Method for obtaining cut-off frequency of water impact load test and related equipment

Abstract

The embodiment of the application discloses a water impact load test cutoff frequency acquisition method and related equipment, dry modal analysis is carried out on a vehicle test model, the natural frequency and modal participation factor corresponding to the modal of different stages are acquired; the modal corresponding to the maximum modal participation factor in the same preset excitation direction is acquired; and the natural frequency corresponding to the maximum modal is taken as the cutoff frequency of the water impact load test. The natural frequency of the vibration response of the vehicle structure is acquired through the dry modal analysis, and is introduced into the data processing process of the signal, the natural frequency corresponding to the maximum modal participation factor of the excitation direction is selected as the cutoff frequency, the subjectivity of the low-pass filter cutoff frequency selection is weakened, and the error of the test data is reduced.

Description

[0001] The present application relates to the technical field of high-speed water entry test technology, and particularly relates to a method for obtaining a cutoff frequency of a water entry impact load test and related equipment.

[0002] With the development of new cross-medium vehicle related technologies, the research on high-speed water entry has attracted extensive attention. High-speed water entry test research is an important supplementary method for researching high-speed water entry. Due to the transient and strong nonlinearity of high-speed water entry, the impact load data collected by the acceleration sensor in the high-speed water entry test process generally consists of three parts: rigid body acceleration, structural response acceleration and other accelerations. The rigid body acceleration is the acceleration formed by the resistance during the water entry process, which is also called rigid body overload. The structural response acceleration is the acceleration signal formed by the dynamic response of the vehicle structure due to the collision between the vehicle and the water surface, including the acceleration signals generated by the axial and lateral vibration responses of the vehicle structure. The other acceleration is mainly the acceleration signal generated by the interference factors, such as the acceleration signal generated by the vibration of the acceleration sensor and the interference noise signal caused by the installation connection mode between the acceleration sensor and the vehicle. The high-speed water entry impact load test data is complex, and how to accurately extract the rigid body overload from the complex measured impact load test data has been a key and difficult problem in data processing.

[0003] The existing method is based on the EEMD method to decompose the original signal, then performs Burg power spectrum analysis on the IMF component to obtain the power spectrum of each IMF component, then obtains the high-frequency part of the vibration of the rigid body according to the specific rigid body modal analysis, and obtains the corresponding critical frequency, finally filters the high-frequency IMF component from the original signal according to the critical frequency, and reconstructs the remaining IMF component to obtain the filtered signal. In this method, the selection of the critical frequency is not given a clear criterion, so the IMF components participating in the signal reconstruction may have a certain subjectivity in selection, which may easily lead to a large error between the filtered signal and the actual required signal.

[0004] Therefore, the present application provides a method for obtaining a cutoff frequency of a water entry impact load test and related equipment.

[0005] ​​​The technical scheme of the first embodiment of the present application is as follows: a method for obtaining a cutoff frequency of a water-entry impact load test, the method comprising: performing dry modal analysis on a test model of a vehicle to obtain natural frequencies and modal participation factors corresponding to modes in different stages; the different stages include a launch stage and a water-entry impact stage of the test model of the vehicle; obtaining a mode corresponding to a maximum modal participation factor in a preset excitation direction; and taking the natural frequency corresponding to the maximum mode as the cutoff frequency of the water-entry impact load test.

[0006] Preferably, the dry modal analysis on the test model of the vehicle to obtain the natural frequencies and the modal participation factors corresponding to the modes in the different stages comprises: performing dry modal analysis on the test model of the vehicle to obtain a structural linear motion control equation of the vehicle; obtaining the natural frequencies and modal shapes corresponding to the modes in the different stages according to a node displacement vector, a node acceleration vector and the structural linear motion control equation; and obtaining the modal participation factors based on the modal shapes and a structural mass matrix.

[0007] Preferably, the obtaining of the natural frequencies and the modal shapes corresponding to the modes in the different stages according to the node displacement vector, the node acceleration vector and the structural linear motion control equation comprises: substituting the node displacement vector and the node acceleration vector into the structural linear motion control equation to obtain a vibration frequency and a modal shape; and obtaining the natural frequencies according to the vibration frequency.

