Stress analysis of a monopile foundation under the hammering loads

132 Pages·2017·8.69 MB·English

by  Rui Xu

Stress analysis of a monopile foundation
under the hammering loads
Rui Xu
Wind Energy
Submission date: July 2017
Supervisor: Zhen Gao, IMT
Co-supervisor: Eliz-Mari Lourens, Delft University of Technology
Norwegian University of Science and Technology
Department of Marine Technology

Structural analysis of the gripper device
during the hammering process of an offshore
wind turbine monopile
Rui Xu
July2017
MASTERTHESIS
DelftUniversityofTechnology&
NorwegianUniversityofScienceandTechnology
Supervisor1: ProfessorAndreiMetrikine
Supervisor2: ProfessorZhenGao
Supervisor3: Dr. ZhiyuJiang
Supervisor4: Dr. PeterMeijers
i
Abstract
Theinstallationofmonopileisaveryimportantprocessinoffshorewindturbineconstruction.
Duringthemonopilebeingdrivendownbyhydraulichammer,hugeenergytransfersfromham-
mer to pile, which may cause monopile inclination. In order to keep the monopile steady in
horizontaldirection, agripperdeviceisappliedbetweenthemonopileandinstallationvessel.
Thegrippercontactswithmonopilebyfourhydrauliccylinders. Inthemosttime,thehydraulic
cylindercontactswiththesmoothsurfaceonthemonopile,anditonlybearsaxialload. While,
the monopile is welded piece by piece, its surface is not perfectly smooth due to welds. The
welds collide with the hydraulic cylinder and induce a vertical force on the hydraulic cylinder,
whichmaydamagethehydrauliccylinder.
This thesis analyzes the installation of monopile by HLV and hydraulic hammer. It presents
modelling and calculation for the collision problem between welds and hydraulic cylinder. A
finiteelementmodelformonopile,weldsandgripperisbuiltinAbaqusCAE.Theexternalloads
includinghammerload,soilresistanceandcylinderforceisobtainedfromhandcalculationor
previousthesisandthenappliedintothefiniteelementmodel.Theeffectsofchangingdifferent
parameters(suchasweldsthickness, hammerenergy, initialpenetrationdepthetc.) iscarried
outforanalyzingthemethodforreducingthegripperstressduringcolliding.
ii
Preface
This thesis presents the work done by Rui Xu for the Master thesis, in order to obtain the MSc
in wind energy degree in NTNU and MSc in offshore engineering and dredging in TU Delft.
The work was carried out during spring 2017, in Trondheim. The supervisor was Prof. Andrei
Metrikine (TU Delft), Prof. Zhen Gao (NTNU), Dr. Zhiyu Jiang (NTNU), Dr. Peter Maijers (TU
Delft.)
iii
Acknowledgements
I want to give my sincere thinks to my master thesis committee: Prof. Andrei Metrikine, Prof.
Zhen Gao, Dr. Zhiyu Jiang and Dr. Peter Maijers. I gain a lot from Andrei’s deep knowledge,
experienceandgreatenthusiasmanddisciplineinscientificresearch. Gaoalwaysuseshiswide
knowledge,thoroughmindandpatiencetoguidemeintotherightpath. Zhiyuisalwayshelp-
ful, and, with his genius thought, he can always point out what makes my thesis better. I am
gratefulforPeterwhogivesmegreatcommentonmymasterthesisandfollowsmywork.
I am also grateful for Wilson Guachamin Acero for the excellent discussion about soil pile in-
teraction. I appreciate previous supervisor Prof. Eliz-Mari Lourens’ valuable discussion and
commentsformythesis.
Finally,IwanttogivemydeepestthankstomyfamilyinChinaandmygirlfriendJingyiforthe
greatsupportonmystudyandlife.
RuiXu
July2017
Trondheim,Norway
iv
Contents
1 Introduction 1
1.1 Introductiontowindenergy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Offshorewindenergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.2 Windturbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.3 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Introductiontowindturbineinstallation . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Installationequipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.1 Vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.2 Hammer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4.3 Gripper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5 Windfarmconstructionmethodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5.1 Procurementanddelivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5.2 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5.3 Windturbineinstallation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.6 Monopileinstallation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2 Problemstatement 12
2.1 Aimandscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Introductiontoproblem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Previousstudy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
v
CONTENTS vi
3 Theoreticalbackground 20
3.1 Soilresistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.2 Undrainedbehavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.3 Axialcapacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2 Theoryofrigidpilemodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3 Cylinderforceduringmonopileinstallation . . . . . . . . . . . . . . . . . . . . . . . 29
3.4 Stresswavetheory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4.1 Introductiontostresswave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4.2 One-dimensionalelasticstresswavepropagation . . . . . . . . . . . . . . . . 30
3.4.3 Propagationvelocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.4.4 Relationbetweenparticlevelocityandstress . . . . . . . . . . . . . . . . . . . 33
3.4.5 Reflectionofone-dimensionalstresswave . . . . . . . . . . . . . . . . . . . . 34
3.5 TheoryforcontactandinteractioninAbaqus . . . . . . . . . . . . . . . . . . . . . . 36
3.6 TheoryfornaturalfrequencyextractioninAbaqus . . . . . . . . . . . . . . . . . . . 40
3.6.1 Overviewofnaturalfrequencyextraction . . . . . . . . . . . . . . . . . . . . . 40
3.6.2 Equationsfornaturalfrequencyextraction . . . . . . . . . . . . . . . . . . . . 40
4 Calculationforexternalloads 41
4.1 Soilresistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1.1 Soilproperty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1.2 Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2 Hammerload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2.1 Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2.2 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2.3 Installationtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.3 CylinderforceresultfromLinLi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5 Finiteelementmodel 51
5.1 IntroductiontoAbaqus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.2 Abaqusmodelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
CONTENTS vii
5.2.1 Geometryandmaterialmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.2.2 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.2.3 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.2.4 Boundarycondition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.2.5 Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2.6 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.2.7 Meshsensitivitycheck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.3 Eigenmodesanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.3.1 Naturalfrequencyforpiston-cylinderassembly . . . . . . . . . . . . . . . . . 66
5.3.2 Axialvibrationnaturalfrequency . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.3.3 Naturalfrequencyforsoilsupportedmonopile . . . . . . . . . . . . . . . . . 68
5.4 Pistondecaytest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.5 Choosingpointforoutputdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.6 Verificationofinputhammerloadandsoilresistance . . . . . . . . . . . . . . . . . 74
6 Parametricstudy 80
6.1 Setupforloadcases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.2 Case1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.3 Case2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.4 Case3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.5 Case4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.6 Case5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.7 Case6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.8 Case7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.9 Case8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7 Conclusion 99
8 Futurework 101
Bibliography 102
A Eigenmodeshapesforpiston-cylinderassembly 104