• Tribology and Lubricants
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• 제34권3호
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• pp.93-107
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• 2018

The purpose of Part I of this study is to find the potential region of wear scarring on engine journal bearings operating at a constant angular crank shaft velocity under firing conditions. To do this, we calculate the applied loads and eccentricities of a big-end journal bearing installed on a four-stroke and four-cylinder engine at every crank angle. Then, we find potential wear regions, such as a minimum oil film thickness, at every crank angle below most oil film thickness scarring wear (MOFTSW) obtained based on the concept of the centerline average surface roughness. Thus, the wear region is defined as a set of each film thickness below the MOFTSW at every crank angle. In this region, the wear volume changes according to the wear depth and wear angle, depending on the minimum oil film thickness at every crank angle. The total wear volume is the summation during one cycle. Graphical views of the region in the two-dimensional coordinates show the crank angle and bearing angle along the journal center path, indicating the position of the minimum oil film thickness. The results of wear analysis show that the possible wear region is located at a few tens of angles behind the upper center of a big-end bearing at maximum power rpm.

• 한국기계가공학회지
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• 제13권2호
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• pp.64-72
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• 2014

In the past, prism patterns have been linear triangular shapeswith a $90^{\circ}$ angle; however, new micro prism patterns having acute angles or obtuse angles have recently been the subject of demandin the display, lighting and photovoltaic industries. Micro-cutting experiments for micro-prism patterns having $60^{\circ}$, $90^{\circ}$, and $120^{\circ}$ angles on an electroplated Ni mold were performed and it was found in this study that the specific cutting resistance increased with a decrease in the tool angles (prism pattern angles). The cause of this variation had been thought to be the increase of the ploughing force due to tip rounding and the friction force due to the edge effect. However, the depth of the cut was large enough that it was possible to neglect these effects. Therefore, this study introduced the concept of representative stress of indentation. The measured stress was varied according to the indentation depth eventhoughthetestedspecimenswereidentical ; the varied stress was termed the representative stress. According to indentation theory, the strain that the Ni mold experienced increased with a decrease in the tool angle. Based on the stress-strain relationship, higher strain means higher stress and higher specific cutting resistance. Therefore, the specific cutting resistance was higher at smaller tool angles that had higher strain and stress.

• International Journal of Aeronautical and Space Sciences
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• 제14권2호
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• pp.133-139
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• 2013

Morphing aircraft capable of varying their wing form can operate efficiently at various flight conditions. However, radical morphing of the aircraft leads to increased structural complexities, resulting in occurrence of dynamic instabilities such as flutter, which can lead to catastrophic events. Therefore, it is of utmost importance to investigate and understand the changes in flutter characteristics of morphing wings, to ensure uncompromised safety and maximum reliability. In this paper, a study on the flutter characteristics of the folding wing type morphing concept is conducted, to examine the effect of changes in folding angles on the flutter speed and flutter frequency. The subsonic aerodynamic theory Doublet Lattice Method (DLM) and p-k method are used, to perform the flutter analysis in MSC.NASTRAN. The present baseline flutter characteristics correspond well with the results from previous study. Furthermore, enhancement of the flutter characteristics of an aluminum folding wing is proposed, by varying the outboard wing folding angle independently of the inboard wing folding angle. It is clearly found that the flutter characteristics are strongly influenced by changes in the inboard/outboard folding angles, and significant improvement in the flutter characteristics of a folding wing can be achieved, by varying its outboard wing folding angle.

• 한국운동역학회지
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• 제22권3호
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• pp.269-276
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• 2012

The purpose of This study's aim is to examine the difference in the changes of body segment movement, variables for ball quality, and carry at golf driver swing according to the ball quality using comparative analysis. Regarding the impact variables according to the ball quality using the track man and carry, club speed was the fastest at draw shot, ball speed was the fastest at straight shot, and smash factor was the lowest at draw shot. About the vertical launch angle, the fade shot showed the highest launch angle while the max height of the ground and ball was the highest at fade shot. And carry was the longest at draw shot. For the flight time, it was the longest at draw shot. The landing angle was the largest at fade shot. About the club head position change and trajectory, at the overall event point, the fade shot drew a more outer trajectory at the point of the follow through(E6) than the straight or draw shot. Regarding the angular speed of shoulder rotation, at the overall event point, the fade shot showed the greatest angular speed change in the follow through(E6). Also, about the angular speed of pelvic rotation, at the overall event point, the draw shot showed the greatest angular speed change at the point of down swing(E4). Concerning the stance angle change, both straight and fade shots were open as the concept of open stance whereas the draw shot was close as that of close stance. Regarding the previous study, the most important factor of deciding Ball Quality is the club face angle's open and close state at Impact. In short, the Ball Quality and carry were decided by this factor.

• 한국산학기술학회논문지
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• 제19권2호
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• pp.64-70
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• 2018

대형트럭으로 견인되는 트레일러는 무게중심이 일반 차량에 비해 상대적으로 높기 때문에 전복사고 위험이 높게 된다. 곡선 주행 구간에서 차체를 기울여 곡선부의 주행속도를 향상시키는 원리를 적용하는 틸팅 시스템은 고속철도 차량에서 먼저 그 개념이 연구되고 사용되어 왔는데, 이 논문에서는 일반 대형트럭의 트레일러 적재함에 이 틸팅 시스템을 적용함으로써 아주 작은 틸팅각의 변화로도 급회전 시 주행 안정성을 크게 개선할 수 있는 가능성에 대해 연구하였다. 틸팅 가능한 트레일러의 동역학적 모델을 사용하여 선회주행 시 운동 관계식을 유도함으로써 주어진 도로 선회반경과 하중조건에 대해 원심력 효과와 수직력의 균형으로 전복임계속도를 결정할 수 있었다. 본 논문에서는 보수적인 기준을 선택하여 한쪽 바퀴가 지면으로부터 떨어지는 순간을 전복임계상태로 정의하였다. 실제로 틸팅 시스템을 작동시키기 위해서는 조향각과 주행속도로부터 최적 틸팅각을 계산해야 한다. 트레일러가 달린 대형트럭을 간단하게 모델링하고 시뮬레이션을 통해 곡선주행시 차량의 틸팅각에 따른 전복임계속도의 변화를 분석하고, 틸팅의 효과를 입증하였다.

