• Proceedings of the KSME Conference
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• 2001.11b
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• pp.729-734
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• 2001

Thermal stratification due to turbulence penetration and in-leakage of valve cause the large thermal stress, which lead to fatigue crack of the piping system of nuclear power plant. So it is needed that numerical and experimental study for the phenomenon is conducted because there have not yet been sufficient study for the relationship between turbulence penetration and thermal stratification. Therefore numerical analysis is done here and respected to give a fundamental method of the approach to the phenomenon.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.2
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• pp.51-60
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. Standard k-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.3
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• pp.239-245
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. $textsc{k}$-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of the main flow in the duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from the main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.230-231
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• 2014

This study is concerned with the root penetration resistance competence and constructability of a waterproofing and root penetration resistance layer of an eco-bridge which is applied with various types of seeding. For the review of root penetration resistance competence, the competence was tested using herbs, woody plants, and tall trees. As a result, there was no tear of or damage to the waterproofing and root penetration resistance layer as well as the sweeping-down phenomenon of a waterproofing and root penetration resistance layer by soil. Also, the effect of the root growth of herbs, woody plants, and tall trees on the root penetration resistance system was confirmed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.188-189
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• 2014

Nowadays, many research execute about sandwich-insulation wall for durability of wall and retaining insulation performance. But sandwich-insulation, different exterior and interior insulation, need to form-tie which supporting both side form. And because of it penetrate concrete wall, it is worried about thermal-bridge phenomenon to form-tie. So, this research classify penetration type and buried type and analysis thermal-phenomenon of each type's form-tie and insulation performance. As a result, all form-tie type little occur thermal-bridge but penetration form-tie have superior insulation performance and low U-value.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.1-8
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• 2014

In this study, the numerical simulation using AUTODYN-3D program was investigated angle trajectory prediction for inclined impacts of projectiles. The penetration and perforation of polycarbonate plate by 7.62 mm projectile was investigated numerically. The characteristic structure of the projectile's trajectory in the polycabonate plates was studied. Two combined failure criteria were used in the target plate, and the target plate was modeled with the properties of polycarbonate for simulating the ricochet phenomenon. The effect of the angle of inclination on the trajectory and kinetic energy of the projectile were studied. The dynamic deformation behaviors tests of polycabonate were compared with numerical simulation results which can be used as predictive purpose. From the simulation, the ricochet phenomenon was occurred for angles of inclination of $0^{\circ}{\leq}{\theta}{\leq}20^{\circ}$. The projectile perforated the plate for ${\theta}{\leq}30^{\circ}$, thus defining a failure envelope for numerical configuration. The numerical analyses are used to study the effect of the projectile impact velocity on the depth of penetration (DOP). It can be observed that the residual velocities were almost linear relative to penetration velocities. It means that polycarbonate has high resistance at higher velocities.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1738-1747
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• 2003

Smoothed Particle Hydrodynamics (SPH), a pure Lagrangian numerical method, is applied to analysis of penetration phenomenon of bumper plate which is installed outside of spacecraft hull to protect the spacecraft against hypervelocity meteorite impact. Effects of SPH parameters, such as artificial viscosities, smoothing lengths, numbers of particles and time increments, are analysed by comparing the SPH simulation results with experimental ones with regard to subsequent formation of debris cloud. An optimum range of parameter values is determined by error analysis and various SPH numerical results are compared with experiments.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.77.1-77.1
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• 2010

Durability problems of gas diffusion layer(GDL) is one of the important issues for accomplishing commercialization of proton exchange membrane fuel cell(PEMFC). GDL is strongly related to the performance of PEMFC because one of the main function of GDL is to work as a path of fuel, air and water. When the GDL is degraded, it causes water balance problems such as the flooding phenomenon. Thus, investigating the durability characteristics of the GDL is important and understanding the GDL degradation process is needed. In this study, the GDLs are degraded by carbon corrosion stress method which is the electrochemical degradation mode. To determine the effects of carbon corrosion of the GDL, 1.45 V of potential is imposed for 96 hours. In this manner, in the previous research, the structure between the substrate and the MPL is weaken. Further investigations are needed to clarify this phenomenon. Therefore, in this study, the carbon corrosion stress method is carried out with GDLs which have various MPL penetration levels and the effects of the MPL penetration level on the characteristics change of the GDL are analyzed. The changes in characteristics are measured with various properties of GDL such as weight, thickness and static contact angle. The degraded GDL shows loss of their properties.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.1
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• pp.137-142
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• 2005

Gas-Assisted Injection Molding(GAIM) is an innovative technology for producing plastic parts and has been received extensive attention in the plastic manufacturing industries. But, due to gas-polymer interacting during the gas injection phase, the process has significantly different characteristics from conventional injection molding and, therefore, the control of the process requires much technical knowledge in processing and materials. The experiment was performed about variations of gas-penetration length that is affected by filling imbalance resulting from the structure of runner. The Taguchi method was used for the design of experiment. The most effective factors for the gas-penetration length were the shot size and mold temperature. The most effective factors for the difference of the gas-penetration length were the melt temperature and shot size. This study also discussed the filling imbalance phenomenon in a unary branch runner type mold that has geometrically balanced runner.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.2
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• pp.25-33
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• 2016

The thermal stratification phenomenon in the nuclear power plant can cause abnormal deformation of the piping, contact with the support, damage to the support system. Repetition of the thermal stratification phenomenon or variation of the thermal boundary layer can cause thermal fatigue. Thermal stratification phenomenon in nuclear power plants is still an ongoing issue and active research has been carried out. In this paper, the current situation in Korean nuclear power plants is described, followed by the status of research and the future problems on the thermal stratification phenomenon in Korea.