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nonlinear-vibrations
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An approximate method for the surge response of the tension leg platform
, Article Journal of Marine Science and Application ; Vol. 13, issue. 1 , March , 2014 , p. 99-104 ; Tabeshpour, M. R ; Sharif University of Technology
Abstract
The solution for the Duffing equation in a nonlinear vibration problem is studied in this paper. Clearly, in the case of the perturb parameter being a larger value, the traditional perturbation method is no longer valid but the Homotopy Perturbation Method (HPM) is applicable usually. HPM is used to solve the weak and strong nonlinear differential equations for finding the perturbed frequency of the response. The obtained frequencies via HPM and the approximate method have good accordance for weak and strong nonlinear differential equations. Additionally, the calculated responses by use of the approximate method are compared with the responses obtained from the Numerical method in the time...
Nonlinear vibration and comfort analysis of high-speed trains moving over railway bridges
, Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 2 , 2004 , Pages 237-246 ; 0791841731 (ISBN); 9780791841730 (ISBN) ; Thompson, D. J ; Younesian, D ; Jones, C. J. C ; Sharif University of Technology
American Society of Mechanical Engineers
2004
Abstract
The ride comfort of high-speed trains passing over railway bridges is studied in this paper. The effects of some nonlinear parameters in a carriage-track-bridge system are investigated such as the load-stiffening characteristics of the rail-pad and the ballast, rubber elements in the primary and secondary suspension systems. The influence of the track irregularity and train speed on two comfort indicators, namely Sperling's comfort index and the maximum acceleration level, are also studied. Timoshenko beam theory is used for modelling the rail and bridge and two layers of parallel damped springs in conjunction with a layer of mass are used to model the rail-pads, sleepers and ballast. A...
A nonlinear double-winged adaptive neutralizer for optimum structural vibration suppression
, Article Communications in Nonlinear Science and Numerical Simulation ; Volume 8, Issue 2 , 2003 , Pages 113-134 ; 10075704 (ISSN) ; Esmailzadeh, E ; Sharif University of Technology
2003
Abstract
A distributed, nonlinear dynamic vibration neutralizer is presented to improve vibration suppression characteristics of harmonically excited structures. The absorber subsection consists of a double-ended cantilever beam carrying intermediate lumped masses. The positions of the moving masses are adjustable along the beam in order to comply with the desired optimal performance. The absorber is assumed to be linearly elastic but with the inextensibility along the neutral axis of the beam. Due to the existence of parametric resonance, nonlinearities of the system begin to affect the motion and hence parametric instability occurs. The necessary and sufficient conditions for the existence of...
Analytical and Experimental Study of Transverse Vibration of Ulerr-Bernoulli Beam with Dry Friction Boundary Condition
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Roohollah (Supervisor)
Abstract
The dry friction and its effect on the dynamics and vibrations of structures have always been one of the remarkable engineering issues. In the structures of engineering, dry friction mostly exists at the joints of structures and substrates and dry friction can lead to the nonlinearity and even chaos in the vibration of structures. There are different theories for the friction modeling and the most famous theory is the relation between the proportional ratio of the force of friction and perpendicular force to the surface. The main characteristic of friction as a damper force is the change of direction along with change in the direction of velocity. In the present study, at first, the nature...
Nonlinear free vibration of simply supported beams considering the effects of shear deformation and rotary inertia, a homotopy perturbation approach
, Article International Journal of Modern Physics B ; Volume 25, Issue 3 , 2011 , Pages 441-455 ; 02179792 (ISSN) ; Moeenfard, H ; Ahmadian, M. T ; Sharif University of Technology
2011
Abstract
The objective of this paper is to apply He's homotopy perturbation method (HPM) to analyze nonlinear free vibration of simply supported Timoshenko beams considering the effects of rotary inertia and shear deformation. First, the equation governing the nonlinear free vibration of a Timoshinko beam is nondimensionalized. Galerkin's projection method is utilized to reduce the governing nonlinear partial differential equation to a nonlinear ordinary differential equation. HPM is then used to find analytic expressions for nonlinear natural frequencies of the pre-stretched beam. A parametric study has also been applied in order to investigate the effects of design parameters such as applied axial...
