Autonomous landing control of highly flexible aircraft based on Lidar preview in the presence of wind turbulence

This paper investigates preview-based autonomous landing control of a highly flexible flying wing model using short range Lidar wind measurements in the presence of wind turbulence. The preview control system is developed based on a reduced-order linear aeroelastic model and employs a two-loop control scheme. The outer loop employs the LADRC (linear active disturbance rejection control) and PI algorithms to track the reference landing trajectory and vertical speed, respectively, and to generate the attitude angle command. This is then used by the inner-loop using H∞ preview control to compute the control inputs to the actuators (control flaps and thrust). A landing trajectory navigation system is designed to generate real-time reference commands for the landing control system. A Lidar (light detection and ranging) simulator is developed to measure the wind disturbances at a distance in front of the aircraft, which are provided to the inner-loop H∞ preview controller as prior knowledge to improve control performance. Simulation results based on the full-order nonlinear flexible aircraft dynamic model show that the preview-based landing control system is able to land the flying wing effectively and safely, showing better control performance than the baseline landing control system (without preview) with respect to landing effectiveness and disturbance rejection. The control system’s robustness to measurement error in the Lidar system is also demonstrated

Effects of POD control on a DFIG wind turbine structural system

This paper investigates the effects power oscillation damping (POD) controller could have on a wind turbine structural system. Most of the published work in this area has been done using relatively simple aerodynamic and structural models of a wind turbine which cannot be used to investigate the detailed interactions between electrical and mechanical components of the wind turbine. Therefore, a detailed model that combines electrical, structural and aerodynamic characteristics of a grid-connected Doubly Fed Induction Generator (DFIG) based wind turbine has been developed by adapting the NREL (National Renewable Energy Laboratory) 5MW wind turbine model within FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. This detailed model is used to evaluate the effects of POD controller on the wind turbine system. The results appear to indicate that the effects of POD control on the WT structural system are comparable or less significant as those caused by wind speed variations. Furthermore, the results also reveal that the effects of a transient three-phase short circuit fault on the WT structural system are much larger than those caused by the POD controller

Optimum microgeometry modifications of herringbone gear by means of fitness predicted genetic algorithm

This paper presents a systematic methodology focused on herringbone gear microgeometry modifications toward vibration reduction. The dynamic model considering the unique characteristics of aviation herringbone gear is developed to study the vibration behavior. The optimal ease-off shape can be defined as the outcome of a multi-objective optimization process, the objective functions are loaded transmission error, meshing impact excitation and root mean square (RMS) of vibration acceleration. With special attention given to computational efficiency, a novel fitness predicted genetic algorithm is developed. An application to herringbone gear are presented, the results show the proposed method can obtain optimal modifications that significantly improve the gear performance over a wide range of operating conditions. Furthermore, the reduction of the vibration also leads to a reduction of bending stresses. Finally, a test on herringbone gear is executed under various combinations of torque and speed to demonstrate the accuracy of the proposed model

Power generation control of a hydrostatic wind turbine implemented by model-free adaptive control scheme

The hydrostatic wind turbine (HWT) is a type of wind turbine that uses hydrostatic transmission (HST) drivetrain to replace the traditional gearbox drivetrain. Without the fragile and expensive gearbox and power converters, HWT can potentially reduce the maintenance costs owing to the gearbox and power converter failures in wind power system, especially in offshore cases. We design an MFAC torque controller to regulate the pump torque of the HWT and compared to an H_inf torque controller. Then we design an MFAC pitch controller to stabilise the rotor speed of HWT and compared to a gain-scheduling proportional-integral (PI) controller and a gain-scheduling PI controller with anti-windup (PIAW). The results indicate that MFAC torque controller provides more effective tracking performance than the H_inf controller, and that MFAC pitch controller shows better rotor speed stabilisation performance in comparison with the gain-scheduling PI controller and PIAW

A Novel Radially Closable Tubular Origami Structure (RC-ori) for Valves

Cylindrical Kresling origami structures are often used in engineering fields due to their axial stretchability, tunable stiffness, and bistability, while their radial closability is rarely mentioned to date. This feature enables a valvelike function, which inspired this study to develop a new origami-based valve. With the unique one-piece structure of origami, the valve requires fewer parts, which can improve its tightness and reduce the cleaning process. These advantages meet the requirements of sanitary valves used in industries such as the pharmaceutical industry. This paper summarizes the geometric definition of the Kresling pattern as developed in previous studies and reveals the similarity of its twisting motion to the widely utilized iris valves. Through this analogy, the Kresling structure’s closability and geometric conditions are characterized. To facilitate the operation of the valve, we optimize the existing structure and create a new crease pattern, RC-ori. This novel design enables an entirely closed state without twisting. In addition, a simplified modeling method is proposed in this paper for the non-rigid foldable cylindrical origami. The relationship between the open area and the unfolded length of the RC-ori structure is explored based on the modeling method with a comparison with nonlinear FEA simulations. Not only limited to valves, the new crease pattern could also be applied to microreactors, drug carriers, samplers, and foldable furniture

