Strong Vibration Research Articles

Experimental study on the sediment movement around monopile under vibration action

Offshore wind monopile foundations are subjected to strong wave current nonlinear effects and horizontal vibration loads caused by strong winds, waves, and rotating blades. In order to understand the rule of sediment movement around monopile under different vibration frequencies and amplitude, a cyclic loading test was carried out in the sand tank. The motion and migration rule of sediment particles around monopile under vibration action was observed by color tracer sand. The development process of the subsidence pit was qualitatively described by comparing the typical moment photos of sediment particle movement on the bed's surface with time. The transition zone of sediment particles was observed by vertical cutting of the sand bed. Then, the relationship between the relative time scale T0 and the vibration intensity under pure vibration load is analyzed, and the relationship between the equilibrium settlement depth and the initial settlement rate is obtained. The experimental results show that under vibration loading, the densification of the sand bed around the monopile foundation along the loading direction and the phenomenon of ratchet convective movement is relatively strong, and the relative time scale of settlement shows a tendency to decrease with the increase of vibration intensity; the multi-stage alternating loading of vibration and wave-flow loading will result in the backfilling and widening of the scouring pits; the rise in the amplitude and the frequency of vibration under the joint action of wave-current-vibration will decrease the depth of the equilibrium scouring, and the width of scouring pits will increase significantly with the increase of amplitude, and the backfilling of the sand will be more evident with the increase of the frequency of vibration.

INVESTIGATION ON CHARACTERISTICS OF TURBOCHARGER VIBRATION USING DIGITAL SIGNAL PROCESSING TECHNIQUE

High-speed rotating machinery such as a turbocharger is always subject to imperfection that causes strong vibrations. The problem is that there is no way of knowing the root causes of these vibrations by just using our five senses. This problem is significant since unattended heavy vibrations on a turbocharger may lead to permanent damage and a high cost to fix them. The purpose of this study is to investigate the vibration characteristics of a running turbocharger using the Digital Signal Processing (DSP) method, hence identifying the sources of such vibration profiles. In this context, DSP is the process of taking vibration signals that have been digitized and then mathematically manipulating them. Usually, it involves converting time domain data into frequency domain using Fast Fourier Transform (FFT). To identify the causes of turbocharger vibrations, a literature review was done by studying past research of the same methodology. An experiment was conducted by running the machine at different speeds and operating conditions across the choke, regular, and surge conditions. Vibrational data was obtained by mounting a piezoelectric accelerometer onto the compressor housing. The data was then later post-processed using MATLAB to execute FFT. The result shows high energy peaks at various frequencies associated with an unbalanced rotor, oil whirl, looseness, misalignment, and surging noise. On this basis, it is concluded that the vibrational data of a turbocharger can be identified using DSP.

Fast charge induced phase evolution and element contribution of nickel-rich layered cathode for lithium-ion batteries

In nickel-rich layered cathode materials, three transition metals (TM = Ni, Co and Mn) play critical roles in Li storage performance. However, rate-dependent phase evolution and elemental contribution of nickel-rich cathode materials are not well understood, but very important for further design and development of these cathodes in high-power applications. Here, the rate-dependent phase evolution and elemental contribution of LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode are investigated thoroughly by using time-resolved synchrotron-based in situ X-ray diffraction and absorption techniques. The increase of Ni content in NMC532 has been found to be the main cause of the complex structural changes, resulting in distortion of TM-O6 octahedron and strong static vibration between TM and O coordination. It is revealed that the fast charge (10 and 30C) of NMC532 leads to intermediate Li-poor phases, shrinking of H2 phase region, and prolonged O1 phase. During high-rate charging, Co is oxidized easily in low voltage region, while Ni mainly dominates charge compensation in high voltage region. It is found that delithiation-induced local structure distortion transfers from Ni to Co sites in fast kinetic process. These findings provide in-depth understanding for the fast charge behavior of Ni-rich layered cathode materials, and help to guide further development of advanced high power lithium-ion batteries.

