曲面辐射屏蔽体的建模及可视化研究

用空间坐标变换法将曲面辐射屏蔽体的数学模型简化成标准型。通过模型变换法,可用球体和圆柱体来代替椭圆球和椭圆柱。对于弯管和环面状几何对象,先在新坐标系上确定其一组组顶点,然后由这些顶点绘制其图形。图形在标准位置上被绘制后,通过坐标平移和旋转转换到给定位置卜进行显示,从而可大幅度简化绘制过程。所绘制的图形能连续变化而且图形的着色和光照可通过菜单、对话框来变更。     

圆管绕流旋涡脱落诱导振动的数值模拟

利用计算流体力学软件Ansys／Flotran CFD,首先对粘性不可压缩流体的固定圆管绕流进行了数值模拟,然后结合逐步积分法完成了同时考虑纵横两向弹性支撑圆管绕流旋涡脱落诱导振动的数值模拟,并通过快速傅立叶变换,得到了弹性支撑圆管和固定圆管的升力及弹性支承圆管横向位移响应的功率谱．通过计算结果分析,得出了一些有价值的结论,可供从事具有圆管绕流构件设备设计的工程技术人员参考．     

The use of NONSAP to compare the Von Mises and a modified Von Mises yield criteria

The NONSAP finite element code was modified to include a modified Von Mises yield criterion. The program was then used to study the differences which exist between a Von Mises and a modified von Mises yield criterion for problems of elastic-plastic deformation.

The particular examples used to study this variation were that of a circular hole in a plate under uniaxial tension, a pressurized hemispherical head, and a pressurized open ended cylinder. The results of the finite element analyses are compared to previously published experimental studies.     

High Order Accurate Solution of Flow Past a Circular Cylinder

A high order method is applied to time-dependent incompressible flow around a circular cylinder geometry. The space discretization employs compact fourth-order difference operators. In time we discretize with a second-order semi-implicit scheme. A large linear system of equations is solved in each time step by a combination of outer and inner iterations. An approximate block factorization of the system matrix is used for preconditioning. Well posed boundary conditions are obtained by an integral formulation of boundary data including a condition on the pressure. Two-dimensional flow around a circular cylinder is studied for Reynolds numbers in the range 7 ≤ R ≤ 180. The results agree very well with the data known from numerical and experimental studies in the literature.     

Shedding of vortices behind a circular cylinder

The process of shedding of vortices from a circular cylinder is discussed by computing an unsteady viscous fluid flow at Reynolds number 200 under natural boundary conditions with a fine mesh near the surface of the cylinder. The phenomena of shedding of vortices is described by drawing streamlines patterns and the equivorticity lines at different times. The variations of the vorticity distribution, the pressure distribution and the drag coefficient at different times are shown by graphs. The Strouhal number for the shedding process is calculated and compared with the known results.     

Circular programs and self-referential structures

A circular program creates a data structure whose computation depends upon itself or refers to itself. The technique is used to implement the classic data structures circular and doubly-linked lists, threaded trees and queues, in a functional programming language. These structures are normally thought to require updateable variables found in imperative languages. For example, a functional program to perform the breadth-first traversal of a tree is given. Some of the examples result in circular data structures when evaluated. Some examples are particularly space-efficient by avoiding the creation of intermediate temporary structures which would otherwise later become garbage. Lastly, the technique can be applied in an imperative language to give an elegant program.     

圆柱绕流的二维数值模拟和尾迹分析

为指导机械设计中参数和布局的选择,研究固定在水流中的圆柱结构件的受力情况和流场分布．利用FLUENT中的三种湍流模型对雷诺数为3900的圆柱绕流进行二维数值模拟并进行对比,得到升力因数、阻力因数、分离角、斯特劳哈尔数和涡街尺寸等参数的模拟结果,与参考文献中的实验结果对比验证二维模拟的预测精度．RKE（Realizable k-ε）和雷诺应力模型（Reynolds Stress Model,RSM）均能在此雷诺数下得出接近实验结果的流场,RSM模型使用POWER LAW离散格式的结果优于QUICK格式．与三维模拟的对比表明二维模拟适合在设计初期的快速估算,能够快速得到合适精度的模拟结果．     

A BASIC microcomputer program to calculate the secondary structure of proteins from their circular dichroism spectrum

A BASIC program (CDPROT) has been developed to calculate the secondary structure of proteins from their far UV circular dichroism spectrum. This implementation can use different reference spectra, calculated either from model polypeptides or proteins of known tertiary structure. Apart from obtaining the alpha-helical, beta-structure, beta-turns or random percentages which would generate the spectrum of best fit with respect to the experimental measures, CDPROT represents on screen both theoretical and experimental spectra indicating the root-mean-square error. The provision of additional reference spectra by the user is also considered, and another program (STOREREF) performs the editing in an adequate format for CDPROT.     

