Fluid-structure interaction vibration fatigue life prediction method of propellant storage tank diaphragm structure

Abstract

The embodiment of the invention provides a fluid-solid coupling vibration fatigue life prediction method of a propellant storage tank diaphragm structure. The method comprises the following steps: acquiring a frequency domain power spectrum density for performing a vibration fatigue test on the propellant storage tank diaphragm; performing inverse Fourier transform processing on the frequency spectrum function of the frequency domain power spectrum density to obtain time domain data of the speed power spectrum density and the displacement power spectrum density; performing internal flow field analysis on the propellant storage tank according to the time domain data of the velocity power spectral density to obtain pressure distribution data at the fluid-solid interface of the diaphragm structure of the storage tank; according to the pressure distribution data and the time domain data of the displacement power spectral density, fluid-solid coupling analysis is carried out on the diaphragm structure, a time-varying curve of stress borne by a sampling point at a preset position of the storage tank diaphragm structure is obtained, fatigue life prediction is carried out on the storage tank diaphragm structure according to the curve, and the fatigue life of the storage tank diaphragm structure is obtained. The method can accurately predict the vibration fatigue life of the diaphragm structure of the propellant storage tank.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of propellant tank performance acquisition, and particularly relates to a fluid-structure coupling vibration fatigue life prediction method for a propellant tank diaphragm structure. BACKGROUND

[0002] The propellant tank is a management and control device in a spacecraft. When the liquid in the propellant tank shakes very violently, a strong impact will be generated on the diaphragm of the propellant tank, and the diaphragm structure will be damaged in severe cases. Therefore, the life of the diaphragm of the propellant tank needs to be predicted according to the liquid shaking condition to ensure the safe use of the propellant tank.

[0003] In the related art, the modal analysis and random vibration analysis of the propellant tank can be performed through the acoustic-structure coupling method to obtain the evaluation result of the fatigue life of the propellant tank.

[0004] However, this method can only consider linear problems, while the diaphragm structure of the propellant tank has the characteristics of material nonlinearity and contact nonlinearity in the vibration process. Therefore, it is difficult to accurately predict the fatigue life of the diaphragm of the propellant tank based on the method of the related art. SUMMARY

[0005] The application provides a fluid-structure coupling vibration fatigue life prediction method for a propellant tank diaphragm structure to solve the technical problem of low accuracy of the fatigue life prediction result of the diaphragm of the propellant tank in the related art.

[0006] In a first aspect, the application provides a fluid-structure coupling vibration fatigue life prediction method for a propellant tank diaphragm structure, which comprises the following steps: obtaining the frequency domain power spectral density of the vibration fatigue test of the diaphragm of the propellant tank; performing inverse Fourier transform processing on the frequency spectrum function of the frequency domain power spectral density to obtain the time domain data of the velocity power spectral density and the time domain data of the displacement power spectral density; performing internal flow field analysis on the propellant tank according to the time domain data of the velocity power spectral density to obtain the pressure distribution data at the fluid-structure interface of the diaphragm structure of the propellant tank; performing fluid-structure coupling analysis on the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectral density to obtain the curve of the stress of the sampling point at a preset position of the diaphragm structure of the propellant tank varying with time; and performing fatigue life prediction on the diaphragm structure of the propellant tank according to the curve of the stress of the sampling point varying with time to obtain the fatigue life of the diaphragm structure of the propellant tank.

[0007] Optionally, the spectrum function of the frequency domain power spectrum density is in complex number form; the inverse Fourier transform processing of the frequency domain power spectrum density to obtain time domain data of a velocity power spectrum density and time domain data of a displacement power spectrum density comprises: inverse Fourier transform processing of the spectrum function of the frequency domain power spectrum density to obtain time domain data of an acceleration power spectrum density; and first integration and second integration processing of the time domain data of the acceleration power spectrum density to obtain the time domain data of the velocity power spectrum density and the time domain data of the displacement power spectrum density.

[0008] Optionally, the inverse Fourier transform processing of the spectrum function of the frequency domain power spectrum density to obtain time domain data of an acceleration power spectrum density comprises: obtaining a modulus of the spectrum function of the frequency domain power spectrum density; obtaining a random phase, and obtaining a two-sided spectrum of the frequency domain power spectrum density within a preset frequency domain range according to the modulus of the spectrum function and the random phase; and inverse Fourier transform processing of the two-sided spectrum to obtain the time domain data of the acceleration power spectrum density.

[0009] Optionally, the internal flow field analysis of the propellant tank according to the time domain data of the velocity power spectrum density to obtain pressure distribution data at a fluid-structure interface of a diaphragm structure of the propellant tank comprises: obtaining a propellant tank flow field simulation model; obtaining preset physical property parameters of a flow field internal medium and gas of the propellant tank; the physical property parameters comprise density and viscosity; and configuring the preset physical property parameters and the time domain data of the velocity power spectrum density to the propellant tank flow field simulation model, and obtaining the pressure distribution data at the fluid-structure interface of the diaphragm structure of the propellant tank by using a computational fluid dynamics method.

[0010] Optionally, the fluid-structure coupling analysis of the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectrum density to obtain a curve of stress variation with time of a sampling point at a preset position of the diaphragm structure of the propellant tank comprises: obtaining a propellant tank structure simulation model; obtaining material performance parameters of each component of the propellant tank; the material performance parameters comprise density, elastic modulus, Poisson's ratio and data of elastic-plastic stress variation with strain of the material; importing the material performance parameters and the pressure distribution data into the propellant tank structure simulation model, determining vibration load at a constrained position of the propellant tank according to the time domain data of the displacement power spectrum density, and obtaining the curve of stress variation with time of the sampling point at the preset position of the diaphragm structure by transient dynamics analysis.

[0011] Optionally, the fatigue life of the propellant tank diaphragm structure is predicted according to the curve of the stress borne by the sampling point changing over time, and the fatigue life of the propellant tank diaphragm structure is obtained, including: obtaining the cycle frequency corresponding to the preset stress mean value according to the curve of the stress borne by the sampling point changing over time; obtaining the change data of the fatigue life of the diaphragm structure with respect to stress; the fatigue life in the change data is an upper limit value of the number of times of impact of the diaphragm on the corresponding stress; obtaining the fatigue life of the propellant tank diaphragm according to the time corresponding to the power spectral density, the cycle frequency corresponding to the preset stress mean value, and the upper limit value; the fatigue life of the sampling point is an upper limit value of the time length of impact of the sampling point on the corresponding stress.

[0012] Optionally, the cycle frequency corresponding to the preset stress mean value is obtained according to the curve of the stress borne by the sampling point changing over time, including: using the rainflow counting method to obtain the stress amplitude and stress mean value corresponding to a plurality of stress cycles in the curve of the stress changing over time; correcting the stress amplitude corresponding to the stress cycle by taking the stress mean value equal to the preset stress mean value as a constraint to obtain an updated stress amplitude; obtaining the cycle frequency of the updated stress amplitude, and determining the cycle frequency of the updated stress amplitude as the cycle frequency corresponding to the preset stress mean value.

[0013] Optionally, the stress amplitude corresponding to the stress cycle is corrected by taking the stress mean value equal to the preset stress mean value as a constraint to obtain an updated stress amplitude, including: obtaining the tensile strength σ u of the diaphragm; obtaining the updated stress amplitude S: u according to the tensile strength σ

[0014]

[0015] wherein σ a is the alternating stress corresponding to the stress amplitude, and σ m is the stress mean value.

[0016] Optionally, the fatigue life of the propellant tank diaphragm is obtained according to the time corresponding to the power spectral density, the stress amplitude and cycle frequency corresponding to the preset stress mean value, and the upper limit value, including: obtaining the ratio of the cycle frequency to the upper limit value; obtaining the fatigue life of the sampling point according to the ratio of the cycle frequency to the upper limit value and the obtained time.

[0017] Optionally, the diaphragm and the inner wall of the propellant tank have a pre-bent edge; the fluid-solid coupling analysis of the diaphragm structure of the propellant tank according to the time-domain data of the pressure distribution data and the displacement power spectral density obtains a curve of the stress of a sampling point at a preset position of the diaphragm structure of the propellant tank varying with time, including: obtaining stress distribution data of a plurality of position points at the pre-bent edge of the diaphragm structure of the propellant tank according to the time-domain data of the displacement power spectral density; obtaining the curve of the stress of the sampling point varying with time from the stress distribution data of the plurality of position points; the sampling point is a position point determined at the pre-bent edge of the diaphragm by a cross-shaped point selection method.

