CN115994477B - Method for determining service life of rocket engine pipeline - Google Patents
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Abstract
The invention discloses a method for determining the service life of a rocket engine pipeline, which relates to the field of analysis of fatigue service life of rocket engine pipelines and aims to provide a technical scheme capable of determining the damage condition of the rocket engine pipeline in a working environment and further predicting the service life of the rocket engine pipeline. The service life determining method of the rocket engine pipeline comprises the following steps: acquiring a startup load spectrum, a shutdown load spectrum and a steady section load spectrum of a rocket engine pipeline; obtaining a damage value of an engine pipeline in the starting and closing process based on the starting load spectrum and the closing load spectrum; harmonic response analysis is carried out on the engine pipeline to obtain amplitude frequency response and phase frequency response of the engine pipeline, and damage values of the engine pipeline in a stable section are obtained; and obtaining a life damage model of the engine pipeline under the working environment based on the damage value of the engine pipeline in the starting and stopping process and the damage value of the engine pipeline in the stable section, and determining the life of the engine based on the damage model of the engine.
Description
Technical Field
The invention relates to the field of fatigue life analysis of rocket engine pipelines, in particular to a method for determining the life of rocket engine pipelines.
Background
The rocket engine pipeline is a channel for providing various liquids and gases, and if the rocket engine pipeline is cracked or even broken, the rocket engine can be caused to be in fault. Along with the gradual increase of the thrust of the liquid rocket engine developed in China, the rocket engine pipeline is required to bear alternating vibration load uninterruptedly, the problems of dynamic damage and fatigue failure under the impact load in the starting and shutting down processes and the random vibration excitation accumulation effect in the stable section in the flying process are increasingly outstanding, and the estimated pipeline service life in the working environment has important significance for improving the reliability of the rocket engine. However, the fatigue test of rocket engine pipelines requires a lot of work and has high cost.
One current solution to the above problems is to calculate the fatigue life parameter of the pipeline result by using the fatigue life Dirlic empirical formula, and then judge whether the pipeline structure is in a safe state according to the parameter, but the solution does not consider the surface processing influence of the materials affecting the fatigue life of the pipeline, and is not suitable for pipeline vibration life estimation under the time sequence load excitation of non-stationary random vibration.
Another solution takes into account both multiaxial vibration fatigue analysis and torsional fatigue conditions. And a vibration fatigue finite element model is established, and transient vibration fatigue analysis is carried out to obtain a total fatigue damage value, but vibration fatigue of random vibration load is not considered.
Disclosure of Invention
The invention aims to provide a service life determining method of a rocket engine pipeline. The technical scheme can determine the damage condition of the rocket engine pipeline in the working environment and further predict the service 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, applied to a rocket engine in a working environment, the method for determining the life of the rocket engine pipeline comprising the steps of:
acquiring a startup load spectrum, a shutdown load spectrum and a plateau load spectrum of the rocket engine pipeline, and acquiring a plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum;
in finite element software, based on the startup load spectrum and the shutdown load spectrum, performing transient dynamics analysis on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline in the startup and shutdown processes;
in the finite element software, harmonic response analysis is carried out on the rocket engine pipeline to obtain amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and a damage value of the rocket engine pipeline in a stable section is obtained based on the random vibration acceleration load spectrum of the stable section and the amplitude-frequency response and the phase-frequency response of the rocket engine pipeline;
and obtaining a life damage model of the rocket engine pipeline in a working environment through a damage accumulation principle based on a damage value of the rocket engine pipeline in a startup and shutdown process and a damage value of the rocket engine pipeline in a stable section, and determining the life of the engine based on the damage model of the engine.
