Offshore wind energy is a key resource in the renewable energy sector, with a growing number of monopile foundations being installed for wind turbines. The installation of these piles generates high levels of underwater noise, which can pose risks to marine species. High-level experiment data sets are essential to quantify the pressure, particle motion in both seawater and seabed and vibration of the monopile, allowing for the monitoring of sound levels and the assessment of environmental impact. This is done by comparing measured noise to regulatory thresholds and auditory injury criteria for marine mammals, fish, sea turtles, and benthic communities. Noise mitigation systems, such as air-bubble curtains, play a significant role in reducing underwater noise. Ensuring their effectiveness requires monitoring key parameters, including the pressure distribution along bubble curtain hoses, which governs air flow through the nozzles and ultimately determines acoustic performance. In this study, medium-scale tests were conducted to measure pressure distribution along hoses at varying air flow rates and compare the results with numerical predictions. Additionally, acoustic measurements were performed during an offshore installation campaign in German waters, with hydrophones deployed at multiple locations and distances from the pile. The collected data serves as a benchmark for validating noise prediction models for offshore pile driving across various scenarios, including those with and without noise mitigation measures. These measurements enable the validation of modelling approaches and the evaluation of the effectiveness of applied noise mitigation techniques. Future work will focus on laboratory-scale tests to monitor particle motion in the water column and seabed vibrations. This will help assess the environmental impact on species that are particularly sensitive to these physical changes.

The present study introduces a coupled contactless control approach for managing both translational and torsional motions of a suspended load. This method utilizes magnet-to-magnet interactions between two pairs of magnetic dipoles, with translational motion controlled by adjusting the polarity and intensity of the electromagnetic actuator, and torsional motion regulated through the orientation of the external magnetic field. The results demonstrate effective motion dissipation in response to external excitations and non-trivial initial conditions. Key control parameters include the initial distance between interacting magnets and the ability of translational control to counteract the attractive forces generated by torsional torque. The proposed magnetic control method presents a promising foundation for non-contact position control in offshore wind turbine installations.

The increasing size of offshore wind turbine foundations necessitates innovative approaches for monopile installation. Traditionally performed through impact driving, the challenges of large stresses induced on the monopile and high levels of underwater noise emissions have driven a shift toward vibratory installation methods. This study investigates the vibro-installation process of steel tubular piles in dense saturated sand through controlled lab-scale experiments. The experiments systematically varied penetration rates and driving frequencies to analyze the interaction between the piles and the surrounding soil. The results reveal critical insights into the influence of vibratory parameters on soil resistance and pile drivability, with a specific focus on the response of the pile tip and shaft under different conditions. These findings contribute to improved predictive models for monopile installation, addressing data gaps in offshore conditions and supporting the optimization of vibratory techniques for sustainable and cost-effective wind energy development.

As the trend shifts toward the installation of larger foundation piles for offshore wind farms, which are associated with lower frequency excitations, accurately predicting the resulting sound and vibrations requires a precise characterization of soil behaviour and pile-soil interaction. In addition to noise emissions caused by pile installation, substrate-borne vibrations are particularly perceptible to various marine biota. Both seabed vibrations and underwater noise raise concerns about ecological impacts, emphasizing the need for predictive models that accurately represent the interactions between pile, soil, and seawater. This paper examines the effects of the inclusion of the pile-soil contact mechanism during impact pile driving both in the underwater soundand the seabed vibrations. The pile-soil mechanism condition is modelled by the introduction of linear springs at thepile-soil interface allowing for relative displacement to develop between the soil and the pile. A case study is conducted to explore the implications of the contact mechanism, focusing on the two key outputs: the noise levels in thesurrounding fluid and particle motion within the substrate. Sensitivity analysis is performed to evaluate how variations in contact conditions during impact piling influence these critical metrics.

Seismic airguns are widely used in offshore environments to investigate sub-seafloor layers, generating intense, impulsive sound waves that propagate through seawater, penetrate the seabed, and travel tens to hundreds of kilometers from the source. The characteristics of these acoustic waves evolve as they interact with sediment layers and the sea surface, which can alter the temporal features of the sound pressure reaching marine life at various distances. Assessing sound pressure wave properties across different environments is essential for selecting metrics that effectively gauge the impact of seismic noise on aquatic ecosystems. One such metric, sound pressure kurtosis, reflects the impulsive nature of sound waves and provides a measure of their impulsiveness, which is particularly relevant for assessing potential effects on marine animals. In this study, Green’s functions for the acousto-elastodynamic problem are employed to model sound propagation from seismic airguns, capturing the influence of the seafloor’s elastic properties on sound dispersion. We investigate variations in sound pressure kurtosis across various sediment types, including sandy, silty, and clay-like substrates, examining how each affects the impulsive characteristics of airgun-generated pulses. Additionally, the temporal dispersion of pressure signals from individual airgun shots is analyzed as they interact with differing marine sediments, providing insights into the impact of the seafloor’s elastic properties on sound emissions affecting marine life.

