GB2145520A - Method of forming random vibration spectrum and device therefor - Google Patents
Method of forming random vibration spectrum and device therefor Download PDFInfo
- Publication number
- GB2145520A GB2145520A GB08322500A GB8322500A GB2145520A GB 2145520 A GB2145520 A GB 2145520A GB 08322500 A GB08322500 A GB 08322500A GB 8322500 A GB8322500 A GB 8322500A GB 2145520 A GB2145520 A GB 2145520A
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- random
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- vibration
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- shaper
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/12—Analysing solids by measuring frequency or resonance of acoustic waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
- G01N29/348—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with frequency characteristics, e.g. single frequency signals, chirp signals
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Acoustics & Sound (AREA)
- Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
Abstract
A method of forming a random vibration spectrum comprises the steps of firstly causing vibration of an article (1) under test in a predetermined frequency range by the use of a variable-frequency harmonic oscillator (10) and then using a multichannel random signal shaper (4) to set characteristic values of spectral vibration acceleration density at each chosen check point on the article (1) in each band of the predetermined frequency range, a random output signal level kn in each channel being computed by solving a set of linear equations. A device for accomplishing the method comprises the multichannel shaper (4) connected to a vibrator (2) mounting the test article (1); vibration pick-ups (3) secured at the check points and connected through a switch (12) to a signal analyzer (13); a unit (16) for setting parameters of a formed random vibration spectrum, and a control unit (17). The device also comprises oscillator (10) and a memory unit (14) connected thereto. A computing unit (15) receives inputs from units (14) and (16) and is connected to the control inputs of adjustable amplifiers (7) in shaper (4). A gate (9) is controlled by unit (17) to pass firstly signals from oscillator (10) to the vibrator and their signals from shaper (4). <IMAGE>
Description
SPECIFICATION
Method of forming random vibration spectrum and device therefor
The present invention relates to strength tests and in particular to vibration tests of articles.
More specifically, it concerns with methods and devices for forming a random vibration spectrum. It may be used to best advantage in laboratory tests of complex articles having flexible structure and limited dimensions, which are installed on moving objects and subjected to random vibration in operation, for example, in aviation and rocket fields, machine building, automobile industries and the like.
The invention resides in that in a method of forming a random vibration spectrum comprising the steps of choosing check points on an article under test, said points being characterized by certain values of spectral vibration acceleration density in each band of a predetermined frequency range, causing vibration of the article in the predetermined frequency range by the use of a multichannel random signal shaper, each channel thereof having an intrinsic amplitudefrequency response and an adjustable random output signal level, checking parameters at the check points in each of said frequecy bands, and subsequently using the obtained vibration data and said values of spectral vibration acceleration density to compute the random output signal levels in each channel of the multichannel shaper, the total value thereof characterizing the formed random vibration spectrum, according to the invention, vibrations of the article in the predetermined frequency range are preliminarily set up by the use of harmonic variablefrequency oscillations, characteristic values of spectral vibration acceleration density being set at each check point on the article under test in each band of the predetermined frequency range, an amplitude-frequency response of a "vibrator-article" system being chosen as a vibration parameter to be checked, the subsequent step being computation oF the random output signal levels kn in each channel of the multichannel shaper by solving a set of linear equations of the form
where q, is a preset value of spectral vibration acceleration density at the Ith check point in the nth frequency band of the predetermined frequency range, the coefficient an, at the Ith check point in the ith frequency band for the nth channel of the multichannel shaper being computed from the formula
where (pn('L') is the amplitude-frequency response of the nth channel of the multichannel shaper; th(w) is the amplitude-frequency response of the "vibrator-article" system at the Ith check point on the article under test; and Açj is the ith band of the predetermined frequency range, the sum of random output signals having the levels k, being used to determine a random signal utilized to form a predetermined random vibration spectrum.
