Статті в журналах з теми "Natural oscillation frequency"
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1
DANA, SYAMAL KUMAR, and SATYABRATA CHAKRABORTY. "GENERATION OF HOMOCLINIC OSCILLATION IN THE PHASE SYNCHRONIZATION REGIME IN COUPLED CHUA'S OSCILLATORS." International Journal of Bifurcation and Chaos 14, no. 04 (April 2004): 1375–83. http://dx.doi.org/10.1142/s0218127404009958.
Повний текст джерелаАнотація:
An experimental method for generating homoclinic oscillations using two nonidentical Chua's oscillators coupled in unidirectional mode is described here. A homoclinic oscillation is obtained at the response oscillator in the weaker coupling limit of phase synchronization. Different phase locking phenomena of homoclinic oscillations with external periodic pulse have been observed when the frequency of the pulse is close to the natural frequency of the homoclinic oscillation or its subharmonics.
2
Fisher, C. E., and K. S. Ball. "Plume Dynamics in Natural Convection in a Horizontal Cylindrical Annulus." Journal of Heat Transfer 121, no. 3 (August 1, 1999): 598–602. http://dx.doi.org/10.1115/1.2826021.
Повний текст джерелаАнотація:
Measurements of the unsteady temperature fluctuations in the plume region between differentially heated horizontal concentric cylinders are reported. In particular, power spectral density estimates of the temperature fluctuations within the plume show the development and breakdown of the oscillatory plume structure at high Rayleigh number, Rad, by two relatively independent processes: (1) the development of harmonic oscillations related to the dominant plume oscillation frequency, and (2) interactions between the oscillating plume and the adjacent relatively stagnant core flow (shear and entrainment). The harmonic oscillations are shown to be the dominant energy transfer mode at moderate Rad (up to Rad = 108), acting to disperse the plume energy without generating a broadband spectrum. The spectral density estimates show that while a distinct plume oscillation is still present near the inner cylinder at Rad = 109, the plume becomes increasingly turbulent as the outer cylinder is approached. A new correlation for the plume oscillation frequency, which is found to be proportional to Rad0.5, is also presented.
3
Eliseev, V. І., S. А. Shevchenko, A. P. Tolstopyat, L. A. Fleer, and А. Р. Shevchenko. "Dynamics of oscillations of the "liquid bath - lance" system during injection processing of the melt in the ledle." Fundamental and applied problems of ferrous metallurgy, no. 34 (2020): 90–100. http://dx.doi.org/10.52150/2522-9117-2020-34-90-100.
Повний текст джерелаАнотація:
The aim of the study was to evaluate the influence of key waveform factors on the dynamics of the process during injection molding of cast iron with granular magnesium in ladles, their significance and relationship between them. Based on the theories of wave motion of liquid layers, a mathematical model has been developed that allows to investigate the oscillatory processes in the ladle during the processing of cast iron melt with granular magnesium. The model involved the processing of cast iron by injection of granular magnesium through the tuyeres of devices that are immersed in the melt. The oscillating system "Liquid bath - lance" is considered on the example of the bath of a heavy - duty filling bucket with its own frequency - 0.47 Hz. The influence of the most probable oscillation sources (natural frequency of the lance oscillation and the frequency of the conditional source) on the amplitude-frequency oscillations of the system elements is calculated. It is established that in addition to the natural frequencies of these elements, the system has two more natural oscillations. Given that the mass of the melt is much greater than the mass of the lance, it practically determines the behavior of the system during its excitation. That is, the system responds only to those excitations in which the frequency is close to the natural frequency of the liquid bath. In turn, it is shown that the natural frequency of the bath is largely determined by its diameter at the top. In practice, it is necessary to know the resonant frequencies of the liquid bath, the tuyere device, as well as all other sources of oscillations (gas jet decay, and oscillations of pop-up bubbles). Accordingly, it is necessary to try to dampen the amplitude with this dangerous resonant frequency. To reduce the oscillation amplitude of the bath surface when treating cast iron with granular magnesium, it is recommended to first estimate the natural resonant frequency of the liquid bath, and then select design solutions and processing parameters, avoiding dangerous frequencies close to the natural frequency of the bath. However, it should be noted that the spectrum of oscillation frequencies in the purl zone is quite wide and, of course, contains dangerous low frequencies.
4
Wang, Wei, Kaiming Yang, and Yu Zhu. "Optimal Frequency and Amplitude of Vertical Viewpoint Oscillation for Improving Vection Strength and Reducing Neural Constrains on Gait." Entropy 23, no. 5 (April 28, 2021): 541. http://dx.doi.org/10.3390/e23050541.
Повний текст джерелаАнотація:
Inducing self-motion illusions referred as vection are critical for improving the sensation of walking in virtual environments (VE). Adding viewpoint oscillations to a constant forward velocity in VE is effective for improving vection strength under static conditions. However, the effects of oscillation frequency and amplitude on vection strength under treadmill walking conditions are still unclear. Besides, due to the visuomotor entrainment mechanism, these visual oscillations would affect gait patterns and be detrimental for achieving natural walking if not properly designed. This study was aimed at determining the optimal frequency and amplitude of vertical viewpoint oscillations for improving vection strength and reducing gait constraints. Seven subjects walked on a treadmill while watching a visual scene. The visual scene presented a constant forward velocity equal to the treadmill velocity with different vertical viewpoint oscillations added. Five oscillation patterns with different combinations of frequency and amplitude were tested. Subjects gave verbal ratings of vection strength. The mediolateral (M-L) center of pressure (CoP) complexity was calculated to indicate gait constraints. After the experiment, subjects were asked to give the best and the worst oscillation pattern based on their walking experience. The oscillation frequency and amplitude had strong positive correlations with vection strength. The M-L CoP complexity was reduced under oscillations with low frequency. The medium oscillation amplitude had greater M-L CoP complexity than the small and large amplitude. Besides, subjects preferred those oscillation patterns with large gait complexity. We suggested that the oscillation amplitude with largest M-L CoP complexity should first be chosen to reduce gait constraints. Then, increasing the oscillation frequency to improve vection strength until individual preference or the boundary of motion sickness. These findings provide important guidelines to promote the sensation of natural walking in VE.
5
Ma, Xindong, and Shuqian Cao. "Bursting Oscillations in Shimizu-Morioka System with Slow-Varying Periodic Excitation." Shock and Vibration 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/5207910.
Повний текст джерелаАнотація:
The coupling effect of two different frequency scales between the exciting frequency and the natural frequency of the Shimizu-Morioka system with slow-varying periodic excitation is investigated. First, based on the analysis of the equilibrium states, homoclinic bifurcation, fold bifurcation, and supercritical Hopf bifurcation are observed in the system under a certain parameter condition. When the exciting frequency is much smaller than the natural frequency, we can regard the periodic excitation as a slow-varying parameter. Second, complicated dynamic behaviors are analyzed when the slow-varying parameter passes through different bifurcation points, of which the mechanisms of four different bursting patterns, namely, symmetric “homoclinic/homoclinic” bursting oscillation, symmetric “fold/Hopf” bursting oscillation, symmetric “fold/fold” bursting oscillation, and symmetric “Hopf/Hopf” bursting oscillation via “fold/fold” hysteresis loop, are revealed with different values of the parameterbby means of the transformed phase portrait. Finally, we can find that the time interval between two symmetric adjacent spikes of bursting oscillations exhibits dependency on the periodic excitation frequency.
