Asynchronous Vibration Research Articles

Earthquake Response Spectra Analysis of Bridges considering Pounding at Bilateral Beam Ends Based on an Improved Precise Pounding Algorithm

Asynchronous vibration was generated between the main bridge and approach spans or abutments due to differences in stiffness and mass during an earthquake, thus further leading to pounding at the bilateral beam ends. By taking a T-shaped rigid frame bridge as an example, the bilateral pounding model was abstracted, and the earthquake response spectra considering pounding at the bilateral beam ends were studied, including the maximum displacement spectrum, the acceleration dynamic coefficient spectrum, the pounding force response spectrum, and the response spectrum for the number of pounding events. An improved precise pounding algorithm was proposed to solve the dynamic equation of the bilateral pounding model. This algorithm is based on the precise integration method for solving the second-order dynamic differential equation and reduces the order thereof by introducing a new velocity vector and uses the series method to find the nonhomogeneous term. The system matrix is simpler, and the inversion of the system matrix can be avoided. On this basis, a multipoint earthquake-induced pounding response spectrum program was developed. A total of 18 seismic waves from Class II sites were selected, and the response spectra of 18 waves were analyzed using this new program. Furthermore, the effects of structural stiffness, mass, stiffness of contact element, pounding recovery coefficient, and peak ground acceleration (PGA) on the earthquake response spectrum were studied. Through the analysis of earthquake response spectra and a parametric study, the phenomenon of earthquake-induced pounding of bridges was clarified to the benefit of the analysis and engineering control of earthquake-induced pounding of bridges.

Correction of the static characteristic of a frequency converter to reduce the amplitudes of resonance vibrations of the vibrating table

It is known that vibration systems of directional vibrations based on asynchronous vibration motors are currently widely used in practice, but at the same time they have a significant drawback - a sharp increase in vibration amplitudes when passing through the resonance zone at the time of acceleration and deceleration of vibration motors, which negatively affects their operation. The article discusses a vibration table with two unbalanced asynchronous vibration motors. The calculation scheme and equations of motion of such a vibration system are presented. It is shown that the vibration table as a control object is an oscillatory link with a pronounced resonant frequency. The equations of motion of asynchronous vibration motors with scalar frequency control are given. A structural diagram of a vibration table with unbalanced exciters has been developed, the modeling of which made it possible to determine the amplitudes of resonant oscillations. It is proposed to apply correction of the static characteristics of the frequency converter, which connects the effective value of the output voltage with the frequency, to reduce the resonance amplitudes. Equations of the desired static characteristics of the inverter and analytical dependences for calculating the necessary coefficients for its implementation are given. A computational model has been developed that makes it possible to take into account the effect of the corrected static characteristic of the frequency converter on the operation of the vibrating table at the stages of acceleration and deceleration. The results of computer simulation are given, convincingly showing that the correction of the static characteristics of the inverter is an effective means of reducing the amplitudes of resonant oscillations. It is shown that modern frequency converters have functionality that makes it easy to correct the dependence of the effective value of the output voltage on the frequency. The need to adjust the static characteristics of the inverter for a specific type of product tested on the vibration table is noted.

Enhancing Virtual Walking Sensation Using Self-Avatar in First-Person Perspective and Foot Vibrations

Walking is a fundamental physical activity in humans. Various virtual walking systems have been developed using treadmill or leg-support devices. Using optic flow, foot vibrations simulating footsteps, and a walking avatar, we propose a virtual walking system that does not require limb action for seated users. We aim to investigate whether a full-body or hands-and-feet-only walking avatar with either the first-person (experiment 1) or third-person (experiment 2) perspective can convey the sensation of walking in a virtual environment through optic flows and foot vibrations. The viewing direction of the virtual camera and the head of the full-body avatar were linked to the actual user's head motion. We discovered that the full-body avatar with the first-person perspective enhanced the sensations of walking, leg action, and telepresence, either through synchronous or asynchronous foot vibrations. Although the hands-and-feet-only avatar with the first-person perspective enhanced the walking sensation and telepresence, compared with the no-avatar condition, its effect was less prominent than that of the full-body avatar. However, the full-body avatar with the third-person perspective did not enhance the sensations of walking and leg action; rather, it impaired the sensations of self-motion and telepresence. Synchronous or rhythmic foot vibrations enhanced the sensations of self-motion, waking, leg action, and telepresence, irrespective of the avatar condition. These results suggest that the full-body or hands-and-feet avatar is effective for creating virtual walking experiences from the first-person perspective, but not the third-person perspective, and that the foot vibrations simulating footsteps are effective, regardless of the avatar condition.

