Special Section on Intelligent Unmanned Systems

Abstract

There has been increased worldwide interest in the research on intelligent unmanned systems in recent decades. The unmannedsystem technologies have been implemented in the underwater, ground, aerial, and space domains within an ever-extending operational envelope. The miniaturization of the hardware footprint coupled with exponentially increased computing power has enabled more efficient application of a wide range of unmanned vehicles. The papers in this special section represent recent contributions to several aspects of intelligent unmanned systems. The papers were largely an extension of select papers presented at the ICIUS2010 held in Bali, Indonesia, in October 2010. Three papers deal with the development of intelligent algorithms for unmanned aerial vehicles, while two papers focus on the software and hardware integration. The rest of the papers cover the application of aerospace technology for unmanned-vehicle design. The paper by Manathara and Ghose addresses the problem of multiple unmanned aerial vehicle (UAV) rendezvous when the UAVs have to perform maneuvers to avoid collisions with other UAVs. The authors proposed a solution that consists of velocity control and a wandering maneuver of the UAVs based on a consensus among them on the estimated time of arrival at the point of rendezvous. This simple algorithm was shown to be useful in tracking stationary or slowly moving targets with a standoff distance. Kim et al. paper present an automatic landing control design using adaptive, integrated guidance and control (IGC) logic. The proposed IGC design uses a combination of an adaptive output feedback inversion and backstepping techniques. The authors formulated the problem as an adaptive output feedback control problem for a line-of-sight–based chasing-flight configuration. The automatic landing system using IGC logic was evaluated using a sophisticated six-degrees-of-freedom nonlinear simulation program with the approach and landing scenario. Jeong et al. focused on the design of a robust H-infinity attitude controller for an unmanned small-scale helicopter. It was demonstrated that the H-infinity controller works amiably when applied to the nonlinear model, even though it is designed using a linear model approximation. The time-domain simulation with the nonlinear model demonstrated that the proposed controller was very robust to the uncertainties as expected, overcoming large gain uncertainties and time delay in each input channel. Formal verification currently plays an important role in guaranteeing the correctness of the operation of safety-critical systems, for example, in UAVs. Lee et al. discuss formal modeling and verification of operational flight programs (OFPs) in a small-scale unmanned helicopter. Two different formal models for the OFP were developed and verified using SPIN and UPPAAL model checkers. Real-time behavior of theOFPwas specified using a timed-automata model. Their verification of the OFP found several safety-critical faults to be reported to and fixed by the development team. One of the key features of autonomous flight of UAVs is the ability to perform localization and map building of flight environments simultaneously. Park et al. present vision-based simultaneous localization and mapping (SLAM) for small UAVs in global-positioningsystem–denied environments. A method that combines onboard and on-ground localization and mapping was proposed. The paper by Thu et al. investigates the nature of vortex structure developed by a double-delta wing. Dye-flow visualization in a small-scale water tunnel was used for the study. The authors identified two types of flow interaction, which are enveloping and coiling-up modes. Characteristics of the two modes were examined for various angles of attack (AOAs) at relatively low Reynolds numbers of 10,000 and 15,000. The authors found that the wing vortex became stronger and the enveloping mode was dominant for a low AOA, while the coiling-up mode was dominant at a high AOA. They also reported that the transition of these two modes occurred at around an AOA of 20 . Another paper in the special section studied the unsteady flow field of a flapping model butterfly under the zero-advance ratio (J 5 0) condition using timeresolved stereoscopic particle image velocimetry. The effect of feathering on thrust generation because of chordwise wing flexibility was identified by focusing on the ejection of airflow from the gap between two wings. Ghosh et al. found that the wing flexibility adds a feathering effect and enhances net lift and thrust generation through ejection of vortex pairs during the downstroke-to-upstroke–motion reversal. They also reported that the thrust produced was positive all over the cycle, even at J 5 0, because of the feathering motion. The special section editors would like to express their sincerest gratitude to all the contributing authors. We hope that the readers will find the content of this section not only relevant but also stimulating and beneficial for their ongoing research endeavors.