Řada strojní. 2009, roč. 55 / Mechanical Series. 2009, vol. 55
http://hdl.handle.net/10084/111974
2019-04-18T16:23:22ZA mathematical model of allocation of aircraft to flights of regular air routes
http://hdl.handle.net/10084/83444
A mathematical model of allocation of aircraft to flights of regular air routes
Smrž, Vladimír; Teichmann, Dušan
The article deals with the problem of aircraft allocation to flights of air routes. For solving the
problem, methods of linear programming that is a very universal solving tool [1] are employed. It
contains the mathematical formulation of the problem, two linear mathematical models and a
concrete example enabling the verification of functionality of mathematical models built. The solving
of the concrete example was performed using optimization software Xpress-IVE.
2009-01-01T00:00:00ZThe contacts on the superelements
http://hdl.handle.net/10084/83442
The contacts on the superelements
Podešva, Jiří
The modeling of the roller bearing brings two important problems. The contact problem means
that two surfaces touch one another. The contact transmits the pressure force but not tensile force. It
is not known neither the contact area nor the distribution of the contact pressure. The second problem
is the largeness of the structure, the number of degrees of freedom (DOF). Nowadays the hardware
allows solving the large systems of equations. Nevertheless if the number of DOF goes over 105 or
106 and the algorithm necessitates the iterative approach this could be the problem. The effective way
of solution can be domain decomposition using so called super-elements. The paper brings the
description of modeling with super-elements and solving the contact problem.
2009-01-01T00:00:00ZDetermination of pulverized coal thermokinetic properties with use of mathematical modelling
http://hdl.handle.net/10084/83441
Determination of pulverized coal thermokinetic properties with use of mathematical modelling
Paluska, Radim; Bojko, Marian; Horák, Jiří
Thermokinetic properties as a mean for better understanding the nature of combustion process,
can be determined by experiment using the Drop Tube Test Facility (DTTF) described further in the
text. DTTF provides conditions occurring in pulverized coal fired boiler by emulated oxygen
concentration, temperature and velocity of reaction gas. The DTTF presented in the paper was built
recently at the Energy Research Center. Experimental data acquired from DTTF are planned to be
used in mathematical modelling using the code Fluent. The paper describes in detail main differences
between used Fluent models of particles combustible fraction and reaction rate. Temperature field
and distribution of species mass fraction is evaluated for comparing with experimental tests. Results
from adjusted mathematical model should provide closer information about combustion process in
real operation.
2009-01-01T00:00:00ZFatigue behaviour of AZ91 magnesium alloy
http://hdl.handle.net/10084/83440
Fatigue behaviour of AZ91 magnesium alloy
Němcová, Aneta; Zapletal, Josef; Podrábský, Tomáš
The paper deals with the determination of principal mechanical properties and the
investigation of fatigue behaviour of AZ91 magnesium alloy. The experimental material was made by
squeeze casting technique and heat treated to obtain T4 state (solution annealing), when hard, brittle
Mg17Al12 intermetallic phase is dissolved. The basic mechanical properties (Young’s modulus,
ultimate tensile strength, yield strength, elongation to fracture and reduction of area) were
determinated by static tensile test. Furthermore, fatigue parameters were investigated and standard
tensile curve was compared with cyclic stress-strain curve. The comparison indicates that studied
material exhibited cyclic hardening at whole lifetime. In addition, the S-N curve on the basis of
smooth test bars tested under symmetrical push-pull loading at room temperature was evaluated. The
measured data were subsequently used for assessing the Manson-Coffin curve and for fitting with
suitable regression function for determination of the fatigue parameters. Fatigue limit σC of the
studied alloy for 108 cycles is approaching 50 MPa. Structure of the studied alloy in the basic state
and after heat treatment was observed by light and scanning electron microscopy.
2009-01-01T00:00:00Z