual impacts of offshore wind development. Here, we examined critical behavioral, physiological, and antipredator impacts of actual pile driving construction on the giant sea scallop (Placopecten magellanicus). Benthic taxa including bivalves are of particular concern because they are sound-sensitive, cannot move appreciable distances away from the stressor, and support livelihoods as one of the world's most economically and socially important fisheries. Overall, pile driving sound impacted scallops across a series of behavioral and physiological assays. Sound-exposed scallops consistently reduced their valve opening (22%), resulting in lowered mantle water oxygen levels available to the gills. Repeated and rapid valve adductions led to a 56% increase in metabolic rates relative to pre-exposure baselines. Consequently, in response to predator stimuli, sound-exposed scallops displayed a suite of significantly weaker antipredator behaviors including fewer swimming events and shorter time-to-exhaustion. These results show aquatic construction activities can induce metabolic and ecologically relevant changes in a key benthic animal. As offshore windfarm construction accelerates globally, our field-based study highlights that spatial overlap with benthic taxa may cause substantial metabolic changes, alter important fisheries resources, and ultimately could lead to increased predation.

Qualitative modeling for representing the social-ecological system of the Groix–Belle-île offshore wind farm project

Abstract The increasing numbers of offshore wind farm (OWF) projects question the impacts of such infrastructures on the social-ecological system (SES) in which they are to be constructed. Some answers can be given using qualitative modeling and loop analysis. We used participatory modeling to co-construct a qualitative model of the socio-ecosystem together with stakeholders of the APPEAL project. The goal of the project was to evaluate the potential impacts of the pilot OWF in the Groix–Belle-île region. Then, loop analysis was used to study the characteristics of the SES created by the setting-up of an OWF. We focused on the impacts of SES variables on each other by evaluating their effects through direct and indirect pathways. Pleasure boating appeared as one of the SES components prone to suffer from the OWF construction, whereas industrial tourism was likely to benefit from it. This article presents the methodology used to obtain such results, for it to be used in spatial planning or in citizen-science processes.

Environmental DNA for monitoring the impact of offshore wind farms on fish and invertebrate community structures

AbstractTo reach the renewable energy targets set by the European Commission, a tenfold expansion of the installed offshore wind farms is needed. Since the construction of offshore wind farms may affect local soft‐sediment fauna, an efficient monitoring technique is needed to monitor the potential effects on the marine ecosystem. Here, we assess whether eDNA metabarcoding is a suitable alternative to monitor fish and epibenthos biodiversity in these difficult to access marine habitats. Water sampling and trawl surveys were conducted in parallel in 12 coastal and 18 offshore sites, the latter located inside and outside two offshore wind farms in the Belgian part of the North Sea. 12S eDNA metabarcoding retrieved 85.7% of the fish species caught in the beam trawls, whereas the COI eDNA metabarcoding only identified 31.4% of the epibenthic invertebrate species. Furthermore, the 12S marker resulted in an additional detection of 26 unique fish species, whereas the COI marker detected an additional 90 invertebrate species. Spatial patterns in alpha diversity recovered with eDNA metabarcoding were not significantly different from those observed with morphological determination. Significant differences were found in fish and invertebrate community structures between the coastal, transition and offshore zones as well as on the smaller wind farm scales, which agreed with the morphological beam trawl data. Indicator species found with morphological beam trawl monitoring for each of the three zones (coastal, transition, offshore) were also detected with 12S eDNA metabarcoding, and the latter method detected an additional 31 indicator species. Our findings show the need for adequate quality control of the obtained species lists and reveal that 12S eDNA metabarcoding analyses offers a useful survey tool for the monitoring of fish communities in offshore wind farms, but the used COI assay did not adequately capture the epibenthic communities as observed with beam trawl data.

Governing offshore wind: is an ‘Asia-Pacific Model’ emerging?

ABSTRACT The Asia-Pacific region is emerging as central to the deployment of offshore wind power. Large scale offshore wind involves complex governance challenges, and governments can choose to centralize and streamline processes enabling the construction of offshore wind farms. We develop a framework for comparing site selection and consenting processes for offshore wind farms, and examine whether a more streamlined and centralized model of offshore wind governance is emerging in the major Asia-Pacific markets of Japan, the People’s Republic of China, South Korea, Taiwan, and Vietnam. We also examine whether policy targets and framework legislation are used in these markets, and whether renumeration schemes are being applied. We find limited evidence of convergence in some aspects of offshore wind governance, but that governance models in the region remain diverse. We suggest there remains scope for facilitating learning across different Asia-Pacific markets as governments work to ensure the governance of siting and consenting meets the needs of stakeholders, while enabling offshore wind supports rapid low carbon energy transition goals.

