Vibration of passenger ship structures by length-scale separation and inertia-induced interaction

Aleksi Laakso

Vibration of passenger ship structures by length-scale separation and inertia-induced interaction

Julkaisun otsikon käännös: Matkustajalaivan rakenteiden värähtely-mittakaavojen erottaminen ja inertian aiheuttama vuorovaikutus

Aleksi Laakso

Energia- ja konetekniikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Matkustusmukavuus on tärkeä laatutekijä matkustaja-aluksissa, joista osan pääasiallisena tarkoituksena on tarjota mukavat puitteet nautinnolliseen lomaan. Laivanvarustajat ja luokituslaitokset määrittelevät kansainvälisten standardien perusteella hyväksyttävät melun ja värähtelyn raja-arvot. Värähtelyvasteanalyysi elementtimenetelmällä on olennainen osa näiden alusten rakennesuunnittelua. Useat epävarmuustekijät rajoittavat laskelmien tarkkuutta, varsinkin kun taajuusaluetta laajennetaan ensimmäisen kertaluvun herätteiden yläpuolelle. Näitä ovat herätevoimien, kuten aaltojen, potkuriherätteiden ja moottoreiden mallinnuksen epävarmuudet, mutta myös globaalin rakennemallin tarkkuudella on rajansa. Tämä opinnäytetyö keskittyy rakennemallin tarkkuuden parantamiseen. Työssä esitetään menetelmä ohutseinäisten rakenteiden vapaan värähtelyn laskentaan huomioimalla mittakaavatasojen välinen dynaaminen vuorovaikutus. Globaali vapaan värähtelyn ominaisarvotehtävä ratkaistaan elementtimenetelmällä soveltamalla homogenisoituja laskentaelementtejä. Paikallisen mittakaavan alimallin suhteellinen vaste lasketaan erillisellä alustaheräteanalyysillä, jonka jälkeen koko systeemin muodonmuutos- ja kineettiset energiat lasketaan analyyttisesti. Tämän jälkeen tutkittavan muodon ominaistaajuutta muutetaan iteroimalla siten, että mekaanisen energian säilyminen aikatasossa toteutuu. Menetelmän todetaan olevan tarkka ominaistaajuuksien laskentaan tapauksissa, jotka edustavat tyypillisiä laivan rakenteita 1D-, 2D- ja 3D-tapauksissa. Menetelmä soveltuu muotojen kautta tehtävään vastelaskentaan, koska yhteys ominaismuodon ja yleistettyjen massan ja jäykkyyden välillä säilyy. Menetelmää soveltamalla homogenisoituihin elementteihin perustuvien laskentamallien tarkkaa taajuusaluetta voidaan laajentaa noin 35-40 Hz:iin tyypillisen kannen tapauksessa. Esitetty menetelmä pystyy tarjoamaan tiheäverkkoisen mallin tasoisen tarkkuuden harvan homogenisoidun mallin laskentakuormalla.

Julkaisun otsikon käännös	Matkustajalaivan rakenteiden värähtely-mittakaavojen erottaminen ja inertian aiheuttama vuorovaikutus
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Romanoff, Jani, Vastuuprofessori Remes, Heikki, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-0818-7
Sähköinen ISBN	978-952-64-0819-4
Tila	Julkaistu - 2022
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

vapaa värähtely
energiamenetelmä
elementtimenetelmä
homogenisointi
mittakaavavuorovaikutus
inertia
ohutseinäinen rakenne
laivan rakenne

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-64-0819-4

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@phdthesis{606e7e6fb55a4cb6bea3921fab3be78e,

title = "Vibration of passenger ship structures by length-scale separation and inertia-induced interaction",

abstract = "Comfort is an essential quality for new passenger ships, some of which have as their main purpose to provide comfortable settings for enjoyable holidays. Ship owners and classification societies define acceptable limit values for noise and vibrations on the basis of international standards for comfort. Vibration response analysis by means of the Finite Element Method is an essential part of the structural design of these ships. Several uncertainties limit the accuracy of the predictive calculations, especially when the response frequency range is extended above first-order excitations. These include uncertainties in excitation forces, such as waves, propulsion, and engines, but also limitations on the accuracy of the structural analysis model. This thesis focuses on improving the structural model. A method is introduced to analyze the free vibration of thin-walled structures where dynamic inertia-induced interaction occurs between structural length-scales. A global length-scale model that uses Finite Elements with structurally homogenized mass and stiffness is used to solve the free vibration eigenvalue problem. The relative response on a local length-scale is analyzed separately by applying base excitation. Analytical equations are then applied to define the kinetic and strain energies of the combined system. Finally, the natural frequency of the mode under study is altered by iteration so that the mechanical energy of the system is conserved in the time domain. The method is found to be accurate in terms of natural frequencies in case studies representing typical ship structures of 1D, 2D, and 3D global domains. It is applicable to modal response analysis, because the link between the mode shape and generalized mass and stiffness properties remains. In the response analysis of a typical deck, the accurate frequency range of homogenized finite elements is extended up to about 35-40 Hz. The method provides fine mesh-like accuracy with the computational cost of a coarse homogenized model.",

