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.

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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

Underwater noise from offshore pile driving has raised significant concerns over its ecological impact on marine life. To protect the marine environment and maintain the sustainable development of wind energy, strict governmental regulations are imposed. Assessment and mitigation of underwater noise are usually required to ensure that sound levels stay within the noise thresholds. The air-bubble curtain system is one of the most widely applied noise mitigation techniques. This paper presents a multi-physics approach for modeling an air-bubble curtain system in application to offshore pile driving. The complete model consists of four modules: (i) a compressible flow model to account for the transport of compressed air from the offshore vessel to the perforated hose located in the seabed; (ii) a hydrodynamic model for capturing the characteristics of bubble clouds in varying development phases through depth; (iii) an acoustic model for predicting the sound insertion loss of the air-bubble curtain; and (iv) a vibroacoustic model for the prediction of underwater noise from pile driving which is coupled to the acoustic model in (iii) through a boundary integral formulation. The waterborne and soilborne noise transmission paths are examined separately, allowing us to explore the amount of energy channeled through the seabed and through the bubble curtain in the water column. A parametric study is performed to examine the optimal configuration of the double bubble curtain system for various soil conditions and pile configurations. Model predictions are compared with measured data. The model allows for a large number of simulations to examine different configurations of a single bubble curtain and a double big bubble curtain@en

This paper presents a computationally efficient modeling approach for predicting underwater noise radiation from offshore pile driving. The complete noise prediction model comprises two modules. First, a sound generation module is adopted to capture the interaction between the pile, the fluid, and the seabed, aiming at modeling the sound generation and propagation in the vicinity of the pile. Second, a sound propagation module is developed to propagate the sound field at larger distances from the pile. To couple the input wavefield obtained from the sound generation module, the boundary integral equations (BIEs) are formulated based on the acousto-elastodynamic reciprocity theorem. To advance the mathematical formulation of the BIEs, the Green's tensor for an axisymmetric ring load is derived using the complex wavenumber integration technique. The model advances the computational efficiency and flexibility of the noise prediction in both near-and far-fields from the pile. Finally, model predictions are benchmarked against a theoretical scenario and validated using measurement data from a recent offshore pile-installation campaign.

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The prediction of underwater noise and the assessment of the influencing factors on noise transmission are significant for the control and mitigation of the noise generated by offshore pile driving. This paper presents a coupled two-step approach for modelling the underwater noise from offshore pile driving, with the focus being placed on examining the influence of the seabed conditions on the near- and far-field sound propagation. The complete model consists of a near-source module and a far from source module. The near-source module captures the coupled vibroacoustic behaviour of the pile and its surrounding fluid and layered soil media. With the input obtained from near-source module, the far-from-source module propagates the sound field at larger distances. The two modules are coupled by applying the boundary integral method. A parametric study is performed to investigate the influence of the seabed properties on the noise levels and the energy distribution at various horizontal distances from the pile. An energy flux analysis is performed by examining the total energy radiated through the cylindrical surface at target distances from the pile. As waves propagate away from the pile, the through-depth distribution of the energy in both seawater and sediment alters. The results indicate the characteristics of noise transmission and energy distribution with respect to different soil conditions; an analysis which is key to the development of effective noise mitigation strategies.@en

Underwater noise pollution generated by offshore pile driving has raised serious concerns over the ecological impact on marine life. To comply with the strict governmental regulations on the threshold levels of underwater noise, bubble curtains are usually applied in practice. This paper examines the effectiveness of an air bubble curtain system in noise reduction for offshore pile driving. The focus is placed on the evaluation of noise transmission paths, which are essential for the effective blockage of sound propagation. A coupled two-step approach for the prediction of underwater noise is adopted, which allows us to treat the waterborne and soilborne noise transmission paths separately. The complete model consists of two modules: a noise prediction module for offshore pile driving aiming at the generation and propagation of the wave field and a noise reduction module for predicting the transmission loss in passing through an air bubble curtain. With the proposed model, underwater noise prognosis is examined in the following cases: (i) free-field noise prediction without the air bubble curtain, (ii) waterborne path fully blocked at the position of the air bubble curtain while the rest of the wave field is propagated at the target distance, (iii) similarly to (ii) but with a non-fully blocked waterborne path close to the seabed, and (iv) air bubble curtain modeled explicitly using an effective medium theory. The results provide a clear indication of the amount of energy that can be channeled through the seabed and through possible gaps in the water column adjacent to the seabed. The model allows for a large number of simulations and for a thorough parametric study of the noise escape when a bubble curtain is applied offshore.

