Experimental Study on the Velocity Dependent Drag Coefficient and Friction in an Automatic Ball Balancer

The paper presents the evaluation of experiments on the drag and friction forces in an automatic ball balancer, which raceway is embodied by the outer ring of a ball-bearing. Due to the throughout contact between the balls andtheracewaywhileoperatingtheballbalancer,efforthasbeenmadetocharacterisetheflowconditionsofthe surrounding fluid by determining the drag coefficient ?? as a function of the Reynolds number Re. By the use of fluids with different viscosities and the postulation of continuity in the run of ??(Re), coefficients for different friction models, e.g. Coulomb friction and rolling friction deduced from Hertzian surface pressure equation can bederived

Dynamic Behaviour of EHD-contacts using a regularised, mass conserving Cavitation Algorithm

The paper deals with the holistic simulation of systems supported in journal bearings, which is demonstrated using the example of a conrod’s big end bearing. For that purpose, primarily the interactions of multibody-, structureand hydrodynamics have to be described. Based on the time integration of the global equations of motions, the non-linear bearing forces in the fluid film and the elastic deformation of the bearings surfaces have to be modelled adequately concerning their mutual influence. The implementation of the elastic structure is carried out by means of a hierarchised, IRS–based1modal reduction in order to represent its eigenbehaviour as realistic as possible and to fulfil the requirement of low computational costs by reducing the number of degree of freedoms. Additionally, the journal bearing is considered by an online solution of the Reynolds equation, whereat the cavitation is handled by a transient acting, mass-conserving algorithm. This is based on the classical Elrod algorithm, but was extended by a regularisation, which enables a faster and more stable solution. Due to the general approach, both mechanical and tribological output quantities are accessible. This provides the possibility to draw a comparison with simpler approaches and to emphasize the benefit of the described procedure

Run-up Simulation of Automatic Balanced Rotors Considering Velocity-dependent Drag Coefficients

The paper at hand presents the modelling approach of a laboratory centrifuge with a vertically mounted rotor and an automatic balancing device, which counterbalances the unbalance in one plane. This device consists of an annulus containing the outer ring of a ball-bearing as well as steel balls and is filled with a newtonian fluid. The fluid, accelerated by the annulus’ walls, flows around the balls and positions them in the annulus. In order to develop a design method for the balancing device the velocity dependency of the drag coefficient is considered and the influence of fluid density and viscosity on the balancing efficiency is examined. An experimental comparison shows that the flow in the concave bearing race can be represented by the flow around a ball in contact with a flat surface. It can be shown that, depending on the run-up acceleration, a selective choice of the fluid properties has a positive influence on the vibrations near the critical speed and the response time of the counterbalancing effect at supercritical speeds

About the Vibration Modes of Square Plate-like Structures

In the experimental vibration analysis of an oil pan, two eigenmodes are observed that did not appear to be those of a standard rectangular plate vibration. As a result, a numerical, analytical and experimental investigation is launched to discover where these modes are originating from. In this paper, the finite element method is applied to determine the vibration behavior numerically, and experimental results are obtained with the help of a laser doppler vibrometer in order to determine the origin of these two eigenmodes

Simulation von schwimmbuchsenlagerungen in Abgasturboladern

Der Beitrag behandelt die Berechnung eines vollständigen Hochlaufs der Turboladerwelle auf Betriebsdrehzahl zur Untersuchung der Stabilität der Lagerung. Aus der Schwimmbuchsenlagerung resultieren zum einen spezielle Randbedingungen, die zur Kopplung von innerem und äußerem Schmierfilm führen. Zum anderen ist dadurch der Rotor in der Lage sich derart schiefzustellen, dass die Berechnung der hydrodynamischen Schmierfilmdrücke unter Annahme eines Parallelspalts nicht mehr gerechtfertigt ist. Die Modellierung erfolgt daher innerhalb eines Mehrkörpersystems (MKS), wobei die Reynolds Differentialgleichung in jedem Zeitschritt unter Verwendung der Finiten-Elemente-Methode gelöst wird. Abschließend erfolgt ein Vergleich zwischen gemessenen Daten und numerischer Simulation. Dabei wird der Einfluss der Berücksichtigung der Wellenschiefstellung sowie der Kommunikationsbohrungen bei der Lösung der Reynolds DGL auf die Ausbildung des instabilen Bereichs diskutiert.This paper deals with the calculation of a full-dynamical run-up of a turbocharger shaft up to operating speed to investigate the stability of the bearing. Due to the full floating ring bearings special boundary conditions result, which lead to a coupling of outer and inner lubrication film. Furthermore the rotor is able to take a skew position in such a way, that for the solution of Reynolds equation the simplistic assumption of a parallel gap isn’t longer valid. Therefore the modeling is done in a multi-body-system (MBS), whereat the finite element method is used for the calculation of hydrodynamic pressures in every timestep. Concluding a comparison is done between measured data and numerical simulation. Thereby the development of the instable region is discussed by the influence of shaft inclination as well as the communication drill-holes

SIMULATION VON SCHWIMMBUCHSENLAGERUNGEN IN ABGASTURBOLADERN

Der Beitrag behandelt die Berechnung eines vollständigen Hochlaufs der Turboladerwelle auf Betriebsdrehzahl zur Untersuchung der Stabilität der Lagerung. Aus der Schwimmbuchsenlagerung resultieren zum einen spezielle Randbedingungen, die zur Kopplung von innerem und äußerem Schmierfilm führen. Zum anderen ist dadurch der Rotor in der Lage sich derart schiefzustellen, dass die Berechnung der hydrodynamischen Schmierfilmdrücke unter Annahme eines Parallelspalts nicht mehr gerechtfertigt ist. Die Modellierung erfolgt daher innerhalb eines Mehrkörpersystems(MKS), wobei die Reynolds Differentialgleichung in jedem Zeitschritt unter Verwendung der Finiten-Elemente-Methode gelöst wird. Abschließend erfolgt ein Vergleich zwischen gemessenen Daten und numerischer Simulation. Dabei wird der Einfluss der Berücksichtigung der Wellenschiefstellung sowie der Kommunikationsbohrungen bei der Lösung der Reynolds DGL auf die Ausbildung des instabilen Bereichs diskutiert.This paper deals with the calculation of a full-dynamical run-up of a turbocharger shaft up to operating speed to investigate the stability of the bearing. Due to the full floating ring bearings special boundary conditions result, which lead to a coupling of outer and inner lubrication film. Furthermore the rotor is able to take a skew position in such a way, that for the solution of Reynolds equation the simplistic assumption of a parallel gap isn’t longer valid. Therefore the modeling is done in a multi-body-system(MBS), whereat the finite element method is used for the calculation of hydrodynamic pressures in every timestep. Concluding a comparison is done between measured data and numerical simulation. Thereby the development of the instable region is discussed by the influence of shaft inclination as well as thecommunication drill-holes