• Journal of the Korean Institute of Gas
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• v.17 no.4
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• pp.1-8
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• 2013

The aim of this study is to assess thermal hazards of polystyrene polymerization process by bulk polymerization with accelerating rate calorimeter(ARC) and Multimax reactor system(MM). From this study, we found out that the polymerization process should be operated at reaction temperature of $120^{\circ}C{\sim}130^{\circ}C$. At reaction temperature over $130^{\circ}C$, there was a runaway reaction hazard due to the temperature control failure following a viscosity increase of reaction products. With a cooling failure of a reactor in the early stage of process operation at the reaction temperature ($120^{\circ}C{\sim}130^{\circ}C$), there was a high thermal hazard of burst of a reactor's rupture disk or explosion of a reactor caused by the rapid rise of temperature and pressure to $340^{\circ}C$, 5.3 bar respectively within 30 - 50 minutes.

• Corrosion Science and Technology
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• v.20 no.1
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• pp.26-36
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• 2021

Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component, as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 ℃ using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.385-393
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• 2019

Potential fire, explosion and safety hazards exist in medium- or small-scale chemical plants using radical batch reaction processes due to the various conditions of materials, works or products. To minimize the potential damage, a study was conducted on qualitative hazard analysis using the HAZOP technique, which is a typical method for a qualitative risk assessment and analysis of the potential risks encountered in these chemical plants. For this purpose, a domestic chemical plant, which produces the acrylic resin by a radical batch reaction process, was selected and a risk assessment and analysis according to the procedure of HAZOP method was performed for the process. As the result of the study, to prevent the hazard, the input of inert gas and the installation of a pressure gauge were indispensable. In addition, the initiator and monomer should also be separated, and inhibiting substances and equipment are also necessary to prevent a runaway reaction.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.178-187
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• 2021

Dual-cooled annular fuel allows a significant increase in power density while maintaining or improving safety margins. However, the dual-cooled design brings much higher Zircaloy charge in reactor core, which could cause a great threaten of hydrogen explosion during severe accidents. Hence, an innovative fuel combined dual-cooled annular geometry and SiC cladding was proposed for the first time in this study. Capabilities of fuel design and behavior simulation were developed for this new fuel by the upgrade of FROBA-ANNULAR code. Considering characteristics of both SiC cladding and dual-cooled annular geometry, the basic fuel design was proposed and preliminary proved to be feasible. After that, a design optimization study was conducted, and the optimal values of as-fabricated plenum pressure and gas gap sizes were obtained. Finally, the performance simulation of the new fuel was carried out with the full consideration of realistic operation conditions. Results indicate that in addition to possessing advantages of both dual-cooled annular fuel and accident tolerant cladding at the same time, this innovative fuel could overcome the brittle failure issue of SiC induced by pellet-cladding interaction.

• Journal of the Korean Institute of Gas
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• v.26 no.1
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• pp.34-40
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• 2022

Gas cylinder cabinets have risks such as cylinder explosion and scattering of debris when a fire occurs. These risks are likely to cause gas spills and cause secondary damage. In order to reduce damage, it is very important to secure the fire resistance performance of the gas cylinder cabinet. In foreign countries, NFPA codes in the United States and EN-14470-2 in Europe stipulate fire resistance test standards for gas cylinder cabinets to protect internal cylinders for a certain period of time in a situation where gas cylinder cabinets are exposed to flames. However, in Korea, only internal pressure performance and airtight performance standards are specified, and the target is limited to piping, and research and regulations for the fire resistance performance of gas cylinder cabinets are insufficient compared to overseas. Therefore, in this study, finite element analysis was used to establish fire resistance standards for domestic gas cylinder cabinets. In the event of a fire, optimal conditions are derived in terms of structure and material.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.151-160
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• 2022

Owing to the recent increase in the frequency of explosion accidents, blast resistive design has garnered attention to reduce the damage of important structural elements. However, domestic research on the blast resistive structures is still insufficient, and domestic design guideline against blast loads are not documented yet. In this study, a numerical study on the RC blast resistive walls, where the test variable was the presence of FRP sheet, was performed using LS-DYNA program. Based on the numerical results, displacement-time hysteretic curve, pressure-impulse diagram, and fragility curve of the test specimens were derived. It was shown that the FRP sheet strengthening method is efficient to improve the blast resistive performance of the RC wall. Also, the strengthening effect of FRP sheet on the RC wall was stronger when the magnitude of the blast load was greater.

