A high resolution inversion method for fluid factor with dynamic dryrock V_(P)/V_(S) ratio squared

As an important indicator parameter of fluid identification,fluid factor has always been a concern for scholars.However,when predicting Russell fluid factor or effective pore-fluid bulk modulus,it is necessary to introduce a new rock skeleton parameter which is the dry-rock VP/VS ratio squared(DVRS).In the process of fluid factor calculation or inversion,the existing methods take this parameter as a static constant,which has been estimated in advance,and then apply it to the fluid factor calculation and inversion.The fluid identification analysis based on a portion of the Marmousi 2 model and numerical forward modeling test show that,taking the DVRS as a static constant will limit the identification ability of fluid factor and reduce the inversion accuracy.To solve the above problems,we proposed a new method to regard the DVRS as a dynamic variable varying with depth and lithology for the first time,then apply it to fluid factor calculation and inversion.Firstly,the exact Zoeppritz equations are rewritten into a new form containing the fluid factor and DVRS of upper and lower layers.Next,the new equations are applied to the four parameters simultaneous inversion based on the generalized nonlinear inversion(GNI)method.The testing results on a portion of the Marmousi 2 model and field data show that dynamic DVRS can significantly improve the fluid factor identification ability,effectively suppress illusion.Both synthetic and filed data tests also demonstrate that the GNI method based on Bayesian deterministic inversion(BDI)theory can successfully solve the above four parameter simultaneous inversion problem,and taking the dynamic DVRS as a target inversion parameter can effectively improve the inversion accuracy of fluid factor.All these results completely verified the feasibility and effectiveness of the proposed method.

An Improved Nonlinear Dynamic Inversion Method for Altitude and Attitude Control of Nano Quad-Rotors under Persistent Uncertainties

Nonlinear dynamic inversion(NDI)has been applied to the control law design of quad-rotors mainly thanks to its good robustness and simplicity of parameter tuning.However,the weakness of relying on accurate model greatly restrains its application on quad-rotors,especially nano quad-rotors(NQRs).NQRs are easy to be influenced by uncertainties such as model uncertainties(mainly from complicated aerodynamic interferences,strong coupling in roll-pitch-yaw channels and inaccurate aerodynamic prediction of rotors)and external uncertainties(mainly from winds or gusts),particularly persistent ones.Therefore,developing accurate model for altitude and attitude control of NQRs is difficult.To solve this problem,in this paper,an improved nonlinear dynamic inversion(INDI)method is developed,which can reject the above-mentioned uncertainties by estimating them and then counteracting in real time using linear extended state observer(LESO).Comparison with the traditional NDI(TNDI)method was carried out numerically,and the results show that,in coping with persistent uncertainties,the INDI-based method presents significant superiority.

NONLINEAR DYNAMIC INVERSION CONTROL WITH ADAPTIVE COMPENSATION FOR FLIGHT CONTROL SYSTEM

A type of nonlinear dynamic inversion control with adaptive compensation is proposed in order to overcome its over sensitivity to parameter uncertainty and disturbance for flight control system using nonlinear dynamic inversion. This control strategy is different from the general strategy of a nonlinear adaptive control by taking into consideration both parameter uncertainty and external disturbance, the two major uncertain forms in flight control. Finally, an analysis of the stabilily of this control structure is given.

Civil aircraft fault tolerant attitude tracking based on extended state observers and nonlinear dynamic inversion

For the problem of sensor faults and actuator faults in aircraft attitude control,this paper proposes a fault tolerant control(FTC)scheme based on extended state observer(ESO)and nonlinear dynamic inversion(NDI).First,two ESOs are designed to estimate sensor faults and actuator faults respectively.Second,the angular rate signal is reconstructed according to the estimation of sensor faults.Third,in angular rate loop,NDI is designed based on reconstruction of angular rate signals and estimation of actuator faults.The FTC scheme proposed in this paper is testified through numerical simulations.The results show that it is feasible and has good fault tolerant ability.

