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Micro/macro properties of geomaterials: a homogenization method for viscoelastic problem
Ichikawa, Yasuaki,Wang, Jianguo,Jeong, Gyo-Cheol Techno-Press 1996 Structural Engineering and Mechanics, An Int'l Jou Vol.4 No.6
Geomaterials such as soil and rock are composed of discrete elements of microstructures with different grains and microcracks. The studies of these microstructures are of increasing interest in geophysics and geotechnical engineering relating to underground space development We first show experimental results undertaken for direct observation of microcrack initiation and propagation by using a newly developed experimental system, and next a homogenization method for treating a viscoelastic behavior of a polycrystalline rock.
Safe Disposal of Radioactive Wastes for Natural Disasters
( Yasuaki Ichikawa ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
Energy is an essential basis of modern human life, and nuclear powers support a major part of the energy supply for many countries. It is urgently important for sustainable supply of nuclear energy to dispose the high-level nuclear wastes (HLW) generated by the nuclear power plants. The safe disposal of HLW is planned in deep underground repositories sited several hundred meters deep. For the disaster-prone countries like Japan, the facilities of HLW disposal must be provided against the severe disasters. Especially we are discussing how to provide for the huge earthquake, like the Great East Japan Earthquake in 2011. The barrier system which prevents radionuclide migration for a long period forms an engineered barrier system (EBS, consisting of the HLW itself, vitrified wastes or spent fuel, a metal overpack and bentonite buffer) and a natural barrier, that is, the rock mass. Bentonite is the key material of the HLW barrier system, which retards the transport radionuclides for extremely long period. We will discuss the properties and behaviors of the bentonite buffer.
( Yuki Mori ),( Fumihiko Iwamoto ),( Yasuaki Ishida ),( Toru Kuno ),( Shoji Kobayashi ),( Takashi Yoshida ),( Tatsuya Yamaguchi ),( Tadashi Sato ),( Makoto Sudo ),( Daisuke Ichikawa ),( Nobuyuki Enomo 대한장연구학회 2020 Intestinal Research Vol.18 No.4
Behçet’s disease (BD) is a multisystem inflammatory disease of unknown origin. Rarely, BD occurs together with myelodysplastic syndrome (MDS). Interestingly, it is speculated that these are not simple coexistence but that the etiology of intestinal BD is at least partly derived from MDS itself. Furthermore, there is a relationship between MDS in patients with intestinal BD and trisomy 8. Immunosuppressive agents alone are insufficient to control MDS-associated BD, and many of these patients die of infection or hemorrhage. Surgery is considered for intestinal BD patients who are unresponsive to medical treatment or those with bowel complications such as perforation or persistent bleeding. We report a case of intestinal BD associated with MDS and trisomy 8. The patient was unresponsive to oral steroids and immunosuppressive treatment; the patient improved by surgical repair of a bowel perforation. Five years after the surgery, the patient is free of recurrence and not on medication. Our experience suggests that surgery may provide an effective therapeutic option for the treatment of MDS-related BD. (Intest Res 2020;18:469-475)
석영광물의 용해 및 수산화 이온의 확산에 관한 균질화해석
최정해 ( Jung Hae Choi ),( Yasuaki Ichikawa ) 대한지질공학회 2010 지질공학 Vol.20 No.3
광물의 용해현상과 밀접하게 관련된 암석의 시간의존성 변형과 파괴현상은 실내시험에서 비교적 용이하게 관찰된다. 본 연구에서는 고준위 방사성폐기물의 지하 처분장 건설시 완충제로 사용되어지는 벤토나이트에 많이 포함된 석영의 고알칼리 환경 하에서의 용해 현상을 정량적으로 관찰하기 위해서 수산화 이온의 확산과 석영의 용해 문제를 균질화 해석법을 이용하여 평가하였다. 해석결과에 의하면 석영의 용해량은 주변 환경의 온도 및 층간수의 두께와 비례한다. 특히 고알칼리환경 하에서는 층간수의 두께가 작아지면서 반응표면적이 커지게 되고 그 결과 용해 속도는 층간수의 두께가 작아질수록 커지는 결과를 나타내고 있다. Time-dependent behavior similar to secondary deformation related to mineral dissolution is easily observed when performing a laboratory pressure experiment. In this research, to observe the dissolution of quartz found in bentonite used as buffer material for the geological disposal of high-level waste (HLW) under conditions of high pH, we calculated the diffusion of OH- ions and the behavior of quartz dissolution using the homogenization analysis method. The results reveal that the rate of quartz dissolution is proportional to the temperature and interlayer water thickness. In particular, in a high-pH environment, the reacted area (and therefore the dissolution rate) increases with decreasing interlayer water thickness.
채병곤,JUNG-HAE CHOI,Yasuaki Ichikawa,YONG-SEOK SEO 한국원자력학회 2012 Nuclear Engineering and Technology Vol.44 No.1
To compute a permeability coefficient along a rough fracture that takes into account the fracture geometry, this study performed detailed measurements of fracture roughness using a confocal laser scanning microscope, a quantitative analysis of roughness using a spectral analysis, and a homogenization analysis to calculate the permeability coefficient on the microand macro-scale. The homogenization analysis is a type of perturbation theory that characterizes the behavior of microscopically inhomogeneous material with a periodic boundary condition in the microstructure. Therefore, it is possible to analyze accurate permeability characteristics that are represented by the local effect of the facture geometry. The Cpermeability coefficients that are calculated using the homogenization analysis for each rough fracture model exhibit an irregular distribution and do not follow the relationship of the cubic law. This distribution suggests that the permeability characteristics strongly depend on the geometric conditions of the fractures, such as the roughness and the aperture variation. The homogenization analysis may allow us to produce more accurate results than are possible with the preexisting equations for calculating permeability.
Chae, Byung-Gon,Choi, Jung-Hae,Ichikawa, Yasuaki,Seo, Yong-Seok Korean Nuclear Society 2012 Nuclear Engineering and Technology Vol.44 No.1
To compute a permeability coefficient along a rough fracture that takes into account the fracture geometry, this study performed detailed measurements of fracture roughness using a confocal laser scanning microscope, a quantitative analysis of roughness using a spectral analysis, and a homogenization analysis to calculate the permeability coefficient on the microand macro-scale. The homogenization analysis is a type of perturbation theory that characterizes the behavior of microscopically inhomogeneous material with a periodic boundary condition in the microstructure. Therefore, it is possible to analyze accurate permeability characteristics that are represented by the local effect of the facture geometry. The Cpermeability coefficients that are calculated using the homogenization analysis for each rough fracture model exhibit an irregular distribution and do not follow the relationship of the cubic law. This distribution suggests that the permeability characteristics strongly depend on the geometric conditions of the fractures, such as the roughness and the aperture variation. The homogenization analysis may allow us to produce more accurate results than are possible with the preexisting equations for calculating permeability.