Tackling underwater noise at source

Reducing the environmental impact of offshore piling activities

Offshore wind turbines have grown significantly in size in recent years, and as a result can generate more renewable energy to meet climate change targets. However, the ever-increasing size and weight of the new generation of wind turbines – and greater water depths – have implications for their installation, particularly regarding the impact of noise from piling activities on marine life.

This is an important consideration for developers. They must comply with international noise mitigation legislation to gain approval for, and continue working on, their offshore wind farm projects. The most stringent legislation is currently in Germany, and applicable to Arcadis Ost, a 257 MW offshore wind project located in the Baltic Sea.

“The noise threshold in German regulations is set at 160 dB Sound, Equivalant Level at a distance of 750m the pile to comply with this, additional noise mitigation is required,” e Offshore Wind Project Specialist at IQIP. “Arcadis Ost is one of the first projects to install ten-metre diameter monopiles – 28 in total – This meant that they were looking for a new method to reduce noise.”

Listening to the market

IQIP is supporting the contractor, DEME, and project developer, Parkwind NV, with an innovative piling method known as Pulse. “The new DP3 offshore installation vessel, ORION, will lift the monopiles and our IQIP’s equipment will be there to drive them down to final penetration,. “Although it’s still under development and this is its first commercial use, IQIP is confident that Pulse will make a significant contribution to staying within the noise limits.”

Pulse is a modular add-on to the standard IQIP Hydrohammer. The unit is positioned between the pile driving hammer and sleeve, and dampens the impact and noise with two steel plungers. The volume in between the plungers can be filled with water, which extends the impact of each blow of the Hydrohammer, resulting in reduced noise levels.

“The main advantage of Pulse is that it uses an adaptable volume of water as a cushion between two pistons, which helps to deliver a softer blow with a longer duration to the pile,”
“This causes less vibrations in the water and soil.”

In addition, the use of water eliminates the risk of wear or breakdown associated with other cushion materials. It is also highly flexible as the settings can be adjusted depending on the penetration required in addition, if something is not going according to plan, the customer can drain the water and go back to using a standard hammer.

Using Pulse will enable customers to complete installation more quickly due to the efficiency of penetration per blow.  Results indicate efficiency improvements of 10%. It also contributes to reduced installation fatigue, which will give developers and monopile designers more opportunities to optimise structure designs and meet the need to lower the levelised cost of energy.

“It could accommodate TP-less monopiles, for example, and in the future even lead to the design of lighter monopiles, reducing the amount of steel required.”

 

Firm foundation

Pulse follows on from IQIP’s HiLo (high frequency, low energy) method used on numerous offshore wind projects over the past decade. “It ensures the amount of energy consumed is minimised, by using only what is required to get the pile down to penetration level. “The higher frequency, with more blows per minute, means we will still get the pile down to penetration within a reasonable timeframe.

“Used largely on piles with up to eight-metre bottom diameters, the HiLo method has been very effective in reducing underwater noise when used in addition to noise mitigation systems or bubble curtains. However, as projects like Arcadis Ost are starting with bottom diameters of ten metres – with probably larger ones in the future – more mitigation at the source is needed to adhere to regulations for underwater noise.”

Game-changing developments

As a new technology, Pulse will be used by Parkwind NV in addition to other noise mitigation measures, such as bubble curtains and mitigation around the pile itself.  On future projects IQIP believe, the use of Pulse will reduce the number of bubble curtains, which will have a large impact on sustainability.

“The vessel and compressors required consume a substantial amount of fossil fuels and release emissions. “Using Pulse could mean customers would no longer need this supporting vessel.”

This further reiterates the beauty of the Pulse concept and the importance of tackling underwater noise at its source. “Noise is created by piling and if the system can reduce that, there is no need to combat it afterwards by covering it up with different additional mitigation methods. Otherwise, eventually the monopiles will become too large to be installed in an environmentally friendly way.”

While IQIP is looking forward to the results of this first project for Pulse, it is also looking ahead to future development for other applications. At Arcadis Ost, it will be applied to the largest hammers in its portfolio, but it could be downsized for smaller hammers used for jacket installation, floating mooring installation and the civil industry.

Considering the size of the monopiles on Arcadis Ost, this project is pushing at the boundaries of what has been achieved to date in the offshore wind industry. Thanks to state-of-the-art equipment and innovative technology, such as IQIP’s Pulse, it will be completed in an environmentally sensitive way to deliver a reliable supply of renewable energy at lower costs.

 

“We see this as a solution across all of our hammers ­– for foundation works, civil and offshore”

IQIP’s Offshore Wind Project Specialist

With the largest monopiles ever installed in Europe, the Arcadis Ost project is pushing at the boundaries of what has been achieved to date in the offshore wind industry. Thanks to state-of-the-art equipment and innovative technology, such as IQIP’s Pulse, it will be completed in an environmentally sensitive way to deliver a reliable supply of renewable energy at lower costs.

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