Underwater noise pollution during the installation of foundation piles offshore using large impact hammers can adversely affect marine fauna. In recent years, several vibratory techniques have been developed to drive large foundation piles offshore. One promising technology is called the gentle driving of piles (GDP). This technology uses a combination of high-frequency torsional excitation together with low-frequency vertical excitation at the pile head to drive the pile into the marine sediment. To date, most of the modelling developments have focused on the installation process with this new method, i.e., the development of the so-called driveability models. This paper discusses the underwater noise that is generated during the installation of piles using the GDP method. A case study is analyzed using experimental data to identify the excitation forces at the top of the pile. The prediction of the noise is then investigated using a linear vibroacoustic model in two cases: the classical installation with vertical excitation alone and the installation by means of the GDP method. The differences between the two methods are highlighted, and some conclusions are drawn that can be of added value for practitioners in the field.@en

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.

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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 installation of foundation piles for offshore wind turbines using traditional hydraulic impact hammers raises concerns about the impact of underwater noise on marine life. To address this issue, the offshore wind industry investigates the use of alternative driving techniques, such as vibratory pile installation, to reduce sound levels and expedite installation. This paper discusses a method for modelling underwater sound generated in vibratory piling and presents sound maps of broadband sound levels. The complete model comprises sub-models, including the generation of the source field and the propagation of the sound in range-dependent shallow water environments. The sound source model utilizes a non-linear three-dimensional pile–soil-water modelling framework tailored for vibratory pile installation in layered media, capturing the coupled pile-soil-water interaction at the source. The sound propagation model employed for generating sound maps is a normal mode model, designed to simulate propagation loss in range-dependent acousto-elastic half-spaces of varying bathymetry. The paper concludes with the theoretical case study of underwater noise emission from vibratory pile installation in the North Sea. Numerical simulations with the adopted modelling framework can be used by marine biologists to assess the environmental impact of underwater sound on marine species.@en

Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). After presenting the development of a purpose-built GDP driving device and the geotechnical characterisation of the site, this paper covers the execution of GDP installation tests. Focus is on the installation performance of GDP-driven piles, which is discussed with the aid of structural and ground monitoring data. The comparison between piling data associated with GDP and standard axial vibro-driving points out the potential of the proposed installation technology, particularly with regard to the beneficial effect of the torsional vibration component. The findings of this study encourage further development of the GDP method and its future extension to offshore full-scale conditions.

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Due to the growing demand in offshore wind, increasing numbers of foundation piles are planned to be installed in the coming decades. Monopiles driven by impact hammers have a large environmental impact on aquatic life. Vibratory pile driving is a promising alternative that generates less noise nuisance. Despite the lower levels of noise expected, modeling of noise radiation from vibratory piling is still required due to the large size of the foundation piles used nowadays and the changes in the radiated spectrum of the noise. The existing models used to assess the noise emission are calibrated against impact piling and are not accurate when it comes to noise radiation from vibratory installation. Existing models either represent the sediment as an acoustic fluid or, when the seabed is modelled as elastic medium, they couple the soil and pile displacements fully at their interface. The effect of both these assumptions on the radiated noise still needs to be verified in vibratory pile installation. Additionally, the effect of the secondary noise path, i.e. noise channeling into the seawater via the soil, is expected to play a more significant role in vibratory pile driving because more energy is concentrated at the lower frequencies. In this paper, a pile-water-soil model to predict the noise emission due to vibratory pile driving is developed which describes the soil as an elastic medium and allows the pile to move relative to the soil during the pile driving process. To maintain a computationally efficient solution method, the effect of friction is linearized via a spring connection between soil and pile. Finally, a study is conducted and the effect of the slip on the noise emission is studied in detail for the first time.

