86 research outputs found
Quantum-Information Theoretic Properties of Nuclei and Trapped Bose Gases
Fermionic (atomic nuclei) and bosonic (correlated atoms in a trap) systems
are studied from an information-theoretic point of view. Shannon and Onicescu
information measures are calculated for the above systems comparing correlated
and uncorrelated cases as functions of the strength of short range
correlations. One-body and two-body density and momentum distributions are
employed. Thus the effect of short-range correlations on the information
content is evaluated. The magnitude of distinguishability of the correlated and
uncorrelated densities is also discussed employing suitable measures of
distance of states i.e. the well known Kullback-Leibler relative entropy and
the recently proposed Jensen-Shannon divergence entropy. It is seen that the
same information-theoretic properties hold for quantum many-body systems
obeying different statistics (fermions and bosons).Comment: 24 pages, 9 figures, 1 tabl
Efficient Thermohydrodynamic Radial and Thrust Bearing Modeling for Transient Rotor Simulations
Hydrodynamic bearings are usually employed to support rotating machines, both in
the axial as well as in the radial direction. Both bearing types influence the vibration
behavior of rotors. Moreover, the oil-temperature influences the hydrodynamic bearing
forces. In this work, efficient thermohydrodynamic bearing models for thrust and
radial bearings are developed. Run-up simulations are performed for the identification
of the influence of the bearings on the nonlinear rotor vibrations.
The Reynolds equation, which describes the hydrodynamic pressure distribution in the
bearings, is solved using a highly efficient approach. The Global Galerkin approach,
using appropriate trial and test functions, is used for the approximation of the solution
of the Reynolds equation, leading to heavily reduced simulation times when compared
with Finite Difference or Finite Element approaches. For radial bearings, a novel
semi-analytical method is developed using also the Global Galerkin approach. The
oil-temperature in the thrust bearings is captured through the energy equation, which
is decoupled from the Reynolds equation under appropriate assumptions. For the
oil-temperature in radial bearings with full- as well as semi-floating rings a global
thermal energy balance is used between the two oil-films and the bearing ring. The
transient temperature terms in this energy balance are taken into consideration and
their significance for the numerical stability of the solver is demonstrated.
A turbocharger rotor is modeled in a multibody simulation software. The complete
system consists of a flexible shaft, a turbine and a compressor wheel, as well as a
thrust bearing and two full-floating ring bearings. The equations of motion of the
turbocharger rotor are coupled with the equations of the thermohydrodynamic bearing
models and they are solved simultaneously at each time-integration step during a run-up
simulation. The simulation results show that the oil-temperature and the gas
forces in the axial direction exert a large influence on the rotor vibrations.
The geometry of the pads in thrust bearings will be optimized using a novel approach.
In this work, statistical and neural network methods are used, avoiding the drawbacks
of optimization algorithms. Usually, thrust bearings are optimized for higher load
capacity and lower friction losses. Using the proposed optimization approach, thrust
bearings can be optimized not only for load capacity and friction losses but also
towards a better vibration behavior of the complete rotordynamic system.
The validation of the thrust and the radial bearing modeling is performed through
comparisons with experimental results. For radial bearings, a standard shaft motion
test is used and for the thrust bearing a new testing approach is implemented. The
simulation results are in a good agreement with the experimental data
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