• 한국추진공학회지
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• 제17권4호
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• pp.25-31
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• 2013

액체로켓 엔진의 시동과 종료 시, 터빈에 가해지는 열충격을 완화시키기 위해 초음속 충동형 터빈로터의 일체형 슈라우드를 여러 조각으로 분할하는 방법을 고안하였다. 구조해석 수행결과 슈라우드 분할은 동익의 허브와 팁에 나타나는 소성변형량을 크게 줄일 수 있는 것으로 나타났다. 그러나 슈라우드 분할은 의도하지 않은 누설손실로 인해 성능손실이 불가피하며 이에 대한 정량적인 성능감소를 측정하기 위해 다양한 슈라우드 분할 형상에 대해 시험을 수행하였다. 연구대상 터빈의 경우 슈라우드 분할 수를 최대로 할 경우 설계점 효율은 2.65% 비율로 감소하는 것으로 나타났다.

• Journal of Ship and Ocean Technology
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• 제10권4호
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• pp.1-11
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• 2006

The finite volume based multi-block RANS code, WAVIS developed at MOERI is applied to the numerical self-propulsion test. WAVIS uses the cell-centered finite volume method for discretization of the governing equations. The realizable $k-{\epsilon}$ turbulence model with a wall function is employed for the turbulence closure. The free surface is captured with the two-phase level set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. The propeller forces are obtained using an unsteady lifting surface method based on potential flow theory. The numerical procedure followed the self-propulsion model experiment based on the 1978 ITTC performance prediction method. The self-propulsion point is obtained iteratively through balancing the propeller thrust, the ship hull resistance and towing force that is correction for Reynolds number difference between the model and full scale. The unsteady lifting surface code is also iterated until the propeller induced velocity is converged in order to obtain the propeller force. The self-propulsion characteristics such as thrust deduction, wake fraction, propeller efficiency, and hull efficiency are compared with the experimental data of the practical container ship. The present paper shows that hybrid RANS and potential flow based numerical method is promising to predict the self-propulsion parameters of practical ships as a useful tool for the hull form and propeller design.

• 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.

• Journal of Acupuncture Research
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• 제39권4호
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• pp.283-296
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• 2022

In this study, the evidence of thread embedding acupuncture (TEA) in treating cervical radiculopathy in randomized controlled trials was investigated. We searched 16 databases up to August 22, 2022. Of the 2,644 studies retrieved, 22 randomized controlled trials (2,483 participants) were selected. Quality assessments were performed using Cochrane's risk-of-bias tool and RevMan 5.4 software. Outcome measures in the included studies typically showed TEA had a significant therapeutic effect compared with simple acupuncture and other remedies, and TEA was better than sham TEA. Catgut and polydioxanone had no difference in effectiveness, however, catgut was considered to be less safe. TEA was shown to be more therapeutic when inserted deeper into the skin. Ultrasound guided TEA was more effective and safer than conventional TEA, and using a flat blade needle was better than conventional needles for TEA. No serious adverse events were reported from using TEA, and only a few mild side effects were observed. However, the limited number and heterogeneity of the included studies, together with the unclear methodological quality, indicate that higher-quality studies need to be conducted to determine the effectiveness and safety of TEA for cervical radiculopathy.

• Smart Structures and Systems
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• 제31권5호
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• pp.469-483
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• 2023

