• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.813-818
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• 2001

The flow characteristics of the vaned diffuser were complicated with geometric shapes. We have studied the effects of various vaned diffuser configurations, such as divergence angles and rectangular and conical cross-section shapes. Numerical analyses are carried out for the diffuser and casing. The pressure recovery coefficient was calculated to estimate the performance of the diffuser, and then compared with the measure data. Results show that the shapes and the divergence angles of the diffuser strongly influence on the performance of the small-size turbo-compressor.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.349-354
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• 2005

본 연구에서는 초음속 충동형 터빈의 유동특성을 알아보기 위해 소형 초음속 풍동을 설계하였으며 Single pass Schlieren system을 이용하여 유동을 가시화하였다. 실험은 2차원 초음속 노즐과 익렬을 조합하여 블레이드 앞전 형상과 노즐-익렬 간극에 따라 실시하였다. 실험을 통해 충격파를 포함한 복잡한 유동 형태와 노즐-익렬, 충격파-경계층 상호작용 등을 관찰할 수 있었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.414-417
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• 2001

SRG (Switched Reluctance Generator) have many advantages such as high efficiency, low cost, high-speed capability and robustness compared with characteristics of other machines. However, the control methods that have been adopted for SRGs are complicated. This paper proposes a simple control method using PID controller that only controls turn-off angles while keeping turn-on angles of SRG constant. The linear characteristics between the generated current and the turn-off angle can be used to control the turn-off angle for load variations. Since the reference current for generation can be produced from an error between the reference and the real voltage, it can be controlled to keep the output voltage constant. The proposed control method enhances the robustness of this system and simplifies the hardware and software by using only the voltage and speed sensors. The proposed method is verified by experimental results.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.268-271
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• 2001

When compared to other composite materials such as FRP and MMC, hybrid composite material is more attractive one due to the high specific strength and the resistance to fatigue. However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. In this study, AE technique has been used to clarify the fracture mechanism and the degree of damage for Al 7075/CFRP hybrid composite material. It was found that AE event, energy and amplitude among AE parameters were effective to evaluate fracture process of Al 7075/CFRP composite material. In addition, the relationship between the AE signal and the characteristics of failure surface using optical microscope was discussed.

• ETRI Journal
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• 제30권6호
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• pp.833-843
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• 2008

The effect of forward and reverse electrostatic discharge (ESD) on the electro-optical characteristics of oxide vertical-cavity surface-emitting lasers is investigated using a human body model for the purpose of understanding degradation behavior. Forward ESD-induced degradation is complicated, showing three degradation phases depending on ESD voltage, while reverse ESD-induced degradation is relatively simple, exhibiting two phases of degradation divided by a sudden distinctive change in electro-optical characteristics. We demonstrate that the increase in the threshold current is mainly due to the increase in leakage current, nonradiative recombination current, and optical loss. The decrease in the slope efficiency is mainly due to the increase in optical loss.

• 한국항공우주학회지
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• 제30권4호
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• pp.84-91
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• 2002

Shroud로 감싸여 있는 제트베인의 추력 방향 조종 특성은 shoroud가 없는 제트베인의 조종 특성보다 매우 복잡하며 그 특성이 매우 특이하다. 이러한 제트 베인 시스템의 조종 특성을 파악하기 위하여 베인과 shroud 고유의 공력 특성은 물론 shroud/베인간의 유동 간섭에 대한 연구가 요구된다. 본 연구에서는 이를 위하여 반실험적인 모델링을 개발하고, 실제 기하학적 모델을 고려한 삼차원 유동해석과 실기형 연소시험을 수행하여 복잡한 물리적현상을 도출하여 shroud로 감싸여 있는 제트베인의 측력 특성을 제시하였다.

• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.112-121
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• 2009

This paper deals with supersonic air-breathing missile system. A supersonic air-breathing missile system has very complicated and incoherent thrust characteristics with respect to outer and inner environment during operation. For this reason, the missile system has many maneuver constraints and is allowed to operate within narrow flight envelope. In this paper, trajectory optimization of the missile is accomplished. The trajectory optimization problem is formulated as a discrete parameter optimization problem. For this formulation, Legendre Pseudo-Spectral method is introduced. This method is based on calculating the state and control variables on Legendre-Gauss-Lobatto (LGL) points. This approach helps to find approximated derivative and integration quantities simply. It is shown that, for this trajectory optimization, trend analysis is performed from thrust characteristics on various conditions so that the trajectory optimization is accomplished with fine initial guess with these results.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2006년도 춘계학술발표회 논문집
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• pp.521-526
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• 2006

As a result of establishing the regional self-government system, regional residents came to take more interest in their land ownership rights and relevant areas. The administrative bodies in South Korea are trying their best to meet the complicated and diversified demands of the residents regarding land and construction administration. However, governmental agencies are having difficulties identifying land characteristics on the field as part of standard lands change every year. Also, the vague boundaries of agricultural and mountainous land areas are causing surveyors problems in spotting the right areas. Thus, this study intends to provide information and guidance on an accurate land price calculation system in connection between the land information system and PDA technology for distribution of accurate information regarding lands and their management.

• 한국측량학회지
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• 제38권2호
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• pp.87-95
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• 2020

South korea has been developing and managing the complete dimensions, around the rivers to rapid economic growth. In Korea, where water resources are scarce, administration and work are complicated and diversified in the computerization of related facilities and hydrologic data due to the indiscriminate development of river facilities. In general, dividing the water system based on object in remote sensing is relatively accurate in the image with the same spectral characteristics. However, the distinction between the reservoir and the river must be made manually due to the characteristics of remote sensing. Therefore, this study performed three classifications using GIS (Geographic Information System) to classify reservoirs and rivers. For the purpose of accuracy analysis, the land cover map provided by EGIS (Environmental Geographic Information Service) was used to evaluate the accuracy, and the average of 85.63% was found to be 75.40% of rivers, 89.50% of reservoirs, and 92.00% of others.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.286-292
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• 2008

Transverse flux machine (TFM) has been developed to drive a machine of large input power at low-speed. However, it has complicated structure and large torque ripple due to its inherent structure In this paper the characteristics of torque of a rotatory two-phase TFM are analyzed by using the 3-dimensional finite to element method and optimal design. This research shows that one of the effective design variables is the skew angle of permanent magnet. The skew angles of permanent magnet are optimized by using a Progressive Quadratic Response Surface Method (PQRSM). It also shows that the proposed optimal skew magnet not only increases average torque but also decreases torque ripple of a rotatory two-phase TFM.