Dynamic characteristics of micro air bearings for microsystems

This paper reports on the dynamic characteristics of micro air bearings that include thrust and journal air bearings for microsystems. The dynamic thrust air bearing employs a spiral groove configuration. Analysis shows that the motion stability and load capacity of a thrust air bearing imposes a contradictive requirement on the groove pattern of the air bearing. The dynamic journal air bearing is realized by using a plain circular trench with a narrow radial clearance of C, and a very small aspect ratio of bearing length versus diameter (L/D). Analysis on the shock tolerance of the journal air bearing shows that the shock tolerance increases with the bearing number, the bearing aspect ratio of L/D and its initial equilibrium eccentricity ratio ε ₀. The optimum values of the bearing parameters are explored and recommended. A prototype of turbine device has been designed based on the recommended bearing configurations and realized via microfabrication.     

Pattern analysis of dermoscopic images based on Markov random fields

In this paper a method for detecting different patterns in dermoscopic images is presented. In order to diagnose a possible skin cancer, physicians assess the lesion based on different rules. While the most famous one is the ABCD rule (asymmetry, border, colour, diameter), the new tendency in dermatology is to classify the lesion performing a pattern analysis. Due to the colour textured appearance of these patterns, this paper presents a novel method based on Markov random field (MRF) extended for colour images that classifies images representing different dermatologic patterns. First, each image plane in L^*a^*b^* colour space is modelled as a MRF following a finite symmetric conditional model (FSCM). Coupling of colour components is taken into account by supposing that features of the MRF in the three colour planes follow a multivariate Normal distribution. Performance is analysed in different colour spaces. The best classification rate is 86% on average.     

Studies on a micro turbine device with both journal- and thrust-air bearings

This paper presents design, fabrication, analysis and test of a silicon-based micro turbine device that is driven by compressed air. To improve the motion stability at high rotational speed, the turbine device employs an enhanced micro air bearing system that includes both journal air bearing and thrust air bearings. The double-sides dynamic thrust air bearings are designed to support the rotor from both its top and bottom sides. The top thrust air bearing employs pump-in spiral groove configuration, and the bottom bearing uses pump-out spiral groove configuration. The dynamic journal air bearing is formed by a plain circular trench with a short journal length (L) and a narrow radial clearance (C). The critical aspect ratio (L/C) over 20:1 is realized through an optimized fabrication process. The micro turbine device has been fabricated, integrated and tested. During the test, the turbine device demonstrated stable operations at a rotational speed of 14,700 rpm.     

Wear identification in rotor-bearing systems by measurements of dynamic bearing characteristics

During operation of rotating machines, journal and bearing mechanisms are progressively worn down. To prevent catastrophic failure of a rotating system, it is necessary both to detect wear precisely, without shutting down and dismantling the machinery and to predict future replacement needs. In this work, Computational Fluid Dynamics (CFD) analysis is used to solve the Navier–Stokes equations. Diagrams of bearing characteristics such as relative eccentricity, attitude angle, lubricant side flow and friction coefficient versus Sommerfeld number are presented for various wear depths and used for online wear identification. A graphical detection method is analytically presented to identify the wear depth associated with the measured dynamic bearing characteristics.     

JChainsAnalyser: an ImageJ-based stand-alone application for the study of magneto-rheological fluids

JChainsAnalyser is a Java-based program for the analysis of two-dimensional images of magneto-rheological fluids (MRF) at low concentration of particles obtained using the video-microscopy technique. MRF are colloidal dispersions of micron-sized polarizable particles in a carrier fluid with medium to low viscosity. When a magnetic field is applied to the suspension, the particles aggregate forming chains or clusters. Aggregation dynamics [P. Domínguez-García, S. Melle, J.M. Pastor, M.A. Rubio, Phys. Rev. E 76 (2007) 051403] and morphology of the aggregates [P. Domínguez-García, S. Melle, M.A. Rubio, J. Colloid Interface Sci. 333 (2009) 221-229] have been studied capturing images of the fluid and analyzing them by using this software. The program allows to analyze automatically the MRF images by means of an adequate combination of different imaging methods, while magnitudes and statistics are calculated and saved in data files. It is possible to run the program on a desktop computer, using the GUI (graphical user interface), or in a cluster of processors or remote computer by means of command-line instructions.

