• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.742-750
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• 1986

The lateral vibrating motion of a railway vehicle over a certain critical speed is a well known problem in the field of train dynamics. It is known that the train equations of motion are strongly coupled and highly nonlinear with the motion and causing that it is very difficult to solve the equations simultaneously. In this paper, a 8 degree of feedom model of a railway vehicle was suggested to solve the rail vehicle lateral motion. In stead of solving the nonlinear equation simultaneously, statistical linearization technique was adopted to solve those equations. The analysis results from the statistical linearization method were directly compared with those from direct nonlinear equations and found that the linearization technique can be very effective and economical for railroad vehicle analysis. By the way, it was found that the analysis results can analytically explain the intermittent hunting phenomena which has been frequently observed in experiments.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.602-605
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• 2011

본 논문에서는 마찰감쇠기가 설치된 건물이 붕괴하중을 받을 때의 에너지소산능력을 고려하여 등가감쇠비를 유도하였다. 마찰감쇠기는 주로 지진과 같은 수평하중에 대한 에너지를 소산하기위해 설치된다. 마찰감쇠기를 대각 가새형으로 설치하면 수평하중에 대한 저항력뿐 만아니라 수직하중에 대한 저항성능도 발휘된다. 건물에 설치된 마찰감쇠기는 외력의 크기에 따라 정지와 운동의 상태를 반복하여 외부 입력에너지를 소산시키기 때문에 외력과 응답관계가 비선형이다. 건물은 고유의 점성감쇠를 가지므로 마찰감쇠기가 설치된 건물은 마찰과 점성감쇠를 동시에 고려해야하므로 해석적인 정해를 구하기가 어렵다. 에너지 평형을 이용하여 등가감쇠비를 구하고 운동방정식을 등가선형화하면 쉽게 저항 성능을 파악할 수 있다. 우선 건물에 영향을 미치는 것은 감쇠이므로 감쇠의 영향력을 마찰력비, ${\gamma}_c$로 나타내었다. 둘째, 정해를 마찰력비로 표현하여 유도하고 응답특성을 파악하였다. 셋째, 에너지 균형식을 통해 등가감쇠비를 산정하였다. 마지막으로 등가감쇠비를 검증하기 위하여 등가감쇠비를 이용하여 등가선형화한 응답과 실제 마찰감쇠기를 설치하여 비선형 수치해석한 결과와 비교, 검증하였다.

• 대한공업교육학회지
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• v.30 no.2
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• pp.115-122
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• 2005

For an analysis of dynamic behavior in carbon nanotube(CNT) which is widely used as micro and nano-sensors, an electrostatic force of CNT was investigated. For larger gaps in between sensor and electrode the van der Waals force can be ignored. The boundary condition in the CNT was assumed to clamped-clamped case at both ends. In this paper electrostatic force is expressed as linear equation along deflection using Taylor series. The first and second terms(${\zeta}_0$ and ${\zeta}_1$) of the linear equation are analyzed. Based on the simulation results nondimensional number ${\Phi}_0$ and ${\Phi}_1$ which came from ${\zeta}_0$ and ${\zeta}_1$ were decreased according to the increment of the gap. Reduction ratio of the second term ${\zeta}_1$ is increased up to 99% along to the increment of the gap. The higher order terms can be ignored and therefore, electrostatic force can be expressed using the first two terms of the linear equation. This results play an important role in analyzing the nonlinear dynamic behavior of the CNT as well as the pull-in voltage of simply supported switches.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.435-443
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• 2010

This study presents key parameters for the structure installed with MR controller in reducing its responses. MR controller is regarded as Bingham model of which control forces are frictional and viscous ones. The parameters are identified as friction force ratios, $R_f$ and $R_h$ which are, respectively, ratio of MR controller friction force to static restoring force for free vibration and ratio of the friction force to amplitude of harmonic force. Structure-MR controller system shows nonlinear response behavior due to friction force. Energy balance strategy is adopted to transform the behavior to linear one with equivalent damping ratio. Finally, proposed equivalent linear process is compared to the nonlinear one, which turns out to give acceptably good results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.21-27
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• 2012

The HLLL scheme, proposed by T. Linde, determines all the wave speeds from the initial states because the middle wave is evaluated by the introduction of a generalized entropy function. The scheme is considered a genuine successor to the original HLL scheme because it is completely separated form the Roe's linearization scheme unlike the HLLE scheme and does not rely on the exact solution unlike the HLLC scheme. In this study, a numerical model was configured by the HLLL scheme with the total energy as a generalized entropy function to solve governing equations, which are the one-dimensional shallow water equations without source terms and with an additional conserved variable relating a concentration. Despite the limitations of the first order solutions, results to three cases with the exact solutions were generally accurate. The HLLL scheme appeared to be superior in comparison with the other HLL-type schemes. In particular, the scheme gave fairly accurate results in capturing the front of wetting and drying. However, it revealed shortcomings of more time-consuming calculations compared to the other schemes.

