Sea ice ridge keel punch through experiments: model experiments and numerical modeling with discrete and combined finite-discrete element methods

Arttu Polojärvi

Sea ice ridge keel punch through experiments: model experiments and numerical modeling with discrete and combined finite-discrete element methods

Julkaisun otsikon käännös: Ahtojäävallin kölin lujuus: mallikokeita ja simulointeja diskreetti- sekä yhdistetyllä diskreetti- ja elementtimenetelmällä

Arttu Polojärvi

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Ahtojäävallin kölin materiaaliominaisuuksia mitataan tavallisimmin kokeilla, joissa levymäinen työntyri painetaan vallimassaan samalla kun työntyriin kohdistuva voima mitataan. Vaikka koemenetelmä on tärkeä ja paljon käytetty, kokeiden tulosten tulkitseminen on hyvin vaikeaa. Toisaalta tulosten tarkka tulkitseminen on välttämätöntä kölin materiaalin tarkassa mallinnuksessa, jota puolestaan tarvitaan Arktisten merirakenteiden suunnittelussa. Tässä työssä kyseisiä kokeita on tutkittu sekä simuloimalla että kokeellisesti. Työn kokeellisessa osassa tehtiin laboratoriossa kokeita kölimassalla, joka koostui muovikappaleista jääkappaleiden sijaan. Tavoitteena kokeissa oli tutkia itse koejärjestelyä ja sen vaikutuksia tuloksiin ja muovikappaleita käytettiin tuloksiin vaikuttavien ilmiöiden lukumäärän vähentämiseksi. Erityisesti tarkasteltiin kuormitusnopeuden vaikutusta, koska aikaisempien laboratoriokokeiden perusteella on epäilty vallin leikkauslujuuden kasvavan kuormitusnopeuden kasvaessa. Tässä työssä näytettin, että tämä leikkauslujuuden kasvuksi tulkittu ilmiö johtuu todennäköisesti koejärjestelystä vallin materiaalin sijaan. Työssä kokeita mallinnettin käyttäen sekä kolmiulotteista diskreettielementtimenetelmää, että kaksiulotteista yhdistettyä elementti- ja diskreettielementtimenetelmää. Molemmissa mallinnustekniikoissa valli mallinnetaan epäjatkuvana materiaalina. Tekniikoita kehitettiin työn aikana erityisesti jäämekaniikan ongelmiin sopiviksi. Vallia, jossa jääkappaleet eivät olleet yhteenjäätyneet, mallinnettiin kolmiulotteisella diskreettielementtimenetelmällä, kun taas osittain jäätyneen vallin mallinnuksessa käytettiin kaksiulotteista yhdistettyä elementti- ja diskreettielementtimenetelmää. Jälkimmäisen mallinnustekniikan yhteyteen kehitettiin menetelmä jääkappaleita yhteensitovien sidosten mallintamiseksi. Simulaatioiden avulla voitiin tarkastella ja analysoida kokeita yksityiskohtaisesti. Mallinnuksen perusteella löydettiin selkeä yhteys vallin deformaatiokentän kehittymisen ja mitattujen kuormien välille. Toisaalta osittain jäätyneen vallin tapauksessa löydettiin yhteys maksimikuorman ja vallin ensimmäisen vaurion geometrian välille. Lisäksi mallin perusteella voitiin näyttää, että aikaisemmin vallin materiaalin pehmenemiseksi tulkittu ilmiö selittyykin vallin deformaatiokentän ja vallin geometrian muutoksilla kokeen aikana. Käyteyt epäjatkuvat mallinnusmenetelmät paljastivat ilmiöitä, joita ei esiinny vallimassan kontinuumimallinnuksessa. Esimerkkinä näistä ilmiöistä voidaan mainita kappaleiden välisten sidosten vedosta johtuvien vaurioiden suhteellisen suuri merkitys.