Program summary

Program title: JChainsAnalyserCatalogue identifier: AEDT_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDT_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 79 071No. of bytes in distributed program, including test data, etc.: 4 367 909Distribution format: tar.gzProgramming language: Java 2Computer: Any computer with Java Runtime Environment (JRE) installedOperating system: Any OS with Java Runtime Environment (JRE) installedRAM: Typically, 3.3 MBClassification: 23External routines: ImageJ, ij-imageIO, jdom, L2FProdNature of problem: The video-microscopy technique usually produces quite a big quantity of images to analyze. Although ImageJ gives the required filters and methods for image analysis, it fails when a large number of images is used. Moreover, an adequate combination of filters is needed for the segmentation and binarization of this kind of images.Solution method: JChainsAnalyser filters and analyses any quantity of MRF images automatically, so the application can be run on a desktop computer or using a cluster of processors. It can be run in a desktop computer using the GUI (graphical user interface) or by a command-line interface. JChainsAnalyser uses XML files to define input/output data and Java to ensure portability between operating systems. It also utilizes an image algorithm based on the application of different and adaptative ImageJ's filters.Running time: The test run provided takes only a few seconds.     

Simulating magnetic positive positioning of cryogenic propellants in a transient acceleration field

A computational simulation of magnetic positive positioning (MP²) is developed to model cryogenic propellant reorientation in reduced gravity. Previous efforts have successfully incorporated an electromagnetic field model into an axisymmetric, two-dimensional, incompressible fluid flow model yielding accurate predictions of fluid motion induced by a magnetic field. To simulate MP², a three-dimensional magnetic field and magnetic force model was developed as a feature of a commercially available fluid flow model which has been well validated. The computational tool was then improved upon to model magnetically induced flows in a transient acceleration field. Simulation predictions obtained with the enhanced model are compared to available reduced gravity experiment data. Evidence is presented and conclusions are drawn that support the continued use of the simulation as viable modeling and predictive tool in the continuing study of MP².     

Performances of journal bearing with MoS2-shot coating for spindle of magnetic recording storage system

MoS₂-shot coating technology is recently focused as one of potential methods of surface modification to realize a low friction state. In this paper, performances of a small-sized journal bearing with MoS₂-shot coating, which we aim to apply to a spindle of magnetic recording storage system, are investigated in detail through both of the observation of surface property and experimental approach from the viewpoints of frictional torque, durability against start–stop repetition, and run-out characteristics. In consequence, we can conclude that the MoS₂-shot coating spindle is suitable for the application of small-sized journal bearing.     

Computer simulation of MHD blood conveying gold nanoparticles as a third grade non-Newtonian nanofluid in a hollow porous vessel

In this paper, heat transfer and flow analysis for a non-Newtonian third grade nanofluid flow in porous medium of a hollow vessel in presence of magnetic field are simulated analytically and numerically. Blood is considered as the base third grade non-Newtonian fluid and gold (Au) as nanoparticles are added to it. The viscosity of nanofluid is considered a function of temperature as Vogel's model. Least Square Method (LSM), Galerkin method (GM) and fourth-order Runge–Kutta numerical method (NUM) are used to solve the present problem. The influences of the some physical parameters such as Brownian motion and thermophoresis parameters on non-dimensional velocity and temperature profiles are considered. The results show that increasing the thermophoresis parameter (N_t) caused an increase in temperature values in whole domain and an increase in nanoparticles concentration just near the inner wall of vessel. Furthermore by increasing the MHD parameter, velocity profiles decreased due to magnetic field effect.     

