• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.920-926
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• 1990

본 연구에서는 Fig.1과 같은 2상 자연순환 회로의 1차원 해석을 수행하고, 액 상의 과냉정도와 각 상 영역에서의 밸브 마찰저항이 순환유속에 미치는 영향을 살펴보 므로써 정적 불안정의 조건을 알아보는데 있다. 본 모델에서는 유한 길이를 갖는 증 발기와 응축기를 고려하였으며, 정적 불안정의 가능성을 해석적으로 보여주기 위해 간 단한 모델(point-heat-source/sink)도 함께 다루었다.

• Journal of Korean Association for Spatial Structures
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• v.3 no.3 s.9
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• pp.20-28
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• 2003

• Journal of Energy Engineering
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• v.13 no.4
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• pp.311-318
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• 2004

In the present study, the combustion characteristics of methane and hydrogen-supplemented methane as alternative fuels for automotive vehicles were investigated at various hydrogen substitution rate, ignition position and ignition methods in a CVCC. The main results obtained from the study can be summarized as follow. In case of center ignition and neat methane-air mixture, the flame propagation processes are propagated with an elliptical shape, but they are changed an instable elliptical shape flame with very regular cells and higher velocity by increasing the hydrogen supplement rate. In case of side, 0.5R ignition and neat methane-air mixture, the flame propagation processes are propagated with an instable elliptical shape flame, but they are changed from an instable elliptical shape to wedge shape flame with very irregular cells and higher velocity by increasing the hydrogen supplement rate. Although the flame propagation shape with ignition position and ignition devices was not differ, the flame area of MSCDI device was a little larger than it of CDI device at the same time.

• Journal of Korean Association for Spatial Structures
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• v.4 no.3 s.13
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• pp.65-75
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• 2004

A shell structure, having a curvature with a curved surface, is an extremely efficient mechanical creation regard to the external load. A basic structural resistance mechanism is the structural system, which is resisted the out-of-plane direction load by in-plane forces using the structure's curvature. Therefore, it has a merit to make thin and lightweight large spacial structures using minimum materials. Among the large spare structural system, the rapid development of the membrane structures, cable structures and the hybrid structures are watched recently. But, this kind of structural system shows the unstable phenomenon by snap-through or bifurcation according to the shape of structure, and the understanding of the collapse mechanism by this phenomenon is very important to the design process. In this study, I investigated the unstable characteristics of the Geiger-type, Zetlin-type and flower-type hybrid cable dome structures, which is the lightweight hybrid structures using compression and tension elements continuously, according to the difference of structural system.

• Journal of Korea Entertainment Industry Association
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• v.14 no.8
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• pp.337-344
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• 2020

The purpose of this study was to investigate the effect of theratainment low extremity complex exercise using unstable surface on knee and static plantar pressure in patient with genu varum. 25 adult subjects were recruited and randomized into stable surface exercise group(SEG) and unstable surface exercise group(UEG). Subjects carried out complex exercise(elastic band exercise & squat exercise) for 40 minutes, 4 times per week for 5 weeks. The knee joint distance and Q-angle of all subjects measured, the foot pressure measured distribution on the front and rear of both foots during pre and post. The most outcome at post was significantly improved than the pre outcome in the both group(p<.05). The result of this study show that the low extremity complex exercise using unstable surface may be appropriate for improving structure of knee joint and static plantar pressure in patient with genu varum. This will enable the application of low extremity complex exercise using unstable surface in rehabilitation therapy of genu varum and it will help guide the selection of the therapist as one therapeutic basis.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.25-34
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• 2001

송전철탑의 기초로써 락앵커는 바람에 의해 반복적인 하중을 받고 있다. 반복하중은 락앵커의 인발 지지력 감소와 누적변위의 증가를 유발할 수 있다. 그러므로 송전철탑의 락앵커 설계시 세심한 주의가 요구된다. 본 논문에서는 세 가지 암반형태에 시공된 모형 락앵커에 대하여 반복하중 시험을 수행한 결과들을 제시하였다. 시험결과에 의하면 정적 극한하중의 50%보다 작은 최대 반복하중(Q$_{max}$)이 락앵커에 작용할 경우, 락앵커의 지지력에 대하여 반복하중의 영향이 없다. 최대 반복하중이 정적 극한하중의 50%에서 75%로 작용할 경우 누적변위의 증가를 유발하고, 정적 극한하중의 75%이상인 경우 락앵커의 지지력에 심각한 영향을 미친다. 따라서 정적 극한하중의 50% 이상의 반복하중을 받는 락앵커는 불안정하다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.407-415
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• 1999

There are two kinds of instability phenomena for shell-type structures which are snap-through and bifurcation buckling. These are very sensitive according to the shape characteristics including rise-span ratio and especially shape initial imperfection. In this study, the equilibrium path of shallow sinusoidal arches supported by hinges at both ends is investigated to grasp the instability behavior of shell-type structures with initial imperfection. The Galerkin method is used to get the nonlinear discretized equation of governing differential equation considering geometric nonlinearity of arches and the perturbation method is also used to transform the nonlinear equation to incremental form.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.417-426
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• 1999

The some papers which deal with the dynamic instability for shell-like structures under the step load have been published, but there are few papers which treat the essential phenomenon of the dynamic buckling using the phase plane for investigating occurrence of chaos. In nonlinear dynamics, examining the characteristics of attractor on the phase plane and investigating the dynamic buckling process are very important thing for understanding why unstable phenomena are sensitively originated by various initial conditions. In this study, the direct and the indirect snap-buckling of shallow arches considering geometrical nonlinearity are investigated numerically and compared with the static critical load.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.1-10
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• 2003

An airship is statically unstable, because it has no wing, comparatively small tail and large hull. Hence, an accurate prediction of dynamic stability is critical. In this study, dynamic stability data of the Mid-Size Airship is acquired through forced oscillation wind tests. The test was done in BAR LAMP which is Birhle Applied Research Inc's facility located in Germany. The test was composed with 16 static runs and 26 dynamic runs. As a result, dynamic characteristics of the airship depends on sideslip angle, angular rate and its direction as well as angle of attack. Generally, it is obtained that 3 directional moments have damping, but normal force, side force, and cross-derivatives are unstable. The dynamic derivatives are not sensitive to control surfaces, but have nonlinear dependency on sideslip angle.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.1083-1088
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• 2004

This paper deals with the vibration and stability of a circular cylindrical shaft, modeled as a tapered thin-walled composite beam and spinning with constant angular speed about its longitudinal axis, and subjected to an axial compressive force. Hamilton's principle and the assumed mode method are employed to derive the governing equations of motion. The resulting eigenvalue problem is analyzed, and the stability boundaries are presented for selected taper ratios and axial compressive force combinations. Taking into account the directionality property of fiber reinforced composite materials, it is shown that for a shaft featuring flapwise-chordwise-bending coupling, a dramatic enhancement of both the vibration and stability behavior can be reached. It is found that by the structural tailoring and tapering, bending natural frequencies, stiffness and stability region can be significantly increased over those of uniform shafts made of the same material. In addition, the particular case of a classical beam with internal damping effect is also included.