An optimal vibration control logic for minimising fatigue damage in flexible structures

One of the most common applications of active control on flexible structures is the mitigation of vibrations to reduce stresses and consequently increase lifetime. However, except for a few particular cases, the fatigue phenomenon has never been taken into account in the design of the control algorithm. Moreover, since fatigue is mainly a local effect, in some cases active control could even worsen the structure's integrity (e.g. consider local damage close to the actuators caused by control strategies requiring high control forces). For this reason, control is not able to achieve the best performance in terms of damage reduction and lifetime maximisation. This paper proposes an optimal active control designed to minimise fatigue damage on the structure. A model of the fatigue phenomenon is introduced and included in the definition of the control parameters. The solution is firstly described from a theoretical point of view and then tested both numerically and experimentally, showing a significant improvement over state-of-the-art techniques.     

Dynamic analysis and optimal design of a passive and an active piezo-electrical dynamic vibration absorber

This paper is concerned with the dynamic analysis and parameter optimization of both passive and active piezo-electrical dynamic vibration absorbers that are strongly coupled with a single degree of freedom vibrating structure. The passive absorber is implemented by using an R_s∥L_s parallel shunt circuit while the active absorber is implemented by feeding back the acceleration of the structure through a second-order lowpass filter. An impedance-mobility approach is used for the electromechanical coupling analysis of both types of absorbers coupled with the structure. Using this approach it is demonstrated that the passive and active absorbers can be made exactly equivalent. A maximally flat frequency response strategy is used to find the optimal damping ratio of the passive absorber while a robust, optimal control theory is used to find that for the active absorber. It is found that the passive optimization strategy corresponds to an optimal, robust feedback control of 2 dB spillover. Simulations and experiments are conducted to support the theoretical findings.     

Minimax design of vibration absorbers for linear damped systems

This paper addresses the issue of design of a passive vibration absorber in the presence of uncertainties in the forcing frequency. A minimax problem is formulated to determine the parameters of a vibration absorber which minimize the maximum motion of the primary mass over the domain of the forcing frequency. The limiting solutions corresponding to the forcing frequency being unrestricted and to that where the forcing frequency is known exactly, are shown to match those available in the literature. The transition of the optimal vibration absorber parameters between the extreme two cases is presented and the solutions are generalized by permitting the mass ratio of the absorber mass and the primary mass to be design parameters. For the specific case where the primary system is undamped, detailed analysis is presented to determine the transition of the optimal vibration absorber parameters between three distinct domains of solutions.     

The optimal design of integrated evaporation systems

The heat integration of evaporators with overall processes leads to optimal designs very different from optimal stand-alone designs. The grand composite curve has been previously suggested for assessing alternative evaporator integration schemes. This paper demonstrates that if the effect of the evaporator integration on the overall capital-energy trade-off is ignored then misleading conclusions can be obtained. A procedure is suggested which takes account of this capital-energy trade-off. Design complications such as boiling point rise and latent heat changes which have often been ignored in the past in the grand composite approach are also considered.     

柔性铰链机构柔节疲劳寿命的设计及研究

围绕基于迈克尔逊干涉仪傅里叶变换光谱仪的动镜支撑机构——柔性铰链机构的柔节疲劳寿命问题,先通过相关公式计算选取出机构柔节的各个参数,并由这些参数建立机构的有限元模型;然后再根据材料属性参数,利用疲劳分析软件msc.fatigue,通过拟合疲劳寿命S-N曲线来对机构的柔节参数进行仿真验证.从分析结果可知:柔节破坏点的寿命...     

浅海声场单模闭环发射的最佳估计算法

提出了一种浅海声场单模闭环发射的最佳估计算法。通过对声场格林函数矩阵估计协方差的分析,设计了一种对格林函数矩阵作最佳估计的最佳发射阵权系数矩阵,此权系数矩阵为酉矩阵且各元素绝对值相等。基于此矩阵的单模发射算法可以使得单模激发过程以最快的速度收敛,并且发射稳定。算法的优势在模拟计算中得到了验证。最后给出了海上实验的结果,单模含量高达97%。     

An analytical model for vibration of clusters of flexible cylinders in turbulent axial flow

This paper describes an analytical model for the flow-induced vibration of clusters of cylinders in axial flow, in the sub-critical flow regime (i.e., at flow velocities below the threshold for fluid-elastic instabilities). The vibration is excited by the random pressure fluctuations in the turbulent flow acting on the cylinders. Correlation of the excitation field is assumed to exist, with appropriate length scales, not only on the same cylinder, but also on adjacent cylinders in the cluster. In the absence of measured correlation functions for the system at hand, numerical calculations were conducted with available pipe-flow correlation functions, due to Bakewell et al., assumed to be approximately valid. Power- and cross-spectral densities of the vibration are presented, as well as r.m.s. amplitudes, for simple systems of two, three and four cylinders, and the characteristics of the flow-induced vibration are then discussed. It is seen that there is remarkable qualitative agreement with measured characteristics of vibration.     

An optimal algorithm for single-mode close-loop excitation in shallow water

An optimal algorithm for single-mode close-loop excitation in shallow water is presented.By analyzing the covariance of estimation value of Green’s function matrix,an optimal source array weights matrix is presented to estimate Green’s function matrix.The weights matrix is a unitary matrix,and absolute values of the matrix elements are equal. Algorithm based on the weights matrix makes single-mode excitation converge at maximum speed and be steady.Advantages of the algorithm are confirmed by numerical simulations. Finally,results of shallow water experiment are presented,and the energy ratio of single mode is higher than 97 percent.     

