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Magneto-rheological (MR) fluids react to magnetic fields undergoing changes in their mechanical characteristics, viscosity in particular. After an analytical and numerical study, an MR squeeze-film damper has been designed and set up on a reduced scale rotor test-rig. Numerical simulations were carried out in order to evaluate the dynamic behaviour of the damped rotor as a function of the current supplied to the adjustable device. A linear model that depicts the main characteristics of the system has been developed as a useful tool in damper and control design. By testing different fluids, an optimal fluid has been singled out. Tests conducted on the selected fluid show that it is possible to have the optimum conditions for each steady rotational speed.

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Aircraft transmissions have the peculiar characteristics of light structures and high operating speeds, therefore relatively low flexural natural frequencies and high excitation frequencies due to rotation and meshing. Resonance vibrations can create serious problems of malfunctions and even catastrophic failures. A reliable numerical model is surely a convenient means to perform preliminary simulations to identify the most critical resonance conditions and evaluate the effect of structural modifications on the dynamic behaviour of the component in the design development phase. Most numerical investigations found in the literature are carried out on simplified models of the rotating bodies likened to discs to reduce the computational effort. In this work a novel approach based on the application of Duhamel’s integral for the determination of the dynamic behaviour of a rotating gear subject to meshing forces has been developed to obtain more reliable results with a realistic model at an affordable computational cost. The gear response to dynamic excitation is obtained by the determination of its response to impulse using a single 3D finite element transient analysis taking afterwards into account the effect of the gear rotation. Subsequently, the Duhamel’s integral is applied using the tooth load time history in order to simulate as realistically as possible the gear load conditions. This paper presents the case of a real bi-helicoidal gear. A test bench was simulated measuring the displacement observed by some non-rotating virtual displacement sensors, located near the gear rim and disc. The signal was processed identifying the most critical rotating speeds on the basis of its RMS value. The numerical Campbell speed/frequency diagrams are in good agreement with experimental results.

Aircraft transmissions have the peculiar characteristics of light structures and high operating speeds, therefore relatively low flexural natural frequencies and high excitation frequencies due to rotation and meshing. Thus some dynamic phenomena, such as traveling wave vibration (TWV), can be more easily encountered. However few papers can be found in the literature on TWV of gears while on the contrary it might be a problem especially for gears having thin rim and disk. This paper deals with the simulation of the disk TWV of bevel gears. 3D FEM is used to obtain the natural modes and frequencies of the gear. The response of a simplified non-rotating model of two meshing gears was entirely simulated in an Ansys environment. The numerical tests were performed considering a variable torque applied to one of the gears, the other being constrained, accounting for the meshing excitation. To simulate the rotating contact condition with respect to the gear reference systems, the dof of the nodes in contact of the two gears were coupled. Preliminary tests were performed considering one of the two gears rigid. The simulation of the TWV of gears makes it possible to identify the most critical conditions for stress and fatigue in the gear disks and therefore estimate the gear structural reliability.