scholarly journals Computation of the Negative Damping Associated to the Hunting Motion of the Railway Wheelset, without Using Geometrical or Tribological Restrictions into the Model

2020 ◽  
Vol 5 (2) ◽  
pp. 210-217
Author(s):  
Barenten Suciu
Keyword(s):  
Characteristic Equation ◽  
Opposite Sign ◽  
Damping Ratio ◽  
Complex Conjugate ◽  
Railway Vehicle ◽  
Real Roots ◽  
Vibration Model ◽  
Hunting Motion ◽  
Negative Damping ◽  
Analytical Expressions

Recently, analytical expressions for the damped natural frequency and damping ratio were proposed for the so-called dynamical hunting, either by assuming that the wheel conicity can be neglected, or by imposing restrictions on the ratio between the lateral and longitudinal creep coefficients, and also, on the ratio of the track span to the yawing diameter. However, instead of a pair of complex conjugate roots, and two real roots, of opposite sign, two pairs of complex conjugate roots were obtained for the characteristic equation. Purpose of this work is to achieve accurate expressions for the damping associated to the hunting motion, without imposing geometrical or tribological limitations into the vibration model, and to evaluate the error on the damping ratio, introduced by the simplified models. Also, nature of the roots of the characteristic equation is discussed, relative to the critical speed of the railway vehicle.

Research on Damage Status of the Reinforced Concrete Ground Floor Columns

2012 ◽  
Vol 226-228 ◽  
pp. 1436-1440
Author(s):  
Li Jun Gao ◽  
Yong Sheng Zhang ◽  
Qin Li
Keyword(s):  
Reinforced Concrete ◽  
Measurement Method ◽  
Damping Ratio ◽  
Simple Calculation ◽  
Dynamic Measurement ◽  
Concrete Column ◽  
Destructive Testing ◽  
Reinforced Concrete Column ◽  
First Order ◽  
Vibration Model

In this paper, dynamic measurement method is applied to test the damage of the bottom reinforced concrete column. The comparison between the calculated first order frequency of the bottom reinforced concrete column and the measured first order frequency shows that the result is consistent. This indicates that this approach is feasible. However, in recent years, dynamic measurement method is widely used in non-destructive testing of bridges and floors. The principle of the dynamic measurement method for the detection of reinforced concrete column utilizes the measured natural frequency, vibration model and damping ratio of reinforced concrete column and such inherent dynamic characteristics of indicators to reflect the damage of reinforced concrete column. And there is no secondary injury for the column. The simplified method of structure dynamics is applied to calculate the frequency of the bottom reinforced concrete column. And the simple calculation method is verified by experiment and practice.

Lateral Vibration Research for Railway Deck Steel Plate Bridges

2011 ◽  
Vol 243-249 ◽  
pp. 1646-1650
Author(s):  
Wen Ping Li ◽  
Shu Li Chen ◽  
Mu Biao Su
Keyword(s):  
Steel Plate ◽  
Lateral Vibration ◽  
Vibration Model ◽  
Hunting Motion ◽  
Before And After ◽  
Vibration Mechanism ◽  
Track Irregularity ◽  
Lateral Reinforcement ◽  
Resonant Velocity

In this paper, the vehicle-bridge lateral vibration mechanism was analyzed; the vehicle-bridge vibration model was built and the lateral reinforcement schemes of open steel plate bridges were designed. Numbers of analysis were carried out for the lateral vibration of 40m deck steel plate bridges before and after reinforcement, under input of random artificial hunting waves and track irregularity. The results showed that, the frequency of hunting motion is approaching loaded frequency of the girder. The larger lateral amplitude appears on the bridge when the hunting wavelength is around 8~9m and the velocity of the train is around 55~70km/h. The wavelength is longer, the resonant velocity of the bridge is higher.

scholarly journals Stability Analysis of a Linear Friction-Induced Vibration Model and Its Prevention Using Active Force Control

2014 ◽  
Vol 6 ◽  
pp. 251594 ◽  
Author(s):  
S. M. Hashemi-Dehkordi ◽  
A. R. Abu-Bakar ◽  
M. Mailah
Keyword(s):  
Force Control ◽  
Pid Controller ◽  
Active Force ◽  
Active Force Control ◽  
Vibration Model ◽  
Control Scheme ◽  
Linear Friction ◽  
Critical Slope ◽  
Negative Damping ◽  
Friction Induced Vibration

