91 research outputs found
Optimization of wind farm layout
U radu je predstavljen metod odreÄivanja optimalnih položaja vetrogeneratora u okviru farme, postavljene na terenu proizvoljne orografije. Optimalni položaji pojedinaÄnih vetrogeneratora su odreÄeni tako da se postigne njihova maksimalna efikasnost. Metod je zasnovan na genetskom algoritmu kao optimizacionoj tehnici. AerodinamiÄki proraÄun vetrogeneratora je izveden na nestacionarnom potencijalnom strujnom polju. Lopatice vetrogeneratora su modelirane kao vrtložne povrÅ”ine, a vrtložni trag je modeliran upotrebom 'freewake' metode. Optimizacioni model je razvijen za dve funkcije cilja. Obe funkcije koriste ukupnu energiju dobijenu iz farme kao jednu od kljuÄnih promenljivih. Druga funkcija cilja ukljuÄuje i ukupno ulaganje u svaku pojedinaÄnu turbinu, tako da optimizacioni proces ukljuÄuje i ukupan broj vetrogeneratora kao promenljivu. Metod je testiran na nekoliko proizvoljnih konfiguracija terena, pri Äemu je posebna pažnja posveÄena izboru parametara genetskog algoritma, kako bi se postigle povoljne performanse optimizacionog procesa.This paper presents a method for determination of optimum positions of single wind turbines within the wind farms installed on arbitrary configured terrains, in order to achieve their maximum production effectiveness. This method is based on use of the genetic algorithm as optimization technique. The wind turbine aerodynamic calculation is unsteady, based on the blade modeled as a vortex lattice and a free-wake type airflow behind the blade. Optimization method is developed for two different fitness functions. Both functions use the total energy obtained from the farm as one of the key variables. The second also involves the total investments in a single wind turbine, so the optimization process can also include the total number of turbines as an additional variable. The method has been tested on several different terrain configurations, with special attention paid to the overall algorithm performance improvements by selecting certain genetic algorithm parameters
Dielectric properties modeling of composite materials
Komponovanje materijala sa aspekta dielektriÄnih karakteristika je postalo veoma važno u cilju zadovoljenja celokupnih zahteva konstrukcija, naroÄito kod problema koji se tiÄu prostiranja radio talasa kroz razliÄite sredine. Kompozitni materijali na bazi polimernih matrica predstavljaju odliÄne kandidate za ovakve primene. U ovom radu predstavljen je model dielektriÄnih osobina kompozitnog materijala, na osnovu kojeg je moguÄe predvideti vrednosti dielektriÄne konstante i dielektriÄnih gubitaka kompozitnog materijala polazeÄi od dielektriÄnih karakteristika faza koje saÄinjavaju kompozitni sistem. U eksperimentalnom delu rada, izmerene su dielektriÄne karakteristike kompozitnog materijala na bazi epoksidne matrice sa staklenim vlaknima, razliÄitog volumetrijskog odnosa i rezultati uporeÄeni sa rezultatima predloženog modela. Sva ispitivanja izvedena su u frekventnom opsegu od 100 kHz do 1 MHz.Tailoring dielectric properties of engineering materials has become very important since many radio wave propagation problems and remote sensing applications depend on correct values of these material properties. Prediction of material dielectric constant and loss tangent is of paramount importance. Polymer matrix composite materials are excellent candidates for these applications. In this paper analytical method for material dielectric constant and loss tangent prediction is presented. The model is experimentally verified for E-glass fibers embedded in epoxy matrix. Test results for 100 kHz to 1 MHz frequency range are presented
Extended finite element method (xfem) applied to aircraft duralumin spar fatigue life estimation
In the present work, duralumin aircraft spar fatigue life is evaluated by extended finite element method (XFEM) under cyclic loading condition. The effect of the crack growth on the fatigue life of aircraft spar is discussed in detail. The values of stress intensity factors (SIFs) are extracted from the XFEM solution. Standard Paris fatigue crack growth law (currently, the only one incorporated in Abaqus) is used for the fatigue life estimation. Obtained results are compared with previously obtained experimental results
