Device for reducing pile-driving noise

Abstract

The invention relates to a device for reducing pile-driving noise when a pile-driving material (1) is introduced into a substrate, comprising at least one support structure (2) and a structure for reducing vibrations (3), which is coupled to the support structure (2), wherein the structure for reducing vibrations (3) has a wavelength-dependent cut-off frequency above which broadband suppression of wave propagation in the material of the support structure (2) takes place.

Description

[0001] Device for reducing pile driving noise

[0002] The invention relates to a device for reducing pile driving noise when driving a pile into a subsoil, as well as a corresponding method for reducing pile driving noise.

[0003] The installation of pilings, such as piles, sheet piles, or steel profiles, into the ground is a construction project that generates a lot of noise. This problem is particularly relevant in the construction of offshore structures such as wind turbines or general offshore platforms. So-called monopiles are used for the foundations here. These round steel pillars are driven into the seabed by ramming from an installation vessel. However, the sound emitted during this process by the monopile structure into the sea poses a threat to many marine animals, which is why operators of offshore construction sites are legally obliged to comply with limit values. For this reason, sound insulation measures are essential when building the foundations of offshore structures. There are currently three proven sound insulation systems for use in offshore foundations with monopiles.

[0004] One approach involves the use of bubble curtains, created by air hoses with outlet openings laid on the seabed around the construction site. The air bubbles introduced into the seawater in this way locally change the speed of sound in the water, thus breaking up the sound emitted by the monopile. While this active measure effectively reduces sound propagation, the installation of a bubble curtain requires additional technology such as a powerful vacuum pump, which entails costs and problems. A passive alternative is the Hydro-Sound-Damper (HSD) system, which essentially creates a curtain made of a net with foam elements attached to it, arranged around the monopile between a circular floating body and a corresponding ballast ring.The differently sized foam elements absorb different frequencies and thus prevent sound propagation. However, due to its design, the HSD system is vulnerable to sea swells and has a very limited service life. A more stable approach is a so-called IHC Noise Mitigation Screen, or IHC duct. This is a double-walled steel duct with an air-filled cavity. The duct can also incorporate a centering device for the monopile to ensure optimal alignment during installation into the seabed. It can also have an integrated bubble curtain on its interior to further enhance the duct's insulation effect. All common noise mitigation approaches have in common that additional equipment must be brought out at sea and installed and operated at the pile-driving position or its surroundings.Furthermore, the on-site noise mitigation measures must be adapted to the local conditions. After the actual construction work, the equipment must be salvaged and removed. Since, for example, there is great interest in accelerating offshore construction projects while complying with legal noise mitigation requirements, innovative measures to reduce pile-driving noise during the installation of monopiles are necessary. Reducing pile-driving noise is also desirable in other areas of application in order to comply with occupational health and safety regulations and protect the environment.

[0005] The object of this patent application is therefore to propose a passive and "near-pile" solution that can reduce sound radiation when driving a pile into the subsoil. This solution directly targets the pile by manipulating the vibroacoustic properties of its structure, which is set into vibration by the driving impacts. For this purpose, two different effects of sound propagation in solids can be exploited. Vibroacoustic metamaterials generate defined stop bands for wave propagation within the material through their arrangement of resonators. They can therefore find diverse applications in the field of sound insulation and vibration suppression, see, for example, DE 10 2022 294790 A1 or DE 10 2022 205 321 A1. Acoustic black holes, on the other hand, are based on the relationship between the propagation speed of a wave in an elastic medium and the propagation distance within the medium.An overview of this research area is provided, for example, by Pelat et al., "The acoustic black hole: A review of theory and applications." By applying these effects to a pile, a significantly reduced sound radiation can be achieved when driving the pile into the subsoil, without the need for additional equipment or the expenditure of energy for active measures. In addition, the necessary preparatory steps can be carried out on the pile before transport to the actual construction project—in the case of a monopile, for example, on land rather than at sea—which can reduce costs. This problem is solved by a device for reducing pile-driving noise according to claim 1 and by a method for reducing pile-driving noise according to claim 11.

