The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform

J. B. Liu - One of the best experts on this subject based on the ideXlab platform.

  • Numerical instabilities of a local transmitting boundary
    Earthquake Engineering & Structural Dynamics, 1992
    Co-Authors: Z. P. Liao, J. B. Liu
    Abstract:

    A local transmitting boundary is presented in a compact form, which can be directly incorporated into finite elements. The accuracy of the boundary is studied thoroughly for a one-dimensional model in order to clarify numerical instabilities introduced by the boundary. Discretization of the model and reflection from the boundary are rigorously considered in the study, and the mechanism of the instability is then illuminated in the frequency domain by the amplification of reflection from the boundary and the multi-reflection of wave motion in a finite Computational Region. Typical characteristics of the instability in the time domain are illustrated by numerical results of the simple model and explained completely by the mechanism. On the basis of this understanding of the mechanism, a modified transmitting boundary is devised and its stability criterion is given for the one-dimensional model.

Ilya B. Simanovskii - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear Marangoni waves in a two-layer film with reflecting lateral boundaries
    Physics of Fluids, 2017
    Co-Authors: Alexander A. Nepomnyashchy, Ilya B. Simanovskii
    Abstract:

    Longwave Marangoni convection in a two-layer film of a finite lateral extent is considered. The analysis is carried out in the lubrication approximation. Numerical simulations are performed in the case of oscillatory instability, which takes place by heating from above. Reflecting conditions are applied on the boundaries of the Computational Region. A sequence of nonlinear wave regimes, which develop by the increase of the Marangoni number, is studied. The multistability of wave patterns has been revealed.

  • Generation of nonlinear Marangoni waves in a two-layer film by heating modulation
    Journal of Fluid Mechanics, 2015
    Co-Authors: Alexander A. Nepomnyashchy, Ilya B. Simanovskii
    Abstract:

    Longwave Marangoni convection in two-layer films under the action of heating modulation is considered. The analysis is carried out in the lubrication approximation. The capillary forces are assumed to be sufficiently strong, and they are taken into account. Periodic or symmetric boundary conditions are applied on the boundaries of the Computational Region. Numerical simulations are performed by means of a finite-difference method. Two Regions of parametric instabilities have been found. In the first Region, one observes the competition or coexistence of standing waves parallel to the boundaries of the Computational Region. The multistability of the flow regimes is revealed. In the second Region, the regimes found in the case of periodic boundary conditions are more diverse than in the case of symmetric boundary conditions.

  • The influence of vibration on Marangoni waves in two-layer films
    Journal of Fluid Mechanics, 2013
    Co-Authors: Alexander A. Nepomnyashchy, Ilya B. Simanovskii
    Abstract:

    The influence of time-periodic vibrations on long Marangoni waves in two-layer films is investigated. The problem is governed by a system of nonlinear equations obtained in the framework of the lubrication approximation. Periodic boundary conditions are applied on the boundaries of the Computational Region. The development of instabilities is investigated by means of nonlinear simulations. Excitation of two-dimensional and three-dimensional subharmonic wavy regimes is studied. A new phenomenon, the excitation of nonlinear waves with a temporal period that is four times larger than that of the gravity modulation, is revealed.

  • Nonlinear Marangoni waves in a two-layer film in the presence of gravity
    Physics of Fluids, 2012
    Co-Authors: Alexander A. Nepomnyashchy, Ilya B. Simanovskii
    Abstract:

    Longwave Marangoni convection in two-layer films under the action of gravity is considered. The analysis is carried out in the lubrication approximation. A linear stability analysis reveals the existence of monotonic and oscillatory instability modes, depending on the way of heating and the value of the Biot number. Numerical simulations are performed in the case of an oscillatory instability, which takes place by heating from above. Periodic boundary conditions are applied on the boundaries of the Computational Region. A sequence of nonlinear wavy regimes, which develop by the increase of the Galileo number, is studied. That sequence includes three-dimensional and two-dimensional structures. The multistability of wavy patterns with different spatial periods has been revealed.

  • The Influence of the Gravity Force on Longwave Marangoni Patterns in Two-Layer Films
    Microgravity Science and Technology, 2011
    Co-Authors: Alexander A. Nepomnyashchy, Ilya B. Simanovskii
    Abstract:

    The effect of gravity on the dynamics of non-isothermic ultra-thin two-layer films is studied. The problem is considered in a longwave approximation. Periodic boundary conditions have been applied on the boundaries of the Computational Region. The problem is solved by means of a linear stability theory and nonlinear simulations. Nonlinear wavy regimes, including two-dimensional and three-dimensional traveling waves, as well as different kinds of three-dimensional standing waves, have been studied.

Lars Ferm - One of the best experts on this subject based on the ideXlab platform.

Aref Meddeb - One of the best experts on this subject based on the ideXlab platform.

