Vibration

Human operators in the transportation sector are exposed to whole-body vibration (WBV) while driving. Occupational exposure to WBV, predominant at low frequencies (<20 Hz), has been linked to spinal injuries and reduced functioning. This study aims at the design development of a novel semi-active seat suspension system featuring magneto-rheological elastomers (MREs) to mitigate the WBV. The proposed suspension system allows a greater range of strokes, while ensuring the MRE remains within an acceptable level of deformation. Several MRE samples were fabricated and characterized under shear mode. Afterward, a field- and frequency-dependent phenomenological model was developed to predict the viscoelastic properties of MREs as functions of both the excitation frequency and applied magnetic field. The MRE material model was subsequently used to design and optimize an adaptive seat suspension system incorporating a C-shaped MRE-based isolator in parallel and series with passive springs. The proposed adaptive seat suspension system demonstrated a frequency shift of 29% by increasing the applied current from 0 to 2 A. Finally, a 6-DOF lumped parameter model of a seated human subject combined with the proposed semi-active suspension system featuring the MRE isolator has been formulated to investigate the vibration transmissibility from the floor to the subject’s head. Full article

Manual wheelchair (MWC) users are daily exposed to vibration during propulsion. The impact of such exposure on the MWC user’s health has yet to be proven. To date, no agreement has been reached, presumably on the account of the wide variety of experimental parameters that need to be controlled. A possible solution relies on the implementation of a User/MWC model to point out the effect of propelling conditions (MWC loads, propulsion methods, speeds, and ground floor types) on the vibration exposure and eventually on the MWC user’s health. To feed such a model, the evaluation of the MWC vibration response during propulsion is required. Following a necessary MWC experimental modal analysis under laboratory conditions, this study presents the vibration response of an MWC under various propelling conditions. For each investigated condition, the identified set of modal parameters was provided and the effect on the MWC response to vibration at the User/MWC interfaces was highlighted. Results mostly underline that the response to vibration is highly dependent on the propelling conditions. The speed and the ground floor type greatly affect the vibration response: doubling speed and increasing ground surface roughness imply threefold and eightfold vibration levels, respectively. Finally, the main outcome is that an empty MWC or an MWC loaded with a dummy generates vibration outside the range measured for an MWC loaded with a human body, resulting in a lower frequency content and an almost two-fold vibration level increase. The findings of this study will help enhance the understanding of the health risks that wheelchair users encounter as a result of vibrations. Full article

Vibration mitigation of moving flexible structures is a key issue in many applications. Examples include antennas, solar arrays, radar reflectors, and manipulator arms, especially in the aerospace sector. These structures typically consist of inter-connected slender and flexible elements moved by external actuators to reach specific configurations and positions. The movements excite vibrations, which lead to the risk of structural and fatigue failures; once in position, residual vibrations can be further amplified by structure lightness, causing bad performance and malfunctioning of onboard sensors. This paper proposes an effective technique to minimise the vibration of moving flexible structures by calculating the control points of a time-parametrised B-spline representing the shape of the motion law. A testing case of a rotating cantilever beam is considered. Validation using multi-flexible-body simulation software has shown the method’s effectiveness in minimising residual vibrations. Full article

Six mode shapes, including bending and torsion, were documented for five different basketball rims and backboards at the United States Military Academy, West Point, New York, NY, USA. The frequency and damping ratio of each mode shape were also determined. The empirical process began with the time-domain excitation and response of each rim-backboard system. The impulse of excitation came from an impact hammer separately applied sequentially to each node. The sinusoidal response was gathered from an accelerometer at a fixed location (node 1). Each time-domain excitation response was then converted to a frequency-domain Bode plot for each node by a Brüel & Kjær 2034 Signal Analyzer, giving transfer functions of output/input versus frequency. Structural Measurements System (SMS) StarStruc software was used to fit mode shapes to the Bode plots. Each of the six mode shapes was fitted to the Bode plots of each node at a specific modal frequency. Each of the six mode shapes was a function of the locations of the nodes, and the Bode plots gathered at each node. The first and second modes were critical for showing that the Energy Rebound Testing Device statistically correlated with the energy transferred to the rim and backboard. A known perturbation mass was selectively attached to the rim to help isolate the dynamic masses and spring rates for the rim and backboard and to ascertain that the kinetic energy transferred to the rim had a 95.67% inverse correlation with rim stiffness. Full article

