CN115994477A - A method for determining the life of a rocket engine pipeline - Google Patents

Abstract

The invention discloses a method for determining the life of a rocket engine pipeline, which relates to the field of rocket engine pipeline fatigue life analysis, to provide a method capable of determining the damage of the rocket engine pipeline in the working environment, and further improving the life of the rocket engine pipeline. A technical solution for forecasting. The life determination method of the rocket engine pipeline includes: obtaining the start-up load spectrum, shutdown load spectrum and steady-state load spectrum of the rocket engine pipeline; ;Analyze the harmonic response of the engine pipeline to obtain the amplitude-frequency response and phase-frequency response of the engine pipeline, and obtain the damage value of the engine pipeline in the stable section; The damage value of the road in the stable section is used to obtain the life damage model of the engine pipeline in the working environment, and the life of the engine is determined based on the damage model of the engine.

Description

A method for determining the life of a rocket engine pipeline

Technical Field

The invention relates to the field of rocket engine pipeline fatigue life analysis, and in particular designs a method for determining the life of a rocket engine pipeline.

Background Art

Rocket engine pipelines provide channels for various liquids and gases. If cracks or even breaks appear in rocket engine pipelines, rocket engine failures will occur. As the thrust of liquid rocket engines developed in my country gradually increases, rocket engine pipelines need to continuously withstand alternating vibration loads. Dynamic damage and fatigue failure problems under the cumulative effects of impact loads during the start-up and shutdown processes and random vibration excitation during the stable phase of flight are becoming increasingly prominent. Estimating the pipeline life under the working environment is of great significance to improving the reliability of rocket engines. However, fatigue testing of rocket engine pipelines requires a lot of work and is costly.

At present, one solution to the above problem is to use the fatigue life Dirlic empirical formula to calculate the fatigue life parameters of the pipeline results, and then judge whether the pipeline structure is in a safe state based on this parameter. However, this solution does not take into account the influence of material surface processing on the fatigue life of the pipeline, and is not suitable for the vibration life estimation of the pipeline under the time-series load excitation of non-stationary random vibration.

Another solution considers two working conditions: multiaxial vibration fatigue analysis and torsional fatigue. A vibration fatigue finite element model was established, and a transient vibration fatigue analysis was performed to obtain the total fatigue damage value, but the vibration fatigue of random vibration loads was not considered.

Summary of the invention

The purpose of the present invention is to provide a method for determining the life of a rocket engine pipeline, so as to provide a technical solution that can determine the damage of the rocket engine pipeline under the working environment and then predict the life of the rocket engine pipeline.

In a first aspect, the present invention provides a method for determining the life of a rocket engine pipeline, which is applied to a rocket engine in a working environment. The method for determining the life of a rocket engine pipeline comprises the following steps:

Obtaining a startup load spectrum, a shutdown load spectrum, and a steady-state load spectrum of the rocket engine pipeline, and obtaining a steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum;

In finite element software, based on the startup load spectrum and the shutdown load spectrum, a transient dynamic analysis is performed on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline during the startup and shutdown process;

In the finite element software, a harmonic response analysis is performed on the rocket engine pipeline to obtain the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and based on the stable section random vibration acceleration load spectrum and the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, a damage value of the rocket engine pipeline in the stable section is obtained;

Based on the damage value of the rocket engine pipeline during the startup and shutdown process and the damage value of the rocket engine pipeline in the stable section, the life damage model of the rocket engine pipeline in the working environment is obtained through the damage accumulation principle, and the life of the engine is determined based on the damage model of the engine.

Compared with the prior art, the life determination method of the rocket engine pipeline provided by the present invention first obtains the startup load spectrum, shutdown load spectrum and stable section load spectrum of the rocket engine pipeline, and then, based on the startup load spectrum and the shutdown load spectrum, performs transient dynamic analysis on the rocket engine pipeline to obtain the damage value of the rocket engine pipeline during the startup and shutdown process; in the finite element software, performs harmonic response analysis on the rocket engine pipeline to obtain the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and based on the stable section random vibration acceleration load spectrum and the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, obtain the damage value of the rocket engine pipeline in the stable section. Based on this, the present invention divides the load spectrum of the rocket engine pipeline under the working environment into a startup load spectrum, a shutdown load spectrum and a stable section load spectrum, and then uses the startup load spectrum and the shutdown load spectrum to obtain the damage value of the rocket engine pipeline during the startup and shutdown process. Then, the rocket engine pipeline is subjected to harmonic response analysis to obtain the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and based on the stable section random vibration acceleration load spectrum and the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, the damage value of the rocket engine pipeline in the stable section is obtained. The amplitude-frequency response and phase-frequency response of the rocket engine pipeline are used to characterize the response of the rocket engine pipeline to the random vibration acceleration load in the stable section. Therefore, compared with the prior art, the present invention takes into account the impact load during the start-up and shutdown process and the random vibration load during the stable section of the flight process, and can obtain more accurate damage prediction results.

