Onset Of Vibrations Research Articles

Effect of Achilles tendon vibration on posture in children

This study investigated the effect of unilateral Achilles tendon vibration on postural response in children and young adults during standing. Thirty healthy subjects participated in this study including ten 6-year-old children (YC group), ten 10-year-old children (OC group), and ten young adults (YA group). Eight-second vibration was elicited in each trial from a small vibrator attached above the right Achilles tendon when participants stood barefoot on a force platform. Three 40-s trials were collected under both eyes-open and eyes-closed conditions. Center of pressure (COP) was calculated to examine postural response during the pre-vibration, vibration and post-vibration phases. Results show that both the YC and OC groups had a greater COP average velocity than the YA group in all three phases. Tendon vibration induced a directionally specific postural response in all three groups such that the onset of vibration induced a posterior and medial COP shift during the vibration phase, and the offset of vibration induced an anterior and lateral COP shift during the post-vibration phase. Timing of the maximal COP shift was comparable among three groups in both anterior–posterior (AP) and medial–lateral (ML) directions. However, only the OC group showed an adult-like magnitude of the maximal COP shift during the post-vibration phase in the AP direction. These results suggest that 6-year-old children may start showing an adult-like directionally specific response and temporal parameter to tendon vibration during standing; however, the development of an adult-like spatial postural response to tendon vibration may take more than 10 years.

Design of Ultrasonic Compaction Tool for Powder Metallurgy

The current study is presented into the investigation of the application of ultrasonic vibration on the lower punch during compaction process of powder metallurgy material. The lower punch is specifically designed of ultrasonic horn which has been tuned at frequency of 20 kHz and vibrates in longitudinal mode. Finite Element modeling was used to assist the design process of the lower punch or horn. The horn was fabricated using high grade aluminium alloy and mounted onto the ultrasonic system test rig and subsequently tested prior the experimental process begins. Various static and ultrasonic compaction procedures have been carried out to confirm the capability of the tool to operate. The compaction force was reduced significantly at the onset of ultrasonic vibration applied compared to without ultrasonic.

Cross-recurrence plot quantification analysis of input and output signals for the detection of chatter in turning

Metal cutting is a complex nonlinear dynamical process. Analysis of signals from turning operation shows that the machining exhibits a low-dimensional chaos. The self-excited vibration caused by the regenerative effect, usually called chatter, can be created during machining by increasing one cutting parameter, while keeping all other cutting parameters constant. A cross-recurrence plot (CRP) enables the study of synchronisation or time differences in two time series. CRP-based methodology is used to find the point of transition from normal cutting to chatter cutting. In this method, two signals, one input signal (power to the lathe motor) and one output signal (cutting tool vibration), are recorded simultaneously at a constant sampling rate during cutting. A time series is generated from the recorded values, and cross-recurrence plot is prepared. This CRP can be quantified using Cross-Recurrence Quantification Analysis (CRQA). Abrupt variation in the CRQA parameters indicates the onset of chatter vibration. The results are verified using permutation entropy (PE) to detect the onset of chatter from the time series. The present study ascertains that this CRP-based methodology is capable of recognising the transition from regular cutting to the chatter cutting irrespective of the machining parameters or work piece material.

Assessment of the Cutting Tooling Effect on Turning Chatter

Machining performance is often limited by chatter vibration at the tool-workpiece interface. Chatter is a type of machining self-excited vibration which originates from the variation in cutting forces and the flexibility of the machine tool structure. Machining chatter is an inherently nonlinear phenomenon that is affected by many parameters such as cutting conditions, tool geometry, cutting speed, feed rate, depth of cut, overhang length of tool, clamping condition of workpiece. This study presents experimental approach for investigation of effects of various cutting tool geometry on the onset of chatter. In turning process, measured cutting force signal and triaxial accelerometer signal was used to know the characteristics of chatter vibration. The static and dynamic component of cutting forces reflect onset of chatter vibration. Proper selection of tooling is an important parameter in terms of chatter elimination in machining.

