Vibration Waveform Research Articles

Lithological Interface Detection Using an Impact Source

Early detection of abnormal geological targets during drilling can enhance the safety of petroleum drilling. An impact source equipped with the advantage of long detection distances can recognize lithological interfaces. However, coda waves in the vibration waveform are significant to reflected waves, which are difficult to recognize in the time domain. This paper presents the design of an impact source that includes a hammer, impacted metal, Teflon, and a metal base. With the length and diameter of Teflon kept constant, the effect of the hammer, impacted metal, and metal base on the coda waves was experimentally investigated. According to the preferred metal materials, the effect of the length and diameter of Teflon on coda waves was also experimentally studied. A distance measurement experiment was implemented on 1.2 m sandstone on the basis of the preferred impact source design. The experimental results show that the coda waves are significantly attenuated by the preferred impact source. Moreover, the reflected waves are clearly identified in the time domain. Therefore, the preferred impact source can be used effectively in lithological interface detection.

Reduction of tunnel blasting induced ground vibrations using advanced electronic detonators

Blasting has been widely used for economical and rapid rock excavation in civil and mining engineering but has great loads, such as vibrations and noises, on the surrounding environment in the case of urban areas near dwellings and important structures. In this study, for the purpose of environmental load reduction, blasting tests were conducted at a tunnel construction site using advanced electronic detonators in which arbitrary ignition times could be set. The test results showed that the peak amplitude of the vibration waveform from each of the blast holes follows the Weibull distribution and that the wave propagation time depends on the location of the blast hole on the tunnel face. The superposition method proposed from these findings reproduced the vibration waveforms in delay blasting from the seed waveform recorded in single-shot blasting. The optimum delay interval determined accurately from the superposition method was almost equal to the one simply estimated from the method with the autocorrelation coefficient or a frequency analysis of the vibration waveform in single-shot blasting. These simple methods were validated at another tunnel construction site and found to be useful for estimating the optimum delay interval from single-shot blasting at each tunnel face on each day. This study is based on the practical consideration of actual tunnel blasting and construction, and these proposed methods will be widely applied to other tunnel construction sites.

Detachable expansion fit ultrasonic head with multiple dovetail structures

Ultrasonic vibration is a powerful processing tool in cutting and bonding. However, because of its high physical energy, there are few methods to suitably fix an ultrasonic head that contacts a workpiece to an ultrasonic horn, and it is also very difficult to make detachment possible. In preliminary experiments, the loss vibration energy of four different methods including double-sided tape, adhesive material, screw clamping, and expansion fit was compared. It was found that the expansion fit fixing method had the largest friction heat generation, and the amplitude of propagated ultrasonic vibration also increased the most. These phenomena were attributed to the presence of a single dovetail structure in the center of the contact surface between the ultrasonic horn and head, which allowed a gap to form between the ultrasonic horn and head. Therefore, we tried to improve the efficiency of vibration energy transmission from the ultrasonic horn to the ultrasonic head by adding multiple dovetail structures to the contact surfaces to narrow the gap. The multiple dovetail structures suppressed deformation caused by collision of the surface edges and generation of frictional heat. Actually, measured and calculated improvement ratios of vibration at the edge of the ultrasonic head are 51% and 43%, respectively. The temperature transition of the joint measured by infrared thermography and the vibration waveform at the bottom surface of the ultrasonic head determined by a laser Doppler vibrometer experimentally confirmed that multiple dovetail structures improved the vibration energy loss at the contact surface of ultrasonic heads and horns.

Pulling Illusion Based on the Phase Difference of the Frequency Components of Asymmetric Vibrations

When presented with asymmetric vibrations, humans experience an illusory force, similar to the sensation of being pulled in a particular direction. A pulling illusion has also been used in new display elements for a virtual reality content and a pedestrian navigation system. However, the basic design of asymmetric vibration stimuli that can induce this illusion has not yet been determined. In particular, it is unclear as to which part of the vibration waveform should be asymmetric to induce an illusion. To better understand the design of asymmetric vibration stimuli that can induce a pulling illusion, we evaluated the effect of the illusion corresponding to the waveform deformation due to a change in phase difference of asymmetric-vibration frequency components. The results of a psychophysical experiment demonstrate that when the phase differences of the fundamental and second harmonic waves of the asymmetric vibration are close to 0° or -180°, the illusion is more likely to occur. This result implies that the difference in the rate by which the acceleration changes at each polarity contributes to the illusion.

