• Journal of the Korean Institute of Gas
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• v.14 no.6
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• pp.15-20
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• 2010

Compressed Natural Gas (CNG) buses have been supplied since the year 2000 in order to resolve severe atmospheric pollution in metropolitan area and contributed on the improvement of urban atmospheric environment. However, it is indispensible to take an adequate measure to guarantee the safety of CNG vehicles because of the possibility of huge fire accident. A receptacle, connecting device between high pressure fuel supply tank and fuel line, plays an important role in CNG supply system. In recent, leakage of CNG from receptacles has been reported. So, the concern about the security and reliability of receptacles has been arisen. Therefore, a lot of efforts to prevent leakage are invested among researchers and the durability of this component should be guaranteed despite repeated operation. This research has performed durability tests of a CNG receptacle regarding the repeated usage, extreme chattering, and continuous full flow test. Although a receptacle used for CNG vehicle satisfies validation requirements in the test results, it has been found that failure in the function of leakage prevention in a receptacle could take place in the case of prolonged exposure to high supply pressure in common quick charging environment on site.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.554-561
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• 2016

In this study, loading tests and a strength evaluation of the bogie frame were conducted to verify the structural safety of the bogie system in an intermodal tram, which runs with cars on a road track. The loads were calculated taking into account the features of the road track with many sharp curves and steep gradients, which are different from the track of conventional railway. They were compared with the loads specified in the previous standard specifications. After the comparison, it was confirmed that the loads acting on the bogie system operating on a road track are slightly different from the specified loads. The specified vertical load of the standard specification for all kinds of trains is conservative, but the specified lateral and longitudinal loads are less than the calculated loads. The application of the actual loads was proven to be reasonable in the development of a new railway system. Based on the defined loads, the bogie frame was fabricated on which strain gauges were attached. It was set on the large loading frame so that the stresses could be measured when loads were applied by hydraulic actuators. After measuring the stresses, it was shown that they were below the allowable stress, which verified the structural safety of the bogie frame.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.213-213
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• 2016

수문조사기기의 검정은 수문조사에 활용할 기기를 일관되고 표준화된 기준으로 검사하여 수문조사에 적합한 기기인지 확인하는 것이다. 이러한 검정은 국가수문자료의 신뢰도를 높이고 유지하는 기본적이고 중요한 업무이다. 검정대상기기는 강수량측정기기, 유속측정기기, 수위측정기기, 부유사측정기기, 토양수분측정기기, 증발산량측정기기로 총 6가지이며, 2009년부터 국토교통부 위탁사업으로 한국건설기술연구원(유량조사사업단)에서 수행하고 있다. 특히 유량조사사업단에서는 유속측정기기를 제외한 나머지 5개 수문조사기기에 대해 검정을 수행하고 있다. 연도별로 2009년부터 2015년까지 98대, 334대, 572대, 539대, 359대, 682대, 690대로 총 3,274대를 검정하였고, 관측기종별로 강수량 1,579대, 수위 1,589대 부유사 23대, 토양수분 33대, 증발산량 50대이다. 신청기관별로는 국토교통부(홍수통제소) 1,847대, 환경부(국립환경과학원) 4대, 한국건설기술연구원(유량조사사업단 포함) 81대, K-water 338대, 한국수력원자력(주) 91대, 일반업체 913대에 대한 검정을 실시하였다. 검정을 실시한 강수량측정기기 1,579대 중 보정없이 합격된 기기는 1,495대, 허용오차기준에 미달되어 보정 실시 후 합격한 기기는 76대이며, 불합격 처리된 기기는 8대이다. 수위측정기기는 합격이 1,586대, 기준에 미달되어 불합격된 기기가 2대로 나타났다. 강수량측정기기의 각 연도대비 통계분석 결과 보정률은 2009년 97대 중 8대(8.2%), 2010년 194대 중 3대(1.5%), 2011년 180대 중 24대(13.3%), 2012년 175대 중 17대(9.7%), 2013년 165대 중 15대(9.1%), 2014년 547대 중 8대(1.5%), 2015년 221대 중 9대(4.1%)로 다소 낮은 수치로 나타났다. 이처럼 보정률이 낮게 나타난 이유는 관할기관의 검정을 위한 유지관리 및 사업자의 사전검사 등을 통해 감소한 것으로 판단되며, 이와 같은 결과는 수문자료의 품질 및 신뢰도 향상으로 이어졌다. 그러나 여전히 선진국에 비해 수문조사기기 검정의 중요성에 대한 인프라 구축이 미흡한 실정이다. 수문조사기기 검정의 선진국이라 할 수 있는 미국의 경우 USGS에서 HIF(Hydrogical Istrumentation Facility)라는 별도 조직을 운영하여 관측기기의 렌탈, 수리, 교정 및 검정, 개발, 교육 등 이러한 작업을 일괄 수행하고 있고 조직 내 자체 시설로 수중펌프 시험소, 자연과 유사한 환경에서 테스트 하는 장소, 대형온도챔버 등을 갖추고 있으며, 이러한 시설을 이용하여 기기의 교정 및 검정, 연구 등을 현장과 비슷한 환경에서 다양한 실험을 통해 검정방법을 비교, 분석하는 것을 볼 수 있다. 현재 우리나라의 수문조사기기는 다양한 방법으로 현장에 설치되어 검정방법의 다양성이 요구된다. 향후 우리나라도 HIF와 같이 다양하고 선진화된 시설과 기술을 개선하고 다각적인 시험 과정을 통해 수준 높은 검정방법체계를 갖추려는 노력이 필요하다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.269-275
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• 2019

