reef dB

What it does

Underwater noise pollution from offshore windfarm operations is devastating the North Sea ecosystem. Reef dB filters out underwater noise pollution while regenerating the ocean floor, allowing humans and marine life to coexist.

Your inspiration

In 2022, the EU finally mandated threshold levels for underwater noise pollution — some 50 odd years after first discovering that noise pollution negatively affects marine life. However, there is currently no solution that can help mitigate underwater noise pollution over a long period of time, or that functions in an ecologically positive way. This project was an opportunity to demonstrate the importance of a post-human-centred design approach, while combining my lifelong passions for sound and the ocean. The solution emerged by synthesising this process with a deeply technical exploration of acoustic metamaterials and phononic crystals.

How it works

The structure suppresses sound transmission via Helmholtz resonance and physical vibrations, dissipating sound energy as heat. Arraying the structure in a super-periodic array (e.g., a hexagonal lattice) around a turbine foundation leverages the Bragg scattering effect for further sound dissipation. This allows broadband sound suppression by 10 – 15 dB from 50 – 1000 Hz. The window through the middle of the structure allows tidal currents to flow uninhibited. This prevents sedimentation (which is otherwise extremely damaging for the benthic environment) and reduces hydrodynamic forces on the structure. The surface texture was designed to reach the measured surface roughness of reefs in the north sea. This provides attachment points for a diverse range of creatures, preventing monocultures and contributing to benthic regeneration. Filter feeders help to improve water quality and calcium carbonate deposition from coral can sequester significant CO2.

Design process

I took a post-human-centred design approach, interviewing proxies who could speak on behalf of marine life (experts in the benthic environment, marine biodiversity, and underwater noise), physically immersing myself in the benthos of the North Sea, and giga-mapping the offshore wind farm system, from pre-planning to decommissioning. This helped me to fully empathise and integrate with the problem. I also undertook a technical investigation, prototyping and testing membrane-type acoustic metamaterials and 3D and 2D phononic crystals. This led me to the metacage window concept, which allows a fluid to pass through a window while suppressing sound transmission. I quickly iterated over this design, using 3D printing to test different prototypes in an underwater environment while measuring the transmission loss via a hydrophone. By integrating insights from the post-human design approach, I was able to refine the design into a final geometry. This includes a textured surface for benthos to attach to, a window to allow the flow of tidal currents, and sound suppression that has been tailored to the range that is most problematic for marine life (< 200 Hz).I subsequently trialled various ways of fabrication at 1:10 scale, including ceramic 3D printing, and concrete formworks.

How it is different

No underwater noise mitigation solutions currently exist for a long period of operation (i.e., longer than one day). Current solutions are only effective for the installation phase of offshore wind farms, and not the operational phase. Hence, reef dB is unique in this context, with a design life of ~120 years. No current solutions are effective below 200 Hz, whereas reef dB is effective from 50 – 1000 Hz. Current solutions are incredibly expensive, requiring a total budget of £10 – 15 million per windfarm. Reef dB is costed at £500,000 per windfarm. Most importantly, however, is that reef dB is the only noise mitigation system that integrates with the environment in an ecologically positive way, regenerating the benthic floor (which is destroyed during windfarm installation). The closest competitor in this regard are artificial reefs; however, no artificial reefs deliver high-level functionality, making reef dB an incredibly unique and pertinent solution.

Future plans

The next stage in this project is to fabricate 97 1:1 prototypes from marine-sustainable concrete, using a large scale 3D printer. These can then be arrayed around an offshore wind turbine in the north sea for in-situ testing. I have initiated discussions regarding materials, testing, and fabrication. Subsequently, the design can be further optimised for full roll-out. In the future, I see reef dB being relevant anywhere with underwater anthropogenic noise emissions for a long period; deep sea mining, oil drilling, underwater construction, aquaculture, etc. With the growth of the blue economy, the true value of reef dB remains to be seen.

Awards