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dynamic-instability
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Dynamic instability responses of the substructure living biological cells in the cytoplasm environment using stress-strain size-dependent theory
, Article Journal of Biomolecular Structure and Dynamics ; 17 April , 2020 ; Jamali, M ; Habibi, M ; Sadeghi, S ; Jung, D. W ; Nabipour, N ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
Over the last few years, some novel researches in the field of medical science made a tendency to have a therapy without any complications or side-effects of the disease with the aid of prognosis about the behaviors of the substructure living biological cell. Regarding this issue, nonlinear frequency characteristics of substructure living biological cell in axons with attention to different size effect parameters based on generalized differential quadrature method is presented. Supporting the effects of surrounding cytoplasm and MAP Tau proteins are considered as nonlinear elastic foundation. The Substructure living biological cell are modeled as a moderately thick curved cylindrical...
Effects of Trim tab on High Speed Vessel‘s Performance
, M.Sc. Thesis Sharif University of Technology ; Sayyadi, Hassan (Supervisor) ; Seif, Mohammad Saeed (Supervisor)
Abstract
Wide range application of high speed marine crafts in marine industry and other related industries results in attempts to improve the performance of such vessels. The main ideas of using control surfaces in high speed planing crafts are the change of the high speed planing craft‘s resistance due to change of their running attitudes and wave response mitigation of this vessels. Control surfaces produce forces and a pitching moment due to a pressure distribution caused by them, which can be used to alter the running attitude of high speed marine crafts. The present work contains a comprehensive study on trim tab as a control surface for the high speed crafts. The results of this study condense...
Maneuvering & Dynamic Stability Study of Planing Hulls
, Ph.D. Dissertation Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor)
Abstract
Planing hulls have been under rapid development during recent years and their maximum speed has increased significantly thanks to advancements in high power engines and light weight hull construction methods. In the past two decades, the main concern have been hydrodynamic characteristics and stability of the planing hulls in straight-line motion in calm and rough water, and no applied mathematical model is proposed for their dynamic motions in different maneuvers in contrast to displacement hulls. Moreover, control loss at high speeds is very prevalent and in most cases this leads to economy and human losses. The main target of this thesis is to develop and validate a mathematical model to...
Dynamic instability of cantilevered composite pipe conveying flow with an end nozzle
, Article 21st International Congress on Sound and Vibration 2014, ICSV 2014 ; Vol. 4, issue , 13- 17 July , 2014 , pp. 3564-3571 ; ISBN: 9781634392389 ; Abtahi, H ; Haddadpour, H ; Sharif University of Technology
Abstract
In this paper, the instability of cantilevered horizontal composite pipes is investigated. To this aim, the lateral flow forces are modelled as a distributed lateral force and the nozzle effect is modelled as a compressive axial follower force and a concentrated end mass. The coupled bending-torsional equations of motion are derived using Hamilton's principal and Galerkin method. In order to obtain the stability margin of the pipe, the standard Eigen value problem is solved. Finally, effects of elastic coupling parameter and nozzle aspect ratio are considered on the stability margin of the pipe and some conclusions are drawn
Dynamic instability characteristics of advanced grid stiffened conical shell with laminated composite skins
, Article Journal of Sound and Vibration ; Volume 488 , 2020 ; Kouchakzadeh, M. A ; Mirzavand, B ; Noghabi, M ; Sharif University of Technology
Academic Press
2020
Abstract
Dynamical instability characteristics of sandwich truncated conical shell are investigated. The three-layered shell is composed of advanced grid stiffened core and laminated composite skins. The core maybe made of three different fiber paths. The conical shell with simply-supported ends is subjected to two different types of time-dependent axial compressions. The equations of motion and compatibility are derived by considering Kirchhoff-Love assumptions and von Karman relations. The solution procedure is divided to two steps. First, the terms consisting of spatial derivatives are eliminated by applying a stress function and following the Galerkin method. Second, the terms with temporal...
Degradation Effects on Seismic Behavior of Soil-structure System
, M.Sc. Thesis Sharif University of Technology ; Mohtasham Dolatshahi, Kiarash (Supervisor)
Abstract
Up till now, various contributions of research to soil-structure-interaction context have been primarily focused on structural systems exhibiting elastic-perfectly plastic material behavior. In this paper, combined effects of material degradation, p-delta, and soil-structure-interaction considering foundation uplift have been deemed to determine seismic response of a single degree of freedom system. The system is composed of a column with a lumped mass on top that is placed on a rigid foundation. The foundation is mounted on Winkler springs and dashpots to account for soil-foundation compliance and material/radiational damping. The springs are tensionless to guarantee that uplift phenomenon...
