Function Of Vibration Frequency Research Articles

Adaptivity of a leaf-inspired wind energy harvester with respect to wind speed and direction

Environmental wind is a random phenomenon in both speed and direction, though it can be forecasted to some extent. An example of that is a gust which is an abrupt, but short-time change in wind speed and direction. Being a free and clean source for small-scale energy scavenging, attraction of wind is rapidly growing in the world of energy harvesters. In this paper, a leaf-like flapping wind energy harvester is introduced as the base structure in which a short-span airfoil is attached to the free end of a double-deck cantilever beam. A flap mechanism inspired by scales on sharks’ skin and a tail mechanism inspired by birds’ horizontal tail are proposed for integration to the base harvester to make it adaptive with respect to wind speed and direction, respectively. The use of the flap mechanism increases the leaf flapping frequency by +2.1 to +11.5 Hz at wind speeds of 1.5 to 6.0 m s−1. Therefore, since the output power of a vibrational harvester is a function of vibration frequency, a figure of merit or an efficiency parameter related to the output power will increase, as well. On the other hand, if there is a misalignment between the harvester’s heading and wind direction due to change of the latter one, the harvesting performance deteriorates. Although the base harvester can realign in certain ranges of sideslip angle at each wind speed, when the tail mechanism is integrated into that, it broadens the range of realignable sideslip angles at all the investigated wind speeds by up to 80 ∘ .

COMPARISON OF THE DYNAMIC PROPERTIES OF THE UNDERFLOOR WHEEL LATHES BODIES

The research results presented in this article are important because information on machine tools for machining wheelsets is scarce in the literature, due to technical limitations related to large machine tool dimensions, a limited number of manufacturers and non-standard variants. This paper presents the findings of experimental and finite element method (FEM) simulation studies on the vibration of bodies used in Underfloor Wheel Lathes. Two bodies, varying in shape, dimensions, and weight, were examined, with their common characteristics being their purpose, material (cast iron), and casting technology. The bodies underwent experimental and numerical modal analyses to determine damping coefficients as a function of vibration frequency. The study was conducted on both free-suspended bodies and bodies positioned and leveled on a foundation. The results of the experimental and numerical tests were compared, showing good convergence in terms of natural vibration frequency and form.

Topology of vibrational modes predicts plastic events in glasses

The plastic deformation of crystalline materials can be understood by considering their structural defects such as disclinations and dislocations. Although also glasses are solids, their structure resembles closely the one of a liquid and hence the concept of structural defects becomes ill-defined. As a consequence it is very challenging to rationalize on a microscopic level the mechanical properties of glasses close to the yielding point and to relate plastic events to structural properties. Here we investigate the topological characteristics of the eigenvector field of the vibrational excitations of a two-dimensional glass model, notably the geometric arrangement of the topological defects as a function of vibrational frequency. We find that if the system is subjected to a quasistatic shear, the location of the resulting plastic events correlate strongly with the topological defects that have a negative charge. Our results provide thus a direct link between the structure of glasses prior their deformation and the plastic events during deformation.

Spectral decomposition of thermal conductivity: Comparing velocity decomposition methods in homogeneous molecular dynamics simulations

The design of new applications, especially those based on heterogeneous integration, must rely on detailed knowledge of material properties, such as thermal conductivity (TC). To this end, multiple methods have been developed to study TC as a function of vibrational frequency. Here, we compare three spectral TC methods based on velocity decomposition in homogenous molecular dynamics simulations: Green-Kubo modal analysis (GKMA), the spectral heat current (SHC) method, and a method we propose called homogeneous nonequilibrium modal analysis (HNEMA). First, we derive a convenient per-atom virial expression for systems described by general many-body potentials, enabling compact representations of the heat current, each velocity decomposition method, and other related quantities. Next, we evaluate each method by calculating the spectral TC for carbon nanotubes, graphene, and silicon. We show that each method qualitatively agrees except at optical phonon frequencies, where a combination of mismatched eigenvectors and a large density of states produces artificial TC peaks for modal analysis methods. Our calculations also show that the HNEMA and SHC methods converge much faster than the GKMA method, with the SHC method being the most computationally efficient. Finally, we demonstrate that our single-GPU modal analysis implementation in GPUMD (Graphics Processing Units Molecular Dynamics) is over 1000 times faster than the existing LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) implementation on one CPU.

