二维非定常跨声速流动的B型反命题:变分理论

A family of variational principles (VP) has been developed for the unsteady inverse problem of the second type IB. It opens new ways for the inverse shape design of unsteady airfoils and can serve as key basis of multipoint inverse shape design of steady airfoils and cascades.     

二维振荡机翼可压缩绕流IA型反命题变域变分有限元解

In this paper, on the basis of the variational principles developed the finite element method (FEM) is employed for numerical solution of the inverse problem of 2-D unsteady compressible flow around oscillating airfoils by incorporating the non-reflecting far-field boundary conditions and a new unsteady Kutta condition. All unknown boundary (airfoil contour) and discontinuities(shocks and free trailing vortex sheets) are determined via the functional variation with variable domain and artificial density concept. For the numerical realization of the variable-domain variation, a special finite element with self-adjusting nodes is also suggested herein. The numerical results show that the present method is effective for the design of unsteady airfoil.     

Variable Domain Variational Finite Element Solution of I A Inverse Problem of 2 D Unsteady Compressible Flow around Oscillating Airfoils

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基于变域变分有限元的翼型气动设计

Designing airfoils according to given pressure (or velocity) distribution is one kind of free boundary problems. Free boundary condition can be coupled with the flow governing equations by variable-domain variational calculus, which makes it possible to calculate simultaneously the flow field and the free boundary. An accurate deduction of the variable-domain variational principles is taken herein to design airfoils in compressible and incompressible flows. Furthermore, two grid types (H and O) are used in the calculation with better results for the O-type grid. It is shown that convergence is accelerated and good results can be obtained even if the initial guessed airfoil shape is a triangle, demonstrating the strong adaptability of this method.     

A structural morphogenesis method based on a linkage mechanism system

This paper presents an elements-grouped morphogenesis method for the design of grid shells based on finding the linkage mechanism system shape that corresponds to the state of minimum potential energy. This method assigns the elements to several groups according to architectural design intentions and requirements to optimize a structural shape. A shape transformation equation is derived to constrain the total length of elements in each element group in the morphogenesis process and the generalized inverse matrix theory is then used to resolve the equation. The positions of nodes are, thus, progressively updated until the system reaches the minimum potential energy state. This method is characterized by the settings of element groups, temporary elements, and temporary forces. Finally, several numerical examples illustrate the characteristics and effectiveness of the proposed method.     

Anode Simulation and Cathode Design for Electrolytic Dressing of Diamond Profile Wheel

The design methods of anode and cathode are proposed for precision profile grinding.Based on the electrolytic machining theory, electrolytic equilibrium condition and Faraday‘s law of electrolysis are applied to establishing the mathematical model of profile diamond dressing processes. A finite element method (FEM) program is developed to solve the inverse boundary problem of Laplace‘s equation. Desired anode contour or cathode shape is determined by computing the distribution of electric potential layer by layer. Electrolytic machining experiment is carried out to verify the simulated anode shape. The research result shows that shape deviation between designed cathode and profile wheel increases with the value of angle between feed rate and the normal to anode surface. The shape of simulated anode is consistent with the contour of metal-bonded diamond profile wheel for a given cathode. Based on the anode contour, cathode shape can also be designed accurately.     

旧住宅水压不稳定原因简析及改造方案

通过对某住宅生活给水水压不稳定原因进行分析，并参考《建筑给水排水设计规范GB50015—2003》及建筑给水排水工程相关知识，提出了解决方法，分析了水压不稳的原因，折射当前旧住宅给水设计存在的普遍问题。     

构形诗中的形状和意义

虽然构形诗(CarmenFiguratum)是因它奇特的形状而命名,但并不是说,诗意的发展仅仅依靠它的奇特形状。在诗意的发展上,形状和诗的长度、韵律、节奏等所起的作用是相辅相承的。甚至在某种意义上来说,形状的作用和诗的长度是成反比例的。过分追求形状奇特会失去诗的本性。     

二维非定常对流扩散方程的高精度紧致半显式差分格

在已有文献的基础上,发展了一种求解二维非定常对流扩散方程的高精度紧致半显式差分格式,其截断误差为O（τ2 ＋h4）,该格式形式上是隐式,但实际上可以显式计算.利用Fourier分析法证明该格式是无条件稳定的.数值实验结果验证了该格式的精确性和可靠性.     

校正装置计算机辅助设计——根轨迹方法

将以时域参量描述的性能指标要求转化为一对期望主导极点位置的参数,引入校正装置改变原系统的根轨迹,使其通过或接近期望主导极点.对一个原来不稳定的系统,采用根轨迹方法设计校正装置,使其满足性能要求.设计过程通过计算机辅助绘图完成,从设计过程可以体会机辅分析与设计技术用在控制系统分析与设计中的一些具体做法,以及这种方法的便捷和优越.     

