Search Results (318)

Ply Curving Termination (PCT) is an effective method to suppress stress concentration at composite ply drop-offs by locally curving the reinforcing fibers to reduce the stiffness. A previous study by the authors confirmed that PCT can suppress fatigue delamination failure in composite ply drop-off. However, the specimens used were external ply drop-offs without cover plies and did not reflect practical structural configurations. Following the basic study, this current study evaluated the fatigue damage suppression characteristic of PCT in practically relevant internal ply drop-offs with cover plies. Finite element analysis, fatigue testing, and detailed observation of the failure process using X-ray CT showed that PCT is effective in suppressing fatigue failure of internal ply drop-offs. In particular, delamination propagation from matrix cracks along the curving fibers, a weak point of PCT, is suppressed in the external ply drop-off. Finite element analysis indicated the importance of stress transfer from the cover ply to the ply drop-off, confirming that the fatigue damage suppression effect of PCT is enhanced in practical composite ply drop-off configurations. Full article

The integration of multiple renewable and storage units in electric vehicle (EV) hybrid energy systems presents significant challenges in stability, dynamic response, and disturbance rejection, limitations often encountered with conventional sliding mode control (SMC) and super-twisting SMC (STSMC) schemes. This paper proposes a condition-based integral terminal super-twisting sliding mode control (CBITSTSMC) strategy, with gains optimally tuned using an improved gray wolf optimization (I-GWO) algorithm, for coordinated control of a multi-source DC–DC converter system comprising photovoltaic (PV) arrays, fuel cells (FCs), lithium-ion batteries, and supercapacitors. The CBITSTSMC ensures finite-time convergence, reduces chattering, and dynamically adapts to operating conditions, thereby achieving superior performance. Compared to SMC and STSMC, the proposed controller delivers substantial reductions in steady-state error, overshoot, and undershoot, while improving rise time and settling time by up to 50%. Transient stability and disturbance rejection are significantly enhanced across all subsystems. Controller-in-the-loop (CIL) validation on a Delfino C2000 platform confirms the real-time feasibility and robustness of the approach. These results establish the CBITSTSMC as a highly effective solution for next-generation EV hybrid energy management systems, enabling precise power-sharing, improved stability, and enhanced renewable energy utilization. Full article

Unmanned Aerial Vehicles (UAVs) have revolutionized various industries due to their adaptability, efficiency, and capability to operate in diverse environments. However, conventional UAV designs face trade-offs between flight endurance and maneuverability. This study explores the design, analysis, and optimization of a biplane quadrotor UAV, integrating the vertical takeoff and landing (VTOL) capabilities of multirotors with the aerodynamic efficiency of fixed-wing aircraft to enhance flight endurance while maintaining high maneuverability. The UAV’s structural design incorporates biplane wings with different NACA airfoil configurations (NACA4415, NACA0015, and NACA0012) to assess their impact on drag reduction, stress distribution, and flight efficiency. Computational Fluid Dynamics (CFD) simulations in ANSYS Fluent 2023 R2 (Canonsburg, PA, USA).reveal that the NACA0012 airfoil achieves the highest drag reduction (75.29%), making it the most aerodynamically efficient option. Finite Element Analysis (FEA) further demonstrates that NACA4415 exhibits the lowest structural stress (95.45% reduction), ensuring greater durability and load distribution. Additionally, a hybrid flight control system, combining Backstepping Control (BSC) and Integral Terminal Sliding Mode Control (ITSMC), is implemented to optimize transition stability and trajectory tracking. The results confirm that the biplane quadrotor UAV significantly outperforms conventional quadcopters in terms of aerodynamic efficiency, structural integrity, and energy consumption, making it a promising solution for surveillance, cargo transport, and long-endurance missions. Future research will focus on material enhancements, real-world flight testing, and adaptive control strategies to further refine UAV performance in practical applications. Full article

Aiming at the control performance degradation of permanent magnet synchronous motor (PMSM) drive systems caused by uncertainties of internal and external disturbances, a robust control algorithm integrating an improved fast terminal sliding mode (IFTSM) surface with a novel adaptive reaching law (NARL) is proposed. A dynamic model of PMSM with disturbances is established, and an improved fast terminal sliding mode surface is designed. By introducing nonlinear terms and error derivative feedback mechanisms, the finite-time rapid convergence of system states is achieved, while solving the singularity problem of traditional terminal sliding mode control. Combined with the novel adaptive reaching law strategy, a state-dependent gain adjustment function is used to dynamically optimize the balance between reaching speed and chattering, enhancing the smoothness of the system′s dynamic response. Through the synergy of the finite-time convergence characteristic of the improved sliding mode surface and the novel adaptive reaching law, the proposed algorithm significantly enhances the system′s anti-interference capability against load mutations and parameter time variations. Experiment results demonstrate that under complex working conditions, the algorithm achieves superior speed tracking accuracy and current stability, providing a control solution with strong anti-interference capability and fast response for PMSM speed control systems. Full article

