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Purpose: In order to facilitate the adjustment of parameters according to various environments during the operation and to increase the energy harvesting efficiency of the system, this article connects an adjustable gear unit and an inertial amplification unit to a structure with five springs. Methods: In this article, the kinetic equation of the system is given and they are solved using the harmonic balance method. The amplitude-frequency response curves were plotted on this basis. Multi-color plots of root mean square (RMS) values of induced voltage and electric power were obtained using the Runge–Kutta method. Results: By rotating the gears, the geometrical parameters of the system can be changed, thus limiting the force–displacement characteristics of the system. The mass element is connected vertically to an inertial amplification device for changing the dynamic mass. Conclusion: The rotation of gears can change the soft and hard characteristics of the nonlinear stiffness of the system and the characteristics of the potential energy curve. And the inertial amplification device can change the intrinsic frequency of the system. [ABSTRACT FROM AUTHOR]

Energy harvesting from external Ultra-low frequency vibrations is currently attracting a lot of attention. However, for the same system, it is difficult to satisfy the need for more efficient energy harvesting in a variety of external environments. Accordingly, an adjustable gearing device connected to the energy harvesting system is used herein for adapting energy harvesting to a wide range of external environments. The device uses four symmetrical inclined springs. One end of the springs is connected to a gear and the other end to a mass element. The geometrical parameters of the system can be varied by rotating the gears, thus varying the dynamic stiffness of the system. The kinetic equations of the system are derived and their nonlinear terms are Taylor-expanded. The amplitude-frequency response curve of the system is obtained by solving using the harmonic balance method. Multi-color plots of RMS values of induced voltage and electric power are obtained using the fourth-order Runge-Kutta method. The results show that the device has excellent adjustable performance. Adjusting the rotation angle of the gears can change the soft and hard characteristics of the system's dynamic stiffness and the intrinsic frequency, thus improving the system's energy harvesting performance in different environments.

Energy harvesting from external Ultra-low frequency vibrations is currently attracting a lot of attention. However, for the same system, it is difficult to satisfy the need for more efficient energy harvesting in a variety of external environments. Accordingly, an adjustable gearing device connected to the energy harvesting system is used herein for adapting energy harvesting to a wide range of external environments. The device uses four symmetrical inclined springs. One end of the springs is connected to a gear and the other end to a mass element. The geometrical parameters of the system can be varied by rotating the gears, thus varying the dynamic stiffness of the system. The kinetic equations of the system are derived and their nonlinear terms are Taylor-expanded. The amplitude-frequency response curve of the system is obtained by solving using the harmonic balance method. Multi-color plots of RMS values of induced voltage and electric power are obtained using the fourth-order Runge-Kutta method. The results show that the device has excellent adjustable performance. Adjusting the rotation angle of the gears can change the soft and hard characteristics of the system's dynamic stiffness and the intrinsic frequency, thus improving the system's energy harvesting performance in different environments. [Display omitted] • An energy harvesting system using a gear unit for regulation is proposed. • The natural frequency of the system is varied by changing the angle of the gears. • The nonlinear form of the system is adjusted by changing the angle of the gears. • The potential energy of the system is adjusted by changing the angle of the gears. • The RMS value of the system is used to analyze its energy harvesting efficiency. [ABSTRACT FROM AUTHOR]

The measurement of low frequency vibration signals is of great significance in seismic monitoring, health monitoring of large and medium-sized engineering structures, resource exploration, etc. A cross spring leaf-based novel FBG accelerometer was designed against the problem that it's hard for FBG acceleration sensors to effectively pick up low frequency vibration signals. Firstly, the vibration model of acceleration sensor was built and its operating principle was analyzed; secondly, the effect of structural parameters of sensor on their sensitivity and natural frequency was analyzed, and the sensor was subjected to static stress analysis and dynamic characteristics analysis through the ANSYS simulation software; finally, the sensors were subjected to performance tests with a low frequency vibration test system. Experimental results suggested that the natural frequency of FBG acceleration sensor was 63.65 Hz, it gives a flat sensitivity response in the low frequency band of 0.1–40 Hz; its sensitivity was not lower than 2000 pm/g, and the transverse interference was not higher than 1.99%; moreover, it offered favorable self-temperature compensation. Such FBG acceleration sensors with high sensitivity response at low frequencies provide important reference for the design of like sensors. [ABSTRACT FROM AUTHOR]

As a key component of the integrated transmission device of tracked armored vehicles, the confluence planetary row has the advantages of high transmission efficiency, high load capacity and compact space structure, but its working condition is very complex and variable, and the vibration characteristics under the extreme high and low temperature environment directly affect the service performance of the integrated transmission device. In this study, a comprehensive test rig for the vibration of the confluence planetary row is designed and built, and the dynamic characteristics tests of the confluence planetary row gear system are carried out under normal temperature conditions and temperature rise conditions. The results show that under normal temperature conditions, the rotational speed and load power have a greater influence on the system vibration amplitude; and under temperature rise conditions, when the temperature is constant, the load power has a greater influence on the system vibration amplitude in the low frequency band, and the rotational speed plays a dominant role in the high frequency band. When the speed and load power are certain, the influence of temperature on the low frequency region is more obvious, and the higher the temperature, the more obvious the influence will be. The research results have theoretical and application values for condition monitoring and health maintenance of the confluence planetary row under complex working conditions.