Modeling the Physical Properties of ZnO Nanoparticles with Selective Hydrogen Using DFT

The impact of hydrogen on the conductivity and vibration for zinc oxide (ZnO) nanoparticles had implicated for nanoscale optoelectronic units. Infrared reflectance spectra for ZnO hydrogen-annealed nanoparticles were calculated at incidence. The theory of density functional theory is applied to the reflectance model and absorption spectra. There is an agreement between both the model suggesting that the nanoparticles have inhomogeneous carriers’ concentrations and the experimental results. A significant decrease in carrier concentration resulted from exposure to oxygen for several hours, according to the adsorption on the nanoparticle surface of negative oxygen molecules. Also, the density of states in deferent wurtzoid’s size has been studied. The experimental energy gap values of bulk ZnO, HOMO and LUMO levels as a function of the total Zn and O atoms number in ZnOH diamondoids were determined, as well as the bond length in deferent wurtzoid’s size where the experimental ZnO bond length at 1.9767 Å has been calculated. The tetrahedral angles in deferent wurtzoid’s size were studied, deferent wurtzoid’s size Reduced mass as a vibration frequency function and force constant as a function of vibrational frequency in deferent wurtzoid’s size were determined. A good result for infrared as a vibration frequency function in deferent wurtzoid’s size has been found, as well as Raman as a vibration frequency function in deferent wurtzoid’s size.

A versatile and fully instrumented test station for piezoelectric energy harvesters

This paper describes the implementation of LabVIEW software to control instruments and acquire data from a piezoelectric energy harvesting test station which is based on a cantilever structure. The experiment is run in the Clean Energy Laboratory on the Ambient Energy Harvester Test Station. A digital multimeter, a programmable resistance selector, an arbitrary waveform generator, a shaker table, an accelerometer and a laser displacement sensor are used to control and acquire data in terms of harvested energy as a function of vibration frequency and load resistance. LabVIEW software is used to control the test station which makes near real-time data measurements, displays waveforms on a PC screen, and stores data for later analysis. Acquired waveforms are presented in terms of frequency versus voltage of the vibrating cantilever at preselected ranges of load resistances in terms of either AC or DC voltages. The vibration of the cantilever beam is measured with an accelerometer and beam movement is measured with a laser displacement meter. Test results are stored in a comma separated variable text file which can be imported into any data analysis software package. All experiments are performed on an isolated optical bench to avoid interference from mechanical noise that may exist in the surrounding environment. The system provides an integrated approach to characterize key performance indicators for energy harvesting materials and devices.

Measurement of Young’s Modulus and Internal Damping of Pork Muscle in Dynamic Mode

Automotive shocks involve various tiers’ speed for different human body tissues. Knowing the behavior of these tissues, including muscles, in different vibration frequency is therefore necessary. The muscle has viscoelatic properties. Dynamically, this material has variable mechanical properties depending on the vibration frequency. A novel technique is being employed to examine the variation of the mechanical impedance of pork muscle as a function of frequency. A force is imposed on the lower surface of the sample and acceleration is measured on its upper surface. These two parameters are measured using sensors. The sample is modeled by Kelvin–Voigt model. These measures allow deducing the change in the mechanical impedance modulus (/[Formula: see text]/ [Formula: see text] /Force: Acceleration/) of pork muscle as a function of vibration frequency. The measured impedance has a resonance of approximately 60[Formula: see text]Hz. Best-fit parameters of theoretical impedance can be deduced by superposition with the experiment result. The variation of Young’s modulus and internal damping of pig’s muscle as a function of frequency are determined. The results obtained between 5[Formula: see text]Hz and 30[Formula: see text]Hz are the same as determined by Aimedieu and al in 2003, therefore validating our technique. The Young’s modulus of muscle increases with the frequency, on the other hand, we note a rating decrease of internal damping.

