Parametric study on smoothed particle hydrodynamics for accurate determination of drag coefficient for a circular cylinder

Simulations of two-dimensional (2D) flow past a circular cylinder with the smoothed particle hydrodynamics (SPH) method were conducted in order to accurately determine the drag coefficient. The fluid was modeled as a viscous liquid with weak compressibility. Boundary conditions, such as a no-slip solid wall, inflow and outflow, and periodic boundaries, were employed to resemble the physical problem. A sensitivity analysis, which has been rarely addressed in previous studies, was conducted on several SPH parameters. Hence, the effects of distinct parameters, such as the kernel choices and the domain dimensions, were investigated with the goal of obtaining highly accurate results. A range of Reynolds numbers (1–500) was simulated, and the results were compared with existing experimental data. It was observed that the domain dimensions and the resolution of SPH particles, in comparison to the obstacle size, affected the obtained drag coefficient significantly. Other parameters, such as the background pressure, influenced the transient condition, but did not influence the steady state at which the drag coefficient was determined.     

泥岩隧道光面爆破的技术参数研究及应用

针对泥岩隧道的特殊性,通过优化光面爆破的爆破参数,讨论泥岩隧道掘进的经济性、安全性。采用预埋振速传感器监测的方式,分析光面爆破对隧道周围岩体的扰动。现场光爆技术应用效果显著,隧道开挖轮廓线内基本未出现超欠挖现象,半孔率达86%以上,爆破进尺提升约15%,孔痕长度基本均匀分布一般都在孔长的66%以上;萨道夫斯基公式的系数K衰减明显、α基本稳定,光爆的振动速度和围岩扰动都得到了有效控制。     

CONTROL AND ESTIMATION FOR PERTURBED NONLINEAR PROCESSES WITH DEADTIME

Feedback linearization techniques are used to deal with the nonlinear controller designs which have attracted many researchers' attention in recent years. The approach has been applied successfully to solve a number of practical nonlinear control problems, but typically requires on-line full state measurement which is usually not the case in real chemical process industries. In this paper, we address the problem of synthesizing nonlinear state feedback controllers for time-delay nonlinear systems which are perturbed by disturbances. On-line estimation of the unmeasurable disturbances and unavailable state variables is introduced to facilitate the implementation of coordinate transformations and state feedback and prediction. Two kinds of dynamic compensators are then proposed to handle the process deadtime. Finally numerical simulations in a CSTR example demonstrate the promising performance of the overall nonlinear control structure in disturbance rejection.     

An integrated approach to hypersonic entry attitude control

This paper presents an integrated approach based on dynamic inversion(DI)and active disturbance rejection control(ADRC)to the entry attitude control of a generic hypersonic vehicle(GHV).DI is frstly used to cancel the nonlinearities of the GHV entry model to construct a basic attitude controller.To enhance the control performance and system robustness to inevitable disturbances,ADRC techniques,including the arranged transient process(ATP),nonlinear feedback(NF),and most importantly the extended state observer(ESO),are integrated with the basic DI controller.As one primary task,the stability and estimation error of the second-order nonlinear ESO are analyzed from a brand new perspective:the nonlinear ESO is treated as a specifc form of forced Li′enard system.Abundant qualitative properties of the Li′enard system are utilized to yield comprehensive theorems on nonlinear ESO solution behaviors,such as the boundedness,convergence,and existence of periodic solutions.Phase portraits of ESO estimation error dynamics are given to validate our analysis.At last,three groups of simulations,including comparative simulations with modeling errors,Monte Carlo runs with parametric uncertainties,and a six degrees-of-freedom reference entry trajectory tracking are executed,which demonstrate the superiority of the proposed integrated controller over the basic DI controller.     

A Discrete‐Time Global Quasi‐Sliding Mode Control Scheme with Bounded External Disturbance Rejection

A global quasi‐sliding mode control (GQSMC) scheme is introduced to ensure zigzag motion with a smaller bound than that offered by Gao's method and to provide disturbance rejection throughout the entire response in discrete time. The design of an augmented forcing function is followed by three conditions in discrete time extended from global sliding mode control (GSMC) in continuous time. Furthermore, we adopt a switching gain, which is auto‐tuned as a function of sliding surface s(k), such that chattering phenomena can be considerably alleviated during the steady‐state, significantly reducing switching control applied to the plant. The proposed GQSMC scheme can provide more advantages such as an even distribution of the control input throughout the entire response and an improvement in the accuracy and speed of the desired performance, guaranteeing a quasi‐sliding mode throughout the entire response. In addition, we also consider the input disturbance rejection according to the norm‐bounded exogenous signal. Results from both the simulation and the experiments are reported. The results further verify that we can use the global sliding surface to curtail reaching the phase stage.     

