• 터널과지하공간
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• 제19권5호
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• pp.440-449
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• 2009

LCM 시험은 TBM에서의 디스크 커터 설계와 굴진성능 예측을 위한 가장 신뢰성 있는 시험 중의 하나이다. 그러나 이는 실대형 암석시료의 채취, 운반 및 거치에 많은 비용이 소요되는 단점을 가지고 있으며, 절리가 포함된 시료에 대한 시험이 용이하지 않아 시험에서 예측된 모델을 설계에 활용하기 어려운 경우가 많다. 따라서 LCM 시험이 갖는 이러한 경제적 시간적 제약점들을 극복할 수 있는 현실성 있는 수치모델링이 고려된다면, 현장에서의 복잡한 검토과정 없이 현장에 직접 적용할 수 있는 적합한 형태의 TBM 절삭모델을 제시할 수 있을 것이다. 본 연구에서는 UDEC을 이용하여 단일절리를 포함한 암석시료에 대한 디스크 커터의 절삭 메커니즘 분석을 위해 디스크 커터의 가압지점의 위치와 절리의 방향성에 따른 균열전파양상을 분석하였으며, 이를 통하여 절리의 방향에 따른 적절한 디스크 커터의 가압지점 위치 및 디스크 커터의 적정 간격을 도출하였다.

• Journal of Plant Biotechnology
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• 제31권2호
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• pp.121-126
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• 2004

금낭화 (Dicentra spectabilis L.)는 개발가치가 있는 국내 자생화 중의 하나로서 우수한 품종의 대량생산이 절실히 요구되는 실정이다. 본 연구는 현탁배양을 통한 배발생세포의 대량증식과 체세포배 발생 및 식물체재생의 적정조건을 구명하여 효율적인 기내묘목의 대량생산 체계를 확립하고자 시도되었다. 1.0mg/L 2,4-D SH고체배지에서 유도된 배발생캘러스를 현탁배지에서 증식시킨 결과, 1.0mg/L 2,4-D를 포함한 SH배지에서 MS배지에 비해 증식율이 높게 나타났으며, 체세포배 발생율은 1/2배 SH기본배지에서 가장 높게 나타났다. 250$m\ell$ 삼각플라스크에서 5,000개 이상의 고빈도로 체세포배가 생산되었다. 체세포배로부터 발아유도시에 GA$_3$는 정상적인 식물체로의 재생을 억제하는 효과를 나타내었으며, 정상적인 식물체 재생은 1/2희석 SH배지에서 양호하였다, 신초와 뿌리를 갖는 유식물체를 모래와 원예용상토(5:1, vol)가 혼합된 토양이 함유된 포트에 이식하여 1개월 후 58%의 생존율을 나타내었다. 이상의 결과를 활용하면 체세포배로부터 금낭화의 묘목을 대량생산 할 수 있을 것으로 생각된다.

• Nuclear Engineering and Technology
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• 제51권8호
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• pp.1897-1904
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• 2019

Three-layer back propagation network (BPN) and genetic neural network (GNN) were developed in this study to predict the flow boiling heat transfer coefficient (HTC) in conventional and small-diameter channels. The GNN has higher precision than BPN (with root mean square errors of 17.16% and 20.50%, respectively) and other correlations. The inputs include vapor quality x, mass flux G, heat flux q, diameter D and physical parameter φ, and the predicted flow boiling HTC is set as the outputs. Influences of input parameters on the flow boiling HTC are discussed based on the trained GNN: nucleate boiling promoted by a larger saturated pressure, a larger heat flux and a smaller diameter is dominant in small channels; convective boiling improved by a larger mass flux and a larger vapor quality is more significant in conventional channels. The HTC increases with pressure both in conventional and small channels. The HTC in conventional channels rises when mass flux increases but remains almost unaffected in small channels. A larger heat flux leads to the HTC growth in small channels and an increase of HTC was observed in conventional channels at a higher vapor quality. HTC increases inversely with diameter before dry out.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.831-847
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• 2012

Impact from water-borne debris during tsunami and flood events pose a potential threat to structures. Debris impact forces specified by current codes and standards are based on rigid body dynamics, leading to forces that are dependent on total debris mass. However, shipping containers and other debris are unlikely to be rigid compared to the walls, columns and other structures that they impact. The application of a simple one-dimensional model to obtain impact force magnitude and duration, based on acoustic wave propagation in a flexible projectile, is explored. The focus herein is on in-air impact. Based on small-scale experiments, the applicability of the model to predict actual impact forces is investigated. The tests show that the force and duration are reasonably well represented by the simple model, but they also show how actual impact differs from the ideal model. A more detailed three-dimensional finite element model is also developed to understand more clearly the physical phenomena involved in the experimental tests. The tests and the FE results reveal important characteristics of actual impact, knowledge of which can be used to guide larger scale experiments and detailed modeling. The one-dimensional model is extended to consider water-driven debris as well. When fluid is used to propel the 1-D model, an estimate of the 'added mass' effect is possible. In this extended model the debris impact force depends on the wave propagation in the two media, and the conditions under which the fluid increases the impact force are discussed.

• 터널과지하공간
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• 제21권1호
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• pp.66-81
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• 2011

암반 내 균열 생성, 진전, 파괴 등과 같은 지하 암반의 역학적 거동과 이들 균열을 통한 지하수 유동 및 온도 변화에 기인한 열응력이 역학적 거동에 미치는 상호작용을 모델링하기 위한 수치해석코드를 개발하였다. 개발된 수치해석코드에서는 기존의 2차원 FRACOD(Shen & Stephasson, 1993)에 열-역학 및 수리-역학 상호 거동을 모델링하기 위한 해석모듈을 개발하여 추가하였다. 열-역학 연계를 위해서는 가상열원법과 시간전진기법을 도입하였으며, 수리-역학 연계에서는 양해법에 의한 반복기법을 적용하였다. 수치해석결과와 해석해와의 비교를 통해 개발된 해석모듈의 유용성을 검증하고 해석사례를 통해 온도변화에 따른 열균열 발생 및 수압파쇄과정에서의 균열 진전 양상과 같은 절리암반 복합거동을 잘 표현할 수 있음을 확인하였다.

