• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 한국방사성폐기물학회 2009년도 학술논문요약집
• /
• pp.187-187
• /
• 2009

Opening of fractures induced by shear dilation or normal deformation can be a significant source of fracture permeability change in fractured rock, which is important for the performance assessment of geological repositories for spent nuclear fuel. As the repository generates heat and later cools the fluid-carrying ability of the rocks becomes a dynamic variable during the lifespan of the repository. Heating causes expansion of the rock close to the repository and, at the same time, contraction close to the surface. During the cooling phase of the repository, the opposite takes place. Heating and cooling together with the, virgin stress can induce shear dilation of fractures and deformation zones and change the flow field around the repository. The objectives of this work are to examine the contribution of thermal stress to the shear slip of fracture in mid- and far-field around a KBS-3 type of repository and to investigate the effect of evolution of stress on the rock mass permeability. In the first part of this study, zones of fracture shear slip were examined by conducting a three-dimensional, thermo-mechanical analysis of a spent fuel repository model in the size of 2 km $\times$ 2 km $\times$ 800 m. Stress evolutions of importance for fracture shear slip are: (1) comparatively high horizontal compressive thermal stress at the repository level, (2) generation of vertical tensile thermal stress right above the repository, (3) horizontal tensile stress near the surface, which can induce tensile failure, and generation of shear stresses at the comers of the repository. In the second part of the study, fracture data from Forsmark, Sweden is used to establish fracture network models (DFN). Stress paths obtained from the thermo-mechanical analysis were used as boundary conditions in DFN-DEM (Discrete Element Method) analysis of six DFN models at the repository level. Increases of permeability up to a factor of four were observed during thermal loading history and shear dilation of fractures was not recovered after cooling of the repository. An understanding of the stress path and potential areas of slip induced shear dilation and related permeability changes during the lifetime of a repository for spent nuclear fuel is of utmost importance for analysing long-term safety. The result of this study will assist in identifying critical areas around a repository where fracture shear slip is likely to develop. The presentation also includes a brief introduction to the ongoing site investigation on two candidate sites for geological repository in Sweden.

• Journal of the Korea Institute of Building Construction
• /
• 제17권1호
• /
• pp.39-46
• /
• 2017

In this research, considering the practical conditions at field, thermal cracking reducing method was suggested based on the comparative analysis between predicted value and actual value obtained from the actual structure member with optimum mix design. The optimum mix design was deduced from the various mix designs with various proportions of cementitious binder for upper and lower placement lifts of mat-foundation mass concrete. Therefore, before field applications, the mix designs were obtained from the theoretical analysis obtained by MIDAS GEN for upper lift was OPC to FA of 85 to 15, and for lower lift was OPC to FA to BS of 50 : 20 : 30. Based on this mix design, the actual concrete for field was determined and all concrete properties were reached within the predicted range. Especially, the temperature properties of mass concrete at core was approximately $39^{\circ}C$ of temperature difference for low-heat mix design, while approximately $54^{\circ}C$ was shown for normal mix design currently used. Additionally, in the case of cracking index, the low heat mix design showed about 1.4 of relatively high value while the normal mix design showed 1.0. Therefore, it can be stated that applying low heat mix design and different heating technique between upper and lower placement lifts for mass concrete are efficient to control the thermal cracking.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• 제30A권7호
• /
• pp.47-59
• /
• 1993

The thermal stability of "stuffed" TiN/Ti barrier matals with different annealing history has been studied to improve the contact reliability of Al/Si contacts in 16M DRAM. The annealing conditions before the Al deposition such as film thickness, the annealing temperature and the annealing ambient have been varied. For TiN(900A)/Ti(300A) annealed at 450 in nitrogen ambient to form a "stuffed barrier" by inducing oxygen atoms into grain boundaries, there is no observation of Al penetrations into Si substrates after the post heat treatment of up to 700 even though there are massive amounts of Al found in TiN film after the post heat treatment of 600 indicating that TiN has a "sponge-like" function due to its ability to absorb several amounts of aluminum at elevated temperature. The TiN/Ti diffusion barrier annealed at 550 has, however, failed after the post heat treatment at 600. The thinner diffusion barriers with TiN(300A)/Ti(100A) failed after the post heat treatment at 600.he post heat treatment at 600.

• Journal of Astronomy and Space Sciences
• /
• 제31권1호
• /
• pp.83-90
• /
• 2014

The NISS onboard NEXTSat-1 is being developed by Korea astronomy and space science institute (KASI). For the study of the cosmic star formation history, the NISS performs the imaging spectroscopic observation in the near-infrared range for nearby galaxies, low background regions, star-forming regions and so on. It is designed to cover a wide field of view ($2{\times}2$ deg) and a wide wavelength range from 0.95 to $3.8{\mu}m$ by using linear variable filters. In order to reduce the thermal noise, the telescope and the infrared sensor are cooled down to 200 K and 80 K, respectively. Evading a stray light outside the field of view and making the most use of limited space, the NISS adopts the off-axis reflective optical system. The primary and the secondary mirrors, the opto-mechanical part and the mechanical structure are designed to be made of aluminum material. It reduces the degradation of optical performance due to a thermal variation. This paper presents the study on the conceptual design of the NISS.