To address the issues of external unknown disturbances and roll motion in the tracking control of underactuated unmanned surface vehicle (USV) formation, a cooperative formation control method based on nonlinear model predictive control (NMPC) algorithm and finite-time disturbance observer is proposed. Initially, a tracking error model for the USV formation is established within a leader–follower framework, utilizing a four-degree-of-freedom (4-DOF) dynamic model to simultaneously account for roll motion and trajectory tracking. This error model is then approximately linearized and discretized. To mitigate the initial non-smoothness in the desired trajectories of the follower USVs, a tracking differentiator is designed to smooth the heading angle of the leader USV. Thereafter, a quasi-infinite horizon NMPC algorithm is developed, in which a terminal penalty function is constructed based on quasi-infinite horizon theory. Furthermore, a finite-time disturbance observer is developed to facilitate real-time estimation and compensation for unknown marine disturbances. The proposed method’s effectiveness is validated both mathematically and in simulation. Mathematically, closed-loop stability is rigorously guaranteed via a Lyapunov-based proof of the quasi-infinite horizon NMPC design. In simulations, the algorithm demonstrates superior performance, reducing steady-state tracking errors by over 80% and shortening convergence times by up to 75% compared to a conventional PID controller. These results confirm the method’s robustness and high performance for complex USV formation tasks. Full article

To address the problems of insufficient trajectory tracking accuracy, pronounced jitter over undulating terrain, and limited disturbance rejection in orchard mobile robots, this paper proposes a trajectory tracking control strategy based on a double-loop adaptive sliding mode. Firstly, a kinematic model of the orchard robot is constructed and a time-varying integral terminal sliding surface is designed to achieve global fast finite-time convergence. Secondly, a sinusoidal saturation switching function with a variable boundary is employed to suppress the high-frequency chattering inherent in sliding mode control. Thirdly, an improved double-power reaching law (Improved DPRL) is introduced to enhance disturbance rejection in the inner loop while ensuring continuity of the outer-loop output. Finally, Lyapunov stability theory is used to prove the asymptotic stability of the double-loop system. The experimental results show that attitude angle error settles within 0.01 rad after 0.144 s, while the position errors in both the x-axis and y-axis directions settle within 0.01 m after 0.966 s and 0.753 s, respectively. Regarding position error convergence, the Integral of Absolute Error (IAE)/Integral of Squared Error (ISE)/Integral of Time-Weighted Absolute Error (ITAE) are 0.7629 m, 0.7698 m, and 0.2754 m, respectively; for the attitude angle error, the IAE/ISE/ITAE are 0.0484 rad, 0.0229 rad, and 0.1545 rad, respectively. These results indicate faster convergence of both position and attitude errors, smoother control inputs, and markedly reduced chattering. Overall, the findings satisfy the real-time and accuracy requirements of fast trajectory tracking for orchard mobile robots. Full article

This paper presents an analysis of the influence of the termination geometry of an undercutting anchor drive bolt and the shape of the bottom of the anchor hole on the initiation and progression of failure processes in a rock medium. The study employed the finite element method (FEM) to model various bolt termination configurations, including cylindrical terminations with a 2 × 2 mm chamfer, a rounded termination with radius R, and a conical termination. The interaction of these bolt geometries with both cylindrical and conical hole bottoms was analyzed. The numerical simulations enabled the identification of stress concentration zones and crack propagation paths, which are critical to understanding the efficiency and mechanism of rock failure. The results indicate that the geometry of the bolt termination significantly influences stress distribution within the contact zone, as well as the extent and morphology of the resulting failure zone. Specifically, employing a cylindrical termination with a 2 × 2 mm chamfer in combination with a conical hole bottom promotes the development of deep fractures, which may lead to the detachment of larger rock fragments. This mechanism may be useful in the development of non-explosive rock fragmentation technologies. The findings provide a foundation for further optimization of anchor designs and the development of targeted excavation methods in mining and geotechnical engineering. Full article

