CN114169144A - Random load spectrum compiling method under force-heat-vibration composite environment - Google Patents
Random load spectrum compiling method under force-heat-vibration composite environment Download PDFInfo
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- CN114169144A CN114169144A CN202111350314.0A CN202111350314A CN114169144A CN 114169144 A CN114169144 A CN 114169144A CN 202111350314 A CN202111350314 A CN 202111350314A CN 114169144 A CN114169144 A CN 114169144A
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Abstract
The application belongs to the field of fatigue life analysis of flight structures, and particularly relates to a random load spectrum compiling method in a force-heat-vibration composite environment. The method comprises the following steps: selecting a fatigue dangerous part according to the stress level of an airplane structure; acquiring a flight-continuation-flight fatigue load spectrum of a typical task section of a fatigue dangerous part, wherein the fatigue load spectrum comprises a vibration fatigue load spectrum, a pneumatic fatigue load spectrum and a thermal fatigue load spectrum; step three, performing linear superposition on the pneumatic fatigue load spectrum and the thermal fatigue load spectrum to obtain a composite static fatigue load spectrum; step four, processing the vibration fatigue load spectrum to obtain a processed vibration fatigue load spectrum; and fifthly, carrying out random interpolation on the processed vibration fatigue load spectrum and the composite static fatigue load spectrum to obtain a new load spectrum. The method and the device can realize compilation of the load spectrum under the force-heat-vibration composite environment, and form the fatigue analysis load spectrum comprehensively considering flight load spectrum damage and environment spectrum damage.
Description
Technical Field
The application belongs to the field of fatigue life analysis of flight structures, and particularly relates to a random load spectrum compiling method in a force-heat-vibration composite environment.
Background
The load spectrum used for designing the airplane refers to the load spectrum compiled by the airplane design stage for carrying out fatigue/durability/damage tolerance analysis and corresponding tests. For the part with airplane maneuvering overload as the main design condition, the flying-continuing-flying fatigue load spectrum is mainly used as the mainstream compiling method. Corresponding environment spectrums are compiled for the areas subjected to temperature and vibration environments. However, for a part affected by a thermal environment and a high-magnitude vibration environment, the damage of the part cannot be truly reflected only by the fly-fly load spectrum. The harsh thermal environment can generate thermal stresses that are not inferior to mechanical stresses. Random vibrational fatigue is fatigue failure caused by the superposition of vibrational stress on the basis of quasi-static stress. Although the amplitude of the dynamic stress caused by a high-magnitude vibration environment is not large, the resultant stress level of the dynamic stress and the quasi-static stress cannot be ignored after the dynamic stress and the quasi-static stress are superposed. In particular, vibration loads at frequencies much higher than flight loads generally exacerbate structural damage. For the area affected by the maneuvering overload, the temperature and the vibration environment of the airplane at the same time, simplifying the load/environment process, compiling a load spectrum under the force, heat and vibration composite environment, representing the preset average design use condition of the airplane, and analyzing the fatigue life and the durability/damage tolerance of the structure.
The traditional fly-continue-fly fatigue load spectrum cannot truly reflect the real damage of the structure influenced by the temperature and the vibration environment. The direct correction method is too coarse to accurately reflect the damage of the structure. The correction method brings great design risk, if the correction damage is small, the result is dangerous, and serious property loss and even personnel injury can be caused; if the repair damage is too large, which leads to a safer result, the structural weight is increased and the performance of the aircraft is reduced.
Accordingly, a technical solution is desired to overcome or at least alleviate at least one of the above-mentioned drawbacks of the prior art.
Disclosure of Invention
The application aims to provide a random load spectrum compiling method under a force, heat and vibration composite environment so as to solve at least one problem in the prior art.
The technical scheme of the application is as follows:
a random load spectrum compiling method under a force-thermal-vibration composite environment comprises the following steps:
selecting a fatigue dangerous part according to the stress level of an airplane structure;
acquiring a flight-continuation-flight fatigue load spectrum of a typical task section of a fatigue dangerous part, wherein the fatigue load spectrum comprises a vibration fatigue load spectrum, a pneumatic fatigue load spectrum and a thermal fatigue load spectrum;
step three, performing linear superposition on the pneumatic fatigue load spectrum and the thermal fatigue load spectrum to obtain a composite static fatigue load spectrum;
step four, processing the vibration fatigue load spectrum to obtain a processed vibration fatigue load spectrum;
and fifthly, carrying out random interpolation on the processed vibration fatigue load spectrum and the composite static fatigue load spectrum to obtain a new load spectrum.
