A new numerical algorithm for 2D moving boundary problems using a boundary element method

Phase change problems are of practical importance and can be found in a wide range of engineering applications. In the present paper, two proposed numerical algorithms are developed; the first one is general for phase change problems, while the second one is for ablation problems. The boundary elements method is used as a mathematical tool in conjunction with the proposed algorithms. Two test examples were solved and the results agree with the physics of the problems.     

High-precision and ultrafast UV laser system for next-generation flexible PCB drilling

Since conventional mechanical punching technology for Flexible Printed Circuit Board (FPCB) drilling has restricted via-hole size and depth control for multi-layer circuit boards, CO₂ and Ultra Violet (UV) laser drilling technologies have been developed. However, the FPCBs for mobile phones and Personal Digital Assistants (PDAs) require smaller via-hole diameters, since the development of thinner and higher circuit density devices is demanded. Currently, UV laser systems are widely used for FPCB drilling of 75–105 μm diameter via-holes and inspectors performs quality test manually using microscopes. We developed a high-precision UV laser microfabrication system for next-generation FPCB drilling of 15 μm diameter via-holes. The degrees of the precision of the microfabricated via-holes of 15, 35, 50 and 85 μm were mean absolute error rate of 4.4, 2.2, 2.3, and 2.2 which was fully satisfied with industrial inspection specification ±10%. The drilling speed of the system of 2800 via-holes per second at stationary state was achieved. In addition, we applied modified Greedy 2-opt algorithm to find out optimal drilling path which reduced the total time of via-hole fabrication. We successfully reduced the production time by 25% compared with the result obtained in the normal Greedy 2-opt algorithm. Moreover, we designed very accurate inspection method using Canny edge detection and geometric pattern matching algorithms and successfully applied it to the Automated Optical Inspection (AOI) module for the inspections of 15 μm diameter via-hole which was required for the fabrication of high density FPCB.     

A micro-adjusting attitude mechanism for autonomous drilling robot end-effector

Drilling end-effector is a key unit in autonomous drilling robot. The perpendicularity of the hole has an important influence on the quality of airplane assembly. Aiming at the robot drilling perpendicularity, a micro-adjusting attitude mechanism and a surface normal measurement algorithm are proposed in this paper. In the mechanism, two rounded eccentric discs are used and the small one is embedded in the big one, which makes the drill＇s point static when adjusting the drill＇s attitude. Thus, removal of drill＇s point position after adjusting the drill attitude can be avoided. Before the micro-adjusting progress, four non-coplanar points in space are used to determine a unique sphere. The normal at the drilling point is measured by four laser ranging sensors. The adjusting angles at which the motors should be rotated to adjust attitude can be calculated by using the deviation between the normal and the drill axis. Finally, the motors will drive the two eccentric discs to achieve micro-adjusting progress. Experiments on drilling robot system and the results demonstrate that the adjusting mechanism and the algorithm for surface normal measurement are effective with high accuracy and efficiency.     

A free boundary approach and keller's box scheme for BVPs on infinite intervals

A free boundary approach for the numerical solution of boundary value problems (BVPs) governed by a third-order differential equation and defined on infinite intervals was proposed recently [SIAM J. Numer. Anal., 33 (1996), pp. 1473–1483]. In that approach, the free boundary (that can be considered as the truncated boundary) is unknown and has to be found as part of the solution. This eliminates the uncertainty related to the choice of the truncated boundary in the classical treatment of BVPs defined on infinite intervals. In this article, we investigate some open questions related to the free boundary approach. We recall the extension of that approach to problems governed by a system of first-order differential equations, and for the solution of the related free boundary problem we consider now the reliable Keller's box difference scheme. Moreover, by solving a challenging test problem of interest in foundation engineering, we verify that the proposed approach is applicable to problems where none of the solution components is a monotone function.     

面向网络攻防演练的操作系统仿真模型研究与实现

针对目前网络攻防演练中对主机行为的表现粒度不足的问题,通过分析操作系统概念以及性质,给出了一种用于网络攻防演练的操作系统仿真模型。该模型反映了操作系统的安全属性。还给出了该仿真系统的体系结构,使得仿真系统具有一定的扩展性。     

A well deliverability model for non-Darcian flow in geothermal reservoirs

A new numerical algorithm is proposed to estimate the deliverability of a geothermal well. The mathematical model assumes a single-component fluid. The model accounts for both the phase change phenomenon and the non-Darcian behavior of the flow. The contemporaneous presence of both effects has to the authors’ knowledge never been fully taken into account. Provided that the numerical solution is based on a finite differences or finite volumes method, the numerical code we developed (called DNDmultiphase) can be plugged as an additional module into existing codes devoted to simulations of a whole reservoir (such as TOUGH2 or HYDROTHERM).     