Compared with the prior art, the service life determining method of the rocket engine pipeline provided by the invention has the advantages that firstly, the startup load spectrum, the shutdown load spectrum and the steady section load spectrum of the rocket engine pipeline are obtained, and then, based on the startup load spectrum and the shutdown load spectrum, the transient dynamics analysis is carried out on the rocket engine pipeline, so as to obtain the damage value of the rocket engine pipeline in the startup and shutdown processes; in the finite element software, harmonic response analysis is carried out on the rocket engine pipeline to obtain amplitude-frequency response and phase-frequency response of the rocket engine pipeline, and damage values of the rocket engine pipeline in a stable section are obtained based on the random vibration acceleration load spectrum of the stable section and the amplitude-frequency response and the phase-frequency response of the rocket engine pipeline. Based on the method, the load spectrum of the rocket engine pipeline in the working environment is divided into a startup load spectrum, a shutdown load spectrum and a steady section load spectrum, and then the damage value of the rocket engine pipeline in the startup and shutdown processes is obtained by using the startup load spectrum and the shutdown load spectrum. And then carrying out harmonic response analysis on the rocket engine pipeline to obtain amplitude frequency response and phase frequency response of the rocket engine pipeline, and obtaining a damage value of the rocket engine pipeline in a stable section based on the random vibration acceleration load spectrum of the stable section and the amplitude frequency response and the phase frequency response of the rocket engine pipeline, wherein the amplitude frequency response and the phase frequency response of the rocket engine pipeline are used for representing the response condition of the rocket engine pipeline to the random vibration acceleration load in the stable section. Therefore, compared with the prior art, the method considers the impact load in the startup and shutdown process and the random vibration load in the flight process stable section, and can obtain more accurate damage prediction results.
The invention also obtains a life damage model of the rocket engine pipeline in the working environment through a damage accumulation principle based on the damage value of the rocket engine pipeline in the starting and stopping process and the damage value of the rocket engine pipeline in a stable section, and determines the life of the engine based on the damage model of the engine. According to the invention, transient dynamics analysis is performed on the on-load spectrum and the off-load spectrum, and amplitude frequency response and phase frequency response of the rocket engine pipeline are obtained by harmonic response analysis on the rocket engine pipeline, so that the life damage model is more accurate, and the life of the engine determined by the life damage model is also more accurate.
Further, before obtaining a startup load spectrum, a shutdown load spectrum and a plateau load spectrum of the rocket engine pipeline and obtaining a plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum, the service life determining method of the rocket engine pipeline further comprises:
and dividing a test load spectrum of the engine into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on the start-up time of the engine during test.
Further, the dividing the test load spectrum of the engine into a start load spectrum, a shutdown load spectrum and a plateau load spectrum based on the start-up time of the engine includes:
acquiring a test loading spectrum of the rocket engine pipeline;
dividing the test load spectrum into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on the start-up time and the shut-down time of the engine during test;
and performing time domain to frequency domain processing on the load spectrum of the stationary segment to obtain the random vibration acceleration load spectrum of the stationary segment.
Further, before obtaining a startup load spectrum, a shutdown load spectrum and a plateau load spectrum of the rocket engine pipeline and obtaining a plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum, the service life determining method of the rocket engine pipeline further comprises:
establishing a finite element model of the rocket engine pipeline by utilizing finite element software;
in finite element software, analyzing a finite element model of the rocket engine pipeline by using modal analysis, so that target parameters of the rocket engine pipeline obtained by the modal analysis meet target parameters of an actual rocket engine pipeline;
the target parameters of the rocket engine pipeline obtained through the modal analysis comprise natural frequencies and modal shapes.
Further, after obtaining a startup load spectrum, a shutdown load spectrum and a plateau load spectrum of the rocket engine pipeline, and obtaining a plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum, the service life determining method of the rocket engine pipeline further comprises:
and in finite element software, carrying out random vibration analysis on the rocket engine pipeline based on the plateau load spectrum to obtain a weak dynamic strength position of the rocket engine pipeline under random vibration.
Further, in the finite element software, based on the plateau load spectrum, performing random vibration analysis on the rocket engine pipeline to obtain a weak dynamic strength position of the rocket engine pipeline includes:
and in the finite element software, the load spectrum of the stable section is acted on the load input position of the rocket engine pipeline, and a first target parameter is set to obtain the weak dynamic strength position of the rocket engine pipeline under random vibration.
Further, in the finite element software, based on the startup load spectrum and the shutdown load spectrum, performing transient dynamics analysis on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline in a startup and shutdown process includes:
in finite element software, based on a modal superposition method, the startup load spectrum and the shutdown load spectrum act on the rocket engine pipeline, a second target parameter is set, transient dynamics analysis is carried out on the rocket engine pipeline, and a damage value of the rocket engine pipeline in the startup and shutdown process is obtained.