In at least one embodiment of the present application, in step four, the processing the vibration fatigue load spectrum to obtain a processed vibration fatigue load spectrum includes:
s401, counting the vibration fatigue load spectrum by a Dirlik counting method to obtain a probability density function of a vibration stress amplitude;
s402, discretizing the probability density function of the vibration stress amplitude to obtain the probabilities of different vibration stress amplitudes;
s403, carrying out high-load interception and low-load interception on the vibration stress amplitude according to the most dangerous working condition;
s404, dividing the vibration stress level again;
s405, calculating frequency numbers of n flights under different stress amplitude values according to the loading time and the vibration average frequency;
and S406, distributing the load frequency according to the action time of different working conditions to obtain the vibration load frequency of each working condition in one flight.
In at least one embodiment of the present application, S403 includes:
carrying out high load interception on peak stress, intercepting high loads with frequency less than 1 time in a service life, and ensuring that the stress level does not exceed the strength limit;
the valley stress was cut off at low load, defining that 60% below the fatigue limit did not cause damage.
In at least one embodiment of the present application, in S405, the frequency count for different stress amplitudes for 50 flights is calculated according to the loading time and the vibration average frequency.
In at least one embodiment of the present application, in step five, a random number is generated by using a hybrid multiplier-congruence method, and a shuffle algorithm is used to perform random interpolation on the processed vibration fatigue load spectrum and the composite static fatigue load spectrum.
In at least one embodiment of the present application, in step five, the generating the random number by using the hybrid multiplier-congruence method includes:
the iterative formula is:
M＝2N
a＝2c+1
b＝2k+1
wherein, XiDenotes the ith random number, Xi+1Represents the (i + 1) th random number, M represents the period of the random number sequence, N is the number of bits for generating the random sequence, a is a multiplier, b is an increment, and c is the minimum odd number greater than or equal to k.
The invention has at least the following beneficial technical effects:
the random load spectrum compiling method under the force-heat-vibration composite environment can realize compiling of the load spectrum under the force-heat-vibration composite environment, form a fatigue analysis load spectrum comprehensively considering flight load spectrum damage and environment spectrum damage, reflect the real stress state and damage level of the airplane structure, and lay a foundation for accurately analyzing the service life of the structure and evaluating the service life index of the airplane.
Drawings
Fig. 1 is a flowchart of a random load spectrum compiling method in a force-thermal-vibration composite environment according to an embodiment of the present application.
Detailed Description
In order to make the implementation objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below with reference to the drawings in the embodiments of the present application. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are a subset of the embodiments in the present application and not all embodiments in the present application. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present application and should not be construed as limiting the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application. Embodiments of the present application will be described in detail below with reference to the accompanying drawings.
In the description of the present application, it is to be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are used merely for convenience in describing the present application and for simplifying the description, and do not indicate or imply that the referenced device or element must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore should not be construed as limiting the scope of the present application.
The present application is described in further detail below with reference to fig. 1.
The application provides a random load spectrum compiling method under a force-heat-vibration composite environment, which comprises the following steps:
selecting a fatigue dangerous part according to the stress level of an airplane structure;
acquiring a flight-continuation-flight fatigue load spectrum of a typical task section of a fatigue dangerous part, wherein the fatigue load spectrum comprises a vibration fatigue load spectrum, a pneumatic fatigue load spectrum and a thermal fatigue load spectrum;
step three, performing linear superposition on the pneumatic fatigue load spectrum and the thermal fatigue load spectrum to obtain a composite static fatigue load spectrum;
step four, processing the vibration fatigue load spectrum to obtain a processed vibration fatigue load spectrum;
and fifthly, carrying out random interpolation on the processed vibration fatigue load spectrum and the composite static fatigue load spectrum to obtain a new load spectrum.
