Influence Of External Vibrations Research Articles

Gravity-driven powder flow and the influence of external vibration on flow characteristics

The controlled and homogeneous flow of dry granular powders through hoppers is essential for applications, namely, packaging of food grains, fertilizers and additive manufacturing processes such as directed energy deposition for better product quality. One of the major issues encountered in the granular flows through hoppers is flow stagnation due to the well-known arching phenomenon. Vibration-assisted granular flow through hoppers is one of the mechanisms used for better mass flow control. In this work, the influence of external mechanical vibration on the powder flow is investigated experimentally and using discrete element simulations. First, the mass flow rate through the hopper increases with an increase in vibration amplitude and then decreases, signifying the existence of an optimal amplitude of vibration. The DEM simulations explained the underlying mechanisms for the existence of an optimal amplitude of vibration corresponding to the maximum mass flow rate. A range of vibration amplitudes from 0 mm to 3.5 mm is used to study the flow behaviour; the maximum flow of around 33 g/s to 35 g/s is observed for 0.75 mm to 1.25 mm vibration amplitude for the hopper-particle combination studied in this work. The work also reports the influence of vibration frequency, hopper, and particle dimension on the flow characteristics. The research facilitates the effective use of mechanical vibration to enhance powder flow that can further be extended to non-spherical and multi-material particles.

Use of Cable Vibration Isolators for Vibration Protection of Quartz Generators

Vibration isolators with damping properties of steel multiwire cables for vibration protection of quartz oscillators have been studied. Modeling of vibration characteristics of structural elements was carried out using numerical methods. The elastic characteristics and design parameters of the cable for the vibration isolator are calculated. A harmonic analysis was carried out with given values of mass and stiffness under the influence of external vibrations. A sample of a cable vibration isolator has been developed and manufactured. To verify the calculated results obtained, the structure of the test bench is proposed, which allows determining the values of na tural re sonant frequencies. The study of the dependence of vibration acceleration on the frequency of oscillations with a disturbing effect according to the sinusoidal and random laws with a variable frequency in the range of 10–2000 Hz was carried out. Tests of the cable vibration isolator have shown the effectiveness of vibration suppression for frequencies above 120 Hz. In the lower range of random vibrations, various resonances have a significant effect on each other. The experiments confirmed the simulation results and the effectiveness of the solution used: the difference in indicators in determining the resonant frequencies was less than 10 % with a decrease in the vibration level to a given indicator.

Influence of External Vibration on the Gravitational Flow Characteristics of Cementitious Materials: A Perspective from Application in Additive Manufacturing

Three-dimensional (3D) printable concretes require high plastic yield stress to retain the shape of the printed layers, however, to enhance the ease of pumping the cementitious system should have as low a plastic yield stress as possible. To address these opposing needs for printing and pumping, a vibration-based active rheology-controlled system which temporarily reduces the plastic yield stress during pumping has been designed. To study the response of the rheological properties of the cementitious system and its response to vibrations, a test setup which can simulate the vibration that occurs during pumping has been developed. An EN445 flow cone was modified by mounting a frequency-controlled vibration setup. The effect of vibration on the flow initiation, flow topology, and flow rate of cementitious systems with three different water-to-binder ratios, two pozzolans (silica fume and metakaolin), and multiple dosage levels of high-range water reducer and viscosity modifying agents was studied. Results from this study suggest a strong correlation between plastic yield stress, and the frequency and amplitude of vibration with implications for 3D printing.

Effect of external vibrations on Electro-Mechanical impedance signatures in damage detection

Piezoelectric Lead Zirconate Titanate (PZT) transducers have gained their application in Structural Health Monitoring (SHM). The surface bonded PZT patches are actuated by an external voltage under a specified frequency range and the Electro Mechanical Impedance (EMI) Signatures are captured which can be utilized to assess and monitor structural health. Generally, with the assumption of the structure is excited only by the PZT actuator the health of the structure is assessed and monitored. However, the changes in the EMI signatures due to external vibrations are not taken into account and interpretation will lead to wrong assessments. The current paper focuses on the study of external vibration with different excitation frequencies and amplitudes on EMI signatures of healthy and damaged beams. Finite element analysis is conducted on a cantilever aluminium flat and the conductance signatures are extracted and the influence of external vibrations on EMI signatures is analyzed and presented.

