• Journal of the Korean Geotechnical Society
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• v.26 no.9
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• pp.71-74
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• 2010

During construction of deep foundation in soft rock under varying soil properties, it is essential to locate the rock stratum, especially when drilling with slurry. When slurry is used for drilling, the bottom of the borehole cannot be seen, thereafter soil cuttings cannot be differentiated from soft rock cuttings. A new static rock penetrometer, known as Rock Penetrometer was developed during this study. It could be a simple mechanical device that is attached to the bottom of a Kelly bar which is used to attach drilling tools such as augers and core barrels while drilling. After its calibration in the laboratory, the performance of the static rock penetrometer was verified in the several field test sites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.965-975
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• 1994

Opening the tip of a PHC pile, under a constant driving energy, can result in an increment of penetration depth due to the decrement of driving resistance. Therefore, the bearing capacity of an open-ended PHC pile may become larger than that of a closed-ended PHC pile by virtue of the increased embedded length. However, two main problems can be caused by opening the end of PHC pile. First problem is the variation of bearing capacity by opening the pile tip, and the second one is whether the tip of an open-ended PHC pile will be failured by a high pressure developed by the soil plug. In this study, model pile tests in calibration chamber were performed to investigate the practicability of open-ended PHC pile in view of both the pile bearing capacity and the possible failure of the pile tip. According to the test results, the total bearing capacity of open-ended piles approaches the total bearing capacity of closed-ended piles with the increase of the penetration depth. The failure of pile tip could be occurred in the region of 0.8~1.1 times as the inside diameter from the pile tip.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.423-430
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• 1999

PIT collector를 이용한 저변형률 건전도시험(low strain pile integrity test)은 충격에 의해 발생하는 응력파장의 특성을 분석하여 말뚝의 길이와 형상을 추정하는 방법이다. PIT시험(Pile Integrity Test)은 장말뚝인 경우와 지반저항이 큰 경우 선단부의 위치가 분명하게 확인되지 않아 해석이 불가능하다는 단점이 있으며 적용할 수 있는 대상말뚝에도 종류에 따라 제한된다. 그러나 이밖의 경우 간편성과 말뚝의 대략적인 단면형상을 파악할 수 있다는 점에서 다른 방법에 비하여 유리하다. 이 때문에 국내에서도 PIT시험의 적용 빈도가 증가하는 추세이며 지난 3~4년 동안 주로 대형 교량건설 현장의 대구경 현장타설말뚝에 대하여 적용되어 왔다. 최근 국내에서는 대구경 현장타설말뚝이 아닌 소구경 현장타설말뚝에 대하여 PIT시험을 실시하는 경우도 증가하고 있다. 현장 조건상 말뚝길이가 길지 않은 경우 시험분석결과 말뚝의 선단부가 분명하게 확인되었고 말뚝 중간부 및 하부의 necking 또는 bulging, 선단부의 단면이 확대되거나 축소되는 형상 등 다양한 단면형상을 나타내었다. 이 결과로부터 건전도시험의 효과적인 분석방안, 시간(양생)효과 등을 판단할 수 있음을 확인할 수 있었다.

• Journal of the Korean GEO-environmental Society
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• v.16 no.3
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• pp.5-13
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• 2015

Wave overflow can cause a failure of sea dike structure. Based on the results of the field surveys on mound-type sea dike, the failure of vicinity of crown and the scouring of toe at the landward was revealed as the most representative failure example. One of the main factors related to this failure pattern is overflow-induced pressure and velocity. Thus, in this study the analytical equations which can determine the pressure and the velocity induced by overflow in sea dike were proposed and verified. To accomplish this, assumed that the flow is quasi-steady and irrotational, and concentric circular streamlines around the vicinity of crown and toe of the sea dike. Flow was assumed as critical state and Bernoulli equation was used to develop the equations that can determine the pressure and velocity at the vicinity of crown and toe of the sea dike. Using these equations, the pressure and the velocity were calculated in condition of various overflow depths and radiuses of circular streamline. Based on the calculation results, while a negative pressure was occurred at the vicinity of crown, a significant amount of positive pressure occurred at the toe. The existence of flow-induced shear stresses was also confirmed. In addition, the limitation of the proposed equations was discussed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1989.06b
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• pp.60-69
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• 1989

안정성과 진동억제 특성이 요구되는 터어빈이나 모터등의 고속 회전기계에서는 틸팅-패드 저어널 베어링이 많이 사용되고 있다. 이는 틸팅-패드 저어널 베어링에서는 패드가 피봇이나 로울러로 지지되어 있으므로 윤활유막에서 발생하는 압력의 합력중심이 항상 이 지지점을 지나게 되어 베어링의 안정특성이 향상되기 때문이다. 틸팅-패드 저어널 베어링은 추력 베어링과 같이 불연속적인 윤활면을 갖는다. 그러므로 베어링의 입구부 선단에서 공급되는 윤활유의 충돌로 인한 압력격변이 일어나는데 이때 패드 입구부에서 발생하는 압력을 선단압력이라 한다. 이러한 선단압력으로 인한 베어링의 성능변화에 관한 연구는 주로 추력 베어링에 대하여 이론 및 실험적으로 수행 되어져 왔으며 그 결과들은 선단압력이 베어링의 성능에 미치는 영향을 무시할 수 없음을 보여주고 있다. 그러나 아직도 선단압력의 영향이 제대로 파악되고 있지 못하며, 특히 틸팅-패드 저어널 베어링에서 선단압력의 영향을 조사한 연구는 많이 부족한 실정이다. 그러므로 본 연구에서는 유한폭 틸팅-패드 저어널 베어링을 모델화한 실험장치를 설계 제작하여 선단압력을 포함한 유막내의 압력분포 및 유막두께를 연속적으로 측정함으로써 틸팅-패드 저어널 베어링의 성능에 미치는 선단압력의 영향을 실험적으로 조사하기로 한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.1
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• pp.85-92
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• 2024

