Finite-time resilient decentralized control for interconnected impulsive switched systems with neutral delay

This paper is concerned with the problem of finite-time control for a class of interconnected impulsive switched systems with neutral delay in which the time-varying delay appears in both the state and the state derivative. The concepts of finite-time boundedness and finite-time stability are respectively extended to interconnected impulsive switched systems with neutral delay for the first time. By applying the average dwell time method, sufficient conditions are first derived to cope with the problem of finite-time boundedness and finite-time stability for interconnected impulsive switched systems with neutral delay. In addition, the purpose of finite-time resilient decentralized control is to construct a resilient decentralized state-feedback controller such that the closed-loop system is finite-time bounded and finite-time stable. All the conditions are formulated in terms of linear matrix inequalities to ensure finite-time boundedness and finite-time stability of the given system. Finally, an example is presented to illustrate the effectiveness of the proposed approach.     

Fault diagnosis of a gearbox using the sliced Wigner fourth order time frequency method smoothed by a new kernel function

The detection of impulsive signals embedded in the broadband noise is useful for the fault diagnosis of a gearbox. The sliced Wigner fourth-order time frequency method (SWFOTFM) has been used for the detection of impulsive signals embedded in the broadband noise. However, one disadvantage of SWFOTFM is that the non-oscillating cross-terms cannot be smoothed by conventional kernel functions. In this paper, a new kernel function is developed to reduce the non-oscillation cross-terms. The SWFOTFM using the new kernel function is successfully applied to the fault diagnosis of a gearbox.     

Backstepping control for periodically time-varying systems using high-order neural network and Fourier series expansion

An adaptive backstepping tracking scheme is developed for a class of strict-feedback systems with unknown periodically time-varying parameters and unknown control gain functions. High-order neural network (HONN) and Fourier series expansion (FSE) are combined into a new function approximator to model each uncertain term in the system. The dynamic surface control (DSC) approach is used to solve the problem of ‘explosion of complexity’ in the backstepping design procedure. Nussbaum gain function (NGF) is employed to deal with the unknown control gain functions. The uniform boundedness of all closed-loop signals is guaranteed. The tracking error is proved to converge to a small residual set around the origin. Two simulation examples are provided to demonstrate the effectiveness of the control scheme designed in this paper.     

Finite time stability and controller design for nonlinear impulsive sampled-data systems with applications

This paper investigates the finite time stability (FTS) for nonlinear impulsive sampled-data systems. By constructing an appropriated Lyapunov function and employing average impulsive interval (AII) method, some FTS criteria for the nonlinear impulsive sampled-data systems are derived in terms of linear matrix inequalities (LMIs), which can be easily verified via the LMI toolbox. The hybrid controller including sampled-data controller and impulsive controller is designed via the established LMIs. Moreover, the impulse effect considered in this paper including stabilizing impulse and destabilizing impulse. Our developed results are less conservative than the recent work in the literature. Finally, two numerical examples are provided to show the applications of the proposed criteria.     

Control of Nonlinear Systems with Output Tracking Error Constraints

A constructive method is presented to design controllers that force the output of nonlinear systems in a strict feedback form to track a bounded and sufficient smooth reference trajectory asymptotically. Under suitable condition with the initial output tracking error, the proposed controllers guarantee the output tracking error within a symmetric or an asymmetric pre-specified limit range, and boundedness of all signals of the closed loop system. A transformation is introduced to take care of the output tracking error constraint. Smooth and/or p-times differentiable step functions are proposed and incorporated in the output tracking error transformation to overcome difficulties due to the asymmetric limit range on the output tracking error. As a result, there are no switchings in the proposed controllers despite of the asymmetric limit range.     

Application of improved morphological filter to the extraction of impulsive attenuation signals

Rotating machinery response is often characterized by the presence of periodic impulses modulated by high-frequency harmonic components. It can be defined with three parameters, which are natural frequency, fault frequency and decay coefficient. In this paper, we propose an improved morphological filter for feature extraction of the above signals in the time domain. Firstly, an average weighted combination of open-closing and close-opening morphological operator, which eliminates statistical deflection of amplitude, is utilized to extract impulsive component from the original signal. Then, according to the geometric characteristic of impulsive attenuation component, the structure element is constructed with an impulsive attenuation function, and a new criterion is put forward to optimize the structure element. The proposed method is evaluated by simulated impulsive attenuation signals with different natural frequencies and vibration signals measured on defective bearings with outer race fault and inner race fault, respectively. Results show that the background noise can be fully restrained and the entire impulsive attenuation signal is well extracted, which demonstrates that the method is an efficient tool to extract impulsive attenuation component from mechanical signals.     

