A method and system for identifying dynamic loads of an underwater propeller

Abstract

The application discloses a kind of underwater propeller dynamic load identification method and system.The method comprises: building underwater propeller dynamic load identification test platform, from propeller structure start, in turn by underwater to water includes watertight force sensor, watertight acceleration sensor, static beam in line with working condition stiffness, water acceleration sensor, base fixed support fixture;Unit force under frequency domain is applied at watertight sensor measuring point, modal damping ratio obtained by adding dynamic response test, the frequency response function of watertight force sensor measuring point to water acceleration sensor measuring point is calculated, and the finite element dynamic calibration model of underwater propeller dynamic load identification is established;Based on the acceleration response at water acceleration point under propeller working condition, dynamic load identification is completed using finite element dynamic calibration model.The application provides a practical and accurate solution for the dynamic load identification problem of underwater propeller.

Description

Technical Field

[0001] This invention belongs to the field of dynamic load identification, specifically relating to a method and system for identifying dynamic loads on underwater propulsion vehicles. Background Technology

[0002] As the second type of inverse problem in structural dynamics, dynamic load identification technology has limited applications in engineering. This is because dynamic load identification is a systemic problem encompassing dynamic response acquisition, modal parameter identification, and matrix ill-conditioned problems. In practical engineering applications, nonlinearity, minute disturbances, complex boundaries, and complex model errors often significantly impact the final dynamic load identification results, leading to poor identification accuracy and weak model adaptability. Underwater propulsion systems operate in complex environments, facing not only the influence of dynamic loads under specific conditions but also challenges such as surrounding fluids, fluid-structure interaction, and the difficulty in obtaining underwater model parameters. Therefore, dynamic load identification in underwater systems, particularly in the shipbuilding field, has always been a challenging problem. Dynamic loads are the "source" of structural dynamics problems; solving the dynamic load problem can effectively address issues related to the structure's dynamic response, vibration troubleshooting, dynamic fatigue, and acoustic radiation. Due to the complexity and specificity of dynamic load problems, a "specific problem, specific analysis" approach is crucial. Traditional dynamic load identification theories cannot perfectly solve specific engineering applications, and improving the accuracy of dynamic load identification is paramount. The complex environmental influences, fluid disturbances, boundary conditions, and many other factors of underwater thrusters pose significant challenges to dynamic load identification. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for identifying the dynamic load of an underwater propulsion device, establish a complete process for identifying the dynamic load of an underwater propulsion device, and provide a system for identifying the dynamic load of an underwater propulsion device.

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

[0005] A method for identifying dynamic loads on underwater thrusters includes the following steps:

[0006] An underwater thruster dynamic load identification test platform was built. Starting from the thruster structure, watertight force sensors, watertight acceleration sensors, statically determinate beams with working stiffness, above-water acceleration sensors, and foundation support fixtures were set up sequentially from underwater to above-water. The statically determinate beams connected the underwater thruster to the watertight force sensors and watertight acceleration sensors, extended out of the water surface, and were fixed to the above-water foundation.

[0007] A unit force in the frequency domain is applied at the watertightness sensor measuring point, and the modal damping ratio obtained from the dynamic response test is added. The frequency response function from the watertightness force sensor measuring point to the surface acceleration sensor measuring point is calculated, and a finite element dynamic calibration model for identifying the dynamic load of the underwater thruster is established.

[0008] Based on the acceleration response at the water acceleration sensor measurement point under the thruster's operating state, dynamic load identification is completed using a finite element dynamic calibration model.

[0009] Furthermore, the dynamic response test includes:

[0010] Without installing water acceleration sensors, a force hammer is used to excite the water acceleration sensor placement points to measure the model parameters of the entire model, which are used for finite element model correction and to obtain the modal damping ratio of each mode.

[0011] With the underwater thruster in operation, the position of the surface acceleration sensor is struck by a force hammer to obtain the transmission relationship between the underwater thruster excitation and the measurement point of the surface acceleration sensor, providing a reference for the dynamic calibration of the finite element model.

