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•  8/2014 table of contents

Hajdú Sándor, Czibere Tibor, Kalmár László
Starting behaviour of cross flow turbine    5
The dynamics specific of a cross flow turbine can be quite complex. The flow field is very unsteady and largely three-dimensional. There is much interference between the shed vortices and blades. In addition, dynamic stall behavior is very prevalent as the blade encounters rapidly changing angles of attack throughout its rotation. Despite this complexity, relevant conclusions are available using a simple calculation model. The paper analyses the changes in the lift and the drag on the airfoil as a function of the angle θ, describing the position of the blade, and of the tip speed ratio λ on the basis of the lifting-line theory. Our calculations were not limited to a single tip speed ratio but we studied the whole relevant rotational speed range of cross-flow turbine.

Farkas József
Optimum design of a storage tank roof constructed from welded stiffened plates    9
The optimization problem of a welded fixed roof for a vertical storage tank is studied. The load from snow and from a 150 mm soil layer is considered.  The roof is constructed from stiffened sectorial trapezoidal plate elements and radial beams. The stiffeners are of halved rolled I-section and the radial beams are constructed from rolled I-sections. To find the minimum cost solution the thickness of the base plate, the position, number and size of circumferential stiffeners, the size of radial beams as well as the number of sectors is varied. The distances of stiffeners are non-equidistant. In the cost function the cost of material, welding and painting is taken into account.

Jármai Károly, Farkas József
Optimization for cost minimum of welded colunms and beams for fire safety    15
The two important principles of welded structures is optimized for cost minimum with and without fire protection. A square box section compressed column is designed for overall and local buckling. For a simply supported box beam the stress, deflection and buckling conditions are taken into account. The cost function includes the cost of materials, welding, painting and fire protection costs. In the case of design without fire protection the critical temperature formula of Eurocode 3 is applied. For both kinds of structures the fire protected version is cheaper than the unprotected one. The reason is that in case of protection much thinner plates are necessary.

Dr. Kota László, Jármai Károly
Discretization of the firefly algorithm for the multiple travelling salesman problem    21
The aim of this research is developing a discrete firefly optimization algorithm to solve the multiple travelling salesmen problem (MTSP) and later the fixed destination multiple route multiple travelling salesmen problem. In this article we will introduce the first steps of this research. We will introduce one proposed discretization of the firefly algorithm at this special problem, which heavily based on the characteristic of the problem and state space

Kovács László, Dr. Szabó Szilárd
Examination of the gas exchange process of an ic engine with the help of 0d/1d engine modell    25
During the initial design phase of an IC engine it is not important to exactly identify all the thermodynamic, fluid mechanical and chemical reactions within the engine in question. What is of interest is the whole system that needs to be optimized to reach the preset targets with sufficient precision. In this work the validation of an engine model is presented and the results of the simulation and measurements are compared and examined. The outcome of the comparison is the clear identification of the cause of the dip in the torque characteristics of the modelled test engine while also presenting a possible solution for this special problem.

Krámer Gyula, Siménfalvi Zoltán, Szepesi L. Gábor
Calculation of data of ammonia-water system to absoption cooling methods    30
This article contains calculations and estimations of the ammonia-water system to make the planning of absorption refrigeration systems easier and more simple, avoiding the use of difficult databases, and to make the planning without expensive program background possible, using the very popular MathCAD software.

Páczelt István, Baksa Attila
Numerical analysis of the wear problems for periodical loading    34
The relative sliding motion of two elastic bodies in contact induces wear process and contact shape evolution. In the case of a substrate sliding under the punch the transient process tends to a periodical steady state occuring at periodical fixed contact stress and strain distribution in the contact zone if the load is acting on punch periodically changing in time. The present paper is aimed to extend the previous analyses [1-3] of steady state conditions for periodical loading.

Péter József, Németh Géza
Load equalization in planetary friction drive based on elastic deflection    38
The relationship between the wheels of a planetary drive is shape closing or force closing. Present paper is dealing with a variant, where there is a force closing planetary friction drive, having external-external-internal cylindrical rolling surfaces, and the power distribution (and partly its equalization) is based on the elastic deflection of the annular wheel.

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