This paper provides an initial investigation of quadruped rotary galloping gait patterns using data from racing greyhounds as they navigate their way around a constant radius bend. This study reviewed actual race data collected over a five month period from 2986 racing greyhounds. Using numerical dynamics modelling and value range analysis important factors were identified and analysed. By cleaning and synthesising simple X and Y data and also processing data for accuracy greyhound motion path dynamics results were produced for analysis. The results show that the galloping path greyhounds took going into the bend was different from the path coming out of the bend. It also shows that more than 50% of the greyhounds naturally optimised their path for a longer transition while minimising jerk when entering and exiting the bend. This research verified that individual greyhounds naturally chose different path transition lengths for accommodating their dynamic conditions. Finally, it was found that the greyhound galloping path dynamics state is less intense during the second half of the bend. Full article

Broadband noise reduction over the low–mid frequency range in the building and transportation sectors requires compact lightweight sound absorbers of a typical subwavelength size. The use of multi-layered, closely spaced (micro-)perforated membranes or panels, if suitably optimized, contributes to these objectives. However, their elasticity or modal behaviors often impede the final acoustical performance of the partition. The objective of this study is to obtain insights into the vibrational effects induced by elastic limp membranes or panel volumetric modes on the optimized sound absorption properties of acoustic fishnets and functionally graded partitions (FGP). The cost-efficient global optimization of the partitions’ frequency-averaged dissipation is achieved using the simulated annealing optimization method, while vibrational effects are included through an impedance translation method. A critical coupling analysis reveals how the membranes or panel vibrations redistribute the locations of the Hole-Cavity resonances, as well as their cross-coupling with the panels’ first volumetric mode. It is found that elastic limp micro-perforated membranes broaden the pass-band of acoustic fishnets, while smoothing out the dissipation ripples over the FGP optimization bandwidth. Moreover, the resonance frequency of the first panels mode sets an upper limit to the broadband optimization of FGPs, up to which a high dissipation, high absorption, and low transmission can be achieved. Full article

The estimation of vertical ground reaction forces (VGRFs) during running is necessary to understand running mechanisms. For this purpose, the use of force platforms is fundamental. However, to extend the study of VGRFs to real conditions, wearable accelerometers are a promising alternative to force platforms, whose use is often limited to the laboratory environment. The objective of this study was to develop a VGRF model using wearable accelerometers and a stepwise regression algorithm. Several models were developed and validated using the VGRFs and acceleration signals collected during 100 stances performed by one participant. The validated models were tested on eight participants. In a sensitivity study, the strongest correlations were observed at cut-off frequencies of ≤25 Hz and in models developed with 30 to 90 stances. After the validation phase, the 10 best models had, on average, low relative differences (≤10%) in the estimation of discrete VGRF parameters, i.e., the passive peak ($\left|{\epsilon }_{pp}\right|=6.26\%$), active peak ($\left|{\epsilon }_{ap}\right|=2.22\%)$, and loading rate ($\left|{\epsilon }_{lr}\right|=2.17\%$). The results indicate that the development of personalized models is more suitable for achieving the best estimates. The proposed methodology opens many perspectives for monitoring VGRFs under real conditions using a limited number of wearable sensors. Full article