  • Spatially Enhanced Bags of Visual Words Representation to Improve Traffic Signs Recognition
    Journal of Signal Processing Systems, 2018
    Co-Authors: Lotfi Abdi, Aref Meddeb
    Abstract:

    Traffic signs play a very vital role in safe driving and in avoiding accidents by informing the driver about the speed limits or possible dangers such as icy roads, imminent road works or pedestrian crossings. Considering the processing time and classification accuracy as a whole, a novel approach for visual words construction was presented, which takes the spatial information of keypoints into account in order to enhance the quality of visual words generated from extracted keypoints using the distance and angle information in the Bags of Visual Words (BoVW) representation. In this paper, we proposed a new Computationally efficient method to model global spatial distribution of visual words by taking into consideration the spatial relationships of its visual words. In the first step, the Region of interest is extracted using a scanning window with a Haar cascade detector and an AdaBoost classifier to reduce the Computational Region in the hypothesis generation step. Second, the Regions are represented with BoVW and spatial information for classification. Experimental results show that the suggested method could reach comparable performance of the state-of-the-art approaches with less Computational complexity and shorter training time. It clearly demonstrates the complementarity of the additional relative spatial information provided by our approach to improve accuracy while maintaining short retrieval time, and can obtain a better traffic sign recognition accuracy than the methods based on the traditional BoVW model.

  • In-vehicle augmented reality TSR to improve driving safety and enhance the driver’s experience
    Signal Image and Video Processing, 2018
    Co-Authors: Lotfi Abdi, Aref Meddeb
    Abstract:

    In-vehicle contextual augmented reality (AR) has the potential to provide novel visual feedbacks to drivers for an enhanced driving experience. In this paper, we propose a new AR traffic sign recognition system (AR-TSR) to improve driving safety and enhance the driver’s experience based on the Haar cascade and the Bag-of-Visual-Words approach, using spatial information to improve accuracy and an overview of studies related to the driver’s perception and the effectiveness of the AR in improving driving safety. In the first step, the Region of interest (ROI) is extracted using a scanning window with a Haar cascade detector and an AdaBoost classifier to reduce the Computational Region in the hypothesis generation step. Second, we proposed a new Computationally efficient method to model global spatial distribution of visual words by taking into consideration the spatial relationships of its visual words. Finally, a multiclass sign classifier takes the positive ROIs and assigns a 3D traffic sign for each one using a linear SVM. Experimental results show that the suggested method could reach comparable performance of the state-of-the-art approaches with less Computational complexity and shorter training time, and the AR-TSR more strongly impacts the allocation of visual attention during the decision-making phase.

  • In-Vehicle Augmented Reality Traffic Information System: A New Type of Communication Between Driver and Vehicle
    Procedia Computer Science, 2015
    Co-Authors: Lotfi Abdi, Faten Ben Abdallah, Aref Meddeb
    Abstract:

    Abstract In order to improve driving safety and minimize driving workload, the information provided should be represented in such a way that it is more easily understood and imposing less cognitive load onto the driver. Augmented Reality Head-up Display (AR- HUD) can facilitate a new form of dialogue between the vehicle and the driver; and enhance intelligent transportation systems by superimposing surrounding traffic information on the users view and keep drivers view on roads. In this paper, we investigated the potential costs and benefits of using AR cues to improve driving safety as new form of dialog between the vehicle and the driver. We present a new approach for marker-less AR Traffics Signs Recognition system that superimposes augmented virtual objects onto a real scene under all types of driving situations, including unfavorable weather conditions. Our method uses two steps: hypothesis generation and hypothesis verification. In the first step, Region Of Interest (ROI) is extracted using a scanning window with Haar cascade detector and AdaBoost classifier to reduce the Computational Region in the hypothesis generation step. The second step verifies whether a given candidate and classified into vehicle and non-vehicle classes using edge information and symmetry measurement to verify them. We employ this approach to improve the accuracy of AR traffic information system to assist the driver in various driving situations, increase the driving comfort and reduce traffic accidents.

T. G. Elizarova - One of the best experts on this subject based on the ideXlab platform.

  • Direct Simulation of Laminar–Turbulent Transition in a Viscous Compressible Gas Layer
    Computational Mathematics and Modeling, 2014
    Co-Authors: I. A. Shirokov, T. G. Elizarova
    Abstract:

    We present simulation results for oscillatory modes in supersonic flow past an aircraft with a hypersonic jet engine. The flow of viscous compressible gas is modeled by a quasi-gas dynamic (QGD) system of equations. A coordinate transformation is applied to adapt the Computational Region to the configuration of the compression shock in supersonic flow past an object. An original method is proposed for the introduction of additional dissipation that smooths the instability in the neighborhood of the compression shock. The spectral characteristics of the oscillatory flow in the turbulence Region follow the Kolmogorov law of oscillation energy decrease with increasing oscillation frequency.

  • Direct Simulation of Laminar---Turbulent Transition in a Viscous Compressible Gas Layer
    Computational Mathematics and Modeling, 2013
    Co-Authors: I. A. Shirokov, T. G. Elizarova
    Abstract:

    We present simulation results for oscillatory modes in supersonic flow past an aircraft with a hypersonic jet engine. The flow of viscous compressible gas is modeled by a quasi-gas dynamic (QGD) system of equations. A coordinate transformation is applied to adapt the Computational Region to the configuration of the compression shock in supersonic flow past an object. An original method is proposed for the introduction of additional dissipation that smooths the instability in the neighborhood of the compression shock. The spectral characteristics of the oscillatory flow in the turbulence Region follow the Kolmogorov law of oscillation energy decrease with increasing oscillation frequency.