[0012] Install a water-based acceleration sensor and test the acceleration response at the sensor's measuring point during the thruster's operation for dynamic load identification.

[0013] Furthermore, obtaining the transmission relationship between the underwater thruster excitation and the surface acceleration sensor measurement point includes: using a hammer to strike the surface acceleration sensor position, taking the acceleration data at the underwater excitation point as a reference point, and using the reciprocity of the frequency response function to obtain the transmission relationship between the underwater thruster excitation point and the surface acceleration response point.

[0014] Furthermore, the method also includes: simplifying the finite element dynamic calibration model to ensure that the differences between the local mass, center of gravity, and moment of inertia in each direction of the simplified model and the model before simplification are within a specified range.

[0015] Furthermore, the simplification of the finite element dynamic calibration model includes: based on the identification task of underwater pulsating pressure under dynamic load, the model is dynamically simplified, including: replacing the real thruster with a cylindrical model with the same mass, center of gravity coordinates, and moment of inertia as the real object; deleting fillets and chamfers in the model that do not affect the dynamic analysis, and patching, adjusting mesh angles, and smoothing the gaps in the model; using the inherent parameters of the model obtained from the real object and actual tests as the standard, repeatedly comparing the results of finite element modal iteration calculations with the actual results to deduce the fixed support conditions of the finite element model.

[0016] Furthermore, simplifying the finite element dynamic calibration model also includes: based on the structural characteristics of the statically determinate beam, performing modal analysis on the simplified model in the direction of the thruster's propulsion to determine whether the natural vibration modes of the structure conform to the corresponding structural dynamics natural vibration theory, and whether the natural frequency errors of each vibration mode test and simulation are within the specified range. If the above conditions are met, the finite element dynamic calibration model is confirmed to be established.

[0017] Furthermore, since the statically determinate beam is a homogeneous I-beam, if the first five modes of vibration are similar to the first to fifth bending modes of an ideal simply supported beam, then it conforms to the natural vibration theory of cantilever beams in structural dynamics.

[0018] Furthermore, the dynamic load identification using the finite element dynamic calibration model includes:

[0019] The thrust is simplified to a concentrated dynamic load transmitted from the thruster to the watertightness force sensor. The dynamic load is identified using the traditional frequency domain method. If the simplified dynamic load consists of multiple concentrated loads, then F = H is used. + X represents the dynamic load, F represents the dynamic load, H represents the frequency response function matrix, and X represents the excitation response matrix. If the simplified dynamic load is a single-point concentrated dynamic load, multiple sets of acceleration data are measured through experiments. Based on the relationship between structural load and structural response, a dynamic load calculation formula is established. The experimental and simulation data are then substituted into the calculation formula to obtain the dynamic load of the underwater thruster.

[0020] Furthermore, the dynamic load calculation formula established based on the relationship between structural load and structural response is as follows:

[0021]

[0022] In the formula, [H 11 H 21 H 31 …H 41 H N1 [X] represents the first column of the frequency response function obtained from the dynamic calibration of the finite element model. i The response vector of the structure at a specified frequency, where N is the number of data sets acquired.

[0023] A dynamic load identification system for underwater thrusters, comprising:

[0024] The test platform, starting from the thruster structure, sequentially includes, from underwater to above water, a watertight force sensor, a watertight acceleration sensor, a statically determinate beam conforming to the operating conditions, an above-water acceleration sensor, and a foundation support fixture. The statically determinate beam connects the underwater thruster to the watertight force sensor and the watertight acceleration sensor, extends above the water surface, and is fixed to the above-water foundation.