6
Alshuaibi, Khaled, Yi Zhao, Lin Zhu, Evangelos Farantatos, Deepak Ramasubramanian, Wenpeng Yu, and Yilu Liu. "Forced Oscillation Grid Vulnerability Analysis and Mitigation Using Inverter-Based Resources: Texas Grid Case Study." Energies 15, no. 8 (April 12, 2022): 2819. http://dx.doi.org/10.3390/en15082819.
Повний текст джерелаАнотація:
Forced oscillation events have become a challenging problem with the increasing penetration of renewable and other inverter-based resources (IBRs), especially when the forced oscillation frequency coincides with the dominant natural oscillation frequency. A severe forced oscillation event can deteriorate power system dynamic stability, damage equipment, and limit power transfer capability. This paper proposes a two-dimension scanning forced oscillation grid vulnerability analysis method to identify areas/zones in the system that are critical to forced oscillation. These critical areas/zones can be further considered as effective actuator locations for the deployment of forced oscillation damping controllers. Additionally, active power modulation control through IBRs is also proposed to reduce the forced oscillation impact on the entire grid. The proposed methods are demonstrated through a case study on a synthetic Texas power system model. The simulation results demonstrate that the critical areas/zones of forced oscillation are related to the areas that highly participate in the natural oscillations and the proposed oscillation damping controller through IBRs can effectively reduce the forced oscillation impact in the entire system.
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Malkin, Evgeny. "Natural Vibration Frequency Definition Of Turbine Blades." E3S Web of Conferences 221 (2020): 03007. http://dx.doi.org/10.1051/e3sconf/202022103007.
Повний текст джерелаАнотація:
A turbine compressor package is used for pipeline gas transmission. When operating, compressor turbine blades develop vibration, which increases the number of dynamic stress cycles and results in the blade failure. The present study aims to determine the frequency of natural blade vibration and to consider it in the context of the blade repair process. In the first stage of the study, an oscillating contour is developed to generate standing oscillation wave which characteristics are used as experimental data. To process those data, a mathematical model is developed to calculate the blade resonant frequency. Finally, the boundaries of the assured quality area are determined. Blade operation capacity analysis method will allow us to reduce the number of environmentally dangerous experiments.
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Pattiaratchi, Charitha, and Sarath Wijeratne. "PROCESSES LEADING TO INFRA-GRAVITY PERIOD OSCILLATIONS AND CURRENTS IN PORTS AND MARINAS." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 78. http://dx.doi.org/10.9753/icce.v36.currents.78.
Повний текст джерелаАнотація:
In this paper, we take the broad definition of tsunami (‘harbour wave’) to describe oscillations in the infragravity (IG) periods (between 30 and 300s) in ports and marinas that often lead to interruption in harbour operations due to excessive vessel movements. The main processes that lead to these oscillations (also called seiches) are examined through the analysis of field measurements of water levels and currents from Western Australia. In a port or marina with lengths of the order of 500m and depths of the order of 10m, the natural oscillation periods are of the order of a few minutes. Changes in water levels in the coastal ocean adjacent to the port can setup oscillations within the port at its natural frequency. This results in water level fluctuations and strong horizontal currents within the port. If the incoming forcing is close to the natural frequency of oscillation resonance conditions may arise resulting in increased agitation inside the port. In addition if the harbour oscillation periods coincide with natural period of moored vessels, harbour operations can be severely interrupted due to strong vessel movements damaging to mooring lines and fenders.
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Becker, E., W. J. Hiller, and T. A. Kowalewski. "Experimental and theoretical investigation of large-amplitude oscillations of liquid droplets." Journal of Fluid Mechanics 231 (October 1991): 189–210. http://dx.doi.org/10.1017/s0022112091003361.
Повний текст джерелаАнотація:
Finite-amplitude, axially symmetric oscillations of small (0.2 mm) liquid droplets in a gaseous environment are studied, both experimentally and theoretically. When the amplitude of natural oscillations of the fundamental mode exceeds approximately 10% of the droplet radius, typical nonlinear effects like the dependence of the oscillation frequency on the amplitude, the asymmetry of the oscillation amplitude, and the interaction between modes are observed. As the amplitude decreases due to viscous damping, the oscillation frequency and the amplitude decay factor reach their asymptotical values predicted by linear theory. The initial behaviour of the droplet is described quite satisfactorily by a proposed nonlinear inviscid theoretical model.
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Bilyk, V. A., E. V. Korobko, G. N. Reizina, E. A. Bashtovaya, E. B. Kaberdina, and V. A. Kuzmin. "Vibration Control of Oscillating System Based on Governing Visco-Elastic Characteristics of Absorber by Means of External Electric Signal." Solid State Phenomena 144 (September 2008): 220–25. http://dx.doi.org/10.4028/www.scientific.net/ssp.144.220.
Повний текст джерелаАнотація:
Electro-rheological fluids (ERF) allow us to create «smart» devices. One of the basic directions of application of such materials is damping in oscillating systems. This work describes simulation model and offers the results of experimental research by rheological properties and damping characteristic of ERF. Control signal is defined by electric field intensity, which is changed within the bounds of 0…0.5 kV/mm. Amplitude of oscillation – up to 5 mm, oscillation frequency is modified within the bounds of 0.5…5 Hz. The logarithmic damping decrement and natural oscillation frequency of oscillating system, shear stress and viscosity of ERF are determined.
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Jamisola, Rodrigo S., Jr., and Elmer P. Dadios. "Experimental Identification of Manipulator Dynamics Through the Minimization of its Natural Oscillations." Journal of Advanced Computational Intelligence and Intelligent Informatics 14, no. 1 (January 20, 2010): 39–45. http://dx.doi.org/10.20965/jaciii.2010.p0039.
Повний текст джерелаАнотація:
This work presents amethod of identifying the dynamics parameters of rigid-body manipulators through the minimization of its natural oscillations. It is assumed that each link has an actuated joint that is different from its center of mass, such that its driving torque is influenced by gravitational force. In this earlier results of our study, it is assumed that the inertias can be expressed in terms of the mass and center of mass. This work utilizes the actual force of gravity for the manipulator link to achieve natural oscillation. The oscillatory motion allows the system to be converted into an optimization problem through the minimization of the frequency of oscillation. The correct dynamics parameters are found when the minimum frequency of oscillation is achieved. The proposed method is analyzed and a theorem is presented that supports the claims presented in this work together with implementation results.
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Pariz, Aref, Ingo Fischer, Alireza Valizadeh, and Claudio Mirasso. "Transmission delays and frequency detuning can regulate information flow between brain regions." PLOS Computational Biology 17, no. 4 (April 15, 2021): e1008129. http://dx.doi.org/10.1371/journal.pcbi.1008129.
Повний текст джерелаАнотація:
Brain networks exhibit very variable and dynamical functional connectivity and flexible configurations of information exchange despite their overall fixed structure. Brain oscillations are hypothesized to underlie time-dependent functional connectivity by periodically changing the excitability of neural populations. In this paper, we investigate the role of the connection delay and the detuning between the natural frequencies of neural populations in the transmission of signals. Based on numerical simulations and analytical arguments, we show that the amount of information transfer between two oscillating neural populations could be determined by their connection delay and the mismatch in their oscillation frequencies. Our results highlight the role of the collective phase response curve of the oscillating neural populations for the efficacy of signal transmission and the quality of the information transfer in brain networks.