A solution-adaptive central-constraint transport scheme for magnetohydrodynamics

The central-constraint transport scheme for magnetohydrodynamics in Ziegler [J. Comput. Phys. 196 (2004) 393] is made adaptive employing a block-structured mesh refinement method. Based on the guidelines in Berger and Collela [J. Comput. Phys. 82 (1989) 64] a mesh refinement variant has been developed which combines a flexible grid adaptation by using small blocks as refinement elements with integration speed by reducing the inherent overhead via block clustering techniques. The algorithms are discussed in detail and the efficiency of the implementation is benchmarked in terms of an efficiency parameter which takes into account both the obtained speedup factor and an error estimate. The three-dimensional benchmark problems are a spherical implosion problem and a shock-cloud collision problem in a magnetic medium. Further examples of astrophysical interest are presented which demonstrate the robustness and versatility of the new adaptive grid code.     

A multigrid algorithm for parallel computers: CPMG

In this article, we present a multigrid algorithm for parallel computers, the chopped parallel multigrid (CPMG) algorithm. The CPMG algorithm improves the processor utilization by reducing the work load on coarse grids without affecting the convergence rate of the algorithm. This is in contrast to earlier approaches (Gannon and van Rosendale, 1986; Frederickson and McBryan, 1989), where unutilized processors are used to improve the convergence rate. The CPMG algorithm reduces the coarse grid work bychopping the alternate cycles of multigrid. Using analytical results and simulations on sequential machines we show that the CPMG can achieve almost the same convergence rate as standard MG for many cases. Analytically we show that the advantage gained by CPMG over standard MG on a mesh connected massively parallel machine is 33% in hardware utilization, 50% in communication overheads and 38% in overall execution time. We have also evaluated the performance of CPMG on an actual massively parallel machine, the DAP-510. The advantage gained by CPMG over standard MG is 35% in overall execution time. Moreover, the CPMG can be integrated with other parallel multigrid algorithms, such as the PSMG algorithm (Frederickson and McBryan, 1989) and Decker's algorithm (Decker, 1990).     

A method for the calibration of a 3-D laser scanner

The calibration of a three-dimensional digitizer is a very important issue to take into consideration that good quality, reliability, accuracy and high repeatability are the features which a good digitizer is expected to have. The aim of this paper is to propose a new method for the calibration of a 3-D laser scanner, mainly for robotic applications. The acquisition system consists of a laser emitter and a webcam with fixed relative positions. In addition, a cylindrical lens is provided with the laser housing so that it is capable to project a plane light. An optical filter was also used in order to segment the laser stripe from the rest of the scene. For the calibration procedure it was used a digital micrometer that move a target with known dimensions. The calibration method is based on the modeling of the geometrical relationship between the 3-D coordinates of the laser stripe on the target and its digital coordinates in the image plane. By this method it is possible to calibrate the intrinsic parameters of the video system, the position of the image plane and the laser plane in a given frame, all in the same time.     

A variable time delay compensator for multivariable linear processes

A variable time delay compensator based on the Smith predictor is proposed. Finite difference and cinematic techniques are employed for a numerical approximation of the variable delay. The resulting multivariable controller is analyzed for robustness using the structured singular value. The technique is demonstrated through two simulated systems: a single-input, single-output numerical example, and a cross-direction paper machine control problem.     

基于本体和CBR的钻井工程风险决策模型研究

为了实现钻井工程风险智能决策,从钻井专家决策过程的特征出发,针对传统的CBR技术的不足,提出并构建了一种基于本体和CBR的钻井工程风险决策模型。通过对风险决策案例的分析,设计了钻井风险决策案例的结构,并结合本体技术构建了风险决策案例本体,使案例表示更规范化、语义化,同时为案例知识提供了良好的可扩展性与共享性;为了提高案例检索效率,按照本体中风险的类别对案例进行分层组织,建立了风险案例库;针对现有的案例相似度计算模型的缺陷,提出了一种改进的基于本体的语义相似度计算模型,并由此构建了风险案例检索模型,经现场实例测试,结果表明该模型有效地提高了案例检索的查准率和查全率。在以上基础上,开发了钻井工程风险决策原型系统,为钻井专家、技术人员提供了高效的决策支持。     

凿岩机器人钻臂定位控制交叉精英反向粒子群算法

在利用粒子群优化算法(particle swarm optimization,PSO)进行凿岩机器人钻臂定位过程中,存在收敛速度慢和易于陷入局部最优解等问题.为此,提出一种交叉精英反向粒子群优化算法(crossover elite opposition-based particle swarm optimization,CEOPSO)并给出算法的流程.建立凿岩机器人钻臂运动学模型并对其逆向运动学进行求解.将交叉算子引入EOPSO中,采用自适应惯性权重和交叉概率参数控制技术,在维护粒子个体与最优解之间信息交换的基础上,增加粒子个体之间的信息交换,提高算法的全局搜索能力和钻臂定位效率.仿真结果表明,CEOPSO的平均位置误差和平均姿态误差均小于PSO和EOPSO算法,且迭代过程平稳,可以有效提高凿岩机器人钻臂的定位控制性能.     