A study on influence of blast-induced ground vibration in dragline bench blasting using signature hole analysis

In dragline bench blasts, large amount of explosives are used in each hole making it the largest blasts of mining industry. The explosives in dragline blast holes liberate huge energy in surrounding rockmass and hence generates higher ground vibration. The generated ground vibration may cause loss to property or irritation to nearby population. In Khadia coal mine opencast project, there is a huge risk of loss to property and sensitive structures as there exist a village Kota basti and also a power plant named Shakti Nagar power plant in near vicinity of the mine. The empirical techniques are not precise and may result in erroneous prediction leading to unsafe blasting. In this paper, the signature hole dragline blasts were conducted and ground vibration waveform recorded is simulated using a signature hole analysis technique to predict the production blast-induced ground vibration. The production blasts were planned using echelon delay sequence and straight-line hole to hole delay sequence keeping the charge per delay the same. With the help of signature hole simulation, the optimum delay sequence was determined and accordingly the production blasts conducted. It was observed that by using straight-line hole to hole delay sequence pattern, the PPV values may be reduced up to 48.26%. Also, it has been found that the predicted PPV values using signature hole simulation techniques are close to the actual values with root mean square error (RMSE) of ± 3.48 mm/s and ± 2.73 mm/s with echelon and straight-line hole to hole delay sequence patterns respectively.

Long-range and wide-band vibration sensing by using phase-sensitive OFDR to interrogate a weak reflector array.

In this paper, we propose and experimentally demonstrate a novel quasi-distributed fiber-optic vibration sensing system, which can achieve vibration measurement with a wide frequency response over a long distance. The system is based on phase-sensitive optical frequency domain reflectometry (ϕ-OFDR). The sensing part is a single-mode fiber (SMF) with auxiliary weak reflection points along it. By detecting the auxiliary weak reflection points, we can obtain the waveform of the vibration signal. In the experiments, single-point and multi-point vibrations with a wide-frequency response at 100 km are successfully measured, which validated the proposed system. To the best of our knowledge, this is the first time to realize a wide-band vibration waveform measurement over such a long range by using reflectometry-based sensing system.

Optimal IMF selection and unknown fault feature extraction for rolling bearings with different defect modes

Rolling bearings are widely used in the rotating machinery. The fault types and fault feature frequencies are usually unknown when rolling bearings fail in the engineering applications, which brings difficulties to accurately recognize the health status of rolling bearings. Realizing the extraction of unknown fault features is of great significance for rolling bearing fault diagnosis in real engineering scenarios. Based on the ensemble empirical mode decomposition (EEMD) and stochastic resonance (SR), an adaptive fault diagnosis method for unknown rolling bearing faults is proposed by designing an effective frequency cut-off criteria and constructing two novel evaluation indicators. For a target signal containing complex frequency components, a frequency cut-off criterion is applied to remove redundant intrinsic mode function (IMF) components and improve the accuracy of unknown fault diagnosis in the process of using EEMD to decompose target signal. For the remaining effective IMFs, the spectral amplification factor (SAF) index is built to estimate the energy of each IMF for selecting the optimal IMF. The adaptive SR with the piecewise mean value (PMV) index is performed to extract the unknown fault features from the optimal IMF. The proposed frequency cut-off criteria obviously reduce the interference of other unknown frequencies. Compared with traditional kurtosis, SAF has good noise immunity and stability. The effectiveness of the proposed method is successfully verified by three rolling bearing experiments with different defect modes. Moreover, the vibration waveform characterizing unknown fault feature is reproduced to some extent based on the adaptive SR response. The proposed method accurately realizes unknown fault diagnosis and provides a reference for condition monitoring of rolling bearings in engineering practice.

The Monitoring of Milling Tool Tipping by Estimating Holder Exponents of Vibration

The gradual tool wear is unavoidable in the machining process, it directly influences the surface integrity and dimensional tolerances of the components. The tool condition monitoring (TCM) systems have the capacity to make full use of the cutting potential of the cutting tools, which is of great significance for improving production efficiency and ensuring product quality. In milling titanium alloys, tool tipping is one of the main failure modes. Therefore, this study focuses on establishing a tool tipping monitoring approach for the milling process. The singularity analysis method based on wavelet transform was employed to characterize the variation of vibration waveforms quantitatively with the Holder Exponent (HE) index. The probability density distribution and statistical analysis were adopted to extract effective HE features from the HE indexes to correlate with the different tool conditions. The mutual information method was adopted to rank the discriminability of the HE statistical parameters. Then, several machine learning (ML) models were established with the screened HE features. Finally, the results of the experiments indicate that the Support Vector Machine (SVM) model has the highest classification accuracy and can provide practical guides on the tool changes.

