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...
详细信息
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.
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 smeare...
详细信息
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.
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 reconstruct...
详细信息
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.
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. M...
详细信息
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.
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...
详细信息
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.
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...
详细信息
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.
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 necessar...
详细信息
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.
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...
详细信息
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.
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, confir...
详细信息
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.
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...
详细信息
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.
暂无评论