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Intelligent feedforward gust alleviation based on neural network

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Chinese Journal of Aeronautics 2024年第3期37卷 116-132页

作者： Yitao ZHOU zhigang wu Chao YANG School of Aeronautic Science and Engineering Beihang UniversityBeijing 100191China

This paper proposes a neural network-based intelligent feedforward gust alleviation framework,which includes a neural network identification model and a neural network controller.A neural network training dataset is formed by collecting flight data and the gust data encountered during the aircraft flight.A neural network identification model is first trained to accurately predict the aircraft’s ***,based on the output of the identification model and the collected flight data,the parameters of the time-delay neural network controller are obtained through a learning *** simulation results show that the designed intelligent controller has good gust alleviation effects for both continuous turbulence excitation and discrete gust *** example,when the aircraft is 40000 kg and the flight speed is 0.81Ma,the controller achieves a 67.82%reduction in wingtip acceleration and a 35.90%reduction in center of mass acceleration under continuous turbulence *** considering the measurement uncertainties,such as noise existing in the collected data,the trained controller can still achieve an acceptable gust alleviation ***,considering a flight in which the aircraft mass is constantly changing,the intelligent controller,which continuously learns from new flight data,maintains a good gust alleviation effect throughout the flight.

关键词： Gust alleviation Intelligent control Feedforward control Neural networks Time-varying aircraft

Aeroelastic dynamic response of elastic aircraft with consideration of two-dimensional discrete gust excitation

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Chinese Journal of Aeronautics 2020年第4期33卷 1228-1241页

作者： Yang YANG Chao YANG zhigang wu School of Aeronautic Science and Engineering Beihang UniversityBeijing 100083China

Design loads generally require a one-dimensional discrete gust profile without consideration of the spanwise effect,and this profile cannot represent the true gust field *** a high aspect ratio aircraft,two-dimensional gusts may cause critical load conditions,and approaches for calculating dynamic responses under two-dimensional discrete gust excitation are rarely *** this paper,a spanwise non-uniform vertical discrete gust field is established based on a onedimensional‘1-cos’gust profile in reference to a DARPA proposal,while frequency and hybrid approaches to the dynamic response analysis of flexible aircraft under this two-dimensional gust excitation are *** techniques have been applied to a high aspect ratio aircraft to assess the different response characteristics with a comparison between one-dimensional and two-dimensional discrete gust field *** results show that the two-dimensional discrete gust model produces a higher bending moment than that of the one-dimensional ***,the critical load conditions that are derived from the two-dimensional discrete gust for high aspect ratio aircraft should be seriously *** to the analysis,an active control scheme to alleviate the bending loads caused by the two-dimensional gust is designed,and alleviation effects in different gust conditions are compared.

关键词： Aeroservoelastic Discrete gust Gust response Gust response alleviation Two-dimensional gust

Active flutter suppression of nonlinear fin-actuator system via inverse system and immersion and invariance method

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Chinese Journal of Aeronautics 2024年第4期37卷 343-362页

作者： Jin LU zhigang wu Chao YANG Chinese Aeronautical Establishment Beijing 100029China School of Aeronautic Science and Engineering Beihang UniversityBeijing 100191China

Structural nonlinearities such as freeplay will affect the stability and even flight safety of the fin-actuator *** is a lack of a practical method for designing Active Flutter Suppression (AFS) control laws for nonlinear fin-actuator systems.A design method for the AFS controller of the nonlinear all-movable fin-electromechanical actuator system is established by combining the inverse system and the Immersion and Invariance (I&I) ***,the composite control law combining the inverse system principle and internal model control is used to offset the nonlinearity and dynamics of the actuator,so that its driving torque can follow the ideal ***,the ideal torque of the actuator is designed employing the I&I *** unfavorable oscillation of the fin is suppressed by making the output torque of the actuator track the ideal *** simulation results reveal that the proposed AFS method can increase the flutter speed of the nonlinear finactuator system with freeplay,and a set of controller parameters is also applicable for wider freeplay within a certain *** power required for the actuator does not exceed the power that can be provided by the commonly used aviation *** method can also resist a certain level of noise and external disturbance.