According to the random load spectrum compiling method under the force-heat-vibration composite environment, firstly, fatigue dangerous parts are selected according to the stress level of an airplane structure, and the flying-continuing-flying fatigue load spectrum of a typical task section of the fatigue dangerous parts is obtained. By analyzing the stress level of the aircraft structure, the aircraft structure is determined to bear the main effects of three stresses: mechanical stress, thermal stress and vibrational stress. The mechanical stress is stress caused by the fact that the airplane is subjected to mechanical loads such as aerodynamic loads and inertial loads; the thermal stress is the stress generated by the structure due to factors such as pneumatic heating, heat source radiation and the like; vibrational stress is the dynamic response that results after a structure is externally excited. Aiming at the same part, the mechanical stress and the thermal stress can be directly and linearly superposed according to the corresponding load condition and used as the composite static stress. The superposition result of the mechanical stress and the thermal stress is used as the mean stress of fatigue, has a certain duration and has different sizes under different working conditions of one flight. In this embodiment, the most dangerous working condition (the mean stress is the largest) in one flight is selected as the spectrum coding basis in the load spectrum coding so as to avoid deleting the low vibration stress amplitude which can cause damage under some working conditions when low-load truncation is performed.
The random load spectrum compiling method under the force-heat-vibration composite environment further needs to process the vibration fatigue load spectrum to obtain the processed vibration fatigue load spectrum, and comprises the following steps:
s401, counting the vibration fatigue load spectrum by a Dirlik counting method to obtain a probability density function of the vibration stress amplitude;
s402, discretizing a probability density function of the vibration stress amplitude to obtain probabilities of different vibration stress amplitudes;
s403, carrying out high-load interception and low-load interception on the vibration stress amplitude according to the most dangerous working condition;
s404, dividing the vibration stress level again;
s405, calculating frequency numbers of n flights under different stress amplitude values according to the loading time and the vibration average frequency;
and S406, distributing the load frequency according to the action time of different working conditions to obtain the vibration load frequency of each working condition in one flight.
According to the random load spectrum compiling method under the force-thermal-vibration composite environment, finally, after the load frequency of primary flight under different working conditions is obtained, the vibration stress amplitude value is required to be interpolated on the pneumatic and thermal stress mean values at random. In the application, a random number can be generated by adopting a mixed congruence method, and random interpolation of vibration stress is realized by adopting a shuffling algorithm to obtain a load spectrum of one flight under one working condition. And then arranging according to the sequence of the flight working conditions to obtain a load spectrum of one flight, and obtaining the load spectrum of the whole life cycle according to the arrangement of different flight sections.
In the preferred embodiment of the present application, in the processing of the vibration fatigue load spectrum, the amplitude probability density function is discretized to obtain probability densities at different amplitudes, and the total vibration frequency cycle number is obtained according to the total flight time and the average loading frequency, as shown in the following table:
TABLE 1
| Stress interval/MPa | Stress amplitude/MPa | Probability of | Frequency of |
| 0-10 | 5 | P1 | P1Tf |
| 10-20 | 15 | P2 | P2Tf |
| …… | -- | -- | -- |
| 100-110 | 105 | Pi | PiTf |
| …… | -- | -- | -- |
Grading the stress amplitudes of different areas to obtain stress amplitude distribution frequency:
TABLE 2
And converting by using a Goodman formula to obtain the fatigue limit of the corresponding orifice plate when R is-1. And (4) superposing the composite stress as the average stress to obtain the vibration stress with the amplitude to obtain the peak stress and the valley stress.
Carrying out high load interception on the peak stress, namely intercepting high loads with frequency less than 1 time in a service life and ensuring that the stress level does not exceed the strength limit;
the valley stress was cut off at low load, defining that 60% below the fatigue limit did not cause damage. Calculating to obtain an amplitude lower limit:
wherein σ6The frequency of the vibration stress amplitude value is less than 10 times. According to the principle of high-load interception and low-load interception, the sigma is intercepted1Low load amplitude below, cut σ6The load amplitude is taken as [ sigma ] interval1，σ6]。
For σ1-σ6The interval stress amplitude is divided into n levels, and the obtained flight stress amplitude distribution frequency is shown in the following table:
TABLE 3
And determining the loading period of one load spectrum block according to the flying times. The length of the loading period has a certain influence on the fatigue test or life estimation result, and is mainly reflected in the aspect of the influence of the loading sequence caused by the length of the loading period. In this embodiment, one loading cycle is temporarily defined as 50 flights.