[0006] Such a device for reducing pile driving noise when driving a pile into a subsoil comprises at least one support structure, a structure for reducing vibrations which is coupled to the support structure, wherein the structure for reducing vibrations has a wavelength-dependent cut-off frequency from which a broadband suppression of the wave propagation in the material of the support structure takes place.

[0007] The device is used to reduce the pile driving noise generated when a pile is driven into the subsoil. A pile is a body suitable for driving into the subsoil, for example a pile, a sheet pile or any type of steel profile. In particular, the pile driving can be a monopile for installation in the seabed. The pile driving is generally driven into the subsoil by the impacts of a piling head. A variety of different types of pile drivers are used for this purpose, on the high seas, for example, by installation vessels. The pile driving is excited to vibrate and emits corresponding sound waves into the surrounding medium, for example air, soil or water. Frequencies below 1000 Hz are particularly relevant for pile driving noise during construction work.

[0008] The device comprises a support structure. This is a structure that serves to position the actual sound-reducing elements on the pile-dried material or in its surroundings. The support structure can be part of the pile-dried material itself, attached to it, or located in its surroundings. In any case, it is designed so that the vibrations of the pile-dried material generated by the ramming impacts can propagate into the support structure. A structure for reducing vibrations is coupled to the support structure. This structure can be attached to the support structure or machined out of it. The structure for reducing vibrations has at least one wavelength-dependent cutoff frequency above which a broadband reduction of the wave propagation occurs in the material of the support structure and thus also in the pile-dried material.In other words, the vibration reduction structure serves to manipulate the dispersion behavior of structure-borne sound waves in the material of the support structure and the pile-driving material in a wavelength-dependent manner in order to achieve strong suppression of wave propagation in certain frequency ranges. The dimensions of the structures used for this purpose are in the order of magnitude of the wavelengths. A generally relevant frequency range is the range below 1000 Hz. By configuring the vibration reduction structure, one or more specific frequency ranges can be selected in which wave propagation is reduced, thus reducing the pile-driving noise emitted into the environment.

[0009] The support structure can be directly formed by the pile-driving material. The vibration-reducing structure can then be applied directly to the pile-driving material. It is also conceivable for the support structure to be a curved plate or sheet metal covering one or more areas of the pile-driving material's surface. The vibration-reducing structure can also be machined directly from the material of the pile-driving material. By enclosing areas of the pile-driving material's surface, the weight and material requirements of the device for reducing pile-driving noise can be reduced.

[0010] The support structure can also include mounting rails that are connected to the pile-driving material via a guide. The individual elements of the vibration-reducing structure are mounted on the mounting rail. Using such mounting rails allows the device for reducing pile-driving noise to be effectively prepared before it is attached to the pile-driving material. Furthermore, the support structure can be easily coupled to the pile-driving material using common joining methods such as welding, riveting, or screwing. The device for reducing pile-driving noise can also include both areas on the surface of the pile-driving material and mounting rails as support structures. The support structures can be coupled to the pile-driving material on land, meaning that no additional steps are necessary when the pile-driving material is actually inserted into the seabed.This reduces the time and effort required for soundproofing at sea and reduces the associated costs.

[0011] Alternatively, a duct can serve as a support structure. The duct can be a single- or double-walled duct that surrounds the pile-driving material as it is driven into the ground. Because the duct is equipped with a vibration-reducing structure, it further reduces the pile-driving noise emitted into the environment. Using a duct as a support structure allows existing processes to be easily improved. With a monopile as the pile-driving material, it makes it possible to transfer the advantages of an IHC duct, such as improved centering of the driven joints and rails for aligning the monopile, to the innovative device for reducing pile-driving noise.

