Complex Vibration Research Articles

Stability and bifurcations of complex vibrations in a nonlinear brush-seal rotor system.

A brush seal has the advantages of adapting to different vibration conditions and increasing the stability of the nonlinear rotor system. In this research, the stability and bifurcations of complex vibrations in a brush-seal rotor system are studied. An analytical seal force model is obtained through the beam theory and mutual coupling dynamics of the bristles and the rotor. The interaction between the bristles and the rotor is clearly depicted by a geometric map. Periodic and chaotic vibrations as well as the corresponding amplitude-frequency characteristics are first predicted by a numerical bifurcation diagram and 3D waterfalls. Discrete dynamic eigenvalue analysis is adopted for a detailed investigation of the stability and bifurcations of nonlinear vibrations. Jumping, quasi-periodic, and half-frequency vibrations are warned during the speeding up and down process. Four separate nonlinear vibration evolving routes are discovered. Two period-doubling bifurcation trees evolving to chaos are illustrated for the observation of global and independent periodic vibrations. Nonlinear vibration illustrations are presented through displacement orbits as well as harmonic amplitudes and phases. Chaotic vibration and unstable semi-analytical vibration solutions are compared. The obtained results and analysis methods provide new perspectives on nonlinear vibrations in the brush-seal rotor system.

A novel formulation for transfer path identification and vibration prediction in the over-track building induced by trains.

Over-track buildings in metro depots become more and more prevalent in metropolis with the increase in population and the decrease of construction land. However, the train-induced vibration greatly reduces the comfort of occupants living in the over-track buildings. Owing to complex vibration sources and numerous transfer paths, it is a challenging task to analyze and predict the vibration characteristics accurately in the building. In this paper, a field measurement campaign of vibration was conducted in the Guanhu metro depot in Guangzhou, China. A novel formulation based on the operational transfer path analysis (OTPA) and singular value decomposition (SVD) is proposed to analyze the measured data and predict the train-induced vibration in the building. In this study, the vibration contributions from each transfer path to the target points in the building were obtained and the predominant transfer paths were identified further. Besides, the vibration at target points in the building was predicted using the vibration at path points and transmissibility functions from transfer paths. This study provides insights into the prediction and evaluation of vibration transmissions from vibration source to upper floors of over-track building.

Novel Model-free Optimal Active Vibration Control Strategy Based on Deep Reinforcement Learning

Neural networks (NNs) can provide a simple solution to complex structural vibration control problems. However, most past NN-based control strategies cannot guarantee an optimal policy in structural vibration control. In this study, a novel active vibration control strategy based on deep reinforcement learning is proposed, which utilizes the learning ability of NN controllers and simultaneously provides control performance comparable to traditional model-based optimal controllers. The proposed learning algorithm can determine the control policy through interaction with the environment without knowing dynamic system models. This study shows that the proposed model-free strategy can provide optimal control performance to various systems and excitations. The proposed control strategy is first verified on a single-degree-of-freedom model and subsequently extended to a multi-degree-of-freedom shear-building model. Its control performance with full-state feedback is nearly the same as that of a classical linear quadratic regulator. Moreover, the learned policy can outperform a traditional output feedback controller in a partially observed system. The robustness of the proposed control strategy against measurement noise is also tested.

Attitude Control of Vehicle Based on Series Active Suspensions

When vehicles with traditional passive suspension systems are driving in complex terrain, large swing and vibrations of the car body make passengers and goods uncomfortable and unstable, even at very low-speed conditions. Considering the actual need for intelligent resource exploration in the sustainable economy, visual-based perception and localization systems of unmanned vehicles still cannot handle the sensor noise coursed by large body motions. In order to improve the stability and safety of vehicles in complex terrain, an attitude control system is proposed for mainly eliminating the external body motions of the vehicle by using series active suspensions. A model predictive control method considered the differences between the simulated and real vehicle, and the performance restrictions of actuators are used to design the attitude controller for reducing the heaving, pitching, and rolling motions of the vehicle. After simulations and real car tests, the results show that the proposed attitude controller can significantly improve the attitude stability of vehicles in harsh terrain.

