Laser Doppler vibrometry is actively used in experimental studies because of its noncontact measurement technique. When using a stationary laser to measure the vibrations of rotating bodies and ...Fourier transform to process the results of such measurements, a problem arises, associated with a decrease in the frequency resolution of the spectra with increasing rotation rate of the body. As a result, at sufficiently high rotation rates, closely spaced discrete components may cease to be resolved. This paper proposes a method for solving such a problem using the least squares method. The operability of this processing method has been demonstrated on experimental data.
•Model allowing synchronous measurement of flow and structure oscillations.•Experimental data used to validate the one-way and two-way FSI calculations.•Appearing harmonics of the vortex shedding and ...natural frequencies for lock-in mode.
This paper presents results of dynamic measurements of the flow and structure oscillations. We proposed a model consisting of two in-tandem flexible cylinders in the water cross-flow. During the studies, vibration acceleration amplitudes at the shedding frequency and at the cylinders natural frequency were obtained as a function of the flow velocity. The velocity pulsation and pressure pulsation spectra were determined in the flow. A relatively simple structure enabled the use of non-contact measurement systems for cross validation and uncertainty quantifications. The mutual influence of flow and structural dynamics induced by the lock-in effect between the vortex shedding frequency (or its harmonics) and the natural frequency was analyzed. These activities were conducted to generate representative data in order to validate the requirements for hydrodynamic force calculation accuracy and the methods of one-way and two-way coupled FSI calculations.
We propose methods for estimation of the number of the sources and their localization in complex mechanical systems. These methods are based on the matching vibrational field obtained using finite ...element modeling with the measured field from vibration sensors. A modification of the MUSIC (Multiple Signal Classification) algorithm, which is often employed in direction-of-arrival estimation of wavefield sources, is effectively used to localize several simultaneously operating sources of vibration. Numerical simulation and experimental testing in mechanical systems showed the superior efficiency of the proposed method in comparison with the methods previously used to solve similar problems.
The authors have performed laboratory modeling of noise-emission processes in turbulent flows of the heat-transfer agent in shutoff and control valves of a pipeline. Experiments were conducted on an ...aeroacoustic bench consisting of a model of the flow chamber of shutoff and control valves (parallelepiped), inlet and outlet tubes, an exhaust fan, and a baffle chamber. Parallel measurements of velocity fields were performed by the PIV method, and of acoustic characteristics, with a microphone. The experiments were conducted with different widths of the gaps between the tubes in the flow-chamber model. At certain values of the gaps, tone sounding was recorded at frequencies of 340 and 680 Hz by the microphone, which, as subsequently shown by results of the velocity-field measurements, is a consequence of the self-oscillating flow regime occurring with a periodic separation of vortices whose scale is comparable with the gap width in the flow chamber.
The development of compact hydroacoustic low-frequency emitters with a high power density is fraught with difficulties due to conflicting requirements on the dimensions, efficiency, radiated power, ...operating bandwidth, and manufacturability. For compact emitters, the body dimensions limit the possibility of combining the resonances of the active element and mechanical oscillatory system, which makes their development difficult. A compact hydroacoustic low-frequency longitudinal-bending type transducer with a complexly shaped radiating surface, 3D LFR, designed for large-scale modeling and verification of theoretical calculations of such design, has relatively small dimensions and demonstrates high efficiency. The paper presents the results, obtained with laser vibrometry, of in-air measurements of the vibrational characteristics of two titanium bodies with different sizes and corrugation patterns. The proposed designs for the transduce with maximum overall dimensions of less than 100 mm and a weight of approximately 1 kg provide a voltage sensitivity of about 1 Pa m/V in the operating frequency band and the fundamental resonance in the 1–2 kHz range. 3D LFR has a high mechanical conversion coefficient and uses the added mass; it also has a number of other advantages over similar designs. It is shown that the 10–12% differences in the sizes of the two emitters and the geometry of the radiating shells (12 and 16 corrugation waves) lead to a difference in the resonance frequencies measured in air (4.0 and 3.5 kHz, respectively). At the same time, the emitter is larger and has a smaller spread of the mechanical conversion coefficient along the ridges and troughs of the body, as well as a denser distribution of the spectral components outside the fundamental frequency band.