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Iudin, Arkadii V., and Viktor S. Shestakov. "Analysis of connections and restrictions occurring due to the oscillations of vibrating screen working member and cantilevered screen deck." Izvestiya vysshikh uchebnykh zavedenii Gornyi zhurnal, no. 1 (February 17, 2020): 97–104. http://dx.doi.org/10.21440/0536-1028-2020-1-97-104.
Повний текст джерелаАнотація:
Research relevance is due to the need of mining companies in a more complete extraction of mineral resources, reduction of crude minerals losses, and extension of deposits’ life. Some enterprises face the problem of complicated high-quality separation of hard-to-screen rock mass. Screen which are common in the industry often become clogged causing decline in the effectiveness of screening. Research aim is to determine the links, build resonant curves and analyze the amplitude oscillations of the working member and cantilevered bars of the screen deck using numerical simulation. Methodology includes the theoretical study of the dual mass oscillatory system with the use of numerical simulation. Results. The motion of the vibrating screen with circular oscillations of the working member, which includes the screen deck of a cascade type with cantilevered bars, is regarded as oscillation of a dual mass system. The amplitudes of oscillations of both masses make in-phase and anti-phase movements relative to the driving force of the drive. The analysis showed that the amplitudes of the working member are practically independent of the screen deck parameters, and bars oscillation amplitudes vary over a wide range. The expressions are given calculating the parameters of cantilevered bars and the values of the initial data of the GIT-51 screen. Resonance curves of amplitude and frequency relations are constructed. The conditions are established under which the oscillation amplitudes of the cantilevered bars take on hyperadmissible values; it is shown that for a particular oscillating system there is a transitional resonance value. Summary. The natural oscillation frequency ratio ranges are established of the entire system with the frequency of forced oscillations in which the oscillation amplitudes of cantilevered bars reach the specified parameters. It is shown that by changing the screen deck parameters at the design stage, it is possible to adjust the inter-frequency range and establish the operating mode of the screen.
14
Pei, Jiang Hong. "Study on the Relation between Oscillation Frequency of Self-Excited Oscillation Pulsed Water Jet and Self-Excited Pulsed Water Jet Devices." Advanced Materials Research 339 (September 2011): 547–52. http://dx.doi.org/10.4028/www.scientific.net/amr.339.547.
Повний текст джерелаАнотація:
Depending on different structure characteristic of nozzle (self-excited oscillation chamber and special boundary condition), the self-excited pulsed water jet can be produced,which can increase the jet pressure and having the cavitation phenomenon. So,it has been applied in oil driven well、mining and building etc.To study the relation among the frequency of the jetting peak pressure,the peak pressure of the plused-jetting and the self-excited pulsed water jet device,based on the theory of fluid network,the mathematical model of the self-excited oscillation pulsed water jet device was established and the dynamic characteristics parameters of the self-excited oscillation pulsed water jet were tested, which shows that the frequency of the self-excited oscillation nozzle depend on the structure parameter and the dynamic state characteristic of the fluid decisive .the frequency of the jetting peak pressure depends on natural frequency and damping ratio of the device.The experiment proves that the frequency of the jetting peak pressure decreases with the length of the self-excited oscillation chamber,increases with the rising of the pump pressure and there is an optimal length of the oscillation chamber corresponding to the jetting surge pressure. lastly, it clearly shows that the device has functions of oscillator and low pass filter and the jetting peak pressure is the highest when the jet dominant frequency close to the natural frequency of the device. The experimental results help to theory analyzing how to improve peak pressure of the self-excited oscillation jet and have some value in engineering.
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Palikhe, Sunit, Jianxu Zhou, and Khem Prasad Bhattarai. "Hydraulic Oscillation and Instability of a Hydraulic System with Two Different Pump-Turbines in Turbine Operation." Water 11, no. 4 (April 4, 2019): 692. http://dx.doi.org/10.3390/w11040692.
Повний текст джерелаАнотація:
Hydraulic oscillation mainly reveals the undesirable pressure fluctuations which can cause catastrophic failure of any hydraulic system. The behavior of a hydraulic system equipped with two different pump-turbines was investigated through hydraulic oscillation analysis to demonstrate severe consequences induced in turbine operation, including S-shaped characteristics. The impedance of a pump-turbine has an essential role in the determination of the instability of the hydraulic system. The conventional way to determine the instability solely using the slope of a characteristic curve was improved, including the effect of guide vane opening in pump-turbine impedance, which consequently modified the instability expression. With this pump-turbine impedance, hydraulic oscillation analysis, including free oscillation analysis and frequency response analysis, was carried out. The free oscillation analysis entails the computation of complex natural frequencies and corresponding mode shapes of the system. These computations provided necessary information about the vulnerable position of vital hydraulic components and the scenario for self-excited oscillation. Further, the analysis illustrates the significant role of guide vane opening to prevent the system from becoming unstable. Lastly, frequency response analysis was performed for the system with an oscillating guide vane to obtain the frequency response spectrum, which revealed that the resonating frequencies are consistent with natural frequencies, and it supported free oscillation results.
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Matsuda, Takeru, and Fumiyasu Komaki. "Time Series Decomposition into Oscillation Components and Phase Estimation." Neural Computation 29, no. 2 (February 2017): 332–67. http://dx.doi.org/10.1162/neco_a_00916.
Повний текст джерелаАнотація:
Many time series are naturally considered as a superposition of several oscillation components. For example, electroencephalogram (EEG) time series include oscillation components such as alpha, beta, and gamma. We propose a method for decomposing time series into such oscillation components using state-space models. Based on the concept of random frequency modulation, gaussian linear state-space models for oscillation components are developed. In this model, the frequency of an oscillator fluctuates by noise. Time series decomposition is accomplished by this model like the Bayesian seasonal adjustment method. Since the model parameters are estimated from data by the empirical Bayes’ method, the amplitudes and the frequencies of oscillation components are determined in a data-driven manner. Also, the appropriate number of oscillation components is determined with the Akaike information criterion (AIC). In this way, the proposed method provides a natural decomposition of the given time series into oscillation components. In neuroscience, the phase of neural time series plays an important role in neural information processing. The proposed method can be used to estimate the phase of each oscillation component and has several advantages over a conventional method based on the Hilbert transform. Thus, the proposed method enables an investigation of the phase dynamics of time series. Numerical results show that the proposed method succeeds in extracting intermittent oscillations like ripples and detecting the phase reset phenomena. We apply the proposed method to real data from various fields such as astronomy, ecology, tidology, and neuroscience.
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Nosko, Oleksii, Takuo Nagamine, Hiroki Mori, and Yuichi Sato. "Friction-Induced Oscillations of a Non-Asbestos Organic Pin Sliding on a Steel Disc." Acta Mechanica et Automatica 9, no. 2 (June 1, 2015): 84–88. http://dx.doi.org/10.1515/ama-2015-0014.
