WO2017068528A1 - System comprising a rotating assembly and related production method - Google Patents

System comprising a rotating assembly and related production method Download PDF

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Publication number
WO2017068528A1
WO2017068528A1 PCT/IB2016/056319 IB2016056319W WO2017068528A1 WO 2017068528 A1 WO2017068528 A1 WO 2017068528A1 IB 2016056319 W IB2016056319 W IB 2016056319W WO 2017068528 A1 WO2017068528 A1 WO 2017068528A1
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WO
WIPO (PCT)
Prior art keywords
soundproofing
frequencies
soundproofing element
band
outer casing
Prior art date
Application number
PCT/IB2016/056319
Other languages
French (fr)
Inventor
Georg Folie
Original Assignee
Windfin B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Windfin B.V. filed Critical Windfin B.V.
Publication of WO2017068528A1 publication Critical patent/WO2017068528A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D80/00—Details, components or accessories not provided for in groups F03D1/00 - F03D17/00
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D1/00—Wind motors with rotation axis substantially parallel to the air flow entering the rotor 
    • F03D1/06—Rotors
    • F03D1/065—Rotors characterised by their construction elements
    • F03D1/0675—Rotors characterised by their construction elements of the blades
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D1/00—Wind motors with rotation axis substantially parallel to the air flow entering the rotor 
    • F03D1/06—Rotors
    • F03D1/065—Rotors characterised by their construction elements
    • F03D1/0691—Rotors characterised by their construction elements of the hub
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2240/00—Components
    • F05B2240/10—Stators
    • F05B2240/14—Casings, housings, nacelles, gondels or the like, protecting or supporting assemblies there within
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2260/00—Function
    • F05B2260/96—Preventing, counteracting or reducing vibration or noise
    • F05B2260/962—Preventing, counteracting or reducing vibration or noise by means creating "anti-noise"
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a system comprising a rotating assembly and to a production method for said system.
  • This system finds application, for example, in wind plants, in cable transport systems and in snow groomer vehicles.
  • a wind plant comprises a nacelle and said system that, in turn, comprises the rotating assembly.
  • the rotating assembly of the system comprises a hub, blades mounted on the hub, and an electrical machine comprising a stator and a rotor kinetically coupled to the hub.
  • the wind strikes the blades and induces rotation of the hub about its axis, in this way transferring kinetic energy from the wind to the hub.
  • the rotation of the hub is transferred to the electrical machine, in particular to the rotor, which is coupled to and rotates with the hub about its axis.
  • the system is part of a cable transport system.
  • the cable transport system comprises a loading and unloading station, the system comprising the rotating assembly, at least one hauling cable, and a transport unit coupled to the hauling cable.
  • the rotating assembly of the system comprises an electrical machine coupled to the hauling cable.
  • the system is part of a snow groomer vehicle.
  • the snow groomer vehicle comprises at least one track, the system comprising the rotating assembly, and at least one working device coupled to the rotating assembly.
  • the rotating assembly comprises an internal combustion engine and a power transmission coupled to the internal combustion engine, to the track and to the working device to transmit kinetic energy from the internal combustion engine to the track and to the working device.
  • a system comprising an assembly rotating about an axis (A2), and at least one soundproofing element installed in proximity to the rotating assembly and comprising a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies located at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and, in particular, the metamaterial having a negative acoustic refractive index value at least partly in the 20 Hz to 1 kHz frequency range.
  • the system has higher cost performance than those of the known art because it can operate at any time during the day and even close to residential areas, as it is quieter than systems of the known art.
  • the reduction in noise is obtained without an excessive increase in weight or space and, in consequence, this solution can also be implemented as a retrofit in existing systems without having to modify the system's supporting structure.
  • the system it is possible for the system to have better cost performance even when it is configured to operate at low rotational speeds.
  • a wind plant comprising the system of claim 1, wherein the rotating assembly comprises a hub, at least one blade coupled to the hub, and a rotor coupled to the hub, and wherein at least one soundproofing element is at least partly installed around the rotating assembly; preferably, the rotating assembly comprises a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • the soundproofing element can be installed around the rotating assembly because it occupies little space and is light. In consequence, a light and low-noise rotating assembly is obtained.
  • at least one soundproofing element at least partly encloses the rotor and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies that comprises the operating angular frequencies of the rotor; preferably, the rotor has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • the metamaterial absorbs the noise at the operating angular frequency of the rotor, thereby reducing costs and increasing soundproofing efficiency.
  • At least one soundproofing element at least partly encloses the hub and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies that comprises the operating angular frequencies of the hub; preferably, the hub has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • At least one soundproofing element is integrated in the blade and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the blade; preferably, the blade has a protective outer casing and the soundproofing element is integrated in the protective outer casing .
  • the wind plant comprises an electrical machine, at least one soundproofing element at least partly encloses the electrical machine and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating frequencies of the electrical machine; preferably, the electrical machine has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • the wind plant comprises an electrical machine and an electrical energy conversion device coupled to the electrical machine, at least one soundproofing element at least partly encloses the conversion device and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating frequencies of the conversion device; preferably, the conversion device has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • the wind plant comprises a gearbox connected to the rotor and configured to transmit kinetic energy from the hub to the rotor with an operating angular frequency equal to a multiple of the operating angular frequency of the hub, at least one soundproofing element at least partly encloses the gearbox and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the gearbox; preferably, the gearbox has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • the wind plant comprises a nacelle, the nacelle being at least partly enclosed by at least one soundproofing element and where the metamaterial of the at least one soundproofing element has a negative refractive index value in a range of soundproofing frequencies comprising the operating frequencies of one of the components housed inside the nacelle; preferably, the nacelle has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
  • the wind plant comprises a supporting structure to support the nacelle at a given height from the ground, the supporting structure (2) being at least partly enclosed by the soundproofing element.