Parametric studies of coupled vibration of cylindrical pipes conveying fluid with the wave propagation approach

The wave propagation approach is extended to the coupled frequency analysis of finite cylindrical pipes conveying dense fluid. The downstream, upstream and mixed frequencies of the pipe are defined and discussed. The effects of fluid and shell parameters on the coupled frequencies are investigated. The difference between the coupled and uncoupled frequencies decreases with the circumferential mode n, but increases with the mode n after the number n where the fundamental frequency is obtained. The fundamental frequency can change from one circumferential mode to another circumferential mode with the h/R ratios. However for a shorter shell the fundamental frequency may keep with the same mode n in the interested h/R ratios. For different boundary conditions the transition of fundamental frequency between circumferential modes occurs at different h/R ratios. The downstream frequency increases with increasing fluid velocity, whereas the upstream frequency decreases as the fluid velocity increases. However, the mixed frequency of the pipe decreases with the increase of the fluid velocity. For a given flow velocity all the three frequencies decrease with decreasing h/R ratios. However the mixed frequency drops more with increasing fluid velocity at small h/R ratios than at large h/R ratios. Therefore negative frequencies may occur for small h/R ratios if the fluid velocity is large enough, which means that instability occurs first for thinner pipes.     

A bi-directional rotating fluid bearing system

 Most fluid bearing systems with grooves on the journal/thrust bearing surfaces were designed to rotate in a specified direction and cannot be reversed. This feature of such fluid bearings limits their application range and hence, a bi-directional rotating fluid bearing system is proposed. The results of numerical simulation on the dynamic characteristics of such bearing system are presented and compared with those of one-directional rotating fluid-bearing system. It shows that for the same load capacity and stiffness requirement, the bi-directional rotating fluid bearing system has a higher power consumption than that of the one-directional counterpart. However, the bi- directional rotating fluid bearing system provides the freedom of rotating spindle motor in either direction and widens the application range of fluid bearing spindle motors. Received: 5 July 2001/Accepted: 17 October 2001     

Dynamic characteristics of a coupled journal and thrust hydrodynamic bearing in a HDD spindle system due to its groove location

 This research numerically analyzes the dynamic characteristics of a coupled journal and thrust hydrodynamic bearing due to its groove location which has the static load due to the weight of a rotor in the axial direction and the dynamic load due to its mass unbalance in the radial direction. The Reynolds equation is transformed to solve a plain member rotating type of journal bearing (PMRJ), a grooved member rotating type of journal bearing (GMRJ), a plain member rotating type of thrust bearing (PMRT), and a grooved member rotating type of thrust bearing (GMRT). FEM is used to solve the Reynolds equations in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or axial displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge–Kutta method. This research shows that the groove location affects the pressure distribution in the fluid film and consequently the dynamic performance of a HDD spindle system. Received: 5 July 2001/Accepted: 17 October 2001     

MHD flow past a circular cylinder using the immersed boundary method

The immersed boundary method (IB hereafter) is an efficient numerical methodology for treating purely hydrodynamic flows in geometrically complicated flow-domains. Recently Grigoriadis et als. [1] proposed an extension of the IB method that accounts for electromagnetic effects near non-conducting boundaries in magnetohydrodynamic (MHD) flows. The proposed extension (hereafter called MIB method) integrates naturally within the original IB concept and is suitable for magnetohydrodynamic (MHD) simulations of liquid metal flows. It is based on the proper definition of an externally applied current density field in order to satisfy the Maxwell equations in the presence of arbitrarily-shaped, non-conducting immersed boundaries. The efficiency of the proposed method is achieved by fast direct solutions of the two poisson equations for the hydrodynamic pressure and the electrostatic potential.The purpose of the present study is to establish the performance of the new MIB method in challenging configurations for which sufficient details are available in the literature. For this purpose, we have considered the classical MHD problem of a conducting fluid that is exposed to an external magnetic field while flowing across a circular cylinder with electrically insulated boundaries. Two- and three-dimensional, steady and unsteady, flow regimes were examined for Reynolds numbers Re_d ranging up to 200 based on the cylinder’s diameter. The intensity of the external magnetic field, as characterized by the magnetic interaction parameter N, varied from N=0 for the purely hydrodynamic cases up to N=5 for the MHD cases. For each simulation, a sufficiently fine Cartesian computational mesh was selected to ensure adequate resolution of the thin boundary layers developing due to the magnetic field, the so called Hartmann and sidewall layers. Results for a wide range of flow and magnetic field strength parameters show that the MIB method is capable of accurately reproducing integral parameters, such as the lift and drag coefficients, as well as the geometrical details of the recirculation zones. The results of the present study suggest that the proposed MIB methodology provides a powerful numerical tool for accurate MHD simulations, and that it can extend the applicability of existing Cartesian flow solvers as well as the range of computable MHD flows. Moreover, the new MIB method has been used to carrry out a series of accurate simulations allowing the determination of asymptotic laws for the lift and drag coefficients and the extent of the recirculation length as a function of the amplitude of the magnetic field. These results are reported herein.     