Повний текст джерелаАнотація:
Abstract Friction-induced oscillations result in deterioration of performance of disc brakes and are generally undesired. We conduct experimental study of friction-induced oscillations in a non-asbestos organic material / steel pair used in disc brakes of motor vehicles. The tests are done by use of a pin-on-disc machine in which the pin sample is supported on a deformable beam. The adjustable friction parameters are the disc velocity, contact pressure and temperature. The tests show that the friction coefficient decreases with the sliding velocity and increases with the temperature. The friction-induced tangential oscillation of the pin sample occurs with a frequency equal to the first natural frequency of the beam. The effects of the disc velocity and temperature on the oscillation characteristics are investigated. The oscillation amplitude increases with the disc velocity on the interval of velocities below 2 m/s. Temperature changes of several tens of degrees Celsius lead to the oscillation occurrence / decay. The obtained results can be useful for prognostication of friction-induced oscillations in disc brakes with non-asbestos organic pads.
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Fabrikant, A. L. "Harbour oscillations generated by shear flow." Journal of Fluid Mechanics 282 (January 10, 1995): 203–17. http://dx.doi.org/10.1017/s0022112095000103.
Повний текст джерелаАнотація:
A new mechanism that could be responsible for excitation of long-period oscillations in partially enclosed harbours is discussed. This mechanism is based on the interaction between a shear flow and the harbour-basin natural mode and does not suppose any external exciting forces caused by wind waves, tsunami, etc. The growth rate of harbour oscillations is found in terms of a plane-wave reflection coefficient integrated on the wavenumber spectrum of the oscillating outflow field near the harbour entrance. Analytical considerations for simple shear flows (vortex sheet and jet) show that the growth rate changes its sign depending on the ratio of oscillation frequency to flow speed.
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Kuznetsov, Alexey S., Nancy J. Kopell, and Charles J. Wilson. "Transient High-Frequency Firing in a Coupled-Oscillator Model of the Mesencephalic Dopaminergic Neuron." Journal of Neurophysiology 95, no. 2 (February 2006): 932–47. http://dx.doi.org/10.1152/jn.00691.2004.
Повний текст джерелаАнотація:
Dopaminergic neurons of the midbrain fire spontaneously at rates <10/s and ordinarily will not exceed this range even when driven with somatic current injection. When driven at higher rates, these cells undergo spike failure through depolarization block. During spontaneous bursting of dopaminergic neurons in vivo, bursts related to reward expectation in behaving animals, and bursts generated by dendritic application of N-methyl-d-aspartate (NMDA) agonists, transient firing attains rates well above this range. We suggest a way such high-frequency firing may occur in response to dendritic NMDA receptor activation. We have extended the coupled oscillator model of the dopaminergic neuron, which represents the soma and dendrites as electrically coupled compartments with different natural spiking frequencies, by addition of dendritic AMPA (voltage-independent) or NMDA (voltage-dependent) synaptic conductance. Both soma and dendrites contain a simplified version of the calcium-potassium mechanism known to be the mechanism for slow spontaneous oscillation and background firing in dopaminergic cells. The compartments differ only in diameter, and this difference is responsible for the difference in natural frequencies. We show that because of its voltage dependence, NMDA receptor activation acts to amplify the effect on the soma of the high-frequency oscillation of the dendrites, which is normally too weak to exert a large influence on the overall oscillation frequency of the neuron. During the high-frequency oscillations that result, sodium inactivation in the soma is removed rapidly after each action potential by the hyperpolarizing influence of the dendritic calcium-dependent potassium current, preventing depolarization block of the spike mechanism, and allowing high-frequency spiking.
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Pirogov, Sergey, and Alexander Chuba. "Development of the theory of oscillations of manometric tubular springs." АгроЭкоИнфо 3, no. 51 (May 24, 2022): 4. http://dx.doi.org/10.51419/202123304.
Повний текст джерелаАнотація:
The paper considers the development of the theory of oscillations of manometric tubular springs (Bourdon tubes). A review of the work in this field is carried out, the development of the theory of vibrations of tubular springs and methods for calculating the parameters of the oscillatory motion of natural frequencies and attenuation coefficients when moving in a viscous medium are shown. Keywords: OSCILLATION THEORY, MANOMETRIC TUBULAR SPRINGS, OSCILLATION PARAMETERS, OSCILLA-TION FREQUENCY
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Akimov, O., V. Dmytriiev, V. Boiarov, and V. Fedenko. "SIMULATION OF NATURAL OSCILLATIONS OF THE AIR ASSAULT RAPPELLING SYSTEM “KANAT-1”." Наукові праці Державного науково-дослідного інституту випробувань і сертифікації озброєння та військової техніки, no. 8 (June 29, 2021): 4–9. http://dx.doi.org/10.37701/dndivsovt.8.2021.01.
Повний текст джерелаАнотація:
The main purpose of the article is to consider the simulation of the natural oscillations of the air assault rappelling system “Kanat-1”.
The object of consideration is a set of removable onboard equipment for rappelling air assault "Kanat-1" for landing from the cargo hatch of Mi-8 helicopters.
Air assault rappelling system is an oscillating system that has certain natural frequencies of oscillation of the item, which depend on the number of paratroopers on the rope and their placement on it. The airframe of the Mi-8 helicopter has its own frequencies within the ranges of 3.1 - 3.3; 8 - 9; 15 - 17 Hz with which, and their divisibles the natural frequencies of the item should not coincide. In real operating conditions, determining the natural frequencies of the elements of the item under load is problematic.
A system of dynamic models is built which allows determining the natural frequencies of air assault rappelling system oscillations at arbitrary placement of up to three paratroopers weighing up to 140 kg each, which can be hung simultaneously on one of the ropes in constant motion while moving the points of contact with the rope. In general, at the maximum load on the rope (three paratroopers), the mathematical model represents a system of three second-order differential equations. Eight variants for loading the rope with paratroopers are considered. The obtained oscillation frequencies of the air assault rappelling system do not coincide with the oscillation frequencies of the helicopter airframe which proves the effectivity of the air assault rappelling system.
Recommendations for regulation of frequency characteristics of air assault rappelling system by replacement of a fastening element of a rope to a traverse are developed.
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Szudarek, Maciej, and Mateusz Turkowski. "Experimental study of a lock-in phenomenon in the case of a mechanical oscillator flowmeter." Mechanik 93, no. 7 (July 2, 2020): 13–15. http://dx.doi.org/10.17814/mechanik.2020.7.13.
Повний текст джерелаАнотація:
Oscillatory flowmeters are susceptible to pulsatile flow and mechanical oscillator flowmeters are no exception. The experimental study was conducted to determine possible measurement errors for specific pulsation amplitude thresholds. The study verified that no frequency lock-in takes place for pulsation frequencies which are subharmonics of the natural oscillation frequency, nor for harmonics higher than the 2nd.
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Khateb, Fabian, Montree Kumngern, Tomasz Kulej, and Dalibor Biolek. "0.3-Volt Rail-to-Rail DDTA and Its Application in a Universal Filter and Quadrature Oscillator." Sensors 22, no. 7 (March 30, 2022): 2655. http://dx.doi.org/10.3390/s22072655.
Повний текст джерелаАнотація:
This paper presents the extremely low-voltage supply of the CMOS structure of a differential difference transconductance amplifier (DDTA). With a 0.3-volt supply voltage, the circuit offers rail-to-rail operational capability. The circuit is designed for low-frequency biomedical and sensor applications, and it consumes 357.4 nW of power. Based on two DDTAs and two grounded capacitors, a voltage-mode universal filter and quadrature oscillator are presented as applications. The universal filter possesses high-input impedance and electronic tuning ability of the natural frequency in the range of tens up to hundreds of Hz. The total harmonic distortion (THD) for the band-pass filter was 0.5% for 100 mVpp @ 84.47 Hz input voltage. The slight modification of the filter yields a quadrature oscillator. The condition and the frequency of oscillation are orthogonally controllable. The frequency of oscillation can also be controlled electronically. The THD for a 67 Hz oscillation frequency was around 1.2%. The circuit is designed and simulated in a Cadence environment using 130 nm CMOS technology from United Microelectronics Corporation (UMC). The simulation results confirm the performance of the designed circuits.