Analysis of dynamic acoustic resonance effects in a sonicated gas–liquid flow microreactor

In this work, we characterize acoustic resonance phenomena occurring between gas bubbles in a segmented gas-liquid flow in a microchannel irradiated with a frequency around 500kHz. A large acoustic amplitude can be reached, leading to gas-liquid interface deformation, atomization of micrometer sized droplets, and cavitation. A numerical approach combining an acoustic frequency-domain solver and a Lagrangian Surface-Evolver solver is introduced to predict the acoustic deformation of gas-liquid interfaces and the dynamic acoustic magnitude. The numerical approach and its assumptions were validated with experiments, for which a good agreement was observed. Therefore, this numerical approach allows to provide a description and an understanding of the acoustic nature of these phenomena. The acoustic pressure magnitude can reach hundreds of kPa to tens of MPa, and these values are consistent with the observation of atomization and cavitation in the experiments. Furthermore, volume of fluid simulations were performed to predict the atomization threshold, which was then related to acoustic resonance. It is found that dynamic acoustic resonance gives rise to atomization bursts at the gas bubble surface. The presented approach can be applied to more complex acoustic fields involving more complex channel geometries, vibration patterns, or two-phase flow patterns.

Structural and magnetic analysis of Cd-Zn spinel ferrite nanoparticles

Sol-gel auto-combustion synthesis technique was employed to synthesize Cd-Zn ferrite nanoparticles with composition Zn1-xCdxFe2O4, where 0.0 ≤ x ≤ 1.0. The physical properties of prepared samples were inspected by using x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and vibration sample magnetometer (VSM) techniques. XRD analysis confirmed the formation of Cd-Zn spinel nanoferrites with an increase in experimental lattice constant from 8.37 Å to 8.74 Å for zinc and cadmium ferrite samples, respectively. Variation of tetrahedral and octahedral hopping lengths, crystallite size, microstrain and dislocation density with Cd-content has been investigated and elucidated. SEM micrographs showed agglomeration of nearly-spherical grains that increased in size with Cd-content increase. FTIR analysis confirmed the existence of the characteristic tetrahedral and octahedral stretching vibrations of metal ion and oxygen complex in the range 429–558 cm−1. VSM measurements revealed a tuning in coercivity to higher values and a decrease in saturation magnetization as Cd-content increased. The calculated cations distribution, bond lengths, bond angles and interionic distances between cations at tetrahedral and octahedral sites attribute the observed decrease in saturation magnetization to weak interaction between cations in the two sites.

Structural optimization to improve the dynamic performance of novel co‐curing damping sandwich composites

AbstractCo‐cured damping composite structures have broad application prospects in high‐tech fields such as aerospace and space vehicles because of their low weight, large damping, and sufficient stiffness. In order to improve dynamic properties of conventional composite structures, a new type of damping composites embedded with multilayer viscoelastic film is proposed in this paper. Based on the complex modulus theory and vibration mechanics of composite plates and shells, vibration differential equation of composite plates with multilayer viscoelastic film is derived. The constitutive relation of the complex structure is established. The consistency of theoretical derivation and numerical simulation results provides a reference for the optimization of dynamic performance of damping sandwich composites. The effects of the distribution of viscoelastic film and the geometric structure parameters on dynamic performance of co‐cured damping composites are also discussed. The results show that the embedding of multi‐layer viscoelastic film can greatly enhance the loss factors of co‐cured composite structures under same damping layer thickness. This work lays a foundation for optimization of dynamic performance of lightweight and large damping composite structures.

Dual-Mode Coupled Triboelectric Nanogenerator for Harvesting Random Vibration Energy.

As a new energy harvesting technology, triboelectric nanogenerators are widely used for vibration mechanical energy harvesting. However, the current schemes ignore the composite characteristics of vibration, with problems such as utilization and low collection efficiency. In this paper, a random resonance cantilever beam triboelectric nanogenerator (RCB-TENG) with dual-mode coupled is presented, the working mode is a coupling form of in-plane sliding and vertical contact-separation that can effectively collect complex vibration energy in transverse and longitudinal directions. The influences of the structural parameters of the RCB-TENG and different dielectric materials on the output performance are systematically investigated. The single vibration module achieved a power density of 463.56 mW/m2 and a transfer charge of 10.7 μC at a vibration frequency of 46 Hz, an increase in power density, and a transfer charge of 4.94 and 3.82 times, respectively, compared to the conventional contact-separation mode. Finally, the RCB-TENG was tested in practice, and it was observed that nine 1 W commercial LED bulbs and 500 5 mm diameter LED lamps were successfully lit. This work offers new ideas for distributed energy harvesting technologies and holds broad promise in the field of energy harvesting from wind, water, wave, and random vibrations caused by mechanical energy.

