Performance Comparison of KOMPSAT-5 Precision Orbit Determination with GRACERead the full article
International Journal of Aerospace Engineering serves the international aerospace engineering community through the dissemination of scientific knowledge on practical engineering and design methodologies pertaining to aircraft and space vehicles.
Chief Editor, Professor Zhao, is based at the University of Canterbury and his research interests include applying theoretical, numerical and experimental approaches to study combustion instability, thermoacoustics and aerodynamics.
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BOC Signal Acquisition Algorithm Based on Similar Enfoldment
A BOC signal has been widely used in the Global Navigation Satellite System (GNSS). Although the BOC signal has many advantages, the autocorrelation function (ACF) of the BOC signal has lots of peaks, which makes signal acquisition difficult. This paper proposes a similar enfoldment acquisition (SEA) algorithm, which can be applied to sin-BOC and cos-BOC signals, with even and odd modulation orders. The SEA algorithm utilizes the similarity between the main peak and the secondary peak to construct a new ACF to eliminate the ambiguity of the BOC signal. This paper simulates the acquisition performance of the SEA algorithm, Martin algorithm, and SCPC algorithm, while the simulation result shows that the SEA algorithm is superior to the Martin algorithm and SCPC algorithm. Since the SEA algorithm does not need filters or auxiliary signals, its complexity is lower than that of the Martin algorithm and SCPC algorithm.
Space-Based Optical Observations on Space Debris via Multipoint of View
In this paper, the space debris catalogue in LEO is fulfilled using multipoint of view (MPOV) observations constructed by a spacecraft formation. The dual-point of view (DPOV) observation is employed because it has higher cost-benefit ratio than other MPOV methods, and it required that the target is detectable for multiple optical sensors simultaneously. This condition is matched by designing the orbit of formation and the installation angles of sensors without frequent attitude maneuvers. The design parameters are optimized to maximize the matching degree of observation constraints to improve the coverage performance of the formation, and the equivalent ranging error is taken into account to ensure the orbit determination accuracy. Finally, the system capabilities of different schemes are compared by simulations. For the schemes with the same number of platforms, simulation results show that the initial orbit determination accuracy of the proposed scheme is higher.
Computational Investigation of Flow Control Methods in the Impeller Rear Cavity
In typical median and small aeroengines, the air used to realize the functions such as cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, adjusting of rotating assembly axial load is normally drawn through the rear cavity of centrifugal impeller, so the thorough understanding of flow characteristics and pressure distribution and the proposal of the corresponding control methods in the cavity are the key to design the rational secondary air system. With an impeller rear cavity in a small turbofan engine as an object, the current study was dedicated to the investigation of flow control methods in the cavity. Two methods, namely, baffle and swirl-controlled orifice, were proposed to regulate the pressure loss and distribution in the cavity. Furthermore, the influence of geometry parameters of the two methods such as the length of baffle, the space between the baffle and rotating disk wall, the orientation, and radial position of swirl-controlled orifice was investigated. The CFD results show that the swirl-controlled orifice which could deswirl the flow is more effective in regulating the pressure loss and its distribution in cavity than baffle. The variation of the radial position of the swirl-controlled orifice had little influence on pressure loss but obvious influence on pressure distribution; therefore, decreasing the radial position could reduce the axial load on the rotating disk without changing the outlet pressure.
Numerical Investigation on Flapping Aerodynamic Performance of Dragonfly Wings in Crosswind
Numerical simulations are performed to investigate the influence of crosswind on the aerodynamic characteristics of rigid dragonfly-like flapping wings through the solution of the three-dimensional unsteady Navier-Stokes equations. The aerodynamic forces, the moments, and the flow structures of four dragonfly wings are examined when the sideslip angle between the crosswind and the flight direction varied from 0o to 90o. The stability of the dragonfly model in crosswind is analyzed. The results show that the sideslip angle has a little effect on the total time-average lift force but significant influence on the total time-average thrust force, lateral force, and three-direction torques. An increase in the sideslip angle gives rise to a larger total time-average lateral force and yaw moment. These may accelerate the lateral skewing of the dragonfly, and the increased rolling and pitching moments will further aggravate the instability of the dragonfly model. The vorticities and reattached flow on the wings move laterally to one side due to the crosswind, and the pressure on wing surfaces is no longer symmetrical and hence, the balance between the aerodynamic forces of the wings on two sides is broken. The effects of the sideslip angle on each dragonfly wing are different, e.g., has a greater effect on the aerodynamic forces of the hind wings than those of the fore wings. When sensing a crosswind, it is optimal to control the two hind wings of the bionic dragonfly-like micro aerial vehicles.
Predictive Functional Control-Based Zenith Pass Controller Design for Roll-Pitch Seeker
A roll-pitch seeker has a wide field of view but suffers from a singularity as the sightline coincides with the outer gimbal (OG) axis. In the vicinity of the singularity, the tracking effectiveness is often degraded or even lost due to the high actuation demand on OG, which is known as the zenith pass problem. To solve this problem, this paper first proposes a novel motion model of sightline to predict the singularity in a receding horizon, where the model parameters are identified using a modified recursive least square estimator. And with the singularity predictions as set points, a predictive functional controller is then designed for the OG position control to minimize the tracking error. This novel combination control scheme is validated in MATLAB/Simulink. Simulation results have confirmed that the proposed scheme can significantly mitigate the zenith pass problem and be applied to the real-time tracking process.
Inflatable Leading Edge-Based Dynamic Stall Control considering Fluid-Structure Interaction
The inflatable leading edge (ILE) is explored as a dynamic stall control concept. A fluid-structure interaction (FSI) numerical method for the elastic membrane structure is constructed based on unsteady Reynolds-averaged Navier-Stokes (URANS) and a mass-spring-damper (MSD) structural dynamic model. Radial basis function- (RBF-) based mesh deformation algorithm and Laplacian and optimization-based mesh smoothing algorithm are adopted in flowfield simulations to achieve the pitching oscillation of the airfoil and to ensure the mesh quality. An airfoil is considered at a freestream Mach number of 0.3 and chord-based Reynolds number of . The airfoil is pitched about its quarter-chord axis at a sinusoidal motion. The numerical results indicate that the ILE can change the radius of curvature of the airfoil leading edge, which could reduce the streamwise adverse pressure gradient and suppress the formation of dynamic stall vortex (DSV). Although the maximum lift coefficient of the airfoil is slightly reduced during the control process, the maximum drag and pitching moment coefficients of the airfoil are greatly reduced by up to 66% and 75.2%, respectively. The relative position of the ILE has a significant influence on its control effect. The control laws of inflation and deflation also affect the control ability of the ILE.