A rotating machine over-critical permanent magnet eddy current damping device and a manufacturing method thereof

Abstract

This invention relates to the field of supercritical high-speed rotating machinery, and particularly to a permanent magnet eddy current vibration damping device for supercritical rotating machinery and its manufacturing method. The device includes a rotor, a bearing mounted at the lower end of the rotor, a motor rotor disk mounted at the lower end of the bearing, and a damper connected to the lower end of the motor rotor disk. A permanent magnet eddy current vibration damping structure is mounted on the upper flange of the rotating machinery above the upper cover of the rotor. A magnetic guiding structure is provided above the permanent magnet eddy current vibration damping structure. The permanent magnet eddy current vibration damping structure and the magnetic guiding structure are concentrically arranged, with a gap between them. The permanent magnet eddy current vibration damping structure of this device is directly mounted on the machine casing as a stationary component, and will not affect rotating components such as the rotor. The device effectively utilizes the upper metal cover of the rotor to generate a damping effect. Through a reasonable design of the permanent magnet array, a damping force can be generated on the upper metal cover through the eddy current effect, thereby suppressing the amplitude of vibration.

Description

Technical Field

[0001] This invention relates to the field of supercritical high-speed rotating machinery, and in particular to a permanent magnet eddy current vibration damping device for supercritical rotating machinery and its manufacturing method. Background Technology

[0002] High-speed rotating machinery is widely used in aviation, aerospace, and automotive fields. Based on the relationship between operating speed and rotor natural frequency, it is classified into subcritical and supercritical types. Supercritical rotors are longer and operate at higher speeds. Their critical speed is lower than the operating speed, and they must pass through the critical speed during acceleration, making them prone to asynchronous precession. Supercritical rotors are driven by a motor for acceleration, and their vibration amplitude is related to unbalanced mass, dampers, bearings, etc. Approaching the critical speed, the amplitude increases rapidly, returning to normal after passing through it. To reach the operating speed, the rotor must pass through multiple critical speeds, facing multiple amplitude increases. Increased amplitude can cause the rotor to rub against the protective bearings, generating impact and heat, leading to deformation or even failure. Therefore, how to suppress the amplitude of the rotor when it passes the critical speed is a key issue that must be addressed in the design of supercritical rotating machinery.

[0003] In existing technologies, a common method for suppressing the vibration amplitude of rotating machinery rotors is dynamic balancing. The deviation between the rotor's center of mass and centroid creates an unbalanced mass; reducing this unbalanced mass reduces the amplitude of the rotor during the supercritical process. By attaching counterweights to the corresponding points of the unbalanced mass, the overall unbalanced mass of the rotor can be reduced. However, applying this technology to a vertical supercritical rotor presents certain challenges. Experiments have shown that the rotor counterweight accuracy needs to reach the mg level. Firstly, it is difficult to control the unbalanced mass to this level through the molding process; secondly, the dynamic balancing process is inefficient and difficult to scale up for mass production.

[0004] Other methods for suppressing the vibration amplitude of rotating machinery rotors include electromagnetic force and pneumatic methods. Electromagnetic bearings are a typical device for controlling rotor vibration, but for supercritical and ultra-high-speed rotating machinery, it is necessary to add magnetically conductive silicon steel sheets to the rotor, which affects the rotor's strength performance, making it difficult to use. Pneumatic bearings are also devices for controlling rotor vibration, but due to the high speed, ultra-high-speed supercritical rotors operate in a high-vacuum environment to reduce energy loss caused by wind resistance, which contradicts the high-pressure gas required for pneumatic bearings, making pneumatic methods difficult to use.

[0005] Permanent magnet eddy current damping is a novel method for suppressing vibration. It utilizes the relative motion of moving and stationary components as the driving force, generating eddy currents in the metal through electromagnetic induction. The vibration energy is then dissipated through Lorentz force and eddy current heat generation. Currently, there is a lack of applications for permanent magnet eddy current damping technology in vibration reduction devices for vertical supercritical rotating machinery. Summary of the Invention

[0006] This invention provides a permanent magnet eddy current vibration damping device for overcritical rotating machinery and its manufacturing method, which solves the problem of the lack of vibration damping devices in the prior art that apply permanent magnet eddy current damping technology to vertical overcritical rotating machinery.

