External Vibration Research Articles

Levenberg–Marquardt method for solving inverse problem of MRE based on the modified stationary Stokes system

Magnetic resonance elastography (MRE) is a developing medical imaging technique which can successfully diagnose liver diseases such as cirrhotic and fibrosis. As a hardware MRE gives an image of a viscoelastic wave in a region of interest (ROI) of a human body. Here the wave is generated by an external vibration system and further transmitted to the human body through a probe. MRE also has a software usually called elastogram which reconstructs viscoelastic modulus from the wave displacement vector. An appropriate model equation or system which connects the wave image to the modulus is known as modified stationary Stokes system if viscoelastic property of the ROI is isotropic (Ammari et al 2008 Q. Appl. Math. 66 139–175; Jiang et al 2011 SIAM J. Appl. Math. 71 1965–1989). Comparing this system with the original stationary Stokes system, it has an extra term with frequency. In most cases the elastogram has been using a more simpler model equation such as scalar model (Manduca et al 2003 Med. Image Anal. 5 237–254). In this paper we discuss about a scheme of solving the equation (*)F(A) = u, where u is the measured wave displacement and F(A) is the solution to the boundary value problem for the modified stationary Stokes system with the modulus A (see subsection for more details). More precisely, we will show the convergence of a Newton type iteration scheme called the Levenberg–Marquardt method by proving that the nonlinear operator F satisfies the tangential cone condition. We will also provide several numerical tests even with noisy data.

Discharge of vibrated granular silo: A grain scale approach

The present work focuses on granular flows in a nearly-2D silo when external vibrations are applied. Experimental measurements and numerical simulations based on discrete element method (DEM) were performed in order to study the impact of both vibrations and opening size on the flow. Although vibrations make the flow possible for small opening sizes, we show that they can either increase or decrease the flow rate depending on the range of experimental parameters (amplitude, frequency, opening size...). The effect of vibrations amplitude (10–16000 μm) and frequency (15–75 Hz) on the flow was investigated. Two regimes are evidenced for the flow, governed by the Froude number Fr and the relative frequency Ω. In the first regime, vibration causes dead zones to flow and increases collision dissipation at the aperture while keeping the particle volume fraction constant. The flow rate decreases and can be described by Benyamine's law by introducing an effective velocity that accounts for the effect of vibrations on the fall of particles at the outlet. In the second regime, the perturbations due to vibrations then surpass the gravity driven flow, leading to periodic shocks in the silo and increasing the apparent flow rate.

Deagglomeration of fine granular materials under low-frequency vertical harmonic vibration

Resonance Acoustic Mixing® (RAM) technology applies an external low-frequency vertical harmonic vibration to mix and deagglomerate fine and ultrafine granular materials. However, although this system is used for various applications, its mechanism is yet not well understood. To address this gap in the knowledge, in this study, a continuum model of powder in a low-frequency vertical harmonic vibration container was established, and spectral proper orthogonal decomposition was used to analyse the slip velocity. The mechanism of fine particle deagglomeration with vertical harmonic vibration is proposed. The slip velocity at the interface between the particles and air has a significant periodic character and produces a persistent drag force on the particles. As the vibrational excitation frequency increases, the bandwidth of the slip velocity becomes narrower and the peak frequency becomes equal to the vibrational frequency. The drag force produced by the periodic slip velocity is the main contribution to the deagglomeration force, which needs to overcome aggregation forces (e.g., van der Waals force). The strength of the deagglomeration force determines the overall deagglomeration performance and the particle size distribution of the agglomerates.

A Novel $\phi$-OTDR System With a Phase Demodulation Module Based on Sagnac Balanced Interferometer

At present, a phase demodulation <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\phi$</tex-math></inline-formula> -OTDR-based on an unbalanced interferometer is widely used, but its demodulation module is easily affected by external vibration noise. To improve the reliability of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\phi$</tex-math></inline-formula> -OTDR, this paper proposed a phase demodulation method based on a balanced interferometer, which uses the Sagnac interferometer to obtain two Rayleigh scattering intensities and then recovers the phase information using an incoherent phase demodulation algorithm. The experimental results show that the proposed method can recover the disturbance signals on the sensing optical fiber well, even when the demodulation module is in serious external vibration noise including a vibration table shaking with different frequencies, opening and closing a door, and a car honking. These results indicate that the proposed method significantly reduces the influence of environmental vibration noise on the demodulation module, and offers a promising solution for the application of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\phi$</tex-math></inline-formula> -OTDR in a harsh environment.

