13 research outputs found
An adaptive unscented Kalman filter for quaternion‐based orientation estimation in low‐cost AHRS
No full textEXPERIMENTAL INVESTIGATION OF VERTICAL CG POSITION CHANGES ON QUADROTOR'S PERFORMANCE VIA FREQUENCY-DOMAIN IDENTIFICATION TECHNIQUES
No full textPayload placement on quad-rotor (QR) is a subject of considerable importance
during its flight and maneuvering phases. In this sense, any changes in the
payload position, especially along the vertical axis, could significantly affect the QR center of gravity (CG) position and, in turn, its performance, dramatically. The current experimental study investigates the effect of payload vertical positioning on the performance and stability characteristics of a typical QR. The QR is test flown for more than eighty times with different payload positions, whose recorded flight data (RFD) are filtered using extended Kalman filter and subsequently utilized for QR frequency domain analysis. The RFDs are used to identify the QR longitudinal and lateral modes. In addition, the mode changes trend against the center of gravity location has led to the determination of the CG position at which instability occurs. The experimental results show that as the QR CG moves up along its vertical axis, its dynamics modes move towards the origin on the real axis taking the QR closer to borderline dynamic instability. Moreover, the damping behavior of the longitudinal and lateral modes with respect to CG has been extracted that in turn can lead to CG based techniques for QR damping control. In addition, in order to generalize the present results to be useful for other QRs, the QR parameters have been nondimensionalized, and an effective nondimensional
parameter through which results can be extended to other QRs is determined. The newly introduced nondimensional parameter is used against another set of data, extracted from a different QR for verification and comparative purposes.
Finally, to account for uncertainties and stochastic noise in the RFD measures,
each experimental stage is repeated four times; and the results of the mean
behavior are reported, too
Non‐linear feedback optimal control law for minimum‐time injection problem using fuzzy system
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Simultaneous Orbit, Attitude and Albedo Parameter Estimation Using Satellite Surface Temperature Data
No full textDevelopment of low-cost small satellites has been at the center of attention in recent years. Concurrent Orbit and Attitude Estimation (COAE) requires fewer sensors onboard and subsequently results in some cost reductions. In this regard, the present paper has focused on addressing the importance of COAE utilizing temperature rate on satellite surfaces. To this end, the thermal model for a low Earth orbiting satellite is introduced first. A three-axis stabilized spacecraft is assumed equipped with small measurement plates that are isolated from each other and from the internal heat sources of the satellite. As the Sun and the Earth are the significant sources of radiation for a near Earth space system, the view factor is the key parameter for observability of the orbital elements, while the Sun radiation is responsible for the attitude observability. The Earth albedo factor is a major uncertain parameter required for the thermal analysis of low Earth orbiting satellites. This parameter is greatly dependent on the Earth’s local terrain and climatic conditions such as instantaneous cloud coverage. To address the problem of albedo factor uncertainty, it is estimated simultaneously with the attitude and orbit of the satellite. NASA's CERES project provides satellite-based observations of the Earth’s radiation budget and clouds over almost 18 years. In this paper, CERES data tables for the Earth’s thermal flux and albedo factor have been used to produce more realistic measurement data. The nonlinear filter of Unscented Kalman Filter (UKF) is also exploited for the state estimation. Lack of sun radiation during the satellite’s eclipse intervals results in the loss of orbit and attitude observability. The performance and viability of the proposed COAE algorithm are verified by Monte Carlo simulations. Moreover, a sensitivity analysis is conducted within a wide range of semi major axes, eccentricities, and inclinations. The results demonstrate the high sensitivity of the algorithm to the orbit altitude and the sun rays direction
A Stigmergy-Based Algorithm for Continuous Optimization Tested on Real-Life-Like Environment
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A parametric study on supersonic/hypersonic flutter behavior of aero-thermo-elastic geometrically imperfect curved skin panel
No full textIn this paper, the effect of the system parameters on the flutter of a curved skin panel forced by a supersonic/hypersonic unsteady flow is numerically investigated. The aeroelastic model investigated includes the third-order piston theory aerodynamics for modeling the flow-induced forces and the Von Kármán nonlinear strain-displacement relation in conjunction with the Kirchhoff plate hypothesis for the panel structural modeling. Structural non-linearities are considered and are due to the non-linear coupling between out-of-plane bending and in-plane stretching. The effects of thermal degradation and Kelvin’s model of structural damping independent on time and temperature are also considered. The aero-thermo-elastic governing equations are developed from the geometrically imperfect non-linear theory of infinitely long two-dimensional curved panels. Computational analysis and discussion of the finding along with pertinent conclusions are presented.Aerospace Engineerin
