Asynchronous Vibration Research Articles

Frequency identification method based on active aliasing of biprobes blade tip timing without once-per-revolution

Rotary blades are the core components of aeroengines, gas turbines and centrifugal compressors. However, due to the complexity of their work environment, monitoring their health is necessary. Blade tip timing (BTT) is an effective non-contact monitoring method for rotating blades. However, conventional BTT rely heavily on once-per-revolution (OPR) signals, which cannot be accurately obtained in complex environments. At the same time, there is a serious under-sampled problem in the BTT signal. Consequently, the extraction of blade vibration parameters from under-sampled BTT signals without relying on OPR signals remains a research hotspot. In this paper, an active aliasing method based on the vibration difference of the blade is proposed to extract the vibration frequency of the blade. In the proposed method, two BTT probes are used to calculate the blade vibration difference, and time delay estimation is used to estimate the approximate value of the natural frequency at small angle delays. Then, a series of aliasing frequencies are generated under various large angle delays. Next, the estimated natural frequency and aliasing frequency are combined to solve the exact natural frequency value. In addition, numerical simulations demonstrate the effectiveness and robustness of the method. Finally, experimental research was conducted on the BTT experimental platform. As a result, this method can accurately identify the inherent frequency of asynchronous vibration of the blades.

The effect of posture on virtual walking experience using foot vibrations

Virtual walking systems for stationary observers have been developed using multimodal stimulation such as vision, touch, and sound to overcome physical limitation. In previous studies, participants were typically positioned in either a standing or a seated position. It would be beneficial if bedridden users could have enough virtual walking experience. Thus, we aimed to investigate the effects of participants’ posture and foot vibrations on the experience of virtual walking. They were either sitting, standing, or lying during observing a virtual scene of a walking avatar in the first-person perspective, while vibrations either synchronized or asynchronized (randomized) to the avatar’s walking were applied to their feet. We found that the synchronized foot vibrations improved virtual walking experiences compared to asynchronous vibrations. The standing position consistently offered an improved virtual walking experience compared to sitting and lying positions with either the synchronous or asynchronous foot vibrations, while the difference between the siting and lying postures was small and not significant. Furthermore, subjective scores for posture matching between real and virtual postures, illusory body ownership, and sense of agency were significantly higher with the synchronous than the asynchronous vibration. These findings suggest that experiencing virtual walking with foot vibrations in a lying position is less effective than a standing position, but not much different from a sitting position.

Enhanced algorithm for predictive maintenance to detect turbocharger overspeed in diesel engine rail vehicles

The reliability and safety of locomotives is crucial for efficient train operation. Repeated turbocharger failures in Israel Railways locomotive fleet have raised serious safety concerns. An investigation into the failures revealed that the uncontrolled acceleration and overspeed transients of the turbocharger shaft occurred before the failure. Early detection of potential turbocharger failures by predicting overspeed conditions is critical to the safety and reliability of locomotives. In this study, an enhanced novel algorithm for estimating the Instantaneous Angular Speed (IAS) of the turbocharger and diesel engines is presented to overcome the challenges of transient operating conditions of diesel engines. Using adaptive dephasing, the algorithm effectively isolates critical asynchronous vibration components that are crucial for the early detection of turbocharger failures. This algorithm is suitable for non-stationary speeds and is applicable to any range of rotational speed and rate of change. The algorithm requires the input of the basic parameters of the system, while all other parameters that control the process are determined automatically. The algorithm was developed specifically for the special operating conditions of diesel engines and improves predictive maintenance and operational reliability. The method is robust as it correlates between several characteristic frequencies of the rotating parts of the system. The algorithm was verified and validated with simulated and experimental data.