keywords = "free vibration, energy method, finite element method, homogenization, equivalent element, length-scale interaction, inertia, thin-walled structures, ship structures, passenger ship, vapaa v{\"a}r{\"a}htely, energiamenetelm{\"a}, elementtimenetelm{\"a}, homogenisointi, mittakaavavuorovaikutus, inertia, ohutsein{\"a}inen rakenne, laivan rakenne, free vibration, energy method, finite element method, homogenization, equivalent element, length-scale interaction, inertia, thin-walled structures, ship structures, passenger ship",

author = "Aleksi Laakso",

year = "2022",

language = "English",

isbn = "978-952-64-0818-7",

series = "Aalto University publication series DOCTORAL THESES",

publisher = "Aalto University",

number = "76",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Vibration of passenger ship structures by length-scale separation and inertia-induced interaction

AU - Laakso, Aleksi

PY - 2022

Y1 - 2022

N2 - Comfort is an essential quality for new passenger ships, some of which have as their main purpose to provide comfortable settings for enjoyable holidays. Ship owners and classification societies define acceptable limit values for noise and vibrations on the basis of international standards for comfort. Vibration response analysis by means of the Finite Element Method is an essential part of the structural design of these ships. Several uncertainties limit the accuracy of the predictive calculations, especially when the response frequency range is extended above first-order excitations. These include uncertainties in excitation forces, such as waves, propulsion, and engines, but also limitations on the accuracy of the structural analysis model. This thesis focuses on improving the structural model. A method is introduced to analyze the free vibration of thin-walled structures where dynamic inertia-induced interaction occurs between structural length-scales. A global length-scale model that uses Finite Elements with structurally homogenized mass and stiffness is used to solve the free vibration eigenvalue problem. The relative response on a local length-scale is analyzed separately by applying base excitation. Analytical equations are then applied to define the kinetic and strain energies of the combined system. Finally, the natural frequency of the mode under study is altered by iteration so that the mechanical energy of the system is conserved in the time domain. The method is found to be accurate in terms of natural frequencies in case studies representing typical ship structures of 1D, 2D, and 3D global domains. It is applicable to modal response analysis, because the link between the mode shape and generalized mass and stiffness properties remains. In the response analysis of a typical deck, the accurate frequency range of homogenized finite elements is extended up to about 35-40 Hz. The method provides fine mesh-like accuracy with the computational cost of a coarse homogenized model.

AB - Comfort is an essential quality for new passenger ships, some of which have as their main purpose to provide comfortable settings for enjoyable holidays. Ship owners and classification societies define acceptable limit values for noise and vibrations on the basis of international standards for comfort. Vibration response analysis by means of the Finite Element Method is an essential part of the structural design of these ships. Several uncertainties limit the accuracy of the predictive calculations, especially when the response frequency range is extended above first-order excitations. These include uncertainties in excitation forces, such as waves, propulsion, and engines, but also limitations on the accuracy of the structural analysis model. This thesis focuses on improving the structural model. A method is introduced to analyze the free vibration of thin-walled structures where dynamic inertia-induced interaction occurs between structural length-scales. A global length-scale model that uses Finite Elements with structurally homogenized mass and stiffness is used to solve the free vibration eigenvalue problem. The relative response on a local length-scale is analyzed separately by applying base excitation. Analytical equations are then applied to define the kinetic and strain energies of the combined system. Finally, the natural frequency of the mode under study is altered by iteration so that the mechanical energy of the system is conserved in the time domain. The method is found to be accurate in terms of natural frequencies in case studies representing typical ship structures of 1D, 2D, and 3D global domains. It is applicable to modal response analysis, because the link between the mode shape and generalized mass and stiffness properties remains. In the response analysis of a typical deck, the accurate frequency range of homogenized finite elements is extended up to about 35-40 Hz. The method provides fine mesh-like accuracy with the computational cost of a coarse homogenized model.

KW - free vibration

KW - energy method

KW - finite element method

KW - homogenization

KW - equivalent element

KW - length-scale interaction

KW - inertia

KW - thin-walled structures

KW - ship structures

KW - passenger ship

KW - vapaa värähtely

KW - energiamenetelmä

KW - elementtimenetelmä

KW - homogenisointi

KW - mittakaavavuorovaikutus

KW - inertia

KW - ohutseinäinen rakenne

KW - laivan rakenne

KW - free vibration

KW - energy method

KW - finite element method

KW - homogenization

KW - equivalent element

KW - length-scale interaction

KW - inertia

KW - thin-walled structures

KW - ship structures

KW - passenger ship

M3 - Doctoral Thesis

SN - 978-952-64-0818-7

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

Vibration of passenger ship structures by length-scale separation and inertia-induced interaction

Abstrakti

Tutkimusalat

Pääsy asiakirjaan

Sormenjälki

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