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Analitical and Numerical Investigation of Mechanical Response of Steel Cable
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
Although many aspects of helical strand have been carried out, there are still some situations which need more studies. Based on previous studies of wire rope the constitutive equations regarding the rope tension and torque to the rope deformations are carried out. In which constitutive constants depend on both the rope material and geometry of the rope. Equations of motion for straghit rope loaded simultaneously in tension and torque are derived, and with using extensional-torsional deformations in both side of the rope, dynamic stiffness matrix is derived. Some experimental results and currently models are compared with my research model numerically. Finally, mechanic response of helically...
Parallel computation of a fully implicit finite volume method using different ordering strategies
, Article 42nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 5 January 2004 through 8 January 2004 ; 2004 , Pages 12306-12316 ; Schneider, G. E ; Bostandoost, S. M ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2004
Abstract
The main purpose of this work is to improve the efficiency and performance of a primitive finite volume element method which provides superior capability on a single platform. This method is suitably extended in order to use the advantages of parallel computing on multiprocessors or multicomputers. The method is fully implicit which renders huge sparse linear algebraic kernels. Nevertheless, the attention is focused on solving the sparse system rather than constructing it. The current method is a cell-centered scheme. Since the grid is unstructured, each non-boundary node engages with nodes on three or more surrounding elements around that node. Depending on global node numbering, the...
Nonlinear stress analysis of shell structures in buckling and snapping problems by exact geometry solid-shell elements through sampling surfaces formulation
, Article International Journal of Non-Linear Mechanics ; Volume 129 , 2021 ; 00207462 (ISSN) ; Bohlooly, M ; Plotnikova, S. V ; Kouchakzadeh, M. A ; Mirzavand, B ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
In this paper, the nonlinear three-dimensional (3D) stress analysis of shell structures in buckling and snapping problems is presented. The exact geometry or geometrically exact (GeX) hybrid-mixed four-node solid-shell element is developed using a sampling surfaces (SaS) method. The SaS formulation is based on the choice of N SaS parallel to the middle surface to introduce the displacements of these surfaces as basic shell unknowns. The SaS are located at the Chebyshev polynomial nodes (roots of the Chebyshev polynomial of degree N), that is, the outer surfaces are not included into a set of SaS. Such choice of unknowns with the consequent use of Lagrange polynomials of degree N–1 in the...
Effective mechanical properties of unidirectional composites in the presence of imperfect interface
, Article Archive of Applied Mechanics ; Vol. 84, issue. 6 , June , 2014 , pp. 807-819 ; Print ISSN: 0939-1533 ; Toozandehjani, H ; Sharif University of Technology
Abstract
In this paper, the equivalent inclusion method is implemented to estimate the effective mechanical properties of unidirectional composites in the presence of an imperfect interface. For this purpose, a representative volume element containing three constituents, a matrix, and interface layer, and a fiber component, is considered. A periodic eigenstrain defined in terms of Fourier series is then employed to homogenize non-dilute multi-phase composites. In order to take into account the interphase imperfection effects on mechanical properties of composites, a stiffness parameter in terms of a matrix and interphase elastic modulus is introduced. Consistency conditions are also modified...
Modeling Mechanical Behavior Of Multilayer Synthetic Fiber Ropes Under Axial Loading
, M.Sc. Thesis Sharif University of Technology ; Ghoreishi, Reza (Supervisor) ; Behzad, Mehdi (Supervisor)
Abstract
Synthetic fiber rope mooring systems, are increasingly finding applications as offshore oil exploration goes to deeper sites. Synthetic fiber cables provide numerous advantages over steel mooring lines, particularly in deeper water that large self-weight of steel lines is prohibitive, synthetic fiber ropes could be a good selection for mooring system. In order to reduce the need for expensive tests under varying parameters and operating conditions it is essential to be able to model the mechanical behavior of very long synthetic mooring lines. The purpose of modeling mechanical behavior of cables is to determine global stiffness matrix Coefficients to correlate the forces and strains for...
