The Experts below are selected from a list of 576 Experts worldwide ranked by ideXlab platform

Erez Gal - One of the best experts on this subject based on the ideXlab platform.

  • The geometric stiffness of thick shell triangular finite elements for large rotations
    International Journal for Numerical Methods in Engineering, 2006
    Co-Authors: Robert Levy, Erez Gal
    Abstract:

    This paper is concerned with the development of the geometric stiffness matrix of thick shell finite elements for geometrically nonlinear analysis of the Newton type. A linear shell element that is comprised of the constant stress triangular membrane element and the triangular discrete Kirchhoff Mindlin theory (DKMT) plate element is ‘upgraded’ to become a geometrically nonlinear thick shell finite element. Perturbation methods are used to derive the geometric stiffness matrix from the gradient, in global coordinates, of the Nodal Force Vector when stresses are kept fixed. The present approach follows earlier works associated with trusses, space frames and thin shells. It has the advantage of explicitness and clear physical insight. A special procedure, tailored to triangular elements is used to isolate pure rotations to enable stress recovery via linear elastic constitutive relations. Several examples are solved. The results compare well with those available in the literature. Copyright © 2005 John Wiley & Sons, Ltd.

  • The geometric stiffness of triangular composite-materials shell elements
    Computers & Structures, 2005
    Co-Authors: Erez Gal, Robert Levy
    Abstract:

    This paper is concerned with the development of the geometric stiffness matrix for Newton type large rotation analysis of composite thin shell structures. The geometric stiffness matrix is derived from load perturbation of the discrete equilibrium equations of a given linear finite element formulation. The geometric stiffness matrix is extracted from the gradient, in global coordinates, of the element Nodal Force Vector when stresses are kept fixed. In order to overcome the difficulties in taking derivatives of the rotation matrix with respect to the Nodal coordinates, gradient evaluations are performed in the local coordinate system to result in an in-plane geometric stiffness matrix. An out-of-plane geometric stiffness matrix is then introduced to account for the effect of rigid body rotations on member Forces. A unique procedure is used for the removal of rigid body displacements and rotations that enables stress recovery via linear, kinematic and constitutive, relationships. The geometric stiffness matrix derived was used to study several examples whose results compare well with the literature.

Yuanhai Zhang - One of the best experts on this subject based on the ideXlab platform.

  • improved finite segment method for analyzing shear lag effect in thin walled box girders
    Journal of Structural Engineering-asce, 2012
    Co-Authors: Yuanhai Zhang
    Abstract:

    AbstractShear lag effect in thin-walled box girders has been studied over several decades. However, the methods adopted in many papers have some deficiencies. In the present work, an improved displacement function for shear lag warping in a box girder with cantilever slabs is established. Based on the concept of generalized Force corresponding to the generalized displacement for shear lag and the relevant geometrical properties, an improved finite-segment method is proposed to simplify the shear lag analysis of complex box girders. The homogeneous solution of the governing differential equation for shear lag is adopted as the element displacement function. The formulas of the element stiffness matrix and the equivalent Nodal Force Vector are derived. A general formula expressed in terms of the generalized moment is presented to calculate the stress. A finite-element computer program is developed by using FORTRAN language and is used to analyze a cantilever box girder model and a continuous prestressed con...

Robert Levy - One of the best experts on this subject based on the ideXlab platform.

  • The geometric stiffness of thick shell triangular finite elements for large rotations
    International Journal for Numerical Methods in Engineering, 2006
    Co-Authors: Robert Levy, Erez Gal
    Abstract:

    This paper is concerned with the development of the geometric stiffness matrix of thick shell finite elements for geometrically nonlinear analysis of the Newton type. A linear shell element that is comprised of the constant stress triangular membrane element and the triangular discrete Kirchhoff Mindlin theory (DKMT) plate element is ‘upgraded’ to become a geometrically nonlinear thick shell finite element. Perturbation methods are used to derive the geometric stiffness matrix from the gradient, in global coordinates, of the Nodal Force Vector when stresses are kept fixed. The present approach follows earlier works associated with trusses, space frames and thin shells. It has the advantage of explicitness and clear physical insight. A special procedure, tailored to triangular elements is used to isolate pure rotations to enable stress recovery via linear elastic constitutive relations. Several examples are solved. The results compare well with those available in the literature. Copyright © 2005 John Wiley & Sons, Ltd.

  • The geometric stiffness of triangular composite-materials shell elements
    Computers & Structures, 2005
    Co-Authors: Erez Gal, Robert Levy
    Abstract:

    This paper is concerned with the development of the geometric stiffness matrix for Newton type large rotation analysis of composite thin shell structures. The geometric stiffness matrix is derived from load perturbation of the discrete equilibrium equations of a given linear finite element formulation. The geometric stiffness matrix is extracted from the gradient, in global coordinates, of the element Nodal Force Vector when stresses are kept fixed. In order to overcome the difficulties in taking derivatives of the rotation matrix with respect to the Nodal coordinates, gradient evaluations are performed in the local coordinate system to result in an in-plane geometric stiffness matrix. An out-of-plane geometric stiffness matrix is then introduced to account for the effect of rigid body rotations on member Forces. A unique procedure is used for the removal of rigid body displacements and rotations that enables stress recovery via linear, kinematic and constitutive, relationships. The geometric stiffness matrix derived was used to study several examples whose results compare well with the literature.

