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Mesh objective tensile cracking via a local continuum damage model and a crack tracking technique

COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2006年第1-3期196卷 304-320页

作者： Cervera, M. Chiumenti, M. Tech Univ Catalonia Int Ctr Numer Methods Engn Barcelona 08034 Spain

This paper describes a procedure for the solution of problems involving tensile cracking using the so-called smeared crack approach, that is, standard finite elements with continuous displacement fields and a standard local constitutive model with strain-softening. An isotropic Rankine damage model is considered. The softening modulus is adjusted according to the material fracture energy and the element size. The resulting continuum and discrete mechanical problems are analyzed and the question of predicting correctly the direction of crack propagation is deemed as the main difficulty to be overcome in the discrete problem. It is proposed to use a crack tracking technique to attain the desired stability and convergence properties of the corresponding formulation. Numerical examples show that the resulting procedure is well-posed, stable and remarkably robust;the results obtained do not seem to suffer from spurious mesh-size or mesh-bias dependence. (c) 2006 Elsevier B.V. All rights reserved.

关键词： tensile cracking smeared crack approach strain softening strain localization damage tracking algorithms mesh dependence

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Smeared crack approach: back to the original track

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INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS 2006年第12期30卷 1173-1199页

作者： Cervera, M. Chiumenti, M. UPC CIMNE Barcelona 08034 Spain

This paper briefly reviews the formulations used over the last 40 years for the solution of problems involving tensile cracking, with both the discrete and the smeared crack approaches. The paper focuses on the smeared approach, identifying as its main drawbacks the observed mesh-size and mesh-bias spurious dependence when the method is applied 'straightly'. A simple isotropic local damage constitutive model is considered, and the (exponential) softening modulus is regularized according to the material fracture energy and the element size. The continuum and discrete mechanical problems corresponding to both the weak discontinuity (smeared cracks) and the strong discontinuity (discrete cracks) approaches are analysed and the question of propagation of the strain localization band (crack) is identified as the main difficulty to be overcome in the numerical procedure. A tracking technique is used to ensure stability of the solution, attaining the necessary convergence properties of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is stable and remarkably robust. As a consequence, the results obtained do not suffer from spurious mesh-size or mesh-bias dependence, comparing very favourably with those obtained with other fracture and continuum mechanics approaches. Copyright (C) 2006 John Wiley & Sons, Ltd.

关键词： tensile cracking strain softening strain localization damage tracking algorithms mesh dependence

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The Fast Track Trigger at the H1 experiment design concepts and algorithms

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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 2006年第1期566卷 130-132页

作者： Schoening, Andre ETH Honggerberg Inst Particle Phys CH-8093 Zurich Switzerland

The HI Collaboration has built a new Fast Track Trigger which performs a full reconstruction of charged particles in a high multiplicity environment. At the first trigger level (2.3 mu s) coarse tracks are reconstructed in two dimensions whereas at the second level (23 mu s) all tracks are reconstructed with high precision in all three dimensions. This allows to identify particle resonances at the third trigger level (<= 100 mu s). The conceptual design and the implementation of the fast track finding algorithms are discussed. First results from the 2005 running period are presented. (c) 2006 Elsevier B.V. All rights reserved.

关键词： H1 experiment track trigger tracking algorithms

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A methodology for image-based tracking of seismic-induced motions

A methodology for image-based tracking of seismic-induced mo...

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Smart Structures and Materials 2005 Conference

作者： Doerr, KU Hutchinson, TC Kuester, F Univ Calif Irvine Dept Elect Engn & Comp Sci Irvine CA 92717 USA

ISBN: (纸本)0819457396

Previous experiences during earthquake events emphasize the need for new technologies for real-time monitoring and assessment of facilities with high value nonstructural elements such as equipment or other contents. Moreover, there are substantial limitations to our ability to rapidly evaluate and identify potential hazard zones within a structure, exposing rescue workers, society and the environment to unnecessary risks. A real-time monitoring system, integrated with critical warning systems, would allow for improved channeling of resources. Ideally such a system would acquire all relevant data non-intrusively, at high rates and resolution and disseminate it with low latency over a trusted network to a central repository. This repository can then be used by the building owner and rescue workers to make informed decisions. In recognition of these issues, in this paper, we describe a methodology for image-based tracking of seismically induced motions. The methodology includes calibration, acquisition, processing, and analysis tools geared towards seismic assessment. We present sample waveforms extracted considering pixel-based algorithms applied to images collected from an array of high speed, high-resolution charged-couple-device (CCD) cameras. This work includes use of a unique hardware and software design involving a multi-threaded process, which bypasses conventional hardware frame grabbers and uses a software-based approach to acquire, synchronize and time stamp image data.

关键词： seismic motions image acquisition image processing tracking algorithms

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A comparative study of predictive transmit power control schemes for S-UMTS

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WIRELESS NETWORKS 2005年第3期11卷 215-222页

作者： Gombachika, HSH Tafazolli, R Evans, BG Univ Malawi Blantyre 3 Malawi Univ Surrey CCSR Surrey GU2 7XH England

Transmit power control is indispensable in Direct Sequence Code Division Multiple Access (DS/CDMA) based systems such as the Satellite Universal Mobile Telecommunication System (S-UMTS). Since S-UMTS aims at achieving close integration with the terrestrial component (T-UMTS) in its complementary role, it is going to implement closed-loop transmit power control (TPC) at a slow rate of once every frame. In addition, predictive schemes can be used to mitigate the effects of delay. In this regard, recursive-least-squares (RLS) and least-mean-square (LMS) algorithms are normally employed. The RLS algorithm has a higher convergence rate than the LMS algorithm: an attractive attribute when the fading process abruptly changes. The LMS algorithm, on the other hand, has better tracking property than the RLS algorithm: an attractive attribute when the changes in the fading process are persistently slow. However, the mobile satellite system channel exhibits both attributes: abrupt changes and slow drifts. In this paper, therefore, we compare the performance of predictive TPC based on the RLS and the LMS algorithms for S-UMTS with the conventional TPC as a reference. We demonstrate that the predictive TPC schemes perform better than the conventional TPC scheme. However, the performance gain achieved depends on the predictive algorithm used, the environment in which the user equipment is operating, and loop delays. We show that, in general, the LMS based predictive TPC offers better performance than the RLS based predictive TPC scheme in S-UMTS environment.