A fully self‐powered, natural‐light‐enabled fiber‐optic vibration sensing solution

AbstractFiber‐optic sensors have been developed to monitor the structural vibration with advantages of high sensitivity, immunity to electromagnetic interference (EMI), flexibility, and capability to achieve multiplexed or distributed sensing. However, the current fiber‐optic sensors require precisely polarized coherent lasers as the lighting sources, which are expensive in cost and suffer from the power supply issues while operating at outdoor environments. This work aims at solving these issues, through developing a fully self‐powered, natural‐light‐enabled approach. To achieve that, a spring oscillator‐based triboelectric nanogenerator (TENG), a polymer network liquid crystal (PNLC), and an optical fiber were integrated. The external vibration drove the PNLC to switch its transparency, allowing the variation of the incident natural light in the optical fiber. Compared with the majority of conventional TENG‐based active vibration sensors, the developed paradigm does not suffer from the EMI, without requirements of the signal preamplification which consumes additional energy. The vibration displacement monitoring was performed to validate the sensing effectiveness of the developed paradigm.

Robust Nonlinear Control Scheme for Electro-Hydraulic Force Tracking Control with Time-Varying Output Constraint

This paper presents a robust nonlinear control scheme with time-varying output constraint for the electro-hydraulic force control system (EHFCS). Two typical double-rod symmetrical hydraulic cylinders are employed to simulate force environments in the EHFCS. Therefore, in order to improve the performance of the EHFCS, firstly, the model of the EHFCS is established with taking external disturbances, parameter uncertainties as well as structural vibrations into consideration. Secondly, in order to estimate external disturbances, parameter uncertainties and structural vibrations in the EHFCS and compensate them in the following robust controller design, two disturbance observers (DOs) are designed according to the nonlinear system model. Thirdly, with two estimation values from two DOs, a time-varying constraint-based robust controller (TVCRC) is presented in detail. Moreover, the stability of the proposed controller is analyzed by defining a proper Lyapunov functions. Finally, in order to validate the performance of the proposed controller, a series of simulation studies are conducted using the MATLAB/Simulink software. These simulation results give a fine proof of the efficiency of the proposed controller. What’s more, an experimental setup of the EHFCS is established to further validate the performance. Comparative experimental results show that the proposed controller exhibits better performance than the TVCRC without two DOs and a conventional proportional integral (PI) controller.

Studies on Impact Resistance of Self-Compacting Concrete with mechanically treated Recycled Coarse Aggregate

Self-compacting concrete (SCC) is an extraordinary type of concrete that is extremely flowable and spreads into the formwork without the need of external vibration. In order to attain self-compatibility SCC obliges extensively surplus quantity of fine particles as compared to conventional concrete. Recycled Coarse Aggregate (RCA) obtained by crushing of old concrete is used in the investigational analysis. Nan-Su method is used to design the SCC mixes A and B (M35 and M45). The current experimental study aims to evaluate the impact energy of Recycled Coarse Aggregate (RCA) based self- compacting concrete by replacing with Natural Coarse Aggregate (NCA) (25%, 50%, 75%, and 100%) in unprocessed and processed states for various number of revolutions (500R, 1000R, 1500R, 2000R). Tests were carried out with a constant mass of hammer (16.38 kg). The impact energy determined for the Mixes A and B is compared with respect to replacement level and processing of RCA. The impact energy calculated is maximum for mix-A (1500 and 2000 revolutions) and mix-B (2000 revolutions) at 75% and 100% replacement of RCA respectively. From the experimental results of obtained Coefficient of Variation (CoV) with respect to processing of aggregate, in both the mixes it is observed that RCA in unprocessed state and processed state (1500R) has good Coefficient of Variation. Comparing the results of Coefficient of Variation with respect to replacement level of aggregate it has a very good CoV at 25% replacement level of RCA for both the mixes.

