Optimization of wind farm layout

U radu je predstavljen metod određivanja optimalnih položaja vetrogeneratora u okviru farme, postavljene na terenu proizvoljne orografije. Optimalni položaji pojedinačnih vetrogeneratora su određeni tako da se postigne njihova maksimalna efikasnost. Metod je zasnovan na genetskom algoritmu kao optimizacionoj tehnici. Aerodinamički proračun vetrogeneratora je izveden na nestacionarnom potencijalnom strujnom polju. Lopatice vetrogeneratora su modelirane kao vrtložne površine, 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 ključnih promenljivih. Druga funkcija cilja uključuje i ukupno ulaganje u svaku pojedinačnu turbinu, tako da optimizacioni proces uključuje i ukupan broj vetrogeneratora kao promenljivu. Metod je testiran na nekoliko proizvoljnih konfiguracija terena, pri čemu je posebna pažnja posvećena 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 dielektričnih karakteristika je postalo veoma važno u cilju zadovoljenja celokupnih zahteva konstrukcija, naročito kod problema koji se tiču prostiranja radio talasa kroz različite sredine. Kompozitni materijali na bazi polimernih matrica predstavljaju odlične kandidate za ovakve primene. U ovom radu predstavljen je model dielektričnih osobina kompozitnog materijala, na osnovu kojeg je moguće predvideti vrednosti dielektrične konstante i dielektričnih gubitaka kompozitnog materijala polazeći od dielektričnih karakteristika faza koje sačinjavaju kompozitni sistem. U eksperimentalnom delu rada, izmerene su dielektrične karakteristike kompozitnog materijala na bazi epoksidne matrice sa staklenim vlaknima, različitog volumetrijskog odnosa i rezultati upoređeni 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

Dynamic analysis of modified composite helicopter blade

U ovom radu izvršena je modalna analiza modifikovane lopatice helikoptera 'Gazela'. Modifikovana lopatica je kompletno kompozitna sa saćastom ispunom. Prikazan je metod određivanja modova oscilovanja i sopstvenih frekvencija. Modifikovana lopatica sastoji se od saćaste ispune, ramenjače od 3D usmerenog kompozita i tankih karbonskih ploča kao oplate. Da bi se odredila matrica krutosti ispune korišćen je metod ekvivalentnih masa. U cilju nalaženja optimalnog metoda za određivanje sopstvenih frekvencija ispitano je nekoliko poznatih metoda. Metod Lancosa pokazao je najtačnije rezultate kroz umereno procesorsko vreme kada je u pitanju određivanje sopstvenih frekvencija i modova oscilovanja kod struktura od kompozitnih materijala sa saćastim ispunama. Ovom metodom izračunata su prva četiri 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 izvršena je modalna analiza modifikovane lopatice helikoptera 'Gazela'. Modifikovana lopatica je kompletno kompozitna sa saćastom ispunom. Prikazan je metod određivanja modova oscilovanja i sopstvenih frekvencija. Modifikovana lopatica sastoji se od saćaste ispune, ramenjače od 3D usmerenog kompozita i tankih karbonskih ploča kao oplate. Da bi se odredila matrica krutosti ispune korišćen je metod ekvivalentnih masa. U cilju nalaženja optimalnog metoda za određivanje sopstvenih frekvencija ispitano je nekoliko poznatih metoda. Metod Lancosa pokazao je najtačnije rezultate kroz umereno procesorsko vreme kada je u pitanju određivanje sopstvenih frekvencija i modova oscilovanja kod struktura od kompozitnih materijala sa saćastim ispunama. Ovom metodom izračunata su prva četiri 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. ALPEMA’s specific propeller and engine are a certain comparative advantage, together with its flight envelope

Numerical prediction of aerodynamic noise generated from missile for low Mach number flows

