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Author:Puolakka, Otto
Title:Modelling wave-structure interaction of wave energy converter
Aaltovoimarakenteen ja aallokon vuorovaikutuksen mallinnus
Publication type:Master's thesis
Publication year:2011
Pages:71 s. + liitt. 25      Language:   eng
Department/School:Sovelletun mekaniikan laitos
Main subject:Laivanrakennusoppi   (Kul-24)
Supervisor:Matusiak, Jerzy
Instructor:Mikkola, Tommi
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  3937   | Archive
Keywords:wave energy converter
vertical flap
intermediate depth
water waves
radiation
diffraction
absorption
aaltovoimala
pystysuora levy
välivesi
pinta-aallot
radiaatio
diffraktio
absorptio
Abstract (eng): In this study a linear model for the interaction of water surface waves and a two dimensional flap-type wave energy converter is constructed.
The converter consists of a wide flat base on the seabed in intermediate depth of water and of a thin vertical flap hinged to it at the lower end and extending to the surface.
Sinusoidal Airy waves are assumed normally incident on the flap.

The hydrodynamic and flap dynamic problems are decoupled by assuming harmonic motion.
Flow around the flap is assumed potential and analysis restricted to first order.
The wave flow is divided into diffraction and radiation parts, for which known analytical solutions are presented.
Flap displacement is taken into account as a linear restoring force.

The linearized hydrodynamic reaction forces are included as stiffness, added mass and damping and a wave excitation moment in the linear equation of motion of the flap.
Analytical solutions for flap motion response, power absorbed by linear mechanism damping and absorption efficiency are derived.

Numerical results are produced for a test case flap over a range of wave periods.
Absorption efficiencies very near to the theoretical maximum of 50 per cent are found at the nominal frequency range with constant flap parameters.
The efficiency is not very sensitive to flap thickness or the chosen mechanism damping.
The bandwidth of high efficiency is found very wide for the flap device in intermediate depth in comparison with other single-mode wave absorbing devices.
Abstract (fin): Tässä työssä luodaan kaksiulotteinen lineaarinen malli pinta-aallokon ja levytyyppisen väliveteen sijoitettavan aaltovoimalan vuorovaikutukselle.
Aaltovoimala koostuu matalasta merenpohjalla makaavasta perustasta sekä siihen nivelöidystä pystysuorasta ohuesta voimalalevystä.
Sinimuotoisten Airyn aaltojen oletetaan kohtaavan levyn meren puolella.

Virtauksen ja levyn liikkeen ongelmat erotetaan toisistaan olettamalla liike harmoniseksi.
Virtaus levyn ympärillä oletetaan potentiaaliseksi ja analyysi rajoitetaan ensimmäiseen kertalukuun.
Aaltovirtaus jaetaan diffraktio- ja radiaatio-ongelmiksi, joille työssä käytetään tunnettuja analyyttisiä ratkaisuja.
Levyn uppouman vaikutus otetaan huomioon lineaarisena palautusvoimana.

Virtauksen linearisoidut reaktiovoimat sisällytetään levyn liikeyhtälöön jäykkyytenä, lisättynä massana ja vaimennuksena sekä aaltoherätemomenttina.
Levyn liikevasteelle, lineaarisen mekanismivaimennuksen absorboimalle teholle sekä absorptiohyötysuhteelle johdetaan analyyttiset ratkaisut.

Numeerisia tuloksia lasketaan esimerkkilevylle merkityksellisille aallon jaksonajoille.
Absorptiohyötysuhteen havaitaan valituilla kiinteillä parametreillä olevan hyvin lähellä teoreettista maksimiaan 50 prosenttia nimellistaajuusalueella.
Valitun levynpaksuuden ja mekanismivaimennuksen vaihtelun vaikutus hyötysuhteeseen on verrattain pieni.
Korkean hyötysuhteen taajuusalueen havaitaan olevan poikkeuksellisen laaja kyseiselle väliveden levyvoimalalle muihin yhden vapausasteen aaltovoimaloihin verrattuna.
ED:2011-11-22
INSSI record number: 42993
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