The effect of near-fault earthquakes and wavelet-generated artificial near-fault earthquakes on the seismic behavior of rockfill dams

Strong earth vibrations may destroy high asphalt concrete core rockfill dams (ACCRDs) and cause unanticipated economic and social losses. Due to favorable geographical, geological, and environmental characteristics, ACCRDs are always near ruptured fault zones. Compared to far-field and non-pulse earthquakes, near-fault (NF) earthquakes with pulse effect may put high dams under stress. However, seismic design and dynamic assessments of high ACCRDs under pulse-type earthquake stimulation are less popular than NF earthquake recordings. The fundamental explanation is that most earthquake data pertain to non-pulse-type seismic occurrences, whereas pulse-type earthquakes have more sophisticated seismology. This work uses the finite element approach to illustrate the seismic behavior of the ACCRD under pulse-type NF, non-pulse-type NF, and far-fault (FF) earthquake excitations. The pulse-type artificial NF earthquakes are generated using wavelet multi-scale decomposition incorporation (WMSDI), a simplified wavelet theory-based approach. Next, the WMSDI approach of artificial NF earthquake synthesis is tested and compared to earthquake data and structure responses. Forward-directivity pulse-type and fling-step pulse-type earthquakes may induce higher horizontal accelerations and stresses of the high ACCRD than FF earthquakes. FS and FD earthquake excitations with high PGV/PGA ratios cause severe residual deformation and relative settlement ratio to the high ACCRD. The dynamic response of the high ACCRD under pulse-type artificial NF earthquakes also depends on the pulse parameters of the artificial equivalent pulse mathematical models. Thus, pulse-type NF earthquake seismology should be included in rockfill dam seismic design assessments.

Self-lubricating rubber-matrix composite incorporated with microcapsules via co-vulcanization: Elimination of friction-induced noise under dry conditions

Under extreme conditions, rubber bearings of marine stern shafts will be in a state of poor lubrication, which could cause severe wear and abnormal noise, endangering the stealth and safety of underwater vehicles. In this paper, a self--lubricating bearing material was designed by co-vulcanization method, where the nitrile butadiene rubber (NBR) and liquid NBR (LNBR) as the co-matrix and the microcapsule as the additive, named Powder-NBR/Microcapsule/LNBR (PNML). The scanning electron microscopy and thermalgravimetric analysis showed that microcapsules were well dispersed in the matrix, and the co-matrix was thermodynamically compatible. The “block-on-ring” friction test was carried out using a tribological test machine with a high-precision vibration acceleration sensor, where the ring material was composed of ZCuSn10Zn2. The results showed that the PNML had significantly lower coefficient of friction and specific wear rate, up to 84.19 % and 73.08 %, respectively, compared to the composite Matrix-NBR/LNBR (MNL) without microcapsule. The analysis of the vibration signals demonstrated that the MNL generated strong vibration and noise during friction, while the total vibration acceleration level of the PNML was reduced by 61.44 dB, as well as the line spectra and broadband noise (3300–5700 Hz) were nearly eliminated. In addition, the mechanical properties of composite were basically maintained. The findings in this study expanded the application scope of self-lubricating microcapsules, providing ideas for the design of rubber bearing materials with engineering application prospects.

Compression behavior of 4D printed metamaterials with various Poisson's ratios

In this study, three types of cellular metamaterials with negative/zero/positive Poisson's ratio and vibration isolation effects were devised and fabricated based on 4D printing of shape memory polymers. The compressive properties and energy absorption capacity of three cellular metamaterials at variable temperatures were evaluated by finite element simulations and compression experiments. To explore the application possibilities of 4D printed cellular metamaterials in deformable structures, shape recovery experiments were carried out, and the results showed that the three types of cellular metamaterials exhibited a high shape recovery rate. The vibration modes and vibration isolation capabilities of 4D printed cellular metamaterials were investigated for three types of cellular metamaterials with negative/zero/positive Poisson's ratio. In addition, based on the deformation reversible capability of the structure, the vibration isolation capability of three cellular metamaterial structures was investigated under different deformation stages. The results demonstrate that the cellular metamaterials with zero Poisson's ratio possess superior vibration isolation capability compared to negative or positive Poisson's ratio cellular metamaterials at different deformation stages by a comprehensive analysis. The methods and conclusions presented in this study will guide the design of functionalized cellular metamaterials with high energy absorption, strong vibration isolation, and autonomous deformation ability.

