dynamics
Masoud Dehnad; Morteza Farhid; Samira Mazhari Anvar
Abstract
In this article, a fault tolerant control based on a virtual actuator is used for the maneuvering of low earth orbit satellites that are subject to the loss of the effectiveness and additive actuator faults as well as natural disturbances such as atmospheric drag, earth's gravity, solar radiation and ...
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In this article, a fault tolerant control based on a virtual actuator is used for the maneuvering of low earth orbit satellites that are subject to the loss of the effectiveness and additive actuator faults as well as natural disturbances such as atmospheric drag, earth's gravity, solar radiation and third body. In the approach used, there is no need for a separate unit to detect, isolate and identify the error. The main feature of this approach is to provide the same performance for the nominal system and the faulty system since the actuator faults and disturbances are hide from the nominal controller due to placing a virtual actuator between the faulty plant and the nominal controller.For the purpose of satellite maneuvering, using Kepler's orbital dynamics, which is affected only by the Earth's gravity, the desired second orbit parameters are calculated. In addition, orbital dynamics based on six modified orbital elements have been used, which avoids singularities. Then, using the desired orbit parameters, the relative motion elements are calculated and used in the control laws. To demonstrate the effectiveness of the control method, a maneuvering scenario of a satellite with Kepler's orbital dynamics that affected by natural disturbances and the actuator faults, is simulated for 42 days. The satellite has an effective cross-sectional area of 0.56 m2, and an actuator fault is occurred since the 32nd day. The results show higher performances the proposed method compared with conventional controllers like LQR.
adel Pourtaghi Marzrood; Arezoo Esmaeili; adel Pourtaghi marzrood; Moharram Shameli
Abstract
Backflow is a phenomenon that occurs due to the increase of upstream pressure compared to downstream pressure. In converging-diverging nozzles, by increasing the outlet pressure compared to the design pressure, the phenomenon of backflow is observed in the divergent part, which causes a decrease in the ...
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Backflow is a phenomenon that occurs due to the increase of upstream pressure compared to downstream pressure. In converging-diverging nozzles, by increasing the outlet pressure compared to the design pressure, the phenomenon of backflow is observed in the divergent part, which causes a decrease in the output velocity and thrust. In this paper, a converging- diverging nozzle with suitable expansion ratio for vacuum condition is selected and the propellant flow, which is considered as butane in this research, is simulated by finite volume method for output pressure equal to vacuum pressure and atmospheric pressure conditions. It has seen that in the atmospheric pressure, backflow occurs in the nozzle in order to determine the appropriate expansion ratio for the nozzle operating in atmospheric pressure, the flow inside the nozzle is simulated for the different expansion ratios and the average outlet axial velocity at the output of theses nozzles is obtained. According to the results, the most suitable expansion ratio of the surface has the highest average axial velocity. Also, to verify the obtained results from finite element simulation, four nozzles with different surface expansion ratios were manufactured and the thrust force obtained from experimental test on the measuring stand with equivalent results obtained from the simulations were compared
