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Author:Määttänen, Pirjo
Title:Potkurin siiven murtuminen
Propeller blade fracture
Publication type:Master's thesis
Publication year:2004
Pages:71      Language:   fin
Department/School:Konetekniikan osasto
Main subject:Lujuusoppi   (Kul-49)
Supervisor:Tuhkuri, Jukka
Instructor:Aho, Jaakko
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark TKK  5834   | Archive
Abstract (eng): The objective of this study was to determine ship propeller's blade brake load and to determine its consequences to the structure of Compact Azipod.
Also the validity of traditional cantilever beam method was studied and the objective was to find a method that would be simple and trustworthy for the determination of blade brake load.

Blade brake loads were calculated with cantilever beam method and also with linear and nonlinear finite element method.
Results were compared and because the amount of non-linear analysis was restricted, a constant was determined, with which linear results could be evaluated to match non-linear results.
The consequences of the transmitted forces for the structure's shaft, bearings and one bolted joint were included in calculations.

It was found, that when brake load affects the weakest parts of the blade, which are on the edges, no damage occurs at surrounding structure.
The structure of the blade is strongest in the mid areas of the blade.
If the fracture load is affecting in that area, the stresses at the shaft and at the bolts are over their yield limit.
Loads affecting the bearings were at acceptable level.

The differences of the calculated loads of beam method and non-linear FEM, which affect at the center of the blade, did not differ much.
When calculating the fracture loads of this type of propeller on the surrounding structure, simple beam method is enough.
But when exact blade brake forces are needed, non-linear FEM is recommended.
Abstract (fin): Työn tavoitteena oli määrittää laivan potkurin siiven murtokuorma ja tutkia kuorman vaikutuksia Compact Azipod ruoripotkurin muiden osien kestävyyteen.
Lisäksi tarkoituksena oli etsiä mahdollisimman yksinkertainen laskentamenetelmä lavan murtokuorman laskemiseksi ja selvittää perinteisen palkkimenetelmän luotettavuus.

Lavan murtokuormia laskettiin yksinkertaisella palkkimenetelmällä, sekä lineaarisella ja epälineaarisella elementtimenetelmällä.
Näistä saatuja tuloksia verrattiin keskenään ja koska epälineaarisia tapauksia voitiin ratkaista vain pieni määrä, etsittiin kerroin, jonka avulla lineaarisista tuloksista voitiin arvioida todellisia murtokuormia.
Ruoripotkurisysteemin akselille, laakereille ja eräälle ruuviliitokselle laskettiin suurimmat sallitut lavan murtumisen aiheuttavat kuormat.

Tutkimus osoitti, että potkurin lavan murtuessa kuorman osuessa sen heikoimpiin kohtiin, jotka ovat kaukana akselilta tai lavan reunoilla, ympäröivälle rakenteelle ei aiheudu vaurioita.
Lavan keskellä on suurin materiaalivahvuus.
Jos murtumisen aiheuttava kuorma osuu tälle alueelle, akselille ja ruuveille välittyy myötölujuuden ylityksen aiheuttavia kuormia.
Laakereiden sallitut kuormat eivät ylity.

Lavan keskialueille kohdistuvien murtokuormien arvot eivät palkkimenetelmällä ja epälineaarisella elementtimenetelmällä laskettuina poikenneet huomattavasti toisistaan.
Todettiin palkkimenetelmän olevan riittävä laskettaessa tutkimuksessa käsitellyn tyyppisten potkureiden lavan murtokuormien valittamia voimia ympäröivälle rakenteelle.
Potkurin lavan tarkan murtokuorman määrittämiseen suositellaan kuitenkin epälineaarista elementtimenetelmää.
ED:2004-11-12
INSSI record number: 26494
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