• Journal of the Society of Disaster Information
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• v.8 no.2
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• pp.197-203
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• 2012

In these days, the design of a structure for reducing or eliminating noise and vibration is getting more important, as the social demands for reducing environmental pollution rise. In this paper, the basic concept and performance verification test results of the recently developed vertical vibration isolator are presented. The isolator attenuates vibration using the damping action from the friction plane made of PTFE and provides the restoring force from the polyurethane springs arranged in vertical and horizontal directions. The performance verification tests consist of a test for identifying performance change during load rate variation and a test for confirming the force-displacement relationship assumption in vibration force range.

• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.29-37
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• 2017

As the behavior of the debris flow due to the torrential rains in mountain is affected by shear strength and rheological properties of the fine fraction in the ground, the evaluation of both properties is necessary to estimate the behavior of the debris flow. The objective of this study is to evaluate the shear strength and rheological properties using the direct shear apparatus. The direct shear tests are conducted for two kinds of fine-grained soil specimens, which are in dry state and liquid limit state. From the direct shear tests, shear strengths are measured according to the normal stresses applied on the specimens to evaluate the cohesion and internal friction angle. In addition, reversal shear tests are performed for the fine-grained soil specimens in liquid limit state according to the shear rate to evaluate the residual shear strength. The results of direct shear tests show that the specimen at the liquid limit state has lower internal friction angle and higher cohesion compared to the dry stated, and the residual friction angle and cohesion at the residual state are lower than those at the peak state. In the result of reversal shear test, the residual shear strength is directly proportional to the shear rate and viscosity is calculated as $73.60Pa{\cdot}s$. This study demonstrates that the direct shear apparatus can be effectively used for the evaluation of the shear strength and rheological properties of the fine-grained soils related with the debris flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2261-2267
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• 1992

The equations are derived for the evaluation of the axial contact force. The contact forces for rubber seals are analyzed as a function of the ratio of real contact length, the thickness of seal lip, the inclined angle of seal lip, and the interference between the edge of seal lip and the rotating inner ring. The design data for rubber seals are presented in terms of the ratio of real contact length, initial inclined lip angle, lip thickness and the interference. The calculated results show that the deflected interference and the circumferential stress cause considerable change of contcat forces for the low sealed pressure.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.177-177
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• 2011

환형수조는 점착성 퇴적물의 침/퇴적실험을 위한 실험장치로서, 수조내부의 수면과 접하여 회전하는 상부링(top ring)의 마찰력에 의해 흐름이 생성되며, 시간의 제약없이 흐름조건을 동일하게 만들 수 있다는 큰 장점을 갖는다. 그러나 환형수조는 원주유속의 속도차이 및 원심력으로 인한 2차 순환류가 형성되어 바닥전단응력이 불균일해지는 단점을 가지고 있으며, 이러한 이유로 인하여 환형수조를 이용한 침/퇴적실험 수행시 수조의 외벽부근에서 더 큰 침식이 발생한다. 따라서, 2차 순환류의 발생을 줄이고 바닥전단응력의 분포를 균등하게 하기 위해 양방향 회전(환형수조의 몸체를 상부링의 회전방향과 반대방향으로 회전)이 가능한 환형수조가 고안되었는데, 이러한 방법으로 2차 순환류의 크기를 저감시키고, 바닥전단응력을 균일하게 만들 수 있다. 한편, 환형수조의 양방향 회전(counter-rotation)은 현장용 환형수조에는 적용될 수 없는 단점을 갖는다. 현장실험에서는 바닥면이 없는 현장용 환형수조를 해저면에 거치시켜 자연상태의 비교란 퇴적물 시료를 저면으로 형성시키는데, 바닥면이 존재하지 않는 환형수조 본체는 회전시킬 수 없으므로 양방향 회전을 통한 2차 순환류의 저감 및 바닥전단응력 균일화의 효과를 기대할 수 없다. 이러한 이유로 환형수조의 양방향 회전은 단지 실내실험용 환형수조에만 적용된다. 이에 본 연구에서는 환형수조 본체를 회전시키지 않고 수조의 측벽과 상부링의 각도 조절을 통해 수조단면의 형상을 변화시켜 2차 순환류를 저감시키고 바닥전단응력을 균등하게 하는 방법에 대한 연구가 수행되었다. 이 방법은 본체의 회전이 필요 없으므로 현장용 환형수조에 적용될 수 있을 뿐만 아니라, 실험장치의 구조가 단순해져 실험장치의 제작비가 절감될 수 있다. 또한 원주속도에 수직한 단면에서 속도구배가 감소되어 2차 순환류가 저감됨과 동시에 바닥전단응력이 균등하게 됨으로서 양방향 회전시와 동일한 효과가 얻어질 수 있을 것으로 예상된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.176-176
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• 2011

