NONLINEAR LOW FREQUENCY WATER WAVES IN A CYLINDRICAL SHELL

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1615-1618 ◽  
Author(s):  
H. W. PENG ◽  
D. J. WANG ◽  
C. B. LEE
Keyword(s):  
High Frequency ◽  
Water Waves ◽  
Water Wave ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Viscous Effect ◽  
First Approximation ◽  
Quantitative Results ◽  
High Frequency Excitation ◽  
Frequency Excitation

The experiment was carried out to study the low frequency surface waves due to the horizontal high frequency excitation. The feature of the phenomenon was that the big amplitude axisymmetric surface wave frequency was typically about 1/50 of the excitation frequency. The viscous effect of water was neglected as a first approximation in the earlier papers on this subject. In contrast, we found the viscosity was important to achieve the low frequency water wave with the cooperation of hundreds of "finger" waves. Photographs were taken with stroboscopic lighting and thereafter relevant quantitative results were obtained based on the measurements with Polytec Scanning Vibrometer PSV 400.

Effect of rail pad stiffness on the wheel/rail force intensity in a railway slab track with short-wave irregularity

2019 ◽  
Vol 233 (10) ◽  
pp. 1038-1049 ◽  
Author(s):  
Amin Khajehdezfuly
Keyword(s):  
High Frequency ◽  
Critical Speed ◽  
Concrete Slab ◽  
Low Frequency ◽  
Short Wave ◽  
Vehicle Speed ◽  
Frequency Range ◽  
Slab Track ◽  
High Frequency Excitation ◽  
Frequency Excitation

In this paper, a two-dimensional numerical model is developed to investigate the effect of rail pad stiffness on the wheel/rail force in a slab track with harmonic irregularity. The model consists of a vehicle, nonlinear Hertz spring, rail, rail pad, concrete slab, resilient layer, concrete base, and subgrade. The rail is simulated using the Timoshenko beam element for considering the effects of high-frequency excitation produced by short-wave irregularity. The results obtained from the model are compared with those available in the literature and from the field to prove the validity of the model. Through a parametric study, the effect of variations in rail pad stiffness, vehicle speed, and harmonic irregularity on the wheel/rail force is investigated. For the slab track without any irregularity, the wheel/rail force is at maximum when the vehicle speed reaches the critical speed. As the rail pad stiffness increases, the critical speed increases. When the amplitude of irregularity is high, wheel jumping phenomenon may occur. In this situation, as the vehicle speed and rail pad stiffness are increased, the dynamic wheel/rail force is increased. In the low-frequency range, the wheel/rail force increases as the rail pad stiffness increases. In the high-frequency range, the wheel/rail force increases as the rail pad stiffness is decreased.

Study of Flow-Induced Vibration Phenomena in Automotive Shock Absorbers

2016 ◽  
Vol 248 ◽  
pp. 204-210 ◽  
Author(s):  
Marian Sikora
Keyword(s):  
High Frequency ◽  
Shock Absorber ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Flow Induced Vibration ◽  
Shock Absorbers ◽  
Time Histories ◽  
Valve Stiction ◽  
High Frequency Excitation ◽  
Frequency Excitation

The purpose of this study was to develop a model of the dynamic behavior of a hydraulic vehicle double-tube shock absorber. The model accounts for the effects of compressibility, valve stiction, inertia, etc. and can be suitable for use in the analyses on flow-induced pressure fluctuations in the device. The author highlights all major variables to influence the output of the shock absorber, and then proceeds by performing a series of simulations using the developed model. The model is demonstrated to operate well in the large amplitude and low frequency range as well as the small amplitude and high frequency excitation operation regimes. The results are presented in the form of time histories of pressures in each fluid volume of the damper, flow rates through the valves, piston rod acceleration and force. Fast Fourier Transform (FFT) graphs are presented, too, in order to identify major components of the pressure fluctuation phenomena in frequency domain.

Performance Simulation and Analysis of New High-Frequency Valve

2011 ◽  
Vol 219-220 ◽  
pp. 1712-1715
Author(s):  
Yong Zhen Zheng ◽  
Ruan Jian ◽  
Yong He
Keyword(s):  
Mathematical Model ◽  
High Frequency ◽  
Excitation Frequency ◽  
Rotary Motion ◽  
Performance Simulation ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Design Idea ◽  
Spool Valve

This article described the design idea, advantages and operation principle of the new high-frequency valve, designed and analyzed its mathematical model. The rotary motion and axial sliding of valve core are used to realize the independence control of excitation frequency and amplitude. The high-frequency excitation can be achieved by increasing in the number of spool table and selecting the matching relationship between the spool and sleeve valve to improve the spool valve cover window grooves and the communication times per revolution.

scholarly journals Динамика магнитных скирмионов в наноточках

2018 ◽  
Vol 60 (6) ◽  
pp. 1135
Author(s):  
З.В. Гареева ◽  
К.Ю. Гуслиенко
Keyword(s):  
Ultrathin Films ◽  
High Frequency ◽  
Linear Array ◽  
Linear Chain ◽  
Low Frequency ◽  
Characteristic Difference ◽  
Frequency Spectra ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Magnetic Skyrmions

AbstractBloch and Neel magnetic skyrmions have been studied in systems of confined geometry (nanodots, a linear array of nanodots). The spectra of low- and high-frequency excitation modes of a skyrmion state have been calculated. It has been shown that skyrmion spectrum asymmetry, namely, the characteristic difference between the frequencies of the azimuthal modes of the azimuthal skyrmion modes rotating clockwise and counterclockwise, is associated with asymmetry in the magnetization profiles of high-frequency spin waves propagating on the background of a skyrmion state in a nanodot. The low-frequency spectrum contains the only gyrotropic mode localized near the center of a nanodot. The gyrotropic frequency depends on the material parameters of a nanodot and the size of a skyrmion. The eigenfrequency of the gyrotropic mode of an isolated skyrmion in a nanodot in ultrathin films ( L ~ 1 nm) does not depend on the internal structure of a skyrmion and is the same for Bloch and Neel skyrmions. The interaction of skyrmions, in particular, in a linear chain of nanodots with the ground skyrmion state, leads to distinctions in low-frequency spectra. The structure of a skyrmion (of Bloch or Neel type) is exhibited as a shift of dispersion curves and a difference between the frequencies of ferromagnetic resonance in a system of interacting skyrmions.