As the national industry is developing gradually due to the expansion of the economic scale, the construction of large and super high-rise structures for building social infrastructure has been increasing, and studies have been conducted actively to transmit the large loads at the upper portion to the lower bedrock. In this study, the PHC was extended to an ultra-high strength PHC, which increased the concrete compressive strength of the PHC from the conventional 80 MPa to 110 MPa, and the PHC, which extended the tip of the pile. After construction with the driving method and injected pile method, the tendency of the bearing capacity was tested through a load test. Measurements of the bearing capacity of the extended PHC using the pile driving method revealed the main surface friction force to be smaller than that of the general PHC, and the stet-up effect was also insignificant. On the other hand, the effect of the friction force on the ground surface when the injected pile method was applied is expected to increase the bearing capacity when the gap between the main surface and the ground is wide and the cement paste is filled tightly. In addition, the ultrahigh strength PHC showed higher bearing capacity than the conventional PHC, and the permissible pile stress was less than 60%. Therefore, it is possible to reduce the number of piles and reduce the construction cost and effect of shortening the length of the pile by designing the tip of the pile on the ground with the intensity of soft rock as a method for utilizing the increased strength of the ultra-high strength PHC.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.559-568
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• 2019

Recently, the infrastructure of the marine environment has been increasing. Therefore, there has been increasing interest in increasing the durability of structures. The FRP Hybrid Bar with improved durability against corrosion was developed in recent years. On the other hand, studies that evaluate the corrosion resistance are insufficient. In this study, the corrosion resistance according to the type of rebar in concrete was assessed and analyzed. The experiment used steel bars and FRP Hybrid Bar. The corrosion test method was a galvanic current and half-cell potential method. The accelerated corrosion test was carried out by four levels (0%, 1.5%, 3%, and 6%) of chloride added to the concrete. The galvanic current measurements revealed no corrosion current in the FRP Hybrid Bar. The half-cell measurement also showed the corrosion resistance of the FRP Hybrid Bar. Therefore. FHB can be used as an alternative steel for structures where a marine environment and steel corrosion are predicted.

• Korean Journal of Construction Engineering and Management
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• v.23 no.2
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• pp.95-101
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• 2022

This study attempts to identify the ways of reducing the floor impact sound, by applying six different types of the reinforced bar girders and stirrup arrangements to the Structure: (1) the longer-direction girder arrangements (2) the shorter-direction girder arrangements (3) the diagonal-direction arrangements (4) the longer-direction girder arrangements with stirrups (5) the shorter-direction girder arrangements with stirrups (6) the diagonal-direction arrangements with stirrups. In order to identify the most effective structural changes, each slab was tested with bang machines, measuring the level of the sound impact. The results showed that the longer-direction girder arrangements with stirrups were the most effective one. In addition, the effectiveness of slab was found to be remarkable, showing the level of minimum 1dB to maximum 5dB, where the slab was compared with the control models without girders and stirrups. In conclusion, it is suggested that the longer-direction girder arrangements with stirrups could possibly be applied to the Wall Structures to minimize the floor impact sound.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.1-7
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• 2022

