This paper proposes a new method which employs the optimal flight controls of a point mass model to a rigid body model in order to realize the optimal guidance controls for an autonomous UAV. In the first stage of this study, we had developed an UAV flight simulator. A point mass model as well as a rigid body model is incorporated into the simulation programs because it is utilized in order to obtain optimal controls by solving two-point boundary-value problems. All proper model parameters of the point mass model were estimated by simulations with the flight simulator. Four control inputs of the rigid body model were produced based on three control inputs of the point mass model. Both models’ simulation results of some flight maneuvers showed good correspondence and our approach was justified by solving a simple optimal control problem of an UAV.
Structure of flow field formed by normal sonic injection into a Mach 1.8 air stream was investigated with acetone planar laser induced fluorescence (acetone PLIF). Parametric calculation of fluorescence intensity indicates that it represent molar concentration within ±2.5% error for the present experimental condition. For the special situation of isentropic flow without any mixing, Mach number can be deduced from the fluorescence intensity. Mach number distribution from PLIF data was compared with one obtained from PIV measurement, and showed good agreement. The jet trajectories obtained from images visualized by acetone PLIF and Mie scattering are compared. We find that the acetone PLIF gives reasonable trajectory while the Mie scattering over estimate the jet penetration.
The cavity enhanced absorption spectroscopy using a tunable diode laser was applied to plasma torch diagnostics. Using cavity mirrors with 99.95% reflectance, the sensitivity was successfully enhanced by three orders of magnitude compared with the conventional single-pass laser absorption spectroscopy. With a 0.6m distance cavity, the spatial resolution of less than 1mm was achieved. The deviation of deduced temperature was below 5% when ten profiles were averaged. Total amount of data acquisition needed for a given plume section was estimated at 100M Sample. The torch plume was found in nonequilibrium electronic excitation state.
This paper reports experimental studies on telescopic aerospikes with multiple disks. The telescopic aerospike is useful as an aerodynamic control device; however, changing its length causes a buzz phenomenon, which many researchers have reported. The occurrence of buzzing might be critical to the vehicle because it brings about severe pressure oscillations on the surface. Disks on the shaft produce stable recirculation regions by dividing the single separation flow into several conical cavity flows. The telescopic aerospikes with stabilizer disks are useful without any length constraints. Aerodynamic characteristics of the telescopic aerospikes were investigated through a series of wind tunnel tests. Transition of recirculation/reattachment flow modes of a plain spike causes a large change in the drag coefficient. Because of this hysteresis phenomenon and the buzzing, the plain spike is unsuitable for fine aerodynamic control devices. Adding stabilizer disks is effective for the improved control of aerospikes.
There are two interesting differences in roll control response characteristics between an aircraft and a paraglider: 1) Opposite roll angle is generated by the same control surface deflection: and 2) to keep the roll angle constant, an aircraft requires a pilot to return the control wheel to the nearly neutral position, but a paraglider requires him to keep the control surface deflection. Although it is commonly accepted that the main factor producing these differences would be the adverse yaw characteristics, the essential mechanism has not yet been clearly determined. This study focuses on features in their airframe configurations, and aims to determine the physical mechanism which produces their differences in roll control responses. Results showed that not only adverse yaw characteristics but also lower center of gravity position and decrease of vertical fin area in a paraglider are the main parameters.
We propose a new framework for spacecraft fault diagnosis based on combined parameter and mode online estimation using a sequential Monte Carlo method. Our method can detect and diagnose faults as parameter changes and hence can be considered as a probabilistic approach for the parameter-estimation-based fault diagnosis method which is one of the methodologies on quantitative model-based diagnosis. We derive an algorithm for spacecraft fault diagnosis by describing the parameter-estimation-based fault diagnosis method as a probabilistic inference problem and applying a modified sequential Monte Carlo method, obtained by incorporating fault-modes, risk-sensitivities on modes and kernel-smoothing techniques into the original method, to the problem. The proposed fault-diagnosis algorithm was applied to an artificial data simulating malfunctions of thrusters in rendezvous maneuver of spacecraft, and the feasibility of the method was confirmed.
This paper proposes a method of early spacecraft anomaly detection by simultaneously estimating its states and parameters. We applied an extended particle filter algorithm in order to estimate not only states but also parameters. In this method, we incorporated artificial evolution of parameters and kernel smoothing of parameters into the ordinary particle filter algorithm. Each parameter is related to each state of the spacecraft components, so we can understand what is happening in the spacecraft by finding out parameters’ changing signs. We tested the algorithm on a simulation of spacecraft attitude motion.