[0018] In a second aspect, the present application provides a fluid-solid coupling vibration fatigue life prediction device for a diaphragm structure of a propellant tank, including: a first obtaining module for obtaining a frequency domain power spectral density of a vibration fatigue test of a diaphragm of a propellant tank; a second obtaining module for performing inverse Fourier transform processing on a frequency spectrum function of the frequency domain power spectral density to obtain time-domain data of a velocity power spectral density and time-domain data of a displacement power spectral density; a third obtaining module for performing internal flow field analysis on the propellant tank according to the time-domain data of the velocity power spectral density to obtain pressure distribution data at a fluid-solid interface of the diaphragm structure of the propellant tank; a fourth obtaining module for performing fluid-solid coupling analysis on the diaphragm structure of the propellant tank according to the pressure distribution data and the time-domain data of the displacement power spectral density to obtain a curve of the stress of a sampling point at a preset position of the diaphragm structure of the propellant tank varying with time; and a fifth obtaining module for performing fatigue life prediction on the diaphragm structure of the propellant tank according to the curve of the stress of the sampling point varying with time to obtain a fatigue life of the diaphragm structure of the propellant tank.

[0019] In the embodiment of the present application, based on the inverse Fourier transform method, the power spectrum density in the frequency domain is effectively converted into the time domain data of the displacement power spectrum density and the velocity power spectrum density, the flow field inside the storage tank is analyzed according to the velocity power spectrum density in the time domain, the pressure distribution data of the fluid-structure interface of the propellant storage tank diaphragm structure are obtained, the displacement power spectrum density and the velocity power spectrum density are analyzed according to the displacement power spectrum density in the time domain and the pressure distribution data at the fluid-structure interface, the stress-time curve of the sampling point at the preset position of the propellant storage tank diaphragm structure is obtained, and the fatigue life of the sampling point is obtained based on the stress-time curve of the sampling point at the fluid-structure interface. The propellant storage tank diaphragm structure has material nonlinearity and contact nonlinearity in the vibration process, the time domain data in the embodiment can consider the characteristics of the material nonlinearity and the contact nonlinearity of the propellant storage tank diaphragm structure in the vibration process, the fatigue life is calculated based on the time domain data, the accuracy of the fatigue life calculation result is improved, and the problem of unable to consider the nonlinearity calculation and low calculation accuracy in the related art of the fluid-structure coupling vibration fatigue life evaluation of the propellant storage tank diaphragm structure is solved. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the embodiments or the related art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Figure 1 is a step flow chart of a fluid-structure coupling vibration fatigue life prediction method of a propellant storage tank diaphragm structure provided by the embodiment of the present application;

[0022] Figure 2 is a structural schematic diagram of a propellant storage tank provided by the embodiment of the present application;

[0023] Figure 3 is a schematic diagram of a power spectrum density provided by the embodiment of the present application;

[0024] Figure 4 is a time domain data schematic diagram of a displacement power spectrum density provided by the embodiment of the present application;

[0025] Figure 5 is a step flow chart of another fluid-structure coupling vibration fatigue life prediction method of a propellant storage tank diaphragm structure provided by the embodiment of the present application;

[0026] Figure 6 is another sampling point distribution schematic diagram provided by the embodiment of the present application;

[0027] Figure 7 is a schematic diagram of a rainflow counting method provided by an embodiment of the present application;

[0028] Figure 8 is a schematic diagram of a rainflow counting method provided by an embodiment of the present application;

[0029] Figure 9 is a schematic diagram of a rainflow counting method provided by an embodiment of the present application;

[0030] Figure 10 is a histogram of a rainflow counting result of a rainflow counting method provided by an embodiment of the present application;

[0031] Figure 11 is a step flow chart of a fluid-structure coupling vibration fatigue life prediction method of a propellant tank diaphragm structure provided by an embodiment of the present application;

[0032] Figure 12 is a structural schematic diagram of a fluid-structure coupling vibration fatigue life acquisition device of a propellant tank diaphragm structure provided by an embodiment of the present application;

[0033] Figure 13 is a structural diagram of an electronic device provided by an embodiment of the present application. DETAILED DESCRIPTION

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

[0035] Figure 1 is a step flow chart of a fluid-structure coupling vibration fatigue life prediction method of a propellant tank diaphragm structure provided by an embodiment of the present application, as shown in the figure, the method can include: Figure 1

[0036] Step 101, acquiring a frequency domain power spectrum density of a vibration test on a propellant tank diaphragm.

[0037] ​Propellant tanks, as the primary management and control devices of spacecraft, are used to supply propellant to engines according to operational requirements. They are a crucial component of the propulsion systems of rockets, satellites, and other spacecraft. With the rapid development of the space industry, there are increasing demands for rockets to improve their carrying capacity, extend satellite on-orbit time, and enhance maneuverability. Based on this trend, the proportion of liquid fuel in the total weight of rockets, satellites, and other spacecraft is constantly increasing. The sloshing of liquid within the propellant tank causes changes in the distribution of additional inertial mass and fluid-structure interaction stiffness, which can severely affect the structural vibration modes. Especially when the liquid sloshing is very intense and the tank diaphragm structure is thin, it can generate strong impacts on the metal diaphragm, potentially leading to structural failure and damage. Therefore, predicting the vibration impacts caused by liquid sloshing within the propellant tank, the structural strength impacts induced by the sloshing torque, and the lifespan of the tank is extremely important.

[0038] In this embodiment, the propellant tank has the following structure: Figure 2 As shown, refer to Figure 2 The propellant tank includes a shell 1 and a chamber 2. The inner wall of the chamber 2 is provided with a diaphragm 3, and the diaphragm 3 has a pre-bent edge portion 4. The pre-bent edge is the curved part where the propellant tank interior meets the diaphragm.

[0039] The frequency domain power spectral density for vibration fatigue life testing of propellant tank diaphragms can be obtained according to relevant test standards. For example, the frequency domain power spectral density can be obtained based on the vibration of the propellant tank diaphragm under the influence of the liquid inside the tank during application, or it can be obtained from an existing database used to store vibration test data. In one embodiment, the frequency domain power spectral density data is as follows: Figure 3 As shown, Figure 3 In the diagram, the horizontal axis represents frequency, and the vertical axis represents PSD, where PSD stands for Power Spectral Density.

[0040] Furthermore, vibration tests were conducted on the propellant tanks to assess their fatigue life. The frequency domain power spectral density (PSD) is a physical quantity characterizing the energy distribution of random vibration signals in the frequency domain during the propellant tank vibration test. More specifically, the frequency domain power spectral density is the distribution of power spectral density in the frequency domain.

[0041] Step 102: Perform inverse Fourier transform on the spectral function of the frequency domain power spectral density to obtain the time domain data of the velocity power spectral density and the time domain data of the displacement power spectral density.

[0042] The time-domain data of velocity power spectral density and displacement power spectral density represent the distributions of velocity power spectral density and displacement power spectral density in the time domain, respectively.

[0043] The spectrum function F(jω) of the power spectral density is a complex number, which is conjugate symmetric in the complex frequency domain. The power spectral density of each frequency point in the complex frequency domain can be expressed as F(ω n )=Re+i×Im, which has a real part Re and an imaginary part Im. The modulus of the spectrum function can be expressed as:

[0044]

[0045] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2. Figure 4 The modulus of the spectrum function can be obtained according to the power spectral density of the frequency point and the interval time Δt, wherein the total number of samples n is obtained by interval sampling at Δt within the total vibration time .

[0046] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2.

[0047] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2.

[0048] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2.

[0049] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2.

[0050] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2.

[0051] In one embodiment, the time-domain data of the displacement power spectral density is as shown in FIG. 2.