• 한국자원식물학회:학술대회논문집
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• 한국자원식물학회 2019년도 춘계학술대회
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• pp.44-44
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• 2019

This study aimed to develop a suitable method for inducing the proliferation of prothallus and producing sporophytes of rock polypody (Polypodium vulgare L.). The prothalli used in all experiments were obtained from spore germination and sub-cultured for 8-week intervals. The most appropriate media for prothallus propagation were investigated by culturing 300 mg of prothallus in MS ($1/4{\times}$, $1/2{\times}$, $1{\times}$, and $2{\times}$ strength) medium and in Knop medium for 8 weeks. Cultures were maintained at a temperature of $25{\pm}1^{\circ}C$, light intensity of $30{\pm}1.0{\mu}mol-m-2{\cdot}s-1$, and a photoperiod of 16/8 h (light/dark). Fresh weight of prothalli was 4.8 g on $1{\times}$ MS, 4.5 g on $1/2{\times}$ MS and 4.3 g on 1/4 MS medium. To select a suitable soil combination for sporophyte formation, 1.0 g of prothallus was ground with distilled water, spread in five combinations onto different soil substrates (decomposed granite, horticultural substrates, peat moss, and perlite), and then cultivated for 13 weeks. The sporophyte cultures were maintained at a temperature of $25{\pm}1^{\circ}C$, light intensity of $43{\pm}2.0{\mu}mol-m-2{\cdot}s-1$, humidity of $84{\pm}1.4%$, and a photoperiod of 16/8 h (light/dark). The results showed that a mixture containing a 2:1 (v:v) ratio of horticultural substrate and perlite, increased sporophyte formation to 462.5 sporophytes per pot (7.5 cm2). The other soil substrates produced from 314.5 to 405.3 sporophytes per pot. Therefore, our results will provide conditions suitable for mass production of Polypodium vulgare L.

• 자원환경지질
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• 제9권4호
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• pp.213-223
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• 1976

해저(海底) 지층(地層)에서의 탄성파(彈性波)의 전파(傳播)와 감쇠(減衰)에 관하여 현재까지 부분적(部分的)으로 알려져있는 연구 결과(決果)를 토대로, 기본이론(基本理論)으로 부터 실제(實際)문제까지 재정리(再整理)를 시도(試圖)하였다. 탄성파(彈性波)의 기본(基本) 관계식을 유도(誘導)하고 해수내(海水內)에서의 전파(傳播), 해저면(海底面)에 의한 탄성파(彈性波)의 반향(反響)과 퇴적물(堆積物)의 물리적성질(物理的性質)의 관계(關係)를 다루었다.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1692-1701
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• 2001

This study describes the combustion characteristics under various condition of air excess ratio and ignition timing in a 2-valve SI optically accessible engine with swirl control valve(SCV). It adapted three different types of SCV(open ratio 72.5%, 78%, 59%) to strengthen a swirl flow. Pressure data were acquired using pressure sensor to investigate the effect of swirl flow on combustion, and from these pressure data, IMEP(indicated mean effective pressure) and MFB(mass fraction burnt) were calculated to explain burn rate and flame speed. From acquired flame images, we inspected the flame propagation direction, flame area, and flame centroid. Flame propagation direction showed different tendency between with/without SCV, and flame area with SCV was faster and larger than that of conventional engine. Finally, the representative flame images at each crank angle were acquired by PDF method to verify flame growth process. It is found that strengthened swirl flow is more beneficial for faster and stable combustion.

• Geomechanics and Engineering
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• 재33권6호
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• pp.529-542
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• 2023

Wave propagation with high transverse deflection could affect the stability of the ball in its trajectory. For low stiffness balls similar to soccer and volleyball balls, the waves are more noticeable in comparison to other balls like ping-pong ball. On the other hand, the soccer balls are under heavy impact loads from shoots and contacting different objects in the field. The maximum recorded speed of a soccer ball after kicking is the 211 km/hr and the average maximum speed is around 112 km/hr. Therefore, in such speeds the aerodynamic forces become important which are directly related to geometrical shape of the ball. In this regard, the wave propagation in soccer ball is examined in the current study using large deformation shear deformable formulations. Classical relations of stress-strain components are taken into consideration along with minimum total energy principle. The final derived relations were solved by using harmonic differential quadrature method. The results are generally presented ion term of phase velocity as function of different influencing parameters of the materials, geometry and mass of the ball.

• Earthquakes and Structures
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• 제5권6호
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• pp.753-779
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• 2013

One of the most important issues in progressive collapse mechanism of the buildings is evaluation of the collapse distribution in presence of the earthquake loads. Here, collapse propagation is investigated by tracking down the location and type of the collapsed beam and column elements, from the first element to the entire buildings. 6-story reinforced concrete ordinary moment resisting frame buildings with one directional mass eccentricity of 0%, 5%, 15% and 25% are studied to investigate differences among the progressive collapse mechanism of the regular and irregular buildings. According to the results of the nonlinear time history analyses, there are some patterns to predict progressive collapse scenarios in beam and column elements of the similar regular and irregular buildings. Results also show that collapse distribution patterns are approximately independent of the earthquake records.