Chinese Journal of Aeronautics最新文献

The influence of local cooling/heating on two types of nonlinear instabilities of the high-speed boundary layer, namely, the First and Second Mode Oblique Breakdown (FMOB and SMOB), is studied using direct numerical simulations. Local cooling and heating are performed at the weak and strong nonlinear stages of the two types of nonlinear instabilities. It is found that for the FMOB, local cooling at the weak nonlinear region will suppress the increase of the fundamental mode, leading to transition delay. Opposite to local cooling, local heating at the weak nonlinear region of the FMOB will promote the growth of the fundamental mode, resulting in the occurrence of more upstream transition onset. However, if local cooling and heating are performed at the strong nonlinear region, the influence of both local cooling and heating on the FMOB can be neglected. Remarkably, both local heating and cooling can delay the SMOB for different mechanisms. Performing local cooling at the weak nonlinear region of the SMOB, the low amplitude of higher spanwise wavenumber steady mode caused by local cooling lies behind transition delay. When local cooling is set at the strong nonlinear region, the low amplitude of harmonic modes around the cooling area can cause transition delay. Additionally, local heating will suppress the SMOB for the slowing amplification rate of various modes caused by the local heating at both the weak and strong nonlinear stages of the SMOB.

This paper describes the design and implementation of a three-axis acceleration control autopilot for an asymmetric tail-controlled, skid-to-turn tactical missile. In an earlier flight test, degraded autopilot performance was attributed to multiple disturbances and uncertainties and the presence of hidden coupling terms, giving rise to a miss distance of greater than 20 m. To address these issues, the missile dynamics are decomposed into the angular rate dynamics as fast and the acceleration dynamics as slow subsystem using the singular perturbation theory to analyze a multi-time-scale property. Multifrequency extended state observers are then incorporated into the gain scheduling technique to attenuate disturbances, thus enhancing the control performance significantly. In the proposed engineering/practical design framework for missile autopilot, simple, conventional, and explicit tuning rules are provided. And the proposed control scheme can achieve input-to-state stability across the entire flight envelope under unknown but bounded disturbances. The advantages of the method over existing benchmark approaches are shown through nonlinear numerical simulations. This is supported by evidence from a new flight test result with a miss distance of only 2 m.

Carbon fiber reinforced thermoplastic composites (CFRTP) and metals hybrid structures have been widely used in aircraft lightweight manufacturing. However, due to the significant difference in physical and chemical properties between CFRTP and metals, there are lots of challenges to connect them with high quality. Laser welding has a good application prospect in CFRTP and metals connection, and a significant research progress has been made in the exploration of CFRTP-metal laser joining mechanism, joining process optimization, joining strength improvement and joining defects controlling. However, there are still some problems need to be solved for this technology application. In this paper, the research progress of CFRTP-metal laser joining was summarized in three major aspects: theoretical modeling and simulation analysis, process exploration and parameter optimization, joint performance improvement and process innovation. And, problems and challenges of this technology were discussed, and the outlook of this research was provided.

This paper proposes a novel self-calibration method for a large-FoV (Field-of-View) camera using a real star image. First, based on the classic equisolid-angle projection model and polynomial distortion model, the inclination of the optical axis is thoroughly considered with respect to the image plane, and a rigorous imaging model including 8 unknown intrinsic parameters is built. Second, the basic calibration equation based on star vector observations is presented. Third, the partial derivative expressions of all 11 camera parameters for linearizing the calibration equation are deduced in detail, and an iterative solution using the least squares method is given. Furtherly, simulation experiment is designed, results of which shows the new model has a better performance than the old model. At last, three experiments were conducted at night in central China and 671 valid star images were collected. The results indicate that the new method obtains a mean magnitude of reprojection error of 0.251 pixels at a 120° FoV, which improves the calibration accuracy by 38.6% compared with the old calibration model (not considering the inclination of the optical axis). When the FoV drops below 20°, the mean magnitude of the reprojection error decreases to 0.15 pixels for both the new model and the old model. Since stars instead of manual control points are used, the new method can realize self-calibration, which might be significant for the long-duration navigation of vehicles in some unfamiliar or extreme environments, such as those of Mars or Earth’s moon.

Tethered Space Net Robot (TSNR) is considered to be a promising approach for space debris removal, and accordingly it is also an interesting control problem due to its time-varying disturbances caused by an elastic and flexible net and a main connected tether. In this situation, the control scheme should be robust enough, low-frequency, and finite-time convergent in presence of external disturbances. In this paper, a robust controller with an advanced adaptive scheme is proposed. To improve robustness, the disturbance is skillfully involved in the adaptive scheme. It is strictly proven that the closed-loop system can converge to the desired trajectory in finite time in both reaching and sliding processes. Based on the theoretical proof, adaptive gains and corresponding dynamic stability characteristics are further discussed. Finally, the efficiency of the proposed control scheme is numerically proven via a TSNR. The proposed control scheme utilizes small and continuous control forces to compensate for the disturbance efficiently and track the desired trajectory quickly.