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Offshore Wind Journal

Low-noise pile driver can outperform noise mitigation systems

Wed 07 Nov 2018 by David Foxwell

Low-noise pile driver can outperform noise mitigation systems
Pile driving using conventional hydraulic hammers can adversely affect marine mammal and fish populations if mitigation measures are not in place

Tests have demonstrated that an innovative water-driven piling unit developed for the offshore wind industry has multiple advantages compared to conventional technology and even outperforms hydraulic piling systems with noise mitigation measures, its developer claims

After a successful series of tests earlier this year, the Blue Hammer piling system developed by Fistuca in the Netherlands and tested in a joint project with The Carbon Trust’s Offshore Wind Accelerator is set to enter into commercial use in 2020. 

Having successfully installed a test pile and then decommissioned it, the Blue Hammer pile driving system needs only minor adjustments and will be ready to undertake its first projects late next year, the man behind the concept, Fistuca’s founder and managing director Jasper Winkes, told OWJ in an exclusive interview in early November.

The Offshore Wind Accelerator first announced details of what it described as “successful execution” of offshore tests by the innovative installation system, that reduces underwater noise and costs, in August 2018.

Describing the results in more detail, Mr Winkes told OWJ that the tests, conducted by The Carbon Trust and Fistuca in conjunction with industry partners Eon, EDPR,  EnBW, Equinor, Ørsted, Shell, Sif, SSE, Van Oord and Vattenfall were “very positive.”

The offshore tests of the BLUE 25M hammer as part of the Blue Pilot project were carried out on 13 August 2018 using Van Oord’s offshore heavy lift installation vessel, Svanen, off the coast of the Netherlands.

“The Blue Hammer proved it is 16-20 dB quieter than any hydraulic hammer and makes piling quieter than is possible with any noise mitigation system used in conjunction with a hydraulic hammer,” Mr Winkes told OWJ. “The remaining noise you get with the system is at a frequency which doesn’t adversely affect mammals or other marine life.

“We also proved the Blue Hammer can be used to drive monopiles with secondary steel structures attached to them.

“Now we plan to undertake a few modifications to the system, and test it again in the course of 2019, which would allow for commercial offshore deployment in 2020.

“The tests demonstrated what we expected, that we have a powerful business case in a number of respects. We are quieter than hydraulic hammers, quieter than noise mitigation systems and when the pile is being driven using the Blue Hammer it suffers from less fatigue-related stress than it otherwise would.”

Fistuca’s strategy is to rent out the Blue Hammer on a project-by-project basis and build more examples of the innovative pile driving system as demand picks up. “We also know that we can design hammers for specific projects, according to the size of monopiles, soil stiffness and water depth,” he explained.  

As highlighted previously by OWJ, the Blue Hammer utilises water to provide a more energetic, but quiet blow to drive a pile into the seabed. It was designed to reduce underwater noise levels significantly and reduce the fatigue damage while installing a pile. As Mr Winkes stated, in many cases, this could not only remove the need for underwater noise mitigation but also enable secondary steel to be prewelded to the monopile before installation, potentially unlocking ‘transition piece free’ designs. By reducing the time piling takes and the number of operations carried out offshore, the innovative piling method could also improve health and safety and significantly reduce costs.

The offshore tests provided significant insights and understanding for future commercial operations. Data was recorded on both acceleration levels on the monopile and underwater noise levels in the surrounding area which have now been analysed and interpreted to validate studies undertaken prior to the test.

Impacts on fish from piling

Much of the attention on noise reduction from piling has focused on potential adverse effects on mammals, but attention has also turned to the possible impact on fish from piling at offshore wind sites. Now, a revised technique for mapping the spawning sites of Atlantic herring in the UK has been developed which will ensure fish are protected during offshore windfarm construction and which could lead to a more efficient and low-cost development process. It was described in a report produced by The Carbon Trust for the Offshore Renewables Joint Industry Programme (ORJIP).

The potential impact of noise from pile driving activity has led to restrictions and conditions placed on UK offshore renewables developers during construction activity when marine mammals and fish are considered to be most vulnerable to disturbance, such as during spawning and migration. It is important to ensure the established controls are appropriately formulated to deliver a protection benefit without unnecessarily burdening development.

The Impacts on Fish from Piling at Offshore Wind Sites project analysed annual fish spawning data in UK waters over the past 10 years to better define fish spawning grounds and to evaluate the potential impacts of new offshore wind sites on Atlantic herring and other fish.

The main spawning sites for Atlantic herring stocks in UK waters are well known. However, due to the specific habitat and environmental conditions that herring need to spawn successfully, there are discrete pockets of spawning bed areas that are less easy to identify as they can change from year to year.

Currently the exact location of spawning beds can only be identified if they are recorded through grab sampling or by drop-down video surveys. This study aims to address the uncertainty of the accuracy of fish spawning information and the impacts of piling activity on fish species.

The objectives of the study were to review and consolidate available data and information to define (where possible) UK populations, spawning areas, and periods for key species of concern; identify any gaps in our understanding of fish populations, spawning areas and periods; define and gain acceptance with consenting authorities and experts on fish populations, spawning areas and periods; and discuss and understand how the current mitigation approaches are agreed by consenting authorities with the aim to understand what is required to support a change in construction restrictions.

The study that forms the basis of the report was launched in 2017 is the first ORJIP study to look in detail about the important subject of fish and windfarm consenting. The analysis shifts the focus of studies from abandoned spawning sites and highlights those regions that have shown recent spawning activity. The techniques and methodology of heat mapping demonstrated the final report study provides clearer information of the areas of spawning and their proximity to offshore wind developments.

If considered in the consenting process this could lead to a reduction in construction times, potentially lowering cost to consumers, and reducing operational disruption for offshore windfarms.


 

Consortium to commercialise low-noise foundation

An industry consortium has been awarded €3.8M (US$4.4M) by the Energy Technology Development and Demonstration Programme to demonstrate the advantages of industrialising an enhanced suction bucket foundation for offshore windfarms.

The partners in the project said the overall aim of the project is to mature the industrialised suction bucket concept towards commercial-scale applications. The consortium includes Siemens Gamesa, Universal Foundation, Aalborg University, Fred Olsen Windcarrier and Offshoreenergy.dk. The funds were awarded via the Danish Ministry of Energy, Utilities and Climate.

The concept merges the noise-free installation advantages of suction buckets with industrialised fabrication techniques using coil steel instead of conventional plate steel.

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