Pointwise multiclass vibration classification for cable-supported bridges using a signal-segmentation deep network

Long-span bridges are inherently vulnerable to vibration, which could result in serviceability failure. Many design codes typically apply a one-size-fits-all approach with predefined thresholds for determining the occurrence of excessive vibration, but these often fail to work properly due to complex vibration patterns. Assessments that are based on vibration type could provide a more accurate assessment. To this end, this study proposes a deep-learning-based framework for the pointwise multiclass vibration classification of long-span bridges. Two abnormal vibration classes are considered here: vortex-induced vibration (VIV) and traffic-induced vibration (TIV). The proposed framework employs a Fourier Synchrosqueezed Transform (FSST) to accomplish time–frequency estimation, a Bidirectional Long-Short-Term-Memory (Bi-LSTM) model for network training, and a median filter for post-processing. In this study, field-monitored wind and weigh-in-motion data from a case study of the Jindo Bridge in South Korea was used to demonstrate the feasibility of the developed framework. The results show that the trained network classified TIVs and VIVs sample-by-sample with an accuracy of 94.35 %. In addition to significant VIVs, the network also successfully detected limited vibrations, which allowed it to outperform statistic-based approaches.

Damage detection method based on defect mode for orthogonal grid stiffened panels

Orthogonal grid stiffened panels are very useful structures widely utilized in many engineering applications. The nondestructive testing and evaluation (NDT&E) methods for these structures are still limited due to the complex vibration modes induced by stiffeners distributed in two periodic directions. A novel method based on defect modes to localize multiple damage in orthogonal grid stiffened panels is proposed in this research. Instead of utilizing defect modes in periodic structures to control vibration or wave propagation, it is proposed to analyze the influence of defects on the dynamic response properties of orthogonal grid stiffened panels. The damage-related modes can then be used to identify multiple damage. The method is successfully verified both numerically and experimentally and shows great potential for broad engineering applications.

Autonomous Resonance‐Tuning Mechanism for Environmental Adaptive Energy Harvesting (Adv. Sci. 3/2023)

Piezoelectric Energy Harvester A piezoelectric energy harvester (PEH) that converts unused ambient vibration energy into useful electricity can alleviate issues related to the battery maintenance and power line installation of IoT sensors. To maximize the harvesting power, the resonance frequency of the PEH should match the dominant frequency of the ambient vibrations. In article number 2205179, Kyung-Hoon Cho, Hyun-Cheol Song, and co-workers report a novel autonomous resonance-tuning (ART) PEH that autonomously adjusts its resonance frequency in accordance with ambient vibrations without any external assistance or human intervention. The PEH design methodology to implement the ART function is provided along with its real-world validation under low-frequency (<100 Hz) complex vibrations in which the acceleration and frequency change simultaneously.

Impact response analysis of vibration system with inerter

This research investigates using an inerter system to control the impact-induced vibration response of a single degree of freedom(SDOF) and two degrees of freedom(TDOF) vibration system. An analytic model of the SDOF system with an inerter is first derived, and simulation is performed to compare the inerter performance in suppressing the maximum acceleration response under shock load. Next, a more complex TDOF vibration model with an inerter is derived, and the effectiveness of the inerter in reducing the large acceleration amplitude is evaluated. The energy analysis is conducted to investigate the energy transfer mechanism during impact. The simulation study shows that one can significantly decrease the maximum acceleration response with an appropriate selection of the inerter parameters. For the SDOF vibration system with an inerter, response reduction is greatly influenced by the system’s natural frequency. In the TDOF vibration system, the maximum acceleration response attenuation is caused by two factors. For a large inerter radius, the acceleration response reduction is mainly influenced by energy transfer between unsprung and inerter mass. However, for a big inerter mass, attenuation of the acceleration response is caused by decreasing the system’s natural frequency. It is observed from the simulation that the maximum acceleration response can be reduced up to 35% by adjusting the inerter radius of gyration. Furthermore, the optimum condition for reducing the acceleration response occurs when the inerter mass is half the unsprung mass ( m i = 0.5 m u). An experimental study is conducted to validate the simulation results.

Arbitrary variable thickness annular piezoelectric ultrasonic transducer based on transfer matrix method

