• 센서학회지
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• 제32권2호
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• pp.75-81
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• 2023

The significance of gas sensors has been emphasized in various industries and applications, owing to the growing significance of environmental, social, and governance (ESG) management in corporate operations. In particular, the monitoring of hazardous gas leakages and detection of fugitive emissions have recently garnered significant attention across several industrial sectors. As industrial workplaces evolve to ensure the safety of their working environments and reduce greenhouse gas emissions, the demand for high-performance gas sensors in industrial sectors dealing with toxic substances is on the rise. However, conventional gas-sensing systems have limitations in monitoring fugitive gas leakages at both critical and subcritical concentrations in complex environments. To overcome these difficulties, recent studies in the field of gas sensors have employed techniques such as mobile robotic olfaction, remote optical sensing, chemical grid sensing, and remote acoustic sensing. This review highlights the significant progress made in various technologies that have enabled accurate and real-time mapping of gas distribution and localization of hazardous gas sources. These recent advancements in gas-sensing technology have shed light on the future role of gas-detection systems in industrial safety.

• 비파괴검사학회지
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• 제22권4호
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• pp.354-360
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• 2002

NDT나 의료용 영장장치에 응용되는 압전복합재는 일반적인 세라믹이나 고분자 압전재료에 비하여 많은 장점을 가진다. 이들 응용분야에서는 전기기계결합계수가 높아야 하고 음향임피던스가 낮아야 한다. 그러나, 압전복합재의 횡방향 단위 크기가 조밀하지 못할 경우 횡방향으로 진행하는 판파에 의한 불필요한 진통이 표면에 발생하게 된다. 횡방향 단위 크기와 세라믹 체적비에 따른 압전 특성을 조사하기 위하여 PMN-PZT 세라믹과 Epofix 에폭시로 에폭시의 폭의 달리하면서 1-3형 압전복합채를 제작하였다. 제작된 1-3형 압전복합재의 두께방향 진동모드의 전기기계결합계 수, 음향임피던스는 각각 $0.36{\sim}0.64,\;9.8{\sim}22.7MRayl$ MRayl로 나타났으며, 횡방향 단위크기가 줄어들수록 횡방향 모드 공진 주파수가 증가하였다.

• Interaction and multiscale mechanics
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• 제2권1호
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• pp.45-68
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• 2009

An aim of the study is to develop an efficient numerical simulation technique that can handle the two-scale analysis of fluid permeation filters fabricated by the partial sintering technique of small spherical ceramics. A solid-fluid mixture homogenization method is introduced to predict the mechanical characters such as rigidity and permeability of the porous ceramic filters from the micro-scale geometry and configuration of partially-sintered particles. An extended finite element (X-FE) discretization technique based on the enriched interpolations of respective characteristic functions at fluid-solid interfaces is proposed for the non-interface-fitted mesh solution of the micro-scale analysis that needs non-slip condition at the interface between solid and fluid phases of the unit cell. The homogenization and localization performances of the proposed method are shown in a typical two-dimensional benchmark problem whose model has a hole in center. Three-dimensional applications to the body-centered cubic (BCC) and face-centered cubic (FCC) unit cell models are also shown in the paper. The 3D application is prepared toward the computer-aided optimal design of ceramic filters. The accuracy and stability of the X-FEM based method are comparable to those of the standard interface-fitted FEM, and are superior to those of the voxel type FEM that is often used in such complex micro geometry cases.

• 대한환경공학회지
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• 제22권4호
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• pp.689-698
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• 2000