Synthesis of single-hole signatures by group delay for ground vibration control in rock blasting

Prediction and control of ground vibrations become essential as with the development of neighborhoods in the proximity of active mining operations or the need for new infrastructure in urban centers, both requiring the use of blasting. Novel ground vibration prediction models attempt to reproduce a whole vibration waveform from a blast and are based, in most cases, on the collection of vibrational information from a single blasthole. A single blasthole should have the same characteristics (geometry and weights of explosives) as the blastholes used in production shots. In some cases, the collection of the fundamental information (the signature) is straightforward. In more complex cases, the fundamental information from ground vibration data is collected from previous production shots. This study presents a novel methodology to assess the fundamental ground vibration information (the signature) using known information such as one event waveform (a production shot waveform) and the timing sequence used (the comb function) for the shot. The methodology is based on the analysis of group delay, a concept widely used in signal processing, and is modified here for the analysis of ground vibration waveforms. The methodology is developed using real data collected in coal and quarry mining operations, and at the end of this document, one case study with step-by-step calculations is presented to show the benefits of the methodology.

Aero-engine bearing fault detection: A clustering low-rank approach

Different from classic exponential-decaying feature waveform, the fault information of high-speed aero-engine bearing presents an overlapping distortion or even approximately-harmonic morphology, which brings a new challenge for popular bearing diagnosis techniques. From the nonlocal similarity perspective of vibration waveforms, this study first reveals the singular value coupled pattern among strong similarity structure, weak similarity structure and noises, which consequently yields the overlapping coherent pathology in the SVD-based low-rank domain. Leveraging an adaptive clustering into the low-rank regularization theory, a tailored diagnostic framework (dubbed AMS-CluLR) is then proposed to address the challenging problem. The main highlight of AMS-CluLR is to adaptively cluster local feature waveforms into multiple isolated groups to guarantee that different similarity structures are reliably concentrated into their matched low-rank domain, which effectively eliminates the singular value overlapping coherent pathology while keeping the structural completeness of relatively weak similarity features. Moreover, an alternative minimization solver is developed for the AMS-CluLR model to rapidly achieve a satisfying stationary solution. The embedded clustering operation’s necessity and AMS-CluLR’s superiority are profoundly investigated through a set of comprehensive numerical studies. An aero-engine bearing experiment under high-speed conditions with rotational speed up to 25,000 rev/min is further conducted to corroborate AMS-CluLR’s superiority. Experimental results show that the proposed framework substantially outperforms state-of-the-art bearing fault detection methods in terms of both information volumes and visual quality.

Direction-resolved homodyne laser-Doppler vibrometry by analyzing space-time fringes created by the successive 1D intensity profiles of the interference fringes.

In this Letter, we introduce a simple direction-resolved homodyne Laser-Doppler vibrometry method by sewing successive one-dimensional images of the interference pattern recorded by a linear array detector and creating a two-dimensional space-time fringe pattern. A space-time fringe pattern visualizes the vibration form, and it can be used for characterizing the vibration of the object. We measure the vibration of a harmonically driven loudspeaker as a known source to demonstrate the capability of the method. We also employ the method to characterize the vibrational properties of the resonator elements of a thin-disk laser. The method reveals the environmental and instrumental sources of the vibration. The use of an array detector in the detection system simplifies the fringe chasing procedure and optical setup and, by the aid of a space-time image, the vibration waveform is directly determined with no requirement for a time-consuming SPS algorithm.

Dynamic compaction of a thick soil-stone fill: Dynamic response and strengthening mechanisms

A large-scale field test to investigate vibration velocities from dynamic compaction of soil-aggregate mixture in a fill at a Chengde airport construction site, China, was carried out. The propagation and evolution of the vibration waveforms, wave amplitudes, and wave frequencies were analyzed and the mechanism by which the strength of the soil-aggregate fill was reinforced by the tamping energy was studied. The results show that there are only two vibration forms, shock waves and vibration waves, in the soil-aggregate mixture under dynamic compaction. The dominant vibration frequency and optimum frequency band for dynamic compaction are determined and the concept of critical elastic vibration velocity for soil-aggregate mixtures is proposed. A method for determining the magnitude of this vibration is demonstrated. During and after compaction, the fill could be divided into three zones, an impact reinforced zone, plastic stress wave reinforced zone, and elastic area in which the soil is not reinforced. These zones are defined by the spatial distribution of the vibration velocities and the correspondingly increased soil densities. Finally, the dynamic compaction reinforcement mechanism for a coarse-grained soil-aggregate mixture is explained and the reinforcement process is divided into two stages. In addition, a suggestion for the best layer thickness for dynamic compaction of fill is proposed.

