• Transactions on Electrical and Electronic Materials
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• 제7권6호
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• pp.313-318
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• 2006

This paper introduces a partial discharge (PD) severity metric, S, based on the evaluation of time-sequence PD data capture and resulting Time-Sequence-Analysis Discharge (TSAD) level distributions. Basically based on an IEC60270 measurement technique, each PD event is time stamped and the discharge level noted. By evaluating the time differences between a previous and subsequent discharge, a 3D plot of time-sequence activity and discharge levels can be produced. From these parameters a measurement of severity, which takes into account dynamic or instantaneous variations in both the time of occurrence and the level of discharge, rather than using standard repetition rate techniques, can be formulated. The idea is to provide a measure of the severity of PD activity for potentially measuring the state of insulation within an item of plant. This severity measure is evaluated for a simple point-plane geometry in $SF_{6}$ as a function of gap distance and applied high voltage. The results show that as the partial discharge activity increases, the severity measure also increases. The importance of future investigations, quantifications and evaluations of the robustness, sensitivity and importance of such a severity measurement, as well as comparing it with typical repetition rate assessment techniques, and other monitoring techniques, are also very briefly discussed.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.78-80
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• 2014

Silicone structural glazing (SSG) is a method utilizing a silicone adhesive to attach glass, metal, or other panel material to the structure of a building. Windload and other impact loads on the facade are transferred from the glass or panel through the silicone structural sealant to the systems' framework. Silicone structural glazing systems are currently a very common method of glazing throughout the world. Locally, structural silicone glazing has become very common to achieve aesthetically pleasing and high utilization of small land for both residential and commercial building. Although structural silicone glazing has been utilized for approximately thirty years in Korea, the understanding of its technology was low and limited. Consequently, Korean projects experienced many quality issues during assembly and construction, even in very recently finished buildings. Adhesion loss and water infiltration occurred on more than one project, and the time and cost to repair these issues were substantial. In general, there are two kinds of structural silicones depending on fabrication methods. 1part structural silicone is for site glazing system and 2part structural silicone is for unitized factory glazing system. In this paper, 2part structural silicone which is very common for factory fabricating curtainwall systems was evaluated with regards to various mixing ratio. Since the structural performance of 2part sealant can be affected by mixing ratios, some extra ranges of recommended mixing ratio were evaluated to see any performance differences. Besides on cure profile, comparative evaluations for mechanical properties and adhesion develop on common building substrates were conducted.

• Wind and Structures
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• 제21권3호
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• pp.353-367
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• 2015

As concrete wind-turbine towers are increasingly being used in wind-farm construction, there is a growing need to understand the behavior of concrete wind-turbine towers. In particular, experimental evaluations of concrete wind-turbine towers are necessary to demonstrate the dynamic characteristics and load-carrying capacity of such towers. This paper describes a model test of a prestressed concrete wind-turbine tower that examines the dynamic characteristics and load-carrying performance of the tower. Additionally, a numerical model is presented and used to verify the design approach. The test results indicate that the first natural frequency of the prestressed concrete wind turbine tower is 0.395 Hz which lies between frequencies 1P and 3P (0.25-0.51 Hz). The damper ratio is 3.3%. The maximum concrete compression stresses are less than the concrete design compression strength, the maximum tensile stresses are less than zero and the prestressed strand stresses are less than the design strength under both the serviceability and ultimate limit state loads. The maximum displacement of the tower top are 331 mm and 648 mm for the serviceability limit state and ultimate limit state, respectively, which is less than L/100 = 1000 mm. Compared with traditional tall wind-turbine steel towers, the prestressed concrete tower has better material damping properties, potential lower maintenance cost, and lower construction costs. Thus, the prestressed concrete wind-turbine tower could be an innovative engineering solution for multi-megawatt wind turbine towers, in particular those that are taller than 100 m.

• 대한화장품학회:학술대회논문집
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• 대한화장품학회 1999년도 IFSCC . ASCS 학술대회 발표 논문
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• pp.123-131
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• 1999

Liquid crystal known as a rheological barrier to coaleseence of oil dorplets. increases. emulsion stability, water-holding capacity and promotes active material penetration to skin. Some investigation for its rheological characteristics have been reported but its relations to consumer perception have been rarely published. In this study oil/water emulsion and oil/liquid crystal/water systems were manufactured using the same composition of Behenyltrimethylammonium chloride/Cetostearyl alcohol/Lanolin oil. and rheological properties of each system were investigated with Cone and Plate rheometer. The formation of liquid crystalline phase was observed with polarized microscope and Differential Scanning Calorimeter. Continuous shear experiment, creep yield and water holding capacity were measured for oil/water and oil/liquid crystal/water systems. The results were compared with sensory evaluations. Oil/liquid crystal/water system showed higher viscosity at the same shear rate, higher viscoelasticity and higher yield stress than oil/water system. These properties were expected to show good spreadability and excellent richness without waxiness I hair care products of creme type. This expectation was consistent with the results of sensory experiments. Water-holding capacity was evaluated by measuring residual water of specimens at specific temperature and relative humidity, Oil/liquid crystal/water system was proved to have ability to hold water in comparison with oil/water system. The results indicated that oil/liquid crystal/water system was of benefit to rheological properties creme type hair care products.

