Řada strojní. 2009, roč. 55 / Mechanical Series. 2009, vol. 55

Permanent URI for this collectionhttp://hdl.handle.net/10084/111974

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Now showing 1 - 20 out of 95 results

A mathematical model of allocation of aircraft to flights of regular air routes
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) 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.
Interparticle forces of powder particles and their coating process
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Slíva, Aleš; Zegzulka, Jiří
Coating is a process, by which fine particles in nano-range are connected to a powder particle material. During the initial phases of coating, surface of powder particle material is sprinkled by nano-particles and thus a lot of powder material properties can be directed and changed especially. A lot of method of surface coatings processing are discovered via commercial devices, and also there are a lot of pioneer devices working without basic knowledge of coating mechanism in laboratory background. The main advantage of the coated material is the possibility to changing the basic properties e.g. wetability, conductivity, electric and electronic properties, rheological properties, flowability, magnetic properties etc. It has been observed that only a few percentages (%W) are enough to ensure a property change and a property direction. In the paper, the coating mechanism and forces involved in coating processing are investigated and mathematical modeling of dry coating is initiated.
The contacts on the superelements
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) 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.
Determination of pulverized coal thermokinetic properties with use of mathematical modelling
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) 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.
Fatigue behaviour of AZ91 magnesium alloy
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) 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.
Changes of mechanical characteristics of extruded aluminium alloys EN-AW 6082 and 7075
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Mazal, Pavel; Liškutín, Petr; Vlašic, František
In the article there are concentrated and partly commented the results of tensile and fatigue tests which were realised on the alloys EN-AW 6082/T6 and alloy EN-AW 7075/T6. Semi products of these materials were produced by extruding technology and their structure demonstrated visually inhomogeneity (directionality). In the frame of experimental tests they were evaluated and mutually compared the mechanical parameters obtained on the samples produced in different directions to the extrusion axis. The reached results indicate that the fatigue properties of tested materials are influenced by the structure orientation only gently.
Precision check of beam bending solution by means of analytical metod
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Macura, Pavel
The paper is devoted to the issues of beam bending with focus on one of possible methods of solution – by analytical method. Principle of this method is based on solution of approximate differential equation of the bending curve, derived from the precise differential equation of the bending curve with omission of one of its member. The bending curves can be spatial or in some simpler cases planar, and it is appropriate to use for their solution a vector analysis, specifically vector functions of the scalar argument. With use of them at first the precise and approximate differential equation of the bending curve is determined and then the deviations between the accurate and approximate solutions are assessed.
The solderability of ceramic materials with active solders under high-intensity ultrasonic conditions
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Koleňák, Roman; Žúbor, Peter; Hlavatý, Ivo
Joints of combined metallic or non-metallic materials prepared by lead-free tin solder. The analysis of phase interface of joints using fractographic techniques, new phase identification by Xray analysis and electron microscopy analysis. Effect of new phase on the mechanical properties of solder joint and the possibility of reaction layer study by in-depth etching technique.
Lead-free solders intended for higher temperatures
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Koleňák, Roman; Hlavatý, Ivo
A design for a lead-free solder intended for higher application temperatures. Alternative solder production. Structural analysis, chemical microanalysis, and semi-quantitative chemical analysis of BiAg11 solder. BiAg11 solder wettability on copper, nickel and silver surfaces.
Critical factors of high-pressure hydrogen compression in hydrogen technologies
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Kaminský, Jaroslav; Vrtek, Mojmír
Hydrogen technology is connected with many problems occurring during storage, liquefaction, distribution and utilization of hydrogen. The economy of all these processes is affected by mediumpressure and high-pressure compressors efficiency, which is with regard to thermodynamic properties of hydrogen function namely of their working space leakage. An experimental study of these phenomena was used to proposition of mathematical model describing the effect of reflux from working space on compressor efficiency.
Simulation of pressure amplitude characteristics of pipe with hydraulic accumulator in Matlab - SimHydraulics
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Hružík, Lumír; Šeděnka, Ladislav; Sikora, Roman
The paper deals with the simulation of pulsating flow in the pipeline for options with and without the hydraulic accumulator, when the throttle valve is at the outlet of pipeline. Time dependent flow through the pipeline is simulated in the software Matlab - SimHydraulics. Numerically simulated amplitude-frequency characteristics of pressure are verified experimentally.
Demonstration of the MatSol library developed for the efficient solution of contact problems and its comparison with ANSYS
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Horyl, Petr; Kozubek, Tomáš; Markopoulos, Alexandros; Brzobohatý, Tomáš
The goal of this contribution is to present the MatSol library developed for the efficient solution of large problems in contact mechanics. The MatSol solvers are based on FETI domain decomposition methods which are well known by their parallel and numerical scalability. The performance is illustrated on a model contact problem of the cantilever cube over the obstacle. Finally, we compare the MatSol solution with the ANSYS one of a simplified contact problem with Coulomb friction of the yielding clamp connection.
Emission factors of selected organic compounds from domestic hardwood combustion
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Hopan, František; Šyc, Michal; Horák, Jiří; Dej, Milan; Krpec, Kamil; Ocelka, Tomáš; Tomšej, Tomáš; Pekárek, Vladimír
