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Design and Experimental Verification of a Roll Control Strategy for Large Wingspan Flapping-Wing Aerial Vehicle

Journal of Bionic Engineering 2024年第4期21卷 1644-1661页

作者： Rui Meng Bifeng Song Jianlin Xuan Xiaojun Yang Dong Xue School of Aeronautics Northwestern Polytechnical UniversityXi’an710072China research and Development institute of northwestern polytechnical university in shenzhen Shenzhen518057China Yangtze River Delta research institute of northwestern polytechnical university Taicang215400China

Most flapping-wing aircraft wings use a single degree of freedom to generate lift and thrust by flapping up and down,while relying on the tail control surfaces to manage ***,these aircraft have certain limitations,such as poor accuracy in attitude control and inadequate roll control *** paper presents a design for an active torsional mechanism at the wing's trailing edge,which enables differential variations in the pitch angle of the left and right wings during *** simple mechanical form significantly enhances the aircraft's roll control *** experimental verification of this mechanism was conducted in a wind tunnel using the RoboEagle flapping-wing aerial vehicle that we *** study investigated the effects of the control strategy on lift,thrust,and roll moment during flapping ***,the impact of roll control on roll moment was examined under various wind speeds,flapping frequencies,angles of attack,and wing ***,several rolling maneuver flight tests were performed to evaluate the agility of RoboEagle,utilizing both the elevon control strategy and the new roll control *** results demonstrated that the new roll control strategy effectively enhances the roll control capability,thereby improving the attitude control capabilities of the flapping-wing aircraft in complex wind field *** conclusion is supported by a comparison of the control time,maximum roll angle,average roll angular velocity,and other relevant parameters between the two control strategies under identical roll control input.

关键词： Roll control Bio-inspired Roll moment Flapping wing aerial vehicle

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research progress of slippage characteristic and gas film stability enhancement methods on biomimetic hydrophobic surfaces

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Journal of Hydrodynamics 2024年第1期36卷 87-101页

作者： Meng-zhuo Zhang Hai-bao Hu Liu-zhen Ren Lu-yao Bao Jun Wen Luo Xie School of Marine Science and Technology Northwestern Polytechnical UniversityXi’an710072China research and Development institute of northwestern polytechnical university in shenzhen Shenzhen518063China

The biomimetic hydrophobic surface is a potentially efficient underwater drag reduction method and the drag reduction mechanism of this kind of surface comes from the interfacial *** now,it is a hotspot to grasp the slippage characteristic and explore slippage enhancement *** paper not only summarizes our numerical simulation and experimental results of slippage characteristic at the solid-liquid interface(SLI)of hydrophobic surfaces(HS)and the gas-liquid interface(GLI)of superhydrophobic surfaces(SHS)in recent years,but also introduces some innovative methods that can effectively improve the gas film stability and drag reduction effect of ***,we used the molecular dynamics(MD)simulation method to figure out the effect of the solid-liquid interaction strength,the system temperature and the shear rate on the slippage of SLI,and expound their action mechanism from molecular ***,by MD and multibody dissipative particle dynamics(MDPD)method,the slippage behavior at the GLI was studied under the influence of the microstructure size and the flow driving *** proposed a new kind of hybrid slip boundary condition model to describe the slippage characteristic on *** addition,we found through experiment that a three-dimensional backflow will appear on the GLI under the interfacial adsorption of surfactants,and the backflow direction will reverse with the change of GLI ***,we put forward the wettability step structure and gas injection method to enhance the stability and drag reduction effect of the gas film on SHS.

