Comparison of novel variable area convergent-divergent nozzle performances obtained by analytic, computational and experimental methods

Different applications of a variable area convergent-divergent nozzle are found in various parts of the industry. This paper presents the development of a new design methodology for a variable area convergent-divergent nozzle, to maintain constant nozzle area ratio for different values of mass flow rates. The validation of the presented model was carried out on an example supersonic ejector using experimental, numerical and analytical data. Analytical (one dimensional) and computational fluid dynamics models showed satisfactory prediction performance in comparison with the experiment. The average entrainment ratio error was between 10% and 7%, respectively. Results confirmed that the velocity of the primary fluid at the nozzle outlet is in accordance with the one dimensional analysis. Although disturbances (strong and weak shock waves) are visible, their effects are negligible. Also, supersonic ejector performances are presented through relations between entrainment ratio, outlet pressure and spindle position. Disadvantages of variable area nozzle utilization in ejector applications are emphasized

Comparison of novel variable area convergent-divergent nozzle performances obtained by analytic, computational and experimental methods

Different applications of a variable area convergent-divergent nozzle are found in various parts of the industry. This paper presents the development of a new design methodology for a variable area convergent-divergent nozzle, to maintain constant nozzle area ratio for different values of mass flow rates. The validation of the presented model was carried out on an example supersonic ejector using experimental, numerical and analytical data. Analytical (one dimensional) and computational fluid dynamics models showed satisfactory prediction performance in comparison with the experiment. The average entrainment ratio error was between 10% and 7%, respectively. Results confirmed that the velocity of the primary fluid at the nozzle outlet is in accordance with the one dimensional analysis. Although disturbances (strong and weak shock waves) are visible, their effects are negligible. Also, supersonic ejector performances are presented through relations between entrainment ratio, outlet pressure and spindle position. Disadvantages of variable area nozzle utilization in ejector applications are emphasized

Ethnic Stereotypes in the Discourse of Former-Yugoslav TV and Cinema

This paper is an attempt to analyze particular scenes from the TV series “Složna braća” and “Crni Gruja” and the film “Balcancan” for the purpose of surveying the featured stereotypical representations of former-Yugoslav ethnicities, identifying their roles within the said examples of film and TV discourse, and proving that familiarity with the discursive practices of these particular cultures (discourse communities) is essential for interpreting these artistic discourses (texts) in the manner intended by their authors. Ethnic stereotypes are, therefore, discussed as socio-cultural constructs or myths generated by the discursive practices of a particular culture, as, it is discourses that “bring cultural objects into being by naming them, defining them and delimiting their field of operation” (Stam, Burgoyne and Flitterman-Lewis 2005: 216). They are also viewed as part of a larger structure – a discursive universe comprised of interrelated mythical texts (Johansen and Larsen 2002: 55–56) shaped by former-Yugoslav discourse communities. For this reason, the mentioned texts will be analyzed as sharing the said discursive universe

Mathematical-geographical analysis of the orientation of St John’s church of the Studenica monastery

Considering the fact that ecclesiastical rules do not precisely say that a church must be directed “to the East” or “to sunrise”, it should always be checked if there is a connection between the orientation of a church and geometry of the Sun. In this paper, such examination is performed on the example of the church of St. John (the 13th century), one of four churches of the Studenica monastery, in the following way: 1) using gnomon method, the azimuth of the main longitudinal axis of the church is measured; 2) the altitude above the horizon of the point in which the extended axis of the church touches the true horizon is determined by cartometry; 3) the most probable dates when the Sun rises at that point are determined: May 7th according to Gregorian calendar, or April 30th according to Julian calendar, in the 13th century. The applied method is described in details and it can be applied for the analysis of the orientation of any other medieval church. This method can determine the time when the church was founded, as well as the fact if the church is original, or possibly erected on the foundations of some older sacral object

Modelling, simulation and control of desalination plant with a liquid jet ejector

U radu je prikazan metod modelovanja, simulacije i upravljanja postrojenja za desalinizaciju vode. Postrojenje za desalinizaciju vode spada u klasu postrojenja koje uparavaju slanu vodu korićenjem vodeno-parnog ejektora. U cilju validacije rezultata simulacije dinamičkog modela, razvijenog u cilju upravljanja, rezultati stacionarne simulacije postrojenja su korišćeni. Dodatno razvijen je PI kontroler koji dovodi sistem do željenih stanja pri uticaju poremećaja. Linearizovani model postrojenja je verfikovan pomoću nelinearnog dinamičkog modela. Pokazano je da navedeni pristup daje zadovoljavajuće rezultate.In this paper, modelling, simulation and control of water desalination plant is presented. The desalination plant is based on vapour compression method acquired utilizing a liquid jet ejector. Nonlinear steady-state model is developed in order to verify simplified dynamic model for control purposes. Furthermore, to design PI controller capable of guiding the system through desired states under the influence of disturbances, the linearized model of the plant has been developed and verified applying the nonlinear dynamical model. It is shown that presented approach can deliver satisfying model and tracking results

