基于最佳相位匹配的减摇鳍低航速控制策略

为了满足工程船舶对低航速下减摇的需求,提高船舶在锚泊和低航速下的耐波性,提出减摇鳍在低航速下的控制策略,重点针对低航速下升力与鳍角之间相位关系对航速十分敏感的问题和船舶横摇模型的不确定性问题进行研究.通过数值迭代解决低航速下升力相位对航速的敏感性和升力与鳍角的非线性关系问题,相位调节器可以克服航速测量误差的影响,保证最...     

分数傅里叶变换理论及其应用研究进展

分数傅里叶变换是傅里叶变换的广义形式,提供了介于时域和频域之间的多分数域信号表征,为非平稳信号处理和线性时变系统分析开辟了新途径,应用十分广泛。本文首先总结近年来分数傅里叶变换的理论研究成果,包括分数傅里叶变换的数值计算、衍生的离散分数变换、分数域采样、分数域滤波与参数估计、多分数域分析。然后介绍分数傅里叶变换在工程和实践中的应用,包括雷达、通信、图像加密、光学干涉测量、医学、生物、机械仪器等。最后对分数傅里叶变换理论及其应用的未来研究方向进行展望。

     

干/湿状态下HFRP搭接接头的剪切蠕变试验及分数阶导数流变模型

搭接是纤维增强复合材料(FRP)的重要连接方式,长期性能是该技术实际工程应用的关键.对不同恒定应力和湿度状态下混杂FRP (HFRP)双搭接接头的剪切蠕变性能进行了试验研究.试验观测到了明显的蠕变变形,测定了蠕变与恒定应力及湿度的关系.进一步采用分数阶导数流变模型对试件的蠕变进行模拟.根据模型所包含的Mittag-Leffler函数的性质采用了改进的Powell优化算法,并确定了合理的初值,结合试验曲线拟合得到模型各参数值.根据搭接接头蠕变的特点,在经典分数阶流变模型中引入了表征应力水平对搭接接头非线性蠕变特性影响的函数,提出了一种改进的分数阶蠕变柔量计算公式.研究结果表明,该流变模型能够采用简单的表达形式和较少的参数对试件的非线性蠕变行为进行拟合,在30%~70%恒定应力范围内准确模拟了双剪搭接接头的蠕变曲线.     

Constrained Fractional Variational Problems of Variable Order

Isoperimetric problems consist in minimizing or maximizing a cost functional subject to an integral constraint. In this work, we present two fractional isoperimetric problems where the Lagrangian depends on a combined Caputo derivative of variable fractional order and we present a new variational problem subject to a holonomic constraint. We establish necessary optimality conditions in order to determine the minimizers of the fractional problems. The terminal point in the cost integral, as well as the terminal state, are considered to be free, and we obtain corresponding natural boundary conditions.      

Pinning Synchronization Between Two General Fractional Complex Dynamical Networks With External Disturbances

In this paper, the pinning synchronization between two fractional complex dynamical networks with nonlinear coupling, time delays and external disturbances is investigated. A Lyapunov-like theorem for the fractional system with time delays is obtained. A class of novel controllers is designed for the pinning synchronization of fractional complex networks with disturbances. By using this technique, fractional calculus theory and linear matrix inequalities, all nodes of the fractional complex networks reach complete synchronization. In the above framework, the coupling-configuration matrix and the innercoupling matrix are not necessarily symmetric. All involved numerical simulations verify the effectiveness of the proposed scheme.      

分数阶导数线性流变固体模型及其应用

采用Koeller 弹壶元件替代标准线性固体模型中的Newton黏壶, 得到分数阶导数线性流变固体模型, 给出了表征模型动态黏弹特性的存储模量、损耗模量和损耗因子以及表征模型静态黏弹特性的蠕变柔量和松弛模量。采用分数阶导数线性流变固体模型、标准线性固体模型和五参量固体模型对聚丙烯材料应力松弛特性进行分析。讨论了Mittag-Leffler函数的求和截断误差。结果表明分数阶导数线性流变固体模型能更准确描述聚丙烯材料的应力松弛行为。     

Separation of Paraffin Wax Using Solvent Fractionation

In order to separate and characterize some grades of paraffin waxes from El-Ameria crude waxes (slack waxes), a one-stage fractional crystallization technique has been done to separate the paraffin waxes with different characteristics by using different solvents and solvent mixtures at ambient temperature of 20°C and fixed dilution and washing solvent ratios (S/F) of 4:1 and 2:1 by weight, respectively. The fractionating solvents used are n-hexane, methyl isobutyl ketone (MIBK), dioxane, ethyl acetate, and butyl acetate as a single solvent and a mixture of methyl ethyl ketone (MEK) containing benzene (B) and toluene (T) as a mixed solvent. The resulting data revealed that dioxane and n-hexane solvents are not suitable for fractional crystallization of slack waxes, and the most suitable solvents for separating paraffin waxes with the standard specifications are ethyl and butyl acetates, MIBK, and the mixture of MEK, B, and T (60:20:20 by weight, respectively).     

金属分步结晶精炼的热力学

分步结晶是一种历程悠久的金属精炼方法。随着科学与技术的不断发展，分步结晶作为一种独立的热分离过程，对金属熔体的分离与精炼具有日益重要的意义。本文将详细讨论该方法的基本概念、特点及其热力学原理。     

Fractional Invariance Principle

Abstract. The paper presents a central limit theorem and an allied invariance theorem related to what Marinucci and Robinson [Journal of Statistics, Planning and Inference (1999) Vol. 21, pp. 111–122] termed type II fractional Brownian motion. To widen the applicability, their independent and identically distributed (i.i.d.) assumption for the innovation process is relaxed, allowing it to be mildly conditionally heteroscedastic and requiring the Martingale‐difference property only asymptotically. Additionally, the paper presents, for contrast, the weak convergence of the conventional partial sum process in a related set‐up.     

Chaos-based discrete fractional Sine transform domain audio watermarking scheme

We proposed a novel discrete fractional Sine transform (DFRST) based watermarking scheme for audio data copyright protection. Chaotic sequences were adopted to improve the security of the proposed watermarking scheme. Simulations under various conditions were given to verify the effectiveness of the audio watermarking scheme. The results show the proposed scheme is secure, and the watermark is imperceptible and robust against various audio signal processing attacks.