Design and development of rotary machinery vibration monitoring system

This paper designs and develops a monitoring system for rotary mechanical vibration. The system uses ARM+FPGA dual processor combination, FPGA control signal acquisition and data transmission, ARM transplantation embedded Linux system with touch screen to complete signal analysis and time domain, frequency domain curve display. The vibration signals of multiple positions on the mechanical device are synchronously sampled, and the FFT analysis of the signals is completed on the terminal, and the vibration waveform diagram and the spectrum diagram of each channel are displayed. At the same time, the system combines current IoT technology and cloud diagnostic technology to provide wired and wireless network communication solutions. The monitoring system can connect to the cloud server through the Ethernet interface and the WiFi interface to perform cloud diagnosis on the device.

An innovative technique of simplified signature hole analysis for prediction of blast-induced ground vibration of multi-hole/production blast: an empirical analysis

Prediction and control of blast-induced ground vibration is a matter of concern in mining industry since long. Several approaches ranging from scaled distance regression, different numerical methods to wave superimposition theories have been tried by many researchers for better prediction and control of blast-induced ground vibration. Signature hole analysis is one of the popular simulation methods to predict the ground vibration generated due to production blast. It superimposes the recorded signature hole waveform using a computer program to predict the production blast-induced vibration. The technique inputs the designated time of detonation of each hole and superimposes the waves generated by each hole to predict the nearest value of peak particle velocity and frequency of blast-induced ground vibration. Although a very useful approach, it requires a computer program to simulate the linear superimposition of waveforms. The simulation is not possible for every blast as it takes time and also is difficult for field engineers to simulate every time, whereas it is always easy for blasting engineers to adapt and use an empirical equation/approach for prediction and control of blast-induced ground vibration than simulation. In this paper, an attempt has been made to develop an innovative and simplified analytical approach of signature hole analysis. The simplified sinusoidal wave equation is obtained from recorded signature hole ground vibration waveform properties and is superimposed mathematically according to the multi-hole blast design to predict the production blast-induced ground vibrations. The validation of the developed approach was done in three different sites, and up to 15% more accuracy in prediction of the blast, vibrations are achieved in comparison with signature hole analysis prediction.

Harvesting ultralow frequency (< 1 Hz) mechanical energy using triboelectric nanogenerator

Mechanical energy has been widely harvested to meet the increasing worldwide energy demands, especially propelled by the breakthrough of Triboelectric nanogenerator (TENG). Although extensive progresses have been achieved in the development of TENGs to harvest low-frequency mechanical energy, the collection of ultralow frequency mechanical energy less than 1 Hz remains challenging so far. Here we report a study on harvesting ultra-low frequency mechanical energy by TENG utilizing modulating the mechanical vibrations. An equivalent circuit model of the TENG is derived to theoretical analyze the influence of ultralow frequency mechanical energy with different vibration waveforms in energy harvesting. The theoretical model provides reasonable interpretation of the harvesting performance for ultralow frequency mechanical energy with different vibration waveforms and contact-release time, which keeps in consistency with our experimental results. By reducing the contact-release time, the collection efficiency of TENGs is significantly improved, even if the mechanical input frequency is 0.1 Hz. This work advances the deep understanding of harvesting ultralow mechanical energy using TENGs, and provides an important insight for the design of the TENGs that can harvest various mechanical energy in wide frequencies.

Vibration-Induced Beat Frequency Offset Compensation in Distributed Acoustic Sensing Based on Optical Frequency Domain Reflectometry

We investigate the impact of the frequency modulation induced by vibration occurring at a preceding distance in distributed acoustic sensing (DAS) based on optical frequency domain reflectometry (OFDR), which analyzes a vibration waveform by calculating the spectrum shift of Rayleigh backscattered light in the same manner as a fiber Bragg grating. When the measurement time of a beat signal is shorter than the period of the vibration at the preceding distance, the vibration-induced frequency modulation can be treated as a frequency offset for the backscattered light. The frequency offset becomes a distance offset through the distance - beat frequency allocation of OFDR, and the distance offset forces us to interrogate the Rayleigh backscattered light spectra at unintentional distances for each measurement since the distance offset is time-varying. Since the spectra at unintentional distances are uncorrelated, the spectrum shift calculated with an uncorrelated spectrum results in a spurious vibration, which is a measured waveform that is different from the actual vibration waveform and that constitutes a measurement error in a DAS measurement. We propose a technique to compensate for the spurious vibration. The technique estimates the vibration-induced distance offset by calculating the cross-correlation between Rayleigh backscattered light waveforms and shifts the spectrum analysis range by the estimated offset in order to track the consistent spectrum. We perform a DAS measurement on a sensing fiber that experiences simultaneous vibrations at different distances and confirm the validity of the proposed technique.