Emission factors were determined during beech logs combustion in four domestic facilities typical for Central European region households. In flue gases there were determined except basic pollutants (NOx, CO, PM and OC as TOC ) also selected organic pollutants as PCBz, PCPh, PAH, PCB, and PCDD/F. Generally, obtained EF values of selected pollutants were lower for modern combustion facilities than for older ones. However, some differences were found between modern facilities in dependence on their type as well. For better understanding results were also subjected to principal component analysis.
Fatigue properties of AZ31 magnesium alloy with calcium addition
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Gejdoš, Pavel; Zapletal, Josef; Podrábský, Tomáš
In the work the AZ31 magnesium alloy with 0.15% calcium was studied which was cast using squeeze casting (SC). Besides the determination of mechanical and fatigue properties also microstructure of the alloy was observed. In addition, fractographic evaluation of the resulting fracture surfaces after fatigue loading was performed.
New applications of conjugated strength criterion
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Fojtík, František; Fuxa, Jan; Poruba, Zdeněk
This article describes experimental results under combined loading of specimens manufactured from construction steel 11523. Specimens were loaded by amplitude of the torque, then by combination of torque and tension prestress. For evaluation of the results the conjugated strength criterion was applied. Further, another approximation based on the same boundary conditions as the described conjugated strength criterion was proposed. The performed experiments and their results embody a good agreement with bellow mentioned conjugated strength criterion. The experiments were performed on modified testing machine.
Fracture surface digitizing of specimen from drop-weight tear
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Ferfecki, Petr; Židlík, Pavel; Strnadel, Bohumír
There is always a need to determine a fraction of the ductile, and respectively, brittle fracture on the fracture surface of specimen examined using a drop-weight tear test (DWTT). Determination of the percentage of ductile fracture (PDF) in accordance with valid national and international recommendations is not entirely unambiguous. Results of evaluation show a large scattering for each criterion, and depend on the subjective view of the evaluator. Criteria are complex in nature and are independent of the fracture morphology. The dimensionless areas ratio criterion has been newly proposed for the evaluation of the DWTT specimens. This criterion is given by the ratio of the fracture surface projection into a base plane to the scanned fracture surface. The fracture surface of the DWTT specimen is scanned using a 3D-Cam scanner into a network of discrete points. A fracture surface area is calculated from the sum of the areas of triangles constructed above the element of the projection of fracture surface. A dimensionless areas ratio criterion is sensitive to a change of the size of fracture surface evaluated and its value depends on the proportion of PDF in the specimen. An application of the proposed assessment of fracture surfaces in the DWTT specimens in engineering practice will contribute to the objectivity of DWTT test results and to improve equipment reliability, in which the DWTT test result is a part of attestations in materials used.
Comparison of methods for computation of electromagnetic forces in the radial active magnetic bearing
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Ferfecki, Petr; František, Ondřej
Rotor systems supported by the radial active magnetic bearings (AMBs) are considered in this paper. If dynamic characteristics of the rotor systems are examined numerically by the finite element method, it is necessary to determine forces in the bearings. Considering supporting by the AMBs, a shaft levitates in an air gap between the rotor and the stator part. Forces of magnetic levitation are caused by the electromagnetic field in the bearing. Electromagnetic forces in AMB are determined by two methods. One is based upon the principle of virtual work and the other one upon the Maxwell stress tensor. The forces computations are provided for three-dimensional and two-dimensional finite element models of the radial AMB. One-dimensional approximation of the magnetic circuit is provided as well. Rates of convergence, efficiencies and accuracies of the electromagnetic forces computations are evaluated from several points of view. These are compared also with used type of material model, methods of the forces calculation and size of AMB model meshes.
Acicular ferrite and bainite microfractographic response
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Mazancová, Eva; Rusz, Stanislav; Rucká, Zdeňka; Mazanec, Karel
The acicular ferrite (AF) and bainite (B) formation is practically connected with the same temperature range. The plates (laths) of the both austenite transformation products show displacive mechanism character. The differences are in nucleation sites. At the non-metallic inclusions or precipitates, the intragranular nucleated AF leads to the microstructure refinement consisting of interlocked plates (laths). The B is formed intergranularly. In impact toughness specimens (CVN-60) the fractal analysis of fracture surfaces was performed. In the AF the determined values of fractal dimenses are higher (cleavage fracture) than in the B microstructure. In the zone of ductile fracture, determined difference of fractal dimension is small.
Comparison of two simplified mathematic models of pneumatic system
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Dvořák, Lukáš; Fojtášek, Kamil
This paper deals with comparison of two methods of pneumatic systems modelling. The first one is mathematical modeling by means of RHD resistances, which are resistance to motion R, resistance to acceleration H and deformation resistance D. The second approach can be called as classical. This method is based on state equation of gas, continuity equation and motion equation. Output characteristics of models are compared with data obtained by measurement in the end.
Contribution to unreliable M/M/1/M queueing systems modelling
(Vysoká škola báňská - Technická univerzita Ostrava, 2009) Dorda, Michal
In the queueing theory we usually assume that a server breakdown can not occur (see for example in [1], [2], [3] or [4]). In other words a utility server works without failures. But in practice this assumption is not correct, the server is often a technical device and every technical device can be broken. During the breakdown the server can not work which means that the consideration of server failures has got an effect on performance measures of studied queueing system. We can say that queueing models with unreliable servers are more closely to a reality than models with reliable servers. On the other hand unreliable queueing models are more complicated. This paper presents two models of Markov queueing systems with an unreliable server.

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