Further, the lifetime damage model has the expression:
wherein,,
for stationary random shaking time +.>
For the damage value of the rocket engine pipeline in the steady section,
for the damage value of the rocket engine pipeline during starting up, < >>
And the damage value of the rocket engine pipeline in the shutdown process is obtained.
Further, determining that a life of the engine meets a requirement based on a damage model of the engine
；
Wherein,,
is the time of one working cycle of the rocket engine pipeline.
Further, the method comprises the steps of,
；
wherein,,Nfor the number of cycles of the rocket engine piping material S-N curve,Candmtwo material parameters in a formula are calculated for the rocket engine pipeline material S-N curve,
the number of zero values of internal stress passing through with positive slope per unit time, T is random vibration time per unit time, sigma is stress amplitude, < >>
Probability density function of stress amplitude;
wherein,,D 1 ，D 2 ，D 3 ，R ，Q，x m to calculate the amount of intermediate substitution in the process,m 0 ，m 1 ，m 2 ，m 3 ，m 4 the 0 th moment of inertia, the first moment of inertia, the second moment of inertia, the third moment of inertia, the fourth moment of inertia of the power spectral density function,
as a function of power spectral densityMoment of inertia of order n>
Spectral pattern irregularity factor for the bandwidth distribution of the power spectral density function with frequency, +.>
Is the regularized amplitude.
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The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation on the invention. In the drawings:
fig. 1 shows a method for determining the service life of a rocket engine pipeline according to an embodiment of the present invention.
Detailed Description
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is only exemplary and is not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the concepts of the present disclosure.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise. The meaning of "a number" is one or more than one unless specifically defined otherwise.
The rocket engine pipeline is a channel for providing various liquids and gases, and if the rocket engine pipeline is cracked or even broken, the rocket engine can be caused to be in fault. Along with the gradual increase of the thrust of the liquid rocket engine developed in China, the rocket engine pipeline is required to bear alternating vibration load uninterruptedly, the problems of dynamic damage and fatigue failure under the impact load in the starting and shutting down processes and the random vibration excitation accumulation effect in the stable section in the flying process are increasingly outstanding, and the estimated pipeline service life in the working environment has important significance for improving the reliability of the rocket engine. However, the fatigue test of rocket engine pipelines requires a lot of work and has high cost.
One current solution to the above problems is to calculate the fatigue life parameter of the pipeline result by using the fatigue life Dirlic empirical formula, and then judge whether the pipeline structure is in a safe state according to the parameter, but the solution does not consider the surface processing influence of the materials affecting the fatigue life of the pipeline, and is not suitable for pipeline vibration life estimation under the time sequence load excitation of non-stationary random vibration.
Another solution takes into account both multiaxial vibration fatigue analysis and torsional fatigue conditions. And a vibration fatigue finite element model is established, and transient vibration fatigue analysis is carried out to obtain a total fatigue damage value, but vibration fatigue of random vibration load is not considered.
Based on this, referring 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, and includes the following steps:
s100, acquiring a startup load spectrum, a shutdown load spectrum and a plateau load spectrum of the rocket engine pipeline, and acquiring a plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum.
Specifically, the test load spectrum of the engine is divided into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on the start-up time and the shutdown time of the engine during test.
It should be appreciated that when an engine is tested, a test load spectrum of a rocket engine pipeline may be obtained, and then the test load spectrum may be divided into a start load spectrum, a shutdown load spectrum, and a plateau load spectrum based on the on-off time of the engine during testing. That is, the test load is cut into three sections according to the on-off time, namely, the load spectrum of the first section when the engine is started, the load spectrum of the second section when the engine is running stably, and the load spectrum of the third section when the engine is shut down. And then performing time domain to frequency domain processing on the load spectrum of the stationary segment to obtain the random vibration acceleration load spectrum of the stationary segment.