The present invention also obtains the life damage model of the rocket engine pipeline in the working environment based on the damage value of the rocket engine pipeline during the startup and shutdown process and the damage value of the rocket engine pipeline in the stable section through the damage accumulation principle, and determines the life of the engine based on the damage model of the engine. Since the present invention combines the transient dynamic analysis of the startup load spectrum and the shutdown load spectrum, as well as the amplitude-frequency response and phase-frequency response of the rocket engine pipeline obtained by the harmonic response analysis of the rocket engine pipeline, the life damage model obtained by the present invention is more accurate, and the life of the engine determined by the life damage model is also more accurate.

Furthermore, before obtaining the startup load spectrum, shutdown load spectrum and steady-state load spectrum of the rocket engine pipeline, and obtaining the steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the rocket engine pipeline life determination method further includes:

Based on the start and stop moments of the engine during the test run, the test run load spectrum of the engine is divided into a start-up load spectrum, a shutdown load spectrum and a steady-state load spectrum.

Furthermore, the engine test load spectrum is divided into a startup load spectrum, a shutdown load spectrum and a stable load spectrum based on the startup and shutdown moments of the engine, including:

Obtaining a test load spectrum of the rocket engine pipeline;

Based on the on/off time of the engine test, the test load spectrum is divided into a start-up load spectrum, a shutdown load spectrum and a stable load spectrum;

The stable section load spectrum is processed from time domain to frequency domain to obtain the stable section random vibration acceleration load spectrum.

Furthermore, before obtaining the startup load spectrum, shutdown load spectrum and steady-state load spectrum of the rocket engine pipeline, and obtaining the steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the rocket engine pipeline life determination method further includes:

Using finite element software to establish a finite element model of the rocket engine pipeline;

In finite element software, the finite element model of the rocket engine pipeline is analyzed by modal analysis, so that the target parameters of the rocket engine pipeline obtained by the modal analysis meet the target parameters of the actual rocket engine pipeline;

Among them, the target parameters of the rocket engine pipeline obtained by the modal analysis include natural frequency and modal vibration shape.

Further, after obtaining the startup load spectrum, shutdown load spectrum and steady-state load spectrum of the rocket engine pipeline, and obtaining the steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the life determination method of the rocket engine pipeline also includes:

In finite element software, random vibration analysis is performed on the rocket engine pipeline based on the stable section load spectrum to obtain the weak positions of dynamic strength of the rocket engine pipeline under random vibration.

Furthermore, in the finite element software, based on the stable section load spectrum, random vibration analysis is performed on the rocket engine pipeline, and the dynamic strength weak positions of the rocket engine pipeline are obtained, including:

In the finite element software, the stable section load spectrum is applied to the load input position of the rocket engine pipeline, and the first target parameter is set to obtain the dynamic strength weak position of the rocket engine pipeline under random vibration.

Furthermore, in the finite element software, based on the startup load spectrum and the shutdown load spectrum, a transient dynamic analysis is performed on the rocket engine pipeline, and the damage value of the rocket engine pipeline during the startup and shutdown process is obtained, including:

In the finite element software, based on the modal superposition method, the startup load spectrum and the shutdown load spectrum are applied to the rocket engine pipeline, the second target parameter is set, and the transient dynamic analysis of the rocket engine pipeline is performed to obtain the damage value of the rocket engine pipeline during the startup and shutdown process.

Furthermore, the expression of the life damage model is:

；

;

为平稳段随机振动时间，

为所述火箭发动机管路在平稳段的损伤值，

为所述火箭发动机管路在开机过程的损伤值，

为所述火箭发动机管路在关机过程的损伤值。in,

is the random vibration time of the stable section,

is the damage value of the rocket engine pipeline in the stable section,

is the damage value of the rocket engine pipeline during the startup process,

It is the damage value of the rocket engine pipeline during the shutdown process.