Trajectory Tracking of Quadrotor Aerial Robot Using Improved Dynamic Inversion Method

This paper presents trajectory tracking control works concerning quadrotor aerial robot with rigid cross structure. The quadrotor consists of four propellers which are two paired clockwise rotate and anticlockwise rotate. A nonlinear dynamic model of the quadrotor is provided, and a controller based on the improved dynamic inverse is synthesized for the purpose of stabilization and trajectory tracking. The proposed control strategy has been tested in simulation that can balance the deviation of model inaccuracy well.

Output Feedback for Stochastic Nonlinear Systems with Unmeasurable Inverse Dynamics

This paper considers a concrete stochastic nonlinear system with stochastic unmeasurable inverse dynamics. Motivated by the concept of integral input-to-state stability （iISS） in deterministic systems and stochastic input-to-state stability （SISS） in stochastic systems, a concept of stochastic integral input-to-state stability （SiISS） using Lyapunov functions is first introduced. A constructive strategy is proposed to design a dynamic output feedback control law, which drives the state to the origin almost surely while keeping all other closed-loop signals almost surely bounded. At last, a simulation is given to verify the effectiveness of the control law.

Dynamic mechanical behavior and nonlinear hyper-viscoelastic constitutive model of SiO_(2) particle-reinforced silicone rubber composite:experimental and numerical investigation

SiO_(2)-particle reinforced silicon rubber composite(SP-RSRC)is a widely utilized material that offers shock absorption protection to various engineering structures in impact environments.This paper presents a comprehensive investigation of the mechanical behavior of SP-RSRC under various strain rates,employing a combination of experimental,theoretical,and numerical analyses.Firstly,quasi-static and dynamic compression tests were performed on SP-RSRC utilizing a universal testing machine and split Hopkinson pressure bar(SHPB)apparatus.Nonlinear stress-strain relationships of SP-RSRC were obtained for strain rates ranging from 1×10^(−3) to 3065 s^(−1).The results indicated that the composite showed evident strain rate sensitivity,along with nonlinearity.Then,a nonlinear visco-hyperelastic constitutive model was developed,consisting of a hyperelastic component utilizing the 3rd-order Ogden energy function and a viscous component employing a rate-dependent relaxation time scheme.The model accurately characterized the dynamic mechanical response of SP-RSRC,effectively mitigating the challenge of calibrating an excessive number of material parameters inherent in conventional viscoelastic models.Furthermore,the simplified rubber material(SRM)model,integrated within the LS-DYNA software,was chosen to depict the mechanical properties of SP-RSRC in numerical simulations.The parameters of the SRM model were further calibrated based on the strain-stress relationships of SP-RSRC,as predicted by the developed nonlinear visco-hyperelastic constitutive model.Finally,an inverse ballistic experiment using a single-stage air gun was conducted for SP-RSRC.Numerical simulations of SHPB experiments and the inverse ballistic experiment were then performed,and the reliability of the calibrated SRM model was verified by comparing the results of experiments and numerical simulations.This study offers a valuable reference for the utilization of SP-RSRC in the realm of impact protection.

基于增量非线性动态逆的导弹解耦控制设计

针对导弹大迎角机动存在强耦合动力学特点,提出了一种基于增量非线性动态逆的解耦控制方法,将自动驾驶仪分为高带宽的快变角速率内回路和低带宽的慢变角回路控制,用部分逆近似求解的方法分别设计了增量形式的动态逆控制律对消不同的耦合项,实现控制解耦的目的。典型工况数字仿真结果表明,所设计的导弹增量非线性动态逆控制解耦律大大改善了强耦合动力学下的稳定控制性能。相比传统PID控制,它能够完全消除过载响应的低频振荡和超调量,同时还使得滚转角响应能够准确跟踪指令。

INVERSION OF A NONLINEAR DYNAMICAL MODEL FROM THE OBSERVATION

A technique for inversion of a nonlinear dynamical model from the observations has been developed, and examined by using the Lorenz system. The results show that the Lorenz system can be accurately inversed by using the observation data set. This technique will be broadly used in establishing the nonlinear dynamical model from an actual data set.

