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Ground Penetrating Radar Imaging of a Circular Patterned Ground near King Sejong Station, Antarctica
( Kwansoo Kim ),( Hyeontae Ju ),( Joohan Lee ),( Changhyun Chung ),( Hyoungkwon Kim ),( Sunjoong Lee ),( Jisoo Kim ) 대한지질공학회 2021 지질공학 Vol.31 No.3
Constraints on the structure and composition of the active layer are important for understanding permafrost evolution. Soil convection owing to repeated moisture-induced freeze-thaw cycles within the active layer promotes the formation of self-organized patterned ground. Here we present the results of ground penetrating radar (GPR) surveys across a selected sorted circle near King Sejong Station, Antarctica, to better delineate the active layer and its relation to the observed patterned ground structure. We acquire GPR data in both bistatic mode (common mid-points) for precise velocity constraints and monostatic mode (common-offset) for subsurface imaging. Reflections are derived from the active layer-permafrost boundary, organic layer-weathered soil boundary within the active layer, and frozen rock-fracture-filled ice boundary within the permafrost. The base of the imaged sorted circle possesses a convex-down shape in the central silty zone, which is typical for the pattern associated with convection-like soil motion within the active layer. The boundary between the central fine-silty domain and coarse-grained stone border is effectively identified in a radar amplitude contour at the assumed active layer depth, and is further examined in the frequency spectra of the near- and far-offset traces. The far-offset traces and the traces from the lower frequency components dominant on the far-offset traces would be associated with rapid absorption of higher frequency radiowave due to the voids in gravel-rich zone. The presented correlation strategies for analyzing very shallow, thin-layered GPR reflection data can potentially be applied to the various types of patterned ground, particularly for acquiring time-lapse imaging, when electric resistivity tomography is incorporated into the analysis.
김남진(Namjin Kim),김형권(Hyoungkwon Kim),박현호(Hyunho Park),임진완(Jinwan Lim),서석훈(Suhkhoon Suh),박익수(Iksoo Park) 한국추진공학회 2017 한국추진공학회 학술대회논문집 Vol.2017 No.5
연속가변 추력기는 비행체의 위치 또는 자세 변경 및 연소실 내부의 압력 조절을 위하여 정밀 추력 조절이 요구된다. 이를 위하여 연소실 내부의 노즐 목 근처에 설치된 핀틀 구조물을 앞/뒤로 움직여 추력을 조절하고, 핀틀 구조물을 움직이기 위하여 구동장치를 사용한다. 본 논문에서는 연속가변 추력 기용 구동장치를 개발하였으며, 운용조건에서의 부하를 모사하기 위한 부하시험장비를 개발하였다. 또한, 개발된 부하시험장비를 이용하여 구동장치의 성능 시험을 수행하였다. Continuous variable thrusters require precise thrust control to change the position or attitude of the aircraft and to control the pressure inside the combustion chamber. For this purpose, the thrust is adjusted by moving the pintle structure near the nozzle neck inside the combustion chamber by moving the pintle structure forward and backward, and the actuator is used to move the pintle structure. In this paper, we developed a actuator system for continuous variable thruster and load test system to simulate the load under operating conditions. Also, the performance test of the actuator was performed using the developed load test system.
Son Seung-Wan,Lee Dong-Hyeon,Kim Insu,Jung Chang-Hyeon,Kim Hyoungkwon,Yoon Dong-Jin,Lee Joohan 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.3
Renewable energy sources reduce irresponsible carbon emissions and have the advantage of being located close to the load as a distributed generation (DG). Thus, various studies have examined the optimal placement and capacity of DG to maximize their eff ect on power grids. However, there was no paper that considered the normalized cost including the fault current in the process of the optimal allocation of DG. The reason that the normalized fault current cost should be included in objective function is that the more DG is connected to the network, the higher fault current will fl ow. Thus, this paper presents a method of optimizing the DG placement and capacity from a novel perspective using normalized costs that minimize the fault current. For this purpose, this study incorporates the particle swarm optimization method to the Newton–Raphson power-fl ow calculation and the sequence network decomposition methods. The proposed normalized cost function includes not only voltage variations determined by the power-fl ow method, installation costs, and power losses but also fault current determined by the sequence method. As a result, the objective function of the new design, adding the normalized fault current cost, enables the solution set to be more optimal than the previous solution set.