  • the metamaterial comprises a rigid structure and flexible membranes supported by the rigid structure; preferably, the rigid structure has a honeycomb shape and the flexible membranes occupy the gaps inside the rigid honeycomb structure.
  • the rigid structure has a cell structure in which the cells can have any shape, in particular, rectangular or square.
  • the flexible membranes incorporate the rigid structure .
  • the wind plant comprises a plurality of soundproofing elements having negative refractive index values in soundproofing frequency intervals differing from one another, and the soundproofing elements are preferably arranged one on top of the other to form layers of soundproofing elements.
  • a cable transport system comprises the system of claim 1.
  • the cable transport system comprises a loading and unloading station, at least one hauling cable and a transport unit coupled to the hauling cable.
  • the rotating assembly comprises at least one electrical machine coupled to the hauling cable and an auxiliary handling system of the transport unit.
  • a snow groomer vehicle comprises the system of claim 1.
  • the snow groomer vehicle also comprises at least one track and a working device coupled to the rotating assembly.
  • the rotating assembly comprises an internal combustion engine and a power transmission coupled to the internal combustion engine, to the track and to the working device, to transmit kinetic energy from the internal combustion engine to the track and to the working device.
  • Another object of the present invention is to provide a production method for a system that reduces the drawbacks of the known art .
  • a production method for producing a system comprising a rotating assembly, the method comprising the steps of determining a first band of operating frequencies of the system, obtaining a second band of frequencies based on comparison between the first band of frequencies and the band of frequencies audible to the human ear, selecting a soundproofing element having a metamaterial with a negative refractive index value in the second band of noise frequencies, and coupling the soundproofing element to the system or to a component of the system.
  • the step of obtaining the first band of frequencies is implemented through analysis of a model of the system or through detection of the noise produced by the system.
  • FIG. 1 is a side elevation view, with parts in section and parts removed for clarity, of a wind plant for the generation of electrical energy comprising a system according to an embodiment of the present invention
  • FIG. 2 is a side elevation view, on an enlarged scale and with parts in section and parts removed for clarity, of a detail in Figure 1 ;
  • FIG. 3 is a perspective, schematic view, with parts in section and parts removed for clarity, of a detail in Figure 1 ;
  • FIG. 4 is a side elevation view, on an enlarged scale and with parts in section and parts removed for clarity, of an alternative embodiment to the embodiment in Figure 1 ;
  • FIG. 5 is a side elevation view, with parts in section and parts removed for clarity, of a cable transport system comprising a system according to an embodiment of the present invention.
  • FIG. 6 is a side elevation view, with parts in section and parts removed for clarity, of a snow groomer vehicle comprising a system according to an embodiment of the present invention.
  • reference numeral 1 indicates a wind plant for the generation of electrical energy.
  • the wind plant 1 is a wind plant with variable angular velocity.
  • the wind plant 1 comprises a tower 2, a nacelle 3, a system 16a that in turn comprises a rotating assembly 16 and a plurality of soundproofing elements 24, an electrical energy conversion device 7, and a control device 8 for controlling the wind plant 1.
  • the rotating assembly 16 comprises a hub 4, three blades 5, and an electrical machine 6.
  • the three blades 5 are mounted on the hub 4, which is mounted on the nacelle 3, which, in turn, is mounted on the tower 2.
  • the nacelle 3 is mounted to rotate about an axis Al with respect to the tower 2 to orient the blades 5 to favour the wind, while the hub 4 is mounted to rotate about an axis A2 with respect to the nacelle 3.
  • each blade 5 is mounted to rotate, with respect to the hub 4, about a respective axis A3.
  • the hub 4 comprises a hollow shaft 9 and a fuselage 10, which have internal diameters such that an operator can access the insides thereof for possible maintenance or inspection operations.
  • the fuselage 10 and the hollow shaft 9 are rigidly connected to each other.
  • the hollow shaft 9 is mounted on the nacelle 3 by means of a bearing 11 and is connected directly to the electrical machine 6.
  • the electrical machine 6 comprises a stator 12 and a rotor 13.
  • the stator 12 defines a portion of the nacelle 3 and comprises stator windings 14, while the rotor 13 is hollow, comprises permanent magnets 15 and is fixed directly to the hollow shaft 9.
  • the electrical machine 6 is of the synchronous type .
  • the hub 4 rotates about axis A2, the rotation of the hub 4 being transferred to the rotor 13, which thus rotates about axis A2.
  • the relative movement of the permanent magnets 15 with respect to the stator windings 14 induces an electric current at the ends of the stator windings 14.
  • the relative movement takes place in the form of rotation of the rotor 13 at an angular velocity that is variable .
  • the hub 4, the blades 5 and the rotor 13 are integral with each other and define the rotating assembly 16, which is rotatable with respect to the nacelle 3 about axis A2.