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Bibikov, Yu N., and V. R. Bukaty. "Stability of the Equilibrium of an Oscillator with an Infinitely High Natural Oscillation Frequency." Vestnik St. Petersburg University, Mathematics 52, no. 3 (July 2019): 259–62. http://dx.doi.org/10.1134/s1063454119030051.
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D'Adamo, Juan, Ramiro Godoy-Diana, and José Eduardo Wesfreid. "Centrifugal instability of Stokes layers in crossflow: the case of a forced cylinder wake." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2178 (June 2015): 20150011. http://dx.doi.org/10.1098/rspa.2015.0011.
Повний текст джерелаАнотація:
The wake flow around a circular cylinder at Re ≈100 performing rotatory oscillations has been thoroughly discussed in the literature, mostly focusing on the modifications to the natural Bénard–von Kármán vortex street that result from the forced shedding modes locked to the rotatory oscillation frequency. The usual experimental and theoretical frameworks at these Reynolds numbers are quasi-two-dimensional, because the secondary instabilities bringing a three-dimensional structure to the cylinder wake flow occur only at higher Reynolds numbers. In this paper, we show that a three-dimensional structure can appear below the usual three-dimensionalization threshold, when forcing with frequencies lower than the natural vortex shedding frequency, at high amplitudes, as a result of a previously unreported mechanism: a pulsed centrifugal instability of the oscillating Stokes layer at the wall of the cylinder. The present numerical investigation lets us in this way propose a physical explanation for the turbulence-like features reported in the recent experimental study by the present authors.
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Yaroslavkina, Ekaterina E., and Anton V. Suslov. "Theoretical-experimental study of dependence of natural frequencies of oscillations plates from application thickness." Vestnik of Samara State Technical University. Technical Sciences Series 29, no. 2 (August 30, 2021): 88–99. http://dx.doi.org/10.14498/tech.2021.2.6.
Повний текст джерелаАнотація:
The paper considers the problem of asphalt-resin-paraffin deposits in the production of oil and oil products. Methods of sediment measurement have been studied. Computer simulation of dependence of natural frequencies of metal plate oscillations on thickness of deposits was carried out. Correlation dependence of oscillation frequency of the control object on thickness of deposits is confirmed. The obtained results allow prospective investigation of pipe-wires deposits thickness.
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Svalov, A. M. "Effect of compact inclusion on the natural frequencies of vibrations of a pipe string in a well." SOCAR Proceedings, no. 1 (March 30, 2021): 73–77. http://dx.doi.org/10.5510/ogp20210100482.
Повний текст джерелаАнотація:
The influence of small-size inclusion of pipes in a well column on the natural frequency of its longitudinal vibrations is investigated. Using the asymptotic expansion in a small parameter, an analytical relation is obtained that describes the change in the period of the column oscillations in the form of some additional small term to the period of the homogeneous column oscillations. Numerical calculations show that the obtained analytical relations almost accurately describe the oscillation period of a column with a massive compact inclusion, while its difference from the oscillation period of a homogeneous column is within ~20%. The results obtained can be useful for preventing resonant phenomena in the drill string when drilling wells, as well as for optimal use of the longitudinal vibrations of the tubing string to influence the bottom-hole zones of producing wells.
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Wang, Xiao Hua, Zhe Xiao, and Kai Zhang. "Numerical Simulation on the Performance of Vertical Jet Flowmeter of Natural Gas." Applied Mechanics and Materials 598 (July 2014): 206–9. http://dx.doi.org/10.4028/www.scientific.net/amm.598.206.
Повний текст джерелаАнотація:
In this paper, SimpleC algorithm and Realizable turbulence model are applied to simulate the detailed flow field of oscillator, which is the key component of the vertical drainage jet flowmeter. Based on analyzing the pressure fluctuation of fluid in the feedback channels of the oscillator at different flowrates, the results indicate that there is an obviously linear relationship between velocity and oscillation frequency of static pressure in the vertical feedback channels within a certain range of flowrate. The achievements can be helpful to the optimization the design of vertical drainage jet flowmeter.
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Og̃uz, H. N., and A. Prosperetti. "The natural frequency of oscillation of gas bubbles in tubes." Journal of the Acoustical Society of America 103, no. 6 (June 1998): 3301–8. http://dx.doi.org/10.1121/1.423043.
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Longuet-Higgins, Michael S. "The sound field due to an oscillating bubble near an indented free surface." Journal of Fluid Mechanics 221 (December 1990): 675–83. http://dx.doi.org/10.1017/s002211209000372x.
Повний текст джерелаАнотація:
The problem is solved of the flow due to a rapidly oscillating source situated near a plane surface with a hemispherical indentation. The strength of the far-field flow is evaluated, and also the natural frequency of oscillation of a small bubble centred at the same position as the source.
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Maykov, O. A., E. A. Kokhonkova, and T. N. Baturin. "On the assessment of the potential for extracting information on defects in the main pipeline by the method of radar analysis of natural oscillation frequency." Journal of Physics: Conference Series 2094, no. 4 (November 1, 2021): 042030. http://dx.doi.org/10.1088/1742-6596/2094/4/042030.
Повний текст джерелаАнотація:
Abstract The paper deals with the issue of diagnostics of main pipelines by the vibration method, exploring the influence of the formation of cracks in the walls of the pipeline on the change in the frequency characteristics of the pipeline. By analyzing the difference in the natural oscillation frequency of a pipe with a crack and without it, it is possible to assess the location of the defect with a certain accuracy. The issue of the possibility of reading the natural oscillations of the main pipeline from the surface of the soil located above the pipeline is also being studied.
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Gelperin, A., L. D. Rhines, J. Flores, and D. W. Tank. "Coherent network oscillations by olfactory interneurons: modulation by endogenous amines." Journal of Neurophysiology 69, no. 6 (June 1, 1993): 1930–39. http://dx.doi.org/10.1152/jn.1993.69.6.1930.
Повний текст джерелаАнотація:
1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives direct axonal projections from the two pairs of noses. This olfactory processing network generates a 0.7-Hz oscillation in its local field potential (LFP) that is coherent throughout the network. The oscillating LFP is modulated by natural odorants applied to the neuroepithelium of the superior nose. 2. Two amines known to be present in the PC lobe, dopamine and serotonin, increase the frequency of the PC lobe oscillation and alter its waveform. 3. Glutamate, another putative neurotransmitter known to be present in the lobe, suppresses the PC lobe oscillation by a quisqualate-type receptor and appears to be used by one of the two classes of neurons in the PC lobe to generate the basic LFP oscillation. 4. The known activation of second messengers in Limax PC lobe by dopamine and serotonin together with their effects on the oscillatory rhythm suggest the hypothesis that these amines augment mechanisms mediating synaptic plasticity in the olfactory network, similar to hypothesized effects of amines in vertebrate olfactory systems. 5. The use of a distributed network of interneurons showing coherent oscillations may relate to the highly developed odor recognition and odor learning ability of Limax.