A wavefront division multiplexing holographic scheme and its application in looking through diffuser

We present a spatial light modulator (SLM) assisted compact holographic method and illustrate its application by imaging through a random scattering medium. The merit of the proposed method is wavefront division multiplexing, i.e. the dual wavefront modulations over a single SLM. Two different wavefront shapes: a reference-light shape and a phase object, are combined over the SLM. One advantage of this scheme is the flexible modulation of the reference light. The experimental implementation of this method is demonstrated by quantitatively reconstructing different phase objects from the randomly scattered light. This new scheme greatly simplifies the experimental configuration and presents a better stability even in presence of external vibrations, opening avenues for the holography-based scattering imaging application.

Design and Research of Bearing Reliability Test Bed Based on Multi-Dimensional Vibration Loading

Rolling bearings are widely used in aviation, aerospace and other important fields, and their reliability is greatly affected by external vibration excitation during service. Due to the large volume and high cost of the combined structure of shaking table and test chamber, this paper designed a dynamic reliability test bed specially for rolling bearings to study the influence of external vibration excitation with different directions, frequencies and amplitudes on vibration signals and service life of rolling bearings. The test bed is loaded with external excitation by means of electromagnetic shakers in two directions, and the flexible material is used to realize the displacement of the test chamber under two external excitation directions at the same time. The bearing vibration loading life test carried out by this test bed has important guiding significance for the design of rolling bearing. The experimental results show that the test bed can apply axial and radial vibration loads of 1-800Hz sinusoidal waveform, and the vibration acceleration can reach 1g, which can simulate the effect of actual working conditions.

A new scaling number reveals droplet dynamics on vibratory surfaces

HypothesisDroplet spreading on surfaces is a ubiquitous phenomenon in nature and is relevant with a wide range of applications. In practical scenarios, surfaces are usually associated with certain levels of vibration. Although vertical or horizontal modes of vibration have been used to promote droplet dewetting, bouncing from immiscible medium, directional transport, etc., a quantitative understanding of how external vibration mediates the droplet behaviors remains to be revealed. MethodsWe studied droplets impacting on stationary and vibratory surfaces, respectively. In analogy to the Weber number We=ρUi2D0/γ, we define the vibration Weber number We*=ρUv2D0/γ to quantitively analyze the vibration-induced dynamic pressure on droplet behaviors on vibratory surfaces, where ρ,γ,D0,UiandUv are liquid density, surface tension, initial droplet diameter, impact velocity of the droplet, and velocity amplitude of vibration, respectively. FindingsWe demonstrate that the effect of vibration on promoting droplet spreading can be captured by a new scaling number expressed as We*/[We1\\2sin(θ/2)], leading to (Dm − Dm0)/Dm0 ∝ We*/[We1\\2sin(θ/2)], where θ is the contact angle, and Dm0 and Dm are the maximum diameter of the droplet on stationary and vibratory surfaces, respectively. The scaling number illustrates the relative importance of vibration-induced dynamic pressure compared to inertial force and surface tension. Together with other well-established non-dimensional numbers, this scaling number provides a new dimension and framework for understanding and controlling droplet dynamics. Our findings can also find applications such as improving the power generation efficiency, intensifying the deposition of paint, and enhancing the heat transfer of droplets.

Self-Powered Acceleration Sensor Based on Multilayer Suspension Structure and TPU-RTV Film for Vibration Monitoring.

In this paper, we designed a triboelectric acceleration sensor with excellent multiple parameters. To more easily detect weak vibrations, the sensor was founded on a multilayer suspension structure. To effectively improve the electrical properties of the sensor, a surface roughening and internal doping friction film, which was refined with a room temperature vulcanized silicone rubber (RTV) and some thermoplastic polyurethanes (TPU) powder in a certain proportion, was integrated into the structure. It was found that the optimization of the RTV film increases the open circuit voltage and short circuit current of the triboelectric nanogenerator (TENG) by 223% and 227%, respectively. When the external vibration acceleration is less than 4 m/s2, the sensitivity and linearity are 1.996 V/(m/s2) and 0.999, respectively. Additionally, when it is in the range between 4 m/s2 and 15 m/s2, those are 23.082 V/(m/s2) and 0.975, respectively. Furthermore, the sensor was placed in a simulated truck vibration environment, and its self-powered monitoring ability validated by experiments in real time. The results show that the designed sensor has strong practical value in the field of monitoring mechanical vibration acceleration.