Bifurcations of a High-Frequency Horizontally Excited Double Pendulum

2011 ◽  
Author(s):  
Hiroshi Yabuno ◽  
Kazuya Endo
Keyword(s):  
Bifurcation Point ◽  
High Frequency ◽  
Excitation Frequency ◽  
Pitchfork Bifurcation ◽  
Vertical Position ◽  
Double Pendulum ◽  
Bifurcation Phenomena ◽  
Underactuated Manipulator ◽  
High Frequency Excitation ◽  
Frequency Excitation

The bifurcation phenomena produced in a double pendulum under high-frequency horizontal excitation are theoretically and experimentally examined. It has been well known as dynamic stabilization phenomenon that vertical high-frequency excitation can stabilize inverted pendulum. The phenomenon is produced through a sub-critical pitchfork bifurcation. On the other hand, under horizontal high-frequency excitation, the pendulum undergoes a supercritical pitchfork bifurcation and is swung up from the downward vertical position. There have so far been many researches on such dynamics of a single pendulum under the vertical and horizontal high-frequency excitations, but few investigations on multi-degrees-of-freedom system. Also, the utilization of these bifurcations phenomena under the high-frequency excitation is proposed for motion control of underactuated manipulators, but most researches on application is confined to a single pendulum to which a free of two-link underactuated manipulator corresponds. In this paper, toward the development of a three-link underactuated manipulator, we deal with a double pendulum to which two free links of the three-link underactuated manipulator correspond, and theoretically and experimentally investigate bifurcation phenomena in the two pendulums. First, we theoretically predict two pitchfork bifurcation points while increasing the excitation frequency by linear amplitude equations derived using the method of multiple scales. Furthermore, we experimentally examine the swing-up of the pendulums after the first pitchfork bifurcation point and observe that the system has the four types of stable configurations beyond the second pitchfork bifurcation point.

scholarly journals Modeling and Simulation Technology of High Frequency Vibratory Stress Relief Treatment for Complex Thin -Walled Workpiece

2018 ◽  
Vol 206 ◽  
pp. 04001 ◽  
Author(s):  
Xian-yang Zhao ◽  
Nian-song Zhang ◽  
Ai-min Wang
Keyword(s):  
High Frequency ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Stress Relief ◽  
Response Analysis ◽  
Finite Element Software ◽  
Frequency Excitation ◽  
Thin Walled ◽  
Harmonic Response Analysis ◽  
Selection Of

The current research based on vibratory stress relief (VSR) is focused on low frequency excitation, but it is seldom mentioned for complex thin-walled workpiece with higher natural frequency. In this paper, the mechanism of high frequency VSR is studied by microdynamic theory. Aiming at the rotating frame of complex thin-walled workpiece in aerospace equipment, the high frequency VSR numerical simulation is carried out by finite element software Abaqus, the modal analysis technology and harmonic response analysis technology are proposed, and the exciting force, excitation frequency and other important parameters are determined. The simulation results are analyzed to verify the superiority of high frequency VSR to eliminate residual stresses of complex thin-walled workpieces, and provide a theoretical basis for optimal selection of excitation parameters for high frequency VSR.

Energy Transfer from High-Frequency to Low-Frequency Modes in Structures

1995 ◽  
Vol 117 (B) ◽  
pp. 186-195 ◽  
Author(s):  
A. H. Nayfeh ◽  
D. T. Mook
Keyword(s):  
Energy Transfer ◽  
High Frequency ◽  
Large Amplitude ◽  
Low Frequency ◽  
Internal Resonances ◽  
Parametric Resonances ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Low Amplitude

A perspective of the mechanisms by which energy is transferred from high- to low-frequency modes is presented. The focus is on some recent experiments that reveal how a low-amplitude high-frequency excitation can produce a large-amplitude low-frequency response. Such a phenomenon is potentially harmful, if not catastrophic. Specifically, these experiments clarify the role of internal resonances, combination external and parametric resonances, and the interactions among modes of widely spaced frequencies.

Energy Transfer from High-Frequency to Low-Frequency Modes in Structures

1995 ◽  
Vol 117 (B) ◽  
pp. 186-195 ◽  
Author(s):  
A. H. Nayfeh ◽  
D. T. Mook
Keyword(s):  
Energy Transfer ◽  
High Frequency ◽  
Large Amplitude ◽  
Low Frequency ◽  
Internal Resonances ◽  
Parametric Resonances ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Low Amplitude

A perspective of the mechanisms by which energy is transferred from high- to low-frequency modes is presented. The focus is on some recent experiments that reveal how a low-amplitude high-frequency excitation can produce a large-amplitude low-frequency response. Such a phenomenon is potentially harmful, if not catastrophic. Specifically, these experiments clarify the role of internal resonances, combination external and parametric resonances, and the interactions among modes of widely spaced frequencies.

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