RU2714897C1 - Method for extraction of impact processes from dynamic loads - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment and can be used to measure impact loads on aircraft. In method, including measurement of vibration loads in locations of onboard equipment of aircraft using vibration transducers, recording of measurement information on a recorder, recorded information is reproduced in the form of centering relative to mathematical expectation of ordinates of vibration acceleration with reception of record on time of this measurement information during measurement of vibration loads. Sharply allocated levels of ordinates of vibration acceleration of measured loads are detected, time interval of action of each selected level between points of intersection of selected pulse with time axis of recording is determined. Determining the pulse speed in the form of a product of the numerical value of the sharply emphasized level of the acceleration of the vibration acceleration by the value of the time interval, comparing the obtained pulse speed value with the predetermined permissible value of the pulse speed value for the aircraft structure and deciding on the impact of the sharply allocated level of the measured process to the impact, if the pulse speed is less than the set limit, and on rejection of the released level, if the pulse speed is more than the set limit. At that, permissible limits of impulse pulse speed for aircraft structure are determined proceeding from standard requirements to load in nodes of equipment fixation to aircraft structure during tests of impact effects and characteristics of reference impact actions.

EFFECT: technical result consists in improvement of reliability of extraction of impact processes from dynamic loads, measured in locations of aircraft onboard equipment, registered in time, and improvement of accuracy of determination of parameters of vibration loads.

1 cl, 3 dwg

Description

The invention relates to the field of measuring equipment and can be used to measure shock loads on aircraft (LA).

The presence in the measurement information during the study of random vibrations on aircraft of individual abnormal, physically inexplicable levels of vibration can lead to results that are completely inconsistent with other data obtained during the test. Examples of recorded vibrational processes before take-off and after landing of an aircraft are shown in FIG. 1 and 2. However, the physical origin of the emissions in these processes is difficult to explain. The following explanations are possible:

- failure and errors in the operation of measuring equipment;

- the appearance of short-term shock processes.

In the fight against such measurement errors, the easiest way out is to exclude abruptly abnormal measurements from the entire array of measurement information and, therefore, from further processing.

A large number of theoretical studies (in particular, those presented in the theoretical literature: R. Storm. Probability theory, Mathematical statistics. Statistical quality control, “Mir”, Moscow, 1970, Chap. 13. Statistical hypothesis testing, devoted to the rejection with confirmation of its necessity). Chapter 14. Statistical estimates; ES Wentzel, Probability Theory, “Science”, Moscow, 1969, chap. 14 Processing of experiments, chap. 15. Basic concepts of the theory of random functions; J. Box. Time series analysis. Forecasting and Management: Issue 1, Mir, Mo kva, 1974; N.V. Smirnov, I.V. Dudin-Barkovsky, “The course of probability theory and mathematical statistics”, “Science”, Moscow, 1969; Orlov A.I., “Applied statistics”, M., "Examination", 2004, etc.), which are based on testing hypotheses about the emissions belonging to the general set of measurement materials. Hypothesis testing when assessing sharply distinguished members of the sample, which are measurement materials, is carried out according to various criteria (Fisher criterion, criterion of type r, etc.).

The decision to reject such sharply distinguished levels of the measured process is made with a certain level of significance, which is set by the researcher himself, i.e. subjectively. In this case, it is necessary to justify the choice of the distribution function, on the analysis of which all the conclusions about the ordinates of the process under study are based on the totality of all measurement materials. To select and obtain a distribution function, it is necessary to select several thousand correct samples (without sharply distinguished levels) from measurement materials.

Another well-known way of highlighting extreme levels in a recorded signal from a vibration transducer is a method of calculating the average value of this signal. If the calculated value centered on the average value significantly differs from 0 at some point in time, this indicates the presence at this moment of a signal of a large level that is not related to the measured process, for example, the presence of a single shock of a large level.

