A composite propeller excitation characteristic test method based on finite element optimization

Abstract

The application belongs to the technical field of composite propeller analysis, and particularly relates to a composite propeller excitation characteristic test method based on finite element optimization. The method comprises the following steps: based on the propeller type value, completing the parametric expression of the propeller and the finite element grid processing; simulating and calculating the propeller excitation characteristic to generate the excitation configuration parameters required for actual measurement; selecting the propeller simulation excitation point according to the propeller simulation mode and the excitation characteristic obtained in steps A and B; establishing a data acquisition system for measuring the excitation response signal; based on the data acquisition system and the excitation configuration parameters, performing the excitation test to obtain the excitation response signal of all the excitation points; the application is convenient for quickly generating and optimizing the test configuration scheme, and then the inherent vibration characteristic of the propeller is measured by using the excitation device, so that the excitation characteristic is determined, thereby laying a foundation for the production and development of a low-noise pre-deformation composite propeller.

Description

Technical Field

[0001] This invention belongs to the field of composite material propeller analysis technology, and in particular relates to a method for testing the vibration characteristics of composite material propellers based on finite element optimization. Background Technology

[0002] Traditional propellers offer high precision and stability, but their rigid rotating blades suffer from limitations such as insufficient adaptability to flow field coupling, poor damping performance of metallic materials, and noise reduction measures limited to geometric optimization, hindering their further development. Composite material propellers, with their material designability advantages, have become a new research focus for improving marine propeller performance. Compared to traditional metal propellers, composite material propellers exhibit significant adaptive hydroelastic characteristics. To rationally utilize this characteristic, pre-deformation design can ensure no loss of speed, while low-noise design can effectively reduce pressure pulsation and excitation noise. However, current research on composite material propellers mainly focuses on theoretical studies and numerical calculations for small-scale model propellers, lacking effective methods for testing and optimizing propellers on actual ships. Support for manufacturing and onshore testing is poor, especially in the development of low-noise pre-deformed composite material propellers, where engineering applications are still largely unexplored. Summary of the Invention

[0003] The purpose of this invention is to propose a method for measuring the vibration characteristics of composite material propellers for actual ships, based on practical needs. First, the optimal excitation point of the propeller blade and the vibration pickup point are found by using finite element simulation and intelligent optimization algorithm, thereby reducing the content of actual measurement and analysis while ensuring the effectiveness of the measurement. Then, the inherent excitation characteristics of the propeller blade are measured using an experimental device, providing a practical basis for the development of low-noise pre-deformed composite material propellers.

[0004] To achieve the above objectives, the present invention adopts the following technical solution.

[0005] A method for testing the vibration characteristics of composite material propellers based on finite element optimization includes the following steps:

[0006] Step A: Based on the blade profile values, complete the parameterized representation of the blade and the finite element mesh processing; specifically including:

[0007] A1. Based on the blade profile data, the cross-sectional shape at each radius of the blade is obtained and a cylindrical coordinate system is established. The parameterized expression of the blade cross-section is obtained based on cosine segmentation.

[0008] A2 Based on the parameterized expression of the blade, the finite element mesh processing of the blade is carried out, the fluid near the blade is simplified into a lifting body, and a double integral relationship is established for the field corresponding to the lifting body in the fluid domain.

[0009] Step B: Simulate and calculate the blade excitation characteristics to generate the excitation configuration parameters required for actual measurement; specifically including:

[0010] B1 Complete the creation and simplification of the finite element simulation model of the blade, and set the blade attribute parameters according to the test configuration scheme;

[0011] B2. Based on the blade structure characteristics and installation and fixing method, determine the connection mode and degree of freedom. The connection mode includes rigid fixed connection and elastic connection. Based on the finite element modal analysis method, establish the dynamic equation of the blade structure and solve it to determine the blade excitation characteristic values, including natural frequency, mode shape and modal damping.

[0012] Step C: Based on the blade simulation mode shape and excitation characteristics obtained in steps A and B, select the blade simulation excitation point; specifically including:

[0013] The sample space for determining the excitation point location is determined. Under different excitation configuration parameters, with the optimization objective of maximizing the spectral amplitude and root mean square error of the monitoring point, an intelligent optimization algorithm is used to find the optimal excitation point location under the excitation configuration parameters in the sample space of the excitation point location; the excitation point and the vibration pickup point are marked.

