Calculation method, system, equipment and medium for equivalent friction damping ratio of stator blades

Abstract

The present invention relates to the technical field of vibration reduction design of stator blades, and discloses a method, system, device and medium for calculating the equivalent friction damping ratio of a stator blade, the method comprising: obtaining the maximum vibration displacement position on the stator blade in a spring constraint model; applying a single-point circumferential exciting force at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement; calculating the total friction energy consumption at the spring connection position according to the spring displacement, and calculating the exciting energy according to the exciting point displacement and the maximum single-point exciting force; obtaining the current damping ratio according to the exciting energy and the total friction energy consumption, and calculating the difference between the current damping ratio and the initial damping ratio to obtain the equivalent friction damping ratio. The method of the present invention is a finite element simulation calculation method for obtaining an equivalent friction damping ratio based on an energy method, and can evaluate the damping ratio of the edge plate mounting structure to the stator blade structure.

Description

Technical Field

[0001] The invention belongs to the field of aeroengines, relates to the technical field of vibration reduction design of stator blades, and specifically relates to a method, system, equipment and medium for calculating the equivalent friction damping ratio of a stator blade. Background Art

[0002] The stator blades are also called rectifying blades. After the airflow speed is reduced in the stator blades to increase the pressure, it flows into the next row of working blades in a certain direction. In order to ensure that the stator blades can work well, the blade shape of the stator blades and the relationship between the blade shapes at each cross section need to be designed well.

[0003] Furthermore, the stator blades may experience large vibration problems due to the excitation of gas, etc. The vibration load caused by the excitation of gas, etc. will affect the normal operation and service life of the engine, and may even cause the fan compressor stator blades to crack and fall off. However, due to the limitations of aerodynamic performance and other aspects of the fan compressor, it is sometimes impossible to make major changes to the stator blade profile, etc. At this time, it is necessary to analyze its damping characteristics and increase the damping to achieve the purpose of reducing vibration and increasing the blade life.

[0004] Therefore, it is necessary to design a method to analyze the damping of stator blades. Summary of the invention

[0005] In order to accurately analyze the damping of the stator blades to achieve the purpose of reducing the vibration stress of the stator blades and improving the high-cycle fatigue life, the present invention discloses a method for calculating the equivalent friction damping ratio of the stator blades, the method comprising the following steps:

[0006] S1. Setting a spring between the stator blade and the engine casing to build a spring constraint model, and obtaining the maximum vibration displacement position on the stator blade in the spring constraint model;

[0007] S2. According to a given initial damping ratio, a single-point circumferential exciting force is applied at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement;

[0008] S3, calculating the total friction energy consumption at the spring connection position according to the spring displacement, and calculating the excitation energy according to the excitation point displacement and the maximum single-point excitation force;

[0009] S4. The initial damping ratio is corrected according to the excitation energy and the total friction energy consumption to obtain a current damping ratio that introduces friction damping, and the difference between the current damping ratio and the initial damping ratio is calculated to obtain an equivalent friction damping ratio.

[0010] Further, in step S1, a spring is set between the stator blade and the engine casing to construct a spring constraint model, and the maximum vibration displacement position on the stator blade in the spring constraint model is obtained, including:

[0011] S11, connecting at least one spring to the edge plate of the stator blade, fixing the other end of each spring to the engine casing, and constructing a spring constraint model;

[0012] S12. Performing vibration stress analysis on the spring constraint model to obtain the maximum vibration displacement position of the stator blade in each mode.

[0013] Further, in step S2, according to a given initial damping ratio, a single-point circumferential exciting force is applied at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement, including:

[0014] S21, giving the initial damping ratio of the stator blade in each mode;

[0015] S22, using simulation technology, gradually loading a single-point circumferential exciting force at the maximum vibration displacement position according to the initial damping ratio, and collecting vibration stress and exciting point displacement in real time;

[0016] S23, taking the single-point circumferential exciting force corresponding to the time when the collected vibration stress is equal to the given maximum vibration stress as the maximum single-point exciting force, and collecting the spring displacement corresponding to the maximum single-point exciting force.

[0017] Further, in step S3, the total friction energy consumption at the spring connection position is calculated according to the spring displacement, including:

[0018] S31, extracting the normal displacement of the spring displacement, and calculating the spring pressure at the spring connection position according to the normal displacement and the spring stiffness;

[0019] S32, calculating the friction force according to the spring pressure and the friction coefficient;

[0020] S33, calculating the tangential displacement of the spring connection position according to the displacements in two directions perpendicular to the normal direction of the spring displacement;

[0021] S34, calculating the spring friction energy consumption according to the tangential displacement and the friction force, and calculating the sum of the spring friction energy consumption of all the springs to obtain the total friction energy consumption.