  • the other non- rotating components of the wind plant 1 constitute the stator assembly . Therefore, in use, the rotating assembly 16 rotates at a given operating angular frequency emitting noise having a certain frequency.
  • the operating angular frequency can vary within a range of operating angular frequencies set by the control device 8 that runs from a minimum operating angular frequency to a maximum operating angular frequency.
  • the minimum and maximum operating angular frequencies are set for correct operation of the wind plant 1 so as to avoid damage to the wind plant.
  • the rotating assembly 16 will rotate at an operating angular frequency having a value delimited by the minimum operating angular frequency and the maximum operating angular frequency.
  • Each soundproofing element 24 comprises a metamaterial having a negative acoustic refractive index in a range of soundproofing frequencies that at least partly covers the band of frequencies audible to the human ear, i.e. the band of frequencies having range limits of 20 Hz and 20 kHz.
  • the metamaterial has a negative acoustic refractive index in a range of soundproofing frequencies that extends at least partly in the range of frequencies between 20 Hz and 1 kHz.
  • each soundproofing element 24 comprises a rigid structure 25 and flexible membranes
  • the rigid structure 25 has a honeycomb shape and the flexible membranes 26 occupy gaps
  • the rigid structure 25 is a cell structure with cells of any shape, in particular, rectangular or square.
  • the flexible membranes 26 incorporate the rigid structure 25.
  • each soundproofing element 24 is characterized by a certain negative acoustic refractive index value in a band of soundproofing frequencies. All of the soundproofing frequency bands cover at least part of the band of frequencies audible to the human ear.
  • one of the soundproofing elements 24 is at least partly installed around the rotating assembly 16.
  • one of the soundproofing elements 24 at least partly encloses the rotor 13.
  • the metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the rotor.
  • Another of the soundproofing elements 24 of the plurality of soundproofing elements 24 at least partly encloses the hub 4, in particular, the fuselage 10 of the hub 4.
  • the metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the hub 4.
  • Another of the soundproofing elements 24 of the plurality of soundproofing elements 24 at least partly encloses the blade 5.
  • the metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the blade 5.
  • the soundproofing element 24 is integrated in the blade 5.
  • Another of the soundproofing elements 24 of the plurality of soundproofing elements 24 at least partly encloses the electrical machine 6.
  • the metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the electrical machine 6.
  • Another element of the soundproofing elements 24 at least partly encloses the electrical energy conversion device 7 coupled to the electrical machine 6.
  • the metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating frequencies of the conversion device 8.
  • the rotating assembly 16 and, in particular, at least one of either the hub 4 or the rotor 3 is fitted with a protective outer casing 30 and the respective soundproofing element 24 is integrated in the protective outer casing 30.
  • the electrical machine 6 has a protective outer casing 30 and the soundproofing element 24 is integrated in the protective outer casing 30.
  • the conversion device 7 has a protective outer casing 30 and the soundproofing element 24 is integrated in the protective outer casing 30.
  • Another element of the soundproofing elements 24 at least partly encloses the nacelle 3.
  • the metamaterial of this soundproofing element 24 has a negative refractive index value in a range of soundproofing frequencies comprising the operating frequencies of one of the components housed inside the nacelle 3.
  • the nacelle 3 comprises a protective outer casing 30 and the soundproofing element 24 is integrated in the protective outer casing 30.
  • the soundproofing frequency bands of each soundproofing element 24 are chosen by defining a first band of acoustic noise frequencies caused by the component of the wind plant 1 to which the soundproofing element will be associated. Then, the soundproofing frequency band will be identified based on comparison between the first band of frequencies and the band of frequencies audible to the human ear.
  • the first band of frequencies is defined through analysis of a model of the component of the wind plant or through direct detection of the noise produced by the wind plant.
  • wind plant 101 replaces wind plant 1 and comprises a hub 104 and an electrical machine 106 comprising a rotor 113.
  • the wind plant 101 comprises a gearbox 150 interposed between the hub 104 and the rotor 113 of the electrical machine 106 to vary the operating angular frequency between the hub 104 and the rotor 113 of the electrical machine 106.
  • the gearbox 150 is configured to transmit kinetic energy to the rotor 113 at an operating angular frequency equal to a multiple of the operating angular frequency of the hub 104.
  • the wind plant 101 comprises a soundproofing element 124 that at least partly encloses the gearbox 150.
  • the metamaterial of this soundproofing element 124 has a negative refractive index in the band of operating frequencies of the gearbox 150.
  • the gearbox 150 has a protective outer casing 130 and the soundproofing element 24 is integrated in the protective outer casing 150.
  • reference numeral 201 indicates a cable transport system comprising a system 216a that comprises a rotating assembly 216 and a plurality of soundproofing elements 24, a loading and unloading station 202, at least one hauling cable 203, and a transport unit 204 coupled to the hauling cable 203.
  • the rotating assembly 216 comprises an electrical machine 206 having a rotor 216 coupled to the hauling cable 203 by a power transmission 208, and a wheel 209 to move the hauling cable 203; in addition, the rotating assembly comprises an auxiliary handling system 205 configured to move the transport unit 204 inside the loading and unloading station 202 when the transport units 204 are not clamped to the hauling cable 203.
  • the soundproofing elements 24 are at least partly installed around the rotating assembly 216; in particular, the soundproofing elements 24 enclose the electrical machine 206 and the auxiliary handling system 205.
