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A proposed strategy for managing airspace and preventing illegal drones from compromising security involves the use of autonomous drones equipped with three key functionalities. Firstly, the implementation of YOLO-v5 technology allows for the identification of illegal drones and the establishment of a visual-servo system to determine their relative position to the autonomous drone. Secondly, an extended Kalman filter algorithm predicts the flight trajectory of illegal drones, enabling the autonomous drone to compensate in advance and significantly enhance the capture success rate. Lastly, to ensure system robustness and suppress interference from illegal drones, an adaptive fast nonsingular terminal sliding mode technique is employed. This technique achieves finite time convergence of the system state and utilizes delay estimation technology for the real-time compensation of unknown disturbances. The stability of the closed-loop system is confirmed through Lyapunov theory, and a model-based hardware-in-the-loop simulation strategy is adopted to streamline system development and improve efficiency. Experimental results demonstrate that the designed autonomous drone accurately predicts the trajectory of illegal drones, effectively captures them using a robotic arm, and maintains stable flight throughout the process.

This paper proposes a cascaded dual closed-loop control strategy that incorporates time delay estimation and sliding mode control (SMC) to address the issue of uncertain disturbances in logistic unmanned aerial vehicles (UAVs) caused by ground effects, crosswind disturbances, and payloads. The control strategy comprises a position loop and an attitude loop. The position loop, which functions as the outer loop, employs a proportional–integral–derivative (PID) sliding mode surface to eliminate steady-state error through an integral component. Conversely, the attitude loop, serving as the inner loop, utilizes a fast nonsingular terminal sliding mode approach to achieve finite-time convergence and ensure a quick system response. The time-delay estimation technique is employed for the online estimation and real-time compensation of unknown disturbances, while SMC is used to enhance the robustness of the control system. The combination of time-delay estimation and SMC offers complementary advantages. The stability of the system is proven using Lyapunov theory. Hardware-in-the-loop simulation and flight tests demonstrate that the control law can achieve a smooth and continuous output. The proposed control strategy can be effectively applied in complex scenarios, such as hovering, crash recovery, and high maneuverability flying, with significant practicality in engineering applications.

Although the linear Mohr−Coulomb criterion is frequently applied to predict the failure of brittle materials such as cast iron, it can be used for ductile metals too. However, the criterion has some significant deficiencies which limit its predictive ability. In the present study, the underlying failure hypotheses of the linear Mohr−Coulomb criterion were thoroughly discussed. Based on Mohr’s physically meaningful concept of fracture plane, a macroscopic strength criterion was developed to explain the failure mechanism of isotropic metals. The failure function was expressed as a polynomial expansion in terms of the stresses acting on the fracture plane, and the quadratic approximation was employed to describe the non-linear behavior of the failure envelope. With an in-depth understanding of Mohr’s fracture plane concept, the failure angle was regarded as a generalized strength parameter in addition to the failure stress (i.e., the conventional basic strength). The undetermined coefficients of the non-linear failure function were calibrated by the strength parameters obtained from the common uniaxial tension and compression tests. Theoretical and experimental assessment for different types of isotropic metals validated the effectiveness of the proposed criterion in predicting material failure.

Summary In present paper, the Kane-Mindlin assumptions are applied to homogeneous anisotropic plates undergoing extensional deformations. A complex potential approach is formulated;to that end, a third complex potential is added to the two Lekhniskii complex potentials, [2]. The components of displacement and stress as well as boundary conditions are represented in terms of these three complex potentials. The advantage of the proposed approach is that problems of anisotropic plates under extensional deformations are treated as a quasi-three-dimensional problem by considering the effect of the transverse normal strain. [ABSTRACT FROM AUTHOR]

A new method to determine the compression after impact (CAI) strength of composite laminates was presented. In this method, an impact damage zone was modeled as an equivalent hole. The most outstanding characteristic of the method was that the simplification of the impact damage was based on the compressive failure mechanisms of impacted laminates. Such a simplification has not been discussed in the literature before. A technique was established for determining the shape and size of the equivalent hole. To the authors' knowledge, it is the first practical method for simplifying the impact damage as a hole, and also the present work was the first attempt to predict the CAI strength by modeling the impact damage as a hole. The stress distribution around damage was calculated using the complex potential method and the classical lamination theory. A lay-up independent failure criterion was used to predict CAI strength. The predictions of the present approach were compared to test results and found to be in very good agreement over a wide variety of materials. The study indicated that the width of damage zone was a key factor governing CAI strength. The influence of damage area, impact energy, impactor shape and dimension, etc. on CAI strength can be essentially characterized by their effects on the damage width. The study provided a very simple and effective approach for CAI strength prediction compared with previous methods. [ABSTRACT FROM AUTHOR]

The present study numerically explores the distinct aerodynamic characteristics of an airfoil flying in proximity to water waves. The water wave is treated by both two-phase-flow wavy water and rigid moving wavy ground, with a specific goal to clarify whether the water wave can be substituted by rigid wavy ground. Results show that for large ground clearance (h/c=0.4), the aerodynamic forces and flow structures of the near-field airfoil are basically dominated by the passage shape between airfoil and wave surface where the wavy water can be replaced by means of using wavy ground. However, it is different for small ground clearance that the airfoil-induced airflow has a strong relative speed to the water flow and subsequently creates a strong shear force on the forthcoming wave to eject water spray from wave crest. The spray has a sufficient influence on the flow topology and consequently leads to a distinct aerodynamic behavior. Particularly, the strong upstream shear on the wave resulted from the stagnation region at a positive angle of attack induces upwind spray, which can be elevated to hit onto the airfoil with larger density and momentum than airflow causing extraordinarily high pressure on the lower surface as well as unstable aerodynamic forces. [ABSTRACT FROM AUTHOR]