应对风切变的四旋翼轨迹跟踪几何控制方法

针对存在风切变环境的四旋翼轨迹跟踪问题,提出了结合增量非线性动态逆的几何控制方法。首先,建立了基于SO(3)群的风切变扰动四旋翼动力学模型,并建立风场模型,引入风切变效应。其次,利用四旋翼的微分平坦特性将轨迹跟踪问题转换为状态跟踪问题,并依据微分平坦特性推导参考高阶状态量实现前馈控制。在控制器设计部分,姿态控制采用几何控制,使姿态具有全局不存在奇异点的特性。对于风场扰动带来的阻力与气动力矩,使用增量非线性动态逆方法进行补偿,实现线加速度和角加速度的控制。最后,基于Simulink在多种风速场景中对不同航迹进行了仿真实验,仿真结果验证了所提方法相较传统方法在面对风切变干扰情况下的有效性。

基于终端滑模的F-16固定翼飞行器有限时间编队控制

以F-16固定翼飞行器为研究对象,采用终端滑模控制方法,实现了六自由度固定翼飞行器的有限时间编队控制。首先,根据奇异摄动理论,将固定翼飞行器十二阶微分运动方程按照响应速度快慢分为外环位置编队控制系统和内环姿态跟踪控制系统。外环应用有限时间稳定性理论和非线性滑模控制方法设计了分布式控制器,实现多固定翼飞行器系统的有限时间编队控制。然后,将外环分布式控制器产生的控制信号转换为内环单架固定翼飞行器的姿态跟踪参考信号,内环应用非线性动态逆(nonlinear dynamic inversion,NDI)控制和增量非线性动态逆(incremental nonlinear dynamic inversion,INDI)控制在可能存在执行器故障的情况下实现单架固定翼飞行器姿态的跟踪控制。最后,通过仿真实例验证了该控制方法的有效性。

多液压缸同步驱动系统DCAT-NDI控制研究

针对多缸同步电液伺服系统(MIMO系统)驱动性能易受执行器冗余和外部扰动等非线性因素影响的问题,建立了MIMO系统最简形式(四缸同步驱动系统)的动力学模型,并引入基于二次规划的动态控制理论DCAT和非线性动态逆控制策略NDI,提出了一种DCAT-NDI的多缸同步控制策略。该控制策略首先计算负载姿态期望的最优映射,实现了MIMO系统各液压缸位移期望输出的解耦;其次,根据跟踪位移误差与速度期望以及跟踪速度误差与加速度期望的相似性原理,引入位移频率带宽和速度频率带宽概念,构造各自通道的逆系统,从而求解各自通道的最优控制。仿真和实际结果表明,该文提出的控制策略比常规PID同步控制策略具有更好的同步性能和稳定性能。

低空风切变下基于NDI-PID的飞机进近控制律设计

针对飞机在进近过程中遭遇低空风切变后的轨迹控制问题,通过建立较真实的风切变工程化模型和飞机非线性数学模型,应用奇异摄动理论对飞机状态变量进行时标划分,采用非线性动态逆方法设计了快、慢状态子系统的控制律以及外回路制导系统的控制律;并引入PID控制,补偿由风切变和其他外界因素引起的飞机气动参数摄动带来的系统逆误差,从而消除系统稳态误差,实现对飞机进近轨迹的有效保持;最后进行了数值仿真验证,结果表明,采用动态逆与PID相结合的控制方法,能使系统具有较好的动态特性和鲁棒性,能有效抵抗一定强度的风切变干扰。

Survey on nonlinear reconfigurable flight control

An overview on nonlinear reconfigurable flight control approaches that have been demonstrated in flight-test or highfidelity simulation is presented. Various approaches for reconfigurable flight control systems are considered, including nonlinear dynamic inversion, parameter identification and neural network technologies, backstepping and model predictive control approaches. The recent research work, flight tests, and potential strength and weakness of each approach are discussed objectively in order to give readers and researchers some reference. Finally, possible future directions and open problems in this area are addressed.