Low-frequency vibration cutting technology can actively generate an intermittent cutting process in which chips are broken up by vibrating the tool in the feed direction synchronized with the spindle rotation. The sinusoidal oscillation superimposed to feed drive motion triggers cutting thickness fluctuations so that air cutting occurs. To attain efficient and practical machining, selection of appropriate conditions for low-frequency vibration cutting is important. From a practical point of view, it is necessary to analyze the cutting process for its effects on tool wear as well as chip breakup. Low-frequency vibration cutting has been reported to reduce average cutting force and average cutting temperature. On the other hand, few studies have analyzed the effect of tool trajectory on the tool life, and thus the mechanism has not been fully clarified. In this study, the effects of low-frequency vibration on the tool life in turning operations were experimentally investigated for carbon steel, stainless steel, and titanium alloys. In low-frequency vibration cutting of ductile materials such as carbon steel and stainless steel, tool damage was significantly improved by designing an intermittent cutting process with large amplitude. On the other hand, the tool life for titanium alloys was deteriorated in low-frequency-vibration cutting. The experimental results indicated that the higher the vibration speed, the faster the tool wear progression in titanium alloy machining. Model-based analysis of the cutting force revealed a characteristic mechanism of the flank wear development that depends on the tool trajectory with low frequency vibration.

In order to understand the effect of low - frequency vibration stimulation on the behavior and physiology of Larimichthys crocea,this study simulated the vibration of breeding cabin by self-made steel sink and actuator,and used the main frequency of underwater noise of traditional knocking operation to catch large yellow croaker. The frequency of 125 Hz (150 dB) and 200 Hz (150 dB) were used to conduct vibration stimulation experiments on 250 g and 500 g groups of large yellow croaker to determine the behavioral response and physiological and biochemical changes of large yellow croaker ( cortisol, epinephrine, thyroxine). The results showed that:(1) In the early stage of acoustic stimulation,the behavioral responses of the two groups of test fish were characterized by random movement,cruising away after slow approach,free or around cruising. After adaptation,the test fish were basically in a regular or free cruising around the wall,cruising away after slow approach,or stagnant,and there was no obvious disturbance response. (2) In 250 g test group,the change of adrenaline at 125 Hz frequency (about 40. 93% increase) was the most significant (P<0. 05). Under the condition of 200 Hz frequency,the change of thyroxine (increased by about 41. 08%) was the most significant (P< 0. 05). Except for increase of other blood indexes except epinephrine was higher than that of 125 Hz frequency group. Therefore,250 g large yellow croaker was more sensitive to 200 Hz. In the 500 g test group, the change of thyroxine ( increased by about 28. 68%) at 125 Hz frequency was the most significant ( P < 0. 05),and other blood indexes decreased. Under the condition of 200 Hz frequency,the change of thyroxine (increased by about 41. 79%) was the most significant (P<0. 05) and higher than that of 125 Hz frequency group,while other blood indexes increased in different degrees in 200 Hz frequency group. Therefore,the 250 g and 500 g groups were more sensitive to 200 Hz vibration stimulation. In this study, the effects of low - frequency vibration stimulation on the behavioral response and physiological and biochemical indexes of large yellow croaker were analyzed. The aim was to improve the growth rate,survival rate and quality of large yellow croaker during the breeding process of large yellow croaker,and to provide data support and reference [ABSTRACT FROM AUTHOR]

In order to prolong the service life of wireless vibration sensors when collecting a large number of high-frequency vibration data, this paper studied the existing vibration data compression algorithms, put forward and analyzed the existing problems, and on this basis, proposed an effective mechanism of K-means clustering-discrete cosine transform (DCT) dual data compression. According to the characteristics of predictive maintenance data, K-means clustering-DCT dual compression algorithm firstly used K-means algorithm to aggregate and classify vibration data, and then carried out DCT compression according to the frequency domain characteristics of vibration signals. The verification results showed that the algorithm significantly improved the data compression efficiency and reduced the transmission of redundant data by aggregating vibration data. In addition, under the condition of the same amount of data, the algorithm had better application performance after improving the peak signal-to-noise ratio compared with other algorithms.

Inspired by the hind limbs of goats, a bio-inspired polygon vibration isolation structure with nonlinear stiffness and damping is proposed. The bionic mechanism consists of four bionic legs with different rods (as skeleton), 12 inclined tension springs (as muscle or tendon), a bearing platform, a base, and so on. A theoretical model is developed to characterize its stiffness nonlinearity through geometrical and mechanical analysis. Theoretical analysis shows that the bionic structure has nonlinear positive stiffness and large working range. The dynamic model of the structure is established based on the Lagrange principle, and the influence of various structural parameters on the vibration isolation performance of the structure was analyzed combined with ADAMS. Thanks to the unique bionic design, the device allows the stiffness and damping characteristics of the system to be adjusted by varying the structural parameters, resulting in excellent stability, high static and low dynamic stiffness, excellent vibration isolation performance, and good load carrying capacity without active control. [ABSTRACT FROM AUTHOR]