Known RF patent No. 26494986 dated 02.15.2018, “Method for measuring impact on the mounting structure of aircraft equipment in the presence of vibration and shock loads in the process being measured”, which provides for the measurement of the total vibration and shock processes at the locations of airborne equipment (BO) at the ends wing and end parts of the aircraft fuselage with the use of converters, the sensitive elements of which respond to the acceleration that occurs at the attachment point of these converters, its recording on the recorder. Additionally, first, the processing of the total measurement information is performed to obtain the measured amplitude spectrum in a given range from the lower frequency to the upper one. For a given requirement in the terms of reference for the development of a BO, a reference shock with a duration and amplitude spectrum described by a well-known analytical expression calculates the cutoff frequency, beyond which the amplitude spectrum is 0. Then, within the range in the measured amplitude spectrum, a frequency with the maximum value of the amplitude spectrum is isolated. Identify the frequency with the calculated value of the frequencies. For this frequency, the ordinate of the amplitude spectrum of the reference shock is calculated from the known analytical expression for this spectrum in relative values, the acceleration amplitude of the measured shock is calculated, and then the calculated value of the shock amplitude is compared with the specified value of the amplitude of the reference shock. In this case, the condition must be fulfilled that the amplitude of the reference shock must be greater than the amplitude of the measured shock, and the obtained mismatch between the experimental and given values of the amplitudes is compared with the permissible value.

However, this method provides for the comparison of real measured processes and reference shocks in the frequency domain, presented in the form of spectra, but a specific reference shock in the form of an analytical dependence for the purpose of comparison cannot always be compared in the frequency domain.

Kepski, Tomasz Barszcz, «Diagnostyka - Applied Structura 1 Health, Usage And Condition Monitoring)), 4(64)/2012, в которой предлагается использовать различные способы проверки сигнала вибрации шахтного оборудования, например, правило минимальной энергии, основанное на вычислении среднеквадратичного значения анализируемого сигнала и сравнении его с заданным пороговым значением; правило динамики диапазона амплитуд, предусматривающее задание правильного диапазона измерений, соответствующего конкретному типу анализируемой технической системы; правило n-точек, основанное на сравнении максимального количества последовательных выборок в сигнале с одинаковыми значениями амплитуды с пороговым значением; правило Z-точек, основанное на определении максимального количества последовательных отсчетов сигнала с одинаковыми знаками, что может быть индикатором насыщения датчика; правило u-точек, основанное на определении количества уникальных выборок в сигнале вибрации.Known work "Validation of vibration signals for diagnostics of mining machinery"("Testing vibration signals for the diagnosis of mine equipment"),

Kepski, Tomasz Barszcz, “Diagnostyka - Applied Structura 1 Health, Usage And Condition Monitoring)), 4 (64) / 2012, which proposes the use of various methods for checking the vibration signal of mine equipment, for example, the minimum energy rule based on the calculation of the rms value the analyzed signal and comparing it with a given threshold value; the rule of the dynamics of the range of amplitudes, providing for setting the correct range of measurements corresponding to a particular type of the analyzed technical system; the n-point rule based on a comparison of the maximum number of consecutive samples in a signal with the same amplitude values with a threshold value; the rule of Z-points based on determining the maximum number of consecutive samples of a signal with the same signs, which can be an indicator of sensor saturation; u-point rule based on determining the number of unique samples in a vibration signal.

However, these methods are highly focused on the specific type of equipment tested for vibration.

The technical result to which the invention is directed is to increase the reliability of the allocation of shock processes from dynamic loads, measured at the locations of the onboard equipment of the aircraft recorded in time, and to increase the accuracy of determining the parameters of vibration loads.