A fixed-point approach for nonlinear discrete boundary value problems

Existence results are established for second-order discrete boundary value problems.     

合金相变材料储热过程的数值仿真研究

传统低熔点相变材料,具有较小的导热系数,严重影响了相变储能装置的吸放热速率和储能效率.Cerrolow-136合金因其具有的良好导热性能和较低的相变点温及,在电子设备散热领域具有巨大的潜力.为了验证Cerrolow-136合金在强化换热方面的优势,首次采用数值仿真的方法对储热性能进行研究,并与石蜡的温控效果和相变过程进行对比.建立了三维相变储能装置的数学模型,利用焓-多孔理论分析相变材料的熔化过程.结果表明:Cerrolow-136合金相变材料相比较石蜡在温控能力和导热均匀性方面都具有较大的优势;在热流密度为1000～ 3000W/m2,环境温度为80℃的高温环境下,Cerrolow-136合金相变储能装置可确保在3988～9922s内将发热面温度控制在70℃以下.仿真结果为以后Cerrolow-136合金的应用提供参考.     

An efficient and reliable model to simulate microscopic mechanical friction in the Frenkel–Kontorova–Tomlinson model

The Frenkel–Kontorova–Tomlinson model is composed of a large number of non-linear, coupled differential equations that reproduce the friction occurring in mechanical systems in which the atomic smooth surfaces of two bodies slide against each other. The problem is very interesting since the possible solutions, which are very sensitive to the parameters of the system, range from simple stable harmonic solutions (in which the spectrum of the movement of individual atoms contains one frequency) to chaotic solutions (where the spectrum contains a series of incommensurable frequencies), passing through intermediate solutions formed by a spectrum of commensurable finite frequencies. The design of the model both for the static and dynamic problem, which follows the network method rules, is explained in detail and the model is run on standard electrical circuit simulation software to provide, in its own graphic ambient, the average total friction force, the Fast Fourier Transforms of atom displacement and the phase diagrams. The influence of the main parameters of the system (interaction force amplitude and stiffness between surface atoms and substrate) on the type of pattern of the solution is studied for a practical range of these parameters.     

A simple model for aquatic plant management

Aquatic plants have become a problem in many freshwater bodies. Several control techniques are available, but mechanical methods (eg. harvesting) have advantages in some circumstances. Since the effectiveness of mechanical methods has been variable, a model has been formulated to investigate the impact on the plants of several harvesting regimes. The model reproduces the observed dynamics of unperturbed growth very well, and shows reasonable dynamics for harvested plants. Results from the model suggest that July is the optimum time to harvest, but that harvesting cannot be viewed as more than a temporary relief to the plant problem.     

A numerical method for deadbeat control of generalized state-space systems

In this paper we give a new numerical method for constructing a rank m correction BF to an n × n matrix A, such that the generalized eigenvalues of λE−(A+BF) are all at λ = 0. In the control literature, this problem is known as ‘deadbeat control’ of a generalized state-space system Ex_i+1 = Ax_i + Bu_i, whereby the matrix F is the ‘feedback matrix’ to be constructed.     

基于加速度计和磁强计的随钻姿态测量观测模型

水平定向钻进中钻具姿态的实时测量是实现导向的关键因素。推导了钻具姿态角的测量方法,给出了姿态转换矩阵的解算公式。针对姿态测量的非线性问题和已有算法的不足,建立了姿态测量系统的线性观测方程,该观测方程利用加速度计和磁强计分别测得的地球重力场分量和地磁场分量来构造新的观测向量,并以姿态四元数的误差向量作为观测模型的输入。给出了线性观测模型的求解方法,最小二乘递推法。仿真结果表明:该算法收敛速度快,能够得到钻具准确的姿态信息,即使起始姿态的估计值与真实值之间的偏差很大,该算法仍能很好地收敛到真实值。     

A multiscale numerical method for the heterogeneous cable equation

Several interesting problems in neuroscience are of multiscale type, i.e. possess different temporal and spatial scales that cannot be disregarded. Such characteristics impose severe burden to numerical simulations since the need to resolve small scale features pushes the computational costs to unreasonable levels. Classical numerical methods that do not resolve the small scales suffer from spurious oscillations and lack of precision.This paper presents an innovative numerical method of multiscale type that ameliorates these maladies. As an example we consider the case of a cable equation modeling heterogeneous dendrites. Our method is not only easy to parallelize, but it is also nodally exact, i.e., it matches the values of the exact solution at every node of the discretization mesh, for a class of problems.To show the validity of our scheme under different physiological regimes, we describe how the model behaves whenever the dendrites are thin or long, or the longitudinal conductance is small. We also consider the case of a large number of synapses and of large or low membrane conductance.