Achilles tendon vibration shifts the center of pressure backward in standing and forward in sitting in young subjects

An Achilles tendon (AT) vibration is known to disrupt the postural control in standing ("vibration-induced falling", VIF) and to backward tilt the postural vertical in restrained sitting position, suggesting a link between AT vibration and internal representations involved in postural control. A recalibration of some troubles in body orientation by oriented sensory manipulations could be of great clinical interest. In order to use the VIF paradigm in a procedure suitable for a rehabilitation context, AT vibration deserves to be more investigated in sitting, for security reasons, and first in young participants. In 12 healthy participants (6 men/6 women; 23.3±1.9 years), posturographic data to AT vibrations (85 Hz) were recorded over 30 s standing and 40 s sitting trials. Surprisingly, four types of differences were found between standing and sitting AT vibrations: presence/absence of VIF and kinesthetic illusion, opposite directions of the centre of foot pressure (CoP) displacements, different temporal profiles. In standing: VIF without kinesthetic illusion, rapid backward shift of CoP with a peak of -54.6±11.3 mm (with respect to baseline P<0.001) 2.8±0.2 s after vibration onset. In sitting: surprising systematic forward shift of the CoP throughout the duration of AT vibration with a maximum of 27.9±18.9 mm (P<0.05 with respect to the baseline) 19.6±0.3 s after vibration onset, associated with a kinesthetic illusion in most subjects. The present study invalidates our idea to extend in sitting the VIF paradigm but the unexpected results open a new window about the basic mechanisms underlying muscle vibration effects.

Plasma-Mediated Nanocavitation and Photothermal Effects in Ultrafast Laser Irradiation of Gold Nanorods in Water

We present a theoretical and experimental study that reveals the physical mechanism underlying the response of an in-resonance gold nanorod (AuNR) in water to a near-infrared ultrafast laser pulse. Results reveal the presence of two different regimes of interaction, depending on the irradiation fluence. For fluences below 3 mJ/cm2, AuNRs are in the so-called absorption regime and are shown to strongly absorb energy, leading to a fast temperature increase revealed by the onset of characteristic mechanical vibration of the structure. In situ measurement demonstrates a permanent deformation of the AuNRs occurring for fluences over 100 μJ/cm2. In the absorption regime, we show the formation of a nanoscale plasma around the structure, dominated by a photothermal emission from the AuNR, and the generation of a pressure wave. However, no cavitation occurs under the deformation threshold fluence (100 μJ/cm2). For fluences over 3 mJ/cm2, in the near-field regime, the energy transfer is dominated by the enhanced near-field around the particle that directly ionizes and heats a nanoplasma in the surrounding water. We theoretically show that bubbles with diameters ≈ 490 nm can be generated in this near-field regime for an incident fluence of 200 mJ/cm2. In situ optical characterization of the produced bubbles supports this result and shows that bubbles with diameters ≈ 200–600 nm can be generated for fluences ranging 100–400 mJ/cm2. Important shielding of the laser–nanostructure interaction by the surrounding plasma is shown to decrease considerably the near-field enhancement, the energy absorption, and the diameter of the generated bubbles and may explain the smaller bubbles generated around in-resonance 10 × 41 nm2 AuNRs when compared to off-resonance 25 × 60 nm2 AuNRs and 100 nm AuNPs.

Suppressing Chatter in a Plunge Grinding Process: Application of Variable Rotational Speed of Workpiece

This paper investigates the regenerative chatter in a plunge grinding process. The effect of the contact force on the onset of chatter vibration is clarified by a proposed continuation algorithm, and the boundary for the chatter-free region in which the grinding process is stable is obtained. By varying the rotational speed of the workpiece continuously, the chatter vibration with the values of the system parameters being near the boundary is suppressed, namely, the chatter-free region is expanded by this spindle speed variation control strategy.