；Further, based on the damage model of the engine, it is determined that the life of the engine meets

;

为火箭发动机管路一个工作周期的时间。in,

It is the time for one working cycle of the rocket engine pipeline.

；Furthermore,

;

为单位时间内应力以正斜率通过零值的数目，T为单位时间内的随机振动时间，σ是应力幅值，

为应力幅值的概率密度函数；Wherein, N is the number of cycles of the rocket engine pipeline material SN curve, C and m are two material parameters in the calculation formula of the rocket engine pipeline material SN curve,

is the number of times the stress passes through zero with a positive slope per unit time, T is the random vibration time per unit time, σ is the stress amplitude,

is the probability density function of stress amplitude;

；

;

；

;

；

;

；

;

；

;

是功率谱密度函数的n阶惯性矩，

为功率谱密度函数随频率的带宽分布情况的谱型不规则因子，

为正则化的幅值。Wherein, D ₁ , D ₂ , D ₃ , R , Q, x _m are the intermediate replacement quantities in the calculation process, m ₀ , m ₁ , m ₂ , m ₃ , m ₄ are the 0th order moment of inertia, the first order moment of inertia, the second order moment of inertia, the third order moment of inertia, the fourth order moment of inertia of the power spectrum density function respectively,

is the nth-order moment of inertia of the power spectral density function,

is the spectral irregularity factor of the bandwidth distribution of the power spectral density function with frequency,

is the regularization amplitude.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

FIG1 shows a method for determining the life of a rocket engine pipeline provided by an embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.

Rocket engine pipelines provide channels for various liquids and gases. If cracks or even breaks appear in rocket engine pipelines, rocket engine failures will occur. As the thrust of liquid rocket engines developed in my country gradually increases, rocket engine pipelines need to continuously withstand alternating vibration loads. Dynamic damage and fatigue failure problems under the cumulative effects of impact loads during the start-up and shutdown processes and random vibration excitation during the stable phase of flight are becoming increasingly prominent. Estimating the pipeline life under the working environment is of great significance to improving the reliability of rocket engines. However, fatigue testing of rocket engine pipelines requires a lot of work and is costly.

At present, one solution to the above problem is to use the fatigue life Dirlic empirical formula to calculate the fatigue life parameters of the pipeline results, and then judge whether the pipeline structure is in a safe state based on this parameter. However, this solution does not take into account the influence of material surface processing on the fatigue life of the pipeline, and is not suitable for the vibration life estimation of the pipeline under the time-series load excitation of non-stationary random vibration.

Another solution considers two working conditions: multiaxial vibration fatigue analysis and torsional fatigue. A vibration fatigue finite element model was established, and a transient vibration fatigue analysis was performed to obtain the total fatigue damage value, but the vibration fatigue of random vibration loads was not considered.

Based on this, with reference to FIG. 1 , an embodiment of the present invention provides a method for determining the life of a rocket engine pipeline, which is applied to a rocket engine in a working environment. The method for determining the life of a rocket engine pipeline comprises the following steps:

S100, obtaining a startup load spectrum, a shutdown load spectrum, and a steady-state load spectrum of the rocket engine pipeline, and based on the steady-state load spectrum, obtaining a steady-state random vibration acceleration load spectrum of the rocket engine pipeline.

Specifically, based on the start and stop times of the engine during the test run, the test run load spectrum of the engine is divided into a start-up load spectrum, a shutdown load spectrum and a steady-state load spectrum.

It should be understood that when testing the engine, the test load spectrum of the rocket engine pipeline can be obtained, and then based on the on/off time of the engine test, the test load spectrum is divided into a start-up load spectrum, a shutdown load spectrum, and a stable load spectrum. In other words, the test load spectrum is divided into three sections according to the on/off time. The first section is the load spectrum when the engine is turned on, the second section is the stable load spectrum when the engine is running smoothly, and the third section is the load spectrum when the engine is turned off. Then, the stable load spectrum is processed from time domain to frequency domain to obtain the stable random vibration acceleration load spectrum.

In practice, before obtaining the startup load spectrum, shutdown load spectrum and steady-state load spectrum of the rocket engine pipeline, and obtaining the steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the rocket engine pipeline life determination method further includes:

A finite element model of the rocket engine pipeline is established using finite element software; specifically, a three-dimensional model of the rocket engine pipeline is established according to a drawing of the rocket engine pipeline structure, and the three-dimensional model of the rocket engine pipeline is imported into the finite element software to set the pipeline material and contact relationship and perform mesh division to obtain a finite element model of the pipeline structure.