[0025] The computing device is used to establish a finite element dynamic calibration model for identifying the dynamic load of the underwater thruster. Based on the acceleration response at the water surface accelerometer measurement point under the thruster's operating state, the dynamic load identification is completed using the finite element dynamic calibration model. The establishment of the finite element dynamic calibration model includes: applying a unit force in the frequency domain at the watertightness sensor measurement point, adding the modal damping ratio obtained from the dynamic response test, and calculating the frequency response function from the watertightness force sensor measurement point to the water surface accelerometer measurement point.

[0026] Beneficial Effects: Based on the working characteristics of underwater thrusters, this invention establishes a complete underwater dynamic load identification test platform under the complex fluid environment and boundary conditions during underwater thruster operation. Through the design of underwater thruster tooling fixtures, modification of test dynamics, and dynamic response testing, the dynamic response of the underwater environment and model parameters are acquired for subsequent dynamic load identification. A precise dynamic calibration model of the underwater thruster is established, and the thruster model is dynamically calibrated based on test data to obtain accurate model parameters, minimizing the influence of fluid and boundary conditions on the dynamic calibration. Using the operating frequency band of the underwater thruster under operating conditions as a reference, the frequency band range of the experimental dynamic response acquisition and dynamic calibration model is adjusted to accurately identify the dynamic loads in the frequency band of interest. This invention provides a highly practical and accurate solution to the problem of dynamic load identification for underwater thrusters, laying a solid foundation for underwater system dynamic analysis. Attached Figure Description

[0027] Figure 1 This is a flowchart of the underwater thruster dynamic load identification method of the present invention;

[0028] Figure 2 This is the dynamic load identification test platform built in the embodiment;

[0029] Figure 3 This is the finite element dynamic calibration model of the overall structure in the embodiment;

[0030] Figure 4 This is the first-order natural vibration mode of the propulsion direction after correction in the embodiment;

[0031] Figure 5 This is the second-order natural vibration mode of the propulsion direction after correction in the embodiment;

[0032] Figure 6 This is the third-order natural vibration mode of the propulsion direction after correction in the embodiment;

[0033] Figure 7 This is the fourth-order natural vibration mode of the propulsion direction after correction in the embodiment;

[0034] Figure 8 This is the fifth natural mode shape of the propulsion direction after correction in the embodiment;

[0035] Figure 9 This is a schematic diagram of the frequency response function obtained from finite element dynamic calibration calculation.

[0036] Figure 10 These are typical acceleration response data obtained from experiments;

[0037] Figure 11 The results show the dynamic load identification of the thruster under full-speed operating conditions. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0039] This invention focuses on a typical, linearly elastic underwater thruster structure, assuming the location of the external excitation force is known. First, an experimental platform for dynamic load identification of the underwater thruster is established. Considering the submerged nature of the thruster structure, a surface-mounted fixture is fabricated. This fixture is sufficiently load-bearing and capable of being excited to the main modes by the propulsion force. The fixture is fixedly supported to the foundation. Next, a precise finite element model of the underwater thruster is established. Based on the natural frequencies, damping ratios, and mode shapes of the overall structure obtained from the previous experiment, the finite element model is modified to ensure that the natural frequency error within the desired frequency band is within acceptable limits. Then, the modified finite element model is used for dynamic calibration to obtain the direct transmission relationship between the thruster excitation point and the fixture structure response point. Finally, dynamic load identification is performed using the dynamic response data obtained from the experiment and the dynamic calibration results obtained from the finite element model. Furthermore, the identified dynamic loads are verified to validate the accuracy of the entire dynamic load identification method. This invention introduces the relative error of the main frequency load amplitude, the decibel error of the total force spectrum level, and the decibel error of one-third octave bands to evaluate the dynamic load identification effect.

[0040] Reference Figure 1 The underwater thruster dynamic load identification process of the present invention includes the following steps:

[0041] Step 1: Build an underwater thruster dynamic load identification test platform.

[0042] The thruster operates underwater. Compared to the terrestrial working environment, the underwater working environment is more challenging due to factors such as noise and fluid coupling, making the dynamic load unpredictable. Furthermore, the dynamic response test data from terrestrial operation cannot be used as the response for dynamic load identification. Therefore, the thruster excitation point must be submerged in water, requiring the construction of a test platform that meets this requirement.

