• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1009-1015
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• 2012

Valves are one of the most important components of a pipeline system in a nuclear power plant, and it is important to ensure their structural safety under seismic loads. A crucial aspect of structural safety verification is the seismic qualification, and therefore, an optimal shape design and experimental seismic qualification is necessary in case the configuration of the valve parts needs to be modified and their performance needs to be improved. Recently, intensive numerical analyses have been performed before the experimental verification in order to determine the appropriate design variables that satisfy the performance requirements under seismic loads. In this study, static and dynamic numerical structural analyses of a 200A butterfly valve for a nuclear power plant were performed according to the KEPIC MFA. The result of static analysis considering an equivalent static load under SSE condition gave an applied stress of 135 MPa. In addition, the result of dynamic analysis gave an applied stress of 183 MPa, where the CQC method using response spectrums was taken into account. These values are under the allowable strength of the materials used for manufacturing the butterfly valve, and therefore, its structural safety satisfies the requirements of KEPIC MFA.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.21 no.2
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• pp.110-115
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• 2011

Objectives: The aim of this study is to survey for finding asbestos containing equipment at the laboratories using picture based questionnaire and polarized light microscopic analysis. Methods: This study was conducted from 2009 to 2010 at a university in Seoul. In 2009, picture based questionnaire was distributed to 100 laboratories during the regular laboratory air quality monitoring. In 2010, we emailed all professors of the same university who have laboratories to participate voluntarily this survey. For the laboratories consented to participate survey, picture based questionnaire was distributed and collected. Suspected asbestos containing material and apparatus were collected at the laboratories which replied they have suspected material and equipment. Collected samples were analyzed with polarized light microscope at the laboratory accredited by ministry of employment and labor in Korea. Results: Total of 18 out of 100 laboratories reported that they had suspected asbestos containing equipment in 2009. Twenty-three samples were collected and three samples (13%), one heating mantle and two pairs of insulation gloves, contained asbestos. Thirty four laboratories reported they had suspected asbestos containing material or equipment in 2010. Sixty samples were collected and four of them (6%), two pairs of insulation gloves, one packing rope in dry oven and, one pair of tongs, contained asbestos. All founded asbestos was chrysotile and the content of chrysotile was more than 90% for all equipment except heating mantle which has less than 1%. Conclusions: We confirmed that asbestos was still used at the laboratories though strict regulations on asbestos use in Korea. The method of picture based questionnaire invented in this study could be applied for asbestos survey to other research institute or university where there are many laboratories because of its simplicity and accessibility without huge man power, cost and time.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.7
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• pp.645-653
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• 2013

Seoul National University flap(SNUF) blade is a small-scale rotor blade incorporating a small trailing-edge flap control surface driven by piezoelectric actuators at higher harmonics for vibration attenuation. Initially, the blade was designed using two-dimensional cross-section analysis and geometrically exact one-dimensional beam analysis, and its material configuration was finalized. A flap-deflection angle of ${\pm}4^{\circ}$ was established as the criterion for enhanced vibration reduction based on an earlier simulation. The flap-linkage mechanism was designed and static bench tests were conducted for verifying the performance of the flap-actuation mechanism. Different versions of test beds were developed and tested with the designed flap and the selected APA 200M piezoelectric actuators. Through significant improvements, a maximum deflection of ${\pm}3.7^{\circ}$ was achieved. High-frequency experiments were conducted for evaluating the performance, and the transfer function of the test bed was determined experimentally. With the static tests almost complete, the rotor power required for testing the blade in a whirl tower (centrifugal environment) was calculated, and further preparations are underway.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.696-701
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• 2016

Multi-stage deep drawing is a widely used industrial manufacturing process, and its applications are gradually expanding to both small products and large metallic products. The USB C-type socket used in smart phones, for example, is manufactured using oval multi-stage deep drawing. The socket is very small and slender and it requires precise manufacturing. The thickness distribution of the final product is guaranteed only if it is uniform throughout the overall process. Therefore, minimizing the height difference between long and short sidewalls after the first operation is important for this goal. An initial blank optimization was performed for an oval-type drawing process based on finite element simulations. The goal was to determine an initial blank geometry that can maintain uniform height and thickness after the first draw operation. The initial blank shape of the sheet metal was optimized, and the results show that it satisfied the conditions of minimal thickness reduction and even thickness distribution. The geometry from the optimized simulation was compared with experimental results, which showed good agreement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.302-307
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• 2016

The technology of multistage deep drawing has been widely applied in the metal forming industry, in order to reduce both the manufacturing cost and time. A battery can used for mobile phone production is a well-known example of multistage deep drawing. It is very difficult to manufacture a battery can, however, because of its large thickness to height aspect ratio. Furthermore, the production of the final parts may result in assembly failure due to springback after multistage deep drawing. In industry, empirical methods such as over bending, corner setting and ironing have been used to reduce springback. In this study, a bottoming approach using the finite element method is proposed as a practical and scientific method of reducing springback. Bottoming induces compression stress in the deformed blank at the final stroke of the punch and, thus, has the effect of reducing springback. Different cases of the bottoming process are studied using the finite element program, DYNAFORM, to determine the optimal die design. The results of the springback simulation after bottoming were found to be in good agreement with the experimental results. In conclusion, the proposed bottoming method is expected to be widely used as a practical method of reducing springback in industry.