[0008] Preferably, the vibration frequency and the modal shape are obtained by using the following formula:

[0009]

[0010] wherein K is a structural stiffness matrix in the structural linear motion control equation, ω i is the vibration frequency, M is a structural mass matrix in the structural linear motion control equation, is the modal shape.

[0011] Preferably, the natural frequencies are obtained by using the following formula:

[0012] f i =ω i / 2π

[0013] wherein ω i is the vibration frequency, f i is the natural frequency.

[0014] Preferably, the modal participation factors are obtained by using the following formula:

[0015]

[0016] wherein γi as the modal participation factor, as the modal shape, M is a structure mass matrix in a structure linear motion control equation, and D is a displacement frequency spectrum of an element in each global coordinate system translational direction and rotational direction; the element is different elements formed after the structure of the vehicle is discretized.

[0017] Preferably, after the natural frequency corresponding to the maximum modal is taken as the cutoff frequency of the water entry impact load test, the method further comprises: taking the cutoff frequency as the cutoff frequency of a low-pass filter to filter nonlinear data obtained by water entry impact simulation to obtain a filtering result.

[0018] The specific technical scheme of the second embodiment of the application is: a cutoff frequency acquisition system for a water entry impact load test, the system comprising: an analysis module, a modal selection module and a cutoff frequency acquisition module; the analysis module is used to carry out dry modal analysis on a vehicle test model to obtain natural frequencies and modal participation factors corresponding to modes at different stages; the different stages include a vehicle test model launch stage and a water entry impact stage; the modal selection module is used to obtain a modal corresponding to a maximum modal participation factor in the same preset excitation direction; and the cutoff frequency acquisition module is used to take the natural frequency corresponding to the maximum modal as the cutoff frequency of the water entry impact load test.

[0019] The specific technical scheme of the third embodiment of the application is: a cutoff frequency acquisition device for a water entry impact load test, comprising a memory and a processor, the memory storing a computer program, and the computer program being executed by the processor to make the processor execute the steps of the method according to any one of the first embodiment of the application.

[0020] The specific technical scheme of the fourth embodiment of the application is: a computer readable storage medium storing a computer program, and the computer program being executed by a processor to make the processor execute the steps of the method according to any one of the first embodiment of the application.

[0021] The application has the following beneficial effects:

[0022] The application carries out dry modal analysis on a vehicle test model to obtain natural frequencies and modal participation factors corresponding to modes at different stages, obtains a modal corresponding to a maximum modal participation factor in the same preset excitation direction, and takes the natural frequency corresponding to the maximum modal as the cutoff frequency of the water entry impact load test. The natural frequency of the vibration response of the structure of the vehicle is obtained through dry modal analysis and is introduced into the data processing process of the signal, the natural frequency corresponding to the modal with the maximum modal participation factor in the excitation direction is selected as the cutoff frequency, the subjectivity in the selection of the cutoff frequency of the low-pass filter is reduced, and the error of the test data is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0024] Figure 1 Flow chart for the step of the cutoff frequency acquisition method for the water impact load test;

[0025] Figure 2 Impact acceleration original data graph;

[0026] Figure 3 Impact acceleration data graph of the intercepted segment;

[0027] Figure 4 First six modal shape graphs;

[0028] Figure 5 Low-pass filter amplitude-frequency response graph;

[0029] Figure 6 Filtering result comparison graph;

[0030] Figure 7 Power spectrum comparison graph;

[0031] Figure 8 Structural schematic diagram of the cutoff frequency acquisition system;

[0032] Figure 9 Internal structure diagram of the computer device;

[0033] Among them, 201, analysis module; 202, modal selection module; 203, cutoff frequency acquisition module.

DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0035] The terms "first", "second", and the like in the description and in the claims of the present application and in the drawings refer to different objects and not to a particular sequence. Furthermore, the terms "comprises", "comprising", "has", "having", "includes", "including", and the like are to be construed open-ended, allowing for instances where there are equivalents to the recited steps or modules that are not listed. For example, a process, method, system, product, or apparatus that comprises a list of steps or modules is not necessarily limited to those listed steps or modules, but can include additional steps or modules not expressly listed or can include steps or modules that are inherent to the process, method, system, product, or apparatus.

