Collaboration to collect data for integrated offshore driveability and noise prediction modelling (COAX)

WHY

Hydraulic impact pile driving is currently the most widely used method for driving monopiles into the seabed. However, this method produces high underwater noise levels that can harm fauna. Therefore, alternative installation technologies are being investigated, developed and tested to deal with this concern. The project description of SIMOX provides additional background information about these new techniques.

To accelerate the development of these alternative installation techniques, a better understanding of their performance and validation of the underlying sound models is required. In this way, we can reduce the uncertainties in predicting the drivability and the relationship between the vibro-piling installation and the offshore underwater noise levels can be established. Less uncertainty will help the industry to design and implement the optimised vibrating drive equipment. It will also provide authorities with better information to develop appropriate regulations regarding noise emissions.

In the SIMOX project, the partners have decided to move from the initially planned nearshore testing to offshore testing. This offers us the opportunity to make use of the already planned offshore campaign in the SIMOX project at a relatively low cost and to collect good noise data.

WHAT

The COAX project aims to collect offshore piling data and associated data on underwater noise emission and vibrations of the seabed. In addition, we strive to bring the vibration driving technology to a higher Technology Readiness Level (TRL).

In this project, we develop an advanced near-field sound measurement system and an advanced pile instrumentation system that will be linked in the time domain, i.e. synchronous measurements of all physical quantities. We will be testing at various offshore locations to carry out more measurements, repeat tests and do more noise and ground vibration measurements during the pile driving. For the execution of the tests, we will purchase a pile with a more representative diameter/thickness ratio (D/T) of 60 to 70 which will be fully instrumented. This pile size represents XXL monopile dimensions more than the initially envisaged pile in the SIMOX project. This is particularly relevant for validating driving characteristics and noise prediction models.

EXPECTED RESULTS

This project will lead to the following three main results.

1. A high-quality time domain coupled data set enables us to see the correlation between pile driving parameters, pile response, seabed vibrations, and underwater noise emission.

This data set is invaluable because coupled vibrohammer-pile-underwater noise data obtained in typical offshore conditions with realistic pile dimensions are currently unavailable. In addition, for the first time, measurements of the seabed vibrations will be collected synchronously with the rest of the physical quantities (i.e. pile-hammer vibrations, acoustic pressures, etc.) and are expected to be particularly important given the relatively low frequencies involved in vibratory driving. This will also contribute to ecological impact models, in particular (future) models that (will) consider particle motion in addition to the underwater noise in the assessment process.

This data is an essential input for the integrated driving parameter and noise prediction model. The generated data set, together with the tuned prediction models (see point 3), are essential assets to understand the main mechanisms causing excessive underwater noise emission and seabed vibrations during vibratory installation. In practice, with this insight, the specific driving parameters that can lead to excessive noise can be avoided.

2. Measurements of underwater noise generated during pile extraction.

This dataset will be used to improve models for predicting underwater noise and seabed vibrations caused by pile extraction using vibro technology. To date, no validated model exists for modelling the noise emissions and seabed vibrations during pile extraction.

3. Obtained data will enable the validation of integrated models for underwater noise prediction.

Well-tuned and validated underwater noise prediction models provide insight into the main components that cause excessive noise emission during pile driving, such as piling parameters, soil conditions and bathymetry. The models will help the offshore wind industry accelerate the introduction of vibro-technology for installing and decommissioning of piles.