• Journal of the Korean GEO-environmental Society
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• v.14 no.4
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• pp.53-58
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• 2013

The design for horizontal drain layer on soft ground starts from the decision that the material could be used or not, by verifying material condition in permeability of horizontal drain material according to the weight percent of the dry soil retained on #200 sieve. In the next step of the design, we estimate the thickness of horizontal drain layer to confirm trafficability of heavy machinery in construction work. Successively, the long-term functionality for good drainage of horizontal drain layer is checked and if needed, some means are considered. In this study, the system to recycle mixed coal ash in ash pond successfully as a horizontal drain material on soft ground is presented through the process and the result of its practical construction work. Namely, the pact is confirmed that mixed coal ash in ash pond should be sorted out by sieve screen to a certain extent and the remainders of this mixed coal ash on sieve openings be recycled, because the amount of finer particles than $75{\mu}m$ contained in mixed coal ash in ash pond is quite massive and irregular depending on the coal power plant or the location in same ash pond. In order to sort at large scale in situ, the dimension of a sieve squre hole and the sort-out method, etc. should be decided before the sort-out process. And, it is described that we need to manufacture classifier to sort out mixed coal ash in ash pond, too.

• Journal of the Korean Society of Safety
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• v.34 no.5
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• pp.144-152
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• 2019

According to the National Police Agency, point-to-point speed enforcement system is being installed and operated in 97 sections across the country. It is more effective than other enforcement systems in terms of stabilizing the traffic flow and inhibiting the kangaroo effect. But it is only 5.1% of the total enforcement systems. The National Police Agency is also aware that its operation ratio is very low and it is necessary to expand point-to-point speed enforcement system. Hence, this study aims to provide the expansion basis of the point-to-point speed enforcement operation through analysis of the quantitative effects and development the accident prediction model. Firstly, this study analyzed the effectiveness of point-to-point speed enforcement system. Naive before-after study and comparison group method(C-G Method) were used as methodologies of analyzing the effectiveness. The result of using the naive before-after study was significant. Total accidents, EPDOs and casualty crashes decreased by 42.15%, 70.64% and 45.30% respectively. And average speed and the ratio of exceeding speed limit decreased by 6.92% and 20.50%p respectively. Moreover, using the C-G method total accidents, EPDOs and casualty crashes decreased by 31.35%, 66.62% and 10.04% respectively. And average speed and the ratio of exceeding speed limit decreased by 3.49% and 56.65%p respectively. Secondly, this study developed a prediction model for the probability of casualty crash. It was dependant on factors of traffic volume, ratio of exceeding speed limit, ratio of heavy vehicle, ratio of curve section, and presence of point-to-point speed enforcement. Finally, this study selected the most danger sections to the major highway and evaluated proper installation sections to the recent installation section by applying the accident prediction model. The results of this study are expected to be useful in establishing the installation standards for the point-to-point speed enforcement system.

• Korean Journal of Optics and Photonics
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• v.30 no.5
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• pp.187-192
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• 2019

In this paper a pump combiner, a key component of a high-power fiber laser, was fabricated, and its output characteristics measured using a high-power performance measuring instrument. The $(18+1){\times}1$ pump combiner consists of an optical-fiber bundle of one signal fiber and 18 pump fibers, an output optical fiber, and housing. The signal and output fibers were fabricated using polarization-maintaining optical fiber. By measuring the loss of signal light along the tapering length of the optical-fiber bundle, the tapering length was optimized to 18 mm. Signal-light insertion loss, pump-light transmittance, and polarization extinction ratio of the fabricated $(18+1){\times}1$ pump combiner were measured as 6.5%, 98.07%, and 18.0 dB respectively. The temperature distribution of the pump combiner, at a high power of 2 kW using 18 pump laser diodes, was measured and analyzed using a thermal-imaging camera.

• Journal of Korea Port Economic Association
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• v.32 no.3
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• pp.123-137
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• 2016

In order to address the crisis of the regional employment structure caused by the recent restructuring of the shipbuilding industry, this study estimates the shipbuilding industry's Employment Linkage Effect(ELE) across regions and industries. Consequently, the study uses the hypothetical extraction method on the shipbuilding industry from the 2013 Regional Input-output Table. The analysis results are as follows. First, the shipbuilding industry's ELE across industries is estimated at its highest in wholesale and retail, followed by shipment, other manufacturing, project supporting service, machine and equipment manufacturing, and metal product manufacturing. These industries either have a high employment to GDP ratio or are directly related to the shipbuilding industry in terms of production activities. Second, the Southeastern Korea's ELE on South Jeolla Province is very low, and, accordingly, South Jeolla Province is isolated in the employment structure of the shipbuilding industry. Therefore, when the government establishes measures to tackle the crisis of employment caused by the shipbuilding industry's restructuring, it should prioritize identifying such regional employment structures, as demonstrated above, and incorporate them into the regional industry policy.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.553-581
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• 2022

Shortly after tunnel boring machine (TBM) was introduced in the tunneling industry, the use of TBM has surprisingly increased worldwide due to its performance together with the benefit of being safely and environmentally friendly. One of the main cost items in the TBM tunneling in rock and soil is changing damaged or worn cutters. It is because that the cutter change is a time-consuming and costly activity that can significantly reduce the TBM utilization and advance rate and has a major effect on the total time and cost of TBM tunneling projects. Therefore, the importance of accurately evaluating the cutter life can never be overemphasized. However, the prediction of cutter wear in soil, rock including mixed face is very complex and not yet fully clarified, subsequently keeping engineers busy around the world. Various prediction models for cutter wear have been developed and introduced, but these models almost usually produce highly variable results due to inherent uncertainties in the models. In this study, a case study of design and construction of disc cutter change is introduced and analyzed, rather than proposing a prediction model of cutter wear. As the disc cutter is strongly affected by the geological condition, TBM machine characteristic and operation, authors believe it is very hard to suggest a generalized prediction model given the uncertainties and limitations therefore it would be more practical to analyze a real case and provide a detailed discussion of the difference between prediction and result for the cutter change. By doing so, up-to-date idea about planning and execution of cutter change in practice can be promoted.