In practice, before acquiring the startup load spectrum, the shutdown load spectrum and the plateau load spectrum of the rocket engine pipeline and acquiring the plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum, the service life determining method of the rocket engine pipeline further comprises:
establishing a finite element model of the rocket engine pipeline by utilizing finite element software; specifically, a three-dimensional model of a rocket engine pipeline is established according to a drawing of the rocket engine pipeline structure, the three-dimensional model of the rocket engine pipeline is imported into finite element software, and pipeline materials, contact relation setting and grid division are carried out to obtain the finite element model of the pipeline structure.
In finite element software, a finite element model of the rocket engine pipeline is analyzed by using modal analysis, so that a first target parameter of the rocket engine pipeline obtained by the modal analysis meets the actual rocket engine pipeline requirement. The first target parameters of the rocket engine pipeline obtained through the modal analysis comprise natural frequencies and modal shapes.
Specifically, in finite element software, the natural frequency and the modal shape of the rocket engine pipeline are combined, the finite element model of the rocket engine pipeline is simplified, the finite element model of the rocket engine pipeline is subjected to contact relation correction, boundary condition correction and grid division correction, and the natural frequency and the modal shape of the rocket engine pipeline obtained after modal analysis meet the natural frequency and the modal shape of the actual rocket engine pipeline. That is, 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 requirement, and the natural frequency of the rocket engine pipeline obtained after the modal analysis is consistent with the modal shape of the actual rocket engine pipeline and the modal shape of the actual rocket engine pipeline. Based on the above, the finite element model of the rocket engine pipeline in the embodiment of the invention is closer to the actual rocket engine pipeline structure, so that the accuracy of determining the damage of the rocket engine pipeline is improved.
S200, in finite element software, based on the startup load spectrum and the shutdown load spectrum, performing transient dynamics analysis on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline in the startup and shutdown process.
Specifically, in finite element software, a load spectrum of startup and shutdown is acted on the whole pipeline based on a modal superposition method, and a third target parameter is set, wherein the third target parameter comprises a damping ratio and a time step, finite element calculation is performed, and a damage value of the rocket engine pipeline in the startup and shutdown processes is obtained. Wherein the damping ratio is generally the material damping or structural damping of rocket engine pipelines; the time step length refers to the length of each time step in the time domain calculation. Based on the above, in the starting and stopping process of the engine, transient dynamics analysis is performed on the rocket engine pipeline, and the damage value of the rocket engine pipeline in the starting and stopping process is obtained, so that the damage condition of the rocket engine pipeline can be calculated more accurately.
Specifically, a stress time history result file calculated in the starting and shutting processes is imported into fatigue analysis software, and the surface processing influence is considered, so that a stress combination method and an average stress correction method are adopted.
Setting material mapping according to a material S-N curve obtained by a standard component tensile test, wherein the material S-N curve is as follows:
wherein,,Candmtwo characteristic parameters in the calculation formula of the S-N curve of the rocket engine pipeline material are calculated, sigma is the stress amplitude,
the number of fatigue failure cycles at stress level sigma.
In fatigue analysis softwareCalculating to obtain damage value in the process of starting and stopping
And->
。
S300, in the finite element software, harmonic response analysis is carried out on the rocket engine pipeline to obtain amplitude frequency response and phase frequency response of the rocket engine pipeline, and damage values of the rocket engine pipeline in a stable section are obtained based on the random vibration acceleration load spectrum of the stable section and the amplitude frequency response and the phase frequency response of the rocket engine pipeline.
Specifically, a harmonic response analysis based on a modal superposition method is firstly carried out on the rocket engine pipeline, a proper damping ratio and a proper frequency range are set, and a harmonic response result of a pipeline structure is obtained through analysis: amplitude-frequency response and phase-frequency response. Wherein the damping ratio is typically a material damping or a structural damping of the rocket engine pipeline.
In practice, the harmonic response of the piping structure may be the harmonic response of the x, y, z axes.
In the embodiment of the invention, after obtaining the startup load spectrum, the shutdown load spectrum and the plateau load spectrum of the rocket engine pipeline and obtaining the plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum, the service life determining method of the rocket engine pipeline further comprises the following steps:
and in finite element software, carrying out random vibration analysis on the rocket engine pipeline based on the plateau load spectrum to obtain a weak dynamic strength position of the rocket engine pipeline under random vibration.
