• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.9
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• pp.866-870
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• 2011

In this paper, the aerodynamic forces of a Korean Traditional Bangpae Kite with the wind hole and spanwise curved dihedral were measured by wind tunnel test. For the flat plate kite without the wind hole, the stall presents at ${\alpha}=35^{\circ}$ with $C_{Lmax}$=1.2. The Korean Traditional Bangpae Kite with the wind hole had $C_{Lmax}$=1.05 at ${\alpha}=30^{\circ}$ without the apparent stall phenomena. As the wind hole size growing, the lift and drag of kite were changed slowly after stalling angle of attack. As increasing the leading edge dihedral angle, lift curves were more increased than drag curves. As the growing of wind hole size, the effect of dihedral angle was constant affect to the lift and drag of kite.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.27-36
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• 2014

This paper presents a numerical investigation of the effect of the rotation speed on the performance in a transonic axial compressor with the dihedral stator. Four stator geometries with different stacking line variables were tested in the flow simulations over the whole operating range. It was found that a large shroud loss at the rotor outlet and the subsequent shroud corner separation in the stator passage occurred at low mass flow rate with the 100 % design speed. The hub dihedral stator could suppress the shroud loss region and consequently improve the stall margin. In case of the 70 % design speed condition as the mass flow rate decreased, it was seen that the high loss region was placed at the midspan of the rotor passage. The dihedral stator slightly affected the local diffusion factor, but the performance of the compressor was not changed.

• The KSFM Journal of Fluid Machinery
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• v.18 no.5
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• pp.5-12
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• 2015

This paper presents a numerical investigation of the effect of the dihedral stator on the loss in a transonic axial compressor. Four stator geometries with different stacking line variables are tested in the flow simulations over the whole operating range. It is found that a large shroud loss at the rotor outlet and the subsequent shroud corner separation in the stator passage occur at low mass flow rate. The hub dihedral stator and bowed blade generate unexpected hub-corner-separation, thereby causing a large total pressure loss over the entire operating range. However, the corresponding blockage forces the high momentum flow near the hub to divert toward the upper part of the passage suppressing the negative axial velocity region. The dihedral stator increases deflection angle and secondary vorticity near the endwall where the dihedral is applied. As a result, the endwall loss which is related to the endwall relative velocity decreases.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1038-1044
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• 2017

We are working on improving the performance by applying the three-dimensional design element to the rotor blades of high pressure supersonic impulse turbine that drives turbo pump of liquid rocket engine. In this paper, based on the shape of a rotor blade of a turbopump turbine designed in the past, a three-dimensional shape is applied to a rotor blade through a stacking line change such as sweep and dihedral. After performing the flow analysis, the changes in the turbine performance characteristics for each design element were carefully examined and the results were summarized.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.409-418
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• 1988

Steam turbines, gas turbines, multistage centrifugal compressors are operated over the range of the first critical speed. In these rotors flexible rotor balancing technique is necessary. In such balancing, influence coefficients are measured by rotating a rotor with trial weight. But for the large rotor, the measurement of influence coefficient takes much time and it reduces the cost efficiency. In this paper the new influence coefficient with rotation of rotor is proposed. First the theoretical background of the method is presented and it is applied to the simple flexible rotor model. Then the experiments are performed and the results of presented method are compared with those of analytical method. By using the obtained influence coefficient, balancing of the flexible rotor is performed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.12
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• pp.931-939
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• 2013

In this paper, we try to find the lifting-line method which is applicable to the conceptual design of aircraft wings, and analyze the accuracy and coverage of the method. Two methods that are extended from the lifting-line theory of Prandtl are selected. One of the methods is Weissinger's method which imposes the velocity boundary condition at the control points located at the quarter chord, and the other is Phillips's method which combines the three-dimensional vortex lifting law. Calculations are performed for an elliptic wing, a swept back wing, and a tapered unswept wing with dihedral angle and geometric twist. The aerodynamic data of the potential flow such as spanwise distributions of circulation and downwash, lift and induced drag are obtained through calculations, and these data are compared with theoretical results and wind tunnel test data. As a result, Weissinger's method showed good accuracy and reliability regardless of wing shapes, but Phillips's method revealed inaccurate results for a swept back wing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.711-717
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• 2012

During the conceptual design phase of a light sport aircraft, the wind tunnel tests were conducted to investigate the static stability of newly-designed configuration. The 1/5 scale-down wind tunnel model consisted of fuselage, main wing, vertical tail and horizontal tail. The main wing and tails were able to be attached or detached from the fuselage. The aerodynamic forces and moments acting on the 6 different configurations compounding each component were measured by using the internal balance system and their static stability derivatives were derived. With these experimental data, the baseline lift and drag characteristics as well as the effects of each component to the longitudinal, directional and lateral static stability were quantitatively analyzed.

