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Effect of wing morphing on stability and energy harvesting in albatross dynamic soaring

Chinese Journal of Aeronautics 2024年第11期37卷 317-334页

作者： Wei WANG Weigang AN Bifeng SONG School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China National Key Laboratory of Aircraft Configuration Design Xi’an 710072China

Dynamic soaring,which harvests energy from the wind,can enhance Unmanned Aerial Vehicles'(UAVs')range and ***,energy harvesting efficiency issues hinder UAV applications,which can be addressed by wing ***,this study investigates the influence of albatross wing morphing during dynamic *** constructing a parametric model,the shape of the albatross wing can be modeled and achieve morphing based on *** the video data,this paper summarizes the typical wing morphing patterns of the albatross and notices that changes primarily occur during the leeward descent *** paper first analyzes the aerodynamic performance of different wing morphing patterns and finds that the drag coefficient can be reduced by 7.75%with a suitable morphing *** paper also explores the drag coefficient reduction mechanism and finds that downwash airflow decreases by 30.32%after wingtip ***,the lift-to-drag ratio shows minimal variation under different morphing patterns,within 2%.From the stability perspective,this study finds that the neutral point position changes after *** maximum longitudinal static margin change is 4.9%,enhancing longitudinal stability by increasing the restorative moment *** lateral neutral point is 4.87%closer to the center of gravity,decreasing the roll and yaw *** can be observed that wingtip anhedral significantly increases the stability of the ***,a flight simulation is carried out to study the morphing influence on trajectory and energy *** results show that maximum energy gained is improved by 47.99%,and endurance is increased by 13.05%.The results also indicate that the effects of wing morphing are global rather than limited to the phase of morphing ***,based on the results,this paper proposes wing morphing regularity about the wingtip for *** bends downward can significantly increase the UAVs'stability and reduce drag,but the

关键词： Dynamic soaring Wing morphing Aerodynamics Stability Energy harvesting

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Learning Bayesian networks by constrained Bayesian estimation

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Journal of Systems Engineering and Electronics 2019年第3期30卷 511-524页

作者： GAO Xiaoguang YANG Yu GUO Zhigao School of Electronics and Information Northwestern Polytechnical University

Bayesian networks (BNs) have become increasingly popular in recent years due to their wide-ranging applications in modeling uncertain knowledge. An essential problem about discrete BNs is learning conditional probability table (CPT) parameters. If training data are sparse, purely data-driven methods often fail to learn accurate parameters. Then, expert judgments can be introduced to overcome this challenge. Parameter constraints deduced from expert judgments can cause parameter estimates to be consistent with domain knowledge. In addition, Dirichlet priors contain information that helps improve learning accuracy. This paper proposes a constrained Bayesian estimation approach to learn CPTs by incorporating constraints and Dirichlet priors. First, a posterior distribution of BN parameters is developed over a restricted parameter space based on training data and Dirichlet priors. Then, the expectation of the posterior distribution is taken as a parameter estimation. As it is difficult to directly compute the expectation for a continuous distribution with an irregular feasible domain, we apply the Monte Carlo method to approximate it. In the experiments on learning standard BNs, the proposed method outperforms competing methods. It suggests that the proposed method can facilitate solving real-world problems. Additionally, a case study of Wine data demonstrates that the proposed method achieves the highest classification accuracy.

关键词： Bayesian networks (BNs) parameter learning constraints sparse data

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Logit prototype learning with active multimodal representation for robust open-set recognition

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Science China(Information Sciences) 2024年第6期67卷 297-312页

作者： Yimin FU Zhunga LIU Zicheng WANG School of Automation Northwestern Polytechnical University

Robust open-set recognition(OSR) performance has become a prerequisite for pattern recognition systems in real-world applications. However, the existing OSR methods are primarily implemented on the basis of single-modal perception, and their performance is limited when single-modal data fail to provide sufficient descriptions of the objects. Although multimodal data can provide more comprehensive information than single-modal data, the learning of decision boundaries can be affected by the feature representation gap between different modalities. To effectively integrate multimodal data for robust OSR performance, we propose logit prototype learning(LPL) with active multimodal representation. In LPL, the input multimodal data are transformed into the logit space, enabling a direct exploration of intermodal correlations without the impact of scale inconsistency. Then, the fusion weights of each modality are determined using an entropybased uncertainty estimation method. This approach realizes adaptive adjustment of the fusion strategy to provide comprehensive descriptions in the presence of external disturbances. Moreover, the single-modal and multimodal representations are jointly optimized interactively to learn discriminative decision ***, a stepwise recognition rule is employed to reduce the misclassification risk and facilitate the distinction between known and unknown classes. Extensive experiments on three multimodal datasets have been done to demonstrate the effectiveness of the proposed method.