Low-frequency vibration cutting is a machining technology in which chips are broken by applying periodic vibrations along a specific axis. Periodic vibration deteriorates the surface roughness and roundness of the workpiece when compared to without vibration cutting. In this study, the properties of a machined surface under low-frequency vibration were simulated. Based on the simulation results, a tool was designed to reduce the effects of periodic vibration on the surface properties. Actual machining experiments were conducted using the proposed tool to clarify the relationship between tool shape, surface roughness, and roundness under low-frequency vibration. Using the proposed tool on low-frequency vibration cutting, the surface roughness was reduced (from 5.74 µm to .94 µm in Ra and 23.09 µm-6.66 µm in Rz), average roundness improved (from 4.73 µm to 2.95 µm), and maximum roundness decreased (from 15.34 µm to 3.61 µm) compared with those of the conventional tool. [ABSTRACT FROM AUTHOR]

Recently, the application of low frequency vibration has been attempted in the turning process. The tool is vibrated in the feed direction by numerical control to break up long continuous chips that adversely affect the surface quality and tool wear, etc., by generating a duration of cutting edge leaving workpiece. In order to achieve higher machining efficiency in vibration cutting, however, it is necessary to focus on chatter stability. When chattering occurs, a higher frequency chatter vibration is superimposed on the low-frequency tool vibration caused by the feed motion of the servo drive. However, the chatter amplitude decreases due to system damping, because the cutting force does not act in the air-cutting section of vibration cutting. In addition, tool displacement is regenerated not only before one spindle rotation, but also before two or more rotations in vibration cutting. Therefore, the application of low frequency vibration has an important influence on the chatter stability. The purpose of this study is to reveal the detailed effects of vibration conditions on the stability limit, and identify the vibration conditions that achieve high chatter stability. We consider the effect of the air-cutting and multi-rotation delayed regeneration described above, in which chatter displacement occurring more than two spindle rotations before is regenerated, and analyze regenerative chatter vibration during vibration cutting in the frequency domain. In this study, the phase difference φ of tool motion in vibration cutting is focused as an important vibration condition parameter that affects the stability limit. In the conventional condition (φ = π), the air-cutting ratio is limited to a relatively low value, and only the dynamic displacements before one and two spindle revolutions are regenerated. On the other hand, setting φ appropriately under the condition φ ≠ π , the air-cutting ratio is increased. Furthermore, the dynamic displacement is regenerated not only before one and two spindle rotations but also before three or more spindle rotations. These results indicate that proper setting of the phase difference φ is effective in suppressing regenerative chatter vibration due to the effects of both the air-cutting phenomenon and multi-rotation delay. Finally, cutting experiments show that the phase difference φ specified by the analysis was effective in suppressing chatter vibration. In summary, the application of low frequency vibration with an appropriately set phase difference φ is an effective strategy for suppressing chatter vibration without reducing the material removal rate in the turning process. [Display omitted] • We performed chatter stability analysis in low frequency vibration cutting. • Chatter stability is affected by vibration cutting parameters. • Phase difference φ and amplitude ratio A / F heavily impact chatter stability. • Using the specific φ depending on A / F is an effective chatter-suppression strategy. [ABSTRACT FROM AUTHOR]

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Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A piezoelectric-electromagnetic collaborative energy extraction circuit (PEC-EC) is presented in this paper to extract low-frequency vibration energy from arm swinging for wearable devices. This circuit simultaneously harvests energy from both the piezoelectric transducer (PZT) and electromagnetic coil generator (ECG). When the piezoelectric output voltage reaches its peak, the peak detection circuit becomes conductive, and the energy of the piezoelectric material is extracted at this moment. At the same time, the PEC-EC circuit can also harvest electromagnetic energy. Especially, even at low electromagnetic voltage input, the electromagnetic voltage can be extracted through the designed switch. The experimental results show that the circuit starts up only when the input voltage reaches 0.5V. The electromagnetic energy conversion efficiency can reach 53 %, and the piezoelectric energy conversion efficiency can reach 56 %. The effectiveness of collaborative extraction was also verified through experimental validation. [ABSTRACT FROM AUTHOR]

We demonstrate a fiber optic accelerometer for low frequency vibration detection in this paper. A slider moving along a guide rail is suspended over an optical fiber into which a fiber Bragg grating (FBG) is inscribed. When acceleration signal acts on our sensing structure, the slider will vibrate vertically under the constraint of the optical fiber, inducing the change of FBG axial strain and we can therefore establish the relationship between vibrational acceleration and wavelength shift. Laboratory measurements validate the effectiveness of the derived theoretical results that the sensor owns a low natural frequency of 9.5 Hz and a high sensitivity up to 926.29 pm/g from 0.5 to 9 Hz. The sensor structure also shows a good ability to resist lateral interference that the cross-sensitivity is calculated as 0.3%. • Compact low-frequency FBG accelerometer using fiber itself as elastic element. • Low natural frequency of 9.5 Hz and high sensitivity up to 926.29 pm/g. • Cross sensitivity of 0.3% indicates its strong ability to resist lateral interference. [ABSTRACT FROM AUTHOR]

