Propeller excitation measurement system and method taking into account shafting bending and torsional vibration influences

Abstract

A propeller excitation measurement system and method taking into account the influence of shafting bending and torsional vibration belong to the field of ship propulsion devices. It includes a propeller, a sealing device, a propeller bearing, a bearing dynamic excitation force sensor, a torque speed instrument rotor, a torque speed instrument stator, a front / rear stern bearing, a diaphragm coupling, a thrust bearing, a counterweight balance disc, a front / rear intermediate bearing, a motor coupling, a driving motor, a frequency conversion controller, a data analysis and acquisition instrument, a test bench base, a rotating shaft, an eddy current displacement sensor, an optical electric speed sensor and a propeller mounting shaft sleeve. It aims to overcome the technical bottleneck of the existing propeller excitation direct measurement method, that is, the difficulty in arranging underwater sensors, high cost and influence on shafting transmission performance. At the same time, it solves the problem that the existing indirect measurement method cannot eliminate mechanical structure excitation interference and the measurement precision is insufficient, so as to realize a propeller hydrodynamic excitation measurement method which can take into account the influence of shafting bending and torsional vibration, has low cost and high precision.

Description

Technical Field

[0001] This invention relates to a propeller excitation measurement system and method that takes into account the effects of shaft bending and torsional vibration, belonging to the field of marine propulsion devices. Background Technology

[0002] The propeller-shaft system, consisting of the propulsion shaft and the propeller, is responsible for transmitting the main engine power and propeller thrust, and is also one of the main sources of vibration and noise in ships. Under the influence of the non-uniform inflow field induced by the hull, the propeller generates hydrodynamic excitation and causes shaft vibration. The propeller's center of mass motion, under the influence of the shaft's bending and torsional vibrations, generates vortices of "rotation + revolution" accompanied by instantaneous speed fluctuations, which in turn leads to changes in the flow field distribution characteristics and generates additional hydrodynamic excitation.

[0003] Ro-Ro ships, ro-ro ships, and container ships typically have their main engines mounted in the middle of the hull, thus generally employing a long shafting arrangement. Furthermore, these ships often use large-diameter, high-area-ratio propellers to achieve better propulsion performance, resulting in a more pronounced cantilever characteristic in the propeller-shaft system. In these long shafting arrangements with prominent cantilever characteristics, the coupling effect between shaft bending and torsional vibrations and propeller hydrodynamic excitation is more significant. The resulting additional propeller excitation leads to severe vibrations in the stern structure and significantly affects low-frequency radiated noise; therefore, it is necessary to study its amplitude-frequency characteristics.

[0004] Over 90% of the energy generated by the propeller excitation is transferred to the hull through bearing excitation, causing structural vibration and generating cabin and underwater radiated noise. Due to the complexity of the propeller-shaft system structure and the difficulty of underwater environmental balance force measurement tests, there are currently many numerical simulation studies on propeller excitation, but few experimental studies that can verify the computational models. Therefore, it is necessary to develop a method for measuring propeller hydrodynamic excitation that can take into account the effects of bending and torsional vibrations of the propulsion shaft.

[0005] In the prior art, the direct measurement method of propeller excitation embedded in the shaft system, such as the patent document with publication number CN104316229A which involves a composite measuring device for dynamic thrust and torque of a propeller, requires consideration of the installation position and connection method of the measuring device during the shaft system design, processing and assembly stages, which affects the transmission performance of the shaft system itself. In addition, the measuring device itself also has many technical problems in terms of water tightness, signal cable lead-out and decoupling between multiple degrees of freedom of force.

[0006] Another indirect measurement method for propeller excitation, such as the patent document with publication number CN119618557A, involves an inverse method for solving ice-induced propeller load based on shaft system measurement. This method overcomes the technical difficulties faced by the direct measurement method mentioned above, but it does not eliminate the mechanical structure self-excitation contained in the actual measured force and torque signals.

