Contactless Excitation of Vibrations of Light Composite Structures Ground Vibration Testing

Testing of the Flying Vehicles Composite Structures Elements


Аuthors

Smotrov A. V.

Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI), 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia

e-mail: andrey.smotrov@tsagi.ru

Abstract

Ground-based vibration testing is a special technological process, during which dynamic characteristics of the mechanical structures are being determined in the assigned frequency range, primarily spectrum of the resonant (close to natural) frequencies, mode shapes, modal damping factorы and generalized masses of the vibration tones. The purpose of such tests consists in creating a frequency passport (certificate), verifying and correcting the test object computed dynamic scheme or its aggregates, comparing dynamic characteristics of the full-scale structure and its model, and monitoring characteristics compliance with the specified requirements. For the external harmonic force application, the electrodynamic type exciters with constant field (vibrators), the force from which is being transmitted to the test object by the special rod with elastic hinge, fixed directly in the selected point of the load, are employed as a rule. The traditional method of contact excitation of vibrations by the attached vibrators has a number of disadvantages for the objects of low specific gravity. Despite modernization of both vibrators themselves (application of rare-earth magnets and and lightweight coils) and application of the force sensors, physical contact inevitably distorts the inertial-and-rigidity properties of the object. To start with, it is worth noting the the additional attached mass and additional rigidity occurrence, the presence of parasitic damping, the existing nonlinear electromagnetic effects in the coil circuit, as well as possible frequency losses in the extended cable lines. This problem is being solved by implementing a non-contact vibration excitation method, which was demonstrated by comparative ground-based vibration testing of the dynamically similar model of a rotor blade from the polymer composite materials. The experiments were conducted by three methods:

1) standard procedure, where attached vibrators and contact sensors (accelerometers) are being employed;

2) a completely contactless method, in which the excitation is being performed with an impact hammer or a special contactless device, while measurement is being conducted with the laser Doppler vibrometer;

3) a “hybrid” method when vibrations are being excited by an attached vibrator, and their measurement is being performed contactless.

Analysis of the obtained results confirmed that the “contact” excitation creates additional parasitic stiffness in the vibrator-rod-structure system when measuring vibrations with a laser vibrometer, which was clearly demonstrated by the increase in the frequency values of the five lowest tones. At the same time, application of the standard “contact” technique leads to a general underestimation of resonant frequencies due to the attached masses of sensors and their cables. The patterns of the mode shapes (nodal lines) herewith remained almost identical for all methods, which confirms the adequacy of the separation of the shapes themselves, but proves the absolute resonant frequency values incorrectness during the contact measurement. The errors elimination method  (the data extrapolation with two vibrators with various weight of the coils) applied by the colleagues is non-effective due to the high labor costs. The technology of fully contactless ground based vibration testing developed at TsAGI became an alternative and optimal solution. Application of the specialized device for the contactless excitation of mechanical vibrations paired with a laser vibrometer completely eliminates negative impact of the test equipment on the recorded data. This approach ensures high reliability of the results for the structures of any scale, from light rotor blades to full-size fuselage floor beams, opening a new frontier of precision in experimental aeroelasticity and strength.

Keywords:

ground vibration testing, electrodynamic type vibration exciters, rotor blade, polymer composite materials, resonant vibration frequency

References

  1. Karkle PG, Malyutin VA, Mamedov OS, Popovsky VN, Smotrov AV, Smyslov VI. On modern methods of ground testing of aircraft in aeroelasticity. Trudy TSAGI. 2012;2708:1-34. (In Russ.).

  2. Templeton JD, Buehrle RD, Gaspar JL, et al. Ares I-X launch vehicle modal test measurements and data quality assessments. In: Proulx T. (ed) Structural Dynamics. Vol. 3. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, New York; 2011. p.1017-1027. DOI: 10.1007/978-1-4419-9834-7_90

  3. Karkle PG, Smyslov VI. Modal tests of aircraft and reproduction of force effects. Moscow: Technosphere; 2017. p. 40-62. (In Russ.).

  4. Dolgopolov AV, Kazancev DA, Markin IV, et al. The modern method of creating dynamically scaled models to study aircraft flutter characteristics. Uchenye Zapiski Kazanskogo Universiteta. Seriya Fiziko-Matematicheskie Nauki. 2020;162(4):441-454. (In Russ.).