[0012] The reduction of pile-driving noise can be based on vibroacoustic metamaterials (VAMM). In this case, the structure for reducing vibrations can comprise an array of local resonators. The local resonators each have at least one common natural frequency in the relevant frequency range. The local resonators each consist of a vibrating mass and a spring element and can additionally comprise a damping element. The spring element has elastic properties and can be formed integrally with the vibrating mass, for example, as a vibrating beam. For example, strip resonators cut from plate material or punched from sheet metal are conceivable. Plastic or rubber elements can serve as damping. The individual resonators or the entire arrangement can be connected to the support structure by gluing, welding, or screwing.By selecting the shape and dimensions of the oscillating mass and the spring element, the natural frequencies of the local resonator can be tuned. The local resonator defines a unit cell. The arrangement of local resonators consists of a spatial repetition of this unit cell in one, two, or three dimensions. Each individual resonator has at least one natural or resonant frequency. When excited at this resonant frequency, the amplitude of the resonator's oscillation is maximized. All local resonators in the arrangement are tuned to at least one identical, or at least approximately identical, resonant frequency, so that when excited externally at this frequency—for example, by the vibration of the pile-driving material following the impact—as much of this kinetic energy as possible is captured in the arrangement of local resonators.This creates a stop band around the natural frequency of the local resonators, which significantly attenuates wave propagation in the metamaterial of the structure and the coupled support structure, reducing vibrations. By tuning the natural frequencies of the local resonators, the position of a stop band can be determined, which significantly reduces the pile-driving noise emitted by the piling material. The width of the stop band depends on the effective vibrating mass of the local resonators, their damping, and deviations in the tuning of the resonators. If the local resonators have multiple natural frequencies in the selected frequency range, multiple stop bands can be created around them. These multiple stop bands can separately reduce vibrations in multiple frequency ranges, or they can overlap to form a large stop band.

[0013] This effect is particularly effective when the arrangement of local resonators is periodic. Deviations from the periodicity result in a wider, but less pronounced, stopband. By selecting the spacing of the local resonators, the stopband can be broadened for the selected frequency range. The spacing of the local resonators in the arrangement of local resonators should be less than half a wavelength of the highest relevant frequency to achieve good oscillation reduction across the entire selected frequency range.

[0014] In addition to the described effect of vibroacoustic metamaterials, the arrangement of local resonators can also exploit the effect of Bragg scattering to create a stop band in the selected frequency range. In Bragg scattering, the local resonators act as inhomogeneities in the structure where the waves are reflected, resulting in destructive interference at certain frequencies. This creates a stop band whose position is defined by the distance between the resonators.

[0015] Another effect based on the dispersive properties of wave propagation in media is the so-called acoustic black hole, also known as an "acoustic black hole" (ABH). Analogous to the black holes of astrophysics, these are regions from which sound waves can no longer escape. One possible implementation of this effect is a thin-walled structure whose thickness steadily decreases along its length until it reaches a theoretical value of zero. Due to the steadily decreasing thickness, the wave propagation velocity in the structure is continuously reduced in the longitudinal direction until, ideally, it also reaches zero, and the wave is thus completely absorbed. In the present application, a freely vibrating end of a plate or beam can serve as a structure to reduce vibrations.The thickness of this element decreases towards a free end with a continuous function and approaches the ideal value of zero. In practice, thicknesses of a few millimeters are achievable, so that this acoustic black hole can already achieve a very good reduction in wave propagation in the material. Such a section of a plate or beam, whose thickness continuously decreases along its length, can be used as a structure to reduce vibrations, for example on a support structure at one end of the pile driving or at any position along the pile driving in order to reduce the emitted pile driving noise. Alternatively, a structure is also conceivable whose thickness decreases continuously from at least two directions down to an ideal value of zero, thus acting as an acoustic black hole.A plate, beam, or a section of the supporting structure at any position along the pile can serve as a vibration-reducing structure, gradually thinning to a minimum value in the center. In practice, thicknesses of a few millimeters can be achieved without compromising the stability of the structure.

