Vibration Cycle Research Articles

Flow Field Simulation and Experimental Investigation of Ultrasonic Vibration Assisted EDM Holes Array

Debris distribution in the bottom and side gap significantly affects machining performance of electrical discharge machining (EDM) of holes array. Therefore, the mechanisms of debris distribution and velocity field of flow field in the discharge gap between tool electrode and work piece during EDM process should be investigated. However, these mechanisms have not been fully understood because it is difficult to observe debris distribution process. In this paper, a two-dimensional model of flow field with liquid and debris phase for the bottom and side gap in ultrasonic assisted EDM of holes array was created by computational fluid dynamics. The debris distribution and velocity field of flow field in the bottom and side gap during an ultrasonic vibration cycle was investigated through the numerical simulation. The results show that holes in the center of the array are larger than those at the periphery, which is caused by difference of debris distribution. Machining experiments were conducted to verify the simulation results of debris distribution during EDM of holes array.

Prediction of three-dimensional crack propagation paths taking high cycle fatigue into account

Engine components are usually subject to complex loading patterns such as mixed-mode Low Cycle Fatigue Loading due to maneuvering. In practice, this LCF Loading has to be superimposed by High Cyclic Fatigue Loading caused by vibrations. The changes brought along by HCF are twofold: first, the vibrational cycles which are superposed on the LCF mission increase the maximum loading of the mission and may alter the principal stress planes. Secondly, the HCF cycles themselves have to be evaluated on their own, assuring that no crack propagation occurs. Indeed, the vibrational frequency is usually so high that propagation leads to immediate failure. In the present paper it is explained how these two effects can be taken care of in a standard LCF crack propagation procedure. The method is illustrated by applying the Finite Element based crack propagation software CRACKTRACER3D on an engine blade.

Prediction of oxidation in ground beef meatballs made with citrus fiber by fourier transform infrared spectroscopy

This paper presents a nonlinear dynamic methodology for monitoring precursors of fatigue damage in metallic structures under variable rotational base excitation. The methodology accounts for important nonlinearities due to the complex loading generated by variable rotation and structural degradation. The sources of the nonlinearities include: structural stiffening due to gyroscopic motion and high-response amplitude at the fundamental mode, softening due to inertial forces and gyroscopic loads, and localized microscopic material damage and micro-plasticity. The loading intensity and number of vibration cycles increase the influence of these effects. The change in the dynamic response due to fatigue damage accumulation is experimentally investigated by exciting a cantilever beam at variable rotational base motions. The observed fatigue evolution in the material microstructure at regions of large stresses (and the resulting progressive structural softening) is tracked by quantifying the growth in the tip response, the change in the fundamental natural frequency of the beam and the skewedness of the stepped-sine response curve. Previous understanding of the structural dynamic behavior is necessary to ascertain the damage precursor location and evolution. Nanoindentation studies near the beam clamped boundary are conducted to confirm the gradual progression in the local mechanical properties as a function of loading cycles, and microstructural studies are conducted to obtain qualitative preliminary insights into the microstructure evolution. This study demonstrates that careful monitoring of the nonlinearities in the structural dynamic response can be a sensitive parameter for detection of damage precursors.

Development of 1 kW Stirling cryocooler using a linear compressor

Cryogenic cooling systems for HTS electric power devices require a reliable and efficient high-capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed a dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of the fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has a gamma-type configuration. The piston and displacer are supported with a flexure spring. A slit-type heat exchanger is adopted for the cold and warm-end, and the generated heat is rejected by cooling water. In the cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. The developed cryocooler reaches 47.8 K within 23.4 min. with no-load. Heat load tests shows a cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

Characterization of laryngealization as irregular vocal fold vibration and interaction with prosodic prominence

This paper introduces an original variant of recurrence analysis to quantify the degree of regularity of vocal fold vibration as captured by electroglottography during phonation. The proposed technique is applied to the analysis of laryngealized phonation as this phonation type typically shows irregular vibration cycles. The reliability of this approach is validated with synthetic vocal fold vibration signals, demonstrating that it permits measuring the regularity of vocal fold vibration, unaffected by changes in fundamental frequency. The method is also applied to real electroglottographic signals recorded at the onset of vowel-initial nonsense words produced in a speeded repetition task by five female German speakers. Results show that the degree of laryngealization during the production of word-initial vowels is modulated by the presence of stress (with stressed vowels being less laryngealized). Due to its robustness to changes of F0, the proposed technique proves to be a suitable tool for studying vocal fold regularity in concatenated speech. Its applications are not limited to the study of glottalization, since the degree of regularity of vocal fold vibration has paralinguistic functions and is a clinically relevant measure of voice pathologies.