Iterative implicit integration procedure for hybrid simulation of large nonlinear structures
, Article Earthquake Engineering and Structural Dynamics ; Volume 40, Issue 9 , October , 2011 , Pages 945-960 ; 00988847 (ISSN) ; Ahmadizadeh, M ; Sharif University of Technology
2011
Abstract
A fully implicit iterative integration procedure is presented for local and geographically distributed hybrid simulation of the seismic response of complex structural systems with distributed nonlinear behavior. The purpose of this procedure is to seamlessly incorporate experimental elements in simulations using existing fully implicit integration algorithms designed for pure numerical simulations. The difficulties of implementing implicit integrators in a hybrid simulation are addressed at the element level by introducing a safe iteration strategy and using an efficient procedure for online estimation of the experimental tangent stiffness matrix. In order to avoid physical application of...
Development of a shell superelement for large deformation and free vibration analysis of composite spherical shells
, Article Engineering with Computers ; Volume 37, Issue 4 , 2021 , Pages 3551-3567 ; 01770667 (ISSN) ; Hosseinzadeh, A ; Movahhedy, M. R ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
Finite element analysis of huge and/or complicated structures often requires long times and large computational expenses. Superelements are huge elements that exploit the deformation theory of a specific problem to provide the capability of discretizing the problem with minimum number of elements. They are employed to reduce the computational cost while retaining the accuracy of results in FEM analysis of engineering problems. In this research, a new shell superelement is presented to study linear/nonlinear static and free vibration analysis of spherical structures with partial or full spherical geometries that exist in many industrial applications. Furthermore, this study investigates the...
An Analitical Model for Grid Stiffened Structures of Various Patterns
, M.Sc. Thesis Sharif University of Technology ; Kouchakzadeh, Mohammad Ali (Supervisor)
Abstract
Structural efficiency is a primary concern in today’s aerospace and aircraft industries. This brings about the need for strong and light weight structures. To increase the strength of a panel without considerable increase in its weight, we may use a lattice of stiffeners which may have shells connected to one side of the lattice or both sides of it. These structures are usually called grid stiffened structures. Aircraft fuselage and launch vehicle fuel tanks are some of the many applications of these structures in aerospace and aircraft industries. These structures include two major groups; isogrids (grid stiffened structures with equivalent isotropic properties) and orthogrids (grid...
An Innovative Method for Vibration Analysis of Nanostructures using Equivalent Lattice Stiffness
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Rouhollah (Supervisor)
Abstract
In the following research a novel method for vibration analysis of nano-structures has been presented. This method is based on equalizing the lattice stiffness to a continuous model. In this method, an equivalent continuous system is considered for each atomic lattice and for the equivalent system a modified differential equation is presented. The governing equation of the continuous system is modified in such a way that the displacement field of the atomic lattice obtained by solving this differential equation gives similar responses to the displacement field of atomic lattice. This differential equation is derived from the Taylor expansion of the displacement field about the lattice atoms....
Determination of the Equivalent Linear Systems of Nonlinear MDOF Steel Moment Resisting Frames
, M.Sc. Thesis Sharif University of Technology ; Rahimzadeh Rofooei, Fayyaz (Supervisor)
Abstract
The purposeof this study isto findthe propertiesof an equivalent linear Multiple Degrees of Freedom (MDOF) system, or so-called substitute structure, that its response is an approximation ofthe target actualnonlinearMDOF structure’s response (Shodja, 2013). In that regard,thestiffness anddampingmatricesofthe substitutestructure are considered as functions ofthe stiffnessand dampingmatrices ofthe actualnonlinear structure. Inthisway,the substitute structurescan be constructedthroughtrial and errorfor structures with different fundamentalperiods, damping ratios and number of floors.Inthat regard, a number of multi-story steel moment resisting frames are considered. The ductilities of these...