The effect of structural stiffness variations on the onset of cross-flow VIV

This brief communication discusses test results in an earlier publication, which reveal that the onset of vortex-induced vibration (VIV) of a cylindrical structure is greatly influenced by its stiffness variations. An explanation is provided and a dimensionless parameter is proposed as an indicator to the onset of the cross-flow motion. The importance of this finding to VIV design of the cylindrical structures for marine applications is suggested.

Temporal features of human tendon vibration illusions

Muscle spindles provide information about the position and movement of our bodies. One method for investigating spindle signals is tendon vibration. Vibration of flexor tendons can produce illusions of extension, and vibration of extensor tendons can produce illusions of flexion. Here we estimate the temporal resolution and persistence of these illusions. In Experiments 1 and 2, sequences of alternating vibration of wrist flexor and extensor tendons produced position illusions that varied with alternation period. When vibrations alternated at 1 Hz or slower, perceived position at the end of the sequence depended on the last vibration. When vibrations alternated every 0.3 s, perceived position was independent of the last vibration. Experiment 2 verified and extended these results using more trials and concurrent electromyographic recording. Although tendon vibrations sometimes induce reflexive muscle activity, we found no evidence that such activity contributed to these effects. Experiment 3 investigated how long position sense is retained when not updated by current information from spindles. Our first experiments suggested that vibrating antagonistic tendons simultaneously could produce conflicting inputs, leaving position sense reliant on memory of position prior to vibration onset. We compared variability in position sense after different durations of such double vibration. After 12 s of double vibration, variability across trials exceeded levels predicted from vibrations of flexor or extensor tendons alone. This suggests that position sense memory had decayed too much to substitute for the current conflicting sensory information. Together, our results provide novel, quantitative insight into the temporal properties of tendon vibration illusions.

Vibration-Induced Motor Responses of Infants With and Without Myelomeningocele

The severity of myelomeningocele (MMC) stems both from a loss of neurons due to neural tube defect and a loss of function in viable neurons due to reduced movement experience during the first year after birth. In young infants with MMC, the challenge is to reinforce excitability and voluntary control of all available neurons. Muscle vibration paired with voluntary movement may increase motoneuron excitability and contribute to improvements in neural organization, responsiveness, and control. This study examined whether infants with or without MMC respond to vibration by altering their step or stance behavior when supported upright on a treadmill. This was a cross-sectional study. Twenty-four 2- to 10-month-old infants, 12 with typical development (TD) and 12 with MMC (lumbar and sacral lesions), were tested. Infants were supported upright with their feet in contact with a stationary or moving treadmill during 30-second trials. Rhythmic alternating vibrations were applied to the right and left rectus femoris muscles, the lateral gastrocnemius muscle, or the sole of the foot. Two cameras and behavior coding were used to determine step count, step type, and motor response to vibration onset. Step count decreased and swing duration increased in infants with TD during vibration of the sole of the foot on a moving treadmill (FT-M trials). Across all groups the percentage of single steps increased during vibration of the lateral gastrocnemius muscle on a moving treadmill. Infants with MMC and younger infants with TD responded to onset of vibration with leg straightening during rectus femoris muscle stimulation and by stepping during FT-M trials more often than older infants with TD. Vibration seems a viable option for increasing motor responsiveness in infants with MMC. Follow-up studies are needed to identify optimal methods of administering vibration to maximize step and stance behavior in infants.

Field emission of electrons from a single carbon fiber with a nanostructured emitting surface

The field emission of electrons from a single fine carbon fiber with a nanostructured emitting surface is studied experimentally. It is found that the fiber can serve as an effective field emitter of electrons at voltages of ∼102–103 under the conditions of technical vacuum and the emission current density may reach ∼102 A/cm2. At a certain threshold voltage, the fiber starts executing flexural mechanical vibrations. The onset of mechanical vibrations is accompanied by a change in the field emission conditions. Namely, in the absence of vibrations, the mode of steady current extraction is observed. When mechanical vibrations set in, the field emission switches to the mode of current periodic oscillations with a constant component.