关键词： logit prototype learning multimodal perception open-set recognition uncertainty estimation

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Endless recrystallization of high-entropy alloys at high temperature

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Journal of Materials Science & Technology 2022年第33期128卷 71-81页

作者： Qingfeng Wu Zhijun Wang Feng He Zhongsheng Yang Junjie Li Jincheng Wang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China

In traditional physical metallurgy,once recrystallization occurs,it will proceed to 100%along with time even at relatively low temperatures,resulting in the limited thermal stability of partially recrystallized ***,we proposed the strategy of achieving the endless recrystallization state at high temperature(~0.6T_(m))in high entropy alloys for the first *** partially recrystallized microstructures remained stable after annealing at 700℃ for 1440 h toward endless recrystallization with kinetics *** from the ultra-thermostable heterostructures,the alloy exhibited excellent mechanical properties of~1.6 GPa tensile strength at room temperature and~1.1 GPa tensile strength at 600°C even after exposure at 700℃ for 720 *** kinetics of recovery,recrystallization,grain growth,and precipitate coarsening were quantitatively analyzed to uncover the mechanisms of endless *** results revealed that the stable state of 50%recrystallization at 700℃ can be attributed to the precipitates inhibited recrystallization and the continued recovery decreased stored energy in the non-recrystallized ***,the grain size was stable in the recrystallized regions due to the strong pinning effect of the intergranular precipitates with slow coarsening *** findings created a brand-new state of endless recrystallization with the combination of recovery and recrystallization,which can significantly broaden the service temperature range of heterogeneous materials.

关键词： Endless recrystallization High-entropy alloy Partial recrystallization Thermal stability High-temperature mechanical properties

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Complex response analysis of a non-smooth oscillator under harmonic and random excitations

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Applied Mathematics and Mechanics(English Edition) 2021年第5期42卷 641-648页

作者： Shichao MA Xin NING Liang WANG Wantao JIA Wei XU School of Astronautics Northwestern Polytechnical UniversityXi’an 710072China National Key Laboratory of Aerospace Flight Dynamics Xi’an 710072China School of Mathematics and Statistics Northwestern Polytechnical UniversityXi’an 710129China

It is well-known that practical vibro-impact systems are often influenced by random perturbations and external excitation forces,making it challenging to carry out the research of this category of complex systems with non-smooth *** address this problem,by adequately utilizing the stochastic response analysis approach and performing the stochastic response for the considered non-smooth system with the external excitation force and white noise excitation,a modified conducting process has *** the multiple nonlinear parameters,the non-smooth parameters,and the external excitation frequency into consideration,the steady-state stochastic P-bifurcation phenomena of an elastic impact oscillator are *** can be found that the system parameters can make the system stability topology *** effectiveness of the proposed method is verified and demonstrated by the Monte Carlo(MC)***,the conclusions show that the process can be applied to stochastic non-autonomous and non-smooth systems.

关键词： non-autonomous system non-smooth system random excitation

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Control of epileptic activities in a cortex network of multiple coupled neural populations under electromagnetic induction

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Applied Mathematics and Mechanics(English Edition) 2023年第3期44卷 499-514页

作者： Zhongkui SUN Yuanyuan LIU Xiaoli YANG Wei XU School of Mathematics and Statistics Northwestern Polytechnical UniversityXi’an 710129China School of Mathematics and Statistics Shaanxi Normal UniversityXi’an 710062China

Epilepsy is believed to be associated with the abnormal synchronous neuronal activity in the brain,which results from large groups or circuits of *** this paper,we choose to focus on the temporal lobe epilepsy,and establish a cortex network of multiple coupled neural populations to explore the epileptic activities under electromagnetic *** demonstrate that the epileptic activities can be controlled and modulated by electromagnetic induction and coupling among *** certain regions,these two types of control are observed to show exactly reverse *** results show that the strong electromagnetic induction is conducive to eliminating the epileptic *** coupling among regions has a conduction effect that the previous normal background activity of the region gives way to the epileptic discharge,owing to coupling with spike wave discharge ***,these results highlight the role of electromagnetic induction and coupling among the regions in controlling and modulating epileptic activities,and might provide novel insights into the treatments of epilepsy.