The variable thickness annular radial piezoelectric ultrasonic transducer can realize impedance transformation and energy concentration, has the advantages of large radiation area and full directivity, and is widely used in power ultrasound, underwater acoustic and other fields. Because solving complex variable thickness metal ring radial vibration wave equation is more difficult, in this paper, the radial vibration of metal rings with variable thickness is transformed into the superposition of the radial vibrations of N metal rings with equal thickness by using the transfer matrix method. The equivalent circuit diagram, the resonance frequency equation and the expression of the displacement amplification coefficient of the radial vibration of the metal thin ring with arbitrary thickness are obtained. The relationship between the displacement amplification coefficient and the geometric size of the cone, power function, exponential and catenary metal rings is analyzed. On this basis, the equivalent circuit and resonance frequency equation of radial vibration of piezoelectric ultrasonic transducer which is composed of a metal ring with variable thickness and a piezoelectric ring with equal thickness are derived. In order to verify the correctness of the theoretical results, the finite element software is used in simulation, and the numerical solutions of the first and second order resonance frequency and displacement amplification coefficients are in good agreement with the theoretical solutions. In this paper, the universal solution of radial vibration of metal ring with arbitrary variable thickness is given, which provides theoretical guidance for designing and optimizing the radial piezoelectric ultrasonic transducers.

Stochastic Mechanism of Shock Disturbances of Rocket Sleigh Supports during High-Speed Track Testing of Aviation Equipment

Tests of ballistic aircraft on rail tracks in conditions close to real ones are an economically viable alternative to flight tests. Rocket rail tracks exist in the USA, Canada, France, China and a number of other countries. The article con-siders potentially self-oscillating mechanical systems that have a threshold mechanism for the transition from a noise vibrational stable state to a self-oscillatory one, depending on the mode parameters. An algorithm for estimating the damping coefficient of the harmonic components of a particular mode of a complex process is proposed. As an indicator of energy loss of the oscillatory component during resonant interaction, the value of the density of the power spectrum related to the width of the frequency range is taken. Based on the solution of the Fokker-Planck equation for a stochastic process, estimates of the “drift” and “diffusion” coefficients are obtained. A technique for estimating the state of potentially self-oscillatory systems in the form of a set of probabilistic stochastic characteristics is proposed. According to the experimental data of vibration accelerations for the structural elements of the rocket sled with the test object, according to the proposed method, it is possible to make the contribution of the self-oscillations of the elements, if they are pre-sent in a complex vibration process, and also to make estimates of their vibration strength at resonances.

Equivalent Static Wind Load for Structures with Inerter-Based Vibration Absorbers

Equivalent Static Wind Loads (ESWL) are desired in structural design to consider peak dynamic wind effects. Conventional ESWLs are for structures without control. For flexible structures with vibration control devices, the investigation of ESWL is required. Inerter-based Vibration Absorbers (IVAs), due to the light weight and high performance, gained much research attention recently. This paper established a generic analytical framework of ESWL for structures with IVAs. The analytical optimal design formulas for IVAs with different configurations and installation locations are provided. Subsequently, the solutions to uncontrolled and controlled wind-induced responses are derived based on the filter approach. Finally, the ESWL for controlled structures are presented with a gust response factor approach. The ESWL estimation for a tall chimney controlled by IVAs is illustrated, and the results revealed a significant ESWL reduction effect of the IVAs, particularly for the cross-wind vortex resonance. In the presented framework, the conventional uncontrolled ESWL can be converted to the controlled one with a control ratio. The closed form solution of the control ratio is provided, which enables a quick estimation of ESWL for controlled structures particularly in the preliminary design stage. The presented approach has the potential to be extended to more complex structures and vibration control devices.

Leakage aperture identification of natural gas pipeline based on compressed acquisition and DSAE

Traditional gas pipeline leak detection methods usually face challenges in that there are redundant data collected on account of the time-domain sampling theory and the valuable leakage information is hidden in the complex vibration signals. This paper put forward an intelligent aperture identification method for natural gas pipeline leakage. This method integrated the compression of monitoring data based on compressed sensing (CS) transformation and automatic feature extraction and identification based on deep neural networks, namely, denoising sparse autoencoder (DSAE). The compressed acquisition can greatly reduce the volume to be processed and effectively extract the aperture information. DSAE combined the merits of sparse auto-encoder (SAE), denoising coding and dropout to achieve robust feature extraction and aperture classification. Experimental results validate the effectiveness and good performance, and the proposed method can realize faster and more accurate identification of different leak sizes compared with the traditional methods.