[0043] According to an embodiment of the present invention, in order to facilitate operation on water, a tooling platform for the propeller is established. The tooling starts from the propeller structure and includes, in sequence from underwater to above water, a watertight force sensor, a watertight acceleration sensor, a statically determinate beam with working stiffness, an above-water acceleration sensor, and a foundation support fixture. Figure 2This serves as a dynamic load testing platform for the propeller. A watertight force sensor acquires the propulsion force under operating conditions for dynamic load identification and verification, validating the accuracy of the method. A watertight accelerometer acquires the structural model parameters and a reference acceleration point for the transfer relationship between the excitation and response points. Since the installation of the exciter and power amplifier is generally inconvenient in a water-bearing environment, a force hammer is used to excite the structure above water. The excitation points are arranged on the water-borne portion of the statically determinate beam. Ideally, the excitation points should be located where the structural stiffness is high to ensure the overall vibration of the structure is excited. Because a homogeneous I-beam is used in this embodiment, the stiffness distribution of the water-borne portion of the statically determinate beam is theoretically uniform. Therefore, five excitation points are evenly arranged on the beam at a distance of 0.8 meters from the tooling fixture. Figure 2 As shown. Using the acceleration data at the underwater excitation point as a reference point, the reciprocity H of the frequency response function is utilized. ij =H ji The transfer relationship between the structural excitation point and the acceleration response point is obtained for reference in subsequent model dynamic calibration; the statically determinate beam connects the underwater thruster and two types of sensors, extends out of the water surface, and is fixed to the foundation above water; the above-water acceleration sensor is arranged at the above-mentioned force hammer excitation point to obtain the dynamic response data of the overall structure. In this invention, the acceleration point of the above-water part is both the excitation point for experimental dynamic calibration and the response point for experimental dynamic response; the foundation fixing fixture ensures that it can be tightly fixed to the foundation, establishing the boundary conditions of complete fixation.

[0044] Dynamic response tests were conducted based on the experimental platform. The tests included three parts: (i) Without installing surface accelerometers, a hammer was used to excite the surface accelerometer placement points to measure the natural frequencies of the entire model, which were used for finite element model correction. Since the accuracy of the natural frequencies has the greatest impact on the accuracy of the simulation model, the correction in this embodiment mainly focused on the structural natural frequencies. Simultaneously, the modal damping ratio of each mode was measured for subsequent frequency response function analysis. (ii) With the underwater thruster operating, a hammer was used to strike the surface accelerometer locations to obtain the transmission relationship between the underwater thruster excitation and the surface acceleration points, providing a reference for the dynamic calibration of the finite element model. (iii) With surface accelerometers installed, the acceleration response at the surface acceleration points under thruster operating conditions was tested for subsequent dynamic load identification.

[0045] Step 2: Establish a finite element dynamic calibration model for identifying the dynamic load of the underwater thruster and perform simulation dynamic calibration.

[0046] For dynamic load identification methods, obtaining accurate model parameters is particularly important. It can be said that the more accurate the model, the higher the accuracy of dynamic load identification. Step 2 of this invention is based on model correction theory to establish an accurate finite element dynamic calibration model for underwater thruster dynamic load identification.

[0047] A unit force in the frequency domain is applied to the corresponding position of the finite element model at the watertightness sensor measuring point in step 1. The modal damping ratio obtained from the dynamic response test in step 1 is added, and the frequency response function from the watertightness force sensor measuring point to the surface acceleration sensor measuring point is calculated, completing the dynamic calibration of the underwater thruster model. In this embodiment, the dynamic calibration calculation of the finite element model analyzes the transmission relationship between the underwater thruster excitation point and the surface acceleration point, also known as the frequency response function, such as... Figure 9 As shown.

