基于偏微分方程方法的Bézier曲面设计

提出了一种Bézier曲面设计方法,该方法通过给定2条边界曲线及对应一阶切矢和二阶切矢基于偏微分方程构造Bézier曲面.该曲面具有PDE曲面的优点,可通过调整边界条件束调整曲面形状.该方法易于实现,可适用于自由曲面的设计以及过渡面的构造.     

对曲面上参数曲线二等分角轨线微分方程的理解

对曲面上参数曲线二等分角轨线微分方程进行求解,解释u-曲线和v-曲线的切向量的表示方法,即以在某点张成二维向量切空间Tps的两个切向量-ru(u,v)和-rv(u,v)为基底,以-δr(u,v)在自然基底{-ru(u,v),-rv(u,v)}下的分量(δu,δv)为其切向量,并对参数曲线的二等分角θ1和θ2关系的两种情况θ1=θ2和θ1+θ2=π进行讨论,利用曲面的第一基本形式求解,使得曲面上参数曲线二等分角轨线微分方程更加易于理解,有助于初学者对微分几何课程更好地学习.     

浅论EViews与期权定价的有限差分法

文章介绍了EViews统计软件在线性代数方面具备强大的计算功能,提出这些功能恰好满足偏微分方程(PDE)数值解法的基本要求,因此EViews非常适合于为期权定价.     

MATLAB在磁场分析中的应用

MATLAB提供了一个图形用户界面的偏微分方程的数值求解工具。它包括了数值分析的前处理,计算和后处理等一套完整的程序。本文介绍了电磁场数值分析基本理论并通过实例介绍了使用MATLAB PDE工具箱实现电磁场偏微分方程的有限元解法。仿真结果表明这一方法具有操作简单、快速、准确等优点。     

MasterCAM中构建昆氏曲面的探讨

昆氏曲面是构建复杂曲面最常见的方法,但昆氏曲面的构造极其复杂,步骤繁琐,使人们难以理解和加以应用。本文从昆氏曲面的基本概念、创建方法、要点等来阐述昆氏曲面在Mas-terCAM中的应用。     

艺术花瓶三维建模方法

针对目前广泛使用的UG和Pro/E软件,以艺术花瓶为例,详细阐述了如何巧妙利用曲线方程来创建复杂曲线,通过网格曲面、曲面缝合、加厚或混合等特征来完成艺术花瓶的三维建模,从中体会这两种软件在创建曲面时的区别和联系。该方法可广泛用于类似曲面的三维设计。     

反求工程中基于特征截面线的曲面重构技术研究

对点云数据截平面的生成、特征截面线的提取、截面线分割以及基于截面线的曲面重构技术进行了研究,并给出适合该理论的算法。     

浅谈线切割曲面加工

本文主要论述线切割关于曲面加工的特点,本文以一个风扇叶片的加工为例,阐述线切割在曲面加工的传统方法,以及线切割曲面加工目前存在的问题以及加工难点。另一方面阐述了线切割加工曲面的可观发展前景。     

Labview下基于高阶PDE的局部放电信号去噪

局部放电检测是预防电力事故的有效手段,因现场强烈的电磁干扰,提取的局部放电信号往往混入了大量的噪声。因此噪声抑制是局部放电检测中的一个重要环节。借鉴偏微分方程(PDE)在图像噪声抑制中的良好表现,将其引入到局部放电信号的去噪中,并在Labview中进行了实现。结果表明,偏微分方程对噪声具有良好的抑制作用。     

汽车钣金模具CAD技术研究

汽车钣金逆向CAD模型建构在汽车业界的发展已久.近年来,国内开始使用逆向工程软件,以建构曲面及特征线的方式,进行钣逆向CAD模型的建构.该方法除可以通过控制曲面质量来改善加工精度,以减少后段工程的钳修部份,更由于CAD的曲面资,可以做为设计后端各工程参考依据,使得整个开发的过程予以计算机化,节省再开发的成本.本文讨论了钣金模具逆向流程,以及汽车钣金逆向CAD模型的建构技术.     

An adaptive iterative learning algorithm for boundary control of a coupled ODE–PDE two-link rigid–flexible manipulator

To perform repetitive tasks, this paper proposes an adaptive boundary iterative learning control (ILC) scheme for a two-link rigid–flexible manipulator with parametric uncertainties. Using Hamilton?s principle, the coupled ordinary differential equation and partial differential equation (ODE–PDE) dynamic model of the system is established. In order to drive the joints to follow desired trajectory and eliminate deformation of flexible beam simultaneously, boundary control strategy is added based on the conventional joints torque control. The adaptive iterative learning algorithm for boundary control scheme includes a proportional-derivative (PD) feedback structure and an iterative term. This novel controller is designed to deal with the unmodeled dynamics and other unknown external disturbances. Numerical simulations are provided to verify the performance of proposed controller in MATLAB.     

