• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.4
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• pp.468-475
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• 2019

An end-line flame arrester allows free venting in combination with flame protection for vertical vent applications. End-line flame arresters are employed in various fields, especially in shipping. In flame arresters, springs are essential parts because the spring load and the spring's elasticity determine the hood opening moment. In addition, the spring has to work under a high-temperature condition because of the burning gas flame. Therefore, it is necessary to analyze the mechanical load and elasticity of the spring when the flame starts to appear. Based on simulations of the working process of a specific end-line flame arrester, a thermal and structural analysis of the spring is performed. A three-dimensional model of a burned spring is built using computational fluid dynamics (CFD) simulation. Results of the CFD analysis are input into a finite element method simulation to analyze the spring structure. The research team focused on three cases of spring loads: 43, 93, and 56 kg, correspondingly, at 150 mm of spring deflection. Consequently, the spring load was reduced by 10 kg after 5 min under a $1,000^{\circ}C$ heat condition. The simulation results can be used to predict and estimate the spring's load and elasticity at the burning time variation. Moreover, the obtained outcome can provide the industry with references to optimize the design of the spring as well as that of the flame arrester.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.75-86
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• 2019

The biggest obstacle in the nuclear power generation is the high level radioactive waste such as the spent nuclear fuel. High level radioactivities and generated heat make the safe treatment of the spent nuclear fuel very difficult. Nowadays, the only treatment method is a deep geological disposal technology. This paper treats the structural safe design problem of the spent nuclear fuel disposal canister which is one of the core technologies of the deep geological disposal technology. Especially, this paper executed the nonlinear structural analysis for the stresses and deformations occurring in the canister due to the impulsive force applied to the spent nuclear fuel disposal canister in the case of an accidental drop and ground impact event from the transportation vehicle in the repository. The main content of the analysis is about that the impulsive force is obtained using the commercial rigid body dynamic analysis computer code, RecurDyn, and the stress and deformation caused by this impulsive force are obtained using the commercial finite element static structural analysis computer code, NISA. The analysis results show that large stresses and deformations may occur in the canister, especially in the rid or the bottom of the canister, due to the impulsive force occurring during the collision impact period.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.488-496
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• 2023

Ship and bridge structures are a type of long box-shaped structure, and resistance to vertical bending moment is a key factor in their structural design. In particular, because box girders are repeatedly exposed to irregular wave loads for a long time, the continuous collapse behavior of structural members must be accurately predicted. In this study, plastic collapse behavior, including buckling according to load changes of the box girder receiving pure bending moments, was analyzed using a numerical analysis method. The analysis targets were selected as three box girders used in the Gordo experiment. The cause of the difference was considered by comparing the results of the structural strength experiment with those of non-linear finite element analysis. This study proposed a combination of the entire and local sagging shape to reflect the effect of the initial sagging caused by welding heat that is inevitably used to manufacture carbon steel materials. The procedures reviewed in the study and the contents of the initial sagging configuration can be used as a good guide for analyzing the final strength of similar structures in the future.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.189-207
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• 2023

In the present study, the thermoshearing experiment on a rough rock fracture were modeled using a three-dimensional grain-based distinct element model (GBDEM). The experiment was conducted by the Korea Institute of Construction Technology to investigate the progressive shear failure of fracture under the influence of thermal stress in a critical stress state. The numerical model employs an assembly of multiple polyhedral grains and their interfaces to represent the rock sample, and calculates the coupled thermo-mechanical behavior of the grains (blocks) and the interfaces (contacts) using 3DEC, a DEM code. The primary focus was on simulating the temperature evolution, generation of thermal stress, and shear and normal displacements of the fracture. Two fracture models, namely the mated fracture model and the unmated fracture model, were constructed based on the degree of surface matedness, and their respective behaviors were compared and analyzed. By leveraging the advantage of the DEM, the contact area between the fracture surfaces was continuously monitored during the simulation, enabling an examination of its influence on shear behavior. The numerical results demonstrated distinct differences depending on the degree of the surface matedness at the initial stage. In the mated fracture model, where the surfaces were in almost full contact, the characteristic stages of peak stress and residual stress commonly observed in shear behavior of natural rock joints were reasonably replicated, despite exhibiting discrepancies with the experimental results. The analysis of contact area variation over time confirmed that our numerical model effectively simulated the abrupt normal dilation and shear slip, stress softening phenomenon, and transition to the residual state that occur during the peak stress stage. The unmated fracture model, which closely resembled the experimental specimen, showed qualitative agreement with the experimental observations, including heat transfer characteristics, the progressive shear failure process induced by heating, and the increase in thermal stress. However, there were some mismatches between the numerical and experimental results regarding the onset of fracture slip and the magnitudes of fracture stress and displacement. This research was conducted as part of DECOVALEX-2023 Task G, and we expect the numerical model to be enhanced through continued collaboration with other research teams and validated in further studies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.575-582
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• 2010

In recent years, several rapid-mold-heating techniques that can be used for the injection molding of thin-walled parts or micro/nano structures have been developed. High-frequency induction heating, which involves heating by electromagnetic induction, is an efficient method for the rapid heating of mold surfaces. The present study proposes an integrated numerical model of the high-frequency induction heating process and the resulting injection molding process. To take into account the effects of thermal boundary conditions in induction heating, we carry out a fully integrated numerical analysis that combines electromagnetic field calculation, heat transfer analysis, and injection molding simulation. The proposed integrated simulation is extended to the injection molding of a thin-wall part, and the simulation results are compared with the experimental findings. The validity of the proposed simulation is discussed according to the ways of the boundary condition imposition.