• Journal of Korean Society of Steel Construction
• /
• 제13권4호
• /
• pp.327-335
• /
• 2001

The characteristics and production mechanism of residual stress generated by multi-pass welding of the steel pipe were elucidated from the results of three-dimensional thermal elastic-plastic FEM analysis. When the steel pipe was jointed by multi-pass welding, the stress components of circumferential direction and radial direction near welded joints on the inner surface and the outer surface of the pope were tensile. The stress component of axial direction on the inner surface was tensile and on the outer surface was compressive. On the other hands, the production mechanism of residual stress generated by multi-pass welding of the steel pipe was investigated. Residual stress generated by welding of the steel pipe was investigated not only by the thermal history but also by geometrical shape. Then, the generality of the production mechanism of residual stress generated by multi-pass welding was confirmed.

• Proceedings of the KWS Conference
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.675-680
• /
• 2002

Cracking and bulging in welded and internally lined pressure vessels that work in thermal-mechanical cycling service have been well known problems in the petrochemical, power and nuclear industries. However, published literature and industry surveys show that similar problems have been occurring during the last 50 years. A better understanding of the causes of cracking and bulging causes is needed to improve the reliability of these pressure vessels. This study attempts to add information required for increasing the knowledge and fundamental understanding required. Typical examples of this problem are the coke drums in the delayed coking units refinery process. This case was selected for experimental work, field study and results comparison. Delayed coking units are among the refinery units that have higher economical yields. To shut down these units represents a high negative economical impact in refinery operations. Also, the maintenance costs associated with repairs are commonly very high. Cracking and bulging occurrences in the coke drums, most often at the weld areas, characterize the history of the operation of delayed coking units. To design and operate more robust coke drums with fewer problems, an improved metallurgical understanding of the cracking and bulging mechanisms is required. A methodology that is based field experience revision and metallurgical analyses for the screening of the most important variables, and subsequent finite element analyses to verify hypotheses and to rank the variables according to their impact on the coke drum lives has been developed. This indicated approach provides useful information for increasing coke drum reliability. The results of this work not only order the most important variables according to their impact in the life of the vessels, but also permit estimation of the life spans of coke drums. In conclusion, the current work shows that coke drums may fail as a combination of thermal fatigue and other degradation mechanisms such as: corrosion at high and low temperatures, detrimental metallurgical transformations and plastic deformation. It was also found that FEA is a very valuable tool for understanding cracking and bulging mechanisms in these services and for ranking the design, fabrication, operation and maintenance variables that affect coke drum reliability.

• Transactions of the Korean Society of Automotive Engineers
• /
• 제14권2호
• /
• pp.174-183
• /
• 2006

The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The role of this rigid beam is simply to transfer the load across the welded components. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. The load calculated from the precise finite element model of the spot-welded region considering the residual stress due to the thermal history during the spot welding procedure is regarded as the reference value and the value of the load is compared with the one obtained from the spot-welded model using the rigid beam with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.

• Journal of the Korean Geosynthetics Society
• /
• 제8권1호
• /
• pp.53-59
• /
• 2009

A new system of modified freeze-thaw testing apparatus is introduced. This system is developed to evaluate the geotechnical parameters and their dependence upon freezing-thawing history of frost-susceptibility soil. A necessary condition for stationary frost heaving is clarified in this paper. The method changes the thermal boundary condition up to the net heat flow at the freezing frost becomes zero. The effectiveness of this method is verified by freeze-thaw tests. Frost heaving observed after the application of the method is found to be due to another frost heaving action called long-term frost heaving. This frost heaving has already been studied and is considered ignorable as engineering factor because of its small heaving amount.

• Journal of Adhesion and Interface
• /
• 제3권3호
• /
• pp.15-21
• /
• 2002

The modified polyethylene(m-PE) films were prepared from aqueous dispersions which were synthesized by reacting poly(ethylene-co-methylacrylate) with aqueous KOH and ammonia solution to attach -COOK, $CONH_2$, and COOH as pendent groups in the polyethylene backbones. Thermal, tensile and heat-seal properties were measured to investigate the effect of the pendent groups. Endothermic peaks on DSC curves were affected by the thermal history of the samples and a melting peak was observed at around $86^{\circ}C$ on the second heating curve while three melting peaks were shown on the first heating curve. A minimum value of tensile strength was shown at 70 mole% of COOK based on pendent groups. Tensile modulus increased with increasing the amide content in pendent groups. The m-PE films were heat-sealed at lower temperature than LDPE films and showed a minimum heat seal strength at around 70 mole% COOK content in pendent groups.

• Solar Energy
• /
• 제15권1호
• /
• pp.13-28
• /
• 1995

In this study, the history of Korean traditional Ondol was investigated and the latent heat materials and bioceramics were selected to develop the latent heat storage-bioceramics Ondol system based on the Korean traditional Ondol(sensible heat storage type), and the thermal characteristics of Ondol were analyzed experimentally The results could be summarized as follows; 1. Korean traditional Ondol has been originated in "Whaduk" which had been utilized continuously for about $2{\times}10^6$ years from the Old Stone Age to the Bronze Age, and Korean traditional Ondol using in these days has been utilized for about 976 years from the Koryu Dynasty to the Modern Ages. 2. $Na_2SO_4{\cdot}10H_2O(SSD)$ was selected as latent heat material for the latent heat storage Ondol. 3. Ondol unit was filled with the latent heat material of 0.63 kg and the dimension of Ondol unit was $400mm{\times}400mm{\times}27mm(width{\t\imes}depth{\times}height)$. 4. The comfortable surface temperature($23{\sim}29^{\circ}C$) of the latent heat storage Ondol was lasted 5 hours at the room temperature of $16{\sim}18^{\circ}C$, whereas that of sensible heat storage Ondol was lasted only 1.0 hours in the same conditions. 5. For the thermal effect of bioceramics, the Ondol air temperature i.n case of bioceramics treatment on the pannel was higher than that of without bioceramics treatment.