  • the soundproofing elements 24 comprise a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and in particular from 20 Hz to 1 kHz.
  • reference numeral 301 indicates a snow groomer vehicle comprising a system 316a that comprises a rotating assembly 316 and a soundproofing element 324, a first and a second track 304, and a plurality of working devices 310 coupled to the rotating assembly 316.
  • the rotating assembly 316 comprises an internal combustion engine 306 and a power transmission 308 coupled to the internal combustion engine 306, to the tracks 304 and to the working devices 310, to transmit kinetic energy from the internal combustion engine to the tracks 304 and to the working devices 310.
  • the soundproofing elements 24 extend at least partly around the rotating assembly 316 and comprise a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies located at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and in particular from 20 Hz to 1 kHz.
  • the electrical machine can be of any other known type, such as the asynchronous type for example.

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Abstract

A system comprising a rotating assembly (16; 216; 316) rotating about an axis (A2 ), and at least one soundproofing element (24) installed in proximity to the rotating assembly (16; 216; 316) and comprising a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies located at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, in particular from 20 Hz to 1 kHz.

Description

SYSTEM COMPRISING A ROTATING ASSEMBLY AND RELATED PRODUCTION
ME THOD TECHNICAL FIELD
The present invention relates to a system comprising a rotating assembly and to a production method for said system.
This system finds application, for example, in wind plants, in cable transport systems and in snow groomer vehicles.
BACKGROUND ART
Generally, a wind plant comprises a nacelle and said system that, in turn, comprises the rotating assembly. In this case, the rotating assembly of the system comprises a hub, blades mounted on the hub, and an electrical machine comprising a stator and a rotor kinetically coupled to the hub. In such a wind plant, in use, the wind strikes the blades and induces rotation of the hub about its axis, in this way transferring kinetic energy from the wind to the hub. The rotation of the hub is transferred to the electrical machine, in particular to the rotor, which is coupled to and rotates with the hub about its axis.
In another embodiment, the system is part of a cable transport system. In greater detail, the cable transport system comprises a loading and unloading station, the system comprising the rotating assembly, at least one hauling cable, and a transport unit coupled to the hauling cable. The rotating assembly of the system comprises an electrical machine coupled to the hauling cable.
In another embodiment, the system is part of a snow groomer vehicle. In greater detail, the snow groomer vehicle comprises at least one track, the system comprising the rotating assembly, and at least one working device coupled to the rotating assembly. In particular, the rotating assembly comprises an internal combustion engine and a power transmission coupled to the internal combustion engine, to the track and to the working device to transmit kinetic energy from the internal combustion engine to the track and to the working device.
One problem of said systems is their cost performance, as they are used in expensive applications and are subject to usage restrictions. In other words, these systems cannot operate under all conditions and at all times and, by being expensive systems, they have low cost performance. In certain environments, the noise of these systems can cause big operability problems, because they can disturb people living nearby such systems, such as, for example, people living near wind plants or cable transport systems or ski slopes that use snow groomer vehicles. In some cases, the noise caused by these systems can be so annoying that there may be usage restrictions on the systems or even bans on using these systems. These bans may regard times when such a system may not operate, or environmental conditions, for example, certain wind speeds corresponding to certain speeds of the rotating assembly in a wind plant. This problem exists in wind plants of the direct drive type, i.e. without a gearbox between the hub and the electrical machine, because the rotating assembly of these wind plants rotates at a relatively low speed and, in consequence, creates a low-frequency noise, in particular in the frequency band audible to the human ear. Furthermore, always with regard to wind plants, direct-drive wind plants comprise large electrical machines and this makes soundproofing them difficult. The noise problem also exists in wind plants having a gearbox placed between the hub and the generator; in fact, the gearbox itself generates noise that is added to the noise caused by the rotating assembly.
DISCLOSURE OF INVENTION
One object of the present invention it to provide a system capable of limiting the drawbacks of the known art. According to the present invention, a system is provided that comprises an assembly rotating about an axis (A2), and at least one soundproofing element installed in proximity to the rotating assembly and comprising a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies located at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and, in particular, the metamaterial having a negative acoustic refractive index value at least partly in the 20 Hz to 1 kHz frequency range.
Thanks to the present invention, the system has higher cost performance than those of the known art because it can operate at any time during the day and even close to residential areas, as it is quieter than systems of the known art. The reduction in noise is obtained without an excessive increase in weight or space and, in consequence, this solution can also be implemented as a retrofit in existing systems without having to modify the system's supporting structure. Furthermore, thanks to the present invention, it is possible for the system to have better cost performance even when it is configured to operate at low rotational speeds.
According to a preferred embodiment of the present invention, a wind plant is provided comprising the system of claim 1, wherein the rotating assembly comprises a hub, at least one blade coupled to the hub, and a rotor coupled to the hub, and wherein at least one soundproofing element is at least partly installed around the rotating assembly; preferably, the rotating assembly comprises a protective outer casing and the soundproofing element is integrated in the protective outer casing.
Thanks to the present invention, the soundproofing element can be installed around the rotating assembly because it occupies little space and is light. In consequence, a light and low-noise rotating assembly is obtained. According to a preferred embodiment of the present invention, at least one soundproofing element at least partly encloses the rotor and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies that comprises the operating angular frequencies of the rotor; preferably, the rotor has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
Thanks to the present invention, the metamaterial absorbs the noise at the operating angular frequency of the rotor, thereby reducing costs and increasing soundproofing efficiency.