Vibration of hard disk drive spindle systems with distributed journal bearing forces

This paper is to analyze vibration of fluid dynamic bearing spindles with distributed journal bearing forces. The dynamical model is developed to predict the transverse vibration of the disk–spindle systems in HDD where an aspect ratio of the bearing width to the shaft length is significant and the shaft is likely flexible. In such spindles the journal bearing functions as a continuous support, providing the distributed restoring and damping forces, and is therefore modeled as distributed linear spring and damping forces through distribution functions of dynamic coefficients. Vibration analysis reveals that the spindle model with distributed bearing forces predicts the same natural frequencies for all transverse modes but higher modal damping of the rocking modes, when compared to the values predicted by the conventional model with discrete bearing forces. The difference in damping prediction is clearer for the flexible-shaft spindle whose ratio of the bearing width to the shaft length becomes larger.

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Fuzzy Modeling and Control for Conical Magnetic Bearings Using Linear Matrix Inequality

A general nonlinear model with six degree-of-freedom rotor dynamics and electromagnetic force equations for conical magnetic bearings is developed. For simplicity, a T–S (Takagi–Sugeno) fuzzy model for the nonlinear magnetic bearings assumed no rotor eccentricity is first derived, and a fuzzy control design based on the T–S fuzzy model is then proposed for the high speed and high accuracy control of the complex magnetic bearing systems. The suggested fuzzy control design approach for nonlinear magnetic bearings can be cast into a linear matrix inequality (LMI) problem via robust performance analysis, and the LMI problem can be solved efficiently using the convex optimization techniques. Computer simulations are presented for illustrating the performance of the control strategy considering simultaneous rotor rotation tracking and gap deviations regulation.     

Distributions of the potential and electric field of an electrode elliptic array used in tumor electrotherapy: Analytical and numerical solutions

To estimate the potential and electric field generated by any electrode array is very useful in effective tumor destruction. At present, an electrode array that takes into account the ellipsoidal geometry of the solid tumors has not been proposed. We present both analytical and numerical solutions for the potential and electric field in a solid tumor established by an electrode array with elliptic shape which may be used in vitro, in vivo and in clinical studies for cancer treatment with electrotherapy. These analytical and numerical solutions are obtained using multipole expansion and the finite difference method. Distributions of potential and electric field magnitudes are computed in function of the eccentricity of an elliptical array and compared with those obtained with a circular array of electrode. Maximum difference and Root Means Square Error are used to compare the distributions of the potential and electric field in leading-order and first-order correction and between the analytical and numerical solutions. The results show a good agreement between these distributions in both orders and the analytical and numerical solutions. It was concluded that the mathematical approach presented in this study is a tool for a rapid design of electrode elliptical arrays in order to induce the maximum destruction of the tumor. Moreover, it is shown that, for all values of eccentricity, there is a good correspondence between the distributions of the potential and the electric field for leading-order and first-order correction and for both the analytical and numerical solutions.     

