In recent years, many offshore wind farm developers have had no choice but to accept the additional cost, energy consumption and vessel requirements of secondary noise mitigation technologies. The problem has been particularly pressing in Europe and Taiwan, where noise reduction legislation and environmental concerns often necessitate technologies such as the Big Bubble Curtain (BBC). To offer an alternative solution, IQIP has been developing PULSE, an add-on technology that will significantly reduce the expense of noise mitigation with minimum effect on the efficiency of installation.
Comprising two plungers with a fluid layer in-between, the PULSE unit is directly placed between the hammer and sleeve. Because of this integration, the difference between conventional piling methods and PULSE is almost non-existent when it comes to the efficiency of installation.
"A key feature is that the amount of fluid between the plungers can be adjusted when the hammer is on the pile, altering the system's stiffness. This allows our operators to optimise the noise reduction for each pile while maintaining driveability and installation speed," explained Jonathan Stolk from IQIP's R&D department.
"Comparable systems are not adjustable, meaning that the stiffness must be decided upfront, and, because of the required safety margins on soil information, the decision is likely to be on the conservative side, strongly decreasing the noise reduction. With PULSE, we are not limited by this, but are always able to achieve the maximum performance on noise reduction with our existing hammer line-up."
Used on its own with no further noise mitigating measures, calculations and tests prove that PULSE can reduce the SEL of conventional hammers with 6-9dB and the SPL with 9-12dB in the right circumstances. And the reductions will improve exponentially when the size of the hammer grows. For even higher reductions, the system can be combined with IQIP's Integrated Monopile Installer, which directly mitigates noise by shielding the pile with a double-walled steel tube into which a bubble curtain can be fed. In most cases, the combination of those two systems would eliminate the need for a bubble curtain.
One of the main issues motivating IQIP to invest in the development of technologies that mitigate noise at the source is the recurring problems experienced by clients when attempting to control the noise in the water. While widely used, BBC are cost and energy-consuming, and their efficiency is highly dependent on depths and currents. PULSE, is unaffected by such factors as it reduces noise at the source by elongating the impact of the hammer through the adjustable fluid cushioning. The fact that the fluid layer can be adjusted, also means that if the system should fail, it is possible to drain all water so that the plungers are on top of each other, providing the function of a conventional hammer again. In that way, it is a secure system.
On top of the predictability of the achievable noise reduction, PULSE also uses significantly less energy than bubble curtains and eliminates the need for an extra CO2 emitting vessel. Further adding to its overall cost- and energy-efficiency is its potential to significantly reduce pile fatigue.
When installing a pile with conventional hammers, fatigue damage is induced in the pile. IQIP tries to minimise this by assisting our clients with smart pile design and piling strategies, but with current equipment, it cannot do more than that. However, with PULSE, fatigue damage in the pile can be reduced by up to 60 per cent. This could potentially lead to a longer lifespan of the offshore monopile and ultimately to a reduction to the costs of offshore wind energy.
The dampened impact of the strike also reduces the risk of damaging secondary steel if and when installing complete monopiles with transition pieces.
Got a story? Email: duncan.moore@aspermontmedia.com