Capillary effect-based selective sealing strategy for increasing piezoelectric MEMS speaker performance

To address the serious acoustic performance deterioration induced by air leakage in the low-frequency range and the asynchronous vibration in electroacoustic transduction structures near the resonant frequency, a novel sealing strategy is proposed that targets one of the most widely reported piezoelectric MEMS speaker designs. This design consists of multiple cantilever beams, in which the air gaps between cantilevers are automatically and selectively filled with liquid polydimethylsiloxane (PDMS) via the capillary effect, followed by curing. In the proof-of-concept demonstration, the sound pressure level (SPL) within the frequency range lower than 100 Hz markedly increased after sealing in an experiment using an IEC ear simulator. Specifically, the SPL is increased by 4.9 dB at 20 Hz for a 40 Vpp driving voltage. Moreover, the deteriorated SPL response near the resonant frequencies of the cantilever beams (18 kHz–19 kHz) caused by their asynchronous vibration induced by the fabrication process nonuniformity also significantly improved, which successfully increased the SPL to approximately 17.5 dB. Moreover, sealed devices feature nearly the same SPL response as the initial counterpart in the frequency band from 100 Hz to 16 kHz and a total harmonic distortion (THD) of 0.728% at 1 kHz for a 40 Vpp driving voltage. Compared with existing sealing methods, the current approach offers easy operation, low damage risk, excellent repeatability/reliability and excellent robustness advantages and provides a promising technical solution for MEMS acoustic devices.

Experimental study on the influence of radial internal clearances of the rolling bearings on dynamics of a flexible rotor system

To investigate the impact of radial internal clearance of rolling bearings on the dynamic response of a flexible rotor system in a turbo-shaft engine, a dynamic similarity model of the power turbine rotor was established. Experimental research was then conducted. Four rolling bearings supporting the rotor were examined, with dynamic response tests carried out under varying radial internal clearances. The influence of the radial internal clearance on the dynamic characteristics of the rotor system was studied using the controlled variable method. The amplitude, orbit, and asynchronous vibration were analyzed through time-domain signal comparison, waterfall diagrams, and spectral analysis. The experimental results demonstrate that: (1) Adjusting the radial internal clearance of the bearings can significantly reduce the dynamic response of the flexible rotor system, with a maximum observed displacement response reduction of 88%. (2) The efficiency of vibration reduction is closely related to the axial location of the bearing. (3) Optimal radial internal clearance is not necessarily achieved at the maximum or minimum values. (4) The "locked-up" frequency phenomenon, which increases the resonance opportunities of the rotor system, can be mitigated by adjusting the radial internal clearance of different bearings. This research is of great significance and engineering value for understanding, diagnosing, and preventing excessive vibration in flexible rotor systems.

Experimental Research Into Aeroelastic Phenomena in Turbine Rotor Blades Inside ARIAS EU Project

Abstract This paper describes an aeroelastic experimental campaign on a low-pressure turbine-bladed rotor in a rotating wind tunnel that took place as a part of the Advanced Research Into Aeromechanical Solutions (ARIAS) EU project. The campaign can be considered a continuation of the free-flutter test that was performed as part of the FUTURE EU project, where the saturation of asynchronous vibrations due to dry friction was characterized. This new campaign studied new aspects of the physics behind saturated flutter, including the non-linear interaction between synchronous excitation and asynchronous vibration, the effectiveness of different mistuning patterns to suppress flutter, and the viability of under-platform dampers as a technology to control the amplitude of asynchronous vibrations. Furthermore, the campaign explored various operation conditions for the turbine rotor, including near-stall. In general, there was a good agreement between the theoretical predictions regarding all these different aspects of turbine flutter and the test results.

Research on Three-Phase Asynchronous Motor Fault Diagnosis Based on Multiscale Weibull Dispersion Entropy.

Three-phase asynchronous motors have a wide range of applications in the machinery industry and fault diagnosis aids in the healthy operation of a motor. In order to improve the accuracy and generalization of fault diagnosis in three-phase asynchronous motors, this paper proposes a three-phase asynchronous motor fault diagnosis method based on the combination of multiscale Weibull dispersive entropy (WB-MDE) and particle swarm optimization-support vector machine (PSO-SVM). Firstly, the Weibull distribution (WB) is used to linearize and smooth the vibration signals to obtain sharper information about the motor state. Secondly, the quantitative features of the regularity and orderliness of a given sequence are extracted using multiscale dispersion entropy (MDE). Then, a support vector machine (SVM) is used to construct a classifier, the parameters are optimized via the particle swarm optimization (PSO) algorithm, and the extracted feature vectors are fed into the optimized SVM model for classification and recognition. Finally, the accuracy and generalization of the model proposed in this paper are tested by adding raw data with Gaussian white noise with different signal-to-noise ratios and the CHIST-ERA SOON public dataset. This paper builds a three-phase asynchronous motor vibration signal experimental platform, through a piezoelectric acceleration sensor to discern the four states of the motor data, to verify the effectiveness of the proposed method. The accuracy of the collected data using the WB-MDE method proposed in this paper for feature extraction and the extracted features using the optimization of the PSO-SVM method for fault classification and identification is 100%. Additionally, the proposed model is tested for noise resistance and generalization. Finally, the superiority of the present method is verified through experiments as well as noise immunity and generalization tests.

