• Korean Chemical Engineering Research
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• 제53권4호
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• pp.412-416
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• 2015

고분자 막 성능 평가 및 내구성 평가에 이용하기 위해 고분자전해질 연료전지(PEMFC) 구동 중에 수소 크로스오버 측정이 필요하다. 수소 크로스오버 측정 시에 불활성 기체 대신에 공기를 cathode에 공급하면서 기체 크로마토그래프로 수소 농도를 cathode 출구에서 분석하였다. PEMFC 구동 중 고분자 막을 통과한 수소는 cathode에서 산소와 반응해 불활성 가스를 공급할 때에 비해 수소 농도가 감소하였다. cathode 공기 공급 유량이 증가하면 수소 농도가 감소했고, 셀의 온도와 습도, 압력이 증가하면 cathode의 수소 농도는 증가했다. 일반적인 PEMFC 구동 조건에서 $120mA/cm^2$ 전류밀도에서 수소농도는 약 5.0 ppm이었다.

• Smart Structures and Systems
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• 제17권1호
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• pp.149-165
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• 2016

Floods have been known to be one of the main causes of bridge collapse. Contrary to earthquakes, flood events tend to occur repeatedly and more frequently in rainfall areas; flood-induced damage and collapse account for a significant portion of disasters in many countries. Nevertheless, in contrast to extensive research on the seismic fragility analysis for civil infrastructure, relatively little attention has been devoted to the flood-related fragility. The present study proposes a novel methodology for deriving flood fragility curves for bridges. Fragility curves are generally derived by means of structural reliability analysis, and structural failure modes are defined as excessive demands of the displacement ductility of a bridge under increased water pressure resulting from debris accumulation and structural deterioration, which are known to be the primary causes of bridge failures during flood events. Since these bridge failure modes need to be analyzed through sophisticated structural analysis, flood fragility curve derivation that would require repeated finite element analyses may take a long time. To calculate the probability of flood-induced failure of bridges efficiently, in the proposed framework, the first order reliability method (FORM) is employed for reducing the required number of finite element analyses. In addition, two software packages specialized for reliability analysis and finite element analysis, FERUM (Finite Element Reliability Using MATLAB) and ABAQUS, are coupled so that they can exchange their inputs and outputs during structural reliability analysis, and a Python-based interface for FERUM and ABAQUS is newly developed to effectively coordinate the fragility analysis. The proposed framework of flood fragility analysis is applied to an actual reinforced concrete bridge in South Korea to demonstrate the detailed procedure of the approach.

• 한국진공학회지
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• 제7권2호
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• pp.104-111
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• 1998

저압 MOCVD 방법을 이용하여 InGaAs/InP 양자우물구조를 성장하였다. 성장 정지 시간에 따른 photoluminescence특성의 변화를 통하여 계면구조를 분석하였다. InP표면을 $PH_3$ 분위기로, InGaAs표면을 $AsH_3$분위기로 유지하며 성장을 정지하는 경우에는 성장 정지 시간이 길어짐에 따라 불순물 유입에 의한 것으로 생각되는 PL반가폭의 증가를 관찰하였다. InP표면에 AsH3을 공급하는 경우에는 As-P교환에 의해 우물층 두께가 증가하여 PL피크가 저에너지로 이동하였고, 반가폭의 변화는 크지 않았다. 계면 양자우물구조를 형성하여 As-P 교환작용에 대해 조사하였고, 1-2monolayer가 InAs유효두께로 계산되었다. InGaAs 표면에 $PH_3$을 공급한 결과, PL피크가 고에너지로 이동하는 것을 관찰하였고 동시에 반가폭도 증가 하였다. 이는 메모리 효과에 의해 InP층으로 As침투를 억제하고, InGaAs표면에서의 국부적 인 As-P교환에 의한 것으로 생각된다.