The invention also resides in that a device for forming a random vibration spectrum comprising a multichannel shaper having several channels, each of which includes such seriesconnected components as a white noise generator, a bandpass filter and an adjustable amplifier, the outputs of all the adjustable amplifiers being connected to the inputs of an adder whose output is connected to the input of a power amplifier, the output of which is, in turn, connected to the input of a vibrator mounting the article under test, vibration pick-ups being mounted at check points on said article, said vibration pick-ups representing means for converting mechanical oscillations into an electrical signal, the outputs of said converting means being connected to the inputs of a switch connected to an analyzer, a unit for setting parameters of a formed spectrum, and a control unit having the first input thereof connected to the control input of the switch, according to the invention, includes a variablefrequency harmonic oscillator whose output is connected to a gate inserted between the output of the adder and the input of the power amplifier and connected to the second output of the control unit, and a memory unit having its output connected to a computing unit whose second input is connected to the unit for setting parameters of a formed spectrum, while the third input thereof is connected to the first output of the control unit connected to the control inputs of the harmonic variable-frequency oscillator and the memory unit, whose second input is connected to the output of the harmonic variable-frequency oscillator and to the output of the analyzer representing an amplitude detector, one output of the computing unit being connected to the input of the adjustable amplifier in each channel of the multichannel random signal shaper, while the other output thereof is connected to the third input of the memory unit.
The method and device for forming a random vibration spectrum accordng to the invention permit obtaining a desired vibration spectrum at several check points on an article under test using one vibrator.
The invention will now be described further with reference to a specific embodiment thereof, taken in conjunction with the accompanying drawings, wherein:
Figure 1 is a block diagram of a device for forming a random vibration spectrum according to the invention; and
Figure 2 is a functional diagram of the device of Fig. 2 according to the invention.
The proposed method of forming a random vibration spectrum essentially consists in the following.
Check points are chosen on an article 1 (Fig. 1) under test, for example, two check points (a and b) determined as a result of analysis of vibration of the article 1 in operation and having different values (q) of spectral acceleration density in a frequency range also found during inservice analysis. If an article being designed is to be tested, the check points a and b may be chosen with due regard for specific conditions set by the designers. For example, the check points a and b may be attachment points and portions of the article 1 particularly sensitive to vibration.
Providing a characteristic value (q,) of spectral vibration acceleration density at each check point (a and b) in each band of a predetermined frequency range allows performing laboratory tests of articles in conditions resembling to a greater extent actual operating conditions.
The article 1 to be tested is secured to a vibrator 2, for example, an electrodynamic or electrohydraulic vibrator. Vibration pick-ups 3 (meand for converting mechanical oscillations into an electrical signal) are secured at the check points a and b on the article 1 under test. The number of the vibration pick-ups corresponds to the number of the check points. Vibration of the article 1 is caused by a multichannel shaper 4 wherein each channel has a characteristic amplitude-frequency response (pn(CO) and an adjustable random output signal level k where n is the number of the channel. Narrow-band random signals of all channels form a sum signal used to cause vibration of the article 1 under test in a desired spectrum.
To determine the required random output signal level kn in each channel of the multichannel shaper 4, vibration of the article 1 under test is preliminarily caused by harmonic oscillations at à continuously variable frequency in a predetermined frequency range. The amplitude-frequency response (o) of the "vibrator-article" system is successively measured at each I-th check point.
The use of the amplitude-frequency response Ik(w) as a vibration parameter under check makes it possible to utilize harmonic analysis which is simplier and more accurate than a random signal analysis.
The next step is to solve a set of linear equations of the form
where q is a preset value of spectral vibration acceleration density at the Ith check point in the ith band of the predetermined frequency range, the coefficients of the set of linear equations, an,;, being determined from the formula
Computing the random output signal level kn in each channel of the multichannel shaper 4 permits obtaining characteristic values q, of spectral vibration acceleration density at each check point on the article under test in all bands of the predetermined frequency range.
The above equations are derived from the known relationships (cf. the cited publication): G,fev) =
where G,(w) is a signal spectrum at the input of the "vibrator-article" system, which is formed by the multichannel shaper; G,(Ç) is a spectrum at the output of the "vibrator-article" system, for example, at the Ith check point; q, is spectral acceleration density, for example, at the Ith check point in the ith frequency band.
For the multichannel spectrum the random output signal spectrum being an input spectrum for the "vibrator-article" system is as follows:
where No is a random signal level of a noise source 5, which is constant in the predetermined frequency range (it may be taken to be unity); and kn is the gain of the nth channel of the shaper 4, which determines its random output signal level at No = 1 and tZ)n (w)max = 1.
