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Torsional vibration of the power transmission system is one of the main factors which affects ride comfort and fatigue of the driveline components. These vibrations are caused by periodic changes in the gas pressure and inertial forces. To reduce these vibrations, dual mass flywheels (DMF) are used in some vehicles. DMFs are usually modelled as two disks connected with linear springs. However large rotation angle in DMFs can invalidate linear assumption. In this research, torsional vibration of a three-cylinder engine with nonlinear DMF is investigated and an analytical solution is obtained for the governing nonlinear equations of torsional vibrations under real engine torsional excitation for the first time. It should be noted that in the previous works, the torsional vibration equations of the DMF had been solved numerically. Analytical solution helps to study the effect of design parameters of DMF more easily. It is shown that the analytical and numerical solutions are well matched in steady-state conditions. Finally, a parametric study is performed and the effects of design parameters on the oscillation amplitude of the engine speed and flywheel output speed are presented. [ABSTRACT FROM AUTHOR]

One of the most important issues for the helicopter pilots is the health risk due to the vibration transmitted to the pilot through the seat. In this article, a seat suspension based on negative stiffness structure is presented to decrease the vibration transmitted to the pilot in both vertical and lateral directions without losing the loading capacity of the system. Here, an integrated model of the suspension–cushion–occupant is derived. To generalize the results of system analysis and its usability in other applications, the impact of parameters on the system performance is studied in dimensionless form. Despite coupling between the lateral and vertical directions, the design parameters of the seat suspension are determined in such a way that the system responds simultaneously as a negative stiffness structure in both directions. The system efficiency in vibration damping is assessed by seat effective amplitude transmissibility and transmissibility criteria. In addition, the whole body vibration and impact of the vibration on the pilot body are evaluated using ISO-2631. To verify the system efficiency in more realistic situation, the simulations are performed using the measured vibration data of a Bell-412 helicopter. The results indicate that the vibration amplitude is decreased by about 45% and 48% in the lateral and vertical directions, respectively. The frequency spectrum comparison of the seat and cabin floor reveals 80% reduction of amplitude in fundamental frequency in the vertical direction, whereas it is about 93% in the lateral direction. Furthermore, the level of pilot's comfort and perception is improved that demonstrates better riding quality and reduced vibration environment. [ABSTRACT FROM AUTHOR]

Rotating machinery support design with the aim of reducing the force transmitted to the foundation has significant importance regarding the various applications of this machinery. This article presents H∞ and H2 methods for calculating the optimum support flexibility and damping of flexible rotors to minimize force transmissibility in the vicinity of the rotor's first critical speed. First, the governing equations for the Jeffcott rotor model mounted on flexible supports are derived and the optimal parameters for the supports are analytically achieved by H∞ and H2 optimization procedures. The proposed approach of the tuned damper support system is similar to that designed for dynamic vibration absorber optimization. The main objective of the H∞ optimization is to minimize the force transmitted based on fixed-point theory and the mean square transmissibility of flexible rotor is minimized in the H2 optimization design as analytical formulae. It is proven by numerical solution that the system optimization design can effectively minimize the force transmitted to the foundation. Comparison of two optimization procedures showed that the force transmitted to the foundation with H2 optimization was smaller than with H∞. [ABSTRACT FROM AUTHOR]

Rotating machinery support design with the aim of reducing the synchronous unbalance response has significant importance regarding the various applications of these machineries. In this paper, we present H∞ and H2 methods for calculating the optimum support flexibility and damping of flexible rotors to minimize vibrational amplitudes in the vicinity of the rotor first critical speed. First, the governing equations for the Jeffcott rotor model mounted on flexible supports are derived and the optimal parameters for the supports have been analytically achieved using H∞ and H2 optimization procedures. The approach method of the tuned damper support system is similar to that designed for dynamic vibration absorber optimization. The H∞ optimum parameters such as tuning frequency and damping ratios are expressed based on fixed-point theory to minimize the rotor amplitudes, as well as, the H2 optimum parameters to minimize the mean square motion of flexible rotor as analytical formulas. It is proven by numerical simulations that the system optimization design can effectively improve the synchronous unbalance response. Comparison of two optimization procedure showed the vibrational amplitudes with H2 optimization was smaller than H∞ one. [ABSTRACT FROM AUTHOR]