Facta Universitatis, Series: Mechanical Engineering

123-131

Authors: Qiang Li, Roman Pohrt

A new model of mixed lubrication is proposed in the frame of the Method of Dimensionality Reduction (MDR). In this model the dynamic lubricated rolling contact between rough surfaces is simulated based on the results from elastohydrodynamic lubrication (EHL). In order to account for the break-up of the additional boundary layer on a local micro contact area, a supplemental criterion is imposed. For comparison, a twin-disc test rig is set up to measure the electrical resistance between two lubricated rolling surfaces under different normal forces, rotation speeds and temperatures. We investigated the probability of boundary layer breakthrough for both experiment and simulation and found good agreement.

141-151

Authors: Dragan Jovanović

Results of reconstruction of potential strain energy surfaces at the region of crack and basic procedures of the reconstruction method are presented. Pertinent limitations and specifications of the method are pointed out in evaluating the best fitting curves and the best fitting three-dimensional surfaces of stress components and potential strain energy. Examples of cracks named in the paper as PR-Z-16 and PR-P-22, with exactly the same geometry of crack and plate are analyzed. The same finite element lattice for calculation in both cases is selected. The first example of a plate is loaded with in y - direction on the outer border of the plate, perpendicularly on the plane of crack, while in the example PR-P-22 the plate is loaded with continually and perpendicularly on the crack contour surface. The reconstruction procedure of potential strain energy surfaces for two sections of plates y=0 and z=0, and graphical presentation of these surfaces, are carried out. Based on reconstructed potential strain energy surfaces, isoenergy lines at the region in front of the crack tip for both analyzed examples, are obtained. It is observed that the distribution of stresses as well as the distribution of potential strain energy are very similar in both cases, which indicates a significant influence of geometric shape of contour surfaces of the crack. For comparison, stress state and potential strain energy state, which are obtained by using relations from literature, are shown.

169-180

Authors: Mića V. Vukić, Goran Vučković, Predrag Živković, Žarko Stevanović, Mladen Tomić

A shell and tube heat exchanger (STHE) is one of the most often used apparatuses in chemical industry. One of the main goals of the STHE manufacturers is to improve their exploitation reliability and efficiency. Two approaches to the STHE design improvement are possible: experimental investigation, which is very expensive and time-consuming because of the shell side complex geometry, and numerical investigations. Numerical simulations can be used to check the old and to develop new and more efficient STHE designs. In this paper, the results of the numerical investigations of fluid flow and heat transfer in the laboratory experimental STHE are presented. Numerical simulation has been performed by using the PHOENICS code. The tube bundle has been modeled by using the concept of porous media. Standard k-e turbulence model is used.

193-202

Authors: Predrag Milić, Dragan Marinković

Finite element method (FEM) is a tool that is mostly used for the structural analysis. The method is based upon approximation of the actual geometry and displacement field of the structure over the finite element domain. In practice, Lagrange polynomials are mostly used as shape functions (approximate functions). They provide only the C0-continuity at the element boundaries. This paper elucidates a possible approach based on the so-called isogeometric analysis to improve this property. The isogeometric FEM analysis applies the same functions to describe the CAD model, the element geometry and the element displacements. The paper represents developed algorithm and the obtained results for a relatively simple test case.