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    Nonlinear analysis of carbon nanotube-based nanoelectronics devices

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Vol. 228, issue. 13 , 2014 , p. 2426-2439 Fakhrabadi, M. M. S ; Rastgoo, A ; Ahmadian, M. T ; Sharif University of Technology
    Abstract
    The paper deals with the investigation of nonlinear static and dynamic behaviors of electrostatically actuated carbon nanotubes with different geometries and boundary conditions. The deflection and pull-in properties are studied in detail in the presence of DC and combined DC+AC electrostatic voltages accompanying the interatomic interactions. The considered nano system can be applied in a wide range of nanoelectronics devices such as nano switches, nano resonators, nano transistors, nano capacitors and random access memories. Moreover, a useful mathematical model of the nano sensor application of the studied nano system to sense the stiffness of the nano particles is presented  

    The Static Behavior of Calcite Cemented Gravely Sand – Tehran Alluvium Case Study

    , M.Sc. Thesis Sharif University of Technology Adl, Mahmoud Reza (Author) ; Haeri, Mohsen (Supervisor)
    Abstract
    An understanding of the effect of degree of cementation on static behavior of cemented soils in becoming increasingly important in design and analysis of geotechnical engineering problems. Naturally cemented coarse-grained soils are widely present in many parts of the world. Misunderstanding of the behavior of such soils could lead to under or overestimate of the soil parameters. Previous studies conducted by Prof. Haeri and his co-workers show that most of the alluvial deposit of Tehran, the capital city of Iran. The amount and characteristics of the cementation of the deposit varies in different parts from highly cemented in the north to non-cemented in the south. This deposit consists of... 

    Static and Dynamic Modeling of Post Fixed Grooved Clay Brick System Behaviour for Wall and Surfaces Construction Without Mortar and With High Planarity

    , M.Sc. Thesis Sharif University of Technology Mahmoodi, Mostafa (Author) ; Esmaeil Pourestekanchi, Homayoon (Supervisor)
    Abstract
    Nowadays using traditional hollow clay brick in buildings to make walls and partitionsisvery common. Non-load-bearing walls in buildings are used as architectural elements for design purposes and protecting the people that are inside the building from cold , heat and sound pollution .Due to the new technologies and developing building codes interms of structure , non-load-bearing walls behaviour that is always neglected seems necessary to be considered. In this research we have investigated the static and dynamic behaviour of a patented non-load-bearing wall made up of a claybrick system with specially-designed-precision grooved faces that eliminates conventional cement mortar and results... 

    Comparison of Dynamic and Static Performances of a Quaternary Distillation Sequence

    , Ph.D. Dissertation Sharif University of Technology Baghmisheh, Gholmarez (Author) ; Shahrokhi, Mohammad (Supervisor) ; Bozorgmehri, Ramin (Supervisor)
    Abstract
    In this work steady state and dynamic performances of quaternary distillation column sequences designed based on steady state and dynamic cost functions have been investigated. To quantify the dynamic performance, product loss due to disturbances has been considered in the objective function. In addition, variations of operating costs such as utilities have been considered in the objective function. To separate a quaternary mixture into four products, twenty two configurations have been used. It has been observed that the feed composition, disturbance frequency and magnitude affect the dynamic behavior strongly. To decrease the optimization computational load, a scheme that provides a... 

    Study of the Static and Dynamic Behaviour of Tieback Walls

    , M.Sc. Thesis Sharif University of Technology Sasar, Mohammad Hassan (Author) ; Haeri, Mohsen (Supervisor)
    Abstract
    The commercially available finite element software, FLAC, was used to provide better understanding of the static and dynamic behavior of tieback and anchored walls. Many of the codes dealing with the design of these structures use empirical methods to estimate the amount of deformation under static conditions. Therefore, in terms of static behavior, this thesis mainly focuses on the deformation patterns of the wall and the retained soil. Mohr-Coulomb elasto-plastic constitutive model was used; however, in elastic part the nonlinear Duncan-Change was implemented. The efforts made for better representation of soil behavior resulted in the suggestion of a modification to Duncan-Chang’s... 

