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Author:Asén, Patrik
Title:Analysis of the flow around a cruise ferry hull by the means of computational fluid dynamics
Risteliylautan rungon virtauksen analysointi laskennallisen virtausmekaniikan keinoin
Publication type:Master's thesis
Publication year:2014
Pages:(9) + 70 s. + liitt. 15      Language:   eng
Department/School:Insinööritieteiden korkeakoulu
Main subject:Teknillinen mekaniikka   (K3006)
Supervisor:Siikonen, Timo
Instructor:Mikkola, Tommi
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201412033092
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  4351   | Archive
Keywords:CFD
openFOAM
hydrodynamics
turbulence modelling
free surface flow
hydrodynamiikka
turbulenssin mallinnus
vapaan nestepinnan virtaus
Abstract (eng):In this thesis computational fluid dynamics (CFD) is used to determine the drag of a cruise ferry in a double hull, as well as a free-surface case.
The computations are done with OpenFOAM-software.
Both cases are computed with five different grid spacings.
The results obtained are compared to findings from towing tank experiments, as well as to each other in order to distinguish between the differences of the two cases.

The computations in OpenFOAM are based on the finite volume method.
Turbulence is modelled with the STT k-$\omega$ method by Menter.
The free surface is treated with the Volume of Fluid (VOF) method.
The computations are done on a set of geometrically similar grids with the number of cells between $0.14-0.44$ million for the double hull cases, and between $0.6 -2.2$ million for the free-surface cases.
All the cases are run with the same Reynolds number of $20$ million.
The ship hull is considered to advance at a constant velocity in deep and calm water.
The flow is considered incompressible.

The results are presented in a non-dimensional form.
The drag is presented as the drag coefficient and it is compared to experimental towing tank results.
The shear stress distributions as well as the pressure distributions for the double hull case are compared to those from the free-surface case.

The results obtained for the total drag are satisfactory when compared to earlier findings.
The results were also accurate enough to distinguish clear differences between the double hull and free-surface cases.
However, the grid refinement was not completely successful, as the solution did not converge on the finer grids.
The reason behind this is not completely understood.
Abstract (fin):Tässä diplomityössä ratkaistaan laskennallista virtausmekaniikkaa käyttäen risteilylautan vastus sekä tuplarunkotapauksessa että vapaan nestepinnan kanssa.
Laskenta on suoritettu avoimen lähdekoodin OpenFOAM-ohjelmistolla.
Laskennassa on kummallekkin tilanteelle käytetty viittä eri hilatiheyttä.
Saatuja tuloksia on verrattu aikaisempiin löytöihin.
Tuloksia on myös verrattu keskenään, jotta eroja virtaustilanteiden välillä löydettäisiin.

Laskenta OpenFOAM-ohjelmassa perustuu kontrollitilavuusmenetelmään.
Turbulenssimalleista käytettiin Menterin STT k-$\omega$ mallia.
Vapaa nestepinta käsiteltiin VOF-nestetilavuusmallilla.
Laskennat on suoritettu geometrisesti samanlaisilla hiloilla joiden koppimäärät ovat välillä $0.14-0.44$ miljoonaa tuplarungolle ja $0.6-2.2$ miljoonaa vapaalle nestepinnalle.
Kaikkissa simuloinnessa pidettiin Reynoldsin lukuna $20$ miljoonaa.
Laivarungon oletetaan etenevän vakionopeudella syvässä ja tyynessä vedessä.
Virtaus on luonteeltaan puristumatonta.

Tulokset on esitetty dimensiottomassa muodossa.
Vastus on esitetty vastuskertoimina ja niitä on verrattu hinausaltaalta saatuihin koetuloksiin.
Tuplarungon ja vapaan nestepinnan antamia leikkausjännityksiä ja painejakaumia rungolla on verrattu toisiinsa.

Tuloksia voidaan pitää kokonaisvastuksen kannalta tyydyttävinä, kun niitä verrataan aikaisempiin tuloksiin.
Tulokset ovat myös riittävän tarkkoja, jotta selviä eroja tuplarungon ja vapaan nestepinnan tilanteiden välillä pystytään havaitsemaan.
Hilatihennystä ei kuitenkaan saatu suoritettua loppuun, sillä suuremmilla hilatiheyksillä laskenta ei konvergoinut.
Syytä tälle ilmiölle ei onnistuttu löytämään.
ED:2014-12-21
INSSI record number: 50177
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