This paper presents friction-induced vibration (FIV) caused by combined mode-coupling and negative damping effects in a simple FIV model. In doing so, a new four-degree-of-freedom linear model which consists of a slider and a block is proposed and then simulated using MATLAB/Simulink. Stability or instability of the FIV model is defined by the convergence or divergence of time domain responses of the slider and the block. Having found critical slope of friction-velocity characteristics that generate instabilities in the model, a conventional closed loop proportional-integral-derivative (PID) controller is first introduced into the main model in order to attenuate the vibration level and subsequently to suppress it. Later, the model is integrated with the active force control (AFC) element to effectively reject the disturbance and reduce the vibrations. It is found that the integrated PID-AFC scheme is effective in reducing vibration compared to the pure PID controller alone. Thus, the proposed control scheme can be one of the potential solutions to suppress vibration in a friction-induced vibration system.

Optimization of Dynamic Vibration Absorbers for Suppressing Sound Radiation of Plate Structures

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Guanghe Huo ◽  
Zhaobo Chen ◽  
Yinghou Jiao ◽  
Xuezhi Zhu
Keyword(s):  
Fixed Points ◽  
Frequency Ratio ◽  
Vibration Suppression ◽  
Damping Ratio ◽  
Sound Radiation ◽  
Thin Plates ◽  
Optimal Frequency ◽  
Radiation Control ◽  
Dynamic Vibration ◽  
Analytical Expressions

Abstract Dynamic vibration absorber (DVA) is a practical tool used for sound and vibration suppression in the specific frequency band. The parameters of DVAs should be optimally tuned to obtain the best sound and vibration suppression application effects. When the DVAs are used for structural vibration reduction, DVAs’ two parameters which are the optimal frequency ratio and damping ratio have simple analytical expressions. However, the concise analytical expressions of the DVAs that are used for suppressing the structural sound radiations have not been reported. First, this paper investigates the characteristics of DVAs in suppressing sound radiation from thin plates. Second, the fixed points’ phenomenon of the sound radiations of the plate carrying DVAs is revealed. In addition, the classical fixed points’ theory is extended into the optimization process of the DVAs that are used for sound radiation control of the plate. The analytical expression of the optimal frequency ratio, as well as the damping ratio optimization method of the DVA, is simultaneously proposed. Third, the installation position of DVAs is also presented to obtain a better acoustic radiation effect. Finally, the numerical simulations are performed to verify the availability of the method. It is showed that the best sound radiation control effect could be obtained by adopting the optimization means proposed in this paper.

Singularities at the Tip of a Crack Terminating Normally at an Interface Between Two Orthotropic Media

1996 ◽  
Vol 63 (2) ◽  
pp. 264-270 ◽  
Author(s):  
J. C. Sung ◽  
J. Y. Liou
Keyword(s):  
Characteristic Equation ◽  
Complex Form ◽  
Stress Singularities ◽  
Real Form ◽  
Antisymmetric Mode ◽  
Real Roots ◽  
Complex Roots ◽  
Principal Axes ◽  
Orthotropic Media ◽  
Set Up

The order of stress singularities at the tip of a crack terminating normally at an interface between two orthotropic media is analyzed. Characteristic equation in complex form for the power of singularity s, where 0 < Re{s} < 1, is first set up for two general anisotropic materials. Attention is then focused on the problem that is composed by two orthotropic media where one of them (say, material #2 ) the material principal axes are aligned while the other one (say, material #1) the principal axes can have an angle γ relative to the interface. For such a problem, a real form of the characteristic equation is obtained. The roots are functions of γ in general. Two real roots exist for most values of γ; however, there are possible ranges of γ that the complex roots will occur. The roots s are found to be independent of γ when material #1 has the property that δ(1) = 1. When γ = 0, two roots are always real. Furthermore, each of these two roots is associated with symmetric or antisymmetric mode and they become equal when Δ = 1. Many other features of the effects of the material parameters on the behaviors of the roots s are further investigated in the present work, where the six generalized Dundurs’ constants, expressed in terms of Krenk’s parameters, play an important role in the analysis.

