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김홍교,박으뜸,송우진,강범수,김정 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.3
Fiber metal laminates (FMLs) are composites that have better mechanical properties (e.g. specific stiffness, strength, and impact resistance) than metallic materials. FMLs can be use in automobile and aviation industries as performance-enhancing or weight-lightening materials. To use FMLs in industries, a numerical analysis process should be established to reduce experimental cost and time. To establish such a process, the properties of adhesive zone materials in FMLs at delamination conditions should be determined. In this study, FMLs were produced, and the properties of the adhesive zone materials were determined from the strain energy release rate. Based on these properties, numerical analysis was performed through LS-DYNA for metallic Al 6061-T6 and by ABAQUS for FMLs. The Johnson-Cook strength and damage model, which can represent the strain rate effect, were used as the material model. The adhesive film was expressed by strain energy release rate, and self-reinforce polypropylene had FLD without cohesive zone model (CZM). Furthermore, the impact resistances of FMLs and Al 6061-T6 were investigated and compared at high velocities by developing an electromagnetic launcher. The impact resistance of the FMLs was investigated using impact test and numerical analysis, showed that FMLs had better impact resistance than metallic materials at high velocities. This numerical analysis also provided an impact prediction method at highvelocity impact phenomenon without CZM.
관정간 도수통로를 설치한 개방형 지열 시스템의 냉방성능 실험
김홍교,배상무,남유진,전운,오종현,이병호 대한설비공학회 2018 설비공학 논문집 Vol.30 No.4
A ground-source heat pump system (GSHP) is more energy efficient than other heat-source systems because it uses annual constant underground and water temperatures. Especially, two-well geothermal systems using groundwater as the heat source can achieve higher performance than closed-loop geothermal systems. However, performance of two-well geothermal systems is decreased by occurring overflow according to scale during long-term operations. Therefore, this study presents a two-well pairing geothermal system that controls the groundwater level of a diffusion well. In addition, a two-well pairing geothermal system and an SCW geothermal system were installed, and a comparative analysis of cooling performance depending on system operation under the same load conditions was conducted. The result was that the average heat pump coefficient of performance (COP) of the two-well pairing system was 6.5, and the entire system COP was 4.3.
최적화 컴파일된 자바스크립트 함수에 대한 최적화 해제 회피를 이용하는 런타임 가드 커버리지 유도 퍼저
김홍교,문종섭 한국정보보호학회 2020 정보보호학회논문지 Vol.30 No.3
The JavaScript engine is a module that receives JavaScript code as input and processes it, among many functions that areloaded into web browsers and display web pages. Many fuzzing test studies have been conducted as vulnerabilities inJavaScript engines could threaten the system security of end-users running JavaScript through browsers. Some of them haveincreased fuzzing efficiency by guiding test coverage in JavaScript engines, but no coverage guided fuzzing of optimized,dynamically generated machine code was attempted. Optimized JavaScript codes are difficult to perform sufficient iterativetesting through fuzzing due to the function of runtime guards to free the code in the event of exceptional control flow. Tosolve these problems, this paper proposes a method of performing fuzzing tests on optimized machine code by avoidingdeoptimization. In addition, we propose a method to measure the coverage of runtime-guards by the dynamic binaryinstrumentation and to guide increment of runtime-guard coverage. In our experiment, our method has outperformed theexisting method at two measures: runtime coverage and iteration by time. 자바스크립트 엔진은 주로 웹 브라우저에 적재되어 웹 페이지를 표시하는 여러 기능 중 자바스크립트 코드를 입력으로 받아 처리하는 모듈이다. 자바스크립트 엔진 내 취약점은 종단 사용자의 시스템 보안을 위협할 수 있어 많은퍼징 테스트 연구가 수행되었다. 그중 일부 연구는 자바스크립트 엔진 내 테스트 커버리지를 유도하는 방식으로 퍼징 효율을 높였으나, 최적화되어 동적으로 생성된 기계어 코드에 대한 커버리지 유도 퍼징은 시도되지 않았다. 최적화된 자바스크립트 코드는 예외적인 흐름 발생 시 코드를 해제하는 런타임 가드의 기능으로 인해 퍼징을 통한 충분한 반복 테스트가 어렵다. 본 논문은 이러한 문제점을 해결하기 위해 최적화 해제를 회피하여 최적화된 기계어 코드에 대해 퍼징 테스트를 수행하는 방법을 제안한다. 또한, 동적 바이너리 계측 방식으로 수행된 런타임 가드의 커버리지를 계측하고 커버리지 증가를 유도하는 방식을 제안한다. 실험을 통해, 본 연구가 제안하는 방식이 런타임 가드커버리지, 시간당 테스트 횟수의 두가지 척도에서 기존의 방식보다 뛰어남을 보인다.
