On the passive control of vibrations with viscoelastic dynamic absorbers of ordinary and pendulum types

Dynamic vibration absorbers (DVA) provide a cheap and efficient means for vibration abatement in many complex systems, ranging from crankshafts of internal combustion engines, overhead transmission lines, machine casings, structural panels and large turbo machinery sets, to quote a few examples. One can provide a simple classification for them by considering the nature of the resilient material it contains as a form of “spring”: it may be viscous (CDVA), hysteretic (HDVA) or viscoelastic (VDVA). Viscous DVAs are the largely studied devices and one of their most remarkable applications is in mitigating crankshafts torsional vibrations and in very tall buildings. The most well known hysteretic DVA is the Stockbridge damper, largely applied in overhead electric power transmission lines. With modern use of fractional calculus, modelling viscoelastic materials became a routine work. The experimental identification of four fractional parameter models for viscoelastic material has become a standard technique amongst the authors of this work. Modelling viscoelastic materials by four fractional parameters has made advanced analysis of structures and systems where it is applied much more straightforward than it was before. This is true also for structures with VDVA and HDVA attached to it. In this paper it is shown that a hysteretic material model can be derived from a viscoelastic material model based on four fractional parameters. Generalized quantities of ordinary and pendulum type absorbers and for both viscoelastic and hysteretic materials are derived and their nature discussed. The performances of a system with absorbers of viscoelastic and hysteretic nature are compared. Input energy and dissipated energy by the absorbers of both natures and types are computed and compared, using the concept of generalized damping parameter of the absorbers. Conclusions are drawn from the comparisons. One of the ideas behind these computations is to check the validity of some international recommendations for the experimental assessment of Stockbridge dampers, which implicitly neglects the effect of the generalized mass parameter.     

Synchronization of fractional-order spatiotemporal complex-valued neural networks in finite-time interval and its application

This paper focuses on the synchronization of fractional-order complex-valued neural networks (FOCVNNs) with reaction–diffusion terms in finite-time interval. Different from the existing complex-valued neural networks (CVNNs), the reaction–diffusion phenomena and fractional derivative are first considered into the system, meanwhile, the parameter switching (the system parameters will switch with the state) is considered, which makes the presented model more comprehensive. By choosing an appropriate Lyapunov function, the driver and response systems achieve Mittag-Leffler synchronization under a suitable controller. In addition, based on the fractional calculus theorem and the basic inequality methods, a criterion of synchronization for the error system in finite-time interval is derived and the upper bound of the corresponding finite synchronization time can be obtained. Finally, two examples are provided, one is a numerical example to explain the effectiveness of the main results, and the other shows that the results of this paper can be applied to image encryption for any size with high-security coefficient.     

Mean-square pinning control of fractional stochastic discrete-time complex networks

This paper considers the mean-square pinning control problem of fractional stochastic discrete-time complex networks. First, a new fractional stochastic discrete-time complex networks model with stochastic noise is established. Then, some pinning controllers and sufficient conditions are developed for the complex networks. By adopting Lyapunov energy function theory and matrix analysis theory, it proved that the synchronization of the fractional stochastic discrete-time complex networks can be achieved in a mean-square sense via pinning control. In addition, these results are extended to solve the synchronization problem of general fractional discrete-time complex networks without noise. Finally, several numerical examples are given to verify the correctness of the obtained theoretical results.     

网络团队协同创新产品迭代开发模式研究

为保持用户满意度,减轻产品运营商的迭代压力,设计网络协同创新产品迭代开发模式。首先利用区块链技术搭建网络协同创新云平台,实现信息共享以及大众参与任务完成等功能;然后组建网络协同创新团队,通过这样的模式实现快速且高质量的创新任务;最后设计网络协同创新迭代开发模式的具体路径,其中包括在此路径中进一步实施快速响应的实现路径。所建立的迭代路径可用于帮助企业提升迭代创新中迭代速度和迭代质量。     

Switched systems with changing derivation order: Stability and applications

This paper deals with systems that can switch their structure, including the differentiation order. It is shown that there are several non-equivalent cases for them, which all coincide when the derivation order is not switched but fixed at 1. For each of these cases, (asymptotic) stability results are obtained in this paper. This is accomplished by generalizing Common Lyapunov Functions (CLF) and Multiple Lyapunov Functions (MLF) methods, the latter when applied to fractional switching systems (FSS) in the resetting. Several examples are presented to illustrate that such Lyapunov functions exist for linear and nonlinear switched order systems. It is shown that the resetting fractional switching can be easily implemented by standard software. Finally, applications in adaptive integer-order problems are made by exploiting features of both fractional and integer-order systems.     

