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

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

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

First Report of Tritrophic Relationships among Soft Scale Physokermes hemicryphus (Dalman, 1826) (Hemiptera), Polyembryonic Parasitoid Pseudorhopus testaceus (Ratzeburg, 1848) (Hymenoptera) and the Predator Anthribus nebulosus Forster, 1770 (Coleoptera)

The tritrophic relationships among the soft scale Physokermes hemicryphus (Dalman, 1826) (Hemiptera), the polyembryonic parasitoid Pseudorhopus testaceus (Ratzeburg, 1848) (Hymenoptera) and the predator Anthribus nebulosus Forster, 1770 (Coleoptera) is documented and reported for the first time. In Belgrade region (Serbia), in scale insects P. hemicryphus, the simultaneous presence of P. testaceus parasitoid larvae and A. nebulosus larvae has been registered. Larvae of A. nebulosus, apart from scales' eggs, also feed on larvae of parasitoids P. testaceus. Competitive interactions between these two species, which are natural enemies of P. hemicryphus, have not been known until now

Design of mold for helicopter composite rotor blade

This paper shows CAD/CAM programming 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 and Pro/Emgineer’s tools were used. For chosen mold segment, machining has been done on machining center