Omid Omidi | University of Tennessee Space Institute (original) (raw)
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Address: Tullahoma, Tennessee, United States
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Malaviya National Institute of Technology, Jaipur
Faculty of Technical & Engineering, Islamic Azad University South Tehran Branch, Tehran, Iran
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Papers by Omid Omidi
Earthquake Engineering & Structural Dynamics, 2013
There are several alternatives to evaluate seismic damage-cracking behavior of concrete arch dams... more There are several alternatives to evaluate seismic damage-cracking behavior of concrete arch dams, among which damage theory is the most popular. A more recent option introduced for this purpose is plasticdamage (PD) approach. In this study, a special finite element program coded in 3-D space is developed on the basis of a well-established PD model successfully applied to gravity dams in 2-D plane stress state. The model originally proposed by Lee and Fenves in 1998 relies on isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity to capture inelastic behaviors of concrete in cyclic or dynamic loadings. The present implementation is based on the rate-dependent version of the model, including large crack opening/closing possibilities. Moreover, with utilizing the Hilber-Hughes-Taylor time integration scheme, an incremental-iterative solution strategy is detailed for the coupled dam-reservoir equations while the damage-dependent damping stress is included. The program is initially validated, and then, it is employed for the main analyses of the Koyna gravity dam in a 3-D modeling as well as a typical concrete arch dam. The former is a major verification for the further examination on the arch dam. The application of the PD model to an arch dam is more challenging because the governing stress condition is multiaxial, causing shear damage to become more important than uniaxial states dominated in gravity dams. In fact, the softening and strength loss in compression for the damaged regions under multiaxial cyclic loadings affect its seismic safety.
International Journal for Numerical and Analytical Methods in Geomechanics, 2013
Formulation and algorithmic treatment of a rate-dependent plastic-damage model modified to captur... more Formulation and algorithmic treatment of a rate-dependent plastic-damage model modified to capture large tensile cracking in cyclic-loaded concrete structures are presented in detail for a three-dimensional implementation. The plastic-damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi-hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic-damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single-element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate.
Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 2006
In this paper, modeling and simulation of an underwater vehicle equipped with manipulator arms, u... more In this paper, modeling and simulation of an underwater vehicle equipped with manipulator arms, using a composite rigid body algorithm, will be discussed. Because of the increasing need for unmanned underwater vehicles (UUVs) in oil and gas projects in the Persian Gulf, for ...
Earthquake Engineering & Structural Dynamics, 2013
There are several alternatives to evaluate seismic damage-cracking behavior of concrete arch dams... more There are several alternatives to evaluate seismic damage-cracking behavior of concrete arch dams, among which damage theory is the most popular. A more recent option introduced for this purpose is plasticdamage (PD) approach. In this study, a special finite element program coded in 3-D space is developed on the basis of a well-established PD model successfully applied to gravity dams in 2-D plane stress state. The model originally proposed by Lee and Fenves in 1998 relies on isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity to capture inelastic behaviors of concrete in cyclic or dynamic loadings. The present implementation is based on the rate-dependent version of the model, including large crack opening/closing possibilities. Moreover, with utilizing the Hilber-Hughes-Taylor time integration scheme, an incremental-iterative solution strategy is detailed for the coupled dam-reservoir equations while the damage-dependent damping stress is included. The program is initially validated, and then, it is employed for the main analyses of the Koyna gravity dam in a 3-D modeling as well as a typical concrete arch dam. The former is a major verification for the further examination on the arch dam. The application of the PD model to an arch dam is more challenging because the governing stress condition is multiaxial, causing shear damage to become more important than uniaxial states dominated in gravity dams. In fact, the softening and strength loss in compression for the damaged regions under multiaxial cyclic loadings affect its seismic safety.
International Journal for Numerical and Analytical Methods in Geomechanics, 2013
Formulation and algorithmic treatment of a rate-dependent plastic-damage model modified to captur... more Formulation and algorithmic treatment of a rate-dependent plastic-damage model modified to capture large tensile cracking in cyclic-loaded concrete structures are presented in detail for a three-dimensional implementation. The plastic-damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi-hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic-damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single-element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate.
Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 2006
In this paper, modeling and simulation of an underwater vehicle equipped with manipulator arms, u... more In this paper, modeling and simulation of an underwater vehicle equipped with manipulator arms, using a composite rigid body algorithm, will be discussed. Because of the increasing need for unmanned underwater vehicles (UUVs) in oil and gas projects in the Persian Gulf, for ...