Bringing free weight areas under acoustic control

Fitness studios that are housed in office, residential, or hotel buildings are repeatedly confronted with the problem that the strong vibrations caused by dropping weights lead to noise and vibrations in the entire building or even cause damage to existing ceiling structures. For these situations, Getzner has developed the g-fit Shock Absorb system with low construction heights and low weight. This is achieved through several layers of polyurethane foam materials including high damping or high elasticity sub-layer. The impact is isolated, the drop energy is absorbed by the material and dangerous rebound of the weights (dumbbell, barbell, kettlebells, etc.) is prevented. But the best flooring system can hardly be used without a proper prognosis of the isolation effect and the achieved sound pressure level in adjacent rooms. This paper is about the development of a prognosis tool that allows to predict the sound pressure level as a function of the impact energy, the type of weight at gym, and the ceiling mass for all g-fit Shock Absorb floor coverings. The extensive drop tests as well as the evaluation and the development of a prediction function is described in detail and explained by examples.

Ruggedized sensor packaging with advanced die attach and encapsulation material for harsh environment

Current gas sensors are typically graded for performance up to 100 °C and limited by the materials used in their packaging. This work aims to select, design and investigate novel materials for die attach and encapsulation technology, such as copper nanoparticles-based die attach and phthalonitrile-based encapsulant, for the fabrication of a packaged gas sensor for harsh environment applications. This is done through a series of test protocols and reliability assessments developed to simulate operations at high temperature and under strong vibration.

Vibration Analysis of a Plate Embedded or Attached with Acoustic Black Hole Using a Virtual Spring Energy Method

Acoustic black hole (ABH) with the power-law profile has the advantages of strong designability and vibration suppression. This study provides a novel virtual spring energy method (VEM) to solve the vibration characteristics of a plate embedded or attached with acoustic black hole. Firstly, the virtual springs in this study can deal with boundary conditions, continuity conditions, and periodic conditions. After solving the kinetic and potential energy of a plate cell embedded with acoustic black hole, the periodic structure’s kinetic and potential energy need not be calculated repeatedly. The method is verified by the finite element method. Secondly, to overcome the stiffness reduction owing to the varying thickness of ABH in the primary bearing structure, a composite ABH structure called “Plate–ABH” is proposed, in which a damping layer is designed with an ABH profile and attached to the primary plate structure. The two layers connect each other through the virtual springs. The vibration characteristics of the composite ABH plate are given by employing the VEM. The composite ABH structure shows strong damping ability and lighter weight compared with a plate attached with the uniform thickness damping layer. Plate–ABH can be effectively used in the engineering of vibration reduction.

Wire bond contact defect identification in battery modules of electric vehicles using pulses and differential voltage analysis

Automotive battery packs for electromobility applications consist of a large number of interconnected battery cells. Different cell-to-busbar joining techniques are utilized, with cylindrical cells frequently being contacted using wire bonding. Failure of individual connections can occur due to strong vibrations during operation and improper stress, making detection by the battery management system a necessity. This study investigates the identification of an electrical wire bond failure in a state-of-the-art electric vehicle module of a Lucid Air with 10 series-connected and 30 parallel-connected cells (10s30p). Four individual cells were characterized extensively in order to generate a simulation model taking into account parameter scatter. The failure case under investigation was simulatively incorporated in one parallel circuit and subsequently replicated in experimental validation measurements at the module level. The results show that this defect can be detected using pulses of C/3 or higher currents at various states of charge. An even more robust detection is achieved using differential voltage analysis of constant current C/20 discharge voltage trajectories. This defect identification method does not require any additional measurement sensors beyond the voltage taps and sensors provided by the manufacturer – with one voltage sensor per parallel circuit – and can therefore be implemented during electric vehicle usage, e.g. at dedicated service checks. A discussion on the applicability and scalability as well as the limitations of the method is provided. All measurement data of the state-of-the-art Lucid battery system is available as open source alongside the article.

