• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1097-1107
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• 2015

General VTOL aircraft uses gas turbine engine which has high power to weight ratio. However, in the VTOL UAV in small sector, the gas turbine as a prime mover is not adequate because of the limitation of the high fuel consumption ratio of the gas turbine. In this research, The Series Hybrid-Electric Propulsion System(SHEPS) has been proposed and technology survey & comparison analysis has conducted to constitute propulsion system for engine, electric motor and battery. To achieve this object a 65kg-class P-UAV from "Company I" was used. And to estimate the validity of power control algorithm and developed power management control, Matlab/simulink$^{(R)}$ has been used for the simulation. As a result, the developed algorithm worked comparatively well and the research has predicted that SHEPS was satisfied enough for 7 hour of endurance for mission profile.

• 전자공학회논문지 IE
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• v.47 no.2
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• pp.73-81
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• 2010

The main purpose of this study was to examine the effects of meta-cognition, learning flow and problem solving ability of the college engineering students on academic achievement. For this purpose, a total of 396 college engineering freshmen of the six different departments was chosen to conduct a survey. A hypothetical model was proposed, which was composed of meta-cognition, problem solving ability and learning flow as the prediction variables, and academic achievement as the outcome variables. The results of this study through multiple regression analysis showed that meta-cognition, learning flow and problem solving ability significantly influenced on the college engineering studnets' academic achievement. In addition, learning flow was used as a significant mediated variable in the relationships among meta-cognition, problem solving ability and academic achievement. Based on these study results, the above variables investigated in this study should be considered in the design and development of the college engineering courses that enable students to facilitate their problem-solving attitude and improve academic achievement.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.2
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• pp.89-99
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• 1997

Although discontinuously reinforced metal matrix composite(MMC) is one of the most promising materials for applications of aerospace, automotive industries, the thermal residual stresses developed in the MMC due to the mismatch in coefficients of thermal expansion between the matrix and the fiber under a temperature change has been pointed out as one of the serious problem in practical applications. There are very limited nondestructive techniques to measure the residual stress of composite materials. However, many difficulties have been reported in their applications. Therefore it is important to establish analytical model to evaluate the thermal residual stress of MMC for practical engineering application. In this study, an elastic model is developed to predict the average thermal residual stresses in the matrix and fiber of a misoriented short fiber composite. The thermal residual stresses are induced by the mismatch in the coefficient of the thermal expansion of the matrix and fiber when the composite is subjected to a uniform temperature change. The model considers two-dimensional in-plane fiber misorientation. The analytical formulation of the model is based on Eshelby's equivalent inclusion method and is unique in that it is able to account for interactions among fibers. This model is more general than past models to investigate the effect of parameters which might influence thermal residual stress in composites. The present model is to investigate the effects of fiber volume fraction, distribution type, distribution cut-off angle, and aspect ratio on thermal residual stress for in-plane fiber misorientation. Fiber volume fraction, aspect ratio, and distribution cut-off angle are shown to have more significant effects on the magnitude of the thermal residual stresses than fiber distribution type for in-plane misorientation.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2292-2314
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• 2006

Efficient numerical method is developed for the prediction of aerodynamic noise generation and propagation in low Mach number flows such as aeolian tone noise. The proposed numerical method is based on acoustic/viscous splitting techniques of which acoustic solvers use simplified linearised Euler equations, full linearised Euler equations and nonlinear perturbation equations as acoustic governing equations. All of acoustic equations are forced with immersed surface dipole model which is developed for the efficient computation of aerodynamic noise generation and propagation in low Mach number flows in which dipole source, originating from unsteady pressure fluctuation on a solid surface, is known to be more efficient than quadrupole sources. Multi-scale overset grid technique is also utilized to resolve the complex geometries. Initially, aeolian tone from single cylinder is considered to examine the effects that the immersed surface dipole models combined with the different acoustic governing equations have on the overall accuracy of the method. Then, the current numerical method is applied to the simulation of the aeolian tones from twin cylinders aligned perpendicularly to the mean flow and separated 3 diameters between their centers. In this configuration, symmetric vortices are shed from twin cylinders, which leads to the anti-phase of the lift dipoles and the in-phase of the drag dipoles. Due to these phase differences, the directivity of the fluctuating pressure from the lift dipoles shows the comparable magnitude with that from the drag dipoles at 10 diameters apart from the origin. However, the directivity at 100 diameters shows that the lift-dipole originated noise has larger magnitude than, but still comparable to, that of the drag-dipole one. Comparison of the numerical results with and without mean flow effects on the acoustic wave emphasizes the effects of the sheared background flows around the cylinders on the propagating acoustic waves, which is not generally considered by the classic acoustic analogy methods. Through the comparison of the results using the immersed surface dipole models with those using point sources, it is demonstrated that the current methods can allow for the complex interactions between the acoustic wave and the solid wall and the effects of the mean flow on the acoustic waves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.7
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• pp.639-646
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• 2014

The comparative analysis of near-wall treatment methods that affect the prediction of heat transfer over the gas turbine nozzle guide vane were presented. To achieve this objective, wall-function and low Reynolds number methods, and the transition model were applied and simulated using NASA's C3X turbine vane. The predicted turbine vane surface pressure distribution data using the near-wall treatment methods were found to be in close agreement with experimental data. However, the predicted vane metal temperature and heat transfer coefficient displayed significant differences. Overall, the low Reynolds method and transition model did not offer specific advantages in the prediction of temperature and heat transfer than did the wall-function method. The Reynolds stress model used along with the wall-function method resulted in a relatively high accuracy of prediction of the vane metal temperature and heat transfer coefficient.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.41-51
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• 2018

