Aerospace Systems最新文献

Considering the complexities of the modern maritime operational environment and aiming for effective safe navigation and communication maintenance, research into the collaborative trajectory tracking problem of unmanned surface vehicles (USVs) and unmanned aerial vehicles (UAVs) clusters during patrol and target tracking missions holds paramount significance. This paper proposes a multi-agent deep reinforcement learning (MADRL) approach, specifically the action-constrained multi-agent deep deterministic policy gradient (MADDPG), to efficiently solve the collaborative maritime-aerial distributed information fusion-based trajectory tracking problem. The proposed approach incorporates a constraint model based on the characteristics of maritime-aerial distributed information fusion mode and two designed reward functions—one global for target tracking and one local for cross-domain collaborative unmanned clusters. Simulation experiments under three different mission scenarios have been conducted, and results demonstrate that the proposed approach possesses excellent applicability to trajectory tracking tasks in collaborative maritime-aerial settings, exhibiting strong convergence and robustness in mobile target tracking. In a complex three-dimensional simulation environment, the improved algorithm demonstrated an 11.04% reduction in training time for convergence and an 8.03% increase in reward values compared to the original algorithm. This indicates that the introduction of attention mechanisms and the design of reward functions enable the algorithm to learn optimal strategies more quickly and effectively.

The shrouded stator is widely used in aero-engines and the leakage flow from the cavity has a strong effect on the performance of the stator. Due to the high degree of geometric freedom of the tooth shape, it is difficult to find the optimal geometry directly through a large number of sample calculations. In this research, a multi-objective optimization design method was used for the structure of labyrinth seal teeth and the optimal shape was found. The effect of the optimal seal teeth on the stator was analyzed in a low-speed research compressor. It is found that two different optimized shapes of seal teeth meet the optimization requirements. There is a significant difference in the cavity depth, but they have similar intervals and angles of inclination of seal teeth. The total pressure loss coefficient below 20% span decreases by 9.18% and the outlet static pressure coefficient below 20% span increases by 1.76%. For both optimal results, the leakage flow becomes closer to the pressure side of the stator. The leakage flow climbs in the radial direction in the rear of the passage. The vortex near the suction side disappears. Instead, two vortexes with opposite rotating directions exist in the passage. The range of the vortex in the radial direction expands.

The stratospheric airship uses the electric thrusters composed of motors and large diameter propellers to generate the forward thrust and heading manipulation torque. As the actuators of flight control, electric thrusters have an important impact on the station-keeping and flight-control performance. Due to the high-altitude environment and low-speed flight of big volumetric stratospheric airships, the operating of electric thrusters is significantly different from that of electric aircraft, which makes the analysis and modeling of electric thrusters difficult. In this paper, the characteristics of motors and propellers for stratospheric airship is analyzed at first. Then, the propeller and motor model expressions are summarized respectively, mainly concentrating on the relationship between torque, thrust, advance speed and rotational speed. Benefited from the methods in the field of marine propellers, a quantitative characterization method for the interaction between propeller and airship hull is introduced. Through the mechanical motion equation of the motor, the dynamic matching model between the motor output electromagnetic torque and the propeller load torque is described. An example is used to illustrate the modeling process. Finally, some of the challenging issues in engineering practice are discussed.

This paper expounds on the development status and relevant works of control and guidance methods of the aerospace vehicle in recent years. The control difficulties and the solutions in the related results are introduced briefly. Moreover, the guidance methods are then expounded in detail according to the flight phases of the whole flight mission. Guidance methods are usually included in each phase, and the corresponding trajectory design theories are also introduced where necessary. In addition, the potential future development direction prospects. Based on the above, a brief conclusion is then made as a summary.

A hybrid rocket engine test bench experiment carried out the thrust 300 N, retaining nitrous gas as an oxidant, and 70 weight percent paraffin and 30 weight percent aluminum as fuel. To enhance the regression rate, new fuels such as paraffin-based fuel have been created, allowing for more compact engine designs with high thrust densities. As a result, the use of hybrid rocket engines in several domains, such as sounding rockets and small satellites for educational purposes and launch vehicle propulsion systems, has become possible. The solid fuel grain diameter is assumed to spread the characterization under different conditions. Estimate the rocket performance in the assumed condition and develop the test bench setup. In this paper, the data are composed of a 165 mm length of grain, external diameter is 79.6 mm and internal/port diameter is 8 mm. The injector plate used in this experiment is three injector holes with 120°. This injector is a showerhead that is simple in design and it is frequently used in hybrid rocket engines. Constraints such as the pressure in the combustion chamber being 50 bar and the SS304 nozzle, thrust were measured. Four separate test series were conducted. In the first test, one hole in the showerhead injector geometry was studied. In the 2nd, 3rd, and 4th tests, injector plates with three injector holes were used. The test bench of a hybrid rocket engine has many components (oxidizer/pressure tank, combustion chamber with the pre-combustion, post-combustion chamber, conical shape nozzle, igniter, injector plate, etc.).

