柔性梁受迫振动时滞变结构控制的试验研究

时滞反馈控制是一种利用时滞进行系统控制的策略,目前对该控制策略的研究多是在理论上进行探讨,少有试验研究报道. 以受简谐激励的柔性悬臂梁为对象,开展时滞反馈控制的试验研究,给出了一个多时滞控制律的设计方法. 首先给出悬臂梁系统含有时滞项的控制模态状态方程; 然后对方程进行离散化和一种特殊的状态变量增广,得到形式上不含有时滞项的标准差分方程; 最后使用离散变结构控制的方法设计控制律. 试验中采用压电片作为作动器和外界激励,应变片作为传感器,分别考虑单时滞和双时滞的情况,通过试验验证了时滞反馈控制的可行性和有效性.关键词:柔性悬臂梁;变结构控制;时滞;实验      

Stabilization control for offshore steel jacket platforms with actuator time-delays

This paper is concerned with the stabilization control for the offshore steel jacket platforms subject to wave-induced force. Two state feedback stabilization control schemes are proposed to reduce the vibration amplitudes of the systems. One scheme is that for the systems without actuator time-delay, a state feedback controller is designed. Compared with the nonlinear controller, both the control force and the vibration amplitudes of the systems under the state feedback controller are much reduced; and compared with the dynamic output feedback controller and the integral sliding mode controller, the required control force under the state feedback controller are significantly reduced. The other scheme is that based on the integral inequality approach, a delay-dependent state feedback controller, which can be solved by using the cone complementarity algorithm, is developed to control the systems with actuator time-delays. Compared with the state feedback controller, the delay-dependent state feedback controller is less conservative with actuator time-delays. In addition, it is capable of improving the control performance of the offshore platforms significantly, which are illustrated by simulation results.     

框架结构主动控制最优时滞研究

在结构振动主动控制中,时滞的大小对结构控制能量和响应均产生影响。在允许时滞的范围内,把结构控制能量和响应作为目标函数,数值仿真发现目标函数随着时滞的变化呈现曲线状态,这说明存在最优时滞。在目标函数处理方面,考虑到控制能量和响应数量级不一致,本文采用了无量纲化处理。同时,考虑到地震波的随机性,本文还推导了含控制力的改进的随机Newmark方法。最后给出了一个计算实例。实例表明本文所提出的方法是有效的。     

A criterion of robustness intelligent nonlinear control for multiple time-delay systems based on fuzzy Lyapunov methods

A control system with state feedback controllers, in which the fuzzy Lyapunov approach is developed for the stability criterion, is studied. The proposed intelligent design provides a systematic and effective framework for the control systems. The global nonlinear controller is constructed based on T–S (Takagi–Sugeno) fuzzy controller design techniques, blending all such local state feedback controllers. Based on this design, the stability conditions of a multiple time-delay system are derived in terms of the fuzzy Lyapunov theory. The effectiveness and the feasibility of the proposed controller design method are demonstrated through numerical simulations.     

Pure delayed non-fragile control for offshore steel jacket platforms subject to non-linear self-excited wave force

This paper is concerned with pure delayed non-fragile control for an offshore steel jacket platform subject to non-linear self-excited wave force. By purposefully introducing a proper time-delay into control channel, a pure delayed non-fragile controller (DNFC) is proposed to improve performance of the offshore steel jacket platform. The positive effects of time-delays on non-fragile stabilization control for the system are investigated. It is shown through simulation results that (i) the DNFC and the delay-free non-fragile controller are capable of attenuating the vibration of the offshore platform to almost the same level, while the required control force under the DNFC is less than that under the delay-free one; and (ii) both the oscillation amplitudes of the offshore platform and the ranges of the control force under the pure delayed state feedback controller (DSFC) are smaller than the ones under the non-linear controller and the dynamic output feedback controller; and (iii) the oscillation amplitudes of the offshore platform under the DSFC are almost the same as the ones under integral sliding mode controller and the delayed dynamic output feedback controller, while the control force required by the former is less than the one by the latter.     

Interplay between internal delays and coherent oscillations in delayed coupled noisy excitable systems

Numerical study of variations in coherence of spike trains produced by two stochastically perturbed FitzHugh–Nagumo excitable systems with internal and coupling time-delays is performed. Both, the internal time-delay and the interaction time-delay in some domains of values can substantially increase the coherence but the interplay of the two delays can also lead to quite incoherent spike trains. Numerically observed dependence of the coherence on the delays is qualitatively explained by considering the bifurcations in the system caused by the variations of the values of the internal and the interaction time-lags.     