A study of vibration behavior in shoe sole using vibration level difference and power flow method

Vibration is a common phenomenon in people’s daily life. As the main bearing part of the human body, the foot can cushion the impact and shock of external force, and alleviate the influence of external vibration on the human body. Footwear with different structures and materials could cause kinematic, kinetic and biomechanical changes in the foot and leg. It is necessary to evaluate the effects of various footwear on the foot. In this paper, a method based on the vibration cushion characteristics of shoes is proposed to discuss the effect of shoes on feet. First of all, the modal test of the common sole was carried out in this paper, and the acceleration vibration level difference of the sole was obtained. Then, based on the finite element method, the power flow method was used to analyze the soles under different gait patterns. Finally, the vibration analysis of the soles filled with different porous structures was carried out by power flow method. The results show that the vibration level difference and power flow method can be used to study the vibration behavior of vibrating body from the aspects of structure and energy accurately and effectively, and the soles filled with triangular and quadrilateral porous structure have better damping performance. This method can be used to further study the biomechanical effect of the sole on foot and as a reference for shoe design.

Влияние внешней воздействующей вибрации на микроэлектромеханические системы-акселерометры

Влияние внешней воздействующей вибрации на микроэлектромеханические системы-акселерометры

Characterization of vibration relative amplitude in direct detection Φ-OTDR using variable gain method

Vibration relative amplitude characterization has always been a tough problem in direct detection phase-sensitive optical time-domain reflectometry (Φ-OTDR) system due to the nonlinear relationship between the optical intensity and vibration amplitude. In this paper, a novel variable gain method is proposed to characterize the relative amplitude of external vibration. The mathematical model of Φ-OTDR is established, and the influence of external vibration on detected coherent Rayleigh back-scattering light in a single-mode fiber is simulated. Then, the vibration signals of different amplitudes imposed on the sensing fiber are further investigated, and the relationship between the interference amplitude peak power and vibration amplitude is derived. On the basis of the theoretical analysis, the variable gain method is carried out and implemented in Φ-OTDR system. The experimental results demonstrate that the calibrated interference peak power increases linearly with the applied vibration amplitude, and a high correlation coefficient (R2 = 0.93071) for linear fitting is obtained.

Influence of external vibrations on bubble coalescence time at water and oil surfaces—Experiments and modelling

We report results of the experiments and numerical simulations on kinetics of collision, bouncing and coalescence of air bubbles at free surface of pure liquids of different viscosities. The bubble collision and bouncing courses on the stagnant and vibrating (with controlled acceleration), water/air and silicone oil/air interfaces are compared. For stagnant interfaces the coalescence time (tc) was found to be the bubble radius (Rb) dependent. For larger bubbles the tc was longer. This was caused by higher impact velocity resulting in an increased bubble deformation and higher tendency of the bubble to rebound from the liquid/gas interface. At oscillating liquid/gas interfaces with proper vibration frequency and amplitude the bubble coalescence time can be prolonged significantly as a consequence of prolongation of the bubble bouncing time. This was due to the fact that the energy dissipated during the bubble collision and bouncing was re-supplied via interface vibrations with a properly adjusted acceleration. The analysis of the bubble deformation showed that this effect is related to the degree of the bubble deformation, which determined size of the liquid film formed at the interface. The bubble was bouncing when radius of the liquid film formed was large enough to prevent the draining film to reach a critical thickness of rupture during the collision time. Moreover, it was found that higher acceleration should be applied to prolong the coalescence time (tc) of the bubbles having higher Laplace pressure. The results obtained prove that mechanism of the bubble bouncing from various interfaces depends on interrelation between rates of two simultaneously going processes: (i) exchange between kinetic and surface energies of the system, and (ii) drainage of the liquid film separating the interacting interfaces.

