Ahmed Bouzidane

Equivalent Stiffness and Damping Investigation of a Hydrostatic Journal Bearing

The aim of this research is to study the dynamic characteristics of a hydrostatic journal bearing, with four hydrostatic bearing flat pads fed by diaphragm restrictors and supporting a rotor. We assumed that the fluid flow is incompressible, laminar, isothermal, and steady-state. Linear modeling was performed using a numerical method in order to investigate the effects of the film thickness, the recess pressure, and the geometric configuration on the equivalent stiffness and damping of a hydrostatic journal bearing. In the first step, the variation of equivalent stiffness and damping is studied according to the pressure ratio for different geometric configurations of a hydrostatic bearing at the point of operation. In the second step, the variation of the equivalent stiffness and damping is studied according to the ratio of the film thickness for different geometric configurations of a hydrostatic bearing when one moves away from the point of operation. The results show that the hydrostatic journal bearing has good dynamic characteristics and excellent stability because of its higher stiffness, damping, and zero cross-coupling terms.

Nonlinear Dynamic Analysis of a Rigid Rotor Supported by a Three-Pad Hydrostatic Squeeze Film Dampers

The aim of this article is to study the nonlinear dynamic behavior of rigid rotors, supported by a new hydrostatic squeeze film damper (HSFD). A nonlinear model of an HSFD is presented. The results are compared with those obtained from a linear approach that is only valid for small vibrations around the equilibrium position. Compared to the four-pad HSFD, the advantage of using a three-pad HSFD consists of reducing the cost due to the need for a feeding system and the volumetric flow rate used in hydrostatic lubrication. In this study, the effects of the pad dimensions ratios, capillary diameters, and rotational speed on the flow rate, unbalance responses, and transmitted forces are investigated using a nonlinear method and the results are analyzed and discussed. The results obtained show that this type of HSFD provides hydrostatic designers with a new bearing configuration suitable to control rotor vibrations and bearing transmitted forces for high speeds.

Nonlinear Dynamic Behavior of a Flexible Shaft Supported by Smart Hydrostatic Squeeze Film Dampers

The aim of this research is to study the nonlinear dynamic behavior of a flexible shaftsupported by smart hydrostatic squeeze film dampers, which are filled with a negativeelectrorheological fluid (NERF). A nonlinear model of the hydrostatic squeeze filmdamper has been developed in order to study the effect of the electrorheological fluid onthe dynamic behavior of a flexible shaft. The results obtained are discussed and com-pared with the linear model, which is restricted to only small vibrations around the equi-librium position. A new smart hydrostatic squeeze film damper is proposed to reduce thetransient response of the shaft and transmitted forces by applying an electric field to theNER fluid, which results in modifying its viscosity. The results show that it is possible toeffectively monitor the electric field and the viscosity of the fluid inside the hydrostaticsqueeze film dampers (HSFD) for a better control of flexible shaft vibration and bearingtransmitted forces. [DOI: 10.1115/1.4023805]Keywords: electrorheological fluid, journal hydrostatic bearing, nonlinear dynamicbehavior, squeeze film dampers, rotor dynamic

Non Linear Transient Response of a Flexible Shaft Controlled by Electro-rheological Hydrostatic Squeeze Film Dampers

The aim of this research is to study the non-linear dynamic behaviour of a flexible shaft supported by hydrostatic squeeze film dampers which are filled with a Negative Electro-Rheological fluid (NERF). In order to study the effect of the electro-rheological fluid on the dynamic behaviour of a flexible shaft, a non linear model of a hydrostatic squeeze film damper has been developed and the results are discussed and compared with the linear model which is restricted to only small vibrations around the equilibrium position. A new control system is proposed to reduce the transient response of the shaft, by applying an electric field in order to modify the viscosity of the NER fluid in the hydrostatic journal, and thus control its damping. The results of this control show that it is possible to effectively monitor the electric field and the viscosity of the fluid inside the hydrostatic squeeze film dampers (HSFD) for controlling flexible shaft vibration.

