Experimental Vibrational Study Research Articles

Experimental study of flow-induced vibration in a two degrees-of-freedom flexibly mounted triangular prism in crossflow

This study experimentally investigates the flow-induced vibration (FIV) of a flexibly mounted triangular prism with two degrees of freedom (DoF), capable of oscillating in its first two vibrational modes in the crossflow direction. The experiments were conducted by varying the angle of attack (α) in the range of 0°–60° and eigenfrequency ratio (R), which is the ratio between the second and first eigenfrequency, from R = 1.5 to 3. For α = 0° and 15°, no significant oscillations were observed. At α=30°, both vortex-induced vibration (VIV) and galloping-type response were detected. For higher angles of attack, α = 45° and 60°, a pure galloping type response was identified. Hydrogen bubble flow visualization was employed to analyze the vortex-dominated wake and to discern the nature of the FIV response—whether it was VIV or galloping. Although the prism was free to oscillate in both its first and second modes, only the first mode contributed to the FIV response at α = 45° and 60°, where galloping was dominant. The FIV response remained primarily influenced by the first mode, except when mode two was externally excited, resulting in pronounced hard mode-two galloping behavior. Because mode one predominantly drives the system's overall FIV response, variations in the eigenfrequency ratio had minimal impact on the system's overall FIV behavior.

Experimental study of vortex-induced vibration of stay cables installed with two types of perforated shroud light devices

To address both illumination issues and the common vortex-induced vibration (VIV) of bridge cables, a perforated shroud light device is proposed. The effect of the different porosities (20%, 35%, 42%, and 55%) on VIV of the rigid segmented shroud cable models is studied first by wind tunnel tests. It reveals that shrouds with porosities of 20% and 35% could reduce the VIV amplitude of the smooth cables by 26% and 46%, respectively. However, shrouds with porosities of 42% and 55% tend to increase the complexity and risk associated with VIV. Vibration measurements on flexible should cable with 20% porosity were conducted for both vertical and inclined models with an inclination of 35° and yaw angles of 0°, 30° and 60°. Shrouds with a porosity of 20% exhibit similar effects on vertical flexible cables as on horizontal rigid cables, in both cases mitigating VIV. The impact on the inclined flexible cables depends on the yaw angle. At the yaw angle of 0°, the shroud effectively mitigates VIV in flexible cables. However, at yaw angles of 30° and 60°, the same porosity level shroud exacerbates the risk of VIV in the inclined flexible cable. This may be due to the enhanced wind velocity along the cable axial direction and decreased penetrating flow rate through the shroud as the wind yaw angle increases. Overall, it was found that a shroud with a porosity of 20%–35% performed the best and was recommended for applications on cables with no inclination and inclined cable at yaw angle β = 0°.

(Invited) Collective Radial Breathing Modes in Homogeneous Nanotube Bundles

Carbon nanotubes (CNTs) exist in many atomic structures typically grow as mixtures of of many chiralities with a vast variety of properties. Identical CNTs that are arranged into two-dimensional hexagonal lattices, their vibrational properties have been predicted to change with additional low-frequency modes appearing in the Raman spectrum. [1] Up to now, the experimental study of collective vibrations has been limited by a lack of pure homogeneous chirality bundles. We overcome this challenge by employing a self-coil mechanism of a very long CNT that loop into itself during the growth process resulting in a tightly packed hexagonal stack [2]. This lattice is perfectly homogeneous in terms of diameter, chiral twist, and even handedness of the tube. By characterizing and comparing the physical properties of the coil with respect to its tails, the bundling effects are clearly visible. We report on two breathing-like modes for quasi-infinite bundles, compared to the single radial breathing mode characteristic for isolated tubes. The exciton-phonon coupling in these modes is probed with resonant Raman spectroscopy, revealing the same resonance energy for both breathing-like peaks. Additionally, we study the dependence of vibrational coupling on the tube diameter by analysing different tube’s diameter coils and other bundling geometries. Our experimental findings align well with previously reported theoretical studies, demonstrating a 1/d scaling for all modes, as well as confirming the relative shift of the modes dependent on intertube interaction. These vibrations provide insight into the role of intertube lattice dynamics in two-dimensional THz-range phononic crystals.[1] Popov, V. N.; Henrard, L. Evidence for the existence of two breathinglike phonon modes in infinite bundles of single-walled carbon nanotubes. Phys. Rev. B 2001, 63, 233407[2] Nakar, D.; Gordeev, G.; Machado, L. D.; Popovitz-Biro, R.; Rechav, K.; Oliveira, E. F.; Kusch, P.; Jorio, A.; Galvao, D. S.; Reich, S.; others Few-wall Carbon Nanotube Coils. Nano Letters 2019, 20, 953–962.