室内设计透视图的反求方法

室内设计透视图反向求解其真实尺寸是室内设计领域中一个有意义的课题。目前设计者可以借助电脑绘图软件,根据经典透视理论方便地实现这一过程,以某室内空间两点透视图为例,分析室内设计透视图反向求解的可能性及一般步骤,并对室内设计中复杂几何空间的透视反求原则进行探讨。     

远场模式反演声波阻尼区域的一种数值解法

研究了时间调和的声波反散射问题,利用散射波的远场模式反演阻尼边界条件中的边界。应用单层位势来逼近散射波,最终把反散射问题转化为一个最优化问题,应用Levenberg—Marquardt算法求解。给出的数值例子说明了该反演方法是可行和有效的。     

Intuitive Interference in Geometry: An Eye‐Tracking Study

Interference of irrelevant salient variables may cause difficulties for students. This study focused on eye tracking during the comparison of perimeters task, in which area is the interfering irrelevant salient variable. There were three trial types: congruent (larger area—larger perimeter), incongruent inverse (larger area—smaller perimeter), and incongruent equal (larger area—equal perimeter). Behavioral findings corroborated previous studies: congruent trials yielded higher accuracy and a shorter reaction time than did incongruent trials. Surprisingly, the area saliency could not be revealed in fixation location and duration measurements in incongruent inverse trials nor in the heat maps for incongruent inverse or incongruent equal trials, suggesting that such processing does not require overt attention; measures of attention shift from one geometrical shape to another were higher for incongruent equal trials, as was pupil dilation, suggesting that greater effort is associated with solving incongruent equal trials.     

Aerobasics — An introduction to aeronautics

Flight at supersonic speeds is accompanied by standing waves, a phenomenon absent in subsonic flows. The standing waves affect the flow radically and lead to wave drag and sonic booms. In this article, we explain the above phenomena and their effect on the performance of airfoils and wings in supersonic flows. In the light of the above, wing configurations suitable for supersonic airplanes are discussed.     

汉字形义联系与其文化蕴涵特征

汉字结构方式对其传载历史文化信息具有非同寻常的影响。汉字形义联系的紧密程度,与其文化符号的价值程度成反比,即形义联系越曲折松散,其传载历史文化信息的可能性就越大,就会有越多的机会深入探讨种种相关的历史文化内容及先民观念意识,进而深入探讨汉字的文化蕴涵。     

Aerobasics — An introduction to aeronautics

This part of the article continues the discussion of the aerodynamic characteristics of airfoils presented in the previous part and extends it to wings at subsonic speeds. The effects of highlift devices and spoilers are considered and their application indicated. The effects of wing sweep and finiteness of aspect ratio are analyzed.     

An approach for shape optimization of stratosphere airships based on multidisciplinary design optimization

Airship shape is crucial to the design of stratosphere airships. In this paper, multidisciplinary design optimization （MDO） technology is introduced into the design of airship shape. We devise a composite objective function, based on this technology, which takes account of various factors which influence airship performance, including aerodynamics, structures, energy and weight to determine the optimal airship shape. A shape generation algorithm is proposed and appropriate mathematical models are constructed. Simulation results show that the optimized shape gives an improvement in the value of the composite objective function compared with a reference shape.     

机械原理课程设计中机器人机构的动力学建模与仿真

为培养学生的机构分析能力,在机械原理课程设计中对3-PRR并联机器人机构动力学建模分析进行研究。推导出3-PRR并联机构位置反解、速度反解和加速度反解等方程。基于第2类拉格朗日方程建立3-PRR并联机器人机构逆动力学模型,据此求出各驱动关节的驱动力。在空载和负载两种情况下进行数值计算,经过与Adams仿真结果对比分析,验证了动力学建模的正确性。本研究为平面3自由度并联机器人机构运动学建模和动力学建模分析提供了有效的方法,为实物样机的优化设计奠定了理论基础。     

无芯模旋压旋轮轨迹曲线对其成形精度影响的仿真研究

研究目的：验证无芯模旋压工艺可行性,同时深入探究此新型工艺机理,研究并获取旋轮轨迹曲线参数化控制及其对于零件成形精度的影响趋势。创新要点：基于贝塞尔曲线实现对于无芯模旋压旋轮轨迹曲线的参数化控制;通过构建包括成形与回弹工艺过程的无芯模旋压仿真模型,研究参数化轨迹曲线对成形件壁厚及形状精度的影响趋势及关系,同时对成形过程变形区应力应变进行了深入探究分析。研究方法：1．基于三次贝塞尔曲线实现对于旋轮轨迹曲线的拟合以及参数化控制（图3）;2．利用LSDYNA软件实现对无芯模旋压成形及回弹工艺综合仿真及其过程、结果数据的提取;3．研究不同参数化轨迹曲线下成形件壁厚及形状精度变化趋钟（图12和13）,获取量化轨迹曲线对于零件成形精度影响关系（表3）,并通过增加实验组验证所获关系模型;4．提取成形过程中及成形后板料变形区应力及应变数据（图14-19）,深入探究上述变形机理。重要结论：凹轨迹曲线下,坯料中部出现最大减薄及变形程度,且降低曲线曲率,形状精度提高;凸轨迹曲线下,最大减薄及变形区域出现在坯料后部,且降低曲线曲率,壁厚及形状精度均提高。     

Interactive sculpting of product shape based on constraint manipulation in virtual environment

In product concept design, not only designers with professional CAD skills, but also final customers take part in the design and evaluation of product shape styling. Because customers usually lack surface modelling background and are not familiar with concrete operations of commercial CAD systems, it is difficult for them to express their change intentions of product shape through professional CAD tools if they are not satisfied with the current shape design. This paper puts forward a method for creating, dragging and manipulating constraint and load represented in form of icon entity in interactive sculpting of product shape in virtual environment. The method supports customers manipulation of sculpting constraints or loads on sculpting shapes in virtual reality interaction to control the deformation of product shape. Constraints management based on icon entity is similar to spline lofting operation that is familiar to engineers, so users do not need to know surface details or have any professional knowledge of surface modelling, by only using their physical and engineering experience, they can manipulate the sculpting of product shape intuitively.