Nonlinear vibration analysis of directional drill string considering effect of drilling mud and weight on bit
, Article Journal of Vibroengineering ; Volume 18, Issue 2 , 2016 , Pages 1280-1287 ; 13928716 (ISSN) ; Monfared, V ; Daneshmand, S ; Abedi, E ; Sharif University of Technology
Vibromechanika
2016
Abstract
In this paper a nonlinear dynamic model for drill string in inclined well drilling is developed. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping on stability and vibration of the drill string are studied. Findings indicate the nonlinear effects are significant on the results. The effects of drilling mud flow rate and weight on bit on the natural frequencies and time responses are evaluated. Enhancement of drilling mud flow rate results in decreasing of natural frequencies and vibrational amplitude, while increasing the weight on bit, leads to decrease of the natural frequencies and increase the vibrational amplitude. © JVE INTERNATIONAL LTD
An Analytical Approach to Nonlinear Vibrations of a Three-Layered Sandwich Beam with a Viscoelastic Core, under the Effects of Internal Resonance, Employing MMS
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor)
Abstract
Vibrations with high amplitudes in continuous systems and models with multiple degrees of freedom, in specific conditions, is concomitant with a phenomenon called internal resonance. In the presence of this phenomenon, energy is transferred from one directly excited mode to the other vibrating modes of the structure results in response of the structure to be combination of the excited modes. In that situation occurrence of the internal resonance may decrease the level of undesired vibrations of the structure. This behavior is of interest especially in sandwich structures with viscoelastic cores that are designated to improve the damping characteristics of the structure and the property may...
Nonlinear Vibration Analysis of a Closed Ends ,Fluid-Filled Beam with Different Boundary Condition, Using Galerkin Method
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
Presence of fluid in closed ends beam can increase beam hardness against pressure and buckling loads. This behavior is due to incompressibility or very low compressibility of fluids. there is a lot of research in the literature focusing on fluid solid interaction in pipe flow, but there is not any reported research studying on fluid filled beam, where fluid doesn’t flow across the beam. In this research hollow beam is modeled with Euler -Bernoulli beam theorem. Potential energy and kinetic energy is derived with considering the incompressibility of fluid. Nonlinear system of equations is derived using Hamilton principle . this system is taken to time domain using Galerkin and assumed mode...
Simulation of Vortex Induced Vibration and Limit Cycle Oscillation on Flexible tall towers and Suspended Cables
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
Vibration of flexible slender structures under vortex induced vibrations is one of the important subjects in the different fields of engineering such as overhead electricity transmission cables, columns, tall towers and suspended bridges. During passes of flow around bluff bodies, in the certain range of velocity, the Von Karman vortices sheds unsynchronized from two sides of bluff bodies. When structure frequency closed to the vortex shedding frequency, resonant vibrations happen and one can observe vibrations with limited amplitude. Simulations of these phenomenons are so complicated and time consuming prosess, but there is an engineering method for simulating this phenomenon. The aim of...
Nonlinear forced vibration of strain gradient microbeams
, Article Applied Mathematical Modelling ; Volume 37, Issue 18-19 , 1 October , 2013 , pp. 8363-8382 ; ISSN: 0307904X ; Kahrobaiyan, M. H ; Alasty, A ; Ahmadian, M. T ; Sharif University of Technology
Abstract
In this paper, the strain gradient theory, a non-classical continuum theory able to capture the size effect happening in micro-scale structures, is employed in order to investigate the size-dependent nonlinear forced vibration of Euler-Bernoulli microbeams. The nonlinearities are caused by mid-plane stretching and nonlinear external forces such as van-der-Waals force. The nonlinear governing equations of the microbeams are solved analytically utilizing the perturbation techniques. The primary, super-harmonic and sub-harmonic resonances of a microbeam are studied and the size-dependency of the frequency responses is assessed. The results indicate that the nonlinear forced vibration behavior...
