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.

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.

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.

Role of very-high-frequency excitation in single-bubble sonoluminescence

2000 ◽  
Vol 62 (2) ◽  
pp. 2233-2237 ◽  
Author(s):  
Francisco J. Moraga ◽  
Rusi P. Taleyarkhan ◽  
Richard T. Lahey ◽  
Fabian J. Bonetto
Keyword(s):  
High Frequency ◽  
Single Bubble ◽  
Very High Frequency ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Single Bubble Sonoluminescence ◽  
Very High

An Experimental Investigation of Energy Transfer from a High- Frequency Mode to a Low-Frequency Mode in a Flexible Structure

1995 ◽  
Vol 1 (1) ◽  
pp. 115-128 ◽  
Author(s):  
Pavol Popovic ◽  
Ali H. Nayfeh ◽  
Kyoyul Oh ◽  
Samir A. Nayfeh
Keyword(s):  
Energy Transfer ◽  
High Frequency ◽  
Power Spectra ◽  
Low Frequency ◽  
Excitation Amplitude ◽  
High Amplitude ◽  
Frequency Mode ◽  
High Frequency Mode ◽  
Beam Frame ◽  
Low Amplitude

The objective of the present article is to experimentally observe and characterize the transfer of energy from low-amplitude, high-frequency modes to high-amplitude, low-frequency modes. The subject of the study is a three-beam frame. The excitation amplitude is restricted to below 2 g peak. The authors have focused on observing, characterizing, and documenting the excitation of the first mode by high-frequency forcing. The energy-transfer processes are identified by power spectra and characterized further by frequency and amplitude sweeps. The energy-transfer routes observed in the experiment are subharmonic resonance of order one-half, combination resonance of the additive type, and interaction between widely spaced modes. In the latter route, an excitation at a frequency that is more than 100 times the first-mode frequency has been observed to excite the first mode.

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.

Calculation-and-experimental estimation of the role of the frequency ratio in changing the endurance at two-frequency deformation modes

2019 ◽  
Vol 85 (1(I)) ◽  
pp. 64-71 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Reduction Factor ◽  
Single Frequency ◽  
Cyclic Loads ◽  
Small Ratio ◽  
Harmonic Components ◽  
Deformation Modes

The cycle configuration at two-frequency loading regimes depends on the number of parameters including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, as well as the phase shift between these harmonic components, the latter having a significant effect only with a small ratio of frequencies. Presence of such two-frequency regimes or service loading conditions for parts of machines and structures schematized by them can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened and cyclically hardened steels under rigid conditions we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operation low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.

scholarly journals The Influence ofNrf2on Cardiac Responses to Environmental Stressors

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Reuben Howden ◽  
Eva Gougian ◽  
Marcus Lawrence ◽  
Samantha Cividanes ◽  
Wesley Gladwell ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
High Frequency ◽  
Low Frequency ◽  
Therapeutic Strategies ◽  
Environmental Stressors ◽  
Total Power ◽  
Airborne Pollutants ◽  
Cardiac Responses

Nrf2protects the lung from adverse responses to oxidants, including 100% oxygen (hyperoxia) and airborne pollutants like particulate matter (PM) exposure, but the role ofNrf2on heart rate (HR) and heart rate variability (HRV) responses is not known. We hypothesized that genetic disruption ofNrf2would exacerbate murine HR and HRV responses to severe hyperoxia or moderate PM exposures.Nrf2-/-andNrf2+/+mice were instrumented for continuous ECG recording to calculate HR and HRV (low frequency (LF), high frequency (HF), and total power (TP)). Mice were then either exposed to hyperoxia for up to 72 hrs or aspirated with ultrafine PM (UF-PM). Compared to respective controls, UF-PM induced significantly greater effects on HR (P<0.001) and HF HRV (P<0.001) inNrf2-/-mice compared toNrf2+/+mice.Nrf2-/-mice tolerated hyperoxia significantly less thanNrf2+/+mice (~22 hrs;P<0.001). Reductions in HR, LF, HF, and TP HRV were also significantly greater inNrf2-/-compared toNrf2+/+mice (P<0.01). Results demonstrate thatNrf2deletion increases susceptibility to change in HR and HRV responses to environmental stressors and suggest potential therapeutic strategies to prevent cardiovascular alterations.

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