关键词： epilepsy electromagnetic induction multiple coupled neural population dynamical transition

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Variational Bayesian Kalman filter using natural gradient

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Chinese Journal of Aeronautics 2022年第5期35卷 1-10页

作者： Yumei HU Xuezhi WANG Quan PAN Zhentao HU Bill MORAN School of Automation Northwestern Polytechnical UniversityXi’an 710072China The Key Laboratory of Information Fusion Technology Ministry of EducationXi’an 710072China Department of Electrical and Electronic Engineering The University of MelbourneMelbourneVIC 3010Australia School of Engineering RMIT UniversityMelbourneVIC 3000Australia School of Computer and Information Engineering Henan UniversityKaifeng 475001China

We propose a technique based on the natural gradient method for variational lower bound maximization for a variational Bayesian Kalman *** natural gradient approach is applied to the Kullback-Leibler divergence between the parameterized variational distribution and the posterior density of *** a Gaussian assumption for the parametrized variational distribution,we obtain a closed-form iterative procedure for the Kullback-Leibler divergence minimization,producing estimates of the variational hyper-parameters of state estimation and the associated error *** results in both a Doppler radar tracking scenario and a bearing-only tracking scenario are presented,showing that the proposed natural gradient method outperforms existing methods which are based on other linearization techniques in terms of tracking accuracy.

关键词： Kullback-Leibler divergence Natural gradient Nonlinear Kalman filter Target tracking Variational Bayesian optimization

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Multiplicative Lévy noise-induced transitions in gene expression

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Science China(Technological Sciences) 2022年第8期65卷 1700-1709页

作者： SONG Yi XU Wei NIU LiZhi Department of Applied Mathematics Northwestern Polytechnical UniversityXi’an 710129China

Gene expression is intrinsically noisy. Experimental studies have shown that random fluctuations are large bursts and heavytailed distributions. Therefore, this study aims to consider transition dynamics in a gene transcriptional regulatory system via the mean first exit time(MFET) and first escape probability(FEP), when the degradation rate is under multiplicative non-Gaussian Lévy fluctuations in the sense of It? and Marcus forms. We find that, in the Marcus form case, the FEP corresponding to different stability index and noise intensity has an intersection point, whereas in the It? form case, the turning point only occurs at stability index. Increasing the initial CI concentration is helpful for improving the likelihood of transcription in both cases. Our results also imply that larger jumps of Lévy noise and smaller noise intensity can shorten the time of state transition to boost protein production.

关键词： gene expression transition dynamics multiplicative Lévy noise It?and Marcus integral

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Improved mechanical properties in titanium matrix composites reinforced with quasi-continuously networked graphene nanosheets and in-situ formed carbides

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Journal of Materials Science & Technology 2022年第1期96卷 85-93页

作者： Q.Yan B.Chen L.Cao K.Y.Liu S.Li L.Jia K.Kondoh J.S.Li State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China School of Materials Science and Engineering Xi’an University of TechnologyXi’an 710048China Joining and Welding Research Institution Osaka University11-1 MihogaokaIbarakiOsaka 567-0047Japan

In order to construct quasi-continuously networked reinforcement in titanium(Ti)matrix composites,in this study,Ti-6 Al-4 V spherical powders were uniformly coated with a graphene nanosheet(GNS)layer by high energy ball milling and then consolidated by spark plasma *** showed that the GNS layer on the powder surface inhibited continuous metallurgy bonding between powders during sintering,which led to the formation of quasi-networked hybrid reinforcement structure consisting of insitu Ti C and remained *** networked GNSs/Ti64 composite possessed noticeably higher tensile strength but similar ductility to the Ti64 alloy,leading to both better tensile strength and ductility than the GNSs/Ti composite with randomly dispersed GNSs and Ti *** formation mechanism and the fracture mechanism of the networked hybrid reinforcement were *** results provided a method to fabricate Ti matrix composites with high strength and good ductility.

关键词： Titanium matrix composites(TMCs) Graphene Network structure Strength Ductility

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Experimental investigation on the yield behavior of metal foam under shear-compression combined loading

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Science China(Technological Sciences) 2021年第7期64卷 1412-1422页

作者： LUO Geng XUE Pu LI YuLong School of Automobile Chang’an UniversityXi’an710064China School of Aeronautics Northwestern Polytechnical UniversityXi’an710072China Joint International Research Laboratory of Impact Dynamics and its Engineering Applications Northwestern Polytechnical UniversityXi’an710072China

Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and quasi-static shear-compression combined loadings is investigated in this study. First, quasi-static and dynamic compression-shear combined tests at different loading angles are conducted using a universal testing machine and a rotatable Hopkinson bar system, respectively. Shear deformation reduces the plateau stress as the loading angle increases. Subsequently, the yield modes of the metal foam under combined loadings are investigated. Only one yield band occurs under a combined loading with large loading angles(mode I),whereas several yield bands occur under a combined loading with small loading angles(mode II). Finally, the yield surface plot of metal foam indicates significant enhancement in terms of normal stress and shear stress under dynamic loading. Quasi-static and dynamic phenomenological yield criteria for a shear-normal stress space are established to provide a brief and precise prediction of the behavior of metal foam under quasi-static and dynamic combined loadings.

关键词： metal foam yield behavior shear-compression combined loading yield mode yield criterion

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