Piezoelectric driven self-powered supercapacitor for wearable device applications

The universal energy demand and pollution have prompted research scientists to explore other energy harvesting technologies that can generate energy from the natural resource environment, mainly due to the use of conventional energy sources. Energy harvester can be extracted and to convert into useful electric energy. The piezoelectric energy harvester is an excellent method of extracting mechanical energy due to its high electric and mechanical combination and piezoelectric harvester coefficient to compare electro-static, electro-magnetic, and triboelectric transitions. Therefore, the harvesting of piezoelectric energy is highly appreciated by the scientific community. Energy harvesters can be used to convert electrical energy into strong vibrations, which can be to store and used on a variety of ultra-low power electronic devices. With the advent of a various variety of wearable digital devices and fitness tracking devices, the piezoelectric generator suitable for portable and wearable electronic power source is one of the most interesting.

Chaotic Effect-Based Array Duffing Systems with Improved Nonlinear Restoring Force for Weak Signal Detection in Dynamic MWD.

In the process of dynamic Measurement While Drilling (MWD), the strong vibration and rapid rotation of the Bottom Hole Assembly (BHA) lead to multi-frequency and high-amplitude noise interference in the attitude measurement signal. The weak original signal and extremely low signal-to-noise ratio (SNR) are always the technical difficulties of dynamic MWD. To solve this problem, this paper uses the chaotic effect of the Duffing system, which takes the expression (-x3 + x5) as a nonlinear restoring force to detect the weak characteristic signal of downhole dynamic MWD. First of all, in order to meet the limit condition of the chaotic phase transition of the system output, the frequency value of the characteristic signal is reconstructed and transformed based on the variable scale theory. Then, in order to solve the influence of the initial phase of the characteristic signal on the detection accuracy, a detection model based on the array Duffing system is presented, and a frequency-detection scheme with all-phase coverage is given. Finally, another array Duffing system is designed for the parameter estimation of the characteristic signal. The critical value of chaotic phase transition is determined by adjusting the amplitude of the driving signal of the array Duffing system, and then the amplitude and phase parameters of the characteristic signal are synchronously estimated. The experimental results show that the proposed method can effectively extract the weak characteristic signal within the strong noise, and the SNR of the characteristic signal can be as low as -21 dB. Through the attitude calculation for the extracted characteristic signal, it can be seen that the proposed method can improve the accuracy of the inclination of the drilling tool significantly, which proves the feasibility and effectiveness of the method proposed in this paper.

Ideal-Pulse-Based Strong-Motion Duration for Multi-Pulse Near-Fault Records

ABSTRACT Serious damage to near-fault structures is caused mainly by velocity pulses in a ground motion, hence, the necessity to develop a pulse-related definition of strong-motion duration to adequately describe the intensity of near-fault ground motion. For a multipulse record, an ideal-pulse-based strong-motion duration, which is defined as the time interval between the beginning of the first pulse and the end of the last pulse in an ideal-pulse signal, is proposed. This strong-motion duration corresponds with the time interval of the occurrence of strong vibrations and energy accumulations in the original record. For near-fault records, pulselike characteristics can be completely presented within this duration. Meanwhile, the ideal-pulse-based strong-motion duration shows good performance in the estimation of structural responses. The elastic and inelastic displacement spectra of the original records agree well with those of the records shortened according to the proposed duration. The validity of applying the proposed duration to structural analysis is further verified by the nonlinear time history analyses of 3-, 9-, and 20-story steel moment-resisting frame structures. The proposed strong-motion duration accurately estimates nonlinear structural responses. It is proven that the ideal-pulse-based strong-motion duration can adequately describe the intensity of near-fault ground motions, both from the perspective of the energy accumulation process in a ground-motion record and that of the structural analyses subjected to these ground motions.