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Wilson, G. J., G. A. Wood, and B. C. Elliott. "Optimal stiffness of series elastic component in a stretch-shorten cycle activity." Journal of Applied Physiology 70, no. 2 (February 1, 1991): 825–33. http://dx.doi.org/10.1152/jappl.1991.70.2.825.
Повний текст джерелаАнотація:
Twelve experienced male weight lifters performed a rebound bench press and a purely concentric bench press lift. Data were obtained pertaining to 1) the benefits to concentric motion derived from a prior stretch and 2) the movement frequency adopted during performance of the stretch-shorten cycle (SSC) portion of the rebound bench press lift. The subjects also performed a series of quasi-static muscular actions in a position specific to the bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's series elastic component (SEC) stiffness and natural frequency of oscillation. A significant correlation (r = -0.718, P less than 0.01) between maximal SEC stiffness and augmentation to concentric motion derived from prior stretch was observed. Subjects were also observed to perform the SSC portion of the rebound bench press movement to coincide with the natural frequency of oscillation of their SEC. These results are interpreted as demonstrating that the optimal stiffness in a rebound bench press lift was a resonant-compliant SEC.
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Paul, Tapas Kumar, and Radha Raman Pal. "New Electronically Tunable Third Order Filters and Dual Mode Sinusoidal Oscillator Using VDTAs and Grounded Capacitors." Advances in Technology Innovation 6, no. 4 (September 1, 2021): 262–81. http://dx.doi.org/10.46604/aiti.2021.7592.
Повний текст джерелаАнотація:
This study introduces a third order filter and a third order oscillator configuration. Both the circuits use two voltage difference transconductance amplifiers (VDTAs) and three grounded capacitors. By selecting the input and output terminals properly, current mode and transimpedance mode low-pass and band-pass filters can be obtained without component matching conditions. The natural frequency (ω0) can be tuned electronically. The oscillator circuit provides voltage and current outputs explicitly. The condition of oscillation (CO) and the frequency of oscillation (FO) can be adjusted orthogonally and electronically. The workability of the configurations is judged using TSMC CMOS 0.18 μm technology parameter as well as commercially available LM13700 integrated circuits (ICs). The simulation results show that: for ±0.9V power supply, the power consumption is 1.08 mW for both the configurations, while total harmonic distortions (THDs) are less than 2.06% and 2.17% for the filter and oscillator configurations, respectively.
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Borozenets, A. S., A. V. Proskurin, and A. V. Shlishevskiy. "Evaluation of the Composite Barrier Natural Oscillations Influence on the Generated Shock Loading." Herald of the Bauman Moscow State Technical University. Series Mechanical Engineering, no. 1 (136) (March 2021): 103–13. http://dx.doi.org/10.18698/0236-3941-2021-1-103-113.
Повний текст джерелаАнотація:
The problem of studying behavior of various structures under the influence of intense impulsive (shock) loads arising during operation of many modern facilities, machines and devices remains relevant for many years. Shock loading in laboratory conditions is generated due to interaction between the test object and the braking device (barrier). In this case, braking device or barrier could be a one-piece or a prefabricated structure. If the braking device (barrier) dimensions commensurate with the test object, the braking device natural oscillation frequencies excited during interaction between the test object and the braking device (barrier) could be found in the range of the test object natural oscillation frequencies. Frequency determination within the signal spectrum registered on the test object and caused by oscillations of the braking device (barrier) or test equipment, would assist in better assessing the test object shock loading and its compliance with real operating conditions
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Eliseev, Sergey, Roman Bolshakov, Duc Huynh Nguyen, and Quang Truc Vuong. "MECHANICAL OSCILLATION SYSTEM NATURAL FREQUENCY DETERMINATION: APPLICATION FEATURES OF FREQUENCY ENERGY FUNCTION. PART II." Proceedings of Irkutsk State Technical University 114, no. 7 (July 2016): 10–23. http://dx.doi.org/10.21285/1814-3520-2016-7-10-23.
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Simonenko, A. A., and E. Z. Kovarskaya. "DETERMINATION OF DENSITY OF WOOD USING LOW-FREQUENCY ACOUSTIC METHOD OF NATURAL OSCILLATION FREQUENCY." Kontrol'. Diagnostika 188, no. 2 (February 2014): 43–48. http://dx.doi.org/10.14489/td.2014.02.pp.043-048.
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Kononov, Yuri, and Yuri Dzhukha. "On the simplification of a frequency equation of the natural axially symmetric oscillations of a perfect liquid in a rigid cylindrical reservoir with elastic base." Proceedings of the Institute of Applied Mathematics and Mechanics NAS of Ukraine 32 (December 28, 2018): 67–77. http://dx.doi.org/10.37069/1683-4720-2018-32-8.
Повний текст джерелаАнотація:
We have simplified the previously received frequency equation of the natural axially symmetric oscillations of a heavy perfect incompressible liquid in a rigid cylindrical reservoir with elastic bases in the form of thin circular plates. The singularity in the frequency equation in the case of the coincidence of mass characteristics of the plates was removed. We have considered arbitrary methods of fixing the contours of the plates and different limiting cases: the degeneration of plates into membranes, absolutely rigid plates, the absence of upper plate (free surface on the liquid), and the case of zero gravity. It has been shown that the frequency spectrum of the coupled axially symmetric oscillations of elastic bases and the ideal liquid consists of two sets of frequencies, corresponding to oscillations of the upper and lower elastic bases, and additional oscillation frequency of a liquid column as a whole.
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Zhou, Qiao-Nian, and W. P. Graebel. "Free-Surface Oscillations in a Slowly Draining Tank." Journal of Applied Mechanics 59, no. 2 (June 1, 1992): 438–44. http://dx.doi.org/10.1115/1.2899539.
Повний текст джерелаАнотація:
The initial behavior of a free surface in a draining (filling) circular tank is analyzed using a linearized model. The withdrawal (injection) of fluid damps (enhances) oscillations which either exist before the withdrawal (filling) or are induced by the withdrawal (injection). The initial growth rate of the drainage-initiated free-surface oscillations strongly depends on the initial behavior of the drain rate function. If the drain is turned on gradually, the drainage-initiated free-surface oscillation is weaker compared to the forced one, so there are no drainage-initiated oscillations. However, if the drain is turned on suddenly, the induced oscillatory motion dominates the forced motion. For periodic drainage, the results show that the strongest resonant oscillation occurs when the drainage frequency w coincides with the first natural frequency of the flow system. All of the nonresonant modes of the oscillations are stable regardless of the initial behavior of the drain rate. If q(t) = sinωt, all of the resonant oscillations are stable. In the case when q(t) = cosωt, the initial jump in the drainage means that the resonance modes can be either unconditionally unstable, unconditionally stable, or conditionally unstable, depending on the various parameters.
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Mahfouz, F. M., and H. M. Badr. "Flow Structure in the Wake of a Rotationally Oscillating Cylinder." Journal of Fluids Engineering 122, no. 2 (November 15, 1999): 290–301. http://dx.doi.org/10.1115/1.483257.