The support stiffness of the turbopump rotor system with angular contact ball bearing varies with the rotational speed, which leads to the inaccurate prediction of the dynamics of the turbopump rotor system. The model of the rotor bearing system was constructed based on the theoretical model of angular contact ball bearing stiffness, and the dynamics characteristics of the turbopump system were calculated. To verify the accuracy of the stiffness and the dynamics model, a test system of the turbopump rotor with angular contact ball bearings was designed. Since the bearing stiffness cannot be measured directly, a stiffness identification model was introduced, and an unbalanced response test was conducted to verify the dynamics model. It was found that the turbopump bearing stiffness increased dynamically with speed and reduced the unbalance response of the rotor. The results show that the angular contact ball bearing stiffness model and the dynamics model of the rotor support system are accurate and provide support for the dynamics design of the turbopump rotor system with angular contact ball bearings. Full article

Despite newly available therapies for acute stroke and innovative prevention strategies, stroke remains the third leading cause of disability-adjusted life-years (DALYs) lost worldwide, mostly because more than half of stroke survivors aged 65 and over exhibit an incomplete functional recovery of the paretic limb. Given that a repeated sensory input is one of the most effective modulators of cortical motor and somatosensory structures, focal muscle vibration (fMV) is gaining growing interest as a safe, well-tolerated, and non-invasive brain stimulation technique to promote motor recovery after stroke with a long-lasting and clinically relevant improvement in strength, step symmetry, gait, and kinematics parameters. In this narrative review, we first summarize the structural (neural plasticity) and functional changes (network relearning) triggered by the stroke lesion and carried out at a brain and spinal cord level in an attempt to recover from the loss of function. Then, we will focus on the fMV’s plasticity-based mechanisms reporting evidence of a possible concurrently acting multisite plasticity induced by fMV. Finally, to understand what the most effective fMV rehabilitation protocol could be, we will report the most recent evidence regarding the different clinical approaches and timing of the fMV treatment, the related open issues, and prospects. Full article

Self-mixing interferometry (SMI) is suitable to sense and measure vibrations of amplitudes ranging from picometers to millimeters at frequencies from sub-Hz to MHz’s. As an optical probe, SMI has the advantage of being non-invasive with the ability to measure without any treatment of the target surface and operate from a substantial standoff distance from the target. As an additional advantage, the SMI configuration is much simpler than that of conventional interferometers as it does not require any optical part external to the laser source. After a short introduction to the basics of SMI, we review the development of configurations of SMI instruments for vibration measurements, based on both analog and digital processing, with record performance to cover the range of vibration amplitudes from 0.1 nm to 1 mm, frequencies up to MHz, and stand-off distances up to 100 m. These performances set a benchmark that is unequaled by other approaches reported so far in the literature. The configurations we describe are (i) a simple MEMS-response testing instrument based on fringe counting, (ii) a half-fringe locking vibrometer for mechanical mode analysis and transfer function measurements, with a wide linear response on six decades of amplitude, (iii) a vibrometer with analog switching cancellation for μm-to-mm amplitude of vibrations, and (iv) a long standoff distance vibrometer for testing large structures at distances up to 100 m and with nm sensitivity. Lastly, as the vibrometer will almost invariably operate on untreated, diffusing surfaces, we provide an evaluation of phase-induced speckle pattern errors affecting the SMI measurement. Full article

The aim of this work is to perform an uncertainty propagation and global sensitivity analysis of a surface acoustic wave (SAW) gas sensor using finite elements and sparse polynomial chaos. The SAW gas sensor is modeled using finite elements (FEM) under COMSOL, and the sensitivity to DCM of its Sezawa mode is considered to be the quantity of interest. The importance of several geometrical (width and PIB thickness), material (PIB Young’s modulus and density), and ambient (pressure, temperature, and concentration) parameters on the sensor’s sensitivity is figured out by means of Sobol’ indices using sparse polynomial chaos expansions. It is shown that when the variability of the input parameters is low (inferior to 5%), the only impacting parameter is the cell width. However, when the variability of the input parameters reaches medium levels (around 10%), all the input parameters except the ambient temperature are impacting the sensor’s sensitivity. It is also reported that in the medium variability case, the sensor’s sensitivity experiences high variations that can lead to a degradation of its performances. Full article