Fuzzy clustering algorithms for unsupervised change detection in remote sensing images

In this paper, we propose a context-sensitive technique for unsupervised change detection in multitemporal remote sensing images. The technique is based on fuzzy clustering approach and takes care of spatial correlation between neighboring pixels of the difference image produced by comparing two images acquired on the same geographical area at different times. Since the ranges of pixel values of the difference image belonging to the two clusters (changed and unchanged) generally have overlap, fuzzy clustering techniques seem to be an appropriate and realistic choice to identify them (as we already know from pattern recognition literatures that fuzzy set can handle this type of situation very well). Two fuzzy clustering algorithms, namely fuzzy c-means (FCM) and Gustafson-Kessel clustering (GKC) algorithms have been used for this task in the proposed work. For clustering purpose various image features are extracted using the neighborhood information of pixels. Hybridization of FCM and GKC with two other optimization techniques, genetic algorithm (GA) and simulated annealing (SA), is made to further enhance the performance. To show the effectiveness of the proposed technique, experiments are conducted on two multispectral and multitemporal remote sensing images. A fuzzy cluster validity index (Xie-Beni) is used to quantitatively evaluate the performance. Results are compared with those of existing Markov random field (MRF) and neural network based algorithms and found to be superior. The proposed technique is less time consuming and unlike MRF does not require any a priori knowledge of distributions of changed and unchanged pixels.     

Magnetohydrodynamic state estimation with boundary sensors

We present a PDE observer that estimates the velocity, pressure, electric potential and current fields in a magnetohydrodynamic (MHD) channel flow, also known as Hartmann flow. This flow is characterized by an electrically conducting fluid moving between parallel plates in the presence of an externally imposed transverse magnetic field. The system is described by the inductionless MHD equations, a combination of the Navier-Stokes equations and a Poisson equation for the electric potential under the so-called inductionless MHD approximation in a low magnetic Reynolds number regime. We identify physical quantities (measurable on the wall of the channel) that are sufficient to generate convergent estimates of the velocity, pressure, and electric potential field away from the walls. Our observer consists of a copy of the linearized MHD equations, combined with linear injection of output estimation error, with observer gains designed using backstepping. Pressure, skin friction and current measurements from one of the walls are used for output injection. For zero magnetic field or nonconducting fluid, the design reduces to an observer for the Navier-Stokes Poiseuille flow, a benchmark for flow control and turbulence estimation. We show that for the linearized MHD model the estimation error converges to zero in the L² norm. Despite being a subject of practical interest, the problem of observer design for nondiscretized 3-D MHD or Navier-Stokes channel flow has so far been an open problem.     

《中国图象图形学报》创刊20年出版情况统计分析

目的 在《中国图象图形学报》创刊20年后,回顾和总结其20年来的发展情况,分析当前状态,并展望未来方向。方法 对1996年创刊以来前20年的出版情况和数据进行统计和分析,包括学报创刊情况,所设栏目（及其文献数量）和主题,所发表的文献综述系列的概况及所反映的特点,以及学报的出版期数、页数、篇数（包括每期页数、每期篇数、每篇页数等）与它们的变化和趋势。结果 将学报的统计数据与其他14种图像工程刊物进行了对比,反映了学报在相关领域的相对专业地位和学术水平,也揭示了若干值得改进的方向。结论 经过20年的努力和发展,学报已是相关专业领域里的一个重要刊物,但还有继续提高的需求和目标。     

摩托车磁流变阻尼器的设计研究

磁流变液（Magnetorheological fuild）是一种新型的智能材料，属于可控流体，具有在外加磁场作用下快速可逆地改变流变性能的特点。本文选择剪切阀式作为本文阻尼器的工作模式，对磁流变阻尼器的磁路进行了设计；优化设计了磁流变阻尼器的结构参数，在此基础上，根据理论分析选择阻尼器的结构尺寸，设计制作了单出杆磁流变阻尼器。对本文设计的磁流变阻尼器的特性进行了实验研究，本文的研究结果对于磁流变阻尼器在摩托车悬挂系统中的应用具有较好的参考价值。