• Journal of Welding and Joining
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• 제27권6호
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• pp.74-79
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• 2009

Titanium and titanium alloy can be reproduced immediately even if oxide films($TiO_2$) break apart in sea water. Therefore, since titanium demonstrates large specific strength and outstanding resistance to stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion in sea water environment, it has been widely applied to heat exchanger for ships. In particular, with excellent elongation, pure titanium may be deemed as optimal material for production of heat exchanger plate which is used with wrinkles formed for efficient heat exchange. Conventional plate type heat exchanger prevented leakage of liquid through insertion of gasket between plates and mechanical tightening by bolts and nuts, but in high temperature and high pressure environment, gasket deterioration and leakage occur, so heat exchanger for LPG re-liquefaction device etc do not use gasket but weld heat exchanger plate for use. On the other hand, since welded plate cannot be separated, it is important to obtain high quality reliable welds. In addition, for better workability and production performance, lasers that can obtain weldment with large aspect ratio and demonstrate fast welding speed even in atmospheric condition not in vacuum condition are used in producing products. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through quantitative analysis of oxygen and nitrogen and measurement of hardness as fundamental experiment for the evaluation of titanium laser welding, and evaluated the welding performance and mechanical properties of butt welding. This study welded specimens in various conditions by using laser and GTA welding machine to apply edge welding to heat exchanger, and evaluated the mechanical strength through tensile stress test. As a result of tensile test, laser weldment demonstrated tensile strength 4 times higher than GTA welds, and porosity could be controlled by increasing and decreasing slope of laser power at overlap area.

• 문화기술의 융합
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• 제5권4호
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• pp.203-208
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• 2019

의료용 컬러 그래픽 연구는 의료용 로봇의 생산 시대를 통해 회사 제품의 디자인 품질을 세계적으로 확대하고 보급하는 기반이 될 것이다. 본 연구에서는 의료 로봇 침대 확대 시대에 걸맞은 기술과 내용, 유니버셜 의료색 적용, 인체공학적 색채 등을 기반으로 하였다. 이와 함께 유니버셜 디자인의 관점에서 의료용 침대 로봇의 색채 연구방향을 제시하였다. 이에 따라, 국내업체에서 개발 중인 의료용 로봇의 기능을 사례로 하여 유니버셜 컬러 설계를 제안하였다. 이 로봇 침대의 특성은 기능별로 3가지로 구분할 수 있는 바, 첫째는 치유성(Curative)으로 욕창 예방을 위한 치료 특성을, 두 번째는 의료 환경을 위한 청결성(Clean)으로 시트 자동교환을, 세 번째는 편의성(Convenient)으로 환자이송을 구현하는 기능을 갖는 것으로 파악된다. 본론으로 이에 적합한 기능 색채의 조합을 제시하였다. 결과적으로 제시한 색채분석 및 유니버설 컬러설계 기법이 첨단 의료용 로봇 침대의 외형과 기능을 잘 표현하는 데 유용한 방법론이 될 수 있을 것이다.

• The Journal of Korean Physical Therapy
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• 제31권5호
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• pp.322-327
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• 2019

Purpose: This study examined the influence of the maximal aerobic capacity on the two-year cardiac-related re-hospitalization in patients with heart failure with a reduced ejection fraction (HFrEF) in Korean society. Methods: The maximal aerobic capacity of the study population (n=95, male 63%) was evaluated using a cardiopulmonary exercise (CPX) testing system. Each patient was followed up for two years to divide the HFrEF patients into two groups according to cardiac-related re-hospitalization: re-hospitalization (RH) group (n=29, 30%) and no re-hospitalization (NRH) group (n=66, 70%). Results: The relative peak $VO_2$ (mL/kg/min, p<0.001), exercise duration (p<0.001), respiratory exchange ratio ($VCO_2/VO_2$, p=0.001), systolic blood pressure (SBP) reserve (p=0.004), heart rate (HR) reserve (p=0.007), SBP max (p=0.02), and HR max (p=0.039) were significantly lower in the RH group than the NRH group during the CPX test. On the other hand, the ventilatory efficiency (VE/VCO2 slope, p=0.02) and age (p=0.022) were significantly higher in the RH group than in the NRH group. In binary logistic regression analysis, the relative peak $VO_2$ (p=0.001, Wald Chi-square 10.137) was the strongest predictive factor on cardiac-related re-hospitalization, which was followed by $VCO_2/VO_2$ (p=0.019, Wald Chi-square 5.54). On the other hand, age (p=0.063, Wald Chi-square 3.445) did not have a significant influence on cardiac related re-hospitalization. Conclusion: The maximal aerobic capacity, especially the relative peak $VO_2$, is the strongest factor on cardiac-related re-hospitalization within two years in patients with HFrEF in Korean society.

