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, placing a first 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 first screen is positioned about the foundation element, and deploying a further screen in the water before driving the foundation element into the ground formation, the further screen comprising a plurality of arms movably attached to the first screen and wherein deploying the further screen comprises moving the arms to deploy the further screen between a retracted position and a deployed position such that the further screen is deployed about the first screen at a distance of at least 3 meters, measured between an outer circumference of the first screen and an outer circumference of the further screen with water separating the first screen from the further screen.

2. The method according to claim 1, wherein deploying comprises deploying a ring about the first screen and generating a bubble screen as the further screen from the ring with water separating the bubble screen from the first screen.

3. The method according to claim 1, wherein deploying comprises deploying the further screen with its bottom end below the bottom end of the first screen.

4. The method according to claim 1, wherein the distance, measured between the outer circumference of the first screen and the outer circumference of the further screen, is at least 5 meters.

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

6. The method of claim 1 wherein moving comprises translating the arms.

7. The method of claim 1 wherein moving comprises rotating the arms.

8. The method according to claim 1, comprising deploying a ring about the first screen and suspending a buoyant screen as the further screen from the ring with water separating the buoyant screen from the first screen.

9. A noise mitigation system comprising a first screen configured 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 is attached to the first screen and comprises a plurality of arms movably attached to the first screen and configured so as to be deployed about the first screen by moving the arms between a retracted position and a deployed position such that in the deployed position the further screen is deployed with a distance between an outer circumference of the first screen and an outer circumference of the further screen of at least 3 meters.

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

11. The system according to claim 9, wherein the further screen comprises a series of nozzles or a buoyant screen.

12. The system according to claim 11, wherein the further screen comprises a plurality of arms slidably and/or pivotably attached to the first screen and a tube provided with the series of nozzles, the tube being attached to the arms near or at ends of the arms.

13. The system according to claim 9, wherein a bottom end of the further screen is configured to be deployable below a bottom end of the first screen.

14. The system according to claim 9, wherein the further screen is attached to the first screen at least 1 meter above a bottom end of the first screen.

15. The system according to claim 9, wherein the further screen is configured so as to be deployed wherein the distance between the outer circumference of the first screen and the outer circumference of the further screen is at least 5 meters.

16. The system of claim 9 wherein the further screen comprises a plurality of arms pivotably attached to the first screen.

17. The system of claim 9 wherein the further screen comprises a buoyant screen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) FIG. 1 is a perspective view of noise mitigation system comprising a further screen in a retracted position.

(3) FIG. 2 is a perspective view of noise mitigation system comprising a further screen in a deployed position.

DETAILED DESCRIPTION

(4) 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.

(5) 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.

(6) 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.

(7) 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.

(8) 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.

(9) 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.

(10) 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 9 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.

(11) 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.

(12) The invention is not restricted to the embodiment described above and can be varied in numerous ways within the scope of the claims. In another embodiment, the further screen comprises a series of nozzles 12 or a buoyant screen 13, e.g. a flexible tube comprising one or more buoys or air chambers.

(13) The ring 9-may provide sufficient weight to maintain the tube at an appropriate depth, e.g. with it bottom end on or in the seabed.