• 수산해양기술연구
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• 제53권4호
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• pp.337-348
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• 2017

The tension of warp from trawler and sea-floor contact can generate tilt and wake turbulence around otter boards. Preliminary measurements of otter board tilt and 3-D flow velocity during bottom trawl operations were taken using a vector instrument to investigate the effects of wake turbulence at the trailing edge of the otter board. Tilt data (i.e., yaw, pitch, and roll) at 1 Hz and flow data (velocities in the towing, lateral, and vertical directions) at 16 Hz were analyzed to determine their periods and amplitudes using global wavelet and peak event analyses. The mean period (${\pm}standard$ deviation) of the tilt from the peak event analysis ($5{\pm}2s$) was longer or double than that of flow velocity ($3{\pm}2s$). The two periods also had a significant linear relationship. The turbulence rate of flow was 30-50% at the trailing edge and was closely related to roll deviation. The frequency of phase difference ratios (i.e., peak time differences between tilts and flow periods) was significantly different from random occurrence in two trials, possibly due to side tidal effects. However, in the other trials, flow peaks were random, as shown by the even peak times between tilts and flows. Future studies should focus on reducing tilt variation, wake turbulence, and bottom contact to stabilize otter board motion.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.208-212
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• 2008

Gas hydrate has been paid attention to study for because: 1) it can be considered as a new energy resources; 2) one of reasons causing the instability of sea floor slope and 3) a factor to the climate change. Bottom simulating reflector (BSR) defined as seismic boundary between the gas hydrate and free gas zone has been considered as the most common evidence in the seismic reflection data for the gas hydrate exploration. BSR has several characteristics such as parallel to the sea bottom, high amplitude, reducing interval velocity between above and below BSR and reversing phase to the sea bottom. Moreover, instantaneous attribute properties such as amplitude envelop, instantaneous frequency, phase and first derivative of amplitude of seismic data from the complex analysis could be used to analyze properties of BSR those would be added to the certain properties of BSR in order to effectively find out the existence of BSR of the gas hydrate stability zone. The output of conventional seismic data processing for gas hydrate data set in Ulleung basin in the East sea of Korea will be used for complex analyses to indicate better BSR in the seismic reflection data. This result of this analysis implies that the BSR of the analyzed seismic profile is clearly located at the two ways time (TWT) of around 3.1 seconds.

• 대한안전경영과학회지
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• 제19권4호
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• pp.301-307
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• 2017

The planing hull is characterized by a large change in the posture according to the speed, and the shape of the propeller varies, so that the hull resistance varies greatly depending on the propeller used. Especially, the Savitsky system, which is widely used for estimating the resistance of planing hull, does not consider the characteristics of these propeller and ship bottom spray rails. In this paper, in order to investigate the difference in resistance characteristics between the propeller and the bottom of the propeller of 6m and 12m class propeller using propeller such as outboard or stern drive, A comparative test was conducted on resistance and attitude posture changes in the Circulating Water Channel of Institute of Medium & Small Shipbuilding. As a result of comparison test, it was confirmed that there is a clear difference in the attitude change due to the presence of the bottom floor spray rail and the change in resistance characteristics due to the installation of the propeller. However, attitude change with the propeller was found to be insignificant.

• 한국환경복원기술학회지
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• 제24권1호
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• pp.111-119
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• 2021

This study was conducted to investigate the growth characteristics of artificially planted trees on top of the underground parking lots. The trees were planted 17 years ago and are now in good condition. The survey results are as follows. The planting depth of the trees was 0.9 - 1.3m. The horizontal roots of the trees were distributed in the depth of 0.2m ~ 0.6m, Growth condition was also considered to be good. Also, in the case of the straight root of the trees, the pine tree(Pinus densiflora) grew near the bottom but tree root was very thin, and the Japanese hackberry tree(Celtis sinensis) and the zelkova tree(Zelkova serrata) were seemed to bend at the bottom and to grow by changing direction. When trees were planted on artificial ground, the roots grew well horizontally, and the forces of growing vertically were much weakened. because the plants were planted in earth ball state. As a result, it was considered that the roots would hardly penetrate the bottom-pressing concrete floor.

• 대한가정학회지
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• 제33권5호
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• pp.63-73
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• 1995

Absolute poverty is redefined as biological existence level poverty and relative poverty is also redefinded as 'the state that relatively insufficient compared to the specific society's average living standard under the condition that basic needs on the biological existence level has been satisfied.' Then absolute poverty and relative poverty lies on the same welfare continuum. Therefore these two can be regarded as one unified concept. Theoretical bottom line of poverty is the biological existence level and ceiling is average income. Poverty line for the social policy is to be drawn between ceiling and floor. Using these standard lines three poverty bands are categorized : minimum subsistence level, minimum decency level.