[0007] Therefore, there is an urgent need to propose a propeller excitation measurement system and method that takes into account the influence of shaft bending and torsional vibration in order to solve the above-mentioned technical problems. Summary of the Invention

[0008] This invention aims to overcome the technical bottlenecks of existing direct measurement methods for propeller excitation, such as the difficulty and high cost of underwater sensor placement, and the impact on shaft transmission performance. It also addresses the problems of existing indirect measurement methods, such as the inability to eliminate interference from the mechanical structure's own excitation and insufficient measurement accuracy. Therefore, it aims to achieve a low-cost and high-precision method for measuring propeller hydrodynamic excitation that can account for the effects of shaft bending and torsional vibration. A brief overview of the invention is provided below to provide a basic understanding of certain aspects of the invention. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention.

[0009] The technical solution of this invention:

[0010] Option 1: A propeller excitation measurement system that takes into account the influence of shaft bending and torsional vibration, comprising a propeller, a sealing device, a propeller bearing, a bearing dynamic excitation force sensor, a torque tachometer rotor, a torque tachometer stator, a front stern bearing, a rear stern bearing, a diaphragm coupling, a thrust bearing, a counterweight balance disc, a front intermediate bearing, a rear intermediate bearing, a motor coupling, a drive motor, a frequency converter, a data analysis and acquisition instrument, a test bench base, a rotating shaft, an eddy current displacement sensor, a photoelectric speed sensor, and a propeller mounting bushing;

[0011] One end of the rotating shaft is connected to the output end of the drive motor via a motor coupling, and the other end of the rotating shaft is connected to the propeller via the propeller mounting sleeve. The rotating shaft is rotatably connected to the test bench base via a sealing device.

[0012] The shaft is axially mounted with a rear intermediate bearing, a front intermediate bearing, a thrust bearing, a diaphragm coupling, a rear stern bearing, a front stern bearing, a torque and tachometer rotor, and a propeller bearing.

[0013] The propeller bearing is connected to the test bench base via a bearing dynamic excitation force sensor, the torque tachometer rotor is connected to the test bench base via a torque tachometer stator, and the front intermediate bearing, rear intermediate bearing, thrust bearing, front stern bearing, and rear stern bearing are respectively connected to the test bench base.

[0014] Two counterweight balance discs are provided, respectively arranged on the front and rear sides of the thrust bearing; an eddy current displacement sensor is provided on the counterweight balance disc.

[0015] Multiple photoelectric speed sensors are respectively disposed on the front intermediate bearing, the rear intermediate bearing, the front stern bearing, the rear stern bearing, and the stator of the torque tachometer;

[0016] The frequency converter is connected to the drive motor and the data analysis and acquisition instrument respectively, and is used to control the drive motor to generate a regular sinusoidal waveform instantaneous fluctuation speed in order to apply a quantitative torsional disturbance;

[0017] The data analysis and acquisition instrument is connected to the frequency converter and the sensor assembly respectively, and is used to receive and process the acquired signals to output the hydrodynamic excitation results at the propeller position.

[0018] Preferably, multiple eddy current displacement sensors and multiple photoelectric speed sensors are provided at multiple positions along the axial direction of the rotating shaft.

[0019] Preferably, the propeller mounting bushing serves as a bending vibration simulation device. By replacing the propeller mounting bushing with one of different eccentricities, a fixed amount of gyratory disturbance is applied to the rotating shaft to simulate bending vibration.

[0020] Option 2: A propeller excitation measurement method that takes into account the influence of shaft bending and torsional vibration, based on the aforementioned propeller excitation measurement system that takes into account the influence of shaft bending and torsional vibration, includes the following steps:

[0021] Step 1: Conduct inherent characteristic tests and frequency response characteristic analysis to eliminate the sources of measurement error of structural resonance, and establish the mapping relationship between the amplitude of the excitation force at each degree of freedom of the propeller and the torque tachometer and bearing dynamic excitation force sensor within the measurement frequency range of interest.