According to a preferred embodiment of the present invention, at least one soundproofing element at least partly encloses the hub and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies that comprises the operating angular frequencies of the hub; preferably, the hub has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
According to a preferred embodiment of the present invention, at least one soundproofing element is integrated in the blade and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the blade; preferably, the blade has a protective outer casing and the soundproofing element is integrated in the protective outer casing .
According to a preferred embodiment of the present invention, the wind plant comprises an electrical machine, at least one soundproofing element at least partly encloses the electrical machine and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating frequencies of the electrical machine; preferably, the electrical machine has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
According to a preferred embodiment of the present invention, the wind plant comprises an electrical machine and an electrical energy conversion device coupled to the electrical machine, at least one soundproofing element at least partly encloses the conversion device and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating frequencies of the conversion device; preferably, the conversion device has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
According to a preferred embodiment of the present invention, the wind plant comprises a gearbox connected to the rotor and configured to transmit kinetic energy from the hub to the rotor with an operating angular frequency equal to a multiple of the operating angular frequency of the hub, at least one soundproofing element at least partly encloses the gearbox and the metamaterial of the at least one soundproofing element has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the gearbox; preferably, the gearbox has a protective outer casing and the soundproofing element is integrated in the protective outer casing.
According to a preferred embodiment of the present invention, the wind plant comprises a nacelle, the nacelle being at least partly enclosed by at least one soundproofing element and where the metamaterial of the at least one soundproofing element has a negative refractive index value in a range of soundproofing frequencies comprising the operating frequencies of one of the components housed inside the nacelle; preferably, the nacelle has a protective outer casing and the soundproofing element is integrated in the protective outer casing. According to a preferred embodiment of the present invention, the wind plant comprises a supporting structure to support the nacelle at a given height from the ground, the supporting structure (2) being at least partly enclosed by the soundproofing element.
According to a preferred embodiment of the present invention, the metamaterial comprises a rigid structure and flexible membranes supported by the rigid structure; preferably, the rigid structure has a honeycomb shape and the flexible membranes occupy the gaps inside the rigid honeycomb structure.
According to another preferred embodiment of the present invention, the rigid structure has a cell structure in which the cells can have any shape, in particular, rectangular or square.
According to another preferred embodiment of the present invention, the flexible membranes incorporate the rigid structure . According to a preferred embodiment of the present invention, the wind plant comprises a plurality of soundproofing elements having negative refractive index values in soundproofing frequency intervals differing from one another, and the soundproofing elements are preferably arranged one on top of the other to form layers of soundproofing elements.
In another embodiment of the present invention, a cable transport system comprises the system of claim 1. In addition, the cable transport system comprises a loading and unloading station, at least one hauling cable and a transport unit coupled to the hauling cable. The rotating assembly comprises at least one electrical machine coupled to the hauling cable and an auxiliary handling system of the transport unit.
In another embodiment of the present invention, a snow groomer vehicle comprises the system of claim 1. The snow groomer vehicle also comprises at least one track and a working device coupled to the rotating assembly. In addition, the rotating assembly comprises an internal combustion engine and a power transmission coupled to the internal combustion engine, to the track and to the working device, to transmit kinetic energy from the internal combustion engine to the track and to the working device.
Another object of the present invention is to provide a production method for a system that reduces the drawbacks of the known art .
According to the present invention, a production method is provided for producing a system comprising a rotating assembly, the method comprising the steps of determining a first band of operating frequencies of the system, obtaining a second band of frequencies based on comparison between the first band of frequencies and the band of frequencies audible to the human ear, selecting a soundproofing element having a metamaterial with a negative refractive index value in the second band of noise frequencies, and coupling the soundproofing element to the system or to a component of the system.
According to a preferred embodiment of the present invention, the step of obtaining the first band of frequencies is implemented through analysis of a model of the system or through detection of the noise produced by the system.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics and advantages of the present invention will become clear from the description that follows of a non- limitative embodiment, with reference to the figures in the accompanying drawings, in which:
- Figure 1 is a side elevation view, with parts in section and parts removed for clarity, of a wind plant for the generation of electrical energy comprising a system according to an embodiment of the present invention;
- Figure 2 is a side elevation view, on an enlarged scale and with parts in section and parts removed for clarity, of a detail in Figure 1 ;
- Figure 3 is a perspective, schematic view, with parts in section and parts removed for clarity, of a detail in Figure 1 ;
- Figure 4 is a side elevation view, on an enlarged scale and with parts in section and parts removed for clarity, of an alternative embodiment to the embodiment in Figure 1 ;
- Figure 5 is a side elevation view, with parts in section and parts removed for clarity, of a cable transport system comprising a system according to an embodiment of the present invention; and
- Figure 6 is a side elevation view, with parts in section and parts removed for clarity, of a snow groomer vehicle comprising a system according to an embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to Figure 1 and 2, reference numeral 1 indicates a wind plant for the generation of electrical energy.
In the case shown, the wind plant 1 is a wind plant with variable angular velocity.