[0022] Furthermore, in step S4, the initial damping ratio is corrected according to the excitation energy and the total friction energy consumption to obtain a current damping ratio that introduces friction damping, including:

[0023] By formula The initial damping ratio is corrected to obtain a current damping ratio with friction damping introduced, where: is the current damping ratio, is the initial damping ratio, To stimulate energy, is the total friction energy consumption.

[0024] An embodiment of the present invention also provides an equivalent friction damping ratio calculation system for a stator blade, the system comprising a spring constraint model construction module, a vibration displacement position acquisition module, an excitation simulation module, a friction energy consumption and excitation energy calculation module and an equivalent friction damping ratio calculation module.

[0025] The spring constraint model building module is used to set a spring between the stator blade and the engine casing to build a spring constraint model;

[0026] The vibration displacement position acquisition module is used to acquire the maximum vibration displacement position on the stator blade in the spring constraint model according to the spring constraint model;

[0027] The excitation simulation module is used to apply a single-point circumferential excitation force at the maximum vibration displacement position through simulation technology according to a given initial damping ratio, and obtain the maximum single-point excitation force, spring displacement and excitation point displacement;

[0028] The friction energy consumption and excitation energy calculation module is used to calculate the total friction energy consumption of the spring connection position according to the spring displacement, and calculate the excitation energy according to the excitation point displacement and the maximum single-point excitation force;

[0029] The equivalent friction damping ratio calculation module is used to correct the initial damping ratio according to the excitation energy and the total friction energy consumption, obtain the current damping ratio introducing friction damping, and calculate the difference between the current damping ratio and the initial damping ratio to obtain the equivalent friction damping ratio.

[0030] An embodiment of the present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements any of the above-mentioned methods for calculating the equivalent friction damping ratio of the stator blades to accurately analyze the damping of the stator blades, thereby achieving the purpose of reducing the vibration stress of the stator blades and improving the high-cycle fatigue life.

[0031] An embodiment of the present invention also provides a computer-readable storage medium, which stores a computer program for executing any of the above-mentioned methods for calculating the equivalent friction damping ratio of the stator blades, so as to accurately analyze the damping of the stator blades, thereby achieving the purpose of reducing the vibration stress of the stator blades and improving the high-cycle fatigue life.

[0032] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least: the equivalent friction damping ratio calculation method of the present invention obtains the maximum vibration displacement position on the stator blade through the established spring constraint model; applies a single-point circumferential exciting force at the maximum vibration displacement position through simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement; calculates the total friction energy consumption at the spring connection position based on the spring displacement, and calculates the exciting energy based on the exciting point displacement and the maximum single-point exciting force; corrects the initial damping ratio based on the exciting energy and the total friction energy consumption to obtain the current damping ratio, and calculates the difference between the current damping ratio and the initial damping ratio to obtain the equivalent friction damping ratio. This method is a finite element simulation calculation method for the equivalent friction damping ratio of the stator blade edge plate mounting structure and the casing mating surface based on the energy method, which can evaluate the damping ratio of the edge plate mounting structure to the stator blade structure, and this method does not require repeated iterations and has the advantage of high computational efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A flow chart of a method for calculating the equivalent friction damping ratio of a stator blade is disclosed in an embodiment of the present invention;

[0035] Figure 2 It is a structural diagram of a system for calculating the equivalent friction damping ratio of a stator blade disclosed in an embodiment of the present invention;

[0036] Among them, 201 is a spring constraint model building module; 202 is a vibration displacement position acquisition module; 203 is an excitation simulation module; 204 is a friction energy consumption and excitation energy calculation module; 205 is an equivalent friction damping ratio calculation module. DETAILED DESCRIPTION

[0037] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0038] The following describes the implementation methods of the present application through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and the features of the embodiments can be combined with each other in the absence of conflict. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0039] In order to reduce the vibration stress of the stator blades and provide them with a high-cycle fatigue life, the present invention designs a method for obtaining an equivalent friction damping ratio for the friction damping at the stator blade edge plate mounting structure. Generally speaking, friction will occur at the contact boundary of the stator blade during the actual operation of the engine, and the stator blade has a small aerodynamic load, unlike the tenon-connected rotor blades whose extrusion surface can be approximately consolidated under the action of centrifugal force. Therefore, the contact boundary will produce damping when the blade vibrates. The present invention calculates the equivalent friction damping ratio by the friction energy consumption introduced by the contact boundary.

