RU2682582C1 - Device of contactless excitation of the mechanical vibrations - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to acoustics. Device of the contactless excitation of the mechanical vibrations contains a loudspeaker and a horn. Surface of the horn is a curvilinear surface of constant negative curvature with a forming line in the shape of a tractor, the horn is fixed by a wide part on the loudspeaker case, the narrow part of the horn smoothly passes into the cylindrical nozzle directed to the surface being excited, and the ratio of the length of the horn to the diameter of the loudspeaker is in the range of 1.4–1.6, with the loudspeaker mounted on a height-adjustable stand that can be rotated relative to the vertical and horizontal axes. Horn surface is a Lobachevsky pseudosphere.

EFFECT: technical results are expanding the range of loudspeakers used, reducing the lower limit of the operating frequency range, better acoustic matching of the loudspeaker as a resonator with the open space of the horn outlet.

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Description

The scope of the non-contact excitation of mechanical vibrations is the determination of the basic dynamic characteristics of structures during ground frequency tests (LFI) in aircraft, rocket engineering, transport engineering, shipbuilding, instrument making, etc.

The invention relates to measuring technique and is intended to provide a given external impact in the form of harmonic, random, pulsed and other types of vibrations on the test object and to provide the necessary boundary conditions when measuring the dynamic characteristics of mechanical structures by conducting ground frequency tests (LFR). The main objective of the NCHI is to determine the basic dynamic characteristics - the spectrum of natural frequencies (in a given frequency range), shapes, damping coefficients and generalized masses of natural tones. The purpose of the NCHI is to create a frequency passport (certificate), verify and correct the calculated dynamic circuit of the test structure or its components, compare the dynamic characteristics of the full-scale structure and its model, control the compliance of the characteristics of materials and structures with the specified requirements (P. Karlle, V. Malyutin A., Mamedov OS, Popovsky VN, Smyslov VI, Smotrov AV On modern methods of ground testing of aircraft in aeroelasticity - Transactions of TsAGI, issue 2708, 2012. - P. 1- 34).

When conducting an NPI, specialists of research enterprises and organizations of a high-tech complex, as a rule, use a set of electrodynamic type vibration pathogens with a constant field - a set of force exciters with different values of dynamic force, to excite vibrations. The force from the exciter to the test object is transmitted using a special rod with an elastic hinge that is directly attached to the test structure at the selected point (Mikishev G.N., Rabinovich B.I. Dynamics of thin-walled structures with compartments containing liquid. - M.: Mechanical Engineering , 1971. - S. 352-356; Shaker excitation tutorial. Considerations and Problems. Young Engineer's Program - IMAC 2001. - Structural Dynamics Research Laboratory. University of Cincinnati (Cincinnati, Ohio 45221-0072 USA), 2001. - C. 20 , 25).

The main disadvantages of the methods in which the exciter is mounted on the test structure or the movable element of the exciter is connected to the structure:

- the influence of the attached mass of the moving node of the exciter, which distorts (usually downward) the value of the determined frequencies of natural vibrations,

- the impact of the exciter traction on the tested structure, which consists in additional dynamic stiffness due to both the stiffness of the traction itself and the action of the induction resistance of the exciter electromagnetic system, including a magnet, magnetic circuit and a moving coil.

These circumstances impose restrictions not only on the weight and size parameters of the test objects, but also make it difficult to determine the dynamic characteristics of non-rigid structures.

The task of providing acceptable boundary conditions when conducting experiments to determine the dynamic characteristics of small-sized, light, and non-rigid elements of mechanical structures, as a result of which the influence of additional mass, stiffness and damping from the exciter is eliminated, comes down to the search for constructive solutions for non-contact excitation of vibrations.

The main three classes of devices for contactless excitation of mechanical vibrations are known, which are briefly described below.

Firstly, non-contact electromagnetic vibrators, which, for example, are used in experiments where the structure under test or its surface layer have good electrical conductivity. A structure with a conductive surface layer is placed in the area where an alternating electromagnetic field created by an external inductor installed at a distance from the test object (usually 1.0-3.0 mm) leads to mechanical resonance causing vibrations of the test structure ( Bad M., Ferrari V., Marioli D. Contactless excitation of MEMS resonant sensors by electromagnetic driving. - Proceedings of the COMSOL Conference 2009 Milan (October 14-16, 2009, Milan, Italy), 2009 [Electronic resource] URL: https: //www.comsol.ru/paper/download/44961/Bau.pdf (accessed October 20, 2017); Brennan SM, Bronowicki AJ, Ryan PJ, Simonian SS, Hurst WE, Mc Monagle R., Sweeney RJ (Northrop Grumman Space Technology). Control Structure Interaction Testbed: Passive Isolation, Simulation & Test. - AIAA 2006-1834. - Proceeding of 47 ^th AIAA / ASME / ASCE / AHS / ASC Structures, Structural Dynamics, and Materials Conference (1-4 May 2006, Newport, Rhode Island), 2006 .-- C. 1-17).