[0036] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that the embodiments described herein are merely examples from a whole class of comparable embodiments which those skilled in the art will readily appreciate. It is also expressly understood that the embodiments described herein have a wide application.

[0037] The cutoff frequency, also known as the turnover frequency, is the frequency point at which the filter response drops to a certain specific value, usually 70.7% of the maximum response, that is, the -3dB point corresponding to a power halving. Below this frequency, the signal can pass through the filter more freely, while the signal with a frequency higher than this point will be significantly attenuated. The cutoff frequency of the low-pass filter determines which frequency signals can pass through the filter without being significantly attenuated, and which frequency signals will be blocked or weakened by the filter. Adjusting the cutoff frequency of the low-pass filter can change the response characteristics of the filter to meet different application requirements.

[0038] Please refer to Figure 1 The step flowchart of the method for acquiring the cutoff frequency of the water entry impact load test in the first embodiment of the application is beneficial to reduce the error of the test data, and the method comprises the following steps:

[0039] In step 101, dry modal analysis is performed on the vehicle test model to acquire the natural frequencies and modal participation factors corresponding to different stages; the different stages include the launch stage and the water entry impact stage of the vehicle test model.

[0040] In step 102, the modal corresponding to the maximum modal participation factor in the preset excitation direction is acquired.

[0041] In step 103, the natural frequency corresponding to the maximum modal is taken as the cutoff frequency of the water entry impact load test.

[0042] Specifically, dry modal analysis is an effective method for studying the dynamic characteristics of a structure, which transforms the physical coordinates in a linear constant system vibration differential equation set into modal coordinates, decouples the equation set, and becomes a set of independent equations described by modal coordinates and modal parameters, so as to obtain the modal parameters of the system. Dry modal analysis is a kind of modal analysis, which does not consider the influence of fluid on the structure mode, and only focuses on the vibration characteristics of the structure itself. First, the dry modal analysis of the vehicle model is carried out, which can be completed by dividing the finite element grid analysis using commercial software. The basic principle is to assume that the vehicle is free vibration and ignore the structural damping to obtain the natural frequency and modal participation factor corresponding to the modal at different stages. The modal participation factor is a function of the mode shape and the excitation direction, which can measure the contribution of the mode to the structural deformation in the excitation direction. If the modal participation factor of a certain mode in a certain direction is larger, it means that the force in the excitation direction will cause larger structural deformation corresponding to this mode. Combined with the structural response, deformation and other characteristics of the vehicle during the water impact process, the modal with the largest modal participation factor in the same excitation direction is found, and the natural frequency corresponding to the modal is used as the cutoff frequency of the low-pass filter

[0043] The method in the embodiment obtains the natural frequency of the vehicle structure vibration response through dry modal analysis, and introduces it into the data processing process of the signal. The natural frequency corresponding to the modal with the largest modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity of the selection of the low-pass filter cutoff frequency and is beneficial to reduce the error of the test data.

[0044] In specific embodiments, the dry modal analysis of the vehicle test model is carried out to obtain the natural frequency and modal participation factor corresponding to the modal at different stages, including: carrying out dry modal analysis on the vehicle test model to obtain the structural linear motion control equation of the vehicle; obtaining the natural frequency and modal shape corresponding to the modal at different stages according to the node displacement vector, the node acceleration vector and the structural linear motion control equation; and obtaining the modal participation factor based on the modal shape and the structural mass matrix.

[0045] Specifically, the vehicle is free vibration and the structural damping is ignored, so the general structural linear motion control equation of the vehicle is:

[0046]

[0047] Wherein: M is the structural mass matrix; K is the structural stiffness matrix; is the node acceleration vector; u is the node displacement vector.