State-space method for dynamic responses of double beams with general viscoelastic interlayer

Due to their effective engineering applications, double-beam systems have intensively been studied in recent decades. The interlayer between beams in the system plays a key role in the structural vibration and energy dissipation. However, existing research efforts only observe the pure elastic interlayer or simplest viscoelastic interlayer such as Kelvin-model interlayer. In this paper, a general viscoelastic interlayer that can consider more complex stiffness and damping effects is investigated. A novel state-space approach with the proposed mode-shape constant is presented to determine the transverse vibration of the double-beams. The given integrals of mode shapes can effectively decouple the governing equations, making it possible to analyze the complex viscoelastic interlayer. Numerical examples demonstrate that the proposed method is accurate and reliable. The viscoelastic interlayer affects the natural frequencies of asynchronous vibration mode more apparently than those of synchronous vibration mode. The damping coefficients of the viscoelastic interlayer have a significant effect on the damping characteristic of the double-beam systems while reducing the dynamic responses of the beams in the forced vibration. The proposed method can be useful to simulate the dynamic responses of double-beam systems with various viscoelastic interlayers in engineering practices and applications.

A Technique for Frequency Converter-Fed Asynchronous Motor Vibration Monitoring and Fault Classification, Applying Continuous Wavelet Transform and Convolutional Neural Networks

In this article, a type of diagnostic tool for an asynchronous motor powered from a frequency converter is proposed. An all-purpose, effective, and simple method for asynchronous motor monitoring is used. This method includes a single vibration measuring device fixed on the motor’s housing to detect faults such as worn-out or broken bearings, shaft misalignment, defective motor support, lost phase to the stator, and short circuit in one of the phase windings in the stator. The gathered vibration data are then standardized and continuous wavelet transform (CWT) is applied for feature extraction. Using morl wavelets, the algorithm is applied to all the datasets in the research and resulting scalograms are then fed to a complex deep convolutional neural network (CNN). Training and testing are done using separate datasets. The resulting model could successfully classify all the defects at an excellent rate and even separate mechanical faults from electrical ones. The best performing model achieved 97.53% accuracy.

Rotation-induced axial oscillation of a composite nanoconvertor at low temperature

We propose a model of a nanostructure which can transform an input rotation into an output oscillation. In the model, the rotor has two identical internally hydrogenated deformable parts. The mechanism is that the rotation-induced centrifugal force and van der Waals force drive the recoverable deformation of the hydrogenated deformable parts, which gives rise to the axial translation of the free end of the rotor. Once the two hydrogenated deformable parts deform periodically, the free end of the rotor oscillates periodically in the axial direction. Molecular dynamics simulations are conducted to reveal the dynamic response of the system at low temperature. Four main types of deformation and the first three orders of vibration responses of the hydrogenated deformable parts are analyzed. Synchronous breathing vibration of the two hydrogenated deformable parts produces ideal oscillation with large amplitude. Asynchronous axial vibration of the hydrogenated deformable parts reduces the oscillation amplitude or produces beat vibration. The way to control the amplitude of the axial oscillation/vibration is given.