[0014] Step D: Establish a data acquisition system for measuring the excitation response signal; specifically including:

[0015] D1 is the accelerometer sensor assembly at each vibration pickup point;

[0016] D2 Based on the excitation configuration parameters, configure the excitation components at the corresponding optimal excitation point positions;

[0017] Step E: Based on the data acquisition system and excitation configuration parameters, conduct excitation tests to obtain the excitation response signals of all vibration pickup points. Specifically, this includes:

[0018] E1 establishes an acceleration calibration program based on the data acquisition system, applies a stable excitation force according to the excitation configuration parameters, and calibrates and adjusts each acceleration sensor;

[0019] E2 establishes the model-measuring point relationship based on the blade model and vibration pickup point location information;

[0020] E3 underwent excitation tests under various excitation configuration parameters, including:

[0021] A single-point excitation method is adopted, using a vibrator to excite the excitation point on the blade surface;

[0022] Repeat steps E1 to E3 until all excitation and response signal measurements are completed under all excitation configuration parameters.

[0023] In a further improved or preferred embodiment of the aforementioned method for testing the vibration characteristics of composite material propellers based on finite element optimization, step A specifically includes:

[0024] Step A: Based on the blade profile values, complete the parameterized expression of the blade, and perform finite element mesh processing of the blade based on the parameterized expression;

[0025] A1. Based on the blade profile values, a parametric model of the blade is presented, specifically:

[0026] Based on the blade profile data, a cylindrical coordinate system is established to obtain the cross-sectional shape of the blade at each radius. The parameterized expression of the blade cross-section is obtained based on cosine segmentation, and is represented as follows:

[0027] ;

[0028] in This refers to the coordinates of a point on the blade profile in cylindrical coordinates. It refers to the distance from a point on the leaf profile to the chordal direction of the guide edge. This refers to the distance from the guide edge of the blade profile to the generatrix. It refers to the pitch value at the blade profile. It refers to the oblique angle of the leaf section. It refers to the pitch angle of the blade profile. It refers to the distance from a point on the underside of the leaf cross-section to the chord. It refers to the distance from a point on the leaf surface to the chord in the leaf cross-section;

[0029] A2. Finite element mesh processing of propeller blades based on parametric representation of the blades, specifically:

[0030] a21 obtains the finite element mesh node parameters using cosine segmentation in both the chordal and spanwise directions, as follows:

[0031]

[0032] in This refers to the chord and span coordinate values ​​of several points in the finite element mesh. This refers to the blade radius. Where is the hub radius. The chord length of the leaf section. , This refers to the total number of grid cells in the spanning direction. , This refers to the total number of chordal grids. Indicates the angle of the spanning node. Indicates the angle at the chord node;

[0033] a22. The blade structure mesh is divided along the blade thickness direction. Using the chordal and spanwise finite element mesh nodes of the blade surface obtained in step a21 as the mesh body surface, the structure mesh is divided into cubic mesh elements to obtain the cosine expression of the structure mesh element coordinates in the thickness direction:

[0034]

[0035] in This refers to the coordinates of the surface mesh nodes in the thickness direction. It is a cosine angle. , This represents the number of structural mesh points in the thickness direction.

[0036] a23 simplifies the fluid near the impeller to the incoming flow velocity. The lifting body, based on the blade model dimensions, determines the structural surface, wake surface, and fluid domain boundary. Define the velocity potential caused by the disturbance of the lifting body. , For any point in the field corresponding to the lifting body within the fluid domain Caused fluid velocity disturbance Based on Green's formula, its relationship with the boundary points is established. Fluid velocity disturbance The double integral relationship between them is expressed as:

[0037] ;

[0038] in, It refers to the position quantity. This refers to the boundary surface normal vector. This refers to the boundary surface of the fluid domain at... The normal derivative of a point, Refers to fluid disturbance exist The derivative of a point, It refers to the field point To the boundary point The distance.