Linear controller analysis and design for systems with input hystereses nonlinearities

An output feedback control analysis and design framework for linear systems with input hystereses nonlinearities is developed. Specifically, by transforming the hystereses nonlinearities into dissipative input-output dynamical operators, dissipativity theory is used to analyze and design linear controllers for systems with hysteretic actuators. The overall framework guarantees partial asymptotic stability of the closed-loop system; that is, asymptotic stability with respect to part of the closed-loop system state associated with the plant and the controller. Furthermore, the remainder of the state associated with the hysteresis dynamics is shown to be semistable; that is, solutions of the hysteretic system converge to Lyapunov stable equilibrium points determined by the system initial conditions.     

A simple approach to mathematical modelling of integer order and fractional order fuzzy PID controllers using one-dimensional input space and their experimental realization

Though over the years, mathematical modelling of fuzzy PID controllers is carried out extensively with two-dimensional and three-dimensional input spaces, the modelling is rarely attempted using one-dimensional input space. In this paper, this gap is reduced by proposing a simple approach where each of the fuzzy P, fuzzy I, and fuzzy D components is modelled using one-dimensional input space and merged to provide the complete PID action. Another speciality of the proposed approach is that it does not require any AND or OR operator for obtaining the mathematical models of individual PID components. To the best of author’s knowledge, such a modelling approach is completely new. This newly introduced idea of modelling is further extended to fractional order fuzzy PID controllers. Applicability of the proposed fuzzy controllers is delineated with four simulation examples and one real-time experimentation case study. To understand the usefulness of the proposed control schemes, performances of the newly obtained controllers are compared with the results available in literature. As the proposed controllers are model-free controllers, they can easily be implemented for other control applications also.     

Computer Models of Hysteresis in Mechanical and Magnetic Components

There is a strong analogy between mechanical structural elements and magnetic circuit components which can be extended to include hysteretic energy losses associated with yielding in mechanical systems and saturation in magnetic components. Procedures for developing finite state models of hysteretic components are presented using a small number of basic elements. Using bond graph techniques, it is shown that, when dual structural models are used, elements may be assembled in arbitrary numbers to achieve any desired accuracy without problems of derivative causality. The reason for the dual structure can be seen from physical reasoning. The shape of the hysteresis curve for magnetic materials generally requires more elements for a given degree of approximation than the shape of the typical mechanical hysteresis curve.     

Adaptive tracking control for quantized nonlinear systems via backstepping design technique

In this paper, the adaptive tracking control problem for a class of strict-feedback nonlinear systems with quantized input signal is investigated. The hysteretic quantizer is introduced to avoid the chattering phenomenon and the backstepping method is used to design the controller. The tracking errors are guaranteed to be bounded in a small neighborhood of zero via appropriate design parameters. Finally, two simulation examples are given, and the simulation results further demonstrate the effectiveness of the proposed method.     

Lag quasi-synchronization of incommensurate fractional-order memristor-based neural networks with nonidentical characteristics via quantized control: A vector fractional Halanay inequality approach

This work realizes lag quasi-synchronization of incommensurate fractional-order memristor-based neural networks (FMNNs) with nonidentical characteristics via quantized control. The motivations behind this research work are threefold: (1) quantized controllers, which generate discrete control signals, can be more easily realized in computers than non-quantized controllers, and can consume smaller communication capacity; (2) incommensurate orders in a single FMNN and nonidentical characteristics in drive-response FMNNs are inescapable due to the differences among the circuit elements used to implement FMNNs; (3) convergence analysis of delayed incommensurate fractional-order nonlinear systems, which is the basis for the derivation of synchronization criterion, has not been handled perfectly. As an effective tool for convergence analysis of delayed incommensurate fractional-order nonlinear systems, especially for estimation of ultimate state bound, a vector fractional Halanay inequality is established at first. Then, a quantized synchronization controller, in which the dead-zone is introduced into some logarithmic quantizers to avoid chattering phenomenon, is designed. By means of vector Lyapunov function together with the newly derived vector fractional Halanay inequality, the synchronization criterion is proved theoretically. Lastly, numerical simulations supplementarily illustrate the correctness of the synchronization criterion. In contrast with the hypotheses in the relevant literature, the hypotheses in this paper are weaker.     

