• Proceedings of the KSME Conference
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• 2003.11a
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• pp.916-921
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• 2003

In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method(FVM). This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications.

• Corrosion Science and Technology
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• v.11 no.4
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• pp.151-156
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• 2012

The cavity formed by the ultrasonic generation in the fluid with the application of water cavitation peening collides into the metal surface. At this time, the surface modification effect such as the work hardening presents by the compressive residual stress formed due to the localized plastic deformation. In this investigation, the water cavitation peening technology in the distilled water with the lapse of time was applied to 5052-O aluminum alloy for aluminum ship of a high value. So, the optimum water cavitation peening time on the effect for surface hardening and anti-corrosion property was investigated. Consequently, the water cavitatin peening time on excellent hardness and corrosion resistance characteristic presented 3.5 min. and 5.0 min, respectively. The surface hardness in the optimum water cavitation peening time was improved approximately 45% compared to the non-WCPed condition. In addition, corrosion current density was decreased.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.713-718
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• 1997

In the TMI-2 accident, approximately twenty(20) tons of molten core material drained into the lower plenum. Early advanced light water reactor (LWR) designs assumed a lower head failure and incorporated various measures for ex-vessel accident mitigation. However, one of the major findings from the TMI-2 Vessel Investigation Project was that one part of the reactor lower head wall estimated to have attained a temperature of 1100$^{\circ}C$ for about 30 minutes has seemingly experienced a comparatively rapid cooldown with no major threat to the vessel integrity. In this regard, recent empirical and analytical studies have shifted interests to such in-vessel retention designs or strategies as reactor cavity flooding, in-vessel flooding and engineered gap cooling of the vessel Accurate thermohydrodynamic and creep deformation modeling and rupture prediction are the key to the success in developing practically useful in-vessel accident/risk management strategies. As an advanced in-vessel design concept, this work presents the COrium Attack Syndrome Immunization Structures (COASIS) that are being developed as prospective in-vessel retention devices for a next-generation LWR in concert with existing ex-vessel management measures. Both the engineered gap structures in-vessel (COASISI) and ex-vessel (COASISO) are demonstrated to maintain effective heat transfer geometry during molten core debris attack when applied to the Korean Standard Nuclear Power Plant(KSNPP) reactor. The likelihood of lower head creep rupture during a severe accident is found to be significantly suppressed by the COASIS options.

• Magazine of korean Tunnelling and Underground Space Association
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• v.1 no.2
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• pp.59-71
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• 1999

Recently, many deformations in tunnel such as crack and leakage were occulted. Specially, the defects of tunnel lining have been a serious problem in safety and stability many repair works for maintenance in tunnel have been carried out. Therefore, it is necessary to estimate the structural cracking for countermeasure in deformed tunnel and to investigate on the characteristics of lining system and the soundness of tunnel. In this study model tests for tunnel lining were carried out using test apparatus and centrifuge, In the direct loading test, the prototype was Kyungbu high-speed railway tunnel and the scale is 1/10, and lining models were made of concrete. Test conditions included load conditions such as direction, shape and type, lining conditions such as single and double lining, thickness, and reinforcement. In centrifuge model test, the prototype was Seoul subway tunnel and the scale is 1/100, and lining models were made of aluminum and hydrostone. Test conditions included tunnel defects such as thickness shortage. behind cavity and longitudinal cracks, reinforcement methods such as epoxy, grouting and carbon sheet. From these model tests , the characteristics of deformation and failure for tunnel lining were estimated, and the structural behaviors of deformed lining and the effects of repair and reinforcement for tunnel lining were researched.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.3
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• pp.42-52
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• 1995

An UBET(Upper Bound Elemental Techniquel) program has been developed to analyze forging load, die-cavity filling and effective strain distribution for flashless non-axisymmetric forging. To analyze the process easily, it is suggested that the deforma- tion is divided into two different parts. Those are axisymmetric part in corner and plane- strain part in lateral. The total power consumption is minimized through combination of two deformation parts by building block method, form which the upper-bound forging load, the flow pattern, the grid pattern, the velocity distribution and the effective strain are deter- mined. To show the merit of flashless forging, the results of flashless and flash-forging processes are compared through theory and experiment. Experiments have been carried out with plasticine billets at room temperature. The theoretical predictions of the forging load and the flow pattern are in good agrement with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1101-1107
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• 2014

