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DNV GL © 2015 SAFER, SMARTER, GREENERDNV GL © 2015

Floating wind turbines: a large range of engineering disciplines in a single system

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SUT Evening Meeting, 3rd November 2016 at Imperial College, London

Ricard Buils Urbano

DNV GL – Energy Advisory, Turbine Engineering

DNV GL © 2015

Contents

Introduction to DNV GL

History, recent and future achievements

Technology summary

Market predictions and developments required

Design stages of floating wind

Conclusions

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DNV GL © 2015

Introduction to DNV GL

3

DNV GL © 2015

DNV GL experience for the offshore wind industry

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DNV + GL + KEMA + Nobel Denton + Garrad Hassan =

DNV GL Energy

The world’s largest certification and advisory firm in renewable energy

DNV GL © 2015

DNV GL Energy Advisory – Floating wind expertise

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ENERGY

RENEWABLE

CERTIFICATIONRENEWABLE

ADVISORY

DNV GL © 2015

DNV GL Energy Advisory – Floating wind expertise

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RENEWABLE

ADVISORY

Support from Concept to Verification, with design support in all areas and stages of the concept design, from blade tip to the anchor, including integrated coupled analysis of the whole system.

Support in technical due diligence

Several teams of engineers working in Bristol, Netherlands, Høvik, China, etc.

DNV GL © 2015

Strategic Decision Support

Third Party

Analysis

Concept Design Support

Software

The Required Push in Floating wind

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1-2

2-3

3-5

5-6

6-8

8-9

Most

appropriate

to lower TRLs

Most

appropriate

to higher

TRLs

Appropriate

to all stages

along the

TRL

Technolo

gy R

eadin

ess L

evels

DNV GL © 2015

Turbine Engineering Support

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Engineering excellence at the service of wind energy and marine renewables technology

Key services:

Technology evaluation

Design load analysis

Control system development

Mechanical engineering design support

Wave & tidal technical services

DNV GL © 2015

Knowledge transfer: tools and training

Device modeling Array modeling Training courses

We empower our customers to enhance their own capability

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DNV GL © 2015

History, recent and future achievements

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DNV GL © 2015

Brief history of floating wind:

1970’s: early concept by Professor E. Heronemus

1990’s: first small scale tests

2000’s: 10-100 kW range

2010’s: several 2 – 2.5 MW prototypes tested

Technical feasibility has been demonstrated now

Current focus: increase TRL and reduce CoE

DNV GL © 2015

Key recent milestones for floating wind technology

2013: Fukushima Compact Semi 2MW

2013: Fukushima floating substation – floating

substation

2015: Fukushima V shaped semi sub 7MW

2016: Fukushima Advanced spar 5MW

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2009: Hywind demo – 1st spar buoy

2011: WindFloat demo – 1st semi-sub – decommissioned in 2016

2012: Kabashima/Goto Spar – 1st concrete/steel

2013: VolturnUS – 1st concrete semi-sub

DNV GL © 2015

Looking forward, the first small projects are coming soon

WindFloat Atlantic

27.5 MW off Portugal’s coast

30 m€ in funding from

NER300

Operation aimed for 2018

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Hywind Scotland

30 MW off Peterhead in

Scotland

5 x 6MW turbines

Financed by ROCs

In operation from 2017

France: 2 out of 4 projects awarded

Gruissan/Mediterranean: Quadran, 4 x 6MW Senvion, IDEOL (damping

pool), Bouygues

Groix/Atlantic: Eolfi + CGN (China), 4 x 6 MW GE Alstom 6MW, DCNS,

Vinci

Installation 2018-2019

2 more projects to be announced this autumn

WindFloat Pacific: abandonned

DNV GL © 2015


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Gicon SOF

First ever large scale TLP

prototype

Siemens 2.3 MW

Baltic Sea

Commissioning planned for

2016

Japan: NEDO funding

Confirmed consortium: Hitachi Zosen, Ideol (platform designer)

Two 3-5MW turbines, steel and concrete Ideol platforms

Commissioning 2017-2018

Kincardine Pilot

wind farm

48 MW south east of

Aberdeen

Semi-subs platforms

Taiwan

Eolfi to develop at least 4 commercial

floating wind farms up to 2GW / 300

turbines in total

By 2025

FLOATGEN

Demonstration project in France

Ideol platform

DNV GL © 2015


Hywind US

First Californian offshore

wind project

In planning stage

765MW

DNV GL has secured first

contract

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VolturnUS array

2 x 12 MW in 95 meters of water depth

3m USD from DoE to assist completion

of a full scale design

40m USD private investments secured

Goal to install up to 5 GW of floating

wind in Maine by 2030

... and many more!

