Multi-body kinematics and dynamics in terms of quaternions: Langrange formulation in covariant form: Rodriguez approach

U ovom radu se predlaže kvaternionski pristup za modeliranje kinematike i dinamike sistema krutih tela. Umesto regularnog 'Njutn-Ojlerovog' i Lagranževog metoda korišćenog na tradicionalan način, upotrebljavaju se Lagranževe jednačine druge vrste u kovarijantnom obliku primenom Rodrigovog pristupa i kvaternionske algebre. Dobijen je model sistema od n krutih tela u kvaternionskoj formi koji je koristan za proučavanje kinematike, dinamike sistema za opšti slučaj kretanja, kao i za sintezu sistema upravljanja.This paper suggests a quaternion approach for the modeling kinematics and dynamics of rigid multi-body systems. Instead of the regular 'Newton-Euler' and Lagrange method used in the traditional way, Lagrange's equations of second kind in the covariant form are used by applying Rodriguez approach and quaternion algebra. A model of multi-body system of n rigid bodies in terms of quaternions is obtained, which is useful for studying kinematics, dynamics as well as for research of control system designs

Stress distribution as a cause of industrial steel chimney root section failure

Ovaj rad razmatra iniciranje otkaza korene sekcije industrijskog čeličnog dimnjaka visine 60 m. Prsline nastale u čeličnoj strukturi spoljašnjeg plašta dimnjaka značajno su uticale na integritet strukture. Izvršena je analitička i numerička analiza pojave prslina. Analiza metodom konačnih elemenata ukazala je na postojanje zona sa visokom koncentracijom napona. Identifikovane zone poklopile su se sa mestima na kojima je došlo do iniciranja prslina. Rezultati analize razjasnili su uzroke otkaza i omogućili izradu programa sanacije i dalje mere održavanja dimnjaka.This paper has studied failure initiation of the root section of 60 m tall industrial steel chimney. Cracks that occurred in steel wall of the wind shield have significantly influenced integrity of the structure. Analytical and numerical analysis of failure occurrence was performed. Location of extreme stress values in the steel structure were identified numerically by finite element method. Identified locations coincided with the location of the cracks initiation. The results of analysis identified causes of the failure initiation and allowed expression of the recommendation for root redesign and further maintenance procedures

Stress distribution as a cause of industrial steel chimney root section failure

Ovaj rad razmatra iniciranje otkaza korene sekcije industrijskog čeličnog dimnjaka visine 60 m. Prsline nastale u čeličnoj strukturi spoljašnjeg plašta dimnjaka značajno su uticale na integritet strukture. Izvršena je analitička i numerička analiza pojave prslina. Analiza metodom konačnih elemenata ukazala je na postojanje zona sa visokom koncentracijom napona. Identifikovane zone poklopile su se sa mestima na kojima je došlo do iniciranja prslina. Rezultati analize razjasnili su uzroke otkaza i omogućili izradu programa sanacije i dalje mere održavanja dimnjaka.This paper has studied failure initiation of the root section of 60 m tall industrial steel chimney. Cracks that occurred in steel wall of the wind shield have significantly influenced integrity of the structure. Analytical and numerical analysis of failure occurrence was performed. Location of extreme stress values in the steel structure were identified numerically by finite element method. Identified locations coincided with the location of the cracks initiation. The results of analysis identified causes of the failure initiation and allowed expression of the recommendation for root redesign and further maintenance procedures

Measurement and analysis of vibrations on the helicopter structure in order to detect defects of operating elements

