Aerospace Systems最新文献

This research is mainly devoted to numerical trade studies of a co-rotating array of mini-air-jet vortex generators (Mi-AJVGs) placed on a supercritical P-18-415 airfoil-based wing model. The numerical simulation is carried out at an angle of attack α = 4° and Mach number M_∞ = 0.75. Three-dimensional compressible Reynolds Averaged Navier–Stokes (RANS) equations coupled with the k-ϵ realizable turbulence model are employed with an assumption of fully turbulent boundary layer. The result is the best design case out of the investigated ones in terms of the skin friction coefficient and the lift-to-drag ratio. When the Mi-AJVGs are activated, streamwise vortices acting on the separation region increase downstream skin friction and the lift-to-drag ratio. The effect of the jet to ambient temperature ratios (T_J/T_∞) on aerodynamic performance is considered.

In order to improve the performance of a navigation systems, scintillation studies and Ionospheric Total electron content (TEC) are important. The amplitude scintillation index (S₄), S₄ corrections and Rate of change of TEC index (ROTI) parameters are analysed for different seasons. For the analysis Visakhapatnam station (Lat: 17.78, Long: 83.22) and Lucknow (Lat: 26.76, Long: 80.88) station, GAGAN receiver data for the year 2016 is considered based on four quiet days and four disturbed days and consider the highest Kp index values for Visakhapatnam station and Lucknow station. This work shows the variation of S₄ index and ROTI parameter variation during different seasons for both the stations. The correlation coefficient (CC) of S₄ index and ROTI are presented. The results show that the CC are high for disturbed days compared to the quiet days for both the considered stations. For Lucknow station, it is observed that CC values are high compared to the Visakhapatnam station.

In this paper, we investigate the critical magneto-aeroelastic behavior of dielectric rectangular isotropic plates. The incident flow of a perfectly conducting supersonic gas and a magnetic field cause the perturbed pressure, which we can determine using magneto-aero-elastic stability and dynamic models as well as find the critical flutter speed of the flowing stream. Here, we present the analytical description of the generalized formula of pressure obtained from the “piston theory” of the classical theory of gas dynamics for the case of elastic plates in a magneto-hydro-dynamic flow. We implemented some parametric studies to show the influence of the magnetic field on the flutter boundary. Influence of magnetic field on the dependency “amplitude–frequency” is investigated for several geometrical parameters of examined plate. It is shown that the noted dependency can be as a single-value, as well as a multi-value function. It is shown also that strong magnetic fields have a great influence on the nature of the amplitude–frequency dependence, which is inherent to the case of nonlinear natural oscillations of shells.

Magnetometer is a highly advantageous sensor for determining a spacecraft’s attitude. This article provides a solution to the problem of spacecraft attitude estimation using magnetometer measurements only. To ensure full observability of spacecraft attitude states, it is necessary to use at least two types of sensors. Consequently, utilizing a single sensor, such as the magnetometer, poses a significant challenge for any attitude estimation algorithm, including the extended Kalman filter (EKF). Moreover, implementing the EKF algorithm, or any other attitude estimation algorithm, is computationally intensive. To address these issues, an algorithm has been developed that estimates spacecraft attitude angles and attitude rates using a sequential extended Kalman filter (SEKF). This algorithm offers numerous benefits over those found in the literature such as high accuracy, low computational resource requirements, the ability to converge even with large initial attitude and angular velocity estimation errors, and the ability to function even if two of the three measurement channels of the magnetometer are not functioning. With these benefits, the developed SEKF algorithm is capable of operating in all spacecraft operational modes, delivering accurate performance and computation time. In spite of measurements with large noise values, the high accuracy achieved by the SEKF algorithm enables the magnetometer to serve as the sole source of attitude information, even if one or two magnetometer measurement channels are not functioning.

This paper presents an adaptive attitude consensus controller for a group of spacecrafts subject to stochastic communication link failure and external disturbances. By leveraging the sliding-mode control technique and the super-martingales convergence method, the proposed adaptive controller is robust to the bounded but unknown disturbances and ensures almost sure consensus on the attitude among multi-spacecraft, respectively. Moreover, when compared with the existing results dealing with attitude consensus control with indeterministic communication topology, our approach can drive the attitude of multi-spacecraft to a desired attitude of a virtual spacecraft. To verify the effectiveness of the proposed approach, an attitude consensus control of a group of six spacecraft with a virtual leader is carried out.

