Coaxial tilt-rotor (CTR) unmanned aerial vehicle (UAV) is a system with the specific configuration of two CTR modules and a rear-rotor module. The CTRUAV is a typical strongly coupled, nonlinear, and underactuated system whose control performance is always adversely affected by various disturbances. To realize robust, stable, and efficient flight control for the CTRUAV is a challenging task. A multivariable cascaded finite-time (FT) controller and an improved nonlinear control allocation law with variable parameters are proposed based on the particular configuration of the CTRUAV. Finally, the superiority and the relationship between the control performance of the proposed control scheme and the control parameters are demonstrated through simulations and real flight experiments. The results show that the proposed control system significantly improves the robustness, transient performance, stability, and efficiency of the CTRUAV. In the flight tests, the root mean square error of the velocity is reduced by 28% in the presence of external disturbance, and the settling time of the attitude is shortened up to 55.8% in tracking the step signal.

Finite-Time Control Design for a Coaxial Tilt-Rotor UAV

This research presents a dual-pronged bibliometric and systematic review of the integration of phase change materials (PCMs) in asphalt pavements to counteract the urban heat island (UHI) effect. The bibliometric approach discerns the evolution of PCM-inclusion asphalt research, highlighting a marked rise in the number of publications between 2019 and 2022. Notably, Chang’an University in China has emerged as a leading contributor. The systematic review addresses key questions like optimal PCM types for UHI effect mitigation, strategies for PCM leakage prevention in asphalt, and effects on mechanical properties. The findings identify polyethylene glycols (PEGs), especially PEG2000 and PEG4000, as prevailing PCMs due to their wide phase-change temperature range and significant enthalpy during phase transitions. While including PCMs can modify asphalt’s mechanical attributes, such mixtures typically stay within performance norms. This review emphasises the potential of PCMs in urban heat management and the need for further research to achieve optimal thermal and mechanical balance.

Advancements in Phase Change Materials in Asphalt Pavements for Mitigation of Urban Heat Island Effect: Bibliometric Analysis and Systematic Review

The regulation of asphalt pavement temperature is crucial in ensuring its durability, promoting traffic safety, and preserving the environment. Phase change materials (PCMs) can play a critical role in preventing thermal distress of asphalt pavements as thermoregulation units. This paper presents a comprehensive review of the classification and performance requirements of PCMs and the methods of synthetic and characterization of composite PCMs (CPCMs). Furthermore, the study delves into the thermoregulation effect of CPCMs and its influence on the performance of asphalt pavements. Results show that the organic solid–liquid PCMs and organic-organic eutectic PCMs meet the requirements of asphalt pavement in terms of phase change temperature, latent heat, thermal conductivity, durability, environmental compatibility, and economic viability, and therefore have a wide range of applications. However, the direct incorporation of PCMs can significantly affect both the performance and thermoregulation properties of the asphalt pavement. Therefore, it is crucial to utilize various methods to prepare CPCMs to avoid liquid leakage. The thermoregulation effect of CPCMs on asphalt pavements can be validated through both experimental characterization and numerical simulation, and the improvement in the mechanical strength of CPCMs holds potential for enhancing the rheological properties and overall performance of asphalt pavements. Furthermore, this paper provides an in-depth analysis of the areas in which CPCM preparation methods, performance characterization, and engineering applications still require further research. It is intended that this paper will serve as a valuable resource for relevant professionals and contribute to the advancement of knowledge in this field. 

A review of recent developments and challenges of using phase change materials for thermoregulation in asphalt pavements

Microencapsulated binary eutectic phase change materials with high energy storage capabilities for asphalt binders

To address issues related to the limited improvement in the performance of phase-change material (PCMs) modified asphalt and the unclear underlying mechanisms, this study developed two structurally stable and thermally efficient coal gangue composite phase-change agents. The impact on enhancing the properties of asphalt was systematically investigated. The study revealed that when the dosage of the phase-change agent is below 20%, there was a pronounced interactive effect between the agent and asphalt. This interaction had the capability to regulate both the non-polar and polar components within the asphalt colloid system. By controlling the dosage of the PCMs agent, it was possible to enhance the high-temperature rheological properties, high-temperature shear resistance and low-temperature flexibility of the asphalt. Additionally, this control improved the adhesion and moisture sensitivity of the PCMs modified asphalt and aggregate system. The maximum temperature-regulating effect of PCMs modified asphalt could reach up to 8.3 °C, with the functional attribute strongly correlated with the low-temperature performance of the asphalt. This research contributes to the promotion and application of PCMs in road engineering. 

Promotional effect of shaped coal gangue composite phase change agents doping in asphalt on pavement properties

Study of Temperature-Adjustment Asphalt Mixtures Based on Silica-Based Composite Phase Change Material and its Simulation

This paper proposed a new fixed-time trajectory tracking control strategy based on the disturbance observer (DOB) for a tilt trirotor unmanned aerial vehicle (TTUAV) which is subject to unknown external disturbances. To facilitate the TTUAV's trajectory tracking controller design, the dynamic model of the TTUAV is divided into two subsystems, the position subsystem (outer-loop) and the attitude subsystem (inner-loop). For the dynamics of the TTUAV's outer-loop, the unknown external disturbances consist of the unknown wind disturbances, the unknown aerodynamic frictions forces, the lateral force generated by the rear servo and the states coupling between the outer-loop and the inner-loop. Then, a nonlinear DOB is designed to estimate the unknown external disturbances, and a nonsingular terminal sliding-mode controller (NTSMC) is further developed to drive the TTUAV's position tracking errors to zero in a fixed time. For the dynamics of the TTUAV's inner-loop, the unknown external disturbances are mainly introduced by the aerodynamic frictions torques. Then, a modified sliding mode controller is designed to reject the unknown external disturbances, and to ensure that the attitude tracking errors converge to zero exponentially. In addition, a composite stability analysis based on Lyapunov stability theory is provided to guarantee the fixed-time convergence of the closed-loop dynamics of the TTUAV. Finally, the results of the real-time experiments are presented to verify the effectiveness of the proposed control strategy. 

Disturbance Observer Based Fixed-Time Tracking Control for a Tilt Trirotor Unmanned Aerial Vehicle

Multi-Frequency-Ranging Positioning Algorithm for 5G OFDM Communication Systems

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Study of Temperature-Adjustment Asphalt Mixtures Based on Silica-Based Composite Phase Change Material and its Simulation

Disturbance Observer Based Fixed-Time Tracking Control for a Tilt Trirotor Unmanned Aerial Vehicle

Multi-Frequency-Ranging Positioning Algorithm for 5G OFDM Communication Systems