Повний текст джерелаАнотація:
The characteristics of the flow in the wake of a circular cylinder performing rotational oscillation about its own axis and placed horizontally in a cross-stream is investigated. The governing equations based on stream function-vorticity formulation are solved numerically to determine the flow field structure. The parameters dominating flow structure are Reynolds number, Re, amplitude of oscillation, ΘA and frequency ratio FR=S/S0 where S is the forcing frequency and S0 is the natural frequency of vortex shedding. The ranges considered for these parameters are 40⩽Re⩽200, 0⩽ΘA⩽π and 0⩽FR⩽2. The lock-on phenomenon has been predicted and its effect on the flow hydrodynamics has been determined. The lock-on phenomenon is found to occur within a band of frequency encompassing the natural frequency. This band, however, becomes wider as the amplitude of oscillation increases. The obtained results show that the flow pattern in the near wake has a strong dependence on the oscillation parameters but not the far wake. [S0098-2202(00)01102-0]
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BLACKBURN, H. M., and R. D. HENDERSON. "A study of two-dimensional flow past an oscillating cylinder." Journal of Fluid Mechanics 385 (April 25, 1999): 255–86. http://dx.doi.org/10.1017/s0022112099004309.
Повний текст джерелаАнотація:
In this paper we describe a detailed study of the wake structures and flow dynamics associated with simulated two-dimensional flows past a circular cylinder that is either stationary or in simple harmonic cross-flow oscillation. Results are examined for Re=500 and a fixed motion amplitude of ymax/D=0.25. The study concentrates on a domain of oscillation frequencies near the natural shedding frequency of the fixed cylinder. In addition to the change in phase of vortex shedding with respect to cylinder motion observed in previous experimental studies, we note a central band of frequencies for which the wake exhibits long-time-scale relaxation oscillator behaviour. Time-periodic states with asymmetric wake structures and non-zero mean lift were also observed for oscillation frequencies near the lower edge of the relaxation oscillator band. In this regime we compute a number of bifurcations between different wake configurations and show that the flow state is not a unique function of the oscillation frequency. Results are interpreted using an analysis of vorticity generation and transport in the base region of the cylinder. We suggest that the dynamics of the change in phase of shedding arise from a competition between two different mechanisms of vorticity production.
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THIRIA, B., and J. E. WESFREID. "Stability properties of forced wakes." Journal of Fluid Mechanics 579 (May 2, 2007): 137–61. http://dx.doi.org/10.1017/s0022112007004818.
Повний текст джерелаАнотація:
Thiria, Goujon-Durand & Wesfreid (J. Fluid Mech. vol. 560, 2006, p. 123), it was shown that vortex shedding from a rotationally oscillating cylinder at moderate Reynolds number can be characterized by the spatial coexistence of two distinct patterns, one of which is related to the forcing frequency in the near wake and the other to a frequency close to the natural one for the unforced case downstream of this locked region. The existence and the modification of these wake characteristics were found to be strongly affected by the frequency and the amplitude of the cylinder oscillation. In this paper, a linear stability analysis of these forced regimes is performed, and shows that the stability characteristics of such flows are governed by a strong mean flow correction which is a function of the oscillation parameters. We also present experiments on the spatial properties of the global mode and on the selection of the vortex shedding frequency as a function of the forcing conditions for Re = 150. Finally, we elucidate a diagram of locked and non-locked states, for a large range of frequencies and amplitudes of the oscillation.
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Huseynov, T. K., T. T. Gadirova, B. K. Amiraslanov, N. A. Abdulova, A. I. Quliyeva, and K. R. Haciyeva. "Theoretical and experimental study of vibration-amplitude liquid densimeter on the basis of a high-quality tubular resonator." E3S Web of Conferences 124 (2019): 03004. http://dx.doi.org/10.1051/e3sconf/201912403004.
Повний текст джерелаАнотація:
This paper is devoted to the current model of vibration-amplitude liquid densimeter developed by the authors. Firstly, the necessity to develop vibration-amplitude liquids densimeters with straigt-flow sensing elements (resonators) belonging to the “low cost low accuracy” category is justified. The resonator structure, developed as the result of the search using the heuristic method, is described. The proposed resonator is a tube rigidly fixed at the ends with additional weights attached symmetrically at the vertical axis at the points of the antinodes of the second fundamental oscillation mode in order to improve the resonator qualityfactor by suppressing parasitic harmonics. The structure provides the possibility to restore the resonator natural oscillation frequency (decreased with time) to the primary one. It may be achieved by sequence screwing rods with different lengths into additional masses. The choice of the operating frequency of oscillations equal to 100 Hz is proved. It ensures invariance to the presence of solid inclusions in measured liquid and simplifies the electromagnetic excitation system. There are also theoretical relations obtained as a result of solving a differential equation of natural oscillations of a rigidly fixed tube with additional point masses, which are symmetrically located relatively vertical axis. They allow determining the own resonator oscillations frequencies for given parameters. The description of the operating model of the vibration-amplitude liquids densimeter, obtained experimentally and its calibration characteristic, is given.
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Indoh, Takaki, and Masaru Aniya. "The Effect of the Anharmonicity in a Perturbation Estimate of the Self-Diffusion Coefficient." Physics Research International 2011 (March 20, 2011): 1–3. http://dx.doi.org/10.1155/2011/645264.
Повний текст джерелаАнотація:
A perturbative expression for the self diffusion coefficient is derived by considering that the particles are executing anharmonic vibrations around the sites with local potential minima and jump to neighbor sites after a certain waiting time. The derived expression is a natural extension of the expression obtained by Zwanzig that assumes harmonic oscillations. The relation between the low frequency oscillation and the deviation from the harmonic behavior is also shown.
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Staubli, Thomas, and Donald Rockwell. "Pressure fluctuations on an oscillating trailing edge." Journal of Fluid Mechanics 203 (June 1989): 307–46. http://dx.doi.org/10.1017/s0022112089001485.
Повний текст джерелаАнотація:
Turbulent boundary layers separating from a blunt trailing edge give rise to organized vortical structures in the downstream wake. The perturbation of this inherent flow-instability at f0 by controlled oscillations of the edge at fe produces corresponding, organized components of unsteady surface pressure along the edge. For edge excitation near the ‘natural’ vortex shedding frequency f0, the phase between the local pressure fluctuations and the edge displacement shows large changes for small changes in excitation frequency. Moreover, in this range of excitation, there is quenching (or attenuation) of the surface pressure component at f0 and resonant peaking of the component at fe. These phenomena are related to the change in sign of the energy transfer between the fluid and the body. Integration of the instantaneous pressure distributions along the surfaces of the edge leads to the instantaneous lift at fe and f0 acting upon the oscillating trailing edge. The location of the lift varies as the cotangent of the dimensionless time during an oscillation cycle. When the edge is excited near, or at, the natural vortex shedding frequency, there is a resonant peak in the amplitude of oscillation of the lift location at fe; that at f0 is invariant. Moreover, the mean location of the lift at fe undergoes abrupt changes in this region of excitation. Flow visualization allows determination of the phasing of the organized vortical structures shed from the trailing edge relative to the edge displacement. Modulation of the flow structure at the frequencies f0 and fe, as well as interaction of small-scale vortices at high excitation frequencies, was observed. These aspects of the near-wake structure are related to the instantaneous pressure field.
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Kirsanov, Mikhail N. "Analytical assessment of the frequency of natural vibrations of a truss with an arbitrary number of panels." Structural Mechanics of Engineering Constructions and Buildings 16, no. 5 (December 15, 2020): 351–60. http://dx.doi.org/10.22363/1815-5235-2020-16-5-351-360.
