With the rapid development of offshore renewable energy technologies, open source solvers for hydrodynamic analysis can become beneficial to meet the numerical challenges within the field, particularly when they are both accurate and computationally efficient. Hydrodynamic Analysis of Marine Structures (HAMS), a recently developed open source Boundary Integral Equation Method (BIEM) frequency domain solver has been shown to be a reliable, robust and computationally efficient for analysing single floating structures. This research enhances the capabilities of HAMS further by developing and incorporating a multiple body interaction formulation (henceforth referred as HAMS-MREL), which allows the solution of the diffraction and the radiation problem for multiple floating structures, taking into account their interaction. To evaluate proper performance of this new multi-body solver, comparisons are performed with semi-analytical solutions, as well as with the commercial solver WAMIT in terms of the hydrodynamic coefficients and exciting forces. The excellent comparison with semi-analytical solutions demonstrates the validity of the enhanced multi-body version of HAMS. In addition, the computational comparison considering lower order panels between HAMS-MREL and WAMIT (no symmetry) show that for deep water cases, HAMS-MREL is generally faster than WAMIT, while for the finite depth cases, it is slower. Finally, the functionality to utilize OpenMP parallelization within the multi-body formulation has been added, aiming to reduce the analysis time significantly for the finite depth cases, offering an expected improvement for the future.

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The paper presents a monolithic finite element model for the hydro-visco-elastic analysis of floating membranes interacting with ocean waves. The formulation couples linearised potential flow and viscoelastic membrane equations, offering a versatile tool for modelling arbitrarily shaped floating membranes in varying sea-bed topography. The paper also presents a wet modal analysis for the coupled problem, accounting for the added mass and stiffness of the surrounding fluid. This model is used to study the dependence of the wet natural frequencies of floating membranes on the material properties. It is also used to analyse the reflection, transmission, scattering and absorption of ocean wave energy by 1D and 2D floating membranes. Notably, the paper underscores the impact of proportional material damping on these observed phenomena. The results highlight local peaks in the viscoelastic behaviour at the calculated wet natural frequencies, and demonstrate the outward dispersion of incoming wave around finite 2D membranes. Furthermore, the model is employed to examine the interaction of viscoelastic membranes with other structures, such as a monopile, under the influence of ocean waves. This comprehensive investigation contributes to a deeper understanding of the fluid–structure interaction inherent to certain floating solar, wave-energy converter and floating breakwater technologies.@en

The increasing demand for renewable energy sources is driving a significant rise in the adoption of offshore wind energy. Offshore wind turbines are typically supported by large foundation piles driven into the seabed. The primary method of installation is by hydraulic impact hammers. However, this method generates excessive underwater noise among other drawbacks. Consequently, alternative techniques are being explored by both researchers and industry. One promising alternative is vibratory driving, which theoretically produces less underwater noise compared to impact driving. Nevertheless, there remains a substantial amount of energy transmitted into the water column, particularly from the higher harmonics of the driving frequency. While energy at the fundamental frequency is essential for efficient driving, the energy associated with higher harmonics does not contribute to this efficiency and can significantly increase radiated underwater noise. To address this issue, this study proposes a mitigation strategy to block energy transfer at super-harmonic frequencies in the pile-water-soil system. To selectively target these frequencies without affecting the fundamental one, a mitigation approach utilizing locally-resonant metamaterials is proposed. This involves integrating a transition piece between the vibratory hammer and the pile, that incorporates periodically inserted multiple-degrees-of-freedom systems. By manipulating the natural frequencies of these periodic inclusions, the transition piece forms band-gaps at the relevant super-harmonics. Initial findings indicate that this design has the potential to effectively mitigate noise and vibration at targeted frequencies. Nonetheless, further investigations employing more sophisticated models are necessary to confirm these outcomes.@en

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.

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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.

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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.