[0022] Step 2: Under air conditions, conduct control group tests for each bending and torsional vibration state to be simulated, and obtain comparative measurement data of bearing dynamic excitation force sensor signal, torque tachometer signal, and step speed mark.

[0023] Step 3: With the propeller in water, repeat the bending and torsional vibration test corresponding to the air condition to obtain measurement data from the bearing dynamic excitation force sensor signal and the torque tachometer signal.

[0024] Step 4: For the time-domain data of air and water under the same bending and torsional vibration state, the actual hydrodynamic excitation force and torque are obtained by subtracting the signals that ensure phase consistency.

[0025] Step 5: Based on the mapping relationship, calculate the actual hydrodynamic excitation force and torque at the propeller position, and perform discrete Fourier transform on the time-domain results to obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration.

[0026] Preferably, step one specifically includes: arranging an eddy current displacement sensor and a photoelectric speed sensor at a non-water-contaminated location of the rotor system to obtain its inherent characteristics by measuring the bending and torsional vibrations of the shaft; arranging a torque tachometer at a non-water-contaminated location of the rotor system, wherein the rotor and stator of the torque tachometer together constitute the torque tachometer; installing a bearing dynamic excitation force sensor at the bearing housing of the propeller bearing to measure instantaneous fluctuating torque and bearing dynamic excitation force; using the speed increase method to test inherent characteristics, and determining the natural frequencies of the bending and torsional vibrations of the rotor system within the range of interest by using the waterfall plot results monitored by the eddy current displacement sensor and the photoelectric speed sensor; based on this, performing frequency response function analysis to obtain the mapping relationship of the excitation amplitudes of each degree of freedom at the bearing dynamic excitation force sensor and the torque tachometer at the propeller within the range of interest.

[0027] Preferably, step two specifically includes: setting a dedicated step speed mark channel during the measurement process to provide phase information in the result analysis; using propellers with different eccentricities to install bushings and apply a quantitative gyratory disturbance to the shaft to simulate bending vibration; controlling the drive motor to generate a regular sinusoidal instantaneous fluctuating speed through a frequency converter and applying a quantitative torsional disturbance to simulate torsional vibration; before performing excitation measurements under water-covered conditions, conducting control group tests in air conditions for each bending and torsional vibration state to be simulated, and obtaining comparative measurement data of bearing dynamic excitation force sensor signals, torque tachometer signals, and step speed marks for subsequent analysis.

[0028] Preferably, step three specifically includes: conducting tests on various bending and torsional vibration states to be simulated while the propeller is submerged in water, and obtaining measurement data from the bearing dynamic excitation force sensor signal and the torque tachometer signal for subsequent analysis.

[0029] Preferably, step four specifically includes: analyzing the time-domain measurement data of the air state and the water-attached state under the same bending and torsional vibration state, and performing signal subtraction to ensure phase consistency through the phase information recorded by the step speed marking channel to obtain the actual hydrodynamic excitation force and torque, thereby eliminating the interference of the mechanical structure's own excitation.

[0030] Preferably, step five specifically includes: within the frequency range of interest, based on the frequency response characteristic analysis, determining the mapping relationship of the excitation amplitudes of each degree of freedom at the propeller and the bearing dynamic excitation force sensor and torque tachometer, and calculating the time-domain data of the actual hydrodynamic excitation force and torque at the propeller using a structural transfer function model; performing a discrete Fourier transform on the obtained time-domain results of the actual hydrodynamic excitation force and torque at the propeller to obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration.

[0031] The present invention has the following beneficial effects:

[0032] 1. This invention, by setting up an air state control group test and performing phase-consistent signal subtraction processing based on the phase information recorded by the step speed marking channel, can effectively eliminate the interference of the mechanical structure's own excitation on the measurement results and significantly improve the measurement accuracy of propeller hydrodynamic excitation.