Повний текст джерелаАнотація:
The aim of the work is to derive a formula for the dependence of the first frequency of the natural oscillations of a planar statically determinate beam truss with parallel belts on the number of panels, sizes and masses concentrated in the nodes of the lower truss belt. Truss has a triangular lattice with vertical racks. The solution uses Maple computer math system operators. Methods. The basis for the upper estimate of the desired oscillation frequency of a regular truss is the energy method. As a form of deflection of the truss taken deflection from the action of a uniformly distributed load. Only vertical mass movements are assumed. The amplitude values of the deflection of the truss is calculated by the Maxwell - Mohrs formula. The forces in the rods are determined in symbolic form by the method of cutting nodes. The dependence of the solution on the number of panels is obtained by an inductive generalization of a series of solutions for trusses with a successively increasing number of panels. For sequences of coefficients of the desired formula, fourth-order homogeneous linear recurrence equations are compiled and solved. Results. The solution is compared with the numerical one, obtained from the analysis of the entire spectrum of natural frequencies of oscillations of the mass system located at the nodes of the truss. The frequency equation is compiled and solved using Eigenvalue search operators in the Maple system. It is shown that the obtained analytical estimate differs from the numerical solution by a fraction of a percent. Moreover, with an increase in the number of panels, the error of the energy method decreases monotonically. A simpler lower bound for the oscillation frequency according to the Dunkerley method is presented. The accuracy of the lower estimate is much lower than the upper estimate, depending on the size and number of panels.
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Pampukha, I. V., M. M. Nikiforov, and V. O. Komarov. "DEVELOPMENT OF METHODOLOGY TO DETERMINE THE RESERVE FACTOR OF COMBAT AIRCRAFT BASED ON THE DYNAMIC RESPONSE ANALYSIS WITH REGARD FOR OPERATIONAL FACTORS." Collection of scientific works of the Military Institute of Kyiv National Taras Shevchenko University, no. 67 (2020): 30–38. http://dx.doi.org/10.17721/2519-481x/2020/67-03.
Повний текст джерелаАнотація:
The article considers the issues of diagnostics of the technical condition of cantilevered aircraft structures based on the dynamic response analysis. This task provides for determining the real technical condition of the damaged structure and, as a result, the reserve factor. The main criterion is to use as little information as possible to obtain a precise objective assessment. It is suggested to use the structural dynamics being the most informative as diagnostic features. These are natural oscillation frequencies (torsional and flexural) and zero-twist axis position (according to the data from volitionally undamaged structures taken as reference). The methodology has been patented. As a technical solution, the methodology provides for frequency tests with dysfunction of flexural and torsional oscillation frequencies under which a minimum frequency of natural oscillations corresponding to the minimum residual strength shall be set for each type of aircraft, namely, for its part - wings, fins (cantilevered structures of the glider). The increased number of analysed natural oscillation frequencies increases the reliability of the residual strength estimation. Based on this, the developed and produced equipment and monitor equipment as a mobile version (which are also patented), can be effectively used when basing aircraft in the combat theatre. Based on the provisions of the NIAS similar monitoring system can be implemented in military units of the Air Force of the Armed Forces of Ukraine during the operation of aircraft according to the technical condition.
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Jin, Y., and L. P. Chamorro. "On the dynamics of three-dimensional slung prisms under very low and high turbulence flows." Journal of Fluid Mechanics 816 (March 7, 2017): 468–80. http://dx.doi.org/10.1017/jfm.2017.104.
Повний текст джерелаАнотація:
The distinctive pendulum-like oscillation and pitching patterns of cubic and rectangular slung prisms were inspected for two aspect ratios at various Reynolds numbers $Re$ under two free-stream turbulence levels. Systematic experiments were performed using high-resolution telemetry and hotwire anemometry to quantitatively characterize the dynamics of the prisms and the wake fluctuation. The results show that the dynamics of the prisms can be characterized by two distinctive regions depending on the prism shape. Specifically, in the case of cubic prisms the regions are defined by the growth rate of the pitching amplitude; whereas the dynamics of the rectangular prisms is more sensitive to the angle of attack. In particular, when the large side initially faces the flow, the regions are defined by the synchronization between the vortex shedding and pure oscillations under very low turbulence. When the smaller side initially faces the flow, the regions are defined by the equilibrium pitching position. Regardless of the geometry of the prism and flow condition the dominant oscillation frequency resulted as being close to the natural frequency of the small-amplitude pendulum-like oscillation.
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Tangsrirat, Worapong, Tattaya Pukkalanun, and Wanlop Surakampontorn. "CDBA-Based Universal Biquad Filter and Quadrature Oscillator." Active and Passive Electronic Components 2008 (2008): 1–6. http://dx.doi.org/10.1155/2008/247171.
Повний текст джерелаАнотація:
The voltage-mode universal biquadratic filter and sinusoidal quadrature oscillator based on the use of current differencing buffered amplifiers (CDBAs) as active components have been proposed in this paper. All the proposed configurations employ only two CDBAs and six passive components. The first proposed CDBA-based biquad configuration can realize all the standard types of the biquadratic functions, that is, lowpass, bandpass, highpass, bandstop, and allpass, from the same topology, and can also provide orthogonal tuning of the natural angular frequency(ωo)and the bandwidth (BW) through separate virtually grounded passive components. By slight modification of the first proposed configuration, the new CDBA-based sinusoidal quadrature oscillator is easily obtained. The oscillation condition and the oscillation frequency are independently adjustable by different virtually grounded resistors. The sensitivity analysis of all proposed circuit configurations is shown to be low. PSPICE simulations and experimental results based upon commercially available AD844-type CFAs are included, which confirm the workability of the proposed circuits.
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Konovalov, A. M., V. I. Kugushev, S. S. Khudyakov, and A. I. Yankevich. "APPLICATION OF LOCAL SPECTRUM OF NATURAL OSCILLATIONS FOR MONITORING OF STRESS STATE IN NON-METALLIC ELEMENTS OF STRUCTURES." Kontrol'. Diagnostika, no. 263 (May 2020): 40–45. http://dx.doi.org/10.14489/td.2020.05.pp.040-045.
Повний текст джерелаАнотація:
This work offers a method based on extraction of specially selected localized forms of oscillations from the general spectrum of frequencies of natural oscillations of a part by means of which non-destructive monitoring of stress state in various points of non-metallic parts is performed. Frequency spectrum is localized by use of special oscillation transducers with adjustable mechanic filter at the inlet before piezoelectric plate. Such filter allows both to extract localized frequency spectrum and to ensure adjustment of frequencies of natural oscillations of transducer rod wrt frequencies of natural oscillations of the part being monitored. The transducers operated as a part of acoustic impedance flaw detector «ДАМИ-С09». Stress variations at the points of the part were captured on the screen of the flaw detector by energy redistribution between the forms of natural oscillations of transducer rod. Captured energy redistribution between the forms of oscillations took place due to shift of frequencies of natural oscillations of the part during stress variation wrt to frequencies of natural oscillations of transducer rod and summing up of their amplitudes. Here, the amplitudes of some oscillations intensified and some subsided. The results which were experimentally gained during monitoring demonstrate variations of local stress state at the point on the perimeter of the square plate made of sphere plastic under effect of compressive stresses on the perimeter of the plate and in the centre. In the first case at the point of measurement “conditional compression” took place and in the second case it was “conditional tension”.