In this study, the design optimization of a low Reynolds number airfoil is performed for a Mars exploration airplane. To achieve this goal, a multi-objective genetic algorithm (MOGA) using the Kriging model is used for optimization and a γ–Reθ model is adopted to predict the laminar-turbulent transition point on the airfoil. Both PARSEC and NURBS representations are used to define the geometry of the airfoil in order to investigate its effect on the transition delay. The aerodynamic performances of the airfoils designed are compared with those of the ss1f airfoil, which was designed for the Mars exploration airplane during the ARES project. The objectives of optimization are to minimize the drag coefficient with a fixed lift coefficient and to minimize the moment sensitivity with respect to the angle of attack. Transition of the airfoil using the PARSEC representation occurs further downstream than that of the ss1f airfoil. Furthermore, the airfoil using the NURBS representation achieves fully laminar flow on the upper surface. The moment sensitivity of the optimized airfoils is also lower than that of the ss1f airfoil.
This investigation was conducted to propose an estimation method for energy dissipation in riveted lap joints. In this study, we made a simple energy dissipation model for riveted lap joint by replacing the joint part with a material that draws a hysteresis loop. This simple model does not require detailed contact analysis. Therefore, the calculation cost can be reduced. Hysteresis loops were obtained from cyclic loading tests. Coefficients were obtained by fitting the hysteresis loop assuming that the shape of the hysteresis loop is symmetric. The coefficients were applied to FEM as material properties. Then, load/displacement curves were obtained from FEM, and energy dissipation was calculated from the hysteresis loop. It was shown that the simple model in this study can reproduce the energy dissipation process with an error of less than approximately 13% in the range of the experiment.
This work analyzes the capturability of the true proportional navigation (TPN) guidance law applied in circular orbital pursuit-evasion, which is a new view compared to the prior method used in orbital pursuit-evasion. The saddle point is a rather difficult problem to resolve when the orbital pursuit-evasion problem is formulated as a zero-sum differential game. The research in this paper focuses on analyzing the capture capability of the pursuer and the escape capability of the evader. The relative motion equations for the line-of-sight (LOS) coordinate and the modified polar coordinate (MPC) system are united. Then, nonlinear transformation is used in the dynamic equations so as to acquire the relative motion equation. The optimal strategies of both satellites are determined and expression of the analytical capture-escape equation is proposed. The capture-escape region of an orbital pursuit-evasion game is defined. The simulation clearly shows the capture region of the pursuer, and the results are in agreement with the analysis. The results of the analytic capturability method proposed in this paper are visual and understandable, which means that it will be very convenient to use in analyzing capturability in orbital pursuit-evasion problems.
The second-generation star tracker estimates pointing knowledge of a satellite without a-priori knowledge. But star trackers are larger in size, heavier, power hungry and expensive for nanosatellite missions. The Arcsecond Pico Star Tracker (APST) is designed based on the limitations of nanosatellites and estimated to provide pointing knowledge in an arcsecond. The APST will be used on the SNUSAT-2, Earth-observing nanosatellite. This paper describes the requirements of APST, trade-off for the selection of image sensor, optics, and baffle design. In addition, a survey of algorithms for star trackers and a comparison of the specifications of APST with other Pico star trackers are detailed. The field of view (FOV) estimation shows that 17° and 22° are suitable for APST and this reduces stray light problems. To achieve the 100% sky coverage, the FOV of 17° and 22° should able to detect the 5.85 and 5.35 visual magnitude of stars, respectively. It is validated by estimating the signal to noise ratio of APST and night sky test results. The maximum earth stray light angle is estimated to be 68° and a miniaturized baffle is designed with the exclusion angle of 27°.
A rotor airfoil design optimization framework based on a surrogate model and unsteady flow is constructed. Two optimization models of unsteady design are founded. A study of these models and comparison of design results based on steady and unsteady flows are conducted using the aforementioned optimization framework. The first optimization model aims to simultaneously reduce the time-averaged drag and time-averaged pitching moment. The Pareto front embodies the relation of drag and pitching moment of the rotor airfoil in an unsteady flow, which shows that a slight relaxation of the drag restrictions may yield a remarkable decrease in pitching moment, thereby improving the synthetic aerodynamic performance of the rotor airfoil. Optimization results also show that an unsteady optimization model must give consideration to low speed performance, which has been neglected by other researchers. Therefore, the second optimization model is designed to improve the time-averaged lift-to-drag ratio and the maximum lift coefficient at low speed. An additional case was designed to validate that a well-designed airfoil in a steady flow may be unsatisfactory in an unsteady flow. The results from the last case show that the unsteady pitching moment characteristic is not always proportional to the static characteristic at high speed.