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LEE, Kyun Ho,LEE, Sung Nam,YU, Myoung Jong,KIM, Su Kyum,BAEK, Seung Wook THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2009 Transactions of the Japan Society for Aeronautical Vol.52 No.177
<P>Satellite attitude is usually controlled by plume exhaust from thrusters into the vacuum of space. To study the plume effects in the highly rarefied region, the Direct Simulation Monte Carlo (DSMC) method is usually used, because the plume flow field contains the entire range of flow regime from the near-continuum near the nozzle exit through the transitional state to free molecular state at the far field region from the nozzle. The purpose of this study is to investigate the behavior of a small monopropellant thruster plume in the vacuum region numerically by using the DSMC method. To obtain more accurate results, the preconditioned Navier-Stokes algorithm is introduced to calculate continuum flow fields inside the thruster to predict nozzle exit properties, which are used for inlet conditions of DSMC method. As a result, the plume characteristics in the highly rarefied flow, such as strong nonequilibrium near nozzle exit, large back flow region, etc., are investigated.</P>
Aircraft Longitudinal Auto-landing Guidance Law Using Time Delay Control Scheme
CHOI, Hyoung Sik,LEE, Sangjong,LEE, Jangho,KIM, Eung Tai,SHIM, Hyunchul THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2010 Transactions of the Japan Society for Aeronautical Vol.53 No.181
<P>The objective of this paper is applying the Time Delay Control scheme for the aircraft auto-landing guidance problem. A stability and control augmentation system and longitudinal auto-landing guidance law, using Time Delay Control, is proposed and evaluated through a simulation with model uncertainties and wind disturbances. The proposed Time Delay Control guidance law shows good performance and is robust to model uncertainties and disturbances.</P>
Extending Operational Area of Pseudolite Using Long Integration Time and Data-less Pseudolites
KEE, Changdon,LEE, Taikjin,SO, Hyungmin THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2009 Transactions of the Japan Society for Aeronautical Vol.52 No.176
<P>A pseudolite can be a solution to strengthen GNSS or create an independent navigation system. However a pseudolite has very serious near-far problem where the operational area becomes smaller and the usage limited. The aim of this work is to extend the pseudolite operational area. To minimize the near-far problem, we split the pseudolite pulse into several pulses. To maintain tracking of weak pseudolite signals, we increased receiver integration time. To validate these solutions, we simulated distributed pulsing and tested the increased integration time. To increase the integration time of conventional and low-cost receivers, we used a data-less pseudolite with no navigation data. Using these solutions, we extended the mid zone of the operational area and reduced the near and far zone.</P>
Effects of Low Reynolds Number on Loss Characteristics in Transonic Axial Compressor
CHOI, Minsuk,BAEK, Je Hyun,PARK, Jun Young,OH, Seong Hwan,KO, Han Young THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2010 Transactions of the Japan Society for Aeronautical Vol.53 No.181
<P>A three-dimensional computation was conducted to understand effects of low Reynolds numbers on loss characteristics in a transonic axial compressor, Rotor 67. As a gas turbine becomes smaller and it operates at high altitude, the engine frequently operates under low Reynolds number conditions. This study found that large viscosity significantly affects the location and intensity of the passage shock, which moves toward the leading edge and has decreased intensity at low Reynolds number. This change greatly affects performance as well as internal flows, such as pressure distribution on the blade surface, tip leakage flow and separation. The total pressure ratio and adiabatic efficiency both decreased by about 3% with decreasing Reynolds number. At detailed analysis, the total pressure loss was subdivided into four loss categories such as profile loss, tip leakage loss, endwall loss and shock loss.</P>
A Systematic Approach for Quantitative Analysis of Multidisciplinary Design Optimization Framework
KIM, Sangho,PARK, Jungkeun,LEE, Jeong-Oog,LEE, Jae-Woo THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2010 Transactions of the Japan Society for Aeronautical Vol.52 No.178
<P>An efficient Multidisciplinary Design and Optimization (MDO) framework for an aerospace engineering system should use and integrate distributed resources such as various analysis codes, optimization codes, Computer Aided Design (CAD) tools, Data Base Management Systems (DBMS), etc. in a heterogeneous environment, and need to provide user-friendly graphical user interfaces. In this paper, we propose a systematic approach for determining a reference MDO framework and for evaluating MDO frameworks. The proposed approach incorporates two well-known methods, Analytic Hierarchy Process (AHP) and Quality Function Deployment (QFD), in order to provide a quantitative analysis of the qualitative criteria of MDO frameworks. Identification and hierarchy of the framework requirements and the corresponding solutions for the reference MDO frameworks, the general one and the aircraft oriented one were carefully investigated. The reference frameworks were also quantitatively identified using AHP and QFD. An assessment of three in-house frameworks was then performed. The results produced clear and useful guidelines for improvement of the in-house MDO frameworks and showed the feasibility of the proposed approach for evaluating an MDO framework without a human interference.</P>
