• 대한기계학회논문집
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• 제17권12호
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• pp.3135-3147
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• 1993

A numerical method is presented which can solve the steady flow and heat transfer from a rotating and heated circular cylinder in a uniform flow for a range of Reynolds number form 5 to 100. The steady response of the flow and heat transfer is simulated for various spin parameter. The effects on the flow field and heat transfer characteristics known as lift, drag and heat transfer coefficient are analyzed and the streamlines, velocity vectors, vorticity, temperature distributions around it were scrutinized numerically. As spin parameter increases the region of separation vortex becomes smaller than upper one and the lower region will vanish. The lift force, a large part is due to the pressure force, increases as the Reynolds number and it increases linearly as spin parameter increases. The pressure coefficient changes rapidly with spin parameter on the lower surface of the cylinder and the vorticity is sensitive to the spin parameter near separation region. As spin parameter increases the maximum heat coefficient and the thin thermal layer on front region are moved to direction of rotation. However, with balance between the local increase and decrease, the overal heat transfer coefficient is almost unaffected by rotation.

• 대한기계학회논문집B
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• 제24권6호
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• pp.822-833
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• 2000

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow has been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제9권3호
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• pp.257-267
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• 2005

When notions of numbers are expanded from natural number to complex number, a similar mathematical phenomenon can be observed in each number. As a case study, to complex number, the phenomenon is investigated carefully and teaching materials are created. Then complex number is expressed with matrices and is geometrically treated, so a new number which is an extension of complex number is discovered. Thus, teaching material regarding to complex number and matrices is made for students of ordinary level. Moreover, for talented students, material about an extension of complex number can be added to the previous one.

• 한국토양비료학회지
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• 제39권4호
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• pp.209-213
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• 2006

본 연구는 미사양토인 호남평야지 논토양에서 벼와 콩의 윤작재배에 의한 토양화학성 변화와 작물생육에 미치는 영향을 구명하였다. 벼 연작, 콩-벼 1년 윤작, 콩 2년-벼 1년 윤작, 콩 3년-벼 1년 윤작의 처리를 두었다. 논 토양에서 벼를 연작 후 토양 중 pH, 토양 유기물, $Ca^{2+}$와 $K^+$함량은 별 변화가 없었으나 유효 인산함량은 점차 감소하였다. 한편 벼와 콩의 윤작으로 토양 중 유기물 함량은 감소하고, 유효인산과 $Ca^{2+}$와 $K^+$함량은 증가하였으며, 벼 생육기간 중 토양 중 암모니아태 질소함량도 높아졌다. 이러한 토양 중 양분함량의 변화로 인해 벼의 $m^2$당 수수와 수당립수가 많아져서, 쌀 수량은 1~4%증가하였다. 콩은 연작 연수가 길어질수록 수량이 낮아지는 경향이어서, 콩 논 재배 시에는 벼와 매년 윤작하는 것이 수량 저하를 방지하였다.

• 한국응용곤충학회지
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• 제55권4호
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• pp.329-336
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• 2016