Stability of uncertain impulsive complex-variable chaotic systems with time-varying delays

In this paper, the robust exponential stabilization of uncertain impulsive complex-variable chaotic delayed systems is considered with parameters perturbation and delayed impulses. It is assumed that the considered complex-variable chaotic systems have bounded parametric uncertainties together with the state variables on the impulses related to the time-varying delays. Based on the theories of adaptive control and impulsive control, some less conservative and easily verified stability criteria are established for a class of complex-variable chaotic delayed systems with delayed impulses. Some numerical simulations are given to validate the effectiveness of the proposed criteria of impulsive stabilization for uncertain complex-variable chaotic delayed systems.     

Impulsive sources localisation in noisy environment using modified beamforming method

When a machine has faults in its rotating part, it normally generates periodic vibration or acoustic signals. These signals are often periodic but impulsive. This paper addresses the way in which we can find where the impulsive sources are. We propose a signal processing method that can identify impulsive sources’ location. The method is robust with respect to noise; spatially distributed noise. Numerical simulation and experiments are performed to verify the method. Results show that the proposed technique is quite powerful for localising the sources in noisy environments. The method also required less microphones than conventional beamforming method.     

声源定位法在检测机械故障位置中的应用

针对旋转机械发出的具有较强噪声的周期性脉冲信号,提出了一种能够找出发出声音脉冲信号的位置的声源定位方法,并将这种方法应用到确定机械设备故障所在的位置中去.仿真结果表明,在具有较强噪声干扰的情况下,该方法能够有效地确定脉冲声源的位置.     

Application of the L-Wigner distribution to the diagnosis of local defects of gear tooth

The detection of impulsive signals causing the fracture of gears is a significant task for the analysis of the characteristics of a damaged gear. However, this impulsive signal is hidden by background noise such as meshing frequencies and broadband noise. Recently, conventional time frequency methods have been used. In the case of a signal with a low SNR, these methods are not sufficient for the detection of impulsive signals; hence, the L-Wigner distribution with an S-method kernel is used and applied to the diagnosis of local defects of a tooth in a gear.     

振动模态固有频率和阻尼比的EMD识别方法

针对机械系统固有频率和阻尼比的识别问题,提出了基于经验模式分解(EMD)的模态参数识别方法.该方法首先对脉冲激励下机械系统的位移响应进行了EMD分解,确定与该系统的各阶模态对应的固有模式函数(IMF),分别对各阶IMF进行希尔伯特变换以得到各自的瞬时幅值和瞬时相位曲线,并对所得曲线进行线性拟合,最后根据拟合曲线的参数来...     

H∞ sliding mode control of discrete switched systems with time-varying delays

The finite-time boundedness issue for a class of discrete switched systems with time-varying delays is investigated via sliding mode control (SMC) approach. By employing the Lyapunov functional and average dwell time method, new sufficient conditions are derived to guarantee the finite-time boundedness of the dynamic system in the novel sliding surface. By solving an optimization problem, the sliding mode controller is synthesized such that the discrete reaching condition is satisfied and the chattering is reduced. A simulation example tests the feasibility of the provided SMC scheme.     

Asynchronous control of discrete-time impulsive switched systems with mode-dependent average dwell time

This paper mainly studies the asynchronous control problem for a class of discrete-time impulsive switched systems, where “asynchronous” means the switching of the controllers has a lag to the switching of system modes. By using multiple Lyapunov functions (MLFs), the much looser asymptotic stability result of closed-loop systems is derived with a mode-dependent average dwell time (MDADT) technique. Based on the stability result obtained, the problem of asynchronous control is solved under a proper switching law. Moreover, the stability and stabilization results are formulated in form of matrix inequalities that are numerically feasible. Finally, an illustrative numerical example is presented to show the effectiveness of the obtained stability results.     