Use of Kane’s Method for Multi-Body Dynamic Modelling and Control of Spar-Type Floating Offshore Wind Turbines

This paper demonstrates the use of Kane’s method to derive equations of motion for a spar-type floating offshore wind turbine taking into account the flexibility of the members. The recently emerged Kane’s method reduces the effort required to derive equations of motion for complex multi-body systems, making them simpler to model and more readily solved by computers. Further, the installation procedure of external vibration control devices on the wind turbine using Kane’s method is described, and the ease of using this method has been demonstrated. A tuned mass damper inerter (TMDI) is installed in the tower for illustration. The excellent vibration mitigation properties of the TMDI are also presented in this paper.

Functional architecture of neural circuits for leg proprioception in Drosophila

SUMMARYTo effectively control their bodies, animals rely on feedback from proprioceptive mechanosensory neurons. In the Drosophila leg, different proprioceptor subtypes monitor joint position, movement direction, and vibration. Here, we investigate how these diverse sensory signals are integrated by central proprioceptive circuits. We find that signals for leg joint position and directional movement converge in second-order neurons, revealing pathways for local feedback control of leg posture. Distinct populations of second-order neurons integrate tibia vibration signals across pairs of legs, suggesting a role in detecting external substrate vibration. In each pathway, the flow of sensory information is dynamically gated and sculpted by inhibition. Overall, our results reveal parallel pathways for processing of internal and external mechanosensory signals, which we propose mediate feedback control of leg movement and vibration sensing, respectively. The existence of a functional connectivity map also provides a resource for interpreting connectomic reconstruction of neural circuits for leg proprioception.

Strength of industrial sandstones modelled with the Discrete Element Method

AbstractSandstone is one of the most popular building materials since the earliest times. It has various textures and colours as well as good technical parameters. Sandstones, having such wide applications, are subjected to various external factors during the period of use. So, it is of utmost importance to have a good knowledge of their strength parameters. We employed a numerical method called Discrete Element Method to examine in a non-invasive manner the mechanical strength of industrial sandstones, that are commonly used as broken stones in road construction, cladding material, paving stones, pavement tiles and so on. Various mechanical external factors were considered, such as breaking, compressional and abrasion forces or impact by external objects and vibrations. Fragmentation of the considered sandstones under compressional regime was a source of knowledge about energy storage inside the material and energy release, as well as appearance of fractures inside the matter and final sandstone fragmentation into crumbs.

The use of the vulnerability factor in the study of vibration signals on the soil surface from the movement of subway electric trains

Microseismic vibrations of the upper part of the soil strata occur continuously under the influence of endogenous and exogenous processes of both natural and artificial origin. Micro-oscillations of technogenic nature are especially characteristic of densely built-up urban areas. The practice of monitoring seismological monitoring observations shows that under such conditions it is possible to observe various types of microseismic vibrations, including elastic vibration signals in the frequency range of 1—100 Hz, generated by passing subway trains. In the calculations of the seismic stability of the designed structures, special attention is paid to the resonance characteristics of the upper part of the soil strata, which at certain frequencies can significantly enhance seismic vibrations, for example, from external vibrations sources. By traditional methods, the characteristics of resonant oscillations and their accounting are carried out, as a rule, with an insufficient degree of reliability and completeness, as a result of whichand so they are usually used as auxiliary ones. In this paper, a methodological complex is considered using modern methods for measuring and processing microseismic signals in order to identify areas with maximum amplitudes of response to external elastic influences in the study area for construction and take them into account in the future in design and construction. The study of vibroseismic noises formed on the surface of the soil layer, for example, by passing subway trains, allows one to estimate the amplitude-frequency properties of these soils, and the spectral ratio of horizontal displacements of soils to vertical H/V and the derivative of these ratios — the coefficient of vulnerability of the Ky — provide a confident selection of weakened zones that are subject to the greatest impact of external elastic vibrations.

Attenuation of external vibrations transmitted into platforms by granular media for special applications

Mitigation of mechanical vibrations from external sources into structures by granular media is investigated to prevent transmission into the structure by surrounding granular media layers. Mechanical properties of granular media can be selected for absorption of specific frequency band of external vibrations. The absorption frequency band of the granular media can be move by design to required frequency band where scattering and dissipation of vibrational energy is maximized. Samples of granular media layers are subjected to external vibrations of different intensity and frequency. Experimental values are presented for attenuation versus frequency for different layers of selected grain sizes, at audible frequencies. The goal is to determine media properties that maximize vibration attenuation for special applications of vibration free platform for such specialized application as supports for atomic force microscopy supports and more recent gravitational-wave detectors.