An Adaptive Online Blade Health Monitoring Method: From Raw Data to Parameters Identification

Blade tip timing (BTT) methods have been increasingly implemented for blade health monitoring (BHM). However, there are two drawbacks of current signal analysis methods preventing them from applying to online monitoring: first, current online monitoring requires the manual judgment of the resonance region, which is time-consuming. Second, existing BTT resonance signal analysis methods are not suitable for online monitoring. The spectral-analysis-based method presents spectral aliasing, while the computational complexity of the sparse-based method is usually high. In this article, we propose an adaptive online BHM method that includes two steps: automatic resonance region recognition and parameters identification in resonance area. For the former step, we demonstrate different methods for synchronous and asynchronous resonances, use the cross correlation to judge the occurrence of synchronous vibration, and use the linear estimation to determine the appearance of asynchronous vibration. For the latter step, an iterative adaptive least-squares periodogram is adopted for its tradeoff between spectral aliasing and computational complexity. The effectiveness of the above steps is first verified using different simulation data separately. Then, the laboratory data are used to test the effectiveness of the whole method. Finally, the online monitoring function of the proposed method is verified by the engineering data with both synchronous and asynchronous resonances.

Experimental investigation of wall-bounded turbulence drag reduction by active control of double piezoelectric vibrator

In order to manipulate large-scale coherent structures in the wall-bounded turbulence and reduce the skin-friction, an active-control experimental investigation was performed through synchronous and asynchronous vibrations of double piezoelectric vibrators embedded spanwisely on a smooth flat plate surface. A TSI-IFA300 hot-wire anemometer and TSI-1621A-T1.5 hot-wire probe were used to measure the time series of instantaneous velocity at different locations. Influence of the vibrations on wall-bounded turbulence are compared in a multi-scale point of view. A disturbance Reynolds Number Red = ρd2f/μ is introduced to represent the disturbance. A probability density functions (PDFs) of the multi-scale components of the turbulence velocity and multi-scale conditional phase-averaged waveform are studied in detail using the Wavelet transform. The results show that the maximum drag reduction rate 18.54% was obtained at 100V/160Hz and Red = 0.54 case with an asynchronous vibration mode. The disturbances generated by the vibrators have a significant influence on the sweep events of burst. The asynchronous vibration model is more effective than synchronous vibration one. A possible physical mechanism is recognized to explain why the disturbance frequency of 160Hz leads to an optimal parameter set for drag reduction.

Parameter Identification and Sensor Configuration in Tip Timing for Asynchronous Vibration of a Deformed Blade With Finite Element Method Simulated Data Verification

Abstract Blade tip timing (BTT) measurement has been used to measure the vibration of turbomachinery blades in recent years. People researches focus on the development of processing methods. Newly developed BTT processing methods are usually tested by numerical simulations. Because blades will deform when loaded, the detected points by sensors relative to the blade tip will deviate from their expected positions. A novel simulated BTT model is proposed to identify the movement of the detected points. Finite element method (FEM) is used, and the blade tip profile is discretized into series of segments, each of which is composed of adjacent nodes from the blade tip grid to avoid the error possibly caused by coarse girds. There are two factors which will deviate the detected points from their initial positions: static deformation and vibration. This method is validated by BTT datasets from three different simulations. In addition, an improved sine fitting method and a displacement modification method are proposed to process the deceptive signal of the detected point. The effect of the sensor configuration on the parameter identification is also studied. The result shows that when the static point cannot be determined, it would be better if the sensor could be mounted at a place where it is far away from the nodal line and the static deformation there is small.

Blade Vibration Stress Determination Method Based on Blade Tip Timing Simulator and Finite Element Method

Abstract Blade tip timing (BTT) measurement technology is more widely used to determine the vibrational stress of rotating blades and play an important role for blade service life prediction. The dynamic blade displacements can be measured by tip timing sensors, and then be converted to blade stress by the modal shape information from finite element method (FEM) analysis. However, there are always two uncertainties between the measured displacements by BTT and the modal shape by FEM analysis. First, the effective positions detected by sensors may shift from where they expected due to the deformation of the blade. This deviation may yield calibration factors with deceptions, which will present an inaccurate correlation for the blade stress level and the tip displacement. Second, when vibrating, blade tip would actually oscillate around the equilibrium position both in circumferential and axial direction, while the sensors can only detect the movements along the circumference direction and neglect the other. This causes the measured displacements to be different from the actual displacements. To deal with these two problems, a novel method based on the vibration amplitudes of blade tip along axial direction is proposed to identify the effective detected position. The vibration stress of the whole blade then can be determined by linking the modified displacements to the mode shape information from finite element (FE) predictions. This method is validated by a numerical BTT simulator, which is trying to simulate the actual testing process of BTT measurement. Both synchronous and asynchronous vibrations are discussed to illustrate the applicability of this method. Moreover, sensitivity analysis is performed to identify the uncertainties from the vibration amplitude and mode shape inaccuracies. Results demonstrate the great potential of the method for vibration stress determination.

