• 한국항공우주학회지
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• 제33권9호
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• pp.81-88
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• 2005

본 논문은 단일 태양전지판으로 구성된 통신해양기상위성(COMS)에 대하여 모멘텀 덤핑에 소요되는 연료량을 분석하였다. 먼저 하루 중 일정한 시간에 모멘텀 덤핑을 수행할 경우를 가정하여 최적의 시간을 선정하는 작업을 수치해석적인 접근을 통하여 수행하였고 요구되는 연료량을 분석하였다. 또한 모멘텀 덤핑에 소요되는 연료량을 절감하기 위하여 남북위치유지 시점과 모멘텀 덤핑시점을 근사적으로 일치시키는 방안을 제안하였다. 마지막으로 제안된 기법의 유효성을 분석하기 위하여 궤도 시뮬레이션을 수행하였다.

• 한국과학교육학회지
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• 제14권2호
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• pp.111-122
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• 1994

This study tried to find the effect to the representation patterns of science concepts upon the momentum effect. The previous studies showed that the momentum effect is influenced by students' cognitive levels and the abstractness of test items. The representation patterns of science concepts are divided into 4 different types: quantitative and qualitative, verbal and image. The research method used in this study is time series design. The period is 50 days. The period is divided into "pre-lest", "intervention-test", "post-test". Pre-test period is 5 days and in this period class instruction does not exist. Intervention-lest period is 30 days and in this period class instruction exist. Post-test period is 15 days and in this period class instruction does not exist. The results showed longer momentum effect on the image-qualitative representation pattern than the other representation patterns. Qualitative concepts is formed better than quantitative. Momentum effects is not artifact but the essential characteristics of science study.

• 한국과학교육학회지
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• 제14권1호
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• pp.70-84
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• 1994

This study tried to find the effect to cognitive structure upon the momentum effect. The previous studies showed that the momentum effect is influenced by students' cognitive levels and the abstractness of test items. The cognitive structure is examined by cognitive level and cognitive style. Cognitive levels and cognitive styles are determined by GALT and GEFT respectively. The research method used in this study is time series design. The period is 50 days. The period is divided into "pre-test", "intervention-test", "post-test". Pre-test period is 5 days and in this period class instruction does not exist Intervention-test period is 30 days and in this period class instruction exist Post-test period is 15 days and in this period class instruction does not exist. Field independent students showed longer momentum effect than field dependent students. Formal level students showed less ratio of decrease on post-test than nonformal level students. Momentum effects is not artifact but the essential characteristics of science study.

• 산업융합연구
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• 제20권11호
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• pp.75-83
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• 2022

본 연구는 투자자 심리와 유동성이 우리나라 주식시장에서 모멘텀현상을 설명하는지와 자산가격결정모형에 대한 위험 요소인지를 분석하는 것이다. 실증분석은 2000~2021년 기간 동안 유가증권시장에 상장된 비금융기업의 월별 수익률을 사용하였다. 분석 결과 첫째, 우리나라의 경우 모멘텀 효과가 존재하는 것으로 나타났다. 이는 기존 연구와 같은 결과로 2000년 이후 우리나라 주식시장에서 모멘텀효과가 일반적인 현상으로 받아들여지고 있다. 둘째, 투자자 심리를 기준으로 구성된 포트폴리오를 보면 투자자의 심리가 모멘텀에 영향을 미치고 있다. 특히 투자자 심리가 부정적일 때 승자포트폴리오의 수익률이 높게 나타나고 있다. 셋째, 유동성을 바탕으로 분석한 결과 모멘텀효과는 사라지고 반전효과가 나타난다. 넷째, 투자자 심리와 유동성이 모멘텀효과에 영향을 주는 것으로 나타났다. 투자자 심리가 부정적이고, 비유동적인 주식집단에서 모멘텀효과가 강하게 보이는 결과이다. 다섯째, 주식수익률에 각 요인이 주는 영향을 분석해 본 결과, 투자자의 심리와 유동성 요인 모두가 수익률에 상당한 영향을 미치는 것으로 나타났다. 추정된 결과는 Carhart 4요인 모형에 이 두 요소를 포함하면 모형의 예측력이 상당히 증가한다는 증거를 제공한다. 따라서 투자자 심리요인과 유동성 요인이 주식수익률결정에 중요한 요인이라 할 수 있다.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1238-1246
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• 2004