Recently, satellites equipped with high-performance electronics have required higher power consumption because of the advancement of satellite missions. For this reason, the size of the solar panel is gradually increasing to meet the required power budget. Increasing the size and weight of the solar panel is one of the factors that induce the elastic vibration of the flexible solar panel during the highly agile maneuvering of the satellite or the mode of vibration coupling to the satellite or the mode of vibration coupling to the micro-jitter from the on-board appendages. Previously, an additional damper system was applied to reduce the elastic vibration of the solar panel, but the increase in size and mass of system was inevitable. In this study, to overcome the abovementioned limitations, we proposed a high -damping yoke structure consisting of a superplastic SMA(Shape Memory Alloy) laminating a thin FR4 layer with viscoelastic tape on both sides. Therefore, this advantage contributes to system simplicity by reducing vibrations with small volume and mass without additional system. The effectiveness of the proposed superelastic SMA multilayer solar panel yoke was validated through free vibration testing and temperature testing using a solar panel dummy.

• Journal of Korea Foundry Society
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• v.43 no.3
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• pp.107-136
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• 2023

Natural silica sand was commonly used for sand casting of cast steel products, and chromites sand was used to suppress seizure defects due to the lack of thermal properties of silica sand. However there are disadvantages such as deterioration by repeated use, system sand mixing problem, difficulty separating and removing, increased during mold according to high density and to being waste containing chrome. Recently, industrial waste reduction and atmospheric environment improvement have been highlighted as important tasks in the casting industry. In order to solve the problems that occur when using foundry Sand and to improve the environment of casting factories, various artificial sands that can be applied instead of natural silica sand have been developed and introduced. Artificial sands can be classified into artificial sand manufactured by the electric arc atomization or gas flame atomization, artificial sand manufactured by the spray drying & sintering process, artificial sand manufactured by the sintering & crushing process and exhibit different physical properties depending on the type of raw-minerals and manufacturing method. In this study, comparative evaluation tests were conducted on the physical properties of various foundry sands, mold strength, physical durability, thermal durability, and casting test pieces. When comprehensively considering the actual amount of molding sand used according to density, the mold strength according to the shape of sand, the physical and thermal durability of foundry sand, and the heat resistance characteristics of foundry sand, 'Molten artificial sand A1' or 'Molten artificial sand B' is judged to be the most suitable spherical artificial sand for casting of heavy steel castings.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.77-84
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• 2008

The existing equations for radial consolidation cannot account for the changes of well resistance with time and cannot predict the appropriate in-situ consolidation curve. In this study, small cylinder cell tests are performed to evaluate the discharge capacity of PVD. Also, a block sample of 1.2 m in diameter and 2.0 m in height was consolidated to observe the change in the drainage capacity with time for three types of PVD. From the test results on a block sample, the drainage curves normalized with initial drainage of each PVD are similar, regardless of the PVD type and the consolidation curve, which is predicted using solutions of radial consolidation based on the discharge capacity measured in a small cylinder cell tests, significantly overestimates the degree of consolidation. The term of well resistance in the radial consolidation solution was back-calculated to fit the consolidation curve of a large block sample and it is defined as the time dependent well resistance factor, L(t). The L(t) was found to be linearly proportional to the dimensionless time factor, Th. It was also shown that the consolidation curve evaluated by using L(t) provides more accurate prediction than the existing solution.

• Korean Journal of Environmental Biology
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• v.41 no.4
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• pp.447-454
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• 2023

This study was conducted to analyze the effects of stand density on fire fuel (FF) changes in a Chamaecyparis obtusa forest. The study site was located in Mt. Munsu in Jeollabuk-do and consisted of a control, 30% thinning treatment(LT), and 50% thinning treatment(HT). Three-year-old seedlings were planted at a density of 3,000trees ha^-1 in 1976, and thinning was carried out in 2000. FF production was measured every 2 months by installing 3 circular litter traps 1.2m above the ground. Litter bags containing 5g of each leaf and branch were made and buried in the organic layer to investigate the FF decomposition rate. The decay constant was calculated after 18 months. FF accumulation was measured by collecting dry-weight organic matter from each plot using a square frame (0.09 m²) in September 2018. The FF production in LT and HT was significantly lower than that of the control(P<0.001). The leaf decay constant for HT was significantly lower than that of the control (P<0.05). The FF accumulation in HT was significantly lower than that of the control (P<0.01), but LT was not significantly different from the control. The results of this study showed that thinning decreased FF production.