• Journal of English Language & Literature
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• v.56 no.6
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• pp.1255-1279
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• 2010

Much has already been learned about what goes on in the minds of second language writers as they compose, yet, oddly enough, until recently little in the L2 research literature has addressed writing and mental imagery together. However, images and imaging (visual thinking) play a crucial role in perception (the basis of mental imagery), in turn, affecting language, thinking, and writing. Many theorists of mental imagery also agree that more than just language accounts for how we think and that imagery is at least as crucial as language. All of these demands, to be sure, are compounded for EFL students, which is why I investigate EFL students' writing process, focusing on the use of mental imagery and its relationship to the writing. First I speculate upon some ways that imagery influences EFL students' composing processes and products. Next, I want to explore how and whether the images in a writer's mind can be shaped effectively into a linear piece of written English in one's writing. I studied two university undergraduate EFL students, L and J. They had fairly advanced levels of English proficiency and exhibited high level of writing ability, as measured by TOEFL iBT Test. Each student wrote two comparison and contrast essays: one written under specified time limitations and the other written without the pressure of time. In order to investigate whether the amount of time in itself causes differences within an individual in imagery ability, the students were placed under strict time constraints for Topic 1. But for Topic 2, they were encouraged to take as much time as necessary to complete this essay. Immediately after completing their essays, I conducted face-to-face retrospective interviews with students to prompt them for information about the role of imagery as they write. Both L and J have spent more time on their second (untimed) essays. Without time constraint, they produced longer texts on untimed essay (149 vs. 170; 186 vs 284 words). However, despite a relatively long period of time spent writing an essay, these students neither described their images nor detailed them in their essays. Although their mental imagery generated an explosion of ideas for their writings, most visual thinking must merely be a means toward an end-pictures that writers spent in purchasing the right words or ideas.

• Geomechanics and Engineering
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• v.36 no.3
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• pp.231-245
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• 2024

In recent decades, the protection and vulnerability of civil structures under explosion loads became a critical issue in terms of security, which may cause loss of lives and structural damage. Concrete retaining walls also restrict soils and slopes from displacements; meanwhile, intensive temporary loading may cause massive damage. In the current study, the modified Johnson-Holmquist (also known as J-H2) material model is implemented for concrete materials to model damages into the ABAQUS through user-subroutines to predict the blasting-induced concrete damages and volume strains. For this purpose, a 3D finite-element model of the concrete retaining wall was conducted in coupled Eulerian-Lagrangian simulation. Subsequently, a blast load equal to 500 kg of TNT was considered in three different positions due to UFC 3-340-02. Influences of the critical parameters in smooth blastings, such as distance from a free face, position, and effective blasting time, on concrete damage rate and destroy patterns, are explored. According to the simulation results, the concrete penetration pattern at the same distance is significantly influenced by the density of the progress environment. The result reveals that the progress of waves and the intensity of damages in free-air blasting is entirely different from those that progress in a dense surrounding atmosphere such as soil. Half-damaged elements in air blasts are more than those of embedded explosions, but dense environments such as soil impose much more pressure in a limited zone and cause more destruction in retaining walls.

• Journal of the Korea Institute of Building Construction
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• v.20 no.3
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• pp.253-260
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• 2020

With increasing interest in an underground-type ammunition storage facility, several design results have been provided recently. However, since not only experts in the tunnel but also military persons in charge of ammunition have not fully understood the safety distance standard, reliable design results are not being produced. In this study, the effective design method of an underground-type ammunition storage facility was provided by analyzing the current safety distance standard. First, the critical safety distances that dominate the size of construction site for underground-type ammunition storage facilities were evaluated, which are the layout of chambers and the configuration of the entrances. Then, the decreasing effect of inter-chamber distance was studied according to the rock type and the storage density of ammunition. In addition, the method of designing tunnels with parallel lines and two-floors was considered for arranging more chambers while complying with the safety distance standards. In particular, numerical simulations were carried out to determine the satisfaction of the safety distance standards when an underground-type ammunition storage facility is composed of two-floor and the decreasing effect of inter-chamber distance according to the inner explosive pressure reduction. Finally, the method to adjust the size of entrances and the path of pressure were studied for decreasing the safety distance at the entrance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.209-214
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• 2017

Most of the present potential transformers of train vehicles are of the oil-type filled with insulating oil and are susceptible to problems such as explosion due to the increase in the internal pressure during train operation and poor reliability near the end of their life cycle. As a solution to this problem, it is necessary to develop a molded dry-type potential transformer with excellent pressure-resistance performance using insulating resin. In order to localize the product, the Korea Railroad Research Institute has been developing a molded dry-type potential transformer. As part of this research, it is necessary to analyze the vibration characteristics of the developed product and to check the transformer performance in a vibration environment. In this study, a resonance test and simulated long-term life test of the developed product were conducted according to the KS R 9144 and IEC 61373 standards, respectively, which are vibration test methods for railway vehicle parts. Their natural frequencies were analyzed by comparing the results of the numerical modal analysis and resonance test, in order to confirm their adherence to the standards. Also, the performance test after the simulated long-term life test confirmed that the operation of the developed transformer was not problematic even in a long-time vibration environment.