Offshore Energy Development in Poland—Social and Economic Dimensions

The development of green technology in the world is progressing extremely rapidly. New possibilities for obtaining energy from renewable sources are constantly being sought and existing solutions are being improved. The multifaceted potential of the seas and oceans is an important aspect being taken into account in the development of the energy systems of a number of economies. One dimension of action in this area is the orientation towards offshore wind energy and the construction of offshore wind farms for this purpose. The purpose of this article is to analyse the importance of offshore wind farms in Poland’s energy system and to assess public perception of the changes taking place in this dimension. The article is based on research and critical analysis of the available literature, legal regulations and industry reports, as well as on the results of our own surveys, the scientific findings of which were developed with the application of statistical instruments using PQstat software, ensuring the expected quality of results. The findings of the article indicate the significant importance of offshore wind farms in the creation of Poland’s energy mix, with differing public attitudes towards their construction. Furthermore, the results of the research indicate a differentiated attitude of society towards the construction of offshore wind farms. The main motivation for majority support of the measure in question are economic reasons, which are connected with the expectation of a real price reduction per 1 kW of energy, as well as increased attractiveness of the region due to investments in this area. The main concern with the measure relates to environmental aspects, with concerns about the functioning of ecosystems in light of the construction and subsequent operation of wind farms. Negative public opinion is also signalled in relation to the potential risk of landscape change in a direction that is undesirable for the studied developed coastal tourist region in Poland.

A new method for quantifying redistribution of seabirds within operational offshore wind farms finds no evidence of within-wind farm displacement

The climate crisis is driving a rapid increase in size and number of offshore wind farms to reduce carbon emissions from electricity generation. However, there are concerns about the potential impact of offshore wind farms on the marine environment. Seabirds are considered to be at risk of being displaced from preferred foraging habitat, by construction and operation of offshore wind farms, resulting in reduced energy intake or elevated energetic costs and consequent decreases in survival and/or productivity. Typically, displacement or avoidance behaviour is assessed by comparing abundance and spatial distributions of seabirds before and after an offshore wind farm is constructed. However, seabird distributions are highly variable through time and space and so discerning a change in distribution caused by an offshore wind farm from other environmental variables can be challenging. We present a new method that controls for temporal variation by examining the location of individual seabirds relative to turbines. Mean seabird density at different distances from individual turbines (0-400m) was calculated from data collected on a total of 12 digital aerial surveys of the Beatrice Offshore Wind Farm (UK), in May-August in 2019 and 2021. Mean densities of common guillemot (Uria aalge), razorbill (Alca torda), Atlantic puffin (Fratercula arctica) and black-legged kittiwake (Rissa tridactyla), both flying and sat on the water, were calculated. If the presence of turbines had no effect on seabird distribution, there should be no relationship between distance from turbine and seabird density. This was tested by simulating a relocation of turbines, relative to seabird distribution, and recalculating seabird density over 0-400m from simulated turbine locations. This was repeated to generate a bootstrapped distribution of expected densities against which observed density was compared. If displacement was occurring, mean observed density close to turbines would be significantly lower than expected density, derived from the bootstrap distribution. Overall, observed mean density did not differ significantly from expected density, i.e. no displacement effect was detected. There was a slight tendency for guillemot and razorbill, when sat on the water, to be at higher densities than expected, near turbines, suggestive of possible attraction to turbines, and for flying birds to be at lower densities than expected, near turbines, suggestive of possible avoidance. No flying razorbills were recorded within 100m of turbines but sample sizes were small. Kittiwake tended to show no avoidance or attraction behaviour, although flying kittiwake density was slightly lower than expected at 200m from turbines. Puffins sat on the water were recorded in densities similar to the expected density. Overall, no effect of turbine rotor speed was found, i.e. birds were not more likely to be displaced/avoid turbines at higher or lower rotor speeds. The results of the turbine relocation analysis gave a more consistent and more easily interpreted assessment of displacement/avoidance behaviour than the typical approaches of comparing abundance and seabird distribution through time. We strongly encourage application of this new approach to post-construction spatial distribution data from other offshore wind farms, to build the evidence base on the effects of offshore wind farms on seabirds.