Quantification of Myofascial Taut Bands

ObjectiveTo assess the correlation of clinician-identified myofascial taut bands with their presence and characteristics on magnetic resonance elastography (MRE) imaging. DesignCross-sectional study. SettingA magnetic resonance imaging (MRI) research laboratory. ParticipantsA convenience sample of adults (N=65; 45 women, 20 men) identified by skilled musculoskeletal physicians as having upper trapezius myofascial pain–associated taut bands. InterventionsSubjects had their taut bands outlined and were positioned within a 1.5T MRI machine. Shear waves were induced with a pneumatic transducer located over the belly of the involved muscle. Wave propagation was visualized with MRE images across a vibration cycle. Imaging data were assessed independently by 2 skilled MRE interpreters. Main Outcome MeasuresThe primary outcome measure was the determination of the intra- and interrater reliabilities of MRE taut band identification and their correlation with clinician identification of band presence. Secondary outcomes consisted of the elucidation of the physical characteristics of taut bands and their surrounding muscle tissue. ResultsMRE intra- and interrater reliability was excellent, with kappa coefficients and 95% confidence intervals (CIs) of .86 (.68–1.00) and .93 (.79–1.00), respectively. Stiffness in MRE-identified taut bands was elevated at a mean ± SD of 11.5±2.4kPa and fell to 5.8±0.9kPa in surrounding muscle tissue (P<.001); muscular tone in trapezius muscles without a taut band was relatively uniform at 6.6±2.1kPa. Agreement between the physicians and the MRE raters, however, was relatively poor (63.1%; 95% CI, 50.2%–74.7%). ConclusionsOur findings suggest that while clinicians may overestimate, and current MRE techniques may underestimate, the presence of taut bands, these bands do exist, can be assessed quantitatively, and do represent localized areas of increased muscle stiffness.

Development of high capacity stirling cryocooler

Abstract Cryogenic cooling system for HTS electric power devices requirea reliable and efficient highs -capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has gamma-type configuration. Piston and displacer are supported with flexure spring. A slit -type heat exchanger is adopted for cold and warm -end, and the generated heat is rejected by cooling water. In cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. Moreover, temperatures of cooling water, housing and l inear motor are recorded and electric power parameters of driving circuit are also obtained. The developed Stirling cryocooler reaches to 47.8 K within 23.4 min. with no -load. From heat load tests, it shows cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

Time-averaged photon-counting digital holography.

Time-averaged holography has been using photo-emulsions (early stage) and digital photo-sensitive arrays (later) to record holograms. We extend the recording possibilities by utilizing a photon-counting camera, and we further investigate the possibility of obtaining accurate hologram reconstructions in rather severe experimental conditions. To achieve this, we derived an expression for fringe function comprising the main parameters affecting the hologram recording. Influence of the main parameters, namely the exposure time and the number of averaged holograms, is analyzed by simulations and experiments. It is demonstrated that taking long exposure times can be avoided by averaging over many holograms with the exposure times much shorter than the vibration cycle. Conditions in which signal-to-noise ratio in reconstructed holograms can be substantially increased are provided.

Design, fabrication and testing of composite sandwich integral structure of spacecraft antenna

An innovative design of the space offset mirror antenna made of composite material is presented in the paper. The antenna body is designed in the form of a composite sandwich conical shell with a cutout made on the side surface. The body geometry is selected to conform to and accommodate the signal transmitting zone. The antenna reflector is located at the bottom part of the sandwich cone and the feed is placed at the top creating a compact antenna configuration. A full-size prototype of the antenna has been designed, built and tested. Design parameters of the sandwich structure have been determined based on the results of finite-element modal analysis. The experimental results of vibration and thermal cycling testing of the prototype provide a proof of concept and evidence of the design feasibility. It is shown that the stiffness characteristics of the proposed integral sandwich antenna ensure efficient applications of such composite structures in the space antennas designed for various ranges of radio wave transmission.

Determination of energy dissipation of a spider silk structure under impulsive loading

Various researches and studies have demonstrated that spider silk is much stronger and more deformable than a steel string of the same diameter from a mechanical approach. These excellent properties have caused many scientific disciplines to get involved, such as bio-mechanics, bio-materials and bio-mimetics, in order to create a material of similar properties and characteristics. It should be noted that the researches and studies have been oriented mainly as a quasi-static model. For this research, the analysis has taken a dynamic approach and determined the dissipation energy of a structure which is made of spider silk “Dragline” and produced by the Argiope-Argentata spider, through an analytical-experimental way, when being subjected to impulsive loading. Both experimental and analytical results, the latter obtained by using adjusted models, have given high levels of dissipation energy during the first cycle of vibration, which are consistent with the values suggested by other authors.

