Lee H.,Gyeongsang National University |
Kim Y.,Korea Institute of Geoscience and Mineral Resources |
Jeong Y.,Korea Aerospace Industries Ltd. |
Kim S.,Gyeongsang National University
Corrosion Science | Year: 2012
In the present study, the effects of testing variables on stress corrosion cracking (SCC) susceptibility of Al 2024-T351 in 3.5% NaCl solution were examined using slow strain rate test (SSRT) method with controlled applied potentials and a constant load test (CLT) method. The SSRTs were conducted at various strain rates and applied potential, while the CLTs were performed with different exposure time, with different grain directions of ST (short-transverse) and L (longitudinal) to understand how the testing parameters affected on the SCC susceptibility of Al 2024-T351. The percent reductions in tensile elongation in an SCC-causing environment over those in air tended to express the SCC susceptibility of Al 2024-T351 most properly for both SSRT and CLT. The present fractographic examination suggested that both anodic dissolution and hydrogen embrittlement played a role in the SCC process of Al 2024-T351 in 3.5% NaCl solution at both anodic and cathodic applied potentials, and the contribution of each mechanism could vary with different testing variables. It was also found that the SCC susceptibility of Al 2024-T351 obtained from the CLT result could provide the similar SCC evaluation result obtained by SSRT with a proper selection of testing variables. The metallurgical aspect of SCC behaviour of Al 2024-T351 was also discussed based on the microstructural and fractographic examinations. © 2011 Elsevier Ltd.
Kim Y.,Korea Institute of Geoscience and Mineral Resources |
Kwon J.,Korea Institute of Geoscience and Mineral Resources |
Jeong Y.,Korea Aerospace Industries LTD |
Woo N.,Korea Institute of Geoscience and Mineral Resources |
Kim S.,Gyeongsang National University
Metals and Materials International | Year: 2013
The through-thickness stress corrosion cracking (SCC) behaviors of thick 2024-T351 and 7050-T7451 extrudates in 3.5% NaCl solution were studied at both anodic and cathodic applied potentials using a slow strain rate test method. The SCC susceptibilities of 2024-T351 extrudate tended to change in the throughthickness direction, with the lowest susceptibility for the surface specimen. 7050-T7451 specimens, on the other hand, did not show a notable change in the through-thickness SCC susceptibility. The fractographic analysis suggested that the grain boundary played an important role in determining the SCC susceptibility. The SCC process of each alloy was discussed based on the microscopic and fractographic examinations. © 2013 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.
Jung S.K.,Korea Aerospace Industries LTD. |
Myong R.S.,Gyeongsang National University
Computers and Fluids | Year: 2013
A second-order positivity-preserving finite volume upwind scheme based on the approximate Riemann solver is developed for computing the Eulerian two-phase flow composed of air and small water droplets in atmospheric icing. In order to circumvent a numerical problem due to the non-strictly hyperbolic nature of the original Eulerian droplet equations, a simple technique based on splitting of the original system into the well-posed hyperbolic part and the source term is proposed. The positivity-preserving Harten-Lax-van Leer-Contact approximate Riemann solver is then applied to the well-posed hyperbolic part of the Eulerian droplet equations. It is demonstrated that the new scheme satisfies the positivity condition for the liquid water contents. The numerical results of one and two-dimensional test problems are also presented as the verification and validation of the new scheme. Lastly, the exact analytical Riemann solutions of the well-posed hyperbolic part of the droplet equations in wet and dry regions are given for the verification study. © 2013 Elsevier Ltd.
Moon Y.H.,Gyeongsang National University |
Yoon K.S.,Korea Aerospace Industries Ltd. |
Park S.-T.,Electronics and Telecommunications Research Institute |
Shin I.H.,Electronics and Telecommunications Research Institute
IEEE Transactions on Multimedia | Year: 2013
In this paper, a new fast encoding algorithm based on an efficient motion estimation (ME) process is proposed to accelerate the encoding speed of the scalable video coding standard. Through analysis of the ME process performed in the enhancement layer, we discovered that there are redundant MEs and some MEs can simply be unified at the fully overlapped search range (FOSR). In order to make the unified ME more efficient, we theoretically derive a skip criterion to determine whether the computation of rate-distortion cost can be omitted. In the proposed algorithm, the unnecessary MEs are removed and a unified ME with the skip criterion is applied in the FOSR. Simulation results show that the proposed algorithm achieves computational savings of approximately 46% without coding performance degradation when compared with the original SVC encoder. © 2012 IEEE.
Han K.H.,Korea Aerospace Industries Ltd |
Koh G.O.,Korea Aerospace Industries Ltd |
Sung J.,Gyeongsang National University |
Kim B.S.,Gyeongsang National University
International Journal of Aeronautical and Space Sciences | Year: 2011
Backlash is common in mechanical and hydraulic systems and severely limits overall system performance. In this paper, the development of an adaptive control scheme for systems with unknown backlash is presented. An adaptive backlash inverse based controller is applied to a plant that has an unknown backlash in its input. The harmful effects of backlash are presented. Compensation for backlash by adding a discrete adaptive backlash inverse structure and the gradient-type adaptive algorithm, which provides the estimated backlash parameters, are also presented. The supposed adaptive backlash control algorithms are applied to an aircraft with unknown backlash in the actuator of control surfaces. Simulation results show that the proposed compensation scheme improves the tracking performance of systems with backlash. © The Korean Society for Aeronautical & Space Sciences.