In this paper, the shear stability of a composite hat-stringer stiffened panel was studied by the means of both shear frame test and theoretical analysis. The test specimen is a typical flat composite stiffened panel composed of skin, five hat-shaped stringers, two Z-shaped transverse frames and reinforcement layers. Firstly, a method that can quantitatively capture the buckling load and buckling morphology was proposed. Then, considering the shear-loading fixture as an elastic system with hinged and bolted connections, a finite element model including both shear-loading fixture and specimen was established. The linear buckling analysis was carried out using the subspace method. The first-order buckling mode was in good agreement with the buckling morphology obtained from the test. Furthermore, the deformed configuration of the first buckling mode was multiplied by the mode scale factor, and then introduced into the model as the initial defect. Based on this model, the nonlinear buckling analysis was performed via arc length method. The analysis results were in good agreement with the test. The relative errors between the predicted buckling loads and the test results were 7.0(%) and (-)3.8(%) from linear and nonlinear buckling analyses, respectively. Nonlinear buckling analysis has higher accuracy and tends to be conservative than linear buckling analysis.

Three-point bending tests on glass-fiber reinforced polymer GFRP/Kraft honeycomb sandwich panels after natural aging were undertaken to explore the bending performance of composite honeycomb sandwich panels after long-term aging. The specimens’ failure modes and ultimate damage patterns were recorded, and the pertinent data from the tests were statistically analyzed. A finite element model was developed to investigate the process of fiber failure based on the Hashin failure criterion. The results showed that the bending performance increased significantly, with a small dispersion of the test data; the specimen failure forms were consistent with expectations; the failure mode and result of FEM are in general agreement with the tests.

Taking off and landing are critical phases and it is easy to happen flight disaster for them due to complex environment and weather. To improve flight safety of the aircraft, an anti-skid control method is proposed. First, the ground dynamics model of the civil aircraft is established. Second, a baseline controller is designed to control the velocity and yaw angle of the civil aircraft by Proportional-Integral (PI) technique. Meanwhile, considering high-speed factor during the braking phase, the braking force of the aircraft is over large, and the wheels are easy to skid. To overcome this, an anti-skid system is built, and the dynamic model of the aircraft anti-skid braking system is established. A backstepping sliding mode control algorithm is proposed to control the braking speed. And the slip ratio of the aircraft wheel is controlled by adjusting braking coefficient ({mu }_{Brake}) and the optimal slip ratio is achieved. Stability of the closed-loop system is proved by Lyapunov stability theory. Simulation results show that the proposed controller can track the desired trajectory well and the braking efficiency is optimal, which effectively shortens the braking distance of the aircraft, reduces wear of tire, and prevents puncture caused by wheel slip.

In this work, for a two-dimensional radar tracking system, a new implementation of the robust adaptive unscented Kalman filter is investigated. This robust approach attempts to eliminate the effects of faults associated with measurement models, and varying noise covariances to improve the target tracking performance. An adaptive threshold value is used to identify the need for adapting the noise covariances rather than a fixed threshold value. A forgetting factor and a weighted mix of the most recent and previous estimate data are employed to update the process and measurement noise covariances. By calculating the root mean square error using Monte Carlo simulations under various circumstances, the efficiency of the proposed approach is examined. It has been found that the proposed approach can successfully handles system uncertainties imposed by variable noise covariance and measurement outliers.

Ground-based simulation has become an integral stage in the design of aviation technology. When solving most problems, flight simulators are increasingly used to simulate the piloting process with the participation of human operators on the ground. For example, flight simulators are used to test out the laws of control systems, study the information display systems, and creating prototypes. When forming a ground-based simulation system, an attempt is made to recreate visual, kinesthetic, and motion information for the pilot (operator). It should be noted, however, that not all tasks require simulating all of the above types of information perceived by the pilot, which significantly reduces the cost of creating a flight simulator. This present work is devoted to substantiating the need to use one of the most expensive systems—a motion cue simulation system—in the tasks of evaluating the effectiveness of next-generation flight information display equipment under various types of atmospheric disturbances. During the experiments, the most dangerous types of disturbances for aircraft in the takeoff and landing modes were simulated, such as a wake vortex from a previously passing aircraft and wind shear caused by a microburst. It is shown that not all types of atmospheric disturbances require simulating motion information.