Analysis and design of ribbon cables for high‐speed digital applications

Ribbon cables have been widely used as subsystem interconnections in a large number of digital systems, because they can convey numerous bits of a digital signal simultaneously. In this article, finite difference and finite difference time domain (FDTD) methods are used to analyze and optimize the electrostatic analysis design of ribbon cables, and measurements are used to verify the numerical results. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 148–158, 2002.     

半波振子天线矩量法的研究

矩量法是将连续方程离散为代数方程组的方法,此法对于求解微分方程和积分方程均适用,本文以半波振子天线为例,系统的阐述了半波振子天线的海伦积分方程的建立,利用矩量法求解海伦积分方程而得半波振子天线上的电流分布,已知电流分布求解半波振子天线在远区的电场表达式和方向图。     

A numerical simulation to verify the stress-free growth of silicon crystal ribbon

Thermal stresses developed during the growth of silicon crystal ribbon have been shown to be negligible, thus eliminating residual stresses and dislocations, if the temperature profile satisfies a second-order partial differential equation inside the ribbon. This has been numerically verified through a finite element model, an outline of which is presented here. This model shows that, for homogeneous isotropic material with temperature independent thermal expansion co-efficients, thermal stresses will vanish if the temperature profile satisfies the Laplacian. A comparison of stresses due to uniform and non-uniform temperature gradients in the plane of the ribbon is also presented. The strategies employed to control the round-off error and to validate the computer model are discussed.     

Application of mortar elements to diffuse-interface methods

An adaptive 2D mesh refinement technique based on mortar spectral elements applied to diffuse-interface methods is presented. The refinement algorithm tracks the movement of the 2D diffuse-interface and subsequently refines the mesh locally at that interface, while coarsening the mesh in the rest of the computational domain, based on error estimators. Convergence of the method is validated using a Gaussian distribution problem and results are presented for a Cahn–Hilliard diffuse-interface model applied to capture the transient dynamics of polymer blends.     

Stabilised finite element methods for a bending moment formulation of the Reissner-Mindlin plate model

This work presents new stabilised finite element methods for a bending moments formulation of the Reissner-Mindlin plate model. The introduction of the bending moment as an extra unknown leads to a new weak formulation, where the symmetry of this variable is imposed strongly in the space. This weak problem is proved to be well-posed, and stabilised Galerkin schemes for its discretisation are presented and analysed. The finite element methods are such that the bending moment tensor is sought in a finite element space constituted of piecewise linear continuos and symmetric tensors. Optimal error estimates are proved, and these findings are illustrated by representative numerical experiments.     

Application of spectral methods to the solution of Navier-Stokes equations

In this paper a number of topics that arise in application of Chebyshev expansion methods to the solution of the Navier-Stokes equations are addressed. These include the equivalence of finite differences and finite elements approaches, a new velocity-pressure formulation that permits easy extension to three dimensions, evaluation of the importance of pressure boundary conditions and the virtues of collocation over the tau method for satisfying boundary conditions. Example results from the velocity-pressure formulation which eliminate a non-linear momentum equation in favor of the linear continuity equation are presented. The results are for a 2-D unsteady flow on a flat plate at large Reynolds numbers. The behavior of an unsteady disturbance in such a flow is examined and compared with previous stream-function vorticity results of Murdock.     

电阻应变计在扭矩测量中的应用

工程和实际中,许多情况下必须控制和知道扭矩的大小。利用电阻应变计式传感器,用液晶显示器显示扭矩大小,设计出一种新型工具———数显扭矩起子。     

Flow characterization of valveless micropump using driving equivalent moment: theory and experiments

A valveless micropump, actuated by a PZT disk bonded to a glass plate, can generate positive flow. In order to estimate flow characteristics of micropumps, it is necessary to theoretically analyze the radial expansion (more specifically, the equivalent moment) of the PZT disk according to the voltage input. Using the equivalent moment, deflection equations are derived for the tri-layer disk (PZT, epoxy bonder and glass plate) and are confirmed to match well with experiments. The flow rate of the valveless micropump is also theoretically and experimentally investigated in terms of input voltage and oscillation frequency. The flow increased at a rate of 0.1 μL/min/V, and the maximum flow rate was obtained at the driving frequency of around 225 Hz.     

Application of parallel computing methods to the processing of sea-surface radar imagery

The capabilities of advanced parallel computing methods in processing and identification of seasurface radar imagery are investigated. Their application for the real-time analysis of large-area images is justified. Based on the methods developed by the authors of this paper, estimates are given for the mass, dimensions, and power consumption of a special-purpose onboard processor needed for processing sea-surface radar imagery.     

