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Friedrich Gruttmann - One of the best experts on this subject based on the ideXlab platform.

  • a robust non linear mixed hybrid quadrilateral shell element
    International Journal for Numerical Methods in Engineering, 2005
    Co-Authors: Werner Wagner, Friedrich Gruttmann
    Abstract:

    In the paper a non-linear quadrilateral shell element for the analysis of thin structures is presented. The variational formulation is based on a Hu–Washizu functional with independent displacement, stress and strain fields. The interpolation matrices for the mid-surface displacements and rotations as well as for the stress resultants and strains are specified. Restrictions on the interpolation functions concerning fulfillment of the patch test and stability are derived. The developed mixed hybrid shell element possesses the correct rank and fulfills the in-plane and bending patch test. Using Newton's method the finite element approximation of the Stationary Condition is iteratively solved. Our formulation can accommodate arbitrary non-linear material models for finite deformations. In the examples we present results for isotropic plasticity at finite rotations and small strains as well as bifurcation problems and post-buckling response. The essential feature of the new element is the robustness in the equilibrium iterations. It allows very large load steps in comparison to other element formulations. Copyright © 2005 John Wiley & Sons, Ltd.

  • a linear quadrilateral shell element with fast stiffness computation
    Computer Methods in Applied Mechanics and Engineering, 2005
    Co-Authors: Friedrich Gruttmann, Werner Wagner
    Abstract:

    Abstract A new quadrilateral shell element with 5/6 nodal degrees of freedom is presented. Assuming linear isotropic elasticity a Hellinger–Reissner functional with independent displacements, rotations and stress resultants is used. Within the mixed formulation the stress resultants are interpolated using five parameters for the membrane forces as well as for the bending moments and four parameters for the shear forces. The hybrid element stiffness matrix resulting from the Stationary Condition is integrated analytically. This leads to a part obtained by one point integration and a stabilization matrix. The element possesses the correct rank, is free of locking and is applicable within the whole range of thin and thick shells. The in-plane and bending patch tests are fulfilled and the computed numerical examples show that the convergence behaviour of the stress resultants is very good in comparison to comparable existing elements. The essential advantage is the fast stiffness computation due to the analytically integrated matrices.

  • a stabilized one point integrated quadrilateral reissner mindlin plate element
    International Journal for Numerical Methods in Engineering, 2004
    Co-Authors: Friedrich Gruttmann, Werner Wagner
    Abstract:

    A new quadrilateral Reissner–Mindlin plate element with 12 element degrees of freedom is presented. For linear isotropic elasticity a Hellinger–Reissner functional with independent displacements, rotations and stress resultants is used. Within the mixed formulation the stress resultants are interpolated using five parameters for the bending moments and four parameters for the shear forces. The hybrid element stiffness matrix resulting from the Stationary Condition can be integrated analytically. This leads to a part obtained by one-point integration and a stabilization matrix. The element possesses a correct rank, does not show shear locking and is applicable for the evaluation of displacements and stress resultants within the whole range of thin and thick plates. The bending patch test is fulfilled and the computed numerical examples show that the convergence behaviour is better than comparable quadrilateral assumed strain elements. Copyright © 2004 John Wiley & Sons, Ltd.

Werner Wagner - One of the best experts on this subject based on the ideXlab platform.

  • a robust non linear mixed hybrid quadrilateral shell element
    International Journal for Numerical Methods in Engineering, 2005
    Co-Authors: Werner Wagner, Friedrich Gruttmann
    Abstract:

    In the paper a non-linear quadrilateral shell element for the analysis of thin structures is presented. The variational formulation is based on a Hu–Washizu functional with independent displacement, stress and strain fields. The interpolation matrices for the mid-surface displacements and rotations as well as for the stress resultants and strains are specified. Restrictions on the interpolation functions concerning fulfillment of the patch test and stability are derived. The developed mixed hybrid shell element possesses the correct rank and fulfills the in-plane and bending patch test. Using Newton's method the finite element approximation of the Stationary Condition is iteratively solved. Our formulation can accommodate arbitrary non-linear material models for finite deformations. In the examples we present results for isotropic plasticity at finite rotations and small strains as well as bifurcation problems and post-buckling response. The essential feature of the new element is the robustness in the equilibrium iterations. It allows very large load steps in comparison to other element formulations. Copyright © 2005 John Wiley & Sons, Ltd.

  • a linear quadrilateral shell element with fast stiffness computation
    Computer Methods in Applied Mechanics and Engineering, 2005
    Co-Authors: Friedrich Gruttmann, Werner Wagner
    Abstract:

    Abstract A new quadrilateral shell element with 5/6 nodal degrees of freedom is presented. Assuming linear isotropic elasticity a Hellinger–Reissner functional with independent displacements, rotations and stress resultants is used. Within the mixed formulation the stress resultants are interpolated using five parameters for the membrane forces as well as for the bending moments and four parameters for the shear forces. The hybrid element stiffness matrix resulting from the Stationary Condition is integrated analytically. This leads to a part obtained by one point integration and a stabilization matrix. The element possesses the correct rank, is free of locking and is applicable within the whole range of thin and thick shells. The in-plane and bending patch tests are fulfilled and the computed numerical examples show that the convergence behaviour of the stress resultants is very good in comparison to comparable existing elements. The essential advantage is the fast stiffness computation due to the analytically integrated matrices.