Dynamic analysis of a spinning composite “deep” hyperbolic coupling

A dynamic analysis of a “deep” hyperbolic composite coupling is presented. A model is developed based on “shell/beam” assumptions, the energy approach, and the application of the extended Lagrange’s Equations. The mathematical model is solved, using the finite element method, to study the effect of the minimum diameter of a specific “deep” coupling on its dynamic characteristics. The results of the developed finite element program are compared with the corresponding 3D-ANSYS ones. The effect of the spinning speed is also investigated. Results indicate that the developed model is very accurate in predicting the axial and meridional/tangential natural frequencies. The model, however, over predicts the flexural natural frequency. The model also successfully captures the branching phenomenon of the flexural natural frequency exhibited with spinning.     

A delay partitioning approach to output feedback control for uncertain discrete time-delay systems with actuator saturation

This paper is concerned with the problems of output feedback control for uncertain discrete time-delay systems with input saturation. The delay partitioning approach is proposed to obtain new stability criteria. The dynamic output feedback controller is designed based on a linear matrix inequality framework. A sufficient condition is developed, which guarantees the existence of dynamic output feedback controllers such that all trajectories of the closed-loop system starting from an admissible initial condition domain converge to a smaller ellipsoid. Simulation examples are provided to show the potential of the proposed techniques.     

Output feedback controller for hysteretic time-delayed MIMO nonlinear systems

In this paper, an H ^?? output feedback controller is developed for a class of time-delayed MIMO nonlinear systems, containing backlash as an input nonlinearity. Particularly, a state observer is proposed to estimate unmeasurable states. The control law can be divided into two elements: An adaptive interval type-2 fuzzy part which approximates the uncertain model. The second part is an H ^??-based controller, which attenuates the effects of external disturbances and approximation errors to a prescribed level. Furthermore, the Lyapunov theorem is used to prove stability of proposed controller and its robustness to external disturbance, hysteresis input nonlinearity, and time varying time-delay. As an example, the designed controller is applied to address the tracking problem of 2-DOF robotic manipulator. Simulation results not only verify the robust properties but also in comparison with an existing method reveal the ability of the proposed controller to exclude the effects of unknown time varying time-delays and hysteresis input nonlinearity.     

考虑间隙反馈控制时滞的磁浮车辆稳定性研究

常导磁吸型(EMS)磁悬浮列车在悬浮控制中的每个环节,时滞是不可避免的,当时滞超过一定程度后,系统有可能失稳.本文针对EMS磁浮列车控制环节的临界时滞与车辆参数(如运行速度、反馈控制增益、导轨参数和悬挂参数)的关系开展研究.建立了磁浮车辆/导轨耦合动力学模型,车辆包含1节车辆和4个磁浮架,考虑车辆的10个自由度,每个磁浮架上包含4个悬浮电磁铁.导轨模拟为一系列简支Bernoulli-Euler梁,采用模态叠加法对导轨振动方程进行求解.采用传统线性电磁力模型实现车辆和轨道的耦合.采用比例-微分控制算法对电磁铁电流进行反馈控制,实现车辆稳定悬浮,并假设时滞均发生在控制环节,且只考虑间隙反馈控制环节的时滞.采用四阶龙格库塔法对耦合系统动力学方程进行求解,编写了数值仿真程序,计算得到车辆导轨耦合系统在考虑间隙反馈控制时滞时的响应.将系统运动发散时的时滞大小视为临界时滞,开展了参数规律影响分析.通过分析,给出了提高时滞条件下车辆稳定性的方法,包括增大导轨的弯曲刚度和阻尼比,减小间隙反馈控制增益并增大速度反馈控制增益,以及增大二系悬挂阻尼.      

结构-模态主动控制系统的最大允许时滞及稳定性探讨

根据Ｎｙｑｕｉｓｔ稳定性准则、特征值原理和ＬＱＲ控制原理,导出了结构－模态控制系统的位移速度反馈的时滞计算公式,进而可求得结构－模态主动控制系统的最大允许时滞。数值分析表明,用两种不同稳定判据得到的两个最大允许时滞计算公式的计算结果是接近的。研究了时滞补偿后结构－模态主动控制系统的稳定性问题。从具有时滞补偿控制系统的特征方法知,具有时滞补偿的控制系统保持理想控制系统的特征值,既时滞补偿结构－模态主     

