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This work is aimed at a theoretical study of the dynamic behavior of a rotor-tilting pad journal bearing (TPJB) system under different lubrication regimes, namely, thermohydrodynamic (THD), elastohydrodynamic (EHD), and hybrid lubrication regime. The rotor modeled corresponds to an industrial compressor. Special emphasis is put on analyzing the stability map of the rotor when the different lubrication regimes are included into the TPJB modeling. Results show that, for the studied rotor, the inclusion of a THD model is more relevant when compared to an EHD model, as it implies a reduction on the instability onset speed for the rotor. Also, results show the feasibility of extending the stable operating range of the rotor by implementing a hybrid lubrication regime.

In order to reduce friction losses and vibrations in main engine bearings, fluid film lubrication is combined to controllable radial oil injection. This work evaluates different geometric hybrid bearing configurations and control pressure rules for applying radial oil injection in main engine bearings of internal combustion engines. The conventional hydrodynamic lubrication (CHL) is combined with hydrostatic lubrication which is actively modified by radially injecting oil at controllable pressures, through orifices circumferentially located around the bearing surface. The behaviour of a main bearing of a medium size combustion engine, operating with radial oil injection and with four different control strategies is analyzed, giving some insights into the minimum fluid film thickness (OFT) and reduction of viscous friction losses. The behaviour of such parameters is compared to the case when the bearing operates with conventional hydrodynamic lubrication.Copyright © 2010 by ASME

The static and dynamic properties of tilting-pad journal bearings with controllable radial oil injection are investigated. The tilting pads are modelled as flexible structures and their dynamics are described using a three dimensional finite element framework and linear elasticity. The oil film pressure and flow are considered to follow the modified Reynolds equation, which includes the contribution from controllable radial oil injection. The Reynolds equation is solved using a two dimensional finite element mesh. The rotor is considered to be rigid. The servo-valve flow is governed by a second order ordinary differential equation, where the right hand side is controlled by an electronic input signal. The constitutive flow pressure relationship of the injection nozzles is that of a fully developed laminar velocity profile and the servo-valve is introduced into the system of equations by a volume conservation consideration. The Reynolds equation is linearized with respect to displacements and velocities of the nodal degrees of freedom. When all nodal points satisfy the static equilibrium condition, the system of equations is dynamically perturbed and subsequently condensed to a 2 by 2 system, keeping only the lateral motion of the rotor. As expected, rotor stability is heavily influenced by the control parameters.Copyright © 2008 by ASME

This work describes in details the steps involved within the mathematical modelling of multibody systems (rigid and flexible) interconnected via controllable thin fluid films. The dynamics of the mechanical components are described with help of multibody dynamics and finite element method. In this paper, the methodology is applied to reciprocating machines such as hermetic reciprocating compressors and internal combustion engines. In previous studies [1], it has been shown that for a light duty vehicle, the friction losses may reach until 48% of the total energy consumption of an engine and from that, almost 30% are coming from bearings and crankshaft. Therefore, considering that the dynamics of the fluid films in the journal bearings can be actively controlled by means of different types of actuators, allowing significant reduction of wear and vibrations, one of the aims of this paper is to study the feasibility of applying active lubrication to the main journal bearings of reciprocating machines. In this framework the paper gives a theoretical contribution to the combined fields of fluid-structure interaction and active vibration control. The hydrodynamic pressure distribution for an active lubricated finite journal bearing dynamically loaded can be calculated by numerically solving the modified Reynold’s equation [2], by means of finite-difference method and integrated over the pressure area in order to obtain the dynamic reaction forces among components. These forces are strongly nonlinear and dependent on the relative kinematics of the system. From the point of view of active lubrication and specifically considered the case of a dynamically loaded journal bearing, the injection pressure should be controlled in the time domain. However, taking into account that the pressures and reaction forces in a reciprocating machine have a cyclic behaviour, the fluid film thickness of the main bearings may be modified by controlling the oil pressure injection, depending on the crank angle and the load bearing condition. It can be mentioned that the pressure and flow may be controlled by mechanical cam systems, piezoelectric nozzles [3] [4] or servovalves [5] [6], therefore, an adequate control strategy has to be defined. The fluid film forces are coupled to the set of nonlinear equations that describes the dynamics of the mechanical system. Such a set of equations is numerically solved giving some insights into the following parameters: a) maximum fluid film pressure, b) minimum fluid film thickness, c) maximum vibration levels and d) viscous frictional forces. The behaviour of such parameters is investigated when the system operate with conventional hydro-dynamic lubrication, passive hybrid lubrication and controlled hybrid lubrication.Copyright © 2008 by ASME