Hence, we get
The proposed method of forming a random vibration spectrum substantially increases accuracy in testing articles for random vibrations, whereby testing conditions resemble to a greater extent actual operating conditions.
The method of forming a random vibration spectrum in compliance with the invention will now be illustrated by the following example in which values of an output signal level are computed in each channel of the multichannel random signal chapter 4.
Assume that the task is to form a random vibration spectrum for testing the blade of a gasturbine engine. Relative values of spectral vibration acceleration density are set at two check points (a and b) on the blade under test in a relative frequency range, for example, from 0.2 to 2 covered in three bands: 0.2-0.8; 0.8-1.4; 1.4-2 - q1, = = 0.18; q" = 0.41; q,3 = 0.53; q2, = 0.46; q22 = 0.5; q23 = 0.34.
In the predetermined relative frequency range random vibrations of the blade are caused by the multichannel shaper 4 having, for example, six channels.
Each channel has a characteristic amplitude-frequency response (pn(CO)
where w, = 0.3; 0.6; 0.9; 1.2; 1.5; 1.8, and an adjustable output signal level kn.
It is necessary to compute the values of k0 which would ensure desired parameters of a vibration spectrum being formed.
The initial step is to cause vibration of the article 1 by the use of a harmonic signal at a continuously variable frequency in the relative frequency range from 0.2 to 2, the subsequent step being measurements of the amplitube-frequency response + ) at the two check points a and b on the blade.
Assume that the measurements yield (w)= O. 1 = O. 1 + 0,4 (w) = 1 3w The next step is to compute the coefficients an,
similarly, referring to tormula (2) we compute the other coettlclents
Then a set of the following equations will be solved: 0,145 K2 +0,202K22 + 0,096K2 + 0,03K2 + 0,014K25 + 0,008K2 = = 0,18; 0,034K21+O,09K22+0,277K23+0, + 0,354K24 + 0,162K25 + 0,05K26 = 0,41; 0,016K2i+0,026 K2 + 0,05 K3 + 0,133 K24+0,409 K25+0,505K26= = 0,53; 0,484 K2 + 0,526 K2 + 0,225 K23+0,073 K24+0,035 K25 +0,02 K2 = 0,46; 0,046 K2 + 0,126 K2 + 0,385 K2 + K2i+0, K24 + 0,176 176 + + 0,05 K2 = 0,5;+O,05K26=0,5; 0,01 K21+0,017 K2 + 0,034 K23+0,094 K24+0,286 K25+ + 0,3 K26=O,34.
Solving the above set of equations yields the values of th output signal level in each channel of the multi-channel random signal shaper 4: K2 =0.005; K2 = 0.65;
K23=0.21; K2 = 0.6; K25=0.33;
K26 = 0.67
At the output of the multichannel random signal shaper 4 we shall have the spectrum G0(#) = #Kn2 #n2(#n2), n=1 which ensures desired values of q of spectral vibration acceleration density in each check point (a, b) in each of the three bands of the predetermined frequency range.
Turning now to Fig. 1 the device for forming a random vibration spectrum accordng to the invention comprises such series-connected components as a white noise generator 5, a bandpass filter 6 and an adjustable amplifier 7 in each channel of the multichannel shaper 4. To enable better understanding of the design of the proposed device for forming a random vibration spectrum, the block diagram of Fig. 1 shows the multichannel shaper 4 with only two channels
I and Il. The outputs of all the adjustable amplifiers 7 are connected to the inputs of an adder 8 having its output connected to one of the inputs of a gate 9 whose other input is connected to a variable-frequency harmonic oscillator 10.The output of the gate 9 is connected to a power amplifier 11 which is connected to the input of a vibrator 2 mounting the article 1 under test, vibration pick-ups 3 being secured at check points a and b on said article. The outputs of all the vibration pick-ups 3 are connected through a switch 12 to an amplitude detector 13 whose output is connected to one of the inputs of a memory unit 14. Connected to the same input is the variable-frequency harmonic oscillator 10. The output of the memory unit 14 is connected to one of the inputs of a computing unit 15 whose other input is connected to a unit 16 for setting parameters of a formed random vibration spectrum. Connected to the third (control) input of the computing unit 15 is the first output of a control unit 17, the same output of the control unit 17 being connected to the control inputs of the variable-frequency harmonic oscillator 10, the memory unit 14 and the switch 12. The second output of the control unit 17 is connected the control input of the gate 9. One of the outputs of the computing unit 15 is connected to the inputs of the adjustable amplifiers 7 in all the channels, while the other output thereof is connected to the third input of the memory unit 14.