Rotating blade vibration parameter identification based on genetic algorithm

In this paper, aiming at the identification of blade vibration parameters such as constant speed synchronization, constant speed asynchronous, and variable speed synchronization, the simulation platform Simulink is used to model the blade vibration system, and the blade tip timing vibration measurement system model is constructed. A method of blade vibration parameter identification based on genetic algorithm is proposed, and numerical simulation and experimental verification are carried out. The results show that the parameter identification of blade vibration by genetic algorithm has high accuracy and strong anti-noise interference ability. The influence of key parameters on the identification of blade vibration parameters is studied. For the constant speed synchronous and constant speed asynchronous vibration of the blade, the angle between the sensors should not be an integral multiple of 2π as far as possible, and the larger DR (Distribution Range) value should be guaranteed. The higher the frequency doubling of blade vibration, the more sensors are needed. For the variable speed synchronous vibration of the blade, the frequency doubling is greater than the influence of the sensor layout on the parameter identification results, but the number of sensors is too small, which will seriously affect the identification accuracy of the frequency doubling. Aiming at the blade vibration test, a blade vibration tester is designed. The blade variable speed synchronous vibration test is carried out by using the strain gauge method and the tip timing method. The measurement results of the strain gauge method are basically consistent with the measurement results based on the genetic algorithm and the tip timing.

Multi-spectrum fusion for single-probe blade tip timing

Blade tip timing (BTT) is currently the most promising method for online turbine blade health monitoring. Single-probe BTT minimizes the number of probes required and has the advantages of low cost and high safety. However, the number of probes in single-probe BTT makes its analytical capability significantly weaker than that of multi-probe BTT. In this study, we propose a multi-spectrum fusion (MSF) single-probe BTT signal analysis method that considerably improves the frequency analysis capability of the single-probe BTT and provides a theoretical upper bound for the frequency analysis. The feasibility and robustness of the MSF are verified through numerical simulations and experiments. In addition, we present methods to determine the number of frequency components of the BTT signal, which further reduces the dependence of MSF on a priori information. Finally, we demonstrate that the single-probe BTT is almost identical to the multiprobe BTT in terms of analyzing the asynchronous vibration of a blade.

A Novel Method for the Determination of Blade Vibration Stress Considering the Change in Blade Tip Timing Sensing Position

Abstract Blade tip timing (BTT) technology is concerned with the estimation of turbomachinery blade stress. The stress is determined from BTT data by relating the measured tip displacement to the stress via finite element (FE) models based on the sensing position. However, the correlation of BTT data with FE predictions involves a number of uncertainties. One of the main ones is the effective positions detected by sensors may deviate from their nominal position due to the blade deformation, which will yield deceptive calibration factors. To deal with this problem, a novel method based on the amplitude ratio and virtual displacement optimization under the distance constraints of sensors installed in different axial positions is proposed to determine the accuracy calibration factors and sensing positions. It realizes the identification of sensing positions without the information of static deformation, and overcomes the inapplicability of the corrected displacement to bending modes. Both synchronous and asynchronous vibrations of five typical vibration modes are discussed to illustrate the applicability of this method. The results show that this method has better performance than traditional method. The prediction errors of bending modes are reduced from 20 ∼ 30% to 7%, and the maximum error of other modes is reduced from 72% to 23%. In addition, sensitivity analysis is performed to investigate the influence of vibration levels and mode shape inaccuracies. Results demonstrate the great potential of this method in vibration stress determination.