[0007] The technical solution of the present invention is as follows: This invention provides a permanent magnet eddy current vibration damping device for over-critical rotating machinery. The device includes a rotor, a bearing, a damper, a motor rotor disk, a magnetic guiding structure, and a permanent magnet eddy current vibration damping structure. The bearing is installed at the lower end of the rotor, and the motor rotor disk is installed at the lower end of the bearing. The damper is connected to the lower end of the motor rotor disk. The permanent magnet eddy current vibration damping structure is installed at the upper end of the rotor and is mounted on the upper flange of the rotating machinery above the upper end cover of the rotor. A magnetic guiding structure is provided above the permanent magnet eddy current vibration damping structure. The permanent magnet eddy current vibration damping structure and the magnetic guiding structure are arranged concentrically, and there is a gap between the permanent magnet eddy current vibration damping structure and the magnetic guiding structure.

[0008] In some embodiments, a magnetic bearing is provided above the magnetically conductive structure, and the interaction between the magnetically conductive structure and the magnetic bearing provides radial stiffness.

[0009] In some embodiments, the permanent magnet eddy current vibration reduction structure includes several magnetic rings, and the magnetic rings are nested together to form a ring-shaped permanent magnet array; the ring-shaped permanent magnet array consists of multiple coaxial magnetic rings arranged radially from the inner diameter to the outer diameter, and the progressive gradient of the remanence of the permanent magnet rings is set according to the requirement of the smoothness of the magnetic field gradient.

[0010] In some embodiments, the magnetic ring is magnetized as a whole or is spliced ​​from multiple arc-shaped tiles. All magnetic rings are axially magnetized, and adjacent nested magnetic rings have opposite polarities. By selecting grades with progressively increasing remanence, an axial trapezoidal magnetic field with gradually increasing radial strength is formed in the working air gap. A magnetic yoke back iron is provided above the annular permanent magnet array.

[0011] This invention proposes a method for manufacturing a permanent magnet eddy current vibration damping device for over-critical rotating machinery, the method comprising: Step 1: Measure the dimensions of the permanent magnet eddy current vibration reduction structure on the upper flange structure of the vertical supercritical rotating machinery, and obtain the initial dimensions of the permanent magnet eddy current vibration reduction structure based on the flange structure dimensions; Step 2: Determine the structural dimensions and material properties of the rotor's upper end cover as input parameters for designing the permanent magnet eddy current vibration reduction structure; Step 3: Design and fabricate permanent magnet eddy current vibration reduction structure; Step 3.1: Calculate the total damping force of the permanent magnet eddy current vibration reduction structure. ; Step 3.2: Adjust the magnetic ring structure dimensions, arrangement, and gap between the magnetic ring and the rotor upper end cover to obtain the total damping force. The optimal solution; Step 3.3: Fabricate the permanent magnet eddy current vibration reduction structure according to the design; Step 4: Connect the permanent magnet eddy current vibration damping structure to the upper flange of the vertical supercritical rotating machinery; Step 5: Adjust the rotor position by adding gaskets to the upper flange of the rotating machinery to ensure that the gap between the permanent magnet eddy current damping structure and the upper end cover of the rotor meets the design requirements.

[0012] In some embodiments, the initial dimensions of the permanent magnet eddy current damping structure in step one include the inner diameter, outer diameter, and thickness.

[0013] In some embodiments, the damping force in step 3.1 The calculation formula is as shown in formula (1). Where c is the damping coefficient and v is the rotor speed. The conductivity of the rotor end cover, For rotor end cover thickness, The magnetic ring and yoke together form an axisymmetric axial magnetic field in the working air gap, and the rotor covers a radial range of... , where r is the rotor radius.

[0014] In some embodiments, in step four, a groove is machined into the flange structure based on the dimensions of the permanent magnet eddy current vibration damping structure, and the permanent magnet eddy current vibration damping structure is installed in the groove by adhesive bonding.

