• 한국터널지하공간학회 논문집
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• 제17권3호
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• pp.393-401
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• 2015

TBM 터널을 건설하는 동안 효율적이고 안전한 작업을 위하여 굴착 암반의 정확한 정보를 획득하는 것은 매우 중요하다. 이 연구에서는 터널 막장 전방의 암반 상태를 예측하기 위하여 선진시추장비와 시추공벽 영상화 장비를 이용한 TBM 전방 지반평가시스템을 개발하였다. TBM 전방 지반평가시스템은 선진시추장비와 시추공벽 영상화 장비, 분석 소프트웨어로 구성된다. 선진시추장비는 논코어링과 코어링 방법이 모두 적용 가능하도록 개발되었다. 또한 굴진 시 획득되는 피드압, 회전압, 회전수, 굴진속도 등의 천공영향 변수를 획득할 수 있다. 천공지수는 코어RMR과의 상관성분석을 통해 천공지수RMR로 환산된다. 개발된 시스템은 비탈면, 터널 현장에서 현장적용을 진행하였다. 현장 적용 결과 논코어링 방법은 코어링 방법에 비해 4배가량 빠른 굴진이 가능한 것으로 확인되었고, 천공지수RMR과 코어RMR은 유사한 분포를 나타내었다. TBM 전방 지반평가시스템은 신속한 지반예측이 가능하므로 공기지연을 최소화할 수 있는 막장 전방 예측 기술로의 활용이 기대된다.

• 한국터널지하공간학회 논문집
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• 제21권2호
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• pp.227-242
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• 2019

토압식(Earth Pressure-Balanced, EPB) 쉴드 TBM 기계데이터 분석을 통해 토사터널의 특징이 반영된 막장 전방 예측 방법을 제안하였다. 기존에 암반과 토사가 혼합된 복합 지반의 예측에 적용하였던 시계열 분석 모델을 토사터널에 적용가능하도록 수정하였다. 또한 수정된 모델을 사용하여, 토사 종류에 따라 쏘일 컨디셔닝 재료를 선택하는 것이 타당한지 연구하였다. 이를 위해 Self-Organizing Map (SOM) 군집화(clustering) 분석을 수행하였다. 그 결과 무엇보다도 지반타입이 #200체 통과량 35% 기준으로 분류되어야 한다는 것을 확인하였다. 또한 TBM 기계데이터 분석을 통해 수정된 모델이 지반 타입을 예측하는데 사용될 수 있음을 확인하였다. 수정된 기준에 따라 지반 타입을 분류하고 시계열 분석을 수행하면, 10막장 전방 지반에 대해서 98%의 높은 예측 정확도를 보였으며, 이를 통해 수정된 방법의 우수성이 입증되었다. 특히 지반 타입 변화 구간에 대한 예측 정확도도 약 93%로, 10막장 전방에서 지반 타입 변화 여부를 미리 확인할 수 있게 되었다.

• 대한조선학회논문집
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• 제44권5호
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• pp.467-473
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• 2007

Cavitation phenomena appearing on ship propellers have long been interested and recent theoretical analysises give good results comparing with model tests. In accordance with a continuous rise in heavy powered and high speed ships, hull forms have been changed and loads acting on the propeller surface have also been increased, and they result in various and particular cavitations. In some cases, cavitation appears not only on the back but also on the face of the propeller and it causes additive pressure fluctuations and erosion of the propeller and reduces propulsion efficiency of the ship. In this study, we predict the face cavity inception using unsteady propeller analysis based on the panel method and compare the results with experimental observations.

• 화약ㆍ발파
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• 제25권1호
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• pp.67-77
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• 2007

본 연구에서는 NATM 터널 시공사이클에서 필수적으로 수행되는 천공작업 시 획득할 수 있는 정보를 통해 굴착 대상 암반의 특성을 평가하는 방안에 대해 고찰하였다. 활용 가능한 천공데이터는 천공속도, 피트압, 토크 등이 있으며, 이러한 인자들과 암반 특성들과의 상관관계를 규명하고자 하며 이러한 결과를 토대로 향후 정량적 발파설계를 위한 가이드라인을 제안하고자 하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1992년도 추계학술대회 논문집
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• pp.28-33
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• 1992

The paper describes a new mean specific cutting pressure model in order to improve the accuracy of prediction of cutting force for face milling. The new mean specific cutting pressure model produces a mean specific cutting pressure and coefficients applied to existing cutting model not by traditional method but by considering intermittence and variation of chip width according to insert cutting position to take into cutter geometry machining condition and width of workpiece, and considering a mean measure force according to spindle eccentricity and mean measure force according to spindle eccentricity and insert initial position errors.. The simulated forces in X, Y, Z directions resulted from the simulated cutting model and the new cutting model are compared with measured forces in the time end frequency domains. The simulated forces in the time and frequency domains. The simulated forces resulted from the new cutting model have a good degreement with measured forces in comparison with these resulted from the existing cutting model

• Geomechanics and Engineering
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• 제19권2호
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• pp.153-165
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• 2019

