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1

Analysis of dynamic characteristics of a sealed ends squeeze film damper considering the fluid inertia force

Zhou Hai Lun, Cang Yang Guang, Zhang Yu Qi, Guo Chao

Journal of Theoretical and Applied Mechanics

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2023

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Vol. 61 nr 3

441--452

EN

In order to effectively calculate dynamic characteristics of a sealed ends squeeze film damper (SFD) under the influence of the inertial force, a computational fluid dynamics model of the sealed ends SFD is established. The fluid inertia coefficient of SFD is investigated by using an energy approximation method. Both the theoretical calculation and numerical simulation are conducted to analyze the effects of eccentricity ratio and whirling frequency on stiffness and damping. In this research, the oil film inertia force of the sealed ends SFD is solved by using long bearing approximation (LBA) theory, which provides guidance for the design and application of the sealed ends SFD.

2

Transient simulation of a squeeze film damped turbocharger rotor under consideration of fluid inertia and cavitation

Drapatow Thomas, Alber Oliver, Woschke Elmar

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2021

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Vol. 69, nr 6

art. no. e139201

EN

Squeeze film dampers (SFDs) are commonly used in turbomachinery in order to introduce external damping, thereby reducing rotor vibrations and acoustic emissions. Since SFDs are of similar geometry as hydrodynamic bearings, the REYNOLDS equation of lubrication can be utilised to predict their dynamic behaviour. However, under certain operating conditions, SFDs can experience significant fluid inertia effects, which are neglected in the usual REYNOLDS analysis. An algorithm for the prediction of these effects on the pressure build up inside a finite-length SFD is therefore presented. For this purpose, the REYNOLDS equation is extended with a first-order perturbation in the fluid velocities to account for the local and convective inertia terms of the NAVIER-STOKES equations. Cavitation is taken into account by means of a mass conserving two-phase model. The resulting equation is then discretized using the finite volume method and solved with an LU factorization. The developed algorithm is capable of calculating the pressure field, and thereby the damping force, inside an SFD for arbitrary operating points in a time-efficient manner. It is therefore suited for integration into transient simulations of turbo machinery without the need for bearing force coefficient maps, which are usually restricted to circular centralized orbits. The capabilities of the method are demonstrated on a transient run-up simulation of a turbocharger rotor with two semi-floating bearings. It can be shown that the consideration of fluid inertia effects introduces a significant shift of the pressure field inside the SFDs, and therefore the resulting damper force vector, at high oil temperatures and high rotational speeds. The effect of fluid inertia on the kinematic behaviour of the whole system on the other hand is rather limited for the examined rotor.

3

Simplified model of the dynamics of magneto-rheological dampers

Alexandridis A. A., Goldasz J. P.

Mechanics / AGH University of Science and Technology

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2005

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Vol. 24, no. 2

47-53

EN

It has been long recognized that the inertia and compressibility of the fluid have a significant effect on the dynamic behavior of Magneto-Rheological (MR) dampers. Previous studies have revealed the nature of the effect through the analysis of a comprehensive, albeit fairly complex, state-space model of the MR monotube damper hydraulies. The present paper outlines a simpler model of the damper and presents simple analytical expressions for the transfer function between the input velocity (or stroke) and the output force. Pistons with single and dual flow passages are analyzed. In addition, simple expressions for the damper natural frequency and damping ratio are given. Finally the transfer functions are presented analytically as well as in the form of Bode plots of the amplitude and the phase angle of the transfer functions vs. the normalized frequency.

PL

Od dawna wiadomo, że bezwładność i ściśliwość cieczy ma znaczący wpływ na właściwości dynamiczne tłumików magnetoreologicznych (MR). W poprzednich badaniach prezentowano model w przestrzeni stanu, powstały w wyniku szczegółowej analizy, aczkolwiek stosunkowo skomplikowanej, opisujący właściwości hydraulicznego tłumika MR z pojedynczym cylindrem. Niniejszy artykuł prezentuje uproszczony model tłumika wraz z prostymi zależnościami określającymi funkcję przejścia pomiędzy wejściem w postaci prędkości (przemieszczenia) a wyjściem w postaci siły. Analizowano układy z tłokiem z pojedynczą oraz podwójną szczeliną przepływową. Ponadto zamieszczono proste wyrażenia na częstotliwość drgań własnych tłumika oraz współczynnik tłumienia. Na zakończenie zaprezentowano funkcje przejścia w postaci analitycznej oraz wykresów Bodego.