The Gentle Driving of Piles (GDP) is a new technology for vibratory (mono)pile installation that is based on simultaneous application of low-frequency/axial and high-frequency/torsional vibrations. In this paper, a numerical modelling framework, that has been developed and successfully applied to axial vibratory driving, is employed to study GDP. In that manner, the major driving mechanism of this method is comprehended on the basis of field observations and numerical analyses. As regards the numerical model, the pile is described as a thin cylindrical shell and the soil medium is treated as a linear elastic layered half-space. The pile-soil coupling is realized via a history-dependent frictional interface, that accounts for friction force degradation due to the accumulation of loading cycles at the soil material points. The redirection of the friction force vector due to the high-frequency torsion manifests as the main driving mechanism of GDP. Finally, the soil disturbance during installation is compared for the cases of GDP and axial vibratory driving, showcasing the dissimilar characteristics of the induced soil motion.

Vibratory offshore pile driving offers a potential solution for reducing the underwater noise generated during the installation of foundation piles compared to using impact hammers. Existing noise prediction models are specifically tailored to impact pile driving scenarios. This paper introduces a novel methodology for underwater noise predictions during vibratory pile driving. A non-linear driveability model is utilised to derive realistic non-linear interface friction forces, which are then incorporated into a noise prediction model. The study emphasises the significance of integrating a driveability analysis, revealing substantial differences from traditional models that assume perfect contact between the pile and soil. The authors argue that the proposed model provides more realistic outcomes when considering smooth driving without refusal, in contrast to traditional models designed for impact piling. The results illustrate noticeable deviations in pressure levels and seabed vibrations between the linear and presented methods at the driving frequency and its superharmonics. Furthermore, the research demonstrates that the noise field is highly sensitive to variations in system dynamics and excitation spectrum during driving, using both small- and large-diameter monopiles as examples. This research contributes to developing more effective driving techniques to reduce underwater noise pollution and facilitate sustainable offshore wind turbine installations.

The successful deployment of offshore wind turbines hinges on the installation process, particularly the temporary suspension of the turbine components during assembly. External factors or imbalances in control forces can induce vibrations, emphasizing the need for precise control, especially in the torsional mode, to ensure the delicate alignment required for bolted connections. This paper introduces a contactless technique to control the torsional vibrations of a rigid cylinder using electromagnetic interaction between two magnets, incorporating magnetically-imposed damping and active control algorithms. The magnetically-imposed dissipation is achieved by introducing nonlinear damping into the system, i.e. by controlling the orientation of the field exerted by the electromagnetic actuator. Leveraging the nonlinear coupling of the interaction between the magnets and the modification of the stable equilibrium position, the results show a satisfactory active control performance (low residual error and swift response). The key parameters for control efficiency are identified as the separation distance between the magnets, the fluctuation step of the actuator’s magnetic field, and the magnetically-induced stiffness relative to the inherent stiffness of the system. Consequently, the proposed method lays a promising foundation for a non-contact control technique, particularly valuable in offshore wind turbine installations.

With the growing demand for renewable energy, an increased number of offshore wind farms are planned to be constructed in the coming decades. The monopile is the main foundation of offshore wind turbines in shallow waters while the installation process itself takes place with large hydraulic impact hammers. This process is accompanied by significant underwater noise pollution which can hinder the life of mammals and fish. To protect the marine ecosystem, strict sound thresholds are imposed by regulators in many countries. Among the various noise mitigation systems available, the air-bubble curtain is the most widely applied one. While several models exist which aim to describe the mitigation performance of air-bubble curtains, they all assume a cylindrically symmetric wave field. However, it is well known that the performance of the air-bubble curtains can vary significantly in azimuth due to the inherent variations in the airflow circulation through the perforated pipes positioned on the seabed surface. This paper presents a new model which is based on a multi-physics approach and considers the three-dimensional behavior of the air-bubble curtain system. The complete model consists of three modules: (i) a hydrodynamic model for capturing the characteristics of bubble clouds in varying development phases through depth; (ii) an acoustic model for predicting the sound insertion loss of the air-bubble curtain; and (iii) a vibroacoustic model for the prediction of underwater noise from pile driving which is coupled to the acoustic model in (iii) through a three-dimensional boundary integral formulation. The boundary integral model is validated against a finite element model. The model allows for a comparison of various mitigation scenarios including the perfectly deployed air bubble curtain system, i.e.no azimuth-dependent field, and an imperfect system due to possible leakage in the bubbly sound barrier along the circumference of the hose.