Overview of Predation by Birds, Cephalopods, Fish and Marine Mammals on Marine Benthic Amphipods

With about 8000 marine benthic species, the amphipod crustaceans form one of the richest animal groups of the worldwide Ocean. They have colonized a wide range of soft- and hard-bottom natural and artificial habitats extending from the intertidal to hadal zones. Moreover, they show a broad size spectrum, with numerous giant species exceeding 20 cm in length and some species smaller than 2 mm. When biofouling artificial hard surfaces, some tube-building species can form very dense populations comprising up to 100,000 individuals per square meter. Amphipods are important prey for fish and mammals. Along with cephalopod juveniles, they are also included in the trophic diet of shorebirds that consume amphipods mostly during the low tide on tidal flats. They display diel migration, which reinforces the predation by demersal fish in the suprabenthic zone just above the sea bed, as well as by pelagic fish in the water column. Despite their importance in terms of biodiversity and trophic transfer, no general overview is available on the role of benthic amphipods in marine ecosystem food webs. Various methods, including laboratory and field experiments, as well as the analysis of stomach contents and DNA extraction, have been used to identify the prey/predator trophic links. Based on an extensive literature review, this study discusses the role of marine benthic amphipods as potential food for higher trophic levels in natural and artificial hard-bottom communities created via the construction of offshore wind farms.

Modelling and Simulation of Grid Connected Wind Turbine Induction Generator for Windfarm

As the power generation sector moving towards the sustainability to achieve clean and renewable energy source, the wind power generation plays a vital role due to its abundance in nature. A big chunk of the decrease in carbon emission is a major attribute to the growth of the wind energy sector. Wind turbine production, structural development, logistics, maintenance and R&D are just some of the areas that could benefit from the growth of the wind energy industry. This brought out the attention of researchers of the electrical engineering to focus on wind power generation. It can be more efficient and cost-effective to operate wind turbines as a wind farm rather than individually. This has led to a surge in the construction of wind farms, both onshore and offshore wind farms. Therefore, in this paper, the study and analyse of single Induction generator with wind turbines and 33MW windfarm performance is presented. The simulation result demonstrates the efficiency of DFIG in producing energy at a constant wind speed, as well as its ability to regulate both active and reactive power at steady-state.

Behavioural responses of Sandwich terns following the construction of offshore wind farms

Behavioural responses of Sandwich terns following the construction of offshore wind farms

The effect of offshore wind farms on the variation of the phytoplankton population

Ocean and coastal areas have the opportunity to harness renewable energy with a rapidly growing rate of investment. Among the categories of marine energy, offshore wind energy produces an enormous amount of electricity for over 15 countries. The devices used for harvesting renewable energy can directly or indirectly affect habitat change, climate change, material-energy cycling, and the development of new communities. Studying their impacts can help fill the knowledge gap related to topics such as global carbon management and the reduction of ecological risks. This study aims to investigate changes in phytoplankton population after offshore wind farm (OWF) construction events at intervals of 2, 4, 7, 11, 18, 30, 50, and 80 days. The wind farms selected for this study are located in the North Sea, which is the most active area for OWF activity. The necessary information for this study was gathered from the Copernicus Marine Environment Monitoring Service (CMEMS) and the 4 C Offshore database. Python package in Jupyter Notebook and SPSS (version 25) were used to identify significant changes with a 95% confidence interval, along with their effect size. The results of the study are reported in four sets based on the eutrophication status of the studied OWFs. The events that have a diminishing effect on the phytoplankton population include foundation installation, array cable installation, and fully commissioning. Turbine installation was the only event where primary producers experienced growth afterward. The occurrence and duration of phytoplankton population changes during different eutrophication zones vary. The findings of this study can be beneficial for governments and various organizations when making decisions about the fishing industry, coastal management, ecosystem-based management, and ecological studies.

Stakeholder insights into embedding marine net gain for offshore wind farm planning and delivery

