• Journal of Korean Tunnelling and Underground Space Association
• /
• v.17 no.6
• /
• pp.695-702
• /
• 2015

Recently, the improvement of mechanical and theoretical issues in geo-centrifuge test enhances the applicability and accuracy of the test. Geo-centrifuge test is appropriate to simulate the behaviors of underground structures like tunnel, since tunnel interacts with the soil and/or rock around it and the test can embody the in-situ stress conditions effectively. In this study, the seismic behaviors of twin tunnel were analyzed based on geo-centrifuge test. Flexible segment to mitigate seismic acceleration were implemented in the model with thin and thick thickness. Based on the test results, it was found that flexible segment can decrease the peak acceleration generally, however, thin flexible segment was not able to reduce peak acceleration in short-period seismic wave. Thick flexible segment was more effective in case of high bedrock acceleration condition. Additionally, 3-dimensional numerical analysis was performed to verify the characteristics of seismic behavior and the effect of flexible segment. Consequently, the numerical analysis result showed good agreement with the test result.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.2
• /
• pp.121-126
• /
• 2005

It is not uncommon to observe tilt of buildings and towers as a result of unexpected differential foundation settlements. Over the years, a number of engineering methods including the soil extraction technique have been attempted to reduce inclination of buildings and towers. In this research, a series of novel geotechnical centrifuge model tests by using a state-of-the-art in-flit robotic manipulator have been conducted to study key factors which govern the restoration of building tilts. In the centrifuge model tests, the robotic manipulator was used to drill and extract soil in-flight near an initially tilted model building. The soil extraction was to induce stress release, thereby mitigating the inclination of the model building. Insights into the effects of different configurations, soil density and sequences of drilling observed during the centrifuge model tests on the restoration of the model building are to be investigated.

• Journal of the Korean GEO-environmental Society
• /
• v.9 no.6
• /
• pp.31-41
• /
• 2008

Consolidation characteristics of reclamated ground with dredged soil and methods of evaluating them are investigated in this paper. For a dredged and reclamated ground with a very high water content, self-weight consolidation being progressed, its consolidation characteristics are difficult to find since it is almost impossible to have a undisturbed sample. In order to overcome such a problem, methods of laboratory tests with disturbed sample were studied to obtain consolidation parameters required to analyze consolidation settlement in practices, using the conventional infinitesimal consolidation theory, were evaluated by carrying out various laboratory tests with disturbed soils such as oedometer test, constant rate of deformation test, Rowe-cell tests with ring diameters of 60 mm, 100 mm and 150 mm and the centrifuge model tests with 40 g-levels. Constitutive relations of void ratio - effective vertical stress - permeability were evaluated by using the inverse technique implemented with the finite strain consolidation theory and results of centrifuge model tests. Design soil parameters related to consolidation such as compression index, swelling index, coefficient of volume change and vertical and horizontal consolidation coefficients were proposed properly by analyzing the various test results comprehensively.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.11
• /
• pp.57-70
• /
• 2018

In this study, verification of the nonlinear effective stress analysis is performed for introducing performance based earthquake resistance design of port and harbor structures. Seismic response of gravitational caisson quay wall in numerical analysis is compared directly with dynamic centrifuge test results in prototype scale. Inside of the rigid box, model of the gravitational quay wall is placed above the saturated sand layer which can show the increase of excess pore water pressure. The model represents caisson quay wall with a height of 10 m, width of 6 m under centrifugal acceleration of 60 g. The numerical model is made in the same dimension with the prototype scale of the test in two dimensional plane strain condition. Byrne's liquefaction model is adopted together with a nonlinear constitutive model. Interface element is used for sliding and tensional separation between quay wall and the adjacent soils. Verification results show good agreement for permanent displacement of the quay wall, horizontal acceleration at quay wall and soil layer, and excess pore water pressure increment beneath the quay wall foundation.