The prevalence of dementia is increasing with the ever-growing population of older adults. Non-pharmacological, music-based interventions, including sensory stimulation, were reported by the Lancet Commission in 2020 to be the first-choice approach for managing the behavioural and psychological symptoms of dementia. Low frequency sinusoidal vibration interventions, related to music interventions through their core characteristics, may offer relief for these symptoms. Despite increasing attention on the effectiveness of auditory music interventions and music therapy for managing dementia, this has not included low frequency vibration. This scoping review, following the JBI methodology guidelines, was conducted to investigate participants’ responses to both sound and mechanical vibration, the characteristics of the delivered interventions, methodological challenges, and the specifics of the research experiments reported. An extensive search was conducted in BMC, CINAHL, Cochrane Central Register of Controlled Trials, EMBASE, ERIC, MEDLINE (OvidSP), Pedro, ProQuest Central, PsycINFO, Scopus, and Web of Science. Current Controlled Trials, Clinical Trials, and Google Scholar were also searched as well as a hand search in relevant journals. Studies on adults with all types of dementia, investigating tactile low frequency sound or mechanical vibration in any context were considered. Data from eight full-length studies (three RCTs, two quasi-experimental, two case reports, and one qualitative) were extracted using the data extraction table developed by the authors and were included in the analysis and critical appraisal. Issues in quality related to, for example, control groups and blinding. Few studies addressed participants’ subjective responses to the interventions. Reporting on the intervention characteristics was unclear. It appeared more frequent sessions led to better outcomes and home-based interventions potentially addressing the issue of access and feasibility. Future research should include neuroimaging to measure and confirm the hypothesised mechanism of cerebral coherence. Standardised reporting of intervention characteristics is also needed to ensure replicability of the experiments. Higher quality research is needed to investigate the impact and effect of low frequency vibration for the symptoms of dementia and compare outcomes in meta-syntheses. [ABSTRACT FROM AUTHOR]

Background: Vibroacoustic therapy (VAT) uses low-frequency sound, often combined with listening to music, for therapeutic purposes. However, the impact of low-frequency vibration (LFV) on physiological functions and subjective perception is relatively unknown. Methods: We conducted a randomized cross-over study with the aim of comparing the effect of constant LFV of 40 Hz, its amplitude modulation, and the placebo condition on heart rate variability (HRV), stress perception (measured by visual analogue scales for stress) and mood (measured by UWIST Mood Adjective Check List). Results: Research experiments with various interventions (constant LFV with sound of nature (river in forest), amplitude modulation of the same LFV with sounds of nature and sounds of nature without LFV) were realised involving 24 participants. It was found there was an effect on HRV, stress perception and mood after the interventions. However, there were only seldomly experienced, and mostly nonsignificant, differences between the intervention conditions, so the effects may be attributed to factors other than LFV. Conclusions: Large scale experimental studies are needed to verify the preliminary findings and to explore various coinciding factors that may have influenced the results of this study, e.g., type of autonomic nervous system. We propose that the effect of LFV exposure may differ when combined with listening to music, and this hypothesis should be investigated in future studies. [ABSTRACT FROM AUTHOR]

The prevalence of dementia is increasing with the ever-growing population of older adults. Non-pharmacological, music-based interventions, including sensory stimulation, were reported by the Lancet Commission in 2020 to be the first-choice approach for managing the behavioural and psychological symptoms of dementia. Low frequency sinusoidal vibration interventions, related to music interventions through their core characteristics, may offer relief for these symptoms. Despite increasing attention on the effectiveness of auditory music interventions and music therapy for managing dementia, this has not included low frequency vibration. This scoping review, following the JBI methodology guidelines, was conducted to investigate participants’ responses to both sound and mechanical vibration, the characteristics of the delivered interventions, methodological challenges, and the specifics of the research experiments reported. An extensive search was conducted in BMC, CINAHL, Cochrane Central Register of Controlled Trials, EMBASE, ERIC, MEDLINE (OvidSP), Pedro, ProQuest Central, PsycINFO, Scopus, and Web of Science. Current Controlled Trials, Clinical Trials, and Google Scholar were also searched as well as a hand search in relevant journals. Studies on adults with all types of dementia, investigating tactile low frequency sound or mechanical vibration in any context were considered. Data from eight full-length studies (three RCTs, two quasi-experimental, two case reports, and one qualitative) were extracted using the data extraction table developed by the authors and were included in the analysis and critical appraisal. Issues in quality related to, for example, control groups and blinding. Few studies addressed participants’ subjective responses to the interventions. Reporting on the intervention characteristics was unclear. It appeared more frequent sessions led to better outcomes and home-based interventions potentially addressing the issue of access and feasibility. Future research should include neuroimaging to measure and confirm the hypothesised mechanism of cerebral coherence. Standardised reporting of intervention characteristics is also needed to ensure replicability of the experiments. Higher quality research is needed to investigate the impact and effect of low frequency vibration for the symptoms of dementia and compare outcomes in meta-syntheses.