[0039] In a further improved or preferred embodiment of the aforementioned method for testing the vibration characteristics of composite material propellers based on finite element optimization, step B specifically includes:

[0040] Step B: Simulate and calculate the blade excitation characteristics using the finite element modal analysis method to obtain blade surface excitation characteristic data, and generate the excitation configuration parameters required for actual measurement based on the excitation characteristic data; specifically including:

[0041] B1 Based on the parametric expression and finite element network structure in step A, complete the creation and simplification of the blade finite element simulation model, and set the blade attribute parameters according to the test configuration scheme;

[0042] Furthermore, to achieve more accurate and efficient simulation analysis, mesh refinement and mesh validity checks can be performed on local areas such as the excitation region, stress concentration region, stiffness abrupt change region, and key deformation region.

[0043] B2 Determine the connection mode and degrees of freedom based on the blade structure characteristics and installation and fixing method. The connection mode includes rigid fixed connection and elastic connection.

[0044] The dynamic equations of the blade structure were established and solved based on the finite element modal analysis method to determine the blade excitation characteristic values, including natural frequency, mode shape and modal damping.

[0045] In a further improvement or preferred embodiment of the aforementioned test method for the vibration characteristics of composite propellers based on finite element optimization, step B1 further includes mesh refinement and mesh effectiveness check analysis for the excitation region, stress concentration region, stiffness abrupt change region, and key deformation region.

[0046] In a further improved or preferred embodiment of the aforementioned test method for the vibration characteristics of composite propellers based on finite element optimization, in step B, the finite element model is created using 3D simulation modeling software and then imported into the finite element program, or it is directly established in the finite element program; simplification includes ignoring minor structural features whose influence on the blade structure or dynamic characteristics is negligible, retaining only the core structural features; the blade property parameters include blade material properties, anisotropic properties of the composite material, and ply configuration scheme; wherein, blade material properties include, but are not limited to, elastic modulus, Poisson's ratio, and density, and the anisotropic properties of the composite material include elastic modulus, Poisson's ratio, and shear modulus along each ply configuration direction of the composite material; the ply configuration scheme of the composite material includes ply angle settings, thickness settings, and sequence settings.

[0047] In a further improved or preferred embodiment of the aforementioned method for testing the vibration characteristics of composite material propellers based on finite element optimization, step C specifically includes:

[0048] Step C: Based on the blade simulation mode shape and excitation characteristics obtained in steps A and B, select the blade simulation excitation point; including:

[0049] C1. Based on the parameterized model and finite element structure determined in step A, determine the sample space for the excitation point location. Use at least four edge points, including the midpoint of the blade in the chordal direction with a radius of 0.4R0, the midpoint of the blade in the chordal direction with a radius of 0.7R0, and the leading edge and following edge of the blade in the chordal direction with a radius of 0.5R0, as the monitoring point location. Use the midpoint of the blade profile in the chordal direction with a radius of 0.5R0 as the initial excitation point location. Use a step size of 0.05R0 in the chordal and spanwise directions to locate new excitation points.

[0050] C2 takes the maximum spectral amplitude and mean square error of the monitoring point as the optimization objective under different excitation configuration parameters. It uses an intelligent optimization algorithm to find the optimal excitation point position in the sample space of the excitation point position and obtains a set of Pareto optimal solutions for the optimal excitation point position. It analyzes the spectrum of the four monitoring points under the optimal solution set and selects one of them as the optimal excitation point position under the corresponding excitation configuration parameters.

[0051] C3 marks the optimal excitation point and pickup point; the pickup point includes at least 15 points in total, including the leading edge, the midpoint of the chord, and the trailing edge at radii of 0.3R0, 0.5R0, 0.6R0, 0.8R0, and 0.95R0.

[0052] In a further improved or preferred embodiment of the aforementioned composite material propeller vibration characteristic testing method based on finite element optimization, step D includes: the acceleration sensor assembly includes an acceleration sensor for acquiring the displacement of the vibration pickup point, and a signal amplifier and a signal acquisition unit for acquiring acceleration sensor data; the excitation assembly includes a signal generator for generating excitation configuration parameters, an amplifier for signal generation and processing, and an exciter.