Application of optimization methods to helicopter rotor blade design

The minimum weight design of helicopter rotor blades with constraints on multiple coupled flap-lag natural frequencies is studied in this paper. A constraint is also imposed on the minimum value of the autorotational inertia of the blade to ensure sufficient autorotational inertia to autorotate in case of an engine failure. A stress constraint is used to guard against structural failure due to blade centrifugal forces. Design variables include blade taper ratio, dimensions of the box beam located inside the airfoil and magnitudes of the nonstructural weights. The program CAMRAD is used for the blade modal analysis and the program CONMIN for the optimization. In addition, a linear approximation involving Taylor series expansion is used to reduce the analysis effort. The procedure contains a sensitivity analysis which consists of analytical derivatives of the objective function, the autorotational inertia constraint and the stress constraints. A central finite difference scheme is used for the derivatives of the frequency constraints. Optimum designs are obtained for both rectangular and tapered blades. The paper also discusses the effect of adding constraints on higher frequencies and stresses on the optimum designs. b box beam width - c chord - f ₁,f ₃,f ₄ first three lead-lag dominated frequencies (elastic modes) - f ₂,f ₅ first two flapping dominated frequencies (elastic modes) - g constraint function - h box beam height - h(z) box beam height variation along blade span - n number of blades - r _j distance from the root to the center of thej-th segment - t ₁,t ₂,t ₃ box beam wall thicknesses - x, y, z reference axes - A box beam cross-sectional area - AI autorotational inertia - E Young's modulus - F objective function - FS factor of safety - GJ torsional stiffness - I _x ,I _y total principal area moments of inertia about reference axes - L _j length ofj-th segment - M _j total mass ofj-th segment - N total number of blade segments - NDV number of design variables - R blade radius - W total blade weight - W() blade weight as a function of design variable - W _b box beam weight - W _o nonstructural blade weight (weight of skin, honeycomb, etc. along with tuning/lumped weights) - prescribed autorotational inertia - design variable increment - _h taper ratio inz direction - _i i-th design variable - _j mass density of thej-th segment - _j stress inj-th segment - _max maximum allowable stress - blade RPM - r root value - t tip value - L lower bound - U upper bound - ^ approximate value This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States     

A simulation study of structure characterization methods

Linear black box modelling often requires an inductive model structure characterization method or expressed in other terms a technique that permits for the determination of the order of the model on the basis of experimental data. Recently a number of different methods like FPE, AIC, LILC and BIC have been proposed. The statistical properties of those criteria are badly known. In the paper, the criteria are shown to be similar, differing only in a threshold level. A systematic Monte-Carlo simulation study with second order autoregressive models has been carried out. It is found that the properties of the structure discriminating statistics are remarkably independent of the parameter values or the location of the poles. For all criteria, the error rate increases as the coefficient of the highest order time lag decreases to zero. The simulation indicates the superiority of BIC over LILC and of LILC over AIC. The study suggests that a new criterium that would be dependent on the highest order time lag parameter could be superior.     

Application of methods of feasible directions to structural optimization problems

A general approach to structural optimization which has received much attention in recent years is that of using mathematical programming (numerical search) techniques. These techniques may be separated into direct and indirect methods. Of the direct methods of attack on general nonlinear inequality constrained problems, the largest class is called methods of feasible directions. This paper presents the application fo Zoutendijk's method of feasible directions [5] to structural optimization problems. The algorithm requires the analytic gradient of the objective function and the constraint functions which are active at a given stage in the design process. A considerable improvement in convergence has been achieved by considering each pushoff factor as a linear function of the corresponding active constraint. A comparison of the half-step versus full-step search procedure is presented. An initial step length based on a present decrement of objective function is used. A discussion of the linear versus quadratic interpolations of a constraint function in search for a bound point is presented. The algorithm is demonstrated with elastic design of a 25-bar space tower, a 3-bay single storey and a double bay double storey rigid jointed plane frames. Data on the differences in the optimum designs obtained from different starting points is reported.     

Application of multivariable frequency response methods to control of turbogenerators

This paper deals with the design, evaluation and testing of an integrated control scheme for a turbogenerator equipped with a high-gain thyristor exciter and an electro-hydraulio governing system. Multivariable frequency response methods are used, and these are demonstrated to be eminently suitable for the design and analysis of turbogenerator controllers. It is shown that a control scheme consisting of an automatic voltage regulator with speed stabilizer, and speed governor with lead compensator, designed by the above methods, can greatly improve the dynamic and transient performance of a turbogenerator.

