A Simulation Study of the Beam Steering Characteristics for Linear Phased Arrays

Ultrasonic beam steering characteristics for linear phased array transducers are simulated numerically by visualizing the full-field acoustic pressure field of the waves radiated from a linear phased array transducer. The influences of various transducer parameters on the beam steering properties are studied, including number of elements, inter-element spacing, element size, frequency of the transducer and the steering angle. In addition, the effects of these parameters on the near field characteristics are investigated by analyzing the acoustic pressure profile in the steering direction. The simulation results agree well with the analytical solutions which are valid only in the far field. A suggested scheme for optimal transducer design is presented.     

A Linearized Approach for Diffraction-free Propagation in a Planar Nonlinear Waveguide

Abstract

The aim of this paper is to show that the superposition of three waves (one strong and two weak), under suitable conditions, can create diffraction free propagation in a nonlinear planar waveguide. The propagation is described by the nonlinear Schrödinger equation, which is suitably linearized.     

A New Approach for Multiple-Response Optimization

The desirability of a response that increases in a linear manner from the lower specification limit to the target value and decreases in a linear manner from the target value to the upper specification limit results in a breakpoint (nondifferentiable point) at the target value of its desirability function. Thus, modified desirability functions were proposed to solve this breakpoint problem so that the generalized reduced gradient can be applied. The modified desirability functions require the fitting of a quartic polynomial in the vicinity of the target. However, the fitting of the quartic polynomial needs to satisfy five conditions and involves numerous computations. Therefore, an approach with less computations and yet that is simple to implement is proposed in this article. This approach is applicable when the lower specification limit, the target value, and the upper specification limit of a response are available. In addition, this approach also allows practitioners to assign different degrees of importance to the responses. An example from the original paper of modified desirability functions is used to illustrate this approach.     

一种新的求解带有非凸二次约束的非凸二次规划问题的加速全局优化方法

本文中,我们结合一种由Qu,Zhang和Ji提出的全局规划问题以及适当的删除技巧提出一种新的加速全局优化算法来解决含有非凸二次约束的非凸二次规划(NQP)问题.这类优化问题能广泛应用于工程设计和非线性系统的鲁棒稳定性分析等实际问题中.这种技术能去掉大部分NQP问题全局最优解不存在的区域,而且它可以看成是NQP问题的全局优化算法的加速算法.同已有方法相比,数值实验显示运用这种方法的有效性显然提高,迭代步骤和运行时间明显减少.     

波传播法分析两端固支轴向运动梁的横向振动

用波传播法分析研究了两端固支轴向运动梁的横向自由振动。应用相位封闭原则导出了系统的频率方程,并求出了固有频率和模态函数。所得结论和传统方法解带有边界条件的微分方程的结果一致。但是,波传播法可以从物理角度更好的解释系统振动的本质,这是传统解法所没有提及的。     

A Nonlocal Operator Method for Partial Differential Equations with Application to Electromagnetic Waveguide Problem

A novel nonlocal operator theory based on the variational principle is proposed for the solution of partial differential equations. Common differential operators as well as the variational forms are defined within the context of nonlocal operators. The present nonlocal formulation allows the assembling of the tangent stiffness matrix with ease and simplicity, which is necessary for the eigenvalue analysis such as the waveguide problem. The present formulation is applied to solve the differential electromagnetic vector wave equations based on electric fields. The governing equations are converted into nonlocal integral form. An hourglass energy functional is introduced for the elimination of zero-energy modes. Finally, the proposed method is validated by testing three classical benchmark problems.     

Shape and Thickness Optimization Performance of a Beam Structure by Sequential Quadratic Programming Method

Successful performance of beam structures is critical to failure prevention, and beam performance can be optimized by careful consideration of beam shape and thickness. Shape and thickness optimization of beam structures having linear behaviour is treated. The first problem considered is the thickness distribution of the beam where the optimization variable is the thickness of the control points. The second problem is the shape optimization where the optimization variables are the ordinates of the control points. The optimization criterion (function objective to be minimized) is defined starting with the Von Mises criterion expressed in plane constraints. The resolution of the mechanical problem is made by the finite element method, and the optimization algorithm is the sequential quadratic programming (SQP) method.     

带非凸二次约束的二次规划问题的全局优化方法

利用二次函数的线形下界函数对带有非凸二次约束的二次规划(QP)提出一种新的求其全局最优解的分支定界算法.为改进算法的收敛性,根据问题的最优性和可行性提出一新的区域剪枝准则以排除(QP)的可行域中不存在全局解的部分.数值算例表明该准则能有效地加速算法的收敛性.     

