• 한국소음진동공학회논문집
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• 제20권7호
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• pp.677-684
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• 2010

Backlashes of gears provide gears for good lubrication and for removal of the interference between teeth by the wear and manufacturing errors. The backlash is the strong nonlinear factor to gears. This study deals with nonlinear modeling of helical gears with backlash. Excitation of helical gears comes from torque variation, the tooth surface error, and the periodical change of mesh stiffness. To study the effect of torque fluctuation, equation of motion for the single degree of freedom torsional model of helical gears with the periodical change of mesh stiffness and the backlash was derived. The Newmark beta method and the Newton-Raphson method were used to obtain the nonlinear behaviors of mesh forces of helical gears. All excitation frequencies initially caused the tooth separation and single-sided impacts of the gear pair and eventually led to the normal tooth contact. However, some special excitation frequencies caused the single-sided impacts in the entire time as well as the initial time. Damping increase reduced the duration of single-sided impacts, and the backlash increase caused those in the entire time domain.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.240-245
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• 2000

This paper presents the experimental study of drilling for duralumin A2024 with intermittently decelerated feed rate. It is achieved through a programmed periodic increase and decrease in the feed rate using a machining center. The following experimental result were performed with the objective of solving chip to disposal problems. In conventional drilling of aluminum, long continuous chips are produced that wind around the drill causing difficulties in eliminating chips from the cutting zone. In order to acquire the basic data necessary to regulate the chip profile, the relationship between cutting variables and chip shape was investigated. The following conclusions are established from the experimental results. At a suitable feed fluctuation ratio, intermittently decelerated feed drilling proved successful in breaking chips to appropriate lengths while maintaining stable cutting. Thus, it is an effective method for improving chip disposal. The amplitude of the dynamic component of cutting force in intermittent feed frilling is influenced by the feed fluctuation ratio.

• 한국생산제조학회지
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• 제9권6호
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• pp.103-110
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• 2000

Experimental study of drilling for duralumin A2024 was conducted with intermittently accelerated and decelerated feedrate. It is achieved through a programmed periodic increase and decrease in the feedrate using a machining center. The following experimental results were performed with the objective of solving chip to disposal problems. In conventional drilling of aluminum, long continuous chips are produced with winding around the drill and causing difficulties in eliminating chips from the cutting zone. In order to acquire the basic data necessary to regulate the chip profile, the relationship between cutting variables and chip shape was investigate. The following conclusions are established from the experimental results. At a suitable feed fluctuation ratio, intermittently decelerated feed drilling proved successful in braking chips to appropriate lengths while maintaining stable cutting. Thus, it is an effective method for improving chip disposal. The amplitude of the dynamic component of cutting force in intermittent feed drilling is influenced by the feed fluctuation ratio.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 A
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• pp.340-343
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• 1992

In this paper, To estimate monthly water distribution volume required optimization control of operating scheme & water distribution management for water transmission system in water supply, both Thomas-Fiering technique and Fourier series are compared and analyzed, respectively. Since water distribution volume is periodically repeated and has a linear fluctuation trend, parameters in each element are estimated through dividing into linear fluctuation trend component and periodical component. Finally, results of time-series analysis are proved to be more reasonable than that of Thomas-Fiering techniques by comparing simulation with observation data.

• 한국지형학회지
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• 제24권1호
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• pp.39-50
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• 2017

This study was conducted to analyze the variation of hydro-geomorphological environment along Baekgok wetland, which experiencing periodical inundation, in that water-level fluctuation of reservoir caused by irrigation. Since the field data is unavailable, modeling techniques, involving models such as HSPF and TELEMAC-2D, have been applied to simulate hydrological cycle in watershed and hydrodynamics in channel scale. The result of simulation indicates that the water-level of reservoir determines both the water surface extension and water depth in the wetland. Furthermore, it also shows that water-level functions as a spatial limit factor for a fluvial environment and woody vegetation such as willow. The fact of which the scale of water-level fluctuation being larger than an average topographical relief along the wetland can explain the result. While the water-level kept high, the wetland is submerged and waterbody becomes lentic. In contrast, while the water-level is lowered, fluvial phenomena of which being dependent on flow rate and channel shape become active. Hence, the valid fluvial process is likely to take place only for 4 months annually just near the channel, and it advances to a conclusion expecting a deposition to be dominant among the wetland except for such area. It is anticipated that such understanding can contribute to establishing plans to preserve the geomorphological and ecological value of the Baekgok wetland.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2007년도 추계학술대회
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• pp.149-154
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• 2007

This study examines the effect of acoustic excitation using forced coaxial air on the flame characteristics of turbulent hydrogen nonpremixed flames. A resonance frequency was selected to acoustically excite the coaxial air jet due to its ability to effectively amplify the acoustic amplitude and reduce flame length and NOx emissions. Acoustic excitation causes the flame length to decrease by 15 % and consequently, a 25 % reduction in EINOx is achieved, compared to a flame without acoustic excitation. Moreover, acoustic excitation induces periodical fluctuation of the coaxial air velocity, thus resulting in slight fluctuation of the fuel velocity. From phase-lock PIV and OH PLIF measurement, the local flow properties at the flame surface were investigated under acoustic forcing. During flame-vortex interaction in the near field region, the entrainment velocity and the flame surface area increased locally near the vortex. This increase in flame surface area and entrainment velocity is believed to be a crucial factor in reducing flame length and NOx emission in coaxial jet flames with acoustic excitation. Local flame extinction occurred frequently when subjected to an excessive strain rate, indicating that intense mass transfer of fuel and air occurs radially inward at the flame surface.