This was confirmed by computer simulation, and by extensive tests on a laboratory model turbogenerator. The controllers in the oxcitor and governor loops are easily implemented, and the results show significant improvements in system damping, transient stability, and post-fault recovery of terminal voltage. It has thus been established that these controllers, designed on the basis of linearized mathematical models, work well in practice, at least in a laboratory environment.     

Selection of appropriate defuzzification methods: Application to the assessment of dam performance

The performance assessment of dams is of major importance for optimizing maintenance management. A methodology is provided here to assess the risk of dam failure using data collected during in-situ inspections and from the design and follow-up files. This assessment takes into account uncertainty associated with the data and the assessment process. The result of this assessment is introduced in a fuzzy frame. This paper presents the approach taken to choose defuzzification methods that allow extracting the information necessary from this possibility distribution so that dam experts can both rank dam maintenance actions and communicate the results of this assessment.This paper first presents the process used to assess dam performance after which it presents the defuzzification methods available. A sensitivity analysis is then performed to select the methods most relevant for our case study. The last part presents the development of a tool useful for the application of defuzzification methods to our problematic and describes a real case study in which the selected defuzzification methods are used.     

Avoiding the CNN moment

The CNN Moment is that agonizing disaster where the dot-com infrastructure fails and its architectural shortcomings end up as a lead story on CNN's financial news. As everyone battles to restore the operational integrity of the site, the hapless company combats angry customers, disappointed analysts, falling stock prices, reduced earnings, lawsuits, and a plethora of other ills that can damage the value of the dot-com brand and, in some cases, imperil the company's very survival. At a minimum it is always the kind of bad publicity that every dot-com wants to avoid. It is vital to take steps now to keep your company from experiencing the CNN Moment     

Assembly simulation of multi-branch cables

Cable assembly simulation is a key issue in the computer-aided design (CAD) of products with complex electrical components. In this study, an assembly simulation method is developed to simulate the assembly process of multi-branch cables. First, based on the Cosserat theory of elastic rods, a novel scheme is introduced to model the joints of multi-branch cables. The potential energy of joints is calculated by taking the topology and anatomical features into consideration. Various physical properties are considered. Various constraints, including connectors, collars, and handles are analyzed, based on which the initial conditions of assembly simulation are determined. The configuration of the cable is then calculated by minimizing its potential energy. To increase computational efficiency, GPU acceleration is introduced, which makes the simulation run at interactive rates even for a cable with resolution up to 1000 discrete points. Finally, the proposed algorithm is integrated into the commercial assembly simulation system, DELMIA. Several simulations were performed with our system. It was demonstrated that the proposed method is able to handle cables with complex topologies. In addition, the proposed method is about four times as efficient as a previous method, and it is able to generate realistic configurations of multi-branch cables at interactive rates. Thus, the proposed method is helpful in the assembly process planning of cables.     

Dynamic response of sagged cables

The equations of motion of the cable are developed for the general case when the cable is supported at two different elevations and subjected to static and dynamic loads between supports. The nonlinear strain-displacement relationship is used, which accounts for the change in cable tension during motion. The equations of motion are solved using the finite difference method for fixed and movable support conditions. The time history of the three components of the displacement and tension in the sagged cable are determined for the following forcing functions: a suddenly applied uniform load constant with time; a load varying sinusoidally with time; and a prescribed time history of motion of one end of cable.     

Application of vanishing variable methods to special structured transportation problems

Methods of determining vanishing variables in transportation problems have appeared in a literature published by Intrator and Lev [4]. This paper implements the theorems to special structured transportation problems in general, and tridiagonal transportation problems in particular. New rules are developed for reducing the amount of computations required for solving tridiagonal transportation problems. The rules will result in assigning optimal values to the variables (the values are often zero) and even decomposition of large problems into smaller sub problems.     

Application of global optimization methods to model and feature selection

Many data mining applications involve the task of building a model for predictive classification. The goal of this model is to classify data instances into classes or categories of the same type. The use of variables not related to the classes can reduce the accuracy and reliability of classification or prediction model. Superfluous variables can also increase the costs of building a model particularly on large datasets. The feature selection and hyper-parameters optimization problem can be solved by either an exhaustive search over all parameter values or an optimization procedure that explores only a finite subset of the possible values. The objective of this research is to simultaneously optimize the hyper-parameters and feature subset without degrading the generalization performances of the induction algorithm. We present a global optimization approach based on the use of Cross-Entropy Method to solve this kind of problem.