Julkaisun otsikon käännös	Ahtojäävallin kölin lujuus: mallikokeita ja simulointeja diskreetti- sekä yhdistetyllä diskreetti- ja elementtimenetelmällä
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Tuhkuri, Jukka, Vastuuprofessori Tuhkuri, Jukka, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-5081-2
Sähköinen ISBN	978-952-60-5082-9
Tila	Julkaistu - 2013
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

jäämekaniikka
ahtojäävallin lujuus
jääkuormat
arktiset merirakenteet
diskreettielementtimenetelmä
yhdistetty diskreetti- ja elementtimenetelmä
epäjatkuvat materiaalit
numeerinen mallinnus

YK:n kestävän kehityksen tavoitteet

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Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-5082-9

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@phdthesis{50171ab43847479d8ffff786f0575493,

title = "Sea ice ridge keel punch through experiments: model experiments and numerical modeling with discrete and combined finite-discrete element methods",

abstract = "Simulations and laboratory-scale experiments were performed to study sea ice ridge keel punch through experiments and ice rubble behavior in them. The punch through experiments are an important method for deriving ice rubble properties, yet the interpretation of the experiment results is far from straightforward. Anyhow, accurate interpretation is important for the material modeling of ice rubble, and further for an accurate modeling of the ice rubble related problems needed when designing marine structures in ice covered waters. The experimental work was performed using rubble consisting of plastic blocks. Plastic blocks made it possible to study of experimental method itself, because the interpretation of the experiment results was simplified from that of the experiments with ice rubble. The effect of indentor velocity was experimentally studied, as earlier laboratory-scale punch through experiments have suggested that the ice rubble sheer strength depends on the loading rate. The loading rate dependency of the rubble shear strength was found to be likely related to the experimental set-up rather than to the rubble material. Simulations of punch through experiments were performed using a three dimensional discrete element method and a two dimensional combined finite discrete element method. In both of these methods, rubble is modelled as a discontinuum. The methods were developed during this work for the research on ice mechanics. Simulations of punch through experiments on non-cohesive rubble were performed using the three dimensional discrete numerical model. A technique for modeling freeze bonds was developed within the framework of two dimensional combined finite discrete element method simulations. The simulations helped to provide insight on the analysis of the punch through experiment results. The simulation results clearly showed that the evolution of the deformation patterns was related to the load records in the experiments. In the case of partly consolidated rubble, the initial failure patterns of the rubble were observed to be related to the measured maximum force values. Furthermore, the behavior that has been earlier understood to be the result of rubble material softening was in fact shown to be due to changes in the rubble geometry during the experiment. The discontinuous modeling of rubble showed that physical phenomena could potentially be rendered out from the more traditional continuum models. These phenomena included, for example, the importance of tensile freeze failures in the failure process of partly consolidated rubble.",

keywords = "ice mechanics, punch through tests, ice loads, arctic offshore structures, discrete element method, combined finite-discrete element method, discontinuous materials, numerical modeling, j{\"a}{\"a}mekaniikka, ahtoj{\"a}{\"a}vallin lujuus, j{\"a}{\"a}kuormat, arktiset merirakenteet, diskreettielementtimenetelm{\"a}, yhdistetty diskreetti- ja elementtimenetelm{\"a}, ep{\"a}jatkuvat materiaalit, numeerinen mallinnus, ice mechanics, punch through tests, ice loads, arctic offshore structures, discrete element method, combined finite-discrete element method, discontinuous materials, numerical modeling",

author = "Arttu Poloj{\"a}rvi",

year = "2013",

language = "English",

isbn = "978-952-60-5081-2",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "50",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Sea ice ridge keel punch through experiments: model experiments and numerical modeling with discrete and combined finite-discrete element methods