  5. Kolesnikov KS, Alexandrov DA, Astashev VK, et al. Dynamics and strength of machines. Theory of mechanisms and machines. In: Mechanical engineering: Encyclopedia. Moscow: Mashinostroenie; 1994. Vol. 1-3. Book 1. p. 389-393.

  6. Olejnik A, Kachel S, Rogólski R, et al. Technology of Ground Vibration Testing and its application in light aircraft prototyping. MATEC Web of Conferences. Vol. 304. 9th EASN International Conference on “Innovation in Aviation & Space” (September 3-6, 2019; Athens, Greece). 2019;304:01005. DOI: 10.1051/matecconf/201930401005

  7. Digital industries software. Aircraft ground vibration testing. Enhancing the efficiency of aircraft structural dynamics testing. Paper 81896-D4 1/22 A, 2022. URL: https://www.sw.siemens.com/en-US/

  8. Mikishev GN, Rabinovich BI. Dynamics of thin–walled structures with compartments containing liquid. Moscow: Mashinostroenie; 1971. p. 352-356. (In Russ.).

  9. Mezhin VS, Obukhov VV. The comparative analysis of experimental methods of spacecraft structure dynamic finite element models verification. Space Engineering and Technology. 2016;(4):14-23. (In Russ.).

  10. Berns VA, Zhukov EP, Lakiza PA, et al. Practice of Aircraft Structures Health Monitoring During Vibration Testing. Aerospace MAI Journal. 2024;31(4):113-122. (In Russ.).

  11. Sobolev EI. (comp.) Theory of ground frequency tests. Referaty TsAGI. 1967(221):18-22. (In Russ.).

  12. Smyslov VI. On experimental methods for studying the vibrations of aircraft. Trudy TsAGI. 1970(1217):36-39. (In Russ.).

  13. Vasiliev KI, Smyslov VI, Ulyanov VI. Experimental investigation of elastic vibrations of aircraft using AVDI-1H multichannel equipment. Trudy TsAGI. 1975(1634):21-25. (In Russ.).

  14. Vasiliev KI. Methodology and results of the study of electrodynamic force exciters. Trudy TsAGI. 1983(2160):100-127. (In Russ.).

  15. Varoto PS, de Oliveira LPR. Interaction between a vibration exciter and the structure under test. Sound and vibration. 2002(36):20–25

  16. Peres MA, Bono RW. Modal testing excitation guidelines. Sound and vibration. 2011;45(11):8–12.

  17.  Prodera modal analysis systems and software. URL: http://www.prodera.com/uk/prodera_software.htm

  18. Ewins DJ. Modal testing: Theory and practice. Taunton (Somerset, England): Research Studies Press Ltd.; 1985. p. 113–117.

  19. Berns VA, Dolgopolov AV, Zhukov EP, et al. Experimental modal analysis of aircraft. Novosibirsk: NGTU; 2017. p. 18–23.

  20. Bryukhanov YuA, Lukashevich YuA. Nonlinear distortion of harmonic signals during quantization. Radiotekhnika. 2009(10):57–60.

  21. Gritsutenko SS. Quantization of sine signals. Vestnik IzhGTU im. M.T. Kalashnikova. 2010(4):173–176.

  22. Yakushev AY, Sereda AG, Vasilenko MN, et al. Analysis of electromagnetic processes in a homogeneous long line. Elektrotekhnika. 2017(10):23–28.

  23. Smotrov AV, Smotrova SA, Zaytsev MV, et al. Noncontact ground vibration test technology for composit elements of propulsion systems and engine-propeller units of aircrafts. Materialy Mezhotraslevogo seminara pamyati professora T.D. Karimbaeva “Primenenie kompozitsionnykh materialov v dvigatelestroenii” (September 12-14, 2023; Moscow). Moscow: CIAM; 2023. p. 58- 60.

  24. Agarkov AV, Mishakov NM, Smotrova SA, et al. Device of contactless excitation of the mechanical vibrations. Patent RU 2682582 C1. Bull. 8, 19.03.2019. (In Russ.). 

  25. Betkovskij JJ, Vershinin GA, Chupin IP. Method for experimental detection of frequencies and generalised masses of internal oscillations of tested object. Patent RU 2499239 C1. Bull. 32, 20.11.2013. (In Russ.).  

mai.ru — informational site of MAI

Copyright © 1994-2026 by MAI