• Journal of Astronomy and Space Sciences
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• 제36권1호
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• pp.35-43
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• 2019

The Optical Wide-field patroL-Network (OWL-Net) is a global optical network for Space Situational Awareness in Korea. The primary operational goal of the OWL-Net is to track Low Earth Orbit (LEO) satellites operated by Korea and to monitor the Geostationary Earth Orbit (GEO) region near the Korean peninsula. To obtain dense measurements on LEO tracking, the chopper system was adopted in the OWL-Net's back-end system. Dozens of angle-only measurements can be obtained for a single shot with the observation mode for LEO tracking. In previous work, the reduction process of the LEO tracking data was presented, along with the mechanical specification of the back-end system of the OWL-Net. In this research, we describe an integrity assessment method of time-position matching and verification of results from real observations of LEO satellites. The change rate of the angle of each streak in the shot was checked to assess the results of the matching process. The time error due to the chopper rotation motion was corrected after re-matching of time and position. The corrected measurements were compared with the simulated observation data, which were taken from the Consolidated Prediction File from the International Laser Ranging Service. The comparison results are presented in the In-track and Cross-track frame.

• 한국항공우주학회지
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• 제46권11호
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• pp.921-933
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• 2018

관성항법장치 순수항법 성능을 개선하는 방법으로 관성센서 오차가 상호 상쇄되도록 관성센서뭉치를 회전시켜 항법 성능을 개선하는 방법이 있으며 이러한 원리로 동작하는 항법장치를 회전형 관성항법장치라 한다. 관성센서 오차에 의한 회전형 관성항법장치의 정확한 항법 성능 분석을 위해서는 이에 대한 이론적 오차해석이 요구되나 기존의 많은 연구에서는 지구회전 각속도 및 중력 가속도에 의한 영향을 무시하고 오차해석을 수행하여 회전형 관성항법장치의 정확한 항법 성능 분석이 수행되지 않았다. 본 논문에서는 링레이저 자이로 기반 회전형 관성항법장치의 정확한 항법 성능 분석을 위하여 지구회전 각속도 및 중력 가속도 항을 포함한 이론적인 오차해석을 수행하고 이를 기반으로 회전형 관성항법장치의 항법 성능 분석 결과를 제시하였다.

• 한국추진공학회지
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• 제25권1호
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• pp.19-28
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• 2021

회전 데토네이션 엔진(Rotating Detonation Engine, RDE)은 기계 장치나 유동이 아닌 데토네이션 파만이 연소실 벽을 따라 회전한다. 따라서 RDE 단면이 원형이어야 할 필요가 없으며 임의 단면의 닫힌 형상이 가능하다. 본 연구에서는 임의의 단면을 가지는 RDE의 한 가지 예로써 tri-arc 단면 형상의 RDE를 설계하였으며, 실험적으로 작동 및 성능 특성을 살펴보았다. 동압 센서와 고속카메라를 통하여 데토네이션 파의 회전을 확인하였으며, 오목 면과 볼록 면에서 질량 유량에 따른 데토네이션파의 특징을 알아보았다. 본 연구에서는 유량 조건에 따라 17.0 N에서 96.0 N의 추력 수준을 얻을 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.102-114
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• 2021

Biofouling represents an important problem in the shipping industry since it causes the increase in surface roughness. The most of ships in the current world fleet do not have good coating condition which represents an important problem due to strict rules regarding ship energy efficiency. Therefore, the importance of the control and management of the hull and propeller fouling is highlighted by the International Maritime Organization and the maintenance schedule optimization became valuable energy saving measure. For adequate implementation of this measure, the accurate prediction of the effects of biofouling on the hydrodynamic characteristics is required. Although computational fluid dynamics approach, based on the modified wall function approach, has imposed itself as one of the most promising tools for this prediction, it requires significant computational time. However, during the maintenance schedule optimization, it is important to rapidly predict the effect of biofouling on the ship hydrodynamic performance. In this paper, the effect of biofilm on the ship hydrodynamic performance is studied using the proposed performance prediction method for three merchant ships. The applicability of this method in the assessment of the effect of biofilm on the ship hydrodynamic performance is demonstrated by comparison of the obtained results using the proposed performance prediction method and computational fluid dynamics approach. The comparison has shown that the highest relative deviation is lower than 4.2% for all propulsion characteristics, lower than 1.5% for propeller rotation rate and lower than 5.2% for delivered power. Thus, a practical tool for the estimation of the effect of biofouling with lower fouling severity on the ship hydrodynamic performance is developed.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2720-2727
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• 2022