[0016] To further enhance this effect, a damping coating can be applied to the thin section. The damping coating can be made of rubber or plastic, and the coating can be assumed to be very thin relative to the thickness of the structure. Since a real thin section cannot, of course, reach the ideal thickness of zero, wave propagation will not completely stop. However, the remaining wave can be absorbed by the damping coating, preventing it from being reflected at the free end of the structure. The sound wave propagating in the supporting structure is thus almost completely extinguished.

[0017] One possible way to implement such an acoustic black hole in a device for reducing pile driving noise is to use a pipe attachment as a support structure. This pipe attachment can be placed on the upper end of the pile. At the open end of the pipe attachment, its wall can then gradually thin to form the freely vibrating end, which represents the acoustic black hole. This design has the advantage that it can be easily attached to the pile driving and removed again after the construction work is completed.

[0018] The described forms of the device for reducing pile-driving noise can be used individually or combined with each other. In particular, the device for reducing pile-driving noise can comprise both support structures and structures for reducing sound propagation in the form of vibroacoustic metamaterials, as well as an additional support structure with a freely vibrating element for forming an acoustic black hole in order to achieve the most effective and broadband reduction of the sound emitted by the pile-driving material.

[0019] A method for reducing pile driving noise when driving a pile into the ground comprises the following steps:

[0020] Applying at least one support structure to a pile or a cladding tube, wherein the support structure is coupled to a structure for reducing vibrations, which has a wavelength-dependent cut-off frequency from which a broadband suppression of the wave propagation in the material of the support structure takes place,

[0021] Insertion of the pile-driving material into the subsoil by ramming.

[0022] Common joining methods can be used to attach at least one support structure to a pile or duct. The support structure can be plates, sheets, rails, pipe attachments, or similar. However, the support structure can also be machined from the pile or duct. The support structure serves to position the actual sound-reducing elements on the pile or duct and is designed so that the vibrations of the pile generated by the driving impacts can propagate into the support structure. The support structure is coupled to a vibration-reducing structure.The structure for reducing vibrations has at least one wavelength-dependent cut-off frequency, above which a broadband reduction of the wave propagation in the material of the support structure and thus also in the pile material occurs and serves to reduce the propagation of sound waves in a selected frequency range of below 1000 Hz in the material of the support structure.

[0023] The installation of the support structure can be carried out separately from the installation of the piles into the subsurface. In particular, in the case of a monopile for installation into the seabed, this can be performed onshore, thus reducing the workload on board an installation vessel at sea.

[0024] The actual insertion of the piles into the subsoil is carried out by ramming, as is generally the case with such construction projects. A casing pipe may be provided to align the piles and enhance sound insulation. The ramming not only drives the piles into the subsoil, but also induces vibrations. Because the pile or casing pipe is equipped with a support structure and a vibration-reducing structure coupled to it, these vibrations are reduced, as is the sound emitted by the piles into the surrounding medium.

[0025] The support structure can be provided, in particular, in the form of mounting rails that are coupled to the piles or the duct via guides. The actual structure for reducing vibrations is located on the mounting rails. Using such mounting rails, the support structure can be easily attached to the piles or the duct and connected to the piles using common joining methods such as welding, riveting, or screwing.

[0026] The structure for reducing vibrations can be applied to the support structure as an array of local resonators. The local resonators each have at least one common natural frequency in a selected frequency range. Such an arrangement of local resonators can be used to form a vibroacoustic metamaterial that generates at least one stopband for wave propagation in the selected frequency range.