• 동굴
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• 제7호
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• pp.11-14
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• 1998

1. Stafford's Cave, named by the miners because a former visitor, Mr. Stafford, broke his leg in it, is the most northern of the three caves. The entrance lies concealed in the undergrowth, but is otherwise wide and open. A steep conical shaft leads down for a depth of about 80 ft from the floor of the cave; at the bottom, rammed in between the two walls, lies a great block of limestone below which a rivulet streams forth, flowing through the cave, which runs from east; in the cave it is joined by a little tributary.(omitted)

• 한국지구과학회지
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• 제37권4호
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• pp.200-210
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• 2016

지음향 모델링은 퇴적층과 기반암의 해저 지층을 통해 전파되는 음파 특성을 예측하기 위해 사용된다. 이 연구는 동해 한국대륙주변부의 정동진 해역에서 50 m 퇴적층 심도의 4개 지음향 모델을 구성하였다. 지층 모델은 고해상 에어건 탄성파 자료, SBP 자료, 퇴적물 코어에 근거한다. P파 속도는 신호투과법에 의해 측정되었고, 압전기 트랜스듀서의 공진 중심 주파수는 1 MHz를 유지하였다. 42개 P파 속도와 41개 음감쇠 측정이 세 개 코어 퇴적물에서 수행되었다. 실제 모델링을 위해, 모델의 P파 속도는 Hamilton 방법을 이용하여 해저면 아래 현장 심도 속도로 보정하였다. 연안 지층의 이 지음향 모델은 동해 정동진 해역에서 지음향 특성의 수직/수평 변화를 반영하는 지음향/수중음향 실험을 위해 활용될 것이다.

• 비파괴검사학회지
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• 제20권1호
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• pp.38-45
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• 2000

본 연구에서는 누설자속법을 적용한 저장용 탱크 바닥판재의 부식측정 기술에 관한 연구를 수행하였다. 시험편은 두께 6mm 및 10mm 강판에 20%, 40% 60% 80%의 깊이를 갖는 홈을 가공한 대비시험편을 사용하였다. 영구자석을 이용하여 요크를 제작하고 홀센서를 이용하여 시험편에서 누설자속을 측정하였다. 실험결과는 인공홈에서 발생된 누설자속을 효과적으로 검출할 수 있다는 것을 보여주었다. 또한 transverse형 홀센서를 이용하여 시험편에 가공한 홈의 크기를 근사적으로 측정할 수 있다는 결과를 제시하였다. 홈의 위치에 따른 누설자속 진폭을 측정한 결과, 누설자속법으로는 판재 상, 하부의 홈 위치를 구별할 수 없다는 것이 밝혀졌고, lift-off 거리에 따라서 진폭이 현저하게 변하기 때문에 고정된 lift-off 거리를 유지하는 것이 중요하다는 사실을 보여주었다.

• 한국공간구조학회논문집
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• 제17권4호
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• pp.85-92
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• 2017

Base isolation system is generally used for low-rise buildings. For high-rise buildings subjected to earthquake loads, a mid-story isolation system was proposed and applied to practical engineering. In this study, seismic responses of high-rise buildings considering the installation story of the mid-story isolation system were evaluated. To do this, the 20-story and 30-story building were used as example structures. Historical earthquakes such as Kobe (1995), Northridge (1994) and Loma Prieta (1989) earthquakes were employed applied as earthquake excitations. The installation location of the mid-story isolation system was changed from the bottom of the $1^{st}$ floor to the bottom of the top floor. The seismic responses of the example building were investigated by changing the location of the isolation layer. Based on the analytical results, when the seismic isolation system is applied, story drift ratio and acceleration response are reduced compared to the case without the isolation system. When the isolation layer is located on the lower part of the building, it is most effective. However, in that case, the possibility that the structure is unstable increases. Therefore, an engineer should consider both structural efficiency and safety when a mid-story isolation system for a high-rise building is designed.

• 한국전산구조공학회논문집
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• 제30권6호
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• pp.469-477
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• 2017

본 논문에서는 실제 공연장을 예제 건물로 하여 공연장에 발생한 진동을 측정한 결과를 바탕으로 공연장 구조물의 안전성에 대해 해석적으로 평가하였다. 수치해석 프로그램은 MIDAS GEN을 사용하였으며, 바닥판은 합성효과를 고려하여 모델링하였다. 해석결과 진동계측실험을 통해 구한 바닥판 고유진동수와 유사한 결과를 보였다. 또한 군중의 율동에 의한 동적하중을 시간이력해석으로 해석하여 진동계측 실험과 유사한 수준의 바닥판 가속도 응답을 확인하였다. 이 모델을 사용하여 예제 공연장의 최대관람인원인 400명의 집단율동 시 발생하는 상황에 대하여 분석하였다. 그 결과 기둥과 보의 가해지는 외력은 설계 내력을 하회하여 안전성에 문제없음을 확인하였다. 또한 공연 시 발생하는 수평방향 진동수준은 지진하중의 2% 수준으로 수직수평 모두 안전성에 문제가 없는 것을 확인하였다.