• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.160.2-160.2
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• 2012

Unified State Model(이후 USM)은 Altman(1972)에 의해 처음 제안된 이후 Chodas(1981), Raol & Sinha(1985), Vittaldev et al.(2012) 등을 거치며 연구 발전되어 왔다. 이 모델은 공간상 6개 성분의 위치, 속도 벡터를 이용해 위성의 운동을 기술하는 기존 계산 방법과 달리 4개의 Quaternion 변수를 도입하여 위성의 위치를, 3개의 Hodograph 변수를 도입하여 위성의 속도를 각각 기술한다. USM의 장점은 직교좌표계로 표현된 위성의 위치, 속도 변수에 비해 USM 변수의 변화량이 상대적으로 작기 때문에 수치 계산 시 계산의 안정도가 높다. 또한 원궤도(${\omega}$ : undefined)와 적도면 궤도(i = 0, ${\Omega}$ : undefined) 계산 시에 나타나는 특이성(singularity) 문제가 발생하지 않는다. 본 연구에서는 USM 계산방법과 기존 방법에 의한 위성궤도 계산결과의 차이를 비교 분석하였다. 지구궤도 위성의 정밀계산을 위해 이체항 이외에 지구타원체 섭동항과 대기 항력에 의한 섭동항을 추가 적용하였다. 비구형 지구 중력 포텐셜에 의한 섭동은 J4항까지 고려하였으며, 대기 항력은 간단한 exponential 모델을 적용하였다. 또한 수치계산 시 적분 간격과 정밀도 차수를 조절하여 각 모델의 계산 안정성을 테스트하였다. 본 연구의 궤도계산 결과 USM 모델을 이용한 계산방법은 그 정밀성과 계산효율성이 매우 우수한 것으로 검증되었다.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.3
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• pp.23-29
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• 2002

A wall-frame type structural system has been widely used to make full use of a limited land in large cities to satisfy the several functional requirement in one building. However, this type of hybrid structure brought some problems due to the vertical discontinuity of a structural system. The response of a wall-frame type structural system having a deep transfer girder was observed. An arch system was introduced to replace the deep transfer girder. The adequacy of an arch system was observed for the various boundary conditions of a system. The proposed system was compared to a general transfer girder system by applying both gravity load and lateral load. It was observed that an arch system fairly distributes the stress without concentrating stress at a certain location of a system differently from the current transfer girder system. The moment decrement effect of a column can also be obtained by eliminating the large mass of a transfer girder. Also it was investigated that an arch system is more economical and effective than the current transfer girder system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.283-290
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• 2020

In this study, a floater was developed for a frame-type solar power plant. The floater supports the frame and the solar panels. A finite element analysis was performed to design its shape and thickness, and the floater was manufactured by a rotational molding method using linear low-density polyethylene. It was found that the floater did not cause collapse and it maintained its stiffness even at 4 times the maximum load of 322.7 kgf. To perform a long-term compression test, a weight-type load application device that uses gravity was designed and manufactured. The amount of compressive deformation was measured for 7 days, and a long-term deformation equation was obtained. Even under small loads, continuous deformation was observed. However, the 10-year deformation amount for a constant load of 100 kgf was predicted to be small at about 4.64 mm. As a result, it was found that the developed floater could be used in a solar power plant on a body of water.

• Korean Journal of Ecology and Environment
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• v.49 no.4
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• pp.258-270
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• 2016

This study was conducted to test the green-tide mitigation technique in the lower part of the Sook Stream (Chusori) of Daecheong Reservoir from June 27 to August 24, 2014. And the effects were compared with weekly monitoring result of the watching station of the algae alert system (AAS) as well as test beds reach. The green-tide in a test bed was begun from the upstream, and it was gradually transferred and spread toward the downstream by the hydrological factors. The total amount of algae removed by algae removal device during the test period was 33,920 kg, and solids dewatered by natural gravity was 8,480 kg. Also chlorophyll-a content was 2.83 kg, the number of blue-green algae cells was equivalent to $78.6{\times}10^{14}$ cells. Compared with the results of the watching station of AAS, the pre-concentrate removal work in the outbreak waters was able to suggest the possibility of green-tide mitigation. In addition, an effective management of the green-tide was required spatial and temporal occurrence information and practical device technology. Particularly, the optimal timing of algae removal in the river-reservoir hybrid system was recommended at times before the monsoon rainy season and reached the lowest water level.

• The Journal of Korean Orthopaedic Ultrasound Society
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• v.1 no.2
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• pp.73-77
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• 2008

Purpose: The purpose of this study was to describe the method of dynamic sonographic measurements in the evaluation of the MCL injury of the knee joint while applying valgus and varus stress. Materials and Methods: Seven cases of MCL injury from January to April of 2008 was used for the study. For the evaluation of the medial instability, sonography was used immediately after injury, 6 weeks and 12 weeks after conservative treatment with limited motion brace. The length between the foot of the medial femoral epicondyle and the most proximal point of the tibial cortex was measured in 30 degrees flexion with valgus and varus stress of the knee joint. Results: The foot of the medial epicondyle and the starting point of the proximal tibial cortex underneath the round portion of the articular cartilage were always able to be seen on ultrasonography, even in varus and valgus stress with gravity in 30 degrees flexion of the knee joint. The results of measurements were always constant. Conclusion: Sonography can be used in evaluation of medial instability under the dynamic valgus and varus stress of the knee joint without further injury.

• Journal of Wetlands Research
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• v.23 no.3
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• pp.201-212
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• 2021

In wetland protection areas, a phytosociological research was conducted on willow forests, which plays an important ecological and environmental role and is the main material for ecological restoration. A total of 61 relevés were collected according to the Z-M(Zürich-Montpellier) school's method and the characteristics of plant communities and the composition of the species were identified. A total of 9 plant communities including 237 taxa were differentiated. Willow species showing the high r-NCD(relative net contribution degree) value in study areas were Salix koriyanagi, Salix chaenomeloides, Salix triandra subsp. nipponica, Salix gracilistyla and Salix pierotii. Poaceae was the most diverse in species, followed by Asteraceae, Apiaceae, Polygonaceae and Fabaceae. Life form type of willow forests in wetland protection areas was determined to be Th(therophytes)-R₅(non-clonal form)-D₄(clitochores)-e(erect form) type. The naturalized plants and invasive alien species were identified as 24 taxa and 4 taxa, respectively. Naturalized and disturbance indices were 10.1% and 41.4%, respectively. The results of the site-species ordination by Non-Metric Multidimensional Scaling(NMDS), wetland types and altitude gradient were the main ecological factors determining the spatial distribution of plant communities. Diversity index and evenness index were high in mountainous palustrine wetlands with relatively high altitude, and the disturbance index, naturalized index and appearance rate of annual plant were high in riverine and lacustrine wetlands with low altitude.