Cut-off frequency obtaining method for water entry impact load test and related equipment

Abstract

The embodiment of the invention discloses a cut-off frequency acquisition method for a water entry impact load test and related equipment, and the method comprises the steps: carrying out the dry modal analysis of an aircraft test model, and obtaining inherent frequencies and modal participation factors corresponding to modals in different stages; obtaining a mode corresponding to the maximum mode participation factor in the same direction as the preset excitation direction; and taking the inherent frequency corresponding to the maximum mode as the cut-off frequency of the water entry impact load test. The inherent frequency of the vibration response of the aircraft structure is obtained through dry modal analysis, the inherent frequency is introduced into the data processing process of the signal, the inherent frequency corresponding to the mode with the maximum excitation direction mode participation factor is selected as the cut-off frequency, the subjectivity during selection of the low-pass filtering cut-off frequency is weakened, and the error of test data is reduced.

Description

[Technical field]

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

[0002] With the development of new cross-media vehicle-related technologies, the study of high-speed water entry has received widespread attention. High-speed water entry test research is an important supplementary method for studying high-speed water entry problems. Since high-speed water entry problems have the characteristics of transient and strong nonlinearity, the impact load data collected by the acceleration sensor during the high-speed water entry test generally consists of three parts: rigid body acceleration, structural response acceleration and other accelerations. Rigid body acceleration is the acceleration formed by the resistance encountered during the water entry process assuming that the vehicle is rigid, also known as rigid body overload; structural response acceleration is the acceleration signal formed by the structural dynamic response caused by the collision between the vehicle and the water surface, including the acceleration signal generated by the axial vibration response and lateral vibration response of the vehicle structure; other accelerations are mainly acceleration signals generated by interference factors, such as the acceleration signal generated by the vibration of the acceleration sensor itself and the interference noise signal caused by the installation and connection method between the acceleration sensor and the vehicle. The high-speed water entry impact load test data is complex. How to accurately extract the rigid body overload from the complex measured impact load test data has always been a key focus and difficulty in data processing.

[0003] The existing method decomposes the original signal based on the EEMD method, and then performs Burg power spectrum analysis on the IMF components to obtain the power spectrum of each IMF component. Secondly, according to the specific rigid body modal analysis, the high-frequency part of the rigid body vibration is obtained, and the corresponding critical frequency is obtained. Finally, the high-frequency IMF components are filtered out from the original signal according to the critical frequency, and the remaining IMF components are reconstructed to obtain the filtered signal. In this method, there is no clear criterion for the selection of the critical frequency. Therefore, the selection of the IMF components involved in the signal reconstruction may be subjective, which may easily lead to a large error between the filtered signal and the actual required signal. [Summary of the invention]

[0004] In view of this, the present invention provides a method for obtaining a cutoff frequency of a water entry impact load test and related equipment.

[0005] The specific technical solution of the first embodiment of the present invention is: a method for obtaining the cutoff frequency of a water entry impact load test, the method comprising: performing dry modal analysis on an aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes in different stages; the different stages include the aircraft test model launch stage and the water entry impact stage; obtaining the mode corresponding to the maximum modal participation factor that is the same as the preset excitation direction; and using 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 is performed on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages, including: performing dry modal analysis on the aircraft test model to obtain the structural linear motion control equations of the aircraft; obtaining the natural frequencies and modal vibration shapes corresponding to the modes at different stages according to the node displacement vectors, node acceleration vectors and the structural linear motion control equations; and obtaining the modal participation factors based on the modal vibration shapes and the structural mass matrix.

[0007] Preferably, the method of obtaining the natural frequencies and modal vibration shapes corresponding to the modes at different stages according to the node displacement vectors, the node acceleration vectors and the structural linear motion control equations includes: substituting the node displacement vectors and the node acceleration vectors into the structural linear motion control equations to obtain the vibration frequencies and modal vibration shapes; and obtaining the natural frequencies according to the vibration frequencies.

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

[0009]

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

[0011] Preferably, the natural frequency is obtained using the following formula:

[0012] f i =ω i / 2π

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

[0014] Preferably, the modal participation factor is obtained using the following formula:

[0015]

[0016] Among them, γi is the modal participation factor, is the modal vibration shape, M is the structural mass matrix in the structural linear motion control equation, and D is the displacement spectrum of the unit in the translational and rotational directions of each global coordinate system; the units are different units formed by discretizing the structure of the aircraft.