More specifically, in the finite element software, a second target parameter is set by applying the plateau load spectrum to a load input position, a load transmission position and a connection position with an engine of the rocket engine pipeline, wherein the second target parameter is a damping ratio, and the damping ratio is generally material damping or structural damping of the rocket engine pipeline. And obtaining the weak dynamic strength position of the rocket engine pipeline under random vibration.
In the embodiment of the invention, based on the random vibration analysis of a modal superposition method, the load spectrum of the stable section is acted on the load input position, the load transmission position and the connection position of the rocket engine pipeline, the damping ratio is set according to the empirical value, the 3 sigma equivalent stress cloud picture of the pipeline under the random vibration is obtained through analysis, and the weak dynamic strength position of the rocket engine pipeline can be obtained. In practice, the weak dynamic strength position of the rocket engine pipeline can be used as a part of the rocket engine pipeline, which is easy to damage, so as to evaluate the service life of the rocket engine pipeline in various dimensions.
S400, obtaining a life damage model of the rocket engine pipeline in a working environment through a damage accumulation principle based on a damage value of the rocket engine pipeline in a startup and shutdown process and a damage value of the rocket engine pipeline in a stable section, and determining the life of the engine based on the damage model of the engine.
Specifically, the damage calculation of the startup and shutdown process to the rocket engine pipeline comprises the following steps:
a. and (3) importing a stress time history result file calculated in the starting and shutting processes into fatigue analysis software, and adopting a stress combination method and an average stress correction method by considering the surface processing influence. The stress combination method and the average stress correction method are methods which are provided in the finite element software calculation and need to be selected, wherein in the software, the stress combination method provides a plurality of methods for selection, and the average stress correction method also provides a plurality of methods for selection.
b. Setting material mapping according to a material S-N curve of a rocket engine pipeline obtained by a standard component tensile test, wherein the material S-N curve is as follows:
wherein m is,
Is a fatigue characteristic parameter, σ is stress amplitude, +.>
The number of fatigue failure cycles at stress level sigma.
c. Calculating damage value in fatigue analysis software
And->
。
Stationary segment random vibration fatigue calculation:
d. and importing the amplitude-frequency response and the phase-frequency response results of the rocket engine pipeline in the stable section into fatigue analysis software. According to the S-N curve of the material of the rocket engine pipeline, setting material mapping, considering the surface machining influence, and considering a stress combination method and an average stress correction method.
e. Establishing a damage model of a frequency domain method:
wherein,,Nfor the number of cycles of the rocket engine piping material S-N curve,Candmtwo constants in the formula are calculated for the rocket engine pipeline material S-N curve,
the number of zero values of internal stress passing through with positive slope per unit time, T is random vibration time per unit time, sigma is stress amplitude, < >>
As a function of probability density of stress amplitude.
f. The pipeline receives a broadband random vibration load in a stable section, and a Dirlik frequency domain method is adopted:
wherein,,D 1 ，D 2 ，D 3 ，R ，Q，x m to calculate the amount of intermediate substitution in the process,m 0 ，m 1 ，m 2 ，m 3 ，m 4 the 0 th moment of inertia, the first moment of inertia, the second moment of inertia, the third moment of inertia, the fourth moment of inertia of the power spectral density function,
n-order moment of inertia, which is a function of the power spectral density,/->
Spectral pattern irregularity factor for the bandwidth distribution of the power spectral density function with frequency, +.>
Is the regularized amplitude.
Calculating to obtain damage value of rocket engine pipeline in stable section
。
h. Using linear lesion accumulation, the Miner criterion considers: the fatigue failure of the sample is caused by the fact that the energy absorbed by the sample reaches a limit value, and under the action of a certain constant-amplitude cyclic load, the energy absorbed by the sample and the load cycle number are in direct proportion, namely
Wherein,,
a number of loading cycles for a certain banner load; />
For load cycle number->
The energy absorbed by the corresponding test piece;Nthe number of the circulation limit which can bear the load under the amplitude before the test piece is damaged;Wis the limit value at which the test piece can absorb the total energy before breaking. The damage criteria for the Miner linear cumulative damage theory are:
calculating to obtain damage value of rocket engine pipeline in stable section
。
h. Obtaining the comprehensive damage of a pipeline in one working period under a working environment by adopting linear damage accumulation
The method comprises the following steps:
wherein,,
for stationary random shaking time +.>
Namely, fatigue failure of the pipeline structure is considered to occur.