• The korean journal of orthodontics
• /
• v.25 no.1 s.48
• /
• pp.73-85
• /
• 1995

Multi-Vertical Loop Arch Wire(MVLAW) is a kind of appliance for uprighting the mesially inclined posterior teeth axes simultaneously. In this study MVLAW was classified as 3 types by modifing the vertical loop design and named type A, B and C. Each MVLAW was fabricated from .017'x.025' TMA wire and preactivated at the distal end of the open vertical loop with 10 degree tip-back bend(type B has an electric welding stop at the distal end of each loop and type C has no electric welding stop). Type A MVLAW was preactivated at the apex of each open vertical loop with 10 degree tip-back bend(the electric welding stop of type A is positionod at the mesial side of each loop). The aim of the present study was to identify when and which MVLAW is more effective to correct the buccal segment axes simultaneously. The Photoelastic overview of the upper and lower right quadrant showed that stress concentrations were observed in its photoelastic model. The obtained results were as follows : 1. Higher level compression can be seen clearly at the distal curvature of the lower 1st and 2nd molar when A type MVLAW was applied without short class m elastic, but mild compression cannot be seen at the distal curvature of lower anterior teeth using the class m elastic. 2. Higher concentration was presented at the mesial curvature from the lower 1st premolar to the 2nd molar than the anterior teeth when B type MVLAW without short class III elastic was applied, but using the short class III elastic, higher concentration of compression was presented in the anterior teeth area. 3. Areas of higher compression and tension were not observed at the mesial and distal curvature of the entire 1ower teeth except lower central and lateral incisors in C type MVLAW without short class III elastic, but using the short class III elastic, higher concentration was seen at the mesial curvature of the lower 1st premolar and 1ower anterior teeth.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.177-177
• /
• 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
• /
• 2011.05a
• /
• pp.176-176
• /
• 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.

• Proceedings of the KIEE Conference
• /
• 2011.07a
• /
• pp.999-1000
• /
• 2011

영구자석을 삽입하는 IPM(Interior Permanent Magnet : 이하 IPM) 방식의 동기전동기 설계에서 브리지의 형상 결정은 기계적인 안정성을 확보하고 출력 요구사양을 만족시키기 위해 구조해석과 자기회로 해석을 병행하여 검토하는 것을 요구한다. 본 논문에서는 IPM타입 동기전동기를 대상으로 회전자 원심력이 정적상태로 인가되는 정하중 조건과 속도변화가 시간에 따라 변하는 동하중 조건일 경우를 구분하여 설계 여유를 분석하였으며, 영구자석의 접착여부에 따라 브리지에 발생하는 응력 분포의 차이를 해석하였다. 또한, 동하중 상태에서 재료의 응력-피로 특성을 통해 피로 한계 조건을 설계단계에서 예측하였다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.12
• /
• pp.1027-1034
• /
• 2014

The shear stress on a surface due to the thin film fluid flow is an important issue. In case of a rotating disk, the fluid is delivered to the edge of the disk by centrifugal force, which acts as a body force on the fluid. Wear of a surface is affected by the shear stress acting on the surface and curvature. In this study, we utilize computational fluid dynamics software to model the ratio of curvature and local shear stress on solid surfaces. The key goal of the study is to determine an optimized curvature for the thin film fluid flow on a solid surface in order to minimize the local shear stress affecting the wear of this surface. Our results on the effects of curvature will be utilized for the design of devices that utilize thin film fluid flow on a solid surface, such as rotating-disk spray systems and thin film coating.

• Journal of the Korean Geotechnical Society
• /
• v.31 no.1
• /
• pp.25-35
• /
• 2015

Penetration resistance of bucket foundations with skirt wall in the silty sand of the western coast of Korea was analyzed by centrifuge modelling. The penetration resistance is induced when the bucket foundations are jacked into the soil without suction, and is directly related to the self-weight penetration depth. The procedure by Houlsby and Byrne (2005), which takes into account the effect of stress increase by frictional resistance of skirt wall, was utilized to generate the penetration resistance similar to the experimental results. This paper describes the methods by which major parameters such as lateral earth pressure coefficient and friction angle between the skirt wall and the soil are evaluated. The effect of changes in these parameters on the predictions is analyzed. Also, observed soil behaviour during jacking penetration is investigated.