[0052] Further, a transient dynamic analysis method can be used to perform vibration simulation analysis on the propellant tank structure simulation model, to obtain the dynamic response characteristics of the propellant tank diaphragm structure. Then, the weak position of the diaphragm structure in the entire time history of the transient analysis is evaluated, and the time-stress response result data of multiple sample points in the weak position are extracted. The time-stress response result data is a curve of the stress borne by the sample point changing with time.

[0053] In step 105, fatigue life prediction is performed on the propellant tank diaphragm structure according to the curve of the stress borne by the sample point changing with time, to obtain the fatigue life of the propellant tank diaphragm structure.

[0054] For example, the rainflow counting method is used to statistically process the time-stress response result of the selected sample point, to obtain stress cycles of different stress amplitudes under different stress mean levels, and to statistically process the frequency of each stress cycle. Then, the Goodman equation is used to correct the stress cycles under different stress mean levels to obtain the equivalent stress amplitude with a stress mean of 0. Combined with the stress-life curve of the material, the Miner linear cumulative damage theory is used to evaluate the fatigue life of the weak position of the diaphragm structure.

[0055] In the related art, the acoustic-solid coupling method can be used to perform modal analysis and random vibration analysis to obtain the equivalent stress of the diaphragm structure under 1σ, 2σ, and 3σ levels, where σ represents stress. Combined with the stress-life curve of the material and the three-interval method, the structural fatigue life is evaluated. The finite element method can also be used to perform random vibration analysis to obtain the power spectral density response curve of the structure at the weak position, and the Monte Carlo method and inverse Fourier transform method are used to convert the power spectral density response curve into a time-stress response curve, and then the rainflow counting method is used to evaluate the fatigue life.

[0056] The method in the related art uses a frequency domain calculation method for simulation analysis. Since the frequency domain calculation method can only consider linear problems, it cannot calculate non-linear problems, and therefore the above method cannot accurately predict the structural fatigue life of the propellant tank diaphragm structure under vibration load.

[0057] In the embodiment of the present application, based on the inverse Fourier transform method, the power spectrum density in the frequency domain is effectively converted into the displacement power spectrum density and the velocity power spectrum density in the time domain, the flow field inside the storage tank is analyzed according to the time-domain velocity data, the pressure distribution data of the fluid-structure interface of the propellant tank diaphragm structure at the preset position are obtained, the diaphragm fluid-structure coupling analysis is performed according to the displacement data in the time domain and the pressure distribution data at the fluid-structure interface, the stress-time curve of the sampling point of the propellant tank diaphragm structure at the preset position is obtained, and the fatigue life of the sampling point is obtained based on the stress-time curve of the sampling point at the fluid-structure interface. The propellant tank diaphragm structure has material nonlinearity and contact nonlinearity in the vibration process, the time-domain data in the embodiment can consider the characteristics of the material nonlinearity and the contact nonlinearity of the propellant tank diaphragm structure in the vibration process, the fatigue life is calculated based on the time-domain data, the accuracy of the fatigue life calculation result is improved, and the problem that the fluid-structure coupling vibration fatigue life evaluation of the propellant tank diaphragm structure cannot consider the nonlinearity calculation and has low calculation accuracy in the related art can be solved.

[0058] With reference to Figure 5 The fluid-structure coupling vibration fatigue life prediction method of the propellant tank diaphragm structure of the present application can further include the following steps:

[0059] Step 201, obtaining the frequency domain power spectrum density of the vibration fatigue test of the propellant tank diaphragm.

[0060] The method of the present step has been described in the foregoing step 101, and will not be repeated here.

[0061] The frequency spectrum function of the frequency domain power spectrum density is in the form of a complex number.

[0062] Step 202, performing inverse Fourier transform processing on the frequency spectrum function of the frequency domain power spectrum density to obtain the time-domain data of the acceleration power spectrum density.

[0063] The frequency spectrum function of the power spectrum density is in the form of a complex number.

[0064] For example, step 202 can include sub-steps A1 to A2:

[0065] Sub-step A1, obtaining the modulus of the frequency spectrum function of the frequency domain power spectrum density.

[0066] Specifically, the modulus of the frequency domain function of the frequency domain power spectrum density is obtained according to the frequency domain data of the power spectrum density of the frequency point.

[0067] For example, the modulus Magnitide of the complex frequency spectrum function F(jω) is obtained according to the following method:

[0068]

[0069] Where Re and Im are the real and imaginary parts of the complex spectrum function F(jω), respectively. Δt is the time interval for equally spaced sampling of the time-domain signal, and n is the total vibration time. The total number of samples taken at intervals of Δt.

[0070] It can be combined with the power spectral density F(ω) at frequency points in the complex frequency domain n The power spectral density (PSD) corresponding to the time-domain load is obtained using the following method:

[0071]

[0072] Preferably, according to the sampling theorem, the sampling frequency is greater than or equal to twice the highest frequency of the signal to avoid spectral aliasing and ensure that the signal can be completely recovered, i.e., fs ≥ 2fmax. Then, the sampling interval Δt = 1 / fs, where fs is the sampling frequency and fmax is the highest frequency of the signal.

[0073] Sub-step A2: Obtain the random phase, and based on the magnitude of the spectral function and the random phase, obtain the bilateral spectrum of the frequency domain power spectral density within the preset frequency domain range.

[0074] For example, the two-sided spectrum F(ω) of the power spectral density in the time domain within a preset frequency domain range can be obtained using the following method:

[0075]

[0076] F(ω)' represents a one-sided spectral function in the [0, +∞] frequency domain; F(ω) represents a two-sided spectral function in the [-∞, +∞] frequency domain.

[0077] Sub-step A3 involves performing an inverse Fourier transform on the bilateral spectrum to obtain the time-domain data of the power spectral density.

[0078] For example, the time-domain data F(t) of the power spectral density can be obtained from the following inverse Fourier transform equation:

[0079]

[0080] The above equation is the inverse Fourier transform equation, where F(jω) is the frequency domain acceleration power spectral density, t is the time variable, jωt is the complex exponential function, dω is the integral of the frequency domain variable, and F(t) is the time domain acceleration load data.

[0081] The real part of the time-domain function is defined as the time-domain acceleration load.

[0082] The power spectral density time-domain function is in complex form. For example, the real part of the power spectral density time-domain function can be obtained by the following code: Acceleration = Real(F(t)).

[0083] Step 203, the time domain data of the acceleration power spectral density is respectively subjected to first integration and second integration processing, to obtain the time domain data of the velocity power spectral density and the time domain data of the displacement power spectral density.

[0084] For example, the time domain-acceleration load data is respectively subjected to first integration and second integration, and is de-trended, to obtain the time domain-velocity load data and the time domain-displacement load data.

[0085] In one embodiment, the time domain-displacement load data is as shown in FIG. 6, wherein the horizontal axis is time, and the vertical axis is displacement. Figure 4 Figure 4 In one embodiment, the time domain-displacement load data is as shown in FIG. 6, wherein the horizontal axis is time, and the vertical axis is displacement.

[0086] Step 204, the propellant tank flow field simulation model is obtained.

[0087] For example, based on the propellant tank diaphragm structure, the Ansys Fluent software is used to generate the propellant tank flow field analysis model, and the geometric model of the propellant tank is simplified and feature cleaned.

[0088] Step 205, the preset physical property parameters of the internal medium and gas of the propellant tank flow field are obtained.

[0089] The physical property parameters include density and viscosity.

[0090] Step 206, the preset physical property parameters and the time domain data of the velocity power spectral density are configured to the propellant tank flow field simulation model, and the computational fluid dynamics method is adopted to obtain the pressure distribution data of the propellant tank diaphragm structure fluid-solid interface.

[0091] For example, the Ansys Fluent software is used to perform computational fluid dynamics analysis on the propellant tank. In the process of performing computational fluid dynamics analysis on the propellant tank by using the Ansys Fluent software, the physical property parameters of the internal medium and gas of the flow field are defined, and the physical property parameters include density and viscosity. The geometric model of the flow field is subjected to structured grid division, and the Navier-Stokes equation (N-S) equation is adopted, and the boundary conditions of the inlet and outlet of the propellant tank and the wall surface are solved, and numerical solution is performed, to obtain the flow characteristics of the propellant tank.

