Anomalous Vibrations Research Articles

Detection and recovery of anomalous vibration signal of rotating machinery based on LOF-MSAMP

The collected vibration signals of rotating machinery contain pulses, missing, and other low-quality anomalous data due to environmental noise interference, unstable data transmission, and data acquisition instrument failure. These low-quality data obstruct the analysis of the healthy operation condition of rotating machinery. This paper proposes a method for anomalous vibration signal detection and recovery based on the local outlier factor algorithm and the modified sparsity adaptive matching pursuit algorithm. The method combines the local outlier factor algorithm and compressive sensing theory to realize anomalous vibration signal detection and recovery. This paper evaluates the recovery performance both qualitatively and quantitatively and discusses how the proposed method’s hyperparameter selection affects the recovery results. A set of simulated signal and measured hob base signal are used to verify the proposed method. The results indicate that, when compared to the other seven reconstruction algorithms, the proposed method’s recovered signal has the lower error level and the higher waveform similarity which reaches more than 98% to the original signal, effectively improving data quality.

AI-Enabled Condition Monitoring Framework for Indoor Mobile Cleaning Robots

Autonomous mobile cleaning robots are ubiquitous today and have a vast market need. Current studies are mainly focused on autonomous cleaning performances, and there exists a research gap on monitoring the robot’s health and safety. Vibration is a key indicator of system deterioration or external factors causing accelerated degradation or threats. Hence, this work proposes an artificial intelligence (AI)-enabled automated condition monitoring (CM) framework using two heterogeneous sensor datasets to predict the sources of anomalous vibration in mobile robots with high accuracy. This allows triggering proper maintenance or corrective actions based on the condition of the robot’s health or workspace, easing condition-based maintenance (CbM). Anomalous vibration sources are classified as induced by uneven Terrain, Collision with obstacles, loose Assembly, and unbalanced Structure, which causes accelerated system deterioration or potential hazards. Here, an unexplored heterogeneous sensor dataset using inertial measurement unit (IMU) and current sensors is proposed for effective recognition across different vibration classes, resulting in higher-accuracy prediction. A simple-structured 1D convolutional neural network (1D CNN) is developed for training and real-time prediction. A 2D CbM map is generated by fusing the predicted classes in real time on an occupancy grid map of the workspace to monitor the conditions of the robot and workspace remotely. The evaluation test results of the proposed method show that the usage of heterogeneous sensors performs significantly more accurately (98.4%) than previous studies, which used IMU (92.2%) and camera (93.8%) sensors individually. Also, this model is comparatively fast, fit for the environment, and ideal for real-time applications in mobile robots based on field trial validations, enhancing mobile robots’ productivity and operational safety.

Anomalous interlayer vibrations in few-layer InSe induced by weak intralayer bonding

Atomically thin InSe is a promising semiconductor that possesses exceptional plasticity, high electron mobility, and wide bandgap tunability, which are thought to be highly sensitive to interlayer coupling. Since the interlayer vibration modes can provide direct access to the interlayer coupling strength, in this study, we systematically investigated the interlayer modes in few-layer InSe using low-frequency Raman spectroscopy. We found that the commonly used linear chain model (LCM), which treats the single layer as a rigid entity, is inadequate in accurately describing the frequencies of interlayer shear modes in InSe due to the influence of weak in-plane intralayer In–In bonding. This issue can be addressed with a modified model that accounts for both the in-plane interlayer coupling between InSe layers and the in-plane intralayer interaction within InSe layers. However, the out-of-plane intralayer In–In bonding is strong enough so that it has negligible impact on the frequency of the interlayer layer-breathing modes, which can be well understood by the LCM. Our study reveals how the weak intralayer bonding in two-dimensional materials gives a non-negligible contribution to the corresponding interlayer vibrations.

Theoretical Study on the Influence of the Anharmonic Effect on the Ionic Conductivity and Thermal Stability of 8 mol% Yttria-Stabilized Zirconia Solid Electrolyte Material.

YSZ is a promising material for resistive memory devices due to its high concentration of oxygen vacancies, which provide the high anion migration rates crucial for the manifestation of resistance switching in metal oxides. Therefore, investigating the ionic conductivity of YSZ is an important issue. The ionic conductivity and thermal stability of 8 mol% YSZ were studied using the theories and methods of solid-state physics and physical chemistry. The impact of anomalous atomic vibrations on the material was also explored, and the variation in the ion vibration frequency, electrical conductivity, and thermal stability coefficient of electrical conductivity with temperature was obtained. The results show that the ion conductivity of an 8 mol% YSZ solid electrolyte increases nonlinearly with temperature, with a smaller increase at lower temperatures and a larger increase at higher temperatures. Considering the anharmonic effect of ion vibrations, the electrolyte conductivity is higher than the result of the harmonic approximation, and the anharmonic effect becomes more significant at higher temperatures. Our research fills the gap in the current literature regarding the theoretical non-harmonic exploration of the ion conductivity and thermal stability factor of YSZ solid electrolytes. These results provide valuable theoretical guidance for the development and application of high-performance YSZ resistive memory devices in high-temperature environments.