김홍교(Hong-Kyo Kim),곽현덕(Hyun-Duck Kwak),최창호(Chang-Ho Choi),김정(Jeong Kim) 한국항공우주학회 2018 韓國航空宇宙學會誌 Vol.46 No.2
전기펌프시스템은 기존 터보펌프의 가스발생기, 구동기 및 터빈이 필요 없는 매우 간결한 구조를 갖고 있어 저가 소형 위성 발사체의 차세대 추진기관으로써 최근 주목받고 있다. 그래서 본 논문에서는 로켓엔진용 전기펌프 시스템의 가장 중요한 핵심부품인 영구자석 동기모터(PMSM)의 개발 및 발사체로의 적용 가능성을 파악하기 위하여 50 kW, 50,000 RPM의 성능을 가지는 전기모터에 대한 개념설계안을 도출하였다. 요구되는 전기모터의 성능을 만족시키기 위해서 전자기장해석을 수행하여 모터의 전체 외경과 회전자의 내경을 결정하였으며, 회전자는 4,000 가우스의 Sm2Co17 원통형 자석을 이용하여 Inconel 718 재료의 캔으로 체결하였다. 또한, 엔진구동시 모터 운전 영역에서의 회전 동역학적 안정성을 검증하기 위해서 회전체 동역학해석을 수행하였으며, Campbell 선도를 통하여 설계한 모터의 단품운전 뿐만 아니라 성능확인을 위한 Dynamo meter 운전 시에도 공진현상이 발생하지 않음을 해석적으로 확인할 수 있었다. Electric pump system is new technology for next generation propulsion unit. The system has simple structure which dose not need gas generator, injector and turbine and might better pump for low cost and low payload rocket. Therefore, this paper suggests conceptual design of electric-pump Permanent-Magnet Synchronous Motor (PMSM) which has 50 kW & 50,000 RPM for rocket. To satisfy the system’s requirement, electromagnetic analysis is conducted for suitable inner and outer diameter of stator and rotor which uses 4000 Gauss cylinder magnet and Inconel 718 can to fix whole rotor. Futhermore, to confirm rotational vibration, rotordynamics analysis is conducted. By this analysis, Campbell diagram is printed. From the diagram, natural frequency could be determined for the only motor and dynamo meter test bench.
중고속 충돌 실험을 위한 전자기력 발사장치의 설계와 제작
김홍교(Hong Kyo Kim),노학곤(Hak Gon Noh),강범수(Beom Soo Kang),김정(Jeong Kim) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.10
항공산업의 발달로 하늘에는 많은 비행기, UAV, 드론이 비행하고 있다. 비행기와 UAV는 빠른 속도로 비행하며 드론의 프로펠러는 빠른 속도로 회전하고 있다. 이렇게 빠른 속도의 비행체간의 충돌은 비행기 운항과 승객의 안전성을 위협하고, 지상에 있는 인명과 재산에 피해를 줄 수 있다. 비행체의 운항속도는 음속(340㎧) 내외이며, 프로펠러의 회전 속도는 그 보다 작은 속도 영역이다. 현재까지의 충돌 실험은 공기의 힘을 이용한 방식으로 충돌 속도를 얻었고, 공기 팽창에 따른 넓은 공간을 필요로 한다. 하지만 전자기력 발사장치는 그보다 작은 공간에서 충분한 속도를 얻을 수 있다.(~500㎧) 본 논문에서는 전자기력 발사장치의 설계와 이에 따른 제작에 관한 방법을 제시하고자 한다. Many plane, UAV and drone fly in the sky as development of aviation industry. Plane and UAV fly and drone’s propellers rotate so fast. Impact between flying objects which have high velocity threats passengers. Also the impact damages people, building and various property. Plane’s operating speed is near sound velocity(340㎧), and propeller’s rotating speed is less than that. Until now, impact experiment uses gas gun to get speed and the gun needs large space to entirely air expansion. Electromagnetic launcher, especially railgun, needs smaller space than gas gun to get enough speed about 500㎧. This paper explains electromagnetic launcher’s operating principle, shows making electromagnetic launcher design guide line and suggests that it is a better apparatus to get low-high velocity.
수자원 관리 정보 시스템을 이용한 수열에너지 잠재량 산정에 관한 연구
김홍교(Hongkyo Kim),남유진(Yujin Nam) 대한설비공학회 2019 대한설비공학회 학술발표대회논문집 Vol.2019 No.-
Recently, the Korean government has proposed the convergence technology of renewable energy as a national vision for the mandatory project of Zero Energy Building, (ZEB). Therefore, various renewable energy technologies are being introduced in buildings, and renewable heat source energies that can cope with heating and cooling loads are attracting attention. The hydrothermal energy includes seawater, river water, pipeline water and dam lake water. However, in Korea, river water, pipeline water and dam lake water excluding seawater were not recognized as renewable energy. Therefore the use of hydrothermal energy such as river, pipeline and dam lake water is limited. In this paper, quantitative analysis of the potential of hydrothermal energy in river water, pipeline water and dam lake water was conducted to examine applicability of hydrothermal energy. As a result, the potential of hydrothermal energy in Seoul is 534,220 TJ/year, Busan is 238,241 TJ/year and Daejeon is 21,134 TJ/year.