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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

This paper presents a computationally efficient modelling approach for the prediction of underwater noise radiation from offshore pile driving. A near-source module is adopted to capture the interaction between the pile, fluid and soil, which is based on a previously developed semi-analytical vibro-acoustic model. This module primarily aims at modelling the sound generation and propagation in the vicinity of the monopile. The Green's tensor for an axisymmetric ring source in a horizontally stratified acousto-elastic half-space emitting both compressional and shear waves is derived using the normal modes and branch line integrations. The boundary integral equations are then formulated based on the reciprocity theorem, which forms the mathematical basis of the far-from-source module for the propagation of the wave field at large radial distances. The complete noise prediction model comprises the two modules, which are coupled through the boundary integral formulation with the input obtained from the near-source module. Model predictions are benchmarked against measurement data from an offshore installation campaign.@en

A model is developed to predict bending vibrations of flood gates with fluid on both sides. The liquid flow is three-dimensional and the gate is represented as a thin plate. The fluid response is considered within the linear potential flow theory including the effect of compressibility and the generation of free surface waves. This way, the hydrodynamic fluid pressure exerted on the gate is predicted accurately in both low and high-frequency regimes. Both the structural and fluid responses are expressed in the modal domain as a superposition of modes. A semi-analytical solution of the fluid-interaction problem is obtained by describing the complete system in terms of in vacuo gate modes, which is computationally efficient compared to existing numerical methods. This allows for the accurate prediction of flood gate vibrations for a large number of simulations, making it possible to perform fatigue calculations and probabilistic evaluations. The case of a typical flat flood gate subjected to an impulsive wave impact is studied with the developed model. Results show the capability of the model to efficiently quantify flood gate vibrations considering the involved fluid-structure interaction, which can lead to more economical designs compared to common engineering practice.@en

In this paper, a pile-water-soil model is developed for the prediction of sound generated due to impact piling. The complete model consists of two modules: i) a near-source module aiming at the accurate description of the pile-water-soil interaction together with the sound generation and propagation in the vicinity of the pile; and ii) a far-from-source module aiming at the propagation of the wave field at larger distances. The input to the far-from-source module is provided by the near-source module through a boundary integral formulation. @en

Anthropogenic underwater noise generated by pile driving has been an issue of serious concern due to the rapid developments in offshore wind farms. The underwater noise pollution poses a threat to marine mammals. To reduce the noise, many offshore companies have developed various mitigation measures and alternatives to impact piling. One of them is the use of underwater acoustic resonators around the foundation pile. In this paper, a three-dimensional vibroacoustic model is developed in order to find the optimal configuration of the underwater acoustic resonator system and to improve the existing noise reduction potential. The model requires the proper description of the noise source, the resonator and the acoustic domain surrounding the pile. To describe the acoustic performance of the resonators for a more generic use, the frequency response function of an open-ended resonator is analytically derived based on the assumption that the resonator behaves as a linear Single-Degree-of-Freedom (SDoF) system. The derivation of the parameters of the equivalent SDoF system representing each individual resonator is based on appropriate fitting of numerical results obtained in COMSOL for a wide class of parameters. The Boundary Element Method (BEM) is then employed for determining the total pressure field in the acoustic domain in the process of pile driving accounting for the presence of multiple resonators. In this work, noise sources are represented by a distributed array of phased point sources which reproduce adequately the source of the noise field. In addition, a parametric study is presented in order to define the principal factors yielding effective noise mitigation and to obtain the optimal configuration on the predicted sound levels at the low-frequency range.@en