In the finite element software, the finite element model of the rocket engine pipeline is analyzed by modal analysis so that the first target parameter of the rocket engine pipeline obtained by the modal analysis meets the requirements of the actual rocket engine pipeline. The first target parameter of the rocket engine pipeline obtained by the modal analysis includes the natural frequency and the modal vibration shape.

Specifically, in the finite element software, the finite element model of the rocket engine pipeline is simplified in combination with the natural frequency and modal vibration shape of the rocket engine pipeline, and the contact relationship, boundary condition and mesh division of the finite element model of the rocket engine pipeline are corrected, so that the natural frequency and modal vibration shape of the rocket engine pipeline obtained after the modal analysis meet the natural frequency and modal vibration shape of the actual rocket engine pipeline. In other words, the natural frequency of the rocket engine pipeline obtained after the modal analysis and the natural frequency of the actual rocket engine pipeline meet the error requirements, and the natural frequency of the rocket engine pipeline obtained after the modal analysis and the modal vibration shape of the actual rocket engine pipeline are consistent with the modal vibration shape of the actual rocket engine pipeline. Based on this, the finite element model of the rocket engine pipeline in the embodiment of the present invention is closer to the actual rocket engine pipeline structure to improve the accuracy of the damage determination of the rocket engine pipeline.

S200. In finite element software, based on the startup load spectrum and the shutdown load spectrum, a transient dynamic analysis is performed on the rocket engine pipeline to obtain the damage value of the rocket engine pipeline during the startup and shutdown processes.

Specifically, in the finite element software, based on the modal superposition method, the load spectrum of opening and closing is applied to the entire pipeline, and the third target parameter is set, wherein the third target parameter includes the damping ratio and the time step, and the finite element calculation is performed to obtain the damage value of the rocket engine pipeline during the opening and closing process. Among them, the damping ratio is generally the material damping or structural damping of the rocket engine pipeline; the time step refers to the length of each time step in the time domain calculation. Based on this, in the embodiment of the present invention, during the process of turning the engine on and off, a transient dynamic analysis is performed on the rocket engine pipeline, and the damage value of the rocket engine pipeline during the process of turning the engine on and off is obtained. Therefore, the damage condition of the rocket engine pipeline can be calculated more accurately.

Specifically, the stress time history result file calculated during the startup and shutdown processes is imported into the fatigue analysis software, and the influence of surface processing is considered, and the stress combination method and the average stress correction method are adopted.

Material mapping is set according to the material S-N curve obtained from the standard part tensile test. The material S-N curve is:

（1）

(1)

为应力水平σ时的疲劳破坏循环次数。Wherein, C and m are two characteristic parameters in the calculation formula of the SN curve of the rocket engine pipeline material, σ is the stress amplitude,

is the number of fatigue failure cycles at stress level σ.

和

。The damage value of the startup and shutdown process is calculated in the fatigue analysis software

and

.

S300. In the finite element software, a harmonic response analysis is performed on the rocket engine pipeline to obtain the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and based on the stable section random vibration acceleration load spectrum and the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, the damage value of the rocket engine pipeline in the stable section is obtained.

Specifically, firstly, the rocket engine pipeline is subjected to harmonic response analysis based on the modal superposition method, and a suitable damping ratio and frequency range are set to analyze and obtain the harmonic response results of the pipeline structure: amplitude-frequency response and phase-frequency response. Among them, the damping ratio is generally the material damping or structural damping of the rocket engine pipeline.

In practice, the harmonic response results of the pipeline structure may be harmonic response results of the x, y, and z axes.

In an embodiment of the present invention, after obtaining the startup load spectrum, shutdown load spectrum and stable section load spectrum of the rocket engine pipeline, and obtaining the stable section random vibration acceleration load spectrum of the rocket engine pipeline based on the stable section load spectrum, the life determination method of the rocket engine pipeline further includes:

In finite element software, random vibration analysis is performed on the rocket engine pipeline based on the stable section load spectrum to obtain the weak positions of dynamic strength of the rocket engine pipeline under random vibration.

