Sharif Digital Repository

Magnetorheological (MR) materials indicate variations in their rheological properties when subjected to different magnetic fields. They have quick time response, in the order of milliseconds, and therefore are potentially applicable to structures and devices when a tunable system response is required. This study presents vibration analysis of laminated composite plate using MR fluid lumps under Random Excitation. A structural dynamic modeling approach is discussed and vibration characteristics of MR adaptive structures are predicted for different magnetic field levels. Linear Quadratic Regulator (LQR) controller is designed to achieve the vibration suppression of the laminated plate. The... 

Earthquake motions are among random excitation loads. For that we used random vibration approach to estimate response of multi-degree of freedom base isolated structures under ground excitation. Some models including linear model ,nonlinear Bouc-Wen and BBW models are studied for modeling the superstructure .Several base isolation models including the laminated rubber bearing, high damping laminated rubber bearing ,resilient-friction base isolator with or without sliding upper plate and the Electricity de France system, are studied . El Centro 1940 and Mexico City 1985 earthquake which preserve the nonstationary evolutions of amplitude and frequency content of ground accelerations... 

In some activities, an almost free of any vibration environment is needed. Semi conductor production process and microelectronic microscopes are two examples in which a quiet environment is essential. The goal of this thesis is to attenuate ambient vibrations effectively and to prepare a suitable environment for two microelectronic microscopes. The designed system must be practical, economical and capable of being made in a short time interval. Considering mentioned properties a steel table with bolt connections supported on 4 air springs was built. To investigate dynamic properties, modal analysis was performed with the aid of finite element packages and experiments. To extract oscillations... 

When vibration of the structure is unrecognized we call it random vibrations which their analysis is very important in space structures because these structures are exposed to acoustic forces or forces produced by turbulence of the atmosphere when a spacecraft is launched. Also in the aviation field, the random vibration analysis use to examine the response of the aircraft and missile structures to atmospheric turbulence and gust. In this research dominated equations of a truncated conical axisymmetric shell structure with linearized approximation of Love’s equations under uniform pressure is utilized. Considering displacements in the form of Frobenius series expansion the frequencies and... 

Laminated composite beams are being widely used in engineering applications, including aerospace and automobile where the structures are highly subjected to non-deterministic random loadings, requiring a reliable technique to ensure the stability of structure during operation. A Novel N-layer model of layerwise theory (LWT) for laminated composite beams incorporated with magnetorheological fluid (MR-laminated beams) is developed. In addition, a finite element model of tapered laminated composite beams incorporated with magnetorheological fluid (MR-tapered beam) based on layerwise theory is developed. The dynamic response of the present model for uniform and tapered beams have been compared... 

Indeterminate behavior of some forces in the aerospace industry due to flight at high speeds, gust, combustion, etc., has led to the exposure of structures to dynamic loads with random behavior in the nonlinear manner. To analyze problems in which the loading is random or the system parameters are random, the only possible way is to describe the system response in statistical values.Since most modern structures have complex geometry and the number of degrees of freedom is very high, advanced numerical solution methods are used to obtain the system response. In this study, the geometric nonlinear vibrations of structures under random loading are investigated by the finite element... 

The main purpose of this study is stochastic analysis of base-isolated structures considering soil-structure interaction. Due to stochastic nature of earthquake and existence of uncertainties in non-linear behavior of and properties of soil, it is better to calculate the responses of the structure via random vibrations approach. In this approach first of all, the differential equations of structure are obtained in deterministic vibration mode and then by the available theories, differential equations of covariance of the responses are obtained. Solving these equations leads to the finding of the standard deviations of the responses of the structure in each moment. In backward differential...