Non-Contact Measurement of Blade Vibration in an Axial Compressor

Complex blade responses such as a rotating stall or simultaneous resonances are common in modern engines and their observation can be a challenge even for state-of-the-art tip-timing systems and trained operators. This paper analyses forced vibrations of axial compressor blades, measured during the bench tests of the SO-3 turbojet. In relation to earlier studies conducted in Poland with a small number of sensors, a multichannel tip-timing system let us observe simultaneous responses or higher-order modes. To find possible symptoms of a failure, blade responses in a healthy and unhealthy engine configuration with an inlet blocker were studied. The used analysis methods covered all-blade spectrum and the circumferential fitting of blade deflections to the harmonic oscillator model. The Pearson coefficient of correlation between the measured and predicted tip deflection is calculated to evaluate fitting results. It helps to avoid common operator mistakes and misinterpreting the results. The proposed modal solver can track the vibration frequency and adjust the engine order on the fly. That way, synchronous and asynchronous vibrations are observed and analysed together with an extended variant of least squares. This approach saves a lot of work related to configuring the conventional tip-timing solver.

The Analysis of the Loss of the Traction Effect during an Intensive Start of a Vehicle

The effect of a significant and sudden loss of the greatest possible average traction during a vehicle’s intense acceleration is found under the asymmetric or asynchronous vertical vibrations of the drive wheels. The effect appears in vehicles with an interwheel differential during an intense start with slipping and can be dangerous when entering highways or crossing uncontrolled intersections. The vibration modes resulting in the partial or almost complete loss of the average traction are specified. The torque supplied to the pair of wheels and ensuring the highest possible acceleration in vibration modes is found. The kinematics of the process are analyzed for motion with the minimum power inputs.

Experimental investigation of accumulation deformation properties of frozen silt clay under different cyclic stress-paths

The long-term serviceability of infrastructures in cold regions is inevitably affected by such dynamic loads in practical works as earthquake loading and vehicle loading. In order to study the deformation characteristics of frozen soil under the seismic loading, namely P-waves and S-waves coupled action, different cyclic stress paths were simulated by using triaxial testing equipment with bidirectional cyclic loading function. The results indicate that the cyclic shear stress was main factor in the development of permanent axial strain of frozen sample, while the cyclic normal stress had limited impact. In the case of same stress path, the clockwise rotational-direction of the cyclic stress path is more conducive to the accumulation of the axial permanent strain. In addition, the residual strain generated is greater in the loading process than in the unloading one under the similar conditions. The synchronous vibration of normal stress and shear stress makes the elastic strain maintain larger value than the reverse synchronous vibration, but the asynchronous vibration makes the residual strain keep larger than the synchronous vibration under the condition of the same number of loading cycle.

Qualitative analysis of the undesirable effect of loss of traction force of a vehicle during an intense start

The effect of a significant and sharp loss of the average traction force during vehicle acceleration with asymmetric or asynchronous vibrations of the driving wheels is found. The effect manifests itself in vehicles with an inter- wheel differential under an intensive start with slipping. The vibrational modes leading to both partial and almost complete loss of the average traction force are specified. It can be dangerous when entering highways or crossing unregulated intersections.

A Real-Time Stability Indicator for Micromilling: An Experimental Validation

In contrast to the well-established stability prediction tools, a robust real-time stability indicator is proposed for micromilling process, and it opens the possibility of online chatter avoidance based on successful detection. In this paper, a robust and easy-to-compute stability indicator is presented. This approach exploits the virtue of a stable milling process—the displacement of the vibrating tool repeats with a period of tooth passing. It has been observed that the standard deviation of the tool displacement sampled at once per tooth passing frequency is indicative of chatter, where a low standard deviation coincides with stable cutting. An increase in standard deviation is the direct consequence of an increase in asynchronous motion of the tool, coinciding with chatter. As it is also well known, this asynchronous vibration of the tool results in distinct marks on the workpiece surface. This paper presents the experimental validation of this real-time stability indicator. The ease of implementation makes the presented stability indicator a strong candidate for applications in chatter avoidance based on detection. The results are also verified against the standard stability prediction method.