More specifically, in the finite element software, the stable load spectrum is applied to the load input position, load transfer position and connection position with the engine of the rocket engine pipeline, and a second target parameter is set, wherein the second target parameter is a damping ratio, which is generally the material damping or structural damping of the rocket engine pipeline. The dynamic strength weak position of the rocket engine pipeline under random vibration is obtained.

In the embodiment of the present invention, based on the random vibration analysis of the modal superposition method, the stable load spectrum is applied to the load input position, load transfer position and connection position with the engine of the rocket engine pipeline, the damping ratio is set according to the empirical value, and the 3σ equivalent stress cloud diagram of the pipeline under random vibration is analyzed to obtain the dynamic strength weak position of the rocket engine pipeline. In practice, the dynamic strength weak position of the rocket engine pipeline can be used as the part of the rocket engine pipeline that is prone to damage, so as to evaluate the life of the rocket engine pipeline in multiple dimensions.

S400. Based on the damage value of the rocket engine pipeline during the power on and off process and the damage value of the rocket engine pipeline in the stable section, the life damage model of the rocket engine pipeline in the working environment is obtained through the damage accumulation principle, and the life of the engine is determined based on the damage model of the engine.

Specifically, the damage calculation of the rocket engine pipeline during the startup and shutdown process includes:

a. Import the stress time history result file calculated during the startup and shutdown process into the fatigue analysis software, consider the influence of surface processing, and use the stress combination method and the average stress correction method. Among them, the stress combination method and the average stress correction method are both methods that need to be selected in the finite element software calculation. In the software, the stress combination method will provide several methods to choose from, and the average stress correction method will also provide several methods to choose from.

b. Set the material mapping based on the material S-N curve of the rocket engine pipeline obtained from the standard parts tensile test. The material S-N curve is:

（1）

(1)

是疲劳特性参数，σ是应力幅值，

为应力水平σ时的疲劳破坏循环次数。Among them, m,

is the fatigue characteristic parameter, σ is the stress amplitude,

is the number of fatigue failure cycles at stress level σ.

和

。c. Calculate the damage value of the startup and shutdown process in the fatigue analysis software

and

.

Random vibration fatigue calculation in stable section:

d. Import the amplitude-frequency response and phase-frequency response results of the stable stage rocket engine pipeline into the fatigue analysis software. According to the S-N curve of the rocket engine pipeline material, set the material mapping, consider the influence of surface processing, and consider the stress combination method and the average stress correction method.

e. Establish the damage model of frequency domain method:

（2）

(2)

为单位时间内应力以正斜率通过零值的数目，T为单位时间内的随机振动时间，σ是应力幅值，

为应力幅值的概率密度函数。Wherein, N is the number of cycles of the rocket engine pipeline material SN curve, C and m are two constants in the calculation formula of the rocket engine pipeline material SN curve,

is the number of times the stress passes through zero with a positive slope per unit time, T is the random vibration time per unit time, σ is the stress amplitude,

is the probability density function of the stress amplitude.

f. The pipeline is subjected to broadband random vibration load in the stable section, using the Dirlik frequency domain method:

（3）

(3)

（4）

(4)

（5）

(5)

（6）

(6)

（7）

(7)

是功率谱密度函数的n阶惯性矩，

为功率谱密度函数随频率的带宽分布情况的谱型不规则因子，

为正则化的幅值。Wherein, D ₁ , D ₂ , D ₃ , R , Q, x _m are the intermediate replacement quantities in the calculation process, m ₀ , m ₁ , m ₂ , m ₃ , m ₄ are the 0th order moment of inertia, the first order moment of inertia, the second order moment of inertia, the third order moment of inertia, the fourth order moment of inertia of the power spectrum density function respectively,

is the nth-order moment of inertia of the power spectral density function,

is the spectral irregularity factor of the bandwidth distribution of the power spectral density function with frequency,

is the regularization amplitude.

。Calculate the damage value of the rocket engine pipeline in the stable section

.

h. Using linear damage accumulation, Miner's criterion believes that the reason for the fatigue failure of the specimen is that the energy that the specimen can absorb reaches the limit value. Under a certain constant amplitude cyclic load, the energy absorbed by the specimen is proportional to the number of load cycles, that is,

（8）

(8)

为某一横幅载荷的加载循环数；

为载荷循环数

所对应试件吸收的能量；N为试件破坏前所能够承受该幅值下载荷的循环极限数；W为试件破坏前能够吸收总能量的极限值。Miner线性累积损伤理论的破坏准则为：in,

is the number of loading cycles for a certain banner load;

is the number of load cycles

The energy absorbed by the corresponding specimen; N is the limit number of cycles that the specimen can withstand under the load of this amplitude before failure; W is the limit value of the total energy that the specimen can absorb before failure. The failure criterion of Miner's linear cumulative damage theory is:

（9）

(9)

。Calculate the damage value of the rocket engine pipeline in the stable section

.