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The Hyperloop, a developing transportation system, reduces air resistance by housing the vehicle within a depressurized tube and eliminates contact friction by using an electro-magnetic suspension/levitation system. Maintaining system stability poses a challenge due to the exceptionally high target velocities. Consequently, it is important to know apriori the velocity regimes in which the system can be unstable. The authors have recently investigated this aspect by, unlike previous studies, properly accounting for the frequency and velocity dependent reaction force provided by the infinite guideway. Furthermore, that study focused on the interplay between two fundamentally different instability sources, namely (i) the electro-magnetic suspension, and (ii) wave-induced instability, showing that stability domains drastically change above a certain vehicle velocity. The current study presents a methodology to distinguish the contribution of each instability mechanism to the overall system stability, and demonstrates that the wave-induced instability mechanism is causing the drastic stability change at large vehicle velocities. This investigation offers physical insight into the mechanisms that can cause instability in the Maglev/Hyperloop systems, and can help engineers that develop this novel transportation system to avoid excessive vibrations and, in extreme cases, derailment.@en

In recent times, railway transportation has received increasing attention, particularly for its ability to operate entirely on electricity sourced from renewable sources. However, the growing demand for railway services has transformed previously acceptable issues into significant challenges, disrupting normal traffic operations. One such issue is ground-borne vibration especially in urban and inter-urban locations. This study explores the efficacy of a novel mitigation technique, termed a "metawedge," in reducing ground-borne vibration at the receiving end. The metawedge consists of a series of periodically arranged barriers that act as resonators. Unlike traditional metamaterials, each resonator within the metawedge possesses slightly different natural frequencies compared to its neighbours. With an appropriate choice of this variation, incoming Rayleigh (surface) waves are converted into body waves, redirecting energy deeper into the ground. Simulation results demonstrate that the metawedge can significantly diminish vibration levels with just a few resonators. Additionally, unlike conventional single trenches, which effectively mitigate vibrations only at specific angles of incoming waves (outside the critical cone), the metawedge remains efficient within this cone. While a theoretical proof-of-concept has been previously presented by the authors, this study makes a step forward by proposing a realizable design. Consequently, this work showcases the potential and feasibility of metamaterials to address present and future challenges in railway transportation.@en

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.

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The paper presents a monolithic finite element model for the hydro-visco-elastic analysis of floating membranes interacting with ocean waves. The formulation couples linearised potential flow and viscoelastic membrane equations, offering a versatile tool for modelling arbitrarily shaped floating membranes in varying sea-bed topography. The paper also presents a wet modal analysis for the coupled problem, accounting for the added mass and stiffness of the surrounding fluid. This model is used to study the dependence of the wet natural frequencies of floating membranes on the material properties. It is also used to analyse the reflection, transmission, scattering and absorption of ocean wave energy by 1D and 2D floating membranes. Notably, the paper underscores the impact of proportional material damping on these observed phenomena. The results highlight local peaks in the viscoelastic behaviour at the calculated wet natural frequencies, and demonstrate the outward dispersion of incoming wave around finite 2D membranes. Furthermore, the model is employed to examine the interaction of viscoelastic membranes with other structures, such as a monopile, under the influence of ocean waves. This comprehensive investigation contributes to a deeper understanding of the fluid–structure interaction inherent to certain floating solar, wave-energy converter and floating breakwater technologies.@en

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.

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The railway transition zone where the track transitions from a ballasted track to a slab track, is a crucial area that can experience amplified dynamic responses. This work aims to develop a deeper insight into the mechanisms leading to the amplified dynamic response in railway transition zones. The study employs a finite element model to investigate the amplification of total strain energy due to the phenomena of reflection and redistribution of energy close to the transition interface. The results of the study are obtained for three case studies involving non-reflecting boundary (representing an energy sink) and homogeneous material along the vertical direction of the track, and the responses are studied for individual and combined effects in comparison to a benchmark case. The findings of the study show that eliminating the phenomena results in no dynamic amplification in total strain energy in railway transition zones. The conclusion highlights the importance of understanding these phenomena in order to design an efficient railway transition structure.@en