Leveraging the Properties of mmWave Signals for 3D Finger Motion Tracking for Interactive IoT Applications

mmWave signals form a critical component of 5G and next-generation wireless networks, which are also being increasingly considered for sensing the environment around us to enable ubiquitous IoT applications. In this context, this paper leverages the properties of mmWave signals for tracking 3D finger motion for interactive IoT applications. While conventional vision-based solutions break down under poor lighting, occlusions, and also suffer from privacy concerns, mmWave signals work under typical occlusions and non-line-of-sight conditions, while being privacy-preserving. In contrast to prior works on mmWave sensing that focus on predefined gesture classification, this work performs continuous 3D finger motion tracking. Towards this end, we first observe via simulations and experiments that the small size of fingers coupled with specular reflections do not yield stable mmWave reflections. However, we make an interesting observation that focusing on the forearm instead of the fingers can provide stable reflections for 3D finger motion tracking. Muscles that activate the fingers extend through the forearm, whose motion manifests as vibrations on the forearm. By analyzing the variation in phases of reflected mmWave signals from the forearm, this paper designs mm4Arm, a system that tracks 3D finger motion. Nontrivial challenges arise due to the high dimensional search space, complex vibration patterns, diversity across users, hardware noise, etc. mm4Arm exploits anatomical constraints in finger motions and fuses them with machine learning architectures based on encoder-decoder and ResNets in enabling accurate tracking. A systematic performance evaluation with 10 users demonstrates a median error of 5.73° (location error of 4.07 mm) with robustness to multipath and natural variation in hand position/orientation. The accuracy is also consistent under non-line-of-sight conditions and clothing that might occlude the forearm. mm4Arm runs on smartphones with a latency of 19 ms and low energy overhead.

NES cell

A broadband adaptive vibration control strategy with high reliability and flexible versatility is proposed. The high vibration damping performance of nonlinear energy sink (NES) has attracted attention. However, targeted energy transfer may cause severe vibration of NES. Besides, it is difficult to realize pure nonlinear stiffness without the linear part. As a result, the reliability of NES is not high. The low reliability of NES has hindered its application in engineering. In addition, the performance of NES depends on its mass ratio of the primary system, and NES lacks versatility for different vibration systems. Therefore, this paper proposes the concept of NES cell. The advantages of the adaptive vibration control of NES are applied to cellular NES. By applying a large number of NES cells in parallel, the reliability of NES and its versatility to complex vibration structures are improved. An elastic beam is used as the primary vibration structure, and a limited NES is used as the cell. The relationship between the vibration suppression effect of NES cells and the number of NES cell is studied. In addition, the effect of the distribution of NES cells on the multi-mode resonance suppression of the beam is also studied. In summary, the mode of the primary structure can be efficiently controlled by a large number of lightweight NES cell. Therefore, the lightweight NES cell is flexible for vibration control of complex structures. In addition, it improves the reliability of NES applications. Therefore, the distributed application of NES cells proposed in this paper is a valuable vibration suppression strategy.

Global performance of multi-story stiffness-eccentric RC structures subjected to progressive seismic excitations: Shaking table investigations

Asymmetric structures have demonstrated poor seismic performance while experiencing major earthquakes in the past. Such structures exhibit complex vibration characteristics under seismic shaking as there is coupling between the lateral and torsional components of vibration. These coupled vibrations tend to cause weak locations under torsional distress, which eventually leads to the global failure of the structure. This paper presents the experimental evaluation of a plan-asymmetric structure with stiffness eccentricity. The experimental investigation was conducted by means of shake table testing on a 1/4-scaled reinforced concrete (RC) frame shear wall structure exposed to progressive seismic excitations. The structural response is monitored from a global failure perspective both in the elastic and inelastic states under increased torsional vibrations. The experimental findings indicate that: (1) irregularities in a structure can lead to significant amplification of the dynamic response due to induced torsional vibrations (2) the damage in the structure influences the dynamic properties of the structure, which eventually tend to influence the global structural response (3) structural acceleration response is more sensitive to seismic excitations and appears to have more influence on local oscillations compared with structural displacement response and (4) floor rotations excessively increase with the increasing damage state of the structure. Based on the physical inspection and extracted measurements, the shear wall sustained severe damage, whereas beams and columns at the flexible edge of the structure formed plastic hinges in critical zones.

Nonlinear dynamic analysis of liquid-solid coupling and rubbing on drill string

Natural deposit of natural gas hydrate (NGH) exists in the colder regions on the earth, which is an unconventional energy and has great potential. About 97% of the NGH is located in the offshore and only 3% is located on the land. Due to its sensitivity to the external environment and easy decomposition, it is necessary to suppress the external environment changes caused by the complex vibration of the drill string during its exploitation. In this paper, the fluid-solid coupling nonlinear vibration of drill string is studied. The nonlinear dynamic model of drill string with drilling fluid is established. The relationship between variable parameters of drill string and complex dynamics of drill string is analyzed. Furthermore, the bifurcation diagram is given. The results have certain significance for discussing the non-linear dynamic mechanism of drill string under complex conditions and reasonably selecting the drilling process parameters of NGH.