DNV GL © 2015

Technology summary

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DNV GL © 2015

The three “classic” floating wind technology types

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SPAR Semi-Submersible

TLP

DNV GL © 2015

Other concepts

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Source: MHI

Source: Ideol

Source: Fukushima Forward

DNV GL © 2015

Semi-submersibles

• Stability achieved by buoyancy

• High deflections and heel angles

• Interaction with aerodynamics and control

system

• Turbine to be designed for acceleration

• Catenary or taut mooring

• Varying complexity

• Dry-docking possible

DNV GL © 2015

Spar-buoy systems

• Stability achieved by ballast

• Simple, inexpensive structure

• High depths required

• High mass

• High deflections and heel angles

• Interaction with aerodynamic control

system and mooring

• Special or modified turbine design

• Catenary or taut mooring

• Yaw control -> complicated taut mooring

DNV GL © 2015

Tension-leg Platforms

• Stability from mooring force

• Stable platform, low roll and pitch angles

• Small mooring area (footprint)

• Expensive taut mooring (pre-stressed

cables)

• Cables have to be always in tension

• Prone to fatigue loading (connections)

• Sensitive to yaw load

• High water depth required

DNV GL © 2015

Market predictions and developments required

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DNV GL © 2015

Why floating wind at all?

Advantages against fixed:

– Deeper water available (better wind resource) – only viable option for some

countries

– ... but also shallower water possible depending on concept

– Easier and cheaper transport/installation and maintenance? (no need of heavy

lift vessels)

– Less site dependent – more standardisation

Disadvantages:

– More coupled dynamics – more overall system motion – more integration

– More Technical integration required

– More Contractual integration required

– CAPEX higher: platform, moorings, dynamic cables, ...

Potential for equal/reduced CoE for offshore wind

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And it’s cool!

DNV GL © 2015

Floating wind landscape

Three geographical areas: Europe, Japan, United States

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Source: DNV Kema for The Crown Estate, “UK Market potential and technology assessment for

floating offshore wind power, 2012”

Source: “Floating Offshore Wind:

Market and Technology Review”,

Carbon Trust, June 2015

DNV GL © 2015

Water depth in Europe

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< 50m depth

DNV GL © 2015

Deep waters close to major population centres

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DNV GL © 2015

Floating wind markets - JAPAN

Steep electricity prices – high feed-in tariff

Generation & transmission capacity shortage

Wind energy targets of 75 GW by 2050 - 18 GW by floating

Strong maritime tradition

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Water depths between 100 – 500 meters, within 50 km from shore is indicated by the yellow areas (DNV GL)

DNV GL © 2015

Floating wind has just started to move into the CRI scale

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Source: http://arena.gov.au/files/2014/02/Commercial-Readiness-Index.pdf

Pilot wind farms developments

TRL CRI

DNV GL © 2015

Commercialization prediction for different concepts

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Source: DNV Kema for The Crown Estate, “UK

Market potential and technology assessment for

floating offshore wind power, 2012”

Source: “Floating Offshore Wind: Market and

Technology Review”, Carbon Trust, June 2015

DNV GL © 2015

CAPEX breakdown for a commercial scale floating wind farm

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Source: “Floating Offshore Wind: Market and Technology Review”, Carbon Trust, June 2015

DNV GL © 2015

CAPEX reduction from prototype to commercial scale floating wind farm

Source: “Floating Offshore Wind: Market and Technology Review”, Carbon Trust, June 2015

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OPEX?

DNV GL © 2015

Floating wind commercialisation initially likely driven by technology improvements

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100 %

55 %

2015 2020 2025 2030

LC

OE

, co

st

ind

ex in

%

Estimated LCOE reduction 2015 – 2030

TECHNOLOGY IMPROVEMENTS

MARKET GROWTH

TECHNOLOGY IMPROVEMENTS

MARKET GROWTH

STABLE POLICY ENVIRONMENT

COMPETITION IN SUPPLY CHAIN

Predictions for 2020s• Potential for reaching cost

parity with fixed bottom• £85-95MWh

DNV GL © 2015

Average LCOE of onshore wind 1984-2011 (Eur/MWh)

Source: Bloomberg New Energy Finance, ExTool

14%

Global

Denmark and

Germany

1984 1990 2000 2004 201110

50

100

500

1000

100 1,000 10,000 100,000 1,000,000

MW

14% drop in LCOE for every

doubling of installed capacity

DNV GL © 2015

Next steps

Currently floating wind depends heavily on public subsidies for demonstrators

Next steps:

– Pilot wind farms

– Increase TRL

– Practical issues: transport/installation

– Gain knowledge from naval/oil&gas industries

– Decrease CoE

– Shared risks!