，即：h. Use linear damage accumulation to obtain the comprehensive damage of the pipeline in a working cycle under the working environment.

,Right now:

（10）

(10)

为平稳段随机振动时间，

即认为管路结构发生疲劳破坏。in,

is the random vibration time of the stable section,

That is, it is considered that the pipeline structure has suffered fatigue failure.

为：Comprehensive life of pipeline

for:

（11）

(11)

为管路一个工作周期的时间。in,

It is the time of one working cycle of the pipeline.

为500s，开、关机时间分别为0.07375s、0.2s，一个工作周期振动时间

为500.27375s。In a specific example, the material of the rocket engine pipeline is S06 steel, and the stable random vibration time is

500s, the on and off time are 0.07375s and 0.2s respectively, and the vibration time of one working cycle is

It is 500.27375s.

(1) Calculation of pipeline time-domain vibration fatigue life during startup and shutdown:

a. Import the rocket engine pipeline geometry model into ANSYS workbench, assign materials and boundary conditions, define contact relationships, perform meshing, and then perform modal analysis. By comparing with modal tests, the modal correction index is that the error between the modal calculation results and the test results of the first three frequency modes of pipeline dynamics does not exceed 15%.

b. Perform transient analysis of the modal superposition method in ANSYS Workbench. The load is the sequential vibration load of turning on and off. Set the time step and obtain the stress time history.

c. Import the calculation result file into ncode, and calculate that the maximum fatigue damage of the pipeline during the startup and shutdown processes is 9.699e-17 and 2.809e-10 respectively, and the locations are nodes 79735 and 79739.

(2) Calculation of random vibration fatigue life of pipeline stable section:

a. Import the rocket engine pipeline geometry model into ANSYS workbench to perform random vibration analysis in the X, Y, and Z directions, and obtain the maximum 1σ equivalent stress of the rocket engine pipeline in the three directions.

为2.997e-5，位置在节点47662。b. Perform harmonic response analysis in the X, Y, and Z directions, import the results into ncode, apply the steady-state vibration load spectrum, and calculate the maximum damage of the rocket engine pipeline in the 1s steady-state random vibration

It is 2.997e-5 and the location is node 47662.

(3) Calculation of comprehensive pipeline life:

为66.7334个工作周期。According to formula (10), the maximum damage of the rocket engine pipeline in one working cycle is 0.014985, and the comprehensive life

It is 66.7334 working cycles.

Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in a claim. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

Although the present invention has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such modifications and variations if they fall within the scope of the claims of the present invention and their equivalents.

Claims (10)