A timoshenko beam element based on the modified couple stress theory
, Article International Journal of Mechanical Sciences ; Vol. 79, issue , 2014 , pp. 75-83 ; ISSN: 00207403 ; Asghari, M ; Ahmadian, M. T ; Sharif University of Technology
Abstract
Since the classical continuum theory is neither able to evaluate the accurate stiffness nor able to justify the size-dependency of micro-scale structures, the non-classical continuum theories such as the modified couple stress theory have been developed. In this paper, a new comprehensive Timoshenko beam element has been developed on the basis of the modified couple stress theory. The shape functions of the new element are derived by solving the governing equations of modified couple stress Timoshenko beams. Subsequently, the mass and stiffness matrices are developed using energy approach and Hamilton's principle. The formulations of the modified couple stress Euler-Bernoulli beam element...
Inverse vibration problem for un-damped 3-dimensional multi-story shear building models
, Article Journal of Sound and Vibration ; Volume 333, Issue 1 , 6 January , 2014 , Pages 99-113 ; ISSN: 0022460X ; Rofooei, F. R ; Sharif University of Technology
Abstract
Various researchers have contributed to the identification of the mass and stiffness matrices of two dimensional (2-D) shear building structural models for a given set of vibratory frequencies. The suggested methods are based on the specific characteristics of the Jacobi matrices, i.e., symmetric, tri-diagonal and semi-positive definite matrices. However, in case of three dimensional (3-D) structural models, those methods are no longer applicable, since their stiffness matrices are not tri-diagonal. In this paper the inverse problem for a special class of vibratory structural systems, i.e., 3-D shear building models, is investigated. A practical algorithm is proposed for solving the inverse...
A coupling atomistic-continuum approach for modeling mechanical behavior of nano-crystalline structures
, Article Computational Mechanics ; Volume 54, Issue 2 , August , 2014 , Pages 269-286 ; ISSN: 01787675 ; Aramoon, A ; Jahanbakhshi, F ; Dormohammadi, H ; Sharif University of Technology
Abstract
In this article, a novel approach is presented for the concurrent coupling of continuum-atomistic model in the nano-mechanical behavior of atomic structures. The study is focused on the static concurrent multi-scale simulation, which is able to effectively capture the surface effects intrinsic in the molecular mechanics modeling. The Hamiltonian approach is applied to combine the continuum and molecular models with the same weight in the overlapping domain. A Lagrange-multiplier method is employed over the overlapping domain for coupling the continuum nodal displacement with the atomic lattice deformation. A multiple-step algorithm is developed to decouple the solution process in the atomic...
A concurrent multi-scale modeling for dynamic behavior of nano-crystalline structures
, Article Computational Materials Science ; Volume 79 , 2013 , Pages 841-856 ; 09270256 (ISSN) ; Aramoon, A ; Jahanbakhshi, F ; Dormohammadi, H ; Sharif University of Technology
2013
Abstract
In this paper, a new multi-scale technique is developed for concurrent coupling of atomistic-continuum domains in modeling nano-mechanical behavior of atomic structures. A Lagrange multiplier method is employed over an overlapping domain to coupling the continuum nodal velocities with atomic lattice velocities. The Hamiltonian method is applied to combine the continuum and molecular Hamiltonians with the same weight in the overlapping domain. The mass and stiffness matrices of the continuum domain are obtained using a linear bridging map of the atomic lattice displacement laid underneath the continuum grid to the element displacements. Numerical examples are performed by presenting the...
Stress-constrained topology optimization: A topological level-set approach
, Article Structural and Multidisciplinary Optimization ; Volume 48, Issue 2 , August , 2013 , Pages 295-309 ; 1615147X (ISSN) ; Takalloozadeh, M ; Sharif University of Technology
2013
Abstract
The objective of this paper is to introduce and demonstrate an algorithm for stress-constrained topology optimization. The algorithm relies on tracking a level-set defined via the topological derivative. The primary advantages of the proposed method are: (1) the stresses are well-defined at all points within the evolving topology, (2) the finite-element stiffness matrices are well-conditioned, making the analysis robust and efficient, (3) the level-set is tracked through a simple iterative process, and (4) the stress constraint is precisely satisfied at termination. The proposed algorithm is illustrated through numerical experiments in 2D and 3D
A size-dependent beam element based on the modified couple stress theory
, Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011, 11 November 2011 through 17 November 2011, Denver, CO ; Volume 8 , 2011 , Pages 591-597 ; 9780791854945 (ISBN) ; Khajehpour, M ; Ahmadian, M. T ; ASME ; Sharif University of Technology
Abstract
In this paper, the modified couple stress theory is employed to develop a size-dependent beam element able to predict the size-dependency observed in microbeams. The stiffness matrix is obtained for the aforementioned beam element. As an example, the deflection of a microcantilever is evaluated using the proposed beam elements and the results of the finite element method are compared to the analytical results obtained by the classical beam theory. The maximum deflection of the beam is depicted versus the ratio of the beam thickness to the material length scale parameter, the parameter appearing in non-classical continuum theories. The results show that when the characteristic size of the...
