• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.467-471
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• 2014

The natural frequencies of a mechanical system are determined by the system parameters such as masses and stiffness of the system. Since material irregularities and manufacturing tolerances always exist in most of practical engineering situations, the system parameters always have uncertainties. As the uncertainties of the parameters increase, the uncertainties of the system natural frequencies also increases. Then, the reliability of the system deteriorates. So, the uncertainty of the system natural frequencies should be analyzed accurately and considered in the design of the system. In order to analyze the uncertainty of the system natural frequencies employing most of existing uncertainty analysis methods, the probability distributions of the uncertain system parameters should be identified. In most practical situations, however, identification of the probability distributions is almost impossible because of limited time and cost. For that case, the reliability should be estimated based on finite samples of the system parameters. In this paper, sample based reliability estimation method employing extreme value theory was proposed. Using the proposed estimation method, sample based reliability design of the system natural frequencies was conducted.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.41-49
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• 2021

Cement-mixed polymer-based waterproofing materials are generally used in the form of application by mixing in the field, and it is necessary to supplement the construction ability for air bubbles and uneven coating thickness due to irregularities during construction. The final purpose of this study is to improve the waterproofing performance by adding a sheet attaching process to the composite construction rather than the single process of painting and applying the construction method when applying the polymer waterproofing material to the field. In this regard, the applicability was evaluated by examining the material, environment, and manufacturing method.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.51-58
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• 2018

In this paper, the organic material Poly(methyl methacrylate) PMMA is used with inorganic $Al_2O_3$ to fabricate organic-inorganic multilayer barrier thin films. The organic thin films are developed using a roll-to-roll electrohydrodynamic atomization system, whereas the inorganic are grown using a roll-to-roll low-temperature atmospheric pressure atomic layer deposition system. For the first time, these two technologies are used together to develop organic-inorganic multilayer barrier thin films in atmospheric condition. The films are grown under optimized parameters and classified into three classes based on the layer structures, when the total thickness of the barrier is maintained at ~ 160 nm. All classes of barriers show good morphological, optical and chemical properties. The $Al_2O_3$ films with a low average arithmetic roughness of 1.58 nm conceal the non-uniformity and irregularities in PMMA thin films with a roughness of 5.20 nm. All classes of barriers show a notably good optical transmission of ~ 85 %. The hybrid organic-inorganic barriers show water vapor and oxygen permeation in the range of ${\sim}3.2{\times}10^{-2}g/m^2/day$ and $0.015cc/m^2/day$ at $23^{\circ}C$ and 100% relative humidity. It has been confirmed that it can be mass-produced and used as a low-cost barrier thin film in various printing electronic devices.

• Korean Journal of Acupuncture
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• v.21 no.4
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• pp.43-51
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• 2004

Objectives : In order to ensure safe acupuncture treatment, the quality of the needle tip is essential. But, there have not been so many studies about the quality of the acupuncture needle tip. For this reason we have been already reported about the quality of acupuncture needle tip in Korea using scanning electron microscope(SEM) in 2002, 2003. In order to compare than other society, we investigated the current condition of the tips of the acupuncture needles sold in Europe. Methods : We obtained the needles made by 7 companies, which are sold currently in Europe, and selected 50 pieces out of 100 pieces from each company by randomized methods. And then we observed the tip of each needle using a scanning electron microscope at ${\times}800$ magnification. Results and Discussion : We found that needles had several defects such as scratch marks on the surface, metallic scuff, lumps and irregularities of the needle tips, stubbed or malformed tips, tips of point off-center, peeled off coated tips, same as Korean needles. There was much difference on the quality of needles among the manufacturers, and some needles seem to need thorough quality control. Allowing for the high price, the quality of some needle in Europe generally are better than that of Korean needles. But some Korean needles hold a top position than European ones in quality. We want a good industrial standard to be made in acupuncture manufacturing fields in the near future, because the safety is not less valuable than the efficacy in medicine.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1643-1646
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• 2003

Drawing is a mechanical operation that attenuates thick material to an appropriate thickness for the next processing or end usage. When the input material has the form of a bundle or bundles made of very thin and long shaped wire or fibers, this attenuation operation is called "bundle drawing" or "drafting" Drafting is being used widely in manufacturing staple yarns. which is indispensable for the textile industry. However, the bundle processed by this operation undertake more or less defects in the evenness of linear density. Such irregularities cause many problems not only for the product quality but also for the efficiency of the next successive processes. Since long there have been many researches tying to find out factors affecting the irregularity of linear desity, to obtain optimal drafting conditions, to develop efficient measuring and analysis methods of linear density of bundle, etc., but there exists yet no fundamental equation describing the dynamic behavior of the flowing bundle during processing. In this research a mathematical model for the dynamic behavior of the bundle fluid is to be set up on the basis of general physical lows representing physical variables, i.e. linear density and velocity as the dynamic state of bundle. The conservation of mass and momentum balance was applied to the fluid field of bundle. while the movement of′ individual material was taken into account. The constitutive model relating the surface force and the deformation of bundle was introduced by considering a representative prodedure that stands for the bundle movement. Then a fundamental equations system could be simplified considering a steady state of the process. On the basis of the simplified model, the simulation was performed and the results could be confirmed by the experiments under various conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.197-202
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• 2014

The efficiency of a catalytic converter depends on the flow distribution across a system's chemically active substrate. If irregularities or non-uniform flow patterns exist, the system's conversion efficiency decreases, whereas the manufacturing cost increases. Therefore, it is important to analyze the internal flow of a catalytic converter. In this study, flow pattern measurements along the minor axis were recorded at the mid and exit planes of a ceramic honeycomb catalytic converter at flow rates of 37.8 l/s and 94.4 l/s. Flow distributions of the measurement plans were compared with an automotive company's computed velocity profiles. Measurements along the minor axis showed uneven velocity profiles. The ${\upsilon}$-velocity components between the honeycomb bricks were small but somewhat erratic opposite the intake side of the converter, however, they became flatter in measurements recorded near the intake entrance. For almost all velocity values, the computer model suggested velocities greater than the measured values.