In this paper a new model is developed to describe the response of MAGNETO-RHEOLOGICAL FLUIDs ((MRF)) in transient state. The models which are developed so far, cover the steady-state flow, or address the transient state, with step-wise input electrical current and constant shear rate. In this paper, a new model for transient state of (MRF) is developed in which the input electrical current is an exponential function in different values of shear rate. Due to the magnetic inertia caused by the inductance of the coil, the real magnetic flux density could not be step-wise. Hence, compare with the other models, this model is in well agreement with reality. To verify the presented model and study the FLUID properties as input parameters, an experimental coupling is designed and fabricated. The coupling applies magnetic field perpendicular to shear direction, and measures the shear stress as a function of time. The results of the proposed model show acceptable agreement with experimental observations. According to experimental and theoretical results, the presented model is applied to a controllable torque coupling and acceptable results were obtained.

MAGNETO-RHEOLOGICAL damper is one of the most widely used mechanical equipment, which absorbs mechanical shocks by use of magnetic FLUID and electrical coil in its structure. In this paper, for the first time, dissipative particle dynamics as a mesoscopic scale modeling method was used to simulate a MAGNETO-RHEOLOGICAL damper and its magnetic FLUID. Data from 3 categories including magnetic FLUIDs with brand names 122-EG, 132-DJ, and 140-CG have been used and effect of their physical properties on power of damping force have been investigated. Results of modeling show that by increasing shear rate of FLUID, shear stress is first increased and, then, it is applied to a constant value, which results in a greater shear stress by applying a stronger magnetic field. It is also observed that, with increasing both maximum piston velocity and strength of magnetic field, maximum power of damping force increased, which in 140-CG is higher than the other FLUIDs. Results of sensitivity analysis show that weight of magnetic particles and strength of dissipative forces have the greatest effect on damping force, in such a way that by increasing weight of magnetic particles and decreasing the dissipative force of particles, accumulation of magnetic particles decrease, so, increasing quality of damping. It was also found that 122-EG is more suitable than other types of magnetic FLUIDs in forming standard magnetic particle chains, and provides a more favorable viscosity distribution for damping.

In the area of semi-active control of civil structures, MAGNETO-RHEOLOGICAL (MR) damper has been an efficient mechanism for reducing the seismic response of structures. In this paper, an effective method based on defining an optimization problem for designing MR dampers has been proposed. In the proposed method, the parameters of semi-active control system are determined so that the maximum response of structure is minimized. To solve the optimization problem, the Genetic algorithm (GA) has been utilized. The modified Bouc- Wen model has been used to represent the dynamic behavior of MR damper while to determine the input voltage at any time step, the clipped optimal control algorithm with LQR controller has been applied. To evaluate the performance of the proposed method, a ten-storey shear frame subjected to the El-Centro excitation and for two different kinds of objective functions, optimal MR dampers have been designed. Then the performance of optimal MR damper has been tested under different excitations. The results of the numerical simulations have shown the effectiveness of the proposed method in designing optimal MR dampers that have the capability of reducing the response of the structures up to a significant level. In addition, the effect of selecting a proper objective function to achieve the best performance of MR dampers in decreasing different responses of structure has been shown.

In this paper, at the first time, free vibration and buckling analysis of the cylindrical sandwich panels whit flexible cores and MAGNETO-RHEOLOGICAL FLUID Layers for simply supported boundary conditions are studied based on an improved higher order sandwich panel theory. In order to validate the results, the obtained results were compared with those obtained using finite element ABAQUS software. In this investigation, the effects of magnetic field, geometrical parameters such as the length to radius ratio, the core thickness to panel thickness ratio, MR layer thickness to panel thickness ratio and Fiber angle on the natural Frequency, buckling Load and loss factors of sandwich structure were investigated. The results suggest that the natural frequencies, critical buckling loads (eigen values) and the modal transverse displacements (eigen vectors) of the cylindrical sandwich panels whit flexible cores and MAGNETO-RHEOLOGICAL FLUID Layers in the face sheets are strongly influenced by the intensity of the applied magnetic field.

In this study, single-objective and multi-objective optimization of curved sandwich panel with composite face sheets and MAGNETO-RHEOLOGICAL core have been done to maximize the first modal loss factor and minimize the mass by using genetic algorithm. The studied sandwich panel was curved with simply support boundary condition. In order to derive the governing equations of motion, an improved high order sandwich panel theory and Hamilton's principle were used for the first time. The face sheet thickness, core thickness, fiber angles and intensity of the magnetic field have been considered as optimization variables. In single-objective optimization, the optimized values of variables were calculated. The results showed that the structures tend to have thick core and thin face sheets which seems physically true. As the MAGNETO-RHEOLOGICAL FLUID placed in the core, it has a significant effect on the increasing of the modal loss factor. For the multi-objective optimization the Pareto front of optimal technique was presented. Then for the first time at this field, the set of optimal points are selected based on TOPSIS method and it was showed that in the case of similar size and mass, modal loss factor of double-curved panel is more than sigle-curved.

In the present article, the free vibration analysis of a multi-layer rectangular plate with two MAGNETO-RHEOLOGICAL (MR) FLUID layers and a flexible core is investigated based on exponential shear deformation theory for the first time. In exponential shear deformation theory, exponential functions are used in terms of thickness coordinate to include the effect of transverse shear deformation and rotary inertia. The displacement of the flexible core is modeled using Frostig’ s second order model which contains a polynomial with unknown coefficients. MR FLUIDs viscosity can be varied by changing the magnetic field intensity. Therefore, they have the capability to change the stiffness and damping of a structure. The governing equations of motion have been derived using Hamilton`s principle. The Navier technique is employed to solve derived equations. To validate the accuracy of the derived equations, the results in a specific case are compared with available results in the literature, and a good agreement will be observed. Then, the effect of variation of some parameters such as magnetic field intensity, core thickness to panel thickness ratio hc h ( )and MR layer thickness to panel thickness ratio hMR h ( ) on natural frequency of the sandwich panel is investigated.

MAGNETO-RHEOLOGICAL FLUIDs are one of the intelligent FLUIDs which have been extensively used in engineering application including MAGNETO-RHEOLOGICAL dampers. Having yield stress in a magnetic field and ability to control and increase their viscosity are their most important characteristics. After three different carbonyl iron powders were subjected to analysis, five different MAGNETO-RHEOLOGICAL FLUIDs were synthesized and were tested for stability and the optimized FLUID obtained. The results obtained from the optimized MAGNETO-RHEOLOGICAL FLUID with 85% (weight %) iron powder was similar to that of LORD oil. Also, a modified non-Newtonian RHEOLOGICAL model was developed to predict the behavior of the optimized MAGNETO-RHEOLOGICAL FLUID which is more accurate than Bingham and Herschel-Bulkley models and could be implemented in computational FLUID dynamic modelling. The modelling of the damper was conducted by implementing modified non-Newtonian and Bingham models using analytical quasi-static, unsteady and computational FLUID dynamicmethods and the results were validated with experimental data. The results show that neglecting factors including FLUID shear thinning, wall shear stress and inertia term effects and effect of magnetic field on plastic viscosity in conventional modelling methods results in considerable error that will increase as magnetic field, Reynolds number and gap are increasing.