Numerical and Experimental Study of Flow-Induced Vibrations in Micro-Tube Heat Exchangers

Abstract Thermal management presents an increasing challenge in future engineering systems, especially in applications like combined cycle precooling, waste heat recovery, and innovative propulsion systems. These systems face a growing demand for managing higher heat loads while coping with limited heat sink. Central to these thermal management systems is the heat exchanger, with micro-tube heat transfer emerging as a promising solution for future technologies. Micro-tube heat exchangers are becoming popular owing to their ability to significantly enhance the heat transfer surface area while maintaining a compact core volume. As the demand for high-performance, lightweight heat exchangers escalates, micro-tube heat exchangers are being designed to be increasingly compact yet highly loaded. This trend poses significant challenges to their structural integrity, particularly under harsh operational conditions. Flow-induced vibrations, a critical concern in the design of tubular heat exchangers, can lead to tube failures, compromising the safe operation of engineering systems. While the flow-induced vibrations of conventional-sized heat exchangers have been extensively studied, there is a noticeable gap in the research on similar phenomena in micro-tube heat exchangers. This paper details ongoing research at Reaction Engines Ltd to aid the design of safe and robust heat exchangers, focusing on the flow-induced vibrations in micro-tube heat exchangers and utilizing a cutting-edge laser vibrometry test facility. A predictive model, employing an unsteady flow simulation approach and eigenvalue analysis, has been formulated.

Determination of the characteristics of drill string vibrations during the drilling process

The object of research is vibration processes of a certain origin in the drill string with typical design deviations depending on the mode parameters of drilling. A drill string is an oscillating system with an infinite number of degrees of freedom of a multifactor system. An exhaustive study of oscillatory processes in the drill string is impossible neither analytically nor experimentally, due to the specifics of the hole deepening in various rocks, the design of the well, its shape, etc. Therefore, in practice, they try to solve the problems of the dynamics of the drill string for an idealized system and, while preserving the main oscillatory properties, solve some problems of the rod system. The work carried out was aimed at experimental studies of vibrations of the drill string during the drilling process. It is shown that the effectiveness of the use of hydrodynamic cavitation requires the development of methods and devices for intensifying the well drilling process. It is proven that the design of the cavitation generator organically fits into the existing well drilling equipment and allows for the intensification of technological processes with lower specific energy consumption. It is found that all oscillatory processes that occur in the drill string are random in nature and must be considered using the mathematical apparatus of the theory of random oscillations. The study of vibrations during well drilling shows that vibrations can be considered as random stationary processes, since transient modes have a sufficiently short duration for homogeneous rocks with fixed drilling modes. The analysis of the vibrations of the drill string elements based on random oscillations in a number of cases allows to increase the reliability of determining the vibration reliability of the drill string elements. It has been proven that the response of drill string elements to broadband random vibration can be defined as the combined effect of several narrowband random vibrations.