[0048] Additionally, the complex thruster structure in the finite element model can be dynamically simplified to ensure that the local mass, center of gravity, and moments of inertia in each direction of the simplified thruster model are similar to those of the unsimplified model. It is important to note that simplification and correction errors must be kept within a very small range. In one implementation, based on the task of identifying underwater pulsating pressure under dynamic loads, the model is dynamically simplified. This includes replacing the actual thruster with a cylindrical model of the same mass, center of gravity coordinates, and moments of inertia as the real object; deleting fillets and chamfers in the model that do not affect the dynamic analysis; patching gaps in the model; adjusting mesh angles and smoothing the surface; and repeatedly comparing the results of iterative calculations of finite element modal parameters with the experimental modal parameter results, using the inherent parameters of the model obtained from the actual object and real tests as a reference. By changing the fixed support area of ​​the boundary conditions and fine-tuning the constraint degree of the model, the fixed support conditions of the finite element model are deduced. This is also part of the model correction work. Furthermore, modal analysis is performed on the corrected dynamic calibration model in the thruster's propulsion direction. For example, the first five vibration modes are similar to the first to fifth bending modes of an ideal simply supported beam, which conforms to the natural vibration theory of a cantilever beam in structural dynamics. Thus, a finite element calibration model for dynamic load identification based on the underwater thruster can be obtained. The finite element dynamic calibration model of the overall structure is as follows: Figure 3 As shown. And ensure that the overall model's mass, center of gravity coordinates, and moments of inertia in the XYZ directions remain consistent with the original model.

[0049] Step 3: Complete dynamic load identification and evaluate the identification effect.

[0050] Based on the dynamic response test data obtained from the experiment in step 1 (iii) and the dynamic calibration frequency response function matrix of the finite element model obtained in step 2, the dynamic load identification work is completed.

[0051] Firstly, the propulsion force of the underwater thruster is simplified to a certain extent. This invention simplifies the propulsion force to a concentrated dynamic load transmitted from the thruster to the watertightness force sensor on the structure, which is a single-point dynamic load. The dynamic load is identified using the traditional frequency domain method. If the simplified dynamic load is multiple concentrated loads, then F=H is used. +Identifying dynamic loads (X) involves key issues such as the generalized inverse of the frequency response function matrix and potential ill-conditioned problems. If the simplified dynamic load is a single-point concentrated dynamic load, and multiple sets of acceleration data are measured in the experiment, the following method is used to identify a single concentrated dynamic load using five sets of acceleration response data as an example:

[0052] Five sets of acceleration response and frequency response functions identify a single-point concentrated load. The load-response relationship of the structure then satisfies:

[0053]

[0054] In the above formula, F is the dynamic load, and H i1 The first column of the frequency response function obtained from the dynamic calibration of the finite element model is X. i Let H be the response vector of the structure at a certain frequency, and let [H be the dynamic response data obtained from the experiment in step 1 (iii). Multiply both sides of the above equation by [H]. 11 H 21 H 31 H 41 H 51 ]get:

[0055]

[0056] In the order

[0057]

[0058] Then we have:

[0059]

[0060] By substituting the processed test and simulation data into the above formula, the dynamic load of the underwater thruster can be obtained.

[0061] Engineering Practice Case: This case follows the underwater thruster dynamic load identification workflow of this invention, strictly adhering to dynamic testing standards to build an underwater thruster dynamic load identification test platform and complete the dynamic load identification work: (1) The underwater thruster tooling fixture for this case was designed; (2) The underwater thruster was experimentally modified; (3) The model parameters of the complete structure and the dynamic response data under working conditions were tested; (4) An accurate underwater thruster dynamic calibration model was established based on model correction theory; (5) The transmission relationship between the thruster excitation point and the response point was obtained; (6) The dynamic load identification work was completed. The complete workflow is illustrated with schematic diagrams and simulation model diagrams.