• 한국수산과학회지
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• 제5권4호
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• pp.108-114
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• 1972

한국 남해의 동물성 플랑크톤 현존량은 $1963\~1971$년간의 자료로 분석한 결과 63개월을 일주기로 주기 변동을 하고 있으며. 그 주기성은 자기 상관 계수 $\gamma_k$=0.86으로 강한 편이다. 계절 순환 변동은 4월과 10월을 극대기로 하는 쌍봉성 변동을 하며, 그 경향은 대단히 뚜렷한데, 이것은 이 해역에 있어서 식물성 플랑크톤의 양적 소장과 중요한 관련성을 가지는 것으로 고찰된다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1996년도 특별강연 및 추계학술발표 개요집
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• pp.19-34
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• 1996

A review was made of fatigue failures of nuclear power plant components in Japan, which were experienced in service and during periodical inspection. No case has been recently reported of a service fatigue failure of a reactor pressure vessel itself, excluding nozzle corner cracks, that occurred many years ago. But, service fatigue failures have been occasionally experienced in piping systems, pumps, and valves, on which fatigue design seems to have been inadequately applied. The causes of fatigue failures can be divided into two categories: mechanical-vibration-induced fatigue and thermal-fluctuation-induced fatigue. Vibration-induced fatigue failure occurs more frequently than is generally thought. The lesson gleaned from the present survey is a recognition that a service fatigue failure may occur due to any one or a combination of the following factors: (1) lack of communication between designers and fabrication engineers, (2) lack of knowledge about a possibility of fatigue failure and poor consideration about the effects of residual stresses, (3) lack of consideration on possible vibration in the design and fabrication stages, and (4) lack of fusion or poor penetration in a welded joint.

• 한국환경과학회지
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• 제3권2호
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• pp.111-128
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• 1994

서귀포와 부산사이를 취항하고 있는 “카페리 제 주1호”에 수온계를 설치하여 1990년 10월 부터 10 개월간 제주해협과 대한해협을 횡단하는 해역에서 표면수온의 관측을 실시하였다. 그 결과 거문도 부근의 해역에서 뚜렷한 수온전선이 형성되고 있 으나, 그 위치는 약간의 변동성을 냐타내고 있었 다. 전선이 북으로 이동할 때는 비교적 느리고 뚜 렷하나 남으로 이동할 때는 전선구조가 분명하지 않았다. 수온전선에는 수십일 주기를 가진 단주기 변동이 관측된다. 이 변동은 동계 강한 북서계절 풍의 영향과 열이동의 효과로 인한 것으로 사료된 다 표변수온의 수평구배가 3월부터 10월에 걸쳐 매우 약하고, 그 이외의 시기에는 확실하다. 이러 한 결과는 제주해협과 대한해협을 횡단하는 표면 수온의 연속적 인 관측이 한국남안수의 소장과 대 마난류수의 출현 동을 모니터하는데 매우 유효함 을 나타내고 있다. 제주해협과 대한해협에서의 해양관측을 통하여 추자도 부근 해역에서 형성되는 연안전선의 구조 를 파악하였다. 이 전선은 연중 형성되고 있으나, 계절과 연에 따라 그 위치 및 분포형상이 매우 다 르다 이같은 연안전선이 대한해협에서는 매우 약 하게 형성되고 있었다.

• 한국산림과학회지
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• 제84권3호
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• pp.369-376
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• 1995

흑백 항공사진을 이용하여 산지급류하천(山地急流河川)의 하상변동(河床變動)을 파악한 결과, 다음과 같은 면에서 항공사진이 유효정보로 사용될 수 있다. 1. 항공사진 및 현지조사에 의한 하도폭(河道幅) 측정값의 직선회귀식은 Y=1.0+0.94X($r^2=0.98$)로, 두 인자간의 높은 상관관계가 확인되어 항공사진이 하도폭 해석에 유효하게 사용될 수 있다. 2. 항공사진 판독에 의해 하도내의 하상퇴적지(河床堆積地)와 유로(流路)의 평면적(平面的) 구분(區分)이 가능하였으며, 또한 하상퇴적지(河床堆積地)의 평면적(平面的) 분포(分布) 상황(狀況)과 유로(流路)의 규모(規模) 및 형성과정(形成過程)을 추정 할 수 있다. 3. 촬영시기가 상이한 항공사진을 판독하므로서 각 시기별 유로특성(流路特性)을 파악할 수 있었으며, 또한 이를 비교, 분석하므로서 하상변동(河床變動)에 강하게 영향하는 유로변동(流路變動) 과정(過程)을 추정할 수 있다. 4. 항공사진상의 하도폭(河道幅) 측정(測定), 하상(河床)의 평면형태(平面形狀) 해석(解析) 및 유로변동(流路變動) 파악(把握) 등에 의해 하상미지형도(河床微地形圖)를 작성할 수 있으며, 이를 기초로 하상퇴적지(河床堆積地)의 평면적(平面的) 해석(解析)이 가능하다.