Effects of rotary inertia and shear deformation on nonlinear vibration of micro/nano-beam resonators
, Article 2005 ASME International Mecahnical Engineering Congress and Exposition, IMECE 2005, Orlando, FL, 5 November 2005 through 11 November 2005 ; Volume 7 MEMS , 2005 , Pages 439-445 ; 1096665X (ISSN); 079184224X (ISBN); 9780791842249 (ISBN) ; Alasty, A ; ASME Micro Electro Mecahnical Systems Division ; Sharif University of Technology
2005
Abstract
In this paper, the large amplitude tree vibration of a doubly clamped microbeam is considered. The effects of shear deformation and rotary inertia on the large amplitude vibration of the microbeam are investigated. To this end, first Hamilton's principle is used in deriving the partial differential equation of the microbeam response under the mentioned conditions. Then, implementing the Galerkin's method the partial differential equation is converted to an ordinary nonlinear differential equation. Finally, the method of multiple scales is used to determine a second order perturbation solution for the obtained ODE. The results show that nonlinearity acts in the direction of increasing the...
Vibration and Dynamic Analysis of Electrostatically Aactuated Micro and Nano Beams Using Nonlocal Theory
, M.Sc. Thesis Sharif University of Technology ; Ahmadiyan, Mohammad Taghi (Supervisor) ; Zohoor, Hassan (Supervisor)
Abstract
Micro and nano electromechanical systems technology has experienced lots of progress in recent years. These systems are widely used in sensors and actuators due to their small size low weight and low energy consumption. Electrostatically actuation is one of the simplest and most prevalent methods of actuation and sensing in these systems. Electrostatically actuated micro and nanobeams are used in many devices such as micro and nano switches, resonators, signal filters, tunable capacitors, pressure and mass sensors, etc. Experimental results and measurements have shown that classical theories contain error in prediction of static and dynamic ...
Coupled Vibration Analysis of Directional Drilling String Considering Effect of Drilling Mud
, M.Sc. Thesis Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor) ; Farrahi, Gholamhossein (Co-Advisor)
Abstract
Vibration is one of the most important factors in design, operation and lifetime of drill strings. There for, investigation of vibrations in drill string, like every other rotary machine, is very important. The main goal of this research is developing a nonlinear model for a drill string system dynamics in an inclined well. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping, on the stability and vibration of a drill string are studied. Dynamic equation of the model is developed considering axial displacement and lateral bending geometric nonlinear coupling. The effect of drilling mud flow is modeled using Paidoussis formulations. Equation of motion...
Dynamic and Vibration Analysis of Micro-Mirrors Made of FGM
, M.Sc. Thesis Sharif University of Technology ; Ahmadiyan, Mohammad Taghi (Supervisor) ; Firoozbakhsh, Keikhosrow (Supervisor)
Abstract
The important role of MEMS devices in optical system has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical systems (MEOMS), which mainly includes micromirrors and torsional microactuators. These devices have found variety of application in optical switches, display, micro scanning mirrors, optical cross-connects interferometry, spectroscopy, aberration correction and biomedical imaging. In this project, the dynamic behavior of electrostatic micromirrors under the effect of intermolecular surface forces and squeezed film damping are studied. The prior art published in the literature have mainly used pure torsion models. In a pure torsion, just the torsion...
Nonlinear Vibration Analysis of Non-Uniform Beam in two Lateral Directions by Multiple Scales Method: Application in Wind Turbine
, M.Sc. Thesis Sharif University of Technology ; Moradi, Hamed (Supervisor)
Abstract
Environmental issues and energy crisis have led the world attention to the renewable energies; especially wind power, since they have low cost and high reliability. One of the most challenging areas of studying for wind power is to increase the capacity of wind turbines. As a result, over the years, wind turbines have got progressively larger. Vibration is one of the problems that reduces the life and efficiency of wind turbines; and the growing size of the blades has worsen this problem due to the importance of nonlinear effects in large scale wind turbines. Researchers have been constantly working on this issue in order to make the wind turbines more efficient. In this research, a...