Comprehensive life of pipeline
The method comprises the following steps:
wherein,,
is the time of one working cycle of the pipeline.
In a specific example, the rocket motor line material is S06 steel, the plateau random vibration time
500s, on/off time of 0.07375s, 0.2s, vibration time of one working cycle +.>
500.27375s.
(1) Calculating the time domain vibration fatigue life of a pipeline in the starting and shutting down process:
a. and (3) importing a rocket engine pipeline geometric model into an ansysworks, giving materials and boundary conditions, defining a contact relation, dividing grids, and then carrying out modal analysis. Compared with a modal test, the modal correction index is that the error of the modal calculation result and the test result of the third-order frequency before pipeline dynamics is not more than 15%.
b. And performing transient analysis of a mode superposition method in an ansys workbench, wherein the load is a time sequence vibration load of on-off, and setting a time step to obtain a stress time history.
c. And (3) importing the calculation result file into a ncode, wherein the maximum fatigue damage of the pipelines in the startup and shutdown processes is 9.699e-17 and 2.809e-10 respectively, and the positions are node 79735 and node 79739.
(2) Calculating the random vibration fatigue life of the pipeline stationary section:
a. and (3) introducing the geometric model of the rocket engine pipeline into an ansysworkbench for X, Y, Z-direction random vibration analysis, and respectively obtaining the maximum 1 sigma equivalent stress of the rocket engine pipeline in three directions.
b. Performing X, Y, Z harmonic response analysis in three directions, importing the result into ncode, applying a vibration load spectrum of a stable section, and calculating to obtain the maximum damage of random vibration of the stable section of the rocket engine pipeline 1s
2.997e-5, located at node 47662.
(3) And (3) calculating the comprehensive service life of the pipeline:
the maximum damage of one working cycle of the rocket engine pipeline is 0.014985 and the comprehensive service life is obtained by the formula (10)
66.7334 duty cycles.
Although the invention is described herein in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
Although the invention has been described in connection with specific features and embodiments thereof, it will be apparent that various modifications and combinations can be made without departing from the spirit and scope of the invention. Accordingly, the specification and drawings are merely exemplary illustrations of the present invention as defined in the appended claims and are considered to cover any and all modifications, variations, combinations, or equivalents that fall within the scope of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (7)
1. The method for determining the service life of the rocket engine pipeline is characterized by being applied to a rocket engine in a working environment, and comprises the following steps of:
acquiring a startup load spectrum, a shutdown load spectrum and a plateau load spectrum of the rocket engine pipeline, and acquiring a plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum; the method comprises the steps of dividing a test load spectrum of an engine into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on a start-up time when the engine is tested;
in finite element software, based on the startup load spectrum and the shutdown load spectrum, performing transient dynamics analysis on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline in the startup and shutdown processes;
in the finite element software, harmonic response analysis based on a modal superposition method is carried out on the rocket engine pipeline to obtain amplitude frequency response and phase frequency response of the rocket engine pipeline, and a damage value of the rocket engine pipeline in a stable section is obtained by adopting a linear cumulative damage theory based on the random vibration acceleration load spectrum of the stable section and the amplitude frequency response and the phase frequency response of the rocket engine pipeline;
obtaining a life damage model of the rocket engine pipeline in a working environment through a damage accumulation principle based on a damage value of the rocket engine pipeline in a startup and shutdown process and a damage value of the rocket engine pipeline in a stable section, and determining the life of the engine based on the damage model of the engine;
before acquiring the startup load spectrum, the shutdown load spectrum and the plateau load spectrum of the rocket engine pipeline and acquiring the plateau random vibration acceleration load spectrum of the rocket engine pipeline based on the plateau load spectrum, the service life determining method of the rocket engine pipeline further comprises the following steps:
dividing a test load spectrum of the engine into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on the start-up time when the engine is tested; the step of dividing the test load spectrum of the engine into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on the start-up time of the engine comprises the following steps:
acquiring a test loading spectrum of the rocket engine pipeline;
dividing the test load spectrum into a start load spectrum, a shutdown load spectrum and a steady section load spectrum based on the start-up time and the shut-down time of the engine during test;
performing time domain to frequency domain processing on the load spectrum of the stationary segment to obtain a random vibration acceleration load spectrum of the stationary segment;
in the finite element software, based on the startup load spectrum and the shutdown load spectrum, performing transient dynamics analysis on the rocket engine pipeline to obtain a damage value of the rocket engine pipeline in the startup and shutdown process, wherein the obtaining comprises the following steps:
in finite element software, based on a modal superposition method, the startup load spectrum and the shutdown load spectrum act on the rocket engine pipeline, a third target parameter is set, transient dynamics analysis is carried out on the rocket engine pipeline, and a damage value of the rocket engine pipeline in the startup and shutdown process is obtained.