关键词： Aeroelasticity Active flutter suppression Fin-actuator system Freeplay Inverse system Immersion and invariance

Space-time estimates of the 3D bipolar compressible Navier-Stokes-Poisson system with unequal viscosities

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Science China Mathematics 2024年第5期67卷 1059-1084页

作者： zhigang wu Weike Wang Department of Mathematics Donghua UniversityShanghai 201620China School of Mathematical Sciences Shanghai Jiao Tong UniversityShanghai 200240China Shanghai Frontier Science Center of Modern Analysis(CMA-Shanghai) Shanghai Jiao Tong UniversityShanghai 200240China

The space-time behavior for the Cauchy problem of the 3D compressible bipolar Navier-Stokes-Poisson(BNSP)system with unequal viscosities is *** space-time estimate of the electric field▽φ=▽(-△)^(-1)(n-Zρ)is the most important in deducing generalized Huygens’principle for the BNSP system and it requires proving that the space-time estimate of n-Zρonly contains the diffusion wave due to the singularity of the operator▽(-△)^(-1).A suitable linear combination of unknowns reformulating the original system into two small subsystems for the special case(with equal viscosities)in wu and Wang(2017)is crucial for both linear analysis and nonlinear estimates,especially for the space-time estimate of▽φ.However,the benefits from this reformulation will no longer exist in general ***,we study an 8×8 Green’s matrix *** importantly,each entry in Green’s matrix contains wave operators in the low-frequency part,which will generally produce Huygens’wave;as a result,one cannot achieve the space-time estimate of n-Zρthat only contains the diffusion wave as *** overcome this difficulty by taking a more detailed spectral analysis and developing new estimates arising from subtle cancellations in Green’s function.

关键词： Green's function bipolar Navier-Stokes-Poisson system unequal viscosities

Large time behavior and pointwise estimates for compressible Euler equations with damping

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Science China Mathematics 2015年第7期58卷 1397-1414页

作者： wu zhigang WANG WeiKe Department of Applied Mathematics Donghua University Department of Mathematics Shanghai Jiao Tong University

The Cauchy problem of the compressible Euler equations with damping in multi-dimensions is considered when the initial perturbation in H3-norm is small. First, by using two new energy functionals together with the Green's function and iteration method, we improve the L2-decay rate in Tan and Wang(2013)and Tan and wu(2012)when(ρ0-ˉρ,m)˙B-s1,∞×˙B-s+11,∞with s∈[0,2]is *** particular,it holds that the density converges to its equilibrium state at the rate(1+t)-34-s2 in L2-norm and the momentum decays at the rate(1+t)-54-s2 in ***,under a weaker and more general condition on the initial data,we show that the density and the momentum have different pointwise estimates in dimension d with d 3on both space variable x and time variable t as|Dαx(ρ-ˉρ)|C(1+t)-d2-|α|2(1+|x|21+t)-rwith r>d2and|Dαxm|C(1+t)-d2-|α|+12(1+|x|21+t)-d2 by a more elaborate analysis on the Green’s *** results improve those in Wang and Yang(2001),where the density and the velocity(the momentum)have the same pointwise estimates.

关键词： Green's function energy functional pointwise estimates

Emergent symmetry at superradiance transition of a Bose condensate in two crossed beam cavities

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Science Bulletin 2018年第9期63卷 542-547页

作者： zhigang wu Yu Chen Hui Zhai Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Shenzhen 518000 China Institute for Advanced Study Tsinghua University Beijing 100084 China Department of Physics Capital Normal University Beijing 100048 China Collaborative Innovation Center of Quantum Matter Beijing 100084 China

Recently an experiment on superradiant transition of a Bose condensate in two crossed beam cavities has been reported by Leonard et al. in Nature 543, 87 （2017）. The surprise is they find that across the superradiant transition, the cavity light can be emitted in any superposition of these two cavity modes. This indicates an additional U（1） symmetry that does not exist in the full Hamiltonian. In this paper we show that this symmetry is an emergent symmetry in the vicinity of the phase transition. We identify all the necessary conditions that are required for this emergent U（I ） symmetry and show that this experiment is a special case that satisfies these conditions. We further show that the superradiant transition in this system can also be driven to a first order one when the system is tuned away from the point having the emergent svmmetrv.