Vibration Isolation by an Actively Compliantly Mounted Sensor Applied to a Coriolis Mass-Flow Meter

In this paper, a vibration isolated design of a Coriolis mass-flow meter (CMFM) is proposed by introducing a compliant connection between the casing and the tube displacement sensors, with the objective to obtain a relative displacement measurement of the fluid conveying tube, dependent on the tube actuation and mass-flow, but independent of external vibrations. The transfer from external vibrations to the relative displacement measurement is analyzed and the design is optimized to minimize this transfer. The influence of external vibrations on a compliant sensor element and the tube are made equal by tuning the resonance frequency and damping of the compliant sensor element and therefore the influence on the relative displacement measurement is minimized. The optimal tuning of the parameters is done actively by acceleration feedback. Based on simulation results, a prototype is built and validated. The validated design shows more than 24 dB reduction of the influence of external vibrations on the mass-flow measurement value of a CMFM, without affecting the sensitivity for mass-flow.

Characterization of Doubled Walled Carbon Nanotubes using Finite Element Method

composites will be developed using carbon nanotubes (CNTs). When compared with the conventional carbon fibers, CNTs in polymer matrices enhance the stiffness and strength of composites. The work is focused on the Double walled carbon nanotubes (DWCNTs) to investigate the mechanical properties. Modulus of elasticity is considered to analyze the behavior of CNTs by adopting the Finite element model (FEM). The experiments conducted on both armchair and zig- zag Nanotubes. By considering the length and radius of the inner and outer tubes of CNTs, the developed stress with the applied load, strain and young's modulus and its response to the load applied is estimated using FEM. The influence of external vibrations on the CNTs considerably minimized with significant stiffness constant (K) of the CNTs. The results obtained are supportive to analyze the behavior of CNTs. KeywordsDWCNTs, FEM, Stress, strain, young's modulus.

Errors in shearography measurements due to the creep of the PZT shearing actuator

Shearography is a modern optical interferometric measurement technique. It uses the interferometric properties of coherent laser light to measure deformation gradients on the µm m − 1 level. In the most common shearography setups, the ones employing a Michelson interferometer, the deformation gradients in both the x- and y-directions can be identified by setting angles on the shearing mirror. One of the mechanisms for setting the desired shearing angles in the Michelson interferometer is using the PZT actuators. This paper will reveal that the time-dependent creep behaviour of the PZT actuators is a major source of measurement errors. Measurements at long time spans suffer severely from this creep behaviour. Even for short time spans, which are typical for shearographic experiments, the creep behaviour of the PZT shear actuator induces considerable deviation in the measured response. In this paper the mechanism and the effect of PZT creep is explored and demonstrated with measurements. For long time-span measurements in shearography, noise is a limiting factor. Thus, the time-dependent evolution of noise is considered in this paper, with particular interest in the influence of external vibrations. Measurements with and without external vibration isolation are conducted and the difference between the two setups is analyzed. At the end of the paper some recommendations are given for minimizing and correcting the here-studied time-dependent effects.

Integrated modeling and realizing of the 2 × 2 array-optical assembly

The development of array technique is a crucial issue for large-scale laser system, and the most important factor effecting optical performance of array system is exacting alignment tolerances, which are always requited to be less than 0.25μrad and λ/13. An integrated model setup for far-field pattern distribution of a 2×2 array-optical system is described, which simulates the combining results under the influence of external vibration in PID control mode. In this model, the ANSYS and MATLAB/SIMULINK are included to respectively perform structure and control analysis. Based on the integrated model analysis, a 2×2 array-optical prototype is designed and fabricated, the simulation and experimental results show that the array-mirror assembly is capable of maintaining high-accuracy tiling stability.