Time-varying lumped disturbance and measurement noise are primary obstacles that restrict the control performance of permanent magnet synchronous motor (PMSM) drives. To tackle these obstacles, an adaptive nonsingular terminal sliding mode (ANTSM) algorithm is combined with augmented recursive sliding mode observer (ARSMO) for PMSM speed regulation system in this paper. Generally, conventional nonsingular terminal sliding mode (NTSM) controller adopts a fixed and conservative control gain to suppress the time-varying disturbance, which will lead to unsatisfactory steady-state performance. Without requiring any information of the time-varying disturbance in advance, a novel barrier function adaptive algorithm is utilized to adjust the gain of NTSM controller online according to the amplitude of disturbance. In addition, the ARSMO is emoloyed to estimate the total disturbance and motor speed simultaneously, thereby alleviating the negative impact of measurement noise and excessive control gain. Comprehensive experimental results verify that the proposed enhanced ANTSM strategy can optimize the dynamic performance of PMSM system without sacrificing its steady-state performance. Full article

Settlement control for tunnel–terminal co-construction projects remains undefined, despite the growing trend of integrating multiple transportation modes within large-scale transport hubs. This study investigates a large underground structure passing beneath an airport terminal, combining field investigations, statistical analyses, and finite element simulations to examine differential settlement behavior under non-uniform loading conditions. The key contribution of this work is the proposal of a differential settlement control standard, defined by the tangent of the rotation angle between adjacent column foundations, with a recommended value of 1/625. Case analysis at cross-section E–E shows that the measured maximum tangent rotation angle was 1/839, corresponding to base slab settlements of 40.5 mm and 33.1 mm for the high-speed railway and metro structures, respectively. Application of the proposed 1/625 criterion yields allowable maximum base slab settlements of 55.28 mm for the high-speed railway and 44.83 mm for the metro, with differential settlement limits of 7.5 mm and 3.13 mm. Numerical simulations confirm the validity of this standard, ensuring the structural integrity of co-constructed systems and providing practical guidance for future airport terminal–tunnel integration projects. Full article

Hybrid AC/DC microgrids (HADCMGs), which integrate renewable energy sources and battery storage systems, often face significant stability challenges due to their inherently low inertia and highly variable power inputs. To address these issues, this paper proposes a novel, robust composite controller based on backstepping fast terminal sliding mode control (BFTSMC). This controller is further enhanced with a virtual capacitor to emulate synthetic inertia and with a fractional power-based reaching law, which ensures smooth and finite-time convergence. Moreover, the proposed control strategy ensures the effective coordination of power sharing between AC and DC sub-grids through bidirectional converters, thereby maintaining system stability during rapid fluctuations in load or generation. To achieve optimal control performance under diverse and dynamic operating conditions, the controller gains are adaptively tuned using the marine predators algorithm (MPA), a nature-inspired metaheuristic optimization technique. Furthermore, the stability of the closed-loop system is rigorously established through control Lyapunov function analysis. Extensive simulation results conducted in the MATLAB/Simulink environment demonstrate that the proposed controller significantly outperforms conventional methods by eliminating steady-state error, reducing the settling time by up to 93.9%, and minimizing overshoot and undershoot. In addition, real-time performance is validated via processor-in-the-loop (PIL) testing, thereby confirming the controller’s practical feasibility and effectiveness in enhancing the resilience and efficiency of HADCMG operations. Full article

Staggered floor frame structures with good spatial adaptability are widely used in large-space civil buildings such as conference halls and terminal buildings. However, the short columns formed by staggered floor slabs significantly affect load transfer, which is unfavorable to the seismic performance of the structure. To address this issue, based on a practical project, this paper establishes a finite element analysis model, sets up steel-tube-reinforced concrete (ST-RC) columns at staggered floors to improve the insufficient ductility of short columns, and adopts the dynamic time–history analysis method combined with performance-based evaluation methods to study the effects of different seismic input angles (0°, 30°, 60°, 90°) on the seismic performance of local staggered floor frame structures at both the overall and member levels. The research results show that at the overall level, the fourth floor of the staggered floor frame structure is the weak floor, and the most unfavorable seismic input angle is 60°; additionally, at the member level, the damage of each member meets the performance objectives. Frame beams are more severely damaged under 0° and 90° seismic input, frame columns are more severely damaged under 30° and 60° seismic input, and the damage degree of ST-RC columns is similar in the four directions. As energy-dissipating members, frame beams have a significantly higher proportion of nonlinear strain energy than frame columns and ST-RC columns, which can effectively consume a large amount of seismic energy and enable the structure to retain more safety reserves. Therefore, for irregular buildings such as staggered floor frame structures that are prone to damage due to insufficient ductility of short columns, setting ST-RC columns at staggered floors can effectively reduce structural damage. The adoption of evaluation methods at both the overall structural and member levels enables a comprehensive understanding of the damage status of staggered floor structures. Full article