[0015] The implementation of this invention has the following beneficial effects: This invention proposes a permanent magnet eddy current vibration damping device for rotating machinery passing through critical speeds. The permanent magnet eddy current vibration damping structure of this device is directly installed on the machine casing as a stationary component, without affecting rotating components such as the rotor. The device effectively utilizes the rotor's metal upper cover to generate a damping effect, avoiding the need to add extra material to the rotor and thus affecting its strength performance. When the rotor passes through the critical speed or precession, the amplitude increases, and the horizontal vibration speed of the metal upper cover increases. By rationally designing the permanent magnet array, it is possible to ensure that damping force is generated on the metal upper cover through the eddy current effect, thereby suppressing the vibration amplitude. Moreover, the damping generated by the device is a direct damping effect on the rotor, which is more effective than the indirect damping effect of a damper on the rotor. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a permanent magnet eddy current vibration damping device for overcritical rotating machinery according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the permanent magnet eddy current vibration reduction structure of a permanent magnet eddy current vibration reduction device for over-critical rotating machinery according to an embodiment of the present invention. Figure 3 This is a cross-sectional view of a permanent magnet eddy current vibration reduction structure for a rotating machinery overcritical vibration reduction device proposed in an embodiment of the present invention. Explanation of reference numerals in the attached drawings: 1. Rotor; 2. Bearing; 3. Damper; 4. Motor rotor disc; 5. Rotor upper end cover; 6. Permanent magnet eddy current vibration reduction structure; 7. Magnetic guiding structure; 8. Magnetic bearing; 9. Magnetic ring. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figures 1 to 2 As shown, the present invention proposes a permanent magnet eddy current vibration reduction device for overcritical rotating machinery. The device includes a vertically mounted rotor 1, a bearing 2, a damper 3, a motor rotor disk 4, a magnetic guiding structure 7, a magnetic bearing 8, and a permanent magnet eddy current vibration reduction structure 6.

[0019] A bearing 2 is installed at the lower end of rotor 1, and a motor rotor disk 4 is installed at the lower end of bearing 2. A damper 3 is connected to the lower end of motor rotor disk 4. The connection between bearing 2 and oil damper 3 provides radial stiffness and damping for this device. The motor drives motor rotor disk 4 to make rotor 1 rotate and increase speed.

[0020] A permanent magnet eddy current damping structure 6 is installed on the upper end of rotor 1. This structure is mounted on the upper flange of the vertical transcritical rotating machinery above the rotor's upper end cover 5. A magnetic guiding structure 7 is located above the permanent magnet eddy current damping structure 6. The permanent magnet eddy current damping structure 6 and the magnetic guiding structure 7 are arranged concentrically, maintaining a certain gap between them. A magnetic bearing 8 is located above the magnetic guiding structure 7. The interaction between the magnetic guiding structure 7 and the magnetic bearing 8 provides radial stiffness.

[0021] like Figure 3 As shown, the permanent magnet eddy current vibration reduction structure 6 includes several magnetic rings 9, which are nested together to form a ring-shaped permanent magnet array. The ring-shaped permanent magnet array consists of multiple coaxial magnetic rings 9 arranged radially from the inner diameter to the outer diameter. The progressive gradient of the remanence of the permanent magnet rings 9 is set according to the requirement of the smoothness of the magnetic field gradient.

[0022] Each magnetic ring 9 can be magnetized as a whole or assembled from multiple arc-shaped tiles. All magnetic rings 9 are axially magnetized, with adjacent rings having opposite polarities (N / S alternation on the upper surface). By selecting grades with progressively increasing remanence (e.g., transitioning from N35 to N52 on the outer ring), an axial trapezoidal magnetic field with gradually increasing radial strength is formed in the working air gap. A magnetic yoke back iron is installed above the annular permanent magnet array to close the magnetic circuit, guide magnetic lines of force downwards to concentrate in the working air gap, enhance the axial magnetic field, and suppress back-side leakage magnetic field. The device is based on the principle of radial eddy current damping: when the rotor 1 rotates concentrically, facing the axisymmetrically distributed axial constant magnetic field, the magnetic flux within the conductor plate remains unchanged, and no rotational eddy current resistance is generated; once the rotor 1 undergoes radial displacement and cuts the axial trapezoidal magnetic field, the local rate of change of magnetic flux increases, inducing eddy currents which are dissipated as conductor resistance heat, forming a damping force opposite to the direction of vibration.