  • Geometric stiffness of membranes using symbolic algebra
    Engineering Structures, 2004
    Co-Authors: Robert Levy, Chuin-shan Chen, Cheng-wei Lin, Yeong-bin Yang
    Abstract:

    This paper is concerned with derivation of the geometric stiffness matrix for membrane shells which are represented by constant stress triangular finite elements. Symbolic algebra is used to calculate the gradient of the member Nodal Force Vector of each element when the stresses are kept fixed. This gradient defines the geometric stiffness matrix of the element in global coordinates. The present approach follows the earlier works associated with trusses, plane frames and space frames. It has the advantage of explicitness in derivation, while showing clear physical insight. For the case of small rotations, all the mathematical manipulations can be handled by hand. However, for the case of finite rotations, one must have recourse to symbolic algebra programs. The geometric stiffness matrices derived were implanted into an existing nonlinear membrane analysis program that was used to study two examples from the available literature.

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

  • The speedy algorithm of response spectrum theory in seismic analysis of grid structures
    Spatial Structures, 2004
    Co-Authors: Liu Feng
    Abstract:

    The response spectrum analysis has become the most sophisticated seismic analysis method in codes for seismic design in the world. When response spectrum method is used in the seismic analysis of long-span grid structures, according to the code, the first step in the response spectrum analysis is forming the equivalent Nodal Force Vector. And then, computing the displacement solution in each mode shape. By the speedy algorithm adopted by this article, the displacement solution in each mode shape can be written directly. Solution time can be saved and at the same time computing errors can be avoided by this method. In this article, the equivalence of the speedy algorithm and the method in the code is verified in theory and a simple example is provided to approve it.

  • The Direct Arithmetic of Response Spectrum Theory in Seismic Analysis of Building Structures
    Building Science, 2003
    Co-Authors: Liu Feng
    Abstract:

    Response spectrum analysis has become the mo st sophisticated seismic analysis method in codes for seismic design in the worl d. According to the specification of the code, the first step in the response sp ectrum analysis is forming the equivalent Nodal Force Vector. And then, computin g the displacement solution in each mode. By the Direct Arithmetic adopted by th e article, the displacement solution in each mode can be written directly. The s olution time can be saved and meanwhile the computing errors can be avoided by t his method. In the article, the equivalence of the Direct Arithmetic to the meth od in the code is verified in theory and a simple example is provided for approv al.

Rakesh K. Kapania - One of the best experts on this subject based on the ideXlab platform.

  • Random Response Analysis of Curvilinearly Stiffened Plates Using Element-Free Galerkin Method
    Journal of Aircraft, 2011
    Co-Authors: Ali Yeilaghi Tamijani, Rakesh K. Kapania
    Abstract:

    An Element Free Galerkin (EFG) formulation is presented for studying the random response of curvilinearly-stiffened plates. The structure is subjected to stationary random stochastic loading. The random loads are assumed as stationary in time but can be nonhomogeneous in space. The spectral density of the Nodal Force Vector is formulated using the displacement shape functions. The direct complex matrix inversion method and modal superposition method are used to obtain the random response of structure. The spectral density of displacement for un-stiffened plate under white noise and plate with straight stiffeners subjected to jet noise are compared with those available in the literature. The power spectral density of displacement of curvilinearly-stiffened plate under white noise is also verified using the commercial finite element software ANSYS. Excellent agreement is seen in all cases. The effect of stiffener stiffness and curvature and in-plane load on spectral density of deflection of curvilinearly-stiffened plate is also investigated.

  • 2010 AIAA SDM Student Symposium Random Response Analysis of Curvilinearly-Stiffened Plate Using Element Free Galerkin Method 1
    2010
    Co-Authors: Ali Yeilaghi Tamijani, Rakesh K. Kapania
    Abstract:

    3An Element Free Galerkin (EFG) formulation is presented for studying the random response of curvilinearly-stiffened plates. The str ucture is subjected to stationary random stochastic loading. The random loads are assumed as stationary in time but can be nonhomogeneous in space. The spectral density of the Nodal Force Vector is formulated using the displacement shape functions. The direct comple x matrix inversion method and modal superposition method are used to obtain the random response of structure. The spectral density of displacement for un-stiffened plate unde r white noise and plate with straight stiffeners subjected to jet noise are compared with those available in the literature. The power spectral density of displacement of curviline arly-stiffened plate under white noise is also verified using the commercial finite element s oftware ANSYS ® . Excellent agreement is seen in all cases. The effect of stiffener stiffnes s and curvature and in-plane load on spectral density of deflection of curvilinearly-stiffened pl ate is also investigated.

  • Reduction methods based on eigenVectors and Ritz Vectors for nonlinear transient analysis
    Computational Mechanics, 1993
    Co-Authors: Rakesh K. Kapania, Chansup Byun
    Abstract:

    Reduction methods using eigenVectors and Ritz Vectors as basis Vectors are empolyed to reduce the finite element nonlinear system of equations using a 48 D.O.F. doubly curved thin plate/shell element. With and without basis updating, the solutions obtained by reduction methods are compared with the direct solutions. It is observed that basis updating is essential to obtain accurate solutions. The present reduction methods need a large number of basis Vectors (eigenVectors and Ritz Vectors) to account for the impact load which has high frequency characteristics. Furthermore, for nonlinear analysis, the reduction achieved in the CPU time are only marginal since most of the CPU time was spent in the calculation of the internal Nodal Force Vector. These considerations indicate that reduction methods may not be efficient for the impact response analysis.