• 한국해양공학회지
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• 제35권1호
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• pp.82-90
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• 2021

Owing to the advantages of assuring the best views and seawater exchange, submerged breakwaters have been widely installed along the eastern coast of Korea in recent years. It significantly contributes to promoting the advancement of shorelines by partially inhibiting incident wave energy. Observations were carried out by a pressure-type wave gauge in the Bongpo Beach to evaluate the coefficients of wave transmission via a submerged breakwater, and the results obtained were compared with those of existing conventional equations on the transmission coefficient derived from hydraulic experiments. After reviewing the existing equations, we proposed a transmission coefficient equation in terms of an error function. Although it exhibited robust relationships with the crest height and breaking coefficient, deviations from the observed data were evident and considered to be triggered by the difference in the incident wave climate. Therefore, in this study, we conducted a numerical experiment to verify the influence of wave period on the coefficients of wave transmission, in which we adopted a parabolic-type mild-slope equation model. Consequently, the deviation from calculated results appears to practically cover all deviation range in the observed data. The wave period and direction of the incident wave increased, the transmission coefficient decreased, and the wave direction was determined to demonstrate a relatively significant influence on the transmission coefficient. It was inferred that this numerical study is expected to be used practically in evaluating the design achievement of the submerged breakwater, which is adopted as a countermeasure to coastal beach erosion.

• 한국수자원학회논문집
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• 제55권1호
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• pp.23-32
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• 2022

본 연구는 지표수-지하수 연계 2차원 흐름 및 용질거동 수치모의를 통해 혼합대 흐름에 의한 지표수-하상 경계층 용질교환이 지표수 내 용질거동에 미치는 영향을 분석하였다. 먼저, 혼합대 흐름이 부재한 불투수성 하상의 경우 사련 하상파에 의해 발달한 바닥면 근처 재순환 흐름의 포착 효과가 용질 파과곡선 형태를 결정하였다. 반면, 용질이 혼합대로 유입되는 투수성 하상에서는 지표수 대비 유속이 느린 혼합대 흐름에 의해 파과곡선 꼬리 부분 농도가 증가하여 파과곡선 꼬리 연장이 급격히 증가하였다. 또한, 지표수 유속 증가는 바닥면 압력 상승과 함께 혼합대 흐름을 빠르게 하여 파과곡선 꼬리의 연장을 단축시켰다. 이러한 본 연구의 결과는 지표수 내 용질 체류시간 예측에 있어 혼합대 흐름의 중요성을 시사하는 바이다.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2184-2194
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• 2021

The Free-Piston Stirling engine (FPSE) is of interest for many research in aerospace due to its advantages of long operating life, higher efficiency, and zero maintenance. In this study, a 1-kW FPSE was proposed by analyzing the requirements of Space Reactor Power Systems (SRPS), of which performance was evaluated by developing a code through the Simple Analysis Method. The results of SAM showed that the critical parameters of FPSE could satisfy the designed requirements. The heater of the FPSE was designed with the copper rectangular fins to enhance heat transfer, and the parametric study of the heater was performed with Computational Fluid Dynamics (CFD) software STAR-CCM⁺. The Performance Evaluation Criteria (PEC) was used to evaluate the heat transfer enhancement of the fins in the heater. The numerical results of the CFD program showed that pressure drop and Nusselt number ratio had a linear growth with the height of fins, and PEC number decreased as the height of fins increased, and the optimum height of the fin was set as 4 mm according to the minimum heat exchange surface area. This paper can provide theoretical supports for the design and numerical analysis of an FPSE for SRPSs.

• 한국군사과학기술학회지
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• 제25권5호
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• pp.487-500
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• 2022

Supercavitation is a phenomenon in which the cavity covers the entire underwater vehicle. The purpose of this paper is to compare and analyze the thermal effect on the cavity characteristics by changing the ventilated gas temperature through computational analysis. For this study, a homogeneous mixture model based on the 3D Navier-Stokes equation was used. As a phase change model, it is its own code considering both pressure change and temperature change. A dimensionless number T_m was presented to analyze the numerical results, and as the T_m increased, the cavity length increased by about 3.6 times and the cavity width by about 3.3 times at 393.15 K compared to room temperature. Analyzing these thermal effects, it was confirmed that rapid heat exchange and heat transfer between the gas phase and the liquid phase occurred at the location where the ventilated gas was sprayed, affecting the cavity characteristics. In addition, it can be confirmed that the initial cavity surface becomes unstable as the ventilated gas temperature increases, and it can be confirmed based on the numerical analysis results that the critical temperature at which the cavity surface becomes unstable is 373.15 K.