Influence of simple harmonic speed variations on the Vuk-T sailplane approach paths and distances

Ukoliko iz bilo kog tehničkog razloga vazdušne kočnice prestanu da funkcionišu tokom leta, najkritičnija faza u proceduri sletanja jedrilice je finalni prilaz. Pored leta sa bočnim klizanjem, kada se disipacija energije vrši kroz povećanje bočne sile otpora, drugo moguće rešenje ovog problema je ponuđeno u literaturi, gde je pokazano da se dužina prilaza može minimizirati primenom složenih oscilatornih putanja leta. Međutim, let po takvim putanjama zahteva izuzetno letačko umeće. Nasuprot tome, u ovom radu izvršena je analiza jednostavnijih prilaznih putanja, baziranih na harmonijskim promenama brzine, koje je mnogo lakše operativno reprodukovati u letu. U radu je prikazan proračunski algoritam koji omogućava brzu konvergenciju rešenja i analizirana su numerička rešenja za nekoliko tipičnih slučajeva. Kao primer korišćeni su podaci za jedrilicu Vuk-T. Dobijeni rezultati pokazuju nešto manja skraćenja putanja, ali jednostavnost primene u praksi i veća bezbednost predloženih tehnika letenja čini ih korisnim rešenjima u slučaju pomenutih problema.When for any technical reason spoilers become inoperable in flight, the most critical phase of a sailplane landing procedure is final approach. Besides the sideslipping flight possibility, where energy is dissipated through the increased sideforce drag, another solution for this problem has been offered in literature, showing that the landing distance could be minimized using rather complex oscillating flight paths. The problem is that performing such paths in practice would require exceptional piloting skills. Instead of that, in this paper much simpler approach profiles have been analyzed, based on the simple harmonic speed variations, which could much easier be reproduced in practice. After establishing a quick convergence algorithm, numerical solutions for several typical cases, taking the Vuk-T sailplane as an example, have been presented. Although distance reductions are generally smaller than obtained by distance-minimizing techniques, their operational simplicity and higher safety prove them as valuable solutions for this kind of problems

Investicije i podsticajne mere za zaštitu životne sredine

U radu se razmatraju investicija i podsticajne mere za zaštitu životne sredine i to posebno u oblasti emisije štetnih materija u vazduh i vodu, te postupanja sa otpadom. Dostupni podaci Ministarstva za prostorno planiranje i zaštitu životne sredine ukazuju na značajno povećanje ukupnih sredstava za finansiranje zaštite životne sredine, koji su u 2010. godini iznosila 0,66% BDP. Pretežan deo tih sredstava predstavljaju u osnovi i ključne podsticajne mere, koje prevashodno realizuje Fond za zaštitu životne sredine Republike Srbije u vidu kredita, dotacije, bespovratna sredstava i pomoć. Ova investiciona ulaganja ne mogu se isključivo smatrati kao trošak, niti kao isključivo ekološko pitanje, s obzirom na brojne direktne i indirektne ekonomske efekte se ogledaju kroz stvaranje bezbednog okruženja za postojeće i buduće generacije, multiplikativne efekte od investiranja, smanjivanje rizika od hemijskih udesa, unapređenje poljoprivrede i turizma, a posebno razvoj industrije reciklaže

Influence of simple harmonic speed variations on the Vuk-T sailplane approach paths and distances

Ukoliko iz bilo kog tehničkog razloga vazdušne kočnice prestanu da funkcionišu tokom leta, najkritičnija faza u proceduri sletanja jedrilice je finalni prilaz. Pored leta sa bočnim klizanjem, kada se disipacija energije vrši kroz povećanje bočne sile otpora, drugo moguće rešenje ovog problema je ponuđeno u literaturi, gde je pokazano da se dužina prilaza može minimizirati primenom složenih oscilatornih putanja leta. Međutim, let po takvim putanjama zahteva izuzetno letačko umeće. Nasuprot tome, u ovom radu izvršena je analiza jednostavnijih prilaznih putanja, baziranih na harmonijskim promenama brzine, koje je mnogo lakše operativno reprodukovati u letu. U radu je prikazan proračunski algoritam koji omogućava brzu konvergenciju rešenja i analizirana su numerička rešenja za nekoliko tipičnih slučajeva. Kao primer korišćeni su podaci za jedrilicu Vuk-T. Dobijeni rezultati pokazuju nešto manja skraćenja putanja, ali jednostavnost primene u praksi i veća bezbednost predloženih tehnika letenja čini ih korisnim rešenjima u slučaju pomenutih problema.When for any technical reason spoilers become inoperable in flight, the most critical phase of a sailplane landing procedure is final approach. Besides the sideslipping flight possibility, where energy is dissipated through the increased sideforce drag, another solution for this problem has been offered in literature, showing that the landing distance could be minimized using rather complex oscillating flight paths. The problem is that performing such paths in practice would require exceptional piloting skills. Instead of that, in this paper much simpler approach profiles have been analyzed, based on the simple harmonic speed variations, which could much easier be reproduced in practice. After establishing a quick convergence algorithm, numerical solutions for several typical cases, taking the Vuk-T sailplane as an example, have been presented. Although distance reductions are generally smaller than obtained by distance-minimizing techniques, their operational simplicity and higher safety prove them as valuable solutions for this kind of problems