Wave energy has immense potential and can provide at least twice as much electricity as globally produced now due to its high energy density. Apart from the vast accessibility of the resource, waves are more predictable and available throughout the year when compared to other forms of renewable energies. This makes the development and utilization of wave energy tech-nologies immensely important, in order to meet the renewable energy targets, an example of which is the 40GW by 2050 set as the offshore energy strategy of the European Commission. For wave energy to become a commercially viable power source, in-dividual wave energy converters (WECs) need to be deployed in large numbers similar to what can be seen in the wind in-dustry. Therefore, numerical tools simulating multiple inter-acting devices becomes highly relevant. This research utilizes the new open-source Boundary Element Method (BEM) based solver HAMS-MREL to analyse the hydrodynamic interactions of mono-array farms of point absorbers inspired by the state-of-the-art Corpower C4 point absorber device in various configurations subjected to waves in different directions. The obtained responses are used to estimate the power absorbed by the arrays in different configurations to obtain the Array Power Matrices, which can be used to study the variability of the q-factors in different sea states and different directions. Furthermore, the obtained Array Power Matrices are used to estimate the power absorbed by the array configurations in the North Sea. This can be a powerful tool for the analysis of the best wave energy farm configurations as it employs a computationally efficient frequency domain-based solver.@en

The Hyperloop, a developing transportation system, reduces air resistance by housing the vehicle within a depressurized tube and eliminates contact friction through an electro-magnetic suspension/levitation system. Maintaining system stability poses a challenge due to the exceptionally high target velocities. The interplay between electro-magnetic and wave-induced instability has been previously studied by the authors, showing that stability domains drastically change above a certain vehicle velocity. The current study demonstrates that the anomalous Doppler waves (i.e., wave-induced instability) are causing this drastic change. This investigation offers physical insight into the mechanisms that can cause instability in the Hyperloop system.@en

With the rapid development of offshore renewable energy technologies, open source solvers for hydrodynamic analysis can become beneficial to meet the numerical challenges within the field, particularly when they are both accurate and computationally efficient. Hydrodynamic Analysis of Marine Structures (HAMS), a recently developed open source Boundary Integral Equation Method (BIEM) frequency domain solver has been shown to be a reliable, robust and computationally efficient for analysing single floating structures. This research enhances the capabilities of HAMS further by developing and incorporating a multiple body interaction formulation (henceforth referred as HAMS-MREL), which allows the solution of the diffraction and the radiation problem for multiple floating structures, taking into account their interaction. To evaluate proper performance of this new multi-body solver, comparisons are performed with semi-analytical solutions, as well as with the commercial solver WAMIT in terms of the hydrodynamic coefficients and exciting forces. The excellent comparison with semi-analytical solutions demonstrates the validity of the enhanced multi-body version of HAMS. In addition, the computational comparison considering lower order panels between HAMS-MREL and WAMIT (no symmetry) show that for deep water cases, HAMS-MREL is generally faster than WAMIT, while for the finite depth cases, it is slower. Finally, the functionality to utilize OpenMP parallelization within the multi-body formulation has been added, aiming to reduce the analysis time significantly for the finite depth cases, offering an expected improvement for the future.@en

Railway transition zones are the most critical part of the railway infrastructures that experience 4-8 times more degradation compared to open tracks. Despite several attempts to reduce the maintenance and operation costs in these critical zones, a robust and comprehensive solution remains unknown. In recent studies, a robust safe hull inspired energy limiting design of a transition structure was proposed for an embankment-bridge transition (without ballast layer over the bridge) to deal with operation-induced degradation. However, this solution was investigated in detail for only this particular type of transition. In this work, the scope of this mitigation measure is extended for an embankment-bridge transition with ballast running over the bridge and its performance is evaluated using a strain-energy criterion. It was concluded in the end that the safe hull inspired energy limiting design can effectively mitigate the operation-induced dynamic amplification for more than one type of railway transition zones. @en

