improved foundation models for integrated design - … stavanger presentasjoner...improved...

SMI, Stavanger, 2016-04-06

Kristoffer S. SkauNorwegian Geotechnical Institute

Improved foundation models for integrated design

Houston – 2002

7 persons

Oslo – 1953

220 persons

Trondheim – 2005

20 persons

Kuala Lumpur – 2009

(JV with G & P)

Perth – 2014

7 persons

NGI - Private independent foundation

Established 1953

Consultancy and R&D

National and international clients

Cooperation with universities and research organizations

Key figures

No. of employees = 250

Turnover = around 380 million NOK

6 % from Norwegian Research Council

About 1/3 turnover within Offshore Energy (100 persons)

Soil testing

33

X Y

4 of 31

Instrumentation and measurements

Foundation design

DONG – London Array – 3D FEA with focus on silt layer and effect of sand waves

DONG – Anholt – 3D FEA accounting for cyclic soil behaviour

Statoil – Dudgeon – 3D FEA accounting for cyclic behaviour of glacial till and chalk

Projects

Statoil – HyWind – FEED and complete detailed geotechnical design including cyclic soil behaviour

DONG – Borkum Riffgrund I – FEED and complete detailed geotechnicaldesign including cyclic soil behaviour

DONG – Borkum Riffgrund II – FEED and complete detailed geotechnicaldesign including cyclic soil behaviourand integrated analyses

Projects

REDWIN - Objectives

REDWIN aims at reducing cost in offshore wind by improving the tools used for describing foundation and soil response.

─ The tools should be implemented/integrated in structural programs.

─ The tools should improve important soil issues such as cyclic behaviour, degradation, drainage and damping.

Suction bucket jacket – design processes and

possible loops

Is foundation response important?

Depends on load case and the part of structure we consider

Important for the overall fatigue life

Two examples

Example 1: Jacket on buckets

Variation of FLS

stiffness:

Best Estimate for a site can

deviate from average by a

factor 2 to 3

High- and Low-Estimate

per location 50-200% of

Best Estimate

Example 1: Jacket on buckets

Variation of FLS stiffness:

Soil stiffness Fatigue life

High Estimate 190% 150-250%

Best Estimate 100% 100%

Low Estimate 65% 10-30%

Example 2: Monopile

• Generic OC3 Phase II monopile support structure with NREL 5-MW wind turbine atop

• Distributed Spring model (API p-y curves)

• Fedem Windpower for integrated analysis in time domain

Numerical model:

Schafhirt S, Page A, Eiksund G, Muskulus M (2016)

Influence of Soil Parameters on Fatigue Lifetime for Offshore Wind Turbines with Monopile Support Structure 13th Deep Sea Offshore Wind R&D Conference, EERA DeepWind'2016, 20-22 January 2016,

Trondheim, Norway

Accumulated DEL at mudline normalized to unscaled model:

Soil stiffness (k)

Fatiguedamage

Example 2: Monopile

Foundation response dependencies

Foundation type and geometry

Foundation stiffness dependencies


Stratigraphy/layering




The soil behaviour within each layer, particularly cyclic behaviour




The soil behaviour within each layer

Load level




The soil behaviour within each layer

Load level

Load history




The soil behaviour within each layer, particularly cyclic behaviour

Load level

Load history

Variability across site and uncertainty

Geotechnical analysis

FE-model include foundation, layers, soil properties onelement level

Soil properties representing a cylic degradation often definedprior to the analyses

Apply relevant loads

F=[V,H,M]

Foundation response in integrated analyses

Soil behaviour

Load level and

history

Soil variability

Foundation type

Nonlinear foundation response

Load

Stif

fnes

s

Displacement

Load

Coupled foundation response

The rotational response depends on the vertical load

Ver

tica

l lo

adMoment load

Foundation model

Foundation model = Macro element = Force resultant model = Super element

F=[V,H,M]

The response is determined by both soil and

foundation properties

Expanding series coupled springs to 3D

Multisurface plasticity

Capture stress reversal and coupled response

Produce hystertic damping

Video

../../../../Documents/My CamStudio Videos/loop2.mp4

Foundation model – theoretical concept

IWAN coupled models

uz

A “plastic” spring gets activated when the slider yields

Model response compared to FEM database

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

H/Hmax

V/V

ma

x

Fcy

/ Fa =0

OCR = 4

N=10

uh =0-0.00475, u

h =0.00025

uv =0.0005-0.01, u

v =0.0005

Foundation model response FE caisson response database

Model response compared to FEM database

Foundation model response FE caisson response database

Macro element / foundation

model

F=[V,H,M]

Improved foundation models

Higher accuracy / more reliable ─ Reducing uncertainty and risk is reducing cost

If simpler model are conservative (they should), the design can be further optimized

Model should be presented with different degrees of sophistication (Difference between concept study and FEED)

The cost reduction potential will be evaluated

Implementation in 3D float

Thank you for your

attention!

Questions and feedback,

please.

@infoNGI

NORGES GEOTEKNISKE INSTITUTTNGI.NO