YUN, Youngsun,KIM, Doyoon,KEE, Changdon THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2008 Transactions of the Japan Society for Aeronautical Vol.50 No.170
<P>For more accurate and reliable aviation navigation systems which can be used for civil and military aircraft or missiles, researchers have employed various filtering methods to reduce the measurement noise level, or to integrate sensors such as global navigation satellite system/inertial navigation system (GNSS/INS) integration. Most GNSS applications including Differential GNSS assume that the GNSS measurement error follows a Gaussian distribution, but this is not true. Therefore, we propose an integrity monitoring method using particle filters assuming non-Gaussian measurement error. The performance of our method was contrasted with that of conventional Kalman filter methods with an assumed Gaussian error. Since the Kalman filters presume that measurement error follows a Gaussian distribution, they use an overbounded standard deviation to represent the measurement error distribution, and since the overbound standard deviations are too conservative compared to actual deviations, this degrades the integrity monitoring performance of the filters. A simulation was performed to show the improvement in performance provided by our proposed particle filter method, which does not use sigma overbounding. The results show that our method can detect about 20% smaller measurement biases and reduce the protection level by 30% versus the Kalman filter method based on an overbound sigma, which motivates us to use an actual error model instead of overbounding, or to improve the overbounding methods.</P>
YOO, Kyungho,SUNG, Sangkyung,LEE, Eunsung,LEE, Sanguk,KIM, Jaehoon,LEE, Ho-Jin,LEE, Young Jae THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2009 Transactions of the Japan Society for Aeronautical Vol.52 No.177
<P>Today Global Navigation Satellite Systems (GNSS) are widely used for determining position. Within the city environment, however, in which there are many tall buildings, GNSS signals are frequently interrupted, making it difficult for users to obtain information on their exact position. This paper analyzed the availability and positioning performance of a GPS augmented system within the Seoul urban area using the Japanese QZSS (Quasi-Zenith Satellite System) and a geostationary satellite. A 3-dimensional reproduction of Seoul that was based on the 3D GIS (Geographic Information System) Digital Map and a satellite tracking algorithm using Ray-Triangle Intersection algorithm were discussed. A satellite tracking algorithm was verified through filed testing and the QZSS orbit simulator was realized using Keplerian parameter. DOP (Dilution of Precision) and availability in the urban area of Seoul were analyzed using a GPS/QZSS/geostationary satellite separately and simultaneously.</P>
Geometrical Attitude Determination Algorithm Based on Vector Measurements
AHN, Hyo-Sung,LEE, Seon-Ho THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2010 Transactions of the Japan Society for Aeronautical Vol.53 No.179
<P>This paper addresses a novel vector-based attitude determination algorithm on the basis of geometrical configuration of external reference vectors. The proposed method called a geometrical attitude determination algorithm can be used for the attitude estimation of moving vehicles when two external reference vectors are partially measured on three orthogonal body axes. Applications of the new method range from the ground robotics navigation to satellite attitude control. Numerical simulations demonstrate that the algorithm can be reliably utilized for the three-axis attitude determination in the presence of inaccurately-measured reference vectors.</P>
Time Delay Fault Tolerant Controller for Actuator Failures during Aircraft Autolanding
LEE, Jangho,CHOI, Hyoung Sik,LEE, Sangjong,KIM, Eung Tai,SHIN, Dongho THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIEN 2012 Transactions of the Japan Society for Aeronautical Vol.55 No.3
<P>A time delay control methodology is adopted to cope with degraded control performance due to control surface damage of unmanned aerial vehicles, especially in the case of the automatic landing phase. It is a crucial challenge to maintain consistent control performance even under fault environments such as stuck and/or incipient actuator faults. Flight control systems designed using conventional feedback control methods in such cases may result in unsatisfactory performance, and even worse, may not guarantee the closed-loop stability, which is fatal for aircraft in the state of auto-landing. To overcome the shortfalls of the conventional approach, the time delay control scheme is adopted. This scheme is known to be robust against disturbance, model uncertainties and so on. Motivated by the fact that the abrupt and/or incipient actuator faults focused on in this paper could be considered as model uncertainties, we consider the application of the time delay controller to designing a fault tolerant control system. To show the effectiveness of the time delay control method, a nonlinear 6-DOF simulation is performed under model uncertainties and wind disturbances, and control performance is compared with that of conventional controllers in the case of multiple and single actuator faults.</P>