The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Jose Herskovits - One of the best experts on this subject based on the ideXlab platform.

  • Material Distribution and sizing optimization of functionally graded plate shell structures
    Composites Part B-engineering, 2018
    Co-Authors: Jose S Moita, A L Araujo, Victor Franco M Correia, Cristovao Mota M Soares, Jose Herskovits
    Abstract:

    Abstract A high order shear deformation theory is used to develop a discrete model for the structural and sensitivity analyses allowing for the Material Distribution and sizing optimization of functionally graded Material (FGM) structures. The finite element formulation for general FGM plate-shell type structures is presented, and a non-conforming triangular flat plate/shell element with 24° of freedom for the generalized displacements is used. The formulation accounts for geometric and Material nonlinear behaviour, free vibrations and linear buckling analyses, and their analytical gradient based sensitivities. The p-index of the power–law Material Distribution and the thickness are the design variables. Mass, displacement, fundamental frequency and critical load are the objective functions or constraints. The optimization solutions, obtained by a Feasible Arc Interior Point gradient-based algorithm, for some plate-shell examples are presented for benchmarking purposes.

Mazaher Salamattalab - One of the best experts on this subject based on the ideXlab platform.

  • thermal effect on size dependent behavior of functionally graded microbeams based on modified couple stress theory
    Composite Structures, 2013
    Co-Authors: Alireza Nateghi, Mazaher Salamattalab
    Abstract:

    Abstract Thermal effect on buckling and free vibration behavior of functionally graded (FG) microbeams based on modified couple stress theory is presented. Classical and first order shear deformation beam theories are adopted to count for the effect of shear deformations. Hamilton’s principle is applied to give the governing equations, boundary and initial conditions of the FG microbeam. Using generalized differential quadrature (GDQ) method buckling load and natural frequency of FG microbeam with different boundary conditions are obtained. Some numerical results are presented to investigate effects of different parameters including temperature changes, Material length scale parameter, beam thickness, Poisson’s ratio and power index of Material Distribution on the FG microbeam behavior. Numerical results show that modified couple stress theory predicts higher values of buckling load and natural frequency for FG microbeams. In addition, it is observed that higher temperature changes signify size dependency of FG microbeam. It is shown that Poisson’s effect on buckling load and natural frequency predicted by the current model differs significantly from classical one. Study of power index of Material Distribution proved that the behavior of FG microbeams differ considerably from homogeneous isotropic ones.

  • size dependent buckling analysis of functionally graded micro beams based on modified couple stress theory
    Applied Mathematical Modelling, 2012
    Co-Authors: Alireza Nateghi, Mazaher Salamattalab, Javad Rezapour, Behrouz Daneshian
    Abstract:

    Abstract Buckling analysis of functionally graded micro beams based on modified couple stress theory is presented. Three different beam theories, i.e. classical, first and third order shear deformation beam theories, are considered to study the effect of shear deformations. To present a profound insight on the effect of boundary conditions, beams with hinged-hinged, clamped–clamped and clamped–hinged ends are studied. Governing equations and boundary conditions are derived using principle of minimum potential energy. Afterwards, generalized differential quadrature (GDQ) method is applied to solve the obtained differential equations. Some numerical results are presented to study the effects of Material length scale parameter, beam thickness, Poisson ratio and power index of Material Distribution on size dependent buckling load. It is observed that buckling loads predicted by modified couple stress theory deviates significantly from classical ones, especially for thin beams. It is shown that size dependency of FG micro beams differs from isotropic homogeneous micro beams as it is a function of power index of Material Distribution. In addition, the general trend of buckling load with respect to Poisson ratio predicted by the present model differs from classical one.

Alireza Nateghi - One of the best experts on this subject based on the ideXlab platform.

  • thermal effect on size dependent behavior of functionally graded microbeams based on modified couple stress theory
    Composite Structures, 2013
    Co-Authors: Alireza Nateghi, Mazaher Salamattalab
    Abstract:

    Abstract Thermal effect on buckling and free vibration behavior of functionally graded (FG) microbeams based on modified couple stress theory is presented. Classical and first order shear deformation beam theories are adopted to count for the effect of shear deformations. Hamilton’s principle is applied to give the governing equations, boundary and initial conditions of the FG microbeam. Using generalized differential quadrature (GDQ) method buckling load and natural frequency of FG microbeam with different boundary conditions are obtained. Some numerical results are presented to investigate effects of different parameters including temperature changes, Material length scale parameter, beam thickness, Poisson’s ratio and power index of Material Distribution on the FG microbeam behavior. Numerical results show that modified couple stress theory predicts higher values of buckling load and natural frequency for FG microbeams. In addition, it is observed that higher temperature changes signify size dependency of FG microbeam. It is shown that Poisson’s effect on buckling load and natural frequency predicted by the current model differs significantly from classical one. Study of power index of Material Distribution proved that the behavior of FG microbeams differ considerably from homogeneous isotropic ones.

