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Numerical Modelling Of Spray Sheet Deflection On Planing Hulls
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems.
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The intent of this paper is to investigate the seemingly untested theories regarding modelling of spray formation on planing hulls. This is done by means of 2D and 3D CFD simulations. The motivation for testing these theories is due to the design factors of a conceptual spray deflection system used on planing hulls. This technology is presented and its performance evaluated by comparison with current spray rail systems. With an appropriate design of the cross section of the deflectors the spray can be redirected aftward and thus recover some of the energy in the spray. It was found that the theory presented by Savitsky and Morabito, where the spray field of a planing hull can be represented by a 2D flat planing plate, will overestimate the spray thickness. However a close match between the spray formation on planing hulls and the theory presented by Wagner was found, this theory is that of a wedge being dropped vertically into a calm water surface. The reduced frictional resistance, when using spray deflectors, accounts for up to 28%reduction of the total drag and redirecting the spray aftward can reduce the total drag an additional 4%. The spray deflectors was found to reduce the wet surface area due to spray to a higher extent than possible with spray rails.

Abstract [sv]

Avsikten med denna artikel ¨ar att testa de till synes otestade teorierna betr¨affande modellering av spray bildning hos planande skrov. Detta g¨ors med hj¨alp av 2D och 3D CFD simuleringar. Motiveringen att testa dessa teorier ¨ar p˚a grund av design faktorer av ett konceptuellt spray deflektions system som anv¨ands p˚a planande skrov. Denna teknologi presenteras och dess prestanda utv¨arderas genom att j¨amf¨ora den med nuvarande spray skenor. Med en l¨amplig design av tv¨arsnittet av deflektorerna kan sprayen riktas bak˚at och genom detta ˚atervinna en del av energin i sprayen. Det visade sig att teorin presenterad av Savitsky och Morabito, d¨ar spray bildningen hos planande skrov representeras av en 2D planande platta, ¨overskattar spray tjockleken. D¨aremot hittades en bra ¨overenst¨ammelse mellan spray bildningen hos planande skrov och teorin presenterad av Wagner, denna teori bygger p˚a en kil som sl¨apps vertikalt ner i en v˚agr¨at vattenyta. Det minskade friktions motst˚andet, vid anv¨andning av spray deflektorer, st˚ar f¨or up till 28% minskning av det totala motst˚andet och bak˚atriktning av sprayen minskar det totala motst˚andet ytterligare 4%. Anv¨andning av spray deflektorer visade sig minska den v˚ata ytan fr˚an spray bildningen till en h¨ogre grad ¨an m¨ojligt med spray skenor.

Place, publisher, year, edition, pages
2015. , 22 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2015:71
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-185173OAI: oai:DiVA.org:kth-185173DiVA: diva2:918983
Examiners
Available from: 2016-04-12 Created: 2016-04-12 Last updated: 2016-04-12Bibliographically approved

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