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최종호(Jongho Choi),구본휘(Bonwhee Koo),김태식(Taesik Kim) 한국지반환경공학회 2015 한국지반환경공학회논문집 Vol.16 No.2
도심지 구간에 위치한 지반공학 관련 공사 현장에서는 충분한 안전율 확보와 더불어 사용성도 확보해야 한다. 이를 위해서는 공사 중 인접지반에 발생하는 변형을 제어해야 하므로 지반구조물과 관련된 기술 요구사항도 더욱 높아지고 있다. 사용성 확보를 위해서는 지반의 변형을 예측해야 하므로 지반의 강성을 분석해야 한다. 특히 강성의 비선형성과 이방성은 주요인자라 할 수 있다. 본 연구에서는 깊은 굴착 중 지반이 경험하는 응력경로에 따른 강성의 비선형성과 이방성에 대해 실내시험 결과와 전산 해석 결과를 비교하였다. 강성은 변형률이 작은 미소변형률 구간에서 비선형성이 두드러졌으며, 응력경로에도 큰 영향을 받는 것으로 나타났다. 실내시험 결과 압축은 작은 강성을 인장은 큰 강성을 나타내었으며, 깊은 굴착 시 지지벽체 뒤는 압축이 앞은 인장이 지배적인 응력경로를 나타내었다. 굴착 중 발생하는 지반의 변형을 정확히 예측하기 위해서는 지반이 경험하는 응력경로에 따라 변하는 강성의 변화 특성을 고려해야 한다. In urban area, many design projects related to geotechnical projects are controlled by serviceability rather than stability requirements. Accordingly, control of ground deformation has become more crucial and many researchers have studied soil stiffness. Recent experimental studies on the stress-strain response of Chicago glacial clays showed that the nonlinearity and anisotropy are the two key factors in evaluating the soil stiffness. In this study, experimental results are applied to analyze the deep excavation site locating in downtown Chicago. The stress paths observed from the observation points located behind and front of the supporting wall yield typical stress paths. Changes in soil stiffness nonlinearity and anisotropy were discussed by comparing experimental and computed stress paths. The stiffness anisotropy were significant even at the first few excavations. The stiffness degradation characteristics are significantly different according to relative location to the support wall even at the same elevation.
Transfer Time, Energy, and Quota-Aware Multi-RAT Operation Scheme in Smartphone
Wonbo Lee,Jonghoe Koo,Yongseok Park,Sunghyun Choi IEEE 2016 IEEE Transactions on Vehicular Technology VT Vol.65 No.1
<P>Today's smartphones integrate multiple radio access technologies (multi-RAT), e.g., third-generation (3G), fourth-generation (4G), Wi-Fi, and Bluetooth, whereas the number of integrated RATs is increasing. Therefore, it is becoming more important to select the best RAT set among the available RATs and determine how much data to transfer via each selected RAT network. We propose a multi-RAT interface activation algorithm with supporting system design for smartphones' file transfer service (e.g., downloading a movie file). We model a multiattribute cost function incorporating file-transfer completion time, energy consumption, and data usage quota together. The goal of this paper is to find out the optimal multi-RAT set to be activated with the corresponding file segment allocation that minimizes the cost function under given energy and quota constraints. By the proposed algorithm, the suboptimal solution can be found without significant performance degradation from the optimal solution while making the computational complexity linear in the number of RATs.</P>
Video multicast over WLANs: Power saving and reliability perspectives
Shin, Yeonchul,Choi, Munhwan,Koo, Jonghoe,Choi, Sunghyun IEEE 2013 IEEE network Vol.27 No.2
<P>Video streaming service via multicast is one promising technology for multimedia services over wireless local area networks. Given that many portable devices are battery-powered while video quality relies on the reliable delivery of video traffic, video multicast frames need to be reliably delivered to power-saving stations. In this article, we study video multicast from the power saving and reliability perspectives. The IEEE 802.11 standard allows multicast receivers to enable power management while receiving multicast frames. However, from measurements with several commercial WLAN devices, we observe that many devices are not standards- compliant, thus severely degrading video multicast performance when multicast receivers are in the power saving mode. We identify various standards-non-compliant malfunctions of both access points and stations, and then categorize these malfunctions. Meanwhile, the legacy 802.11 standard is known to support only unreliable multicast service due to the lack of retransmissions. We present various reliable multicast schemes including application layer forward error correction and reliable multicast protocols defined in the emerging IEEE 802.11v and 802.11aa, and comparatively evaluate them via simulations.</P>