Solid-State-LiDAR-Inertial-Visual Odometry and Mapping via Quadratic Motion Model and Reflectivity Information

This paper proposes a solid-state-LiDAR-inertial-visual fusion framework containing two subsystems: the solid-state-LiDAR-inertial odometry (SSLIO) subsystem and the visual-inertial odometry (VIO) subsystem. Our SSLIO subsystem has two novelties that enable it to handle drastic acceleration and angular velocity changes: (1) the quadratic motion model is adopted in the in-frame motion compensation step of the LiDAR feature points, and (2) the system has a weight function for each residual term to ensure consistency in geometry and reflectivity. The VIO subsystem renders the global map in addition to further optimizing the state output by the SSLIO. To save computing resources, we calibrate our VIO subsystem’s extrinsic parameter indirectly in advance, instead of using real-time estimation. We test the SSLIO subsystem using publicly available datasets and a steep ramp experiment, and show that our SSLIO exhibits better performance than the state-of-the-art LiDAR-inertial SLAM algorithm Point-LIO in terms of coping with strong vibrations transmitted to the sensors due to the violent motion of the crawler robot. Furthermore, we present several outdoor field experiments evaluating our framework. The results show that our proposed multi-sensor fusion framework can achieve good robustness, localization and mapping accuracy, as well as strong real-time performance.

A tristable nonlinear energy sink to suppress strong excitation vibration

As well known, the vibration reduction efficiency of the nonlinear energy sink (NES) is poor under strong excitation. In this paper, a tristable NES (TNES) is proposed. The TNES can degenerate into bistable and mono-stable NES by adjusting the geometric parameters of the springs. The governing equations of a linear oscillator coupled with the TNES under harmonic excitation are derived. The approximate analytical solution of the coupled system is obtained by using the harmonic balance method and verified numerically. The vibration suppression efficiency of TNES and NES is compared. The dynamic behavior of TNES under strong excitation is demonstrated. The results show that the nonlinear restoring force is softened due to the wide distribution of the three stable points of TNES. Therefore, compared with NES, the proposed TNES can suppress stronger excitation vibration. In addition, the low side barrier depth is conducive to TNES to perform chaotic inter-well oscillation, which can effectively suppress the strong excitation vibration and obtain good vibration reduction performance. As a result, the proposed TNES can eliminate the detached resonance curve and enlarge the effective range of the NES. Under relatively weak excitation, the vibration suppression efficiency of TNES is slightly lower than that of NES, although the TNES is also relatively significant. Therefore, this paper reveals the vibration suppression mechanism of TNES, and provides a way to effectively solve the problem of low vibration reduction efficiency of NES under strong excitation.

Investigate the full characteristic of a centrifugal pump-as-turbine (PAT) in turbine and reverse pump modes

Large centrifugal pumps can generate electricity in reverse, reducing the power supply pressure of the power grid. However, S region may occurs during the operation and regulation of the pump as a steam turbine (PAT). The S region can cause unstable unit startup, not only causing hydraulic system oscillation, but also accompanied by strong vibration and noise. Understanding the characteristic curve of the S region is of great significance for improving unit stability and efficiency. Previously, the main research object in S area was small generator units. This article conducted unsteady numerical simulation and experimental research on a large centrifugal pump. Analysed the internal flow rate, blade load, entropy generation, and pressure pulsation under three special operating conditions: the optimal operating condition, runaway operating condition, and braking operating condition in the S region. In addition, a comparative analysis was conducted on three pairs of operating conditions: S region turbine mode and reverse pump mode, with opposite flow direction, similar flow rate, and the same speed. Research has found that in the S region of large centrifugal pumps, the flow chaos in the turbine mode mainly occurs in the impeller section, and the maximum pressure occurs in the stationary blade section. The flow chaos under reverse pump operation mainly occurs in the stationary blade section, and the maximum pressure occurs in the impeller section.

Time-lapse imaging of seismic scattering property and velocity in the northeastern Japan

Investigating spatio-temporal changes in crustal structure is a key to understanding the dynamic processes in the earth's crust associated with large earthquakes and volcanic activities. The dense seismic network in the northeast part of Japan (Tohoku region) allows us to apply seismic interferometry to continuous records of ambient noise data for studying crustal changes related to the 2008 Mw 6.9 Iwate-Miyagi Nairiku earthquake and the 2011 Mw 9.0 Tohoku-oki earthquake. We track changes in both seismic scattering properties and velocities over five years and spatially localize them based on the coda wave decorrelation and travel time sensitivity kernels calculated from the solution of the radiative transfer equation. The 2008 Iwate-Miyagi Nairiku earthquake caused significant changes in both seismic scattering properties and seismic velocities in the vicinity of the epicenter subjected to dynamic or/and static stress perturbations. Changes in scattering properties associated with the 2011 Tohoku-Oki earthquake around some active volcanoes in the Tohoku region are likely related to geofluid migrations triggered by strong vibrations during the large earthquake. The decrease in seismic velocity exists mainly along the eastern coastal region and extends to the central Quaternary volcanic chains under the combined dynamic and static stress changes by the earthquake. The waveform correlation is possibly sensitive to the fluid content and might be a useful indicator of fluid migration in the crust. This is the first comprehensive demonstration and comparison of the spatio-temporal changes of seismic scattering properties and velocities at long-term and regional scales under the influence of two large earthquakes.

