Dynamics of a Rocking Horizontal Pendulum Under High Frequency Excitation

2012 ◽  
Author(s):  
Si Mohamed Sah ◽  
Clark McGehee ◽  
Brian P. Mann
Keyword(s):  
Dynamic Equation ◽  
High Frequency ◽  
Slow Dynamic ◽  
Numerical Investigations ◽  
Stable Equilibria ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Parameter Values ◽  
Horizontal Pendulum ◽  
Good Agreement

In this work, we investigate the effect of high frequency excitation on a pendulum positioned at a given distance from a tilted platform. The tilted platform is subjected to high frequency excitation. The method of direct partition of motion is applied to the governing equation to obtain the slow dynamic equation. It is shown that two stable equilibria may coexist for certain parameter values. The analytical results are in a good agreement with the numerical investigations.

scholarly journals Empirical Expression for AC Magnetization Harmonics of Magnetic Nanoparticles under High-Frequency Excitation Field for Thermometry

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2506
Author(s):  
Zhongzhou Du ◽  
Dandan Wang ◽  
Yi Sun ◽  
Yuki Noguchi ◽  
Shi Bai ◽  
...  
Keyword(s):  
Magnetic Nanoparticles ◽  
High Frequency ◽  
Planck Equation ◽  
Magnetization Dynamics ◽  
Excitation Field ◽  
Fokker Planck Equation ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Ac Magnetization ◽  
Fokker Planck

The Fokker–Planck equation accurately describes AC magnetization dynamics of magnetic nanoparticles (MNPs). However, the model for describing AC magnetization dynamics of MNPs based on Fokker-Planck equation is very complicated and the numerical calculation of Fokker-Planck function is time consuming. In the stable stage of AC magnetization response, there are differences in the harmonic phase and amplitude between the stable magnetization response of MNPs described by Langevin and Fokker–Planck equation. Therefore, we proposed an empirical model for AC magnetization harmonics to compensate the attenuation of harmonics amplitude induced by a high frequency excitation field. Simulation and experimental results show that the proposed model accurately describes the AC M–H curve. Moreover, we propose a harmonic amplitude–temperature model of a magnetic nanoparticle thermometer (MNPT) in a high-frequency excitation field. The simulation results show that the temperature error is less than 0.008 K in the temperature range 310–320 K. The proposed empirical model is expected to help improve MNPT performance.

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.

Inductance effect of passive electromagnetic dampers on building-damper system subjected to near-fault earthquakes

2019 ◽  
Vol 23 (2) ◽  
pp. 320-333
Author(s):  
Wei Guo ◽  
Xiaoli Wu ◽  
Xinna Wei ◽  
Yao Cui ◽  
Dan Bu
Keyword(s):  
High Frequency ◽  
Large Error ◽  
Client Server ◽  
Near Fault ◽  
Electromagnetic Model ◽  
High Frequency Excitation ◽  
Frequency Excitation ◽  
Near Fault Earthquakes ◽  
Story Building ◽  
Electromagnetic Damper

The passive electromagnetic damper was commonly simplified into the linear viscous model in numerical analysis, while this simplification may produce large error when the damper inductance is obvious. In this article, an optimal passive electromagnetic damper with good performance and economy characteristic is proposed by parameter optimization, where the damping density is set as the optimization objective. The hysteresis behavior of the passive electromagnetic damper is verified, and by neglecting the inductance effect, the passive electromagnetic damper can be simplified into the linear viscous model in some cases, but actually the inductance effect is obvious under the high-frequency excitation. Subsequently, the effect of inductance on seismic performance of building damper system under the near-fault earthquake is investigated by comparing the simplified linear viscous model and the accurate passive electromagnetic model. The passive electromagnetic damper was supplemented in a 9-story building, and the analysis of the accurate passive electromagnetic model was carried out by the co-simulation of MATLAB and OpenSees based on the client–server technology. It concludes that the inductance effect is obvious and causes large error when the building damper system is subjected to the near-fault earthquake, and the energy dissipation performance described by the linear viscous model is overestimated.

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