  • size dependent buckling analysis of functionally graded micro beams based on modified couple stress theory
    Applied Mathematical Modelling, 2012
    Co-Authors: Alireza Nateghi, Mazaher Salamattalab, Javad Rezapour, Behrouz Daneshian
    Abstract:

    Abstract Buckling analysis of functionally graded micro beams based on modified couple stress theory is presented. Three different beam theories, i.e. classical, first and third order shear deformation beam theories, are considered to study the effect of shear deformations. To present a profound insight on the effect of boundary conditions, beams with hinged-hinged, clamped–clamped and clamped–hinged ends are studied. Governing equations and boundary conditions are derived using principle of minimum potential energy. Afterwards, generalized differential quadrature (GDQ) method is applied to solve the obtained differential equations. Some numerical results are presented to study the effects of Material length scale parameter, beam thickness, Poisson ratio and power index of Material Distribution on size dependent buckling load. It is observed that buckling loads predicted by modified couple stress theory deviates significantly from classical ones, especially for thin beams. It is shown that size dependency of FG micro beams differs from isotropic homogeneous micro beams as it is a function of power index of Material Distribution. In addition, the general trend of buckling load with respect to Poisson ratio predicted by the present model differs from classical one.

Konstantin Nikolaou - One of the best experts on this subject based on the ideXlab platform.

  • dual energy ct for the assessment of contrast Material Distribution in the pulmonary parenchyma
    American Journal of Roentgenology, 2009
    Co-Authors: Sven F Thieme, Thorsten R C Johnson, Christopher Lee, Justin P Mcwilliams, Christoph R Becker, Maximilian F Reiser, Konstantin Nikolaou
    Abstract:

    OBJECTIVE. The purpose of this study was to assess the feasibility and diagnostic value of dual-energy CT iodine mapping at pulmonary CT angiography.SUBJECTS AND METHODS. Ninety-three patients underwent CT angiography with the dual-energy technique on a dual-source CT scanner. Postprocessing was used to map iodine in the lung parenchyma on the basis of its spectral behavior, and image quality was assessed by two readers. Iodine Distribution patterns were rated as homogeneous, patchy, or circumscribed defects. Conventional CT angiographic images reconstructed from the same data sets were reviewed for the presence and localization of pulmonary embolism, whether embolic occlusion was partial or complete, and the presence of changes in the lung parenchyma. Dual-energy perfusion findings were correlated with the CT angiographic and lung-window CT findings in per-patient and per-segment analyses.RESULTS. Iodine Distribution was homogeneous in 49 patients, of whom CT angiography showed no pulmonary embolism in 4...

  • dual energy ct for the assessment of contrast Material Distribution in the pulmonary parenchyma
    American Journal of Roentgenology, 2009
    Co-Authors: Sven F Thieme, Thorsten R C Johnson, Justin P Mcwilliams, Christoph R Becker, Maximilian F Reiser, Konstantin Nikolaou
    Abstract:

    OBJECTIVE. The purpose of this study was to assess the feasibility and diagnostic value of dual-energy CT iodine mapping at pulmonary CT angiography.SUBJECTS AND METHODS. Ninety-three patients underwent CT angiography with the dual-energy technique on a dual-source CT scanner. Postprocessing was used to map iodine in the lung parenchyma on the basis of its spectral behavior, and image quality was assessed by two readers. Iodine Distribution patterns were rated as homogeneous, patchy, or circumscribed defects. Conventional CT angiographic images reconstructed from the same data sets were reviewed for the presence and localization of pulmonary embolism, whether embolic occlusion was partial or complete, and the presence of changes in the lung parenchyma. Dual-energy perfusion findings were correlated with the CT angiographic and lung-window CT findings in per-patient and per-segment analyses.RESULTS. Iodine Distribution was homogeneous in 49 patients, of whom CT angiography showed no pulmonary embolism in 4...

Paulo R Fernandes - One of the best experts on this subject based on the ideXlab platform.

  • a Material based model for topology optimization of thermoelastic structures
    International Journal for Numerical Methods in Engineering, 1995
    Co-Authors: H C Rodrigues, Paulo R Fernandes
    Abstract:

    This paper presents the development of a computational model for the topology optimization problem, using a Material Distribution approach, of a 2-D linear-elastic solid subjected to thermal loads, with a compliance objective function and an isoperimetric constraint on volume. Defining formally the augmented Lagrangian associated with the optimization problem, the optimality conditions are derived analytically. The results of analysis are implemented in a computer code to produce numerical solutions for the optimal topology, considering the temperature Distribution independent of design. The design optimization problem is solved via a sequence of linearized subproblems. The computational model developed is tested in example problems. The influence of both the temperature and the finite element model on the optimal solution obtained is analysed.