[0027] To exploit the acoustic black hole effect instead or in addition, the structure for reducing vibrations can comprise a section of a thin-walled structure whose thickness decreases along its length with a continuous function and approaches a theoretical minimum value of zero. In the present application, a free, thinning end of a plate, a beam or a region of the support structure or a region thereof that continuously thins in its center down to a minimum value can serve as the structure for reducing vibrations. In particular, a pipe attachment can be applied to the upper end of the pile or the cladding tube as the support structure. One end of the pipe attachment can then act as a structure for reducing vibrations in that the thickness of the end decreases along its length with a continuous function and approaches a theoretical minimum value of zero.In reality, the wall thickness of the pipe attachment can be reduced to a thickness of just a few millimeters, which is already sufficient to achieve a strong suppression of wave propagation in the support structure.

[0028] Once the pile has been driven into the ground, the support structure can be removed from the pile or the duct. In the case of a support structure in the form of a pipe attachment, this can be removed again from the placed pile. If mounting rails are used as the support structure and are coupled to the pile using detachable joining methods, these can also be easily detached. This allows the support structures and vibration reduction structure to be reused for future construction projects. If the support structures are coupled to a duct, the entire duct is removed, as in all common methods for driving piles, and can be reused together with the support structure and vibration reduction structure. Of course, the support structure and vibration reduction structure can also remain attached to the pile to reduce the necessary labor.

[0029] The proposed method for reducing pile-driving noise when driving piles into the ground can reduce noise pollution during construction projects, particularly offshore construction projects. At the same time, the method requires less time and material to implement than conventional noise mitigation measures in this area. In particular, it has the advantage that not all work steps need to be carried out on-site at sea; instead, the monopile or a duct, for example, can be prepared accordingly onshore, thus accelerating the overall construction work and saving further costs.

[0030] The described embodiments of the present application can be used both individually and in combination to achieve additional effects and to provide a device and a method for reducing pile driving noise when driving a pile into the subsoil, which have improved sound insulation and reduced costs.

[0031] The above-mentioned and further aspects of the invention will become apparent from the detailed description of the embodiments given with the aid of the following drawings, of which:

[0032] Fig. 1: two versions of a device for

[0033] Reduction of pile-driving noise in perspective,

[0034] Fig. 2a and 2b: two versions of a device for

[0035] Show the reduction of the ram sound cladding tube in perspective,

[0036] Fig. 3: schematically shows a mounting rail provided with an array of local resonators,

[0037] Fig. 4a: an arrangement of strip resonators with

[0038] Damping elements in top view,

[0039] Fig. 4b: an arrangement of punched from a sheet

[0040] Resonators shown in perspective,

[0041] Fig. 5: shows the general structure of a wedge-shaped acoustic black hole,

[0042] Fig. 6: an embodiment of the device for reducing

[0043] Ramming sound as a pipe attachment with acoustic black hole, and

[0044] Fig. 7: an embodiment of the device for reducing

[0045] Ramming sound with acoustic black hole as thinning in the support structure.

[0046] The claimed subject matter and methods will be explained in more detail below based on the accompanying drawings. Like reference numerals refer to like elements. The pile 1 described here is a monopile 1 that is driven into the seabed. However, the embodiments presented can also be applied to other piles such as piles, planks, and steel profiles in onshore construction and civil engineering.

[0047] Fig. 1 shows how a monopile 1 can be provided with a device for reducing pile driving noise when a pile driver 1 is driven into the subsoil. The surfaces 2, 3 represent the areas of the monopile 1 that are provided with support structures 2 and structures for reducing vibrations 3. These can be attached both along the longitudinal axis of the monopile, as shown on the left in Fig. 1, and in the circumferential direction, as shown on the right in Fig. 1. The support structures 2 can be applied to the surface of the monopile 1 as plates or sheets, or fastened to it in the form of mounting rails, as described later with reference to Fig. 4. The support structures 2 can be welded, screwed, or riveted to the monopile 1. Structures for reducing vibrations 3 are applied to the support structures 2. Likewise, the support structures 2 can also be directly on the surface of the monopile.In this case, the vibration reduction structures 3 are applied directly to the surface of the monopile 1 or machined from it. The support structures 2 are coupled to the pile 1 in such a way that vibrations of the pile 1 are transmitted to the support structures 2.