Experimental Study of Rotor Vibrations on Oil-Lubricated Foil Bearings of Various Designs

Experimental Study of Rotor Vibrations on Oil-Lubricated Foil Bearings of Various Designs

Theoretical and experimental study of rigid rapier weft insertion vibration

In this study, vibration equations and models were established utilizing D’Alembert’s principle to address the resonance challenge of a rigid rapier loom operating in high-speed reciprocating motion, and the equations were subsequently solved using Galyokin’s methodology. A laboratory apparatus was constructed to evaluate the findings of the first-order vibration frequency under various rapier extension lengths to validate the precision of the theoretical model, which necessitated recalibration. The accuracy of the theoretical model is confirmed by comparing its predicted results with those of the experiments. In this report, the rigid rapier is further examined in order to correct the trapezoidal acceleration within the perspective of the vibration of the rigid rapier influenced by varied rapier head masses. The results demonstrate that as the mass of the rapier head increases, the maximum apex deviation of the rigid rapier during the weft-induced process also escalates. To enhance the stability of the rigid rapier gravitating process and to provide theoretical guidance and design implications in engineering, the theoretical model of this research can also examine the influence of gravity, rapier material, rapier dimension, and other variables on the oscillation of the rigid rapier gravitation process.

Experimental study of wind-field characteristics and torsional vortex-induced vibrations for a split three-box deck sitting above water waves

The wind-field characteristics of a split three-box deck sitting above water waves and its torsional vortex-induced vibrations (VIVs) were experimentally investigated using wind-tunnel and wave-flume tests. The wind field was measured using turbulent flow instrumentation (TFI) Cobra probe. To test the VIVs of the split three-box deck, a test system that could elastically suspend the deck sectional model by eight springs and guarantee free oscillation of the deck sectional model only in the heaving and torsional directions was constructed. The test results indicated that the regular wave height (H) and regular wave period (T) mainly promoted the overall turbulence-intensity (Iuvw) and turbulence-intensity component (Iw). These contributions were further strengthened by an increase in H and a decrease in T, respectively. In general, the variations in Iuvw and Iw, particularly the latter, should be regarded as the major cause of the change in the maximum torsional VIV amplitudes of the deck sectional model with a scale ratio of 1:60 when compared to the mean local wind speed (U) and wind-speed component (w). The differences in these amplitudes under different cases in the first lock-in regions were not evident, whereas those in the second lock-in regions were significant. In the second regions, the smaller the relative bridge clearance (a/H), the smaller the maximum torsional VIV amplitudes, and the maximum torsional VIV amplitudes increased with T, which were all smaller than those in the corresponding wind-only case. Moreover, the larger the bridge clearance (a), the larger the maximum torsional VIV amplitudes in the wind-only cases (a = 0.30, 0.42, 0.50, and 0.58 m). Evidently, the presence of water waves is conducive to the suppression of torsional VIVs of the split three-box deck when VIVs occur.

Experimental and numerical study of lateral vibration of a rotor–stator rubbing system

AbstractIn this paper, lateral vibration of a rotating system with rotor–stator rubbing is investigated experimentally and numerically. An experimental study is conducted using a simple test rig to model a horizontal rotating system with a fixed stator device to simulate rubbing. Furthermore, a lumped parameter model with two degrees of freedom is established with a viscoelastic contact model that considers the stiffness and damping properties of the stator. The fourth/fifth order Runge–Kutta technique is used to solve the nonlinear equations of motion of the rotor system. The effect of changing mass unbalance and radial clearance on the dynamic response is investigated experimentally and numerically. The observed results are presented in detail through bifurcation diagrams, frequency spectra, Poincaré’s points, orbit plots, and time waveforms. The experimental results show that changing the mass unbalance and radial clearance yield significant effects on the system response. The 2 × and 3 × harmonic components are found to serve as good indicators of increasing rub severity. The numerical results show the dynamic characteristics of rub responses such as periodic no-contact, periodic with contact, quasi-periodic, and chaotic responses. The response characteristics are very sensitive to the changes in system parameters and initial conditions. Both the experimental and numerical results show qualitatively that the lateral vibration response exhibits coexistence and alternation of periodic and chaotic responses. Also, quasiperiodic response shows up in some numerical case studies. The obtained results contribute toward a better diagnosis of rotor–stator rub fault in rotating machines.