• Journal of Astronomy and Space Sciences
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• v.24 no.4
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• pp.315-326
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• 2007

Recently introduced, several explicit solutions of relative motion between neighboring elliptic satellite orbits are reviewed. The performance of these solutions is compared with an analytic solution of the general linearized equation of motion. The inversion solution by the Hill-Clohessy-Wiltshire equations is used to produce the initial condition of numerical results. Despite the difference of the reference orbit, the relative motion with the relatively small eccentricity shows the similar results on elliptic case and circular case. In case of the 'chief' satellite with the relatively large eccentricity, HCW equation with the circular reference orbit has relatively larger error than other elliptic equation of motion does.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.6
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• pp.55-64
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• 2001

Industrial machines are sometimes exposed to the danger of earthquake. In the design of a mechanical system, this factor should be accounted for from the viewpoint of reliability to analyze a complex nonlinear structure system under random excitation is proposed. First, the actual random excitation, such as earthquake, is approximated to the corresponding Gaussian process for the statistical analysis. The modal equations of overall system are expanded sequentially. Then, the perturbed equations are synthesized into the overall system and solved in probabilistic way. Several statistical properties of a random process that are of interest in random vibration are evaluated in each substructure. Comparing with the results of the numerical simulation proved the efficiency of the proposed method.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.2
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• pp.71-82
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• 1984

A programme, called BIPOLE, for the numerical analysis of twotimensional n-p-n bipolar transistors was developed. It has included the SRH and Auger recolnbination processes, the mobility dependence on the impurity density and the electric field, and the band-gap narrowing effect. The finite difference equations of the fundamental semiconductor equations are formulated using Newton's method for Poisson's equation and the divergence theorem for the hole and electron continuity equations without physical restrictions. The matrix of the linearized equations is sparse, symmetric M-matrix. For the solution of the linearized equations ICCG method and Gummel's algorithm have been employed. The programme BIPOLE has been applied to various kinds of the steady-state problems of n-p-n transistors. For the examples of applications the variations of common emitter current gain, emitter and diffusion capacitances, and input and output characteristics are calculated. Three-dimensional representations of some D.C. physical quantities such as potential and charge carrier distributions were displayed. This programme will be used for the nome,rical analysis of the distortion phenom ana of two-dimensional n-p-n transistors. The BIPOLE programme is available for everyone.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.1
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• pp.122-128
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• 1989

In this paper we propose a new method for solving a set of nonlinear algebraic equations encountered in the DC and transient analyses of electronic circuits. This method will be called Quadratic Newton-Raphson Method (QNRM), since it is based on the Newton-Raphson Method (NRM) but effectively takes into accoujnt the second order derivative terms in the Taylor series expansion of the nonlinear algebraic equations. The second order terms are approximated by linear terms using a carefully estimated solution at each iteration. Preliminary simulation results show that the QNRM saves the overall computational time significantly in the DC and transient analysis, compared with the conventional NRM.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.261-266
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• 1995

본 연구에서는 자기부상시스템에 대해 흡인식 자기부상방식을 채택하고 쇠구슬에 대한 운동을 상하 1자유도로 가정하여 운동방정식을 세운다. 이때 전자석이 자기 부상력은 전자석에 흐르는 전류와 인덕턴스의 함수라 가정하고, 모델의 불확실성은 자기부상계의 운동 방정식으로부터 선형화 할 때 발생하는 오차 및 파라미터 변동으로 생각한다. 또한 모델의 불확실성이 존재하더라도 정상편차 없이 부상하는 서보제어계를 설계한다. 그런데 저자등은 강인성 문제 및 정상편차 없는 것에 역점을 두어 H$_{\infty}$ 제어이론에 기초한 1형 로바스트 서보 제어기를 구하여 자기부상 시스템의 안정화 제어계로써 적용한 적이 있다. 이때 중심해 이외의 해를 이용하여 설계한 서보 제어계는 자기부상계의 과도상태시에 일어나는 오버슈트를 줄일 수 없었다. 따라서 시스템 내부 안정화를 위하여 H$_{\infty}$ 제어이론에 의해 설계된 피드백(feedback) 제어기와 물체가 부상할 때 오버슈트를 줄이고 제어량이 목표치에 잘 추종하기 위해 설계된 피드 포워드(feed forward) 제어기로써 2자유도를 갖는 제어계를 설계한다. 이렇게 설계한 2자유도 제어계를 가지고 모의 응답실험과 본 연구자들이 만든 자기부상 시스템의 실험결과를 비교함으로써 설계된 제어기의 타당성을 조사한다.