Crack modelling and detection in Timoshenko FGM beam under transverse vibration using frequency contour and response surface model with GA

In the present work, dynamic response of cracked Timoshenko beam with functionally graded material properties are obtained by a numerical technique using Ritz approximation. In order to verify the applicability and performance of the formulation, comparisons of the present numerical method with three-dimensional FEM models are made. Crack is assumed to be transverse and open throughout the vibration cycle. Two different crack detection techniques have been proposed. Results obtained by the numerical technique are used in both of the crack detection techniques. In the first technique, the frequency contours with respect to crack location and size are plotted and the intersection of contours of different modes helps in the prediction of crack location and size. In the second technique, crack is modelled using response surface methodology (RSM). The sum of the squared errors between the numerical and RSM regression model natural frequencies is used as the objective function. This objective function is minimised using genetic algorithm optimisation technique. Both the crack detection techniques and the numerical analysis have shown good agreement with each other.

단주기 진동에너지에 의한 그라우팅 보강효과

Grouting method has been widely used for the ground improvement and stabilization: mostly to block or control the ground water in the early years and to improve the ground, repair the structure in recent years, ever increasing its use. Despite many advantages so far, the existing grouting method also has some shortcomings including uncertain permeation of grouting with gravity type if the voids between the soil particles are narrow, and problems due to the relaxation of the neighboring ground when injected using injection pressure. As an alternative, a vibration injection method with constant amplitude and frequency has been developed in recent years, with the vibration grouting being reported to have a permeability increasing effect of grout material compared with the positive pressure injection type. Accordingly, the purpose of this study is to investigate the improvement effect of the vibration grouting that applies short-period vibration energy by varying vibration cycle, vibration time and ground conditions to evaluate the strength enhancing effect of grouting materials, expansion effect of grouting body, ground improvement effect of the grouting and the penetration characteristics of the rock joint. The findings of this study show the improved compressive strength of grout, expansion of grouting body and increased penetration rate, according to the vibration compared with non-vibration under the loose soil condition.

Development of an Optimal Operation Approach in the MPC Framework for Heavy-Haul Trains

An operation control approach for heavy-haul trains to optimize their performance, including operation safety, service quality, and energy consumption, is proposed. Following a model predictive control method, the controller is capable of scheduling a train to operate optimally during a long section of the rail track. In the cost function, two penalty factors are presented, i.e., one for the braking forces and one for coupler damping effects. The penalty for braking forces is employed to reduce the energy waste incurred by braking. The penalty for coupler damping is introduced to alleviate the cyclic vibration of couplers, which link adjacent cars in the train. The damping penalty is also expected to reduce energy wasted by coupler damping and corresponding maintenance/replacement cost of the dampers. In addition, the weight of the velocity tracking term in the objective function is modified to vary dynamically, according to the train's velocity, to improve the train's overall performance. Simulations verify the effectiveness of the proposed control approach. Discussions over the impacts of the two penalty factors and the dynamic weight method are provided, together with some suggestions on their applications.

Processing and energy-harvesting ability of (Na,K)NbO3 particle-dispersed fibrous polyvinylidene fluoride multilayer composite

Piezoelectric vibration energy harvesters are expected to be used as power sources for sensors in ubiquitous networks, and improvements in the materials and structures of harvesters are ongoing. We produced a novel vibration energy harvester with a unique material obtained by mixing lead-free piezoelectric (Na0.5K0.5)NbO3 (NKN) ceramic particles with a polyvinylidene fluoride (PVDF) fabric formed by electrospinning. The PVDF/NKN fabric showed high flexibility and was stretchable in the longitudinal-direction. Furthermore, a harvester with a multilayer structure of alternating PVDF/NKN fabrics and polyvinyl alcohol (PVA) sheets was designed and then fabricated by hot pressing. Electric power output results for the harvester suggest that the high flexibility of the fabric in the longitudinal-direction was effectively utilized and the electric power output was enhanced by incorporating NKN powder into PVDF fabric. This harvester showed a maximum power output of 145nW/cm2 per vibration cycle at 170Hz.

Piecewise constrained optimization harmonic balance method for predicting the limit cycle oscillations of an airfoil with various nonlinear structures

A method is proposed to calculate the periodic solutions of piecewise nonlinear systems. The method is based on analytical derivation of nonlinear multi-harmonic equations of motion. Since periodic variations of nonlinear forces are characterized by different states, the vibration cycle is broken into sequential transition intervals according to the instant sets of state transitions. Analytical formulations of the harmonic coefficients of the nonlinear forces and its derivatives with respect to the harmonic coefficients of displacements are developed. Sensitivities of the harmonic coefficients of periodic solutions are determined for constructing explicit expressions for vibration amplitude levels as a function of structural parameters. Numerical investigations of the limit cycle oscillations and its sensitivities of an airfoil with different piecewise nonlinearities have been performed. The results show that the developed method is capable of determining the periodic solutions and its sensitivities with respect to the structural parameters. In order to guarantee time continuity of the nonlinear force, for the hysteresis model it is not right to track the periodic solutions by using the preload or freeplay as the continuation parameters.