Experimental study of parametric vibrations of arc-shaped tubes with pulsating fluid flow

The dynamics of curved tubes with fluid flow fixed on both sides was studied experimentally. Two cases were studied in which the curved tubes differed in curvature. Tests were performed with the flow without pulsation to determine the natural frequencies and with pulsation to determine the interesting dynamic phenomena occurring in the system. Two alternative measurement systems were used to study the motion of the tubes, a contact one based on accelerometers and a non-contact one based on optical technology. Acceleration and displacement time-series were analysed to determine the nature of the motion of the tubes. It was confirmed that the eigenfrequencies of the curved systems are insensitive to flow velocity which is consistent with the extensible centreline hypothesis. The interesting dynamics of tubes with pulsatile flow, the possibility of excitation of simple, combination parametric resonances, including several different combination resonances simultaneously, were identified. The vibrations in the simple resonances were polyharmonic and in the combination resonances quasi-periodic. The motion of the tubes was three-dimensional in nature and its complexity increased with increasing excitation amplitude. It was found that increasing the curvature of the tube reduced the possibility of excitation of parametric vibration.

Numerical and experimental study of vibrations in a non-smooth electromechanical system

The effects of discontinuity in the elasticity and damping on the dynamics of a non-smooth electromechanical system are numerically and experimentally studied in this paper. The amplitude curves are obtained, bifurcation diagrams, phase portraits, and time traces showing the transition from periodic to chaotic motion. A prototype device is designed and built. The experimental results of this device are consistent with results from theoretical investigation and convincingly show the phenomenon of discontinuity, bifurcation and chaos. The non-smooth electromechanical system proposed and studied in this paper can be used for drilling, cutting and vibration absorber.

Transformational deformation models of continuous thin‐walled structural elements with support elements of finite sizes: Theoretical foundations, computational, and physical experiments

AbstractA method of experimental study of forced bending vibrations of unfixed spans of continuous thin‐walled structural element fixed on rigid support elements of finite dimensions has been developed using instrumental means for registration of vibration acceleration amplitudes. The technique is realized on beams with different types of their fixing under the loading of one of the beam section with an external force that varies in time according to a harmonic law. Experimental dependences of amplitude values of vibration accelerations in specific points of certain spans of the beam on the frequency of external load have been obtained. These results indicate the passage of vibrations through the fixed sections due to the transformation of bending vibration modes of the loaded section into longitudinal transverse‐shift vibrations of the fixed sections during the transition across the boundary from the unfixed section to the fixed one (from the fixed to the unfixed section). For the theoretical study of the described phenomenon a transformational model of the flat beam deformation is constructed on the basis of the refined Timoshenko model with additional account of the deformability of the section with fixation to a rigid support element of finite length on one of its face surfaces. The corresponding equations of motion of the unfixed and fixed sections are derived. The corresponding kinematic and force conditions of their conjugation are formulated. On their basis, analytical solutions of two specific problems are found in the linear approximation. One‐dimensional finite elements for modeling the dynamic response of continuous beam of the considered class are also constructed. Numerical experiments have been carried out for a flat beam made of aluminum alloys D16AT, AMg‐6 and unidirectional fiber reinforced plastic. The presence of a significant transformation of the stress‐strain state parameters of the considered beams at the transition across the boundary from unfixed to fixed sections and a significant increase in the level of transverse tangential stresses on the fixed section of the beam in the vicinity of the interface of the unfixed section with the fixed one have been revealed.

