一种基于声散射特性的有鳔鱼特征获取方法

鱼分类技术在渔业资源评估中的重要性日益凸显,而分类中能够得到不同鱼种的本质声散射特征尤为重要。文章基于鱼的声散射特性,提出一种有鳔鱼种特征获取新方法。鱼的目标强度反映了鱼的本质声散射特征,其主要取决于鱼鳔的大小、形状及声波入射角度、频率,文章基于基尔霍夫模式模型和图像处理方法进行建模,不仅可对鱼体和鱼鳔进行更真实的近似,而且可以得到精确的目标强度仿真结果。通过图像识别方法,对鱼体及鱼鳔图像进行灰度变换、二值化、边缘识别、轮廓提取等处理,得到鱼体及鱼鳔边缘坐标,利用得到的信息进行建模,并给出了相应的计算机仿真结果。最后进行了水池试验,对仿真数据与试验数据进行了对比分析,并提取得到有鳔鱼的目标强度特征,为鱼分类特征获取提供了一条新的途径。     

基于分形理论的超音速等离子喷涂层界面结合行为研究

为研究结合界面形貌与涂层体系结合强度之间的关系,采用超音速等离子喷涂设备制备Fe基合金涂层,选用(Ni,Al)涂层作为黏接底层.通过改变Ar气流量,获得不同粗糙表面的黏接底层.采用对偶件拉伸法测量复合合金涂层体系的结合强度,同时引入分形理论对结合界面形貌进行定量表征,结果表明:黏接底层能显著提高涂层的结合强度,随着Ar气流量的升高,黏接底层表面分形维数不断降低,涂层体系的结合强度则呈现出先增大后减小的趋势.     

利用源强密度声辐射模态重建声场

为了利用声场中少量测点声压数据精确重建复杂结构的辐射声场,提出了源强密度声辐射模态分析理论和声场重建公式.在结构表面定义的空间上,利用以源强密度分布函数为参量的结构辐射声功率泛函表达式定义了一个线性自伴正辐射算子,该算子的特征函数为结构的源强密度声辐射模态.然后通过对矩形平板和带有半球帽的圆柱体的源强密度声辐射模态的分析,证明了源强密度声辐射模态具有空间滤波特性,并利用该性质建立了声场重建公式.球体仿真和平板实验验证了所提出的声场重建方法的可行性和稳健性.基于源强密度声辐射模态的声场重建方法简单,利用较少测点数据就可以获得较高的声场重建精度,特别适合于复杂结构的低频声场重建.     

Global residue harmonic balance method to periodic solutions of a class of strongly nonlinear oscillators

A new approach, namely the global residue harmonic balance method, was advanced to determine the accurate analytical approximate periodic solution of a class of strongly nonlinear oscillators. A class of nonlinear jerk equation containing velocity-cubed and velocity times displacements-squared was taken as a typical example. Unlike other harmonic balance methods, all the former residual errors are introduced in the present approximation to improve the accuracy. Comparison of the result obtained using this approach with the exact one and simplicity and efficiency of the proposed procedure. The method can be easily extended to other strongly nonlinear oscillators.     

Application of homotopy analysis method for fractional Swift Hohenberg equation – Revisited

In this article, the homotopy analysis method is used to obtain the approximate analytical solutions of the non-linear Swift Hohenberg equation with fractional time derivative. The fractional derivative is described in Caputo sense. Numerical results reveal that the method is easy to implement, reliable and accurate when applied to time fractional nonlinear partial differential equations. Effects of parameters of physical importance on the probability density function and the convergence of the approximate series solution using residual error formula with the proper choices of auxiliary parameter for various fractional Brownian motions and standard motion are depicted through graphs and tables for different particular cases.     

A novel criterion for cluster synchronization of complex dynamical networks with coupling time-varying delays

This paper investigates the cluster synchronization problem for the time-varying delays coupling networks with nonidentical delayed dynamical systems by using pinning control method. We derive some simple and useful criteria for cluster synchronization for any initial values through an effective feedback control scheme and propose an adaptive feedback strategy that adjusts automatically the coupling strength. Finally, some numerical examples are then given to illustrate the theoretical results.     

乙烯基酯树脂的微观结构及其力学性能研究

树脂的微观结构决定其力学性能 ,乙烯基酯树脂微观结构的一个重要特征就是凝胶粒子和两相结构的存在 .采用SEM、DSC研究了乙烯基酯树脂固化过程中凝胶粒子的形成过程及两相结构对固化放热的影响 ,结果表明 ,凝胶粒子在固化树脂中呈群状分布 ,每群凝胶粒子的最大尺寸为 2 0 μm左右 ,每群凝胶粒子由许多独立凝胶粒子组成 ;凝胶粒子的形成使树脂产生了两相结构 ,使树脂的恒温DSC残余放热呈双峰分布 ;树脂的固化条件影响其微观结构 .力学性能测试的结果表明树脂的固化条件影响其力学性能 ,低温固化树脂(80℃固化 )的后固化可以提高其拉伸强度和弯曲强度 ,对于高温固化树脂 (12 0℃固化 ) ,则出现相反的趋势 ,后固化降低了树脂的拉伸强度和弯曲强度 .     

Circumferentially-symmetric finite eigenstrains in incompressible isotropic nonlinear elastic wedges

Eigenstrains are created as a result of anelastic effects such as defects, temperature changes, bulk growth, etc., and strongly affect the overall response of solids. In this paper, we study the residual stress and deformation fields of an incompressible, isotropic, infinite wedge due to a circumferentially symmetric distribution of finite eigenstrains. In particular, we establish explicit exact solutions for the residual stresses and deformation of a neo-Hookean wedge containing a symmetric inclusion with finite radial and circumferential eigenstrains. In addition, we numerically solve for the residual stress field of a neo-Hookean wedge induced by a symmetric Mooney–Rivlin inhomogeneity with finite eigenstrains.     

基于数字图像处理的含缺陷花岗岩破裂力学分析1）

在细观尺度上,采用数字图像处理技术研究花岗岩中由石英、长石和云母等材料的形状、大小及分布对花岗岩材料造成的非均匀性,结合RFPA-DIP 程序建立了能准确反映材料真实细观结构的含缺陷花岗岩数值模型,并进行了常规单轴压缩模拟试验,研究不同矿物颗粒结构与缺陷对其细观破裂力学行为的影响,再现了外载荷作用下不同数值模型的真实破裂过程与最终破坏模式. 试验结果表明:缺陷对试样强度的影响比改变矿物颗粒的形态构造对其强度的影响更加显著,缺陷的存在削弱了颗粒形态对花岗岩强度影响的能力;缺陷及矿物颗粒的形态构造对试样裂纹的萌生、扩展以及最终破坏模式有直接影响,缺陷与矿物颗粒的空间结构关系是导致岩石形成各种复杂破坏模式的主要因素. 起裂应力水平受试样内部细观介质构造和缺陷的影响,而缺陷的存在对起裂应力的影响更加显著.     

恒定主应力偏转角下黏土不排水剪切特性分析

天然土的结构性、各向异性对其强度有影响.进行固结压力100kPa、主应力轴恒定偏转角为0°,15°,30°,45°,60°的恒定主应力轴偏转角的固结不排水剪切试验,分析了不同恒定主应力轴偏转角对饱和软黏土固结不排水剪切强度影响;推导了总应力控制恒定主应力轴偏转角剪切试验总应力路径,编制了总应力控制剪切三维点积分程序,对比恒定主应力轴偏转角饱和软黏土固结不排水剪切强度计算值与试验结果,表明程序能很好地反应各向异性对土剪切强度影响.