[0033] 2. This invention adopts an indirect measurement method by arranging a dynamic excitation force sensor and a torque tachometer in a non-water-contaminated location. By analyzing the frequency response characteristics, the mapping relationship between the force and torque amplitude at the propeller and the sensor is established, avoiding the cumbersome operation and high cost of arranging watertight sensors and cables in the underwater environment. The test system is simple to debug and highly reliable.

[0034] 3. This invention applies a quantitative gyratory disturbance to the shaft by replacing the propeller mounting bushing with one of different eccentricities, and applies a quantitative torsional disturbance by controlling the drive motor to generate a regular sinusoidal waveform instantaneous fluctuation speed through a frequency converter. This achieves independent, quantitative, and accurate simulation of the shaft bending and torsional vibrations, providing controllable experimental conditions for studying the coupling effect between bending and torsional vibrations and propeller hydrodynamic excitation.

[0035] 4. By performing a discrete Fourier transform on the time-domain results obtained from the measurement, this invention can obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration, providing reliable data support for the design of vibration reduction and noise reduction of ship propulsion shafts and the verification of related numerical simulation models. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a propeller excitation measurement system that takes into account the effects of shaft bending and torsional vibration.

[0037] Figure 2 This is a schematic diagram of the structure for mounting the propeller bushing.

[0038] In the diagram, 1-propeller, 2-sealing device, 3-propeller bearing, 4-bearing dynamic excitation force sensor, 5-torque tachometer rotor, 6-torque tachometer stator, 7-front stern bearing, 8-rear stern bearing, 9-diaphragm coupling, 10-thrust bearing, 11-counterweight balance disc, 12-front intermediate bearing, 13-rear intermediate bearing, 14-motor coupling, 15-drive motor, 16-frequency converter, 17-data analysis and acquisition instrument, 18-test bench base, 19-shaft, 20-eddy current displacement sensor, 21-photoelectric speed sensor, 22-propeller mounting bushing. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0040] Example 1: Combining Figures 1-2 This embodiment describes a propeller excitation measurement system that takes into account the effects of shaft bending and torsional vibration. The system includes the following components: a propeller 1, a sealing device 2, a propeller bearing 3, a bearing dynamic excitation force sensor 4, a torque tachometer rotor 5, a torque tachometer stator 6, a front stern bearing 7, a rear stern bearing 8, a diaphragm coupling 9, a thrust bearing 10, a counterweight balance disc 11, a front intermediate bearing 12, a rear intermediate bearing 13, a motor coupling 14, a drive motor 15, a frequency converter 16, a data analysis and acquisition instrument 17, a test bench base 18, a rotating shaft 19, an eddy current displacement sensor 20, a photoelectric speed sensor 21, and a propeller mounting bushing 22.

[0041] One end of the rotating shaft 19 is connected to the output end of the drive motor 15 via a motor coupling 14, and the other end of the rotating shaft 19 is connected to the propeller 1 via the propeller mounting sleeve 22. The propeller mounting sleeve 22 has different eccentricities; by replacing the sleeve with different eccentricities, a fixed amount of gyratory disturbance can be applied to the rotating shaft 19 to simulate bending vibration. The rotating shaft 19 is rotatably connected to the test bench base 18 via a sealing device 2, which is used to achieve dynamic sealing between the water-contaminated and non-water-contaminated parts.

[0042] The rotating shaft 19 is axially mounted with a rear intermediate bearing 13, a front intermediate bearing 12, a thrust bearing 10, a diaphragm coupling 9, a rear stern bearing 8, a front stern bearing 7, a torque tachometer rotor 5, and a propeller bearing 3. Two diaphragm couplings 9 are provided, respectively located on the front and rear sides of the thrust bearing 10, for connecting different sections of the rotating shaft 19. Two counterweight balance discs 11 are provided, respectively arranged on the front and rear sides of the thrust bearing 10, for adjusting the balance of the rotating shaft 19.