Momentum exchange theory has been generally used for an analysis of the regenerative turbomachines due to its direct description of the complicate circulatory flow. However, because its application is limited only to linear region and its model equations are incomplete on three variables, it needs further refinements. In the present study it is improved by introducing a central pivot of circulatory flow. Also, by assuming linear circulatory velocity distribution, mean radii of inlet and outlet flows through the impeller are newly suggested. By applying control volume analysis to both linear region and the acceleration region, the governing equation on the circulatory velocity is derived. As a result, systematic performance analysis on the entire region of the incompressible regenerative turbomachines can be carried out based on the proposed model equations.

• 한국전산유체공학회지
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• 제14권3호
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• pp.86-94
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• 2009

The non-conservative form of momentum equations is often used for some two-phase flow codes instead of a conservative form because of numerical convenience. Another non-conservative form, so called, a semi-conservative form can improve the numerical solution of these codes maintaining the numerical convenience. It is close to the conservative form but still maintains the feature of the non-conservative form. A semi-conservative form of the momentum equations and a non-conservative form of the momentum equations are implemented in CUPID[1] code. The numerical results of the semi-conservative and the non-conservative forms are compared against analytical solutions and the solutions of the FLUENT code that uses the conservative form. The results clearly showed that the semi-conservative form of the momentum equations provides better solutions than the non-conservative form, especially for heterogeneous two-phase flows.

• 대기
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• 제25권4호
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• pp.591-600
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• 2015

We have analyzed wind and eddy covariance data collected within roughness sublayer over sloping terrain. The study site is located on non-flat terrain with slopes in both south-north and east-west directions. The surface elevation change is smaller than the height of roughness element such as building and tree. This study examines the directional wind shear for data collected at three levels in the lowest 10 m in the roughness sublayer. The wind direction shear is caused by drag of roughness element and terrain-induced motions at this site. Small directional shear occurs when wind speed at 10 m is strong and wind direction at 10 m is southerly which is the same direction as upslope flow near surface at this site during daytime. Correlation between vertical shear of lateral momentum and lateral momentum flux is smaller over steeply sloped surface compared to mildly sloped surface and lateral momentum flux is not down-gradient over steeply sloped surface. Quadrant analysis shows that the relative contribution of four quadrants to momentum flux depends on both surface slope and wind direction shear.

• 한국추진공학회지
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• 제11권2호
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• pp.37-46
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• 2007

본 연구에서는 접선형 산화제 주입기를 갖는 end-burning 하이브리드 연소기에서 산화제 운동량비에 따른 연소 유동장을 해석하였다. 산화제의 운동량비가 감소할수록 연소효율은 연소기 전 영역에 걸쳐 증대되는 경향이 포착되었으며 이론 혼합분율과 온도장을 통해 연소실 전 영역에서 최적의 연소가 저 운동량비에서 발생됨을 확인하였다. 강한 선회류가 연소실 내부 유동장을 지배하지만 압력장은 비교적 균일한 분포를 보였다. 접선형 산화제 주입기를 가진 연소기는 운동량비에 관계없이 공통적으로 연료와 산화제가 만나는 연소실 상부에서 환형의 고온부가 발생했으며 향후 주요 개선 사항으로 판단되었다.

