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Seongnam, South Korea

Yun J.,LIG Nex1 | Yun J.,Precision Guided Munition and Avionics Research and Development Center | Ryoo C.-K.,Inha University
Journal of Guidance, Control, and Dynamics | Year: 2014

This paperpresentsaninteractive multiple-model-based guidance law estimation filter.Anantiship missile's threat index, such as the remaining time of flight and impact angle, can be estimated by using the guidance law estimation filter. The filter bank of the filter was composed of models based on proportional navigation and impact angle control guidance laws. In the guidance law estimation filter, state variables, rather than fixed values of navigation constant or impact angle,are used for estimation.Tothat end, the modified interactive multiple model, which is a modified version of the conventional interactive multiple model method is presented in this paper. The modified interactive multiple model method minimizes the degradation of estimation performance by systematic approach for different state vectors. The effectivenessof the modified interactive multiple model method and the performanceofthe guidance law estimation filter are examined through the numerical simulation of various engagement scenarios. Copyright © 2013 by Joongsup Yun and Chang-Kyung Ryoo.

Jeong Y.,Sungkonghoe University | Kim J.,LIG Nex1 | Han S.-J.,Yonsei University
Wireless Networks | Year: 2011

Scalability is one of the most important features that future wireless sensor networks (WSNs) should provide, and clustering is widely considered as a viable approach for high scalability. In the cluster-based architecture, the cluster heads play a key role in relaying messages between the sensor nodes and the sink. While the cluster heads are involved in both intra-cluster and inter-cluster communication, the latter typically requires transmission over much longer distance than the former. In this paper, we consider a scenario in which each cluster head is equipped with dual radios: IEEE 802.15.4 and IEEE 802.11 for intra-cluster and inter-cluster communication, respectively. IEEE 802.11 links between the cluster heads and the sink provide a high capacity backbone for large-scale WSNs. IEEE 802.15.4 and IEEE 802.11 share a lot of similarities including CSMA/CA MAC. Their operating spectrum also overlaps at the 2.4 GHz ISM band, and this may cause interference. We first experimentally measure how severe the interference can be, when two radios are concurrently used in a WSN. We, then, propose an interference mitigation solution which relies on adaptive aggregation of packets and adaptive transmission scheduling. Through prototyping and experimental evaluation, we show that the proposed scheme significantly reduces the interferences between the two types of radios. © 2011 Springer Science+Business Media, LLC.

Suh C.,Center for Intelligent Robotics | Um T.T.,LIG Nex1 | Kim B.,Seoul National University | Noh H.,Center for Intelligent Robotics | And 2 more authors.
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2011

Motion planning for robots subject to holonomic constraints typically involves planning on constraint manifolds. In this paper we present the Tangent Space Rapidly Exploring Random Tree (TS-RRT) algorithm for planning on constraint manifolds. The key idea is to construct random trees not on the constraint manifold itself, but rather on tangent space approximations to the constraint manifold. Curvature-based methods are developed for constructing bounded tangent space approximations, as well as procedures for random node generation and bidirectional tree extension. Extensive numerical experiments suggest that the TS-RRT algorithm, despite its increased preprocessing and bookkeeping, outperforms existing constrained planning algorithms for a wide range of benchmark planning problems. © 2011 IEEE.

Khil T.,LIG Nex1 | Khil T.,General Electric | Chung Y.,Seoul National University | Bazarov V.G.,Moscow Aviation Institute | Yoon Y.,Seoul National University
Journal of Propulsion and Power | Year: 2012

Combustion instability is generally generated by mutual coupling between heat release and acoustic pressure in the combustor. Acoustic pressure causes the mass flow rate of propellant injected from atomizers to oscillate, which affects the combustion process. Since the early 1970s, great efforts have been made in Russia to elucidate the underlying mechanisms of the injector's dynamic characteristics to better manage combustion instability. In the current work, to characterize the injector dynamics, a mechanical pulsator was developed to produce forced pressure oscillation. An analytical method was also developed to quantify the mass flow rate of the propellant oscillating at the injector exit. The pulsating values of the mass flow rate, pressure, liquid film thickness, and axial velocity generated at the simplex swirl injector exit were all measured and quantified in real time in a low frequency range of the fluctuating pressure. Furthermore, the dynamic characteristics of each parameter were analyzed using these pulsating values. Because of the measured time and position differences between the manifold and the orifice of the swirl injector, phase and amplitude differences were identified and further characterized between the input and output values. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.

Kim T.-H.,Agency for Defense Development | Park B.-G.,LIG Nex1 | Park B.-G.,PGM R and D Laboratory | Tahk M.-J.,Korea Advanced Institute of Science and Technology
Journal of Guidance, Control, and Dynamics | Year: 2013

The proposed suboptimal guidance with a terminal body-attitude constraint for reentry vehicles in appears to be the first attempt to design an impact-angle-constrained guidance. In a modified proportional navigation (PN) guidance with a time-varying bias, which is a function of relative range, was proposed using a nonlinear planar engagement and Lyapunov-like function. Although various guidance laws to control the impact angle have been developed so far, most of these laws are difficult to implement, especially for a passive homing missile equipped with an infrared seeker, because an accurate time-to-go estimation or range information is required. Thereafter, BPN with zero bias is implemented during the remaining flight because the bias is no longer needed. The proposed shaping method provides valuable features. First, the method does not require a time-to-go estimation and range information. Second, the method has a simple and feasible structure for implementation because only the line-of-sight rate information is required.

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