In this paper, we developed an intuitive teaching and control system that directly teaches a task by holding the tip of a robotic arm and moving it to a desired position. The developed system consists of a 6-axis force sensor that measures position and attitude forces at the tip of the robot arm, an algorithm for generating robot arm joint speed control commands based on the measured forces at the tip, and a self-made 6-axis robot arm and control system. The six-dimensional force/torque of the position posture of the robot arm operator steering the handler is detected by the force sensor attached to the handler at the leading edge and converted into velocity commands at the leading edge to control the 7-axis robot arm. The verification of the research method was carried out with a self-made 7-axis robot, and it was confirmed that the proposed force sensor-based robot end-of-arm control method operates successfully through experiments by teaching the operator to adjust the handler.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1989.11a
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• pp.59-68
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• 1989

유압베인 펌프는 소형으로 유량이 많으나, 발생압력 면에서는 피스톤식 펌프에 미치지 못하기 때문에 고압화에 대한 노력이 계속 되어져 왔다. 또한 자원화, 성에너지화의 일환으로 고압, 고효율, 장수명화에 대한 요구가 다른 형의 펌프, 모터와 더불어 더욱더 강력해 지고 있는 실정이다. 이 문제를 해결하기 위하여는 베인펌프의 슬라이딩 부분, 특히 베인 선단부의 윤활 상태를 파악할 필요가 있다. 캠링에 대한 베인의 수직작용력을 파악하기 위하여는 베인 주위의 압력을 여러 위치에서 뿐만아니라 동시에 연속적으로 측정하지 않으면 안된다. 따라서 저자들은 압력평형형의 인트라베인식 유압베인 펌프를 이용하여 베인 주위 4개소의 비정상 압력을 특정하였다. 본 논문에서는 압력측정 결과를 기초로 하여 베인선단 슬라이딩부에 가하여지는 가중을 구하여 압력측정의 조건하에서의 베인과 캠링간의 윤활상태에 대하여 어떠한 윤활 이론을 적용할 것인가를 명확히 하고자함이 이 연구의 목적이다.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.40 no.1
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• pp.98-102
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• 1995

Popped popcorn generally have a regular popping direction and typical shape. But the reason and mechanism are not clear yet. This experiment was carried out to investigate the shape moulding factor of popped popcorn. Pericarp thickness of tip-cap section of kernels is slightly thicker than that of top section and this fact provides the important information to the reason. Popping starts when the moisture pressure of heated popcorn is increased and reaches at the critical pressure. Therefore, in the same moisture pressure conditions, top sections are bursted first because their pericarp section is thinner than that of tip-cap section. At the very moment tip-cap sections pull down the top sections of peri carp as bi-metal does. So kernels which removed tip-cap section showed the irregular popping shape because they lost the tip-cap pericarp function. How-ever, kernels which removed embryo showed the typical popping shape but their popping volume was small due to emition and shortage of critical moisture pressure. But kernels which removed the whole pericarp and top pericarp were not popped at all because moisture was entirely emitting out of kernels. These results suggest that the shape moulding factor of popped popcorn is the pericarp thickness differences between the top and tip-cap section of kernels.

• Geotechnical Engineering
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• v.6 no.4
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• pp.53-64
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• 1990

There have been numerous methods proposed to predict the pile bearing capacity, but except for the prediction by the pile loading test, not one method is suitable to give a reliable result. Even so, the pile loading test has seldom been performed due to the time and money consuming procedures. In this research, a new way of carrying out the pile loading test, "Simple Pile Loading Test(SPLT)" is introduced. In SPLT technique, the test pile is designed to have a separable shoe with a reduced sized sliding core, so that the skin friction acts as the reaction force to cause the pile tip settlement. Therefore the preparation, installation, loading and unloading of the loading frames and the kentledge can be eliminated.liminated.

• Geotechnical Engineering
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• v.14 no.4
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• pp.141-150
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• 1998

Based on the authors' previous research, we have conducted more researches on finding out the coefficient of consolidation from Piezocone dissipation test results, especially measured behind the cone tip which is mostly used in Korea, by adopting the optimization technique. By analyzing numerical and real field examples, it can be found that the adopted optimum technique that minimizes the differences between the predicted dissipation curve and the measured one gives consistent and convergent results, irrespective of initial values. Such technique also provides horizontal coefficient of consolidation which is able to simulate real field consolidation behavior more effectively.