    Submitted to the Department of Mechanical Engineering in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Mechanical Engineering

    , Ph.D. Dissertation Sharif University of Technology Taati, Ehsan (Author) ; Asghari, Mohsen (Supervisor) ; Fallah Rajabzadeh, Famida (Supervisor)
    Abstract
    Circular cylindrical shells have been widely used in many engineering structures such as spacecraft, submarines, offshores, and storage tanks. Their high stiffness-to-weight ratio and load-carrying capability make them well suited for use in civil and aerospace structures. The consecutive development of material engineering along with the increasing demands for lightweight, heat-resistant, and high strength structures have led to the usage of advanced materials namely functionally graded (FG) materials in designing such structures. In this thesis, the nonlinear static analysis of thin FG cylindrical shells is carried out using the Donnell’s shell theory with first-order approximation and the... 

    Static pull-in analysis of micro-cantilevers in wet etching fabrication process

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 9 November 2012 through 15 November 2012 ; Volume 9, Issue PARTS A AND B , November , 2012 , Pages 347-350 ; 9780791845257 (ISBN) Darvishian, A ; Moeenfard, H ; Ahmadian, M. T ; Sharif University of Technology
    2012
    Abstract
    Parallel micro actuators are mostly fabricated using the wet etching process within which the presence of capillary force and the resulting pull-in instabilities can severely affect the success of the fabrication process. In the case the capillary force is large enough then the beam like structure of the micro actuators is collapsed. The current paper investigates; static behavior of microcantilevers under effect of capillary force. It is observed that with increasing the instability number defined in the paper, the deflection of the micro-cantilevers is increased. This study shows in the wet etching fabrication process, if the distance between the beam and substrate is small enough, the... 

    Characterization of static behavior of electrostatically actuated micro tweezers using modified couple stress theory

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 9 November 2012 through 15 November 2012 ; Volume 9, Issue PARTS A AND B , Novembe , 2012 , Pages 581-585 ; 9780791845257 (ISBN) Darvishian, A ; Moeenfard, H ; Ghaderi, N ; Ahmadian, M. T ; Sharif University of Technology
    2012
    Abstract
    In this paper, static behavior and pull-in of micro tweezers is studied. The micro tweezer is modelled as two cantilever beams. Static behavior of the micro tweezer under the effect of electrostatic actuation is modelled using the Euler-Bernoulli beam theory. In order to capture size effects on the behavior of micro tweezers, modified couple stress theory is utilized. It is shown when the voltage between two electrodes increased from some specific value, micro beams adhere to each other and it is observed that the pull-in voltage predicted by the modified couple stress theory considerably differs with that of the classical theory of elasticity. Results of this paper can be used for accurate... 

    An analytical approach to modeling static behavior of torsional nano-/micro-actuators under effect of van der Waals force

    , Article Japanese Journal of Applied Physics ; Volume 51, Issue 3 PART 1 , 2012 ; 00214922 (ISSN) Moeenfard, H ; Darvishian, A ; Ahmaidan, M. T ; Zohoor, H ; Sharif University of Technology
    Abstract
    In this research, the static behavior of torsional nano-/micro-actuators under van der Waals (vdW) force is studied. First, the equilibrium equation governing the static behavior of torsional nano-/micro-actuators under vdW force is obtained. Then the energy method is utilized to investigate the statical stability of nano-/micro-actuator equilibrium points and a useful equation is suggested for the successful and stable design of nano-/micro-actuators under vdW force. Then, the equilibrium angle of nano-/micro-actuators is calculated both numerically and analytically using the homotopy perturbation method (HPM). It is observed that, with increasing instability number, defined in this paper,... 

    Numerical investigation into the static behavior of stepped soil nail walls

    , Article Scientia Iranica ; Volume 25, Issue 1 , 2018 , Pages 140-151 ; 10263098 (ISSN) Ahmadi, M. M ; Borghei, A ; Sharif University of Technology
    Sharif University of Technology  2018
    Abstract
    This paper presents a numerical investigation into the static behavior of stepped soil nail walls constructed in dry sandy soils. The finite element method was used to study influence of wall geometry and soil parameters on behavior of the walls. We analyzed walls with heights of 10, 15, and 20 m. This study shows that the wall deformation and the nail tensile forces of the stepped soil nail wall are smaller than those of the typical soil nail wall. If properties of soils such as friction angle, cohesion, and elastic modulus decrease, more decrease in the wall lateral displacement and nail tensile forces of a stepped soil nail wall would occur. Therefore, stepped soil nail walls are more... 