关键词： S-UMTS power control tracking algorithms predictive TPC

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An improved Morris Water Maze tracking algorithm for psychophysical studies

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ANNALS OF BIOMEDICAL ENGINEERING 2004年第8期32卷 1141-1152页

作者： Hval, ES Barrett, SF Wilcox, M Bailey, TA Univ Wyoming Coll Engn Dept Elect & Comp Engn Laramie WY 82071 USA USAF Acad Dept Biol Colorado Springs CO USA Univ Wyoming Coll Engn Dept Comp Sci Laramie WY 82071 USA

An algorithm to track a rat swimming in a Morris Water Maze has been developed. The system is automatically configured to any pool and relative suitable light conditions. It tracks the rat's position and head pose 10 times per second. The output data is displayed in a bitmap and also in a text file. The system was tested with an X - Y plotter using a simulated rat swimming in the maze. Known signals were provided to a model rat and compared to the position and pose information provided by the tracking algorithm. The algorithm was able to track rat velocities up to 2.32 m/s, localize rat position to 4 mm within the maze. and provide head pose information. Early prototypes of the algorithm were also used to track actual rats in a water maze.

关键词： Morris Water Maze tracking algorithms template matching

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Bias phenomenon and compensation in multiple target tracking algorithms

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MATHEMATICAL AND COMPUTER MODELLING 2000年第8-9期31卷 147-165页

作者： Hong, L Cong, S Wright State Univ Dept Elect Engn Dayton OH 45435 USA

Bias phenomenon in multiple target tracking has been observed for a long time. This paper is devoted to a study of the bias resulting from the miscorrelation in data association. One result of this paper is a necessary condition for miscorrelation to cause bias. Relying on the necessary condition and a model for data association process, techniques are developed to give general directions for where and how to compensate the bias related to miscorrelation in general tracking algorithms. Case studies on the bias phenomenon in two tracking algorithms, i.e., global nearest neighborhood (GNN) and joint probabilistic data association (JPDA), are launched as a practice of the ideas and results presented in this paper. The outcome of the examples illustrates and strongly supports our results. A discussion of several statistical issues is given in the end of this paper, in which the behavior for the bias in GNN and JPDA is studied. (C) 2000 Elsevier Science Ltd. All rights reserved.

关键词： tracking algorithms track bias bias compensation miscorrelation data association

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Multiphase bubbly flow visualization using particle image velocimetry

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VISUALIZATION AND IMAGING IN TRANSPORT PHENOMENA 2002年第1期972卷 223-228页

作者： Hassan, YA Texas A&M Univ Dept Nucl Engn College Stn TX 77843 USA

This article describes advances made in using particle image velocimetry (PIV) techniques in the study of multiphase bubbly flow. One of the fundamental issues in bubbly flow is the prediction of the velocity field. A methodology that allows for velocity field measurements of both components of a two-phase bubbly flow is presented. The bubble shape is also constructed via a shadow imaging technique combined with PIV.

关键词： bubbly flow particle image velocimetry tracking algorithms turbulence

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Target perceivability and its applications

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2001年第11期49卷 2588-2604页

作者： Li, N Li, XR Univ New Orleans Dept Elect Engn New Orleans LA 70148 USA

A concept of target perceivability is introduced, which is related to such concepts as target existence and target observability. Its probability provides a basis for an integrated approach to track initiation, confirmation, termination, and refinement of track maintenance algorithms. This paper proposes the concepts of target perceivability and presents a recursion of its probability based on hidden Markov models (HMMs) and their applications to tracker analysis, development, and design, in particular, in the context of the PDA method. Specifically, several important quantities and track life are analyzed;a perceivability-based probabilistic approach to track confirmation and termination is proposed;two versions of perceivability-based PDA trackers are presented. Simulation results are provided to demonstrate their performance.

关键词： aircraft detection and tracking missile detection and tracking radar tracking sonar tracking target detection and tracking track decision tracking tracking algorithms tracking filters track initiation track maintenance

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Simulation of infrared imaging seeking missiles

Simulation of infrared imaging seeking missiles

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Conference on Acquisition, tracking, and Pointing XV

作者： Morin, A Def Res Estab Valcartier DREV Val Belair PQ Canada

ISBN: (纸本)0819440604

This paper will describe a digital simulation model to assess the effectiveness of infrared imaging seeking missiles in presence of background and countermeasures. The model reproduces the infrared (IR) scene observed by the imaging seeker and generates the images at the detector output. The model replicates the image processing for automatic detection of potential targets in the seeker's field of view (FOV), and the target selection by the tracking algorithm. A model of a two-degree-of-freedom gyro stabilized seeker platform is also presented. The seeker platform is driven by the tracking algorithm to reduce the error between the seeker axis and the line of sight. The simulation also includes models for the missile aerodynamics in six degrees of freedom, the missile guidance and control system and the target and missile trajectories. As an illustration of the model, some results of simulation are shown for a target engaged by an infrared seeking missile using an imaging sensor.

关键词： infrared tracker tracking algorithms Image Processing seeker simulation

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