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Novi Sad, Serbia

Stasevic M.,NIS Petroleum | Maksimovic S.,Ratka Resanovica | Geric K.,University of Novi Sad | Burzic Z.,Ratka Resanovica | Maksimovic M.,Belgrade Waterworks and Sewerage
Strojarstvo | Year: 2011

The goal of this paper is the establishment of computation methods for the evaluation of the residual life of structural elements in the presence of initial damage which appears in the form of cracks. Initial cracks appear during the exploitation of structures in stress concentration zones. Therefore in this paper computation method for the evaluation of the residual life of structural elements with initial damage subjected to cyclic loading of constant amplitude is presented. Calculational methods for the evaluation of the residual life of structural elements with initial damage basically rely on crack propagation analysis. In this investigation for crack propagation analysis Strain Energy Density (SED) method will be used. This method uses the low-cycle fatigue properties of the material, which are also being used for the lifetime evaluation until the occurrence of initial damage. Therefore experimentally obtained dynamic properties of the material such as Paris' constants are not required when this approch is concerned. The complete method for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the structural element in the form of a plate with a hole and a single initial crack. Results of numerical simulation for crack propagation based on strain density method have been compared with experimental results.


Stasevic M.,NIS Petroleum | Geric K.,University of Novi Sad | Vasovic I.,Institut Gosa
Technics Technologies Education Management | Year: 2012

This paper's objective is to establish convenient and efficient numerical models for the crack propagation analysis of structural elements with initial damages. The goal of this paper is the establishment of computation methods for the evaluation of the residual life of structural elements in the presence of initial damage which appears in the form of cracks. Initial cracks appear during the exploitation of structures in stress concentration zones. Therefore in this paper computation method for the evaluation of the residual life of structural elements with initial damage subjected to cyclic loading of constant amplitude is presented. Calculational methods for the evaluation of the residual life of structural elements with initial damage basically rely on crack propagation analysis. In this paper two numerical simulation approaches to crack propagation are presented. First approach is based on the conventional Paris' law of crack propagation, while the other utilizes the strain energy density method during the analysis of crack propagation. The Strain Energy Density Method (SED) uses the low-cycle fatigue properties of the material. Therefore experimentally obtained dynamic properties of the material such as Paris' constants are not required when this approch is concerned. For the S355 J2 G3 steel, which was used in the research, low-cycle properties of the material and Paris' constants for the crack propagation analysis have been determined experimentally. The complete method for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the structural element in the form of a plate with a hole and a single initial crack. Results of numerical simulation for crack propagation based on strain density method and conventional Paris' law of crack propagation have been compared with experimental results.


Dukanovic Z.,NIS Petroleum | Durickovic I.,University of Belgrade | Glisic S.,University of Belgrade | Orlovic A.,University of Belgrade
19th International Congress of Chemical and Process Engineering, CHISA 2010 and 7th European Congress of Chemical Engineering, ECCE-7 | Year: 2010

Hydrotreating of middle distillates is one of the key processes in modern refining technology. Results of hydrotreating of gas oil and LCO blends, obtained in an industrial hydrotreater, are presented. Increasing temperature differences in the reactor with increasing content of LCO in the blend were observed along with substantial decrease of total sulfur in the product. A mathematical model of the industrial hydrotreater was developed to simulate the reactor behavior under different operating conditions. Cubic EOS were applied to model VLE of the reacting fluid for the ternary mixture composed of hydrogen, methane, and n-hexadecane. Validation of the model was performed using the available data obtained during the industrial test run. This is an abstract of a paper presented at the 7th European Congress of Chemical Engineering-7 and the 19th International Congress of Chemical and Process Engineering CHISA (Prague, Czech Republic 8/28/2010-9/1/2010).


Vujicic D.,University of Novi Sad | Comic D.,NIS Petroleum | Zarubica A.,University of Novi Sad | Micic R.,NIS Petroleum | Boskovic G.,University of Novi Sad
Fuel | Year: 2010

Calcium oxide as a heterogeneous catalyst was investigated for its effect on the biodiesel synthesis from refined sunflower oil. Experiments were carried out using a commercial bench stirred tank reactor of 2 dm3 volume, at 200 rpm, with a methanol to oil ratio 6 to 1 and 1 mas.% catalyst loading as constant parameters. Ester yields were followed as a function of temperature (60-120 °C), pressure (1-15 bars) and reaction time (1.5-5.5 h). The temperature of 100 °C was found to be optimal for the maximum (91%) conversion to methyl esters, while pressure had a positive impact up to 10 bars at 80 °C. The catalyst activation in air leading to the formation of strong basic sites was found to occur at 900 °C. Catalyst particle coalescence took place during the reaction, giving a gum-like structure, and resulted in a significant catalyst deactivation. The pseudo-first order reaction was established, with a "knee" at 80 °C in the Arrhenius plot separating the kinetic and diffusion regimes. During the reaction progress, an activation energy decrease from 161 to 101 kJ/mol, and from 32 to (-3) kJ/mol, was found for the kinetic and diffusion regimes, respectively. © 2010 Elsevier Ltd. All rights reserved.

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