Numerical solutions of time-dependent incompressible Navier-Stokes equations using an integro-differential formulation

A numerical method for the solution of the Navier-Stokes equations is developed using an integro-differential formulation of the equations. The method permits the actual computation to be confined to the viscous region of the flow and offers a drastic reduction in the number of data points required in the numerical procedure. The integro-differential formulation is presented along with discussion of the kinetic and kinematic aspects of the problem and the interplay between the two aspects. Results for several parallel flow problems and for the flow past a circular cyliner are presented. For the circular cylinder, it is shown that the introductions of a splitter plate behind the cylinder suppresses vortex shedding.     

ADOXI-PLOT: a computer program for plotting pedigrees illustrating autosomal dominant and X-linked inheritance

A FORTRAN program ADOXI-PLOT (Autosomal Dominant Or X-linked Inheritance Plot) has been developed. Different symbols are used to characterize individual family members. Depending on the size of the kindred, the pedigree automatically obtains a rectangular or circular appearance. The program can be used alone, or be connected to a register of families from which the input information for the plot program is obtained.     

RESIN,a FORTRAN IV program for determining the area of influence of samples or drill holes in resource target search

A FORTRAN IV program that calculates the area of influence of drill holes or samples with respect to the size and shape of elliptical or circular resource targets is presented. Program options include determination of the degree to which areas within a region have been explored and estimation of probabilities that points are centers of undiscovered deposits. Errors of recognition can be utilized in the program input.     

Diffusioosmosis of electrolyte solutions in fibrous porous media

An analytical study is presented for the diffusioosmotic flow of an electrolyte solution in the fibrous medium constructed by an ordered array of parallel charged circular cylinders at the steady state. The prescribed electrolyte concentration gradient is constant but can be oriented arbitrarily with respect to the axes of the cylinders. The electric double layer surrounding each cylinder may have an arbitrary thickness relative to the radius of the cylinder. A unit cell model which allows for the overlap of the double layers of adjacent cylinders is employed to account for the effect of fibers on each other. The electrostatic potential distribution in the fluid phase of a cell is obtained by solving the linearized Poisson–Boltzmann equation, which applies to the case of low surface potential of the cylinders. The macroscopic electric field induced by the imposed electrolyte concentration gradient through the fluid phase in a cell is determined as a function of the radial position. A closed-form formula for the fluid velocity profile of the electrolyte solution due to the combination of electroosmotic and chemiosmotic contributions as a function of the porosity of the array of cylinders correct to the second order of their surface charge density or zeta potential is derived as the solution of a modified Navier–Stokes equation. The diffusioosmotic velocity can have more than one reversal in direction over a small range of the zeta potential. For a given electrolyte concentration gradient in a cell, the fluid flow rate does not necessarily increase with an increase in the electrokinetic radius of the cylinder, which is the cylinder radius divided by the Debye screening length. The effect of the radial distribution of the induced axial electric field in the double layer on the diffusioosmotic flow is found to be of dominant significance in most practical situations.     

Self-calibration from one circular motion sequence and two images

This paper describes a new method for self-calibration of camera with constant internal parameters under circular motion, using one sequence and two images captured with different camera orientations. Unlike the previous method, in which three circular motion sequences are needed with known motion, the new method computes the rotation angles and the projective reconstructions of the sequence and the images with circular constraint enforced, which is called a circular projective reconstruction, using a factorization-based method. It is then shown that the images of the circular points of each circular projective reconstruction can be readily obtained. Subsequently, the image of the absolute conic and the calibration matrix of the camera can be determined. Experiments on both synthetic and real image sequence are given, showing the accuracy and robustness of the new algorithm.     

Non-hydrostatic finite volume model for non-linear waves interacting with structures

An efficient non-hydrostatic finite volume model is developed and applied to simulate non-linear waves interacting with structures. The unsteady Navier–Stokes equations are solved in a 3D grid made of polyhedrons, which are built from a 2D horizontal unstructured grid by adding several horizontal layers. A new grid arrangement in the vertical direction is proposed, which renders the resulting model is relatively simple. Moreover, the discretized Poisson equation for pressure is symmetric and positive definite, and thus it can be solved effectively by the preconditioned conjugate gradient method. Several test cases including solitary wave interacting with a submerged structure, solitary wave scattering from a vertical circular cylinder and an array of four circular cylinders are used to demonstrate the capability of the model on simulating non-linear waves interacting with structures. In all cases, the model gives satisfactory results in comparison with analytical solutions, experimental data and other published numerical results.     

