Mitigating offshore wind farm noise

One of the hot topics at the recent International Quiet Ocean Experiment in Paris was the noise impacts of offshore wind farms. It seems that while the American Oilmen are furiously trying to carve up the Arctic for fossil fuel, the Europeans are rapidly developing wind power. Much of this is happening in the North Sea between the United Kingdom and the European continent.

North Sea Wind Farm

While wind power has significantly lower environmental impact than fossil fuel, it does not come without drawbacks. From a noise standpoint the concerns include the noise of installation, and the ongoing noises of operation.

The operation noises include gearbox vibration transmitted down the mast, and the thumping noise generated by the tip vortices as they pass by a boundary (like the ocean surface).

Pile Driving with bubble curtain

The installation noises in the shallow North Sea are from pile-driving the foundations to mount the mast. Percussive noise from pile driving was found to be deadly to fish, and pernicious to marine mammals.

Mitigation for pile driving noise was first developed during the San Francisco Bay Area bridge retrofits and involves the use of “bubble curtains.” By surrounding a driving pile with a ring of air bubbles, the water and noise within the ring can be acoustically isolated from the surrounding environment.

The drawback here is that the process is energy intensive because a high volume of air needs to be continuously forced down to the depth of the seabed to be released in a continuous stream. This can get really expensive: This mandated mitigation doubled the cost of the Richmond Bridge seismic retrofit.

But researchers at the University of Texas, Austin have developed an improvement on the bubble curtain – by encapsulating the bubbles in a latex envelope, a curtain can be installed while pile driving, and then relocated when needed elsewhere.

This promising technology could decrease the expense as well as the noise of developing wind farms in the North Sea – or even off the coast of America!