Performance evaluation of laminar micromixer based on two-degree-of-freedom flow-induced vibration

Solution mixing in microfluidic devices is very common in chemical, biological, medical and other fields, and it is challenging to achieve rapid mixing in laminar flow. In this paper, flow-induced vibration is introduced to promote laminar mixing and the influence of two-degree-of-freedom vibration of bluff body on the mixing performance of solutions are studied numerically. The vibration response of body, mixing concentration, vorticity, and mixing index under different blocking ratios are analyzed, and the motion trajectory under the optimal blocking ratio is presented. It is found that the blocking ratio directly affects the vibration of cylinder, and then has a significant impact on the mixing performance. When the blocking ratio β=1/4, although the mixing index is not the maximum of all the blocking ratios considered, the kinetic energy loss of the fluid is lower than that at larger blocking ratio, resulting in excellent comprehensive mixing performance. When the reduced velocity U*=4 for β=1/4, the best mixing performance is achieved with a mixing index of 0.55, and the pressure drop of the fluid during the mixing process is very small. Besides, the motion trajectory of the cylinder presents a typical shape of "8″. The strong vibration in the y direction and the shedding vortex at the downstream position of the cylinder can effectively promote fluid mixing.

Coherent-Phonon-Driven Intervalley Scattering and Rabi Oscillation in Multivalley 2D Materials.

Resolving the complete electron scattering dynamics mediated by coherent phonons is crucial for understanding electron-phonon couplings beyond equilibrium. Here we present a time-resolved theoretical investigation on strongly coupled ultrafast electron and phonon dynamics in monolayer WSe_{2}, with a focus on the intervalley scattering from the optically "bright" K state to "dark" Q state. We find that the strong coherent lattice vibration along the longitudinal acoustic phonon mode [LA(M)] can drastically promote K-to-Q transition on a timescale of ∼400 fs, comparable with previous experimental observation on thermal-phonon-mediated electron dynamics. Further, this coherent-phonon-driven intervalley scattering occurs in an unconventional steplike manner and further induces an electronic Rabi oscillation. By constructing a two-level model and quantitatively comparing with abinitio dynamic simulations, we uncover the critical role of nonadiabatic coupling effects. Finally, a new strategy is proposed to effectively tune the intervalley scattering rates by varying the coherent phonon amplitude, which could be realized via light-induced nonlinear phononics that we hope will spark experimental investigation.

Real-Time Bucket Pose Estimation Based on Deep Neural Network and Registration Using Onboard 3D Sensor.

Real-time and accurate bucket pose estimation plays a vital role in improving the intelligence level of mining excavators, as the bucket is a crucial component of the excavator. Existing methods for bucket pose estimation are realized by installing multiple non-visual sensors. However, these sensors suffer from cumulative errors caused by loose connections and short service lives caused by strong vibrations. In this paper, we propose a method for bucket pose estimation based on deep neural network and registration to solve the large registration error problem caused by occlusion. Specifically, we optimize the Point Transformer network for bucket point cloud semantic segmentation, significantly improving the segmentation accuracy. We employ point cloud preprocessing and continuous frame registration to reduce the registration distance and accelerate the Fast Iterative Closest Point algorithm, enabling real-time pose estimation. By achieving precise semantic segmentation and faster registration, we effectively address the problem of intermittent pose estimation caused by occlusion. We collected our own dataset for training and testing, and the experimental results are compared with other relevant studies, validating the accuracy and effectiveness of the proposed method.