In order to achieve the named technical result in the proposed method for isolating shock processes from dynamic loads, including measuring vibration loads at the aircraft’s onboard equipment using vibration transducers, recording the measurement information to the recorder, the recorded information is reproduced in the form of ordinates of vibration acceleration centered relative to the mathematical expectation with obtaining time records of this measurement information during measurements of vibration loads. The sharply distinguished levels of the ordinates of vibration acceleration of the measured loads are detected, the time interval of each distinguished level between the points of intersection of the selected pulse with the time axis of the recording is determined, the pulse velocity is determined as the product of the numerical value of the ordinate of the sharply distinguished level of acceleration of the pulse by the value of the time interval. The obtained value of the pulse velocity is compared with a predetermined allowable limit of the magnitude of the impact pulse velocity for the aircraft structure and a decision is made on whether the shock level of the measured process belongs to the impact, provided that the pulse velocity is less than the set limit, and the rejection of the released level if the pulse velocity is greater set limit. In this case, the permissible limits of the impact pulse velocity for the aircraft structure are determined based on the regulatory requirements for the load at the attachment points of the equipment to the aircraft structure during impact testing and the characteristics of the standard impact impact.

To assess the presence of a single impact in the signal recording, it is proposed to use the following characteristics of the impact in the time domain:

- functional dependence of shock acceleration on time, i.e. j (t);

- the duration of the process from the beginning of the impact until its end τ;

- acceleration momentum as an integral value of acceleration over a time duration τ.

where v ₀ and v _τ are the initial and final speeds at the process measurement point by the vibration transducer, respectively.

This integral characteristic is an increment of velocity during the impact time τ. It is proposed to use this property to determine the presence of shock in the process under study.

As illustrative examples, we consider the standard forms of impact - sinusoidal and rectangular, as the most important from a practical point of view. The expression for the shape of the shock in the form of a half-wave of a sinusoid has the form:

j _n is the amplitude of the acceleration of impact,

The shape of the impact velocity change is accordingly expressed by the formula:

where 0 <t <τ.

The maximum value of speed for a shock sinusoidal acceleration pulse is equal to (“Protection of apparatuses from dynamic influences”, M., “Energy”, 1970):

The expression for the shape of the impact of a rectangular shape is:

j (t) = j _n ;

Where

Shape of impact velocity change:

ν (t) = j _n t, where 0 <t <τ.

The maximum value of the impact velocity for a rectangular shock acceleration pulse is:

ν _n = j _n τ.

In order to determine the permissible limits of the magnitude of the speed of the impact pulse for the design of the aircraft, the speed of impact parameters calculated in the regulatory document “Qualification Requirements KT-160G / 14G. Operating and environmental conditions for avionics. Requirements, norms and test methods ”, IAC AR, 2015:

test for "functioning":

impact amplitude j _n = 6g

impact duration τ = 20 ms

half-sinusoidal shock;

test for "safety of destruction":

impact amplitude j _n = 20g

impact duration τ = 20 ms

Rectangular punch.

In this document, in section 7.0 “Shock operational loads and fracture safety” it is stated that “on an aircraft in the conditions of its operation, the mechanical loads attributed to shock should not exceed the value of 6g for which the equipment was tested for operation prior to installation on the aircraft” .

Tests of “safety of destruction” simulate an emergency landing in terms of impact levels and regulatory requirements are imposed on the attachment points of the equipment to the aircraft structure.

Maximum speed of impact during tests for "functioning":

Given the upper tolerance of 15%, ν = 0.9 m / s

Maximum impact speed when tested for "safety of destruction":

ν _n = j _n τ = 20 * 9.8 * 0.02 = 3.92 m / s.

Given the upper tolerance of 15%, the maximum impact velocity will be ν _max = 4.5 m / s.

The obtained values of ν _n are selected as a sign for determining the presence of single impacts in the records of loads from vibration transducers installed on the aircraft at the locations of the onboard equipment. In this case, you can enter the safety factor K, adopted for aircraft, i.e. the established limit is taken equal to K * ν _max. .

The proposed method is illustrated by the following figures:

in FIG. 1 shows records of vibrational processes with superposition of single impacts before takeoff and after landing;

in FIG. 2 shows a record of the vibro-shock process j (t);

in FIG. 3 shows a block diagram of the allocation of shock processes from dynamic loads, where:

1 - vibration transducer and recorder;

2 - an identification block of a sharply distinguished level of vibration accelerations j (t) of a vibration acceleration pulse recorded in time;

3 - unit for determining the time interval for the action of vibration acceleration levels between the points of intersection of the emitted pulse with the time axis of the record;

4 - block determining the magnitude of the speed of the selected pulse;

5 - a block of predetermined characteristics of single strokes during the test “for operation”, “for failure safety” by increment of the impact velocity ν _n , v _max at the locations of the onboard equipment of the aircraft;

6 is a block comparing the speed of the emitted pulse of the measured loads ν _ISM with a set allowable limit of the value of the pulse velocity ν _max for the aircraft structure: ν _max > ν _ISM or ν _max <ν _ISM ;

7 - decision block;

8 - block excluding the selected pulse from further processing.