Learning-based attitude tracking control with high-performance parameter estimation

This paper aims to handle the optimal attitude tracking control tasks for rigid bodies via a reinforcement learning-based control scheme, in which a constrained parameter estimator is designed to compensate system uncertainties accurately. This estimator guarantees the exponential convergence of estimation errors and can strictly keep all instant estimates always within pre-determined bounds. Based on it, a critic-only adaptive dynamic programming (ADP) control strategy is proposed to learn the optimal control policy with respect to a user-defined cost function. The matching condition on reference control signals, which is commonly employed in relevant ADP design, is not required in the proposed control scheme. We prove the uniform ultimate boundedness of the tracking errors and critic weight's estimation errors under finite excitation conditions by Lyapunov-based analysis. Moreover, an easy-to-implement initial control policy is designed to trigger the real-time learning process. The effectiveness and advantages of the proposed method are verified by both numerical simulations and hardware-in-loop experimental tests

Detect Depression from Social Networks with Sentiment Knowledge Sharing

Social network plays an important role in propagating people's viewpoints, emotions, thoughts, and fears. Notably, following lockdown periods during the COVID-19 pandemic, the issue of depression has garnered increasing attention, with a significant portion of individuals resorting to social networks as an outlet for expressing emotions. Using deep learning techniques to discern potential signs of depression from social network messages facilitates the early identification of mental health conditions. Current efforts in detecting depression through social networks typically rely solely on analyzing the textual content, overlooking other potential information. In this work, we conduct a thorough investigation that unveils a strong correlation between depression and negative emotional states. The integration of such associations as external knowledge can provide valuable insights for detecting depression. Accordingly, we propose a multi-task training framework, DeSK, which utilizes shared sentiment knowledge to enhance the efficacy of depression detection. Experiments conducted on both Chinese and English datasets demonstrate the cross-lingual effectiveness of DeSK

Lithosphere thinning beneath west North China Craton: Evidence from geochemical and Sr-Nd-Hf isotope compositions of Jining basalts

This study shows lithosphere evolution history in the west North China Craton (NCC) from the early Cretaceous to Quaternary by studying the major element, trace element and Sr-Nd-Hf isotope compositions in Jining basalts of 119.6-108.6. Ma, 23.5-21.9. Ma and 1.3-0.11. Ma.The early Cretaceous basalts (119.6-108.6Ma) display enriched characteristics with high contents of incompatible elements, high 87Sr/86Sri, low εNd(t) and low εHf(t). These basalts resulted from partial melting of ancient metasomatized lithospheric mantle, and we consider the 119.6-108.6Ma magmatism as indicating lithosphere thinning in the west NCC. Although the Pacific slab seen seismically in the mantle transition zone beneath eastern China is no older than 60Ma, there exists convincing evidence for the presence of the Paleo-Pacific slab in the transition-zone in the Mesozoic. Thus we propose that the water released from the transition-zone slab hydrated the overlying lithosphere and further converted the base of the lithosphere into asthenosphere. This is the most likely mechanism responsible for the lithosphere thinning in the west NCC and the petrogenesis of the Jining 119.6-108.6Ma basalts.The Jining 23.5-21.9Ma basalts also have high contents of incompatible elements, but they display high εNd(t), high εHf(t) and variably low 87Sr/86Sri. We propose that these Miocene basalts were derived from the asthenosphere with contributions from ancient metasomatized lithospheric mantle during melt ascent. The Jining Quaternary basalts (1.3-0.11Ma) represent the melt of upwelling asthenosphere with low 87Sr/86Sri, high εNd(t) and high εHf(t). Upwelling and decompression melting of the eastward flowing asthenosphere from beneath western plateaus to beneath eastern hilly plains in the Cenozoic is the most plausible mechanism for the petrogenesis of Jining Cenozoic basalts (both of 23.5-21.9Ma and 1.3-0.11Ma), but the Jining 1.3-0.11Ma basalts must have been produced beneath even thinner lithosphere.Taken together geophysical studies and our petrological and geochemical studies of all these three episodes of the Jining basalts, we propose that the lithosphere in the west NCC has been thinning since the early Cretaceous and the thinning continues to the present