[0062] Taking a certain type of underwater thruster operating at full speed (1200 r / min) in the propulsion direction as an example, Figure 2 This is a dynamic load identification test platform that has been built. Figure 3 This is a finite element dynamic calibration model for the overall structure. Figures 4 to 8The first five natural modes of the corrected dynamic calibration model are given in Table 1. The errors of the first five natural frequencies in the XYZ directions of the test and simulation are all within 5%, which is within the acceptable range for engineering applications of underwater thrusters.

[0063] Table 1 Comparison of natural frequencies between the finite element dynamic calibration model and the actual test specimen

[0064]

[0065]

[0066] Figure 9 This is a schematic diagram of the frequency response function within 200Hz obtained from the dynamic calibration of the finite element model. Figure 10 The two figures show the acceleration response obtained from the experiment. As can be seen from the results, under the experimental conditions and with an accurate finite element model, both the frequency response function curve and the acceleration response curve can characterize the main frequencies in the vibration signal. Furthermore, the acceleration response shows relatively obvious fundamental and harmonic characteristics. Figure 11 The results of dynamic load identification under full-speed operating conditions of the thruster are shown in Tables 2 and 3, which compare the identified dynamic load with the actual dynamic load. Tables 2 and 3 present the total force spectrum error and the one-third octave band error. It can be seen that both errors are less than 3dB, which meets the technical specifications for dynamic load identification of underwater thrusters and is within the acceptable range for engineering applications.

[0067] Table 2. Overall force spectrum error for dynamic load identification

[0068] Identify payload / RMS Actual load / RMS Error 1 / % Error 2 / dB 10.8981 9.2981 17.21％ 1.38dB

[0069] Table 3. One-third octave band error of dynamic load identification force spectrum

[0070] 1 / 3 octave band / Hz Identify payload / RMS Actual load / RMS Error 1 / % Error 2 / dB 1.78～2.24 0.4240 0.3565 18.93％ 1.51dB 2.24～2.82 0.3942 0.2855 38.09％ 2.80dB 2.82～3.55 0.2832 0.2605 8.71％ 0.73dB 3.55～4.47 0.3362 0.3873 13.19％ 1.23dB 4.47～5.62 0.4104 0.4858 15.53％ 1.47dB 5.62～7.08 0.4682 0.5375 12.90％ 1.20dB 7.08～8.91 0.5745 0.6679 13.98％ 1.31dB 8.91～11.2 0.6159 0.6691 7.94％ 0.72dB 11.2～14.1 0.7626 0.6015 26.78％ 2.06dB 14.1～17.8 1.1577 1.2456 7.06％ 0.64dB 17.8～22.4 5.1064 4.8430 5.44％ 0.46dB 22.4～28.2 1.1256 1.0874 3.51％ 0.30dB 28.2～35.5 0.9354 0.8678 7.78％ 0.65dB 35.5～44.7 3.3830 3.4586 2.18％ 0.19dB 44.7～56.2 0.9372 0.9215 1.70％ 0.15dB 56.2～70.8 1.4343 1.8913 24.16％ 2.40dB 70.8～89.1 2.3600 3.0556 22.76％ 2.24dB 89.1～112 3.3902 3.3865 0.11％ 0.01dB 112～141 2.6401 2.8438 7.16％ 0.65dB 141～178 2.9019 3.7376 22.36％ 2.20dB

[0071] This invention provides a dynamic load identification system for underwater thrusters, comprising:

[0072] The test platform, starting from the thruster structure, sequentially includes, from underwater to above water, a watertight force sensor, a watertight acceleration sensor, a statically determinate beam conforming to the operating conditions, an above-water acceleration sensor, and a foundation support fixture. The statically determinate beam connects the underwater thruster to the watertight force sensor and the watertight acceleration sensor, extends above the water surface, and is fixed to the above-water foundation.