[0053] In a further improved or preferred embodiment of the aforementioned test method for the excitation characteristics of composite propellers based on finite element optimization, step E further includes: processing the data acquired by the data acquisition system through time-frequency conversion to obtain an average estimated frequency response function, and performing modal parameter identification on the average estimated frequency response function to obtain the natural frequency, mode shape, and modal damping of the composite propeller blade.

[0054] In a further improvement or preferred embodiment of the aforementioned test method for the excitation characteristics of composite propellers based on finite element optimization, step E3 further includes setting the range of each channel of the acquisition instrument to ensure that the acquired signal meets the requirements of the analysis frequency band, so that the signal amplitude is 50% to 80% of the range of each channel.

[0055] In a further improved or preferred embodiment of the aforementioned test method for the vibration characteristics of composite propellers based on finite element optimization, step E further includes: applying an adjustment window to the excitation signal applied by the exciter to reduce random noise, conducting the test in a quiet environment; making the excitation head of the exciter perpendicular to the blade surface; averaging the data in the frequency domain, repeating the excitation 3-10 times, and when the response signal basically decays to 0, performing the next excitation and acquisition, keeping the intensity and duration of each excitation the same.

[0056] This application proposes a test method for the excitation characteristics of composite material propellers based on finite element optimization. First, the optimal excitation point and vibration pickup point of the propeller blade are found by finite element simulation and intelligent optimization algorithm, which facilitates the rapid generation and optimization of the test configuration scheme. Then, the inherent vibration characteristics of the propeller blade are measured by the excitation device, thereby determining its excitation characteristics, laying the foundation for the production and development of low-noise pre-deformed composite material propellers. Attached Figure Description

[0057] Figure 1 This is a flowchart illustrating the principle of a test method for the vibration characteristics of composite material propellers based on finite element optimization.

[0058] Figure 2 These are the mode shapes of the simulated blades at various orders;

[0059] Figure 3 This is a schematic diagram showing the range of changes in the positions of the simulation monitoring points and excitation points;

[0060] Figure 4 This is a schematic diagram showing the distribution of vibration pickup points and excitation points. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0062] This invention relates to a method for testing the vibration characteristics of composite material propellers based on finite element optimization. The invention first performs vibration analysis on the blades of a real ship's composite material propeller using finite element simulation. An intelligent optimization algorithm is then used to determine the optimal excitation point of the blades. Next, an exciter (or impact hammer) is used to apply excitation to the blades. An accelerometer and a data acquisition and analysis system are used to simultaneously measure and acquire the excitation and response signals at each measuring point. After time-frequency conversion and modal parameter identification, the results are compared and analyzed with the simulated natural frequencies and mode shapes of the blades. Finally, the natural frequencies, mode shapes, and modal damping of the real ship's composite material propeller blades are obtained, laying the foundation for further analysis of their inherent characteristics and noise reduction optimization design.

[0063] like Figure 1 As shown, its main steps include:

[0064] Step A: Based on the blade profile values, complete the parameterized expression of the blade, and perform finite element mesh processing of the blade based on the parameterized expression;

[0065] A1. Based on the blade profile values, a parametric model of the blade is presented, specifically:

[0066] like Figure 1 As shown, a cylindrical coordinate system is established based on the blade profile data to obtain the cross-sectional shape at each radius of the blade. The parameterized expression of the blade cross-section is obtained based on cosine segmentation, and is represented as follows:

[0067] ;

[0068] in This refers to the coordinates of a point on the blade profile in cylindrical coordinates. It refers to the distance from a point on the leaf profile to the chordal direction of the guide edge. This refers to the distance from the guide edge of the blade profile to the generatrix. It refers to the pitch value at the blade profile. It refers to the oblique angle of the leaf section. It refers to the pitch angle of the blade profile. It refers to the distance from a point on the underside of the leaf cross-section to the chord. It refers to the distance from a point on the leaf surface to the chord in the leaf cross-section;

[0069] A2. Finite element mesh processing of propeller blades based on parametric representation of the blades, specifically:

[0070] a21 obtains the finite element mesh node parameters using cosine segmentation in both the chordal and spanwise directions, as follows:

[0071]

[0072] in This refers to the chord and span coordinate values ​​of several points in the finite element mesh. This refers to the blade radius. Where is the hub radius. The chord length of the leaf section. , This refers to the total number of grid cells in the spanning direction. , This refers to the total number of chordal grids. Indicates the angle of the spanning node. Indicates the angle at the chord node;

[0073] a22. The blade structure mesh is divided along the blade thickness direction. Using the chordal and spanwise finite element mesh nodes of the blade surface obtained in step a21 as the mesh body surface, the structure mesh is divided into cubic mesh elements to obtain the cosine expression of the structure mesh element coordinates in the thickness direction:

[0074]

[0075] in This refers to the coordinates of the surface mesh nodes in the thickness direction. It is a cosine angle. , This represents the number of structural mesh points in the thickness direction.