Multimode Tip-Timing Analysis of Steam Turbine Rotor Blades

Presented in this paper is a multimode tip-timing analysis of steam turbine rotor blades using the Least Squares Technique. The rotor blade velocity obtained from the measured time of rotor blade arrival is used in the functional of the Least Square Technique, which is a novelty. The approach requires only two sensors in the casing for the algorithm to find blade multi-mode vibration components. For comparison, three and four sensors have also been used. An additional technique has been devised to determine the frequencies of blade vibration coupled modes, which is also a novelty. Verification of the algorithm is based on experimental and numerical analyses of steam turbine Low Pressure last stage rotor blades vibrating during run-down in a vacuum spin chamber, for synchronous vibrations, and during nominal work at 3000 rpm in a real working turbine for asynchronous vibrations. A multimode analysis is carried out for blade vibration at a nominal rotation speed of 3000 rpm. The considered steam turbine rotor blade is found to vibrate with two-mode shapes. This article considers the use of this method in BTT measurement uncertainties in the form of noise uniform distribution and noise normal distribution.

OPR-free single probe blade tip timing for monitoring rotating blade

Condition monitoring is crucial for a rotating blade working in harsh conditions. Blade tip timing (BTT) is a potential technique for operational blade health monitoring owing to its non-contact and efficiency, which identifies the vibration parameters characterizing the blade condition. However, severe undersampling and difficult probe/sensor installation hinder its application. Moreover, minimizing probe number, including once per revolution (OPR) sensor, to reduce modifications to turbomachinery is advocated in the field of health monitoring, especially for high-end equipment, such as aero-engines. In this paper, we proposed a single probe OPR-free BTT based parameters identification method for both synchronous and asynchronous vibrations. To avoid the use of OPR signal, rotating including angle (RIA) replaced the tip displacement as a signal to be analyzed. In addition, a sampling aliasing frequency (SAFE) map was constructed using the RIA signal, which provided the guidelines for parameter identification. Finally, the effectiveness and robustness of the proposed method were validated by a series of simulations and experiments. By reducing installation and hardware costs, the proposed method significantly improved the practicability of BTT measurement.

Experimental research on new hole-making method assisted with asynchronous mixed frequency vibration in TiBw/TC4 composites

With the gradual promotion and the application of difficult-to-machine materials such as titanium matrix composites in the aerospace field, high-quality hole-making technology has become a major demand in aviation manufacturing. In order to improve the hole-making quality of TiBw/TC4 composites, asynchronous mixed frequency vibration-assisted hole-making (AMFVAHM) method is proposed. The process consists of two steps: ultrasonic vibration-assisted drilling (UVAD) base hole and low-frequency torsional vibration-assisted helical milling (LFTVAHM) target hole. Based on this process, the cutting trajectory modeling is established, and the hole-making experiment on TiBw/TC4 composites is conducted. The experimental data show that during the hole expansion stage, the maximum XY-plane average milling force decreases by 30.96% and the maximum axial average milling force decreases by 24.49% compared with conventional helical milling (HM) when the torsional vibration frequency and the milling frequency are the same in LFTVAHM. The hole-making experiment shows that AMFVAHM can reduce the chip size, tool wear, and some other defects such as entrance/exit burrs, scratches, and fractures of the hole wall. Comparing with HM and UVAD, the verticality of hole wall increases by 71.43% and 86.21%, the inlet damage decreases by 27.98% and 31.60%, the outlet damage decreases by 2.80% and 14.47%, the hole wall roughness (Ra) decreases by 36.29% and 63.43%, and the maximum white layer thickness decreases by 19.99% and 67.66%. Meanwhile, AMFVAHM process not only reduces the cutting force and cutting temperature but also improves the hole-making quality due to the fretting friction effect of LFTVAHM in secondary hole expansion, which meets the need for high-quality hole-making of difficult-to-machine materials in practical engineering applications.