[0017] Preferably, after using the natural frequency corresponding to the maximum mode as the cutoff frequency of the water entry impact load test, it also includes: using the cutoff frequency as the cutoff frequency of the low-pass filter to filter the nonlinear data obtained from the vehicle water entry impact simulation to obtain a filtering result.

[0018] The specific technical solution of the second embodiment of the present invention 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 perform dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes in different stages; the different stages include the aircraft test model launch stage and the water entry impact stage; the modal selection module is used to obtain the mode corresponding to the maximum modal participation factor that is the same as the preset excitation direction; the cutoff frequency acquisition module is used to use the natural frequency corresponding to the maximum mode as the cutoff frequency of the water entry impact load test.

[0019] The specific technical solution of the third embodiment of the present invention 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 when the computer program is executed by the processor, the processor executes the steps of the method described in any one of the first embodiments of the present application.

[0020] The specific technical solution of the fourth embodiment of the present invention is: a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to perform the steps of the method described in any one of the first embodiments of the present application.

[0021] Implementing the embodiments of the present invention will have the following beneficial effects:

[0022] The present invention performs dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; obtains the mode corresponding to the maximum modal participation factor that is the same as the preset excitation direction; and uses the natural frequency corresponding to the maximum mode as the cutoff frequency of the water impact load test. The natural frequency of the vibration response of the aircraft structure is obtained through dry modal analysis, and is introduced into the data processing process of the signal. The natural frequency corresponding to the mode with the largest modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity in the selection of the low-pass filter cutoff frequency and is conducive to reducing the error of the test data.

Brief Description of the Drawings

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A flow chart showing the steps of a method for obtaining the cut-off frequency of a water impact load test;

[0025] Figure 2 It is the original data diagram of impact acceleration;

[0026] Figure 3 This is the intercepted segment impact acceleration data diagram;

[0027] Figure 4 are the vibration shape diagrams of the first six modes;

[0028] Figure 5 It is the amplitude-frequency response diagram of the low-pass filter;

[0029] Figure 6 This is a comparison chart of filtering results;

[0030] Figure 7 It is a power spectrum comparison diagram;

[0031] Figure 8 A schematic diagram of the cut-off frequency acquisition system;

[0032] Fig. 9 It is a diagram of the internal structure of a computer device;

[0033] Among them, 201 is an analysis module; 202 is a mode selection module; 203 is a cutoff frequency acquisition module. [Specific implementation method]

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] The terms "first", "second", etc. in the specification, claims and drawings of this application are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or modules is not limited to the listed steps or modules, but optionally includes steps or modules that are not listed, or optionally includes other steps or modules that are inherent to these processes, methods, products or devices.

[0036] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] The cutoff frequency, also known as the corner frequency, refers to the frequency point at which the filter response drops to a certain value (usually 70.7% of the maximum response, which is the -3dB point, corresponding to half the power). Below this frequency, signals can pass through the filter more freely, while signals with frequencies above this point will be significantly attenuated. The cutoff frequency of a 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 a low-pass filter can change the response characteristics of the filter to meet different application requirements.

[0038] See also Figure 1 , is a flowchart of a method for obtaining a cutoff frequency of a water impact load test in the first embodiment of the present application, which is helpful to reduce the error of the test data. The method includes:

[0039] Step 101: performing dry modal analysis on the aircraft test model to obtain natural frequencies and modal participation factors corresponding to modes at different stages; the different stages include a launch stage and a water impact stage of the aircraft test model;

[0040] Step 102, obtaining a mode corresponding to a maximum modal participation factor in the same direction as a preset excitation direction;

[0041] Step 103: Using the natural frequency corresponding to the maximum mode as the cutoff frequency of the water entry impact load test.

[0042] Specifically, dry modal analysis is an effective method to study the dynamic characteristics of structures. It transforms the physical coordinates in the linear steady-state system vibration differential equations into modal coordinates, decouples the equations, 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 type of modal analysis that does not consider the influence of fluid on structural modes, but only focuses on the vibration characteristics of the structure itself. First, the dry modal analysis of the aircraft model is carried out, which can be completed by dividing the finite element mesh analysis using commercial software. The basic principle is to assume that the aircraft is free vibration and ignore the structural damping to obtain the natural frequency and modal participation factor corresponding to the mode at different stages. The modal participation factor is a function of the vibration mode and the excitation direction, which can measure the contribution of the mode to the structural deformation in the excitation direction. If the vibration mode participation factor of a certain order mode in a certain direction is larger, it means that the force in the excitation direction will cause a larger structural deformation corresponding to this mode. Combined with the structural response and deformation characteristics of the vehicle during water impact, find the mode with the largest modal participation factor in the same direction as the excitation, and use the natural frequency corresponding to this mode as the cutoff frequency of the low-pass filter.