This paper introduces an experiment-based recognition and grasping control method for aerial manipulators. The method consists of two parts: an automatic grasping process using a finite state machine, and an ultrasonic ranging principle. The D–H parameter method is utilized for analyzing the manipulator’s degree of freedoms, equipped with bus servos controlled via serial communication. The proposed strategy is evaluated using a practical experiment of the aerial manipulator system. This research contributes to the field of aerial manipulators by providing a robust and flexible way of grasping targets.

Supersonic airflow deceleration in a conventional mixed-compression intake is studied numerically. The simulation of turbulent two-dimensional flow is based on the Reynolds-averaged Navier–Stokes equations and the k-ω SST turbulence model. Numerical solutions are obtained with ANSYS-18.2 CFX finite-volume solver of second-order accuracy. The solutions reveal flow hysteresis with step-by-step changes in the free-stream Mach number M_∞. The hysteresis is caused by the instability of an interaction of a shock wave with the local region of flow acceleration formed near the throat of intake. Oscillations of the Mach number M_∞ in time are considered as well, and the existence of hysteresis is confirmed at small values of the amplitude A and period τ of the oscillations. The hysteresis shrinks with increasing amplitude A and eventually disappears at sufficiently large amplitudes. The dependence of shock wave oscillations on the period τ is also studied and transitions between different flow regimes are discussed.

A homing guidance law combined with terminal angle constraint and seeker’s field-of-view limit is proposed in this paper for hitting a stationary target. The proposed guidance scheme is composed of proportional navigation guidance and a continuous feedback term with respect to a newly defined angle error. Considering that many existing methods use switching logic strategy to address the specific constraint which will generate discontinuous acceleration command, the proposed scheme overcomes the limitation by not using switching logic. Furthermore, the finite-time convergence of angle error before interception is guaranteed via a Lyapunov-like approach, a shaping function is also designed to lengthen the range at which the error becomes zero. Numerical simulations demonstrate the characteristics and advantages of the proposed guidance law.

In this paper, the limits of models different accuracy applicability in the simulation of aircraft rough landing on a runway was analyzed. Three models were considered: a detailed global model, an elastic beam model that takes into account stiffness and mass-inertial characteristics, and an absolutely rigid beam model that takes into account only mass-inertial characteristics. The reduction of the detailed model to the beam ones was carried out according to the beam theory. As a result, the forces acting to the main landing gear were obtained for various combinations of vertical and horizontal speeds, pitch and roll angles. The errors of the beam models relative to the detailed one were obtained and the limits of their applicability were given.

Nearly equiatomic NiTi shape memory alloy exhibits superelasticity, i.e., it can be strained up to ~ 7% and recover completely upon unloading, and consequently, the stress–strain response forms a closed hysteresis. The mechanical behavior of superelastic NiTi is characterized by significant tension–compression asymmetry, which leads to complexity in the stress–strain responses and deformation patterns of thin-walled superelastic NiTi tubes loaded by axial force and internal pressure simultaneously. In the reported biaxial experiments, the NiTi tube exhibits hardening responses and essentially homogeneous deformation in a neighborhood of equibiaxiality. In other cases, its stress–strain responses trace stress plateaus associated with localized deformation patterns, and the level of plateaus, magnitude of transformation strains, and orientation of the localization bands are strongly dependent on the axial-to-hoop stress ratio. In this paper, finite element modeling is performed to analyze numerically the mechanical response of biaxially loaded superelastic NiTi tube. A numerical feedback control scheme is developed to maintain the stress ratio to follow the target value. The simulations reproduce successfully the observed phenomena in the experiments, such as the localization of helical bands, the variation of band angles with stress ratio, as well as the hardening and uniform deformation near the state of equibiaxial stress. In addition, the variation of axial and hoop stress–strain responses with different stress ratios are also studied, which are reasonably close to the experimental ones. The presented work demonstrates the validity of the developed finite element analysis framework and paves the way for analysis of superelastic shape memory alloy structures under multiaxial loading.