[0092] ​Further, in the process of performing computational fluid dynamics analysis on the propellant tank by using Ansys Fluent software, the finite volume method (FVM) of second order accuracy is used to discretize the control equation in space; implicit format is used for iteration in time discretization; second-order upwind format is used for the convection term to facilitate calculation; the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm of pressure-coupled equation set is used to couple pressure and velocity, so as to accelerate the convergence speed and save the amount of calculation.

[0093] Further, in the process of performing computational fluid dynamics analysis on the propellant tank by using Ansys Fluent software, the finite volume method (FVM) of second order accuracy is used to discretize the control equation in space; implicit format is used for iteration in time discretization; second-order upwind format is used for the convection term to facilitate calculation; the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm of pressure-coupled equation set is used to couple pressure and velocity, so as to accelerate the convergence speed and save the amount of calculation.

[0094] In addition, the entire fluid domain is set for calculation load, and time-velocity load data is loaded.

[0095] For example, the computational fluid dynamics analysis method is used to perform vibration simulation analysis on the propellant tank flow field structure simulation model. After the calculation is completed, the flow-solid interface of the tank diaphragm is selected, the pressure distribution data of the flow-solid interface of the tank diaphragm are stored in a.csv format file, and a data transmission file is outputted for subsequent analysis.

[0096] Step 207, obtaining a propellant tank structure simulation model.

[0097] For example, Ansys Fluent software is used to construct a propellant tank structure simulation model.

[0098] Based on the propellant tank diaphragm structure, a structure analysis model is generated, and the geometric model is simplified and feature cleaned.

[0099] Step 208, obtaining material performance parameters of each component of the propellant tank.

[0100] The material performance parameters include density, elastic modulus, Poisson's ratio, and material elastic-plastic stress change data with strain (elastic-plastic stress-strain data).

[0101] In step 209, the material performance parameters and the pressure distribution data are imported into the propellant tank structure simulation model, the vibration load of the propellant tank constraint position is determined according to the time domain data of the displacement power spectrum density, and the stress curve of the sampling point at the preset position of the diaphragm structure with time is obtained through transient dynamics analysis.

[0102] In the method, the vibration load of the propellant tank constraint position is determined according to the time domain data of the displacement power spectrum density, including: configuring the time domain data of the displacement power spectrum density to the constraint position of the propellant tank structure. Further, the constraint position of the propellant tank structure is the position of fixing the propellant tank on the test bench for vibration fatigue test, which can be the lug of the propellant tank. When the propellant tank is subjected to vibration fatigue test, the vibration load needs to be loaded at the lug, and the vibration load of the propellant tank constraint position is determined according to the time domain data of the displacement power spectrum density, that is, the vibration load is loaded at the constraint position of the propellant tank according to the time domain data of the displacement power spectrum density.

[0103] Specifically, a structure analysis model is generated based on the diaphragm structure of the propellant tank, and the geometric model is simplified and feature cleaned.

[0104] In the process of transient dynamics analysis of Ansys software, the material properties of each component of the propellant tank are defined, including density, elastic modulus, Poisson's ratio and material elastic-plastic stress-strain data. Because the metal material produces plastic deformation under alternating load and presents plastic strain softening, which meets the Bauschinger effect, therefore, in this embodiment, the material strengthening criterion is preferably a multi-linear follow-up strengthening criterion.

[0105] Further, the geometric model of the propellant tank structure is structured and meshed, and the propellant tank structure includes a shell and a diaphragm structure; the contact relationship between the shell and the diaphragm structure is defined by friction contact.

[0106] Further, the pressure distribution data of the fluid calculation fluid-solid interface are imported into the structure analysis module Ansys Transient in Ansys software to obtain the pressure distribution load of the propellant tank medium acting on the inner surface of the diaphragm in the vibration process at different times. The X, Y, RX, RY and RZ fixed constraints are applied to the lug hole of the whole shell, the Z direction freedom is released for displacement load setting, the time-displacement load data are loaded, and then the structure fluid-solid coupling simulation calculation is performed.

[0107] For example, the diaphragm and the inner wall of the propellant tank have a diaphragm pre-bending edge; step 209 can include the following sub-steps:

[0108] Sub-step B1, according to the time domain data of the velocity power spectral density, stress distribution data of multiple position points at the fluid-structure interface of the propellant tank diaphragm structure are obtained.

[0109] Sub-step B2, from the stress distribution data of the multiple position points, a curve of stress suffered by the sampling point changing with time is obtained.

[0110] The sampling point is a position point determined at the pre-bent edge of the diaphragm by a cross-shaped selection method. In an embodiment, the sampling point at the pre-bent edge is as shown in FIG. 4. The pre-bent edge is a position where the inside of the propellant tank and the diaphragm meet. Figure 6

[0111] For example, the transient dynamics analysis method is used to perform vibration simulation analysis on the propellant tank structure simulation model, to obtain the dynamic response characteristics of the propellant tank diaphragm structure, and through the transient dynamics analysis method, the weak positions of the propellant tank structure under the entire vibration fatigue test time history are evaluated, and then the time-stress response result data of the sample points at the multiple weak positions are extracted.

[0112] For example, the frequency domain power spectral density has a corresponding acquisition time; further, after step 209, the method further includes the following steps:

[0113] Step 210, according to the curve of the stress changing with time, a cycle frequency corresponding to a preset stress mean value is obtained.

[0114] For example, the rainflow counting method is used to statistically process the time-stress response results of the selected sample points, to obtain stress cycles of different amplitudes under different stress mean levels, and to count the frequencies of each stress cycle.

[0115] For example, step 210 can include the following sub-steps:

[0116] Sub-step C1, using the rainflow counting method, the stress amplitude and the stress mean value corresponding to each stress cycle in the curve of the stress changing with time are obtained.

[0117] The method of counting using the rainflow counting method is further exemplarily described below in combination with Figure 7 , Figure 8 and Figure 9 .

[0118] ​According to the sampling theorem, data is collected, if the cut-off frequency is fmax, the sampling interval needs to satisfy Δt≤1 / 2fmax, based on the sampling interval, data is sampled, and the stress-time history data record is obtained; the stress-time history data record includes a plurality of sampling data distributed in time sequence. According to the continuous three sampling data, the data points which are neither peak value nor valley value are deleted, and the peak-valley value sequence is obtained. The rain flow counting is carried out for the peak-valley value sequence by using the four-point method rain flow counting principle, and the counting conditions are as follows:

[0119] a. If A>B, B≥D, C≤A, record a cycle (full wave) BCB'.

[0120] Based on this, the stress range value, the stress amplitude value, and the stress mean value are obtained.

[0121] b. If A<B, B≤D, C≥A, record a cycle (full wave) BCB'.

[0122] Wherein, A, B, C and D are sampling data, and B' is a data point of reconstituted load cycle.

[0123] After repeating the above steps for counting, a divergent-convergent sequence can be obtained, which no longer satisfies the counting conditions of conditions a and b. Further, the variable range-mean counting method can be used to obtain the counting result distribution of the stress range and mean value, respectively, and the counting result distribution is: X1-X2, X2-X3……, and (X1+X2) / 2, (X2+X3) / 2……a series of half cycles (i.e. one half wave), wherein X1, X2, X3……Xn are data points at different times. Two half waves with the same stress range and mean value are combined into a complete cycle (i.e. one full wave). The above results are combined together to complete the rain flow cycle counting of the stress-time history data.

[0124] For example, the Matlab software can be used to write a rain flow counting calculation program, and the selected sample point time-stress response result is statistically processed to obtain different stress cycles of different amplitude under different stress mean value levels, and the frequency n of each stress cycle is counted.

[0125] In one embodiment, the rain flow counting statistical histogram obtained based on the method of the embodiment is as shown in Figure 10 .

[0126] Sub-step C2, correcting the stress amplitude corresponding to the stress cycle with the constraint that the stress mean value is equal to the preset stress mean value, to obtain the updated stress amplitude.

[0127] The Goodman equation is used to correct the average stress of the stress cycle under different stress mean value levels, wherein the expression of the Goodman equation is as follows:

[0128]

[0129] wherein σ a is the alternating stress, σ m is the mean stress, σ u is the tensile strength of the material, and S is the modified equivalent stress amplitude.