[0048] The vibration reduction structures 3 reduce wave propagation in a selected frequency range in the material of the support structure 2 by exploiting vibroacoustic effects that generate a wavelength-dependent cutoff frequency for wave propagation. Since the support structure is coupled to the monopile 1, the vibration of the monopile 1 is also reduced, as is the pile-driving noise emitted by it. The frequency range can be freely selected by selecting the design of the vibration reduction structures 3; however, frequencies below 1000 Hz, for example, are relevant for sound insulation when driving monopiles into the seabed.

[0049] Fig. 2a and 2b show an embodiment in which the device for reducing pile driving noise when driving a pile 1 into the subsurface is instead attached to a cladding tube 8. Fig. 2a shows a simple cladding tube 8 that surrounds a monopile 1 during installation in the seabed. As in Fig. 1, the surfaces 2, 3 represent the areas of the cladding tube 8 that are provided with support structures 2 and structures for reducing vibrations 3. The further construction of the support structures also corresponds to that described with reference to Fig. 1. The monopile 1 can be guided through the cladding tube 8 during the driving impacts. The sound emitted by the monopile 1 during installation in the seabed is in turn reduced by structures for reducing vibrations 3, so that the cladding tube 8 does not transmit these outwards into the surrounding medium, here water. Fig.Figure 2b shows a double-walled cladding tube 8 with an air-filled gap between the walls. This design further enhances the soundproofing effect. Figure 3 schematically shows a support structure 2 onto which a vibration reduction structure 3 in the form of an array of local resonators 6 is mounted. The support structure 2 is a mounting rail 4 with a guide 5. Such a guide 5 enables particularly simple attachment of the support structure 2 to a pile 1 such as the monopile 1 or the cladding tube 8, which can also be removed again after the pile 1 has been driven into the ground. The mounting rail 4 is coupled to the pile 1 or a cladding tube 8 via the guide 5, so that the vibrations of the pile 1 or the cladding tube 8 are transmitted to the support structure 2.

[0050] The vibration reduction structure 3, shown schematically in Fig. 3, comprises an arrangement of local resonators 6. Each of these consists of an oscillating mass m, a spring element k, and a damping element d. Taken together, such an arrangement of local resonators 6 forms a vibroacoustic metamaterial. The periodically arranged resonant structures in the form of the local resonators 6 impart negative mass properties to the vibration reduction structure 3 and the support structure 2 coupled to it for a specific frequency range, so that wave propagation is severely impeded and a stop band is created. The position of the stop band can be adjusted by tuning the frequency of the local resonators 6: Each individual local resonator 6 has at least one natural or resonant frequency.All local resonators 6 of the arrangement can be tuned to at least one identical, or at least approximately identical, resonant frequency, so that upon external excitation at this frequency, i.e., by the vibration of the monopile 1 as a result of the piling impact, the resonance of the local resonators 6 is excited. Since these absorb the kinetic energy of the vibration, the oscillation of the support structure 2 is suppressed, and a stopband is created around the resonant frequency. However, the local resonators 6 can also be tuned to different resonant frequencies in order to create a wider, less defined stopband. The width of the stopband depends on the elastic spring properties k and the effective oscillating mass m of the local resonators 6, their damping d, and deviations in the tuning of the resonators 6 from one another.If the local resonators 6 have several natural frequencies in the selected frequency range, several stop bands can be created around them or a stop band can be broadened.

[0051] Fig. 4a and 4b show examples of structures for reducing vibrations 3 based on vibroacoustic metamaterials. Fig. 4a shows strip resonators. Here, an arrangement of local resonators 6 is cut from a plate material, for example, using a water jet. The resulting gaps can be filled with a damping material 7 in the form of rubber or plastic elements to determine the shape of the stop band. Fig. 4b shows another simple form of an arrangement of local resonators 6, in which they are punched from a sheet metal. Structures for reducing vibrations 3 in the form of vibroacoustic metamaterials are relatively easy to manufacture and allow precise control of the suppressed frequency range, which is why they are attractive for reducing the pile-driving noise radiated by a pile-driving element 1.