After obtaining the frequency table of not less than one time of flight, calculating the residual frequency of the vibration stress amplitude of less than one time of flight in one loading period (50 times of flight) each time, and making the residual frequency table.
Δf′ij＝PjTfRi-ΔfijNi
Wherein, PjTfRiThe total frequency number N of the ith and jth loads under 50 flight conditions in a loading period is calculatediIndicating the total number of i-th conditions in 50 flights.
And for the vibration load peak frequency less than one time in one working condition in one flight, calculating the position index PI of each stress level according to the flight times of one loading period, and parallel forming a position index table. The position index calculation formula is as follows:
wherein, PIijDenotes per PIijThe second flight adds the jth load of the ith condition.
After the stress amplitude frequency statistics are completed, random interpolation is needed for the amplitudes. In this embodiment, a random number is generated by a hybrid multiplier-congruence method. The generation of random numbers using hybrid multiply-accumulate is described below. The iterative formula is as follows:
M＝2N
a＝2c+1
b＝2k+1
wherein, XiDenotes the ith random number, Xi+1Represents the (i + 1) th random number, M represents the period of the random number sequence, N is the number of bits for generating the random sequence, a is a multiplier, b is an increment, and c is the minimum odd number greater than or equal to k.
In this embodiment, the random number is calculated according to a hybrid multiplier-congruence method formula, a shuffle algorithm is adopted to realize random arrangement of the loads during random arrangement, N is 16, and the initial values generated by the random number are shown in the following table:
TABLE 4
| X0 | N | M | k | a | b | c |
| System time | 16 | 65536 | 8 | 129 | 257 | 7 |
The value of M is 65536, and the range of the rest numbers is [0, 65535]The maximum generated non-repeated random number is 65536, and the use requirement is completely met. In addition, it is necessary to explain the initial value X0Determining by the current system time, and when the random number is obtained, taking three parameters of minute (min), second(s) and millisecond (ms) as initial values according to the current system time, wherein the calculation formula is as follows:
X0＝60000*min+1000*s+ms
randomly pairing the peak and valley values of the primary flight load, wherein the random pairing of the peak and valley values of the primary flight load is realized in the following process:
(1) and randomly pairing load peak-valley values in one flight under each working condition by adopting a shuffling algorithm.
(2) In one flight, if the load peak-valley value under a certain working condition occurs less than one time, the load peak-valley value is normalized to be an integer more than one time, and the j-th level load under the i-th working condition is added every n flights according to the index position of the load residual number table so as to be randomly distributed in the flight working condition.
(3) And arranging stress spectrums of different working conditions under each flight according to the process until a loading period is completed.
Random arrangement of each working condition and flight: in this embodiment, a loading cycle includes 50 flights, and after a random spectrum of each working condition in 50 flights is obtained, different working conditions are randomly arranged according to a task profile of the airplane to obtain a complete 50 flight spectrum.
Random alignment of 50 flights: the obtained load spectrum numbers of the working conditions under 50 flights are shown in the following table, one flight is formed according to LC2-LC1-LC3- … … LC N, the random number is taken for each working condition, 50 flights are formed, and a load spectrum of one loading period is completed, which is shown in the table 5.
TABLE 5
| Working conditions | Code for one flight landing music score |
| LC1 | LC1-1、LC1-2、LC1-3……LC1-49、LC1-50 |
| LC2 | LC2-1、LC2-2、LC2-3……LC2-49、LC2-50 |
| LC3 | LC3-1、LC3-2、LC3-3……LC3-49、LC3-50 |
| …… | …… |
| LC N | LC N -1、LC N -2、LC N -3……LC N -49、LC N -50 |
The random load spectrum compiling method under the force-heat-vibration composite environment is based on the traditional flying-continuing-flying fatigue load spectrum, forms a composite static fatigue load spectrum by the linear superposition of the pneumatic fatigue load spectrum and the thermal fatigue load spectrum, and carries out random interpolation on the vibration fatigue load spectrum and the composite static fatigue load spectrum, so that the simulation of structural damage under the stress-heat-vibration composite load in the whole life cycle is realized, and the compiling of the random load spectrum under the force-heat-vibration composite environment is completed. The method and the device can realize the compilation of the load spectrum under the force-heat-vibration composite environment, form the fatigue analysis load spectrum comprehensively considering the damage of the flight load spectrum and the damage of the environment spectrum, reflect the real stress state and the damage level of the airplane structure, and lay a foundation for accurately analyzing the service life of the structure and evaluating the service life index of the airplane.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (6)
1. A random load spectrum compiling method under a force, heat and vibration composite environment is characterized by comprising the following steps:
selecting a fatigue dangerous part according to the stress level of an airplane structure;
acquiring a flight-continuation-flight fatigue load spectrum of a typical task section of a fatigue dangerous part, wherein the fatigue load spectrum comprises a vibration fatigue load spectrum, a pneumatic fatigue load spectrum and a thermal fatigue load spectrum;
step three, performing linear superposition on the pneumatic fatigue load spectrum and the thermal fatigue load spectrum to obtain a composite static fatigue load spectrum;
step four, processing the vibration fatigue load spectrum to obtain a processed vibration fatigue load spectrum;
and fifthly, carrying out random interpolation on the processed vibration fatigue load spectrum and the composite static fatigue load spectrum to obtain a new load spectrum.
