Slim Bouaziz

HYDRODYNAMIC AND ELASTOHYDRODYNAMIC STUDIES OF A CYLINDRICAL JOURNAL BEARING

In this article, the effect of the bearing elastic deformation on the performance characteristics of a cylindrical journal bearing is analyzed. The variety of simulation models covers hydrodynamic (HD) and elastohydrodynamic (EHD) lubrication theories. The Reynolds equations governing the flow in the clearance space of the journal bearing are obtained by considering the effect of mass transfer across the fluid film. The finite element method with an iteration scheme was employed to solve both the Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell. The converged solutions for the lubricant flow and elastic deformation vector are obtained. Dynamic characteristics of the journal bearing are computed for HD and EHD theories. Numerical simulation results show that the flexibility of bearing liner has a significant influence on the performance of a cylindrical journal bearing. Indeed, the elastic deformations of the bearing liner extend the pressure area in the bearing and increase the minimum film thickness. Although, dynamic coefficient, load capacity and attitude angle decrease.

Vibrations monitoring of high speed spindle with active magnetic bearings in presence of defects

The use of Active Magnetic Bearings (AMBs) in the High Speed Machining (HSM) field is increasing. In fact, they have important advantages such us: high speed which can reach 150000 rpm, high stiffness and absence of lubrication. Indeed, these bearings operate through magnetic interaction generated between the stator and the rotor. The spindle, principal component in the HSM, supported by AMBs, is considered as a source of vibration in machine tool spindles when it is affected by some defects during their functioning. These defects can affect either the rotor of the spindle like the unbalance defect, or the AMBs such us misalignment of bearings, failure of actuators, sensors, amplifier and also the eccentricity defect. This paper studies the influence of spindle or AMBs defects on the dynamic behavior of a spindle supported by two AMBs. The system modeling is based on the finite element method. Four degrees of freedom is used and the coupling between elastic and rigid displacements is taken into account.

Acoustic analysis of hydrodynamic and elasto-hydrodynamic oil lubricated journal bearings

The purpose of the present paper is to investigate the effect of elastic deformation of bearing liner on the acoustic behavior of oil lubricated journal bearings. Analysis is performed for hydrodynamic(HD) and elasto-hydrodynamic (EHD) lubrications. Dynamic behavior and acoustical properties are investigated through an analysis of pressure fluctuation calculated from the Reynolds equation governing the flow in the clearance space of the journal bearing. This is solved numerically using the finite difference method with the successive over relaxation technique. In elasto-hydrodynamic lubrication, the finite element method with in iteration scheme is adopted to solve both Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell. The results show that the sound pressure level of the bearing is markedly influenced by the flexibility of the bearing liner, the viscosity of lubricant and the load applied to journal. HD analysis shows that the journal centre’s orbit, from a disturbed position, converges to the static equilibrium position faster than EHD lubrication. The results of the present paper could aid in the design of low-noise rotor-bearing systems supported by oil lubricated journal bearings.

Numerical Analysis of a Segmented Wind Turbine Blade Using the Substructure Method

The wind turbine blade segmentation development remains a tough challenge for constructors to reduce the blade manufacturing and transport cost. In this paper, numerical analysis is developed in order to study the dynamic characteristics of a segmented wind turbine blade assembled with a spar. The spar and the blade segments are assimilated to a shell structure with different homogeneous and isotropic materials. Accordingly, the three nodes triangular shell element DKT18 is adopted to model the blade. To reduce the problem size the Craig–Bampton substructure method is applied. This study covers the effects the of twist angle on the blade natural frequencies. To validate the accuracy and reliability of the proposed substructuring approach, numerical results obtained from the present study were compared with those determined by modal analysis using ABAQUS software. Results showed that the blade natural frequencies are not monotonically varying with respect to the twist angle which must be investigated to be well above the wind turbine system frequencies.

Non-linear Stiffness and Damping Coefficients Effect on a High Speed AMB Spindle in Peripheral Milling

During the milling operation, some factors such as the cutting parameters and the spindle type and speed can influence the cutting force attitude consequently the state of the finished part. In this work, a High Speed Milling (HSM) spindle supported by a pair of Active Magnetic Bearings (AMB) is modeled. The shaft is discretized with Timoshenko beam finites elements. The six degrees of freedom of both rigid and elastic motions are considered. Electromagnetic forces are modeled by linear springs and dampers. A peripheral milling model is suggested to predict the dynamic cutting force and the tool tip response. Dynamic coefficients of bearings with four, six and eight electromagnets are considered and plotted to study the spindle dynamic behavior.

Dynamic behaviour of active magnetic bearings spindle in high-speed domain

High speed machining (HSM) is a new technology used to product parts in different sectors. This technology permits time and processing cost reduction. One of the principal components of the HSM is the spindle. It is generally supported by active magnetic bearings (AMBs), in order to guarantee the greatest speed without affecting the dynamic characteristics of the machine. In this paper, a spindle supported by two AMBs is modelled using the finite element method. It is discretised with Timoshenko beam finite element with different circular sections. Both flexible and rigid movements are taken into account. The non-linear electromagnetic loads exerted by bearings are computed in terms of the nominal air gap between bearings and spindle, the control current and the degrees of freedom of each node. A parametric study is performed to determine the influence of some parameters on the magnetic forces and subsequently the dynamic behaviour of the spindle.