• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제48권10호
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• pp.809-819
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• 2020

In this study, the twist angle and wing planform shapes were selected as design variables and optimized to secure the stability of the flying-wing type UAV. Flying-wing aircraft has no separated fuselage and tails, which has advantages in aerodynamic characteristics and stealth performance, but it is difficult to secure the flight stability. In this paper, the sweep back angle and twist angle were optimized to obtain the lateral stability, the static margin and wing planform shapes were optimized to improve the longitudinal stability of the flying-wing, then effect of the twist angle was confirmed by comparing the stability of the shape with the winglet and the shape with the twist angle. In the optimization formulation, focusing on improving stability, constraints were established, objective functions and design variables were set, then design variable sensitivity analysis was performed using the Sobol method. AVL was used for aerodynamic analysis and stability analysis, and SQP was used for optimization. The CFD analysis of the optimized shape and the simulation of the dynamic stability proved that the twist angle can be applied to the improvement of the lateral stability as well as the stealth performance in the flying-wing instead of the winglet.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제43권6호
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• pp.548-556
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• 2015

The highly maneuverable fighter aircraft such as F-22, F-16 and F-15have the high maneuverability to maximize the combat performance, whereas the high maneuver characteristics might degrade the pilot's mission efficiency due to fatigue's increase by exposing him to the high gravity and, in the worst case, the pilot could face GLOC (Gravity-induced Loss Of Consciousness). The advanced aerospace company has applied the various technologies to improve the pilot's tolerance to the gravity acceleration, in order to prevent the pilot from entering the situation of the loss of consciousness. Especially, the Anti-G Suit(AGS) equipment to protect the pilot against the high gravity in flight could improve the mission success rate by decreasing the pilot's fatigue in the combat maneuver as well as prevent the pilot from facing GLOC. In this paper, a control algorithm is developed and verified to provide an optimal air pressure to AGS according to the gravity increase during the high performance maneuver. This result is expected, as the key technology, to contribute to the KF-X(Korean Fighter eXperimental), project in the near future.

• Transactions of the Korean Society of Automotive Engineers
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• 제14권3호
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• pp.10-21
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• 2006

The aim in this study is to develop the combined EGR system with a non-thermal plasma reactor for reducing exhaust emissions and improving fuel economy in turbo intercooler ECU common-rail diesel engines. At the first step, in this paper, the characteristics of performance and $NO_x{\cdot}THC$ emissions under four kinds of engine loads are experimentally investigated by using a four-cycle, four-cylinder, direct injection type, water-cooled turbo intercooler ECU common-rail diesel engine with a combined plasma exhaust gas recirculation(EGR) system operating at three kinds of engine speeds. The EGR system is used to reduce $NO_x$ emissions, and the non-thermal plasma reactor and turbo intercooler system are used to reduce THC emissions. The plasma system is a flat-to-flat type reactor operated by a plasma power supply. The fuel is sprayed by pilot and main injections at the variable injection timing between BTDC $15^{\circ}$ and ATDC $1^{\circ}$ according to experimental conditions. It is found that the specific fuel consumption rate with EGR is increased, but the fuel economy is better than that of mechanical injection type diesel engine as compared with the same output. Results show that $NO_x$ emissions are decreased, but THC emissions are increased, as the EGR rate is elevated. $NO_x$ and THC emissions are also slightly decreased as the applied electrical voltage of the non-thermal plasma reactor is elevated. Thus one can conclude that the influence of EGR in $NO_x$ and THC emissions is larger than that of the non-thermal plasma reactor, but THC emissions are greatly influenced by the non-thermal plasma reactor as the EGR rate is elevated.

• Journal of Convergence for Information Technology
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• 제9권12호
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• pp.141-146
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• 2019

Economic analysis predicts that the drone market will grow, and the growth of the toy and hobby drone market is expected to gradually expand. Drone expectations are rising due to the net economic function of drone market growth, but accidents due to improper management and operations are also increasing. The difference in toy drone performance is incomparably small compared to industrial drone performance, but the ordinary buyer can not know whether the difference can cause an accident during use. The toy drones used in this study were obtained from KC and CE certification, and 20 kinds of drones were used. The flight time ranged from a minimum of 3 minutes to a maximum of 12 minutes, and the control distance ranged from a minimum of 20m to a maximum of 380m. Therefore, it is necessary to secure product safety through sampling inspection of the radio wave output of toy drones, and it is also necessary to mount an algorithm that automatically lowers the altitude or hover when exceeding the limit flight distance. For future research, we will build data to establish toy drone safety standards through a altitude testing and impact testing of toy drone.

• Journal of Korea Water Resources Association
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• 제56권2호
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• pp.91-101
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• 2023

In this study, we estimated the concentration of chlorophyll-a (Chl-a) using hyperspectral water surface reflectance in an inland weir (Baekjae weir) and estuarine reservoir (Namyang Reservoir) for monitoring the occurrence of algae in freshwater in South Korea. The hyperspectral reflectance was measured by aircraft in Baekjae Weir (BJW) from 2016 to 2017, and a drone in Namyang Reservoir (NYR) from 2020 to 2021. The 30 reflectance bands (BJW: 400-530, 620-680, 710-730, 760-790 nm, NYR: 400-430, 655-680, 740-800 nm) that were highly related to Chl-a concentration were selected using permutation importance. Artificial neural network based Chl-a estimation model was developed using the selected reflectance in both water bodies. And the performance of the model was evaluated with the coefficient of determination (R²), the root mean square error (RMSE), and the mean absolute error (MAE). The performance evaluation results of the Chl-a estimation model for each watershed was R²: 0.63, 0.82, RMSE: 9.67, 6.99, and MAE: 11.25, 8.48, respectively. The developed Chl-a model of this study may be used as foundation tool for the optimal management of freshwater algal blooms in the future.