    Static behavior of nano/micromirrors under the effect of Casimir force, an analytical approach

    , Article Journal of Mechanical Science and Technology ; Volume 26, Issue 2 , FEB , 2012 , Pages 537-543 ; 1738494X (ISSN) Moeenfard, H ; Darvishian, A ; Ahmaidan, M. T ; Sharif University of Technology
    2012
    Abstract
    In this paper, static behavior of nano/microm1irrors under Casimir force is studied. At the first, the equilibrium equation governing the statical behavior of nano/micromirrors is obtained. Then energy method is employed to investigate statical stability of nano/micromirrors equilibrium points and a useful equation is suggested for successful and stable design of nano/micromirrors under Casimir force. Then, equilibrium angle of nano/micromirrors is calculated both numerically and analytically using the homotopy perturbation method (HPM). It is observed that with increasing the instability number defined in the paper, the rotation angle of the mirror is increased and suddenly, pull-in occurs.... 

    A coupled two degree of freedom pull-in model for micromirrors under capillary force

    , Article Acta Mechanica ; Volume 223, Issue 2 , 2012 , Pages 387-394 ; 00015970 (ISSN) Darvishian, A ; Moeenfard, H ; Ahmadian, M. T ; Zohoor, H ; Sharif University of Technology
    Abstract
    The current paper presents a two degree of freedom model for the problem of micromirrors under capillary force. The principal of minimum potential energy is employed for finding the equilibrium equations governing the deflection and the rotation of the micromirror. Then, using the implicit function theorem, a coupled bending-torsion model is presented for pull-in characteristics of micromirrors under capillary force and the concept of instability mode is introduced. It is observed that with increasing ratio of bending and torsion stiffness, the dominant instability mode changes from bending mode to the torsion mode. In order to verify the accuracy of the coupled model, static behavior of a... 

    Application of a new spherical super element in predicting the deformation of biological cells in microinjection

    , Article Proceedings of the ASME Design Engineering Technical Conference, 28 August 2011 through 31 August 2011 ; Volume 7 , August , 2011 , Pages 41-49 ; 9780791854846 (ISBN) Sarvi, M. N ; Ahmadian, M. T ; Sharif University of Technology
    2011
    Abstract
    Biological cell injection is a sensitive and important work which is implemented in injection of foreign materials into individual cells. Microinjection is significantly developed in the field of drug discovery and genetics so predicting the behavior of cell in microinjection is remarkably important because a tiny excessive manipulation force can destroy the tissue of the biological cell. There are a few analytical methods available to simulate the cell injection, hence the numerical methods such as FEM are suitable to be used to model the microinjection. In this study, a new spherical super element is presented to model the biological cells and deformation of a specific cell under an... 

    Comparison of deformation analysis of a biological cell under an injection force using analytical, experimental and finite element methods and Artificial Neural Network

    , Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011 ; Volume 2 , 2011 , Pages 499-507 ; 9780791854884 (ISBN) Sarvi, M. N ; Ahmadian, M. T ; ASME ; Sharif University of Technology
    Abstract
    Biological cell injection is a sensitive and important work which is implemented in injection of foreign materials into individual cells. Microinjection is significantly developed in the field of drug discovery and genetics so predicting the behavior of cell in microinjection is remarkably important because a tiny excessive manipulation force can destroy the tissue of the biological cell. There are a few analytical methods available to simulate the cell injection, hence the numerical methods such as FEM are suitable to be used to model the microinjection. In this study, a new spherical super element is presented to model the biological cells and deformation of a specific cell under an... 