Rad predstavlja numeričko predviđanje aerodinamične buke koja se generira s projektila. Simulacija turbulentnog strujanja je urađena rješavanjem Navier-Stoksove jednadžbe za nestlačiv fluid, gde je turbulencija modelirana metodom orthogonalne podgrupne ljestvice (OSGS) s dinamičkim podljestvicama. Zbog usporedbe, ista simulacija je urađena i s metodom LES (Large Eddy Simulation). Pokazano je kako simulacija turbulentnog strujanja utječe na predviđanje akustičnih izvora koji su izračunati Lighthill analogijom. Translacija s vremenskog područja ka frekventnom području je urađena s DFT (Direct Fourier Transform), što dovodi do manje uporabe memorije. Akustični izvori su korišteni u nehomogenoj Helmholtz jednadžbi da bi se simuliralo širenje tlaka u područje. Pokazano je da ova metoda dovodi do bolje prezentacije spektra. Općenito, bolje predviđanje energetskog transfera između malih i velikih vrtloga dati će mogućnost bolje i snažnije prezentacije akustičnog izvora. Ovakvi izvori će promjeniti širenje vala u akustičnom polju.Paper describes numerical prediction of aerodynamic noise generated from the missile. Simulation of turbulent flow is done solving incompressible Navier-Stokes equation, where turbulence is modelled with the orthogonal subgrid scale (OSGS) method with dynamical subscales. Because of comparison, the same simulation is done using the LES (Large Eddy simulation). It is shown how simulation of turbulent flow affects the prediction of acoustic sources calculated using Lighthill\u27s analogy. Translation from time to frequency domain is done through DFT (Direct Fourier Transform), which gives smaller usage of memory. Acoustic sources are used in inhomogeneous Helmholtz equation to simulate pressure wave propagation in the domain. It is shown that OSGS with dynamical subscales gives better representation of the spectrum. Overall, better prediction of energy transfer across large and small eddies will give better allocation and presentation of acoustics sources. These sources will change wave propagation of the pressure in acoustic field

Review of impact damages modelling in laminated composite aircraft structures

Laminatni kompoziti imaju značajnu primjenu u suvremenim zrakoplovnim konstrukcijama. Oni imaju izvanredna svojstva, kao što su visoka čvrstoća, krutost i mala težina. Bez obzira na to, ozbiljna prepreka za mnogo širu uporabu ovih materijala je njihova osjetljivost na udarna opterećenja. Kao posljedica toga, u njima se pojavljuju inicijacija i razvoj udarnih oštećenja. Otkazi koji nastaju u laminatnim kompozitnim konstrukcijama mogu biti intralaminarni i interlaminarni. Do sada je razvijeno mnogo modela za udarna oštećenja u laminatima, s većom ili manjom točnošću. Ovi modeli mogu zamjeniti realna i skupa testiranja u laminatnim konstrukcijama, s izvjesnom aproksimacijom. Uporabom specijaliziranih softvera mogu se predvidjeti parametri oštećenja u laminatnim konstrukcijama letjelica (pri specifičnim uvjetima). Na taj način može se provesti numerička simulacija udara u određene laminate, a dobiveni rezultati ove simulacija mogu se predstaviti u obliku grafičkih distribucija oštećenja.Laminated composites have an important application in modern aeronautical structures. They have extraordinary properties, like high strength, stiffness and lightweight. Nevertheless, a serious obstacle to more widespread use of those materials is their sensitivity to impact loads. As a consequence of that, impact damage initiation and growth are appearing in them. Failures that occur in laminated composite structures can be intralaminar and interlaminar. To date a lot of models for impact damages in laminates have been developed with higher or lower accuracy. Those models can replace real and expensive testing in laminated structures with some approximation. By using specialized software the damage parameters in laminate aircraft structures can be predicted (at certain conditions). In that way numerical simulation of impact on certain laminates can be done and the obtained results from the simulations presented in a form of graphic damage distributions

Numerical modeling of Nomex honeycomb core composite plates at meso scale level

Kompozitne ploče sa saćastom ispunom se sve više 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 površina kao što su spojleri i eleroni. Da bi se odredila polja napona i deformacija opterećene strukture neophodno je poznavanje svih elastičnih koeficijenata. U ovom radu, metod za određivanje svih potrebnih elastičnih koeficijenata ispune i ploča je predstavljen. Koristeći se eksperimentalno dobijenim rezultatima za papir NOMEH (tip 410 ) kao i fenolnu matricu materijalni model je predstavljen, izrađen je model konačnih elemenata kompozitne ploče sa saćastom ispunom i numerički je simuliran test savijanja u tri tačke. Dobijeni rezultati upoređeni su sa rezultatima dobijenim eksperimentom. Primećeno je dobro slaganje između 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