The device for forming a random vibration spectrum according to the invention operates as follows.
A control signal from the control unit 1 7 transfers the device into a "tuning" mode. In this case the output of the variablefrequency harmonic oscillator 10 is connected to the input of the power amplifier 11 through the gate 9. Simultaneously a control signal from the output of the control unit 1 7 triggers the variable-frequency harmonic oscillator 10, its output signal being applied through the power amplifier to the input of the vibrator 2, thus causing harmonic oscillations of the article 1 under 1, and to the control input of the switch 1 2 which alternately connects the vibration pick-ups 3 to the input of the amplitude detector 1 3. The output signals of the amplitude detector 1 3 are the measured values of the amplitude-frequency responses Ih(w) of the "vibrator-article" system at the check points a and b on the article 1 under test, which are stored in the memory unit 14 in conjunction with the current frequency of the variable-frequency harmonic oscillator 10. The memory unit 14 also stores the amplitudefrequency responses zPn(X) of the bandpass filters 6 of the multichannel shaper 4.
Before measurements in the "tuning" mode, the signal from the first output of the control unit 1 7 is fed to the control inputs of the memory unit 14 and the computing unit 1 5 to set them to the initial state.
On completion of measurements of the amplitude-frequency responses + ) at each check point a, b, the output signal of the memory unit 14 comes to the input of the computing unit 1 5. The computing unit 1 5 successively computes the coefficients an using formula (2) and the obtained values are stored in the memory unit 14. After the coefficients an, are computed, all values of an, are supplied to the input of the computing unit 1 5. Simultaneously the other input of the computing unit 1 5 accepts the output signal of the unit 16 for setting parameters of a formed random vibration spectrum in the form of q,.
Thereafter the computing unit 1 5 solves the set of linear equations (1) and computes the gain k0 of the adjustable amplifiers 7. The computation over, the control unit 17 disconnects the variable-frequency harmonic oscillator 10 from the input of the power amplifier 11 and connects thereto the output of the multichannel shaper 4, thereby transferring the device to the "testing" mode.
In the "testing" mode wide-band random signals having uniform spectral power density in a predetermined frequency range are applied from the outputs of the white noise generators 5 to the inputs of the bandpass filters 6 which pass to their output only those components of the wide-band random signal which are within the transmission band thereof. The output signals of the bandpass filters 6 come to the inputs of the adjustable amplifiers 7 whose gain has been set using the computed and fixed values of kng The random output signals of channels I and II of the multi-channel shaper 4 are fed to the inputs of the adder 8 whose output signal is applied through the gate 9 and the power amplifier 11 to the input of the vibrator 2, thus causing random vibration of the article 1 in a desired vibration spectrum.
The use of the variable-frequency harmonic oscillator 10 to the proposed device has made it possible to measure amplitude-frequency responses rh(w) of the "vibrator-article" system at check points by the use of a conventional amplitude detector 1 3 having a small integration contact, an advantage eliminating the need for such an intricate unit as a multichannel random signal analyzed. Thus, no stringent requirements are placed for squareness and similarity of amplitude-frequency responses (p0(w) of bandpass filters in shaper channels and of band pass filters in similar channels of an analyzer, which generally eliminates a control error. So, the device forming the subject of the invention permits both obtaining characteristic values ql of spectral vibration acceleration density at each check point on an article under test using one vibrator and solving more accurately the problem of forming a random vibration spectrum at one check point in bands of a predetermined frequency range.
