Guidance laws are proposed to enable unmanned aerial vehicles (UAVs) to accomplish stationary target observation missions. In this paper, a nonlinear guidance law is designed utilizing the characteristics of distance error dynamics. The turning direction of the UAVs is very important for multiple UAVs operation. The turning direction of UAV is related to the line-of-sight angular acceleration of the UAV. The proposed guidance law is analyzed to provide a guideline for selecting guidance gains taking into consideration the turning direction. Numerical simulations are performed to verify the performance of the proposed guidance law.
Unmanned air vehicles should be operated by various flight modes, such as point navigation, loitering, preprogrammed mode and so forth. Since all flight modes can be applied by combining the line-of-sight and loitering guidance laws, the performance and formulation are dependent on the reliability and accuracy of both guidance laws. This paper presents the modified guidance laws and shows the enhanced performance via simulation. In addition, the logical operation and transition logic should be made according to real implementation of the flight modes by considering various flight conditions. This paper also proposes enhanced operation logics for the auto-approach mode, which are formulated after successfully reflecting a variation of the vehicle's current position. Finally, the evaluation is performed through simulations of several flight scenarios.
Design of morphing wings is being considered as a potential way to improve aircraft performance. Composite materials are identified as suitable candidates to achieve some of the future morphing capabilities of aircraft wings. In this work, a morphing airfoil is designed and manufactured using a woven carbon fiber reinforced plastic (CFRP) composite material and a vacuum bagging technique. The layup arrangement and stacking sequence are chosen for maximum out-of-plane deflection under the applied actuation force using finite element analysis (FEA) and composite plate bending experiments. Additionally, manual actuation loads are applied simultaneously at various feasible locations on the airfoil top surface. The morphed airfoil new shape is studied using a JavaFoil airfoil analysis program to investigate its aerodynamic characteristics in terms of lift vs. angle of attack and lift-to-drag ratio vs. angle of attack. It is found that the numbers and locations of actuation forces depend on the flight envelope stage (e.g., take-off and cruising). In general, four factors are identified to have significant effects on the maximum deflection and consequently the ease of the airfoil to morph. These factors are the ply angles, the unbalanced stacking sequence, and the number of actuation forces and their location along the airfoil skin.
In this study, a novel method for the on-orbit calibration for shape control parameters of a self-sensing reflector antenna equipped with surface adjustment mechanisms is developed and verified. These control parameters are related to the control inputs for shape control and changes in the antenna gains caused by intentional deformations. In the antenna system, intentional deformations are added to the reflector surface using surface adjustment mechanisms, and the corresponding changes in the antenna gains are measured. The control inputs for correcting the shape of the deformed reflector are determined directly from information on the changes in the strengths of received radio waves using the calibrated shape control parameters. Some numerical simulations are performed to investigate the feasibility of the developed method. A demonstrator equipped with surface adjustment mechanisms is under development, and the corresponding numerical model is employed for the numerical simulations. The results of these simulations show that the parameters are calibrated appropriately and the deformation of the antenna reflector is properly corrected by the developed method. The results clearly indicate that the developed method is an effective means of controllingthe shape of a reflector antenna equipped with surface adjustment mechanisms.
Aiming at transfer alignment of gimbaled inertial navigation systems (INS) on a moving base, we propose an attitude matching alignment model to align the attitude of the slave platform. This method is achieved by applying an unscented Kalman filter to estimate the fixed misalignment angle, and the misalignment angle can be obtained only with attitude maneuvers, which are very easy for the ship to implement. Firstly, the frame dynamics equations are introduced. Then, frame angular error differential equations, which include the ship-body flexure and other alignment errors, are set up via the frame angle information from the master and the slave INS platform. With these frameworks, the nonlinear attitude matching alignment model is designed based on unscented Kalman filter technology. The simulation results show that the proposed method can obtain an alignment to an accuracy of 1.5′ and alignment time of 50 sections.
Two-photon absorption laser induced fluorescence (TALIF) is applied to atomic oxygen and nitrogen generated in the JAXA 750 kW arc-heated wind tunnel in order to obtain velocity, translational temperature and atomic number density distributions. Free stream velocity is estimated by Doppler shift and the translational temperature distributions are deduced from spectral broadening. The absolute center excitation wavelength and laser line width are estimated with the TALIF profiles from a static reference cell which is called as a flow reactor. In this flow reactor, atomic species are generated by microwave discharge. The spatial distributions of atomic number density are deduced from the integrated TALIF profiles. The absolute atomic number densities inside the flow reactor are estimated with a titration method. From the mass fraction estimation, it is found that the number densities of atomic oxygen are overestimated owing to the saturation effect. When oxygen is assumed to be totally dissociated, the fractional enthalpies are estimated.
In this paper, a robust design optimization framework is proposed with a variable fidelity Kriging model. By the use of the variable fidelity Kriging model approach, an accurate surrogate model can be constructed efficiently by the absolute values of a high-fidelity function as well as the trends obtained by low-fidelity function values. The high- and low-fidelity levels can be defined by utilizing different physical models, computational meshes and so on. The robustness of a candidate design is efficiently evaluated by a Monte Carlo simulation which is executed on the variable fidelity Kriging model. The efficiencies of robust design optimization approaches are investigated in a 2D airfoil drag minimization problem. In this problem, free-stream Mach number as well as target lift coefficient are supposed as uncertain parameters. The mean and standard deviation of drag coefficient are simultaneously minimized to obtain non-dominated robust optimal designs. The developed robust design optimization approach via the variable fidelity Kriging model is shown to be useful for efficient search of robust airfoil designs.