Pula - cultural tourism destination - developmental challenges

Ovaj rad objašnjava koliko kultura može utjecati na razvoj grada Pule kao turističke destinacije, koje kulturne resurse grad Pula posjeduje, te kako njima racionalno raspolagati, da bi se grad i dalje turistički razvijao. Poslije sunca i mora, kultura je najvažniji faktor, te izrazito jaki “adut” za razvoj turizma grada Pule. Postoje svi preduvjeti da grad Pula postane Europska prijestolnica kulture 2020. godine, s obzirom na svoju bogatu i različitu povijest (Rimski i austrougarski spomenici kulture). Dakako postoji još dosta neiskorištenog potencijala za svrhu razvoja kulturnog turizma, kao što su npr. Sveta Katarina i Muzil. Bez obzira da li su kulturološki resursi iskorišteni ili neiskorišteni oni zahtjevaju racionalnu i održivu upotrebu. Drugi problem kojeg je potrebno riješiti u gradu Puli je sezonalnost, jer se kulturološke manifestacije održavaju samo tijekom turističke sezone. Potrebno je osmisliti i provesti manifestacije i izvan turističke sezone, kako bi se privukao veći broj posjetitelja, ostvarila veća konkurentnost na turističkom tržištu, te samim time bi i grad Pula dobio na “živosti”, te tako povećao svoje šanse da postane Europska prijestolnica kulture 2020. godineThis bachelor thesis explains the influence of the culture on the further development of the town of Pula, as a touristic destination, what cultural resources town of Pula contains, and how to use them in a rational way to develop the future tourism of the town. After sun and the sea, the culture is the most important factor for the touristic development of the town of Pula. The town of Pula has all the prerequisites to become the European Capital of Culture in the year 2020, because of its rich and various history (Roman and Austrohungarian cultural monuments). There is also a lot of unused potential, that can be used to develop the cultural tourism. Regardless if the cultural resources are used or still unused, they require rational and sustainabe use. Another issue in the town of Pula that must be solved is seasonality, because all the touristic manifestations are held during touristic season. Manifestations must be held outside the period of touristic season as well, so more visitors can come to Pula, Pula can be more competitive on the touristic market, and the town could become more “liveliness” and improve its chances to become the European Capital of Culture 2020

Pula - cultural tourism destination - developmental challenges

Ovaj rad objašnjava koliko kultura može utjecati na razvoj grada Pule kao turističke destinacije, koje kulturne resurse grad Pula posjeduje, te kako njima racionalno raspolagati, da bi se grad i dalje turistički razvijao. Poslije sunca i mora, kultura je najvažniji faktor, te izrazito jaki “adut” za razvoj turizma grada Pule. Postoje svi preduvjeti da grad Pula postane Europska prijestolnica kulture 2020. godine, s obzirom na svoju bogatu i različitu povijest (Rimski i austrougarski spomenici kulture). Dakako postoji još dosta neiskorištenog potencijala za svrhu razvoja kulturnog turizma, kao što su npr. Sveta Katarina i Muzil. Bez obzira da li su kulturološki resursi iskorišteni ili neiskorišteni oni zahtjevaju racionalnu i održivu upotrebu. Drugi problem kojeg je potrebno riješiti u gradu Puli je sezonalnost, jer se kulturološke manifestacije održavaju samo tijekom turističke sezone. Potrebno je osmisliti i provesti manifestacije i izvan turističke sezone, kako bi se privukao veći broj posjetitelja, ostvarila veća konkurentnost na turističkom tržištu, te samim time bi i grad Pula dobio na “živosti”, te tako povećao svoje šanse da postane Europska prijestolnica kulture 2020. godineThis bachelor thesis explains the influence of the culture on the further development of the town of Pula, as a touristic destination, what cultural resources town of Pula contains, and how to use them in a rational way to develop the future tourism of the town. After sun and the sea, the culture is the most important factor for the touristic development of the town of Pula. The town of Pula has all the prerequisites to become the European Capital of Culture in the year 2020, because of its rich and various history (Roman and Austrohungarian cultural monuments). There is also a lot of unused potential, that can be used to develop the cultural tourism. Regardless if the cultural resources are used or still unused, they require rational and sustainabe use. Another issue in the town of Pula that must be solved is seasonality, because all the touristic manifestations are held during touristic season. Manifestations must be held outside the period of touristic season as well, so more visitors can come to Pula, Pula can be more competitive on the touristic market, and the town could become more “liveliness” and improve its chances to become the European Capital of Culture 2020