Background: The purpose of this study was to validate the applicability of a new screening parameter of VPTW defined as the difference between the ascending and descending thresholds of vibrotactile perception to evaluation of the increasing risk of the neurological components of hand-arm vibration syndrome (HAVS) for repeated exposure to hand-arm vibration (HAV). Methods: Thirty subjects—10 old exposed (G1), 10 old non-exposed (G2), and 10 young non-exposed subjects (G3)—were required to carry out three 3 min grip tasks with exposure to two intensities of HAV at 10 min intervals. Vibration perception measurements, each of which lasted 90 s, were performed at 5 min intervals at the right index finger. Results: VPTWs calculated from pairs of the vibrotactile ascending and descending thresholds at the fingertips were not significantly affected by repeated HAV exposure. Moreover, the VPTWs measured for non-exposed subjects were almost invariant regardless of the subjects’ age or the time elapsed after repeated exposure to HAV. Residual TTSs at 125 Hz gradually recovered in all subject groups under both HAV exposure conditions. The residual TTSs of non-exposed subject groups significantly increased as the number of iterations of HAV exposure increased. Conclusions: VPTWs measured after exposure to repeated HAV are invariant and independent of the individual neurosensory characteristics of the fingertips, which supports the hypothesis that VPTWs can be used as a screening parameter to detect potential patients only with neurosensory components observed as early signs of HAVS. Full article

The widespread use of smartphones and smart wearable devices has created a great demand for vibrators with complex vibration patterns driven by simple circuits. In our previous studies, we observed that a filiform shape-memory alloy (SMA) wire will shrink and then return to its initial length, perfectly synchronizing with a given pulse current. Here, we developed a novel vibrator whose structure allows the micro-vibrations of an SMA wire to be amplified up to a recognizable level without directly touching the wire. The vibrator has the advantage of independently controlling its magnitude and frequency together with a simple driving circuit since it is directly driven by a frequency-modulated pulse current with a controlled duty ratio. We measured the power consumption and the acceleration generated by the vibrator. The results showed that the vibrator consumed only 4–77 milliwatts of power with a quick vibration response within 5 milliseconds, and the acceleration increased significantly in a duty ratio range of around 1%. Furthermore, user evaluations demonstrated that differences in the magnitude and frequency of the generated vibrations were sufficiently recognized when the vibrator was driven by different duty ratios and frequencies, and the vibrator provided various tactile and haptic sensations to users. Full article

New applications introduced capsule designs with features that have not been fully analysed in the literature. In this study, thin shells of revolution are used to model drug delivery capsules both with closed and open designs including perforations. The effects of internal boundary layers and sensitivity on frequency response are discussed in the special case with symmetric concentrated load. The simulations are carried out using high-order finite element method and the frequency response is computed with a very accurate low-rank approximation. Due to the propagation of the singularities induced by the concentrated loads, the most energetic responses do not necessarily include a pinch-through at the point of action. In sensitive configurations, the presence of regions with elliptic curvature leads to strong oscillations at lower frequencies. The amplitudes of these oscillations decay as the frequencies increase. For efficient and reliable analysis of such structures, it is necessary to understand the intricate interplay of loading types and geometry, including the effects of the chosen shell models. Full article

An experimental study was performed examining the effectiveness of a multi-compartment damper in attenuating the response of structures under random and earthquake excitations. The damper consisted of four compartments of unequal size; it was mounted on a small one-story steel structure. The same number of steel spherical particles were placed inside each compartment, resulting in filling area ratios (the total area of the squares around the projected particles divided by the area of the compartment) from 40% to 70%. The damper was effective in reducing the response displacement and acceleration of the structure considerably. The use of different filling area ratios enabled the damper to be effective for a wide range of excitation levels. Full article