Unraveling the role of Sm 4f electrons in the magnetism of SmFeO3

Magnetic rare-earth orthoferrite perovskites ($R$FeO${}_{3})$ host a variety of functional properties particularly suitable for next-generation, ultrafast spintronic devices. A key ingredient is the complex magnetic interaction at play between the two magnetic substructures. SmFeO${}_{3}$ has attracted particular interest because of its high-temperature spin reorientation transition and anomalous temperature-dependent lattice vibrational modes. Through first-principles calculations, the authors unveil here the interplay of the Sm-Fe exchange with the strong Sm $f$ anisotropy as the dominant microscopic mechanism, and the nature of the anomalous vibrations.

An optical flow-based method for condition-based maintenance and operational safety in autonomous cleaning robots

Autonomous professional cleaning robots are ubiquitous today, coexist with humans, and the demand continues to improve hygiene and productivity, especially in large indoor workplaces. Hence, a proper maintenance strategy is essential to monitor the robot’s health, assuring flawless operation and safety. Manual supervision and periodic maintenance are adopted in general, which is challenging to detect failures in advance, resulting in higher maintenance costs and operational hazards. Anomalous vibration due to system degradation or environmental factors is an early symptom of failure or potential threats. Hence, predicting the sources of such abnormal vibration will help prompt maintenance action or set a hazard-free environment. However, such condition-monitoring research studies are not common for indoor cleaning robots. To fill this gap, we proposed an automated Condition Monitoring (CM) system, predicting the abnormal vibration sources that will enhance Condition-based Maintenance (CbM) and Operational Safety. A novel vibration-based CM method is presented for mobile robots, suitable for indoor environments under typical illumination states, using a monocular camera and optical flow technique instead of their usual perception-related applications. The sources of abnormal vibration were classified as terrain, collision, loose assembly, and structural imbalance. We modelled vibration as sparse optical flow, and the change in optical flow vector displacement due to the robot’s vibration is derived from consecutive camera frames used as vibration data. A practical framework is developed adopting the One Dimensional Convolutional Neural Network (1D CNN) model to fit this vibration data and tested predicting the vibration source class with an average accuracy of 93.8%. In addition, a vibration source map (CbM map) is proposed by fusing the predicted class in the workplace environment map for real-time monitoring. The case studies conducted using our in-house-developed cleaning robot show that the proposed CM framework will help the maintenance team for CbM, operational safety, and select proper maintenance strategies.

Anomalous impact and vibration damping by liquid crystal elastomers

Anomalous impact and vibration damping by liquid crystal elastomers Liquid Crystal Elastomers (LCE), invented over 30 years ago, have been considered a highly promising material system for soft actuators and artificial muscles ever since. In this second academic piece for Open Access Government, Professor of Polymer Physics, Eugene M. Terentjev explores the anomalous impact and vibration damping by liquid crystal elastomers. There is considerable interest in developing thin conformal coatings of materials that can efficiently dissipate mechanical energy, thus suppressing vibration and noise and protecting from impacts. Traditionally, to create vibration-damping materials one exploits the loss aspect of the viscoelastic response when the energy dissipates as heat in either free or constrained layer configurations.

Characterization of the Anomalous Vibration Response of an Intentionally Mistuned LPT Rotor

The wind tunnel facility at the Centro de Tecnologías Aeronáuticas was used to perform a set of experiments to study the effect of intentional mistuning on the forced response behavior of an aerodynamically unstable low-pressure turbine rotor. The intentional mistuning patterns were implemented by adding a small extra mass to some of the blades. The forced response of the rotor was therefore expected to show two resonance peaks with similar amplitudes, corresponding, respectively, to the vibration frequencies of the blades with and without added mass. However, on the post-processing of the measurements, some anomalous behavior was observed. Near resonance, the system response was synchronous with the forcing, and the frequency sweeps exhibited two resonance peaks, but it was found that the two peaks were clearly different, with the peak at lower frequency showing a much higher vibration amplitude than the high-frequency peak, and with some blades responding at both frequencies with a similar amplitude. In order to give a correct interpretation of the experimental results, a reduced-order model is derived that takes into account only the traveling wave modes coupled by the mistuning. This model, although extremely simple, is capable of reproducing the unexpected behavior of the experiments, and gives a clean explanation of the system response. It is shown that the relative size of the mistuning with respect to the frequency difference of the involved traveling-wave modes is the key parameter for the appearance of this phenomenon.