Aerodynamic shape optimization of guided missile based on wind tunnel testing and computational fluid dynamics simulation
This paper presents modcation of the existing guided missile which was done by replacing the existing front part with the new five, while the rear part of the missile with rocket motor and missile thrust vector control system remains the same. The shape of all improved front parts is completely different from the original one. Modification was performed based on required aerodynamic coefficients for the existing guided missile. The preliminary aerodynamic configurations of the improved missile front parts were designed based on theoretical and computational fluid dynamics simulations. All aerodynamic configurations were tested in the T-35 wind tunnel at the Military Technical Institute in order to determine the final geometry of the new front parts. The 3-D Reynolds averaged Navier-Stokes numerical simulations were carried out to predict the aerodynamic loads of the missile based on the finite volume method. Experimental results of the axial force, normal force, and pitching moment coefficients are presented. The computational results of the aerodynamic loads of a guided missile model are also given, and agreed well with
Numerical modeling of Nomex honeycomb core composite plates at meso scale level
Kompozitne ploÄe sa saÄastom ispunom se sve viÅ”e koriste pri izradi primarnih vazduhoplovnih struktura. Ovi materijali koriste se pri konstrukciji oplata trupova letelica, centralnih i spoljnih torzionih kutija krila, oplata pogonskih grupa, vrata stajnih trapova, komandnih povrÅ”ina kao Å”to su spojleri i eleroni. Da bi se odredila polja napona i deformacija optereÄene strukture neophodno je poznavanje svih elastiÄnih koeficijenata. U ovom radu, metod za odreÄivanje svih potrebnih elastiÄnih koeficijenata ispune i ploÄa je predstavljen. KoristeÄi se eksperimentalno dobijenim rezultatima za papir NOMEH (tip 410 ) kao i fenolnu matricu materijalni model je predstavljen, izraÄen je model konaÄnih elemenata kompozitne ploÄe sa saÄastom ispunom i numeriÄki je simuliran test savijanja u tri taÄke. Dobijeni rezultati uporeÄeni su sa rezultatima dobijenim eksperimentom. PrimeÄeno je dobro slaganje izmeÄu predloženog modela materijala i eksperimentalno dobijenih vrednosti.Honeycomb core composite plates are becoming more important in the construction of primary aerospace structures. Nowadays, these types of materials are used for construction of fuselage skins, central and outer wing boxes, engine tail cones, landing gear doors, command surfaces like spoilers and ailerons etc. To determine the stress strain field in loaded honeycomb plates elastic coefficients are required. In the present work, a method for determining all required elastic coefficients for the core and plates is presented. Using experimentally obtained values for Nomex paper (type 410) and phenolic resin material model is presented and FEA model of composite plate with honeycomb core is created and three point bend test is simulated. Numerically obtained stress and strain values are compared to the experiment. Good agreement between proposed material model and experimentally obtained values is observed
Dynamic analysis of modified composite helicopter blade
U ovom radu izvrÅ”ena je modalna analiza modifikovane lopatice helikoptera 'Gazela'. Modifikovana lopatica je kompletno kompozitna sa saÄastom ispunom. Prikazan je metod odreÄivanja modova oscilovanja i sopstvenih frekvencija. Modifikovana lopatica sastoji se od saÄaste ispune, ramenjaÄe od 3D usmerenog kompozita i tankih karbonskih ploÄa kao oplate. Da bi se odredila matrica krutosti ispune koriÅ”Äen je metod ekvivalentnih masa. U cilju nalaženja optimalnog metoda za odreÄivanje sopstvenih frekvencija ispitano je nekoliko poznatih metoda. Metod Lancosa pokazao je najtaÄnije rezultate kroz umereno procesorsko vreme kada je u pitanju odreÄivanje sopstvenih frekvencija i modova oscilovanja kod struktura od kompozitnih materijala sa saÄastim ispunama. Ovom metodom izraÄunata su prva Äetiri moda oscilovanja modifikovane kompozitne lopatice, i prikazani su rezultati