• 한국운동역학회지
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• 제15권4호
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• pp.191-203
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• 2005

It was to study a following research of "A Kinematical Traits Analysis when Performing Uchimata(inner thigh reaping throw) by Posture and Voluntary Resistance Levels(VRL) of Uke in Judo[1]" and. "A Case Study of Center of Gravity(COG) when Performing Uchimata(inner thigh reaping throw) by Posture and Voluntary Resistance Levels(VRL) of Uke in Judo[II]". The purpose of this study was to analyze an angular momentum of trunk and lower extremity when performing uchimata by two postures and voluntary resistance levels(VRL) of uke(reciver) in Judo. The subjects, who were one male judoka(YH) for 1992 Barcelona Olympic Games Olympian(silver medalist), was filmed on two S-VHS 16mm video cameras(60fields/sec.) through 3-dimensional motion analysis methods, that postures of uke were shizenhontai (straight natural posture:NP) and jigohontai (straight defensive posture:DP), VRL of uke were 0% and 100%, respectively. The variables were angular momentum of trunk, lower extremity of attacking leg and supporting leg of tori(the thrower). The data of this study collection were digitized by SIMI Motion Program computed the mean values and the standard deviation calculated for each variables. When performing uchimata according to each posture and VRL of uke and classifying. From the data analysis and discussion, the conclusions were as follows : Angular momentum of trunk when performing uchimata was showed the largest among another angular momenta, and the posture displayed more different than resistant of uke(reciver), but the pattern similar in judo. Angular momentum of trunk of X axis was the largest and Y, Z axis order. Angular momentum of attacking the thigh-leg when performing uchimata was showed the largest among another angular momenta, and the posture displayed more different than resistant of uke(reciver), X axis and Y axis similar, but angular momentum of Z axis of thigh-leg the largest, in kake(application) event in 0% resistance of DP than other variables. Angular momentum in X,Y axis of attacking the lower-leg when performing uchimata was showed that the resistance level displayed more different than posture, but Z axis the largest, in kake(E3) phase in 0% resistance of DP than other variables as same thigh-leg, and the largest from tsukuri(set-up:E2) to kake(E3) phase. X and Z axis Angular momentum of supporting the thigh-leg were similar, regardless of posture and resistance of uke, but Y axis was resistance level. Angular momentum of supporting the thigh-leg was showed the largest in X axis, increased from EO event to E2, and decreased in E3, and angular momenta of Y, X axis were showed the largest in kuzushi(balance breaking) phase when performing uchimata. Angular momentum of supporting the lower leg were similar pattern, regardless of posture and resistance of uke, in Y axis, resistance displayed more difficult the position in NP, and showed opposite angular momentum in tsukuri phase. In conclusion, angular momentum of trunk when performing uchimata was showed the largest, and pattern was similar, regardless of posture than resistant of uke(reciver), magnitude and direction were different each other, and uchimata was Ashi -waza(foot and leg techniques) division but important of trunk action.

• 품질경영학회지
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• 제48권1호
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• pp.13-27
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• 2020

Purpose: The purpose of this study is to present a recoil measurement and analysis of K2 rifle for the development of a virtual reality marksmanship training in the Republic of Korea Army. Methods: For the recoil measurement, a test-bed is built by a barrel that has exact dimensions of K2 rifle and three piezoelectric pressure sensors mounted on the barrel. Data of over 200 rounds of 5.56mm M193 and K100 bullets are collected and analyzed from live fire experiments. For the recoil analysis, both the free recoil method and the gas exhaust aftereffect method are used to calculate a recoil velocity, momentum and kinetic energy of K2 rifle by applying the law of conservation of momentum. In addition, a new method is proposed that uses the third law of motion and the chamber pressure model for the recoil measurement Results: The results show how different between the previous and proposed methods with respect to M193 and K100 bullets of K2 rifle. In M193, the free recoil method demonstrates 1.113, 4.197, and 2.335, the gas exhaust aftereffect method computes 1.698, 6.407, and 5.441, and the proposed method calculates 0.990, 3.734, and 1.848 in recoil velocity, momentum and kinetic energy, respectively. In K100, the free recoil method demonstrates 1.190, 4.487, and 2.669, the gas exhaust aftereffect method computes 1.776, 6.699, and 5.949, and the proposed method calculates 1.060, 3.998, and 2.119 in recoil velocity, momentum and kinetic energy, respectively. Conclusion: This study implements live fire experiments to provide recoil velocity, momentum, and kinetic energy of K2 rifle using both M193 and K100 bullets. For the development of the army virtual reality marksmanship, the results in this paper would be useful to design and produce a gun and/or a rifle of virtual reality.