[0023] This invention proposes a method for manufacturing a permanent magnet eddy current vibration damping device for over-critical rotating machinery, the method comprising: Step 1: Measure the dimensions of the permanent magnet eddy current vibration damping structure 6 on the upper flange structure of the vertical transcritical rotating machinery, and give the initial dimensions of the permanent magnet eddy current vibration damping structure 6, including the inner diameter, outer diameter, and thickness.

[0024] Step 2: Determine the structural dimensions and material properties of the rotor upper cover 5 by consulting the design drawings and material test reports, as input parameters for the design.

[0025] Step 3: Design a permanent magnet eddy current vibration reduction structure 6; Step 3.1: Establish a physical model for the permanent magnet eddy current vibration reduction structure 6 and calculate the total damping force. , The calculation formula is as shown in formula (1): Where c is the damping coefficient and v is the rotor speed. The conductivity of rotor end cap 1 is The thickness of rotor end cap 1 The magnetic ring 9 and the magnetic yoke together form an axisymmetric axial magnetic field in the working air gap, and the rotor 1 covers a radial range of... , where r is the rotor radius.

[0026] The specific derivation of the formula is as follows: the eddy current damping force provided by the trapezoidal magnetic field during rotor lateral vibration can be derived based on the eddy current field equation in the thin conductor plate. The two magnetic rings 9 and the magnetic yoke together form an axisymmetric axial magnetic field in the working air gap. It varies only radially and has a trapezoidal distribution, therefore The calculation is as shown in formula (2): (2) in For radial gradient, Let r be the magnetic flux density at the inner and outer boundaries, r be the radius of the magnetic ring, r1 be the inner boundary radius of the magnetic ring, and r2 be the outer boundary radius of the magnetic ring.

[0027] The rotor end cover is a conductive component, which is a conductive ring or disk with a conductivity of ,thickness The radial range covered by rotor 1 is It coincides with the trapezoidal magnetic field region.

[0028] Rotor 1 along The rotor 1 undergoes a small lateral vibration, and its displacement is... Rotor 1 speed At low frequencies, the feedback of the induced magnetic field is ignored.

[0029] In the coordinate system of a stationary magnet, the translation of rotor 1 causes the magnetic field experienced by each point of the conductor to change with time. For an axisymmetric field, the rate of change of magnetic flux caused by vibration is specifically given by Faraday's law of electromagnetic induction as shown in formula (3): This time-varying term is the excitation source for generating eddy currents. The magnetic ring and yoke together form an axisymmetric axial magnetic field in the working air gap, where t is time. Let x be the speed of rotor 1, and let x be the displacement of rotor 1. ϕ represents the radial gradient of the magnetic field, and cosϕ is the direction factor related to the position of rotor 1.

[0030] Current density in thin conductor plate satisfy Introducing stream functions Increase surface current density The eddy current function equation can be derived from Faraday's law and Ohm's law as shown in formula (4): No current flows out of the boundary. The inner and outer boundaries are zero.

[0031] The total Joule loss power p is obtained from the stream function, as shown in formula (5). Where S is the surface of the rotor upper end cover 5.

[0032] Equivalent to incentive The Poisson equation can be solved by separating variables, and under typical boundary conditions, it can be integrated to obtain formula (6): The damping coefficient is For the radial gradient of the magnetic field in the linear trapezoidal region As a constant, the above equation is explicitly integrated into formula (7). Formula (7) needs to be adjusted for constants based on the actual boundary conditions. (7) Energy dissipation and damping force satisfy Therefore, the damping force opposite to the velocity is calculated. As shown in formula (1), the derivation is now complete.

[0033] Substitute the trapezoidal gradient into formula (1) This yields a linear damping force determined solely by geometry, material properties, and magnetic field gradient.