환형수조는 점착성 퇴적물의 이송특성 연구를 위해 가장 선호되는 실험 장치로 알려져 있다. 과거 많은 연구자들은 퇴적물의 이송특성, 특히 침식/퇴적 특성 조사를 위해 주로 수로를 이용한 실험적 연구를 수행하였는데, 최초의 실험적 연구들은 주로 직선수조에서 수행되었다. 그러나 입자간의 응집이 중요한 역할을 하는 점착성 퇴적물의 경우에, 직선수조 끝단에서의 자유낙하 및 재순환 펌프의 날개에 의해 응집된 토사가 쉽게 분리될 수 있어 그 타당성이 의문시 되어 왔으며, 이러한 단점을 보완하기 위해 환형수조가 고안되었다. 환형수조는 수면과 접하여 회전하는 상부링의 마찰력에 의해 흐름이 생성되기 때문에 시간의 제약 없이 흐름조건을 동일하게 만들 수 있다는 큰 장점을 갖는다. 그러나 환형수조는 원주유속의 속도차이 및 원심력으로 인한 2차 순환류를 형성시켜 반경 방향(radial direction)에서의 바닥전단응력을 불균일하게 하는 단점을 갖는다. 이러한 2차 순환류와 바닥전단응력의 불균일을 저감시키기 위하여 환형수조의 몸체를 상부링의 회전 방향과 역방향으로 직접 회전시키는 방법이 채택되어져 왔다. 한편, 환형수조의 상부링과 몸체를 서로 역방향으로 동시에 회전시키는 양방향 회전(counter-rotation)의 적용을 위해서는 2차 순환류가 최소가 되며 바닥전단응력이 균일해지는 최적 회전속도비에 대한 분석은 필수적 사항이다. 이를 위하여, 상부링과 몸체의 회전속도에 따라 변화하는 수조내부의 흐름특성 및 평균바닥전단응력에 대한 연구가 선행되어야만 한다. 이에 본 연구에서는 전산유체역학을 이용하여 전북대에 설치된 환형수조의 상부링과 몸체의 회전속도에 따라 변화하는 수조내부에서의 흐름특성 및 바닥전단응력에 대한 분석이 수행되었다. 또한, 이를 기초로, 환형수조의 최적 회전속도비 산출을 위한 연구가 수행 중에 있다. 이러한 결과들은 추후 환형수조를 이용한 점착성 퇴적물의 침식/퇴적 등과 같은 이송특성 연구시, 퇴적물에 작용하는 흐름조건의 정밀산정을 위한 기초자료로 활용될 수 있을 것이다.