基于特征缺失修复的人脸三维运动形变估计算法

人脸由于其非刚性明显,受到运动背景变化、形变程度复杂、特征丢失等因素的影响,使得在进行三维动态人脸形变估计时,面临着估计不准,误差较大的问题。为了解决这些问题,提出一种基于特征缺失修复的人脸三维运动形变估计算法,将非刚体人脸运动的形变估计过程中,运用特征补偿方法,补偿由于噪声、形变程度复杂带来的特征丢失缺陷,运用较多的人脸形变特征进行形变分析,准确计算人脸的形变程度。实验结果表明,这种方法得到的解误差较小,效果明显。     

Boundary stabilization of a class of reaction–advection–diffusion systems via a gradient-based optimization approach

In this paper, the boundary stabilization problem of a class of unstable reaction–advection–diffusion (RAD) systems described by a scalar parabolic partial differential equation (PDE) is considered. Different the previous research, we present a new gradient-based optimization framework for designing the optimal feedback kernel for stabilizing the unstable PDE system. Our new method does not require solving non-standard Riccati-type or Klein–Gorden-type PDEs. Instead, the feedback kernel is parameterized as a second-order polynomial whose coefficients are decision variables to be tuned via gradient-based dynamic optimization, where the gradients of the system cost functional (which penalizes both kernel and output magnitude) with respect to the decision parameters are computed by solving a so-called “costate” PDE in standard form. Special constraints are imposed on the kernel coefficients to ensure that the optimized kernel yields closed-loop stability. Finally, three numerical examples are illustrated to verify the effectiveness of the proposed approach.     

产品开发经验在企业国际扩张中的作用机制

拥有丰富的产品开发经验(PDE)是否能帮助国际化的企业提升创新绩效呢？一方面,动态能力理论认为企业积累产品开发经验可以在对外直接投资过程中发挥作用进而提高创新绩效。另一方面,路径依赖理论表明企业的PDE是针对国内市场的,经验的积累可能会限制它们利用国际化机会从事创新的能力。基于这样的“母国能力悖论”本研究提出竞争性假设,通过对2002-2012年间80家企业400个样本观测值的实证分析,证实了在中国情境下产品开发经验的深度负向调节国际扩张与创新绩效关系,我们的发现支持了路径依赖效应的假说。     

高效节能低噪风扇优化设计

根据扭曲风叶成型原理和叶栅理论,推导出扭曲风叶风扇气动设计计算方法,分析叶轮结构与其气动性能参数的内在关系,编制成风扇优化设计软件。通过该软件得到了用户需要的座舱风扇的扇叶几何图形及气动特性曲线,并与实测的数据相比较,误差在设计范围内。     

A probabilistic approach to polycrystalline plasticity part II: applications

Using our constitutive theory for polycrystalline plasticity, we have calculated characteristic yield conditions for several sample materials in which the dependence of the dislocation velocity on stress is given by an empirical power function. The shape of the yield surfaces for these materials varies resembling that of von Mises when the stress exponent is small and that of Tresca when the exponent is large. Additional examples illustrate the ability of the proposed theory to model such phenomena as the development of anisotropy during plastic deformation, material hardening and softening, the occurrence of upper and lower yield points, and a Bauschinger effect.     

The dynamics and stability of lubricating oil films during droplet transport by electrowetting in microfluidic devices

The operation of digital microfluidic devices with water droplets manipulated by electrowetting is critically dependent on the static and dynamic stability and lubrication properties of the oil films that separate the droplets from the solid surfaces. The factors determining the stability of the films and preventing surface fouling in such systems are not yet thoroughly understood and were experimentally investigated in this study. The experiments were performed using a standard digital microfluidic cartridge in which water droplets enclosed in a thin, oil-filled gap were transported over an array of electrodes. Stable, continuous oil films separated the droplets from the surfaces when the droplets were stationary. During droplet transport, capillary waves formed in the films on the electrode surfaces as the oil menisci receded. The waves evolved into dome-shaped oil lenses. Droplet deformation and oil displacement caused the films at the surface opposite the electrode array to transform into dimples of oil trapped over the centers of the droplets. Lower actuation voltages were associated with slower film thinning and formation of fewer, but larger, oil lenses. Lower ac frequencies induced oscillations in the droplets that caused the films to rupture. Films were also destabilized by addition of surfactants to the oil or droplet phases. Such a comprehensive understanding of the oil film behavior will enable more robust electrowetting-actuated lab-on-a-chip devices through prevention of loss of species from droplets and contamination of surfaces at points where films may break.     

On the Classification of the Bonnet Surfaces

In this paper,we will prove that the Bonnet surfaces can beclassified into three different types and the first or second types areequivalent to helicoidal surfaces(including surfaces of revolution andcylinders)under Bonnet deformations.     

低渗透油藏双线渗流油井指示曲线研究

考虑启动压力梯度和介质变形系数的影响,建立了低渗透油藏垂直裂缝井双线流模型。根据此模型可得到不同地层参数条件下的油井指示曲线。计算结果表明：随着介质变形系数的减小,指示曲线的斜率逐渐增大,随着启动压力梯度的增大,指示曲线逐渐向下平移。