• Geomechanics and Engineering
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• 제39권1호
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• pp.1-11
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• 2024

Geotechnical parameter estimation is critical to the design, performance, safety, and cost and schedule management in Tunnel Boring Machine projects. Since these parameters vary within a certain range, relying on mean values for evaluation introduces significant risks to the project. Due to the non-homogeneous characteristics of geological formation, data may not exhibit a normal distribution and the presence of outliers might be deceptive. Therefore, the use of reliable analyses and simulation models is inevitable in the course of the data evaluation process. Advanced modeling techniques enable comprehensive analysis of the project data and allowing to model the uncertainty in geotechnical parameters. This study involves using Monte Carlo Simulation method to predict probabilistic distributions of field data, and therefore, establish a basis for designs and in turn to minimize project risks. In the study, 166 sets of geotechnical data Obtained from 35 boreholes including Standard Penetration Test, Limit Pressure, Liquid Limit, and Plastic Limit values, which are mostly utilized parameters in estimating project requirements, were used to estimate the geotechnical data distribution of the study field. In this context, firstly, the data was subjected to multi-parameter linear regression and variance analysis. Then, the obtained equations were implemented into a Monte Carlo Simulation, and probabilistic distributions of the geotechnical data of the field were simulated and corresponding to the 90% probability range, along with the minimum and maximum values at the 5% probability levels presented. Accordingly, while the average SPT N30 value is 42.86, but the highest occurrence rate is 50.81. For Net Limit Pressure, the average field data is 17.07 kg/cm², with the maximum occurrence between 9.6 kg/cm² and 13.7 kg/cm². Similarly, the average Plastic Limit value is 22.32, while the most probable value is 20.6. The average Liquid Limit value is 56.73, with the highest probability at 54.48, as indicated in the statistical data distribution. Understanding the percentage distribution of data likely to be encountered in the project allows for accurate forecasting of both high and low probability scenarios, offering a significant advantage, particularly in ordering TBM requirements.

• Geomechanics and Engineering
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• 제38권5호
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• pp.477-486
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• 2024

The process of inspecting and replacing cutting tools in a shield tunnel boring machine (TBM) is called cutterhead intervention (CHI) (Farrokh and Kim 2018). Since CHI is performed by a worker who enters the chamber in TBM, the worker is directly exposed to high water pressure and huge water inflow, especially in areas with high ground water levels, causing health problems for the worker and shortening of available working hours (Kindwall 1990). Ham et al. (2022) proposed a method of reducing the water pressure and water inflow by injecting a grout solution into the ground through the shield TBM chamber, and named it the new face grouting method (NFGM). In this study, the TBM mechanical characteristics including the injection pressure of the grout solution and the cutterhead rotation speed were determined for the best performance of the NFGM. To find the appropriate injection pressure, the water inflow volume according to the injection pressure change was measured by using a water inflow test apparatus. A model torque test apparatus was manufactured to find the appropriate cutterhead rotation speed by investigating the change in the status of the grout solution according to the rotation speed change. In addition, to prove the validity of this study, comprehensive water inflow tests were carried out. The results of the tests showed that the injection pressure equal to overburden pressure + (0.10 ~ 0.15) MPa and the cutterhead rotation speed of 0.8 to 1.0 RPM are the most appropriate. In the actual construction site, it is recommended to select an appropriate value within the proposed range while considering the economic feasibility and workability.

• Wind and Structures
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• 제27권4호
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• pp.213-221
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• 2018

In the desert and Gobi regions with strong wind and large sediment discharge, sand transporting engineering is more effective than sand blocking and sand fixing measures in sand prevention. This study uses the discrete phase model of 3D numerical simulation to study the motion trail, motion state and distribution rule of sand particles with different grain diameters when the included angle between the main shaft of the feather-row lateral transportation sand barrier and the wind direction changes, and conducts a comparison in combination with the wind tunnel test and the flow field rule of common sand barrier. According to the comparison, when wind-sand incoming flow passes through a feather-row sand barrier, sand particles slow down and deposit within the deceleration area under the resistance of the feather-row sand barrier, move along the transportation area formed by the transportation force, and accumulate as a ridge at the tail of the engineering. With increasing wind speed, the eolian erosion of the sand particles to the ground and the feather-row sand barrier is enhanced, and the sand transporting quantity and throw-over quantity of the feather-row sand barrier are both increased. When sand particles with different grain diameters bypass the feather-row sand barrier, the particle size of the infiltrating sands will increase with the included angle between the main shaft of the feather-row sand barrier and the wind direction. The obtained result demonstrates that, at a constant wind speed, the flow field formed is most suitable for the lateral transportation of the wind-drift flow when the included angle between the main shaft of the feather-row sand barrier lateral transportation engineering and the wind speed is less than or equal to $30^{\circ}$.