U radu je prezentovan praktičan primer merenja i analize vibracija na helikopterskoj strukturi sa ciljem da se otkriju potencijalna oštećenja radnih elemenata. Sveobuhvatna metodologija merenja vibracija je predstavljena u ovom članku i sprovedena sa ciljem da se utvrdi ispravan rad rotirajućih komponenata. Poseban osvrt je dat na analizi uzdužnih i vertikalnih vibracija trupa helikoptera u frekventnom domenu za različite profile leta. Merenje i analiza vibracija na određenim lokacijama helikopterske strukture, rezultiralo je blagovremenim tehničkim pregledom odgovarajuće komponente i otkrivanjem njenog površinskog oštećenja. Praktična upotreba predložene metodologije merenja i analize je moguće implementirati na više vrsta letelica u cilju produženja životnog veka.A practical example of the measurement and analysis of vibrations on helicopter structures in order to detect defects on operating elements is presented in this paper. A comprehensive methodology of vibration testing is presented in this article and implemented in order to determine the correct operation of rotating components. A particular attention is given to the analysis of longitudinal and vertical vibrations on the helicopter fuselage in the frequency domain for different flight profiles. The vibration measurement and analysis on specific locations on a helicopter structure resulted in a timely technical review of a relevant component and a disclosure of the damage on its surface. The proposed methodology of measurement and analysis can be implemented on different types of aircraft in order to extend their life expectancy.

Measurement and analysis of vibrations on the helicopter structure in order to detect defects of operating elements

U radu je prezentovan praktičan primer merenja i analize vibracija na helikopterskoj strukturi sa ciljem da se otkriju potencijalna oštećenja radnih elemenata. Sveobuhvatna metodologija merenja vibracija je predstavljena u ovom članku i sprovedena sa ciljem da se utvrdi ispravan rad rotirajućih komponenata. Poseban osvrt je dat na analizi uzdužnih i vertikalnih vibracija trupa helikoptera u frekventnom domenu za različite profile leta. Merenje i analiza vibracija na određenim lokacijama helikopterske strukture, rezultiralo je blagovremenim tehničkim pregledom odgovarajuće komponente i otkrivanjem njenog površinskog oštećenja. Praktična upotreba predložene metodologije merenja i analize je moguće implementirati na više vrsta letelica u cilju produženja životnog veka.A practical example of the measurement and analysis of vibrations on helicopter structures in order to detect defects on operating elements is presented in this paper. A comprehensive methodology of vibration testing is presented in this article and implemented in order to determine the correct operation of rotating components. A particular attention is given to the analysis of longitudinal and vertical vibrations on the helicopter fuselage in the frequency domain for different flight profiles. The vibration measurement and analysis on specific locations on a helicopter structure resulted in a timely technical review of a relevant component and a disclosure of the damage on its surface. The proposed methodology of measurement and analysis can be implemented on different types of aircraft in order to extend their life expectancy.

Comparative analysis of numerical computational techniques for determination of the wind turbine aerodynamic performances

The purpose of this paper is to explore and define an adequate numerical setting for the computation of aerodynamic performances of wind turbines of various shapes and sizes, which offers the possibility of choosing a suitable approach of minimal complexity for the future research. Here, mechanical power, thrust, power coefficient, thrust coefficient, pressure coefficient, pressure distribution along the blade, relative velocity contoure, at different wind speeds and streamlines were considered by two different methods: the blade element momentum and CFD, within which three different turbulence models were analyzed. The estimation of the mentioned aerodynamic performances was carried out on two different wind turbine blades. The obtained solutions were compared with the experimental and nominal (up-scaled) values, available in the literature. Although the flow was considered as steady, a satisfactory correlation between numerical and experimental results was achieved. The comparison between results also showed, the significance of selection, regarding the complexity and geometry of the analyzed wind turbine blade, the most appropriate numerical approach for computation of aerodynamic performances

CAD/CAM of mold for helicopter rotor composite blade

U radu se predstavlja programiranje primenom CAD/CAM sistema, udubljenja u kalupu za lopaticu glavnog rotora helikoptera. Pri proizvodnji ovakvih lopatica neophodno je postići visoku geometrijsku tačnost. Zbog velikih dimenzija duž jedne ose za izradu je planiran segmentni kalup. U radu je pokazana procedura programiranja za jedan takav segment kalupa. Ostvarena je simulacija putanje alata, dobijanje APT i NC koda kao i verifikacija putanje simulacijom uklanjanja materijala. Za realizaciju je korišćeno okruženje progama CATIA V5.This paper shows CAD/CAM technique of mold recess for helicopter main rotor blade. It is necessary to achieve high precision in this process. Due to the dimensions along one of the blade axis, the segmented mold is found necessary. In this paper the programming procedure is shown for one of these mold segments. The tool path simulation is shown as well as producing of APT and NC code with the verification of material removal. For realization of these processes CATIA’s tools were used.Tehnički urednici: Prof. dr Ljubodrag Tanović, Doc. dr Radovan Puzović, Mr Mihajlo Popović, Mr Goran Slavković Nenad Nešić, dipl. maš. ing