Interface effect on the formation of a dipole of screw misfit dislocations in an embedded nanowire with uniform shear eigenstrain field
, Article European Journal of Mechanics, A/Solids ; Volume 51 , May–June , 2015 , Pages 154-159 ; 09977538 (ISSN) ; Enzevaee, C ; Gutkin, M. Y ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
The critical condition for the generation of a screw misfit dislocation dipole (MDD) at the interface between a nanowire (NW) with uniform shear misfit strain and its surrounding unbounded matrix within surface/interface elasticity theory is of particular interest. The analysis is carried out using the complex potential variable method. It is shown that the critical radius of the NW corresponding to the onset of the MDD generation decreases with the increase in the uniform shear eigenstrain inside the NW as well as when the stiffness of the NW increases with respect to the matrix. The critical radius strongly depends on the non-classical interface parameter. Comparison is made with classical...
On the analysis of simple shear problem using the micro-polar hypoelasticity Cosserat theory
, Article European Journal of Mechanics, A/Solids ; Volume 29, Issue 4 , July–August , 2010 , Pages 664-674 ; 09977538 (ISSN) ; Khoei, A. R ; Sharif University of Technology
2010
Abstract
In this paper, an analysis of kinematics of the isotropic elastic Cosserat continuum is presented in infinitesimal and finite deformations. Emphasis is given on the applicability of corotational stress rates for hypoelasticity in micro-polar continua. A non-linear finite element analysis is performed with an explicit formulation of tangent stiffness matrices in the case of Truesdell stress and couple stress rates. A comprehensive path-dependent procedure is employed based on the arc-length method to calculate the stability points and handle the snap-back problem. Finally, the accuracy and efficiency of method are illustrated by numerical examples
A comparative study of collagen matrix density effect on endothelial sprout formation using experimental and computational approaches
, Article Annals of Biomedical Engineering ; Volume 44, Issue 4 , 2016 , Pages 929-941 ; 00906964 (ISSN) ; Mohammadaliha, N ; Heilshorn, S. C ; Bauer, A. L ; Sharif University of Technology
Abstract
A thorough understanding of determining factors in angiogenesis is a necessary step to control the development of new blood vessels. Extracellular matrix density is known to have a significant influence on cellular behaviors and consequently can regulate vessel formation. The utilization of experimental platforms in combination with numerical models can be a powerful method to explore the mechanisms of new capillary sprout formation. In this study, using an integrative method, the interplay between the matrix density and angiogenesis was investigated. Owing the fact that the extracellular matrix density is a global parameter that can affect other parameters such as pore size, stiffness,...
Modeling of stiffening and strengthening in nano-layered silicate/epoxy
, Article International Journal of Engineering, Transactions A: Basics ; Volume 30, Issue 1 , 2017 , Pages 93-100 ; 17281431 (ISSN) ; Pearson, R. A ; Bagheri, R ; Sharif University of Technology
Abstract
The aim of this paper is to investigate adhesion property between nano-layered filler and the polymer matrix using a combination of experimental and micromechanical models as well as the changes in yield strength and stiffness of a layered silicate-filled epoxy nanocomposite. The results indicate that addition of intercalated layered silicate particles increased Young's modulus and yield strength of the epoxy resin, although the increases in stiffness and yield strength are modest, 30% and 4%, respectively. In addition, experimental results were compared with predictive stiffening and strengthening models. The rule of mixtures provides an upper bound for the modulus in these materials, while...