Study of valveless electromagnetic micropump by volume-of-fluid and OpenFOAM

The paper reports the first study on the backpressure of a valveless electromagnetic micropump using the volume-of-fluid (VOF) technique and open-source code OpenFOAM. The micropump consists of a vibrating diaphragm and fluidic microchannel connected to inlet and outlet tubes. The imbalance in fluid resistance of the fluidic microchannel during a vibration cycle of the diaphragm creates backpressure in the pump, which in turn produces a difference in water level between the inlet and outlet tubes. In this study, VOF was used in a transient simulation to obtain this difference in water level and then the backpressure. The obtained backpressure showed a slight discrepancy with the experimental data. The discrepancy was probably due to the difference in the wall surface quality of the fluidic microchannel between the simulation model and experimental device. These results are useful for analytical and numerical research on these types of micropumps and can easily be applied in an open-source code simulator with almost zero cost.

Causal and passive interpolation of structural acoustic matrices

The present work investigates the causal and passive interpolation of structural acoustic matrices in the frequency domain. Interpolations significantly ease computational burdens involved in computing these matrices from models. For example, one may wish to compute a small admittance matrix, relating forces to velocities at points on a structure, from a large finite element model with over one million degrees of freedom. In many structural acoustic systems, the elements of such matrices vary smoothly with frequency and therefore interpolation can be accurate and effective. In the time domain, causality requires no effect before its cause. In the frequency domain, this takes the form of Hilbert transform relations that relate the real and imaginary parts of scalar transfer functions. Passivity requires that the net power dissipated by the structure over a cycle of vibration be positive semidefinite. The present work develops series expansions in which these conditions may be implicitly satisfied by the proper choice of basis functions. Coefficients of in the series expansion are found by matching the series to the known values at the interpolation points. Examples demonstrate situations in which the satisfaction of these physical conditions yields more accurate interpolations.

On the formation of limit cycle of the friction-induced stick-slip vibration in oilwell drillstring

Abstract In this paper, the stick-slip vibration in oilwell drillstring is studied. The drilling system is modelled as a lumped-parameter torsional pendulum and the interaction between the drill bit and the rock is treated as Coulomb friction. Equation of motion of the drill bit is established and the dynamic responses of the drill bit are obtained. A drilling system with the drillstring length 3000 m is analysed, in which the system parameters are selected by reference to the actual drilling situation. After the slip vibrations in the initial stage, final state of the drill bit is a stable stick-slip vibration of which the limit cycle is a closed loop. In order to find the stability of the limit cycle corresponds to the periodically stick-slip vibration, different initial conditions for the drill bit are studied. Results show that the drill bit will lead to a periodic motion and the phase trajectories ultimately converge to the same limit cycle corresponds to stable stick-slip vibration.

Analysis on Corona Discharge Characteristics of the Overhead Conductor

LGJ150/25 steel core aluminum stranded wires were selected as the test wires, and the aeolian vibrations which work in different cycle times of wire that is under the conditions of dry and acidic corrosion were simulated by the self-made test bed. The electronic number of corona discharge of each pre-set conductor was measured, when applying AC high voltage on the wearing wires step by step,so that the corona inception voltages of the conductors could be confirmed. And the effect of the vibration cycle times and environmental conditions on the corona discharge was researched. Taking the sum of all aluminium stands wear area of a pre-set wire as the fretting wearing capacity, the relationship between the wire wearing capacity and the corona discharge was studied. The results indicate that the corona inception voltages of the conductors decrease with the increase of the cycle times and the wires wear capacity. In general, the wear capacity of the acidic corrosion conductors is larger, and its corona inception voltage is lower. Therefore the decrease of the conductor fretting wear can effectively reduce the corona loss of transmission lines and other hazards.

Free and forced vibration characteristics of bimodular composite laminated circular cylindrical shells

The free and forced vibration characteristics of bimodular cross-ply laminated clamped–clamped circular cylindrical shells are studied using Bert’s and a recently proposed model considering first order shear deformation theory. The free vibration frequencies in positive and negative half cycles are found to be same for all asymmetric modes and for axisymmetric modes with even number of axial half waves, and different for axisymmetric modes with odd number of axial half waves. However, the negative half cycle amplitude is significantly greater than the positive half cycle amplitude due to the local stiffness of bimodular cylindrical shells being different for positive and negative half cycles even though the natural frequencies are same for positive and negative half cycles of asymmetric vibrations. The relative difference of positive and negative half cycle frequencies is very less for single layer orthotropic shells, and it is significant for cross-ply shells for axisymmetric mode of vibration. The vibration characteristics predicted using proposed and Bert’s constitutive models are quite close except for the transverse to the fiber direction normal stress.