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The growing interest in offshore wind leads to an increasing number of wind farms planned to be constructed in the coming years. Installation of these piles often causes high underwater noise levels that harm aquatic life. State-of-the-art models have problems predicting the noise and seabed vibrations from vibratory pile driving. A significant reason for that is the modeling of the sediment and its interaction with the driven pile. In principle, linear vibroacoustic models assume perfect contact between pile and soil, i.e., no pile slip. In this study, this pile-soil interface condition is relaxed, and a slip condition is implemented that allows vertical motion of the pile relative to the soil. First, a model is developed which employs contact spring elements between the pile and the soil, allowing the former to move relative to the latter in the vertical direction. The developed model is then verified against a finite element software. Second, a parametric study is conducted to investigate the effect of the interface conditions on the emitted wave field. The results show that the noise generation mechanism depends strongly on the interface conditions. Third, this study concludes that models developed to predict noise emission from impact pile driving are not directly suitable for vibratory pile driving since the pile-soil interaction becomes essential for noise generation in the latter case.@en

This paper presents a computationally efficient mode-matching method to predict the relative axial motion of two elastic rods in frictional contact. The motion is of the stick-slip type and is non-uniform along the rods. The proposed method utilizes the piecewise linearity of the problem in time and space. The original set of nonlinear partial differential equations describing the dynamics of the coupled system is first reduced to a system of linear, per time interval, ordinary differential equations by means of modal decomposition. The global modes are used for one of the two rods, while for the other rod, different modes are identified per time interval based on the regions in stick or slip phase. Subsequently, the system response is obtained by combining the piecewise linear solutions. A comparison of the solution method proposed with standard numerical techniques shows its advantage both in terms of computational time and accuracy. Numerical examples demonstrate the capability of the method to analyse cases involving either harmonic- or impact-type forces that drive the relative motion. Although the discussion in this paper is limited to the one-dimensional configuration, the approach is generic and can be extended to problems in more dimensions.

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In the original publication, Eqs. (11) and (17) are published incorrectly, and this has been corrected as follows: (Formula presented.) The original article has been revised.

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The paper establishes a computationally inexpensive method to deal with the dynamic response of liquid storage tanks subjected to seismic excitation including dynamic soil-structure interaction. The tank is modelled as a thin shell, the stored liquid is described asan inviscid and incompressible fluid and the soil medium is modelled as an elastic continuum.The dynamic response of the tank-liquid-soil system is derived in the frequency domain usingdynamic substructuring and mode matching. The tank vibrations are first expressed in terms ofthe in-vacuo shell modes while the liquid motion is described as a superposition of linear po-tentials. The soil reaction to the plate of the tank is derived on the basis of a boundary integralformulation with the excitation field being the seismic free-field ground motion. Due to its highcomputational efficiency, the proposed method is suitable when a large number of simulations isrequired as is the case in seismic risk analysis. It overcomes the limitations of most mechanicalanalogues used nowadays, while at the same time maintains an accuracy comparable to that offinite element models within a fraction of the computation time of the latter.@en

In this paper, a new model is developed to describe the nonlinear dynamics of twoaxially deformable bars sliding relative to each other in which the interaction is governed byfriction. The first bar is fixed at one end and is subjected to a distributed normal force perpen-dicular to its axis to activate friction at the common interface, while the second bar is allowed toslide relative to the fixed one. A semi-analytical solution method is developed in which only thenonlinear interaction is addressed numerically. The dynamic behaviour of the bars is expressedas a summation of vibration modes including the necessary rigid body mode to allow for thepermanent sliding of one bar relative to the other. This results in a computationally efficientscheme without compromising the accuracy of the solutions. The developed model can be usedin pile driveability studies. In this case the fixed bar resembles the soil column while the secondbar describes the dynamics of the driven pile.@en

A novel pile-driving technique, named Gentle Driving of Piles (GDP), that combines axial low-frequency and torsional high-frequency vibrations has been developed and tested recently. During the experimental campaign, several piles were installed onshore, making use of the GDP shaker. Besides those, a number of additional piles were installed using conventional pile-driving techniques, i.e. impact piling and axial vibratory driving. After the completion of the installation phase, the installed piles have been subjected to impact hammer tests with the following goals. First, the in-situ dynamic properties of the pile-soil system have been identified. Second, the post-installation soil state has been investigated, along with its evolution in time for each pile driving scenario. Preliminary analyses, of the data collected during the impact tests show dissimilar trends in the overall dynamic response between the piles installed with impact hammer and those installed with the axial and the GDP shakers.This observation suggests a difference in the post-installation dynamic behaviour of the pile-soil systems related to different pile-driving techniques. In this paper, a first attempt is made to identify the differences in the overall pile-soil dynamic behaviour of the piles installed by means of the three different pile-driving techniques.

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