Stability analysis of sample data systems with input missing: A hybrid control approach

In this paper, we establish exponential stability criteria for the sampled-data impulsive control of the linear time-invariant system. With average impulse interval (AII), less conservative conditions are obtained on the exponential stability problem for the sampled-data systems. It is proved that when the AII of the impulsive sequences is fixed, the upper bound of the impulsive intervals could be very large, which guarantees the less conservativeness of the obtained result concerning the sampling intervals. The control input missing is also studied and we establish a new stability criterion for the exponential decay rate and the sampling period which is less conservative than the ones obtained for variable sampling intervals. Two examples are given to show the effectiveness of the obtained result.     

基于小波包域噪声能量分布的脉冲噪声消除

针对信号被平稳脉冲噪声污染的场合,提出了一种从含噪信号中检测脉冲噪声并降噪的脉冲噪声消除方法.该方法选择脉冲噪声能量相比含噪信号能量最为显著的小波包树节点,并利用该节点小波包系数重构信号进而检测脉冲噪声的时域分布.在降噪中,该方法于小波包域内估计脉冲噪声的能量分布并依据估计结果计算每段脉冲噪声的滤波阀值.将该方法用语音增强实验验证,结果表明所提出的检测算法能获得较好的检测结果,而提出的降噪算法能显著地改善信噪比,获得较好的降噪效果.将文中的检测算法应用于轴承故障检测的信号预处理,进一步验证了方法的有效性.     

Three-dimensional computations of the impulsive wave discharged from a duct

A sudden discharge of mass flow from the exit of a duct can generate an impulsive wave, generally leading to undesirable noise and vibration problems The present study develops an understanding of unsteady flow physics with regard to the impulsive wave discharged from a duct, using a numerical method A second order total variation diminishing scheme ts employed to solve three-dimensional, unsteady, compressible Euler equations Computations are performed for several exit conditions with and without ground and wall effects under a change in the Mach number of an initial shock wave from 11 to 15 The results obtained show that the directivity and magnitude of the impulsive wave discharged from the duct are significantly influenced by the initial shock Mach number and by the presence of the ground and walls     

A numerical study on the transient impulsive pressure of a water jet impacting nonplanar solid surfaces

This paper presents an in-depth investigation into the transient impulsive pressure of an arc-curved water jet impacting a solid surface. The emphasis of this study is on the variations of the surface shape, which are classified into four types: The flat surface, the concave surface, the convex surface and the inclined surface. The numerical tool of arbitrary Lagrangian-Eulerian formulations is used to model the arc-curved jet impacting these different solid surface types. Elaborately designed experiments were conducted to test the impulsive pressure profile; the experimental results are found to be in approximate agreement with the numerical results. The impulsive pressure profiles of water jet impacting the flat and inclined solid surface are observed to exhibit two quintessential stages, in line with the traditional pressure profile; however, a double/multiple-peaked pressure structure is observed for the cases of the water jet impacting the concave and convex solid surfaces. Additionally, the value of the peak pressure is found to be a quadratic representation with the jet velocity, and the duration of the peak pressure is found to be an exponential representation with the jet velocity. The compression degrees of the liquid jet impacting the different surfaces are validated to be the root cause for the discrepancy of the impulsive pressure.     

IMPULSIVE CHIP BREAKING IN METAL MACHINING: A PROOF-OF-CONCEPT STUDY

An innovative non-conventional technique, called impulsive chip breaking, is developed in the present study to break difficult-to-break chips that are often generated in machining high toughness or soft gummy materials, such as pure aluminum, pure copper, aluminum alloys, copper alloys, low carbon steels, and stainless steels. These materials have a wide variety of engineering applications. In impulsive chip breaking, the machine tool spindle rotational speed periodically increases to a prescribed higher speed within a set short period of time and then resumes to its normal constant speed to continue machining operations. The experimental investigations covering a range of cutting conditions on a selected work material are preformed to confirm the feasibility of impulsive chip breaking and study its basic mechanism as well as the characteristic variations of machining performances, including the chip morphology, the cutting forces, the machining vibrations, and the surface roughness of the machined workpiece. It is demonstrated that as long as the impulsive rotational speed of the machine tool spindle is appropriately selected or optimized, both requirements of breaking chips and maintaining the machined surface quality can be simultaneously satisfied.