Solvent role in electronic energies, experimental vibrational studies, surface and biological analysis of Ethyl Gallate: In-vitro cytotoxicity assay

Ethyl Gallate is a phytochemical molecule found in the seeds of maprange mangoes that has significant biological effects, including anti-autoimmune behavior. Experimental and theoretical analysis of Ethyl Gallate was carried out to understand the structural and biological activity of the compound. A stable molecular structure of Ethyl Gallate was found, and the geometrical variables were depicted using density functional theory (DFT), a popular approach for electronic structure computation. The structure is spectroscopically characterized using FT-IR and FT-RAMAN methods. Various solvents were utilized to record the UV–visible spectra of Ethyl Gallate, and electronic characteristics, including HOMO-LUMO energies, were measured. Software packages Multiwfn 3.7 and Multiwfn 3.8 are used to provide a thorough topological study of Ethyl Gallate. Natural bond orbital study was also performed. Molecular docking research shows that the inhibitory nature of Ethyl Gallate with 2axj protein functions as an anti-immune agent for Rheumatoid arthritis medication discovery. Additionally, Cell growth and survival were assessed using the MTT assay. By MTT assay, the IC50 value of Ethyl Gallate was 275 μg. Anti-inflammatory activity was obtained as well.

Experimental and computational study on the spectroscopic approach, chemical reactivity, hyperpolarizabilities and in-silico ligand-protein docking of 5-Chloro-2,4,6-trifluoropyrimidine

The 5-Chloro-2,4,6-trifluoropyrimidine (5CTFP) was chosen for extensive investigation of its theoretical and experimental vibrational assignments, structural discussion, and spectroscopic studies of Fourier-transform infrared (FT-IR), Fourier transform-Raman (FT-Raman), Ultraviolet–visible (UV–vis), and Nuclear magnetic resonance (NMR) by Hartree-Fock (HF) functional with 6-311+G(2d,p) basis set. The spectrum of detailed vibrational interpretation was to be provided by the MOLVIB software. Bonding orbitals participate in all stages of NBO analysis as donors and acceptors, which stabilises molecules through intermolecular charge transfer. Molecular docking research was used to foreseen the binding interactions of 5CTFP derivative with the estrogen receptor 3WZD. Auto-dock software was used to conduct receptor-ligand docking investigation. According to the molecular docking results, the highest mean negative binding affinity (−5.639 kcal/mol) was exhibited by the current chemical. Based on five-point rule of Lipinski, drug similarity was determined, and the ADMET variables were also predicted.

Experimental Studies on the Vibration Control of Epoxy Clay Nanocomposites

Fabrication of nanocomposites for different-clay (alumino-silicate) concentrations (1, 3, 5 and 10 wt%) with the matrix (epoxy) is done by using shear mixer. This paper presents the experimental study of free vibration and damping characteristics. The work also involves vibration control of nanocomposite laminates by reinforcing organically modified montmorillonite clay in the epoxy matrix by resin casting technique. Theoretical study is also carried out to study the vibration and damping characteristics of epoxy clay nanocomposites. Dynamic result shows that the second phase nanoscale dispersion in the matrix significantly enhances the internal damping of nanocomposites. This work also presents the active vibration control of nanocomposite beams. Piezoelectric patches are bonded on the surface of beam and control algorithms are applied to the system. Feed forward (open loop) control algorithms are used to control the vibration. Maximum control is obtained for sample with 3 wt.%OC.

Water on ceria{111}: Comparison between 23 experimental vibrational studies in the literature and new modeling.

Theoretical and experimental vibrational signatures of H2O and OH- (dissociated water) adsorbed on stoichiometric ceria{111} surfaces are compared. The experimental ones were collected from low-coverage experiments in the literature, and the theoretical anharmonic frequencies were generated using density functional theory calculations employing the optPBE-vdW functional for coverages from 0.5 to a few monolayers. It is found that (i) the experiments and our calculations overall agree well, lending credibility to both; (ii) the calculations manage to resolve the large class of H-bonded motifs into frequency classes that can guide experimental assignments; (iii) it is possible to find a geometrical H-bond definition that also captures the OH vibrational frequency downshifts well: R(H⋯O) ≤2.5 Å and the O-H⋯O angle θ ≥ 100°; and (iv) the frequency vs electric field relations for water and hydroxides (i.e., dissociated water) follow different and well-separated curves.