– New investment and risk sharing mechanisms needed

– Wind turbine OEMs still a bit skeptical/lack of engagement: some interested,

some keep dropping out of projects... Risk-averse mentality to new

technology... especially after offshore fixed experience?

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DNV GL © 2015

Historical offshore wind CAPEX trends

Source: DNV GL

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DNV GL © 2015

IN-FLOAT concept: example of industrialization

https://www.youtube.com/watch?v=ypzkuV8d_Mc

(4min video)

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DNV GL © 2015

Design stages of floating

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DNV GL © 2015

Turbine+platform: iterative design process

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Turbinedesign

Platformdesign

Numericalmodelling

Scale model testing

Numericalmodel

validation

Control design

Loadcalculations

Certification

Prototype +

commercialization

Platform strength analysis/optimisation

Control re-tune/turbine re-design?

DNV GL © 2015


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Turbinedesign

Platformdesign

Numericalmodelling

Scale model testing

Numericalmodel

validation

Control design

Loadcalculations

Certification

DNV GL © 2015

Turbine design

• Normally pre-designed to type class

• Very flexible

• Frequency constraints

• Active controller

Platform design

• Normally pre-designedaccording to naval experience

• Relatively rigid

• Often self-called “turbineagnostic”

Turbine + floating platform

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Strong coupling

between the two!

Close interaction is

needed between two

parts from early start

Turbine changes typically needed:

- Re-design controller

- Re-design tower and perhaps other

components

DNV GL © 2015

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Sp

ectr

al

Den

sit

y

Frequency (Hz)

Excitation frequencies

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1P 3P

Wave energy spectrum

Platform rigid

body modes

Controller

bandwith

Rule of thumb: avoid freqs

(periods) in the range of

0.04Hz (25s) to 0.25Hz (4s)

DNV GL © 2015


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Turbinedesign

Platformdesign

Numericalmodelling

Scale model testing

Numericalmodel

validation

Control design

Loadcalculations

Certification

DNV GL © 2015

Critical Design Issue: Load Analysis

• Aerodynamic and hydrodynamic loading

• Consideration of dynamics

– Rigid body movement

– Mooring

– Large deflections

– Interaction with control system

– A range of simulation codes exist and

ongoing further development, but need

to be validated further

– Model tests

– Prototype tests

– New load cases needed

DNV GL © 2015

Different levels of modelling fidelity

Full CFD-FEM methods

– Navier-Stokes equations

– Continuum mechanics

Aero-hydro-servo-elastic codes

– State-of-the-art for coupled dynamic analysis

– BEM aerodynamics

– Morison/Potential flow for hydro

– Include effect of the controller

Reduced order models

– Coupled/de-coupled

– Semi-empirical

– Frequency domain methods

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Detailed component

design

Wind turbine +

platform dynamics,

control design and

loads analysis

Accura

cy

Com

puta

tionalspeed

Initial studies

DNV GL © 2015

Floating turbine modelling in Bladed

Industry standard turbine design software

In 2010 Bladed had its structural dynamics core

replaced with a multi-body formulation to make it

simpler and more accurate to model complex

structures

A floating module was released for the first time

with Bladed v4.1 (2011)

This allows fully coupled simulations which include

– both wind and wave loading

– structural dynamics

– global support structure translations and rotations

‘Advanced hydrodynamics’ in Bladed v4.6 (2014)

4 November 2016Private and confidential

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DNV GL © 2015

Hydrodynamics Modelling Options in Bladed


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Morison Model

• Semi-empirical

• Added mass radiation

• Froude Krylov excitation

• Instantaneous hydrostatics

• Viscous drag

• Wide range of sea state

definition options

• Diffraction correction based

on MacCamy Fuchs

BEM Model

• Analytical, reliant on

potential flow solver

• Added mass and damping

radiation

• Froude Krylov and diffraction

excitation

• Linear hydrostatics

• Viscous drag (from Morison)

• Linear, Airy waves only

Future/ongoing developments:

Dynamic moorings

Second order wave forcing

DNV GL © 2015

Iterative design process

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Turbinedesign

Platformdesign

Numericalmodelling

Scale model testing

Numericalmodel

validation

Control design

Loadcalculations

Certification

Main purpose is to validate/calibrate numerical model and reduce design risk. May lead to design optimisationNote wave/wind scaling issues

DNV GL © 2015


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Turbinedesign

Platformdesign

Numericalmodelling

Scale model testing

Numericalmodel

validation

Control design

Loadcalculations

Certification

DNV GL © 2015

The wind turbine controller


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Controller

Flexible blades

Flexible shafts

Pitch actuators

Flexible tower

Flexible mountings

Power and speed transducers

Torque drive

Measured powerMeasured speedWind speedYaw errorBlade loadsTower acceleration…

Pitch demandsTorque demandYaw demandBrake on/offContactor on/off…

The controller is the heart of the wind turbine. It makes use of the available inputs to determine its operation and is responsible for its performance & safety.