On the response spectrum of Euler-Bernoulli beams with a moving mass and horizontal support excitation
, Article Mechanics Research Communications ; Volume 47 , January , 2013 , Pages 77-83 ; 00936413 (ISSN) ; Khaloo, A. R ; Nikkhoo, A ; Sharif University of Technology
Elsevier Ltd
2013
Abstract
Abstract In this study, the response spectrum of a time-varying system such as a beam subjected to moving masses under a harmonic and earthquake support excitations is explored. The excitations are supposed to act on the horizontal directions of the beam axis. The inertial effect of the moving masses on the natural frequencies of the beam for different cases of loading is investigated and a critical value of a so called parameter "mass staying time" is presented to avoid dynamic instability of the system. Finally, some 3D response spectra for different supports excitations as well as the beam natural frequencies are depicted
Modeling the coupled effects of surface layer and size effect on the static and dynamic instability of narrow nano-bridge structure
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 39, Issue 5 , 2017 , Pages 1735-1744 ; 16785878 (ISSN) ; Koochi, A ; Kanani, A ; Navazi, H. M ; Abadyan, M ; Sharif University of Technology
Springer Verlag
2017
Abstract
For modeling the electromechanical behavior of nano-bridge structures with slender narrow-width beam elements, not only the simultaneous effects of surface layer and size dependency should be taken into account but also corrected force models should be considered. In this paper, the instability of a narrow-width nano-bridge is studied based on strain gradient theory and Gurtin–Murdoch surface elasticity. The mid-plane stretching is incorporated in the governing equation as well as corrected force distribution. Using Rayleigh–Ritz method, a parametric analysis is conducted to examine the impacts of surface layer, size dependence, dispersion forces and structural damping on static and dynamic...
Planing craft control using pneumatically driven trim tab
, Article Mathematics and Computers in Simulation ; Volume 178 , December , 2020 , Pages 439-463 ; Zeinali, H ; Tamaddondar, M. H ; Sharif University of Technology
Elsevier B. V
2020
Abstract
Dynamic instabilities are quite common in planing crafts. This study deals with the elimination of one type of dynamic instabilities known as porpoising. The controller device is a pneumatically driven trim tab that applied to the transom of the boat. The governing dynamic equations of the planing craft and the pneumatically driven system are derived. The stability analysis of the system is carried out and porpoising instability is shown under some conditions. A dual control scheme consisting of the actuator control subsystem (inner control subsystem) and the planing craft (outer control subsystem) is proposed in order to control the planing craft from porpoising instability. Since the...
The oscillatory behavior, static and dynamic analyses of a micro/nano gyroscope considering geometric nonlinearities and intermolecular forces
, Article Acta Mechanica Sinica/Lixue Xuebao ; Volume 29, Issue 6 , 2013 , Pages 851-863 ; 05677718 (ISSN) ; Ahmadian, M. T ; Firoozbakhsh, K ; Sharif University of Technology
2013
Abstract
The nonlinear dynamic and static deflection of a micro/nano gyroscope under DC voltages and base rotation are investigated. The gyroscope undertakes two coupled bending motions along the drive and sense directions and subjected to electrostatic actuations and intermolecular forces. The nonlinear governing equations of motion for the system with the effect of electrostatic force, intermolecular tractions and base rotation are derived using extended Hamilton principle. Under constant voltage, the gyroscope finds the preformed shape. First, the deflection of the micro/nano gyroscope under electrostatic forces is obtained by static and dynamic analyses. Furthermore, the static and dynamic...
Dynamic stability analysis of single walled carbon nanocone conveying fluid
, Article Computational Materials Science ; Volume 113 , 2016 , Pages 123-132 ; 09270256 (ISSN) ; Noorian, M. A ; Haddadpour, H ; Fotouhi, M. M ; Sharif University of Technology
Elsevier
2016
Abstract
This report aims the study of dynamic stability of single walled carbon nanocone for some axial length conditions and declination angles of 60°, 120°and 240°. For dynamic stability analysis of Single Walled Carbon Nanocone (SWCNC), the mode shapes and frequencies of the carbon nanocone are extracted using the molecular mechanics approach. The mechanical properties of SWCNC were obtained by the Molecular Mechanics (MM) method. The obtained parameters are used for extraction of the conical shell virtual model of nanocone with the same dimensions. The equations of coupled fluid-structural dynamics of SWCNC are derived using the modal expansion for the structural displacements of the conical...
Application of piezoelectric and functionally graded materials in designing electrostatically actuated micro switches
, Article Proceedings of the ASME Design Engineering Technical Conference, 15 August 2010 through 18 August 2010 ; Volume 4 , August , 2010 , Pages 613-620 ; 9780791844120 (ISBN) ; Ahmadian, M. T ; Design Engineering Division and Computers in Engineering Division ; Sharif University of Technology
2010
Abstract
In this research, a functionally graded microbeam bonded with piezoelectric layers is analyzed under electric force. Static and dynamic instability due to the electric actuation is studied because of its importance in micro electro mechanical systems, especially in micro switches. In order to prevent pull-in instability, two piezoelectric layers are used as sensor and actuator. A current amplifier is used to supply input voltage of the actuator from the output of the sensor layer. Using Hamilton's principle and Euler-Bernoulli theory, equation of motion of the system is obtained. It is shown that the load type (distributed or concentrated) applied to the microbeam from the piezoelectric...