• 한국지반공학회논문집
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• 제18권4호
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• pp.285-294
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• 2002

연약지반상에 제방 성토시 예상되는 연약지반의 측방유동을 적극 억지할 수 있는 성토지지말뚝공법은 말뚝두부에 캡을 설치하는 형태에 따라 크게 말뚝슬래브공법, 캡보말뚝공법 및 단독캡말뚝공법으로 구분할 수 있다. 이들 공법중 캡보말뚝공법 및 단독캡말뚝공법에서는 성토지지말뚝과 지반간의 상대적인 강성차이로 인해 성토지반 속에 지반아치가 발생하게 되고, 대부분의 성토하중은 발달된 지반아치를 통해 말뚝으로 전달된다. 두 공법에서 발생되는 지반아치의 차이는 그 형태가 캡보말뚝공법의 경우 터널의 형태와 유사하게 2차원적이고, 단독캡말뚝공법에서는 돔의 형태와 유사하게 3차원적이라는 것이다. 따라서 이 두 경우의 지반아치로 인한 성토지지말뚝의 하중분담효과에 관한 이론식을 각각 유도 제안하여 비교하였으며, 두 이론식의 타당성을 입증하기 위한 일련의 모형실험을 수행하였다.

• 한국항공우주학회지
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• 제41권5호
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• pp.342-349
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• 2013

무인항공기가 외형손상을 입는 경우, 비행역학 특성이 변하기 때문에 손상 이전 설계된 제어기는 더 이상 안정적인 제어성능을 보장하지 않는다. 본 논문에서는 주익의 손상이 일어난 무인항공기에 대해서도 강건한 제어성능을 보장하는 신경회로망 적응제어기법을 소개한다. 구동기의 특성에 의한 제어기의 성능저하를 방지하기 위해 Pseudo Control Hedging (PCH)를 추가적으로 사용하였다. 기체고정좌표계의 중심이 항공기의 무게중심에 위치하지 않는 비대칭 동역학을 사용하였으며, 전익형 무인기를 대상 비행체로 하였다. 날개가 손상되지 않은 모델과 손상된 모델의 풍동시험을 통해 얻은 공력데이터를 이용하여 시뮬레이션을 수행하였다. 시뮬레이션의 결과를 통해 제안된 제어기법이 주익의 손상이 발생한 항공기에 대해서도 여전히 안정적인 조종성능을 보장하는 제어기법임을 검증하였다.

• 한국항공우주학회지
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• 제30권7호
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• pp.20-28
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• 2002

본 연구에서는 로터의 후류 효과 및 실속 후 특성을 고려하여 30kW급 상반회전 풍차 시스템에 대한 공력성능 해석을 수행하였다. 기본 공력이론은 모멘텀 이론과 2차원 준정상 공기력 이론을 통합한 형태를 사용하였다. 로터의 후류영향을 고려하기 위해 축소형 풍차 블레이드 모델에 대한 풍동시험 결과를 적절히 이용하였으며, 이로부터 보조로터를 지난 후류의 축속도 및 각속도 성분을 결정하였다. 또한, Glauert의 최적 작동판 이론과 Prandtl의 익단손실 효과를 고려하여 30kW급 풍차 시스템에 대한 최적 시위 및 비틀림 분포를 구하였으며, 기존의 단일 로터 시스템과의 공력성능 비교를 통하여 상반회전 풍차 시스템의 효율성 및 우수성을 입증하고자 하였다.