modova oscilovanja i deformacione energije lopatice.In the present study, modal analysis has been performed on modified Gazelle helicopter blade. The construction of the blade is fully composite with the honeycomb core. The approach to determining structure mode shapes and natural frequencies is presented. Modified blade consists of core material, 3D unidirectional composite spar and thin carbon composite facesheets as blade skin. To determine the stiffness of the honeycomb core, the equivalent mass approach was used. Several methods of eigenvalue extraction have been investigated in order to find optimal method which can be used in dynamic analysis of composite structures containing honeycomb cores. Among all extraction methods investigated, it was found that combined Lanczos method is most effective in terms of accuracy and CPU time for eigenvalue extraction in composite structures with honeycomb core having large number of degrees of freedom. Strain energies for first four mode shapes of modified helicopter blade have been calculated using numerical approach and results are presented
Dynamic analysis of modified composite helicopter blade
U ovom radu izvrÅ”ena je modalna analiza modifikovane lopatice helikoptera 'Gazela'. Modifikovana lopatica je kompletno kompozitna sa saÄastom ispunom. Prikazan je metod odreÄivanja modova oscilovanja i sopstvenih frekvencija. Modifikovana lopatica sastoji se od saÄaste ispune, ramenjaÄe od 3D usmerenog kompozita i tankih karbonskih ploÄa kao oplate. Da bi se odredila matrica krutosti ispune koriÅ”Äen je metod ekvivalentnih masa. U cilju nalaženja optimalnog metoda za odreÄivanje sopstvenih frekvencija ispitano je nekoliko poznatih metoda. Metod Lancosa pokazao je najtaÄnije rezultate kroz umereno procesorsko vreme kada je u pitanju odreÄivanje sopstvenih frekvencija i modova oscilovanja kod struktura od kompozitnih materijala sa saÄastim ispunama. Ovom metodom izraÄunata su prva Äetiri moda oscilovanja modifikovane kompozitne lopatice, i prikazani su rezultati modova oscilovanja i deformacione energije lopatice.In the present study, modal analysis has been performed on modified Gazelle helicopter blade. The construction of the blade is fully composite with the honeycomb core. The approach to determining structure mode shapes and natural frequencies is presented. Modified blade consists of core material, 3D unidirectional composite spar and thin carbon composite facesheets as blade skin. To determine the stiffness of the honeycomb core, the equivalent mass approach was used. Several methods of eigenvalue extraction have been investigated in order to find optimal method which can be used in dynamic analysis of composite structures containing honeycomb cores. Among all extraction methods investigated, it was found that combined Lanczos method is most effective in terms of accuracy and CPU time for eigenvalue extraction in composite structures with honeycomb core having large number of degrees of freedom. Strain energies for first four mode shapes of modified helicopter blade have been calculated using numerical approach and results are presented
Conceptual Design and Flight Envelopes of a Light Aircraft for Mars Atmosphere
In this paper is presented a new conceptual design of the light aircraft for Mars atmosphere, ALPEMA. It allows atmospheric dropping (aeroshell), as well as direct take-off from Martian surface. Complex atmosphere demanded for simplified yet efficient wing geometry, capable of maximizing Lift-to-Drag ratio. Martian atmospheric pressure, density, temperature and speed of sound variations, demand a scrutinized powerplant choice. Efficient aspect ratio and drag polar lead to optimal flight envelopes as a proof of sustainability of ALPEMA project. Special performances and basic aerodynamics provide boundaries and constraints of the project, in line with similar approaches. Chosen propeller allows for ALPEMA to use maximum power capabilities of its engine, described through Vmin and Vmax, which are significant inputs for flight envelope. Envelope provides effective width and profile for a variety of possible missions. ALPEMAās specific propeller and engine are a certain comparative advantage, together with its flight envelope