Analysis on vibration rejection ratio of scanning probe microscope

In order to investigate the influence of external vibration on the tip-sample interaction in scanning probe microscope, a concept, vibration rejection ratio (VRR), was proposed by Thompson et al. In the present article, a concise theoretical background was introduced, a vibration stimulating and measuring system for SPM was built up, and an experimental research of the influence on SPM VRR was carried out with different SPM probes, samples, tip preloads, and open/close loops of tip-sample interaction. Based on the experiments, it was proved that SPM VRR had correlations with the spring constant, the air damping constant, the effective mass of the cantilever, the contact spring constant, the contact damping constant between tip and sample, etc. Being different from the traditional theoretical analysis, other than the resonant frequency, a “leading coefficient” was proposed to describe the VRR. A conclusion was drawn after an experimental analysis that SPM’s vibration rejecting ability can be improved by longer cantilever probe, softer sample surface, greater tip preload, and close-loop control for tip-sample interaction. More attention should be paid to a proper combination of the above parameters.

Influence of external vibration on tether chain in ligand-receptor binding

The tethered ligand-receptor binding is an important biological phenomenon. The conformation of tether chain greatly affects the binding process. By using molecular dynamics, the influence of environmental vibration on the conformation of the tether chain is studied. The phase diagram shows that the radius of gyration of the tether chain becomes large when there is vibration due to the vibrational disturbance. However, when the vibration frequency is high enough, the average value of radius of gyration will reduce. Under high frequency vibration, the chain has an inerratic variation on its radius of gyration. These properties provide the frequency modulation on the dimension of the chain. The scaling relation proves the dimension of chain increases faster under low frequency vibration. There are also weak resonance and stochastic-resonance-like behaviors in the chain system. These behaviors probably have biological importance.

Static and dynamic friction processes under the influence of external vibrations

The influence of external vibrations on the frictional force has been studied, using different frequencies, amplitudes, loads and materials. The results show that it is possible to affect the frictional force between two surfaces in contact through vibration. The frictional force can be weakened chiefly through a separation of the surfaces or strengthened by welding phenomena in the contact surfaces. Experiments have shown that either an increase or a decrease in the frictional forces can be obtained when one of the parameters, surface pressure, frequency or amplitude, is changed. Surface roughness, vibration direction, relative speed and materials may also play a determining role. With vibration assistance, the tendency to stick-slip is decreased or eliminated.

Position error occurrence in self balancers used on rigid rotors of rotating machinery

A self balancing method is presented which utilizes freely moving balancing bodies rotating in unison with a rotor to be balanced. Because of resistance to motion, eccentricity of race over which the balancing bodies are moving and the influence of external vibrations, it is impossible to attain a complete balance. Each one of these three factors has been analyzed and their influence on the magnitude of balancing body position errors determined. As a result of some inaccuracy in positioning the balancing bodies, certain residual unbalance always remains.

Static friction processes under dynamic loads and vibration

The influence of external vibration on friction phenomena was investigated. The influence of vibration on the primary displacement was assessed. The influence of the normal pressure and the amplitude of external vibration on the static friction was also investigated. Non-linear relations between the coefficient of static friction and the external vibration and between the coefficient of static friction and the normal pressure where vibration occurs were established. Static and dynamic loads on the same friction pair were studied. Sinusoidal vibration in the contact area caused a decrease in the coefficient of static friction of about 60% which is important practically, especially in this design of machine connections where vibration occurs.

The sliding friction process—effect of external vibrations

The sources of vibrations in machines, and the influence of external vibrations upon friction processes are analysed. Investigations carried out over the range of vibration parameters (frequency 20–120 c/sec, amplitude 5–40 μm) are discussed. The effect of vibrations on technically dry static and kinetic friction at sliding speeds of 0–1.5 m/sec has been examined using steel and cast iron specimens with an antisample of cast iron. A distinct effect of induced vibrations on the values of the force of friction for low sliding speeds has been observed which results in a decrease in the friction force values of up to 15 % of the original value. Considerable changes in the form of frictional vibrations have been proved to exist. Induced vibrations can damp the phenomenon of stick-slip.