• Journal of the Korean Society of Safety
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• v.14 no.4
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• pp.3-12
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• 1999

This research concentrates on the influence of non-linearities associated with impact for the nonlinear rocking behavior of rigid block subjected to one dimensional sinusoidal excitation of horizontal direction. The transition of two governing rocking equations, the abrupt reduction in the kinetic energy associated with impact, and sliding motion of block. In this study, two type of rocking vibration system are considered. One is the undamped rocking vibration system, disregarding energy dissipation at impact and the other is the damped rocking system, including energy dissipation and sliding motion. The response analysis using non-dimensional rocking equation is carried out for the change of excitation parameters and friction coefficient. The chaos responses were discovered in the wide response region, particularly, for the case of high excitation amplitude and their chaos characteristics were examined by the time history, Poincare map, power spectra and Lyapunov Exponent of rocking responses. The complex behavior of chaos response, in the phase space, were illustrated by Poincare map. The bifurcation diagram and Poincare map were shown to be effective in order to understand chaos of rocking system.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.1-6
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• 2011

Flow instability is investigated in a two-dimensional channel with thin baffles placed symmetrically in the vertical direction and periodically in the streamwise dircetion. At low Reynolds numbers, the flow is steady and symmetric. Above a critical Reynolds number, the steady flow undergoes a Hopf bifurcation leading to unsteady periodic flow. As Reynolds number further increases, we observe the onset of secondary instability. At high Reynolds numbers, the two-dimensional periodic flow becomes three dimmensional. To identify the onset of secondary instability, we carry out Floquet stability analysis. We obseved the transition to 3D flow at a Reynolds number of about 125. Also, we computed dominant spanwise wavenumbers near the critical Reynolds number, and visualized vortical structures associated with the most unstable spanwise wave.

• Journal of KSNVE
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• v.11 no.2
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• pp.265-275
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• 2001

This research has been performed to reveal the hysteresis phenomena of the hunting motion in a railway passenger cars. It is found that there are some factors and its operation region to make the nonlinear critical speed reacts to them more sensitively than the linear critical speed. The simulation results show that a self steering bogie system can be a substitute proposal to improve curving Performance together with the reduction of hysteresis of critical speed. Full scale roller rig test is carried out for the validation of the numerical results. Finally, it is certified that wear of wheel profile and stiffness discontinuities of wheelset suspension caused by deterioration have to be considered in the analysis to predict the hysteresis of critical speed precisely.

• Magazine of the Korean Society of Agricultural Engineers
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• v.28 no.2
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• pp.87-92
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• 1986

The differential equation, which can determine the dynamic critical loads for low parabcoic arches, is derived in this study. The dynamic critical loads of the parabolic arches subjected to a concentrated step load are nummerically analyzed for the changes of load positions. In cases of arches with different end conditions (both hinged, fixed hinged, both fixed), the effect of end conditions and that of the rises are investigated in detail. The summary of the results are the following: 1)The snapthrough does not occur when the rise of arch is very low, and the bifurcation appears clearly as the rise of arch increases. 2)The regions in which the dynamic critical loads are not defined for the both ends fixed are broader than that for the both ends hinged. 3)For all case, the load positions of minimum dynamic critical loads exsit at the near position from the end hinged. Thus, the results obtained in present study show that the magnitude of dynamic critical loads, the load positions of minimum dynamic critical loads and the regions in which the dynamic critical loads are not defined depend on end conditions of arches.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.11
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• pp.41-44
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• 1995

A numerical technique is employed to simulate the flow patterns in the human carotid artery and a phantom of the carotid artery made of acrylic material is used to observe the flow phenomena in the carotid artery. For numerical analysis the idealized geometric shape of the carotid artery is constructed to portray the phantom. Steady momentum equation is solved by the finite element method and the numerical results are compared with the results of MRA and color Doppler images.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.2
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• pp.131-139
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• 1996

This paper describes the chaotic neuron model to represent the complicated states of brain and analyzes the dynamical responses of chaotic neuron such as periodic, bifurcation, and chaotic phenomena which are simulated iwth numerical analysis. Next, the chaotic neuron circuit is implemented w ith the analog electronic devices. The transfer function of chaotic neuron is given by summed the linear and nonlinear property. The output function of chaojtic neuron is designed iwth the two cMOS inverters and a feedback resistor. By adjusting the external voltage, the various dynamical properties are demonstrated. In addition, we construt the chaotic neural networks which are composed of the interconnection of chaotic neuroncircuit such as serial, paralle, and layer connection. On the board experiment, we proved the dynamci and chaotic responses which exist in the human brain.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2233-2235
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• 2004

This paper presents a therapy that uses a constant drug dosage for leading a HIV patient to a LTNP (Long-Tenn Non-Progressor). From analysis of CTLp (Cytotoxic T Lymphocyte precursor) concentration at equilibrium point and bifurcation of equilibrium points, we found the therapy with a drug whose efficacy is less than one brings higher CTLp concentration at the equilibrium point. From this fact, we propose a treatment with constant drug dosage. which can induce LTNP.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.110-115
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• 1995

In this paper, the problem of non-linear torsional oscillation of a system incorporating a Hooke's joint is studied. Classical perturbation methods including higher order averaging and bifurcation theory are adopted for analysis. The equation of motion derived by Porter[1] is presented and the type of the system is identified. It has been found that two important cases deserve extensive study. Method of higher order averaging which is a main research tool in this study is introduced briefly. The averaged equations are studied analyticallyand numerically and the method of averaging has been found to be effective to study complex non-linear system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.65-72
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• 2001

직사각형 평판이 수직방향으로 조화가진력을 받을 때 그 변위가 큰 경우 두 개의 모드 간의 비선형적 상호작용에 대한 연구이다. 폰 칼만 운동방정식에서 유도된 두 개의 상미분 방정식으로부터 수차에 걸친 좌표변환을 거쳐 자유진동의 경우 정지해와 주기해를 구한다. 말굽형태의 분기 현상이 일어날 수 있는 조건을 호모클리닉 또는 헤테로클리닉 궤적의 유무로부터 결정한다. 혼돈 현상의 발생조건을 구하기 위해 멜니코프 방법이 적용되어질 수 있는 형태로 변환하여 광역섭동법의 수학적 결과를 직접적으로 적용할 수 있는 형태로 변환한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.449-454
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• 2000

A three-parameter model of viscoelastic damper, which has a non-linear spring as an element is incorporated into an oscillator. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by three-dimensional non-linear dynamical system of equations. The harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurences of such non-linear phenomena. A direct time integration of the original equation of motion validifies the use of the harmonic balance method to this sort of problem.