Contents of the Journal of Mechanical Engineering 50, 5 (1999)

BUDLOVSKY, Z.: An inflatable elastic contactless sealing ring for 
hydrodynamic runners                                                     289

MAGDOLEN, L., STAREK, L.: Control of vibration of rigid rotor 
supported by magnetic bearings (in Slovak)                               301

BOUCARD,  P.-A., LADEVEZE, P.: A multiple-solution method 
for non-linear structural mechanics                                      317

DOBIAS, J., HOSCHL, C.: Paradoxical loosening of press-fitted
pivots                                                                   329

STEGIC, M., KRANJCEVIC, N., VRANKOVIC, N.: Computational
stability analysis of Laval rotor in journal bearings                    346

In this note a new type of inflatable sealing ring for hydrodynamic impellers is presented. Due to its elasticity it is able to decrease substantially the volume and friction losses of hydraulic turbines and pumps. This paper informs on its design and presents the results of model measurements, its comparison with conventional wearing rings, a calculation method, and some exploitation possibilities.

This article presents a model of rigid rotor supported by active magnetic bearings (AMB). Mathematical formulation of magnetic forces generated by AMB has been developed. Equations of motion of rigid rotor supported by controllable AMB with and without control law are presented. Eigenstructure assignment method is used to change the eigenfrequency of mechatronical system. Numerical simulations are compared with experimental measured data. The simulations presented in this paper correspond with measurement.

The numerical solution process for complex, time-dependent non-linear problems (material stamping, cyclic viscoplasticity, crashes, etc.) requires, even with the most powerful computers, a computation time which turns out to be prohibitive. Moreover, with respect to those structural analyses involving multiple solution sequences (parametric studies, probabilistic analyses, flawed structures, etc.), each series of data necessitates performing a full calculation, even if the problems to be solved do resemble one another. The goal of the work presented herein is to develop a strategy that is well-suited to multiple-solution problems. Such a strategy is to be based on the LATIN method and, more specifically, on its capacity to reuse the solution to a given problem in order to solve similar problems. Then, the goal is both to assess the major obstacles encountered during this computational procedure and to define and apply a strategy that enables minimizing total computing costs with respect to multiple-solution problems.

If a press-fitted clamped-free pivot is exposed to alternating loading at its free end while the forces act normal to its central axis, a gradual global displacement of the pivot in the axial direction may occur under some circumstances. Eventually, the pivot can get completely loosened.
This phenomenon was studied in detail on an analogous plane stress elastic model consisting of a cantilever compressed by two rectangular blocks. The finite element computing system equipped with tools for solution of contact problems was made used of.

In this paper the Crandall's bearing force-velocity model is applied to stability analysis of a radial loaded Laval rotor in cylindrical fluid film bearings. A domain of rotor speed and transverse bearing loads, which provides a stable support and introduces heavy damping of rotor vibration, is obtained by standard computational routines. As a result of this analysis, the stability boundary is determined for different values of rotor damping and bearing parameters. The stability regions based on the Crandall's force-velocity model agree with practical observations of rotor dynamic behavior and with the experimental data.