• The Journal of Engineering Geology
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• v.1 no.1
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• pp.121-136
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• 1991

The focal mechanism of the Hongsung Earthquake (1978. Oct. 7, M$_L$=5.0, Latitude 36.62N, Longitude 1 26.67E) was evaulated using the polarity distribution of the P-Waveforms. Through the non-linear computer process, the compatibility of polarity distributions of the 9 P-Waveforms observed at teleseismic distances from the Hongsung Earthquake epicenter was investigated to those of the focal mechanism determined from the varying strike, dip and rake angles. The resultant values for the strike and dip angle of the principal fault plane, which apparently matches very well the sunface lineament of the Hongsung region, are determined to be about 247 degree and 78 degree with uncertainties, respectively. However, the rake angle of the focal mechanism has wide range of 40 degree to 160 degree, which is mainly due to the poor coverage of the azimuthal angle of the observed seismic stations. Due to the consistency of principal stress axes, the resultant focal mechanism could support the current stress regime of that region, which may be caused by subduction of the Pacific Plate under the Eurasia Plate along the Japan Trench. It also provides information of seismic source characteristics of the part of the Korean Peninsula for aseismic design criteria such as Site Specific Response Spectrum and Strong Ground Motion Time History for the nuclear power plants and related nuclear waste disposal facility sites.

• Environmental and Resource Economics Review
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• v.5 no.2
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• pp.185-202
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• 1996

일반적으로 국민경제의 상태를 평가할 때, 경제성장, 물가상승률, 고용사정 및 국제수지 등 각 부문의 성과를 종합적으로 고려한다. 이들 각 부문의 성과는 개선되거나 악화되는데 있어서 동일한 추세를 보이기도 하지만 서로 상반된 움직임을 보이기도 한다. 또한 각 부문간에는 상충관계가 존재하기도 하므로, 부문간의 조화를 달성하기가 매우 어렵다는 사실도 잘 알려져 있다. 본 논문은 평균 분산 개념을 이용하여, 국민경제의 전체적 상황 및 부문간 격치를 반영하면서 직관적으로도 이해하기 쉬운 경제성과지수를 제시하고 이를 이용하여 석유파동 등이 각국경제에 미친 영향을 파악한다. 먼저 경제 각 부문별로 성과를 나타내는 경제지표로부터 시계열 평균과 분산을 계산하고 이를 이용하여 각 부문의 연도별 성과를 지수화한다. 이와같이 계산된 각 부문 지수들의 연도별 평균을 구하고 이를 해당연도의 평균적 경제성과로 해석한다. 또한 연도별로 부문별 지수간의 분산을 계산하여 이를 각 연도별 경제부문간 편차로 해석한다. 평균지수가 높을수록, 그리고 분산지수가 낮을수록 경제성과가 우수하다고 할 수 있다. 본 논문에서 제시된 방법에 따라 한국, 미국, 일본, 대만의 평균 분산 지수를 도출하여 비교 분석한 결과, 동지수가 각국의 경제실상을 잘 나타내고 있으며 두차례의 석유파동이 각국에 미친 영향을 비교하는데 유용하게 활용될 수 있음을 확인하였다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10b
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• pp.463-465
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• 2003

본 논문은 MPEG-4 컨텐츠의 객체 기반 특징을 이용하여 네트웍 환경의 대역폭 변화에 대처하는 적응적 MPEG-4 스트리밍 서비스를 제안한다. 이를 위해서 MPEG-4 컨텐츠를 구성하는 각 미디어 객체를 다양한 비트 레이트로 인코딩하여 계층화하고 미디어 객체가 서비스되어야할 때의 네트웍 대역폭에 적합한 비트 스트림의 계층을 선택하여 전송한다. 이 때 서비스되는 스트림의 품질을 최대로 유지하면서 동시에 대역폭에 적합한 스트림을 전송하는 상반된 목적을 달성하기 위해 대역폭을 제한 조건으로 하고 전송되는 스트림의 화질을 최대화하는 문제로 접근하고, 실험 결과를 통해서 제안한 MPEG-4 컨텐츠 적응 기술이 효과적임을 보인다.