The wind plant 1 comprises a tower 2, a nacelle 3, a system 16a that in turn comprises a rotating assembly 16 and a plurality of soundproofing elements 24, an electrical energy conversion device 7, and a control device 8 for controlling the wind plant 1. The rotating assembly 16 comprises a hub 4, three blades 5, and an electrical machine 6. The three blades 5 are mounted on the hub 4, which is mounted on the nacelle 3, which, in turn, is mounted on the tower 2. In particular, the nacelle 3 is mounted to rotate about an axis Al with respect to the tower 2 to orient the blades 5 to favour the wind, while the hub 4 is mounted to rotate about an axis A2 with respect to the nacelle 3. In turn, each blade 5 is mounted to rotate, with respect to the hub 4, about a respective axis A3.
Referring to Figure 2, the hub 4 comprises a hollow shaft 9 and a fuselage 10, which have internal diameters such that an operator can access the insides thereof for possible maintenance or inspection operations. The fuselage 10 and the hollow shaft 9 are rigidly connected to each other.
The hollow shaft 9 is mounted on the nacelle 3 by means of a bearing 11 and is connected directly to the electrical machine 6.
The electrical machine 6 comprises a stator 12 and a rotor 13. The stator 12 defines a portion of the nacelle 3 and comprises stator windings 14, while the rotor 13 is hollow, comprises permanent magnets 15 and is fixed directly to the hollow shaft 9.
In the case shown, the electrical machine 6 is of the synchronous type .
Under the action of the wind, the hub 4 rotates about axis A2, the rotation of the hub 4 being transferred to the rotor 13, which thus rotates about axis A2. The relative movement of the permanent magnets 15 with respect to the stator windings 14 induces an electric current at the ends of the stator windings 14. In particular, the relative movement takes place in the form of rotation of the rotor 13 at an angular velocity that is variable .
The hub 4, the blades 5 and the rotor 13 are integral with each other and define the rotating assembly 16, which is rotatable with respect to the nacelle 3 about axis A2. The other non- rotating components of the wind plant 1 constitute the stator assembly . Therefore, in use, the rotating assembly 16 rotates at a given operating angular frequency emitting noise having a certain frequency. The operating angular frequency can vary within a range of operating angular frequencies set by the control device 8 that runs from a minimum operating angular frequency to a maximum operating angular frequency. The minimum and maximum operating angular frequencies are set for correct operation of the wind plant 1 so as to avoid damage to the wind plant. In other words, in use, the rotating assembly 16 will rotate at an operating angular frequency having a value delimited by the minimum operating angular frequency and the maximum operating angular frequency.
Each soundproofing element 24 comprises a metamaterial having a negative acoustic refractive index in a range of soundproofing frequencies that at least partly covers the band of frequencies audible to the human ear, i.e. the band of frequencies having range limits of 20 Hz and 20 kHz. In a preferred embodiment, the metamaterial has a negative acoustic refractive index in a range of soundproofing frequencies that extends at least partly in the range of frequencies between 20 Hz and 1 kHz.
Referring to Figure 3, the metamaterial of each soundproofing element 24 comprises a rigid structure 25 and flexible membranes
26 supported by the rigid structure 25. The rigid structure 25 has a honeycomb shape and the flexible membranes 26 occupy gaps
27 formed by the honeycomb structure. According to another embodiment, the rigid structure 25 is a cell structure with cells of any shape, in particular, rectangular or square.
In another embodiment, the flexible membranes 26 incorporate the rigid structure 25.
The rigid structure 25 and the flexible membranes 26 are sized according to the refractive index value and the soundproofing frequencies it is wished to achieve. In consequence, each soundproofing element 24 is characterized by a certain negative acoustic refractive index value in a band of soundproofing frequencies. All of the soundproofing frequency bands cover at least part of the band of frequencies audible to the human ear.
Referring to Figure 2, one of the soundproofing elements 24 is at least partly installed around the rotating assembly 16. In greater detail, one of the soundproofing elements 24 at least partly encloses the rotor 13. The metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the rotor.
Another of the soundproofing elements 24 of the plurality of soundproofing elements 24 at least partly encloses the hub 4, in particular, the fuselage 10 of the hub 4. The metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the hub 4.
Another of the soundproofing elements 24 of the plurality of soundproofing elements 24 at least partly encloses the blade 5. The metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the blade 5. In a preferred embodiment, the soundproofing element 24 is integrated in the blade 5.
Another of the soundproofing elements 24 of the plurality of soundproofing elements 24 at least partly encloses the electrical machine 6. The metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating angular frequencies of the electrical machine 6.
Another element of the soundproofing elements 24 at least partly encloses the electrical energy conversion device 7 coupled to the electrical machine 6. The metamaterial of said soundproofing element 24 has a negative refractive index in a band of soundproofing frequencies that at least partly overlaps the band of operating frequencies of the conversion device 8. Furthermore, in one non-limitative embodiment of the present invention, the rotating assembly 16 and, in particular, at least one of either the hub 4 or the rotor 3 is fitted with a protective outer casing 30 and the respective soundproofing element 24 is integrated in the protective outer casing 30.
In another embodiment, the electrical machine 6 has a protective outer casing 30 and the soundproofing element 24 is integrated in the protective outer casing 30. In another embodiment, the conversion device 7 has a protective outer casing 30 and the soundproofing element 24 is integrated in the protective outer casing 30.