Metabolic Responses to Whole-Body Vibration Varying in Frequency and Amplitude

Whole-body vibration (WBV) has been shown to provide neurological potentiation, thereby enhancing muscular activity. To date, how WBV might influence energy metabolism has not been fully elucidated. PURPOSE: This study was undertaken to assess the effect of various vibratory loads on metabolic responses during WBV and subsequent aerobic exercise. METHODS: Sixteen subjects (21.0±2 yr) including eight men and eight women underwent six WBV sessions that differed in frequency (e.g., 30-Hz, 40-Hz, and 50-Hz) and amplitude (e.g., 1-2 mm and 2-3 mm) in a randomized order. In each WBV session, subjects performed 10 sets of 10 body weight squats with each set lasting 30 sec and 1-min rest period between sets on a vibration platform with a vibration load that represented one of the six frequency-amplitude combinations. Each vibration treatment was immediately followed by 20 min of a constant load cycle exercise at 65% VO2peak. Oxygen uptake (VO2) and respiratory exchange ratio (RER) were measured throughout WBV and subsequent exercise. The average VO2 and RER of both WBV and exercise were analyzed using 2-way (frequency × amplitude) repeated measure ANOVA followed by pairwise comparisons involving Bonferroni correction. RESULTS: During WBV, VO2 demonstrated a progressive increase as a function of vibration frequency and amplitude. A significant main effect of amplitude was observed for VO2 in l·min-1 (F=6.326, p=0.02) and ml·kg-1·min-1 (F=5.497, p=0.03). The highest VO2 occurred at 50-Hz and 2-3 mm (e.g., 13.1±2.4 ml·kg-1·min-1). During subsequent exercise, VO2 responded similarly to that seen in WBV, and there were trends (p = 0.08-0.10) towards a greater VO2 at higher frequencies or amplitudes. No effects of vibration frequency or amplitude on RER were found during either WBV or subsequent exercise. CONCLUSIONS: WBV can augment metabolic responses in a load-dependent manner when administered concurrently with body-weight squats. Such a stimulating effect seems to persist during aerobic exercise that commences immediately after WBV.

Microstructure refinement of commercial 7xxx aluminium alloys solidified by the electromagnetic vibration technique

This paper examines the microstructure refinement of commercial 7xxx aluminium alloys solidified by the electromagnetic vibration technique (EMV) as a function of vibration frequency, f. The microstructure evolution reveals that at the low frequency of f = 62.5 Hz, the solidified microstructure is coarse and with the increase of vibration frequency to f = 500 Hz, the grain size becomes the finest and further increase of frequency to f = 2000 Hz results in coarsening of microstructures. The refinement mechanism is clarified when considering the significant difference in electrical resistivities of the solid and the liquid in mushy zone, in which both phases coexist and subject to vibration. The frequency-dependent refinement behaviour is revealed when the displacement of the mobile solid and sluggish liquid is taken into account during solidification. In contrast to 3xxx aluminium alloys, no giant compounds have been discerned in the present 7xxx alloy regardless of the solidification condition. The formation of crystalline twin is briefly discussed when considering the vibration condition.

Manufacture and Characterisation of Piezoelectric Broadband Energy Harvesters Based on Asymmetric Bistable Cantilever Laminates

In this paper a bistable asymmetric laminate is manufactured and coupled to a ferroelectric material for potential energy harvesting applications. A cantilever configuration is explored and the harvester response as a function of vibration frequency, vibration level and electrical load resistance examined. The harvester is characterised at low and high vibration levels where the device exhibits either single well oscillations (at low vibration amplitude) or snap-through events (at high vibration amplitude). As the vibration levels increase and the device approaches snap-through it exhibits ‘softening’ where the peak power moves to lower frequencies with differences in power levels during up-sweep and down-sweep of frequencies. Examination of the frequency dependence of power for a range of load resistances indicates a broadening of the harvester performance at higher vibration levels and during snap-through.

Vibration assisted extrusion of polypropylene

A new homemade apparatus, i.e. vibration assisted extrusion equipment, is employed to extrude polypropylene. Vibration assisted extrusion is based on the application of a specific macroscopic shear vibration field. Reduction of apparent melt viscosity as a function of vibration frequency is measured at different screw speeds and die temperatures. The effect of the process is investigated by performing mechanical tests, differential scanning calorimetry studies, polarized light microscopy and wide-angle X-ray diffraction. It is found that, compared with conventional extrusion, vibration assisted extrusion could effectively improve the rheological properties of PP melt by incorporating an extra shear vibration field. Both the tensile strength and elongation at break increased under the shear vibration field. For vibration assisted extrusion samples, both the melting temperature and crystallinity increased, accompanied by remarkable grain refinement. Vibration assisted extrusion induced a significantly enhanced bimodal orientation with a high fraction of a*-oriented α-crystallites, while only a limited improvement in the flow direction orientation. A structural model, i.e. bimodal c-axis and a*-axis orientation of PP macromolecular chains, was adopted to explain the experimental results.