• 한국해양공학회지
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• 제30권4호
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• pp.294-302
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• 2016

Because of the importance of steel material saving and rational ship structural design due to the rapid increase in steel prices, a ship structural design system was developed for plate members reinforced by doubler plates subjected to biaxial in-plane compressive loads. This paper mainly emphasizes the design system improvement and upgrade according to the change in the in-plane loading condition of the doubler plate from the single load discussed in a previous paper to the biaxial in-plane compressive load discussed in this paper. A direct design process by a structural designer was added to this developed optimized system to increase the design efficiency and provide a way of directly inserting a designer's decisions into the design system process. As the second stage of preliminary steps of doubler design system development, design formulas subjected to these biaxial loads used in the doubler plate design system were suggested. Based on the introduction of influence coefficients $K_t_c$, $K_t_d$, $K_b_d$ and $K_a_d$ based on the variations in the doubler length, breadth, doubler thickness, and average corrosion thickness of the main plate reinforced by the doubler plate, respectively, the design formulas for the equivalent plate thickness of the main plate reinforced by the doubler plate were also developed, and a hybrid design system using these formulas was suggested for the doubler plate of a ship structure subjected to a biaxial in-plane compressive load. Using this developed design system for a main plate reinforced by a doubler plate was expected to result in a more rational reinforced doubler plate design considering the efficient reinforcement of ship plate members subjected to these biaxial loads. Additionally, a more detail structural analysis through local strength evaluations will be performed to verify the efficiency of the optimum structural design for a plate member reinforced by a doubler plate.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.149-149
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• 2018

Prediction on initial motion of sediment is crucial to evaluate sediment transport and channel stability. The condition of incipient movement of sediment is characterized by bed shear stress, which is generated from force of moving water against the bed of the channel, and by critical shear stress, which depends on force resisting motion of sediment due to the submerged weight of the grains. When the bed shear stress exceeds the critical shear stress, sediment particles begin rolling and sliding at isolated and random locations. In Mountain River, debris flow frequently occurs due to heavy rainfall and can lead some natural stones from mountain slope into the bed river. This phenomenon could add additional forces to sediment transport system in the bed of river and also affect or change direction and magnitude of sediment movement. In this paper, evaluations on incipient motion of uniform coarse gravel under falling spheres impacts using small scale flume channel were conducted. The drag force of falling spheres due to water flow and length movement of falling spheres were investigated. The experiments were carried out in flume channel made by glass wall and steel floor with 12 m long, 0.6 m wide, and 0.6 m deep. The bed slopes were selected with the range from 0.7% to 1.5%. The thickness of granular layer was at least 3 times of diameter of granular particle to meet grain placement condition. The sphere diameters were chosen to be 4cm, 6 cm, 8 cm, 10 cm. The spheres were fallen in to the bed channel for critical condition and under critical condition of motion particle. Based on the experimental results, the Shields curve of particles Reynold number and dimensionless critical shear stress were plotted. The relationship between with drag force and the length movement of spheres were plotted. The pathways of the bed material Under the impact of spheres falling were analyzed.

• 한국의류산업학회지
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• 제21권3호
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• pp.336-345
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• 2019

This study evaluated the preference and wearing characteristics of existing fitness compression wear for elderly women and identified the problems and improvements of existing fitness apparel. Preference and wearing characteristics for 6 types (A-F) of upper and lower fitness compression wear were evaluated. Photos and drawings as well as the preferred designs and details were investigated after presenting the evaluation clothing. Evaluations were made on a 5 point Likert scale for the fitness, allowance, pressure, ease of movement, fabric material, and overall satisfaction after wearing. The design preference indicated that B type (26.6%) and C type (23.4%) were preferred in the top with C, E and F type preferred to the same ratio of 19.4% in the slacks. The fitness and allowance amount of the top B type were the most appropriate (${\geq}4$), the C type was in close contact (2.86), and the F type was inadequate in the neck circumference (1.77). The feeling of pressure was high in the waist, abdomen, thighs, and knees. The area where the elderly people want to improve their strength was the legs; in addition, a pattern design was needed to strengthen leg muscles when designing fitness compression wear. However, a design with excessive adhesion due to a muscle support band was shown to be not preferred. Therefore, depending on the activity, it is necessary to develop a fitness compression wear that applies an optimum stretching ratio of fabric based on body surface area changes.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제45권1호
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• pp.34-42
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• 2019