AU - Polojärvi, Arttu

PY - 2013

Y1 - 2013

N2 - Simulations and laboratory-scale experiments were performed to study sea ice ridge keel punch through experiments and ice rubble behavior in them. The punch through experiments are an important method for deriving ice rubble properties, yet the interpretation of the experiment results is far from straightforward. Anyhow, accurate interpretation is important for the material modeling of ice rubble, and further for an accurate modeling of the ice rubble related problems needed when designing marine structures in ice covered waters. The experimental work was performed using rubble consisting of plastic blocks. Plastic blocks made it possible to study of experimental method itself, because the interpretation of the experiment results was simplified from that of the experiments with ice rubble. The effect of indentor velocity was experimentally studied, as earlier laboratory-scale punch through experiments have suggested that the ice rubble sheer strength depends on the loading rate. The loading rate dependency of the rubble shear strength was found to be likely related to the experimental set-up rather than to the rubble material. Simulations of punch through experiments were performed using a three dimensional discrete element method and a two dimensional combined finite discrete element method. In both of these methods, rubble is modelled as a discontinuum. The methods were developed during this work for the research on ice mechanics. Simulations of punch through experiments on non-cohesive rubble were performed using the three dimensional discrete numerical model. A technique for modeling freeze bonds was developed within the framework of two dimensional combined finite discrete element method simulations. The simulations helped to provide insight on the analysis of the punch through experiment results. The simulation results clearly showed that the evolution of the deformation patterns was related to the load records in the experiments. In the case of partly consolidated rubble, the initial failure patterns of the rubble were observed to be related to the measured maximum force values. Furthermore, the behavior that has been earlier understood to be the result of rubble material softening was in fact shown to be due to changes in the rubble geometry during the experiment. The discontinuous modeling of rubble showed that physical phenomena could potentially be rendered out from the more traditional continuum models. These phenomena included, for example, the importance of tensile freeze failures in the failure process of partly consolidated rubble.

AB - Simulations and laboratory-scale experiments were performed to study sea ice ridge keel punch through experiments and ice rubble behavior in them. The punch through experiments are an important method for deriving ice rubble properties, yet the interpretation of the experiment results is far from straightforward. Anyhow, accurate interpretation is important for the material modeling of ice rubble, and further for an accurate modeling of the ice rubble related problems needed when designing marine structures in ice covered waters. The experimental work was performed using rubble consisting of plastic blocks. Plastic blocks made it possible to study of experimental method itself, because the interpretation of the experiment results was simplified from that of the experiments with ice rubble. The effect of indentor velocity was experimentally studied, as earlier laboratory-scale punch through experiments have suggested that the ice rubble sheer strength depends on the loading rate. The loading rate dependency of the rubble shear strength was found to be likely related to the experimental set-up rather than to the rubble material. Simulations of punch through experiments were performed using a three dimensional discrete element method and a two dimensional combined finite discrete element method. In both of these methods, rubble is modelled as a discontinuum. The methods were developed during this work for the research on ice mechanics. Simulations of punch through experiments on non-cohesive rubble were performed using the three dimensional discrete numerical model. A technique for modeling freeze bonds was developed within the framework of two dimensional combined finite discrete element method simulations. The simulations helped to provide insight on the analysis of the punch through experiment results. The simulation results clearly showed that the evolution of the deformation patterns was related to the load records in the experiments. In the case of partly consolidated rubble, the initial failure patterns of the rubble were observed to be related to the measured maximum force values. Furthermore, the behavior that has been earlier understood to be the result of rubble material softening was in fact shown to be due to changes in the rubble geometry during the experiment. The discontinuous modeling of rubble showed that physical phenomena could potentially be rendered out from the more traditional continuum models. These phenomena included, for example, the importance of tensile freeze failures in the failure process of partly consolidated rubble.

KW - ice mechanics

KW - punch through tests

KW - ice loads

KW - arctic offshore structures

KW - discrete element method

KW - combined finite-discrete element method

KW - discontinuous materials

KW - numerical modeling

KW - jäämekaniikka

KW - ahtojäävallin lujuus

KW - jääkuormat

KW - arktiset merirakenteet

KW - diskreettielementtimenetelmä

KW - yhdistetty diskreetti- ja elementtimenetelmä

KW - epäjatkuvat materiaalit

KW - numeerinen mallinnus

KW - ice mechanics

KW - punch through tests

KW - ice loads

KW - arctic offshore structures

KW - discrete element method

KW - combined finite-discrete element method

KW - discontinuous materials

KW - numerical modeling

M3 - Doctoral Thesis

SN - 978-952-60-5081-2

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Sea ice ridge keel punch through experiments: model experiments and numerical modeling with discrete and combined finite-discrete element methods

Abstrakti

Tutkimusalat

YK:n kestävän kehityksen tavoitteet

Pääsy asiakirjaan

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