Numeričko istraživanje utjecaja bočnih stijenki bazena na otpor broda

master's thesis

• Title (english): Numerical investigation into the blockage effect on ship resistance
• Author: Mislav Štefok
• Mentor: Nastia Degiuli (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2020-12-03, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Shipbuilding; Hydromechanics of Floating and Maritime Structures

Abstract

Prilikom provedbe pokusa otpora broda u bazenu manjih dimenzija, moguća je pojava utjecaja bočnih stijenki na izmjerene vrijednosti. Utjecaj stijenki postaje sve izraženiji povećanjem brzine i dimenzije modela broda te je stoga potrebno korigirati izmjerenu silu otpora broda. Numeričke simulacije strujanja fluida oko trupa broda za jednotrupni Wigley-ev model te tri katamaranske konfiguracije s Wigley-evim modelom broda u neograničenoj i ograničenoj vodi provedene su primjenom komercijalnog programskog paketa za računalnu dinamiku fluida STAR-CCM+. Ispitivanja su provedena s ciljem određivanja utjecaja bočnih stijenki bazena na ukupni otpor broda. Proračunska domena diskretizirana je metodom konačnih volumena te su definirani rubni uvjeti i fizikalni model. Detaljno je prikazan matematički model temeljen na Reynoldsovim osrednjenim Navier-Stokesovim jednadžbama (RANS). U numeričkim simulacijama je primijenjen k-ω SST model turbulencije. Za praćenje i određivanje položaja slobodne površine primijenjena je metoda udjela volumena u fluidu (eng. “Volume of Fluid-VOF“). Za modeliranje strujanja u blizini stijenke primijenjene su zidne funkcije. Proveden je postupak verifikacije za gustoću geometrijske mreže i vremenski koraka za jednotrupni Wigley-ev model i katamaranske konfiguracije u neograničenoj i ograničenoj vodi. Dobiveni numerički rezultati validirani su s eksperimentalnim rezultatima dostupnim u literaturi. Određen je utjecaj razmaka između trupova katamarana na ukupni otpor preko faktora interferencije. Konačno, provedena je analiza utjecaja stijenki bazena na ukupni otpor, sliku valova, hidrodinamički tlak i tangencijalna naprezanja.

Abstract (english)

When carrying out the resistance test in small towing tank the blockage effect may occur. Influence of the blockage effect becomes more and more pronounced with the increased of the ship speed and model dimension. Therefore it is necessary to correct dimension value of total resistance. Numerical simulations of flow round the ship hull for Wigley monohull and three catamaran configuration with Wigley model in unrestricted and restricted water are preformed using the commercial software package for Computational Fluid Dynamics STAR-CCM+. The investigations are performed with the aim of determining the blockage effect on ship resistance. Computational domain is discretized by the finite volume method and boundary conditions and physical model are defined. Mathematical model based on the Reyolds Averaged Navier-Stokes (RANS) equations is presented in detail. The k-ω SST turbulence model is applied in numerical simulations, the volume of fluid method is used for tracking and locating the free surface. Wall functions are applied for modelling the flow near the wall. The verification study regarding grid size and time step for Wigley monohull and three catamaran configurations in unrestriced and restricted water is carried out. The obtained numerical results are validated with the experimental available in the literature. The influence of separation between demihulls on total resistance by means of interference factor is determined. Finally, the analysis of blockage effect on total resistance, wave pattern, hydrodynamic pressure and wallocl shear stresses is carried out.

• Keywords: Računalna dinamika fluida (RDF); RANS; k-ω SST model turbulencije; VOF; utjecaj stijenki; faktor interferencije
• Keywords (english): Computational Fluid Dynamics; RANS; k-ω SST turbulence model; VOF; blockage effect; interference factor
• Language: croatian
• URN:NBN: urn:nbn:hr:235:057298
• Study programme: Title: Naval Architecture; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka brodogradnje (magistar/magistra inženjer/inženjerka brodogradnje)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2020-12-03 19:49:12