Objectives: Various bone graft substitute materials are used to enhance bone regeneration in the maxillofacial skeleton. In the recent past, synthetic graft materials have been produced using various synthetic and natural calcium precursors. Very recently, eggshell-derived hydroxyapatite (EHA) has been evaluated as a synthetic bone graft substitute. To assess bone regeneration using EHA in cystic and/or apicectomy defects of the jaws through clinical and radiographic evaluations. Materials and Methods: A total of 20 patients were enrolled in the study protocol (CTRI/2014/12/005340) and were followed up at 4, 8, 12, and 24 weeks to assess the amount of osseous fill through digital radiographs/cone-beam computed tomography along with clinical parameters and complications. Wilcoxon matched pairs test, means, percentages and standard deviations were used for the statistical analysis. Results: The sizes of the lesions in the study ranged from 1 to 4 cm and involved one to four teeth. The study showed significant changes in the formation of bone, the merging of material and the surgical site margins from the first week to the first month in all patients (age range, 15-50 years) irrespective of the size of the lesions and the number of teeth involved. Bone formation was statistically significant from the fourth to the eighth week, and the trabecular pattern was observed by the end of 12 weeks with uneventful wound healing. Conclusion: EHA showed enhancement of bone regeneration, and healing was complete by the end of 12 weeks with a trabecular pattern in all patients irrespective of the size of the lesion involved. The study showed enhancement of bone regeneration in the early bone formative stage within 12 weeks after grafting. EHA is cost effective and production is environment friendly with no disease transfer risks. Thus, natural bioceramics will play an important role in the reduction of costs involved in grafting and reconstruction.

• Journal of Korea Trade
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• 제24권7호
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• pp.73-92
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• 2020

Purpose - The letter of credit has been playing a major role to diminish overall risks which exist among concerned parties even though there are differences such as language, culture, law, and distance. This paper reviews essence of the letter of credit and its transaction principles, as well as overall practical questions based on the L/C transaction principle. It also investigates the risk of fraud occurrences in L/C transactions and the importance of fraud prevention and preventive measures in international L/C transactions, including the Fraud Rule, which is a major topic to consider in business transactions. Design/methodology - It is considered that an importing country's concerned parties and an exporting country's concerned parties face different situations. This study employs the existing framework to identify liability, responsibility, and obligation for all concerned parties across countries. Using a quite direct measurement of principles in the letter of credit, such as principle of independence, principle of abstraction, and principle of strictness and coincidence, we studied these differences. Findings - Our main findings can be summarized as follow. The paper enhances the efficiency of the L/C payment method to provide fraud generated from L/C transactions, presentation of a theoretical framework about fraud and fraud prevention, which international trading companies should acknowledge in a material way based on fraud risk resulting from taking advantage of L/C transaction principles. Originality/value - Existing studies focus on fraud accidents in L/C transactions by taking bad advantage of the characteristics of the letter of credit without suggesting risks of fraud. This paper attempts to evaluate and provide preventive measures as a solution for fraud and risky international business in a letter of credit transaction. This area of trade studies is underexplored, both empirically and theoretically, although the issue has long been important to Korean and world community foreign trade.

• 열처리공학회지
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• 제35권3호
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• pp.121-129
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• 2022

Recently the growth of the renewable energy production has caused the flexible operation in LNG combined cycle power plant. Due to the rapid start and stop operations, large CrMoV castings used for turbine casings and valve bodies could be distorted and lead to replacement or welding repair. This study was performed to find out the characteristics of the repair welding for a damaged CrMoV casting steel. A typical field repair method (arc & TIG welding) was applied to making specimens. The degraded N2 packing head sample from the steam turbine was used. The evaluations of weldments were carried out in terms of microstructural characterization, microhardness measurements, tensile, creep-rupture and fatigue tests. Color etching was also applied for better understanding of welding microstructures. As the boundary between HAZ and base material was deteriorated by welding, it caused microstructural changes formed during PWHT and the shortening of the remaining residual life. By comparing the properties according to repair welding method, it was possible to derive what important welding factors were. As a result, arc welding method is more suitable for repair welding on CrMoV castings.