Application of photoelasticity to a weld-penetration problem

The need for more information on the “initiation period” in fatigue tests of weld specimens with penetration defects is discussed and the literature which relates the elasticity stress-concentration factor and Irwin's stress-intensity factor is reviewed. A series of photoelasticity tests on two-dimensional plane-stress models of typical penetration defects is described. In particular a method for casting “ready to use” very narrow defects is explained. The results are presented in a graph of stress-concentration factor against defect length. This graph has a “knee” at defect length-to-plate thickness ratios around 0.2. Below the “knee”, the stress-concentration factor changes very little with changes in defect length but, for lengths beyond the knee, i.e., ratios larger than 0.2, the stress concentrations increase linearly with defect length. It is concluded that such a critical defect length should have a strong effect on fatigue life of defective welds and that it may constitute a first approach to the specification of an “acceptable” level of penetration defects for production processes.     

Design and experimental verification of multiple delay feedback control for time-delay nonlinear oscillators

This study aims to show that a multiple delay feedback control method can stabilize unstable fixed points of time-delay nonlinear oscillators. The boundary curves of stability in a control parameter space are derived using linear stability analysis. A simple procedure for designing a feedback gain is provided. The main advantage of this procedure is that the designed controller can stabilize a system even if the controller delay times are long. These analytical results are experimentally verified using electronic circuits.     

Nonlinearly Viscoelastic Nanoindentation of PMMA Under a Spherical Tip

The Oliver-Pharr method has been well established to measure Young’s modulus and hardness of materials without time-dependent behavior in nanoindentation. The method, however, is not appropriate for measuring the viscoelastic properties of materials with pronounced viscoelastic effects. One well-known phenomenon is the formation of unloading “nose” or negative stiffness during unloading that often occurs during slow loading-unloading in nanoindentation on a viscoelastic material. Most methods in literature have only considered the loading curve for analysis of viscoelastic nanoindentation data while the unloading portion is not analyzed adequately to determine the nonlinearly viscoelastic properties. In this paper, nonlinearly viscoelastic effects are considered and modeled using the nonlinear Burgers model. Nanoindentation was conducted on poly-methylmethacrylate (PMMA) using a spherical indenter tip. An inverse problem solving approach is used to allow the finite element simulation results to agree with the nanoindentation load–displacement curve during the entire loading and unloading stage. This approach has allowed the determination of the nonlinearly viscoelastic behavior of PMMA at submicron scale. In addition, the nanoindentation unloading “nose” has been captured by simulation, indicating that the negative stiffness in the viscoelastic material is the result of memory effect in time-dependent materials.     

Subharmonic generation in physical systems: An interaction-box approach

A so-called “interaction-box” formalism, which has recently been introduced to describe hysteresis in dynamical systems in the case of higher harmonic generation, is further discussed and generalized to describe the phenomenon of subharmonic generation. In this case, the increase in the periodicity of the response is reflected in the formation of multiple loops in the Effect (output) vs. Cause (input) diagrams. Conversely, we show how this type of response represents a sort of “signature” of the system, and can thus be employed to draw general conclusions about the features of the latter. A specific example of a nonlinear system is chosen to illustrate the approach, namely a vibrating cantilever beam with a breathing crack. Effect vs. Cause curves are calculated for this system in the presence of higher harmonics and subharmonics.     

负刚度时滞反馈控制动力吸振器的等峰优化

相比于传统动力吸振器, 负刚度动力吸振器同时具有更好的减振能力和更宽的有效减振频带宽度, 为了进一步降低共振峰幅值, 在负刚度吸振器系统耦合时滞反馈控制. 对负刚度时滞反馈控制动力吸振器系统进行等峰优化设计, 优化设计的准则是:第一和第二共振峰的峰值相等; 同时兼顾两个目标, 一个目标是在优化时的最大共振峰幅值小于被动负刚度吸振器系统的反共振峰幅值, 另一目标是在优化时共振峰幅值与反共振峰幅值差小于被动吸振器系统. 接着, 通过设计和调节负刚度系数、吸振器阻尼系数和时滞反馈控制系数对控制系统进行等峰优化设计. 最后, 在降低幅值的同时, 分析结构参数对有效减振频带宽度的影响. 经过等峰优化之后, 选择本文的一组结构参数与两个典型的模型进行对比. 为了定量比较不同模型的降幅效果, 定义了减幅百分比, 研究发现在有效减振频带区间内减幅百分比超过40%以上. 结果表明, 通过等峰优化准则对结构参数进行优化设计和调节增益系数和时滞量, 共振峰幅值的减幅百分比也近似达到40%, 也可以调节增益系数和时滞量, 使得幅频响应曲线具有较宽的有效减振频带和较低的共振峰幅值与反共振峰幅值的差值.      