• Journal of the Korea Furniture Society
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• v.24 no.1
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• pp.60-69
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• 2013

Timber is an eco-friendly material that is suitable for low carbon and green growth, and recently, studies on utilization and manufacture of timber are increasing. Thus, we need a stable supply of wood working materials for the formative element and widespread function of timber. It is necessary to develop the use of timber because it enhances the added value of this material by making the most of it. In this way, skin-timber is an appropriate material for life articles because skin-timber has a variety of functions including the ability for storage use, the beauty of structure, the ability to maintain heat and insulation, and the capability to control humidity. In this study, I developed household items using skin-timbers that are made up of circular columns and square columns of pine, larch, and yellow popular. The circular and square columns have an inner hole that is approximately 90% of the external structure's width. I intended for the concept of these designs to display creativity considering functionality and productivity. These items are life articles and furniture for modern people. They are eco-friendly products that are varnished with traditional lacquer and natural oil. According to the result of this study, skin-timbers are made of domestic pine, larch, and yellow popular and are resource of furniture, household items, and woodcraft. I believe skin-timber is not only a useful material for processability and design applicability, but it also has the capability to be a multifunctional and high value-added material. Also, if the standards, such as cortex thickness, outside diameter, and length, of skin-timber are producted diversely, I believe skin-timber can be have more the possibility of industrial products' development.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.1879-1884
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• 2014

Recently, the micro bonding technology comes into the spotlight as the miniaturization of the electronic product. The micro bonding technique can classify by way of laser welding and ultrasonic bonding and etc. However, the research on the micro bonding is much lacks. In this paper, carried out the cooling analysis of the 60 [kHz] ultrasonic bonding equipment to know heat effect of the piezoelectric element when the ultrasonic bonding equipment was operated. The ultrasonic horn having the natural frequency with 60 [kHz] for the dissimilar material bonding of the glass and solder tried to be designed. The parameters and response was set through the basic experiment. The dissimilar material bonding strength analysis using the 60 [kHz] ultrasonic bonding equipment was done. We carried out the bonding for improving bonding strength to using the silver paste. air thightness of bonding surface was confirmed by analysis of bonding interfaces.

• Corrosion Science and Technology
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• v.15 no.3
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• pp.120-124
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• 2016

The effect of alloying element Ca (0, 1, and 2 wt%) on corrosion resistance and bioactivity of the as-received and anodized surface of rolled plate AM60 alloys was investigated. A plasma electrolytic oxidation (PEO) was carried out to form anodic oxide film in $0.5mol\;dm^{-3}\;Na_3PO_4$ solution. The corrosion behavior was studied by polarization measurements while the in vitro bioactivity was tested by soaking the specimens in Simulated Body Fluid (1.5xSBF). Optical micrograph and elemental analysis of the substrate surfaces indicated that the number of intermetallic particles increased with Ca content in the alloys owing to the formation of a new phase $Al_2Ca$. The corrosion resistance of AM60 specimens improved only slightly by alloying with 2 wt% Ca which was attributed to the reticular distribution of $Al_2Ca$ phase existed in the alloy that might became barrier for corrosion propagation across grain boundaries. Corrosion resistance of the three alloys was significantly improved by coating the substrates with anodic oxide film formed by PEO. The film mainly composed of magnesium phosphate with thickness in the range $30-40{\mu}m$. The heat resistant phase of $Al_2Ca$ was believed to retard the plasma discharge during anodization and, hence, decreased the film thickness of Ca-containing alloys. The highest apatite forming ability in 1.5xSBF was observed for AM60-1Ca specimens (both substrate and anodized) that exhibited more degradation than the other two alloys as indicated by surface observation. The increase of surface roughness and the degree of supersaturation of 1.5xSBF due to dissolution of Mg ions from the substrate surface or the release of film compounds from the anodized surface are important factors to enhance deposition of Ca-P compound on the specimen surfaces.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.576-584
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• 2020

In order to obtain basic information for using polyvinyl alcohol (PVA) gel as a tissue mimicking phantom for temperature visualization, the temperature change characteristics due to the focused ultrasound were examined for different concentration of PVA. To obtain the basic acoustic characteristics, the speed of sound, the attenuation coefficient, and the density depending on the PVA concentration were measured, and the thermodynamic characteristics, such as thermal conductivity and heat capacity, were measured. The range of temperature rising in the vicinity of the focal point due to the focused ultrasound was observed using a thermochromic film that changes color at 30 degree or more, and the discolored area was obtained by image processing of the recorded image. As the concentration of PVA increases in the given range of 2 wt% ~ 16 wt%, the area that rises above 30 degree inside the gel increases linearly. It is confirmed that the discolored area increases as the power applied to the focused ultrasonic transducer increases. These results showed good agreement with the simulation results using the finite element method.

• Journal of the Korean Society of Radiology
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• v.11 no.5
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• pp.353-359
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• 2017

The sonophoresis, a representative low-intensity ultrasonic therapy, is a technique for delivering the drugs into the epidermis, dermis and skin appendages by using physical vibration and heat effects of the ultrasonic waves. Sonophoresis could increases the delivering and absorption efficiency of the drugs usually consisting of hydrophilic molecules and macromolecules. In addition, it has the advantage of being effective in delivering drugs with relatively large molecular sizes such as insulin or lipid. In this study, we proposed a multi-structure ultrasonic transducer assembly with a large-size single piezoelectric element and a drug delivery function at the treatment site for efficient sonophoresis treatment. Futhermore, a transducer assembly structure capable of raising and maintaining the temperature of the treatment site was proposed and evaluated for effectiveness. The transducer assembly proposed in this study is expected to improve the efficiency of sonophoresis by providing a constant amount of drug, and assisting drug delivery through heating the treatment site.