2. The method for compiling the random load spectrum in the combined force, heat and vibration environment according to claim 1, wherein in the fourth step, the step of processing the vibration fatigue load spectrum to obtain the processed vibration fatigue load spectrum comprises the following steps:
s401, counting the vibration fatigue load spectrum by a Dirlik counting method to obtain a probability density function of a vibration stress amplitude;
s402, discretizing the probability density function of the vibration stress amplitude to obtain the probabilities of different vibration stress amplitudes;
s403, carrying out high-load interception and low-load interception on the vibration stress amplitude according to the most dangerous working condition;
s404, dividing the vibration stress level again;
s405, calculating frequency numbers of n flights under different stress amplitude values according to the loading time and the vibration average frequency;
and S406, distributing the load frequency according to the action time of different working conditions to obtain the vibration load frequency of each working condition in one flight.
3. The method for compiling the random load spectrum under the combined force, heat and vibration environment according to claim 1, wherein the step S403 comprises the following steps:
carrying out high load interception on peak stress, intercepting high loads with frequency less than 1 time in a service life, and ensuring that the stress level does not exceed the strength limit;
the valley stress was cut off at low load, defining that 60% below the fatigue limit did not cause damage.
4. The method for compiling the random load spectrum under the force thermal vibration composite environment according to claim 3, wherein in S405, the frequency numbers under different stress amplitudes of 50 flights are calculated according to the loading time and the vibration average frequency.
5. The method for compiling the random load spectrum under the combined force, heat and vibration environment according to claim 4, wherein in the fifth step, a random number is generated by adopting a mixed multiplication-and-remainder method, and random interpolation is carried out on the processed vibration fatigue load spectrum and the combined static fatigue load spectrum by adopting a shuffling algorithm.
6. The method for random load spectrum compilation in a force, thermal and vibration composite environment according to claim 5, wherein in the fifth step, the generating random numbers by using a hybrid multiplier-congruence method comprises:
the iterative formula is:
M＝2N
a＝2c+1
b＝2k+1
wherein, XiDenotes the ith random number, Xi+1Represents the (i + 1) th random number, M represents the period of the random number sequence, N is the number of bits for generating the random sequence, a is a multiplier, b is an increment, and c is the minimum odd number greater than or equal to k.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114878123A (en) * | 2022-07-12 | 2022-08-09 | 中国飞机强度研究所 | Acceleration model-based combined load spectrum compilation method in aircraft fatigue strength test |
| WO2024021369A1 (en) * | 2022-07-28 | 2024-02-01 | 四川航天烽火伺服控制技术有限公司 | Load-spectrum-based test method, apparatus and device, and medium |
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2021
- 2021-11-15 CN CN202111350314.0A patent/CN114169144A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114878123A (en) * | 2022-07-12 | 2022-08-09 | 中国飞机强度研究所 | Acceleration model-based combined load spectrum compilation method in aircraft fatigue strength test |
| CN114878123B (en) * | 2022-07-12 | 2022-09-16 | 中国飞机强度研究所 | Acceleration model-based combined load spectrum compilation method in aircraft fatigue strength test |
| WO2024021369A1 (en) * | 2022-07-28 | 2024-02-01 | 四川航天烽火伺服控制技术有限公司 | Load-spectrum-based test method, apparatus and device, and medium |
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