Numerical Study of Flow Field Optimization for Forebay and Suction Chamber to Solve the Vibration of Pumps in a Parallel Circulation Pumping Station

The water inlet channel is an essential component of the thermal power plant’s circulating water system. It primarily arranges the water flow in the channel so that it is introduced into the pump room smoothly, steadily, and uniformly. Significantly, the operation state of the circulating water pump is impacted by the flow condition of the water inlet channel. The coal-fired generating set’s water input channel was chosen as the research object in this work, and the Computational Fluid Dynamics (CFD) Method was used to examine hydraulic issues impacting anomalous vibration of circulating pumps. Nine optimization options were also suggested, and the effects of the various plans on the water inlet channel’s flow state were examined—the simulation’s outcomes. The simulation’s findings indicate that the arc deflector can enhance the water entry channel’s flow pattern. The wall-attached bias flow of the suction chamber vanished, and the constant flow state is present around the pump’s bellmouth. The thermal power unit’s circulating water pump’s vibration was eliminated, and the circulating pump’s operating efficiency increased due to the curved deflector’s rectification procedures being implemented in the forebay. The study’s findings can guide the hydraulic performance optimization of channels for water inlets with similar sideways or high slopes.

Detecting the Presence of Intrusive Drilling in Secure Transport Containers Using Non-Contact Millimeter-Wave Radar

We employ a 77–81 GHz frequency-modulated continuous-wave (FMCW) millimeter-wave radar to sense anomalous vibrations during vehicle transport at highway speeds for the first time. Secure metallic containers can be breached during transport by means of drilling into their sidewalls but detecting a drilling signature is difficult because the large vibrations of transport drown out the small vibrations of drilling. For the first time, we demonstrate that it is possible to use a non-contact millimeter-wave radar sensor to detect this micron-scale intrusive drilling while highway-speed vehicle movement shakes the container. With the millimeter-wave radar monitoring the microdoppler signature of the container’s vibrating walls, we create a novel signal-processing pipeline consisting of range–angle tracking, time–frequency analysis, horizontal stripe image convolution, and principal component analysis to create a robust and powerful detection statistic to alarm if drilling is present. To support this pipeline, we develop a statistical model combining the vibrating container and the random vibrations induced by vehicle movement to explore the robustness of the sensor’s detection capabilities. The presented results strongly support the inclusion of a millimeter-wave radar vibration sensor into a transport security system.

Triggering mechanisms of Gayari avalanche, Pakistan

A massive snow avalanche occurred on April 2012 at Gayari, located in NE part of Pakistan, close to India and China Border. The catastrophic avalanche killed nearly 148 people, majority of which were Pakistan army personnel destroying army base camp. To mitigate its future hazard, different triggering mechanisms have been investigated in this study. We contemplate that the avalanche was triggered due to snow pack existence on favorable slope in combination with different meteorological conditions and anomalous ground vibration. The avalanche occurrence clock was advanced by two earthquakes: M 4.1 at a distance \(\sim\) 125 km that occurred about 21 h before and another comparatively larger (M 5.6) earthquake that occurred comparatively at larger distance (\(\sim\) 370 km) and longer time (\(\sim\) 25 days) before which have significantly changed the loading conditions. The latter event (M 5.6) has imparted maximum peak dynamic stress and cumulative seismic moment a month before the avalanche. Interestingly the avalanche occurred within the seismic coda of M 2.8 earthquake from Hindu Kush region, located at 560 km distance. Although the size and its expected impact on avalanche might be minor, its role in instantaneous triggering cannot be ruled out. Even smaller events at larger distance have been reported to cause snow avalanches in same environments. The presence of cracks within the avalanche was further weaken by persistence of extremely low temperature (lowest in the past decade), causing high precipitation rate along with altering the mechanical properties of the weak layer within the snow pack. Robust wind pressure pattern highest and lowest in March and April 2012, respectively, might be responsible for abrupt changes in loading conditions.

