DSpace Kolekce:
http://hdl.handle.net/11025/1898
2021-05-09T02:42:18ZStudy of coupling between bending and torsional vibration of cracked rotor system supported by radial active magnetic bearings
http://hdl.handle.net/11025/1965
Název: Study of coupling between bending and torsional vibration of cracked rotor system supported by radial active magnetic bearings
Autoři: Ferfecki, Petr
Abstrakt: The coupling of bending and torsional vibration due to the presence of transverse fatigue crack in a rotor
system supported by radial active magnetic bearings (AMB) is investigated. For this purpose the modified stiffness
matrix with six degrees of freedom per node is used and takes into account all the coupling phenomena that
exists in a cracked rotor. The partial opening and closing of crack is considered by means of status of stress intensity
factor along the crack edge. The equation of motion of rotor system is nonlinear due to response dependent
non-linear breathing crack model and nonlinear force coupling introduced by AMB. A response of the rotor
system is obtained by direct integration of nonlinear equation of motion. When the torsional harmonic excitation
is applied to the rotor system with the crack then the sum and difference of torsional frequency around a bending
natural frequency is observed in the lateral vibration spectrum. Influence of different values of crack parameters
for two different speeds of rotor is investigated with help of frequency spectra.2007-01-01T00:00:00ZFerfecki, PetrVehicle dynamic effects in the course of passing over turnouts
http://hdl.handle.net/11025/1964
Název: Vehicle dynamic effects in the course of passing over turnouts
Autoři: Zelenka, Jaromír; Hába, Aleš; Kohout, Martin
Abstrakt: For the quantification of vehicle dynamic effects at passing over turnouts at a higher speed there was developed
a methodology for evaluating of acceleration measured on vehicle axle boxes in the year 2003. The methodology
is based on statistical evaluation of lateral and vertical acceleration measured values at passing over
both critical parts of a turnout (tongue, frog). The created methodology was used for investigation of vehicle dynamic
effects by running at speed up to 230 km/h in the year 2004 in terms of high-speed tests of tilting-body
unit class 680 CD. There was found relatively high values of dynamic effects already at a speed 160 km/h. In
terms of tilting-body unit class 680 tests at a higher speed in curves of chosen track lines of 1st and 2nd corridor
of Czech Railways there was carried out also verification of curved turnouts state according to methodology
mentioned above with a view to possibility of speed increasing at curved throats of chosen stations. Lateral vehicle
dynamic effects at passing over a curved turnout frog area were evaluated. There were carried out simulation
calculations of vehicle passing over a turnout based on measured geometric parameters of wheelset as well as
chosen turnouts. Results of the calculations were compared with measurements. The increased vehicle dynamic
effects found in pulsed beats character influence negatively the turnouts part (not only wheel contacting parts) as
well as operating life all unsuspended parts of vehicles.2007-01-01T00:00:00ZZelenka, JaromírHába, AlešKohout, MartinSystem model reduction for MBS optimization
http://hdl.handle.net/11025/1963
Název: System model reduction for MBS optimization
Autoři: Zavřel, Jan; Valášek, Michael
Abstrakt: A disadvantage of optimization of flexible multibody systems (MBS) is a computing time, mainly for large
systems, especially designed by FEM. The computing time rises with the complexity of the model significantly. A
reduction techniques allow decreasing of degrees of freedom and it contributes to the reduction of the computing
time. These techniques can be used for the reduction from thousands and more degrees of freedom to tens, but
some limits exist. A reduction degree (ratio between number of DOFs before and after the reduction) is the most
important feature because it predicts the final accuracy of the model. The next one is the selection of master and
slave degrees of freedom that play an important role in connecting all bodies together within the MBS (e.g. by
joints). There are many reduction methods, but they differ in available accuracy, speed, efficiency and suitability
for the same reduction degree. A dimension of the original system is decisive for the reduction method suitability,
many methods require an inversion matrix from the part of the stiffness matrix. The inversion matrix are than large
and the computing time grows up. This paper deals with the reduction techniques, their disadvantages, suitability
and applicability.2007-01-01T00:00:00ZZavřel, JanValášek, MichaelAnalysis of blood flow through a three-dimensional bypass model
http://hdl.handle.net/11025/1962
Název: Analysis of blood flow through a three-dimensional bypass model
Autoři: Vimmr, Jan; Jonášová, Alena
Abstrakt: The purpose of this study is to analyze the steady laminar blood flow through a complete idealized threedimensional
bypass model with regard to the bypass hemodynamics and to compare the obtained results with
the ones from the two-dimensional model. The type of flow restriction in the native artery is represented by
either an occlusion or a 75% symmetric stenosis. In both cases, the blood is considered to be an incompressible
Newtonian fluid. The walls are assumed to be impermeable and rigid. In order to solve the non-linear system of
incompressible Navier-Stokes equations, the pseudo-compressibility method and the finite volume formulation of
the central explicit fourth order Runge-Kutta scheme are applied using own computational software developed for
unstructured hexahedral grids.2007-01-01T00:00:00ZVimmr, JanJonášová, Alena