Download - Van Buren, Eric_NTNU
-
8/3/2019 Van Buren, Eric_NTNU
1/22
1
Wind Power R&D Seminar Dee Sea Offshore Wind
Royal Garden Hotel, Trondheim, NorwayJanuary 21, 2011
Effect of Foundation ModelingEffect of Foundation ModelingMethodology on the Dynamic Response ofMethodology on the Dynamic Response ofOffshore Wind Turbine Su ort StructuresOffshore Wind Turbine Su ort Structures
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
2/22
2
AgendaAgenda
Motivations for research
Research Questions
Project details and methods
esu s
Conclusions
Further work
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
3/22
3
To reduce the costs while increasing the performance and reliability ofoffshore wind energy through advancements in foundation modelingtechniques and design methods
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
Courtesy: GL-Garrad Hassan 2009
-
8/3/2019 Van Buren, Eric_NTNU
4/22
4
offshore support structuresoffshore support structures
Support structures make up a much higher percentage of the total costs offshore This trend is likel to continue as water de th increases at wind farm sites
Contribution to Total Cost
Com onent Onshore Offshore
OFFSHORE Turbines (excludingworks)
68-84% 49%
Su ort Structure 1-9% 21%
Grid Connection 2-10% 16%
Consultancy 2-8% 9%
-
Other 2-10% 1%
Courtesy: EWEA 2010
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
5/22
5
Installation DifficultiesInstallation Difficulties ery arge an expens ve ns a a on vesse s are requ re
Foundations and tower must be installed to very precise tolerances
Many components must be installed in calm weather to avoid damage Bad weather can lead to large amounts of downtime , running up costs
Foundation installation is the most time consuming part of the process Extremely large diameter piles or immensely heavy gravity based must be installed
Preparation of the seabed and scour protection may be required Offshore foundations cost 2.5x more than for a similar land-based wind turbine
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
6/22
6
Reducing the costs...Reducing the costs...
Efficiently designed support structures and foundations Specifically engineer foundations for loads and site conditions at each offshore wind
turbine
Develop computer software tools specifically produced for offshore wind turbine
foundation design
Towers and foundations must be designed in a way that is economical to mass-produce
Efficient use of materials, manufacturing facilities, and manpower
Pur ose built offshore wind su ort structure manufacturin facilities will be needed
Improved installation techniques and equipment New foundation technology which is easier and quicker to install
Pur ose-built installation vessels to install wind turbines in a cost effective manner
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
7/22
7
Pile Foundations ModelsPile Foundations Models
Fully coupled finite element model simulation Most comprehensive modeling technique, includes many additional non linear effects
Includes interactions between soil layers (vertical) and between adjacent piles (horizontal) Very time consuming and expensive, requires extensive soil lab testing
S
I
MP
C
E
Sequential analysis with finite element simulations Combines the capabilities of the multiple non-linear spring model with finite element simulations
Allows for dynamic FE simulations of the foundation without the need for a fully coupled model
Multiple non-linear spring representation (p-y curves)
L
I
C
I
T
A
I
N
Dependant on accurate soil profile and characteristic parameters Single non-linear spring representation Entire foundation modeled with single springs at mudline for each DOF
Does not account for pile flexibility or soil profile non-homogeneity
T
Y
&
T
Y
& o e w an equ va en x y ep pparen x y eng
Very simple and fast in computations, more representative than fixed condition
Does not capture any soil-structure interaction
Assume fixed boundary conditions Extremely simple, fast computations
S
P
E
C
O
S Gross misrepresentation of stiffness of the foundation
D
Eric Van Buren, PhD Offshore Wind
-
8/3/2019 Van Buren, Eric_NTNU
8/22
8
efficiency?efficiency? Separately design each pile to give the minimum installation time and maximum
structural efficiency Each foundation designed to only the minimum required length and diameter
Less overall material use, reduced fabrication effort, less time and effort for installation
More time, man-hours, and money spent during the testing and design phase
Develop a single pile design that can be utilized for all structures in the entire wind park ,
Higher overall material use, increased fabrication effort, more difficult installation Less time, effort and money spent in the testing and design phase
VSVS
Eric Van Buren, PhD Offshore Wind
-
8/3/2019 Van Buren, Eric_NTNU
9/22
9
Research QuestionsResearch Questions
1. Do the most sim le modelin techni ues rovide and accurate enou hdescription of the dynamic characteristics to be used for preliminarydesign and analysis?