Industrial systems operating under severe mission environment are frequently confronted with intricate failure behaviors arising from system internal degradation and extrinsic stresses, posing an elevating challenge to system survivability and mission reliability. Mission termination strategies are attracting increasing attention as an intuitive and effective means to mitigating catastrophic mission-induced risk. However, how to manage coupled risk arising from competing fault processes, particularly when these modes are interdependent, has been rarely reported in existing works. To bridge this gap, this study delves into a dynamic risk control policy for continuously degrading systems operating under a random shock environment, which yields competing and dependent fault processes. An optimal mission termination policy is developed to minimize risk-centered losses throughout the mission execution, whose optimization problem constitutes a finite-time Markov decision process. Some critical structural properties associated with the optimal policy are derived, and by leveraging these structures, the alerting threshold for implementing mission termination procedure is formally established. Alternative risk control policies are introduced for comparison, and experimental evaluations substantiate the superior model capacity in risk mitigation. Full article

This study proposes a hierarchical composite adaptive sliding-mode control strategy to address the strong nonlinear dynamics of a hexarotor Unmanned Aerial Vehicle (UAV) and the external disturbances encountered during flight. First, within the position-control loop, a Terminal Sliding Mode Control (TSMC) is designed to guarantee finite-time convergence of the system states, thereby significantly improving the UAV’s rapid response to complex trajectories. Concurrently, an online Adaptive rates mechanism is introduced to estimate and compensate unknown disturbances and modeling uncertainties in real time, further enhancing disturbance rejection. In the attitude-control loop, a Super-twisting Sliding Mode Control (STSMC) method is employed, where an Adaptive rate law dynamically adjusts the sliding gain to prevent overestimation and high-frequency chattering, while ensuring fast convergence and smooth response. To comprehensively validate the feasibility and superiority of the proposed scheme, a representative helical trajectory-tracking experiment was conducted and systematically compared, via simulation, against conventional control methods. Experimental results demonstrate that the proposed approach achieves stable control within 0.15 s, with maximum position and attitude tracking errors of 0.05 m and 0.15°, respectively. Moreover, it exhibits enhanced robustness and adaptability to external disturbances and parameter uncertainties, effectively improving the motion-control performance of hexacopter UAVs in complex missions. Full article

Rehabilitation devices such as actuated lower-limb exoskeletons can provide essential mobility assistance for pediatric patients with gait impairments. Enhancing their control systems under conditions of user variability and dynamic disturbances remains a significant challenge, particularly in active-assist modes. This study presents a human-in-the-loop control architecture for a pediatric lower-limb exoskeleton, combining outer-loop admittance control with robust inner-loop trajectory tracking via a non-singular terminal sliding-mode (NSTSM) controller. Designed for active-assist gait rehabilitation in children aged 8–12 years, the exoskeleton dynamically responds to user interaction forces while ensuring finite-time convergence under system uncertainties. To enhance adaptability, we augment the inner-loop control with a twin delayed deep deterministic policy gradient (TD3) reinforcement learning framework. The actor–critic RL agent tunes NSTSM gains in real-time, enabling personalized model-free adaptation to subject-specific gait dynamics and external disturbances. The numerical simulations show improved trajectory tracking, with RMSE reductions of 27.82% (hip) and 5.43% (knee), and IAE improvements of 40.85% and 10.20%, respectively, over the baseline NSTSM controller. The proposed approach also reduced the peak interaction torques across all the joints, suggesting more compliant and comfortable assistance for users. While minor degradation is observed at the ankle joint, the TD3-NSTSM controller demonstrates improved responsiveness and stability, particularly in high-load joints. This research contributes to advancing pediatric gait rehabilitation using RL-enhanced control, offering improved mobility support and adaptive rehabilitation outcomes. Full article

In this study, a current vector pattern is analyzed for inter-turn fault (ITF) diagnosis of induction machines (IMs), and an ITF diagnosis algorithm is proposed. When an ITF occurs in IMs, a negative-sequence current is generated due to fault resistance, even though a positive-sequence voltage is applied to IMs. Based on the mathematical model of IMs with an ITF, the current vector patterns in the stationary coordinate frame are analyzed. The superposition of positive- and negative-sequence components results in an elliptical current vector trajectory, and its orientation varies depending on the fault conditions. The co-simulation using finite element analysis and circuit simulation is implemented to analyze the current vector pattern of IMs with an ITF. The ITF diagnosis is proposed based on the current vector pattern. A 12 kW, four-pole, three-phase IM and terminal box, which was used to implement an ITF, is manufactured, and an experiment setup is established to verify the ITF algorithm. The effectiveness of the proposed ITF algorithm is validated through experimental verification of the manufactured IM and terminal box. Full article