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The turning process is a standard machining process employed in diverse sectors. However, it produces long continuous chips that can affect the efficiency of the process, accelerate the tooling's wear, or damage the machined surface. As a solution, low frequency vibration cutting synchronizing with the spindle rotation has recently been developed as a new machining method in turning operation. It applies vibrations in the tool feed direction and can synchronously control the applied vibrations and the spindle rotation. It can also effectively divide the long continuous chips generated by the turning process and has the potential to reduce thermo-mechanical load on the tool by periodically enabling the tool to leave the workpiece due to the vibrations. Low frequency vibration cutting, the cutting characteristics of which differ from those of conventional turning, induces residual stresses in the machined surface; however, the properties of these stresses have not yet been studied. Residual stress can have both beneficial and negative effects on the fatigue life of products. While compressive residual stress increases the fatigue life of the product, tensile residual stress facilitates the growth of fine cracks on the product's surface and reduces fatigue life. Therefore, it is important to understand the characteristics of the residual stress developed on a machined surface. In this study, an annealed 0.45% C steel bar was machined via straight turning of the vibration cutting process synchronizing with the spindle rotation, and the residual stress on the finished surface was measured. Particular focus was placed on analyzing the effects of the spindle phase on the characteristics of the residual stress inside the machined surface, especially the effects of the number of vibrations per spindle rotation, D , which is a unique parameter defining the vibration condition. Our results revealed that the residual stress varied depending on the position of the finished surface owing to the change in feed with the spindle phase during the process. Furthermore, D was observed to heavily influence the distribution of the residual stress on the finished surface. By means of adjusting its value, the residual stress value could either fluctuate periodically according to the phase of the workpiece or not fluctuate. [Display omitted] • Straight turning was performed while vibrating the tool in the feed direction in synchronization with the spindle rotation. • In the process, the residual stress on the finished surface is not uniform. • The residual stress may fluctuate depending on the workpiece rotation phase. • The residual stress fluctuation can be created by adjusting the number of vibrations per spindle rotation D. [ABSTRACT FROM AUTHOR]

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This study proposed a 4 degrees of freedom dynamic model for the two-axle heavy truck to investigate the low frequency vibration characteristics of the suspension system. Unlike the previous research works, the vibration equations of heavy truck model were solved in the frequency domain instead of the traditional time domain based on a calculation method in the complex domain. In order to evaluate the vibration characteristics of the suspension system, parameters of the vehicle velocity, wavelength of the road, load condition, stiffness coefficient, and height of the random road surfaces were then taken into account to clarify their influence on the acceleration frequency characteristics of the suspension system, respectively. The simulation results reveal that the resonant frequency of the suspension system was not affected by the vehicle velocities and road surface profile, while it is greatly influenced by the loading conditions and stiffness of the suspension system. In addition, under different working conditions, the acceleration frequency response characteristics of the vertical and pitch vibration of the heavy truck body and the vertical vibration of the front and rear axles were greatly affected, especially when the vehicle was traveling on the rod of level C at a speed of 30 m s−1. [ABSTRACT FROM AUTHOR]

The annular antenna is a typical large flexible space truss structure featured by small damping and low modal frequencies. The external disturbances, e.g. impulse load resulting from satellite attitude adjusting, may induce the low frequency large amplitude vibrations of annular antenna for a long time and thus reduce working precision and cause even its damage. The active control of vibration of annular antenna under impulse excitation is investigated in the paper. The voice coil actuator instead of piezoelectric stack actuator is used in order to meet the demand of large output displacement. The governing equation of active vibration control system is established by use of finite element method. The proportional differential (PD) control and fuzzy control algorithms are firstly studied in the active control. The results show that the fuzzy control exhibits worse control performance than PD control due to weak control function near structural equilibrium position. To circumvent the drawback of fuzzy control, a fuzzy PD hybrid control strategy is proposed which can combine the merits of both control methods. The simulated and experimental results show that the fuzzy PD hybrid control can yield the best control effect under impulse excitation comparing with the PD control and ordinary fuzzy control. The work provides a promising control way for active control of low frequency and large displacement vibration of annular antenna in satellite engineering. [ABSTRACT FROM AUTHOR]

Visual information can be easily obtained nowadays with more access to various photographic facilities. Appropriate logical analysis and processing of massive visual information could apply to flexible environment pollution detection. In this paper, we present a visual-based non-contact sensing method to detect the low frequency vibration pollution in daily life. The edge points of vibrating objects with more vibration information are extracted using bilateral filtering and Sobel operator. The Sobel operator weights the influence of the pixel position, which make the edge feature extraction effect better and the edge feature obtained more obvious. After that, the continuous frames of the vibration objects with edge information are transformed into several one-dimensional pixel level signals as the input of multi-scale network, which also improves the generalization ability. Experiments on daily objects under low frequency vibration are conducted. The detection accuracy is above 99%, which proves the reliability of the proposed method for the detection of low frequency vibration circumstance pollution. [ABSTRACT FROM AUTHOR]

Copyright of Journal of National University of Defense Technology / Guofang Keji Daxue Xuebao is the property of NUDT Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aiming at the problem that the unclear removal mechanism of CFRP could not ensure machining quality of Al and CFRP at the same time during low-frequency vibration-assisted drilling process of Al/CFRP laminated structure, the tool path during vibration-assisted drilling was analyzed by theoretic method. Based on this, the effect of low frequency vibration on material removal and processing quality at Al entrance, CFRP exit and hole wall of the laminated structure was revealed. The influence of low-frequency vibration parameters was further studied, a drilling platform including low-frequency vibration tool holder was built, based on which low-frequency vibration-assisted drilling experiments with special designed tools for CFRP at different amplitudes were conducted. The results indicate that low-frequency vibration can effectively achieve aluminum alloy chip breaking, avoiding scratching of long chips and improving the processing quality of Al part. The introduction of low-frequency vibration can increase the maximum axial force and excessive amplitude can exacerbate tear damage of CFRP at the exit and reduce the quality of drilled hole wall. [ABSTRACT FROM AUTHOR]