[0076] a23 simplifies the fluid near the impeller to the incoming flow velocity. The lifting body, based on the blade model dimensions, determines the structural surface, wake surface, and fluid domain boundary. Define the velocity potential caused by the disturbance of the lifting body. , For any point in the field corresponding to the lifting body within the fluid domain The resulting disturbance is used to establish its relationship with the boundary points based on Green's formula. The double integral relation is expressed as:

[0077] ;

[0078] in, It refers to the position quantity. This refers to the boundary surface of the fluid domain at... The normal derivative of a point, It refers to the field point To the boundary point The distance;

[0079] Step B: Simulate and calculate the blade excitation characteristics using the finite element modal analysis method to obtain blade surface excitation characteristic data, and generate the excitation configuration parameters required for actual measurement based on the excitation characteristic data; specifically including:

[0080] B1 Based on the parametric expression and finite element network structure in step A, complete the creation and simplification of the blade finite element simulation model, and set the blade attribute parameters according to the test configuration scheme;

[0081] The finite element model is created using 3D simulation modeling software and then imported into the finite element program, or it can be created directly in the finite element program.

[0082] The simplification includes ignoring minor structural features that have negligible impact on the blade structure or dynamic characteristics, and retaining only the core structural features;

[0083] The blade property parameters include blade material properties, anisotropic properties of composite materials, and layup configuration scheme.

[0084] Among them, the blade material properties include, but are not limited to, elastic modulus, Poisson's ratio, and density; the anisotropic properties of the composite material include elastic modulus, Poisson's ratio, and shear modulus along the direction of each layup of the composite material; the layup configuration scheme of the composite material includes the layup angle setting, thickness setting, and sequence setting of the composite material.

[0085] Furthermore, to achieve more accurate and efficient simulation analysis, mesh refinement and mesh validity checks can be performed on local areas such as the excitation region, stress concentration region, stiffness abrupt change region, and key deformation region.

[0086] B2 Determine the connection mode and degrees of freedom based on the blade structure characteristics and installation and fixing method. The connection mode includes rigid fixed connection and elastic connection.

[0087] The dynamic equations of the blade structure were established and solved using the finite element modal analysis method to determine the blade's vibration characteristic values, including natural frequencies, mode shapes, and modal damping. Figure 2 As shown;

[0088] Step C: Based on the blade simulation mode shape and excitation characteristics obtained in steps A and B, select the blade simulation excitation point;

[0089] like Figure 3 , Figure 4 As shown, in the specific implementation process, the selection should avoid structural symmetry, areas with low stiffness, and modal vibration nodes. To ensure the rationality and effectiveness of subsequent excitation point optimization, multiple simulation monitoring points are selected. The initial excitation point position and the range of excitation point position variation are given. The variation range should not be too large, and should be selected from the middle of the chord direction of the blade and the radial middle to near the blade tip. This ensures both optimization efficiency and that the found excitation point can cover the blade surface to a large extent, so as to reflect the average excitation level of the blade and achieve the function of reflecting the excitation response characteristics by using a point to represent the surface. The specific steps include:

[0090] C1. Based on the parameterized model and finite element structure determined in step A, determine the sample space for the excitation point location. Use at least four edge points, including the midpoint of the blade in the chordal direction with a radius of 0.4R0, the midpoint of the blade in the chordal direction with a radius of 0.7R0, and the leading edge and following edge of the blade in the chordal direction with a radius of 0.5R0, as the monitoring point location. Use the midpoint of the blade profile in the chordal direction with a radius of 0.5R0 as the initial excitation point location. Use a step size of 0.05R0 in the chordal and spanwise directions to locate new excitation points.