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

[0044] In a specific embodiment, the dry modal analysis is performed on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages, including: performing dry modal analysis on the aircraft test model to obtain the structural linear motion control equations of the aircraft; obtaining the natural frequencies and modal vibration shapes corresponding to the modes at different stages according to the node displacement vectors, node acceleration vectors and the structural linear motion control equations; and obtaining the modal participation factors based on the modal vibration shapes and the structural mass matrix.

[0045] Specifically, the spacecraft is in free vibration and the structural damping is ignored. Then the general structural linear motion control equation of the spacecraft is:

[0046]

[0047] Where: 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 a specific embodiment, the natural frequencies and modal vibration shapes corresponding to the modes at different stages are obtained according to the node displacement vectors, the node acceleration vectors and the structural linear motion control equations, including: substituting the node displacement vectors and the node acceleration vectors into the structural linear motion control equations to obtain the vibration frequencies and modal vibration shapes; and obtaining the natural frequencies according to the vibration frequencies.

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

[0050]

[0051] Will u, Substitute into the structural linear motion control equation, the natural frequency and modal vibration shape corresponding to the modes in different stages.

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

[0053]

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

[0055] The conditions for the above equation to be valid are It is expressed as a vibration-free situation, or satisfies the following formula:

[0056]

[0057] Solving the above equation, we get the vibration frequency ω i and mode shapes

[0058] In a specific embodiment, the natural frequency is obtained using the following formula:

[0059] f i =ω i / 2π

[0060] Among them, ω i is the vibration frequency, f i is the natural frequency. Indicates that the structure is moving at its natural frequency f i The shape of vibration when vibrating.

[0061] The mode shapes can be normalized with respect to the mass matrix M or with respect to the identity matrix I:

[0062]

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

[0064]

[0065] Among them, γ i is the modal participation factor, is the modal vibration shape, M is the structural mass matrix in the structural linear motion control equation, and D is the displacement spectrum of the unit in the translational and rotational directions of each global coordinate system; the units are different units formed by discretizing the structure of the aircraft.

[0066] In a specific embodiment, after using the natural frequency corresponding to the maximum mode as the cutoff frequency of the water entry impact load test, it also includes: using the cutoff frequency as the cutoff frequency of the low-pass filter to filter the nonlinear data obtained from the vehicle water entry impact simulation to obtain a filtering result.

[0067] Specifically, find out the mode with the largest modal participation factor in the same direction as the excitation, and use the natural frequency corresponding to the mode as the cutoff frequency of the low-pass filter. Design the low-pass filter through self-programming, and observe whether the amplitude-frequency response diagram of the designed filter meets the requirements. Finally, complete the low-pass filtering of the original data, and compare whether the difference between the filtered signal and the original signal meets the requirements.

[0068] The inherent properties of the vibration response of the vehicle structure are obtained through dry modal analysis and introduced into the data processing process of the impact signal. The natural frequency corresponding to the mode with the largest modal participation factor in the excitation direction is selected as the cutoff frequency of the low-pass filter, which reduces the subjectivity in the selection of the low-pass filter cutoff frequency and is beneficial to reducing the error of the test data. At the same time, the low-pass filter is designed through self-programming to achieve autonomous control of the code. Finally, the principle of this method is clear, which simplifies the processing flow and steps of the high-speed water entry test data and greatly improves the efficiency of the test data processing.

[0069] In a specific embodiment, a specific method of low-pass filtering includes: clarifying filter parameters, filter design, filter implementation, and filter verification and adjustment.

[0070] 1. Clarify filter parameters

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

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

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

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

[0075] Stopband cutoff frequency (f3): The frequency point where the stopband begins to attenuate, usually used to determine the transition band width of the filter.

[0076] 2. Filter Design

[0077] Select filter type: Select the type of low-pass filter based on application requirements, such as FIR filter or IIR filter. FIR filter has linear phase characteristics and is suitable for phase-sensitive applications; IIR filter has higher frequency selectivity, but the phase characteristics may not be as good as FIR filter.