Metavalent bonding induced abnormal phonon transport in diamondlike structures: Beyond conventional theory

A phenomenon appears in a few examples of the chalcopyrites (space group $I$-42 $d$) where heavier atoms do not necessarily lead to lower lattice thermal conductivity, in contradiction with Keyes expression that formulates an inverse relation of thermal conductivity with mean atomic mass. Herewith, the thermal conductivity of $\mathrm{CuIn}{\mathrm{Se}}_{2}, \mathrm{CuIn}{\mathrm{Te}}_{2}, \mathrm{AgIn}{\mathrm{Se}}_{2}$, and $\mathrm{AgIn}{\mathrm{Te}}_{2}$ was calculated and compared at room temperature from the linearized Boltzmann transport equation using ab initio density functional theory. $\mathrm{CuIn}{\mathrm{Se}}_{2}$ and $\mathrm{AgIn}{\mathrm{Se}}_{2}$ solids exhibit lower lattice thermal conductivity than that of $\mathrm{CuIn}{\mathrm{Te}}_{2}$ and $\mathrm{AgIn}{\mathrm{Te}}_{2}$, respectively, despite the fact that Te atoms are significantly heavier than Se. A comparison between dispersion relation, the Gr\"uneisen parameter, and projected density of states leads to the conclusion that anharmonic transverse acoustic modes in the form of anomalous vibrations of Cu and Ag cause the lower values of the thermal conductivity. By analyzing the electronic structure, the compounds under study fit perfectly into a recently defined region of the metavalent bonding well known for its pronounced anharmonicity. The insight gained from the current results deepens our understanding of the unusual heat transfer phenomenon related to the metavalent bonding and sheds light on design and discovery of thermally functional materials that break the prediction by the conventional theory.

Conformable solution of fractional vibration problem of plate subjected to in-plane loads

This study provides an approximate analytical solution to the fractional vibration problem of thin plate governing anomalous motion of plate subjected to in-plane loads. The method of variable separable is employed to transform the fractional partial differential equations under consideration into a fractional ordinary differential equation in temporal variable and a bi-harmonic plate equation in spatial variable. The technique of conformable fractional derivative is utilized to solve the resulting fractional differential equation and the approach of finite sine integral transform method is used to solve the accompanying bi-harmonic plate equation. The deflection field which measures the transverse displacement of the plate is expressed in terms of product of Bessel and trigonometric functions via the temporal and spatial variables respectively. The obtained solution reduces to the solution of the free vibration problem of thin plate in literature. This work shows that conformable fractional derivative is an efficient mathematical tool for tracking analytical solution of fractional partial differential equation governing anomalous vibration of thin plates.

Anomalous lattice vibrations of CVD-grown monolayer MoS2 probed using linear polarized excitation light.

A novel physical phenomenon and advanced application have been explored in 2D low-dimensional van der Waals layered materials due to their reduced in-plane symmetry. The light-matter interaction is observed upon rapid characterization of the 2D material's crystal orientation. Here, the effects of the sample's rotation angle and the incident light's linear polarization angle on the Raman scattering of chemical vapor deposition (CVD)-grown monolayer MoS2 were investigated. The results show that the crystal orientation of monolayer MoS2 can be distinguished by analyzing the intensity ratio and frequency difference of its two dominant Raman vibration modes. In addition, an increase in the incident light's power intensity causes the Raman peaks to red shift due to the photothermal effect. Strikingly, it was found that, with an increase in the incident linear polarization angle, the out-of-plane A1g phonon mode red shifts, while the in-plane E2g1 phonon mode blue shifts. The frequency difference consequently decreases from 19.5 cm-1 to 17.4 cm-1. The anomalous lattice vibrations of monolayer MoS2 originate from the built-in strain introduced by the SiO2/Si substrate. This work paves the way for the investigation and characterization of 2D MoS2, providing further understanding of the light-matter interaction in 2D materials, which is beneficial for advanced studies on anisotropic MoS2 based electronic and photoelectric information technologies and sensing applications.

Detection of ferroresonance occurrence in inductive voltage transformers through vibration analysis

Steady state ferroresonances in isolated neutral electrical systems result in sustained abnormal system oscillations, which can damage inductive voltage transformers (IVTs) and other system elements. During this phenomenon, the IVT becomes saturated; consequently, the dimensions of the ferromagnetic material of the IVT change owing to magnetostriction. Because of this inherently nonlinear behaviour, the natural vibration modes of the IVT are excited. The aim of this study is to take advantage of these anomalous vibration modes to reveal the occurrence of ferroresonance in IVTs. The methodology for ferroresonance detection in IVTs through vibration analysis is described and demonstrated experimentally.