[0130] By the Goodman mean stress correction, a plurality of equivalent stress amplitude cycle curves under the condition of stress mean value of 0 can be obtained.

[0131] For example, the sub-step C2 can include sub-steps C21 to C22:

[0132] Sub-step C21, the tensile strength σ u of the diaphragm is obtained.

[0133] For example, the tensile strength of the diaphragm can be obtained, or the existing database can be queried to obtain the tensile strength of the diaphragm.

[0134] Sub-step C22, according to the tensile strength σ u , the updated stress amplitude S is obtained:

[0135]

[0136] wherein σ a is the alternating stress corresponding to the stress amplitude, and σ m is the stress mean value.

[0137] Sub-step C3, the cycle frequency of the updated stress amplitude is obtained, and the cycle frequency of the updated stress amplitude is determined as the cycle frequency of the stress amplitude corresponding to the preset stress mean value.

[0138] After the Goodman mean stress correction, a plurality of equivalent stress amplitude cycle curves under the condition of stress mean value of 0 are obtained, and the cycle frequency of the updated stress amplitude is obtained according to the plurality of equivalent stress amplitude cycle curves.

[0139] Step 211, obtaining the diaphragm structure fatigue life change data with stress.

[0140] wherein the fatigue life in the fatigue life change data with stress is the upper limit value of the number of times of impact of the diaphragm under the corresponding stress.

[0141] For example, the S-N curve equation in the form of power function can be used to fit the material stress-life acquisition data to obtain the diaphragm structure fatigue life change data with stress.

[0142] At step 212, the fatigue life of the diaphragm of the propellant tank is obtained according to the time corresponding to the power spectral density, the cycle frequency corresponding to the preset average stress, and the upper limit value of the number of times.

[0143] The fatigue life of the sampling point is the upper limit value of the duration of the sampling point subjected to the corresponding stress impact.

[0144] For example, step 212 can include sub-steps D1 to D2:

[0145] At sub-step D1, the ratio of the cycle frequency and the upper limit value of the number of times is obtained.

[0146] For example, there are multiple stress amplitudes, and the ratio of the cycle frequency and the upper limit value of the number of times for each stress amplitude is summed. The ratio can reflect the fatigue cumulative damage value D of the diaphragm structure:

[0147]

[0148] In the formula, N(S i ) represents the theoretical fatigue failure cycle frequency when the stress level is S i on the S-N curve, n(S i ) represents the actual cycle frequency per second when the stress level is S i .

[0149] At sub-step D2, the fatigue life of the sampling point is obtained according to the ratio of the cycle frequency and the upper limit value of the number of times of the stress amplitude and the time.

[0150] Wherein, the time is the time corresponding to the power spectral density, and further, the time is the time of the vibration test based on the power spectral density.

[0151] For example, the fatigue life T of the sampling point is obtained according to the following method:

[0152]

[0153] Wherein, D CR is the critical damage value.

[0154] In the embodiment, the spectrum function of the frequency domain power spectrum density is subjected to inverse Fourier transform processing to obtain time domain data of the acceleration power spectrum density, the time domain data of the acceleration power spectrum density is subjected to first integration and second integration processing respectively to obtain time domain data of the velocity power spectrum density and time domain data of the displacement power spectrum density, the preset physical property parameters and the time domain data of the velocity power spectrum density are configured to the propellant tank flow field simulation model, the pressure distribution data at the fluid-structure interface of the propellant tank diaphragm structure are obtained by using the computational fluid dynamics method, the material performance parameters and the pressure distribution data are imported into the propellant tank structure simulation model, the vibration load of the propellant tank constraint position is determined according to the time domain data of the displacement power spectrum density, and the stress curve of the sampling point at the preset position of the diaphragm structure with time is obtained through transient dynamics analysis, the stress amplitude and the cycle frequency corresponding to the preset stress average are obtained according to the stress curve of the sampling point with time, the change data of the fatigue life of the diaphragm structure with stress are obtained, and the fatigue life of the propellant tank diaphragm is obtained according to the time corresponding to the power spectrum density, the cycle frequency of the stress amplitude corresponding to the preset stress average, and the upper limit value of the number of times. By converting the frequency domain power spectrum density into time domain displacement signals (time domain data of the displacement power spectrum density) and time domain velocity signals (time domain data of the velocity power spectrum density) through inverse Fourier transform processing of the spectrum function of the frequency domain power spectrum density, time domain load data can be provided for subsequent transient fluid-structure coupling vibration analysis (i.e., transient dynamics analysis) based on the time domain displacement signals and the time domain velocity signals. By using the time domain transient dynamics fluid-structure coupling calculation method, the characteristics under the conditions of material nonlinearity and contact nonlinearity can be considered. Compared with the frequency domain calculation method in the related art, the analysis result of the embodiment is more reasonable and accurate, the accuracy of the fatigue life calculation result is improved, and the problem that the fluid-structure coupling vibration fatigue life evaluation of the propellant tank diaphragm structure cannot consider nonlinear calculation and has low calculation precision in the related art can be solved.

[0155] In one embodiment, with reference to Figure 11 The fluid-structure coupling vibration fatigue life prediction method of the propellant tank diaphragm structure of the embodiment can include the following steps:

[0156] Step S1, obtaining time domain acceleration load.

[0157] According to the following method, the time domain acceleration load is obtained:

[0158] According to the frequency domain data of the power spectrum density, the module Magnitude of the complex frequency spectrum density is obtained: Magnitude=sqrt(PSDxnfs).

[0159] Since the power spectrum density on the complex frequency domain lacks phase information, a random phase is generated in the embodiment. The generated random phase

[0160] According to the modulus and random phase, a spectrum function in the [0, +∞] frequency domain is obtained Wherein, j is the imaginary unit.

[0161] According to the conjugate symmetry, a double-sided spectrum in the [-∞, +∞] frequency domain is obtained

[0162] Inverse Fourier transform is performed on the double-sided spectrum to obtain a time domain function F(t) = IFFT(F(ω)).

[0163] The real part of the time domain function is taken as the real part of the time domain acceleration load by Acceleration = Real(F(t)).

[0164] Step S2, inverse Fourier transform is performed on the frequency domain data to obtain a time domain-velocity load and a time domain-displacement load.

[0165] The method of this step has been described in the foregoing step 204, and will not be repeated here.

[0166] Wherein, the time domain-velocity load and the time domain-displacement load can be used as external loads for subsequent flow field numerical simulation and structural numerical simulation, respectively.

[0167] A propellant tank flow field structure simulation model is established, including generating a flow field analysis model, defining internal medium physical property parameters, performing fluid domain grid division, performing difference format and multiphase flow model setting, and performing time domain calculation load setting.

[0168] Step S3, based on the propellant tank diaphragm structure, an Ansys Fluent software is used to generate a flow field analysis model, and the geometric model is simplified and feature cleaned.

[0169] Step S4, the internal medium and gas physical property parameters of the flow field are defined, including density and viscosity.

[0170] The medium and gas physical property parameters in this step are the preset physical property parameters in the foregoing embodiment.

[0171] Step S5, the flow field geometric model is subjected to structured grid division.

[0172] Step S6, according to the time-velocity data, the flow calculation model is subjected to working condition setting.

[0173] Further, in step S6, the N-S equation and the boundary conditions of the inlet and outlet and the wall surface are used to solve the flow characteristics by numerical method.

[0174] The control equation can be discretized in space by using a finite volume method (FVM) of the second order of accuracy, and the time discretization can be iterated and transient operation by using an implicit format, the convection term can be calculated by using a second-order upwind format, the SIMPLE algorithm can be used for pressure-velocity coupling to accelerate the convergence speed and save the operation amount. The multiphase flow model adopts a VOF model. The entire fluid domain is calculated and loaded with time-velocity load data.

[0175] Step S7, simulation calculation based on the flow calculation model.

[0176] The simulation analysis of the vibration of the propellant tank flow field structure simulation model is performed by using the computational fluid dynamics analysis method, and the pressure distribution of the propellant tank internal medium acting on the diaphragm structure is obtained.

[0177] The simulation analysis of the vibration of the propellant tank flow field structure simulation model is performed by using the computational fluid dynamics analysis method.

[0178] Step S8, establishing a structure calculation model of the propellant tank.

