Some aspects of design ventilation system in road tunnels

In the base, working of ventilation system can be analyzed in regular and incidental modes of operation. This paper concerns the specification of the longitudinal ventilation necessary to prevent upstream movement of combustion products in a tunnel fire. In this work the objective of the study is to analyze the road way tunnel ventilation system using CFD software to create comfort ventilation system in the tunnel. The comfort ventilation concept refers to the situation when air quality within the tunnel is reduced due to presence of polluted air in the tunnel. This paper is focused on ventilation system in a road traffic tunnel in moment of accident situation as fire. In this investigation numerical simulation of fire was carried out and determination of a critical air velocity depending on the power of the fire was conducted. The output results of the software developed for this purpose, which is also used in the realization of practical projects, are shown

Selecting hardfacing technologies for ventilation mill suction plates and extending its working life

This paper presents results of the suction plate surface modification by hardfacing, of the ventilation mill in the Kostolac B power plant. Before applying hardfaced suction plates to exploitation conditions, it is necessary to study model hardfaced samples for determining the optimal tech-nology and filler material for revitalization. Experimental tests of revitalized mill suction plates in real exploitation conditions show that the proposed modification, hardfacing technologies and filler materials give good results. The relative weight loss of the suction plates after 1440 h period of exploitation in real conditions is 1-3%. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Selecting hardfacing technologies for ventilation mill suction plates and extending its working life

This paper presents results of the suction plate surface modification by hardfacing, of the ventilation mill in the Kostolac B power plant. Before applying hardfaced suction plates to exploitation conditions, it is necessary to study model hardfaced samples for determining the optimal tech-nology and filler material for revitalization. Experimental tests of revitalized mill suction plates in real exploitation conditions show that the proposed modification, hardfacing technologies and filler materials give good results. The relative weight loss of the suction plates after 1440 h period of exploitation in real conditions is 1-3%. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Total Fatigue Life Estimation Of Aircraft Structural Components Using Strain Energy Density Method

This paper is aimed at developing a suitable computation method for estimating the fatigue life of structural elements exposed to the load spectrum. The total fatigue life can be divided into two parts, until the appearance of the initial damage and the other part represents the remaining life, i.e. until the effective fracture. The conventional approach to estimating the total life requires that low-cycle fatigue characteristics of the material be used until the initial damage occurs, and dynamic characteristics of the material for the remaining life. In order to obtain a more efficient method, the Strain Energy Density (SED) method was used in this paper. The essence of this approach is to use the same low - cycle fatigue characteristics of the material to estimate the life expectancy and the remaining life. This work is focused to developing efficient computation method and software for total fatigue life of metal aircraft structural components. To obtain efficient computation method, here the same fatigue low cyclic material properties for crack initiation and crack growth are used together with finite element method (FEM) for stress analyzes. To validate quality computation methods and in-house software for fatigue life estimations computation results are compared with experiments. The results show that the predicted results agree well with the test dat

Residual life estimation of cracked aircraft structural components

Predmet ovog istraživanja je usmeren na uspostavljanje proračunske procedure za analizu čvrstoće elemenata avionskih konstrukcija sa aspekta zamora i mehanike loma. Za tu svrhu ovde će biti uspostavljena proračunska procedura za procenu preostalog veka elemenata avionskih konstrukcija tipa dela oplate krila i uški pod dejstvom cikličnih opterećenja konstantne amplitude i spektra opterećenja. Poseban aspekt istraživanja se odnosi na primenu gustine energije deformacije (GED) za procenu preostalog veka elemenata konstrukcija sa inicijalnim oštećenjima tipa prskotina. Za određivanje analitičkih izraza za faktore intenziteta napona ovde su korišćeni specijalni singularni konačni elementi. Verifikacija proračunskih procedura za procene preostalog veka je podržana sa sa analitičkim i eksperimentalnim rezultatima uključivši i testove na zamor posebno sa aspekta eksperimentalnog određivanja malociklusnih zamornih karakteristika materijala.The subject of this investigation is focused on developing computation procedure for strength analysis of damaged aircraft structural components with respect to fatigue and fracture mechanics. For that purpose, here will be defined computation procedures for residual life estimation of aircraft structural components such as wing skin and attachment lugs under cyclic loads of constant amplitude and load spectrum. A special aspect of this investigation is based on using of the Strain Energy Density (SED) method in residual life estimation of structural elements with initial cracks. To determine analytic formulae for the stress intensity factors here singular finite elements are used. Verification of computation procedures for residual life estimations will be supported with corresponding experimental tests for determination of low cyclic fatigue properties of materials and corresponding parameters of fracture mechanics, including fatigue tests of representative aircraft structural elements