Synthesis and characterization of polyurethane copolymers based on poly(propylene oxide)-block- poly(dimethylsiloxane)-block- poly(propylene oxide) and their nanocomposites with organomodified clay.

Dve serije segmentiranih poliuretanskih kopolimera (SPU) i njihovih nanokompozita (SPUNC) su sintetisane na bazi α,ω-dihidroksi-poli(propilen-oksid)-b-poli(dimetilsiloksan)-b-poli(propilen-oksida) (PPO-PDMS, Mn = 3060 g mol-1) kao dela mekog segmenta i 4,4'-metilendifenildiizocijanata (MDI) i 1,4-butandiola (BD) kao komonomera tvrdog segmenta. Serija SPU-a je sintetisana dvostepenim postupkom poliadicije u smeńi rastvarača tetrahidrofurana (THF) i N,N-dimetilacetamida (DMAc) (1/1, v/v), uz prisustvo kalaj-oktoata kao katalizatora...Two series of segmented polyurethane copolymers (SPU) and their nanocomposites (SPUNC) were synthesized based on α,ω-dihydroxy-poly(propylene oxide)-b-poly(dimethylsiloxane)-b-poly(propylene oxide) (PPO-PDMS, Mn = 3060 g mol-1) as the part of the soft segment and 4,4'-methylenediphenyldiisocyanate (MDI) and 1,4-butanediol (BD) as the comonomers of the hard segment. Series of SPU was synthesized via a two-step polyaddition reaction in solvent mixture of tetrahydrofuran (THF) and N,N-dimethylacetamide (DMAc) (1/1, v/v) and in the presence of tin-octoate as a catalyst..

Entrepreneurial Framework Conditions for the SME Development in Serbia

The SME development in Serbia, like in the most of the Western Balkans countries, shows a significant improvement. Serbia has adopted the SME development policy which is in accordance with the EU policies and is actively engaged on improvement of the business environment in order to foster the SME further expansion. It has moved from the phase of formulating policy and defining strategic objectives to implementing policy, particularly in the field of start-ups, provision of business services and dissemination of information. Analysis of the current framework conditions for the SME sector, and its role and significance, demonstrate considerable enhancements in transition period. However, SMEs in Serbia still face numerous problems, that this sector encounters in its business operating. The analysis of business environment for SMEs in Serbia has been performed through consideration of poll survey Global Entrepreneurship Monitor (GEM) as well as annual reports „SME Policy Index 2007” and „SME Policy Index 2009” which show realized progress in application of the European Charter for Small Enterprises in the Western Balkans with special emphasis on Serbia. The most important findings in the paper suggest that, despite realized progress, business environment in Serbia is still under-stimulating for SMEs development due to certain limitations of legal, procedural and financial nature, whereby defined recommendations for improvement of framework for business operating of SMEs in Serbia have been formulated

CFD modeling of supersonic airflow generated by 2D nozzle with and without an obstacle at the exit section