2. Does the added accuracy and certainty in analysis and design of anoffshore wind turbine foundation when using more advanced modeling
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
10/22
10
Fixed boundary conditions
Apparent Fixity Length (AFL)
Distributed non-linear spring model using force-displacement (p-y) curves
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
11/22
11
certain depth (AFL) below the seabed
AFL chosen to match the stiffness of the pile with distributed spring model - -
Can also be determined based on soil properties
~
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
12/22
12
,
uncoupled spring stiffnesses
Can be determined using two different approaches pp e orce omen me o
Forced displacement/rotation method
Can be modeled with linear or non-linear springs
Borrowed from Zaaijer (2002)
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
13/22
13
Distributed NL spring modelsDistributed NL spring models Force displacement (p-y) curves found in the design standard are used
for horizontal and vertical displacements ISO 19902:2007(E) Petroleum and natural gas industries fixed steel offshore structures (Ch 17)
Dependant on undrained shear strength profile, friction angle, unit weight of soil, and pile diameter
Not really suitable to extremely large diameter piles (such as those used on monopile wind turbines)
Hyperbolic force displacement relationship used for torsional stiffness -
Dependant on undrained shear strength profile, unit weight of soil, pile stiffness, pile diameter
1200p-y curve for clay at depth z=16
12000t-z curve for clay at depth z=16
800
1000
tion(kN/m
2)
8000
10000
tion
(kN/m2)
200
400
600
Subgrade
Reac
2000
4000
6000
SubgradeRea
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
Horizontal Displacement (meters)
Eric Van Buren, PhD Offshore Wind
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
Vertical Displacement (meters)
Effects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
14/22
14
Monotower
Chose a generic design, representative of currently producing turbines
120m height, 35mm wall thickness, diameter tapering from 5.5m to 3m
Full-height lattice tower Designed by former NTNU PhD student Haiyan Long
120m height, 4 legs, 10 sections. 21 meters wide at base, 4 meters at nacelle
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
15/22
15
Monotower ComparisonMonotower Comparison
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
16/22
16
Lattice tower comparisonLattice tower comparison
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
17/22
17
ConclusionsConclusions
Significant discrepancies noted between the different foundation models
Not immediately clear which is most accurate, but worth investigating further
Response is very sensitive to changes in the selected soil parameters More detailed soil descriptions and response models are needed
No interaction between soil layers or between adjacent piles Future models must include 3-D soil interaction effects
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
18/22
-
8/3/2019 Van Buren, Eric_NTNU
19/22
19
Se uential Anal sis FE Method Method used to investigate the response of a piled foundation to the loads experienced on an offshore
wind turbine structure using the finite element method
An iterative process of finite element simulations of the soil-pile structure and the wind turbine structure
Static FEMNL Soil Springs HAWC2 Simulation
oes no a ow a a o ee n o e aero-e as c co e a eac me s ep, on y as n a con ons
Eric Van Buren, PhD Offshore Wind
Dynamic FEM
Time Series Force Data
-
8/3/2019 Van Buren, Eric_NTNU
20/22
20
Full -Cou led FE Model
Foundation, or Geo module to be develop using open source FEM foundation code (such as
OpenSees, Code Aster, etc.)
Geo Module then fully coupled with an Aero-Servo-Hydro-Elastic code (FAST, FLEX5, ADAMS, etc.) ng an ana ys s oo or e oun a on sys em s e as p ece nee e o prov e a proper ana ys s o
the entire wind turbine system
Eric Van Buren, PhD Offshore Wind
-
8/3/2019 Van Buren, Eric_NTNU
21/22
21
Further WorkFurther Work
Develop a FEM code for foundation response which can be coupled to a
Aero-Servo-Hydro-Elastic simulation (Aero-Servo-Hydro-Geo-Elastic) Can be implemented and coupled with FAST/ADAMS or other open source code
Allows for a time domain analysis of the entire wind turbine system
Investigate dynamic processes of scour and the impacts on soil stiffnessand damping Changes in soil properties can have significant impacts on the fatigue life of the structure
Impact will be more significant with shallow foundations such as suction caissons
Extend investigations to suction caissons and other foundation solutions Potential foundation concepts can be used in conjunction with a number of different
tower concepts
a a e numer ca mo e s w e a a
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology
-
8/3/2019 Van Buren, Eric_NTNU
22/22
22
Questions?Questions?
an you or your a en on
Contact:
Eric Van Buren, Ph.D. Candidate, NTNU
Eric Van Buren, PhD Offshore WindEffects of Foundation Modeling Methodology