A heavy ion accelerator is a device that accelerates heavy ions in the radio frequency (RF) range. The electric field that flows into the RF cavity continuously accelerates heavy ions in accordance with the phase of the input electromagnetic wave. For the purpose, it is necessary to design a coupler shape that can stably transfer the RF wave into the cavity. The RF coupler in a heavy ion accelerator has a large temperature difference between the input port and output port, which radiates the RF waves. It is necessary to consider the heat deflection on the RF coupler that occurs as a result of the rapid temperature gradient from an ultra-low temperature about 0 K to a room temperature about 300 K. The purpose of this study was to improve the system performance through an analysis of the intensity of the output electric field and temperature distribution considering various shapes of the RF coupler, along with an analysis of the durability considering the heat deflection and heat loss.

• Journal of the Korean Geosynthetics Society
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• v.18 no.1
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• pp.91-101
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• 2019

Recently, small-scale excavation like ground cavity restoration and buried pipe replacement works are being carried out in urban area, in order to improve living convenience. This paper describes experiment results on the ground reinforcement method that can reduce the buried pipe damage, when the differential settlement occurred due to poor compaction of ground below the buried pipe. Plate load tests were conducted to evaluate a reinforcement effect of ground using concrete mat and expansion mat in the ground below the buried pipe. The results showed that the stress reduction ratio by concrete mat and expansion mat according to the surcharge load was about 46%~48% and 39%~42%, respectively. Therefore, the differential settlement of the buried pipe and the ground deformation below the buried pipes were reduced by the reinforcement effect of the concrete mat and expansion mat. This means that it is possible to prevent a buried pipe damage due to underground cavity and ground subsidence, if concrete mat and expansion mat are reinforced in the ground below the buried pipe or on the ground between the buried pipes.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.270-278
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• 1992

The effect of Ni-rich phase on the stress-rupture properties of Ni mlcroalloyed W were studied using direct load creep tester at 100$0^{\circ}C$, 110$0^{\circ}C$, and 120$0^{\circ}C$ in $H_2.$ The stress rupture strength of 100hrs. of W-0.4wt% Ni was 43% higher at 100$0^{\circ}C$ and 35% higher at 110 $0^{\circ}C$than that of W-0.2wt% Ni due to the larger initial grain size, the higher relative density and the higher grain growth during test. That of W-0.8wt% Ni was 90% higher at 100$0^{\circ}C$ and 60% higher at 110$0^{\circ}C$ than that of W-0.2wt% Ni. The activation energy of W-0.4wt% Ni for creep was 81.3 Kcal/mole. It was considered that creep deformation was controlled by the diffusion of W in the Ni rich phase between the grains and the deformation of grains. All of the specimens showed intergranular fracture by grain boundary cavitation and growth of cavity throughout the entire spcimen cross-section.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.227-236
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• 2003

The evaluation of the reliable strength and deformation characteristics of weathered granite masses is very important for the design of geotechnical structure under working stress conditions. Various types of laboratory test such as triaxial compression test can be performed to determine the strength parameters. However, it is very difficult to obtain the representative undisturbed samples on the site and also the rock specimen cannot represent rock mass including discontinuities, fracture zone, etc. This study aims to investigate the strength and deformation characteristics of granite masses corresponding to its weathering and develop a practical strength parameter evaluation method using the results of PMT. To predict weathering intensity and strength parameters of the weathered granite masess in the field, various laboratory tests and in-situ tests including field triaxial test and PMT are carried out. Based on the results of weathering index tests, the classification method is proposed to identify the weathering degree in three groups for the weathered granite masses. Using the analytical method based on the Mohr-Coulomb failure criteria and the cavity expansion theory, the strength parameters of rock masses were evaluated from the results of PMT. It shows that weathering intensity increases with decreasing the strength parameters exponentially. The strength parameters evaluated with the results of PM almost coincide with the results of field triaxial test.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.177-184
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• 2012

An optical defect detection method using ESPI(electronic speckle pattern interferometry) is proposed. ESPI is widely used as a non-contact measurement system which show deformation and phase map in real time. ESPI can be divided as the in-plane, out-of-plane and shearography by operation principle and target object and also divided with bulk type and optic fiber type by the optic configurations. This paper is focused on optic fiber type out-of-plane ESPI, which has the following advantages: (1) low cost; (2) reduction of the unreliable factors generated by separated optic components; (3) simplification of the optic configuration; (4) great reduction of volume; (5) flexibility, to be easily designed into different structures to adapt to inaccessible environments such as pipeline cavity and so on.