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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.

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The unbalancing is a destructive phenomenon and is a major cause of undesired vibrations in rotating machinery. One of the new methods used to reduce the imbalance is the implementing of automatic dynamic ball balancer. In previous studies the dynamic behavior of automatic ball balancer has been investigated. These studies indicate numerous advantages of automatic ball balancer. However, the traditional automatic ball balancer has two major deficiencies: First, the rotor vibration amplitude is larger than that of a rotor without an automatic ball balancer in speeds below the first critical speed and, the second deficiency is that it has a limited stable region of the perfect balancing configuration. In this paper, a new design of a three-ball automatic balancer is introduced. The governing equations of motion are derived using the Lagrange's equations, and the balanced stable region is obtained. It is shown that this type of automatic ball balancer can prevent from increasing the vibrations of the rotor at the speed range below the first critical speed. Moreover, the new type of balancer increases the balance stable region of the system. Reducing the vibration amplitude in the mentioned range causes the life time of the system to be increased. Moreover, increasing the balanced stable range makes the new design of balancer can balance the systems with a wider range of parameters.

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One of the new methods for reducing the vibrations of rotors with variable imbalance is implementing automatic ball balancer (ABB). Although, the ABB has numerous advantages, it has one major deficiency; increasing the rotor vibration amplitude at transient state that limits the use of this type of balancers. In the previous studies for diminishing the mentioned deficiency, a new type of ball balancer which is called the ball-spring ABB, is introduced and the dynamic behavior of Jeffcott rotor equipped with the ball-spring ABB is investigated. In the Jeffcott rotor model the gyroscopic effect is not considered, however, in practice and in many applications, due to asymmetry which comes from the offset of the rotor from the shaft mid-span, the gyroscopic effect is generated. In such conditions, the results of Jeffcott model are not reliable and dynamic behavior of the ball-spring ABB should be investigated in the presence of gyroscopic effect. In this paper by considering the asymmetry in the rotor-shaft system and taking into account the gyroscopic effect, the equations of motion of a rotor equipped with the ball-spring ABB are derived. The time responses of the system are computed and based on the Lyapanov first method, the stable regions are extracted. The results show that not only the gyroscopic effect does not affect on the performance of the ball-spring ABB, but also the magnitude of the Eulerian angles of the rotor equipped with the ball-spring ABB is less those the rotor equipped with the traditional one.