[0052] Another possibility for reducing pile-driving noise is a device that uses the acoustic black hole (ABH) effect. Fig. 5 shows a schematic representation of the structure of such an acoustic black hole 11. It is a section 9 of a plate or a beam 10. This is freely vibrating, which means that the other end of the beam 10 (not shown here) is firmly clamped. The beam 10 has a thickness ho, but thins continuously at its free end with the function h(x). This has the general form / i(x) = sx m, where x is the axial coordinate (in Fig. 5 from right to left), E is a constant and m is a real number that specifies the shape of the profile. Ideally, the thickness of the beam 10 would therefore asymptotically approach zero, as shown in dashed lines in Fig. 5. Due to this continuously decreasing thickness h(x), the wave propagation velocity in the beam 10 is also continuously reduced until it is completely absorbed. However, since a real beam 10 can never reach a thickness of zero, the actual profile of section 9 is given by the formula / i(x) = E(X + x T )' m where XT describes the end point of the beam and h(x T ) = sx T mthe remaining thickness. In practice, depending on the basic structure, thicknesses of a few millimeters can be achieved, which already provides good vibration reduction. However, the effect can be enhanced by applying a damping coating 12 to section 9. The damping coating 12 thus also absorbs the remaining energy of the wave trapped in the acoustic black hole 11.

[0053] An application of the acoustic black hole principle is shown in Fig. 6, again using the example of a monopile 1 as a pile drive. The support structure 2 is formed by a tubular attachment 13, and the vibration reduction structure 3 is formed by thinning the wall of the tubular attachment 13 in the form of an acoustic black hole 11. A damping coating 12 is additionally applied to the free end 9 of the acoustic black hole 11. The tubular attachment 13 is placed on the monopile 1. If the monopile 1 is set into vibration by ramming impacts, these waves propagate via the tubular attachment 13 into the acoustic black hole 11 and are absorbed there. The sound emitted by the monopile 1 is thus effectively reduced.

[0054] Fig. 7 shows an alternative embodiment of the device for reducing pile driving noise with an acoustic black hole 11. Here, the acoustic black hole 11 is formed by thinning the wall of the monopile as pile driving material 1. The wall of the monopile 1 thus forms the support structure 2, from which the structure for reducing vibrations 3 in the form of the acoustic black hole 11 is formed. The wall of the monopile 1 thins down to a minimum value that approaches the ideal value of zero, whereby the cross-sectional profile of the wall in this region is described by a continuous function. In the area of ​​the acoustic black hole 11, a damping coating 12 is additionally applied. If the monopile 1 is now set into vibration by pile driving impacts, these waves propagate into the acoustic black hole 11 and are absorbed there.

[0055] The embodiments of the device for reducing pile driving noise described with reference to Figs. 1 to 7 can be used to effectively reduce pile driving noise when driving piles into the subsurface. The corresponding method is described using the example of driving a monopile 1 into the seabed and involves attaching support structures 2 and vibration reduction structures 3 to the monopile 1 or a cladding tube 8. This preparatory step can be carried out onshore in the harbor, for example during the winter months when work would otherwise be at a standstill, or even directly during the construction of the monopile 1 and cladding tube 8. During the actual driving of the monopile 1 into the seabed by piling, no further soundproofing equipment is then required, which makes offshore construction work significantly simpler and reduces costs.After completion of the installation of the monopile 1, support structures 1 may also be removed and reused under certain circumstances.