The dynamic characteristics of wind turbine blades are usually monitored by contact sensors with the disadvantages of high cost, difficult installation, easy damage to the structure, and difficult signal transmission. In view of the above problems, based on computer vision technology and the improved YOLOv5 (You Only Look Once v5) deep learning model, a non-contact dynamic characteristic monitoring method for wind turbine blade is proposed. First, the original YOLOv5l model of the CSP (Cross Stage Partial) structure is improved by introducing the CSP2_2 structure, which reduce the number of residual components to better the network training speed. On this basis, combined with the Deep sort algorithm, the accuracy of structural displacement monitoring is mended. Secondly, for the disadvantage that the deep learning sample dataset is difficult to collect, the blender software is used to model the wind turbine structure with conditions, illuminations and other practical engineering similar environments changed. In addition, incorporated with the image expansion technology, a modeling-based dataset augmentation method is proposed. Finally, the feasibility of the proposed algorithm is verified by experiments followed by the analytical procedure about the influence of YOLOv5 models, lighting conditions and angles on the recognition results. The results show that the improved YOLOv5 deep learning model not only perform well compared with many other YOLOv5 models, but also has high accuracy in vibration monitoring in different environments. The method can accurately identify the dynamic characteristics of wind turbine blades, and therefore can provide a reference for evaluating the condition of wind turbine blades.

• 아시안잔디학회지
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• 제1권1호
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• pp.7-17
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• 1987

The experiment with two levels of nitrogen (0. and 300kg / ha / year) and two levels of clipping height (1.5cm and 4cm) was conducted on the field during the period 3 June to 23 October 1985. Clonal lines of korean lawngrass ( Zoysia japonica Steud.) and manilagrass ( Zoysia matrella ( L.) Merr.)of Daejon origin were established in June, as individual clone in rows 30cm apart with a 40cm spacing between clones, actually 4 clones each plot. The results obtained were as follows : 1. When no nitrogen was applied to korean lawngrass, leaf blade which appeared during the August / early September period remained green for a period of about 10 weeks and even leaves emerged in late September lived for 42 days. However, leaf longevity did not exceed 8 weeks as nitrogen was applied. In contrast the leaf longevity of manilagrass which emerged during the mid - August / early September period was 11 weeks and, under the nitrogen applied, 9 weeks, indicating that the life - saen of individual leaf of manilagrass may be longer than that of korean lawngrass. Meanwhile, clipping height had no effect on the leaf longevity in both grasses. 2. During the July / August period, tiller number, green leaf number and DM weight of korean lawngrass were increased significantly with fertilizer nitrogen, but were not with two levels of clipping height. This trend was reversed after late September : no effect of nitrogen was appeared. Instead, lax clipping increased tiller number, green leaf number and DM weight. Green leaves stimulated by lax clipping resulted in the occurrance of more dead leaves in late October. 3. The increase of tiller number, green leaf number, and DM weight of korean lawngrass due to nitrogen application appeared to be of significance in early September. Unlike korean lawngrass, however, this significant increase was maintained to late October when new green leaves still emerge. Clipping height had little effect on the growth of manilagrass by early September, but since then, lax clipping stimulated leaf appearance, possibly resulting in a remained green color of manilagrass turf. 4. Among the stolons outgrown until early September, the primary stolon was not influenced by nitrogen and clipping treatments to produce only 2 - 3 stolons. However, 1st branch stolon as affected by nitrogen increased significantly, so most of stolons which occurred consisted of 1st branch stolon. 5. Until early September, stolon length obtained at nil nitrogen level was chiefly caused by lengthening the primary stolons. By applying nitrogen the primary stolons of korean lawngrass was longer than 1st branch stolons when severe clipping was involved and in turn, shorter than 1st branch stolons when lax clipping was concerned. In manilagrass, 1st branch stolons were much longer than the primary stolons when turf was clipped severely but in conditions of lax clipping, there was little difference in length between primary and 1st branch stolons. 6. Stolon nodes of both korean lawngrass and manilagrass were positively influenced by nitrogen, but no particular increases by imposing clipping height treatment was marked in manilagrass. Although the stolon of korean lawngrass was grown until late october, the growth stimulated by nitrogen was not so remarkable as to exceed that a by nil N. 7. The thickness of korean lawngrass and manilagrass was greatest in late September, but that of manilagrass did not differ significantly from that in late October. 8. The response of stolon length of korean lawngrass to lax clippings was not so great in late October as to that to severe clippings. On the other hand, the positive effect of lax clippings to stolon length in m anilagrass was confirmed even in late October.