    Closed form solutions for the statical behavior of micromirrors under capillary forces

    , Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011 ; Volume 11 , 2011 , Pages 131-137 ; 9780791854976 (ISBN) Moeenfard, H ; Darvishian, A ; Ahmadian, M. T ; Sharif University of Technology
    2011
    Abstract
    In this paper, the static behavior of micromirrors under the effect of capillary forces is studied. First the equation governing the static behavior of micromirrors is obtained using both Newton method and minimum potential energy principle. Then energy method is employed to investigate the static instability of micromirrors equilibrium points. It is proved that when there exist two equilibrium points, the smaller one is stable and the larger one is unstable. Furthermore a design equation is suggested for the successful fabrication process of micromirrors in the stable operatives range. Then the statical behavior of micromirrors is investigated numerically and analytically using the Homotopy... 

    Analytical solutions for the static instability of nano-switches under the effect of casimir force and electrostatic actuation

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 12, Issue PART A , 2010 , Pages 63-69 ; 9780791843857 (ISBN) Mojahedi, M ; Moeenfard, H ; Ahmadian, M. T ; Sharif University of Technology
    Abstract
    This paper deals with the problem of static instability of nano switches under the effect of Casimir force and electrostatic actuation. The nonlinear fringing field effect has been accounted for in the model. Using a Galerkin decomposition method and considering only one mode, the nonlinear boundary value problem describing the static behavior of nano-switch, is reduced to a nonlinear boundary value ordinary differential equation which is solved using the homotopy perturbation method (HPM). In order to ensure the precision of the results, the number of included terms in the perturbation expansion has been investigated. Results have been compared with numerical results and also with... 

    Investigation of TLP behavior under tendon damage

    , Article Ocean Engineering ; Volume 156 , 15 May , 2018 , Pages 580-595 ; 00298018 (ISSN) Tabeshpour, M.R ; Ahmadi, A ; Malayjerdi, E ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    Exact calculation of stiffness matrix of TLP is important for investigation of its behavior in intact and tendon damage conditions and it is necessary to design a reliable TLP. A serious attention has been concentrated on this problem in API-RP-2T and various aspects of that such as dynamic and static behavior of TLP, tendon tensions after one tether failure. Also it has introduced safety factors in different loads and healthy conditions. This paper deals with effect of damage tendon condition of TLP on behavior and tensions of tendons in wave frequency range. Equilibrium of TLP is studied and stiffness matrix of TLP is derived in tendon damage condition. Wave loads and hydrodynamic... 

    Static analysis of electrically actuated nano to micron scale beams using nonlocal theory

    , Article Proceedings of the ASME Design Engineering Technical Conference, 28 August 2011 through 31 August 2011 ; Volume 7 , August , 2011 , Pages 391-396 ; 9780791854846 (ISBN) Vaghasloo, Y. A ; Pasharavesh, A ; Ahmadian, M. T ; Fallah, A ; Sharif University of Technology
    2011
    Abstract
    In this paper, size dependent static behavior of micro and nano cantilevers actuated by a static electric field including deflection and pull-in instability, is analyzed implementing nonlocal theory. Euler-bernoulli assumptions are made to model the relation between deflection of the beam and bending moment. Differential form of the constitutive equation of nonlocal theory is used to find the revised equation for bending moment and substituting in the equilibrium equation of electrostatically actuated beams final nonlinear ordinary differential equation is arrived. Also the boundary conditions for solving the equation are revised and to analyze the size effect better governing equation is... 

    Multi sensing grasper for minimally invasive surgery

    , Article IEEE/ASME International Conference on Advanced Intelligent Mechatronics, AIM, 3 July 2011 through 7 July 2011, Budapest ; July , 2011 , Pages 344-349 ; 9781457708381 (ISBN) Fattahi, S. J ; Zabihollah, A ; Adldoost, H ; Sharif University of Technology
    2011
    Abstract
    In the present work, a multi sensing grasper has been developed for minimally invasive surgery with embedded ZnO piezoelectric and Fiber Bragg Grating sensors. In this model, a sensing patch equipped with three FBG sensors to sense the temperature in rage of 800 n.m and two separated FBG in range of 1550 m.m to detect the displacement in x and y directions. ZnO piezoelectric is highly sensitive to time and provides a good resistance to temperature. Therefore, this sensor is used for measuring the rate of strain and creep coefficient. A finite element approach based on the viscous material theory and plane displacement theory of anisotropic materials has been utilized to obtain the compliance...