• 수산해양기술연구
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• 제34권3호
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• pp.294-301
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• 1998

Towing performance of a midwater trawl system was examined aboard the training ship KAYA(2900ps) at the East Sea using the midwater trawl gear that had been designed and manufactured in accordance with the vessel. In this experiment, the trawl system data, the towing speed, the length and tension of the warp, net mouth height, and the depth of otter boards and net were measured and analyzed. The results are as follows: 1. In case of heaving in the warp with constant towing speed, the tension was suddenly increased and then again was reduced and after returned to the original steady state tension. At this time, net height was reduced a bit by ascension of ground rope, but returned to it’s original value. In the case where the warp was paid out, the tension was suddenly decreased and after increased and then returned to the tension of the original state, and the net height was greatly increased instantly by the sinking of the ground rope and then returned to the steady state 2. In the case of increased towing speed mm constant warp length, the tension was increased, and reducing the net height, the gear depth was decreased. On the other hand, in the case where towing speed was reduced, the tension was reduced and the gear depth and net height was increased. 3. Otter boards show a swing motion in the scope of 5~ 10m continuously. Otter boards responded to the state change of the trawl system at first, and then the motion of the net appeared. 4. The depth of net center was about 20m deeper than that of the otter boards, it shows about 0.4 times the warp length at the 4knots towing speed.

• 한국건축시공학회지
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• 제15권6호
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• pp.631-639
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• 2015

유닛모듈러 공법에서는 정밀 제작된 유닛모듈과 시공정밀도가 낮은 기초부의 접합부에서 수평 정밀도 차이가 발생한다. 이러한 정밀도 차이로 인하여 상부 유닛모듈이 뒤틀리거나, 간격이 벌어지는 등 다양한 문제가 야기될 수 있다. 이러한 배경에서 본 연구는 Pre-Fab 독립기초의 높이조절이 가능한 공법을 개발하는 것을 목적으로 하였다. 이를 위하여 본 연구에서는 볼트와 너트를 이용한 높이조절 공법을 제안하고 시공 상세도와 시공순서를 제시하였다. 그리고 구조 시뮬레이션을 수행하여 구조적 안정성을 확인하였다. 향후 개발된 높이조절 공법의 mock-up 시험, 경제성 분석 등을 실시하여 시공성과 유용성을 검토할 예정이다.

• 대한산업공학회지
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• 제24권2호
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• pp.167-173
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• 1998

Many workers like welders work in squatting postures with the object on the ground during an entire work shift. It is suspected that such prolonged squatting without any supporting stool would gradually cause musculoskeletal injuries to workers. This study is to examine the physical stress caused by the prolonged squatting and to recommend a safe work/rest schedule for a welding task with squatting posture based on the lab experiments. In this study, 8 healthy student subjects participated in the experiment. They maintained a squatting work posture for 16 minutes with 4 different stool height conditions: no stool; 10cm height; 15cm height; and 20cm height. Every 2 minutes, the discomfort was subjectively assessed with the magnitude estimation method for the whole body, lower back, upper leg and lower leg. Based on discomfort ratings, we found that a 10cm height stool relieved the workload most. Discomfort rating results also indicated that a 20cm height stool showed the highest workload, and the there were no difference in workload between a 15cm height stool and no stool. We recommend to use low height stools and to maintain such working postures no longer than 6 minutes for prolonged squatting tasks.

• Journal of Biosystems Engineering
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• 제41권3호
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• pp.153-160
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• 2016

Purpose: This study was conducted to experimentally investigate the structural safety of and identify critical locations in a front-end loader under impact loads. Methods: Impact and static tests were conducted on a commonly used front-end loader mounted on a tractor. In the impact test, the bucket of the front-end loader with maximum live load was raised to its maximum lift height and was allowed to free fall to a height of 500 mm above the ground where it was stopped abruptly. For the static test, the bucket with maximum live load was raised and held at the maximum lift height, median height, and a height of 500 mm from the ground. Strain gages were attached at twenty-three main locations on the front-end loader, and the maximum stresses and strains were measured during respective impact and static tests. Results: Stresses and strains at the same location on the loader were higher in the impact test than in the static test, for most of measurement locations. This indicated that the front-end loader was put under a severe environment during impact loading. The safety factors for stresses were higher than 1.0 at all locations during impact and static tests. Conclusions: Since the lowest safety factor was higher than 1.0, the front-end loader was considered as structurally safe under impact loads. However, caution must be exercised at the locations having relatively low safety factors because failure may occur at these locations under high impact loads. These important design locations were identified to be the bucket link elements and the connection elements between the tractor frame and front-end loader. A robust design is required for these elements because of their high failure probability caused by excessive impact stress.