[0179] The structure calculation model of the propellant tank is the structure simulation model in the foregoing embodiment.

[0180] Specifically, the structure analysis model is generated, the material properties and the constitutive relation are defined, the structured mesh is divided, the contact setting is performed, the fluid pressure load mapping is performed, and the time domain calculation load setting is performed. For example, the structure analysis model is generated based on the diaphragm structure of the propellant tank, and the geometric model is simplified and feature cleaned.

[0181] Step S9, setting the material properties and the strengthening criterion of each component of the propellant tank.

[0182] For example, the material properties include density, elastic modulus, Poisson's ratio, and material strengthening criterion. Because the metal material presents plastic strain softening after plastic deformation under alternating load, it meets the Bauschinger effect, and therefore the material strengthening criterion adopts a multi-linear kinematic hardening criterion.

[0183] Step S10, structured mesh division is performed for the structure geometric model, including the shell and the diaphragm structure.

[0184] Step S11, the contact relationship between the shell and the diaphragm structure is defined by using friction contact to perform contact setting.

[0185] Step S12, the fluid calculation flow-solid interface pressure distribution result and the time-displacement data are imported into the structure calculation model, and the working condition setting is performed.

[0186] The fluid calculation fluid-solid interface pressure distribution result is introduced into the Ansys Transient structure analysis module to obtain the pressure distribution load of the medium in the propellant tank acting on the inner surface of the diaphragm in the vibration process at different times.

[0187] X, Y, RX, RY, RZ fixed constraints are applied to the lug hole of the whole shell of the propellant tank, the Z direction freedom degree is released for displacement load setting, and the time-displacement load data are loaded. X, Y, RX, RY, RZ and Z are different degrees of freedom.

[0188] Further, the time-domain vibration data of the diaphragm structure of the liquid-filled tank in actual operation are combined to set the load, and then the structure fluid-solid coupling simulation calculation is performed.

[0189] In step S13, the simulation calculation is performed on the structure calculation model to obtain the time-stress data of the weak position sample points.

[0190] For example, the transient dynamics analysis method is used to perform vibration simulation analysis on the propellant tank structure simulation model, to obtain the dynamic response characteristics of the propellant tank diaphragm structure, to evaluate the weak position of the structure in the whole time history of the transient analysis, and to extract the time-stress response result data of multiple sample points.

[0191] Further, the transient dynamics analysis method is used to perform fluid-solid coupling vibration simulation analysis on the propellant tank structure simulation model. For a linear system with n degrees of freedom, the vibration equation can be expressed as:

[0192]

[0193] In the formula, [M] is the mass matrix, [C] is the damping matrix, [K] is the stiffness matrix, F(t) is the vibration load, and x is the vibration displacement.

[0194] After the simulation calculation is completed, the dynamic response characteristics of the propellant tank diaphragm structure are obtained. The maximum stress position in the time history is selected to improve the accuracy of the evaluation result. For the diaphragm structure, the maximum stress position of the diaphragm structure at different times is located at the pre-bending edge of the diaphragm. Therefore, the "Chinese" character-shaped sampling method is used to select multiple sample points along the pre-bending edge of the diaphragm, and the time-stress response result data of all sample points are extracted.

[0195] In step S14, the rainflow counting method is used to obtain the stress cycle frequency.

[0196] The rainflow counting method is used to statistically process the time-stress response results of the selected sample points to obtain stress cycles of different amplitudes under different stress mean levels, and to count the frequencies of each stress cycle.

[0197] According to the sampling theorem, the data is collected, if the cut-off frequency is fmax, the sampling interval should satisfy Δt≤1 / 2fmax, and the stress-time history data is recorded.

[0198] According to the continuous 3 sampling data, the data points which are neither peak value nor valley value are deleted, and the peak-valley value sequence is obtained; the rain flow counting principle of four-point method is used for rain flow counting, and the counting conditions are as follows:

[0199] a. If A>B, B≥D, C≤A, record a cycle (full wave) BCB'. The stress range value, stress amplitude and average value are obtained;

[0200] b. If A<B, B≤D, C≥A, record a cycle (full wave) BCB';

[0201] After repeating the above steps for counting, a divergent-convergent sequence is obtained: this sequence no longer satisfies the counting conditions of a and b. At this time, the variable range-average value counting method can be used to obtain the counting results of the stress range and average value distribution as follows: and a series of half cycles (i.e. one half wave). Then two half waves with the same stress range and average value are combined into a complete cycle (i.e. one full wave); the results of the foregoing steps are combined together, and the rain flow cycle counting of the stress-time history data is completed.

[0202] The rain flow counting method calculation program can be written by using Matlab software, and the time-stress response results of the selected sample points are statistically processed to obtain stress cycles of different amplitudes under different stress average levels, and the frequencies n of each stress cycle are counted.

[0203] Step S15, the Goodman algorithm is used for average stress correction.

[0204] The stress cycles under different stress average levels are corrected for average stress to obtain the equivalent stress amplitude under the condition of stress average value of 0.

[0205] The Goodman equation is used to correct the average stress of the stress cycles under different stress average levels, and the Goodman equation expression is as follows:

[0206]

[0207] Where σ a is the alternating stress, σ m is the average stress, σ u is the tensile strength of the material, and S is the corrected equivalent stress amplitude.

[0208] After the Goodman average stress correction, multiple equivalent stress amplitude cycle curves under the condition of stress average value of 0 are obtained.

[0209] Step S16, in combination with the S-N curve of the material, the fatigue life of the weak position of the diaphragm structure is evaluated by using the Miner linear cumulative damage theory.

[0210] In an example, the S-N curve equation in the form of a power function can be used to fit the stress-life data of the material, wherein the S-N curve equation in the form of a power function is as follows:

[0211] S m ·N=C

[0212] In the above formula, m and C are material constants, and N represents the life. After taking the logarithm of both sides of the above formula, the following is obtained:

[0213] lg N=a+b·lgS

[0214] In the above formula, a and b are material constants, and the power function formula of the S-N curve is a straight line in the double logarithmic coordinate system.

[0215] In combination with step S15, the theoretical fatigue failure cycle number N corresponding to each stress amplitude cycle curve is obtained by using the power function S-N equation.

[0216] In an example, the damage value of the time-stress response data of each sample point is calculated by using the Miner linear cumulative damage theory. According to the Miner theory, the fatigue cumulative damage value D of the structure is obtained.

[0217] The calculation method of the fatigue cumulative damage value D is described in the foregoing embodiment, which will not be described here.

[0218] Further, by introducing a critical damage value D Cr to determine the fatigue failure of the structure, for example, D CR = 1, so that the fatigue life T of the structure can be obtained as:

[0219]

[0220] According to the present embodiment, the fatigue life of each sample point of the weak position of the diaphragm structure can be calculated. In an example, the fatigue life of a node with a certain number obtained based on the method of the foregoing embodiment is the shortest, which is 623s.

[0221] The application provides a propellant tank structure fluid-solid coupling vibration fatigue life evaluation method, based on an inverse Fourier transform method, power spectral density can be effectively converted into time domain displacement signals and time domain velocity signals by writing a Matlab code for frequency domain signal-frequency domain signal conversion, thereby providing time domain load data for subsequent transient fluid-solid coupling vibration analysis; compared with a frequency domain calculation method in the related art, the application adopts a time domain transient dynamics fluid-solid coupling calculation method, and the application considers material nonlinearity and contact nonlinearity, and the analysis result is more reasonable and accurate.

[0222] In addition, the application relates to a propellant tank diaphragm structure, and solves the problem that the propellant tank diaphragm structure fluid-solid coupling vibration fatigue life evaluation cannot consider nonlinear calculation and has low calculation precision in the related art. The application provides a propellant tank diaphragm structure fluid-solid coupling vibration fatigue life evaluation method, based on an inverse Fourier transform method, power spectral density can be effectively converted into time domain displacement signals and time domain velocity signals, thereby providing time domain load data for subsequent transient fluid-solid coupling vibration analysis.