The influence of feed rate on process damping in milling: modelling and experiments

The performance of milling operations is limited by the onset of unstable self-excited vibrations known as regenerative chatter. Over the past few decades there has been a great deal of research to help predict and explain regenerative chatter. Consequently, high-speed milling operations are now frequently employed, with judicious choice of spindle speeds and depths of cut so as to avoid chatter whilst maintaining high productivity. However, many materials that are increasingly used in aerospace components are difficult to machine at high spindle speeds because of their thermal properties. Examples include titanium and nickel alloys. For these materials, low-speed machining must be employed, and in this regime the role of regenerative chatter is less clearly understood due to the phenomenon of process damping. In the present study, a time domain model of process damping is developed. This model is used to explore the relationship between cutting conditions and the amplitude of chatter vibrations. A qualitative agreement is found between experimental behaviour and the numerical model. In particular, the model predicts a strong relationship between the workpiece feed rate (expressed as a feed per tooth), and the acceptable chatter stability defined by the process damping wavelength. Further work is needed to properly calibrate some of the model parameters.

Sensitivity of Sub-critical Mode-coupling Instabilities in Non-conservative Rotating Continua to Stiffness and Damping Modifications

Mode-coupling instability is a widely accepted mechanism for the onset of friction-induced vibrations in car brakes, wheel sets, paper calendars, to name a few. In the presence of damping, gyroscopic, and non-conservative positional forces the merging of modes is imperfect, that is two modes may come close together in the complex plane without collision and then diverge so that one of the modes becomes unstable. In non-conservative rotating continua that respect axial symmetry this movement of eigenvalues is very sensitive to the variation of parameters of the system. Our study reveals some general rules that govern sub-critical mode-coupling instabilities in non-conservative rotating continua to stiffness and damping modifications and provide useful insight for optimisation of such systems and interpretation of experimental results.

A Comparison of Sung and Spoken Phonation Onset Gestures Using High-Speed Digital Imaging

Phonation onset is important in the maintenance of healthy vocal production for speech and singing. The purpose of this preliminary study was to examine differences in vocal fold vibratory behavior between sung and spoken phonation onset gestures. Given the greater degree of precision required for the abrupt onset sung gestures, we hypothesize that differences exist in the timing and coordination of the vocal fold adductory gesture with the onset of vocal fold vibration. Staccato and German (a modified glottal plosive, so named for its occurrence in German classical singing) onset gestures were compared with breathy, normal, and hard onset gestures, using high-speed digital imaging. Samples were obtained from two subjects with no history of voice disorders (a female trained singer and a male nonsinger). Simultaneous capture of acoustical data confirmed the distinction among gestures. Image data were compared for glottal area configurations, degree of adductory positioning, number of small-amplitude prephonatory oscillations (PPOs), and timing of onset gesture events, the latter marked by maximum vocal fold abduction, maximum adduction, beginning of PPOs, and beginning of steady-state oscillation. Results reveal closer adductory positioning of the vocal folds for the staccato and German gestures. The data also suggest a direct relationship between the degree of adductory positioning and the number of PPOs. Results for the timing of onset gesture events suggest a relationship between discrete adductory positioning and more evenly spaced PPOs. By contrast, the overlapping of prephonatory adductory positioning with vibration onset revealed more unevenly spaced PPOs. This may support an existing hypothesis that less well-defined boundaries interfere with normal modes of vibration of the vocal fold tissue.

