CN117521379A - Equivalent calculation method for system installation strength under amphibious aircraft vibration environment - Google Patents
Equivalent calculation method for system installation strength under amphibious aircraft vibration environment Download PDFInfo
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- 238000009434 installation Methods 0.000 title claims abstract description 38
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Abstract
The invention belongs to the technical field of aircraft strength calculation, and relates to a system installation strength equivalent calculation method under an amphibious aircraft vibration environment. Dividing the vibration environment spectrum into independent phase spectrums at different rotating speeds to calculate the response of system installation, and obtaining the duration and the number of frames occupied by the rotating speeds of the propellers at each task stage of ground shutdown, ground/water surface taxi, take-off & climb, cruising and the like by statistics, and equivalently converting the duration and the number of frames into the duration related to the rotating speeds; and converting the fatigue S-N curve into parameter equations such as root mean square acceleration, fatigue stress factors and the like, calculating the root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion, determining the limiting acceleration of system installation based on Gaussian distribution, comparing with maneuver overload, and selecting a value with severe acceleration for calculation. The safety and reliability of the aircraft in the running process are greatly improved; design level and efficiency can be effectively improved.
Description
Technical Field
The invention belongs to the technical field of aircraft strength calculation, and relates to a system installation strength equivalent calculation method under an amphibious aircraft vibration environment.
Background
The amphibious aircraft power plant adopts a turbo-propeller engine and a 6-blade propeller. In the normal operation process of the aircraft, the vibration of the machine body structure is mainly caused by the unbalance of the mass of the propeller blade, the unbalance of aerodynamic force caused by the manufacturing error of the blade or the installation inclination, and the vibration is transmitted to the aircraft from the rotating shaft through the engine bracket, wherein the transmission path is as follows: shaft-engine-wing-fuselage. In turn, movement of the body structure excites vibration of the fuel, hydraulic, pneumatic and other system devices coupled thereto. Therefore, it is necessary to ensure that the installation of the system devices is able to withstand the vibration environment encountered during service. Currently, the calculation of system installation only considers motor overload in the running process of the aircraft, and the system installation strength in the vibration environment is not fully considered due to the lack of a proper method.
Disclosure of Invention
Object of the Invention
The invention aims to provide a system installation strength equivalent calculation method under an amphibious aircraft vibration environment, which is used for guiding the intensity calculation of the system installed under the vibration environment.
Technical proposal
A system installation intensity equivalent calculation method under amphibious aircraft vibration environment divides vibration environment spectrum into independent phase spectrum under different rotation speeds to calculate system installation response, obtains the time and the number of frames occupied by the rotation speed of a propeller in each task phase of ground shutdown, ground/water surface coasting, take-off & climbing, cruising and the like by statistics, and converts the time and the number of frames into time related to the rotation speed in an equivalent way; and converting the fatigue S-N curve into parameter equations such as root mean square acceleration, fatigue stress factors and the like, calculating the root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion, determining the limiting acceleration of system installation based on Gaussian distribution, comparing with maneuver overload, and selecting a value with severe acceleration for calculation.
Further, the equivalent calculation method for the system installation strength under the amphibious aircraft vibration environment comprises the following steps:
step 1, dividing a full envelope spectrum of a vibration environment according to the rotating speed of an airplane propeller, and calculating the response of system installation;
step 2, obtaining the duration and the number of times of the rotating speed of the propeller in each task stage of ground shutdown, take-off, climb, cruising and the like by using statistics, and equivalently converting the duration and the number of times into duration related to the rotating speed;
step 3, converting the fatigue S-N curve into a related equation of parameters such as root mean square acceleration, fatigue stress factors and the like;
step 4, calculating root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion;
step 5, determining the limit acceleration of system installation based on Gaussian distribution;
and 6, comparing the maneuver overload and selecting a value with a severe acceleration for calculation.