A case study of monitoring and analysis of surface settlement induced by tunneling of Tabriz metro line 2 (TML2) is presented in this paper. The TML2 single tunnel has been excavated using earth pressure balanced TBM with a cutting-wheel diameter of 9.49 m since 2015. Presented measurements of surface settlements, were collected during the construction of western part of the project (between west depot and S02 station) where the tunnel was being excavated in sand and silt, below the water table and at an average axis depth of about 16 m. Settlement readings were back-analyzed using Gaussian formula, both in longitudinal and transversal directions, in order to estimate volume loss and settlement trough width factor. In addition to settlements, face support and tail grouting pressures were monitored, providing a comprehensive description of the EPB performance. Using the gap model, volume loss prediction was carried out. Also, COB empirical method for determination of the face pressure was employed in order to compare with field monitored data. Likewise, FE simulation was used in various sections employing the code Simulia ABAQUS, to investigate the efficiency of numerical modelling for the estimating of the tunneling induced-surface settlements under such a geotechnical condition. In this regard, the main aspects of a mechanized excavation were simulated. For the studied sections, numerical simulation is not capable of reproducing the high values of in-situ-measured surface settlements, applying Mohr-Coulomb constitutive law for soil. Based on results, for the mentioned case study, the range of estimated volume loss mostly varies from 0.2% to 0.7%, having an average value of 0.45%.

• 한국공작기계학회논문집
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• 제11권2호
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• pp.1-8
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• 2002

Cutting force is obtained as a sum of chip removing force and ploughing force. Chip removing force is estimated by multiplying specific cutting pressure by cutting area. Since ploughing force is caused from dullness of a tool, its magnitude is constant if depth of cut is bigger than a certain value. Using the linearity of chip removing force to cutting area and the constancy of ploughing force regardless of depth of cut which is over a certain limit each force is separated from measured cutting force and used to establish cutting force model. New rotation matrix to convert the measured cutting force in reference axes into the forces in cutter axes is obtained by considering that tool angles are projected angles from cutter axes to reference axes.. Spindle tilt is also considered far the model. The predicted cutting force estimated from the model is in good agreement with the measured force.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1596-1607
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• 2000

The optimal design of auto-catalyst needs a good compromise between the pressure drop and flow uniformity in the substrate. One of the effective methods to achieve this goal is to use the concept of radially variable cell density. But this method has not been examined its usefulness in terms of chemical behavior and conversion performance. In this work, two-dimensional performance prediction of catalyst coupled with turbulent reacting flow simulation has been used to evaluated the benefits of this method n the flow uniformity and conversion efficiency. The results showed that two cell combination of 93cpsc and 62 cpsc was the most effective for improved pressure drop and conversion efficiency due to balanced space velocity and efficient usage of geometric surface area of channels. It was also found that large temperature difference between the bricks in case that the edge of the frontal face of brick has too much lower cell density(less than 67% of cell density of the center of the brick). This study has also demonstrated that the present computational results show the better prediction accuracy in terms of CO, HC and NO conversion efficiencies compared to those of conventional 1-D adiabatic model by comparison with experimental results.

• 지질공학
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• 제19권4호
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• pp.483-492
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• 2009

터널 및 지하구조물 시공 중 굴착 대상 지반에 대한 정확한 정보 획득은 작업의 효율성과 안전성을 위해 매우 중요하다. 본 연구에서는 굴착 중 굴진 대상 암반의 지질 구조를 신속하고 정확하게 감지하기 위하여 천공탐사 기법을 이용하였다. 유압 착암기 천공 시 발생하는 천공속도, 회전압, 피드압 등의 기계량을 측정하여 분석하였으며, 이를 통해 암석과 지질 구조적 특성에 의해 변화되는 암반 특성을 평가 하였다. 터널 시공현장에서 굴착 중 획득된 천공데이터 분석에 의해 평가된 암반 정보는 굴착 전 수행된 선진수평시추 및 TSP 탐사 결과와 비교하여 신뢰성을 검토하였으며, 그 결과 천공 데이터의 변화가 암반 특성 및 불연속면 예측을 위해 효율적으로 활용될 수 있음을 확인하였다.

• KDI Journal of Economic Policy
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• 제41권4호
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• pp.1-44
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• 2019

The contingent convertible bond (or CoCo) is designed as a bail-in tool, which is written down or converted to equity if the issuing bank is seriously troubled and thus its trigger is activated. The trigger could either be rule-based or discretion-based. I show theoretically that the bail-in is less implementable and that the associated bail-in risk is lower if the trigger is discretion-based, as governments face greater political pressure from the act of letting creditors take losses. The political pressure is greater because governments have the sole authority to activate the trigger and hence can be accused of having 'blood on their hands'. Furthermore, the pressures could be augmented by investors' self-fulfilling expectations with regard to government bailouts. I support this theoretic prediction with empirical evidence showing that the bail-in risk premiums on CoCos with discretion-based triggers are on average 1.13 to 2.91%p lower than CoCos with rule-based triggers.