• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.75-80
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• 2011

In the area of wheel on rail vehicle, hunting stability which is generated by lateral motion is one of important characteristics for running safety. It might cause not only oscillation of vehicle but also derailment in an unstable area of the high speed. A Maglev vehicle is usually controlled the voltage to maintain the air gap between electromagnet and track. However, in Maglev system, an occurrence possibility of hunting motion could be high, because Maglev vehicle is not controlled directly lateral force between electromagnet and track in the curved guideway. In this paper, running safety is evaluated when Maglev vehicle run on guideway at high speed according to installment of damper between maglev vehicles and bogies, and to analyze the effect of it. Also, the parametric study is carried out for selecting effective lateral damper properties through the simulation. To accurately predict the running safety, 3d multibody dynamics models which are included air spring, guideway conditions and irregularities profile are used. With the results acquired, suggestions were made whether to adopt the damper and how to optimize the damping characteristics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.255-261
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• 2002

A four-degree of freedom model is suggested to understand the basic dynamical behaviors of the normal interaction between two masses of the friction induced normal vibration system. The two masses may be considered as the pad and the disk of the brake. The phase space analysis is performed to understand complicated in-plane dynamics of the non-linear model. Attractors in the phase space are examined for various conditions of the parameters. In certain conditions, the attractor becomes a limit cycle showing the stick-slip phenomena. In this paper, on the basis of the in-plane motion not only the existence of the limit cycle but also the size of the limit cycle is examined o demonstrate the non-linear dynamics that leads the unstable state and then the normal vibration is investigated as the state of the in-plane motion For only one case of the system frequency(two masses with same natural frequencies), the propensity of the normal vibration is discussed in detail. The results show an important fact that it may be not effective when too much damping is present in the only one part of the masses.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.1185-1190
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• 2007

In this paper the vibration system is consisted of a rotating cantilever pipe conveying fluid. The equation of motion is derived by using the Lagrange's equation. Also, the equation of motion is derived applying a modeling method that employs hybrid deformation variables. Generally, the system of pipe conveying fluid becomes unstable by flutter. So, we studied about the influences of the rotating angular velocity, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method. The influences of mass ratio, the velocity of fluid, the angular velocity of a cantilever pipe and the coupling of these factors on the stability of a cantilever pipe are analytically clarified. The critical fluid velocity$(u_{cr})$ is proportional to the angular velocity of the cantilever pipe. In this paper Flutter(instability) always occur in the second mode of the system.

• International Journal of Aeronautical and Space Sciences
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• 제15권1호
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• pp.82-90
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• 2014

In this paper, the effect of Lorentz force on the stability of attitude orientation of a charged spacecraft moving in an elliptic orbit in the geomagnetic field is considered. Euler equations are used to derive the equations of attitude motion of a charged spacecraft. The equilibrium positions and its stability are investigated separately in the pitch, roll and yaw directions. In each direction, we use the Lorentz force to identify an attitude stabilization parameter. The analytical methods confirm that we can use the Lorentz force as a stabilization method. The charge-to-mass ratio is the main key of control, in addition to the components of the radius vector of the charged center of the spacecraft, relative to the center of mass of the spacecraft. The numerical results determine stable and unstable equilibrium positions. Therefore, in order to generate optimum charge, which may stabilize the attitude motion of a spacecraft, the amount of charge on the surface of spacecraft will need to be monitored for passive control.

• 한국지능시스템학회논문지
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• 제22권1호
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• pp.69-74
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• 2012

본 논문에서는 무게중심 변동이 존재하는 차륜형 역진자가 경사면을 주행하는 경우에 대한 일반적인 운동방정식이 유도되었고 기존 역진자와의 차별점들이 고찰되었다. 차륜형 역진자는 점유면적이 작은 특성 때문에 협소한 장소에서 운용되는 다양한 분야에서 이동 플랫폼으로 채용되고 있다. 차륜형 역진자는 기존 역진자의 불안정한 특성을 그대로 계승하고 있으며, 넘어지지 않고 직립하게 위해서 지속적인 제어가 실행되어야 한다. 차륜형 역진자용 고성능 제어기를 설계하기 위해서는 다양한 환경과 운용조건에서 동작하는 차륜형 역진자를 대상으로 하는 운동방정식과 그 특성을 고려하는 것은 필수적이다.