답전윤환 옥수수 8품종 및 수수 7품종 재배포장에서 조명나방 발생 및 수확 특성을 조사하였다. 매주 이뤄진 성충 트랩 조사에서 조명나방 밀도는 정식 2주 후부터 급격히 증가하여 6월 중순에 최성기에 도달 후 감소하다 9월 초 소폭 증가 후 감소하였다. 조명나방 유충에 의한 피해주수와 침입공수를 매주 옥수수 미백2호와 대학찰 그리고 수수 남풍찰과 동안메를 대상으로 조사하였다. 그 결과, 대학찰과 미백2호에서 피해주가 각 20주당 19주와 18주였고, 주당 침입공수도 6월말부터 꾸준히 증가하여 수확기인 7월말에 대학찰은 주당 평균 1.8개, 미백2호는 1.4개로 나타났다. 수확기에 옥수수 8품종에 대한 피해율과 침입공수를 조사한 결과, 대학찰 94%, 미백2호 92%, 일미찰 71%, 얼룩찰1호 64%, 찰옥4호 54%, 미흑찰 52%, 흑점2호 45%이었다. 주당 침입공수는 일미찰이 1.21개였고 나머지 품종들에서는 1개 미만이었다. 또한 옥수수 각 품종별로 이삭 10개씩 3반복으로 조명나방 유충에 의한 이삭 피해율을 조사한 결과, 일미찰 50%, 흑진주찰 40%, 대학찰 37%, 미흑찰과 흑점2호 13%, 얼룩찰 7% 그리고 미백2호 3% 등이었다. 수수 주요 재배품종들인 남풍찰 및 동안메는 정식 후 2개월까지 20주 평균 4주 미만으로 피해를 입다가 8월 초에 피해가 급증하여 평균 피해주는 남풍찰이 13주, 동안메는 9.2주였고 주 당 침입공수도 8월 초부터 나타나기 시작해 남풍찰은 주당 평균 1.06개, 동안메는 주당 평균 0.46개였다. 수확기 수수 품종별 조명나방에 의한 피해율을 조사한 결과, DS-202 95%, 목탁수수 76%, 소담찰 75%, 남풍찰 67%, 앉은뱅이수수 57%, 동안메 46% 그리고 황금찰 34%로 7품종 모두 조명나방에 의해 높은 피해를 입었다. 침입공수 또한 피해율에 비례해서 DS-202(1.7개), 목탁수수(1.4개), 소담찰(1.3개), 남풍찰(1.1개), 앉은뱅이수수(1개), 동안메(0.5개) 그리고 황금찰(0.4개)로 관찰되었다. 한편, 답전윤환 옥수수 및 수수 포장에서 조명나방 피해와 수확 특성은 인과관계를 보이지 않는 것으로 나타났다. 이상의 결과는 답전윤환 옥수수 및 수수 재배포장에서 조명나방의 관리대책을 구축하는데 활용될 수 있을 것으로 기대한다.

• Journal of Computational Design and Engineering
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• 제3권4호
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• pp.337-348
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• 2016

An experimental approach is presented for the measurement of wear that is common in the threading of cold-forged steel. In this work, the first objective is to measure wear on various types of roll taps manufactured to tapping holes in microalloyed HR45 steel. Different geometries and levels of wear are tested and measured. Taking their geometry as the critical factor, the types of forming tap with the least wear and the best performance are identified. Abrasive wear was observed on the forming lobes. A higher number of lobes in the chamber zone and around the nominal diameter meant a more uniform load distribution and a more gradual forming process. A second objective is to identify the most accurate data-mining technique for the prediction of form-tap wear. Different data-mining techniques are tested to select the most accurate one: from standard versions such as Multilayer Perceptrons, Support Vector Machines and Regression Trees to the most recent ones such as Rotation Forest ensembles and Iterated Bagging ensembles. The best results were obtained with ensembles of Rotation Forest with unpruned Regression Trees as base regressors that reduced the RMS error of the best-tested baseline technique for the lower length output by 33%, and Additive Regression with unpruned M5P as base regressors that reduced the RMS errors of the linear fit for the upper and total lengths by 25% and 39%, respectively. However, the lower length was statistically more difficult to model in Additive Regression than in Rotation Forest. Rotation Forest with unpruned Regression Trees as base regressors therefore appeared to be the most suitable regressor for the modeling of this industrial problem.

• 천문학회지
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• 제21권1호
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• pp.79-95
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• 1988

To examine relations between stellar activity and rotation we estimated parameters of stellar activity such as $R'_{HK}$, $R'_{MgII}$, $R'_{CII}$, $R'_{CIV}$ and $R'_{X-ray}$ from the published data which measure the activity levels of stellar chromospheres, transition regions and coronae. In the present study we considered only the main sequence stars in an attempt to minimize the influence of other stellar parameters such as radius, age and stellar convection on stellar activity since they are also known to affect the magnetic field generation. In the present analysis we selected only those stars that satisfy the following conditions: (1) flux measurements are available together with Ca II fluxes and (2) rotation periods are determined by Ca II observations. We derived relations between the ${\bar{R}}ossby$ number $R_o$ and stellar activity $R'_{HK}$, $R'_{MgII}$, $R'_{CII}$, $R'_{CIV}$ and $R'_{X-ray}$ and assessed the relations by plotting $R'_{HK}$, $R'_{MgII}$ and $R'_{X-ray}$ against rotation period $P_{rot}$ for comparison with observations. From the comparison it is found that as far as the rotation-activity relation is concerned, (1) normalized surface flux $R'_{HK}$ is better than the surface flux $F'_{HK}$, in the sense that $R'_{HK}$ differentiates the color dependence better and (2) $R'_{HK}$ defined by Rutten (1984) describes the observations notably better than $R'_{HK}$ of Noyes et al. (1984).