Refinement of intermetallic compounds and aluminum matrix in 3xxx aluminum alloys solidified by an electromagnetic vibration technique

The industrial 3xxx aluminum alloy was solidified in a superconducting magnet, in which electromagnetic vibration (EMV) was imposed throughout the entire solidification process. The microstructure was examined as a function of vibration frequency. It is revealed that the microstructure contains intermetallic compounds and aluminum solid solution (Al(ss)) regardless of solidification condition. For both structures, quantitative characterization shows that their average grain sizes decrease to minima when vibration frequency, f, increases and further increases of f leads to an increase of average grain sizes. Moreover, the general uniformity of intermetallic compound becomes poor when f goes beyond 1000Hz. The microstructure transition behavior can be elucidated when considering the electrical resistivities of phases, i.e., Al(ss), intermetallic compounds and remaining liquid that coexist in mushy zone. The different electrical resistivities of these phases produce different Lorentz forces and thus lead to different vibration amplitudes and eventually generate uncoupled movement between the leading phase and sluggish phase during vibration. The microstructure transition can be clarified when the distance covered by the leading phase is revealed as a function of frequency. The morphological appearance of intermetallic compounds is dependent on f in EMV processing; however, their phase species and volume proportion are independent of processing conditions.

Vibration and shock reliability of MEMS: modeling and experimental validation

A methodology to predict shock and vibration levels that could lead to the failure of MEMS devices is reported as a function of vibration frequency and shock pulse duration. A combined experimental–analytical approach is developed, maintaining the simplicity and insightfulness of analytical methods without compromising on the accuracy characteristic of experimental methods. The minimum frequency-dependent acceleration that will lead to surfaces coming into contact, for vibration or shock inputs, is determined based on measured mode shapes, damping, resonant frequencies, and an analysis of failure modes, thus defining a safe operating region, without requiring shock or vibration testing. This critical acceleration for failure is a strong function of the drive voltage, and the safe operating region is predicted for transport (unbiased) and operation (biased condition). The model was experimentally validated for over-damped and under-damped modes of a comb-drive-driven silicon-on-insulator-based tunable grating. In-plane and out-of-plane vibration (up to 65 g) and shock (up to 6000 g) tests were performed for biased and unbiased conditions, and very good agreement was found between predicted and observed critical accelerations.

The solidification behavior of the AZ61 magnesium alloy during electromagnetic vibration processing

In the present study, we solidified the magnesium-based AZ61 alloy using an electromagnetic vibration technique and investigated the microstructure development as a function of vibration frequency. The microstructure evolution was quantitatively examined in terms of the total average grain size and the individual grain size distribution. The texture was profiled under two different vibration conditions. With respect to the microstructure formation, one can find that a significant difference arises in electrical resistivity between a primary solid and its surrounding liquid in the mushy zone of the alloy, making the solid move faster than the liquid and thus generating uncoupled motion, from which melt flow may be initiated. The influence of this kind non-synchronous motion on microstructure formation is discussed as a function of vibration frequency when considering the intensity of melt flow during EMV processing. For the Mg-based alloy with a hexagonal closed-packed crystal lattice, it is subject to magnetization torque due to the anisotropic magnetic susceptibility along c-axis and a, b-axes. The Lorentz force induces melt flow that stirs the semisolid slurry to form random textures while the magnetization torque suppresses melt flow that rotates crystals to align along their easy magnetization direction. The resultant structure and texture can be well elucidated when considering the competition of two kinds of force under two different vibration conditions by terminating the vibration at different temperatures during processing.

A new vibrator to stimulate muscle proprioceptors in fMRI

Studying cognitive brain functions by functional magnetic resonance imaging (fMRI) requires appropriate stimulation devices that do not interfere with the magnetic fields. Since the emergence of fMRI in the 90s, a number of stimulation devices have been developed for the visual and auditory modalities. Only few devices, however, have been developed for the somesthesic modality. Here, we present a vibration device for studying somesthesia that is compatible with high magnetic field environments and that can be used in fMRI machines. This device consists of a poly vinyl chloride (PVC) vibrator containing a wind turbine and of a pneumatic apparatus that controls 1-6 vibrators simultaneously. Just like classical electromagnetic vibrators, our device stimulates muscle mechanoreceptors (muscle spindles) and generates reliable illusions of movement. We provide the fMRI compatibility data (phantom test), the calibration curve (vibration frequency as a function of air flow), as well as the results of a kinesthetic test (perceived speed of the illusory movement as a function of vibration frequency). This device was used successfully in several brain imaging studies using both fMRI and magnetoencephalography.