[0043] The propeller bearing 3 is connected to the test bench base 18 via a bearing dynamic excitation force sensor 4, used to measure the dynamic excitation force transmitted from the propeller 1 to the bearing. The torque-tachometer rotor 5 is connected to the test bench base 18 via a torque-tachometer stator 6, used to measure the instantaneous fluctuating torque and rotational speed of the shaft 19. The front intermediate bearing 12, rear intermediate bearing 13, thrust bearing 10, front stern bearing 7, and rear stern bearing 8 are respectively connected to the test bench base 18, used to support the shaft 19 and transmit loads.

[0044] An eddy current displacement sensor 20 is installed on the counterweight balance plate 11 to measure the shaft vibration displacement at the counterweight balance plate 11. Multiple photoelectric speed sensors 21 are respectively installed on the front intermediate bearing 12, the rear intermediate bearing 13, the front stern bearing 7, the rear stern bearing 8, and the stator 6 of the torque tachometer, to measure the speed signal and phase information at each position. Multiple eddy current displacement sensors 20 and multiple photoelectric speed sensors 21 are also installed at multiple positions along the axial direction of the rotating shaft 19 to comprehensively monitor the bending and torsional vibration state of the rotating shaft 19.

[0045] The frequency converter 16 is connected to both the drive motor 15 and the data analysis and acquisition instrument 17. The frequency converter 16 is used to control the drive motor 15 to generate a regular sinusoidal instantaneous fluctuating speed in order to apply a quantitative torsional disturbance.

[0046] Specifically, the frequency converter 16 outputs a sinusoidal modulation signal to the drive motor 15 to achieve quantitative simulation of torsional vibration.

[0047] The data analysis and acquisition instrument 17 is connected to the frequency converter 16 and the sensor assembly, respectively, and is used to receive and process the acquired signals to output the hydrodynamic excitation result at the propeller position. The sensor assembly includes a bearing dynamic excitation force sensor 4, a torque tachometer rotor 5 and a torque tachometer stator 6 forming a torque tachometer, an eddy current displacement sensor 20, a photoelectric speed sensor 21, etc.

[0048] Example 2: Combination Figures 1-2 This embodiment describes a propeller excitation measurement method that takes into account the effects of shaft bending and torsional vibration. This method is based on the system described in Embodiment 1 and includes the following steps:

[0049] Step 1: Inherent Characteristic Testing and Frequency Response Analysis

[0050] First, inherent characteristic tests and frequency response characteristic analysis are conducted to eliminate the sources of measurement error of structural resonance, and establish the mapping relationship between the amplitude of the excitation force at each degree of freedom of the propeller 1 and the torque tachometer and bearing dynamic excitation force sensor 4 within the measurement frequency range of interest.

[0051] Specifically, an eddy current displacement sensor 20 and a photoelectric speed sensor 21 are arranged in the non-water-contaminated area of ​​the rotor system to obtain the inherent characteristics of the shaft 19 by measuring its bending and torsional vibrations. A torque tachometer is also arranged in the non-water-contaminated area of ​​the rotor system. The torque tachometer rotor 5 and the torque tachometer stator 6 together constitute the torque tachometer. A bearing dynamic excitation force sensor 4 is installed at the bearing housing of the propeller bearing 3 to measure the instantaneous fluctuating torque and the bearing dynamic excitation force.

[0052] The inherent characteristics were tested using the increasing rotational speed method. The natural frequencies of the rotor system's bending and torsional vibrations within the range of interest were determined by analyzing the waterfall plot results monitored by the eddy current displacement sensor 20 and the photoelectric speed sensor 21. The horizontal and vertical axes of the waterfall plot represent frequency and rotational speed, respectively, while the contour plot represents amplitude. By observing the bright resonance band region perpendicular to the frequency axis, the natural frequencies of the system can be identified.

[0053] Based on this, frequency response function analysis is performed to obtain the mapping relationship between the excitation amplitudes of each degree of freedom at propeller 1 and the bearing dynamic excitation force sensor 4 and torque tachometer within the measurement frequency range of interest. This mapping relationship reflects the correspondence between the excitation at the propeller position and the measured value at the sensor position at each frequency.