Fem analysis of pressure vessel with an investigation of crack growth on cylindrical surface

To ensure reliability of pressure vessels during service it is necessary to (1) know properties of materials used in their design and (2) evaluate vessels' behaviour under different working conditions with satisfying accuracy. Due to various technical and/or technological requirements, nozzles are usually welded on vessel's shell producing geometrical discontinuities that reduce the safety factor. To evaluate their influence, vessels with two different nozzles were experimentally studied and critical areas for crack initiation have been identified by 3D Digital Image Correlation (DIC) method. After that, the numerical analysis of equivalent 3D finite element model was performed and obtained results were compared with experimental values. In the most critical area, next to the one of the nozzles, crack was initiated and then growth of the damage was simulated using extended finite element method (XFEM). In this paper evaluation of stress intensity factors (SIFs) along crack path is presented, as well as the most probable direction of the crack propagation on the shell. Based on SIFs values, critical length of the crack and number of pressure cycles to the final failure were estimated

Large canyons in Dinaric and Prokletije mountains region of Montenegro

Montenegro occupies relatively small, southeastern part of the Dinaric mountains. Geological composition, which is predominantly carbonate, enabled formation of a great number of deep canyons and gorges. Canyons of Montenegro were formed in several ways, during multiple phases. Regardless of polygenetic and polymorphic character of the canyons, they can be classified into three main groups. By incision of melt-water rivers of Pleistocene glaciers, deep and particularly narrow canyons of small width were formed. The rivers that presently flow through these canyons have a nival regime - during the summer, their discharge is minimal, or they completely dry out. Depths of these canyons are up to 500 m. Rivers that directly feed into the Adriatic sea are of torrential character. They have pluvial regime, and dry out during the summer. Their canyons are short, several hundreds of meters deep. Deepest and longest canyons have been formed by incision of rivers that have changed their regimes during a longer period of time. Melt-water of Pleistocene glaciers has incised the greatest parts of canyons at the beginning of Holocene. Presently, river courses have nival-pluvial regime. In this group, single-phase and multiple-phase canyons can be distinguished (alteration of erosional and accumulation processes). Depths of these canyons exceed 1000 m

Mathematical-geographical analysis of the orientation of St John's church of the Studenica monastery

Considering the fact that ecclesiastical rules do not precisely say that a church must be directed 'to the East' or 'to sunrise', it should always be checked if there is a connection between the orientation of a church and geometry of the Sun. In this paper, such examination is performed on the example of the church of St. John (the 13th century), one of four churches of the Studenica monastery, in the following way: 1) using gnomon method, the azimuth of the main longitudinal axis of the church is measured; 2) the altitude above the horizon of the point in which the extended axis of the church touches the true horizon is determined by cartometry; 3) the most probable dates when the Sun rises at that point are determined: May 7th according to Gregorian calendar, or April 30th according to Julian calendar, in the 13th century. The applied method is described in details and it can be applied for the analysis of the orientation of any other medieval church. This method can determine the time when the church was founded, as well as the fact if the church is original, or possibly erected on the foundations of some older sacral object

The cycles of revolution: how Wegener and Milanković changed the earth sciences

The year 1912 is annus mirabilis for Earth sciences. In two crucial papers Alfred Wegener and Milutin Milanković independently set up revolutionary theories based on far-reaching visions of continental drift and climate orbital forcing. Their contributions simultaneously did for the Earth sciences what the theory of evolution did for biology and what the theory of relativity did for physics. They provided Earth sciences with a comprehensive perspective of Earth’s dynamics in both astronomical and terrestrial terms, and revolutionized geology by abandoning the ideas of a climatologically self-sufficient Earth and unmovable continents – remnants of the old geocentric picture of the unmoving, centered Earth. In the secular sense they finally completed the heliocentric theory that was set up by Copernicus. This paper follows the strange synchronicity in their life and work cycles

Chemometric characterization of the hydrogen bonding complexes of secondary amides and aromatic hydrocarbons

The paper reports the results of the study of hydrogen bonding complexes between secondary amides and various aromatic hydrocarbons. The possibility of using chemometric methods was investigated in order to characterize N-H•••π hydrogen bonded complexes. Hierarchical clustering and Principal Component Analysis (PCA) have been applied on infrared spectroscopic and Taft parameters of 43 N-substituted amide complexes with different aromatic hydrocarbons. Results obtained in this report are in good agreement with conclusions of other spectroscopic and thermodynamic analysis