개별요소법(DEM)과 네트워크 모델을 이용한 불포화토의 열전달 거동에 관한 연구
- 주제(키워드) 유효 열전도도 , 네트워크 모델 , 개별요소법 , 불포화토
- 발행기관 고려대학교 대학원
- 지도교수 최항석
- 발행년도 2012
- 학위수여년월 2012. 2
- 학위구분 석사
- 학과 일반대학원 건축·사회환경공학과
- 원문페이지 111 p
- 실제URI http://www.dcollection.net/handler/korea/000000033447
- 본문언어 한국어
- 제출원본 000045696141
초록/요약
Thermal conduction of the particulate composites or granular materials can be widely used in porous materials, geotechnical engineering and etc. Especially, thermal conduction in soils has been highlighted in a geotechnical engineering such as geothermal energy, buried earth-structures, radioactive waste disposal, geological sequestration of carbon dioxide and hydrocarbon energy recovery (Yun and Evans, 2010). And it has been continued to develop “effective thermal conductivity” of medium by modelling energy relationship among particles in medium. The classical effective medium approximations for evaluating the effective thermal conductivity of particulate composites or granular materials can be broadly classified as: the Maxwell model (maxwell’s approximation based models; Maxwell, 1873), Self-consistent model (Landauer, 1952) and Different effective medium (Bruggeman’s asymmetric model (BAM), Bruggeman, 1935; Landauer, 1952). Such models will enable one to optimize the structure and arrangement of the material (Kanuparthi et al., 2008). It has been suggested that thermal conductivity of soils is dominated by soil properties and boundary conditions such as grain size and shape, mineralogy, porosity, coordination number, pore fluid characteristics, overburden stress and drainage conditions (Gangadhara and Singh, 1999; Singh and Devid, 2000; Tarnawaski et al., 2002; Weidenfeld et al., 2004; Yun and Evans, 2010). Thus, the multi-scale governing factors as well as the heterogeneity and complex configuration of particle skeleton often challenge the accurate estimation and interpretation of thermal conductivity in soils (Yun and Evans, 2010). This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the novel network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at the various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From the series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. However, thermal conductivity from the modified network model at the relatively dried zone (5~20% in degree of saturation) shows slightly higher values than experimental values. It seems that the equivalent radius of thermal cylinder at particles becomes smaller values at relatively dried zone. And an empirical correlation between the fraction of the mean radius (χ) and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conducvity of the granular soils, to estimate thermal conductivity of granular soils.
more목차
Abstract I
목 차 III
그림목차 IV
표목차 VII
제 1장. 서론 1
1.1 개요 1
1.2 연구목적 및 범위 6
1.3 논문구성 7
제 2장. 이론적 배경 8
2.1 기존 열전도 모델 8
2.2.1 Maxwell’s Approximation 9
2.2.2 Self-Consistent Approximaion 12
2.2.3 Differential Effective-Medium Approximation 16
2.2.4 Kersten model 19
2.2.5 Johansen model 22
2.2 네트워크(network) 모델 24
2.2.1 네트워크 모델 적용을 위한 입자간 전도력 산정 27
제 3장. 실내 열전도도 측정 및 불포화 특성 곡선 36
3.1 시료의 기본 물성 36
3.1.1 글라스비즈의 기본 물성 36
3.1.2 주문진규사의 기본 물성 40
3.2 열전도도 측정 41
3.2.1 비정상 열선법 44
3.3 흙의 불포화 특성 48
3.3.1 배경이론 48
3.3.2 흙-수분 특성곡선(SWCC) 53
3.3.3 Van Genuchten (VG) 모델(1980) 57
3.3.4 압력판 추출시험 59
3.4 실내 열전도도 및 불포화 특성 곡선 측정 결과 62
제 4장. 네트워크 모델을 이용한 열전달 해석 68
4.1 PFC3D 프로그램 68
4.2 시험 시료에 대한 3차원 개별요소 입자 생성 72
4.3 네트워크 모델을 이용한 입자간 열전달 해석 알고리즘 76
4.4 불포화 상태를 고려한 네트워크 모델 78
4.4.1 포화상태의 χ로 정규화된 불포화 열전달 해석 78
4.4.2 SWCC를 이용한 불포화 열전달 해석 83
제 5장. 결론 95
References 98