New model and scheme for compressible fluids of the finite difference lattice Boltzmann method and direct simulations of aerodynamic sound

A new scheme for the finite difference lattice Boltzmann method is proposed, in which negative viscosity term is introduced to reduce the viscosity and the calculation time can be remarkably reduced for high Reynolds number flows. A model with additional internal degree of freedom is also presented for diatomic gases such as air, in which an additional distribution function is introduced. Direct simulations of aero-acoustics by using the proposed model and scheme are presented. Speed of sound is correctly recovered. As typical examples, the Aeolian tone emitted by a circular cylinder is successfully simulated even very low Mach number flow. Full three-dimensional sound emission is also given.     

A pressure-correction method and its applications on an unstructured Chimera grid

In this paper, an unstructured Chimera mesh method is used to compute incompressible flow around a rotating body. To implement the pressure correction algorithm on unstructured overlapping sub-grids, a novel interpolation scheme for pressure correction is proposed. This indirect interpolation scheme can ensure a tight coupling of pressure between sub-domains. A moving-mesh finite volume approach is used to treat the rotating sub-domain and the governing equations are formulated in an inertial reference frame. Since the mesh that surrounds the rotating body undergoes only solid body rotation and the background mesh remains stationary, no mesh deformation is encountered in the computation. As a benefit from the utilization of an inertial frame, tensorial transformation for velocity is not needed. Three numerical simulations are successfully performed. They include flow over a fixed circular cylinder, flow over a rotating circular cylinder and flow over a rotating elliptic cylinder. These numerical examples demonstrate the capability of the current scheme in handling moving boundaries. The numerical results are in good agreement with experimental and computational data in literature.     

Declarative solutions to partitioned‐grid problems

The problem of partitioning grid‐based applications for parallel computing can be solved easily and intuitively in a logic programming language such as Prolog, using only the single assignment property of the logic variable, and not the backtracking. We show that such a logic program can be transformed in a systematic way into a circular functional program, which runs 10 times faster than the original logic program. The transformation proceeds in a number of steps. The first step is novel, and we give a correctness proof. Our reasoning also uses a novel combination of concepts from both the logical and functional paradigms. Copyright © 1999 John Wiley & Sons, Ltd.     

Flat-end cutter orientation on a quadric in five-axis machining

The authors have recently developed methods for cutter orientation and tool path generation in 5-axis sculptured surface machining, where the design surface is approximated locally by a quadric. This paper presents, from a purely geometric perspective, the fundamental theory for optimising the cutter orientation on a quadric, which maximises the machined strip width whilst avoiding local and rear gouging. The analysis focuses on the flat-end cutter which is modelled by a circular cylinder but can be generalised for any fillet-end cutter using an appropriate offset of the design surface and the concept of geometric equivalency. The theory is illustrated by three examples.     

碳纤维层合板冲击吸能有限元模拟

为预测复合材料结构的冲击吸能效果,用三维有限元法模拟金属圆柱体冲击碳纤维层合板的过程．层合板被简化为三维正交各向异性材料板;采用Abaqus提供的vumat等扩展编程接口,用FORTRAN编写程序表征材料的弹性、强度和累积失效,实现动态破坏过程仿真;计算结果与冲击试验结果具有可比性．Abaqus的显式分析方法结合编程接口可用于层合板的冲击吸能仿真,结果的准确性取决于用户建立的材料模型．对不同速度、质量和直径的金属圆柱体的冲击进行计算,结果表明在穿透情况下,随着圆柱体速度的增加,圆柱体的动能衰减增多,而系统动能的减少相对稳定,因此后者更适合于临界速度的计算．     

On the use of incomplete sensitivities for feedback control of laminar vortex shedding

A feedback control method based on incomplete sensitivities and gradient evaluation by complex variable method is proposed and applied to the problem of the control of the laminar vortex shedding past a circular cylinder. This procedure results in a low-cost control algorithm, which does not require to compute the gradient of the Navier–Stokes solution with respect to the controllers. For the sake of usability for practical applications, realistic sensors and actuators are used. Validation simulations aiming at controlling the drag of the cylinder are presented and compared with previous published results, proving the efficiency of the proposed method. Application to the control of the cylinder lift is also shown.