Qualitative Analysis of the Undesirable Effect of Loss of Traction Force of a Vehicle during an Intense Start

The effect of a significant and sharp loss of the average traction force upon vehicle acceleration during asymmetric or asynchronous vibrations of the driving wheels is found. The effect manifests itself in vehicles with an interwheel differential under an intensive start with slip. The vibrational modes leading to both partial and almost complete loss of the average traction force are specified. It can be dangerous when driving on highways or crossing unregulated intersections.

Исследование конденсаторного противовключения в режиме торможения асинхронного вибродвигателя

Исследование конденсаторного противовключения в режиме торможения асинхронного вибродвигателя

Reconstructed Order Analysis-Based Vibration Monitoring under Variable Rotation Speed by Using Multiple Blade Tip-Timing Sensors.

On-line vibration monitoring is significant for high-speed rotating blades, and blade tip-timing (BTT) is generally regarded as a promising solution. BTT methods must assume that rotating speeds are constant. This assumption is impractical, and blade damages are always formed and accumulated during variable operational conditions. Thus, how to carry out BTT vibration monitoring under variable rotation speed (VRS) is a big challenge. Angular sampling-based order analyses have been widely used for vibration signals in rotating machinery with variable speeds. However, BTT vibration signals are well under-sampled, and Shannon’s sampling theorem is not satisfied so that existing order analysis methods will not work well. To overcome this problem, a reconstructed order analysis-based BTT vibration monitoring method is proposed in this paper. First, the effects of VRS on BTT vibration monitoring are analyzed, and the basic structure of angular sampling-based BTT vibration monitoring under VRS is presented. Then a band-pass sampling-based engine order (EO) reconstruction algorithm is proposed for uniform BTT sensor configuration so that few BTT sensors can be used to extract high EOs. In addition, a periodically non-uniform sampling-based EO reconstruction algorithm is proposed for non-uniform BTT sensor configuration. Next, numerical simulations are done to validate the two reconstruction algorithms. In the end, an experimental set-up is built. Both uniform and non-uniform BTT vibration signals are collected, and reconstructed order analysis are carried out. Simulation and experimental results testify that the proposed algorithms can accurately capture characteristic high EOs of synchronous and asynchronous vibrations under VRS by using few BTT sensors. The significance of this paper is to overcome the limitation of conventional BTT methods of dealing with variable blade rotating speeds.

Active control of wall-bounded turbulence for drag reduction with piezoelectric oscillators**Project supported by the National Natural Science Foundation of China (Grant Nos. 11332006, 11732010, 11572221, and 11502066).

An experimental investigation was performed for active control of coherent structure bursting in the near-wall region of the turbulent boundary layer. By means of synchronous and asynchronous vibrations with double piezoelectric vibrators, the influence of periodic vibration of the double piezoelectric vibrators on the mean velocity profile, drag reduction rate, and coherent structure bursting is analyzed at Reθ = 2766. The case with 100 V/160 Hz-ASYN is superior to other conditions in the experiment and a relative drag reduction rate of 18.54% is exciting. Asynchronous vibration is more effective than synchronous vibration in drag reduction at the same voltage and frequency. In all controlled cases, coherent structures at large scales are regulated while the small-scale structures are stimulated. The fluctuating velocity increases significantly. A periodic regulating effect on the coherent structure can be seen in the ASYN control conditions at the frequency of 160 Hz.

RESEARCH OF BRAKING MODES OF ASYNCHRONOUS VIBRATION MOTOR DEBELYANOVO

The possibility of braking the asynchronous unbalanced vibration motor through the capacitor of the opposition. The results of mathematical modeling modes, coasting and braking by condensing opposition asynchronous vibration motor.