[0048] In specific embodiments, the obtaining of the natural frequency and the modal shape corresponding to the modal shape of different stages according to the node displacement vector, the node acceleration vector and the structural linear motion control equation comprises: substituting the node displacement vector and the node acceleration vector into the structural linear motion control equation to obtain a vibration frequency and a modal shape; and obtaining the natural frequency according to the vibration frequency.

[0049] Specifically, assuming a harmonic response motion, the node displacement vector and the node acceleration vector can be expressed as:

[0050]

[0051] Substituting u, into the structural linear motion control equation, the natural frequency and the modal shape corresponding to the modal shape of different stages are obtained.

[0052] In specific embodiments, the vibration frequency and the modal shape are obtained by using the following formula:

[0053]

[0054] wherein K is a structural stiffness matrix in the structural linear motion control equation, ω i is the vibration frequency, M is a structural mass matrix in the structural linear motion control equation, is the modal shape.

[0055] The condition for the above equation to be true is is expressed as a non-vibration case, or satisfies the following formula:

[0056]

[0057] Solving the above equation, the vibration frequency ω i and the modal shape

[0058] In specific embodiments, the natural frequency is obtained by using the following formula:

[0059] f i = ω i / 2π

[0060] wherein ω i is the vibration frequency, f i is the natural frequency. represents the vibration shape of the structure when vibrating at the natural frequency f i .

[0061] The modal shape can be normalized with respect to the mass matrix M or with respect to the unit matrix I:

[0062]

[0063] In specific embodiments, the modal participation factor is obtained using the following formula:

[0064]

[0065] where γ i is the modal participation factor, is the modal shape, M is the structural mass matrix in the linear motion control equation of the structure, and D is the displacement spectrum of the element in the translational and rotational directions of each global coordinate system; the element is a different element formed after the structure of the vehicle is discretized.

[0066] In specific embodiments, after the natural frequency corresponding to the maximum modal participation factor is used as the cutoff frequency of the water entry impact load test, the method further comprises filtering the nonlinear data obtained from the water entry impact simulation of the vehicle using the cutoff frequency as the cutoff frequency of a low-pass filter to obtain a filtering result.

[0067] Specifically, the modal with the maximum modal participation factor in the same excitation direction is found, and the natural frequency corresponding to the modal is used as the cutoff frequency of the low-pass filter. A low-pass filter is designed by self-programming, and whether the amplitude-frequency response graph of the designed filter meets the requirements is observed. Finally, low-pass filtering of the original data is completed, and whether the difference between the filtered signal and the original signal meets the requirements is compared.

[0068] The natural properties of the vehicle structure vibration response are obtained through dry modal analysis and introduced into the data processing process of the impact signal. The natural frequency corresponding to the modal with the maximum modal participation factor in the excitation direction is selected as the cutoff frequency of the low-pass filter, which reduces the subjectivity in selecting the cutoff frequency of the low-pass filter and helps to reduce the error of the test data. At the same time, the low-pass filter is designed by self-programming, realizing the self-controlling of the code. Finally, the method has clear principles and simplifies the processing flow and steps of the high-speed water entry test data, greatly improving the efficiency of the test data processing.

[0069] In specific embodiments, the specific method of low-pass filtering includes: defining filter parameters, filter design, filter implementation, and filter verification and adjustment.

[0070] I. Define filter parameters

[0071] Cutoff frequency (f1): This is the key parameter of the low-pass filter, which determines which frequencies below the signal can pass through the filter without being significantly attenuated.

[0072] Sampling frequency (Fs): The frequency at which the signal is sampled, which is particularly important for digital filter design.

[0073] Passband attenuation (rp): The maximum amount of attenuation allowed for signals within the passband.

[0074] Stopband attenuation (rs): The minimum amount of attenuation for signals within the stopband.

[0075] Stopband cutoff frequency (f3): The frequency point at which the stopband begins to attenuate, often used to determine the transition bandwidth of the filter.

[0076] II. Filter Design

[0077] Selecting filter type: Choose a low-pass filter type based on application requirements, such as FIR (Finite Impulse Response) or IIR (Infinite Impulse Response) filters. FIR filters have linear phase characteristics, suitable for applications sensitive to phase; IIR filters have higher frequency selectivity but may not have as good phase characteristics as FIR filters.