• 한국작물학회지
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• 제42권4호
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• pp.459-465
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• 1997

담수표면산파 벼의 생육시기별 경수변화, 건물 생산 특성 그리고 질소시비량에 따른 수량 및 건물생산 정도를 기계이앙재배 벼와 비교하였던 바 그 결과를 요약하면 다음과 같다. 1. 담수표면산파 벼는 기계이앙재배 벼에 비하여 생육 중기까지 경수 증가속도가 빠른 반면, 생육중기 이후 분얼수 감소시기 및 속도가 상대적으로 빠르고 컸으며 단위 면적당 수수는 초기 분얼수가 많았던 담수표면산파 벼에서 많았다. 2. 엽면적지수는 담수표면산파 벼에서 수수분화기까지 높았으나, 그 이후부터는 기계이앙재배 벼에서 다소 높은 경향을 나타내었다. 3. 엽신 질소함량은 파종 후 40일까지는 담수표면산파 벼가 많았으나 그 후부터는 점차 적어지는 경향이었으며, 군락광합성 및 생육시기별 건물생산속도 역시 파종 후 50∼60일을 기점으로 기계이앙재배 벼에 비해 담수표면산파 벼에서 점차 적어졌고 이런 경향은 출수기 이후에도 계속 유지되었다. 4. 질소시비량 증가에 따라 기계이앙재배 벼 및 담수표면산파 벼 모두 수확기 총 건물중, 출수기 엽면적지수 및 군락광합성량 모두 많아지는 경향이었다. 총 건물중은 담수표면산파 벼에서 많았으며 엽면적지수 및 군락광합성은 기계이앙재배 벼에서 많았다. 또한 단위 엽면적당 질소함량은 두 재배법 모두 시비량 증가에 따라 증가하였으나 기계이앙재배 벼에서 많았다.

• 한국환경복원기술학회지
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• 제8권1호
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• pp.73-78
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• 2005

본 연구는 실내에서의 관수주기, 토양처리, 배수층에 따른 생육과 생리적 반응을 살펴봄으로 써 실내에서 도깨비고비의 적정 생육환경을 밝히고자 수행하였다. 실험구의 관수주기는 2회/주와 7회/주로 하였으며 각 실험구의 세부처리로서 토양처리와 배수층처리는 배수층-피트모스 : 버미큘라이트 : 펄라이트=1 : 1 : 1(D-PVP), 피트모스 : 버미큘라이트 : 펄라이트=1 : 1 : 1(PVP), 배수층-부엽토 : 마사토=1 : 1(D-SL) 그리고 부엽토 : 마사토=1 : 1(SL)로 각각 처리하였으며 그 결과는 다음과 같다. 1. 실내환경에서 도깨비고비는 주 2회 관수처리보다 주 7회 관수처리에서 지상부의 생육은 촉진되었으나 낙엽수 증가로 인해 실내적응성은 감소될 뿐 아니라 황화되는 현상을 보였다. 2. 토양에 있어서는 마사토 : 부엽토=1 : 1처리가 피트모스 : 버미큘라이트 : 펄라이트=1 : 1 : 1처리보다 생육이 양호한 것으로 나타났으나 낙엽수의 증가로 인해 실내적응성은 감소하였다. 3. 배수층에 유 무에 따른 생육에 있어서는, 관수주기와 토양에 관계없이 배수층이 없을 경우 초장과 소엽장이 촉진되나, 실내적응성, 포자엽수, 신엽수는 배수층이 있을 때 더 높은 것으로 나타났다. 4. 생리적 변화에 있어 광합성률은 관수주기, 배수층, 토양처리에 따라 차이를 보였으며 주 2회 관수처리구에서는 배수층이 있는 피트모스 : 버미큘라이트 : 펄라이트=1 : 1 : 1처리에서 가장 높게, 주 7회 관수처리구에서는 배수층이 없는 마사토 : 부엽토=1 : 1처리에서 가장 낮은 것으로 나타났다.