• Atmosphere
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• 제23권2호
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• pp.171-186
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• 2013

Recently, the number of observations used in a data assimilation system is increasing due to the enormous amount of observations, including satellite data. However, it is not clear that all of these observations are always beneficial to the performance of the numerical weather prediction (NWP). Therefore, it is important to evaluate the effect of observations on these forecasts so that the observations can be used more usefully in NWP process. In this study, the adjoint-based Forecast Sensitivity to Observation (FSO) method with the KMA Unified Model (UM) is applied to two high-impact weather events which occurred in summer and winter in Korea in an effort to investigate the effects of observations on the forecasts of these events. The total dry energy norm is used as a response function to calculate the adjoint sensitivity. For the summer case, TEMP observations have the greatest total impact while BOGUS shows the greatest impact per observation for all of the 24-, 36-, and 48-hour forecasts. For the winter case, aircraft, ATOVS, and ESA have the greatest total impact for the 24-, 36-, and 48-hour forecasts respectively, while ESA has the greatest impact per observation. Most of the observation effects are horizontally located upwind or in the vicinity of the Korean peninsula. The fraction of beneficial observations is less than 50%, which is less than the results in previous studies. As an additional experiment, the total moist energy norm is used as a response function to measure the sensitivity of 24-hour forecast error to observations. The characteristics of the observation impact with the moist energy response function are generally similar to those with the dry energy response function. However, the ATOVS observations were found to be sensitive to the response function, showing a positive (a negative) effect on the forecast when using the dry (moist) norm for the summer case. For the winter case, the dry and moist energy norm experiments show very similar results because the adjoint of KMA UM does not calculate the specific humidity of ice properly such that the dry and moist energy norms are very similar except for the humidity in air that is very low in winter.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제46권1호
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• pp.1-9
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• 2018

Lambda wing type Unmanned Combat Aerial Vehicle(UCAV) which adopts Blended Wing Body(BWB) has relatively less drag and more stealth performance than conventional aircraft. However, Pitching moment is rapidly increased at a specific angle of attack affected by leading edge vortex due to leading edge sweep angle. Wind tunnel testing and numerical analysis were carried out with UCAV 1303 configuration on condition of 50 m/s of flow velocity, $-4^{\circ}{\sim}28^{\circ}$ of the range of angle-of-attack. The effect of wing twist for longitudinal stability at the various angles of attack was verified in this study. When negative twist is applied on the wing, Pitch-break was onset at higher angle of attack due to delayed flow separation on outboard of the wing. On the other hand, pitch-break was onset at lower angle of attack and lift-to-drag ratio was increased when positive twist is applied on the wing.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제37권5호
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• pp.431-439
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• 2013

A cooling system is adopted to control the thermal load from the avionic equipments in an aircraft for stable operation. In this study, an avionic cooling system was designed and manufactured by adopting a vapor compression cycle with a closed-loop air-circulation system to investigate the operating characteristics of an alternative refrigerant. The performance characteristics of a cooling system adopting R236fa as an alternative refrigerant were experimentally determined by varying the refrigerant charging amount, expansion valve opening, and compressor rotation speed. The experimental results were analyzed and compared with those of a cooling system adopting R124 as a refrigerant. The possibility of the adoption of R236fa as an alternative refrigerant was verified, and design solutions were suggested to improve the system efficiency.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제21권5호
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• pp.1-6
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• 2020

UAV (Unmanned Aerial Vehicles) are used widely for military purposes because they are more economical than general manned aircraft and satellites, and have easy access to the object. Recently, owing to the development of IT technology, UAV equipped with various sensors have been released, and their use is increasing in a wide range of fields, such as surveying, agriculture, meteorological observation, communication, broadcasting, and sports. An increasing number of studies and attempts have made use of it. On the other hand, existing research was related mostly to photogrammetry, but there has been a lack of analytical research on LiDAR (Light Detection And Ranging). Therefore, this study examined the characteristics of a UAV LiDAR sensor for the application of a geospatial information field. In this study, the performance of commercialized LiDAR sensors, such as the acquisition speed and the number of echoes, was investigated, and data acquisition and analysis were conducted by selecting Surveyor Ultra and VX15 models with similar accuracy and data acquisition distances. As a result, a DSM of each study site was generated for each sensor, and the characteristics of data density, precision, and acquisition of ground data from vegetation areas were presented through comparison. In addition, the UAV LiDAR sensor showed an accuracy of 0.03m ~ 0.05m. Hence, it is necessary to select equipment considering the characteristics of data for effective use. In the future, the use of UAV LiDAR may be suggested if additional data can be obtained and analyzed for various areas, such as urban areas and forest areas.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제21권5호
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• pp.93-102
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• 2020

The design of large complex mechanical systems, such as automobile, aircraft, and ship, is a kind of Multidisciplinary Design Optimization (MDO) because it requires both experience and expertise in many areas. With the rapid development of technology and the demand to improve human convenience, the complexity of these systems is increasing further. The design of such a complex system requires an integrated system design, i.e., MDO, which can fuse not only domain-specific knowledge but also knowledge, experience, and perspectives in various fields. In the past, the MDO relied heavily on the designer's intuition and experience, making it less efficient in terms of accuracy and time efficiency. Process integration and the design optimization framework mainly support MDO owing to the evolution of IT technology. This paper examined the procedure and methods to implement an efficient MDO with reasonable effort and time using RCE, an open-source PIDO framework. As a benchmarking example, the authors applied the proposed MDO methodology to a bulk carrier's conceptual design synthesis model. The validity of this proposed MDO methodology was determined by visual analysis of the Pareto optimal solutions.