[0078] Determining filter order: The order of the filter determines the steepness of its frequency response. Higher order filters have steeper frequency responses but also higher computational complexity. Filter design methods such as Chebyshev, Butterworth, etc. can be used to determine the filter order.

[0079] Calculating filter coefficients: Based on the selected filter type, order, and cutoff frequency, calculate the numerator and denominator coefficients of the filter. These coefficients will be used to implement the difference equation or transfer function of the filter.

[0080] III. Filter Implementation

[0081] Analog filter implementation: For low-pass filters in analog circuits, RC circuits can be constructed using resistors and capacitors. According to the cutoff frequency formula, select appropriate resistor and capacitor values to meet the design requirements of the filter.

[0082] Digital filter implementation: For digital filters, filter design toolboxes in programming tools such as MATLAB, Python, etc. can be used to design and implement filters. These tools provide a wealth of filter design methods and optimization algorithms, making it easy to generate filter coefficients and apply them to signal processing.

[0083] Programming implementation: Use programming languages such as C, C++, MATLAB, etc. to write filter implementation code. According to the difference equation or transfer function of the filter, perform filter processing on the input signal to obtain the output signal.

[0084] IV. Filter Verification and Adjustment

[0085] Simulation verification: Use simulation tools (such as MATLAB Simulink, SPICE, etc.) to simulate and verify the filter. By inputting signals of different frequencies and observing the output response of the filter, you can verify whether it meets the design requirements.

[0086] Practical testing: Apply the filter to a real system and conduct actual testing. Evaluate the filter's performance by comparing the input and output signals.

[0087] Adjustment and optimization: Based on the results of simulation verification and actual testing, the filter parameters are adjusted and optimized to improve its performance.

[0088] Figure 2 The impact load test data collected during the test includes the model launch stage and the water impact stage. Since the water impact stage is the main research stage, the test data is intercepted, such as Figure 3 As shown in the figure, it can be seen that the test data contains high-frequency components and low-frequency components. According to the test data processing process, the dry modal analysis is carried out on the aircraft model. At the beginning of the model entering the water, the head of the model collides with the water surface at high speed, and the water medium is discharged to the surrounding areas. At this time, the end face of the head of the model is in a wet state, and the entire body is wrapped in the water cavitation. Therefore, when carrying out the dry modal analysis, the end face of the head of the model is fixed. The natural frequencies, modal vibration shapes and modal participation factors corresponding to each order mode obtained by the dry modal analysis are shown in Table 1 below. The first six order modal vibration shapes are shown in Table 1. Figure 4 shown.

[0089]

[0090]

[0091] Table 1: Schematic table of natural frequency, mode shape and modal participation factor parameters

[0092] Since the aircraft model is an axisymmetric structure, symmetrical modes appear in its modes, and the symmetrical modes show the characteristics of close natural frequencies and similar modal vibration shapes. Combined with the deformation of the model during the water impact, the Z axis is the longitudinal axis of the model and the main deformation direction. Therefore, the focus is on the modal participation factor of the deformation along the Z axis. As can be seen from the above, the participation factors of the 1st, 2nd, 6th, and 7th order modes are large, and from the modal vibration shape diagram, it can be seen that the 6th and 7th order modal vibration shapes are bending deformations, which is consistent with the actual deformation of the model after the water impact. Therefore, the natural frequency corresponding to the 7th order mode is used as the cutoff frequency of the low-pass filter. The FIR low-pass filter is designed through self-programming, and the cutoff frequency is 2318Hz. The amplitude-frequency response diagram of the low-pass filter is shown as follows: Figure 5The amplitude-frequency response graph is shown. It can be seen from the amplitude-frequency response graph that the signal component with a frequency higher than 2318Hz is greatly attenuated when passing through the filter, and the signal component with a frequency lower than 2318Hz is less attenuated. Figure 6 The comparison between the original signal before filtering and the rigid body overload obtained after filtering is shown. It can be seen from the graph that, compared with the original signal, the curve becomes smoother due to the elimination of high-frequency interference, and can well reflect the overall change trend of the signal. Figure 7 The power spectrum of the original signal and the signal after filtering can be seen. At low frequencies, the curves of the two are basically coincident, and at high frequencies, the power of the signal after filtering is smaller. The method well extracts the rigid body overload component contained in the original signal. The method has simple operation steps, greatly improves the efficiency of test data processing, weakens the subjectivity of test data processing parameter setting, reduces the error between the data after filtering and the real data, and lays a foundation for the filtering technology of high-speed water impact load test data.