Quantum transfer through small networks coupled to phonons: Effects of topology versus phonons.

Particle or energy transfer through quantum networks is determined by network topology and couplings to environments. This study examines the combined effect of topology and external couplings on the efficiency of directional quantum transfer through quantum networks. We consider a microscopic model of qubit networks coupled to external vibrations by Holstein and Peierls couplings. By treating the positions of the network sites and the site-dependent phonon frequencies as independent variables, we determine the Hamiltonian parameters corresponding to minimum transfer time by Bayesian optimization. The results show that Holstein couplings may accelerate transfer through suboptimal network configurations but cannot accelerate quantum dynamics beyond the limit of the transfer time in an optimal phonon-free configuration. By contrast, Peierls couplings distort the optimal networks to accelerate quantum transfer through configurations with less than six sites. However, the speed-up offered by Peierls couplings decreases with the network size and disappears for networks with more than seven sites. For networks with seven sites or more, Peierls couplings distort the optimal network configurations and change the mechanism of quantum transfer but do not affect the lower limit of the transfer time. The machine-learning approach demonstrated here can be applied to determine quantum speed limits in other applications.

Highly efficient pyroelectric generator for waste heat recovery without auxiliary device

Waste heat is very abundant and widespread in our lives. Using pyroelectric generators (PEG) to capture the ambient heat energy is meaningful. Here we fabricated a highly efficient PEG using nanocomposite. The nanocomposite was made of P(VDF-TrFE-CFE) and barium strontium titanate (BST) nanoparticles and boron nitride (BN) nanosheets, which has excellent thermal conductivity and high polarization. The output current density of PEG can reach 1.7 μA/cm2, it is a great improvement for PEG devices. In addition, we present a new evaluation method for standardizing the performance of a PEG, which is use η (the ratio between the power density and the heat flux) as the thermos-electric conversion efficiency of PEG. Furthermore, a PEG-unit was designed and fabricated, which was cleverly connected by PEG and a plane spiral spring, it can better utilize external vibration to realize waste heat recovery without auxiliary device. The PEG-unit can be used for energy recovery in the process of train running and it can light up the LED lamp bead for 10 s within five minutes operation.

Characterization of a double torsion pendulum used to detect spin-induced torque based on Beth's experiment.

We characterized a double torsion pendulum system, including measurements of the photon-spin-induced torque. Our experimental strategy was similar to that used in Beth's experiment, which was performed in 1936 to measure photon-spin-induced torque using forced oscillation caused by polarization modulation of light incident on a suspended object. Through simple passive isolation of the suspended object from external vibration noise, the achieved torque sensitivity was 2 × 10-17 N m in a measurement time of 104 s, which is close to the thermal noise limit and one order smaller than the minimum torque measured in Beth's experiment. The observed spin-induced torque exerted on the light-absorbing optics is consistent with the angular momentum transfer of ℏ per photon.

Smart hybrid sensor for magnetic field and vibration detection based on PMN-PT/Terfenol-D magnetoelectric composites and suspended magnetic vibrator

A smart hybrid sensor for magnetic field and vibration detection is presented. We propose a novel structure of the hybrid sensor consisting of two longitudinally magnetized and thickness polarized mode (L–T mode) Terfenol-D alloy 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal (PMN–PT) magnetoelectric laminate composites and a suspended magnetic vibrator which can convert external vibration to internal alternating magnetic field. The hybrid sensor exhibits a giant vibration responsivity of 12 V/g at 400 Hz and a useful magnetic field responsivity of 6 mV/μT at 23 Hz. The detection limit for AC acceleration and magnetic field is as low as 8.16 ng/Hz1/2 at 400 Hz and 16.4 pT/Hz1/2 at 23 Hz, respectively. The sensor output shows linear response with low distortion both to AC acceleration and magnetic field. In the end, the sensor's capability for detection of magnetic and non-magnetic moving target has been proven to be useful in intelligent transportation by an outdoor (open) test.