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 deployment of Offshore Wind Turbines (OWTs) necessitates larger steel monopiles, whose design currently includes additional steel to account for fatigue damage during installation. Traditional contact-based sensors, such as strain gauges and accelerometers, are challenging to deploy in offshore environments and are susceptible to damage under high stress. To overcome these limitations, a novel non-contact sensor system has been developed, utilizing the magnetomechanical effect to measure strain and an optical method to measure velocity. This paper presents the results of a test series using a full-scale impact hammer on a thin-walled steel pile, comparing the new system’s performance to a conventional Pile Driving Analyzer (PDA). Sources of error in the non-contact sensor measurements were identified, and post-processing techniques were applied to obtain acceptable time signals. Despite some residual errors, the system effectively captured strain and velocity behaviour. These findings demonstrate the feasibility of contactless monitoring for steel structures subjected to impact pile driving, representing a promising step toward more efficient and cost-effective monopile 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.

This paper presents the development and testing of a lab-scale Gentle Driving of Piles (GDP) shaker. Conventional impact piling for offshore monopile installation faces challenges due to noise regulations and its adverse marine environmental impacts. The GDP method, which integrates high-frequency torsional vibrations with low-frequency axial vibrations, aims to mitigate these issues. In this work, a new GDP shaker is designed and tested to enhance vibratory pile driving by independently controlling torsional and vertical vibration amplitudes and frequencies. Laboratory tests were conducted using the newly designed shaker for pile driving in sandy soil to evaluate its performance. The results indicate a significant reduction in power consumption and improved pile drivability with high-frequency, low-amplitude torsional vibrations. This study highlights the importance of optimizing dynamic inputs for enhanced pile penetration and reduced environmental impact, showcasing the potential of the GDP method as a promising alternative to traditional impact piling techniques.

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.

To monitor the growth of fatigue cracks in steel specimens, several methods exists. In this paper, the magnetic stray field, which is generated by the magnetisation of the specimen, was measured during loading to investigate how to utilise this data to reliably monitor fatigue crack initiation and growth. Data was collected in a series of fatigue tests on Compact Tension specimens with different force ratios. The evolution of the mean value of the dominant stray field component displayed a sensitivity to stress, plastic deformation and displacement of the specimen. By analysing the stress field induced by the loading, these three causes were distinguished from another. Crack initiation was marked by a large change of the mean magnetic stray field. Moreover, the amplitude of the magnetic stray field components showed a clear peak, at which moment 20% of the life time of the specimen is remaining, indicating that the magnetic stray field might provide a useful method to monitor the evolution of fatigue cracks.

Europe has set an ambitious target to increase the offshore wind power capacity to approximately 30 GW by 2026. With nearshore locations already allocated, future wind farms must be installed in deeper waters, pushing the operational limits of currently used jack-up vessels. Utilizing existing floating heavy-lift vessels presents a viable alternative. This paper disseminates data gathered during the full-scale testing campaign of a floating installation of an offshore wind turbine tower. For this purpose, novel time-synchronized motion-tracking units were developed. Analysis of the obtained data reveals that approximately 96% of the motion response of the tower is due to wave action and 3% to vortex-induced vibrations caused by the presence of a passive tugger line, which shifted one of the system's natural frequencies towards the tower's vortex-shedding frequency. Next to wind and wave-induced motion, the data reveal that the hoisting itself induces tower vibrations, accounting for less than 1% of the tower motion response. The collected data offer a distinctive perspective on this type of installation, which is unlikely to be replicated at model scale due to the scaling limitations associated with the interdependence of waves and wind. The data can be used to validate motion control strategies to enhance the efficiency, safety, and workability of floating offshore wind turbine installations.

To study the irreversible changes in the magnetic stray field surrounding a steel structure caused by impact-induced elastic and plastic deformations, a steel cylinder was repeatedly subjected to axial impacts of various magnitudes. Due to impacts that induce elastic deformation, the measured magnetic stray field of the structure converges to a global magnetic equilibrium. However, as soon as plastic deformation develops, a deviation from this trend is observed. From the spatial distribution of the stray field, the location of the plastic deformation is determined. Subsequently, the underlying processes of the measured evolution of the stray field are discussed and successfully incorporated into an elementary model of the structure's magnetisation to simulate the results from the experiment. It is expected that the reported observation is useful for a class of engineering applications in which non-contact and non-collocated measurements can be utilised to identify structural damage under dynamic loading.

Recent developments in the construction of offshore wind turbines have created the need for a method to detect whether a monopile foundation is plastically deformed during the installation procedure. Since measurements at the pile head are difficult to perform, a method based on measurements at a certain distance below the pile head is proposed in this work for quantification of the amount of plasticity. By considering a onedimensional rod model with an elastic-perfectly plastic constitutive relation, it is shown that the occurrence of plastic deformation caused by an impact load can be detected from these measurements. Furthermore, this plastic deformation can be quantified by the same measurement with the help of an energy balance. The effectiveness of the proposed method is demonstrated via a numerical example.

The use of bolted connections between the tower and a support structure of an offshore wind turbine has created the need for a method to detect whether a monopile foundation plastically deforms during the installation procedure. Small permanent deformations are undesirable, not only because they can accelerate fatigue of the structure; but also because they can lead to misalignment between the tower and the foundation. Since direct measurements at the pile head are difficult to perform, a method based on non-collocated strain measurements is highly desirable. This paper proposes such a method. First, a physically non-linear one-dimensional model is proposed, which accounts for wave dispersion, effects that are relevant for large-diameter piles currently used by the industry. The proposed model, combined with an energy balance principle, gives an upper bound for the amount of plastic deformation caused by an impact load based on simple strain measurements. This is verified by a lab-scale experiment with a uni-axial stress state. Second, measurement data collected during pile driving of a large-diameter pile show that the proposed one-dimensional model, while able to predict the peak stresses, fails to accurately predict the full time history of the measured stress state. In contrast, an advanced model based on shell membrane theory is able to do that, showing that a bi-axial stress state is needed for these type of structures. This requires an extension of the theory for plasticity quantification presented in this paper.