• 대한기계학회논문집B
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• 제41권4호
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• pp.277-283
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• 2017

본 연구에서는 높이에 따른 점프 전략 변화를 이해하기 위해 반동을 이용한 수직 점프 시 상변화 시점에서의 지면반력 벡터가 높이에 따라 어떻게 변하는지 분석하였다; 반동과 추진 구간에서 유사한 힘 작용선을 갖는 수직 점프의 경우, 상변화 시점에서 반동의 이득을 나타내는 합력 벡터의 크기와 방향이 일정한 경향성을 가지고 높이에 따라 변화할 것이라 가정하였다. 9명의 청년군 모두는 정해진 5 종류의 높이를 총 5세트에 걸쳐 랜덤 방식으로 점프하였으며, 해당 높이를 유도하기 위해 지면으로부터 191 cm에서 221 cm 사이에 일정한 간격을 두고 마커를 배치하였다. 점프 높이가 증가함에 따라 반동 시 무게중심을 낮추고, 수평, 수직 방향의 힘을 증가시키는 것이 관찰되었는데, 이는 추진일을 증가시키기 위해 관절의 가용범위를 넓히고 초기 힘(또는 가속도) 이득을 늘리기 때문으로 생각된다.

• 융합정보논문지
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• 제10권12호
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• pp.132-139
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• 2020

본 연구의 목적은 착지 시 키 높이 깔창 높이에 따라 젊은 남성의 최대지면반발력시 하지관절각도와 근 활성도에 미치는 영향을 분석하는데 있다. 20대 남성을 대상으로 총 3주에 걸쳐 한 주당 0, 3, 5cm 의 폴리우레탄 소재의 깔창 중 무작위로 하나를 착용하여 40cm 높이의 플랫폼 위에서 Force plate로 착지 동작을 시행하였다. 착지 동작 중 최대 지면반발력 시 하지의 관절 각도와 넙다리곧은근, 넙다리두갈래근, 앞정강근, 장딴지근의 근활성도를 측정하였다. 깔창의 높이에 따른 하지관절 각도와 근활성도의 변화를 비교하기 위해 반복요인이 있는 분산분석(one-way ANOVA)을 실시하였다. 하지관절각도 분석 결과 깔창의 높이가 높아질수록 좌측 발목관절 각도에 영향을 주었으며, 근활성도 분석 결과 깔창의 높이가 높아질수록 우측 앞정강근과 양쪽 넙다리 두갈래근에 영향을 주었다. 하지 근육의 충분한 근력증가를 통하여 착지시 신체를 보호할 수 있을 것이라고 생각되며 깔창의 종류에 따라 영향을 미치는 근육과 하지관절의 각도도 다를 수 있으므로 그에 대한 연구가 필요할 것으로 사료된다.

• Structural Engineering and Mechanics
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• 제54권1호
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• pp.19-33
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• 2015

Open ground storey (OGS) buildings are characterized by the sudden reduction of stiffness in the ground storey with respect to the upper infilled storeys. During earthquakes, this vertical irregularity may result in accumulated damage in the ground storey members of OGS buildings without much damage in the upper storeys. Hence, the structural design of OGS buildings needs special attention. The present study suggests a modification of existing displacement-based design (DBD) procedure by proposing a new lateral load distribution. The increased demands of ground storey members of OGS buildings are estimated based on non-linear time history analysis results of four sets of bare and OGS frames having four to ten storey heights. The relationship between the increased demand and the relative stiffness of ground storey (with respect to upper storeys) is taken as the criterion for developing the expression for the design lateral load. It is also observed that under far-field earthquakes, there is a decrease in the ground storey drift of OGS frames as the height of the frame increases, whereas there is no such reduction when these frames are subjected to near-field earthquakes.