Experimental and Numerical Study of Nonlinear Vibration in Compressor Stator Blade with Holding Ring Structure Considering Contact Friction

At present, there are very few vibration test designs for compressor stator blades in damped blade test research, and there is a lack of consideration of the holding ring structure of the blade installation. In recent years, compressor designs have become more elaborate, and their structures have become more compact. For improving compressor stator blade design, it is necessary to study the blade vibration response considering contact and friction. In this paper, a compressor stator blade vibration test system with a holding ring structure is designed and built. The composition of the system and the flow of vibration are tested. Then, the nonlinear vibration rules of the model stator blades are experimentally studied through the built test bench. The experimental conditions include excitation forces of 1 N, 2 N, 3 N and 4 N, respectively. At the same time, the normal load of the outer holding ring and the blade contact surface includes 10 N, 20 N, 30 N and 40 N working conditions. The nonlinear vibration law of the test model blade considering contact friction is analyzed using a numerical method and experimental data. The experimental data agree well with the numerical analysis results, and the relative error of measurement is basically less than 5%. It is concluded that the damping vibration rule of the test model blade is related to the exciting force applied by the exciter and the contact surface normal load applied by the adjusting bolt. When these two parameters change, the movement behavior of the contact surface will switch between macro-slip, fretting slip and even a viscous state. Therefore, the amplitude of the blade will change and show nonlinear vibration characteristics. The experimental data in this paper can provide a reference for research on stator ring vibration safety in compressors.

An experimental study of forced vibration on natural convection between closed ended concentric and eccentric annular of horizontal cylinder

An experimental study of forced vibration on natural convection between closed ended concentric and eccentric annular of horizontal cylinder

Experimental Study Results Processing Method for the Marine Diesel Engines Vibration Activity Caused by the Cylinder-Piston Group Operations

The article discusses the method and results of processing statistical data from an experimental study of vibrations in marine diesel engines caused by the operation of cylinder-piston groups. The results of the application of a ranking method for identifying factors that influence vibration in marine diesel engines are presented to determine the most significant ones. A series of experiments were conducted according to special plans to actively implement the random balance method. This helped to establish the correctness of selecting the most significant factors from a variety of factors that influence the process under study. The article presents a mathematical model that enables the calculation of current values and prediction of changes in the most significant indicators, with the clearance between the piston and the cylinder liner being the most important.

Experimental Study of Coupled Torsional and Lateral Vibration of Vertical Rotor-to-Stator Contact in an Inviscid Fluid

Diagnosis of faults in a rotor system operating in a fluid is a complex task in the field of rotating machinery. In an ideal scenario, a forced shutdown due to rotor-stator contact failure would necessitate the replacement of the rotor or stator. However, factors such as time constraints, economic considerations, and the aging of infrastructure make it imprudent to abruptly shut down machinery that can still be safe to operate. The purpose of this paper is to present an experimental study that validates the theoretical results of the dynamic behavior and friction detection using the wavelet synchrosqueezing transformation (WSST) method for recurrent rotor-stator contacts in a fluid environment, as presented in a previous study. The investigation focused on the analysis of whirl orbits, shaft deflection, and fluctuation frequency during passage through critical speeds. The WSST method was used to decompose the dynamic responses of the rotor in the supercritical speed zone into several supercomponents. The variation of the high-frequency component was studied based on the fluctuation of the instantaneous frequency (IF) technique. Additionally, the fast Fourier transform (FFT) method, in conjunction with the WSST technique, was used to calculate the variation in the amplitude of high-order frequencies in the vibration signal spectrum. The experimental study revealed that the split in resonance caused by rubbing effects is reduced when the rotor and stator interact with an inviscid fluid. However, despite the effects of elasticity and fluid boundaries generating self-excitation at low frequencies and uneven motion due to stator clearance, the experimental results were consistent with the theoretical analysis, demonstrating the effectiveness of the contact detection method based on WSST.