[0078] Determine the filter order: The order of the filter determines the steepness of its frequency response. The higher the order, the steeper the frequency response, but the higher the computational complexity. You can use filter design methods such as Chebyshev and Butterworth to determine the filter order.

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

[0080] 3. Filter Implementation

[0081] Analog filter implementation: For low-pass filters in analog circuits, you can use resistors, capacitors and other components to build an RC circuit to implement it. According to the cut-off 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 and Python can be used to design and implement filters. These tools provide a wealth of filter design methods and optimization algorithms, which can easily 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 differential equation or transfer function of the filter, the input signal is filtered to obtain the output signal.

[0084] 4. 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, it can be verified whether it meets the design requirements.

[0086] Practical test: Apply the filter to the actual system and conduct actual test. Evaluate the performance of the filter by comparing the input signal and the output signal.

[0087] Adjustment and optimization: Based on the results of simulation verification and actual testing, the parameters of the filter 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 entry impact stage. Since the water entry impact stage is the main research, 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 flow, a 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 discharges the water medium to the surrounding areas. At this time, the end face of the model head is wet, and the entire body is wrapped in the water entry cavitation. Therefore, when carrying out the dry modal analysis, the end face of the model head 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, symmetric modes appear in its modes, and the symmetric 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, so the focus is on the modal participation factor along the Z axis. From the above, it can be seen that 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 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 in the figure Figure 5As shown in the amplitude-frequency response diagram, it can be seen that the signal components with a frequency higher than 2318 Hz will be greatly attenuated when passing through the filter, while the signal components with a frequency lower than 2318 Hz will be attenuated less. Figure 6 The figure shows the comparison between the original signal before filtering and the rigid body overload after filtering. It can be seen from the figure that compared with the original signal, the filtered result has a smoother curve due to the elimination of high-frequency interference, and can well reflect the overall change trend of the signal. Figure 7 From the power spectrum of the original signal and the filtered signal, it can be seen that the two curves are basically overlapped at low frequencies, and the power of the filtered signal is small at high frequencies. This method can better extract the rigid body overload component contained in the original signal. This method has simple operation steps, greatly improves the efficiency of test data processing, and weakens the subjectivity of test data processing parameter setting, reduces the error between filtered data and real data, and lays the foundation for filtering technology of high-speed water entry impact load test data.

[0093] In the specific embodiments, see Figure 8 , is a structural diagram of a cutoff frequency acquisition system for a water entry impact load test in the second embodiment of the application, the system comprising: an analysis module 201, a mode selection module 202 and a cutoff frequency acquisition module 203; the analysis module 201 is used to perform dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; the different stages include the launch stage and the water entry impact stage of the aircraft test model; the mode selection module 202 is used to obtain the mode corresponding to the maximum modal participation factor in the same direction as the preset excitation direction;

[0094] The cut-off frequency acquisition module 203 is used to use the natural frequency corresponding to the maximum mode as the cut-off frequency of the water entry impact load test.

[0095] The system in this embodiment performs dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; obtains the mode corresponding to the maximum modal participation factor that is the same as the preset excitation direction; and uses the natural frequency corresponding to the maximum mode as the cutoff frequency for the water entry impact load test. The natural frequency of the aircraft structure vibration response is obtained through dry modal analysis, and is introduced into the data processing process of the signal. The natural frequency corresponding to the mode with the largest modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity in the selection of the low-pass filter cutoff frequency and helps reduce the error of the test data.

[0096] In a specific embodiment, the third embodiment of the present application provides a cutoff frequency acquisition device for a water entry impact load test, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method described in any one of the first embodiments of the present application. The device in this embodiment performs dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; obtains the mode corresponding to the maximum modal participation factor that is the same as the preset excitation direction; and uses the natural frequency corresponding to the maximum mode as the cutoff frequency of the water entry impact load test. The natural frequency of the vibration response of the aircraft structure is obtained through dry modal analysis, and is introduced into the data processing process of the signal, and the natural frequency corresponding to the mode with the largest modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity in the selection of the low-pass filter cutoff frequency and is conducive to reducing the error of the test data.