[0056] Thus, the device presented here for reducing pile driving noise when driving a pile into the subsoil and the corresponding method for reducing pile driving noise when driving a pile into the subsoil have considerable advantages over conventional noise protection measures, particularly in offshore construction projects with monopiles, both in terms of improved performance in reducing pile driving noise and in economic terms.

[0057] The embodiments shown here are therefore not limiting. In particular, these embodiments can be combined with one another to achieve additional effects. It will be obvious to those skilled in the art that modifications can be made to these embodiments without departing from the fundamental principles of the subject matter of this patent application, the scope of which is defined in the claims.

Claims

Patent claims 1. Device for reducing pile driving noise when driving a pile (1) into a subsoil, comprising at least one support structure (2), a structure for reducing vibrations (3) which is coupled to the support structure (2), wherein the structure for reducing vibrations (3) has a wavelength-dependent cut-off frequency from which a broadband suppression of the wave propagation in the material of the support structure (2) takes place.

2. Device according to claim 1, wherein the support structure (2) comprises regions of the piling material (1) and the structure for reducing vibrations (3) is applied directly to the regions of the piling material (1) or is machined out of them.

3. Device according to claim 1 or 2, wherein the support structure (2) comprises mounting rails (4) which are connected to the pile (1) via a guide (5).

4. Device according to claim 1, characterized in that the support structure is coupled to a casing tube (8) which surrounds the pile (1) during its introduction into the subsoil.

5. Device according to one of the preceding claims, characterized in that the structure for reducing vibrations (3) comprises an array of local resonators (6) each having at least one common natural frequency in a selected frequency range, the array of local resonators (6) being configured to generate at least one stop band for wave propagation in the selected frequency range.

6. Device according to claim 5, characterized in that the arrangement of local resonators (6) is periodic and / or that a distance between the local resonators (6) is less than half a wavelength of a largest natural frequency of the local resonators (6).

7. Device according to one of claims 5 or 6, characterized in that a stop band for the wave propagation in the selected frequency range is formed by the arrangement of local resonators (6) due to Bragg scattering.

8. Device according to one of the preceding claims, characterized in that the vibration reduction structure (3) uses the effect of the acoustic black hole (11), the vibration reduction structure (3) comprising a section (9) of a plate or a beam (10) whose thickness decreases along its length with a continuous function and approaches a theoretical minimum value of zero.

9. Device according to claim 8, characterized in that a damping coating (12) is additionally applied to the section (9).

10. Device according to claim 8 or 9, characterized in that the support structure (2) is a pipe attachment (13) which is placed on an upper end of the piling material (1).

11. Method for reducing pile driving noise when driving a pile driver (1) into the subsoil, comprising the following steps: Applying at least one support structure (2) to a pile (1) or a cladding tube (8), wherein the support structure (2) is coupled to a structure for reducing vibrations (3) which has a wavelength-dependent cut-off frequency from which a broadband suppression of the wave propagation in the material of the support structure (2) takes place, Insertion of the ramming material (1) into the subsoil by ramming.

12. Method according to claim 11, characterized in that the support structure (2) in the form of mounting rails (4) which have a guide (5) for coupling to the pile (1) or the cladding tube (8) are applied to the pile (1) or the cladding tube (8).

13. The method according to claim 11 or 12, characterized in that the structure for reducing vibrations (3) is applied to the support structure (2) as an arrangement of local resonators (6), wherein the local resonators (6) each have at least one common natural frequency in the selected frequency range, wherein the arrangement of local resonators (6) is configured to generate at least one stop band for the wave propagation in the selected frequency range 14. Method according to claim 11 to 13, characterized in that the structure for reducing vibrations (3) uses the effect of the acoustic black hole (11), wherein the vibrating element is a section (9) of a plate or a beam (10) whose thickness decreases along its length with a continuous function and approaches a theoretical minimum value of zero 15. The method according to claim 11 to 14, additionally comprising the step Removing the support structure (2) from the pile (1) or the cladding tube (8) after the pile has been inserted into the subsoil.

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