[0054] Step 2: Air-condition control group test

[0055] In air, control group tests were conducted for each bending and torsional vibration state to be simulated, and comparative measurement data were obtained from the bearing dynamic excitation force sensor signal, torque tachometer signal, and step speed mark.

[0056] Specifically, a dedicated step speed marking channel is set up during the measurement process to provide phase information in the result analysis. This marking channel records the pulse signal generated by the rotating shaft 19 for each revolution, providing a phase reference for subsequent signal processing.

[0057] By employing propeller mounting sleeves 22 with different eccentricities, a fixed amount of gyratory disturbance is applied to the rotating shaft 19 to simulate bending vibration. By replacing the sleeves with different eccentricities e, the rotation axis of the propeller 1 is deviated from the theoretical axis of the rotor system, thereby generating centrifugal force. , where m is the propeller mass and ω is the propeller speed, to achieve quantitative simulation of bending vibration.

[0058] The variable frequency controller 16 controls the drive motor 15 to generate a regular sinusoidal instantaneous fluctuation in speed, and applies a quantitative torsional disturbance to simulate torsional vibration. The variable frequency controller 16 outputs a modulation signal to the drive motor 15, causing the instantaneous speed of the motor to fluctuate regularly. By adjusting the amplitude and frequency of the fluctuation, the quantitative simulation of torsional vibration is achieved.

[0059] Before conducting excitation measurements under water-covered conditions, control group tests were conducted under air conditions for each bending and torsional vibration state to be simulated. Comparative measurement data of bearing dynamic excitation force sensor signals, torque tachometer signals, and step speed markers were obtained for subsequent analysis.

[0060] Step 3: Excitation Measurement of Water Attachment State

[0061] With the propeller 1 submerged in water, the bending and torsional vibration state corresponding to the air state was repeatedly tested to obtain measurement data from the bearing dynamic excitation force sensor signal and the torque tachometer signal.

[0062] Specifically, water is filled into the water tank of the test bench base 18 so that the propeller 1 is submerged in water. For each bending and torsional vibration state simulated in step two, i.e., the same eccentricity of the propeller mounting bushing 22 and the same torsional disturbance parameters, the test is carried out in the water-covered state to obtain the measurement data of the bearing dynamic excitation force sensor signal and the torque tachometer signal for subsequent analysis.

[0063] Step 4: Subtract phase-consistent signals

[0064] By subtracting the time-domain data of air and water under the same bending and torsional vibration conditions to obtain the actual hydrodynamic excitation force and torque, the signals are kept in phase.

[0065] Specifically, the time-domain measurement data of air and water-covered states under the same bending and torsional vibration conditions are analyzed. First, based on the pulse signal recorded by the step speed marker channel, the start time of the air and water-covered state measurement data is determined, and the two signal segments are synchronously captured. Then, the phase difference between the two signal segments is determined using signal processing methods, and the water-covered state signal is time-shifted to align the phases of the two signals. Finally, the two phase-aligned signals are subtracted to obtain the actual hydrodynamic excitation force and torque time-domain signals. This method eliminates interference from the mechanical structure's own excitation.

[0066] Step 5: Mapping Transformation and Amplitude-Frequency Response Acquisition

[0067] Based on the mapping relationship obtained from the analysis in step three, the actual hydrodynamic excitation force and torque at propeller position 1 are calculated, and the time-domain results are subjected to discrete Fourier transform to obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration.

[0068] Specifically, within the frequency range of interest, the mapping relationship of the excitation amplitudes of each degree of freedom at propeller 1 and bearing dynamic excitation force sensor 4 and torque tachometer obtained from the frequency response characteristic analysis is used to calculate the time-domain data of the actual hydrodynamic excitation force and torque at propeller 1 through the structural transfer function model.