강우시 발생되는 강우유출수는 배수구역내 지표오염물질로부터 기인한 다양한 오엽물질을 포함하고 있으며 전세계적으로 이에 대한 많은 연구가 진행중에 있다. 초기강우시 신업공단에서 발생되는 지표유출수내 오염물질의 특성은 아직도 완벽하게 이해되지 못하고 있다. 일반적으로 분류식 배제방식이 채택된 공단에서 발생되는 우수유출수는 다양한 오염물질을 함유한 채 미처리 상태로 전량 지천으로 배출되고 있다. 본 연구는 산업공단을 대상으로 강우시 지표유출수의 수질과 특성을 분석 평가하였고 시료 채취는 공단을 배수구역별 4개 구역으로 구획 후 해당 배수구역에 대해 grab sampling 방법을 적용하였다. 석유 화학산업과 일반 야적장 등에서는 BOD, COD, SS, TN 등의 일반오염물 항목들이 주로 검출된 반면, 기계 금속산업, 고철 야적장 지역에서는 중금속항목의 오염물이 고농도로 측정되었다. 초기강우유출시 전 조사지점의 지표유출수에서 Fe, Zn, Cu 등의 항목이 주로 검출된 반면, Pb, As, Cd, Cr, Ni 등은 미량으로 검출되었고 Hg는 어느 지점에서도 검출되지 않았다. 산업공단에서 발생하는 지표유출수내 오염물질들은 대부분 업종과 연관성을 나타내었고, 각 지점별 발생 오염물질의 농도는 오염물질의 노출정도 및 강우사상의 특성에 따라 결정되어지는 것으로 나타났다.

• 대한금속재료학회지
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• 제56권11호
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• pp.805-812
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• 2018

High pressure die casting is one of the precision casting methods. It is highly productivity and suitable for manufacturing components with complex shapes and accurate dimensions. Recently, there has been increasing demand for efficient heat dissipation components, to control the heat generated by devices, which directly affects the efficiency and life of the product. Die cast aluminum alloys with high thermal conductivity are especially needed for this application. In this study, the influence of elements added to the die cast aluminum alloy on its thermal conductivity was evaluated. The results showed that Mn remarkably deteriorated the thermal conductivity of the aluminum alloy. When Cu content was increased, the tensile strength of cast aluminum alloy increased, showing 1 wt% of Cu ensured the minimum mechanical properties of the cast aluminum. As Si content increased, the flow length of the alloy proportionally increased. The flow length of aluminum alloy containing 2 wt% Si was about 85% of that of the ALDC12 alloy. A heat dissipation component was successfully fabricated using an optimized composition of Al-1 wt%Cu-0.6 wt%Fe-2 wt%Si die casting alloy without surface cracks, which were turned out as intergranular cracking originated from the solidification contraction of the alloy with Si composition lower than 2 wt%.

• 청정기술
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• 제27권2호
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• pp.174-181
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• 2021

본 연구에서는 경상남도 지역의 오염감시전용측정망의 5년간(2013 ~ 2017) 자료를 이용하여 주오염원과 분기별 지하수 수질특성을 분석하였다. 주오염원은 산업단지지역, 광산·폐광산지역 및 하수처리시설로 구별하였다. 분석 항목은 현장측정 항목(수온, pH, 전기전도도, 용존산소, 산화물환원전위), 양이온 그리고 음이온이었다. 수온과 pH는 주오염원에 따라 크게 변하지 않았다. 양이온과 음이온의 평균농도의 합은 산업단지지역에서 가장 높았고, 하수처리시설 그리고 광산·폐광산지역 순이었다. 산업단지지역에서는 전기전도도의 값이 가장 높았고, 용존산소의 값이 가장 낮았다. 산업단지지역은 나트륨이온이 가장 높은 구성비를 보인 반면 하수처리시설과 광산·폐광산지역에서는 칼슘이온이 가장 높은 값을 나타내었다. 모든 주오염원에서 중탄산염의 농도가 가장 높게 나타났다. 수온, pH 그리고 양이온과 음이온의 농도는 분기마다 크게 다르지 않았다. 수질유형 중 Na-HCO₃ 유형이 가장 높은 비율을 차지하였으나, 외부 오염의 가능성이 높은 Na-Cl 유형도 오염감시전용측정망의 전체 자료 중 약 20%를 차지하였다.