Stability of a Rotor Partially Filled With Fluid: Test Facility and Experimental Results

Abstract Fluid trapped in a hollow, rotating component may lead to subsynchronous vibrations, resulting in high vibration amplitudes. This asynchronous response is observed around 0.55–0.92× after passing through the first critical frequency and affects large rotating equipment such as centrifuges, fluid-cooled gas turbines, and jet engines. A test rig is designed to evaluate this self-excited asynchronous vibration. The high-speed rig comprises of a flexibly-mounted rotor partially filled with fluid, with an overhung test chamber providing an unobstructed view of the liquid surface. A squeeze film damper provides external damping and allows operation through the asynchronous response when the test chamber contains a large amount of fluid. The results show the rotor response with different fluid depths and external damping values as the rotor-bearing system transverses the first critical speed (cylindrical mode). The experiments show that only a small amount of oil (∼20 mL) is required to induce asynchronous excitations, and increasing the fluid depth increases the amplitude of vibration. External damping slightly decreases the response, but it also expands the range of frequencies where asynchronous vibrations occur. At a given speed ratio, the vibrations reach a limit cycle, and subsequently, begin to drop as the rotor speed increases past the first critical speed.

Research on the identification of asynchronous vibration parameters of rotating blades based on blade tip timing vibration measurement theory

The identification of rotating blade vibration parameters is crucial for diagnosing the health of the blades. While there are many rotating blade vibration measurement techniques, the tip timing vibration theory is currently used by most for non-contact rotating blade vibration measurements, which presents a number of challenges in its practical implementation. However, the traditional bladetip timing vibration measurement method is less involved in the calculation of vibration displacement and vibration data pre-processing and the frequency mixing problem brought on by undersampling is not fully analyzed. The majority of methods to increase measurement accuracy are studied in depth in data post-processing. The accuracy of identifying the spinning blade vibration parameters is lowered, and even identification error arises, as a result of measuring noise interference and the impact of frequency overlap. This work adjusts the calculation of blade tip vibration displacement based on the theory of blade tip timing vibration measurement and applies the Savitzky-Golay noise filtering technique to increase calculation accuracy. To combat the effect of frequency confusion brought on by undersampling and increase the precision of asynchronous vibration parameter detection of spinning blades, the synthetic phase difference spectrum correction method is adopted. In the experiments described in this work, a revolving blade is excited by an electromagnetic exciter to create vibrations at a single frequency. To determine the blade asynchronous vibration characteristics at various rotation speeds, rotating blade asynchronous vibration tests were carried out on a rotor blade table. The outcomes demonstrate that the blade asynchronous vibration parameters can be accurately identified using the parameter identification method, and the maximum vibration frequency identification error is 7.2%, demonstrating the accuracy of the blade asynchronous vibration parameter identification method.

Energy Harvesting in a System with a Two-Stage Flexible Cantilever Beam.

The subject of the research contained in this paper is a new design solution for an energy harvesting system resulting from the combination of a quasi-zero-stiffness energy harvester and a two-stage flexible cantilever beam. Numerical tests were divided into two main parts-analysis of the dynamics of the system due to periodic, quasiperiodic, and chaotic solutions and the efficiency of energy generation. The results of numerical simulations were limited to zero initial conditions as they are the natural position of the static equilibrium. The article compares the energy efficiency for the selected range of the dimensionless excitation frequency. For this purpose, three cases of piezoelectric mounting were analyzed-only on the first stage of the beam, on the second and both stages. The analysis has been carried out with the use of diagrams showing difference of the effective values of the voltage induced on the piezoelectric electrodes. The results indicate that for effective energy harvesting, it is advisable to attach piezoelectric energy transducers to each step of the beam despite possible asynchronous vibrations.

Vibrations of complex composite double-column system by extended Laplace transform method

PurposeDouble-beam/column systems have drawn much attention in many engineering fields. This work aims to present the free and forced vibrations of a novel and complex double-column system with concentrated masses, axial loads and discrete viscoelastic supports subjected to the excitation of ground acceleration are solved by the extended Laplace transform method (ELTM).Design/methodology/approachIn this work, the authors proposed an extended Laplace transform method (ELTM), which is an exact and explicit analytical method. Firstly, the mathematical model simulating the vibrations of the double-column system is reformulated with Dirac's delta function. Secondly, the exact and explicit mode shape solutions are obtained, based on which the natural frequencies and dynamic responses are obtained. An illustrating example is presented to show the validity of the proposed method. A parametric study is carried out to investigate the influences of the non-dimensional column stiffness ratio and the support stiffness ratio on the peak dynamic displacement and velocity.FindingsIt is shown that the proposed method can give exact and explicit solutions of the mode shapes and natural frequencies. It is found that the asynchronous vibrations of the proposed double-column systems can be implemented to efficiently dissipate seismic energy, as shown in the time-histories of displacement and velocity.Practical implicationsThis research systematically studied the free and forced vibrations of the complex double-column system. The proposed extended ELTM is a general method. Its application to studying the energy dissipation capability implicates that the double-column system can be utilized to reduce responses in structures under earthquake attacks.Originality/valueThe proposed extended ELTM is original and powerful. Its application to study the complex double-columns system with discrete supports, concentrated masses and axial loads is novel.