Nonlinear Vibrations of Inclined Timoshenko Beam on Pasternak Foundation with Moving Force
, M.Sc. Thesis Sharif University of Technology ; Kargarnovin, Mohammad Hossein (Supervisor)
Abstract
In the first part of this thesis, the linear and nonlinear governing differential equations of motion of an inclined Euler-Bernoulli beam are used by tacking into account the effect of beam’s mid-plane stretching. Then nonlinear coupled governing partial differential equations of vibrations by including rotation of cross section, longitudinal and transverse displacements in the Timoshenko beam theory on Pasternak foundation under the act of moving concentrated force and as wll as moving mass are drived. To do this the energy method (Hamilton’s principle) based on the large deflection theory in conjuncture with the von-Karman relations is used. These equations are solved by applying...
Nonlinear Vibrations of Conical Shells with Concurrent Internal and External Flows
, Ph.D. Dissertation Sharif University of Technology ; Dehghani Firouz Abadi, Ruhollah (Supervisor)
Abstract
In the current study, nonlinear vibration and stability of conical shells with both separate and concurrent internal and external flows are studied. External and internal flows are in the supersonic and subsonic regimes, respectively. The Krumhar’s aerodynamic piston theory is utilized to model the external loading on the structure as well as the compressible potential flow model to capture the internal fluid dynamics. The so-called compressible fluid model is obtained via simplification of the Navier-Stockes equations after applying the inviscid and irrotational assumptions. The nonlinear structural equations of motion are derived using the Hamiltonian dynamics approach and utilizing the...
Bending-torsional Stability and Vibrations of Beams Conveying Pulsating Flow in the Presence of Free Stream
, Ph.D. Dissertation Sharif University of Technology ; Haddadpour, Hassan (Supervisor) ; Dehghani Firouzabadi, Rohollah (Co-Advisor)
Abstract
In the current study, stability and nonlinear vibration of bending-torsional extensible beams conveying internal pulsatile and uniform external flow are studied. The internal and external fluid flows are assumed to be incompressible and frictionless. Applying the extensibility to the pipe along its length and using the nonlinear Euler-Bernoulli beam model and including some appropriate additional assumptions, the 3D nonlinear equations of motion of a cantilevered composite pipe is obtained. In order to derive the equations governing the fluid-structure interaction, the internal flow effect is modeled as a distributed load along the pipe which contains the inertia, Coriolis and centrifugal...
Nonlinear Vibration Analysis of Circular Microplate Based on Strain Gradient Theory
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
Nowadays the combination of mechanical and electronic systems in small scales is gaining attention. Micro electro-mechanical systems are widely used in various industries such as car manufacturing and electronic chips. In these devices, the most important and useful mechanical structures are beams and plates. Therefore, investigating the mechanical properties of these structures in very small scales (micro and nano) is of great importance. Decreasing the size to these scales leads to the dependence of the behavior of these structures to size. Accordingly, some theories for prediction of these behaviors have been presented, one of which is the strain gradient theory. This theory is used in...
Analytical and Experimental Analyses of Nonlinear Vibrations in a Rotary Inverted Pendulum
, M.Sc. Thesis Sharif University of Technology ; Khayyat, Amir Ali Akbar (Supervisor) ; Pasharavesh, Abdolreza (Co-Supervisor)
Abstract
Investigation of possible vibratory responses of dynamical systems around their stable equilibria is an essential step which must be taken before their both design and application. The attained results of such a study can largely help to prevent instability in closed-loop stabilized systems by avoiding excitation of the system in the neighborhood of its resonance. In this paper, nonlinear oscillations of a Rotary Inverted Pendulum (RIP) enjoying a full-state feedback controller is investigated. Lagrange’s equations are employed to derive an accurate 2-DoF mathematical model whose parameters are extracted by both measurement and 3D modeling of the real system components. The perturbative...