DNV GL © 2015

Why it is important


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Rotor diameter (m)

Rated power (kW)

The role of control algorithm design

• Reducing component cost and increasing component lifetime

• A real enabler with constantly increasing rotor sizes

• The larger benefits are obtained where control design is integrated at

an early stage in the overall design process to explore trades

DNV GL © 2015

Elements of the turbine controller

Power production control

– Regulation of power and/or speed

– Avoiding excessive actuator demands

– Alleviating turbine loads

– Maximise controller robustness against model uncertainties and nonlinearities

Supervisory control

– Logic for start-up, shutdown

– Alarms, fault detection and handling

– Health monitoring and data collection

Safety system

– It is NOT part of the control algorithm

– Simple hardware to ensure failsafe operation

– Activated when, as a result of an internal or external failure or of a dangerous

event, a wind turbine is not kept within its normal operating limits


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DNV GL © 2015

Floating wind controllers: low frequency dynamics challenge

Platform natural periods chosen to avoid wave excitation

However they clash with the wind excitation

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Flo

atin

g tu

rbin

e s

urg

e m

ode

Flo

atin

g tu

rbin

e s

urg

e m

ode

Wave spectrum Wind spectrum

Wind Spectrum based on work by van der Hoven (1957)Wave spectra of a fully developed sea for different wind

speeds according to Moskowitz 1964

DNV GL © 2015

Damping of tower/platform motion

Pitch control can have adverse effects on the damping of the 1st tower fore-aft

mode (or, in floating turbines, of the platform surge and pitching modes)

Damping of these modes can be increased by adding a parallel control loop, which

uses the nacelle fore-aft acceleration signal to generate an additional pitch demand

This results in a decrease in the structural loads related to these modes


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WIND TURBINE

TOWER/PLATFORM STABILISATION

PITCH-SPEED CONTROL

+

GENERATOR SPEED

NACELLE FORE-AFT ACCELERATION

PITCHDEMAND

DNV GL © 2015


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Turbinedesign

Platformdesign

Numericalmodelling

Scale model testing

Numericalmodel

validation

Control design

Loadcalculations

Certification

DNV GL © 2015

Standards relating to floating wind

• DNV, Design of Floating Wind Turbine Structures DNV-OS-J103, 2013

• GL RC, Guideline for the Certification of Offshore Wind Turbines, 2012

• IEC 61400-3-2: under development

• Bureau Veritas, Classification and Certification of Floating Offshore Wind Turbines, 2010

In addition to this, industry needs to develop best practices for floating wind load calculations – and to share new knowledge within industry!

DNV GL © 2015

How do environmental conditions differ from offshore fixed?

Prone to larger misalignments wind-waves due to swells?

– Wind-wave misalignment more onerous?

– Two peaked spectra appropriate?

Ice accumulation: turbine and platform?

Sea ice: to platform, moorings,..?

Breaking waves?

Slamming, sloshing, green water

Particular gust cases for floating: EOG, EDC, ECD

Additional fault cases?

4 November 2016

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DNV GL © 2015

New DNV GL Design of floating wind turbine structures standard under development based on DNV-OS-J103

DNV-OS-J103 developed through a Joint Industry Project (JIP), first issued in

2013. Can be downloaded for free on www.dnvgl.com

Being updated during 2016 as part of the harmonization of the DNV GL codes for

the wind industry after the DNV GL merger in 2013

Since 2013 the industry has developed:

– numerous guidelines for the design of floating wind turbine structures have

been published by various certifying bodies

– an IEC technical specification on the subject is under way

– several prototypes have been installed and the first small array of floating

turbines are currently being developed

The new revision is intended to reflect

– the experience gained after the first issue was published in 2013

– the current trends within the industry

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DNV GL © 2015

DNV GL JIP on Recommended Practices for Floating wind turbines

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TLP Spar Semi Barge

Modelling & validation

Model Test Analysis

Industrial agreed recommended practices, based on:

Experience from the selected case studies

Experience from all participants

New analysis run during the project to validate/integrate

the state of art experience

DNV GL © 2015

Next steps

Priority areas for further technology development:

– Reduce platform size / CAPEX

– Installation and maintenance procedures (particularly for TLP and spar buoys)

– Improved mooring and anchoring systems

– Advanced control systems

Maintain/increase public funding

Gain more engagement from turbine OEMs and private investors

New mechanisms for shared investments / risks within the consortiums

Technology has been demonstrated, now it needs to be made cost effective

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DNV GL © 2015

SAFER, SMARTER, GREENER

www.dnvgl.com

Let’s make this happen!

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Ricard Buils Urbano

[email protected]

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