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Hyunwoo Song,Jeong-Min Lee,Yongseok Kim,양승호,Soo Park,구재민,Chang-Sung Seok 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.2
Recently, because global warming has become increasingly severe, CO2 emission regulations have become strict. Accordingly, there is an increasing demand for a combined cycle power plant that is eco-friendly and capable of high-efficiency generation using natural gas, which has a relatively low carbon content. In order to improve the efficiency of a combined cycle power plant by increasing the operating temperature, the durability of the hot-section components must be secured. Therefore, thermal barrier coating (TBC) technology has been applied. The TBC is damaged by thermal fatigue during operation. The delamination of the TBC could lead to core component damage. Therefore, studies on the prediction of TBC durability should be conducted before increasing the operating temperature. In particular, because the thermal fatigue life is affected by changes in the TBC structure, there is a demand for a durability evaluation technique that takes this into consideration. In this study, a thermal fatigue analysis was performed that considered the growth of the oxide layer, and a thermal fatigue life prediction equation for the TBC was derived based on the results. The thermal fatigue life was predicted, according to the change in the TBC structure, using the life prediction equation, and it was verified by comparing it with the thermal fatigue test results.
Hyunwoo Song,Jeong-Min Lee,Junghan Yun,Soo Park,Yongseok Kim,Kyoung-Sup Kum,Young-Ze Lee,Chang-Sung Seok 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.1
Combined-cycle power generation is a high-efficiency power generation method using natural gas that can reduce the emissions of carbon dioxide and other harmful substances by increasing the power generation efficiency. Therefore, the turbine inlet temperature should be increased to improve the power generation efficiency. However, given that the operating environment becomes extreme as the turbine inlet temperature increases, ensuring the sufficient durability of the gas turbine components is a necessity. Thermal barrier coatings (TBCs) applied to ensure the durability of the gas turbine components in a high temperature environment can peel off by stress generated through the difference in the thermal expansion coefficient of each layer. Because internal gas turbine components are damaged if peeling occurs, it is essential to ensure sufficient durability of the TBC. In particular, to enhance the efficiency of the combined-cycle power plant, and to withstand higher operating temperatures, it is essential to develop a TBC with an improved durability performance, when compared with currently commercialized TBCs. In this study, we attempted to improve the durability of the TBCs by mitigating the stress concentration phenomenon by gently controlling the rumpling of the oxide layer. For this purpose, the vertical crack design conditions required to reduce the buckling stress were derived through a finite element analysis. Isothermal degradation and thermal fatigue tests were conducted on the fabricated specimens to verify whether the oxide layer rumpling of the designed TBC was controlled gently and whether the durability was improved. Base on the results, a TBC structure with improved durability using oxide layer rumpling control technology is proposed.
Hyunwoo Song,Daniel Hernandez,Kyoung-Nam Kim 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.4
This article intends to present the electromagnetic (EM) insight of the operation of a double loop shaped dual loop dipole (DLD) antenna as a single-channel transceiver coil and in an array configuration of multi-channel transceiver coil, designed to provide high signal-to-noise ratio (SNR) by using numerical simulations for 300 MHz magnetic resonance imaging (MRI). Thus, this section includes the comparison of DLD antenna and commonly used loop coils through EM simulations. The use of a DLD antenna is proposed to address the length issue that traditional straight dipole have by making a spiral type in a loop style, while having the same effective physical length of the straight dipole. The magnetic flux density (|B1|)-fields of the DLD antenna and the traditional loop coil are compared by field maps acquired by EM simulations. In addition, the DLD antenna has been extended to a 7-channels array, for which the magnetic field coupling between each coil is analyzed and presented through the noise correlation matrix. The use of the DLD antenna exhibits higher |B1|-field intensity while keeping the similar uniformity than a surface loop coil. We use the DLD antenna 7-channel array to observe its utility as multi-channel with short distance overlap between elements; each element is approximately 37 mm away from neighboring element. Transceiver array arrangements also show improved coil performance, especially the interleaving configuration with loop coil indicates lowered mutual inductance coupling at calculated noise correlation matrix. The proposed DLD antenna is expected to induce rapid imaging and high |B1|-field, when expanded to multi-channel planar or volume configuration since it can maximize the number of configuring coil elements within limited imaging area leading effective parallel imaging and deeper penetration depth due to the traveling wave.
무인선박의 자율운항을 위한 저가형 LiDAR센서 기반의 장애물 회피 시스템 구현
송현우(HyunWoo Song),이광국(Kwangkook Lee),김동헌(Dong Hun Kim) 대한전기학회 2019 전기학회논문지 Vol.68 No.3
In this paper, we propose an obstacle avoidance system for an unmanned ship to navigate safely in dynamic environments. Also, in this paper, one-dimensional low-cost lidar sensor is used, and a servo motor is used to implement the lidar sensor in a two-dimensional space. The distance and direction of an obstacle are measured through the two-dimensional lidar sensor. The unmanned ship is controlled by the application at a Tablet PC. The user inputs the coordinates of the destination in Google maps. Then the position of the unmanned ship is compared with the position of the destination through GPS and a geomagnetic sensor. If the unmanned ship finds obstacles while moving to its destination, it avoids obstacles through a fuzzy control-based algorithm. The paper shows that the experimental results can effectively construct an obstacle avoidance system for an unmanned ship with a low-cost LiDAR sensor using fuzzy control.
DMA 내 막대형 시스 유동 층류화 장치에 의한 샘플 유동 정렬 및 입자 분류 효율 향상
송현우(Hyunwoo Song),이상면(Sang-Myun Lee),김용준(Yong-Jun Kim),송준호(Soonho Song) 대한기계학회 2020 大韓機械學會論文集B Vol.44 No.4
경제성을 고려한 독자적인 설계로 제작된 DMA의 시스 흐름 층류화 장치 장착에 따른 입자 분류 효율 개선에 대하여 연구하였다. DMA는 평행판형 구조를 채택하여 제작되었고, 넓은 목표 입경 범위를 충족하기 위해 높은 에어로졸/시스 유량비를 사용하였다. 시스 흐름 층류화 장치는 유로 내 중심선 상에 수직으로 위치한 원기둥형 막대 모양이며, 간단한 CFD를 통해 에어로졸 흐름 정렬도 향상을 목표로 최적화하였다. 연구 결과, 층류화 장치가 장착되었을 때 유로 상단 벽 방향으로의 에어로졸 흐름 정렬도가 크게 개선된 것을 확인하였다. 시스 층류화 장치로 인한 에어로졸 흐름 정렬 개선이 실제로 입자 분류 효율에 미치는 영향을 검증하기 위해 실험을 수행하였고, 200nm 단분산 입자 샘플과 1:5의 에어로졸/시스 유량비 조건에서 91.1%의 분류 효율 향상이 관찰되었다. The improvement in particle classification performance of a differential mobility analyzer (DMA), based on an original cost-effective design, was investigated using a simple sheath flow laminarizing structure. The DMA was designed as a parallel-type, and was used with high aerosol/sheath flow ratios to achieve a wide particle diameter range. The sheath flow of the laminarizing structure consisted of a vertical rod located at the center of the flow channel. A computational fluid dynamics (CFD) optimization was performed for enhancing aerosol flow alignment. With the flow laminarizer, the aerosol flow alignment toward the channel upper wall significantly improved. Subsequently, experiments were performed to examine the effects of the sheath flow laminarization and aerosol flow alignment on the particle classification performance of the DMA. As a result, the classification efficiency increased by 91.1, with a 200 nm particle sample and aerosol/sheath flow ratio of 1:5.