• 한국항공우주학회지
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• 제35권9호
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• pp.753-760
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• 2007

3-D 날개짓 운동은 왕복운동과 회전운동으로 구성된다. 3-D 날개짓 운동은 왕복운동하는 동안 날개 길이방향의 유동이 발생된다. 또한 각각의 왕복운동의 끝에서 날개 회전에 의하여 회전에 의한 순환이 발생한다. 본 연구에서는 날개 길이방향 유동과 날개 회전이 3-D 날개짓 운동의 공기역학적 특성에 미치는 영향을 알아보기 위하여 3-D 날개짓 운동과 2-D 병진운동을 비교하였다. 각각의 날개짓 운동에서 받음각과 레이놀즈수에 따라 공력을 측정하였다. 2-D 병진운동의 공력이 3-D 날개짓 운동의 공력 보다 크다. 하지만 3-D 날개짓 운동시 발생되는 양력은 왕복운동의 중반부에서 받음각 $50^{\circ}$까지 증가하였고 2-D 병진운동시 발생되는 양력은 받음각 $30^{\circ}$이상에서 감소하였다. 또한 각각의 왕복운동의 끝에서 날개 회전에 의하여 공력이 급격하게 증가하였다.

• 식물병연구
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• 제7권1호
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• pp.42-48
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• 2001

참외 연작지에서 문제가 되는 뿌리혹선충의 효율적인 방제법을 구명하기 위하여, 땅콩뿌리혹선충이 감염된 성주과채류시험장 온실에서 실험을 실시하였다. 재배적 방제로는 참깨, 파, 옥수수 및 벼를 참외 심기 전에 윤작작물로 재배하였고, 물리적 방제는 건토, 태양열처리 및 객토였으며, 화학적 방제약제로는 forthizate 입제를 사용하였다. 방제효율은 방제 방법간 큰 차이가 있었는데, 벼 윤작, 태양열처리, 객토에서 방제효과가 가장 높아 뿌리혹선충 밀도는 90% 감소하였고 참외 수량은 무처리에 비해 2배 증수되었다. 그러나 이러한 처리구에서 선충밀도가 6월 이후 다시 증가하여 처리효과는 참외 한 작기에만 유효하였다. 다음으로 효과가 높은 것은 옥수수 윤작, 건토, forthizate 처리였다. Forthizate 처리는 초기 수량에서 유의한 증수 효과가 인정되었으나(P=0.05) 후기 수량과 전체 수량에서는 증수 효과가 없었다. 윤작작물로 참깨와 파는 선충 방제 효과가 없었다.

• Earthquakes and Structures
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• 제26권5호
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• pp.349-361
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• 2024

Excessive torsional behaviour is one of the major reasons for failure of buildings, as inferred from past earthquakes. Numerous seismic codes across the world specify a displacement-based or drift-based criterion for classifying buildings as torsionally irregular. In recent years, quite a few researchers have pointed out some of the inherent deficiencies associated with the current codal guidelines on torsional irregularity. This short communication paper aims to envisage the need for a revision of the displacement-based guidelines on torsional irregularity, and further highlight the appropriateness of a rotation-based criterion. A set of 6 reinforced concrete building models with asymmetric shear walls are analysed using ETABS v18.0.2, by varying the number of stories from 1 to 9, and the torsional irregularity coefficient of various stories is calculated using the displacement-based formula. Since rotation about the vertical axis is a direct indication of the twist experienced by a building, the calculated torsional irregularity coefficients of all stories are compared with the corresponding floor rotations. The conflicting results obtained for the torsional irregularity coefficients are projected through five categories, namely mismatch with floor rotations, inconsistency in trend, lack of clarity in incorporation of negative values, sensitivity to low values of displacement and error conceived in the mathematical formulation. The findings indicate that the irregularity coefficient does not accurately represent the torsional behaviour of buildings in a realistic sense. The Indian seismic code-based values of 1.2 and 1.4, which are used to characterize buildings as torsionally irregular are observed to be highly sensitive to the numerical values of displacements, rather than the actual degree of rotation. The study thus emphasizes the revision of current guidelines based on a more relevant rotation-based or eccentricity-based approach.