[0069] Discrete Fourier transform was performed on the time-domain results of the actual hydrodynamic excitation force and torque at propeller 1 to obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration. The amplitude-frequency characteristics are presented as a curve with frequency on the abscissa and excitation amplitude on the ordinate, reflecting the intensity distribution of propeller hydrodynamic excitation at different frequencies.

[0070] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A propeller excitation measurement method that takes into account the influence of shaft bending and torsional vibration, which is based on a propeller excitation measurement system that takes into account the influence of shaft bending and torsional vibration, characterized in that; The measurement system includes a propeller (1), a sealing device (2), a propeller bearing (3), a bearing dynamic excitation force sensor (4), a torque tachometer rotor (5), a torque tachometer stator (6), a front stern bearing (7), a rear stern bearing (8), a diaphragm coupling (9), a thrust bearing (10), a counterweight balance disc (11), a front intermediate bearing (12), a rear intermediate bearing (13), a motor coupling (14), a drive motor (15), a frequency converter (16), a data analysis and acquisition instrument (17), a test bench base (18), a rotating shaft (19), an eddy current displacement sensor (20), a photoelectric speed sensor (21), and a propeller mounting bushing (22). One end of the rotating shaft (19) is connected to the output end of the drive motor (15) through the motor coupling (14), and the other end of the rotating shaft (19) is connected to the propeller (1) through the propeller mounting bushing (22). The rotating shaft (19) is rotatably connected to the test bench base (18) through the sealing device (2). The shaft (19) is axially mounted with a rear intermediate bearing (13), a front intermediate bearing (12), a thrust bearing (10), a diaphragm coupling (9), a rear stern bearing (8), a front stern bearing (7), a torque tachometer rotor (5), and a propeller bearing (3). The propeller bearing (3) is connected to the test bench base (18) through the bearing dynamic excitation force sensor (4), the torque tachometer rotor (5) is connected to the test bench base (18) through the torque tachometer stator (6), and the front intermediate bearing (12), rear intermediate bearing (13), thrust bearing (10), front stern bearing (7), and rear stern bearing (8) are respectively connected to the test bench base (18). Two counterweight balance discs (11) are provided, which are respectively arranged on the front and rear sides of the thrust bearing (10); An eddy current displacement sensor (20) is provided on the counterweight balance plate (11). Multiple photoelectric speed sensors (21) are respectively disposed on the front intermediate bearing (12), the rear intermediate bearing (13), the front stern bearing (7), the rear stern bearing (8), and the torque speed meter stator (6); The frequency converter (16) is connected to the drive motor (15) and the data analysis and acquisition instrument (17) respectively, and is used to control the drive motor (15) to generate a regular sinusoidal instantaneous fluctuation speed to apply a quantitative torsional disturbance; The data analysis and acquisition instrument (17) is connected to the frequency converter (16) and the sensor assembly respectively, and is used to receive and process the acquired signals to output the hydrodynamic excitation results at the propeller position. Multiple eddy current displacement sensors (20) and multiple photoelectric speed sensors (21) are provided at multiple positions along the axial direction of the rotating shaft (19). The propeller mounting bushing (22) serves as a bending vibration simulation device. By replacing the propeller mounting bushing (22) with different eccentricities, a fixed amount of gyroscopic disturbance is applied to the rotating shaft (19) to simulate bending vibration. The measurement method includes the following steps: Step 1: Conduct inherent characteristic testing and frequency response characteristic analysis to eliminate the source of measurement error of structural resonance, and establish the mapping relationship between the amplitude of the excitation force of each degree of freedom at the propeller (1) and the torque tachometer and bearing dynamic excitation force sensor (4) within the measurement frequency range of interest. Step 2: Under air conditions, conduct control group tests for each bending and torsional vibration state to be simulated, and obtain comparative measurement data of bearing dynamic excitation force sensor signal, torque tachometer signal, and step speed mark. Step 3: With the propeller (1) in the water-covered state, repeat the bending and torsional vibration test corresponding to the air state to obtain the measurement data of the bearing dynamic excitation force sensor signal and the torque speed meter signal; Step 4: For the time-domain data of air and water under the same bending and torsional vibration state, the actual hydrodynamic excitation force and torque are obtained by subtracting the signals that ensure phase consistency. Step 5: Based on the mapping relationship, calculate the actual hydrodynamic excitation force and torque at the propeller (1) position, and perform discrete Fourier transform on the time domain results to obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration.