An Active Disturbance Rejection Approach to Leader‐Follower Controlled Formation

This article describes the design of a linearizing, observer‐based, robust dynamic feedback control scheme for output reference trajectory tracking tasks in a leader‐follower non‐holonomic car formation problem. The approach is based on the cars' kinematic models. A radical simplification in the form of a global ultra‐model is proposed on the follower's exact open loop position tracking error dynamics obtained via flatness considerations. This results in a system described by an additively disturbed set of two, second order integrators with non‐linear velocity dependent control input gain matrix. The unknown additive disturbances are modeled as absolutely uniformly bounded time signals which may be locally approximated by arbitrary elements of a sufficiently high degree family of Taylor polynomials. Linear high‐gain Luenberger observers of the generalized proportional integral (GPI) type may be readily designed. These observers include the self updating internal model of the unknown disturbance input vector components in the form of generic, instantaneous, time‐polynomial models. The proposed (GPI) observers, which are the dual counterpart of GPI controllers [17], achieve a simultaneous disturbance estimation and tracking error phase variables estimation. This on‐line gathered information is used to advantage on the follower's feedback controller thus allowing for a simple, yet efficient, disturbance and control input gain cancelation effort. The results are applied to have the follower track a time‐delayed version of the actual leader's trajectory. Experimental results are presented which illustrate the robustness and viability of the proposed approach.     

分布式多输入系统的自律鲁棒自适应分散控制

为了实现一类分布式多输入系统的分散鲁棒自适应控制, 基于状态扩张和反演干扰抑制控制, 提出一种自律鲁棒自适应分散控制的新方法. 结合直接反馈线性化和最优控制, 给出了自律最优鲁棒自适应分散控制的设计方法. 仿真结果表明, 所提出方法能够有效实现各子系统的自律鲁棒稳定、全系统整体鲁棒稳定和不确定参数自适应, 同时通过求解LMI, 具备了最优干扰抑制的功能.

     

改进LQR技术的飞翼式无人机控制算法研究

针对飞翼式布局无人机存在纵向操稳性能差和易受阵风干扰问题,采用一种指令跟踪增广LQR方法设计了飞翼式无人机纵向姿态控制律,该方法将系统的输出误差和外界恒值阵风干扰信号引入到性能指标函数中,使设计出来的控制器不仅能保证飞行姿态的无静差跟踪,而且能有效抑制外界的阵风干扰。考虑到系统的迎角变量不易检测,结合降维观测器得到了一种准指令跟踪增广LQR方法,该方法不仅具有良好的鲁棒性和跟踪性,而且便于工程实现。最后利用获得的控制律对ICE飞翼式无人机进行仿真实验和对比分析,结果表明,采用改进后的LQR方法设计的控制器不仅改善了飞翼式无人机纵向模态的飞行品质,同时与输出反馈线性二次型跟踪方法和LQG/LTR方法相比,具有更好的控制性能。     

无人直升机姿态通道模型预测控制

针对无人直升机姿态通道中存在的测量干扰与控制输入受限等问题,利用包含时变柔化因子的模型预测控制算法设计了一种姿态通道控制器。具体而言,首先对姿态通道的传递函数进行了等效变换,得到嵌入了积分环节的状态空间(SSEI)模型,并进一步建立了姿态通道的预测模型;然后综合分析了姿态通道系统在初始响应速度和减小测量干扰影响两个方面的要求,设计了含时变柔化因子的柔化轨迹;接着考虑到舵机的输出限制,分析了姿态通道的控制输入约束条件;最后基于上述三点内容,设计了滚动优化过程。论文还以无人直升机的偏航通道为例进行了飞行实验测试,结果表明该控制算法可明显地加快系统响应速度,减小模型不确定性与测量干扰等因素的影响,具有较好的工程应用价值。     

基于互相关定位法的干涉仪分析与仿真

首次提出用时域互相关法处理Sagnac/Mach-Zehnder分布式光纤传感系统的干涉输出信号, 对扰动进行检测和定位。首先对Sagnac/Mach-Zehnder分布式光纤传感系统进行了扰动检测和定位的理论分析, 推导出扰动引起的干涉输出信号的表达式, 利用Bessel函数展开, 确定了该系统的两路干涉输出满足时域互相关的特性。在此基础上进一步分析了两路干涉信号的表达式, 提出基频定位法和微分定位法两种时域互相关方法处理干涉信号, 确定扰动位置。对两种扰动定位方法进行了Matlab仿真, 并通过实验在多个扰动位置多次验证了两种方法的正确性。