NOISE MITIGATION SYSTEM

Abstract

A method of and a noise mitigation system for installing a foundation element, in particular a (mono)pile, includes a screen to be placed about a foundation element, in particular a (mono)pile, during driving of the foundation element in an underwater ground formation, to reduce noise input resulting from the driving into the surrounding water, e.g. a river or sea. The method and system comprise a further screen to be deployed about the (first) screen.

Claims

1. A method of installing a foundation element, in an underwater ground formation by means of a driver, comprising: placing a foundation element on the underwater ground formation- 4), placing a screen for reducing noise input from the driver into surrounding water, driving the foundation element into the ground formation by means of the driver while the screen is positioned about the foundation element, and deploying, before driving the foundation element into the ground formation, a further screen about the screen.

2. The method according to claim 1, comprising deploying the further screen from the first screen.

3. The method according to claim 2, wherein the further screen comprises a plurality of arms attached to the first screen and wherein these arms are translated and/or rotated to deploy the further screen.

4. The method according to claim 1, comprising deploying a ring about the first screen and generating a bubble screen from the ring and/or suspending a buoyant screen from the ring.

5. The method according to claim 1, comprising deploying the further screen with its bottom end below the bottom end of the first screen.

6. The method according to claim 1, wherein the further screen is deployed at a distance, measured between the outer circumference of the first screen and the outer circumference of the further screen, of at least 3 meters, preferably at least 5 meters, preferably at least 7 meter, and/or preferably less than 50 meter, preferably less than 40 meters, preferably less than 30 meters.

7. The method according to claim 1, wherein the first screen reduces noise by at least 15 dB and the further screen reduces noise reduction by at least 5 dB.

8. A noise mitigation system comprising a screen to be placed about a foundation element, during driving of the foundation element in an underwater ground formation, to reduce noise input resulting from the driving into the surrounding water and a further screen deployed about the screen.

9. The system according to claim 8, wherein the further screen is attached to the first screen and movable between a retracted position and a deployed position.

10. The system according to claim 9, wherein the further screen comprises a plurality of arms slidably and/or pivotably attached to the first screen.

11. The system according to claim 8, wherein the further screen comprises a series of nozzles or a buoyant screen.

12. The system according to claim 11, comprising a tube or duct provided with a plurality of nozzles and attached to the arms near or at the ends of the arms.

13. The system according to claim 8, wherein the bottom end of the further screen is deployable below the bottom end of the first screen.

14. The system according to claim 8, wherein the further screen is attached to the first screen at least 1 meter, preferably at least 2 meters, above the bottom end of the first screen.

15. The system according to claim 8, wherein, when the further screen is deployed, the distance between the outer circumference of the first screen and the outer circumference of the further screen is at least 3 meters, preferably at least 5 meters, preferably at least 7 meter, and/or preferably less than 50 meter, preferably less than 40 meters, preferably less than 30 meters, preferably less than 20 meters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Aspects of the invention will now be explained in more detail with reference to the Figures, which show a preferred embodiment of the present method and system.

[0018] FIG. 1 is a perspective view of noise mitigation system comprising a further screen in a retracted position.

[0019] FIG. 2 is a perspective view of noise mitigation system comprising a further screen in a retracted position.

DETAILED DESCRIPTION

[0020] It is noted that the Figures are schematic in nature and that details, which are not necessary for understanding the present invention, may have been omitted.

[0021] FIG. 1 shows an embodiment of a system 1 for installing a monopile 2 in an underwater ground formation 3, e.g. a seabed. In this example, the monopile 2 has a circular cross-section and a diameter of five meters and is intended to serve, after installation, as the foundation of a wind turbine.

[0022] The system 1 comprises an hydraulic driver 4 (depicted in FIG. 2), e.g. an IHC Hydrohammer S-1800, connected to a power pack on board of a surface vessel, such as a ship or jack-up barge (not shown), a driver sleeve 5 for securely mounting the driver on the monopile and an anvil (hidden from view by the driver screen) for transmitting impact energy from the driver 4 to the monopile.

[0023] The system further comprises a noise mitigation screen 6, made of e.g. steel, to be placed about the foundation element to reduce noise input from the driver into the surrounding water. In this example, the screen comprises an inner wall and an outer wall, i.e. it is double walled, has a circular cross-section and an inner diameter of six meters. In general, it is preferred that, once in place, the sound-insulating screen extends to above the water level W.

[0024] The system comprises a further screen to be deployed about the screen 6. In this example, a plurality of arms 7 is attached to the first screen 6 by means of hinges 8 and hydraulic cylinders (not shown), such that the arms are pivotable about substantially horizontal axes. The arms 7 have a length of 15 meters and are made of e.g. metal rods or tubes. The hinges 8 are located approximately 2 meters above the bottom end of the first screen 6 and comprise torsion bars (not shown) to facilitate folding out and folding in. A flexible tube 9 is attached to the ends of the arms 7 and provided with a plurality of nozzles.

[0025] Installation of a monopile is carried out for instance as follows. The cables of the crane are attached to the upper end of a monopile stored on the deck of the ship and the monopile is lifted overboard, manipulated to an upright position, lowered onto the seabed or, as in this example, a scour protection 10. At this stage, the monopile is driven, e.g. by means of a vibratory device, into the scour protection and, depending on the circumstances, the seabed to a depth of some meters to further stabilize the monopile.

[0026] The driver 4 is positioned on top of the monopile 2 and the screen 6 is lifted over the monopile 2 and the driver 4 . Alternatively, the screen 6 is placed and the driver 4 is subsequently placed inside the screen 6 and on top of the pile. The further noise mitigation screen 9 is deployed by lowering the arms 7 onto the seabed. In this position, the tube forms a ring that circumscribes the first screen 6 and the scour protection 10. By feeding air to the tube, e.g. by means of a pump on deck of a surface vessel and via one or more of the arms 7, a bubble screen is generated, which screen surrounds the scour protection 10 and the first screen 6.

[0027] Finally, the pile 2 is driven to the required depth and when driving is completed, the driver 4 is removed, the further screen 7, 9 retracted, the screens 6, 9 lifted over the pile 2 and placed back on deck or into the sea, and installation is completed.

[0028] The invention is not restricted to the embodiment described above and can be varied in numerous ways within the scope of the claims. For instance, the further screen may comprise a buoyant and/or flexible tube, e.g. provided with air chambers or buoys, and the ring may provide sufficient weight to maintain the tube at an appropriate depth, e.g. with it bottom end on or in the seabed.