Nam Y.-S.,Defence Agency for Technology and Quality |
Jeong Y.-I.,Korea Aerospace Industries Ltd. |
Shin B.-C.,Gyeongsang National University |
Byun J.-H.,Gyeongsang National University
Materials and Design | Year: 2015
Shot peening leads to local plastic deformations in the near-surface regions, which result in the development of residual stress and the improvement of surface hardness in the aerospace structural components. These properties can be enhanced by careful selection of the peening parameters. 2124-T851 aluminum alloy is widely used in the aerospace industry due to its high specific static strength. In this study, a response surface methodology is presented to optimize the surface properties of microhardness and residual stress. The effects of four peening parameters (nozzle distance, pressure, impact angle, and exposure time) on microhardness and residual stress are investigated. Box-Behnken design, a popular second-order response surface design, is employed to systematically estimate the empirical models of microhardness and residual stress in terms of the four parameters. Based on the estimated models, optimum peening conditions are recommended by using the desirability function approach, which is the most popular technique for optimizing multiple responses. Additionally, to verify the validity of the optimal conditions obtained from experimental results, metallurgical analyses of the shot-peened aluminum alloy were conducted with respect to hardness, residual stress, surface morphology, X-ray diffraction analysis, and surface roughness. © 2015 Elsevier Ltd.
Hyun J.,Korea Aerospace Industries Ltd. |
Kim K.H.,Gyeongsang National University
Proceedings - 18th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications, RTCSA 2012 - 2nd Workshop on Cyber-Physical Systems, Networks, and Applications, CPSNA | Year: 2012
As real-time systems become complex and require high-performance, Hierarchical Real-Time Scheduling Framework (HRTSF) has been investigated to schedule real-time tasks to meet their deadlines by sharing resources hierarchically under various scheduling algorithms. In this paper, we focus on fault-tolerant scheduling in the hierarchical real-time scheduling framework. Thus, we introduce a new component interface model which provides abstract information about a component's fault-tolerant real-time requirement. The upper-layer component can use the interface model to share its resource with consideration of both real-time and fault-tolerance. We also provide the schedulability analysis of Rate Monotonic (RM) algorithm under the proposed framework and apply it to a case study of designing avionics software as an example of Cyber Physical Systems (CPS). © 2012 IEEE.
Song M.-G.,Gyeongsang National University |
Kweon J.-H.,Gyeongsang National University |
Choi J.-H.,Gyeongsang National University |
Byun J.-H.,Gyeongsang National University |
And 3 more authors.
Composite Structures | Year: 2010
The present paper experimentally addresses the effect of manufacturing methods on the strength of composite bonded joints. A total of 391 specimens, manufactured by four different fabrication methods, were tested. For each method, various overlap lengths, adherend thicknesses and lay-up patterns were examined. The failure strength was higher in thicker adherend joints and lower in specimens with larger overlap length. Results showed that the secondary bonded joints had higher strength than the co-bonded and adhesively cocured joints and yielded similar strength compared with the non-adhesive cocured case. Changes in the stacking sequence also affected the interlaminar stresses and failure loads. © 2009 Elsevier Ltd.
Han K.-H.,Korea Aerospace Industries Ltd. |
Koh G.-O.,Korea Aerospace Industries Ltd. |
Sung J.-M.,Gyeongsang National University |
Kim B.-S.,Gyeongsang National University
International Conference on Control, Automation and Systems | Year: 2011
Backlash which severely limits the overall system performance is common in mechanical and hydraulic systems. In this paper, the development of an adaptive control scheme for systems with unknown backlash is presented. An adaptive backlash inverse based controller is applied to the plants that have an unknown backlash at its input. The harmful effects of backlash and the compensation of backlash by adding a discrete adaptive backlash inverse structure and the gradient type adaptive algorithm which provides the estimated backlash parameter are presented. The supposed adaptive backlash control algorithms are applied to the aircraft with unknown backlash in the actuator of control surfaces for demonstration. Simulation results show that the proposed compensation scheme is the way of improving the tracking performance of the systems with backlash. © 2011 ICROS.
Hur J.-W.,Kumoh National Institute of Technology |
Jang J.-H.,Korea Aerospace Industries LTD.
International Journal of Precision Engineering and Manufacturing | Year: 2013
Crashworthiness model for Korean Utility Helicopter was built by employing KRASH, a kinetic analysis program, and the characteristics and performance of crashworthiness were assessed by the analysis. As a result of the analysis considering crashworthiness impact velocity of military standard, the vertical impact velocity became 0 after 0. 124 second and the predicted values for the maximum acceleration of the engine and power transmission gear were 33G and 27G respectively. Cabin space height before and after the crash were 1. 59 m and 1. 40 m respectively; it led to 12% reduction in survival space but managed to fulfill the engineering requirement of "below 15%." The predicted maximum displacement of crew and passenger seats were 126 mm and 188 mm respectively, fulfilling each of the acceptable standard. In addition, according to the results evaluated by Eiband Curve, passenger acceleration level was found out to be insufficient to cause a severe damage to passengers. © 2013 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.