Modeliranje složenih nadzvučnih strujnih polja korišćenjem računara predstavlja jedan od najvećih izazova u oblasti CFD analiza. U radu su predstavljeni prvi koraci u numeričkoj analizi takvog strujanja, generisanog konvergentno- divergentnim mlaznikom sa Mahovim brojem M = 2.6 na izlazu iz mlaznika. Cilj je bio postići dobra poklapanja sa raspoloživim eksperimentalnim podacima, dobijenim tokom ispitivanja u nadzvučnom aerotunelu instituta VTI Žarkovo, gde su ispitivane mogućnosti vektorisanja potiska mlaznika sa vazduhom kao radnim fluidom, postavljanjem različitih tipova prepreka na izlazu iza mlaznika. U radu se analiziraju slučajevi strujanja sa slobodnim izlazom i sa jednim izabranim tipom prepreke na izlazu iz mlaznika. Za oba slučaja korišćene su strukturirane proračunske mreže za rešavanje RANS jednačina sa k-w SST turbulentnim modelom. Nakon kvalitativnih i kvantitativnih poređenja sa raspoloživim eksperimentalnim rezultatima, utvrđena su dobra poklapanja, pri čemu je CFD analiza bila u mogućnosti da pruži i dodatne podatke o strujnom polju, koji nisu mereni tokom eksperimenata.Computational modeling of complex supersonic airflow patterns is one of the greatest challenges in the domain of CFD analyses. The paper presents initial steps in numerical analysis of such flow, generated by convergentdivergent nozzle with Mach number M = 2.6 at nozzle exit. The aim was to achieve good agreements with available experimental data, obtained during supersonic wind tunnel tests at VTI Žarkovo institute, where nozzle thrust vectoring possibilities had been investigated using air as test fluid, by placing different types of obstacles at the exit section. Paper is focussed on free exit flow, and flow with one selected obstacle type. Using structured mesh for both cases, the RANS equations with k-w SST turbulent model have been applied. After quantitative and qualitative comparisons with available experimental data, good agreements have been obtained, where CFD was also able to provide additional flowfield data, not measuted during experiments

Aerodynamic analysis of a light aircraft at different design stages

Tokom aerodinamičkog projektovanja aviona, shodno njegovoj kategoriji i fazi razvoja projekta, potrebno je koristiti adekvatne proračunske metode i softverske alate. U slučaju lakih aviona, uobičajeno se koriste analitičke i semiempirijske metode u inicijalnoj fazi, kombinovane sa jednostavnim - neviskoznim CFD proračunskim modelima, dok se u kasnijim fazama obavljaju relativno kompleksne CFD analize sa uticajem viskoznosti. U današnje vreme se, u kategoriji lakih aviona, podrazumeva da savremeni proračunski alati za svaku od faza razvoja moraju biti adekvatno izabrani, tako da se njima dobijeni rezultati međusobno verifikuju i dopunjavaju. U radu su prikazane proračunske metode korišćene tokom aerodinamičke analize novog lakog aviona u različitim fazama njegovog razvoja i izvršeno je poređenje dobijenih rezultata, u cilju verifikacije ispunjenja navedenog uslova.During the evolution of an airplane aerodynamic design, proper calculation methods and software tools should be utilized, which correspond to the airplane category and project development level. In case of light aircraft, the general trend is the application of analytical and semiempirical methods at the initial stages, combined with simplified - inviscid CFD computational models, and fairly complex viscous CFD analyses at higher design levels. At the present stage of light aviation development, it is assumed that the contemporary design tools for each of those steps should be appropriate enough, so that they actually verify and additionally fine-tune each other's results. This paper describes the calculation tools and methods applied during the aerodynamic analyses of a new light aircraft at different development stages, and compares the results obtained by them, with the aim to verify and support the above statement, considering light aircraft aerodynamic design

Aerodynamic analysis of a light aircraft at different design stages

Tokom aerodinamičkog projektovanja aviona, shodno njegovoj kategoriji i fazi razvoja projekta, potrebno je koristiti adekvatne proračunske metode i softverske alate. U slučaju lakih aviona, uobičajeno se koriste analitičke i semiempirijske metode u inicijalnoj fazi, kombinovane sa jednostavnim - neviskoznim CFD proračunskim modelima, dok se u kasnijim fazama obavljaju relativno kompleksne CFD analize sa uticajem viskoznosti. U današnje vreme se, u kategoriji lakih aviona, podrazumeva da savremeni proračunski alati za svaku od faza razvoja moraju biti adekvatno izabrani, tako da se njima dobijeni rezultati međusobno verifikuju i dopunjavaju. U radu su prikazane proračunske metode korišćene tokom aerodinamičke analize novog lakog aviona u različitim fazama njegovog razvoja i izvršeno je poređenje dobijenih rezultata, u cilju verifikacije ispunjenja navedenog uslova.During the evolution of an airplane aerodynamic design, proper calculation methods and software tools should be utilized, which correspond to the airplane category and project development level. In case of light aircraft, the general trend is the application of analytical and semiempirical methods at the initial stages, combined with simplified - inviscid CFD computational models, and fairly complex viscous CFD analyses at higher design levels. At the present stage of light aviation development, it is assumed that the contemporary design tools for each of those steps should be appropriate enough, so that they actually verify and additionally fine-tune each other's results. This paper describes the calculation tools and methods applied during the aerodynamic analyses of a new light aircraft at different development stages, and compares the results obtained by them, with the aim to verify and support the above statement, considering light aircraft aerodynamic design