2. A method of determining the life of a rocket engine conduit according to claim 1, wherein prior to obtaining a start-up load spectrum, a shut-down load spectrum, and a plateau load spectrum of the rocket engine conduit, and obtaining a plateau random vibration acceleration load spectrum of the rocket engine conduit based on the plateau load spectrum, the method further comprises:
establishing a finite element model of the rocket engine pipeline by utilizing finite element software;
in finite element software, analyzing a finite element model of the rocket engine pipeline by using modal analysis, so that a first target parameter of the rocket engine pipeline obtained by the modal analysis meets the requirement of an actual rocket engine pipeline;
the first target parameters of the rocket engine pipeline obtained through the modal analysis comprise natural frequencies and modal shapes.
3. A rocket engine line life determining method according to claim 1, wherein after obtaining a start-up load spectrum, a shut-down load spectrum, and a plateau load spectrum of the rocket engine line, and obtaining a plateau random vibration acceleration load spectrum of the rocket engine line based on the plateau load spectrum, the rocket engine line life determining method further comprises:
and in finite element software, carrying out random vibration analysis on the rocket engine pipeline based on the plateau load spectrum to obtain a weak dynamic strength position of the rocket engine pipeline under random vibration.
4. A method of determining the life of a rocket engine line according to claim 3, wherein said performing a random vibration analysis of said rocket engine line based on said plateau load spectrum in finite element software to obtain a location of weakness in the dynamic strength of said rocket engine line comprises:
and in the finite element software, the load spectrum of the stable section is acted on the load input position of the rocket engine pipeline, and a second target parameter is set to obtain the weak dynamic strength position of the rocket engine pipeline under random vibration.
5. A method of determining the life of a rocket engine circuit according to claim 1, wherein the life damage model is expressed as:
wherein,,
for stationary random shaking time +.>
Damage value for the rocket engine line in the plateau,/->
For the damage value of the rocket engine pipeline during starting up, < >>
And the damage value of the rocket engine pipeline in the shutdown process is obtained.
6. A rocket engine circuit life determining method according to claim 5, wherein determining said engine life satisfies, based on a damage model of said engine:
；
wherein,,
for the time of one duty cycle of the rocket engine line.
7. A method of determining the life of a rocket engine circuit according to claim 5,
wherein,,Nfor the number of cycles of the rocket engine piping material S-N curve,Candmtwo of the calculation formulas for the S-N curve of the rocket engine pipeline materialThe number of characteristic parameters of the device is,
the number of zero values of internal stress passing through with positive slope per unit time, T is random vibration time per unit time, sigma is stress amplitude, < >>
Probability density function of stress amplitude;
wherein,,D 1 ，D 2 ，D 3 ，R ，Q，x m to calculate the amount of intermediate substitution in the process,m 0 ，m 1 ，m 2 ，m 3 ，m 4 the 0 th moment of inertia, the first moment of inertia, the second moment of inertia, the third moment of inertia, the fourth moment of inertia of the power spectral density function,
n-order moment of inertia, which is a function of the power spectral density,/->
Spectral pattern irregularity factor for the bandwidth distribution of the power spectral density function with frequency, +.>
Is the regularized amplitude.
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