• 한국항공우주학회지
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• 제39권6호
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• pp.505-516
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• 2011

통합유도조종(IGC, Integrated Guidance and Control)은 기존의 분리형 유도조종루프의 성능한계를 극복하기 위해 제안된 개념이다. 본 논문에서는 입사각제어가 가능한 새로운 형태의 IGC 기법을 제안하였다. 제안된 IGC는 자동조종성능과 유도성능을 동시에 얻기 위해 받음각, 피치각속도, 피치각, 시선각을 상태변수로 고려한다. 제안된 IGC의 제어특성을 고찰하기 위하여 비선형 상태방정식에 대한 가제어성 해석 및 평형점 해석을 수행 하였다. IGC 모델에 대한 제어기법으로는 LQR(Linear Quadratic Regulator)을 사용하였으며 LQR을 IGC에 적용하기 위한 방법을 상세하게 설명하였다. 수치 시뮬레이션을 통해 분리형 유도조종루프와 IGC의 성능을 비교하였다. 성능 비교 결과 IGC는 급격한 기동이 필요한 유도기하에 대하여 분리형 유도조종루프에 비해 우수한 유도성능을 보임을 확인하였다.

• 대한전자공학회논문지SD
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• 제45권9호
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• pp.14-20
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• 2008

최근 LCD나 PDP와 같은 Slim 평판디스플레이의 급속한 성장에 대응하기 위하여, 기존의 부피가 큰 CRT의 두께 축소를 위한 광각화 기술이 요구 되어 지고 있다. 그러나 이러한 광각화한 Screen을 가진 CRT를 만드는 데는 많은 문제점이 있다. 특히 Screen의 Black Matrix를 형성함에 있어서, 설계자의 의도 대비 과도하게 형성되거나, 미형성 되는 큰 문제가 발생한다. 이러한 문제는 광각화 됨으로 인하여 민감도가 증가하여 발생하게 된다. 이러한 부분을 해결하기 위해서 본 논문에서는 새로운 filter system을 제안한다. 기존에 사용하던 filter to panel 방식에서 panel to filter control 방식을 사용함으로써, 설계자의 의도대로 쉽게 Black Matrix를 조절할 수 있다. 본 논문은 새로운 광각화된 CRT에서 좀 더 나은 screen품질을 확보할 수 있도록 새로운 귄ter design 방법을 제안한다.

• 대한수학교육학회지:수학교육학연구
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• 제27권4호
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• pp.833-855
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• 2017

본 연구는 삼각함수 각의 크기를 표현하기 위해 라디안 단위를 새로 도입하는 이유로서 호의 길이를 이용한 각의 측도라는 호도법의 의미와, 삼각함수의 정의역이 일반각을 나타내는 실수로 확장된 이유를 재조명하고자 한다. 이를 위해 라디안 개념의 다각적인 교수학적 분석을 하고자, 역사적, 수학적, 응용수학적 분석을 수행하였다. 이를 통해 첫째, 호도법은 각도에 내재된 본질이고, 라디안은 원주율(${\pi}$)과 밀접한 이론적이고 절대적인 단위이며, 삼각함수를 실함수로 함을 밝혔다. 둘째, 라디안은 동심원에서 비와 비례 관계의 공변성을 거쳐 불변성을 인식하도록 할 것, 라디안으로 표현한 코사인과 사인의 직교성이 임의의 함수의 급수 표현을 가능하게 함, 라디안은 호의 길이를 반지름으로 측도하는 가장 단순화한 표준임을 인식하도록 할 것, 분할 전략을 통해 육십분법과의 연결성을 찾을 수 있음을 밝혔다. 셋째, 각과 각도의 구별로, 라디안 단위의 생략 여부에 대한 정당화와, 호와 반지름 사이의 곱셈 관계 전략이 필요함을 밝혔다. 이로써 도출한 교수학적 시사점은 라디안 개념의 유용성과 가치를 드러내고, 호도법의 실질적인 지도에 기여할 수 있다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.471-478
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• 2000

Endmill is one of the most important cutting tool, not only for machining of mold and die, but also for manufacturing of car industrial. Futhermore with spindle speeds on the increase and machined-surface quality aspiring to higher levels. The purpose of this study is an analysis of endmill's rake angle for appropriate tools design and making for the high speed machining. In this study, Experimental works are also executed to measure shape of endmills, cutting force, on different shape of endmills. Finally, To get concept of endmill design, Tool life was experimented on various design of tool from this study.

• 터널과지하공간
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• 제6권2호
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• pp.166-174
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• 1996

Stability of rock slope is greatly affected by the geometry and strength of discontinuities developed in the rock mass. In this study an analytical method which is capable of analyzing the effect of relative orientation between the discontinuities and the slope face on the safety of slope by assessing their vector components was used to evaluate the stability and the maximum cut-angle for the proposed slope design. The results of computerized vector analysis revealed that slope area under investigation might be divided into 3 sections of different face directions. The safety factors for benches in each 3 sections were calculated using the limit-equilibrium theory. Then, by utilizing the concept of probabilistic risk analysis, the susceptibility of entire slope failure was estimated. Based on the distribution of safety factor in each bench, the maximum cut angle of each section could be selected differently ot achieve the permanent stability of the entire slope.