• Restorative Dentistry and Endodontics
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• 제30권3호
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• pp.184-192
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• 2005

회전식 NiTi file은쉽게 파절되는 단점이 있으나 이에 대한 연구는 아직 부족하다. 본 연구에서는 회전식 NiTi file을 이용해 실제 치아에서 근관을 형성하고, 이 때 발생하는 파절 및 변형을 연구, 분석하였다. 상악 대구치의 근심협측 치근 (n = 150)과 하악 대구치의 근심치근 (n = 150)을 실험대상으로 하여 Profile, ProTaper 및 K3로 각각 근관형성 하였다. 각 file은 파절되거나 변형이 생길 때까지 계속하여 사용한 다음 그 사용횟수를 기록하였다. 파절의 양상을 관찰하기 위해 방사선 및 주사현미경 사진을 촬영하였다. 1 세 군간의 유의할만한 사용횟수의 차이는 없었다. 2. Flaring file 간의 비교에서는 K3의 사용횟수가 통계적으로 유의성 있게 적었으며 (p < 0.05), shaping file 간에는 유의할만한 차이가 없었다. 3, 회전식 NiTi file의 파절은 근관의 최대 만곡부에서 발생하였다. 4. 주사전자현미경으로 파절면을 관찰한 결과 연성파괴의 전형적인 양상인 얕은 딤플이 관찰되었다. 일반적으로 회전식 NiTi file의 평균 사용횟수는 제조회사의 사용지침보다는 길었으며, NiTi file의 수명에 대한 새로운 사용지침을 만들기 위한 부가적인 연구가 있어야 되리라 사료된다.

• 한국산림과학회지
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• 제59권1호
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• pp.1-8
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• 1983

한국산(韓國産) 능수버드나무류(類)에 대한 식별(識別)과 형질변이(形質變異)에 관한 분류학적(分類學的) 문제(問題)들을 해결(解決)하기 위하여 수원시내(水原市內)에 가로수(街路樹)로 식재(植栽)된 능수버드나무류(類) 5종(種)에 대하여 1982년(年) 4월(月)부터 10월(月)에 걸쳐 꽃과 잎의 36 가지 특성(特性)을 측정(測定)하여 유집분석(類集分析), 주요인분석(主要因分析) 및 요인분석(要因分析) 등(等)의 방법(方法)을 이용(利用)하여 수량적(數量的) 분류(分類)를 시도(試圖)하였다. Mahalanobis distance에 의한 분류결과(分類結果)는 능수버들과 수양버들이 가장 먼저 연관(聯關)되고, 개수양버들과 용버들은 다음에 연관(聯關)되었으며 버드나무는 이들 종(種)으로부터 떨어져서 이들과 연관(聯關)되었는데, 이 결과(結果)는 Lattice distance와 Euclidean distance에 의(依)한 결과(結果)와 동일(同一)하였다. 유집분석(類集分析)을 함에 있어서 기관수(器官數)와 형질수(形質數)를 늘릴 수록 종(種)들 상호간(相互間)에 유집(類集)이 더욱 효율적(效率的)으로 나타났고, 주요인분석(主要因分析)에 의(依)한 종간(種間) 관계(關係)는 유집분석(類集分析)에 의한 결과(結果)와 같았으며, 제(第)1, 제(第)2, 제(第)3의 주요인자(主要因子)가 종간관계(種間關係)를 설명(說明)할 수 있는 분산(分散)은 62.2%이었는데, 요인분석(要因分析)의 결과(結果) 엽신폭(葉身幅), 거치수(鋸齒數), 엽각(葉角), 한 화수(花穗)에 달린 꽃의 수(數) 및 엽병장비(葉柄長比) 등(等)이 이들 종(種)을 분류(分類) 식별(識別)함에 있어서 주요(主要)한 형질(形質) 요인(要因)임이 확인(確認)되었다. 이러한 수량적(數量的) 분류(分類)는 종간(種間) 관계(關係)를 설명(說明)하고 주요형질요인(主要形質要因)을 추론(推論)하는데 효과적(效果的)이었다.