Further, in the step 1, dividing the full envelope spectrum of the vibration environment into independent spectrums at different rotating speed stages according to the rotating speed of the aircraft propeller;
further, in the step 2, the time length and the number of frames of each stage of long-term flight, short-term flight, training flight and task flight are counted according to the fatigue typical task;
further, in the step 2, the duration of each stage is calculated according to ground shutdown, ground sliding, water surface sliding, take-off & climbing, high-level cruising, low-level cruising, descending & approaching, water surface sliding, ground sliding and ground shutdown;
further, in step 3, the fatigue S-N curve equation is:
S m ·N＝C
wherein S is a fatigue stress peak; n is the load cycle number before failure; c is the level of damage required for failure to occur; m is fatigue stress index;
further, in step 3, it is assumed that the number of failure cycles is proportional to the failure duration, and the fatigue stress peak is proportional to the root mean square acceleration;
further, in step 4, the root mean square acceleration is calculated as:
in G_RMS flight Root mean square acceleration for total time of flight; G_RMS alt The root mean square acceleration is the cruising stage; G_RMS take_off For take-off&Root mean square acceleration at climbing stage; t (T) alt Is equivalent cruising duration; t (T) take_off Is equivalent take-off duration; t (T) flight Is the total flight time; m is the fatigue stress index.
The beneficial effects of this application lie in:
the invention provides a system installation strength equivalent calculation method under an amphibious aircraft vibration environment, aiming at random vibration environments suffered by amphibious aircraft system installation and related systems in the ground, water surface and air operation processes, the fatigue equivalent method is adopted to convert the vibration of each stage of aircraft operation into root mean square acceleration under the total flight time and is used for strength check, the situation that the conventional aircraft design system installation only considers static load and does not consider dynamic load such as vibration environment is broken through, and the safety and reliability in the aircraft operation process are greatly improved; the method solves the problem that the intensity calculation method of the system installation design is deficient in a vibration environment, the calculation process is simple and easy to understand, the flow is clear, the method can be used for guiding the design and calculation of the installation intensity of the aircraft system, and the design level and efficiency can be effectively improved.
Drawings
FIG. 1 is a schematic diagram of a system installation;
wherein: 1-system support, 2-hydraulic hose and 3-hydraulic hard tube
FIG. 2 is a typical vibration environment spectrum in the present invention.
FIG. 3 is a Gaussian graph of the present invention.
Fig. 4 is a schematic diagram of a system installation calculation result.
Detailed Description
The invention is further described below with reference to examples. The following description is of some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Fig. 1 shows a typical installation of an aircraft system, with hydraulic hoses and hydraulic hard tubes being fastened to the aircraft structure by means of system brackets.
The invention relates to a system installation strength equivalent calculation method under an amphibious aircraft vibration environment, which comprises the following specific implementation processes:
step one, preparing parameters including the rotating speed of the propeller, the full envelope spectrum of the vibration environment, damping coefficients, fatigue stress factors and the like.
And step two, taking the rotating speeds of different propellers as central frequencies, taking a narrow frequency band as a range of +/-5% of the central frequencies, and keeping a spectrum peak value unchanged to form a vibration environment spectrum at each rotating speed.
Step three, calculating the natural frequency f of the system installation structure n 。
Step four, calculating a displacement transfer function Q:
in the formula (1), f n The natural frequency of the system installation structure is in Hz; f (f) 0 Is random motion and forcing frequency, in Hz; alpha is the damping coefficient.
Step five, taking the vibration environment spectrum in the step two as an acceleration spectrum density input, solving to obtain an acceleration spectrum density response, wherein a calculation formula is as follows:
ASD OUT ＝Q 2 ·ASD IN ..................................................(2)
in the formula (2), ASD OUT In g, the unit of the acceleration spectral density response 2 /Hz；ASD IN In g as a vibration environmental spectrum 2 /Hz。
Step six, calculating step five to obtain square root acceleration G_RMS of the area under the acceleration spectral density response curve:
and step seven, counting the time length of each stage of long-term flight, short-term flight, training flight and mission flight and the number of frames according to the fatigue typical mission.
And step eight, converting the statistical result in the step seven into the duration occupied by flight stages such as ground stop, ground sliding, water surface sliding, take-off and climbing, high-level cruising, low-level cruising, descending and approaching, water surface sliding, ground stop and the like.
Step nine, accumulating the duration under the same rotation speed in the step eight to obtain the equivalent task duration T under each rotation speed i 。
Step ten, based on the assumption that the number of failure cycles N is proportional to the failure duration, and that the fatigue stress peak S is proportional to the root mean square acceleration g_rms, the S-N curve can be written as:
G_RMS m ·T＝K..............................................(4)
in the formula (4), m is fatigue stress index; t is the task duration; k is the proportion of damage level required for failure to occur.