关键词： Hydrophobic surface superhydrophobic surface interfacial slip underwater drag reduction

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A quasi-zero stiffness energy harvesting isolator with triple negative stiffness

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Acta Mechanica Sinica 2024年第8期40卷 219-238页

作者： Xiangyu Cai Tao Yang Weiyang Qin Zhongliang Xie research&Development institute of northwestern polytechnical university in shenzhen Shenzhen518057China Department of Engineering Mechanics Northwestern Polytechnical UniversityXi’an710072China

Vibration isolation for low frequency excitation and the power supply for low power monitoring sensors are important issues in bridge *** main problem is how to effectively combine the vibration isolator with the energy harvester to form a multi-functional *** this paper,a system called quasi-zero stiffness energy harvesting isolator(QZS-EHI)with triple negative stiffness(TNS)is *** TNS structure consists of linear springs,rigid links,sliders,and ring permanent ***’s second law and Kirchhoff’s law construct dynamic equations of the QZS-EHI,and a comparison is made to contrast it with other QZS and linear *** comparison field includes the QZS range,amplitude-frequency relationship,force transmissibility,and energy harvested *** isolator can be applied to many engineering fields such as bridges,automobiles,and railway *** paper selects bridge engineering as the main field for the dynamic analysis of this *** the multi-span beam bridge,this paper compares different situations including the bridge with QZS-EHI support,with linear stiffness isolator support,and with single beam *** results show that the QZS-EHI is not only better than the traditional isolator with linear stiffness under both harmonic and stochastic excitation,but also better than some QZS isolators with double or single negative stiffness in bridge vibration isolation and energy *** analysis is verified to correspond to the simulation analysis,which means the proposed QZS-EHI has practical application value.

关键词： Quasi-zero stiffness Triple negative stiffness Vibration isolation Energy harvesting

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Dendritic tip selection during solidification of alloys:Insights from phase-field simulations

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Chinese Physics B 2024年第9期33卷 467-472页

作者： Qingjie Zhang Hui Xing Lingjie Wang Wei Zhai School of Physical Science and Technology Northwestern Polytechnical UniversityXi’an710072China research&Development institute of northwestern polytechnical university in shenzhen Shenzhen 518063China

The effect of undercooling DT and the interface energy anisotropy parameter e4 on the shape of the equiaxed dendritic tip has been investigated by using a quantitative phase-field model for solidification of binary *** was found that the tip radius r increases and the tip shape amplitude coefficient A4 decreases with the increase of the fitting range for all *** dendrite tip shape selection parameter sdecreases and then stabilizes with the increase of the fitting range,and sincreases with the increase of *** relationship between sand e4 follows a power-law function sµea 4,and a is independent of DT but dependent on the fitting *** results demonstrate that the predicted sis consistent with the curve of microscopic solvability theory(MST)for e4<0.02,and sobtained from our phase-field simulations is sensitive to the undercooling when e4 is fixed.

关键词： phase-field simulations dendritic structure interface energy anisotropy tip shape selection parameter

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Resonance mechanism of flapping wing based on fluid structure interaction simulation

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Chinese Journal of Aeronautics 2024年第5期37卷 243-262页

作者： Yueyang GUO Wenqing YANG Yuanbo DONG Dong XUE National Key Laboratory of Science and Technology on Aerodynamic Design and research School of AeronauticsNorthwestern Polytechnical UniversityXi'an 710072China research&Development institute of northwestern polytechnical university in shenzhen Shenzhen 518063China Yangtze River Delta research institute of northwestern polytechnical university Taicang 215400China

Certain insect species have been observed to exploit the resonance mechanism of their *** order to achieve resonance and optimize aerodynamic performance,the conventional approach is to set the flapping frequency of flexible wings based on the Traditional Structural Modal(TSM)***,there exists controversy among researchers regarding the relationship between frequency and aerodynamic *** that the structural response of wings can be influenced by the surrounding air vibrations,an analysis known as Acoustic Structure Interaction Modal(ASIM)is introduced to calculate the resonant *** this study,Fluid Structure Interaction(FSI)simulations are employed to investigate the aerodynamic performance of flapping wings at modal frequencies derived from both TSM and ASIM *** performance is evaluated for various mass ratios and frequency ratios,and the findings indicate that the deformation and changes in vortex structure exhibit similarities at mass ratios that yield the highest aerodynamic ***,the flapping frequency associated with the maximum time-averaged vertical force coefficient at each mass ratio closely aligns with the ASIM frequency,as does the frequency corresponding to maximum ***,the ASIM analysis can provide an effective means for predicting the optimal flapping frequency for flexible ***,it enables the prediction that flexible wings with varying mass ratios will exhibit similar deformation and vortex structure *** paper offers a fresh perspective on the ongoing debate concerning the resonance mechanism of Flexible Flapping Wings(FFWs)and proposes an effective methodology for predicting their aerodynamic performance.