This paper presents the discrete state space mathematical model of the end-effector in industrial robots and designs the linear-quadratic-Gaussian controller, called LQG controller for short, to solve the low frequency vibration problem. Though simplifying the end-effector as the cantilever beam, this paper uses the subspace identification method to determine the output dynamic response data and establishes the state space model. Experimentally comparing the influences of different input excitation signals, Chirp sequences from 0 Hz to 100 Hz are used as the final estimation signal and the excitation signal. The LQG controller is designed and simulated to achieve the low frequency vibration suppression of the structure. The results show that the suppression system can effectively suppress the fundamental natural frequency and lower vibration of end-effector. The vibration suppression percentage is 95%, and the vibration amplitude is successfully reduced from ±20 μm to ±1 μm. The present work provides an effective method to suppress the low frequency vibration of the end-effector for industrial robots. [ABSTRACT FROM AUTHOR]

By use of the concept of impedance, this paper establishes a random energy harvester output model of double-ended fixed beam piezoelectric energy harvester under random White Gaussian noise excitation, which is based on the discussion of the output characteristics influenced by changing vibration beam shape and piezoelectric sheet length under random excitation, while improving piezoelectric structure of double-ended fixed beam piezoelectric energy harvester. It also deduces the output voltage, current and power of energy harvester with Fokker–Planck equation, which are verified by Monte Carlo simulation and experimental testing. It can be found that improving vibration beam shape can reduce resonant frequency and increase average output power of the system. The optimal value of piezoelectric sheet length can be different corresponding to different structures, which proves that double-ended fixed beam piezoelectric energy harvester under random White Gaussian noise excitation can achieve maximum output with optimal piezoelectric sheet length. In addition, in order to further improve the output performance of piezoelectric energy harvester under random excitation, it is necessary to increase the acceleration spectral density under random excitation and set an optimal value of the piezoelectric loading resistance, which is more suitable for energy harvester applied under random low-frequency environment. [ABSTRACT FROM AUTHOR]

• Theoretical analysis of the combined harmonic response of the structure when it is simultaneously excited by low-frequency vibration and ultrasonic guided waves is completed. • De-icing experiments under low-frequency resonance mode, ultrasonic guided waves, and different types of low-frequency excitation modes combined with ultrasonic guided waves are completed. • The application power of low-frequency vibration and ultrasonic guided wave needs to reach a certain level to achieve effective de-icing. • Experimental results show that the low-frequency vibration can significantly enhance the de-icing efficiency of ultrasonic guided waves. This paper presents a novel hybrid de-icing system combining ultrasonic guided waves and low frequency resonance. This new system uses low-frequency vibration-assisted ultrasonic guided waves to remove ice from the leading edge of the blade. Ultrasonic transducers are used to generate ultrasonic guided waves for breaking and detaching ice, and piezoelectric ceramics are used to excite low-frequency resonant modes of the structure to induce additional acceleration and stress. Theoretical analysis and finite element simulation of the combined harmonic response of the structure when it is simultaneously excited by low-frequency vibration and ultrasonic guided waves is completed. Modal analysis is used to determine the mounting location of the piezoelectric ceramics. Transient analysis is calculated to study the effect of low-frequency resonance on ultrasonic guided wave de-icing. De-icing experiments under low-frequency resonance mode, ultrasonic guided waves, and different types of low-frequency excitation modes combined with ultrasonic guided waves are completed. These results show that the application power of low-frequency vibration and ultrasonic guided wave needs to reach a certain level to achieve effective de-icing, and low-frequency resonance vibration is crucial for ultrasonic guided wave de-icing. Compared with ultrasonic guided wave de-icing technology, the combination of low-frequency excitation vibration and ultrasonic guided wave excitation can greatly improve the de-icing efficiency. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesters (PEH) are widely used to collect piezoelectric energy. However, adapting to different engineering application environments is difficult for traditional PEHs. To improve the engineering application value of PEH, a hanger piezoelectric energy harvester (HPEH) based on low frequency vibration of hanger is proposed in this paper. A dynamic electromechanical coupling model was established for hanger structure, and the effects of the external load resistance, the polyvinylidene fluoride (PVDF) piezoelectric film installation location, the stability of the PVDF piezoelectric film with different winding methods, and the external excitation amplitude on the energy output performance of the HPEH were studied. Results indicate that the optimal load resistance of the HPEH studied in this paper is 1.0 MΩ; the PVDF piezoelectric film location has a significant impact on the performance of the HPEH, and the output power is highest at hanger L c/4; the PVDF piezoelectric films during ring winding is better than those in spiral winding for the same external cycle excitation; in the external excitation amplitude range of 2 d –6 d (d : hanger diameter), appropriately increasing the external excitation amplitude is conducive to improving the output voltage of the HPEH, with the root mean square voltage increasing by 95.11 % at external excitation amplitude A = 6 d compared with that at the initial excitation amplitude. It provides an innovative solution for the field of cable structures and new energy sources, and the further research and application of this technology is expected to have a profound impact in the field of energy sustainability and engineering technology. • This paper proposes a novel hanger piezoelectric energy harvester. • The key parameters affecting the energy harvesting performance are analyzed. • The engineering application value is increased compare with conventional harvesters. • It is suitable for low-frequency vibrations of cable structures. • It provides a new idea for energy harvesting of cable structures. [ABSTRACT FROM AUTHOR]