Blade Tip Timing Signal Filtering Method Based on Sampling Aliasing Frequency Map

The rotor blade is the core turbomachinery component with high failure risk. Thus, condition monitoring of blades is critical to ensure engine safety. Blade tip timing (BTT) is one of the most promising approaches to measure vibration, which is used for monitoring the health of blades. In reality, blade displacement contains several unwanted components that cause measurement uncertainty. However, because undersampling leads to spectrum aliasing, and the aliasing frequency changes with speed fluctuation, conventional filtering techniques fail to remove the portion of the signal that causes uncertainty. In this work, two filtering methods for the BTT signal are proposed based on sampling aliasing frequency (SAFE) map, namely, single-probe data detrending and tracking sliding bandpass filtering, which can extract synchronous vibration and denoise the reserved signal (asynchronous vibration) due to the clear distribution of different components in the SAFE map. The former eliminates the rotation frequency and its harmonic components by detrending of the BTT signal, whereas the latter effectively reduces the noise of the BTT signal by bandpass filters whose limit frequencies are adjusted according to sampling frequency and the trajectory in the SAFE map. Furthermore, the time-domain signal and the spectrum obtained by the orthogonal matching pursuit (OMP) algorithm are used to show the filtering effect. The effectiveness and interpretability of the proposed method are verified by simulation and experimental data.

Variable friction‐tuned viscous mass damper and power‐flow‐based control

The passive tuned viscous mass damper (TVMD), i.e., a classic inerter system, has been proven as an efficient vibration mitigation device that is characterized by a damping-enhancement effect for enhanced energy absorption and dissipation. However, due to the sensitivity of the tuning frequency, the effective frequency band of TVMD for vibration reduction is limited, so that the enhanced energy absorption and dissipation are limited. Dealing with this, this study proposes a novel variable friction TVMD (VF-TVMD) by incorporating a sub-device with variable friction forces into the TVMD, successively maximizing the energy dissipation efficiency of VF-TVMD by employing a power-flow-based algorithm. A power-flow analysis is performed for TVMD-structures, which explicitly determine the optimal phase deviation of the dashpot-deformation in TVMD with respect to structural displacement. Given this finding, the friction device in VF-TVMD is employed by the proposed power-flow-based control strategy to adjust the asynchronous vibration between the TVMD and primary structure. Through the implementation of VF-TVMD, the feasibility and effectiveness are illustrated by numerical examples. The results show that a desired phase lag of the TVMD with respect to the structure is −90° to guarantee TVMD the maximum power flow for energy dissipation. Benefitting from the variable friction force, the VF-TVMD is more effective for structural vibration control and exhibits a more significant damping-enhancement effect, in comparison with the TVMD. Applicable in a wider frequency band, the structural vibration can be significantly mitigated by the optimized VF-TVMD or even by VF-TVMD with un-optimized stiffness and damping ratios.

Optimizing probes positioning in Blade Tip Timing systems

The monitoring of the blades in bladed disk assembly is done via a continuous determination and analysis of the blade dynamics, which is mostly subjected to different type of excitation forces inducing the synchronous and asynchronous vibration of the blades. These vibrations can cause fatigue and crack of the blade, which can damage the overall turbo-machinery. Thus, avoiding such a damage motivates the determination of the blade’s vibration. Which is done traditionally by the used of strain gauge, which unfortunately monitor only the instrumented blade but not all the blade at the same time. Nowadays, such vibration measurements are done by Blade Tip Timing (BTT) system, where the arrangement of the probe is extremely important in order to extract useful information of the blade’s vibration signal. Thus, this article proposes a simple approach for the determination of the optimal probe positioning based on the minimization of the coherence of the measurement matrix derived from the mathematical model used to infer the vibration parameters, while the blade exhibits synchronous and asynchronous vibrations.