• The KIPS Transactions:PartB
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• v.12B no.2 s.98
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• pp.157-166
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• 2005

In 3D virtual environment the description of character' s movement that has utilized the conventional key-frame technique is gradually being developed toward the application of motion control method to generate more realistic and natural motion. Even the motion control method, however, has the limitation for expression of character's motion adapted to the ground properties of virtual world. That is, the walking motions of character are not only, for the most part, so uniform simple and repeated often as to feel to be tedious, but also the unnatural motion in which the tips of the toes soak through a plane or float in the air discording with the conditions of terrain lowers the semblance of reality. This paper proposes an adaptive motion control method for human figure locomotion in virtual environments or games, in which the walking motion is dynamiccally adapted to the ground's sliding properties. We compute an optimal parameters for one cycle of walking motion adapted to the ground properties by combining the coefficient of friction and centripetal force, and therefrom we induce a set of nonskid speed corresponding to various sliding properties of the ground.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.9-18
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• 2013

Two-phase vapor-liquid flows exist in many shell and tube heat exchangers such as condensers, evaporators, and nuclear steam generators. To understand the fluid dynamic forces acting on a structure subjected to a two-phase flow, it is essential to obtain detailed information about the characteristics of a two-phase flow. The characteristics of a two-phase flow and the flow parameters were introduced, and then, an experiment was performed to evaluate the pressure loss in the tube bundles and the fluid-dynamic force acting on the cylinder owing to the pressure distribution. A two-phase flow was pre-mixed at the entrance of the test section, and the experiments were undertaken using a normal triangular array of cylinders subjected to a two-phase cross-flow. The pressure loss along the flow direction in the tube bundles was measured to calculate the two-phase friction multiplier, and the multiplier was compared with the analytical value. Furthermore, the circular distributions of the pressure on the cylinders were measured. Based on the distribution and the fundamental theory of two-phase flow, the effects of the void fraction and mass flux per unit area on the pressure coefficient and the drag coefficient were evaluated. The drag coefficient was calculated by integrating the measured pressure on the tube by a numerical method. It was found that for low mass fluxes, the measured two-phase friction multipliers agree well with the analytical results, and good agreement for the effect of the void fraction on the drag coefficients, as calculated by the measured pressure distributions, is shown qualitatively, as compared to the existing experimental results.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.25-33
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• 2011

Suction buckets have been widely used for offshore structures such as anchors for floating facilities, and the foundations of offshore wind energy turbines. However, the design guidelines for suction buckets have not been clearly suggested. Therefore, this study performed the numerical analysis by using ABAQUS (2010) to evaluate bearing capacities and load-movement behaviors of the suction bucket in NC clay. For the numerical analysis, the depth ratio L/D (L=embedded length of skirt; D=diameter of a bucket) was varied from 0.25 to 1.0. The analysis results showed that the L/D ratio has a significant effect on the bearing capacity, and the vertical and horizontal capacities respectively increased by about 40% and 90%, when L/D ratio increased from 0.25 to 1.0. At the vertical loading, the bucket showed the similar failure mode with a deep foundation, so the shaft and toe resistances can be separately evaluated. At the horizontal loading, the bucket with L/D=O.25 showed the sliding failure mode and the bucket with $L/D{\geq}0.5$ showed the rotational failure mode.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.25-32
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• 2004

This paper examines the results of full-scale field tests on micropiles and side resistance is evaluated with respect to axial displacements and soil properties. Both cohesive and cohesionless soils are included in this evaluation. For all practical purposes, the developed load-displacement relationship and the geotechnical soil properties for each micropile and soil type can be used to represent the available data well through normalized average values and empirical correlations. There is a significant difference in load-carrying capacity between micropiles and drilled shafts that results primarily from the micropile pressure-grouting installation effects on the state of stress in the ground. The results show that micropiles can have a significant increase of capacity over larger-diameter drilled shafts at shallower depths with D/B < 100 or so. In cohesive soils, the typical increase is on the order of 1.5 with values as high as 2.5. For cohesionless soils, the typical increases are in the range of 1.5 to 2.5 with values as high as 6.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.383-386
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• 2005

An integrated analytical model which should have essential dynamics on the longitudinal railway vehicle is developed. The model consists of translational movement, rotational movement, brake actuator, adhesion force between rail and wheel, and brake friction force between wheel and pad. Thus, during the deceleration for stopping, a feedback controller controlling the brake cylinder pressure is designed to improve ride quality and to release friction problems. Through the developed model, the feasibility of controlling the cylinder pressure is verified for the better performances during braking.