Bifurcation analysis in the system with the existence of two stable limit cycles and a stable steady state

Van der Pol–Duffing oscillator, which can be used a model for many dynamical system, has been widely concerned. However, most of the systems by scholars are either stable steady states or limit cycles. Here, the self-sustained oscillator with the coexistence of steady state and limit cycles, which is famous for describing the flutter of airfoils with large span ratio in low-speed wind tunnels, is treated in this paper. Using the energy balance method, the deterministic bifurcation of the tristable system with time-delay feedback is investigated. The presence of time-delay feedback expands the bifurcation range of the parameters, making the bifurcation phenomenon more abundant. In addition, according to the stationary probability density function obtained by the stochastic averaging method, stochastic bifurcation of the system with time-delay feedback and noise is explored theoretically. The numerical results confirm the correctness of the theoretical analysis. Transition between the unimodal structure, the bimodal structure and the trimodal structure is found. Many rich bifurcations are available by adjusting the time-delay and noise intensity, which may be conductive to achieve the desired phenomenon in the real-world application.

     

General framework for the identification of constitutive parameters from full-field measurements in linear elasticity

In this paper, several approaches available in the literature for identifying the constitutive parameters of linear elastic materials from full-field measurements are presented and their sensitivity to a white noise added to the data is compared. The first investigated approach is the virtual fields method (VFM). It is shown that the uncertainty of the parameters identified with the VFM when a white noise is added to the data depends on the choice of a relevant set of virtual fields. Optimal virtual fields exist, thus minimizing the uncertainty and providing the “maximum likelihood solution”. The other approaches investigated in this paper are based on finite element model updating (FEMU). It is proved that FEMU approaches actually yield equations similar to the ones derived from the VFM, but with nonoptimal sets of virtual fields. Therefore, the FEMU approaches do not provide the “maximum likelihood solution”. However, the uncertainty of FEMU approaches varies dramatically with the cost function to minimize. On one hand, the FEMU approach based on the “displacement gap” minimization yields equations which are very close to the ones of the VFM approach and therefore, its uncertainty is almost the same as the VFM one. On the other hand, it is shown that other approaches based on the “constitutive equation gap” minimization or the “equilibrium gap” minimization provide biased solutions. For all the approaches, very fast algorithms, converging in only two iterations, have been devised. They are finally applied to real experimental data obtained on an orthotropic composite material. Results confirm the success of two methods: the VFM approach which provides the “maximum likelihood solution” and the FEMU approach based on the “displacement gap” minimization.     

低雷诺数下串列布置双圆柱涡激振动特性研究

基于四步半隐式特征线分裂算子有限元方法,对串列布置双圆柱双自由度涡激振动问题进行了数值模拟计算,并分析了间距比、剪切率、频率比以及折减速度4个参数对圆柱结构动力响应的影响.研究发现:不同固有频率比与剪切率对下游圆柱振动幅值影响较大,然而对上游圆柱振动幅值影响较小.上游圆柱在两个自由度方向达到最大值的折减速度不同,然而下...     

时滞耦合质量摆动力吸振器减振系统的等峰优化理论与实验

摆式调谐质量阻尼器因其便于安装、维修、更换,且经济实用,广泛应用于结构减振.它通过将摆的自振频率调谐到接近主系统的控制频率,使摆产生与主系统相反的振动,从而抑制或消除主系统的振动.本文通过对主系统无阻尼的被动减振系统和主系统有阻尼的时滞反馈主动减振系统进行多目标优化设计,实现了对主系统幅频响应曲线的等峰控制和共振峰与反共振峰差值的有效控制.首先,建立了时滞耦合质量摆动力吸振器减振系统的力学模型和振动微分方程,通过对主系统无阻尼的被动减振系统进行等峰优化,获得了减振系统的最优频率比和质量摆的最优阻尼比.对于主系统存在阻尼的被动减振系统,在该优化参数下主系统的幅频响应曲线等峰优化失效.其次,对于主系统存在阻尼的时滞反馈优化控制系统,采用CTCR方法得到了反馈增益系数和时滞的稳定区域.在保证系统稳定的前提下,通过调节反馈增益系数和时滞量两个控制参数能够实现对主系统幅频响应曲线的等峰控制.再次,对共振点处主系统振幅放大因子时滞敏感度和反馈增益系数敏感度进行分析,表明共振点幅值对反馈增益系数比对时滞更为敏感.最后,通过实验分别在频域和时域内对理论结果进行了验证.研究表明,通过采用时滞反馈对摆式调...