The main disadvantage of such a constructive implementation of a non-contact method of creating an external force impact on the test structure is the requirement that it has an electrically conductive surface at the point of application of force.

Secondly, pneumatic exciters of mechanical vibrations, in which a continuous stream of compressed air passing, for example, in a special cylindrical chamber through a perforated rotating disk, is converted into a pulsating air stream, while the pulsation frequency of this stream is controlled by the angular velocity of rotation of the perforated disk (Di Maiol D., Magil F. Endurance tests performed using contact and contactless excitation methods: application to composites components. - Dynamic environmental testing. Proceedings of ISMA2014 including USD2014, 2014. - C. 753-766 or [Electronic resource] URL: http: / /past.isma-isaac.be/downloads/isma2014/papers/isma20 14_0668.pdf (accessed date: 10/20/2017)).

Among the main disadvantages of these analog devices, you can specify the following:

- the requirement for either a compressed air line at the test site or the presence of a container containing compressed air — a gas tank,

- cumbersome device pneumatic excitation of mechanical vibrations,

- the frequency range of the exciting force limited from above (determined by both the speed of rotation of the perforated disk and the compressibility of the air), usually up to 100 Hz.

Thirdly, acoustic exciters, where the basis is a loudspeaker. This approach to solving the problem of eliminating the influence of additional mass, stiffness and damping from the exciter on the measured characteristics is most common because of the apparent simplicity of the technical implementation. This class of devices for contactless excitation of mechanical vibrations can be divided into three types according to the complexity of practical implementation and design, that is, the equipment of an acoustic signal source — a loudspeaker with additional accessories, devices, devices, instruments, etc. (Aldoshina I.A. Electrodynamic loudspeakers. - M. : Radio and communications, 1989. - 272 p .; Kutsenko AN, Raskita MA Methodological manual for the course "Electroacoustics and sound broadcasting. Part 1" Loudspeakers. - Taganrog: I Health TTI SFU, 2007. - 103 p.):

1) Acoustic pathogens, which are actually a single loudspeaker (a sound-emitting speaker or, according to GOST 16122-87, the loudspeaker head), the front side of which is placed in the immediate vicinity of the surface of the tested structure. An example is the long-term and numerous experiments of foreign scientists and engineers (for example, Cawley R. Defect location in structures by vibration technique. Dissertation. - Department of Mechanical Engineering. Bristol University, 1978. - C. 30-33; Parloo E. Application of frequency-domain system identification techniques in the field of operational modal analysis. Dissertation. - Faculteit Toegepaste Wetenschappen, Vrije Universiteit Brussel, Belgium, 2003 .-- C. 91-95, 220-222; Stults JA Computational Aeroelastic Analysis of Micro Air Vehicle with Experimentally Determined Modes. Thesis. Paper AFIT / GAE / ENY / 05-M23 - Department of the Air Force. Air University. Air Force institute of Technology. Wright-Patterson Air Force Base, Ohio, 2005.- C. 17-25 )

The disadvantages of such analog devices include the following:

- the coefficient of performance (COP) of the sound-emitting speaker is only 1-2%,

- the design of a single loudspeaker does not allow the formation of a given radiation directivity characteristic, which may lead to the impossibility of exciting all the tones of the natural vibrations of the tested structure in the range of interest,

- a single loudspeaker is structurally unsuitable for use as part of a standard set of equipment and devices designed to carry out low-frequency tests.

Operational Modal Analysis of a Wind Turbine Wing using Acoustical Excitation. - Application note BO 0500-11, 02/2002. - Denmark:

- C. 1-8;

F.,

Hagara M. Results and Experiences from the Application of Digital Image Correlation in Operational Modal Analysis. - Acta Poly-technica Hungarica, Vol. 10, No. 5, 2013. - C. 159-174).2) Acoustic pathogens, which are acoustic systems (containing one or more loudspeakers, filters, housing and other parts), designed for high-quality reproduction of music, the so-called “speakers” (Vanwalleghem J., De Baere I., Loccu-fier M ., Van Paepegem W. Practical aspects in measuring vibration damping of materials (Paper Ref: 2762) .- Proceeding of the 15th International Conference on Experimental Mechanics - ICEM 15 / Editors: JF Silva Gomes and Mario AP Vaz (Porto, Portugal, 22- July 27, 2012), 2012 .-- C. 1-10; Herlufsen H.,

Operational Modal Analysis of a Wind Turbine Wing using Acoustical Excitation. - Application note BO 0500-11, 02/2002. - Denmark:

- C. 1-8;

F.,

Hagara M. Results and Experiences from the Application of Digital Image Correlation in Operational Modal Analysis. - Acta Poly-technica Hungarica, Vol. 10, No. 5, 2013 .-- C. 159-174).