[0223] The application also provides a propellant tank diaphragm structure fluid-solid coupling vibration fatigue life prediction device 30. Figure 12 The device 30 comprises: a first acquisition module 301 configured to acquire frequency domain power spectral density of vibration fatigue test on the propellant tank diaphragm; a second acquisition module 302 configured to perform inverse Fourier transform processing on a frequency spectrum function of the frequency domain power spectral density, to obtain time domain data of velocity power spectral density and time domain data of displacement power spectral density; a third acquisition module 303 configured to perform internal flow field analysis on the propellant tank according to the time domain data of the velocity power spectral density, to obtain pressure distribution data at a fluid-solid interface of the propellant tank diaphragm structure; a fourth acquisition module 304 configured to perform fluid-solid coupling analysis on the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectral density, to obtain a curve of stress variation with time of a sampling point at a preset position of the propellant tank diaphragm structure; and a fifth acquisition module 305 configured to perform fatigue life prediction on the propellant tank diaphragm structure according to the curve of stress variation with time of the sampling point, to obtain fatigue life of the propellant tank diaphragm structure.

[0224] Optionally, the frequency spectrum function of the frequency domain power spectral density is in a complex number form; the second acquisition module comprises: a first acquisition submodule configured to perform inverse Fourier transform on the frequency spectrum function of the frequency domain power spectral density, to obtain time domain data of acceleration power spectral density; and a second acquisition submodule configured to perform first integration and second integration processing on the time domain data of the acceleration power spectral density, to obtain the time domain data of the velocity power spectral density and the time domain data of the displacement power spectral density.

[0225] Optionally, the first obtaining sub-module comprises: a first obtaining unit, configured to obtain a modulus of a spectrum function of the frequency domain power spectrum density; a second obtaining unit, configured to obtain a random phase, and obtain a two-sided spectrum of the frequency domain power spectrum density within a preset frequency domain range according to the modulus of the spectrum function and the random phase; and a third obtaining unit, configured to perform inverse Fourier transform processing on the two-sided spectrum to obtain time domain data of the acceleration power spectrum density.

[0226] Optionally, the third obtaining module comprises: a third obtaining sub-module, configured to obtain a propellant tank flow field simulation model; a fourth obtaining sub-module, configured to obtain preset physical property parameters of a medium and gas in a flow field of the propellant tank; the physical property parameters comprise density and viscosity; and a fifth obtaining sub-module, configured to configure the preset physical property parameters and the time domain data of the velocity power spectrum density to the propellant tank flow field simulation model, and obtain pressure distribution data at a fluid-structure interface of a diaphragm structure of the propellant tank by using a computational fluid dynamics method.

[0227] Optionally, the fourth obtaining module comprises: a sixth obtaining sub-module, configured to obtain a propellant tank structure simulation model; a seventh obtaining sub-module, configured to obtain material performance parameters of components of the propellant tank; the material performance parameters comprise density, elastic modulus, Poisson's ratio and data of elastic-plastic stress change of the material with strain; and an eighth obtaining sub-module, configured to import the material performance parameters and the pressure distribution data into the propellant tank structure simulation model, determine vibration load at a constraint position of the propellant tank according to the time domain data of the displacement power spectrum density, and obtain a curve of stress change with time of a sampling point at a preset position of the diaphragm structure by transient dynamics analysis.

[0228] Optionally, the fifth obtaining module comprises: a ninth obtaining sub-module, configured to obtain a cycle frequency corresponding to a preset stress mean value according to the curve of stress change with time of the sampling point; a tenth obtaining sub-module, configured to obtain data of fatigue life change of the diaphragm structure with stress; the fatigue life in the data is an upper limit value of the number of times of stress impact borne by the diaphragm; and an eleventh obtaining sub-module, configured to obtain fatigue life of the diaphragm of the propellant tank according to the time corresponding to the power spectrum density, the cycle frequency corresponding to the preset stress mean value and the upper limit value of the number of times.

[0229] Optionally, the ninth obtaining sub-module comprises: a fourth obtaining unit, configured to obtain stress amplitudes and stress mean values corresponding to a plurality of stress cycles in the curve of stress change with time by using a rainflow counting method; a fifth obtaining unit, configured to correct the stress amplitudes corresponding to the stress cycles to obtain updated stress amplitudes, with the stress mean value being equal to a preset stress mean value as a constraint; and a sixth obtaining unit, configured to obtain a cycle frequency of the updated stress amplitudes, and determine the cycle frequency of the updated stress amplitudes as the cycle frequency corresponding to the preset stress mean value.

[0230] Optionally, the fifth acquisition unit includes: a first acquisition subunit, used to acquire the tensile strength σ of the diaphragm. u The second acquisition subunit is used to obtain the tensile strength σ. u Obtain the updated stress amplitude S:

[0231]

[0232] Where, σ a For the alternating stress corresponding to the stress amplitude, σ m This represents the average stress value.

[0233] Optionally, the eleventh acquisition submodule includes: a seventh acquisition unit, used to acquire the ratio of the cycle frequency to the upper limit of the number of cycles; and an eighth acquisition unit, used to obtain the fatigue life of the sampling point based on the ratio of the cycle frequency to the upper limit of the number of cycles and the acquisition time.

[0234] Optionally, a pre-bent edge is provided at the junction of the diaphragm and the inner wall of the propellant tank; the fourth acquisition module includes: a twelfth acquisition submodule, used to obtain stress distribution data at multiple locations at the pre-bent edge of the propellant tank diaphragm structure based on the time-domain data of the displacement power spectral density; a thirteenth acquisition submodule, used to obtain the curve of stress change over time at the sampling point from the stress distribution data at multiple locations; the sampling point is a location determined at the pre-bent edge of the diaphragm by a star-shaped point selection method.

[0235] Based on the time-domain data in this embodiment, the nonlinear characteristics of materials and contact during vibration of the propellant tank diaphragm structure can be taken into account. Fatigue life calculation based on time-domain data improves the accuracy of fatigue life calculation results and solves the problem in related technologies that the fatigue life assessment of fluid-structure interaction vibration of propellant tank diaphragm structures cannot consider nonlinear calculations and has low calculation accuracy.

[0236] The present invention also provides an electronic device, see [link to relevant documentation]. Figure 13 The system includes a processor 901, a memory 902, and a computer program 9021 stored in the memory and executable on the processor. When the processor executes the program, it implements the fluid-structure interaction vibration fatigue life prediction method for the propellant tank diaphragm structure of the aforementioned embodiment.

[0237] The present invention also provides a readable storage medium that, when the instructions in the storage medium are executed by the processor of an electronic device, enables the electronic device to execute the fluid-structure interaction vibration fatigue life prediction method for the propellant tank diaphragm structure of the foregoing embodiments.

[0238] For the apparatus embodiments, since they are substantially similar to the method embodiments, the description is relatively simple, and the relevant parts are referred to the part of the description of the method embodiments.

[0239] It should be noted that the various information and data acquired in the embodiments of the present application are acquired with the authorization of the information / data holder.

[0240] The algorithms and displays presented herein are not inherently related to any particular computer, virtual system, or other apparatus. Various general purpose systems can be used with programs in accordance with the teachings herein, or it can prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will be apparent from the description above. In addition, the present application is not intended to be limited to any particular programming language. It will be appreciated that there are many programming languages that can be used to implement the teachings herein, and any such programming language can be used in connection with the various aspects of the present application.

[0241] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the application can be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been described in detail in order to not obscure the understanding of this description.

[0242] Similarly, it is to be understood that the mechanical details of the application are sometimes grouped into single embodiments, figures, or descriptions for the convenience of the reader. However, the disclosure is not to be interpreted as reflecting an intention that the application requires more features than are explicitly recited in each claim. Rather, the inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following, are hereby expressly incorporated into this detailed description, with each claim acting as a separate embodiment of the application. The application has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of words of description rather than limitation.

[0243] Those skilled in the art will appreciate that the modules in the apparatuses in the embodiments can be adapted and placed in one or more apparatuses other than those in the embodiments. The modules or units or components in the embodiments can be combined into one module or unit or component, and furthermore can be divided into multiple sub-modules or sub-units or sub-components. Any combination of all the features disclosed in the specification (including the accompanying claims, abstract and drawings), and any method or apparatus so disclosed, can be taken, except that at least some of such features and / or processes are mutually exclusive, unless explicitly stated otherwise. Each feature disclosed in the specification (including the accompanying claims, abstract and drawings), can be replaced by alternative features providing the same, equivalent or similar functionality, unless explicitly stated otherwise.