The Timing of Onset of Mechanical Systole and Diastole in Reference to the QRS-T Complex: a Study to Determine Performance Criteria for a Non-Invasive Diastolic Timed Vibration Massage System in Treatment of Potentially Unstable Cardiac Disorders

Our institution is in development of a low frequency, non-invasive Diastolic Timed Vibrator (DTV) for use in emergency treatment of ST Elevation Myocardial Infarction (STEMI). It is preferable to avoid vibration emissions during the IsoVolumetric Contraction Period (IVCP) and at least the majority of mechanical systole thereafter, as systolic vibration may cause a negative inotropic effect in the ischemic heart. Furthermore diastolic vibration should preferably include the IsoVolumetric Relaxation Period (IVRP) which has been shown in clinical studies to improve cardiac performance and enhance coronary flow. Electrocardiographic (ECG) monitoring can be used to enable diastolic tracking, however, the timing of the phases of the cardiac cycle in relation to the ECG waveform must first be verified. The objective of this study was therefore to determine timing of onset of mechanical systole and diastole in reference to the QRS-T Complex. One hundred and twenty-three adult echocardiographic studies were assessed for the point of mitral and aortic valve closure in relation to the QRS complex and T wave in a representative population. We found that onset of mechanical systole occurred on and usually shortly after the peak of a first dominant QRS complex deflection, and onset of diastole occurred at the earliest on and most commonly beyond the peak or midpoint of the T wave. A DTV should ideally be able to stop vibrating on or before the peak of the first dominant deflection of a QRS complex, and begin vibrating near the peak of the T wave. Given early detection of ventricular depolarization can occur 10-20ms prior to R wave peak, it is proposed that a DTV should preferably be able to stop vibrating within 10ms of a triggered stop command. Onset of vibration during peak of T wave could be approximated by a rate adapted Q-T interval regression equation, and then fine tuned by manual adjustment during therapy.

Linear analysis of chatter vibration and stability for orthogonal cutting in turning

The productivity of high speed milling operations is limited by the onset of self-excited vibrations known as chatter. Unless avoided, chatter vibrations may cause large dynamic loads damaging the machine spindle, cutting tool, or workpiece and leave behind a poor surface finish. The cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. Many researchers focused on the development of analytical and numerical methods for the prediction of chatter. However, the applicability of these methods in industrial conditions is limited, since they require accurate modelling of machining system dynamics and of cutting forces. In this study, chatter prediction was investigated for orthogonal cutting in turning operations. Therefore, the linear analysis of the single degree of freedom (SDOF) model was performed by applying oriented transfer function (OTF) and \ au decomposition form to Nyquist criteria. Machine chatter frequency predictions obtained from both forms were compared with modal analysis and cutting tests.

A Semi-Analytical Study of Stick-Slip Oscillations in Drilling Systems

Rotary drilling systems are known to exhibit torsional stick-slip vibrations, which decrease drilling efficiency and accelerate the wear of drag bits. The mechanisms leading to these torsional vibrations are analyzed using a model that includes both axial and torsional drill string dynamics, which are coupled via a rate-independent bit-rock interaction law. Earlier work following this approach featured a model that lacked two essential aspects, namely, the axial flexibility of the drill string and dissipation due to friction along the bottom hole assembly. In the current paper, axial stiffness and damping are included, and a more realistic model is obtained. In the dynamic analysis of the drill string model, the separation in time scales between the fast axial dynamics and slow torsional dynamics is exploited. Therefore, the fast axial dynamics, which exhibits a stick-slip limit cycle, is analyzed individually. In the dynamic analysis of a drill string model without axial stiffness and damping, an analytical approach can be taken to obtain an approximation of this limit cycle. Due to the additional complexity of the model caused by the inclusion of axial stiffness and damping, this approach cannot be pursued in this work. Therefore, a semi-analytical approach is developed to calculate the exact axial limit cycle. In this approach, parametrized parts of the axial limit cycle are computed analytically. In order to connect these parts, numerical optimization is used to find the unknown parameters. This semi-analytical approach allows for a fast and accurate computation of the axial limit cycles, leading to insight in the phenomena leading to torsional vibrations. The effect of the (fast) axial limit cycle on the (relatively slow) torsional dynamics is driven by the bit-rock interaction and can thus be obtained by averaging the cutting and wearflat forces acting on the drill bit over one axial limit cycle. Using these results, it is shown that the cutting forces generate an apparent velocity-weakening effect in the torsional dynamics, whereas the wearflat forces yield a velocity-strengthening effect. For a realistic bit geometry, the velocity-weakening effect is dominant, leading to the onset of torsional vibrations.

