فهرست مطالب sajjad nikoei

In most of the structural optimization approaches analysis and sensitivities are carried out by using the conventional finite element method. Due to the variations of the problem geometry within the shape optimization iterations, updating the computational model by several remeshings is required that is quite time consuming and computationally costly. As a remedy for this problem, the NURBS-based isogeometric analysis method is here adopted that combines the Computer Aided Design (CAD) and finite element techniques. In this study, in the shape optimization of the structures the Method of Moving Asymptotes (MMA), which is a gradient-based method, is employed and to calculate the required sensitivities a fully analytical approach is presented. To demonstrate the performance of the suggested approach, various numerical examples are solved.

This paper presents isogeometric analysis of free form shells based on Kirchhoff-Love and Reissner-Mindlin theories. The isogeometric approach utilizes Non-Uniform Rational B-Splines (NURBS) for different order approximation of the variables defining the geometry as well as the unknown functions. The geometry is defined for both theories by the NURBS technique for surface generation. In the employed Reissner-Mindlin shell theory, by making use of the anchor point concept the normal vector is calculated accurately. The Kirchhoff-Love shell theory uses three displacements degrees of freedom per node, but the Reissner-Mindlin theory uses five degrees of freedom, three displacements and two rotations. Also, for Kirchhoff-Love shell theory C1 continuity of the NURBS basis functions is needed, while for the Reissner-Mindlin shell theory C0 continuity is sufficient. Several standard benchmark examples with available analytical solutions are presented to demonstrate the performance and accuracy of the approaches. Also, a new benchmark problem is designed to study the performance of the methods as well as the convergence behavior of the presented approach when applied to completely free form shells.

This paper presents an isogeometric analysis approach for static and free vibration analysis of laminated composite plates covered with piezoelectric layers using the Reissner-Mindlin theory. Isogeometric analysis (IGA) aims at simplifying the Computer Aided Design (CAD) and Computer Aided Engineering (CAE) by using the functions describe the geometry (CAD) and the unknown fields (Analysis). The isogeometric approach has here been employed that utilizes the Non-Uniform Rational B-Splines (NURBS) of quadratic, cubic and quartic orders to approximate the variables defining geometry as well as the unknown functions. Using the Reissner-Mindlin first order shear deformation theory requires the C0-continuity of generalized displacements and the NURBS basis functions are well suited for this purpose. The electric potential is assumed to vary linearly through the thickness for each piezoelectric sublayer. To alleviate the shear locking problem, a stabilization technique is employed in the stiffness formulation. Since study of the performance and accuracy of IGA in solving laminated composite plates is one of the main objectives of this article. Several numerical examples are presented and compared with those available in the literature. The obtained results indicate desirable accuracy and efficiency of the proposed approach.