[0040] Specifically, the present invention discloses a method for calculating the equivalent friction damping ratio of a stator blade, see Figure 1 As shown, the method comprises the following steps:

[0041] S1. Setting a spring between the stator blade and the engine casing to build a spring constraint model, and obtaining the maximum vibration displacement position on the stator blade in the spring constraint model;

[0042] S2. According to a given initial damping ratio, a single-point circumferential exciting force is applied at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement;

[0043] S3, calculating the total friction energy consumption at the spring connection position according to the spring displacement, and calculating the excitation energy according to the excitation point displacement and the maximum single-point excitation force;

[0044] S4. The initial damping ratio is corrected according to the excitation energy and the total friction energy consumption to obtain a current damping ratio that introduces friction damping, and the difference between the current damping ratio and the initial damping ratio is calculated to obtain an equivalent friction damping ratio.

[0045] Furthermore, the blade consumes energy during the vibration process. To analyze the vibration resistance generated during the vibration, the maximum vibration displacement position on the stator blade under each mode can be obtained based on the modal calculation results of the spring constraint model. Specifically, in step S1, a spring is set between the stator blade and the engine casing to construct a spring constraint model, and the maximum vibration displacement position on the stator blade in the spring constraint model is obtained, including:

[0046] S11, connecting at least one spring to the edge plate of the stator blade, fixing the other end of each spring to the engine casing, and constructing a spring constraint model;

[0047] S12. Performing vibration stress analysis on the spring constraint model to obtain the maximum vibration displacement position of the stator blade in each mode.

[0048] Further, in step S2, according to a given initial damping ratio, a single-point circumferential exciting force is applied at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement, including:

[0049] S21, given the initial damping ratio of the stator blade in each mode ;

[0050] S22, using simulation technology, gradually loading a single-point circumferential exciting force at the maximum vibration displacement position according to the initial damping ratio, and collecting vibration stress and exciting point displacement in real time;

[0051] S23, taking the single-point circumferential exciting force corresponding to the time when the collected vibration stress is equal to the given maximum vibration stress as the maximum single-point exciting force , collect the maximum single-point exciting force The corresponding spring displacement.

[0052] In specific implementation, the corresponding initial damping ratio under each mode is different, and the maximum single-point exciting force on the stator blade under each mode and its corresponding spring displacement can be obtained through step S2. The given maximum vibration stress is the blade high cycle fatigue limit / n, n is the reserve coefficient, and the blade high cycle fatigue limit can be obtained from the material manual. When the vibration stress reaches the maximum vibration stress, the maximum vibration stress level of the stator blade reaches the blade high cycle fatigue limit level.

[0053] When step S22 is implemented, when the initial damping ratio is input, the mode of the stator blade simulation can be known, that is, the maximum vibration displacement position can be determined. At the same time, in actual operation, each mode can be simulated and analyzed to obtain the equivalent friction damping ratio under each mode. The dangerous mode can also be determined based on experiments or experience, and only the dangerous mode is simulated and analyzed to obtain the equivalent friction damping ratio under the dangerous mode.

[0054] Further, in step S3, the total friction energy consumption at the spring connection position is calculated according to the spring displacement, including:

[0055] S31, extracting the normal displacement of the spring displacement , according to the normal displacement and spring rate Calculation of the spring pressure in the spring connection ,Right now ;

[0056] S32, according to the spring pressure and friction coefficient Calculating Friction ,Right now ;

[0057] S33, according to the displacements in two directions perpendicular to the normal direction of the spring displacement ( , ), calculate the tangential displacement of the spring connection position ,Right now ;

[0058] S34, according to the tangential displacement and the friction Calculation of spring friction energy loss , calculate the sum of the spring friction energy consumption of all the springs to obtain the total friction energy consumption .

[0059] In specific implementation, the spring friction energy consumption of the i-th spring is Equal to the friction force within one excitation cycle Tangential displacement in radial plane The work done in the direction .

[0060] It should be noted that if there is only one spring in the spring constraint model, the total friction energy consumption Equal to the friction energy consumption of the spring If there are multiple springs, the total friction energy consumption is Equal to the spring friction energy dissipated by all springs The sum of .