The solution of the Bagley-Torvik equation with the generalized Taylor collocation method

In this paper, the Bagley-Torvik equation, which has an important role in fractional calculus, is solved by generalizing the Taylor collocation method. The proposed method has a new algorithm for solving fractional differential equations. This new method has many advantages over variety of numerical approximations for solving fractional differential equations. To assess the effectiveness and preciseness of the method, results are compared with other numerical approaches. Since the Bagley-Torvik equation represents a general form of the fractional problems, its solution can give many ideas about the solution of similar problems in fractional differential equations.     

Lag projective synchronization of fractional-order delayed chaotic systems

This paper considers the lag projective synchronization of fractional-order delayed chaotic systems. The lag projective synchronization is achieved through the use of comparison principle of linear fractional equation at the presence of time delay. Some sufficient conditions are obtained via a suitable controller. The results show that the slave system can synchronize the past state of the driver up to a scaling factor. Finally, two different structural fractional order delayed chaotic systems are considered in order to examine the effectiveness of the lag projective synchronization. Feasibility of the proposed method is validated through numerical simulations.     

On the approximate discrete KLT of fractional Brownian motion and applications

This paper establishes connection between discrete cosine transform (DCT) and the discrete-time fractional Brownian motion process (dfBm). It is proved that the eigenvectors of the auto-covariance matrix of a dfBm can be approximated by DCT basis vectors in the asymptotic sense. This shows that DCT basis acts as discrete Karhunen–Loève transform (DKLT) for these processes in the approximate sense. Analytic perturbation theory of linear operators is used to prove this result. This result will be of great practical significance in applications where one is looking for an appropriate basis to work with signals that can perhaps be modeled as belonging to fBm processes. The utility of the proposed work has been illustrated with two real-life data (a) on compressive sampling based reconstruction of financial time-series and (b) in denoising gravitational wave event GW150914 data obtained from a binary black hole merger.     

Robust extended fractional Kalman filter for nonlinear fractional system with missing measurements

Accurate and effective state estimation is essential for nonlinear fractional system, since it can provide some vital operation information about the system. However, inevitably missing measurements and additive uncertainty in the gain will affect the performance of estimation result. Thus, in this paper, in order to deal with these problems, a novel robust extended fractional Kalman filter (REFKF) is developed for states estimation of nonlinear fractional system, by which the states can be estimated accurately even with missing measurements. Finally, simulation results are provided to demonstrate that the proposed method can achieve much better estimation performance than the conventional extended fractional Kalman filter (EFKF).     

Chaotic synchronization between different fractional-order chaotic systems

Based on the idea of tracking control and stability theory of fractional-order systems, a novel synchronization approach for fractional order chaotic systems is proposed. We prove that the synchronization between drive system and response system with different fractional order q can be achieved, and the synchronization between different fractional-order chaotic systems with different fractional order q can be achieved. Two examples are used to illustrate the effectiveness of the proposed synchronization method. Numerical simulations coincide with the theoretical analysis.     