The Oscillating Water Column (OWC) wave energy converter has been shown to have high potential, thus rendering extensive development in recent years. In order to further accelerate its development, highly accurate yet computationally efficient tools are necessary particularly when studying the interaction of multiple OWC devices. This paper proposes a new framework for fixed OWC devices with an orifice, that uses the input from a high fidelity non-linear numerical model to improve the accuracy of a low fidelity linear numerical model keeping computational costs low. This is done by accounting for the non-linearities in the pressure-flow of an orifice in the input to the linear numerical model. Experimental data is used to validate the framework, thus providing an accurate and computationally efficient linear numerical model, that can be used for the preliminary analysis of fixed OWC devices.@en

Railway transition zones present a major challenge in railway track design mainly due to abrupt jumps in stiffness and differential settlements that result from crossing stiffer structures such as bridges or culverts. Despite numerous efforts to mitigate these transition effects at both the superstructure and substructure levels, a comprehensive solution remains elusive. Substructure-level interventions have demonstrated some effectiveness but are often cost-prohibitive and challenging to implement in existing operational railway transition zones. In contrast, mitigation measures at the superstructure (rail, sleepers, rail-pads, under-sleeper pads) level can be easily installed but have shown limited improvement in site measurements. This study evaluates the influence of different sleeper configurations in transition zones and reduced sleeper spacings on the operation-driven dynamic amplifications in railway transition zones, employing a recently proposed criterion based on the total strain energy in the track-bed layers (ballast, embankment, and subgrade). In addition to this, the influence of the loss of contact between sleepers and ballast (i.e., hanging sleepers), which typically results from the differential settlement, is studied. The first part of the paper provides useful insights regarding the interventions (and/or initial design) in the sleeper configuration and spacing, whereas the second part of the work highlights the need for interventions to deal with the loss of contact between sleeper and ballast. A 2-dimensional finite element model of an embankment-bridge transition was used for the analysis. The results show that it is not possible to mitigate the transition effects completely using the interventions involving sleeper spacing and configuration.@en

Railway transition zones (RTZs) are regions where abrupt track stiffness changes occur that may lead to dynamic amplifications and subsequent track deterioration. The design challenges for these zones arise due to variations in material properties in both the depth (trackbed layers composed of different materials) and longitudinal directions of the track, as well as temporal variations in mechanical properties of materials due to several external factors over the operational period. This research aims to investigate the effects of these variations in material properties (i.e., of the resulting stiffness distributions in vertical and longitudinal directions) on the behaviour of RTZs, assess from this perspective the performance of a novel transition structure called the SHIELD, and establish a methodology for designing a robust solution to mitigate the dynamic amplifications in these zones. Results indicate that stiffness variations in both vertical and longitudinal directions significantly influence the dynamic behaviour of the RTZs. The study also suggests a permissible range of stiffness ratios to control the amplification of strain energy in the most critical components of RTZs, both in the initial state as well as during the operational phase (where material properties may vary over time). Moreover, the proposed methodology offers a valuable tool for the design and evaluation of RTZs and is applicable to various transition types and a broad spectrum of material properties.@en

This paper presents a new shaker design for the Gentle Driving of Piles method. Specifically, a lab-scale vibratory device has been developed that can simultaneously apply axial and torsional vibrations, both possessing frequency-amplitude decoupling. This design was implemented and tested in a lab-scale experimental campaign, where both pile and soil were extensively instrumented. The monitoring of the dynamic pile and soil behaviours during driving with various installation settings is of utmost importance to comprehend the governing mechanisms of the process. In that manner, the optimization of pile installation may be realized both for axial vibratory driving and GDP. In this work, the frequency-amplitude decoupling is pivotal, as it is showcased that both enhanced installation performance and reduced power consumption can be attained with proper selection of the installation settings and exploitation of high-frequency torsion.

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