Anomalous interlayer vibrations in strongly coupled layered PdSe2**Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this

In this work, we show unusual effects of strong interlayer coupling on low-frequency (LF) Raman scattering in exfoliated PdSe2 crystals with different number of layers. Unlike many other layered materials, it is found that the measured frequencies of the breathing modes cannot be simply described by a conventional linear chain model (LCM) that treats each layer as a single rigid object. By using first-principles calculations, we show that strong deviations from layer rigidity can occur for the LF breathing vibrations of PdSe2, which accounts for the observed disagreement with the conventional LCM. The layer non-rigidity and strong interlayer coupling could also explain the unusual strong intensities of the LF breathing modes that are comparable with those of the high-frequency Raman modes. These strong intensities allowed us to use a set of the measured LF Raman lines as unique fingerprints for a precise assignment of the layer numbers. The assignment of the layer numbers was further confirmed using second harmonic generation that appeared only in the noncentrosymmetric even-layer PdSe2 crystals. This work thus demonstrates a simple and fast approach for the determination of the number of layers in 2D materials with strong interlayer coupling and non-rigid interlayer vibrations.

CFD three dimensional wake analysis in complex terrain

Even if wind energy technology is nowadays fully developed, the use of wind energy in very complex terrain is still challenging. In particular, it is challenging to characterize the combination effects of wind ow over complex terrain and wake interactions between nearby turbines and this has a practical relevance too, for the perspective of mitigating anomalous vibrations and loads as well improving the farm efficiency. In this work, a very complex terrain site has been analyzed through a Reynolds-averaged CFD (Computational Fluid Dynamics) numerical wind field model; in the simulation the inuence of wakes has been included through the Actuator Disk (AD) approach. In particular, the upstream turbine of a cluster of 4 wind turbines having 2.3 MW of rated power is studied. The objective of this study is investigating the full three-dimensional wind field and the impact of three-dimensionality on the evolution of the waked area between nearby turbines. A post-processing method of the output of the CFD simulation is developed and this allows to estimate the wake lateral deviation and the wake width. The reliability of the numerical approach is inspired by and crosschecked through the analysis of the operational SCADA (Supervisory Control and Data Acquisition) data of the cluster of interest.

Anomalous lattice vibrations in self-nanostructured graphene on Ru(0001)

Momentum-resolved high-resolution electron energy loss spectroscopy has been used to probe the phonon dispersion of periodically rippled graphene grown on Ru(0001). Optical phonons in this system show anomalies with respect to other graphene/metal interfaces. Novel modes with weak intensity are observed at ∼86 and ∼150 meV. Moreover, the dispersion relation of the highest optical branches in the Γ-K direction strongly deviates from the expected behavior. These unusual features in the phonon dispersion should be related to the corrugated and chiral structure of the graphene overlayer on Ru(0001).

Fault Diagnosis for Centre Wear Fault of Roll Grinder Based on a Resonance Demodulation Scheme

Roll grinder is one of the important parts in the rolling machinery, and the grinding precision of roll surface has direct influence on the surface quality of steel strip. However, during the grinding process, the centre bears the gravity of the roll and alternating stress. Therefore, wear or spalling faults are easily observed on the centre, which will lead to an anomalous vibration of the roll grinder. In this study, a resonance demodulation scheme is proposed to detect the centre wear fault of roll grinder. Firstly, fast kurtogram method is employed to help select the sub-band filter parameters for optimal resonance demodulation. Further, the envelope spectrum are derived based on the filtered signal. Finally, two health indicators are designed to conduct the fault diagnosis for centre wear fault. The proposed scheme is assessed by analysing experimental data from a roll grinder of twenty-high rolling mill. The results show that the proposed scheme can effectively detect the centre wear fault of the roll grinder.

Breakthrough of regenerative chatter modeling in milling by including unexpected effects arising from tooling system deflection

Self-excited anomalous vibrations called chatter affected milling operations since the beginning of the industrial era. Chatter is responsible for bad surface quality of the machined part and it may severely damage machining system elements. Although the significant advances of recent years, state of the art dynamic models are not yet able to completely explain chatter onset even when some conventional cutting tools are applied for conventional milling operations. In this work, a more general model of regenerative chatter is presented. The model takes into account some additional degrees of freedom and cutting forces which are neglected in the classical approach. By so doing, a more accurate representation of milling dynamics is obtained, especially when considering large diameter cutters. An improved mathematical formulation of regenerative cutting forces is provided with respect to a very recent publication where the new model has been first outlined. This approach allows −45 % of computation time. Moreover, here a new, independent, and stronger experimental validation is provided, where the new model successfully predicts an increase of about +(50 ÷ 100) % of the stability boundaries with respect to the classical prediction, thus showing the potential breakthrough of the new approach.