• Spatial Information Research
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• 제16권3호
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• pp.373-383
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• 2008

지표면에 대한 정보를 취득하는 기법 중 지금까지 주로 사용되어온 기법은 항공사진 및 위성영상과 같이 평면적인 정보 수집에 중점을 두고 있는 반면, 본 논문에서 다루는 LiDAR(Light Detection And Ranging)는 레이저 측량기술을 이용하여 지표면에 대한 고해상도의 비정규분포 Point 형태의 3차원 정보의 획득이 가능하다. GPS(Global Positioning System) 수신기와 INS(Inertial Navigation System)의 결합을 통해 좌표 값을 제공하게 된다. 이러한 LiDAR의 3차원 Point 정보와 좌표 값을 활용하여 보다 정밀한 3차원 모델링 수행이 가능하다. 본 연구에서는 LiDAR의 반사강도와 기하/지형 자료를 이용하여 도시지역을 대상으로 정밀한 3차원 공간정보자료를 취득하고, 그 자료를 분석하여 도시지역을 높이와 밀도를 기반으로 하여 3차원으로 분류하였다. LiDAR를 통해 획득된 원시자료로부터 지표면에서 반사되는 Point Data의 개수를 지면과 비지면 요소의 비율로 추정하여 지형과 공간적 특성을 파악하고 이에 따라 3차원 토지피복분류도를 작성하였다. 신호의 강약을 구분하는 기준은 통계적 방법(Jenk's Natural Break)을 통해 추정된 값을 사용하였으며, 지표면 반사비율에 따라 세부지역으로 구분하여 크게 고밀도 저밀도 식생지역과 비식생지역으로 구분하였다.

• 한국환경복원기술학회지
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• 제18권3호
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• pp.97-107
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• 2015

Research was initiated to investigate a vegetation characteristics of the species of ground cover plants mixed with herbeceous and woody plants on a cut slope. 4 different ground cover plants (Miscanthus sinensis var. purpurascens, Pennisetum alopecuroides, Festuca arundinacea and Zoysia japonica) were seeded at the same rate of $10.0g/m^2$ with herbaceous plants (Lotus corniculatus var. japonicus, Dianthus sinensis, Aster yomena, Chrysanthemum zawadskii and Coreopsis drummondii L) at the total seeding rate of $7.5g/m^2$ and native woody plants (Lespedeza bicolor Turcz, Indigofera pseudo-tinctoria and Albizzia julibrissin) at the total seeding rate of $7.5g/m^2$, respectively. This experiment was treated with 3 replications on a randomized block design. Data such as surface coverage rate(%), the germinating number, plant height and visual quality were analyzed. There were no statistic differences observed in the soil hardness and the soil moisture content while a significant difference was observed in the surface coverage rate and the germinating number. The surface coverage rate and the germinating number were significantly high in the Pennisetum alopecuroides plot when compared with the Miscanthus sinensis var. purpurascens plot, the Festuca arundinacea plot and the Zoysia japonica plot, respectively from the viewpoint of ground covers. Especially, the surface coverage rate was considerably low in the Festuca arundinacea plot. However, the surface coverage rate and the germinating number were no statistic differences observed in this treatment from the viewpoint of herbaceous and woody plants. Also, both of the plant height and visual quality were high in the Pennisetum alopecuroides plot when compared with the Miscanthus sinensis var. purpurascens plot, the Festuca arundinacea plot and the Zoysia japonica plot, respectively. We concluded that Pennisetum alopecuroides was the optimum plant from the treated ground covers mixed with native woody and herbaceous plants for the balanced emergence from the viewpoint of the ecological slope vegetation.

• 한국지반환경공학회 논문집
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• 제8권2호
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• pp.29-39
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• 2007

본 연구에서는 제방축조에 의해 연약점토지반에서 발생되는 지반의 변위 및 변형형태를 파악하기 위하여 제방높이, 지반의 비배수 전단강도, geotextile의 설치여부와 중력수준을 변화시키면서 원심모형시험을 실시하였다. 실험결과, 제방하중에 의한 지반의 치환단면은 geotextile을 설치하지 않은 경우 포물선 형태를 나타내었고, geotextile을 설치한 경우에는 제방하부에서 균일한 침하단면을 나타내는 사다리꼴 형태를 나타내었다. 치환각도는 제방높이와 중력수준이 증가할수록 그리고 지반의 비배수 전단강도가 작을수록 거의 선형적으로 증가하는 것으로 나타났다. 최대 수평변위가 발생하는 위치는 지표면에서 점토층 깊이의 $0.24{\sim}0.35H_0$($H_0$ : 초기 모형지반의 높이) 지점으로 평균 0.3H0인 것으로 나타났으며, geotextile을 설치하지 않은 경우 지반의 최대침하량(S)과 최대 수평변위(${\delta}_m$)는 ${\delta}_m$ = 0.54S, geotextile을 설치한 경우에는 ${\delta}_m$ = 0.60S의 관계를 나타내었다.