The rapid expansion of offshore wind farms plays a key role in meeting global Net Zero targets by 2050 and if delivered sustainably could address the dual challenges of climate change and biodiversity loss. Many countries are embracing ambitious approaches to environmental impact reduction by implementing concepts such as Biodiversity Net Gain, Nature Positive and No Net Loss. Such policies are now recognized in European and UK legislation, although generally only applicable to terrestrial activities. For the marine realm, there is little consensus on how Marine Net Gain can provide optimal environmental and societal outcomes from marine activities such as offshore wind farm construction, operation and decommissioning. This study sought to clarify the key issues that need to be addressed for effective implementation of Marine Net Gain. Following recruitment through a stakeholder mapping exercise, in-workshop and follow-up questionnaires sought to elicit expert opinions from multi-sector UK offshore wind farm stakeholders on a range of aspects of Marine Net Gain policy formulation and delivery. Over 80 % of participants indicated that certain external inputs, including information for climate change adaptation options and habitat mapping data, were important to enable delivery of Marine Net Gain. The most important ecosystem services to include within Net Gain measures were perceived as those relating to fisheries (mean 4.50, SD 0.51), maintaining nursery habitats (mean 4.41, SD 0.59), and climate regulation (mean 4.20, SD 1.). Stakeholders felt the most important Net Gain actions for environmental restoration/enhancement for future offshore wind deployment were shellfish/mussel bed (ave rank score 4.06) and invertebrate habitat restoration (ave rank score 4.60), and actions supporting plankton communities (ave rank score 4.67). Stakeholders agreed (83 %) that Net Gain actions should be considered at the decommissioning stage, and the preferred decommissioning option was the complete removal or abandonment of all structures. Stakeholders felt that strategic Net Gain assessments should prioritize fishing pressures (dredging: mean 4.27, SD 1.03; line and net: mean 4.21, SD 0.89) and those arising from physical structures (mean 4.0, SD 0.85). Aquaculture farming was deemed most feasible to co-exist with fixed offshore wind farms (means 3.93–4.19), while floating wind farms were felt to be more co-locatable with fishing practices (means 3.94–4.06) and carbon capture storage devices (mean 3.87) compared to fixed structures. Recommendations are suggested for future policy development and scientific research in relation to the application of Marine Net Gain assessment for offshore wind farm projects.

Background Topography Affects the Degree of Three‐Dimensionality of Tidal Sand Waves

AbstractOffshore tidal sand waves on the sandy bed of shallow continental shelf seas are more three‐dimensional (3D) in some places than others, where 3D refers to a pattern that shows variations in three spatial directions. Such sand waves have crestlines that meander, split or merge. The degree of three‐dimensionality seems to vary especially when large‐scale bedforms, such as tidal sand banks, are present underneath the sand waves. Understanding this behavior is important for offshore activities, such as offshore windfarm construction or the maintenance of navigation channels. In this study, the degree of three‐dimensionality of sand waves at five sites in the North Sea is quantified with a new measure. Results show that tidal sand waves on top of tidal sand banks are more two‐dimensional (2D) than those on bank slopes or in open areas. These differences in sand wave pattern are supported by numerical simulations performed with a new long‐term sand wave model. The primary cause of these differences is attributed to the deflection of tidal flow over a sand bank, which causes sand wave crests to be more aligned with the bank at its top than at its slopes. It is subsequently made plausible that the different patterns result from the competition between two known mechanisms. These mechanisms are nonlinear interactions between sand waves themselves (SW‐SW interactions) and nonlinear interactions between sand banks and sand waves (SB‐SW interactions). On bank tops, SB‐SW interactions favor a 2D pattern, while SW‐SW interactions, which elsewhere produce a 3D pattern, are less effective.

Evolution of excess pore water pressures around monopiles subjected to moderate seismic loading

The sustained growth of the offshore wind sector is leading to the construction of offshore wind farms in highly seismic regions of the world. Hence, a large proportion of the potential sites may be exposed to liquefaction risk. Monopiles are directly affected by this phenomenon given their preference as a support system for offshore wind turbines over other foundation types. This paper includes a comprehensive study of the lateral response of monopiles against the combined action of earthquake induced liquefaction and environmental loading using centrifuge modelling. The experimental setup was designed to compare the amount of excess pore pressure generated within the soil adjacent to the monopile with and without operational wind/wave loading. The results revealed higher accumulation of excess pore pressure in the non-laterally loaded case, and significant differences in the amount of excess pore pressure recorded in the windward and leeward sides of the monopile in the laterally loaded scenario. In addition, the study provides data on the rotation experienced by monopile supported offshore wind turbines in liquefiable soils.

Comparison of Extreme Wind and Waves Using Different Statistical Methods in 40 Offshore Wind Energy Lease Areas Worldwide

With the ongoing global drive towards renewable energy, several potential offshore wind energy lease areas worldwide have come into focus. This study aims to estimate the extreme wind and wave conditions across several newly designated offshore wind lease sites spanning six continents that are crucial for risk assessment and the design of offshore wind turbines. Firstly, the raw data of wind speeds and wave heights prevailing in these different lease areas were obtained. Following this, an in-depth extreme value analysis was performed over different return periods. Two principal methodologies were applied for this comparative study: the block-maxima and the peaks-over-threshold (POT) approaches. Various statistical techniques, including the Gumbel method of moments, Gumbel maximum likelihood, Gumbel least-squares, and the three-parameter GEV, were employed under the block-maxima approach to obtain the distribution parameters. The threshold for the POT approach was defined using the mean residual life method, and the distribution parameters were obtained using the maximum likelihood method. The Gumbel least-squares method emerged as the most conservative estimator of extreme values in the majority of cases, while the POT approach generally yielded lower extreme values compared to the block-maxima approach. However, the results from the POT approach showed large variations based on the selected threshold. This comprehensive study’s findings will provide valuable input for the efficient planning, design, and construction of future offshore wind farms.