The Generation IV Lead-cooled fast reactor (LFR) take the liquid lead or lead-bismuth eutectic alloy (LBE) as the coolant of the primary cooling circuit. Combined with the natural characteristics of lead alloy and the design features of LFR, the system is the simplest and the number of equipment is the least, which reflects the inherent safety characteristics of LFR. The nuclear main coolant pump (MCP) is the only power component and the only rotating component in the primary circuit of the reactor, so the various operating characteristics of the MCP are directly related to the safety of the nuclear reactor. In this paper, various working conditions that may occur in the normal rotation (positive rotating) of the MCP and the corresponding internal flow characteristics are analyzed and studied, including the normal pump condition, the positive-flow braking condition and the negative-flow braking condition. Since the corrosiveness of LBE is proportional to the fluid velocity, the distribution of flow velocity in the pump channel will be the focus of this study. It is found that under the normal pump condition and positive-flow braking conditions, the high velocity region of the impeller domain appears at the inlet and outlet of the blade. At the same radius, the pressure surface is lower than the back surface, and with the increase of flow rate, the flow separation phenomenon is obvious, and the turbulent kinetic energy distribution in impeller and diffuser domain shows obvious near-wall property. Under the negative-flow braking condition, there is obvious flow separation in the impeller channel.

• Physical Therapy Rehabilitation Science
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• 제9권4호
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• pp.230-237
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• 2020

Objective: To investigate the physical appearance and therapeutic changes that occur with the performance of Schroth exercise in patients with scoliosis. Design: Randomized controlled trial. Methods: Fifteen subjects with maximum curvature of the lumbar who were diagnosed with idiopathic scoliosis had volunteered to participate in the study. Eight subjects were included in the experimental group where they performed the Schroth Therapeutic Exercise and the other seven were included in the control group. The experimental group underwent 2 hours of weekly treatment for 12 weeks, while the control group did not during the same period based on the decisions of patients or guardians. The Mann-Whitney rank test was carried out to compare the treatment results of the two groups, and the comparison within the group was done by Wilcoxon signed-rank test. The vertebral rotation angle (VRA) was by Scoliometer, and difference of rotated and curved portion volume (DV) between both sides on the major curvature portion measured by 3D human body scanning system. Results: In the experimental group, 12 weeks of Schroth exercise therapy has significant improved in correction rate (CR) in Cobb's angle (CA), VRA, and DV between both sides on the major curvature portion (p<0.05), while significant differences were not found between the groups regarding weight bearing difference in both feet (WD) and DV (p<0.05). Conclusions: Schroth exercise performance showed significant changes in the patient's therapeutic changes (CA, VRA), but the physical appearance (DV, WD) was not significant, indicating that external changes in the treatment goal setting are more difficult goals to achieve.

• 한국농공학회논문집
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• 제64권3호
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• pp.53-61
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• 2022

This study evaluated the impacts of subsurface drainage design, i.e., spacing and depth, on agricultural productivity and environmental sustainability in two tile-drained fields (Sites A and E) under a corn-soybean rotation in the Midwestern United States. A calibrated and validated Root Zone Water Quality Model (RZWQM) was used to simulate Nitrate-N (nitrogen) losses to tile drainage and crop yields of 30 tile spacing and depth scenarios over 24 years (1992-2015). Our results presented that the narrower and deeper the tile drains are placed, the greater corn yield and Nitrate-N losses, indicating that the subsurface drainage design may cause a trade-off between agricultural productivity and environmental sustainability. The simulation results also presented that up to about 255.7% and 628.0% increase in Nitrate-N losses in Sites A and E, respectively, far outweigh the rate of increase in corn yield up to about 1.1% and 1.6% from the adjustment of tile spacing and depth. Meanwhile, the crop yield and Nitrate-N losses according to the tile configuration differed depending on the field, and the soybean yield presented inconsistent simulation results, unlike the corn yield, which together demonstrate the heterogeneous characteristic of agro-environmental systems to a subsurface drainage practice. This study demonstrates the applicability of agricultural systems models in exploring agro-environmental responses to subsurface drainage practices, which can help guide the introduction and installation of tile systems into farmlands, e.g., orchards and paddy fields, in our country.