Another element of the soundproofing elements 24 at least partly encloses the nacelle 3. The metamaterial of this soundproofing element 24 has a negative refractive index value in a range of soundproofing frequencies comprising the operating frequencies of one of the components housed inside the nacelle 3. In one embodiment, the nacelle 3 comprises a protective outer casing 30 and the soundproofing element 24 is integrated in the protective outer casing 30.
The soundproofing frequency bands of each soundproofing element 24 are chosen by defining a first band of acoustic noise frequencies caused by the component of the wind plant 1 to which the soundproofing element will be associated. Then, the soundproofing frequency band will be identified based on comparison between the first band of frequencies and the band of frequencies audible to the human ear. The first band of frequencies is defined through analysis of a model of the component of the wind plant or through direct detection of the noise produced by the wind plant.
Furthermore, in one embodiment a plurality of soundproofing elements 24 having negative refractive index values in soundproofing frequency intervals differing from one another are arranged one on top of the other and form layers of soundproofing elements 24. The layers of soundproofing elements 24 enclose any one of the above-mentioned components of the wind plant 1. In a further embodiment of the present invention shown in Figure 4, wind plant 101 replaces wind plant 1 and comprises a hub 104 and an electrical machine 106 comprising a rotor 113. The wind plant 101 comprises a gearbox 150 interposed between the hub 104 and the rotor 113 of the electrical machine 106 to vary the operating angular frequency between the hub 104 and the rotor 113 of the electrical machine 106. In particular, the gearbox 150 is configured to transmit kinetic energy to the rotor 113 at an operating angular frequency equal to a multiple of the operating angular frequency of the hub 104.
The wind plant 101 comprises a soundproofing element 124 that at least partly encloses the gearbox 150. The metamaterial of this soundproofing element 124 has a negative refractive index in the band of operating frequencies of the gearbox 150. In another embodiment, the gearbox 150 has a protective outer casing 130 and the soundproofing element 24 is integrated in the protective outer casing 150.
Referring to Figure 5, reference numeral 201 indicates a cable transport system comprising a system 216a that comprises a rotating assembly 216 and a plurality of soundproofing elements 24, a loading and unloading station 202, at least one hauling cable 203, and a transport unit 204 coupled to the hauling cable 203. The rotating assembly 216 comprises an electrical machine 206 having a rotor 216 coupled to the hauling cable 203 by a power transmission 208, and a wheel 209 to move the hauling cable 203; in addition, the rotating assembly comprises an auxiliary handling system 205 configured to move the transport unit 204 inside the loading and unloading station 202 when the transport units 204 are not clamped to the hauling cable 203. The soundproofing elements 24 are at least partly installed around the rotating assembly 216; in particular, the soundproofing elements 24 enclose the electrical machine 206 and the auxiliary handling system 205. The soundproofing elements 24 comprise a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and in particular from 20 Hz to 1 kHz. Referring to Figure 6, reference numeral 301 indicates a snow groomer vehicle comprising a system 316a that comprises a rotating assembly 316 and a soundproofing element 324, a first and a second track 304, and a plurality of working devices 310 coupled to the rotating assembly 316. The rotating assembly 316 comprises an internal combustion engine 306 and a power transmission 308 coupled to the internal combustion engine 306, to the tracks 304 and to the working devices 310, to transmit kinetic energy from the internal combustion engine to the tracks 304 and to the working devices 310. The soundproofing elements 24 extend at least partly around the rotating assembly 316 and comprise a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies located at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and in particular from 20 Hz to 1 kHz.
It is understood that although specific reference has been made to a synchronous type of electrical machine, the electrical machine can be of any other known type, such as the asynchronous type for example.
Finally, it is clear that modifications and variants can be made to the apparatuses and to the method described herein without departing from the scope of the appended claims.

Claims

1. A system comprising a rotating assembly (16; 216; 316) rotating about an axis (A2), and at least one soundproofing element (24) installed in proximity to the rotating assembly (16; 216; 316) and comprising a metamaterial having a negative acoustic refractive index value in at least one range of soundproofing frequencies located at least partly inside the band of frequencies audible to the human ear, preferably from 20 Hz to 20 kHz, and in particular from 20 Hz to 1 kHz.
2. A wind plant comprising the system of claim 1, wherein the rotating assembly (16) comprises a hub (4), at least one blade (5) coupled to the hub (4), and a rotor (13; 113) coupled to the hub (4), and wherein at least one soundproofing element (24) is at least partly installed around the rotating assembly (16); preferably, the rotating assembly (16) comprises a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
3. The wind plant according to claim 2, wherein the at least one soundproofing element (24) at least partly encloses the rotor (13) and the metamaterial of the at least one soundproofing element (24) has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the rotor (13); preferably, the rotor (13) has a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
4. The wind plant according to claim 2 or 3, wherein the at least one soundproofing element (24) at least partly encloses the hub (4) and the metamaterial of at least one soundproofing element (24) has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the hub (4) ; preferably, the hub (4) has a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
5. The wind plant according to any one of claims 2 to 4, wherein the at least one soundproofing element (24) is integrated in the blade (5) and the metamaterial of at least one soundproofing element (24) has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the blade (5) ; preferably, the blade (5) has a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
6. The wind plant according to any one of claims 2 to 5, comprising an electrical machine (6), wherein the at least one soundproofing element (24) at least partly encloses the electrical machine (6) and the metamaterial of at least one soundproofing element (24) has a negative refractive index value in a band of soundproofing frequencies comprising the operating frequencies of the electrical machine (6) ; preferably, the electrical machine (6) has a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
7. The wind plant according to any one of claims 2 to 6, comprising an electrical machine (6) and an electrical energy conversion device (7) coupled to the electrical machine (6) , wherein the at least one soundproofing element (24) at least partly encloses the conversion device (7) and the metamaterial of the at least one soundproofing element (24) has a negative acoustic refractive index value in a band of soundproofing frequencies comprising the operating frequencies of the conversion device (7); preferably, the conversion device (7) has a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
8. The wind plant according to any one of claims 2 to 7, comprising a gearbox (150) connected to the rotor (113) and configured to transmit kinetic energy from the hub (4) to the rotor (113) with an operating angular frequency equal to a multiple of the operating angular frequency of the hub (104), wherein the at least one soundproofing element (24) at least partly encloses the gearbox (150) and the metamaterial of the at least one soundproofing element (24) has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of the gearbox (150); preferably, the gearbox (150) has a protective outer casing (130) and the soundproofing element (24) is integrated in the protective outer casing (150) .