Claims (4)
1. A method of forming a random vibration spectrum comprising the steps of preliminarily causing vibration of an article in a predetermined frequency range by the use of variablefrequency harmonic oscillations and selecting check points on the article under test, said check points having characteristic values of spectral vibration acceleration desity in each band of the predetermined frequency range, the next step being the setting of characteristic values of spectral vibration acceleration density at each check point on the article under test in each band of the predetermined frequency range whereupon the article is subjected to vibration in the predetermined frequency range by the use of a multichannel random signal shaper wherein each channel has a characteristic anzplitude-frequency response and an adjustable random output signal level, vibration parameters being subseqently checked at the chosen check points, said parameters representing the arnplitude-frequency responses of a "vibrator-article" system at said points, the final step being computation of random output signal levels k0 in each channel of the multichannel shaper by solving a set of linear equations::
where q, is a preset value of spectral vibration acceleration density at the Ith check point in the ith frequency band in the predetermined frequency range, the coefficient an, at the Ith check point in the ith frequency band for the nth channel of the multichannel shaper being computed from the formula
where cp,(w) is the amplitude-frequency response of the nth channel of the multichannel shaper; rC(w) is the amplitude-frequency response of the "vibrator-article" system at the Ith check point on the article under test; and Axj is the ith band of the predetermined frequency range, the sum of the random output signals having the levels k0 being used to determine a random signal utilized to form a desired random vibration spectrum.
2. A device for forming a random vibration spectrum comprising: a multichannel shaper having several channels, each of which includes such series-connected components as a white noise generator, a bandpass filter and an adjustable amplifier, and an adder having its outputs connected to the outputs of the adjustable amplifiers; a vibrator mounting an article under test, which is connected to the output of the adder through a power amplifier; vibration pickups secured at chosen check points, which represent means for converting mechanical oscillations into an electrical signal, the outputs of the vibration pick-ups being connected to the inputs of a switch connected to the input of an analyzer; a unit for setting parameters of a formed random vibration spectrum and a control unit having the first output thereof connected to the control input of said switch; the device being also provided with a variable-frequency harmonic oscillator; a gate connected to the output of said variable-frequency harmonic oscillator and inserted between the output of said adder and the input of said power amplifier, the control input of the gate being connected to the second output of said control unit; a memory unit having one of its inputs connected to the output of said variable-frequency harmonic oscillator and to the output of said analyzer representing an amplitude detector, and a computing unit whose first input is connected to the output of said memory unit, the other input of said computing unit being connected to said unit for setting parameters of a formed random vibration spectrum, one output of said computing unit being connected to the control input of said adjustable amplifier in each channel of said multichannel random signal shaper, while its second output is connected to the other input of said memory unit; said first output of said control unit being also connected to the control inputs of said variable-frequency harmonic oscillator, said memory unit and said computing unit.
3. A method of forming a random vibration spectrum substantially as hereinabove described with reference to and as shown in the accompanying drawings.
4. A device for accomplishing the proposed method of forming a random vibration spectrum substantially as hereinabove described with reference to and as shown in the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08322500A GB2145520B (en) | 1983-08-22 | 1983-08-22 | Method of forming random vibration spectrum and device therefor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08322500A GB2145520B (en) | 1983-08-22 | 1983-08-22 | Method of forming random vibration spectrum and device therefor |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8322500D0 GB8322500D0 (en) | 1983-09-21 |
| GB2145520A true GB2145520A (en) | 1985-03-27 |
| GB2145520B GB2145520B (en) | 1986-11-12 |
Family
ID=10547663
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08322500A Expired GB2145520B (en) | 1983-08-22 | 1983-08-22 | Method of forming random vibration spectrum and device therefor |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2145520B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100371692C (en) * | 2003-12-22 | 2008-02-27 | 欧洲直升机公司 | Device for indicating the vibration level of an apparatus |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1110156A (en) * | ||||
| GB927195A (en) * | 1960-08-15 | 1963-05-29 | Textron Electronics Inc | Improvements in vibration testing systems |
-
1983
- 1983-08-22 GB GB08322500A patent/GB2145520B/en not_active Expired
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1110156A (en) * | ||||
| GB927195A (en) * | 1960-08-15 | 1963-05-29 | Textron Electronics Inc | Improvements in vibration testing systems |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100371692C (en) * | 2003-12-22 | 2008-02-27 | 欧洲直升机公司 | Device for indicating the vibration level of an apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8322500D0 (en) | 1983-09-21 |
| GB2145520B (en) | 1986-11-12 |
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| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |