Growth through Research, development & demonstration in Offshore Wind
Installing offshore monopiles with impact hammers requires systems to reduce low-frequency noise, as this type of noise can harm marine life. Traditional noise reduction methods work well for frequencies between 500 Hz and 5 kHz, but their effectiveness drops for frequencies below 500 Hz. For example, bubble curtains — commonly used for noise mitigation — need large air bubbles to reduce low-frequency noise, which requires a lot of energy. Moreover, large bubbles are unstable and tend to break into smaller bubbles.
Combining different systems has been tried to improve low-frequency noise reduction, but these solutions are costly to install and operate. Additionally, current systems mainly focus on reducing the primary noise (sound waves travelling directly from the pile to the water) and overlook secondary noise (elastic waves travelling through the soil to the water).
Therefore, it is crucial to explore new designs targeting low-frequency noise to protect marine life and ensure efficient offshore wind farm installation. The entire Metacurtain project will focus on developing a lightweight, flexible metasurface to reduce low-frequency noise during pile-driving.
The Metacurtain project consists of three phases:
In this Metacurtain-1 project, we aim to create a numerical model for a system that reduces noise caused by sound waves travelling directly from the pile to the water. This system will feature an innovative metamaterial-based curtain with two key parts. The first part is for blocking low-frequency sound waves which are caused by monopile vibrations. It consists of a silicone-textile membrane containing air-filled cavities, or unit cells, created by injecting air from below (see blue membrane in Fig. 1). These cavities are arranged in a specific pattern to fit environmental conditions and achieve the desired level of noise reduction, especially for low frequencies. Different cavity shapes can be used to target various frequency ranges, improving noise reduction. The design also allows easy adaptation to reduce secondary noise (purple membrane in Fig. 1).
The design of the unit cells and the entire metacurtain will consider practical aspects like installation and operation. Models will be used to predict noise levels during pile driving, with and without the curtain, and tests will be conducted to compare the metacurtain’s effectiveness with other noise reduction systems.
We will use an existing model developed by TU Delft to assess how well the new metacurtain works and compare it to current systems. The curtain’s performance will also be tested under different environmental conditions, such as varying current speeds, to ensure it effectively reduces vibration and remains structurally sound. Once these aspects are confirmed, we will build a small-scale prototype and conduct tests in a controlled lab environment at TU Delft. The Maritime and Transport Technology Department in the Faculty of Mechanical Engineering has large tanks, and we recently tested another noise reduction system on a 2-meter monopile. We will reuse this monopile and the existing setup to demonstrate that the metacurtain concept works.
The project will be executed in close cooperation with Boskalis, Huisman, IQIP and Seaway7. The partners will share their experiences from the field with the current noise mitigation systems and the challenges they anticipate in the low frequency domain. Their expertise will be crucial in setting the design requirements for the metacurtain, as well as the performance criteria.
The Metacurtain-1 project will deliver an initial metacurtain design that has been both manufactured and tested, along with a validated numerical model for evaluating the noise mitigation performance of the new design.
The project will also present a complete proposal for the Metacurtain-2 project, focusing on further refining the conceptual design and developing, studying, and testing the attenuation of the secondary noise source.
Jovana Jovanova
+31 6 2730 9630
Hybrid mechanical metamaterials: advances of multi-functional mechanical metamaterials with simultaneous static and dynamic properties (Adaptive Metastructures, Mechanisms and Machines website - TU Delft, 2025)
Hybrid mechanical metamaterials: advances of multi-functional mechanical metamaterials with simultaneous static and dynamic properties (Heliyon, 2025)
A metamaterial-based interface for the structural resonance shielding of impact-driven offshore monopiles (Engineering Structures, 2024)
A small-scale pile impact test for demonstrating the coupling between structural vibration and underwater noise generation (INTER-NOISE and NOISE-CON Congress and Conference Proceedings, 2023)
Metacurtain-1 is a GROW Common Fund project with an additional contribution from the Dutch Ministry of Economic Affairs and Green Growth and TKI Offshore Energy.