2. The propeller excitation measurement method considering the influence of shaft bending and torsional vibration according to claim 1, characterized in that, Step one specifically includes: An eddy current displacement sensor (20) and a photoelectric speed sensor (21) are arranged in the non-water-contaminated position of the rotor system to obtain its inherent characteristics by measuring the bending vibration and torsional vibration of the shaft (19); a torque tachometer is arranged in the non-water-contaminated position of the rotor system, the rotor (5) and the stator (6) of the torque tachometer together constitute the torque tachometer; a bearing dynamic excitation force sensor (4) is installed at the bearing seat of the propeller bearing (3) to measure the instantaneous fluctuation torque and the bearing dynamic excitation force; The inherent characteristics were tested by increasing the rotational speed. The natural frequency of the bending and torsional vibration of the rotor system within the range of the measurement interest was determined by the waterfall diagram results monitored by the eddy current displacement sensor (20) and the photoelectric speed sensor (21). Based on this, frequency response function analysis is performed to obtain the mapping relationship of the excitation amplitude of each degree of freedom at the bearing dynamic excitation force sensor (4) and torque tachometer at the propeller (1) within the range of the measurement frequency of interest.

3. The propeller excitation measurement method considering the influence of shaft bending and torsional vibration according to claim 2, characterized in that, Step two specifically includes: A dedicated step speed marking channel is set up during the measurement process to provide phase information in the result analysis; By using propeller mounting bushings (22) with different eccentricities, a fixed amount of gyroscopic disturbance is applied to the rotating shaft (19) to simulate bending vibration; The variable frequency controller (16) controls the drive motor (15) to generate a regular sinusoidal instantaneous fluctuation speed, and applies a quantitative torsional disturbance to simulate torsional vibration. Before conducting excitation measurements under water-covered conditions, control group tests were conducted under air conditions for each bending and torsional vibration state to be simulated. Comparative measurement data of bearing dynamic excitation force sensor signals, torque tachometer signals, and step speed markers were obtained for subsequent analysis.

4. The propeller excitation measurement method considering the influence of shaft bending and torsional vibration according to claim 3, characterized in that, Step three specifically includes: With the propeller (1) in the water-adjacent state, tests were conducted on various bending and torsional vibration states to be simulated, and measurement data of bearing dynamic excitation force sensor signal and torque speed meter signal were obtained for subsequent analysis.

5. The propeller excitation measurement method considering the influence of shaft bending and torsional vibration according to claim 4, characterized in that, Step four specifically includes: The time-domain measurement data of air state and water state under the same bending and torsional vibration conditions are analyzed. By using the phase information recorded by the step speed marking channel, signal subtraction to ensure phase consistency is carried out to obtain the actual hydrodynamic excitation force and torque, eliminating the interference of mechanical structure self-excitation.

6. The propeller excitation measurement method considering the influence of shaft bending and torsional vibration according to claim 5, characterized in that, Step five specifically includes: Within the frequency range of interest, the mapping relationship between the excitation amplitudes of each degree of freedom at the propeller (1) and the bearing dynamic excitation force sensor (4) and torque tachometer obtained from the frequency response characteristic analysis is used to calculate the time-domain data of the real hydrodynamic excitation force and torque at the propeller (1) through the structural transfer function model. Discrete Fourier transform is performed on the time-domain results of the actual hydrodynamic excitation force and torque at the propeller (1) to obtain the propeller excitation amplitude-frequency characteristics that take into account the influence of shaft bending and torsional vibration.

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