[0244] Embodiments of the various components of the application can be implemented in hardware, or as software modules running in one or more processors, or combinations thereof. Those skilled in the art will appreciate that a microprocessor or digital signal processor (DSP) can be used in practice to implement some or all of the functionality of some or all of the components in the sequencing apparatus according to the application. The application can also be implemented as a program for executing part or all of the methods described herein on a device or apparatus. Such a program can be stored on a computer readable medium which can be any medium, tangible or intangible, in which data can be stored. The program can also be in the form of one or more signals. The signal can be downloaded from an Internet website, or can be available for copying from a computer readable medium. It should be noted that the above-mentioned embodiments illustrate rather than limit the application, and that one skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of elements or steps other than those listed in a claim. The word 'a' or 'an' preceding an element does not exclude the presence of a plurality of such elements. The application can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claim enumerating several devices, the various devices can be embodied by one and the same item of hardware. The use of the words 'first','second', and 'third', etc. do not imply any order. These words are to be interpreted as names.

[0245] The user information (including but not limited to user device information, user personal information, etc.) and related data involved in the application are information authorized by the user or authorized by each party.

[0246] Those skilled in the art can clearly understand the specific working process of the system, device and unit described above for the convenience and brevity of description, which can refer to the corresponding process in the foregoing method embodiments, and will not be repeated here. The above is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which shall be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A fluid-structure coupling vibration fatigue life prediction method of a propellant tank diaphragm structure, characterized by, The method comprises the steps of: obtaining a frequency domain power spectrum density of a propellant tank diaphragm subjected to vibration fatigue test; performing inverse Fourier transform on a spectral function of the frequency domain power spectrum density to obtain time domain data of a velocity power spectrum density and time domain data of a displacement power spectrum density; performing internal flow field analysis on the propellant tank according to the time domain data of the velocity power spectrum density to obtain pressure distribution data at a fluid-structure interface of a diaphragm structure of the propellant tank; performing fluid-structure coupling analysis on the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectrum density to obtain a curve of stress variation with time of a sampling point at a preset position of the diaphragm structure of the propellant tank; performing fatigue life prediction on the diaphragm structure of the propellant tank according to the curve of stress variation with time of the sampling point to obtain fatigue life of the diaphragm structure of the propellant tank.

2. The method of claim 1, wherein, The spectral function of the frequency domain power spectrum density is in complex number form; the inverse Fourier transform on the spectral function of the frequency domain power spectrum density to obtain the time domain data of the velocity power spectrum density and the time domain data of the displacement power spectrum density comprises the steps of: performing inverse Fourier transform on the spectral function of the frequency domain power spectrum density to obtain time domain data of an acceleration power spectrum density; performing first integration and second integration on the time domain data of the acceleration power spectrum density to obtain the time domain data of the velocity power spectrum density and the time domain data of the displacement power spectrum density.

3. The method of claim 2, wherein, The inverse Fourier transform on the spectral function of the frequency domain power spectrum density to obtain time domain data of an acceleration power spectrum density comprises the steps of: obtaining a modulus of the spectral function of the frequency domain power spectrum density; obtaining a random phase, and obtaining a bilateral spectrum of the frequency domain power spectrum density within a preset frequency domain range according to the modulus of the spectral function and the random phase; performing inverse Fourier transform on the bilateral spectrum to obtain the time domain data of the acceleration power spectrum density.

4. The method of claim 1, wherein, The internal flow field analysis on the propellant tank according to the time domain data of the velocity power spectrum density to obtain pressure distribution data at a fluid-structure interface of a diaphragm structure of the propellant tank comprises the steps of: obtaining a propellant tank flow field simulation model; obtaining preset physical property parameters of internal medium and gas of the propellant tank; the preset physical property parameters comprise density and viscosity; configuring the preset physical property parameters and the time domain data of the velocity power spectrum density to the propellant tank flow field simulation model, and obtaining the pressure distribution data at the fluid-structure interface of the diaphragm structure of the propellant tank by using computational fluid dynamics method.

5. The method of claim 1, wherein, The fluid-structure coupling analysis on the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectrum density to obtain a curve of stress variation with time of a sampling point at a preset position of the diaphragm structure of the propellant tank comprises the steps of: obtaining a propellant tank structure simulation model; obtaining material performance parameters of each component of the propellant tank; the material performance parameters comprise density, elastic modulus, Poisson's ratio and data of elastic-plastic stress variation with strain of the material; The material performance parameters and the pressure distribution data are imported into the propellant tank structure simulation model, vibration loads at the constraint positions of the propellant tank are determined according to time domain data of the displacement power spectrum density, and a curve of stress variation with time of a sampling point at a preset position of the diaphragm structure is obtained through transient dynamics analysis.

6. The method of claim 1, wherein, The fatigue life of the propellant tank diaphragm structure is predicted according to the curve of stress variation with time of the sampling point, and the fatigue life of the propellant tank diaphragm structure is obtained. The cycle frequency corresponding to the preset stress mean value is obtained according to the curve of stress variation with time of the sampling point. The change data of the fatigue life of the diaphragm structure with stress are obtained; the fatigue life in the change data is an upper limit value of the number of times of stress impact borne by the diaphragm; The fatigue life of the propellant tank diaphragm is obtained according to the time corresponding to the power spectrum density, the cycle frequency corresponding to the preset stress mean value, and the upper limit value of the number of times; the fatigue life of the sampling point is an upper limit value of the time length of stress impact borne by the sampling point.

7. The method of claim 6, wherein, The cycle frequency corresponding to the preset stress mean value is obtained according to the curve of stress variation with time of the sampling point, and the cycle frequency corresponding to the preset stress mean value is obtained. The stress amplitude and stress mean value corresponding to a plurality of stress cycles in the curve of stress variation with time are obtained by using rainflow counting method; The stress amplitude corresponding to the stress cycle is corrected by taking the stress mean value equal to the preset stress mean value as a constraint to obtain an updated stress amplitude; The cycle frequency of the updated stress amplitude is obtained, and the cycle frequency of the updated stress amplitude is determined as the cycle frequency corresponding to the preset stress mean value.

8. The method of claim 7, wherein, The stress amplitude corresponding to the stress cycle is corrected by taking the stress mean value equal to the preset stress mean value as a constraint to obtain an updated stress amplitude, and the stress amplitude corresponding to the stress cycle is corrected by taking the stress mean value equal to the preset stress mean value as a constraint to obtain an updated stress amplitude. obtaining the tensile strength σ of the diaphragm u ; According to the tensile strength σ u , the updated stress amplitude S is obtained: where σ a is the alternating stress corresponding to the stress amplitude, σ m is the stress mean value.

9. The method of claim 6, wherein, The fatigue life of the propellant tank diaphragm is obtained according to the time corresponding to the power spectrum density, the cycle frequency corresponding to the preset stress mean value, and the upper limit value of the number of times, and the fatigue life of the propellant tank diaphragm is obtained according to the time corresponding to the power spectrum density, the cycle frequency corresponding to the preset stress mean value, and the upper limit value of the number of times. The ratio of the cycle frequency to the upper limit value of the number of times is obtained; The fatigue life of the sampling point is obtained according to the ratio of the cycle frequency to the upper limit value of the number of times and the time.

10. The method according to any one of claims 1 to 9, characterized in that, The diaphragm and the inner wall of the propellant tank have a pre-bent edge; the stress variation with time of a sampling point at a preset position of the diaphragm structure of the propellant tank is obtained by fluid-structure coupling analysis of the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectrum density, and the stress variation with time of a sampling point at a preset position of the diaphragm structure of the propellant tank is obtained by fluid-structure coupling analysis of the diaphragm structure of the propellant tank according to the pressure distribution data and the time domain data of the displacement power spectrum density. Stress distribution data of a plurality of position points at the pre-bent edge of the diaphragm structure of the propellant tank are obtained according to the time domain data of the displacement power spectrum density; The stress variation with time of the sampling point is obtained from the stress distribution data of the plurality of position points; the sampling point is a position point determined at the pre-bent edge by a cross-shaped point selection method.

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