Solidification Behavior of AZ31 Magnesium Alloys Using an Electromagnetic Vibration Technique

The commercial magnesium-based AZ31 alloy was solidified in a static magnetic field when an alternating electric current, perpendicular to the direction of the magnetic field, passes through the alloy. In this case, the periodical Lorentz force is generated, making the conductor vibrate centering on the initial equilibrium position. In this paper, we investigated the microstructure evolution of the alloy as a function of vibration frequency, magnetic flux density and electric current, respectively. The solidification behavior was discussed and the mechanism for the formation of the microstructure was proposed when considering the electrical properties of solid and liquid at high temperature. Because the electrical resistivity of liquid in the mushy zone is about twice that of the solid, this significant difference drives the solid to move faster than the liquid and thus generating a leading displacement for the solid over the liquid even within one vibration cycle. The uncoupled movement between the solid and liquid also gives rise to melt flow, which may be the reason to segment dendrites into fine particles. Meanwhile, the uncoupled movement makes it difficult to establish a steady state for solute redistribution during solidification and thus favoring equiaxed structures instead of dendrites. Considering these two factors, we examine the solidification behavior of the alloy separately when vibration frequency, magnetic flux density, and electric current are set as independent variables and the microstructure evolution as a function of these processing parameters can be well interpreted.

Low frequency properties of micro power generator using a gold electroplated coil and magnet

Abstract Micro power generating devices were fabricated by using a gold electroplated coil and a permanent magnet. The electrical power was generated when the magnet reciprocated on the fabricated electroplated coil. The output power was increased as a function of vibration frequency. A measurement system, which convert a rotational motion of a motor into a linear motion, was designed and fabricated. The purpose of this work is to develop the micro power generating devices which convert the ambient vibration or oscillating energy into useful electrical energy. With changing vibration frequency from 0.5 to 8 Hz, the generated power increased linearly. The generated voltage was 106 mV at 3 Hz and 198 mV at 6 Hz. After using the step up circuit, the measured voltage was 81 mV at 3 Hz and 235 mV at 6 Hz. From above the frequency of about 4.5 Hz, the gain obtained by using the quadrupler circuit becomes larger than the loss without using that circuit.

Effects of Hand-Tool Coupling Conditions on the Isolation Effectiveness of Air Bladder Anti-Vibration Gloves

The goals of this study were to determine the vibration isolation effectiveness of a typical (air bladder) anti-vibration glove as a function of vibration frequency, and to investigate the effects of hand-tool coupling action and applied force level on the effectiveness. Six male volunteers were used in the study. A palm adapter method similar to that recommended in the current ISO standard for anti-vibration glove testing (ISO-10819, 1996) was used to measure the transmissibility of the glove. Three different handgrip actions (grip-only, push-only and combined grip and push), three force levels (50, 75 and 100 N), and a broad-band random spectrum were used in the experiment. This study found that the effectiveness of the glove generally increased with an increase in vibration frequency, while the glove did not provide any effective vibration isolation at frequencies less than or equal to 25 Hz. Under the same force level, the push-only action produced the greatest vibration attenuation while the grip-only action resulted in the lowest glove performance among the three actions. Increasing the force tended to increase vibration transmissibility at low frequencies (< 31.5 Hz), while transmissibility decreased at the middle frequencies (63 – 250 Hz). The knowledge generated by this study can be used to augment vibration exposure risk assessments and to promote the appropriate application of anti-vibration gloves at workplaces.

Frequency-dependent effects of muscle tendon vibration on corticospinal excitability: a TMS study.

The aim of the present study was to investigate the effects of muscle tendon vibration at different frequencies on corticospinal excitability by means of transcranial magnetic stimulation (TMS). A second objective was to describe whether the observed modulations in motor evoked potentials (MEPs), as a function of vibration frequency, reflect the behavior of Ia afferents during and after vibration. In ten subjects, muscle tendon vibration (duration 30 s) was applied to the flexor carpi radialis (FCR) muscle at three different frequencies (20, 75 and 120 Hz). MEPs following single-pulse TMS were recorded from the targeted muscle during a previbration, vibration, and postvibration period. Muscle tendon vibration at 75 Hz increased the MEP amplitude significantly during vibration, whereas a smaller but still significant effect was observed during 120 Hz vibration. No significant MEP changes could be observed during 20 Hz vibration and during the postvibration period for each frequency. Our findings indicate that muscle tendon vibration exerts a frequency-dependent effect on corticospinal excitability. Furthermore, evidence is provided for the notion that the excitatory effect of muscle tendon vibration on the primary motor cortex is mediated by Ia afferent input.

Optimization approach to the suppression of vibration errors in phase-shifting interferometry.

An optimization-based strategy is introduced for suppressing errors due to vibration in phase-shifting-interferometry algorithms. A norm-square integral criterion of the error as a function of vibration frequency is used as the basis of the optimization procedure. Analytical results are obtained for certain classes of problems, and numerical algorithms are used when these are not available. It is also shown that the effect of vibration-induced errors in the computation of a time-averaged phase estimate diminishes as the measurements are averaged. Simulations are used to validate the analysis and demonstrate the overall efficacy of the approach. Generalizations to multiple objective optimization problems are briefly discussed.