• 터널과지하공간
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• 제13권2호
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• pp.100-107
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• 2003

본 암석에 외력을 가하면 내부 응력이 발생하고, 이로 인해 변형이 발생하게 된다. 암석재료에서 크리프 변형이 장기간 지속되어 어느 한계에 도달하면 급작스런 파괴로 이어진다. 따라서 구조물의 장기적 안정성 검토 시에 지반의 크리프 특성 파악이 필수적이라 할 수 있다. 본 논문에서는 일축압축강도의 40% 50%, 60%, 70%에 해당하는 하중을 가하여 변형률을 측정하였다. 크리프 특성을 비교 . 분석한 결과로써 변형률 속도의 경우 하중 이 증가함에 따라 변형률 속도 상수$\alpha$ , ${\gamma}$ 도 증가하는 경향이 나타났다. 크리프 곡선에서 Griggs가 제안한 식이 Li와Xia, Singh식 보다 적합하였으며, Burger's model을 적용하여 구한상수 G$_2$는 응력수준의 증가에 파라 감소하며, η$_1$,η$_2$, G$_1$의 경우 불규칙하게 나타났다.

• 한국항해항만학회지
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• 제37권2호
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• pp.137-142
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• 2013

The displacement Deep-V catamaran concept was developed in Newcastle University(UNEW) through development of the systematic Deep-V catamaran series. One of the most important Deep-V catamaran launched to date is Newcastle University's own multi-purpose research vessel, The Princess Royal. The vessel was launched in 2011 and enhanced the Deep-V catamaran concept further with the successful adoption of a novel anti-slamming bulbous bow and tunnel stern for improved efficiency. It was however identified that the vessel has substantial amount of dynamic trim that limited the visibility of the captain. The dynamic trim also increased the wave-making resistance thereby preventing the vessel from attaining its maximum speed in certain sea states. This paper therefore presents the application of devices such as Trim Tabs, Interceptors, Transom Wedges and Integrated Transom Wedges-Tabs to control the dynamic trim and improvement of fuel efficiency of the vessel. All of these energy saving devices were fitted into a model for tests in Newcastle University's Towing Tank. Model test verification confirmed that the optimum appendage was the interceptors, they produced a 5% power saving and 1.2 degree trim reduction at 15 knots, and investigations of full scale trials will be scheduled with and without application of device to compare the improvement of performance.

• Structural Engineering and Mechanics
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• 제57권5호
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• pp.951-968
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• 2016

Long-span cross-strait bridges extending into deep-sea waters are exposed to complex marine environments. During the construction stage, the flexible freestanding bridge towers are more vulnerable to environmental loads imposed by wind and wave loads. This paper presents an experimental investigation on the dynamic responses of a 389-m-high freestanding bridge tower model in a test facility with a wind tunnel and a wave flume. An elastic bridge model with a geometric scale of 1:150 was designed based on Froude similarity and was tested under wind-only, wave-only and wind-wave combined conditions. The dynamic responses obtained from the tests indicate that large deformation under resonant sea states could be a structural challenge. The dominant role of the wind loads and the wave loads change according to the sea states. The joint wind and wave loads have complex effects on the dynamic responses of the structure, depending on the approaching direction angle and the fluid-induced vibration mechanisms of the waves and wind.

• 터널과지하공간
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• 제28권6호
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• pp.651-669
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• 2018

본 연구에서는 유전자 프로그래밍과 개체군집최적화기법을 이용하여 픽 커터의 비에너지를 예측하기 위한 모델을 제안하였다. 기계굴착장비의 굴진성능을 평가하는 것은 터널의 설계 초기 단계에서 매우 중요하며, 비에너지를 이용한 기계 굴착장비의 굴진성능평가방법은 모든 기계굴착공법에 적용될 수 있는 표준화된 방법이다. 본 연구에서는 코니컬형상의 픽 커터가 암석을 절삭할 때 요구되는 비에너지와 암석의 강도특성, 절삭조건 간의 상관관계를 분석하고자 하였으며, 선행연구를 통해 총46개의 선형절삭시험 결과를 수집하여 분석에 활용하였다. 본 연구에서 제안한 예측모델을 이용하여 산정된 픽 커터의 비에너지는 다중선형회귀분석에 비해 작은 평균제곱오차를 나타내었으며, 결정계수 또한 본 연구에서 제안한 모델이 다중선형회귀분석에 비해 우수한 예측결과를 나타내는 것을 확인할 수 있었다.