  • a stabilized one point integrated quadrilateral reissner mindlin plate element
    International Journal for Numerical Methods in Engineering, 2004
    Co-Authors: Friedrich Gruttmann, Werner Wagner
    Abstract:

    A new quadrilateral Reissner–Mindlin plate element with 12 element degrees of freedom is presented. For linear isotropic elasticity a Hellinger–Reissner functional with independent displacements, rotations and stress resultants is used. Within the mixed formulation the stress resultants are interpolated using five parameters for the bending moments and four parameters for the shear forces. The hybrid element stiffness matrix resulting from the Stationary Condition can be integrated analytically. This leads to a part obtained by one-point integration and a stabilization matrix. The element possesses a correct rank, does not show shear locking and is applicable for the evaluation of displacements and stress resultants within the whole range of thin and thick plates. The bending patch test is fulfilled and the computed numerical examples show that the convergence behaviour is better than comparable quadrilateral assumed strain elements. Copyright © 2004 John Wiley & Sons, Ltd.

Xiaohong Li - One of the best experts on this subject based on the ideXlab platform.

  • Short-Term Traffic Flow Prediction Based on Ensemble Real-Time Sequential Extreme Learning Machine Under Non-Stationary Condition
    2016 IEEE 83rd Vehicular Technology Conference (VTC Spring), 2016
    Co-Authors: Dong Wang, Zhu Xiao, Jie Xiong, Xiaohong Li
    Abstract:

    Short-term traffic flow forecasting has been a crucial component in the area of intelligent transportation systems (ITS), which plays a significant role in operating traffic management systems and dynamic traffic assignment effectively as well as proactively. In this paper, a novel short-term traffic flow prediction method called Ensemble Real-time Sequential Extreme Learning Machine (ERS-ELM) with simplified single layer feed- forward networks (SLFN) structure under freeway peak traffic Condition and non-Stationary Condition is proposed. By quickly training historical data and incrementally updating model with new arrived data, ERE-ELM has the characteristics of less training time consumption and high prediction accuracy. Ensemble mechanism is also used to improve stability and robustness. Experiment results show that average mean absolute percentage error (MAPE), test root mean square error (RMSE) as well as training time consumption of proposed method is superior to classical Wave-NN, MLP-NN and ELM methods.

Luigi Pizzamiglio - One of the best experts on this subject based on the ideXlab platform.

  • cortical control of optokinetic nystagmus in humans a positron emission tomography study
    Experimental Brain Research, 1999
    Co-Authors: Gaspare Galati, Sabina Pappata, Patrizia Pantano, G L Lenzi, Yves Samson, Luigi Pizzamiglio
    Abstract:

    Positron emission tomography (PET) was used to address the issue of physiological changes in the cerebral cortex associated to optokinetic nystagmus (OKN) in humans. We studied regional cerebral blood flow in eight volunteers during reflexive induction of OKN by a pattern of dots moving unidirectionally (toward the left side). We used two control Conditions, with subjects passively viewing either Stationary or incoherently moving dots. This paradigm was designed in order to differentiate the OKN-related activations from blood flow changes related to visual motion. When compared with the Stationary Condition, OKN activated a set of occipital areas known to be sensitive to visual motion. Bilateral activation was found in the striate cortex (V1) and the parieto-occipital fissure, while area V5, the intraparietal sulcus, and the pulvinar were activated only in the left hemisphere. When compared with incoherent motion, OKN activated the V1 and the parieto-occipital fissure bilaterally and the right lingual gyrus, while a signal decrease was observed in the V5 region in both hemispheres. No significant signal changes were found in areas implicated in saccades or in processing vestibular information. These results indicate that processing of OKN-related information is associated with neural activity in a specific set of visual motion areas and suggest that this network can be asymmetrically activated by a strictly unidirectional stimulation. Results are also discussed in terms of the specific kinds of OKN-related information processing subserved by each area in this network.

Kai Wang - One of the best experts on this subject based on the ideXlab platform.

  • experimental study of heat transfer characteristic on jet impingement cooling with film extraction flow
    Applied Thermal Engineering, 2014
    Co-Authors: Kai Wang, Jianqin Zhu
    Abstract:

    An experimental investigation was carried out to examine the heat transfer characteristics on impingement cooling with extraction flow under Stationary Condition. The local heat transfer coefficient was measured by the transient method using TLC. Special techniques and devices were developed to make this method feasible and to produce reliable experimental data. The Reynolds number based on the inlet velocity of the jet air and the diameter of impingement hole changes from 2000 to 12,000. Various test models with relative impingement distance H/d = 1.0, 3.0, 6.0 and position of impingement cooling hole = 1/3,1/2 were conducted to get the effects of H/d and f/l. The local Nu on the target surface was measured by a transient method with TLC. Experimental results reveal that the position of impingement cooling hole f/l has great influence on the heat transfer characteristics of the target surface. The averaged Nu of f/l = 1/3 configuration is about 9% higher than that of f/l = 1/2 configuration. It is also found that the maximum local Nu is mostly affected by H/d. And the higher Nusselt number is achieved with smaller H/d, the averaged Nu of H/d = 6 model is about 22%-38% lower than that of H/d = 1 for different Reynolds numbers. (C) 2014 Elsevier Ltd. All rights reserved.