[0061] Furthermore, in step S3, when the excitation energy is calculated based on the excitation point displacement and the maximum single-point excitation force, the excitation point displacement can be obtained when the simulation analysis is performed in step S2. , the excitation energy can be obtained by integrating the displacement of the excitation point within an excitation cycle ,Right now .

[0062] Furthermore, in step S4, the initial damping ratio is corrected according to the excitation energy and the total friction energy consumption to obtain a current damping ratio that introduces friction damping, including:

[0063] By formula The initial damping ratio is corrected to obtain a current damping ratio with friction damping introduced, where: is the current damping ratio, is the initial damping ratio, To stimulate energy, is the total friction energy consumption.

[0064] Based on the same inventive concept, an equivalent friction damping ratio calculation system for a stator blade is also provided in an embodiment of the present invention, as described in the following embodiment. Since the principle of solving the problem by the equivalent friction damping ratio calculation system is similar to the equivalent friction damping ratio calculation method disclosed in the above embodiment, the implementation of the equivalent friction damping ratio calculation system can refer to the implementation of the equivalent friction damping ratio calculation method, and the repeated parts will not be repeated. As used below, the term "unit" or "module" can be a combination of software and / or hardware that implements predetermined functions. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceived.

[0065] Figure 2 is a structural block diagram of a stator blade equivalent friction damping ratio calculation system disclosed in an embodiment of the present invention, such as Figure 2 As shown, the equivalent friction damping ratio calculation system includes a spring constraint model construction module 201, a vibration displacement position acquisition module 202, an excitation simulation module 203, a friction energy consumption and excitation energy calculation module 204 and an equivalent friction damping ratio calculation module 205. The structure is described below.

[0066] The spring constraint model building module 201 is used to set a spring between the stator blade and the engine casing to build a spring constraint model;

[0067] The vibration displacement position acquisition module 202 is used to acquire the maximum vibration displacement position on the stator blade in the spring constraint model according to the spring constraint model;

[0068] The excitation simulation module 203 is used to apply a single-point circumferential excitation force at the maximum vibration displacement position through simulation technology according to a given initial damping ratio, and obtain the maximum single-point excitation force, spring displacement and excitation point displacement;

[0069] The friction energy consumption and excitation energy calculation module 204 is used to calculate the total friction energy consumption of the spring connection position according to the spring displacement, and calculate the excitation energy according to the excitation point displacement and the maximum single-point excitation force;

[0070] The equivalent friction damping ratio calculation module 205 is used to correct the initial damping ratio according to the excitation energy and the total friction energy consumption, obtain the current damping ratio introducing friction damping, and calculate the difference between the current damping ratio and the initial damping ratio to obtain the equivalent friction damping ratio.

[0071] The equivalent friction damping ratio calculation method of the present invention obtains the maximum vibration displacement position on the stator blade through the established spring constraint model; applies a single-point circumferential exciting force at the maximum vibration displacement position through simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement; calculates the total friction energy consumption at the spring connection position based on the spring displacement, and calculates the exciting energy based on the exciting point displacement and the maximum single-point exciting force; corrects the initial damping ratio based on the exciting energy and the total friction energy consumption to obtain the current damping ratio, and calculates the difference between the current damping ratio and the initial damping ratio to obtain the equivalent friction damping ratio. This method is a finite element simulation calculation method for the equivalent friction damping ratio of the stator blade edge plate mounting structure and the casing mating surface based on the energy method, which can evaluate the damping ratio of the edge plate mounting structure to the stator blade structure, and this method does not require repeated iterations and has the advantage of high calculation efficiency.

[0072] In this embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, any of the above-mentioned methods for calculating the equivalent friction damping ratio of a stator blade is implemented.

[0073] Specifically, the computer device may be a computer terminal, a server or a similar computing device.

[0074] In this embodiment, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program for executing any of the above-mentioned methods for calculating the equivalent friction damping ratio of a stator blade.