This is Part I of a two-part series of papers describing the effects of high pressure injection pockets on the operating conditions of tilting-pad thrust bearings. A numerical model based on the Reynolds equation is developed extending the three dimensional thermo-elasto-hydrodynamic (TEHD) analysis of tilting-pad thrust bearings to include the effects of high pressure injection and recesses in the bearing pad. The model is applied to the analysis of an existing bearing of large dimensions and the influence of the pocket is analyzed. It is shown that a shallow pocket positively influences the performance of the bearing as it has characteristics similar to those of a parallel step bearing.Copyright © 2006 by ASME

Journal bearings under active lubrication regime are controlled by servo valves and well-tuned feedback control laws. The servo valves dynamically modify the journal pressure distribution generating active oil film forces. Such forces are dependent on the following parameters: Sommerfeld number, bearing pre-load factor, orifice diameter, excitation frequency, feedback control gain and dynamic parameters of the servo valves, i.e. their natural frequencies, damping factors and pressure-flow coefficients. The theoretical and experimental characterization of such active forces is the main focus and the main contribution of this work. The theoretical analyzes are based on the Modified Reynolds’ equation for active lubrication. The experimental analyzes are carried out by using a special test rig, designed to investigate the behavior of tilting-pad bearings (TPJB) under active lubrication. Relative good agreement between theoretical and experimental behavior of the active oil film forces as a function of the excitation frequency and control gain is achieved. Limitations of the characterization procedure is critically discussed in order to explain some discrepancies between theoretical and experimental results.Copyright © 2005 by ASME

In the present paper, the dynamic response of a rotor supported by an active lubricated tilting-pad bearing is investigated in the frequency domain. The theoretical part of the investigation is based on a mathematical model obtained by means of rigid body dynamics. The oil film forces are inserted into the model by using two different approaches: (a) linearized active oil film forces and the assumption that the hydrodynamic forces and the active hydraulic forces can be decoupled, and (b) equivalent dynamic coefficients of the active oil film and the solution of the modified Reynolds equation for the active lubrication. The second approach, based on the equivalent dynamic coefficients, leads to more accurate results because it includes the frequency dependence of the active hydraulic forces. Theoretical and experimental results reveal the feasibility of reducing resonance peaks by using the active lubricated tilting-pad bearing. By applying a simple proportional controller, it is possible to reach 30% reduction of the resonance peak associated with the first rigid body mode shape of the system. One of the most important consequences of such a vibration reduction in rotating machines is the feasibility of increasing their operational range by attenuating resonance peaks and reducing vibration problems.

This is the first paper in a two-part study on active rotor-blade vibration control using electro-magnetic actuation. Emphasis is focused on theoretical aspects of implementing active control into coupled rotor-blade systems, more precisely, into systems where rotor lateral motion is coupled to blades flexible motion. The theoretical investigation includes controllability and observability analyses of such a system in order to determine optimal actuator and sensor placement. An analysis methodology based on modal analysis in time-variant systems, due to the periodic time-variant nature of this kind of system, is presented. The method takes into account the strong vibration coupling which has a significant effect on the controllability and observability of bladed rotor systems. The analyses show that, for tuned bladed rotors, actuators will have to be located within the blades in order to make all vibration modes controllable. However, if the system is deliberately mistuned, rotor and blade vibrations can be controlled using shaft-based actuation and sensing only. Moreover, a controller design procedure for obtaining active periodic time-variant modal controllers, capable to cope with the time-periodicity of the system, is presented. Controllers are designed for a tuned as well as a deliberately mistuned system. The tuned system is controlled using both blade and shaft actuators while the mistuned system is controlled using only shaft actuation. Numerical simulations are provided to show the efficiency of the designed controllers.