一种多基阵机动目标被动跟踪算法

由多部声纳基阵获取的方位信息对水中机动目标的跟踪实质上是一个非线性状态估计问题,文中首先依据各基阵的方位信息,采用最小二乘法得到目标位置在各采样时刻的初步估计,然后将其作为测量值用于交互多模型算法(IMM)并结合线性卡尔曼滤波(KF)得到目标运动速度和轨迹,避免了应用非线性估计算法直接进行多个方位数据融合过程中存在的各种问题。仿真结果表明这一算法简便,与双基阵纯方位机动目标被动跟踪相比具有较快的收敛速度和较高的跟踪精度。     

Instantaneous optimal method for vibration control of linear sampled-data systems with time delay in control

In an actively controlled system, time delay exists inevitably. Neglecting time delay may cause degradation of control performance or even induce instability to the dynamic system. In this paper, instantaneous optimal control method for vibration control of linear sampled-data systems with time delay in control is investigated. By a peculiar integral transformation, the first order state equation with time delay is transformed into the standard first order state equation, which contains no time delay. Then the optimal controller is designed based on the numerical algorithm of the regular fourth order Runge-Kutta method. Since the obtained controller contains integral term, which is not practical for control implementation, the numerical algorithm for this integral term is investigated too. Since the controller is deduced directly from the time-delay differential equation, the control method presented is prone to guarantee system stability. Thus the presented control method can be applicable to the case of large time delay. The performance of the control method is demonstrated by numerical simulation. Simulation results indicate that this control method is feasible and is an attractive strategy for dealing with the time delay in vibration control systems and is effective in suppressing maximum structural responses. Instability in structural responses may occur if the systems with time delay are controlled using the controller designed in the case of no time delay.     

An algorithm for terrain-aided inertial navigation based on nonlinear optimal filtering

When the initial position error or the altimeter measurement noise is large,the BUAA Inertial Terrain-Aided Navigation (BITAN) algorithm based on extended Kalman filtering can not be located accurately.To solve this problem,we propose a modified BITAN algorithm based on nonlinear optimal filtering.The posterior probability density correction is obtained by using the prior probability density of the system's state transition model and the most recent observations.Hence,the local unobservable system caused by...     

An efficient algorithm for optimal manycast routing problem over WDM networks

In this paper, we discuss the problem of supporting resource optimization of manycasting service over wavelength division multiplexing (WDM) optical networks. Manycast is a novel group communication paradigm wherein the source is required to send data packets to a certain number of a set of pre-specified group members. Since it integrates the characteristic of multicast and anycast, manycast is attracting increasing interest from researchers over wavelength division multiplexing (WDM) optical networks. Splitter, cost, wavelength channel are three parameters which are taken into consideration for the first time in WDM. Finding a manycast tree which span the resource and selected nodes with minimum number of splitter, cost and wavelength channel is an NP-complete problem, and therefore we propose a simple and efficient heuristic solution: based-frequency manycast routing (BFM) algorithm to construct manycast trees with the aim of reducing the use of network resources. For a set of manycast requests, the simulation result shows BFM builds manycast trees with the smallest number of resources than other algorithms.     

An optimal adaptive quantization index modulation watermarking algorithm

A novel adaptive watermarking algorithm in discrete wavelet transform （DWT） based on quantization index modulation （QIM） technique is presented. The host image is decomposed into wavelet subbands, and then the approximation subband is divided into non-overlapping small embedding blocks. The secret watermark bit is embedded into singular value vector of each embedding block by applying QIM. To improve the invisibility and robustness of watermarking system, the quantization step for each embedding block is set by combining statistical model with particle swarm optimization （PSO） algorithm. The experimental results show that the proposed algorithm not only preserves the high perceptual quality, but also effectively stands against joint photographic experts group （JPEG） compression, low-pass filtering, noise addition, scaling, and cropping attacks, etc. The comparison analysis demonstrates that our scheme has better performance than the previously reported watermarking algorithms.     

Experimental verification of the optimal tuning of a tunable vibration neutralizer for global vibration control

A theoretical method has been previously proposed by the authors to optimize a tunable vibration neutralizer for global vibration control. However, experimental verification of the tuning method has yet to be presented. This paper aims to do this. It is shown that by using the proposed optimization method, the tunable vibration neutralizer can be as effective as an active control device in reducing global vibration of a structure. One particularly interesting finding is that although the vibration neutralizer is a passive device which is incapable of supplying energy to a system, it appears to be as effective as active control in reducing the global vibration of a structure, even in the frequency range where the control device is required to supply energy.     

Multi-objective optimal design and experimental validation of tracking control of a rotating flexible beam

This paper investigates the tracking control problem for a rotating flexible beam. A proportional-integral-derivative control is designed to meet multiple objectives including overshoot, peak time, tracking error of the rigid movement of the rotating base, and the defectional angle of the flexible beam. A multi-objective optimization problem is then formulated for the control design and is solved with the cell mapping method. Numerical simulations and experiments are carried out to demonstrate the effect of the different control gains in the Pareto set, and to study the difference between a linear and a nonlinear model of the flexible beam.     

On the stability of delayed feedback controllers for discrete time systems

We consider the stability of delayed feedback control (DFC) scheme for multi-dimensional discrete time systems. We first construct a map whose fixed points correspond to the periodic orbits of the uncontrolled system. Then the stability of the DFC is analyzed as the stability of the corresponding equilibrium point of the constructed map. For each periodic orbit, we construct a characteristic polynomial whose Schur stability corresponds to the stability of DFC scheme.