[0073] The computing device is used to establish a finite element dynamic calibration model for identifying the dynamic load of the underwater thruster. Based on the acceleration response at the water surface accelerometer measurement point under the thruster's operating state, the dynamic load identification is completed using the finite element dynamic calibration model. The establishment of the finite element dynamic calibration model includes: applying a unit force in the frequency domain at the watertightness sensor measurement point, adding the modal damping ratio obtained from the dynamic response test, and calculating the frequency response function from the watertightness force sensor measurement point to the water surface accelerometer measurement point.

[0074] It should be understood that the computing device in the underwater thruster dynamic load identification system is capable of performing the operations described in steps 2 and 3 of the above method embodiments, namely, model calibration and correction through calculation, and dynamic load identification using the model. The specific implementation process will not be elaborated here.

[0075] Based on the operational characteristics of underwater thrusters, this invention establishes a complete underwater dynamic load identification test platform considering the complex fluid environment and boundary conditions encountered during underwater thruster operation. Through tooling and fixture design, experimental dynamics modification, and dynamic response testing, the platform acquires dynamic responses and model parameters for subsequent dynamic load identification. A precise dynamic calibration model of the underwater thruster is established, and the model is dynamically calibrated based on experimental data to obtain accurate model parameters, minimizing the influence of fluid and boundary conditions on the dynamic calibration. Using the operating frequency band of the underwater thruster under its operating conditions as a benchmark, the frequency band range of the experimental dynamic response acquisition and dynamic calibration model is adjusted to accurately identify dynamic loads in the frequency band of interest. This invention provides a highly practical and accurate solution to the challenge of dynamic load identification for underwater thrusters, laying a solid foundation for underwater system dynamic analysis.

Claims

1. A method for identifying dynamic loads on underwater thrusters, characterized in that, Includes the following steps: An underwater thruster dynamic load identification test platform was built. Starting from the thruster structure, watertight force sensors, watertight acceleration sensors, statically determinate beams with working stiffness, above-water acceleration sensors, and foundation support fixtures were set up sequentially from underwater to above-water. The statically determinate beams connected the underwater thruster to the watertight force sensors and watertight acceleration sensors, extended out of the water surface, and were fixed to the above-water foundation. A unit force in the frequency domain is applied at the watertightness sensor measuring point, and the modal damping ratio obtained from the dynamic response test is added. The frequency response function from the watertightness force sensor measuring point to the surface acceleration sensor measuring point is calculated, and a finite element dynamic calibration model for identifying the dynamic load of the underwater thruster is established. Based on the acceleration response at the waterborne accelerometer measurement points during propulsion operation, dynamic load identification is performed using a finite element dynamic calibration model. This includes: simplifying the propulsion force into a concentrated dynamic load transmitted from the propulsion unit to the watertightness force sensor; identifying the dynamic load using the traditional frequency domain method; and if the simplified dynamic load consists of multiple concentrated loads, then... Identify the dynamic load, where F is the dynamic load, H is the frequency response function matrix, and X is the excitation response matrix. If the simplified dynamic load is a single-point concentrated dynamic load, multiple sets of acceleration data are measured experimentally. A dynamic load calculation formula is established based on the relationship between structural load and structural response. The experimental and simulation data are then substituted into the calculation formula to obtain the dynamic load of the underwater thruster. The dynamic load calculation formula established based on the relationship between structural load and structural response is as follows: In the formula, The first column of the frequency response function obtained from the dynamic calibration of the finite element model. The response vector of the structure at a specified frequency, where N is the number of data sets acquired.

2. The method according to claim 1, characterized in that, Dynamic response testing includes: Without installing water acceleration sensors, a force hammer is used to excite the water acceleration sensor placement points to measure the model parameters of the entire model, which are used for finite element model correction and to obtain the modal damping ratio of each mode. With the underwater thruster in operation, the position of the surface acceleration sensor is struck by a force hammer to obtain the transmission relationship between the underwater thruster excitation and the measurement point of the surface acceleration sensor, providing a reference for the dynamic calibration of the finite element model. Install a water-based acceleration sensor and test the acceleration response at the sensor's measuring point during the thruster's operation for dynamic load identification.