• Clinics in Shoulder and Elbow
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• 제24권3호
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• pp.166-171
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• 2021

Background: This study aims to compare the clinical outcomes of steroid injections during the rehabilitation period after arthroscopic rotator cuff repair (ACRC). Methods: Among patients who underwent ARCR, 117 patients who met the inclusion and exclusion criteria were enrolled. Pain and range of motion (ROM) recovery at the 3-, 6-, and 24-month follow-up visits and functional outcome at the 24-month follow-up were compared between 45 patients who received ultrasound-guided subacromial steroid injection at postoperative week 4 or 6 and 72 patients who did not. Functional outcome was assessed using the American Shoulder and Elbow Surgeons (ASES) score and Constant score. Healing of the repaired tendon and retear were observed at the 6-month follow-up via magnetic resonance imaging (MRI) or computed tomography (CT) arthrography. Results: At the 3-month follow-up, the steroid injection group showed lower visual analog scale scores than the control group (p<0.05) and showed faster recovery of forward flexion and internal rotation (p<0.05). From the 6-month follow-up, the two groups did not show differences in pain and ROM, and the ASES score and Constant score also did not significantly differ at the 24-month follow-up. The two groups did not differ in retear rate as determined by MRI or CT arthrography at the 6-month follow-up. Conclusions: This study demonstrated that ultrasound-guided subacromial steroid injection at 4 or 6 weeks after ARCR leads to quick pain reduction and ROM recovery until 3 months after surgery. Therefore, subacromial steroid injection is speculated to be an effective and relatively safe method to assist rehabilitation.

• 한국습지학회지
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• 제24권3호
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• pp.196-203
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• 2022

본 논문은 자유수면에서 마이크로 중력식 와류 수차의 성능에 블레이드 상대위치 변화의 영향을 이해하는 것이다. 일정한 와류 유동에서 자유수면 아래 상대 와류 수심비(y/h_v)의 범위 0 ~ 0.778 지점에 설치된 블레이드의 위치 변화에 따른 마이크로 와류 수차의 회전수, 전압 및 전류를 측정하였다. 유량은 0.0063 ~ 0.00662 m³/s 범위이다. 실험 결과는 유입되는 유속과 난류강도의 분포가 변하기 때문에 블레이드의 상대위치가 마이크로 와류 수차의 성능에 영향을 미치는 것으로 나타났다. 와류 수차에서 발생하는 에너지의 최대량은 상대 와류 수심비 0.111 ~ 0.222 지점에서 발생했다. 상대 와류 수심비 0.111 지점의 출력은 자유수면 아래 상대 와류 수심비 0.588 지점보다 약 2.4배 더 크게 나타난다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.319-319
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• 2023

Flows of water in the environment (e.g. in a river or estuary) generally occur in complex conditions. This complexity can hinder a general understanding of flows and their related sedimentary processes, such as erosion and deposition. To gain insight in simplified, controlled conditions, hydraulic flumes are a popular type of laboratory research equipment. Linear flumes use pumps to recirculation water. This isn't appropriate for the investigation of cohesive sediments as pumps can break fragile cohesive sediment flocs. To overcome this limitation, the rotating annular flume (RAF) was developed. While not having pumps, a side-effect is that unwanted secondary circulations can occur. To counteract this, the top and bottom lid rotate in opposite directions. Furthermore, a larger flume is considered better as it has less curvature and secondary circulation. While only a few RAFs exist, they are important for theoretical research which often underlies numerical models. Many of the first-generation of RAFs have come into disrepair. As new measurement techniques and models become available, there is still a need to research cohesive sediment erosion and deposition in facilities such as a RAF. New RAFs also can have the advantage of being automatic instead of manually operated, thus improving data quality. To further advance our understanding of cohesive sediment erosion and deposition processes, a large, automatic RAF (1.72 m radius, 0.495 m channel depth, 0.275 m channel width) has been constructed at the Hydraulic Laboratory at Chungnam National University (CNU), Korea. The RAF has the ability to simulate both unidirectional (river) and bidirectional (tide) flows with supporting instrumentation for measuring turbulence, bed shear stress, suspended sediment concentraiton, floc size, bed level, and bed density. Here we present the current status and future prospect of the CNU RAF. In the future, calibration of the rotation rate with bed shear stress and experiments with unidirectional and bidirectional flow using cohesive kaolinite are expected. Preliminary results indicate that the CNU RAF is a valuable tool for fundamental cohesive sediment transport research.