[0075] Specifically, computer-readable storage media include permanent and non-permanent, removable and non-removable media that can be used to store information by any method or technology. Information can be computer-readable instructions, data structures, program modules or other data. Examples of computer-readable storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, tape disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable storage media does not include temporary computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0076] Obviously, those skilled in the art should understand that the modules or steps of the above-mentioned embodiments of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order from that here, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. In this way, the embodiments of the present invention are not limited to any specific combination of hardware and software.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the equivalent friction damping ratio of a stator blade, characterized in that: include: A spring is set between the stator blade and the engine casing to build a spring constraint model, and the maximum vibration displacement position on the stator blade in the spring constraint model is obtained; According to a given initial damping ratio, a single-point circumferential exciting force is applied at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement; Calculating the total friction energy consumption at the spring connection position according to the spring displacement, and calculating the excitation energy according to the excitation point displacement and the maximum single-point excitation force; The initial damping ratio is corrected according to the excitation energy and the total friction energy consumption to obtain a current damping ratio with friction damping introduced, and the difference between the current damping ratio and the initial damping ratio is calculated to obtain an equivalent friction damping ratio, including: The initial damping ratio is corrected to obtain a current damping ratio with friction damping introduced, where: is the current damping ratio, is the initial damping ratio, To stimulate energy, is the total friction energy consumption.

2. The method for calculating the equivalent friction damping ratio of a stator blade according to claim 1, characterized in that: A spring is set between the stator blade and the engine casing to build a spring constraint model, and the maximum vibration displacement position on the stator blade in the spring constraint model is obtained, including: At least one spring is connected to the edge plate of the stator blade, and the other end of each spring is fixed to the engine casing to construct a spring constraint model; Vibration stress analysis is performed on the spring constraint model to obtain the maximum vibration displacement position of the stator blade in each mode.

3. The method for calculating the equivalent friction damping ratio of a stator blade according to claim 1, characterized in that: According to the given initial damping ratio, a single-point circumferential exciting force is applied at the maximum vibration displacement position by simulation technology to obtain the maximum single-point exciting force, spring displacement and exciting point displacement, including: Given an initial damping ratio of the stator blade in each mode; By using simulation technology, a single-point circumferential exciting force is gradually loaded at the maximum vibration displacement position according to the initial damping ratio, and vibration stress and exciting point displacement are collected in real time; The single-point circumferential exciting force corresponding to the vibration stress collected when it is equal to the given maximum vibration stress is taken as the maximum single-point exciting force, and the spring displacement corresponding to the maximum single-point exciting force is collected.

4. The method for calculating the equivalent friction damping ratio of a stator blade according to claim 1, characterized in that: The total friction energy consumption at the spring connection position is calculated based on the spring displacement, including: Extracting the normal displacement of the spring displacement, and calculating the spring pressure at the spring connection position according to the normal displacement and the spring stiffness; Calculating friction force based on the spring pressure and friction coefficient; Calculate the tangential displacement of the spring connection position according to the displacements in two directions perpendicular to the normal direction of the spring displacement; The spring friction energy consumption is calculated according to the tangential displacement and the friction force, and the sum of the spring friction energy consumptions of all the springs is calculated to obtain the total friction energy consumption.

5. A calculation system for the equivalent friction damping ratio of a stator blade, characterized in that: include: A spring constraint model building module, wherein the spring constraint model building module is used to set a spring between the stator blade and the engine casing to build a spring constraint model; A vibration displacement position acquisition module, wherein the vibration displacement position acquisition module is used to acquire the maximum vibration displacement position on the stator blade in the spring constraint model according to the spring constraint model; An excitation simulation module, wherein the excitation simulation module is used to apply a single-point circumferential excitation force at the maximum vibration displacement position through a simulation technology according to a given initial damping ratio, and obtain the maximum single-point excitation force, spring displacement, and excitation point displacement; A friction energy consumption and excitation energy calculation module, wherein the friction energy consumption and excitation energy calculation module is used to calculate the total friction energy consumption of the spring connection position according to the spring displacement, and calculate the excitation energy according to the excitation point displacement and the maximum single-point excitation force; An equivalent friction damping ratio calculation module is used to correct the initial damping ratio according to the excitation energy and the total friction energy consumption to obtain a current damping ratio with friction damping introduced, and calculate the difference between the current damping ratio and the initial damping ratio to obtain an equivalent friction damping ratio, including: The initial damping ratio is corrected to obtain a current damping ratio with friction damping introduced, where: is the current damping ratio, is the initial damping ratio, To stimulate energy, is the total friction energy consumption.

6. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method for calculating the equivalent friction damping ratio of the stator blade according to any one of claims 1 to 4 is implemented.

7. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program for executing the method for calculating the equivalent friction damping ratio of a stator blade according to any one of claims 1 to 4.

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