3. The method according to claim 2, characterized in that, The process of obtaining the transmission relationship between the underwater thruster excitation and the surface acceleration sensor measurement point includes: using a hammer to strike the surface acceleration sensor position, taking the acceleration data at the underwater excitation point as a reference point, and using the reciprocity of the frequency response function to obtain the transmission relationship between the underwater thruster excitation point and the surface acceleration response point.

4. The method according to claim 3, characterized in that, It also includes: simplifying the finite element dynamic calibration model to ensure that the differences between the local mass, center of gravity, and moment of inertia in each direction of the simplified model and the model before simplification are within a specified range.

5. The method according to claim 4, characterized in that, The simplification of the finite element dynamic calibration model includes: based on the identification task of underwater pulsating pressure under dynamic load, the model is dynamically simplified, including: replacing the real thruster with a cylindrical model with the same mass, center of gravity coordinates, and moment of inertia as the real object; deleting fillets and chamfers in the model that do not affect the dynamic analysis, and filling gaps in the model, adjusting mesh angles, and smoothing the surface; using the inherent parameters of the model obtained from the real object and real tests as the standard, the results of finite element modal iteration calculations are repeatedly compared with the actual results to deduce the fixed support conditions of the finite element model.

6. The method according to claim 5, characterized in that, The simplification of the finite element dynamic calibration model also includes: based on the structural characteristics of the statically determinate beam, performing modal analysis on the simplified model in the direction of the thruster to determine whether the natural vibration modes of the structure conform to the corresponding structural dynamics natural vibration theory, and whether the natural frequency errors of each vibration mode test and simulation are within the specified range. If the above conditions are met, the finite element dynamic calibration model is confirmed to be established.

7. The method according to claim 6, characterized in that, A statically determinate beam is a homogeneous I-beam. If the first five modes of vibration are similar to the first to fifth bending modes of an ideal simply supported beam, then it conforms to the natural vibration theory of cantilever beams in structural dynamics.

8. A dynamic load identification system for underwater thrusters, characterized in that, include: The test platform, starting from the thruster structure, includes a watertight force sensor, a watertight acceleration sensor, a statically determinate beam with working stiffness, an above-water acceleration sensor, and a foundation support fixture, which connects the underwater thruster to the watertight force sensor and the watertight acceleration sensor, extends out of the water surface, and is fixed to the above-water foundation. as well as The computing device is used to establish a finite element dynamic calibration model for identifying the dynamic load of the underwater thruster. Based on the acceleration response at the water surface accelerometer measurement point under the thruster's operating state, the dynamic load identification is completed using the finite element dynamic calibration model. The establishment of the finite element dynamic calibration model includes: applying a unit force in the frequency domain at the watertightness sensor measurement point, adding the modal damping ratio obtained from the dynamic response test, and calculating the frequency response function from the watertightness force sensor measurement point to the water surface accelerometer measurement point. Dynamic load identification is performed using a finite element dynamic calibration model, including: simplifying the propulsion force into a concentrated dynamic load transmitted from the propeller to the watertightness force sensor; identifying the dynamic load using the traditional frequency domain method; and if the simplified dynamic load consists of multiple concentrated loads, then... Identify the dynamic load, where F is the dynamic load, H is the frequency response function matrix, and X is the excitation response matrix. If the simplified dynamic load is a single-point concentrated dynamic load, multiple sets of acceleration data are measured experimentally. A dynamic load calculation formula is established based on the relationship between structural load and structural response. The experimental and simulation data are then substituted into the calculation formula to obtain the dynamic load of the underwater thruster. The dynamic load calculation formula established based on the relationship between structural load and structural response is as follows: In the formula, The first column of the frequency response function obtained from the dynamic calibration of the finite element model. The response vector of the structure at a specified frequency, where N is the number of data sets acquired.

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