Noise and whole-body vibrations (WBV) inside commercial vehicles can lead to annoyance and reduced comfort. As a result, negative effects on the driver can occur even below the legal exposure limits. In order to understand the annoyance perception and the interaction between noise and WBV, two perception experiments were conducted. For both experiments, recorded signals inside different commercial vehicles were used. Sound pressure and acceleration levels varied. In addition, the frequency content of the recorded vertical seat vibrations was reproduced in different modified variants. The varied parameters (sound pressure level, acceleration level and vibration frequency) were investigated within a three-factorial experimental design. It was found that noise and vibration levels, as well as the vibration spectrum, had a significant effect on total annoyance. Furthermore, an interaction between noise and vibration levels in both experiments could be observed. The results show that for the highest noise level, changing vibration exposure influences annoyance ratings less than the lowest noise level. The results also show that despite the same W_k-weighted RMS level of the WBV according to ISO 2631-1, vibration spectra with sinusoidal components or narrowband vibrations below <10 Hz were significantly perceived as more annoying during a ride in a vehicle. Full article

The evaluation of the vibration behavior of railway vehicle car bodies based on the results of numerical simulations requires the adoption of an appropriate theoretical model of the suspension which considers the important factors that influence the vibration level of the car body. In this paper, the influence of the secondary suspension model on the vertical vibration behavior of the railway vehicle car body is investigated, based on the results of numerical simulations on the frequency response functions of the acceleration, the power spectral density of the acceleration and the root mean square of the acceleration of the car body. Numerical simulation applications are developed based on a rigid-flexible coupled vehicle model with seven degrees of freedom, corresponding to car body vibration modes: bounce, pitch, and first vertical bending mode, and bogie vibration modes: bounce and pitch. Four different models of secondary suspension are integrated into the vehicle model, namely a reference model and four analysis models. Analysis models include systems through which the pitch vibration of the bogies is transmitted to the car body, influencing its vibration behavior and, respectively, a system that takes the relative angular displacement between the car body and the bogie and a system that models the transmission system of the longitudinal forces between the bogie and the car body are analyzed. The effects of these two systems on the vibration behavior of the railway vehicle car body are analyzed both for each system separately and together. In the conclusions of the paper, the influence of the secondary suspension model on the vibration level at the resonance frequencies of the vertical bending of the car body and the pitch of the bogie is pointed out. It also highlights the important contribution of the transmission system of the longitudinal forces between the bogie and the car body in transmitting pitch vibrations of the bogies to the car body, with effects on the vibration level of the car body at high speeds. Full article

Steel cylindrical tanks are vital structures for storing various types of liquid in industrial plants or as a component in a water distributing system. As they sometimes are used to store toxic, flammable, and explosive material, their inapt performance during an earthquake may lead to catastrophic consequences. Therefore, practicing engineers, researchers, and industry owners are concerned about their structural safety. Meanwhile, the seismic performance of liquid storage tanks is rather complex. Thus, this subject has garnered many researchers’ interest in the past decades. This paper aims to briefly review the most significant studies on the seismic performance of on-ground steel cylindrical tanks. It focuses on analytical approaches and does not include experimental and on-site ones. Finally, the new horizons for the seismic performance assessment of such structures are presented herein. Full article

In the design of lightweight structures, both the dynamics and durability must be taken into account. In this paper, a methodology for the combined optimization of structural dynamics, lightweight design, and lifetime with discrete vibration engineering measures is developed and discussed using a demonstration structure. A two-sided welded bending beam is excited at the centre and optimal parameters for tuned mass dampers (TMD) are searched, satisfying the requirements for the dynamic behaviour, the overall mass, and the lifetime of the weldings. It is shown that the combination of a reduced order model with the implementation of the structural stress approach at critical welds enables an efficient evaluation of certain design concepts in the time domain. Using this approach, multi-criterial optimization methods are used to identify the best set of parameters of the TMD to reduce the structural vibrations and enhance the durability. Full article