Analytical and numerical method of velocity fields for the explosively formed projectiles
Ovaj rad predstavlja analitiÄki i numeriÄki pristup procenu performansi brzine za Eksplozivno Formirane Projektile (EFP). Predložene analitiÄke metode matematiÄki razvijaju parametre brzina pojedinaÄnih segmenata za EFP disk pogonjen eksplozivnim procesom. Ovaj model baziran je na dobro poznatim teorijskim pristupima distribucije energije na plastiÄnim telima u dinamiÄkim uslovima formiranjem integralnih reÅ”enja za konaÄnu brzinu projektila. Paralelno sa analitiÄkim takoÄe je razvijen i numeriÄki metod u cilju obezbeÄenja procene ponaÅ”anje projktila u toku vrmena procesa formiranja EFP-a pogonjenog eksplozivom. Oba modela su validna za procenu performansi EFP bojevih glava i projektnih podatka za optimalno projektivanje oblika EFP-a. Simulacije su podržane softverima Matlob i Autodin kako za ananlitiÄko tako i numeriÄko modeliranje. Dobijeni numeriÄki i analitiÄki rezultati uporeÄeni su sa raspoloživivim eksperimentalnim rezultatima. PR Projekat Ministarstva nauke Republike Srbije, br. III-47029.The current paper presents analytical and numerical approaches of velocity performances estimations for the EFP (Explosively Formed Projectiles). The proposed analytical methods mathematically develop velocities parameters of a particular segment for EFP liner propelled by explosive process. This model is based on the well-known theoretical approaches of energy distribution on plastic body in dynamical conditions providing integral solution for projectile final velocity. The redundant to analytical, the numerical method is also developed, to provides estimations about behavior of projectile vs. time in the EFP forming process powered by explosion. Both models are valid for performances estimations of EFP warheads and design data for optimal EFP configuration. Simulations are supported by the software Matlab and Autodyn for analytical and numerical modeling respectively. The obtained numerical and analytical results are compared with the available experimental data
Analytical and numerical method of velocity fields for the explosively formed projectiles
Ovaj rad predstavlja analitiÄki i numeriÄki pristup procenu performansi brzine za Eksplozivno Formirane Projektile (EFP). Predložene analitiÄke metode matematiÄki razvijaju parametre brzina pojedinaÄnih segmenata za EFP disk pogonjen eksplozivnim procesom. Ovaj model baziran je na dobro poznatim teorijskim pristupima distribucije energije na plastiÄnim telima u dinamiÄkim uslovima formiranjem integralnih reÅ”enja za konaÄnu brzinu projektila. Paralelno sa analitiÄkim takoÄe je razvijen i numeriÄki metod u cilju obezbeÄenja procene ponaÅ”anje projktila u toku vrmena procesa formiranja EFP-a pogonjenog eksplozivom. Oba modela su validna za procenu performansi EFP bojevih glava i projektnih podatka za optimalno projektivanje oblika EFP-a. Simulacije su podržane softverima Matlob i Autodin kako za ananlitiÄko tako i numeriÄko modeliranje. Dobijeni numeriÄki i analitiÄki rezultati uporeÄeni su sa raspoloživivim eksperimentalnim rezultatima. PR Projekat Ministarstva nauke Republike Srbije, br. III-47029.The current paper presents analytical and numerical approaches of velocity performances estimations for the EFP (Explosively Formed Projectiles). The proposed analytical methods mathematically develop velocities parameters of a particular segment for EFP liner propelled by explosive process. This model is based on the well-known theoretical approaches of energy distribution on plastic body in dynamical conditions providing integral solution for projectile final velocity. The redundant to analytical, the numerical method is also developed, to provides estimations about behavior of projectile vs. time in the EFP forming process powered by explosion. Both models are valid for performances estimations of EFP warheads and design data for optimal EFP configuration. Simulations are supported by the software Matlab and Autodyn for analytical and numerical modeling respectively. The obtained numerical and analytical results are compared with the available experimental data
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