Post-installation performance of piles installed with a novel driving method: field tests and numerical modelling

Since the industrial revolution, humanity's impact on the planet has increased significantly. The growth of global economies and population size in the 20th century was fueled by the combustion of fossil fuels. In an effort to reduce the impact of human kind on the environment, governments ratified landmark agreements such as the Montreal Protocol in 1987, the UNFCCC in 1992, the Kyoto Protocol in 2005, and the Paris Agreement in 2015.
 To support this effort, the European implemented the European Green Deal (2019), which aims to achieve no-net greenhouse gas emissions by 2050. Offshore wind energy, particularly large-diameter monopiles, is expected to play a substantial role in this transition. Europe has already developed over 28 GW of offshore wind power, with a global capacity of 37 GW as of 2021 [8]. However, to meet the goals of the European Green Deal, offshore wind capacity needs to scale up significantly in the next 28 years.
 The installation of monopiles, the most selected foundation option for offshore wind turbines, has traditionally relied on impact hammering. This method has drawbacks such as lengthy installation times, and noise emissions harmful to marine life. An alternative approach is axial vibratory pile driving, which offers faster and quieter installation. However, certification bodies have yet to endorse its use for offshore wind farm construction owing to uncertainties relating to the post-installation monopile performance. Research efforts are being devoted to understanding the dynamic behaviour of the soil during vibro-driving and the effects of vibro-installation on pile performance. Several geotechnical research teams are investigating the post-installation lateral behaviour of monopiles and comparing the performance of impact piling and vibratory piling [1-7,9-13].
 To complement the effort towards noiseless pile driving researchers from TU Delft proposed the novel Gentle Driving of Piles (GDP) method which aims to enhance traditional axial vibro-pile driving by incorporating high-frequency torsional vibrations [9]. The addition of torsional vibrations is expected to consume/redirect soil frictional resistance and limit radial expansion during pile driving, resulting in faster and quieter installation – the GDP shaker is presented in Figure 1.a.
 To demonstrate the GDP technology and compare its performance with traditional pile-driving methods (impact pilling and axial vibratory driving), comprehensive medium-scale field tests were conducted in an inhomogeneous sand deposit at the Port of Rotterdam. Eight identical test piles with a diameter of 0.762 m and an embedded length of 8 m were installed using impact hammering, traditional axial vibratory piling, and the GDP method. Out of the eight test piles, four were heavily instrumented out of which two were GDP-driven, and the remaining two were installed with impact pilling (IH) and axial vibro-driving (VH).
 The tests performed on the four main test piles consisted of two stages: the first stage focused on driving performance, while the second stage examined the cyclic lateral behaviour of the piles under repeated loading for different installation methods -cyclic loading programme in Figure 1.b. The test results highlighted the promise of the method towards faster (Figure 1.c.) and less perturbing pile driving [1,9,13] but also enhanced post-installation lateral response [5,6,7] compared to the traditional alternative installation methods (Figure 1.d.).

Quantifying the effect of rock armour scour protection on eigenfrequencies of a monopile supported OHVS

It is common practice to install scour protection systems during the construction of offshore wind farms. This is because the guidelines allow for a more optimal structural design, as the potential effects of scouring may be ignored. However, multiple sources, as well as measurements, suggest that there is an additional gain in stiffness which is not being taken into account by current guidelines. Scour protection has the ability to provide extra foundational stiffness to the monopile, which results in higher natural eigenfrequencies and mode shapes. In this paper the focus will be on an offshore high voltage station (OHVS) located in the North Sea and the impact of a rubble riprap scour protection on the foundational stiffness of the structure. Furthermore, a proposal is made on how to take these effects into account when calculating for design. This site was equipped with a mobile measurement system containing a multi-axial accelerometer, which was active in a period both before and after installation of the scour protection rock armour layer. In case of similar environmental circumstances, the eigenfrequencies of the OHVS were noticeably higher after the scour protection was installed, thus substantiating the claim of increased foundational stiffness. To perform numerical studies on the impact of the scour protection system on structural dynamics, an OHVS support structure finite element model was built. As no formally agreed upon formulation to include scour protection exists, two possible methods are proposed. One is adding a global accretion layer to model the scour protection as an additional soil layer. The other calculates an overburden pressure due to the scour protection weight, which translates to the stiffening of the upper soil layers of the foundation. Both methods have their own strengths and weaknesses, but more research on different locations and offshore structures is needed to formalize the definitive description for modelling scour protection.