[0097] In a specific embodiment, the fourth embodiment of the present application provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of the method described in any one of the first embodiments of the present application. The storage medium in this embodiment performs dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; obtains the mode corresponding to the maximum modal participation factor that is the same as the preset excitation direction; and uses the natural frequency corresponding to the maximum mode as the cutoff frequency of the water entry impact load test. The natural frequency of the vibration response of the aircraft structure is obtained through dry modal analysis, and is introduced into the data processing process of the signal. The natural frequency corresponding to the mode with the largest modal participation factor in the excitation direction is selected as the cutoff frequency, which reduces the subjectivity in the selection of the low-pass filter cutoff frequency and is conducive to reducing the error of the test data.

[0098] Fig. 9 The internal structure of a computer device in one embodiment is shown. The computer device can be a terminal or a server. Fig. 9 The computer device includes a processor, a memory, etc. connected via 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 may also store a computer program. When the computer program is executed by the processor, the processor can implement the method in this embodiment. The internal memory may also store a computer program. When the computer program is executed by the processor, the processor can implement the method in this embodiment. Those skilled in the art can understand that Fig. 9The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may 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 methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0100] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for obtaining the cutoff frequency of a water impact load test, characterized in that: The method comprises: Conduct dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; the different stages include the launch stage and the water impact stage of the aircraft test model; Obtain the mode corresponding to the maximum modal participation factor in the same direction as the preset excitation; The natural frequency corresponding to the maximum mode is used as the cutoff frequency of the water entry impact load test.

2. The method for obtaining the cutoff frequency of the water impact load test according to claim 1, characterized in that: The dry modal analysis is performed on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages, including: Conduct dry modal analysis on the aircraft test model to obtain the aircraft's structural linear motion control equations; Obtaining the natural frequencies and modal vibration shapes corresponding to the modes at different stages according to the node displacement vectors, the node acceleration vectors and the linear motion control equations of the structure; Modal participation factors are obtained based on the mode shapes and the structural mass matrix.

3. The method for obtaining the cutoff frequency of the water impact load test according to claim 2, characterized in that: The method of obtaining the natural frequencies and modal vibration shapes corresponding to the modes at different stages according to the node displacement vectors, the node acceleration vectors and the structural linear motion control equations includes: Substituting the node displacement vector and the node acceleration vector into the structural linear motion control equation to obtain the vibration frequency and mode shape; The natural frequency is obtained according to the vibration frequency.

4. The method for obtaining the cutoff frequency of the water impact load test according to claim 3, characterized in that: The vibration frequency and the mode shape are obtained using the following formula: Where K is the structural stiffness matrix in the structural linear motion control equation, ω i is the vibration frequency, M is the structural mass matrix in the structural linear motion control equation, is the mode shape.

5. The method for obtaining the cutoff frequency of the water impact load test according to claim 3, characterized in that: The natural frequency is obtained using the following formula: f i =ω i / 2π Among them, ω i is the vibration frequency, f i is the natural frequency.

6. The method for obtaining the cutoff frequency of the water impact load test according to claim 2, characterized in that: The modal participation factor is obtained using the following formula: Among them, γ i is the modal participation factor, is the modal vibration shape, M is the structural mass matrix in the structural linear motion control equation, and D is the displacement spectrum of the unit in the translational and rotational directions of each global coordinate system; the units are different units formed by discretizing the structure of the aircraft.

7. The method for obtaining the cutoff frequency of the water impact load test according to claim 1, characterized in that: After the natural frequency corresponding to the maximum mode is used as the cutoff frequency of the water entry impact load test, the method further includes: The cut-off frequency is used as the cut-off frequency of a low-pass filter to filter the nonlinear data obtained by the simulation of the impact of the vehicle entering water to obtain a filtering result.

8. A cutoff frequency acquisition system for water impact load test, characterized in that: The system comprises: an analysis module, a mode selection module and a cutoff frequency acquisition module; The analysis module is used to perform dry modal analysis on the aircraft test model to obtain the natural frequencies and modal participation factors corresponding to the modes at different stages; the different stages include the launch stage and the water impact stage of the aircraft test model; The mode selection module is used to obtain the mode corresponding to the maximum mode participation factor that is the same as the preset excitation direction; The cut-off frequency acquisition module is used to use the natural frequency corresponding to the maximum mode as the cut-off frequency of the water entry impact load test.

9. A cutoff frequency acquisition device for a water impact load test, comprising a memory and a processor, characterized in that: The memory stores a computer program, and when the computer program is executed by the processor, the processor is caused to perform the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the processor is caused to perform the steps of the method according to any one of claims 1 to 7.

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