1. A method for determining the life of a rocket engine pipeline, characterized in that the method is applied to a rocket engine in a working environment, and the method for determining the life of the rocket engine pipeline comprises the following steps: Obtaining a startup load spectrum, a shutdown load spectrum, and a steady-state load spectrum of the rocket engine pipeline, and obtaining a steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum; In finite element software, based on the startup load spectrum and the shutdown load spectrum, a transient dynamic analysis is performed on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline during the startup and shutdown process; In the finite element software, a harmonic response analysis is performed on the rocket engine pipeline to obtain the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and based on the stable section random vibration acceleration load spectrum and the amplitude-frequency response and phase-frequency response of the rocket engine pipeline, a damage value of the rocket engine pipeline in the stable section is obtained; Based on the damage value of the rocket engine pipeline during the startup and shutdown process and the damage value of the rocket engine pipeline in the stable section, the life damage model of the rocket engine pipeline in the working environment is obtained through the damage accumulation principle, and the life of the engine is determined based on the damage model of the engine. 2. The method for determining the life of a rocket engine pipeline according to claim 1 is characterized in that, before obtaining a startup load spectrum, a shutdown load spectrum and a steady-state load spectrum of the rocket engine pipeline, and obtaining a steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the method for determining the life of the rocket engine pipeline further comprises: Based on the start and stop moments of the engine during the test run, the test run load spectrum of the engine is divided into a start-up load spectrum, a shutdown load spectrum and a steady-state load spectrum. 3. The method for determining the life of a rocket engine pipeline according to claim 2 is characterized in that the test load spectrum of the engine is divided into a startup load spectrum, a shutdown load spectrum and a stable load spectrum based on the startup and shutdown moments of the engine, including: Obtaining a test load spectrum of the rocket engine pipeline; Based on the on/off time of the engine test, the test load spectrum is divided into a start-up load spectrum, a shutdown load spectrum and a stable load spectrum; The stable section load spectrum is processed from time domain to frequency domain to obtain the stable section random vibration acceleration load spectrum. 4. The method for determining the life of a rocket engine pipeline according to claim 1 is characterized in that, before obtaining a startup load spectrum, a shutdown load spectrum and a steady-state load spectrum of the rocket engine pipeline, and obtaining a steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the method for determining the life of the rocket engine pipeline further comprises: Using finite element software to establish a finite element model of the rocket engine pipeline; In finite element software, a finite element model of the rocket engine pipeline is analyzed using modal analysis, so that a first target parameter of the rocket engine pipeline obtained by the modal analysis meets the requirements of an actual rocket engine pipeline; Among them, the first target parameters of the rocket engine pipeline obtained by the modal analysis include natural frequency and modal vibration shape. 5. The method for determining the life of a rocket engine pipeline according to claim 1 is characterized in that, after obtaining a startup load spectrum, a shutdown load spectrum and a steady-state load spectrum of the rocket engine pipeline, and obtaining a steady-state random vibration acceleration load spectrum of the rocket engine pipeline based on the steady-state load spectrum, the method for determining the life of the rocket engine pipeline further comprises: In finite element software, random vibration analysis is performed on the rocket engine pipeline based on the stable section load spectrum to obtain the weak positions of dynamic strength of the rocket engine pipeline under random vibration. 6. The method for determining the life of a rocket engine pipeline according to claim 5, characterized in that in the finite element software, based on the stable section load spectrum, random vibration analysis is performed on the rocket engine pipeline, and the dynamic strength weak positions of the rocket engine pipeline are obtained, including: In the finite element software, the stable section load spectrum is applied to the load input position of the rocket engine pipeline, and the second target parameter is set to obtain the dynamic strength weak position of the rocket engine pipeline under random vibration. 7. The method for determining the life of a rocket engine pipeline according to claim 1, characterized in that in the finite element software, based on the startup load spectrum and the shutdown load spectrum, a transient dynamic analysis is performed on the rocket engine pipeline to obtain the damage value of the rocket engine pipeline during the startup and shutdown process, which includes: In the finite element software, based on the modal superposition method, the startup load spectrum and the shutdown load spectrum are applied to the rocket engine pipeline, the third target parameter is set, and the transient dynamic analysis of the rocket engine pipeline is performed to obtain the damage value of the rocket engine pipeline during the startup and shutdown process. 8. The method for determining the life of a rocket engine pipeline according to claim 1, wherein the expression of the life damage model is:

; in,

is the random vibration time of the stable section,

is the damage value of the rocket engine pipeline in the stable section,

is the damage value of the rocket engine pipeline during the startup process,

It is the damage value of the rocket engine pipeline during the shutdown process. 9. The method for determining the life of a rocket engine pipeline according to claim 8, characterized in that the life of the engine is determined based on the damage model of the engine to satisfy:

; in,

It is the time of one working cycle of the rocket engine pipeline. 10. The method for determining the life of a rocket engine pipeline according to claim 8, characterized in that:

; Wherein, N is the number of cycles of the rocket engine pipeline material SN curve, C and m are two characteristic parameters in the calculation formula of the rocket engine pipeline material SN curve,

is the number of times the stress passes through zero with a positive slope per unit time, T is the random vibration time per unit time, σ is the stress amplitude,

is the probability density function of stress amplitude;

;

;

;

;

; Wherein, D ₁ , D ₂ , D ₃ , R , Q, x _m are the intermediate replacement quantities in the calculation process, m ₀ , m ₁ , m ₂ , m ₃ , m ₄ are the 0th order moment of inertia, the first order moment of inertia, the second order moment of inertia, the third order moment of inertia, the fourth order moment of inertia of the power spectrum density function respectively,

is the nth-order moment of inertia of the power spectral density function,

is the spectral irregularity factor of the bandwidth distribution of the power spectral density function with frequency,

is the regularization amplitude.

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