Critical Flow Method: A New Reliability Allocation Approach for a Thermonuclear System

In the present work, starting from well‐known methodologies, a new reliability allocation method [critical flow method (CFM)] has been proposed. We focused on the most important conventional methods and discussed their limitations in order to motivate the current research. The results show the main common problem of the most conventional reliability allocation methods: they are developed for complex systems with series configurations but not for series–parallel ones. The consequence is an increase of the required units' reliability (series configuration) in order to guarantee the reliability system target. Actually, the design and manufacturing of a subsystem with an extremely low failure rate would consume a considerable amount of economic resources. The proposed method can solve the shortcomings of the conventional methods with a new reliability approach useful to series–parallel configurations in order to obtain an important cost saving. The CFM has been applied to a liquid nitrogen cooling installation in a thermonuclear system, with many series–parallel configurations in order to guarantee the whole safety system. The proposed technique can be applied to working complex systems, and, in general, in the design phase of new installations. By comparing the CFM application results with real parameters, the new technique has been validated. The computational results clearly demonstrate the advantages of the proposed method. In particular, by applying the method to series–parallel configurations, it allocates failure rates higher than conventional methods, with a component cost reduction. Copyright © 2015 John Wiley & Sons, Ltd.     

求解高分子结构预测问题的新直接搜索方法

高分子结构预测问题是目前国际上最热门的研究课题之一,它具有重要的理论意义和实用价值。本文探讨了其中的一类热门模型:势能函数模型。根据目前研究的现状和存在的不足,首次提出了求解该问题的直接搜索算法。首先,本文根据模型的特点改进了筛选子,然后优化了相应的算法。其次,本文进行的数值试验证了该方法的可行性和有效性。与其他方法相比,新算法针对大规模问题的求解具有明显的优势。     

一种新型的谐振梁频率测量方法研究

谐振梁是一种应用广泛的谐振器。谐振式传感器可以通过测量谐振梁谐振频率的变化,解算谐振梁所受的轴向载荷的大小,从而达到测量目的。目前谐振梁常用的频率测量方法对于动态测量问题的效果并不理想,在很多应用场合都受到限制。本文针对双端固支型谐振梁的频率测量问题,设计了一种基于希尔伯特变换的频率测量方法。使用数值方法对谐振梁振动方程进行求解,获得多种典型的测试信号。仿真实验表明,该方法能很好地获取动态信号频率。     

ZnO棒晶阵列薄膜的水溶液法生长

采用低温水溶液法, 在涂覆ZnO种子层的ITO基底上制备了高度取向的ZnO棒晶阵列, 考察了棒晶的生长过程以及生长液浓度、生长时间对薄膜形貌的影响. 用扫描电子显微镜(SEM),X射线衍射(XRD), 场发射扫描显微镜(FESEM)以及高分辨透射电镜(HRTEM)对ZnO纳米棒的结构和形貌进行了表征. 结果表明, ZnO薄膜的形貌强烈依赖于生长溶液的浓度和生长时间, ZnO棒是单晶, 属于六方纤锌矿结构, 具有沿(002)晶面择优生长的特征, 生长方式为层层台阶生长, 反应时间达到48h后, 通过二次生长形成特殊的板状晶.     

采用协方差矩阵评定测量不确定度的方法

本文首先评述了测量不确定度估计的研究动向。接着,论述了一种用协方差矩阵来表示和处理测量结果不确定度的方法,详细推导并阐述了其不确定度传播的规律.这种方法以矩阵形式严密、清晰、统一地表达出来,其优点是:评定模型通用性好,应用范围广;概率分布可以是未知的;用矩阵运算,算法简洁,适用于计算机快速测量与计算。本文最后通过两个实例来说明该方法的应用。     

对流扩散方程的一种新的显式方法

基于作者建立的一类新的指数型非对称半显式差分方法,提出了一种数值求解对流扩散方程的指数型交替组显方法。该方法具有固有并行性,而且无条件稳定,数值结果表明,该方法精度优于Evans和Abdullah在1985年提出的交替组显格式。     

一种用子结构求解特征灵敏度的新方法

提出了一种利用子结构在p=p0处的固定界面主模态和约束模态作为Ritz基综合出非亏损对称系统的特征灵敏度的方法.与其它子结构灵敏度综合方法相比,该方法不需要对子结构的约束模态以及固定界面主模态作一阶或二阶灵敏度分析,只要有子结构的约束模态和固定界面主模态就可以得到整体结构的灵敏度.算例表明了该方法的有效性.