Downwash from helicopter rotor blades and external winds from various maneuvering make an unguided rocket change its trajectory and range. For the prediction of the trajectory and range, it is essential to consider the downwash effect. In this study, an algorithm was developed to calculate 6-Degree-Of-Freedom(6 DOF) forces and moments exerting on the rocket, and total flight trajectory of a 2.75-inch unguided rocket in a helicopter downwash flow field. Using Actuator Disk Model(ADM) analysis result, the algorithm could analyze the entire trajectory in various initial launch condition such as launch angle, launch velocity, and external wind. The algorithm that considered the interference between a fuselage and external winds could predict the trajectory change more precisely than inflow model analysis. Using the developed algorithm, the attitude and trajectory change mechanism by the downwash effect were investigated analyzing the effective angle of attack change and characteristics of pitching stability of the unguided rocket. Also, the trajectory and range changes were analyzed by considering the downwash effect with external winds. As a result, it was concluded that the key factors of the rocket range change were downwash area and magnitude which effect on the rocket, and the secondary factors were the dynamic pressure of the rocket and the interference between a fuselage and external winds. In tailwind case which was much influential on the range characteristics than other wind cases, the range of the rocket rose as increasing the tailwind velocity. However, there was a limit that the range of the rocket did not increase more than the specific tailwind velocity.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.5
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• pp.539-550
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• 2014

High resolution satellite images have to be oriented and geometrically processed from GCPs(Ground Control Points) to generate precise DEMs(Digital Elevation Models) and topographic maps. In Korea, thousands of national UCPS(Unified Control Points) are established and distributed all over the country by the Korean NGII(National Geographic Information Institute). For that reason, UCPs can be easily searched and downloaded by the national-control-point-record-issues system. Following the study, we suggested the sky-view and road-view from web-portals for searching and identifying UCPs on the images. To evaluate the usefulness of UCPs in RPCs(rational polynomial coefficients) adjustment of the high resolution satellite images, the one UCP, which of using simple the control point, has been applied to adjust the vendor-provided RPCs of the KOMPSAT-3 images. As a result, the positioning error of corrected RPCs was approximately one pixel and one meter. From this experiment, we conclude that the UCPs will be able to replace the survey GCPs for mapping with the satellite images or aerial images.

• Korean Journal of Remote Sensing
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• v.30 no.6
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• pp.829-837
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• 2014

The KOMPSAT-3 can acquire panchromatic stereo image with 0.7 m spatial resolution, and provides Rational Polynomial Coefficient (RPC). In order to determine ground coordinate using the provides RPC, which include interior-exterior orientation errors, its adjustment is needed by using the Ground Control Point (GCP). Several thousands of national Unified Control Points (UCPs) are established and overall distributed in the country by the Korean National Geographic Information Institute (NGII). UCPs therefore can be easily searched and downloaded by the national-control-point-record-issues system. This paper introduced the point-extraction method and the distance-bearing method to detect of UCPs. As results, the distance-bearing method was better detected through the experiment. RPC adjustment using this method was compared with that by only one UCP and GCPs using GPS. The proposed method was more accurate than the other method in the horizontal. As demonstrated in this paper, the proposed UCPs detection method could be replaced GPS surveying for RPC adjustment.

• The Korean Journal of Air & Space Law and Policy
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• v.25 no.2
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• pp.79-112
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• 2010

The Beijing Convention of 2010 taken together effectively establishes a new broader and stronger civil aviation security framework. This adoption would significantly advance cooperation in prevent of the full range of unlawful acting relation to civil aviation and the prosecution and punishment of offenders. First, the Beijing Convention of 2010 will require parties to criminalize a number of new and emerging threats to the safety of civil aviation, including using aircraft as a weapon and organizing, directing and financing acts of terrorism. These new treaties reflect the international community's shared effort to prevent acts of terrorism against civil aviation and to prosecute and punish those who would commit them. Second, this convention will also require States to criminalize the transport of biological, chemical, nuclear weapons and related material. These provisions reflect the nexus between non-proliferation and terrorism and ensure that the international community will act to combat both. Third, this Convention shall not apply to aircraft used in military, customs or police services. As a substitute, International Humanitarian Law will be applied in a case. Moreover, the National Jurisdiction and the application of the law will be extended farther. The treaty promotes cooperation between States while emphasizing the human rights and fair treatment of terrorist suspects.

• The Korean Journal of Air & Space Law and Policy
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• v.25 no.2
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• pp.201-230
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• 2010

With starting the industry of automobiles, railroads and mining, the legal principle of "erlaubtes Risiko" that began as a means of maintaining the revitalized world for the cause of social utility has interpreted as a system of negligence theory in the precedent while it has gained academic recognition. Yet in aircraft operation, which is one area of high technology, CAT which can be the cause of some accidents or events or thunderstorm with turbulence is an abnormal meteorological phenomenon with frequent change that cannot be monitored perfectly just as some patient with unstable condition and that cannot be ascertained about not only the possibility of its happening but also the degree of how big the accident is. Yet the use of jet current which has the possibility of CAT can be an act of high social utility where we not only drastically cut down on time fuel also guarantee the arrival and departure on schedule when landing in airports that have thunderstorm which does not appear as fatal risk. Although we could take some measures where we can predict and avoid the potential risk, easing the regular duty of care is necessary by applying the legal principles of permitted risk concerning the incidents and accidents caused by operating in areas with the risk of turbulence or CAT with the low probability by the reason of social utility.