Output regulation of nonaffine nonlinear systems using singular perturbation theory

A control synthesis method for output regulation based on singular perturbation theory combined with inverting design is considered for a class of nonaffine nonlinear systems. The resulting control signal is defined as a solution to ＂fast＂ dynamics which inverts a series error model, whose state is exponentially stable. It is shown that, under sufficient conditions being consistent with the assumptions of singular perturbation theory, this problem is solvable with （ε） tracking error if and only if a set of first-order nonlinear partial differential equations are solvable. The control law can be easily constructed and the simulations show the feasibility and effectiveness of the controller.

Nonlinear Accelerator Beam Transport Operator

This paper deals with the theory of nonlinear accelerator beam transport op-erator.For nonautonomous accelerator dynamics,a theorem of finding the inversenonlinear beam transport operator is developed.Several concrete examples are workedout in detail to show the practical applications of this theory.

基于动态逆控制的高超声速飞行器飞/发一体化控制方法研究

为了减小高超声速飞行器飞/发耦合效应对自身的影响,开展了高超声速飞行器飞/发一体化控制研究。建立面向控制的高超声速飞行器飞/发一体化数学模型。分别采用非线性动态逆控制与增量非线性动态逆控制方法,设计了姿态慢变外回路、角速率快变内回路控制算法。基于包含高超声速飞行器飞/发耦合特性的在线本体模型,以操纵交联的形式设计了高超声速飞行器姿态与发动机的耦合控制方案。在非线性动态逆控制器中引入参考模型、误差控制、在线估计等模块,保证了高超声速飞行器的飞行品质和鲁棒性要求。仿真实验结果表明,采用了非线性动态逆控制设计的飞/发耦合控制方案达到了预期的控制性能。

四旋翼无人机非线性轨迹跟踪控制

针对四旋翼轨迹跟踪在高频情况下易出现系统不稳定的问题,设计一种基于动态逆技术(Dynamic Inverse,DI)的轨迹跟踪方法。由于四旋翼是典型的欠驱动系统,本文考虑双闭环设计,通过各种数值实验验证在低频率与高频率情况下控制器的追迹性能,并与PID控制器进行比较。仿真结果表明,频率为0.6πrad/s时本文方法的位置跟踪均方误差比PID方法的误差小0.0514 m,当频率大于1.15πrad/s时PID控制方法使得系统出现不稳定,而本文方法仍可以完成较好的轨迹跟踪。

Practical compensation for nonlinear dynamic thrust measurement system

The real dynamic thrust measurement system usually tends to be nonlinear due to the complex characteristics of the rig, pipes connection, etc. For a real dynamic measuring system, the nonlinearity must be eliminated by some adequate methods. In this paper, a nonlinear model of dynamic thrust measurement system is established by using radial basis function neural network （RBF-NN）, where a novel multi-step force generator is designed to stimulate the nonlinearity of the system, and a practical compensation method for the measurement system using left inverse model is proposed. Left inverse model can be considered as a perfect dynamic compensation of the dynamic thrust measurement system, and in practice, it can be approximated by RBF-NN based on least mean square （LMS） algorithms. Different weights are set for producing the multi-step force, which is the ideal input signal of the nonlinear dynamic thrust measurement system. The validity of the compensation method depends on the engine＇s performance and the tolerance error 0.5%, which is commonly demanded in engineering. Results from simulations and experiments show that the practical compensation using left inverse model based on RBF-NN in dynamic thrust measuring system can yield high tracking accuracy than the conventional methods.

基于INDI的倾转旋翼无人机过渡模式控制方案

针对倾转旋翼无人机(TRUAV)过渡模式控制问题,提出了一种基于增量非线性动态逆(INDI)的控制方案。首先,基于四轴倾转旋翼无人机动力学特性,建立了面向控制的纵向运动模型;随后,研究了虚拟控制量与控制量分配方法,在此基础上设计了倾转旋翼无人机过渡模式自适应倾转方案;然后,基于增量非线性动态逆控制理论,分别设计了高度、速度和姿态回路过渡模式下内/外环控制器,以及旋翼和舵面控制量混合策略。最后,仿真实验验证了基于虚拟控制量分配的自适应倾转方案的有效性,以及高度、速度和姿态回路控制器的鲁棒性。