Nonlinear Dynamic Behavior of a Rigid Rotor Supported by Hydrostatic Squeeze Film Dampers

This research project aims to study the nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers (HSFDs). The investigated HSFD consists of four hydrostatic bearing flat pads fed by capillary restrictors. A nonlinear hydrostatic squeeze film damper model is developed, and the results are compared with those obtained using a linear approach. The effect of unbalance eccentricity on the vibration response and the transmitted force of the HSFD are investigated using the linear and nonlinear models. The results show good agreement between the linear and nonlinear methods when the unbalance force is small. However, as the unbalance forces become larger, the results obtained using the linear models cease to be representative of the real behavior of rotor dynamics and a nonlinear approach must be conducted. The effects of supply pressure, viscosity, pressure ratio, and rotational speed on the response and the force transmitted to the HSFD are investigated using a nonlinear approach.

Performance characteristics of a three-pad hydrostatic squeeze film damper compensated with new electrorheological valve restrictors

A numerical analysis is carried out in order to investigate the effect of the electric field on the performance characteristics of a three-pad hydrostatic squeeze film damper compensated with new electrorheological valve restrictors. The bearing design is composed of three identical hydrostatic bearing pads. Each hydrostatic bearing pad is fed with a negative electrorheological fluid through an electrorheological valve. The numerical analysis showed that the viscosity of a smart fluid inside to each electrorheological valve can be controlled by using an electric field in order to control the static and dynamic characteristics. The results presented in this study can be made more useful to control rotor vibrations and force transmissibility especially around the critical speeds.

Performance analysis of four-pad hydrostatic squeeze film dampers loaded between pads under laminar and turbulent flow conditions

Abstract This paper presents a theoretical study of the effects of Poiseuille Reynolds number and eccentricity ratio on the performance of four-pad hydrostatic squeeze film dampers. The finite difference method has been used to solve Reynolds equation based on Constantinescu’s turbulent lubrication theory. The numerical results obtained are analysed and compared between three and four-lobe hybrid journal bearings. The computed results indicate that the performance of a hydrostatic squeeze film damper loaded between pads is significantly influenced by the flow regimes. The results presented in this work can be useful to the bearing designers.

Numerical analysis of a rigid rotor mounted on four-pad hydrostatic squeeze film damper lubricated with micropolar lubricant

The present work deals with a numerical resolution of the modified Reynolds equation using micropolar lubrication theory to study the effects of coupling number and the characteristic length of the micropolar lubricant on the performance characteristics of hydrostatic squeeze film damper, which consists of four hydrostatic pads fed through four capillary restrictors. According to the results, the bearing operating with micropolar lubricant shows an increase in the value of pressure inside the recess. These results suggest that the influence of micropolar effect on the bearing performance is predominantly affected by the pressure ratio. Therefore, the bearing operator must judiciously choose an appropriate value of the pressure ratio in order to get an overall enhanced bearing performance.

Dynamic analysis of a rigid rotor supported by three-pad hydrostatic squeeze film damper lubricated with ferrofluid

Abstract This work describes an analytical study on the dynamic behaviour of a three-pad hydrostatic journal bearing lubricated with ferrofluids. Each pad is fed with an external pressure through a capillary restrictor-type hydraulic resistance. Ferrofluid or magnetic fluid is a colloidal dispersion of magnetic nano-particles in a carrier liquid. In this study, a non-linear method was performed using Jenkins model in order to investigate the effect of ferrofluids lubrication on the vibrations amplitude and the transmitted forces of hydrostatic squeeze film dampers. The results presented in this paper showed that the ferrofluid lubrication is useful in controlling the bearing vibrations and transmitted forces. The results illustrated in this work are expected to be quite useful to the bearing designers.

Pressure distribution in orifice-compensated turbulent hydrostatic bearing with fluid inertia effects using numerical simulations via Navier-Stokes

Abstract Significant progress in turbo-machinery’s speed is made recently. To cope with that; many fluids having large differences in rheological properties are introduced as lubricant in hydrostatic bearing systems. The present study aims to improve the understanding of the pressure patterns within hydrostatic bearing flat pads according to different parameters. The main ones are the squeeze film velocity, the feeding pressure and the fluid viscosity. To consider efficiently, the influence of the turbulent and inertia effects numerical simulation are based on transient Navier-Stokes equations. The results of the present study confirm many patterns already mentioned by other authors, and also showed different flow behaviour in terms of vortex evolution according to the studied parameters combinations.