9. The wind plant according to any one of claims 2 to 8, comprising a nacelle (3), the nacelle (3) being at least partly enclosed by at least one soundproofing element (24), wherein the metamaterial of the at least one soundproofing element (24) has a negative refractive index value in a band of soundproofing frequencies comprising the operating angular frequencies of one of the components housed inside the nacelle (3); preferably, the nacelle (3) has a protective outer casing (30) and the soundproofing element (24) is integrated in the protective outer casing (30) .
10. The wind plant according to any one of claims 2 to 9, comprising a supporting structure (2) to support the nacelle (3) at a given height from the ground, the supporting structure (2) being at least partly enclosed by the soundproofing element (24) .
11. The wind plant according to any one of claims 2 to 10, wherein the metamaterial comprises a rigid structure (25) and flexible membranes (26) supported by the rigid structure (25) ; preferably, the rigid structure (25) has a cell structure with rectangular, square or honeycomb cells and the flexible membranes (26) occupy the gaps (27) inside the rigid structure (25) or incorporate the rigid structure (25) .
12. The wind plant according to any one of claims 2 to 11, comprising a plurality of soundproofing elements (24) having negative refractive index values in soundproofing frequency intervals differing from one another, wherein the soundproofing elements (25) are preferably arranged one on top of the other to form layers of soundproofing elements (24) .
13. A cable transport system comprising the system of claim 1 and a loading and unloading station (202), at least one hauling cable (203) and a transport unit (204) coupled to the hauling cable (203), and wherein the rotating assembly (216) comprises an electrical machine (206) coupled to the hauling cable (203) .
14. A snow groomer vehicle comprising the system of claim 1, at least one track (304) and at least one working device
(310) coupled to the rotating assembly (316), and wherein the rotating assembly (316) comprises an internal combustion engine (306) and a power transmission (308) coupled to the internal combustion engine (306), to the track (304) and to the working device (310), to transmit kinetic energy.
15. A production method of a system, the system comprising a rotating assembly (16; 216; 316), and the method comprises the steps of determining a first band of operating frequencies of the system, obtaining a second band of frequencies based on comparison between the first band of frequencies and the band of frequencies audible to the human ear, selecting a soundproofing element (24) having a metamaterial with a negative acoustic refractive index value in the second band of noise frequencies, and coupling the soundproofing element (24) to the system (16a; 216a; 316a) or to a component of the system (16a; 216a; 316a) .
16. The production method of claim 15; wherein the step of obtaining the first band of frequencies is implemented through analysis of a wind model of the system (16a; 216a; 316a) or through detection of the noise produced by the system (16a; 216a; 316a) .
PCT/IB2016/056319 2015-10-20 2016-10-20 System comprising a rotating assembly and related production method WO2017068528A1 (en)

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Citations (5)

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EP1515040A1 (en) * 2003-09-10 2005-03-16 General Electric Company Wind turbine with outer noise shell
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KR20130051696A (en) * 2011-11-10 2013-05-21 현대자동차주식회사 Noise reduction material using acoustic meta-material
US20140238734A1 (en) * 2013-02-27 2014-08-28 United States Government, As Represented By The Secretary Of The Navy Electromagnetic Cloak Using Metal Lens
WO2015007221A1 (en) * 2013-07-18 2015-01-22 The Hong Kong University Of Science And Technology Extraordinary acoustic absorption induced by hybrid resonance and electrical energy generation from sound by hybrid resonant metasurface

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1515040A1 (en) * 2003-09-10 2005-03-16 General Electric Company Wind turbine with outer noise shell
CN101235801A (en) * 2007-02-01 2008-08-06 上海电气风电设备有限公司 Wind-driven generator group machinery space sound-insulating structure
KR20130051696A (en) * 2011-11-10 2013-05-21 현대자동차주식회사 Noise reduction material using acoustic meta-material
US20140238734A1 (en) * 2013-02-27 2014-08-28 United States Government, As Represented By The Secretary Of The Navy Electromagnetic Cloak Using Metal Lens
WO2015007221A1 (en) * 2013-07-18 2015-01-22 The Hong Kong University Of Science And Technology Extraordinary acoustic absorption induced by hybrid resonance and electrical energy generation from sound by hybrid resonant metasurface

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