Atypical antipsychotic clozapine binds fibrinogen and affects fibrin formation

Clozapine is an atypical antipsychotic used for the treatment of schizophrenia. The prescribed target daily doses may reach 900 mg. Literature studies report a connection between clozapine usage and thrombosis development. Our in vitro study aimed to provide insight into molecular bases of this observation, investigating clozapine binding to fibrinogen, the main plasma protein involved in hemostasis. Fibrinogen/clozapine interaction was confirmed by protein fluorescence quenching, with an affinity constant of 1.7 × 105 M−1. Direct interactions did not affect the structure of fibrinogen, nor fibrinogen melting temperature. Clozapine binding affected fibrin formation by reducing coagulation speed and thickness of fibrin fibers suggesting that in the presence of clozapine, fibrinogen may acquire thrombogenic characteristics. Although no difference in fibrin gel porosity was detected, other factors present in the blood may act synergistically with altered fibrin formation to modify fibrin clot, thus increasing the risk for development of thrombosis in patients on clozapine treatment. ORAC and HORAC assays showed that clozapine reduced free radical-induced oxidation of fibrinogen. All observed effects of clozapine on fibrinogen are dose-dependent, with the effect on fibrin formation being more pronounced.This is the peer-reviewed version of the article: Gligorijević, N.; Vasović, T.; Lević, S. M.; Miljević, Č.; Nedić, O.; Nikolić, M. Atypical Antipsychotic Clozapine Binds Fibrinogen and Affects Fibrin Formation. International Journal of Biological Macromolecules 2020, 154, 142–149. [https://doi.org/10.1016/j.ijbiomac.2020.03.119

Buckling and post-buckling behavior of shell type structures under thermo mechanical loads

The thermo mechanical buckling and post-buckling behavior of layered composite shell type structure are considered with the finite element method under the combination of temperature load and applied mechanical loads. To account for through-thickness shear deformation effects, the thermal elastic, and higher-order shear deformation theory is used in this study. The refined higher order theories, that takes into account the effect of transverse normal deformation, is used to develop discrete finite element models for the thermal buckling analysis of composite laminates. Attention in this study is focused on analyzing the temperature effects on buckling and post-buckling behavior of thin shell structural components. Special attention in this paper is focused on studying of values of the hole in curved panel on thermal buckling behavior and consequently to expend and upgrade previously conducted investigation. Using finite element method, a broader observation of the critical temperature of loss of stability depending on the size of the hole was conducted. The presented numerical results based on higher-order shear deformation theory can be used as versatile and accurate method for buckling and post-buckling analyzes of thin-walled laminated plates under thermo mechanical loads

Fracture mechanics analysis of damaged turbine rotor discs using finite element method

This paper presents evaluation fracture mechanics parameters in low pressure turbine components. Critical locations such as keyway and dovetail area are experiencing stress concentration leading to crack initiation. Stress intensity factors were evaluated using the J-Integral approach available within ANSYS software code. The finite element method allowed the prediction of the point of crack initiation and the crack propagation using the orientations of the maximum principal stresses. Special attention in this investigation is focused to develop analytic expressions for stress intensity factors at critical location of low pressure steam turbine disc

Fracture mechanics analysis of damaged turbine rotor discs using finite element method

This paper presents evaluation fracture mechanics parameters in low pressure turbine components. Critical locations such as keyway and dovetail area are experiencing stress concentration leading to crack initiation. Stress intensity factors were evaluated using the J-Integral approach available within ANSYS software code. The finite element method allowed the prediction of the point of crack initiation and the crack propagation using the orientations of the maximum principal stresses. Special attention in this investigation is focused to develop analytic expressions for stress intensity factors at critical location of low pressure steam turbine disc

Determination of Stress Intensity Factors in Low Pressure Turbine Rotor Discs

An attention in this paper is focused on the stress analysis and the determination of fracture mechanics parameters in low pressure (LP) turbine rotor discs and on developing analytic expressions for stress intensity factors at the critical location of LP steam turbine disc. Critical locations such as keyway and dovetail area experienced stress concentration leading to crack initiation. Major concerns for the power industry are determining the critical locations with one side and fracture mechanics parameters with the other side. For determination of the critical locations in LP turbine rotor disc conventional finite elements are used here. For this initial crack length and during crack growth it is necessary to determine SIFs. In fatigue crack growth process it is necessary to have analytic formulas for the stress intensity factor. To determine analytic formula for stress intensity factor (SIF) of cracked turbine rotor disc special singular finite elements are used. Using discrete values of SIFs which correspond to various crack lengths analytic formula of SIF in polynomial forms is derived here. For determination of SIF in this paper, combined J-integral approach and singular finite elements are used. The interaction of mechanical and thermal effects was correlated in terms of the fracture toughness