Active vibration isolation is gaining increased attention in the ultra-high precision application of atom interferometry to effectively treat the unavoidable ground vibration. In this system, a digital control subsystem is used to process and feedback the vibration measured by a seismometer. A voice coil actuator is used to control and cancel the motion of a commercial passive vibration isolation platform. The system level simulation model is established by Simulink software, The simulation results demonstrate the asymptotic stability of the system and the robustness of the control algorithm. Compared with the conventional lead–lag compensation type controller, the algorithm adopted uses sliding mode control, taking advantage of its easy computer implementation and its robust high performance properties. With the feedback path closed, the system acts like a spring system with a natural resonance frequency of 0.02 Hz. The vibration noise in the vertical direction is about 20 times reduced during 0.1 and 2 Hz, The experimental results verify that the isolator has significant vibration isolation performance, and it is very suitable for applications in high precision gravity measurement.

This paper is aims to study the influence mechanism of low frequency vibration on coal seepage in mining process. By adding vibrating device to triaxial seepage test and combining with Meso-scomic test, the evolution law of coal rock permeability and internal Meso-structure disturbed by vibration under effective volume stress is analyzed. The results show that vibration can increase the permeability of coal and rock. When the vibration frequency is 10 Hz, the resonance effect of coal and rock is produced, and the permeability of coal and rock reaches the maximum. The permeability of coal and rock decreases with the increase of effective volume stress. The porosity and gray value are used to describe the permeability change of coal and rock specimens, that is, the permeability increases with the increase of porosity and decreases with the increase of gray value. The research conclusion has a new understanding of coal and gas outburst induced by low frequency vibration, which is conducive to reduce the occurrence of coal mining safety accidents. [ABSTRACT FROM AUTHOR]

In order to study the influence mechanism of vibration on the safety of coal mining in the process of excavation, the vibration disturbance system is added on the basis of triaxial seepage test, and the evolution law of permeability of coal petrography under low frequency vibration and different effective stress is analyzed. And the process of internal fracture of coal petrography during loading is analyzed by combining with microscopic test. The test result shows that the greater the effective stress applied, the smaller the permeability under the load condition, and decrease in the form of negative exponential; under the effect of low frequency vibration, the higher the frequency of disturbance, the greater the permeability and rise exponentially. The CT image processing can clearly observe the expansion law of the original fracture after vibration and loading, and analyze quantitatively the evolution law of coal-rock fracture by using the porosity. The conclusions obtained will be used to guide the engineering practice and so as to effectively prevent the occurrence of coal mining safety accidents. [ABSTRACT FROM AUTHOR]

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This paper presents the discrete state space mathematical model of the end-effector in industrial robots and designs the linear-quadratic-Gaussian controller, called LQG controller for short, to solve the low frequency vibration problem. Though simplifying the end-effector as the cantilever beam, this paper uses the subspace identification method to determine the output dynamic response data and establishes the state space model. Experimentally comparing the influences of different input excitation signals, Chirp sequences from 0 Hz to 100 Hz are used as the final estimation signal and the excitation signal. The LQG controller is designed and simulated to achieve the low frequency vibration suppression of the structure. The results show that the suppression system can effectively suppress the fundamental natural frequency and lower vibration of end-effector. The vibration suppression percentage is 95%, and the vibration amplitude is successfully reduced from ±20 μm to ±1 μm. The present work provides an effective method to suppress the low frequency vibration of the end-effector for industrial robots.

Low frequency vibration monitoring has significant implications on environmental safety and engineering practices. Vibration expressed by visual information should contain sufficient spatial information. RGB-D camera could record diverse spatial information of vibration in frame images. Deep learning can adaptively transform frame images into deep abstract features through nonlinear mapping, which is an effective method to improve the intelligence of vibration monitoring. In this paper, a multi-modal low frequency visual vibration monitoring system based on Kinect v2 and 3DCNN-ConvLSTM is proposed. Microsoft Kinect v2 collects RGB and depth video information of vibrating objects in unstable ambient light. The 3DCNN-ConvLSTM architecture can effectively learn the spatial-temporal characteristics of muti-frequency vibration. The short-term spatiotemporal feature of the collected vibration information is learned through 3D convolution networks and the long-term spatiotemporal feature is learned through convolutional LSTM. Multi-modal fusion of RGB and depth mode is used to further improve the monitoring accuracy to 93% in the low frequency vibration range of 0–10 Hz. The results show that the system can monitor low frequency vibration and meet the basic measurement requirements.

Periodic vibration in the form of distorted sine wave or other complex shapes are most common in the real moving objects, where the device can be exploited on the basis of flexible modules. This kind of exposure directly affects the reliability of the construction in general. The objective of the work was the creation of an experimental device for the study of mechanical vibrations and the dependencies of their impact on the operated device.Research of mechanical vibrations and the dependencies of their influence on the device will allow finding solutions to the problems of reliability of radio electronic devices. It developed an experimental device and automatic adaptive system for control own resonant frequency of the flexible module. As a result of the experiments has been identified according to mechanical influences on the output parameters of the devices. This will take into account and to apply this experience in the design and manufacture of devices with the use of flexible printed circuit boards.