[0034] Step 3.2: Adjust the structural dimensions and arrangement of the magnetic ring 9, and the gap between the magnetic ring 9 and the upper cover 5 of the rotor, to obtain the optimal value of the damping force. At the optimal value, the over-critical vibration amplitude of the rotor 1 is minimized, and the design results are given. The following design is based on the parameters in Table 1. The first part of the table contains the material and structural dimensions of the inner and outer magnetic rings of the permanent magnet; the second part contains the material and structural dimensions of the yoke; the third part contains the material and structural dimensions of the conductive layer of the upper cover 5 of the rotor 1; the fourth part contains the axial distance between the magnetic ring and the upper cover 5 of the rotor, i.e., the air gap; and the fifth part contains the over-critical vibration velocity of the rotor 1.

[0035] Table 1 Design Examples Total damping force in this invention The calculation example is as follows: Step 1: Calculate the magnetic field gradient; assume the difference between the inner and outer diameters of the 5 conductive layers on the upper end cover of the rotor. mm. The approximate calculation of the magnetic flux density in the working air gap is as follows: T T The meanings of the parameters in B1 and B2 are the same as the corresponding names in the symbol column of Table 1. The selected values ​​are those in Table 1. Step 2: Damping coefficient. The radial range covered by rotor 1 is... , Assuming a value of 0.02m, Assuming a value of 0.08m, The conductivity of rotor end cap 1 is Assuming S / m, For rotor end cover thickness, Assuming a value of 0.002m, The radial gradient of the magnetic field is calculated using the above formula as follows: The calculation is as follows: Step 3: Calculate the damping force when At m / s, the damping force F is calculated as follows: The damping force F is always in the opposite direction to the velocity, thus suppressing lateral vibration.

[0036] Step 3.3: Fabricate the permanent magnet eddy current vibration reduction structure according to the design.

[0037] Step 4: Connect the permanent magnet eddy current vibration damping structure 6 to the upper flange of the vertical overcritical rotating machinery. The upper flange structure is machined with grooves based on the dimensions of the permanent magnet eddy current vibration damping structure 6, and the permanent magnet eddy current vibration damping structure 6 is installed in the grooves using adhesive bonding.

[0038] Step 5: Adjust the relative position of the rotor by adding gaskets to the upper flange of the vertical overcritical rotating machinery to ensure that the gap between the permanent magnet eddy current vibration reduction structure 6 and the upper end cover of the rotor meets the design requirements.

[0039] like Figures 1 to 2 As shown, this invention proposes a permanent magnet eddy current vibration reduction device for over-critical rotating machinery, and its specific implementation process is as follows: For critical operating conditions, the motor drives the rotor disk 4 to drive the rotor 1 to rotate and increase speed. When approaching the critical speed, the amplitude of rotor 1 increases rapidly. As the amplitude increases, the speed of horizontal vibration of the upper cover 5 of the rotor increases. At this time, the damping force generated on the upper cover 5 of the rotor by the permanent magnet eddy current damping structure 6 through electromagnetic induction also increases, so that the vibration amplitude of rotor 1 no longer increases rapidly and remains within a certain amplitude. As the speed of rotor 1 increases and exceeds the critical speed, the amplitude of rotor 1 naturally decreases, and the damping force generated also decreases. The permanent magnet eddy current damping structure 6 returns to the waiting state.

[0040] During precession, when rotor 1 precesses due to various reasons while steadily accelerating or operating at its normal speed, the vibration amplitude of rotor 1 will gradually increase or periodically increase and decrease. When the amplitude increases, the horizontal vibration speed of the upper cover 5 of the rotor increases. At this time, the damping force generated on the upper cover 5 of the rotor by the permanent magnet eddy current damping structure 6 through electromagnetic induction also increases, preventing the vibration amplitude of rotor 1 from increasing further and maintaining it within a certain range, thus avoiding damage to rotor 1 due to precession. The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A permanent magnet eddy current vibration damping device for overcritical rotating machinery, characterized in that, The device includes a rotor (1), a bearing (2), a damper (3), a motor rotor disk (4), a magnetic guiding structure (7), and a permanent magnet eddy current damping structure (6). The bearing (2) is installed at the lower end of the rotor (1), and the motor rotor disk (4) is installed at the lower end of the bearing (2). The damper (3) is connected to the lower end of the motor rotor disk (4). The permanent magnet eddy current damping structure (6) is installed at the upper end of the rotor (1). The permanent magnet eddy current damping structure (6) is installed on the upper flange of the rotating machinery above the upper end cover (5) of the rotor. A magnetic guiding structure (7) is provided above the permanent magnet eddy current damping structure (6). The permanent magnet eddy current damping structure (6) and the magnetic guiding structure (7) are arranged concentrically, and there is a gap between the permanent magnet eddy current damping structure (6) and the magnetic guiding structure (7).