The method is as follows.

Under the conditions of a test flight of an aircraft in places where on-board equipment is located on the structure of its mount, dynamic loads are measured using vibration transducers and recorded on a recorder (1). The measured vibration accelerations from the output of block (1) are transferred to the input of block (2), where they form a functional dependence of the acceleration of shock centered relative to the mathematical expectation on time j (t) and identify in this dependence a sharply distinguished level of pulse acceleration, which then arrives at the input of the block ( 3), fixing the time interval of the action of a sharply distinguished level of vibration acceleration and the duration of the action of this level τ between the points of intersection of the emitted pulse with the time axis of the recording of vibration acceleration . In block (4), the magnitude of the velocity of this selected pulse is determined as the product of the numerical value of the ordinate of the sharply distinguished level of vibration acceleration of the pulse by the value of the time interval τ.

A predetermined allowable limit of the magnitude of the impact pulse velocity for the design of the aircraft ν _max during the test is fixed in block (5) on the basis of the specified characteristics of standard single impacts during the test “for operation”, “for failure safety” according to the increment of the impact velocity ν (t) in locations of aircraft onboard equipment and is transmitted to the block (6). In block (6), ν _{max is} compared with the obtained value of the pulse velocity ν _ISM received from the output of block (4). If, as a result of the comparison, it was found that ν _meas <ν _max , then in block (7) a decision is made on whether the shock-marked level of the measured process belongs to the shock, this level remains in the recording of vibration measurements, and the transition to block (2) is carried out with the aim of further analysis for the presence of shock processes in the measurement information. If, as a result of the comparison, it was found that ν _meas > ν _max , then in block (7) a decision is made to exclude a sharply distinguished level from the measurement record, and this decision from block (7) is transmitted to block (8) in order to reject the distinguished level, after which the transition to block (2) is carried out for further analysis.

Thus, the sign of the belonging of sharply distinguished ordinates of the measured loads to the impact is not a mathematical interpretation of the ratio of such levels to the general population, which is all the ordinates of the loads, but the physical value of the speed calculated according to these distinguished levels. Moreover, if the calculated speed is higher than the normative limit obtained from the impact parameters acceptable for aircraft, then such distinguished levels are excluded from further processing and are considered gross measurement errors, and if the velocity is lower than the normative limit, then such levels are considered to be impacts and are subject to further processing.

Claims (1)

A method for isolating shock processes from dynamic loads, including measuring vibration loads at the aircraft on-board equipment locations using vibration transducers, recording measurement information to a recorder, characterized in that the recorded information is reproduced in the form of ordinal vibration acceleration centered relative to the mathematical expectation with obtaining a time record this measurement information during the measurement of vibration loads, identify sharply distinguished levels of ordinates of vibration acceleration of the measured loads, determine the time interval of each distinguished level between the points of intersection of the selected pulse with the time axis of the recording, determine the pulse speed in the form of the product of the numerical value of the ordinate of the sharply distinguished level of vibration acceleration of the pulse by the value of the time interval, compare the obtained value of the pulse speed with a predefined allowable limit of the magnitude of the impact impulse velocity for the aircraft structure of the apparatus and make a decision about the impact of a sharply distinguished level of the measured process, provided that the pulse speed is less than the set limit, and rejection of the allocated level, if the pulse speed is greater than the set limit, while the allowable limits of the impact pulse speed for the aircraft design are determined based on regulatory requirements for the load in the attachment points of the equipment to the design of the aircraft during impact testing and character Teak reference impact.

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