• 산업기술연구
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• 제26권B호
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• pp.199-206
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• 2006

Internet telephony provides voice communication services with added flexibility for multimedia extension at a lower cost compared to traditional telephone systems. We implemented an internet telephony system as an overlay network without a centralized server, using a distributed hash table (DHT). Compared to the current server-based internet telephony system, our system is fault-tolerant, scalable, and can be flexible extended to various services and advanced to integrated service. To demonstrate the high flexibility of our DHT-based internet telephony system, we made our system cooperate with web servers. Web users can check up others' online stales and establish voice communication sessions to online users at a mouse click. This technology can be applied to more complex services such as multimedia messaging or video conference service.

• 청정기술
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• 제30권3호
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• pp.211-219
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• 2024

3D printing technology has created a paradigm shift in industries by achieving breakthrough innovations and enabling the fabrication of complex products. However, 3D printed parts are inferior in terms of their strength and surface quality compared to parts fabricated by conventional manufacturing methods. This study aims to improve the surface roughness of stereolithographic parts by experimental analysis of the generated area error. A photocurable polymer material was used for fabrication, and the effect of important parameters, such as the material viscosity, printing speed, pneumatic pressure, UV intensity, and pattern spacing, on the surface roughness were analyzed. The results showed that a high-viscosity (12,000 cP) thixotropic material formed a constant pattern with an aspect ratio of 1:1, and the pattern shape was maintained after printing. A pattern with a minimum thickness of 145 ㎛ was formed at a printing speed of 70 mm/s and a pneumatic pressure of 20 kPa. These parameters were found to be suitable for low surface roughness. A UV laser at an intensity of 10 ~ 30 mW/cm² was used to form a smooth surface at low curing intensities. Moreover, it was seen that with a pattern spacing of 110 ~ 130 ㎛, a stereolithographic part with a low surface roughness of Ra 1.29 ㎛ could be fabricated.

• 한국주조공학회지
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• 제29권6호
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• pp.257-264
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• 2009

The effects of silicon and molybdenum on the temperature-dependent properties of high silicon and high molybdenum ductile cast iron were investigated. Microstructure was composed of ferrite, cell boundary complex carbide, carbide precipitated in the grain and graphite. The number and size of carbide decreased with the increase of silicon content and increased with the increase of molybdenum content, however, the size of cell boundary carbide increased above 0.81wt%Mo. The room temperature tensile strength increased with the increase of silicon and molybdenum contents. That did not increase with the latter with more than 0.8wt%. Meanwhile the high temperature tensile strength showed the similar trend to that of room temperature one, that of the specimen with 0.55wt%Mo was the highest. The $A_1$ transformation temperature increased with the silicon and molybdenum contents, and showed similar tendency with the variation of strength. It was discussed due to the solubility limit of Molybdenum in ferrite, of which value was assumed to be in the vicinity of 0.81wt%Mo. The weight after oxidation at 1,173K showed the result caused by the difference in solubility of molybdenum in the matrix. That and the thickness change after oxidation did not show any consistent trend with the silicon and molybdenum contents.

• Design & Manufacturing
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• 제14권4호
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• pp.65-70
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• 2020

Partial reinforcement of sheet metal parts with CFRP patch is a technology that can realize ultra-lightweight body parts while overcoming the high material cost of carbon fiber. Performing these patchworks with highly productive press equipment solves another issue of CFRP: high process costs. The A-pillar is the main body part and has an undercut shape for fastening with other parts such as roof panels and doors. Therefore, it is difficult to bond CFRP patches to the A-pillar with a general press forming tool. In this paper, a flexible system that applies uniform pressure to complex shapes using ceramic particles and silicone rubber is proposed. By benchmarking various A-pillars, a reference model with an undercut shape was designed, and the system was configured to realize a uniform pressure distribution in the model. The ceramic spherical particles failed to realize the uniform distribution of high pressure due to their high hardness and point contact characteristics, which caused damage to the CFRP patch. Compression equipment made of silicone rubber was able to achieve the required pressure level for curing the epoxy. Non-adhesion defects between the metal and the CFRP patch were confirmed in the area where the bending deformation occurred. This defect could be eliminated by optimizing the process conditions suitable for the newly developed flexible system.