DSpace Kolekce:
http://hdl.handle.net/11025/30245
2020-09-19T22:14:49ZMathematical modelling of biogenous filter cake and identification of oilseed material parameters
http://hdl.handle.net/11025/1900
Název: Mathematical modelling of biogenous filter cake and identification of oilseed material parameters
Autoři: Očenášek, Jan; Voldřich, Josef
Abstrakt: Mathematical modeling of the filtration and extrusion process inside a linear compression chamber has gained a lot of attention during several past decades. This subject was originally related to mechanical and hydraulic properties of soils (in particular work of Terzaghi) and later was this approach adopted for the modeling of various technological processes in the chemical industry (work of Shirato). Developed mathematical models of continuum mechanics of porousmaterials with interstitial fluid were then applied also to the problem of an oilseed expression. In this case, various simplifications and partial linearizations are introduced in models for the reason of an analytical or numerical solubility; or it is not possible to generalize the model formulation into the fully 3D problem of an oil expression extrusion with a complex geometry such as it has a screw press extruder. We proposed a modified model for the oil seeds expression process in a linear compression chamber. The model accounts for the rheological properties of the deformable solid matrix of compressed seed, where the permeability of the porous solid is described by the Darcy’s law. A methodology of the experimental work necessary for a material parameters identification is presented together with numerical simulation examples.2009-01-01T00:00:00ZOčenášek, JanVoldřich, JosefDynamic wheelset drive load of the railway vehicle caused by short-circuit motor moment
http://hdl.handle.net/11025/1559
Název: Dynamic wheelset drive load of the railway vehicle caused by short-circuit motor moment
Autoři: Zeman, Vladimír; Hlaváč, Zdeněk
Abstrakt: The paper deals with mathematical modelling of dynamic response of the railway vehicle wheelset drives caused
by short-circuit traction motor torque. The individual wheelset drive with hollow graduated shaft is one of subsystems
of the two-axled vehicle bogie with two wheelset drives. The model respects the viscoelastic suspension of
the both engine stators with gear housings mounted on the bogie frame and all the other couplings among bogie
drive components. The dynamic response is investigated in dependence on longitudinal creepage and forward velocity
of the vehicle at the moment of the sudden short-circuit in one asynchronous traction motor. The method is
applied to bogie of the electric locomotive developed for speed about 200 km/h by the company ŠKODA TRANSPORTATION,
s. r. o. The wheelset drive vibration is confronted with stability conditions of the whole bogie.2009-01-01T00:00:00ZZeman, VladimírHlaváč, ZdeněkA computational investigation of vibration attenuation of a rigid rotor turning at a variable speed by means of short magnetorheological dampers
http://hdl.handle.net/11025/1558
Název: A computational investigation of vibration attenuation of a rigid rotor turning at a variable speed by means of short magnetorheological dampers
Autoři: Zapomněl, Jaroslav; Ferfecki, Petr
Abstrakt: Rotors of all rotating machines are always slightly imbalanced. When they rotate, the imbalance induces their lateral
vibration and forces that are transmitted via the bearings into the foundations. These phenomena are significant
if the rotor accelerates or decelerates and especially if it passes over the critical speeds. The vibration can be reduced
if the rotor supports are equipped with damping elements. To achieve optimum performance of the damper,
the damping effect must be controllable. At present time, semiactive magnetorheological squeeze film dampers
are a subject of intensive research. They work on a principle of squeezing a thin film of magnetorheological liquid.
If magnetic field is applied, the magnetorheological liquid starts to flow only if the shear stress between two
neighbourhood layers exceeds a limit value which depends on intensity of the magnetic field. Its change enables
to control the damping force. In the mathematical models, the magnetorheological liquid is usually considered as
Bingham one. Application of the computer modelling method for analysis of rotors supported by rolling element
bearings and magnetorheological squeeze film dampers and turning at variable angular speed requires to set up the
equations of motion of the rotor and to develop a procedure for calculation of the damping force. Derivation of
the equations of motion starts from the first and second impulse theorems. The pressure distribution in the thin
lubricating film can be described by a Reynolds equation modified for the case of Bingham liquid. In cavitated
areas, it is assumed that pressure of the medium remains constant. The hydraulic force acting on the rotor journal
is then obtained by integration of the pressure distribution around the circumference and along the length of the
damper. Applicability of the developed procedures was tested by means of computer simulations and influence of
the control of the damping force on vibration of the rotor was analyzed.2009-01-01T00:00:00ZZapomněl, JaroslavFerfecki, PetrAn evaluation of the stress intensity factor in functionally graded materials
http://hdl.handle.net/11025/1557
Název: An evaluation of the stress intensity factor in functionally graded materials
Autoři: Ševčík, Martin; Hutař, Pavel; Náhlík, Luboš; Knésl, Zdeněk
Abstrakt: Functionally graded materials (FGM) are characterised by variations in their material properties in terms of their
geometry. They are often used as a coating for interfacial zones to protect the basic material against thermally or
mechanically induced stresses. FGM can be also produced by technological process for example butt-welding of
polymer pipes. This work is focused on a numerical estimation of the stress intensity factor for cracks propagating
through FGM structure. The main difficulty of the FE model creation is the accurate description of continual
changes in mechanical properties. An analysis of the FGM layer bonded from both sides with different homogenous
materials was performed to study the influence of material property distribution. The thickness effect of the
FGM layer is also discussed. All analyses are simulated as a 2D problem of an edge cracked specimen. In this
paper, the above effects are quantified and conclusions concerning the applicability of the proposed model are
discussed.2009-01-01T00:00:00ZŠevčík, MartinHutař, PavelNáhlík, LubošKnésl, Zdeněk