Field Measurement and Numerical Study of the Vibration in the Pipeline of Centrifugal Compressor

During compressor operation, vibration of the connecting pipeline often occurs which potentially has an impact on safety. Field vibration measurements are carried out on a pipeline for a centrifugal compressor, and the vibration waveform and spectrum characteristics are obtained. Numerical studies are conducted to investigate the relationship between the natural frequency of the pipeline and the fluid excitation frequencies. These numerical results are verified by comparison with the field measurement values, which shows that the numerical method can be useful for engineering applications. Some preliminary conclusions are drawn from the results of the field measurements and the numerical simulation. Pressure fluctuations spread through the pipeline over an appreciable distance. The sensitive frequencies of the pipeline vibration are determined, and the fundamental causes of the flow induced vibration revealed. Accordingly, the pipeline structure can be modified to reduce the vibration and ensure the safety of the equipment and the pipeline.

Effect of Static Respiratory Volume on the Waveform of Cardiac-induced Sternal Vibrations.

Cardio-respiratory activity originating in the chest creates vibrations that diffuse through the organs to the thoracic wall. The vibrational waves were detected in all six degrees of freedom by an inertial motion sensor at the xiphoid process of the sternum. Vibrational cardiography (VCG) combines the detection of vibrations via acceleration, termed as seismocardiography, and gyration, termed as gyrocardiography. The objective of this study was to determine the effect of static respiration volume on the morphology of cardiac-induced waveforms in the VCG signal. In this study, 24 subjects were tested while holding breath at peak inhalation, and at peak exhalation. Ensemble averages of the waveforms showed larger variations in the signal when the lungs were inhaled for both the primary and secondary heart sounds. Inter-subject variability was accounted for by averaging all waveforms and calculating the root mean squared value over a sliding window of 60 milliseconds. The peak amplitudes of both heart sounds were consistently larger for high lung volumes. However, the ratio of primary to the secondary heart sound was found to be inversely proportional to lung volume. These opposing effects offer a strong analysis tool for the determination of relative inhalation volume using VCG morphology alone.

A new evaluation method for dependence of width of transmitted waves on accuracy in multipoint simultaneous ultrasonic measurements of cardiac wall vibration waveform

It has been revealed that the ultrasound measurement with high temporal resolution is useful for diagnosis of myocardial tissue properties. However, it is considered that the dynamic measurement of the target tissue is affected by the motion of neighbor tissues because of the wide width of the transmitted wave. For this reason, the measurement error is affected by spatial and temporal factors. In the present study, we constructed an experimental system for measuring these effects quantitatively and investigated the accuracy of the velocity measurement using some transmitted waves such as focused, plane, and diverging waves. In the conditions of the present study, the measurement error is minimized at 9° of the angular width of the transmitted wave. This method is useful for evaluating the conditions of transmitted waves for measurements of other targets which need a high temporal resolution such as shear wave, cardiac blood flow, and so on.

Dynamic performance analysis and quantitative evaluation for ultraprecision aerostatic spindle

For optics used in high-power laser beams, high accuracy requirements in full spatial frequency must be fulfilled. Among them, the allowable root mean square value is less than 5 nm in the PSD1 band. In order to evaluate the dynamic performance of the spindle system and put forward a quantitative index, a novel accurate model of the spindle system was built and a series of dynamic simulations were performed. Harmonic response analysis reveals natural frequencies and frequency response functions. Transient analysis indicates vibration waveforms of the tool-tip. Furthermore, by analyzing surface topography, it can be found that the medium-frequency waviness in the machined surface matches the vibration waveform. Obviously, the medium-frequency waviness is generated by the modal vibration of the spindle system. So that a quantitative index for the aerostatic spindle is proposed: when the amplitude of vibration in transient analysis is smaller than 8 nm, the allowable error in the PSD1 band can be fulfilled.