[0093] In specific embodiments, please refer to Figure 8 Fig. 1 is a structural schematic diagram of an application second embodiment of a cutoff frequency acquisition system for a water impact load test. The system comprises an analysis module 201, a modal selection module 202 and a cutoff frequency acquisition module 203. The analysis module 201 is used to carry out dry modal analysis on the vehicle test model to obtain the natural frequency and modal participation factor corresponding to the modal at different stages. The different stages include the launch stage and the water impact stage of the vehicle test model. The modal selection module 202 is used to obtain the modal corresponding to the maximum modal participation factor in the same preset excitation direction.

[0094] The cutoff frequency acquisition module 203 is used to take the natural frequency corresponding to the maximum modal as the cutoff frequency of the water impact load test.

[0095] The system in this embodiment obtains the natural frequency and modal participation factor corresponding to the modal at different stages by carrying out dry modal analysis on the vehicle test model, obtains the modal corresponding to the maximum modal participation factor in the same preset excitation direction, and takes the natural frequency corresponding to the maximum modal as the cutoff frequency of the water impact load test. The natural frequency of the vehicle structure vibration response is obtained by dry modal analysis and is introduced into the data processing process of the signal, the natural frequency corresponding to the modal with the maximum modal participation factor in the excitation direction is selected as the cutoff frequency, the subjectivity in selecting the cutoff frequency of the low-pass filter is weakened, and the error of the test data is reduced.

[0096] In specific embodiments, the third embodiment of the present application provides a device for obtaining the cutoff frequency of a water-entry impact load test, comprising a memory and a processor, the memory stores a computer program, and the computer program is executed by the processor to make the processor execute the steps of the method according to any one of the first embodiment of the present application. The device in this embodiment obtains the natural frequency and modal participation factor corresponding to the modal at different stages by carrying out dry modal analysis on the vehicle test model; obtains the modal corresponding to the maximum modal participation factor in the preset excitation direction; and takes the natural frequency corresponding to the maximum modal as the cutoff frequency of the water-entry impact load test. The natural frequency of the vibration response of the vehicle structure is obtained by dry modal analysis and introduced into the data processing process of the signal, and the natural frequency corresponding to the modal with the maximum modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity in selecting the cutoff frequency of the low-pass filter and is beneficial to reducing the error of the test data.

[0097] In specific embodiments, the fourth embodiment of the present application provides a computer-readable storage medium storing a computer program, which is executed by a processor to make the processor execute the steps of the method according to any one of the first embodiment of the present application. The storage medium in this embodiment obtains the natural frequency and modal participation factor corresponding to the modal at different stages by carrying out dry modal analysis on the vehicle test model; obtains the modal corresponding to the maximum modal participation factor in the preset excitation direction; and takes the natural frequency corresponding to the maximum modal as the cutoff frequency of the water-entry impact load test. The natural frequency of the vibration response of the vehicle structure is obtained by dry modal analysis and introduced into the data processing process of the signal, and the natural frequency corresponding to the modal with the maximum modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity in selecting the cutoff frequency of the low-pass filter and is beneficial to reducing the error of the test data.

[0098] Figure 9 An internal structure diagram of a computer device in an embodiment is shown. The computer device can be a terminal or a server. Please refer to Figure 9 The computer device includes a processor, a memory, and the like connected through a system bus. The memory includes a non-volatile storage medium and an internal memory. The non-volatile storage medium of the computer device stores an operating system and can also store a computer program, which, when executed by the processor, can make the processor implement the method in this embodiment. The internal memory can also store a computer program, which, when executed by the processor, can make the processor execute the method in this embodiment. Those skilled in the art can understand that Figure 9The structure shown in the figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. A specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0099] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that, for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

[0100] The above is only a preferred embodiment of the present application, and is not a limitation on other forms of the present application. Any person skilled in the art can use the disclosed technical content to make changes or modifications to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solution content of the present application, still belongs to the protection scope of the technical solution of the present application.