关键词： Bose-Einstein condensate Emergent symmetry Superradiance transition Cavity

Dynamic stiffness testing-based flutter analysis of a fin with an actuator

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Chinese Journal of Aeronautics 2015年第5期28卷 1400-1407页

作者： Zhang Renjia wu zhigang Yang Chao School of Aeronautic Science and Engineering Beihang University

Engineering-oriented modeling and synthesized modeling of the fin-actuator system of a missile fin are introduced, including mathematical modeling of the fin, motor and multi-stage gear reducer. The fin-actuator model is verified using dynamic stiffness testing. Good agreement is achieved between the test and theoretical results. The parameter-variable analysis indicates that the inertia of the motor rotor, reduction ratio of the reducer, connection stiffness and damping between the actuator and fin shaft have significant impacts on the dynamic stiffness characteristics. In flutter analysis, test data are directly used in the frequency domain method and indirectly used in the time domain method through the updated fin-actuator model. The two methods play different roles in engineering applications but are of equal importance. The results indicate that dynamic stiffness and constant stiffness treatments may lead to completely different flutter characteristics. Attention should be paid to the design of the fin-actuator system of a missile.

关键词： Actuator Aeroelasticity Dynamic stiffness Flutter Ground vibration test Structural dynamics

Structural Nonlinear Flutter Characteristics Analysis for an Actuator-fin System with Dynamic Stiffness

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Chinese Journal of Aeronautics 2011年第5期24卷 590-599页

作者： YANG Ning wu zhigang YANG Chao School of Aeronautic Science and Engineering Beihang University Beijing 100191 China

The flutter characteristics of an actuator-fin system are investigated with structural nonlinearity and dynamic stiffness of the electric motor. The component mode substitution method is used to establish the nonlinear governing equations in time domain and frequency domain based on the fundamental dynamic equations of the electric motor and decelerator. The existing describing function method and a proposed iterative method are used to obtain the flutter characteristics containing preload freeplay nonlinearity when the control command is zero. A comparison between the results of frequency domain and those of time domain is studied. Simulations are carried out when the control command is not zero and further analysis is conducted when the freeplay angle is changed. The results show that structural nonlinearity and dynamic stiffness have a significant influence on the flutter characteristics. Limit cycle oscillations （LCOs） are observed within linear flutter boundary. The response of the actuator-fin system is related to the initial disturbance. In the nonlinear condition, the amplitude of the control command has an influence on the flutter characteristics.

关键词： aeroelasticity flutter actuators dynamic stiffness structural nonlinearity component mode substitution method describing functions

Aeroelastic scaling laws for gust load alleviation control system

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Chinese Journal of Aeronautics 2016年第1期29卷 76-90页

作者： Tang Bo wu zhigang Yang Chao School of Aeronautic Science and Engineering Beihang University

Gust load alleviation （GLA） tests are widely conducted to study the effectiveness of the control laws and methods. The physical parameters of models in these tests are aeroelastic scaled, while the scaling of GLA control system is always unreached. This paper concentrates on studying the scaling laws of GLA control system. Through theoretical demonstration, the scaling criterion of a classical PID control system has been come up and a scaling methodology is provided and veri- fied. By adopting the scaling laws in this paper, gust response of the scaled model could be directly related to the full-scale aircraft theoretically under both open-loop and closed-loop conditions. Also, the influences of different scaling choices of an important non-dimensional parameter, the Froude number, have been studied in this paper. Furthermore for practical application, a compen- sating method is given when the theoretical scaled actuators or sensors cannot be obtained. Also, the scaling laws of some non-linear elements in control system such as the rate and amplitude sat- urations in actuator have been studied and examined by a numerical simulation.

关键词： Actuator Aeroelasticity Control Systems Froude number Gust loads alleviation Scaling laws