Buckling behaviour of dented aluminium alloy cylindrical shell subjected to uniform axial compression

Tankozide cilindrične strukture imaju veoma visoku primenu u industriji. Pošto su obično opterećene na aksijalni pritisak, najčešći uzrok njihovog otkaza je pojava izvijanja. U ovom članku se prikazuje numerička analiza izvijanja tankozide cilindrične strukture izrađene od legure aluminijuma sa imperfekcijom u vidu udubljenja na sredini strukture i eksperimentalna verifikacija rezultata dobijenih tom analizom. Numerička analiza je odrađena pomoću softvera ANSYS 16.2, a eksperimentalna ispitivanja pomoću hidraulične prese Armavir, PSU-50, na kojoj je uzorak podvrgnut aksijalnom pritisku čiji se intenzitet postepeno povećavao do pojave izvijanja. Poređenjem rezultata eksperimenta uočeno je značajno smanjenje vrednosti kritičnog napona na izvijanje između epruveta bez imperfekcije i epruveta sa imperfekcijom od 2 mm, dok su vrednosti kritičnog napona za epruvete sa imperfekcijama od 2 mm i 4 mm približne.Thin-walled cylindrical shells are commonly used in numerous branches of industry. Since they are subjected to axial load, the most common cause of their failure is buckling. This paper provides numerical analysis and experimental verification of the buckling of the thin-walled aluminium alloy cylindrical shell with special regard to the influence of dent, positioned in the middle of the shell. Numerical simulation was performed using ANSYS 16.2, and experimental verification was performed by means of hydraulic press Armavir, PSU-50, which was used to subject the specimen to the increasing axial load until the occurrence of buckling. Comparing the results it was concluded that there is significant decrease of the buckling resistance if compared the values of the specimen with no dent, and the specimen with 2 mm deep dent. On the contrary, resistance of the 2 mm and 4 mm dented specimen is quite similar. Position and shape of the deformations occurred due to buckling are matching if experimental and numerical results are compared

VAWT optimization using genetic algorithm and CST airfoil parameterization

Vetroturbina sa vertikalnom osom Dareiusovog tipa optimizovana je primenom genetskih algoritama (GA). Oblik aeroprofila parametrizovan je pomoću Klasa-Oblik transformacionog (CST) metoda. Metod dvojne višestrujne cevi sa Gormont modifikacijom za dinamički slom uzgona je kori-ćen za određivanje performansi vetroturbine sa vertikalnom osom. Kad su numerički kodovi validirani sa dostupnim eksperimentalnim rezultatima, parametri aeroprofila su varirani kako bi se postigla optimalna vrednost funkcije cilja genetskog algoritma. PR Projekat Ministarstva nauke Republike Srbije, br. 35035.Darrieus type vertical axis wind turbine (VAWT) is optimized using the genetic algorithm (GA). The airfoil shape is parameterized using the Class-Shape Transformation (CST) method. The double multiple stream tube (DMST) method with the Gormont dynamic stall modification is used for the calculation of the VAWT performance parameters. Once the numerical codes are validated using available experimental results, the airfoil parameters are varied as to achieve the optimum value of the genetic algorithm fitness function

Symbiosis of intermodal terminals and free zones

Globalism is entering a new phase that creates space for regional investments. The trend of offshoring is beginning to weaken and trend of nearshoring investments are increasing. Jobs and new investments are returning to regions, neighboring countries and parent companies. The new course of development requires the need for spaces where investors will receive customs and tax benefits with a greater need for efficient logistics. Free zones, which offer facilities for investment and business, will have to pay more attention to efficient logistics. The benefits of infrastructure-equipped land, exemptions from paying customs duties and taxes with built-in capacities for intermodal transport, along with other state support measures, will additionally make certain locations attractive for investors. The paper proposed a model of symbiosis of logistics centers and free zones, as well as analyzed instruments that should be used in order to create efficient centers that enable savings in business for future investors