Modeling and analytic optimization of dynamic comfort for wheelchair robots undergoing random roads

2018 ◽  
Vol 09 (05) ◽  
pp. 1850044
Author(s):  
Leilei Zhao ◽  
Yuewei Yu ◽  
Changcheng Zhou ◽  
Xiaohan Li ◽  
Fuxing Yang
Keyword(s):  
Root Mean Square ◽  
Damping Ratio ◽  
Analytic Formula ◽  
Dynamic Coefficient ◽  
Mean Square ◽  
Dynamic Parameters ◽  
Vibration Model ◽  
Optimal Damping ◽  
System Optimal ◽  
Optimal Dynamic

To make a rapid comfort assessment and a reasonable dynamic parameters choice of wheelchair robots, this paper proposes a dynamic comfort coefficient [Formula: see text] and analytically optimizes the cushion damping. Firstly, a traveling vibration model of the occupant-wheelchair system for wheelchair robots running on random roads was created. Secondly, the analytic formula of the occupant RMS (root mean square) acceleration was deduced. Moreover, the dynamic coefficient [Formula: see text] was proposed and its influence laws were revealed. Finally, the cushion system optimal damping ratio was calculated based on [Formula: see text]. The results show that the [Formula: see text] value is only determined by the parameters of the occupant-wheelchair system. The smaller the [Formula: see text] value is, the better the dynamic comfort is for wheelchair robots running on random roads. By minimizing [Formula: see text], the occupant-wheelchair system can achieve a statistically optimal dynamic comfort effect.

Asymptotic error analysis of constant‐velocity viscoacoustic migration

Geophysics ◽  
1999 ◽  
Vol 64 (4) ◽  
pp. 1036-1045 ◽  
Author(s):  
Emmanuel Causse ◽  
Bjørn Ursin
Keyword(s):  
Phase Velocity ◽  
Approximate Expression ◽  
Spatial Filter ◽  
Complex Conjugate ◽  
Complex Frequency ◽  
Good Resolution ◽  
Prestack Migration ◽  
Amplitude Versus Offset ◽  
Dissipation Model ◽  
Analytical Expressions

The deterioration of prestack migration images caused by an erroneous velocity or dissipation model can be represented by a space‐variant filter. We have derived an approximate expression of this spatial filter for the case of a plane horizontal reflector between two homogeneous half‐spaces, using analytical expressions for the Green’s functions and a stationary phase approximation of the Kirchhoff integral. We have used complex, frequency‐dependent velocities to represent a general homogeneous viscoacoustic medium. Hence, the filter can describe the effects of errors in phase velocity and absorption on the image of the reflector for different situations. A pure phase velocity error deforms the reflector, affects the value of the recovered reflectivity, and creates a spurious amplitude versus offset (AVO) effect. Neglecting dissipation destroys the phase of the image, decreases the resolution, and causes an underestimation of the reflectivity. To have a true‐amplitude, good‐resolution migration with Claerbout’s crosscorrelation imaging principle, the forward extrapolation of the downgoing wavefield should be done with the complex conjugate of the velocity in the viscoacoustic medium, and the backward extrapolation of the upgoing wavefield should be done with the complex velocity. In both cases, this amplifies the wavefields to compensate for the effects of attenuation on wave propagation.

Three-Dimensional Elasticity Solution for Sandwich Plates With Orthotropic Phases: The Positive Discriminant Case

2008 ◽  
Vol 76 (1) ◽  
Author(s):  
George A. Kardomateas
Keyword(s):  
Characteristic Equation ◽  
Orthotropic Material ◽  
Three Dimensional ◽  
Sandwich Plates ◽  
Elasticity Solution ◽  
Material Constants ◽  
Real Roots ◽  
Three Dimensional Elasticity ◽  
Rectangular Sandwich Plates ◽  
Positive Discriminant

A three-dimensional elasticity solution for rectangular sandwich plates exists only under restrictive assumptions on the orthotropic material constants of the constitutive phases (i.e., face sheets and core). In particular, only for negative or zero discriminant of the cubic characteristic equation, which is formed from these constants (case of three real roots). The purpose of the present paper is to present the corresponding solution for the more challenging case of positive discriminant, in which two of the roots are complex conjugates.

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