电信运营商官方微博影响力评价研究——基于30个电信运营商官方微博影响力的实证研究

微博依靠其较强的信息扩散能力成为众多企业进行线上营销的主要渠道。较高的微博影响力水平对企业营销信息的推广传播具有一定的推动作用,而电信运营商的官方微博尚存在影响力较为欠缺的情况。本文首先通过文献研究、因子分析等方法归纳聚合出3个微博影响力的主要因素,据此构建了微博影响力评价指标体系。因子分析的结果表明微博账号的信息传播能力对微博影响力的方差贡献率最高,其次为账号活跃度。最后,本文基于因子得分对30个电信运营商官方微博的影响力进行实证分析,分别计算得出各微博账号的指标因子得分及影响力综合得分。依据得分情况对各电信运营企业提出具体的微博影响力提升策略。     

小农户与新型农业经营主体的灌溉用水效率及其影响因素比较

基于对黄淮海平原2017年的实地调研数据,选取冬小麦作为研究对象,应用随机前沿模型对小农户和种粮大户、家庭农场与农民专业合作社3类新型农业经营主体冬小麦的农业灌溉用水效率进行测算,并运用Tobit模型探究影响不同农业经营主体农业灌溉用水效率的因素。研究发现：①小农户、种粮大户、家庭农场和农民专业合作社样本中农业灌溉用水效率值的差异较大。家庭农场和农民专业合作社的农业灌溉用水效率值集中在70%以上的水平,而小农户集中在10%~30%的水平;②结合各个农业经营主体的技术效率可知,小农户和新型农业经营主体的农业灌溉用水效率均有一定的提高空间;③小农户和新型农业经营主体在农业灌溉用水效率的影响因素方面有显著的不同,农业收入占比、用水成本和是否采用灌溉技术等因素对所有农业经营主体的农业灌溉用水效率都会有正向影响。在新型农业经营主体中,农户的年龄、灌溉面积、灌溉设施等因素能够影响其农业灌溉用水效率,但是对于小农户的农业灌溉用水效率无显著的影响。小农户是促进节水灌溉技术应用和提高农业灌溉用水效率的重要对象。加快传统农户向新型农业经营主体转型、加大公共服务建设等措施有助于农业灌溉用水效率的提高。     

Fractional-order global sliding mode controller for an uncertain quadrotor UAVs subjected to external disturbances

In the present paper, the problem of designing a global sliding mode control scheme based on fractional operators for tracking a quadrotor trajectory is investigated. The model of the quadrotor system is given with disturbances and uncertainties. To converge in short finite time of the sliding manifold, a classical quadratic Lyapunov function was used and also a global stabilization of the quadrotor system is ensured. The proposed controller can be ensured the robustness against external disturbances and model uncertainties. Some scenarios are illustrated in this paper. Finally, a comparative study to three other controllers is provided to show the validity and feasibility of the proposed method.     

Dynamic output-feedback control for nonlinear continuous-time systems based on parametric uncertain subsystem and interval type-2 fuzzy model

This paper addresses the interval type-2 fuzzy robust dynamic output-feedback control problem for a class of nonlinear continuous-time systems with parametric uncertainties and immeasurable premise variables. First, the parametric uncertainties are assumed to be a subsystem based on the control input matrix and output matrix, and described as a linear fractional. Secondly, the nonlinear continuous-time systems are described by the interval type-2 fuzzy model. Thirdly, the new dynamic output feedback controller is designed based on the interval type-2 fuzzy model and the linear fractional (parametric uncertainties), the sufficient conditions for robust stabilization are given in the form of linear matrix inequalities (LMIs). Compared with previous work, the developed methods not only have abilities to handle the fuzzy system with immeasurable premise variables but also can deal with the parametric uncertainties effectively. The results are further extended to a mobile robot case and a chemical process case. Finally, two simulation examples are performed to show the effectiveness of the propose methods.     

基于PSR模型的房地产调控政策对房价影响的研究—以北京市为例

研究房地产调控政策对房价的影响,可为政府制定合理的调控政策、平抑房价提供参考。在综合分析房价影响因素的基础上,分别筛选了压力、状态和响应指标,构建了基于PSR模型的房地产调控政策对于房价影响的评价体系。采用层次分析法确定了各指标的权重,并对北京市房地产政策的调控效果进行了初步量化。研究结果表明,北京市房价随着政策调控周期的变化而呈现出有规律的升降变化,在政策鼓励期,房价总体呈上升趋势,在政策收缩期,房价呈下降趋势,说明房价对政策的调控反应敏感。并发现政策对房价的调控具有一定的滞后性,滞后周期为3个月左右。为了平抑当前过高的房价,建议从土地政策、税收政策、保障房政策等方面来加强调控力度。