This study aimed to compare the effect of local vibration (LV) and whole body vibration (WBV) on lower body flexibility and to assess whether vibration treatments were more effective than traditionally used static and dynamic stretching methods. Twenty-four well-trained male combat athletes (age: 22.7 ± 3.3 years) performed four exercise protocols – LV (30 Hz, 4 mm), WBV (30 Hz, 4 mm), static stretching (SS), and dynamic stretching (DS) – in four sessions of equal duration 48 hours apart in a randomized, balanced order. During a 15-minute recovery after each protocol, subjects performed the stand and reach test (S&R) at the 15th second and the 2 nd , 4 th , 6 th , 8 th , 10 th and 15 th minute. There was a similar change pattern in S&R scores across the 15-minute recovery after each protocol (p = 0.572), remaining significantly elevated throughout the recovery. A significant main protocol effect was found for absolute change in S&R scores relative to baseline (p = 0.015). These changes were statistically greater in LV than WBV and DS. Changes in SS were not significantly different from LV, but were consistently lower than LV with almost moderate effect sizes. After LV, a greater percentage of subjects increased flexibility above the minimum detectable change compared to other protocols. Subjects with high flexibility (n = 12) benefited more from LV compared with other methods (effect size ≥ 0.862). In conclusion, LV was an effective alternative exercise modality to acutely increase lower extremity flexibility for well-trained athletes compared with WBV and traditional stretching exercises.

Foam injection is widely applied in amounts of fields to drilling, production, and formation protection. Sometimes, the application result is disappointing, which is caused by the failure of bubble generation in foam flooding. Therefore, it is necessary to seek ways for improving the performance of foam injection. An increased disturbance to the stratum, like the vibration caused by a seismic oil recovery technique, would be helpful. In the current work, the seepage of air foam in porous media under low frequency (LF) vibration is analyzed with experiments and an investigation of bubble creation/destruction rate change is carried out using mathematical modeling. The resistance factor of foam flooding under indoor vibration increases by 1.5 times and the valid time is obviously extended compared with when no vibration is used. The optimal vibrating acceleration and frequency of 0.7 m/s2 and the natural frequency of the cores-nearby of 18 Hz are achieved in the indoor experiments. Under vibration, the bubble generation rate increases, while bubble break rate by internal expansion or by gas diffusion and transfer decreases. An interesting phenomenon is also observed, which might develop a power level formula between the initially defined dimensionless MRF (maximum foam flooding resistance factor) and dimensionless DMRF (duration of maximum foam flooding resistance factor). The power product and sum of the power exponents of the above formula both equal approximately to 1. With the assistance of LF vibration, the increase of security, adaptability, and efficiency in foam injection may improve the reservoir recovery and extend its application.

It is necessary to increase the damping of a machine support structure (support damping) to reduce the residual vibrations caused by rocking vibration. The stiffness of the machine support system (support stiffness) is also an important parameter that needs to be considered while designing machine tools, to avoid low frequency vibrations. However, conventional passive damper supports decrease the support stiffness while increasing the damping. In our previous study, a passive viscoelastic non-linear damper system for shear vibrations, where the vertical preload determines its damping coefficient, was developed to increase the support damping without decreasing the stiffness by focusing on the horizontal component of rocking vibration. The magnitude dependency of the damping capacity has been modeled. However, this damper system has a tradeoff relationship between natural frequency and damping capacity caused by changes in the preload distribution. Thus, adjustment of the vertical preload applied on the damper is essential for the model-based installation of this damper system. So far, no method has been proposed considering this issue. The vertical preload has been adjusted by trial and error methods. This study proposes a method to determine the damper preload conditions systematically by considering the tradeoff relationship between natural frequency and damping capacity caused by changes in the preload distribution. This method is described based on the case study of a machining center. First, the relationship between preload distribution and support stiffness is investigated using the support stiffness model. Then, the relationship between damping capacity and vertical preloads on the damper is investigated based on material test results. Based on these investigations, the tradeoff relationships are simulated on a machining center by utilizing the damper model. The simulation results are verified with the experimental results. The results show that the proposed method can estimate the tradeoff relationship between natural frequency and damping capacity caused by the changes in the preload distribution. By utilizing this estimated relationship, the preferred preload condition can be decided depending upon the user's demand. [ABSTRACT FROM AUTHOR]

CFRP/Ti stacks have been widely used in aviation industry. Mechanical characteristics of Carbon fiber reinforced plastic(CFRP) is greatly different from that of the titanium alloy. The low thermal coefficient and elastic modulus of Titanium alloy lead to long spiral chips with high temperature during drilling which may cause surface scratches of machined hole and damages to the CFRP layer. In the paper three types of drilling methods:conventional drilling,rotary ultrasonic assisted drilling and low-frequency vibration assisted drilling are compared and analyzed from the following points of view: Cutting temperate,drilling quality and chip morphology. It is shown that compared with conventional drilling,both the ultrasonic vibration and low frequency vibration assisted drilling could reduce the temperature and improve the drilling quality. The low frequency vibration assisted drilling method could break the cutting chips belts of titanium alloy material to small chips. Due to the reason,the cutting temperature could be reduced by 45%. As a result,the CFRP damages caused by over heated cutting chips belts of titanium alloy could be avoided,and the drilling quality could be improved to a great deal. [ABSTRACT FROM AUTHOR]