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.

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.

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.

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.

Impact pile driving is a transient anthropogenic underwater sound source that can potentially affect marine life. Mathematical modelling tools are essential for predicting sound levels before installing new offshore wind farms. Different modelling approaches are required for modelling the sound generation in proximity to the pile, the mitigation of the noise with the use of air-bubble curtains, and the sound propagation at a larger distance. In addition, the interface and coupling between the different modelling approaches should be carefully considered without losing important details. In this work, a multi-model approach for estimating pile-driving sound in a realistic environment is described. The shortrange predictions (up to 750 m) provide detailed spectral and temporal output in various metrics in the water (acoustic pressure, particle velocity) and the seabed (stress and displacement vectors). For the long-range predictions beyond 750 m, only the acoustic pressure metric is calculated, including the range-dependent properties of the acoustic environment. Based on the combination of short- and long-range models, sound maps can be created to identify the contribution of the pile driving to the underwater soundscape.

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.

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.

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.