| Abstract | U radu su istražene promjene hidrodinamičkog otpora uronjenog dijela trupa jedrilice klase Optimist. Promatrana je ovisnost hidrodinamičkog otpora jedrilice o pet parametara: volumenu istisnine, dubini urona kobilice, uzdužnom i poprečnom (bočnom) nagibu jedrilice te o brzini kretanja jedrilice.
Analiza je napravljena nizom numeričkih simulacija pri čemu su parametri promatrani nezavisno. Utjecaj svakog od parametara je istražen variranjem samo tog parametra u odnosu na referentni slučaj. Za referentni slučaj je odabran volumen istisnine s masom jedriličara od 45 kg uz maksimalnu dubinu urona kobilice bez uzdužnih i poprečnih nagiba jedrilice (ravno uronjena jedrilica) pri brzini od 1,5 m/s (3 čvora).
Za varijaciju volumena istisnine koji ovisi o masi jedriličara odabrane su mase jedriličara od 30, 40, 45, 50 i 60 kg. Pri dubini urona kobilice promatrana su četiri slučaja: maksimalna dubina urona kobilice od 717,41 mm a zatim dubine urona kobilice za 478 mm, 268,84 mm i 238 mm. Za poprečni (bočni) nagib jedrilice promatrani su nagibi od 0, 8, 10, 13 i 15 stupnjeva a za uzdužni nagib su odabrani nagibi od -4 i -2 stupnja, gdje je krma uronjenija, slučaj ravnog urona za 0 stupnjeva te slučaj za 1 stupanj, gdje je pramac uronjeniji. Također su promatrane brzine kretanja jedrilice koje iznose 0,2, 0,5, 1,5, 3, 3,5 i 4 čvora.
Za svaki od slučajeva je napravljen je 3D model koji je diskretiziran te je izrađena odgovarajuća mreža konačnih volumena. Model s pripadajućom mrežom je učitan u računalni program 'Fluent' pomoću kojega je proveden numerički proračun za stacionarne uvjete strujanja s k - ε modelom turbulencije uz zanemaren utjecaj valova. Numerički postupak je verificiran eksperimentalno za slučajeve promjene volumena istisnine i brzine kretanja jedrilice. U radu su prikazana polja različitih fizikalnih veličina te je izvršena analiza i usporedba rezultata. |
| Abstract (english) | This thesis presents the research on hydrodynamic resistance of the immersed part of an Optimist sailboat hull with respect to five parameters: displacement, lowering of the keel, pitch, roll and speed of the sailboat.
A number of numerical simulations were carried out, considering the selected parameters individually. In order to examine the impact of each parameter, various values of the parameters were tested with respect to the reference case. The selected reference case features: displacement of the sailboat with the sailor who has the mass of 45 kg, with the maximum lowering of the keel without pitch and roll (upright position of the sailboat) and at a speed of 1.5 m/s (3 knots).
To determine the effect of displacement, which is dependent on the sailor's mass, the sailor's mass values of 30, 40, 45, 50 and 60 kg were tested. As far as lowering of the keel is concerned, four cases were considered: the maximum lowering of the keel of 717.41 mm followed by those of 478 mm, 268.84 mm and 238 mm. With regard to the pitch, the motion of the sailboat about its transverse axis, the deviations of 0, 8, 10, 13 and 15 degrees were examined. The deviations of -4 and -2 degrees, with the stern being more immersed, were selected for the roll, the motion of the sailboat about its longitudinal axis. The case of the upright position of the sailboat and the deviation of 1 degree, with the bow being more immersed, were also examined. In addition, the effect of the speeds of 0.2, 0.5, 1.5, 3, 3.5 and 4 knots on displacement was observed.
For each of the aforementioned cases a 3D model was designed and discretized. The model with the corresponding finite volume mesh was loaded into the 'Fluent' computer program. A numerical computation for the steady flow conditions with the k – ε turbulence model was performed, without taking the effect of waves into consideration. The numerical procedure was verified experimentally for the effects of displacement and sailboat speed. This thesis also presents the fields of various physical quantities together with the analysis and the comparison of the results. |