Investigation of sound pressure waveforms helps the selection of appropriate metrics to evaluate their effects on marine life in relation to noise thresholds. As marine animals move farther away from a sound source, the temporal characteristics of sound pressure may be influenced by interactions with the sediment and the sea surface. Sound pressure kurtosis and root-mean-square (rms) sound pressure are quantitative characteristics that depend on the shape of a sound pulse, with kurtosis related to the qualitative characteristic “impulsiveness.” After verifying the propagation modeling approach using selected test cases from the JAM Workshop held in Cambridge, UK, in 2022, the time dispersion values of pressure signals produced by an individual airgun shot across various sediment types are analyzed. The results reveal that there is significant pulse dispersion when the seabed consists of predominantly sand-type sediments: i.e., the airgun signal duration increases considerably over long distances, thus decreasing the kurtosis of a sequence of pulses, whereas the pulse dispersion is more limited for clay and silt-type sediments. The range variations of frequency weighted kurtosis and rms sound pressure differ from those of the unweighted kurtosis, depending on the corresponding lower and upper roll-off frequencies corresponding to different marine animal groups.

Periodic fluid-solid layered media exhibit distinctive features that can be utilized in various engineering disciplines, such as selective transmission of guided waves, omnidirectional band-gaps and Fano resonances, depending on the spatial configuration and the material properties of the fluid and solid layers involved. This work utilizes the Thin-Layer Method (TLM) in the study of layered fluid-solid media, by extending the original normal modes-based method to acousto-elastic problems. By means of this development, the band-gap structure of these periodic systems can be analysed and their effect when incorporated in fluid or solid full-/half-spaces can be investigated seamlessly for different periodic arrangements. Conclusively, this study presents a framework to analyse these systems, serving as a basis for non-local continuum theories, as well as unveiling desirable dispersion characteristics for the design of metamaterials.

Offshore wind energy holds significant promise as a solution in the energy transition. However, installing offshore pile foundations can generate substantial levels of underwater noise, posing potential risks to marine life. This paper examines the influence of asymmetric impact forces and pile inclination on producing underwater noise and seabed vibrations based on cases of a small- and large-diameter monopile. The study focuses on scenarios involving inclined and eccentric forces and tilted piles. The analysis reveals that non-symmetrical conditions significantly impact the sound pressure levels around the ring frequency of the pile due to various noise generation mechanisms. However, it is observed that the vertical component of the impact force predominantly contributes to the generation of underwater noise, primarily due to its considerably higher amplitude.

This paper studies the mechanism that leads to the reduction of frictional soil reaction forces during pile driving, termed friction fatigue. We focus on axial vibratory driving, an environmentally friendly monopile installation method, and examine two friction fatigue formulations, i.e. a penetration-based and a cyclic memory mechanism. Friction fatigue plays a pivotal role in pile drivability and post-installation bearing capacity for piles installed via axial vibratory driving. Through numerical analyses and validation against field data from onshore experiments, the efficacy of these memory mechanisms is assessed. The results reveal that the proposed cyclic memory mechanism provides consistently more accurate predictions than the corresponding penetration-based approach, offering a promising option for modelling friction fatigue in vibratory driving. This study advances our understanding of friction fatigue in the context of vibratory driving for offshore monopile installation, emphasizing the need for further numerical and experimental works in this topic.

Current offshore wind turbine installation and positioning methods require mechanical equipment attached on the lifted components and human intervention. The present paper studies the development of a contactless motion compensation technique by investigating a magnetically controlled pendulum. The technique involves the interaction of a magnetic pendulum with an electromagnetic actuator. Two control modes are considered: the imposition of a desired motion to the mass and the motion attenuation of a prescribed pivot excitation. The numerical model is validated and calibrated against experiments and demonstrates excellent predictive capabilities. The control exerted is effective for a broad range of excitation frequencies and amplitudes. Important parameters associated with the performance of the technique such as the separation distance of the magnets and the saturation of the controller are identified. The controllability regions for effective control depending on the characteristics of the excitation are derived. The force amplitude of the contactless actuator is comparable to currently-used active tugger line control systems, but with the additional advantage of both attractive and repulsive forces. The findings of this paper illuminate the path for the further development of a non-contact control technique which has the potential to increase the efficiency of offshore wind installations.