Algorithms are realized for localizing vibration activity sources in complex mechanoacoustic systems using finite element modeling. For the case of one source, the localization method was used in the ...least squares form applied to the first eigenvector of the sample correlation matrix. It is shown that frequency summation can significantly increase the localization accuracy in this case. Considerable attention is paid to assessing the number of simultaneously operating vibration sources and the possibility of correctly localizing them. The efficiency of two source localization methods was compared: the maximum likelihood method calculated for a single source and the MUSIC (Multiple Signal Classification) method specially modified for this problem. It is shown that the modified MUSIC method is more efficient in solving the localization problem with two sources compared to the maximum likelihood method calculated for a single source. It is noted that the maximum likelihood method calculated for two or more sources cannot be applied because of the too high computational complexity.
New Applications of Laser Vibrometry Stulenkov, A. V.; Korotin, P. I.; Suvorov, A. S.
Bulletin of the Russian Academy of Sciences. Physics,
06/2020, Letnik:
84, Številka:
6
Journal Article
Recenzirano
The possibility of using lasers for non-contact vibration measurements has been known since the mid-60s. This work describes the development of some applied areas: the use of laser vibrometry in ...near-field acoustic holography, verification of numerical models of vibrations of complex structures, and vibration flaw detection.
Structure vibration under the influence of unsteady hydrodynamic forces caused by the flow around their surfaces can adversely affect durability and rupture life. Reducing the adverse effects of ...hydrodynamic forces is currently possible with the help of linked
CFD
and vibration calculations. However, for an adequate description of the associated processes one should use calculation models and approaches specific to the hydro-vibration problem. To justify and validate such approaches, an experimental model was developed and a series of structure excitation tests in water flow was carried out.
The model comprises two cylinders installed sequentially in water crossflow. Vibration levels, pressure and velocity fluctuations were measured in the tests as a functions of the flow velocity. The application of different non-intrusive measurement techniques was possible due to relatively simple test model construction which may be used for cross-validation and experimental uncertainty quantification.
Flow-structure interaction, caused by synchronization effect of the flow separation frequency (or it’s spectral components) and eigenfrequency of cylinder, was analyzed based on simultaneously measured data. The tests performed gave the information about dynamical characteristics of the flow and vibration parameters of cantilevered cylinders. The experimental results are used for identification of required accuracy of hydrodynamic forces calculation by
CFD
and validation of oneand two-way linked methods for flow excitation frequency calculation.
The paper describes the results of an experiment on studying long-range surface reverberation in the deep-water part of the Black Sea. The experiment employed tone pulses with a filling frequency of ...2 kHz and a duration sufficient for narrowband spectral analysis. The source and receiver of acoustic signals were spatially offset in the water area; therefore, directional reception and time strobing made it possible to study different situations: forward scattering, bistatic scattering, and monostatic (back) scattering. The paper analyzes the Doppler scattering spectra for different values of the bistatic scattering angle.
The paper presents the results of processing measurement data on the spatiotemporal structures of sound fields in Lake Ladoga. Measurements were taken with an extended vertical receiver array. The ...aim of processing was to isolate the field components that were stable with respect to small variations in the waveguide parameters. Since a model of the medium is inevitably inaccurate, such components can be predicted with greater accuracy than the total field. In terms of the ray approach, a stable component is generated by a beam of rays propagating over close trajectories. The discussed experiment analyzed sound fields excited by a point source that emitted wideband pulses, as well as the fields of wave beams excited by the emitting vertical array at fixed frequencies. In both cases, the processing results showed that the isolated stable components, as expected, coincide substantially better with the prediction of theoretical calculation (by the wide angle parabolic equation method) than with the total wave field.
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