The disadvantages of acoustic systems as devices for non-contact excitation of mechanical vibrations are also: a wide directivity of radiation, which leads to the excitation of a wide range of tones of natural vibrations of the tested design, and the lack of adaptability of the designs of known acoustic systems to use as part of a standard set of equipment and devices designed to perform LFR.

3) Acoustic pathogens, which are specially designed devices, the sound source of which is a frameless (single loudspeaker) or a loudspeaker enclosed in a housing (acoustic system). In this case, the sound wave emitted by the loudspeaker, which creates external exciting force, passes through a special device that gives it the properties required by the developer (Vuye C. Measurement and modeling of sound and vibration fields using a scanning laser Doppler vibrometer. - Faculteit Ingenieursweten-schappen, Vrije Universiteit Brussel , Belgium, 2011 - C. 26-27; Marquez-Chisolm DJ Natural frequencies and mode shapes of a nonlinear, uniform cantilevered beam. Thesis. Paper AFIT / GAE / ENY / 06-S06 - Department of the Air Force. Air University. Air Force Institute of Technology. Wright-Patterson Air Force Base, Ohio, 2006. - C. 16-19), for example, the ability to target a selected location of a test structure (Garcia Lopez JF, Knec hten T., Pluym L., Kazanci Deblauwe MV, Tekeli A. Contactless acoustic excitation for experimental modal analysis in composite components. - Proceeding of the 21 ^st International Congress on Sound and Vibration - ICSV21 (13-17 July 2014, Beijing, China ), 2014 .-- C. 1-8).

The main disadvantage of these devices is the requirement for a special rack to which a sound-emitting nozzle (horn) is attached, which makes it difficult to place a contactless power exciter when creating an NCH test bench, requires the use of lifting equipment or additional special devices, that is, these analog devices without contact excitation of mechanical vibrations do not adapted for use as part of a standard set of equipment and devices designed to perform NCHI.

The closest technical solution adopted for the prototype is a non-contact excitation device for mechanical vibrations that provides point excitation of vibrations of the studied structure (Gunawan L. Experimental Study of Nonlinear Vibrations of Thin-walled Cylindrical Shells. Proefschrift. - Faculty of Aerospace Engineering, Delft University of Technology , Delft, The Netherlands, 1998 .-- C. 41-56). This device is a ∅0250 mm loudspeaker equipped with a horn representing a 490 mm cone with a generatrix line of exponential shape; a cylindrical nozzle is attached to the narrow part of the horn, the free end of which is located at a distance of 25 mm from the excited surface of the test structure; moreover, the horn is widely attached to the speaker housing, that is, the loudspeaker is enclosed in a closed rectangular wooden case, lined with vibration-damping material from the inside, and the loudspeaker diffuser has the shape of a straight cone.

The main disadvantages of the prototype device:

- inability to use in conditions of LFD, for example, the lack of mechanical interface with devices used in standard LFDs intended for mounting vibration excitation devices (trunnions, seismic suspension racks (the so-called "cribs"), height-adjustable racks for installing exciters under the product and other)

- incomplete acoustic matching of the loudspeaker, as a resonator, with the open space of the outlet of the exponential speaker, which can lead to beating and nonlinear distortions of the sound wave, which should excite vibrations of the tested structure,

- the lower limit of the working frequency range (cutoff frequency) is 280 Hz, which does not allow to excite natural (resonant) frequencies in a wide class of structural elements, for example, aircraft propeller blades and their models, the lowest natural frequencies of which lie in the range of 5-15 Hz .

The technical result of the proposed invention is the maximum adaptability of the application (mechanical pairing) of a non-contact excitation device for mechanical vibrations to a standard set of equipment and devices designed to perform LFD, first of all, the possibility of fixing the developed device in the axle of the exciter, as well as the convenience of transporting the device (including in assembled form) and handling it during assembly, commissioning of the test bench, its dismantling, which is determined It is due to the small weight and size parameters of the developed device, reducing the cost of testing equipment and reducing the complexity of the NCHI.

The technical result is also the expansion of the range of speakers used (the presence or absence of their housing, the shape of their diffusers, the dimensions of the outer diameter of the speaker) and lower the lower limit of the working range of operating frequencies; better acoustic matching of the loudspeaker, as a resonator, with the open space of the mouth outlet.