2. The permanent magnet eddy current vibration damping device for overcritical rotating machinery according to claim 1, characterized in that, A magnetic bearing (8) is provided above the magnetic conductive structure (7), and the magnetic conductive structure (7) and the magnetic bearing (8) work together to provide radial stiffness.

3. The permanent magnet eddy current vibration damping device for overcritical rotating machinery according to claim 2, characterized in that, The permanent magnet eddy current vibration reduction structure (6) includes several magnetic rings (9), which are nested and combined into a ring permanent magnet array. The ring permanent magnet array consists of multiple coaxial magnetic rings (9) arranged radially from the inner diameter to the outer diameter. The progressive gradient of the remanence of the permanent magnet rings (9) is set according to the requirement of the smoothness of the magnetic field gradient.

4. The permanent magnet eddy current vibration damping device for overcritical rotating machinery according to claim 3, characterized in that, The magnetic ring (9) is magnetized as a whole or spliced ​​from multiple arc-shaped tiles. All magnetic rings (9) are axially magnetized. Adjacent nested magnetic rings (9) have opposite polarities. By selecting grades with progressive residual magnetism, an axial trapezoidal magnetic field with gradually increasing radial strength is formed in the working air gap. A magnetic yoke back iron is set above the annular permanent magnet array.

5. A method for manufacturing a permanent magnet eddy current vibration damping device for overcritical rotating machinery, the method being used in the device described in any one of claims 1-4, characterized in that, The method includes: Step 1: Measure the dimensions of the permanent magnet eddy current vibration reduction structure (6) on the upper flange structure of the vertical transcritical rotating machinery, and obtain the initial dimensions of the permanent magnet eddy current vibration reduction structure (6) based on the flange structure dimensions; Step 2: Determine the structural dimensions and material properties of the rotor upper end cover (5) as input parameters for designing the permanent magnet eddy current vibration reduction structure (6); Step 3: Design and fabricate permanent magnet eddy current vibration reduction structure (6); Step 3.1: Calculate the total damping force of the permanent magnet eddy current damping structure (6). ; Step 3.2: Adjust the structural dimensions and arrangement of the magnetic ring (9) and the gap between the magnetic ring (9) and the upper end cover (5) of the rotor to obtain the total damping force. The optimal solution; Step 3.3: Fabricate the permanent magnet eddy current vibration reduction structure according to the design (6); Step 4: Connect the permanent magnet eddy current vibration reduction structure (6) to the upper flange of the vertical overcritical rotating machinery; Step 5: Adjust the rotor position by adding gaskets to the upper flange of the rotating machinery to ensure that the gap between the permanent magnet eddy current damping structure (6) and the upper cover (5) of the rotor meets the design requirements.

6. A method for manufacturing a permanent magnet eddy current vibration damping device for overcritical rotating machinery according to claim 5, characterized in that, The initial dimensions of the permanent magnet eddy current damping structure (6) in step one include the inner diameter, outer diameter, and thickness.

7. A method for manufacturing a permanent magnet eddy current vibration damping device for overcritical rotating machinery according to claim 6, characterized in that, The damping force in step 3.1 The calculation formula is as shown in formula (1). Where c is the damping coefficient and v is the rotor (1) speed. For the conductivity of the rotor (1) end cap, For the thickness of the rotor (1) end cap, The magnetic ring (9) and the magnetic yoke together form an axisymmetric axial magnetic field in the working air gap, and the rotor (1) covers the radial region as follows: , where r is the rotor radius.

8. A method for manufacturing a permanent magnet eddy current vibration damping device for overcritical rotating machinery according to claim 5, characterized in that, In step four, a groove is machined on the flange structure based on the dimensions of the permanent magnet eddy current damping structure (6), and the permanent magnet eddy current damping structure (6) is installed in the groove by adhesive bonding.

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