• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.983-988
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• 2001

Dynamic behaviors and stability of an optical disk drive coupled with an automatic ball balancer(ABB) are analyzed by a theoretical approach. The feeding system is modeled a rigid body with six degree-of-freedom. Using Lagrange's equation, we derive the nonlinear equations of motion for a non-autonomous system with respect to the rectangular coordinate. To investigate the dynamic stability of the system in the neighborhood of the equilibrium positions, the monodromy matrix technique is applied to the perturbed equations. On the other hand, time responses are computed by the Runge-Kutta method. We also investigate the effects of the damping coefficient and the position of ABB on the dynamic behaviors of the system.

• Journal of KSNVE
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• v.9 no.2
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• pp.363-370
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• 1999

In this study, we establish a theory for dynamic behaviors of an automatic ball balancer, analyze its dynamic characteristics, and provide its design guide line. Equations of motion are derived by using the polar coordinate system instead of the rectangular coordinate system which was previously used in other researches. After nondimensionalization of the equations, the perturbation method is applied to locate the equilibrium positions and to obtain the linearized equations of motion around the equilibrium positions. The Eigenvalue problem is used to verify the dynamic stability around the equilibrium positions. On the other hand, the time responses are computed from the nonlinear equations of motion by using a time integration method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.10
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• pp.900-906
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• 2010

This note proposes vibration-free motor control through modified LQG/LTR methodology. A conventional LQG/LTR method is a design tool in the frequency domain. However, unlike the conventional one, the proposed one is a time response based design method. This feature is firstly designed by parameterized settling time control gain through the target loop design procedure and the feature is secondly realized by loop transfer recovery. In order to show convergence to the target loop transfer functions, asymptotic behaviors of the open and the closed loop transfer functions are shown. At the conclusion, it is verified that the proposed method is robustly stable to parametric uncertainties through ${\mu}$-plot.

• Journal of Energy Engineering
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• v.8 no.4
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• pp.583-591
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• 1999

this paper proposes a new approach for calculating the reliability indices of generation system, such as interruption frequency and duration, by using the moment matching technique Two separate expressions are derived, one for the loss of load expectation(LOLE) and the other for the loss of load frequency (LOLF). These expressions are combination of exponentials and are therefore easily integrable and can be readily evaluated. In this paper, the parameters of the distribution functions of the LOLE and LOLF are evaluated by using Genetic Algorithm and Complex Method, and the proposed approach is quite comparable with the other methods at the aspect of accuracy and efficiency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.20-20
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• 2000

2개의 경사 충격파와 하나의 수직 충격파로 초음속 유동을 압축하는 초음속 공기 흡입구의 수치적 연구를 수행하였다. 지배방정식으로는 Navier-Stokes방정식을 사용하였고 난류모델로는 SST 모델을 사용하였다. 지배방정식의 점성항 계산에는 중심차분법을 사용하였고 대류항 계산에는 풍상차분법인 Roe의 FDS기법을 MUSCL기법과 결합하여 이용하였다. 유한 체적법을 이용하여 차분된 방정식은 LU분할 기법을 이용한 완전 내재적 방법으로 2차 정확도 시간 적분으로 비정상 과정의 연구를 수행하였다. 흡입구 배압을 정해주어야 하는 어려움을 해결하기 위해 흡입구 후면에 노즐을 달고 노즐의 면적을 조절하여 배압이 형성되도록 하였다.(중략)

• IEMEK Journal of Embedded Systems and Applications
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• v.16 no.6
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• pp.307-312
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• 2021

This paper proposes an adaptive time-delayed control approach with the integral sliding-mode surface for the fast convergence rate of robot manipulators. Adaptive switching gain aims to guarantee the system stability in such a way as to suppress time-delayed estimation error in the proposed control approach. Moreover, it makes an effort to increase the convergence ability in reaching the phase. An integral sliding-mode surface is employed to achieve a fast convergence rate in the sliding phase. The stability of the proposed one is proved to be asymptotically stable in the Lyapunov stability. The efficiency of the proposed control approach is illustrated with a tutorial example in robot manipulator, which is compared to that of the existing control approach.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.92-94
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• 2018

본 논문은 SiC MOSFET 디바이스를 사용하는 전력변환장치에서 Rogowski 코일을 이용하여 SiC MOSFET 디바이스에 흐르는 전류를 측정하여, 과전류를 검출하고 게이팅 신호를 차단하는 기법에 관하여 연구한다. SiC MOSFET는 소자의 특성으로 보편적으로 사용되는 과전류 검출 방법인 DeSAT 적용이 어렵기 때문에 Rogowski 코일을 사용하여 스위치 전류를 측정, 과전류를 검출한다. 본 논문에서는 PCB패턴 Rogowski 코일의 설계 방법뿐만 아니라 Rogowski 코일과 적분기의 대역폭에 대해서도 논의한다. 실험은 직류링크 커패시터에 SiC MOSFET 스위치 레그를 병렬로 연결하고, 직류링크 커패시터에 직류전압을 충전 후 스위치 레그를 약 6us정도 단락시켜 SiC MOSFET에 과전류를 발생시킨다. 이 때, 제안한 Rogowski 코일을 이용한 과전류 검출 및 차단 기법의 적용 전후를 비교하여 동작 및 성능(검출 및 차단 소요시간)을 확인한다. 마지막으로 실험 결과를 통해 본 논문에서 제안한 PCB패턴 Rogowski 코일을 이용하여 과전류 검출 및 차단 기법이 검증되었다.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.2
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• pp.25-31
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• 1989

Two-dimensional large-amplitude motions in regular harmonic wave are treated in time domain, by satisfying the exact body boundary condition and the linear free surface condition. For the present numerical calculation, the method of free-surface spectral representation with simple source distribution on the instantaneous body surface has been extended to include the effect of the incident wave. Calculations of the wave exciting force are performed for a submerged circular cylinder fixed or oscillating with large amplitude. Especially, nonlinear effects on the time-mean forces are studied in detail. It is shown that relative motion between the body and the fluid particle gives a significant effect on the lift and drift forces. Also, large-amplitude motion of a submerged circular cylinder and that of a floating Lewis-form cylinder are directly simulated in time domain. In the calculation results, some nonlinear effects are shown.

• Journal of Soil and Groundwater Environment
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• v.13 no.6
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• pp.40-49
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• 2008

Matrix diffusion from planar fractures was studied mathematically and through physical model experiments. Mathematical models were developed to simulate diffusion from 2D and 3D instantaneous disk sources and a 3D continuous disk source. The models were based on analytical solutions previously developed by Carslaw and Jaeger (1959). The mathematical simulations indicated that the 2D scenario produces significantly different results from the 3D scenario, the time for mass disappearance is significantly larger for continuous sources than for instantaneous sources, the normalized concentration generally decreased over time for instantaneous sources while it increased over time for continuous sources, diffusion rates decrease significantly over time and space, and the normalized mass loss from the source zone never reaches 1 for continuous sources due to the semi-infinite integral. The simulations also showed that disappearance times increase exponentially with increasing source radii and matrix porosity, and decrease with increasing aqueous-phase NAPL solubilities.