Human Muscle Spindles Act as Forward Sensory Models

Modern theories of motor control incorporate forward models that combine sensory information and motor commands to predict future sensory states. Such models circumvent unavoidable neural delays associated with on-line feedback control. Here we show that signals in human muscle spindle afferents during unconstrained wrist and finger movements predict future kinematic states of their parent muscle. Specifically, we show that the discharges of type Ia afferents are best correlated with the velocity of length changes in their parent muscles approximately 100-160 ms in the future and that their discharges vary depending on motor sequences in a way that cannot be explained by the state of their parent muscle alone. We therefore conclude that muscle spindles can act as "forward sensory models": they are affected both by the current state of their parent muscle and by efferent (fusimotor) control, and their discharges represent future kinematic states. If this conjecture is correct, then sensorimotor learning implies learning how to control not only the skeletal muscles but also the fusimotor system.

Acute effects of whole body vibration during passive standing on soleus H-reflex in subjects with and without spinal cord injury

Whole-body vibration (WBV) is being used to enhance neuromuscular performance including muscle strength, power, and endurance in many settings among diverse patient groups including elite athletes. However, the mechanisms underlying the observed neuromuscular effects of WBV have not been established. The extent to which WBV will produce similar neuromuscular effects among patients with neurological impairments unable to voluntarily contract their lower extremity muscles is unknown. We hypothesized that modulation of spinal motorneuronal excitability during WBV may be achieved without voluntary contraction. The purpose of our study was to describe and compare the acute effects of WBV during passive standing in a standing frame on the soleus H-reflex among men with and without spinal cord injury (SCI). In spinal cord intact participants, WBV caused significant inhibition of the H-reflex as early as 6 s after vibration onset (9.0 ± 3.9%) ( p < 0.001). The magnitude of the H-reflex gradually recovered after WBV, but remained significantly below initial values until 36 s post-WBV (57.5 ± 22.0%) ( p = 0.01). Among participants with SCI, H-reflex inhibition was less pronounced with onset 24 s following WBV (54.2 ± 18.7%) ( p = 0.03). The magnitude of the H-reflex fully recovered after 60 s of WBV exposure. These results concur with prior reports of inhibitory effects of local vibration application on the H-reflex. Our results suggest that acute modulation of spinal motoneuronal excitability during WBV can be achieved in the absence of voluntary leg muscle contractions. Nonetheless, WBV has implications for rehabilitation service delivery through modulation of spinal motoneuronal excitability in individuals with SCI.

Generalised modal stability of inclined cables subjected to support excitations

Parametric excitation is of concern for cables such as on cable-stayed bridges, whereby small amplitude end motion can lead to large, potentially damaging, cable vibrations. Previous identification of the stability boundaries for the onset of such vibrations has considered only a single mode of the cable, ignoring non-linear coupling between modes, or has been limited to special cases. Here multiple cable modes in both planes are included, with support excitation close to any natural frequency. Cable inclination, sag, parametric and direct excitation and nonlinearities, including modal coupling, are included. The only significant limitation is that the sag is small. The method of scaling and averaging is used to find the steady-state amplitude of the directly excited mode and, in the presence of this response, to define stability boundaries of other modes excited parametrically or through nonlinear modal coupling. It is found that the directly excited response significantly modifies the stability boundaries compared to previous simplified solutions. The analysis is validated by a series of experimental tests, which also identified another nonlinear mechanism which caused significant cable vibrations at twice the excitation frequency in certain conditions. This new mechanism is explained through a refinement of the analysis.