[0091] C2 takes the maximum spectral amplitude and mean square error of the monitoring point as the optimization objective under different excitation configuration parameters. It uses an intelligent optimization algorithm to find the optimal excitation point position in the sample space of the excitation point position and obtains a set of Pareto optimal solutions for the optimal excitation point position. It analyzes the spectrum of the four monitoring points under the optimal solution set and selects one of them as the optimal excitation point position under the corresponding excitation configuration parameters.

[0092] C3 marks the optimal excitation point and vibration pickup point; the vibration pickup point includes at least 15 points in total, including the leading edge, the midpoint of the chord, and the trailing edge at radii of 0.3R0, 0.5R0, 0.6R0, 0.8R0, and 0.95R0.

[0093] D. Establish a data acquisition system for measuring excitation response signals;

[0094] D1 Accelerometer assembly at each vibration pickup point, the acceleration sensor assembly including an acceleration sensor for acquiring the displacement of the vibration pickup point and a signal amplifier and signal acquisition unit for acquiring acceleration sensor data;

[0095] D2. Based on the excitation configuration parameters, configure the excitation component at the corresponding optimal excitation point position; the excitation component includes a signal generator for generating the excitation configuration parameters, an amplifier for signal generation and processing, and an exciter.

[0096] E. Based on the data acquisition system and excitation configuration parameters, excitation tests were conducted to obtain the excitation response signals of all vibration pickup points:

[0097] E1 establishes an acceleration calibration program based on the data acquisition system, applies a stable excitation force according to the excitation configuration parameters, and calibrates and adjusts each acceleration sensor to ensure data validity; note that the equipment should be placed on a stable plane to avoid excessive calibration error caused by equipment shaking;

[0098] E2 establishes the model-measuring point relationship based on the blade model and vibration pickup point location information;

[0099] E3 underwent excitation tests under various excitation configuration parameters, including:

[0100] A single-point excitation method is adopted, using a vibrator to excite the excitation point on the blade surface;

[0101] On the basis of ensuring that the acquired signal meets the requirements of the analysis frequency band, the range of each channel of the acquisition instrument is set so that the signal amplitude is 50% to 80% of the range of each channel. This prevents signal clipping caused by too small a range or excessive electrical noise interference caused by too large a range, which would affect the quality of the frequency response function.

[0102] Repeat steps E1 to E3 until the excitation and response signal measurements are completed under all excitation configuration parameters;

[0103] The data acquired by the data acquisition system is processed by time-frequency conversion to obtain the average estimated frequency response function. Modal parameter identification is performed on the average estimated frequency response function to obtain the natural frequency, mode shape and modal damping of the composite material propeller blade.