Claims

1. A method for obtaining a cut-off frequency in a water impact load test, characterized by, The method comprises: carrying out dry modal analysis on the vehicle test model to obtain natural frequencies and modal participation factors corresponding to modes in different stages; the different stages include a launch stage and a water-entry impact stage of the vehicle test model; obtaining a mode corresponding to a maximum modal participation factor in a preset excitation direction; taking the natural frequency corresponding to the maximum mode as a cutoff frequency of the water-entry impact load test; wherein the carrying out of the dry modal analysis on the vehicle test model to obtain the natural frequencies and the modal participation factors corresponding to the modes in the different stages comprises: carrying out dry modal analysis on the vehicle test model to obtain a structural linear motion control equation of the vehicle; obtaining natural frequencies and modal shapes corresponding to modes in different stages according to node displacement vectors, node acceleration vectors and the structural linear motion control equation; obtaining modal participation factors based on the modal shapes and a structural mass matrix; the obtaining of the natural frequencies and the modal shapes corresponding to the modes in the different stages according to the node displacement vectors, the node acceleration vectors and the structural linear motion control equation comprises: substituting the node displacement vectors and the node acceleration vectors into the structural linear motion control equation to obtain vibration frequencies and modal shapes; obtaining the natural frequencies according to the vibration frequencies; the vibration frequencies and the modal shapes are obtained by using the following formula: wherein, is the structural stiffness matrix in the structural linear motion control equation, is the vibration frequency, is the structural mass matrix in the structural linear motion control equation, is the modal shape; the modal participation factors are obtained by using the following formula: wherein, is the modal participation factor, is the modal shape, is the structural mass matrix in the structural linear motion control equation, is the displacement frequency spectrum of the element in each translational and rotational direction of the global coordinate system; the element is a different element formed after the structure of the aircraft is discretized.

2. The method of claim 1, wherein the cutoff frequency is obtained by the following equation: ###0001### where, f is the cutoff frequency, A is the amplitude of the input signal, and T is the period of the input signal. the natural frequencies are obtained by using the following formula: wherein, is the vibration frequency, is the natural frequency.

3. The method of claim 1, wherein the cutoff frequency is obtained by the following equation: ###0001### where, f is the cutoff frequency, f0 is the natural frequency of the test vehicle, and ζ is the damping ratio of the test vehicle. after the taking of the natural frequency corresponding to the maximum mode as the cutoff frequency of the water-entry impact load test, the method further comprises: taking the cutoff frequency as a cutoff frequency of a low-pass filter to filter nonlinear data obtained through water-entry impact simulation of the vehicle to obtain a filtering result.

4. A system for acquiring a cutoff frequency of a water-entry impact load test, the system performing the steps of the method for acquiring a cutoff frequency of a water-entry impact load test according to any one of claims 1 to 3, characterized by The system comprises an analysis module, a mode selection module and a cutoff frequency acquisition module; the analysis module is configured to carry out dry modal analysis on the vehicle test model to obtain natural frequencies and modal participation factors corresponding to modes in different stages; the different stages include a launch stage and a water-entry impact stage of the vehicle test model; the mode selection module is configured to obtain a mode corresponding to a maximum modal participation factor in a preset excitation direction; the cutoff frequency acquisition module is configured to take the natural frequency corresponding to the maximum mode as a cutoff frequency of the water-entry impact load test.

5. A device for obtaining a cut-off frequency in a water impact load test, comprising a memory and a processor, characterized in that The memory stores a computer program, and the computer program is executed by the processor to cause the processor to perform the steps of the method according to any one of claims 1 to 3.

6. A computer readable storage medium storing a computer program, characterized in that, The computer program is executed by the processor to cause the processor to perform the steps of the method according to any one of claims 1 to 3.

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