The technical result is achieved by the fact that in a non-contact excitation device of mechanical vibrations containing a loudspeaker and a horn, the horn surface is a curved surface of constant negative curvature with a generatrix line in the form of a tractor, the horn is wide mounted on the loudspeaker body, the narrow part of the horn smoothly passes into a cylindrical nozzle directed to the surface to be excited, and the ratio of the length of the speaker to the diameter of the speaker is in the range 1.4-1.6, and The micro-speaker is mounted on a height-adjustable stand with the possibility of rotation relative to the vertical and horizontal axes.

The surface of the horn is the Lobachevsky pseudosphere.

The invention is illustrated by figures, which depict the following.

In FIG. 1 is a sketch of a horn whose surface is a curved surface of constant negative curvature with a generatrix line in the form of a tractor.

In FIG. 2 shows a schematic representation of the main elements of the proposed device in one of the acceptable options for the technical implementation of its fastening on a height-adjustable stand with the possibility of rotation relative to the vertical and horizontal axes.

In FIG. Figure 3 shows a photograph of one of the possible applications of a non-contact excitation device for mechanical vibrations.

For non-contact excitation of vibrations of the tested design, the developed device (Fig. 2), for example, containing a single loudspeaker 1, mounted in an annular latch 2 by a bolt connection 3, and the annular latch on both sides is provided with shafts 4, which are clamped by bolts 5 in which the latch with the loudspeaker rotates around the horizontal axis of the standard axle 6 of the exciter; the trunnion can be hung on a lifting mechanism or screwed to a platform of a height-adjustable stand 7, with the possibility of a loudspeaker 1 installed in the latch 2, rotate around a vertical axis; the standard rack at the same time is equipped with telescopic 10

supports the tripod 8, equipped with a control wheel 9 for selecting the required height of the rack rod 10, and on the front side of the loudspeaker body 1 a horn 11 is fixed with bolts 12. The horn 11 is wide mounted on the loudspeaker body 1, the narrow part of the horn 11 smoothly passes into a cylindrical nozzle, directed to the surface to be excited. The ratio of the length of the speaker 11 to the diameter of the speaker 1 is in the range 1.4-1.6.

The horn is a shell in the form of the Lobachevsky pseudosphere (Fig. 1), that is, a curved surface of constant negative curvature (Ignatyev Yu.G. Differential geometry of curves and surfaces in Euclidean space. Study guide. IV semester. Kazan: Kazan University, 2013. - S. 179-187; Kolbrek B. Horn Theory: An Introduction, Part 2. - AudioXpress (www.audioXpress.com), 2008. - P. 3), obtained by rotating the tractor along the axis of symmetry of the speaker, while achieving acoustic matching the loudspeaker as a resonator with open space Twomey outlet speaker from which the sound wave without beats and non-linear distortions oscillates the test structure.

In the embodiment of FIG. In the 3rd version of the application of the non-contact excitation device for mechanical vibrations, the standard axle of the power exciter Prodera EX58 (Exciter EX58. Data sheet No. 94/1005-b. -Vibration shakers [Electronic resource] URL: http://www.prodera.com/uk/amplificateur is used. htm (accessed date: 03/26/2009). When using loudspeakers of other sizes, trunnions of other exciters can be used or made to satisfy the conditions described above.

When conducting LFD to excite oscillations, the proposed device is placed in close proximity to the test structure, directing the nozzle to a selected point on the surface.

In the transport position, the developed device is disconnected from the trunnion and placed in a separate box. Due to the small dimensions of the non-contact excitation of mechanical vibrations, such a package is one baggage claim.

Significant features (distinguishing features) of the claimed invention were implemented in a specific device operated by TsAGI, with which a number of experiments were carried out to determine the dynamic characteristics of the following structures:

- a power composite beam of the fuselage floor of a promising Russian near-medium-haul passenger aircraft,

- a series of saber-shaped blades of the model of 8-bladed propeller of a promising aircraft engine,

- structurally similar steering model of the product X-22,

- a set of large-scale demonstrator models (full-sized) helicopter tail rotor blades.

The result of the trial operation of the developed device was the confirmation of the above technical results.

Claims (2)

1. The device of non-contact excitation of mechanical vibrations, comprising a loudspeaker and a horn, characterized in that the horn surface is a curved surface of constant negative curvature with a generatrix line in the form of a tractor, the horn is wide mounted on the loudspeaker body, the narrow part of the horn smoothly passes into a cylindrical nozzle, directed to the surface to be excited, and the ratio of the length of the horn to the diameter of the loudspeaker is in the range 1.4-1.6, and the loudspeaker is fixed ene in a height-adjustable rack pivotable about vertical and horizontal axes. 2. The device according to claim 1, characterized in that the surface of the horn is a Lobachevsky pseudosphere.

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