关键词： Flexible Flapping Wing(FFW) Acoustic Structure Interaction Modal(ASIM) Fluid Structure Interaction(FSI) Resonance mechanism Aerodynamic performance

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Secure Tracking Control via Fixed-Time Convergent Reinforcement Learning for a UAV CPS

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IEEE/CAA Journal of Automatica Sinica 2024年第7期11卷 1699-1701页

作者： Zhenyu Gong Feisheng Yang the School of Automation Northwestern Polytechnical UniversityXi’an 710129 the research&Development institute of northwestern polytechnical university in shenzhen Shenzhen 518063China

Dear Editor,This letter is concerned with the secure tracking control problem in the unmanned aerial vehicle(UAV) system by fixed-time convergent reinforcement learning(RL). By virtue of the zero-sum game,the false da... 详细信息

关键词： Secure Fixed false

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Ensemble successor representations for task generalization in offline-to-online reinforcement learning

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Science China(Information Sciences) 2024年第7期67卷 240-255页

作者： Changhong WANG Xudong YU Chenjia BAI Qiaosheng ZHANG Zhen WANG Space Control and Inertial Technology research Center Harbin Institute of Technology Shanghai Artificial Intelligence Laboratory shenzhen research institute of northwestern polytechnical university School of Cybersecurity Northwestern Polytechnical University

In reinforcement learning(RL), training a policy from scratch with online experiences can be inefficient because of the difficulties in exploration. Recently, offline RL provides a promising solution by giving an initialized offline policy, which can be refined through online interactions. However, existing approaches primarily perform offline and online learning in the same task, without considering the task generalization problem in offline-to-online adaptation. In real-world applications, it is common that we only have an offline dataset from a specific task while aiming for fast online-adaptation for several tasks. To address this problem, our work builds upon the investigation of successor representations for task generalization in online RL and extends the framework to incorporate offline-to-online learning. We demonstrate that the conventional paradigm using successor features cannot effectively utilize offline data and improve the performance for the new task by online fine-tuning. To mitigate this, we introduce a novel methodology that leverages offline data to acquire an ensemble of successor representations and subsequently constructs ensemble Q functions. This approach enables robust representation learning from datasets with different coverage and facilitates fast adaption of Q functions towards new tasks during the online fine-tuning *** empirical evaluations provide compelling evidence showcasing the superior performance of our method in generalizing to diverse or even unseen tasks.

关键词： offline reinforcement learning online fine-tuning task generalization successor representations ensembles

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Enhancing Strength-Ductility Synergy of CoCrNi-Based Medium-Entropy Alloy Through Coherent L1_(2)Nanoprecipitates and Grain Boundary Precipitates

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Acta Metallurgica Sinica(English Letters) 2024年第1期37卷 78-88页

作者： Leilei Li Kaikai Song Qingwei Gao Changshan Zhou Xiaoming Liu Yaocen Wang Xiaojun Bai Chongde Cao School of Physical Science and Technology Northwestern Polytechnical UniversityXi’an710016China Weihai research institute of Industrial Technology Shandong UniversityWeihai264209China research and Development institute of northwestern Polytechnical University in ShenzhenShenzhen518057China

The L1_(2)-strengthened Co_(34)Cr_(32)Ni_(27)Al_(4)Ti_(3)medium-entropy alloy(MEA)with precipitations of grain boundaries has been developed through selective laser melting(SLM)followed by cold rolling and annealing,exhibiting excellent strength-ductility *** as-printed alloy exhibits low yield strength(YS)of~384 MPa,ultimate tensile strength(UTS)of~453 MPa,and uniform elongation(UE)of 1.5%due to the existence of the SLM-induced *** cold rolling and annealing,the YS,UTS,and UE are significantly increased to~739 MPa,~1230 MPa,and~47%,*** enhancement primarily originates from the refined grain structure induced by cold rolling and *** presence of coherent sphericalγ'precipitates(L1_(2)phases)and Al/Ti-rich precipitates at the grain boundaries,coupled with increased lattice defects such as dislocations,stacking faults,and ultrafine deformation twins,further contribute to the property’s *** study highlights the potential of SLM in producing high-strength and ductile MEA with coherent L1_(2)nanoprecipitates,which can be further optimized through subsequent rolling and annealing *** findings offer valuable insights for the development of high-performance alloys for future engineering applications.

关键词： Medium-entropy alloy Selective laser melting Precipitation Strength Ductility

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Effects of dynamical spanwise retraction and stretch on flapping-wing forward flights

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Chinese Journal of Aeronautics 2024年第4期37卷 181-202页

作者： Kang LIU Bifeng SONG Ang CHEN Zhihe WANG Dong XUE Wenqing YANG School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China Intelligent Aircraft research Center Chengdu Technological UniversityChengdu 610031China research&Development institute of northwestern polytechnical university in shenzhen Shenzhen 518057China Harbin institute of Technology Shenzhen 518055China

Birds and bats retract and stretch their wings dynamically during each flap in level flights, implying intriguing mechanisms for the aerodynamic performance improvement of flapping wings. A numerical investigation into the aerodynamic effects of such bio-inspired concept in forward flights has been performed based on a three-dimensional wing in plunging motion and a twosection wing in flapping motion. The currently considered Reynolds number and Strouhal number are Re=1.5×10^(5) and St=0.3, respectively. During the research, the mean angle of attack is varied in relatively wide ranges to achieve lift-thrust interconversion for the wings. The conclusive results show that dynamical spanwise retraction and stretch has induced three absolutely desirable scenarios for the oscillating wings in forward flights, namely producing more lift and consuming less power for a given thrust generation, producing more thrust and consuming less power for a given lift generation, and producing more lift and more thrust while consuming less power. Furthermore,the morphing wings have alleviated periodical aerodynamic load fluctuations compared with the non-morphing baseline. The mechanism of the aerodynamic effects of the bionic morphing mode is analyzed with the aid of field visualization. The current article is the first to reveal the absolute advantages of the bionic spanwise morphing. Hopefully, it may help comprehend the behaviors of natural fliers and provide inspirations for performance enhancement of micro artificial flappingwing vehicles.

关键词： Flapping wing Morphing wing Bionic Aerodynamics Vortex Flight

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Reheat effect on the improvement in efficiency of the turbine driven by pulse detonation

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Defence Technology（防务技术） 2024年第1期31卷 200-210页

作者： Junyu Liu Zhiwu Wang Zixu Zhang Junlin Li Weifeng Qin Jingjing Huang School of Power and Energy Northwestern Polytechnical UniversityXi’an 710072China shenzhen research institute of northwestern polytechnical university Shenzhen 518057China Mechanical Engineering College Xi’an Shiyou UniversityXi’an 710065China

Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine *** that the flow losses are dissipated into the gas as heat energy,some of them can be recycled during the expansion process in subsequent stages by the reheat effect,which should be helpful to improve the detonationdriven turbine *** this into account,this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine,and a stoichiometric hydrogen-air mixture was *** improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage *** research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation,which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled,so that the efficiency of the two-stage turbine was *** a 95%confidence level,the efficiency improvement was stable at 4.5%—5.3%,demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.

关键词： Pulse detonation turbine engine Hydrogen detonation Turbine efficiency Reheat effect Multi-cycle detonation

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