• 대기
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• 제16권4호
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• pp.351-358
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• 2006

The structure of frontal thunderstorm in winter time is different from that of in summer time over the Korean peninsula, due to dry tongue and upward motion. The dry tongue, that is propagation of dry zone from upper level to lower level, was formed after front passage and the upward motion is intensified by the strengthened low level jet. Since this mechanism makes the structure more unstable, thunderstorm occurs at relatively low cloud top height. This study suggests a forecast guidance of winter time frontal thunderstorm that thunderstorms develop when one of the following conditions are satisfied: 1) total totals (TT) >40, 2) K index >-10, 3) mixing ratio ${\geq}$ 3.5 g/kg.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.597-600
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• 2004

A two-degree-of-freedom out-of-plane model with contact stiffness is presented to describe dynamical interaction between the pad and disc of a disc brake system. It is assumed that the out-of-plane motion of the system depends on the friction force acting along the in-plane direction. Dynamic friction coefficient is modelled as a function of both in-plane relative velocity and out-of-plane normal force. When the friction coefficient depends only on the relative velocity, the contact stiffness has the role of negative stiffness. The results of stability analysis show that the stiffness of both pad and disc are equally important. Complex eigenvalue analysis is conducted for the case that the friction coefficient is also dependent on the normal force. The results further verify the importance of the stiffness. It has also been found that increasing the gradient of friction coefficient with respect to the normal force makes the system more unstable. Nonlinear analysis is also performed to demonstrate various responses. Comparing the responses with experimental data has shown that the proposed model may qualitatively well represent a certain type of brake noise.

• 대한정형외과스포츠의학회지
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• 제2권2호
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• pp.119-126
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• 2003

Overhead athletes에서 특히 자주 볼 수 있는 불안정성 SLAP 병변, Internal impingement, 회전근 개 병변 등의 질환은 개별적으로 나타나는 것이 아니라 여러 질환이 동반되어 나타나므로 진단이나 치료에 어려움이 많다. 어깨 관절 손상의 성공적인 치료 및 운동으로의 복귀를 위하여는 각각의 운동의 생역학적인 측면과 개개의 질환의 증상 및 정확한 진단, 병리기전에 대한 확실한 이해가 선행되어야한다.

• 한국해양공학회지
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• 제7권1호
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• pp.13-24
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• 1993

해양오염은 환경파괴의 주요 인자이다. 해양바닥에 가라않은 오염물질을 근본적으로 제거하는 문제와는 별도로, 파동(wave)에 의해 그것이 자동적으로확산될 수가 있다. 파문(ripple)으로 덮혀진 해저(sea bottom)에서 표면의 중력파에 의한 물의 수평방향 요동운동은 와류(vrotices)를 발생시칸다. 이런한 유동장은 해저 침전물을 부유시켜 멀리까지 화가신시키는 작용을 한다.파문주위의 유동장을 살펴보면 모서리(crest)에서 발생된 와류로 인해 정상유동성분이 존재하며 이런한 정상유동은 파문의 주기적 형상으로인해 다분히 순환적이다. 이ㅔ 파동에 의한 요동운동이 가세하면 Taylor 와류와 같은 효과를 보여 줄 것이다. 해저부근에서의 이러한 확산효과를 보기 위하여, 해양유동을 단순화하여 최근 널리 이용되고 있는 혼돈이론을 가미시켰다. 아주 단순한 유동이라도 복잡한 입자의 궤적을 나타내며 입자의 확산과 연관됨을 수치해석을 이용하여 보여준다.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1164-1176
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• 1996

A magnetically levitated micro-positioner is implemented to avoid mechanical friction and increase precision. Since magnetic levitation system is inherently unstable, most concern is focused on a magnetic circuit design to increase the system dynamic stability. For this, the proposed levitation system is constructed by using an antagonistic structure which permits a simple design and robust stability. From the dynamic equations of motion, it is verified that the proposed magnetically levitated system is decoupled in 6 degree-of-freedom motion. Experimental results are presented in terms of time response and accuracy.