Step eleven, calculating root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion:
G_RMS flight m ·T flight ＝∑G_RMS i m ·T i ...................................(5)
in formula (5), G_RMS flight Root mean square acceleration as total time of flight; t (T) flight Is the total flight time; G_RMS i Is the square root acceleration at each rotational speed.
Step twelve, according to the Gaussian distribution curve of the attached figure 3, the ratio of the transient acceleration to the root mean square acceleration is 68.3% of time within +/-1, the curve also shows that 99.73% of time is within +/-3, and the limiting vibration acceleration is 3 times of the root mean square acceleration, so that the system installation acceleration can be basically covered within 100% of time.
Step thirteen, comparing with the motor overload, and selecting an acceleration severity value to calculate aiming at the system bracket in the figure 1.
According to the equivalent calculation method for the system installation strength under the amphibious aircraft vibration environment, the vibration environment spectrum is divided into independent phase spectrums under different rotation speeds to calculate the response of system installation, the time and the number of frames occupied by the rotation speeds of the propellers in each task phase of ground shutdown, take-off, climb, cruise and the like are obtained through statistics, and the equivalent conversion is carried out to the time related to the rotation speeds; and converting the fatigue S-N curve into a related equation of parameters such as root mean square acceleration, fatigue stress factors and the like, calculating the root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion, determining the limit acceleration of system installation based on Gaussian distribution, comparing with maneuver overload, and selecting a harsh value of the acceleration for strength calculation. The method solves the problem that the intensity calculation method of the system installation design in the vibration environment is not available, the flow is clear, and the design level and the efficiency can be effectively improved.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.
Claims (8)
1. A method for equivalently calculating the system installation strength under the vibration environment of an amphibious aircraft is characterized in that the vibration environment spectrum is divided into independent phase spectrums under different rotation speeds to calculate the system installation response, and the time and the number of frames occupied by the rotation speeds of propellers in each task stage of ground shutdown, ground/water surface taxi, take-off & climb, cruising and the like are obtained by statistics and are equivalently converted into time related to the rotation speeds; and converting the fatigue S-N curve into parameter equations such as root mean square acceleration, fatigue stress factors and the like, calculating the root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion, determining the limiting acceleration of system installation based on Gaussian distribution, comparing with maneuver overload, and selecting a value with severe acceleration for calculation.
2. The method of claim 1, characterized by the steps of:
step 1, dividing a full envelope spectrum of a vibration environment according to the rotating speed of an airplane propeller, and calculating the response of system installation;
step 2, obtaining the duration and the number of times of the rotating speed of the propeller in each task stage of ground shutdown, take-off, climb, cruising and the like by using statistics, and equivalently converting the duration and the number of times into duration related to the rotating speed;
step 3, converting the fatigue S-N curve into a related equation of parameters such as root mean square acceleration, fatigue stress factors and the like;
step 4, calculating root mean square acceleration in the total flight time according to an equivalent fatigue damage criterion;
step 5, determining the limit acceleration of system installation based on Gaussian distribution;
and 6, comparing the maneuver overload and selecting a value with a severe acceleration for calculation.
3. The method according to claim 2, characterized in that in step 1, the vibration environment full envelope spectrum is divided into separate spectrums at different rotational speed phases depending on the rotational speed of the aircraft propeller.
4. A method according to claim 3, wherein in step 2, the long-term flight, short-term flight, training flight, the duration of each stage of the mission and the number of frames are counted according to the fatigue-typical mission.
5. The method of claim 4, wherein in step 2, the phase durations are calculated in terms of ground stop, ground taxi, water taxi, take-off & climb, high level cruise, low level cruise, descent & approach, water taxi, ground stop.
6. The method of claim 5, wherein in step 3, the fatigue S-N curve equation is:
S m ·N＝C
wherein S is a fatigue stress peak; n is the load cycle number before failure; c is the level of damage required for failure to occur; m is the fatigue stress index.
7. The method of claim 6, wherein in step 3, the number of failure cycles is assumed to be proportional to the length of the failure time and the fatigue stress peak is assumed to be proportional to the root mean square acceleration.
8. The method of claim 7, wherein in step 4, the root mean square acceleration is calculated as:
in G_RMS flight Root mean square acceleration for total time of flight; G_RMS alt The root mean square acceleration is the cruising stage; G_RMS take_off For take-off&Root mean square acceleration at climbing stage; t (T) alt Is equivalent cruising duration; t (T) take_off Is equivalent take-off duration; t (T) flight Is the total flight time; m is the fatigue stress index.
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