The ratio between thrust generated by a micronozzle and the theoretical thrust under assumption of quasi-one-dimensional compressible fluid generally drops as the Reynolds number of fluid gets lower. Therefore many experiments have been done to measure and reveal the characteristic values in the micronozzle flow including density distribution. However, the method in previous research could measure only one point at same time and simultaneous multi-dimension measurement was not possible. In this study, we proposed a new method to measure simultaneous 2-D density distribution by using camera and electron beam induced fluorescence. We found out that the 2-D absolute density distribution at the downstream of a micronozzle with the Reynolds number around 100 could be obtained by the proposed method.
GNSS positioning technology is used for various kinds of vehicles such as drones because of the convenient position detection regardless of location. However, there is a problem that the accuracy of GNSS positioning in an urban environment deteriorates significantly. One of the causes is that signals reflected by buildings are used for positioning. This problem must be solved to improve safety of automated vehicles using GNSS in urban areas. Therefore, in this research, we developed a model to detect reflected signals using machine learning. As a results of static and rover experiments, improvement of positioning accuracy was demonstrated by excluding the reflected signals from the positioning calculation.
Control of crosswind kites is very important subject in the pumping kite system, which is one of expected ways of wind power generation. Although many ways to control them are proposed before, any commercial operations haven't been succeeded for some reasons. In this study, stability verified controller for the pumping kite system is designed. In order not to make the controller too complicated, the kite model is simplified to be independent to some variables. Controller for the traction phase of the pumping kite system is designed based on the method proposed in the field of robotics. In that method, trajectories generation by optimal control, designing time varying LQR, and stability verification are repeated. About the controller for the retraction phase, standard LQR is designed and stability is verified using SOS programming. Designed two controllers are switched by length of the tether of the kite. Then, simulation is conducted with more practical kite model than control model.
GNSS (Global Navigation Satellite System) spoofing is one of the threats to GNSS users include airplane or UAV (Unmanned Aerial Vehicle). It can generate mock GNSS signal and broadcast it, and GNSS user is confused by fake position, velocity and timing information given by attacked GNSS receiver. We researched GNSS spoofing risk and proposed a detection method by monitoring multipath. Multipath caused by spoofing signal achieves to GNSS antenna through same path for all satellites signals and we focused on this similarity among the multipath. Multipath signal parameters are estimated using dual polarization antenna and dual channel SDR (Software Defined Radio) GNSS receiver and then we distinguished spoofing signal by clustering algorithm. Our proposed methods are evaluated on sea environment and we succeeded to detect spoofing with low false detection rate and miss detection rate.
This study focuses on the aerodynamic characteristics of a high speed compound helicopter with a maximum cruise speed of 500km/h which JAXA is proposing for the use of EMS (Emergency Medical Service). The aerodynamic properties of the airframe are evaluated by the wind tunnel testing with various configurations carried out in JAXA 2 m × 2 m Low-Speed Wind Tunnel. In order to realize this high speed flight condition, the essential requirement is to achieve a very low drag/aerodynamic interference airframe. The test results show 15% lower than the target airframe drag by adopting the hub fairing and 12% improvement of lift/drag ratio by differential deployment of the flap equipped on the wing combining the synergistic effect with the lift offset generated by the main rotor.