[0104] Specifically, an appropriate adjustment window should be applied to the excitation signal applied to the vibrator to reduce random noise, and the experiment should be carried out in a quiet environment as much as possible; the excitation head of the vibrator should be as perpendicular to the blade surface as possible; in order to reduce the influence of unrelated noise, the data needs to be averaged in the frequency domain, so repeated excitation is required, 3-10 times. When the response signal is basically decayed to 0, the next excitation and acquisition should be carried out, and the intensity and duration of each excitation should be kept the same.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for testing the vibration characteristics of composite material propellers based on finite element optimization, characterized in that, Includes the following steps: Step A: Based on the blade profile values, complete the parameterized representation of the blade and the finite element mesh processing; specifically including: A1. Based on the blade profile data, the cross-sectional shape at each radius of the blade is obtained and a cylindrical coordinate system is established. The parameterized expression of the blade cross-section is obtained based on cosine segmentation. A2 Based on the parameterized expression of the blade, the finite element mesh processing of the blade is carried out, the fluid near the blade is simplified into a lifting body, and a double integral relationship is established for the field corresponding to the lifting body in the fluid domain. Step B: Simulate and calculate the blade excitation characteristics to generate the excitation configuration parameters required for actual measurement; specifically including: B1 Complete the creation and simplification of the finite element simulation model of the blade, and set the blade attribute parameters according to the test configuration scheme; B2. Based on the blade structure characteristics and installation and fixing method, determine the connection mode and degree of freedom. The connection mode includes rigid fixed connection and elastic connection. Based on the finite element modal analysis method, establish the dynamic equation of the blade structure and solve it to determine the blade excitation characteristic values, including natural frequency, mode shape and modal damping. Step C: Based on the blade simulation mode shape and excitation characteristics obtained in steps A and B, select the blade simulation excitation point; specifically including: The sample space for determining the excitation point location is determined. Under different excitation configuration parameters, with the optimization objective of maximizing the spectral amplitude and root mean square error of the monitoring point, an intelligent optimization algorithm is used to find the optimal excitation point location under the excitation configuration parameters in the sample space of the excitation point location; the excitation point and the vibration pickup point are marked. Step D: Establish a data acquisition system for measuring the excitation response signal; specifically including: D1 is the accelerometer sensor assembly at each vibration pickup point; D2 Based on the excitation configuration parameters, configure the excitation components at the corresponding optimal excitation point positions; Step E: Based on the data acquisition system and excitation configuration parameters, conduct excitation tests to obtain the excitation response signals of all vibration pickup points. Specifically, this includes: E1 establishes an acceleration calibration program based on the data acquisition system, applies a stable excitation force according to the excitation configuration parameters, and calibrates and adjusts each acceleration sensor; E2 establishes the model-measuring point relationship based on the blade model and vibration pickup point location information; E3 underwent excitation tests under various excitation configuration parameters, including: A single-point excitation method is adopted, using a vibrator to excite the excitation point on the blade surface; Repeat steps E1 to E3 until all excitation and response signal measurements are completed under all excitation configuration parameters.

2. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step A specifically includes: Step A: Based on the blade profile values, complete the parameterized expression of the blade, and perform finite element mesh processing of the blade based on the parameterized expression; A1. Based on the blade profile values, a parametric model of the blade is presented, specifically: Based on the blade profile data, a cylindrical coordinate system is established to obtain the cross-sectional shape of the blade at each radius. The parameterized expression of the blade cross-section is obtained based on cosine segmentation, and is represented as follows: ； in This refers to the coordinates of a point on the blade profile in cylindrical coordinates. It refers to the distance from a point on the leaf profile to the chordal direction of the guide edge. This refers to the distance from the guide edge of the blade profile to the generatrix. It refers to the pitch value at the blade profile. It refers to the oblique angle of the leaf section. It refers to the pitch angle of the blade profile. It refers to the distance from a point on the underside of the leaf cross-section to the chord. It refers to the distance from a point on the leaf surface to the chord in the leaf cross-section; A2. Finite element mesh processing of propeller blades based on parametric representation of the blades, specifically: a21 obtains the finite element mesh node parameters using cosine segmentation in both the chordal and spanwise directions, as follows: in This refers to the chord and span coordinate values ​​of several points in the finite element mesh. This refers to the blade radius. Where is the hub radius. The chord length of the leaf section. , This refers to the total number of grid cells in the spanning direction. , This refers to the total number of chordal grids. Indicates the angle of the spanning node. Indicates the angle at the chord node; a22. The blade structure mesh is divided along the blade thickness direction. Using the chordal and spanwise finite element mesh nodes of the blade surface obtained in step a21 as the mesh body surface, the structure mesh is divided into cubic mesh elements to obtain the cosine expression of the structure mesh element coordinates in the thickness direction: in This refers to the coordinates of the surface mesh nodes in the thickness direction. It is a cosine angle. , This represents the number of structural mesh points in the thickness direction. a23 simplifies the fluid near the impeller to the incoming flow velocity. The lifting body, based on the blade model dimensions, determines the structural surface, wake surface, and fluid domain boundary. Define the velocity potential caused by the disturbance of the lifting body. , For any point in the field corresponding to the lifting body within the fluid domain The resulting disturbance is used to establish its relationship with the boundary points based on Green's formula. The double integral relation is expressed as: ； in, It refers to the position quantity. This refers to the boundary surface of the fluid domain at... The normal derivative of a point, It refers to the field point To the boundary point The distance.

3. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step B specifically includes: Step B: Simulate and calculate the blade excitation characteristics using the finite element modal analysis method to obtain blade surface excitation characteristic data, and generate the excitation configuration parameters required for actual measurement based on the excitation characteristic data; specifically including: B1 Based on the parametric expression and finite element network structure in step A, complete the creation and simplification of the blade finite element simulation model, and set the blade attribute parameters according to the test configuration scheme; Furthermore, to achieve more accurate and efficient simulation analysis, mesh refinement and mesh validity checks can be performed on local areas such as the excitation region, stress concentration region, stiffness abrupt change region, and key deformation region. B2 Determine the connection mode and degrees of freedom based on the blade structure characteristics and installation and fixing method. The connection mode includes rigid fixed connection and elastic connection. The dynamic equations of the blade structure are established and solved using the finite element modal analysis method to determine the blade excitation characteristic values, including natural frequency, mode shape and modal damping.

4. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 3, characterized in that, Step B1 further includes mesh refinement and mesh validity check analysis for the excitation region, stress concentration region, stiffness change region, and key deformation region.

5. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 3, characterized in that, In step B, the finite element model is created using 3D simulation modeling software and then imported into the finite element program, or it is created directly in the finite element program; simplification includes ignoring minor structural features that have negligible impact on the blade structure or dynamic characteristics, and retaining only the core structural features; The blade properties include blade material properties, composite material anisotropic properties, and layup configuration. Blade material properties include, but are not limited to, elastic modulus, Poisson's ratio, and density. Composite material anisotropic properties include elastic modulus, Poisson's ratio, and shear modulus along each layup direction. Composite material layup configuration includes layup angle settings, thickness settings, and sequence settings.

6. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step C specifically includes: Step C: Based on the blade simulation mode shape and excitation characteristics obtained in steps A and B, select the blade simulation excitation point; including: C1. Based on the parameterized model and finite element structure determined in step A, determine the sample space for the excitation point location. Use at least four edge points, including the midpoint of the blade in the chordal direction with a radius of 0.4R0, the midpoint of the blade in the chordal direction with a radius of 0.7R0, and the leading edge and following edge of the blade in the chordal direction with a radius of 0.5R0, as the monitoring point location. Use the midpoint of the blade profile in the chordal direction with a radius of 0.5R0 as the initial excitation point location. Use a step size of 0.05R0 in the chordal and spanwise directions to locate new excitation points. C2 takes the maximum spectral amplitude and mean square error of the monitoring point as the optimization objective under different excitation configuration parameters. It uses an intelligent optimization algorithm to find the optimal excitation point position in the sample space of the excitation point position and obtains a set of Pareto optimal solutions for the optimal excitation point position. It analyzes the spectrum of the four monitoring points under the optimal solution set and selects one of them as the optimal excitation point position under the corresponding excitation configuration parameters. C3 marks the optimal excitation point and pickup point; the pickup point includes at least 15 points in total, including the leading edge, the midpoint of the chord, and the trailing edge at radii of 0.3R0, 0.5R0, 0.6R0, 0.8R0, and 0.95R0.

7. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step D includes: the acceleration sensor assembly includes an acceleration sensor for acquiring the displacement of the vibration pickup point, and a signal amplifier and a signal acquisition unit for acquiring acceleration sensor data; the excitation assembly includes a signal generator for generating excitation configuration parameters, an amplifier for signal generation and processing, and an exciter.

8. The method for testing the excitation characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step E further includes: processing the data acquired by the data acquisition system through time-frequency conversion to obtain an average estimated frequency response function, performing modal parameter identification on the average estimated frequency response function, and obtaining the natural frequency, mode shape, and modal damping of the composite material propeller blade.

9. The method for testing the vibration characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step E3 further includes setting the range of each channel of the acquisition instrument to ensure that the acquired signal meets the analysis frequency band requirements, so that the signal amplitude is 50% to 80% of the range of each channel.

10. The method for testing the excitation characteristics of composite material propellers based on finite element optimization according to claim 1, characterized in that, Step E further includes applying an adjustment window to the excitation signal applied to the exciter to reduce random noise and conducting the test in a quiet environment; making the excitation head of the exciter perpendicular to the blade surface; averaging the data in the frequency domain; repeating the excitation 3-10 times; and when the response signal basically decays to 0, performing the next excitation and acquisition, keeping the intensity and duration of each excitation the same.

Images