wave and wind power seminar - cesos.ntnu.no · 1 introduction by torgeir moan, cesos wave and wind...

1

Introduction by

Torgeir Moan, CeSOS

Wave and wind power seminarwith a focus on

the use of floating facilities

CeSOS, May 27. 2008

2

WIND

LAND

HEAT

OCEAN-waves

-currents

Sources of renewable energy- of primary interest to Norway

Facilities for transforming the energy into- electrical energy- possibly other uses

Solar cell

3

Source: Tande, SINTEF

Wind in Norway4

Wind turbine concepts

Bottom supported Buoyantsupport structures

tower

bladehub

nacelle

5 MW

5

PelamisWaves

Prototype: 750 kW

Power conversion module

The Pelamis during sea trials (Picture from Ocean Power Delivery)

6

Fred Olsen conceptWaves

Rotor/flywheel for smoothing energy

Transfer of wave motioninto electric power:- hydraulics- mechanical- direct drive (linear generator)

7

3D Model of the Point absorber (Picture from Danish Wave Energy)

Principal drawing of thePoint Absorber (Picture from Rambøll)

Schematic of the Aquabouy

Other devices for converting wave power

And devices for converting current power(resembling wind turbines)

8

Site specific design criteria• Wave- wind climate • Bathymetry• Facilities for maintenance

Platform hierarchy/clustering• Platform grouping• Farm control• Replacement of units

Electrical infrastructure• Net connection• Connection between

platforms to main platform(s)• Smooting power

System configuration of power- producing units

9

Data, methods,criteria

Fabrication & Operation

data

Layout/Scantlings

Design for- serviceability &- producability- safety

Fabrication &installation- Fabrication plan -- Inspection/repair

Operation- Operation plan

Inspection/monitoring/ repair / maintenance

Removal and reuse

Reassessment

Life Cycle Phases of Marine Structures

Example: Spar wind turbine

+ Installation ofthe mooring system

10 The challenges

A) Power production- Power = Force · velocity- Power smoothing

B) Safety for Man, Environment and PropertyEnvironmental issues relating to

- occupation of space - oil leaks

Life cycle costs- fabrication & installation- maintenance and repair due todamages due to extreme events, fatigue and wear and tear

Optimal solution ?

Ratio of power producing forces and maximal forces in the system n)- shut down during worst load scenarios (”load shedding”)

Survivability beforePower Capture Effect

11

Aim & Scope of this seminar• Power production

- basic principles- equipment

• Availability & Safety

• Dynamic modelling of the integrated system

Functionality BeforeLunch

Afternoon

the environment mechanical/ electricalhydraulic generator

Identify challenges

12

Program

Power generation 0915 Wave power – some basic principles and use of latching by Professor Johannes Falnes, NTNU 1000 System modelling and application of automatic control of wave power

(wave motion, hydraulics, electric generator) by Jørgen Hals, CeSOS

1030 Power production in a wave energy converter – Effect of controls and operational constraints by dr. Karl Erik Kaasen, MARINTEK

1100 Break

1115 Wind induced power – basic principles of power take-off and equipment by Professor Ole Gunnar Dahlhaug, NTNU 1215 Lunch Dynamic analysis of floating systems subjected to wave- and wind loads 1315 Introduction by Professor Torgeir Moan, CeSOS 1330 Dynamic modelling of multi-body structures – for wave power generation by Reza Taghipour, CeSOS 1400 Dynamic modelling of wind turbines under combined wave and wind loading by Dr. Rune Yttervik, StatoilHydro 1430 Coffee break 1445 Mooring of floating plants by Dr. Zhen Gao, CeSOS 1515 Discussion: Challenges for the future. 1600 End of the day

1

1

Wave power:Some basic principles and use of latching control

Johannes Falnes

Lecture at CeSOS seminar,

NTNU, Trondheim, 27 May 2008:

Institutt for fysikk, NTNU&

Centre for Ships and Ocean Structures, NTNU

http://folk.ntnu.no/falnes http://www.ntnu.no/fysikk http://www.cesos.ntnu.no

<[email protected]>

2

Renewable energy

WIND

LAND

HEAT

OCEAN

Global resource of renewable energy:

Energy flow from the sun to our planet: ∼1017 W

Power in all the world’s winds: ∼1015 W

Power in all the world’s ocean waves: ∼1013 W

2

3

Wind energy is more persistant than solar energy. Winds may blow during nights.

Wave energy is more persistant than wind energy. Swells may exist in cases of no wind.

We have more wind energy and wave energy in winter than in summer.

4

•

••• Wave energy: 2 - 3 kW/m2

• Average energy intensity:

• Solar energy: 100 - 200 W/m2

•

•• Wind energy: 400 - 600 W/m2

3

5

• As we have seen, the water particles move in circles with decreasing radius in the depth. Consequently, the energy flow density decreases as we go deeper in the water. In fact, on deep water, 95 % of the energy transport takes place between the surface and the depth L/4. (L is the wavelength).

Vertical distribution of wave-energy transport

Dep

th

2

4

6

8

3,0 kW/m2

1,3 kW/m210 m

Water level

H = 2 m and T = 10 s

kW/m21 0 3 2

J = 40 kW/m

6

Ring-shaped waves from a stone dropped into a calm lake

Photo: Magne Falnes, 1999

4

7

Swells propagating across the Pacific

• Since the group velocity is proportional to the period, low-frequency waves move faster away from a storm centre than high-frequency waves. The figure shows the situation 4 days after a storm with centre located at 170º east and 50º south.

T = 20 s

T = 18 s

T = 16 s

T = 14 s

T = 12 s

T = 10 s

Period

-10

-20

-30

-40

180 190 200Source: OCEANOR, Norway

8

Energy content of waves• For a sinusoidal wave of height H, the average energy E stored on a

horizontal square metre of the water surface is:

• Half of this is potential energy due to water lifted from wave troughs to wave crests. The remaining half is kinetic energy due to the motion of the water.

2HkE E=

2s/mkW 52m:Example ⋅=⇒= EH

kE = ρ g / 8 = 1.25 kW ·s/m4

ρ = mass density of sea water ≈ 1020 kg/m3

g = acceleration of gravity ≈ 9.8 m/s2

5

9

Energy transport in waves• The energy transport per metre width of the wave front is

2THkJ J=

kW/m402m and s10:Example

=⇒== JHT

EcJ g=

On deep water the group velocity is cg=gT/4π, which gives

kJ = ρ g2 / 32 π ≈ 1 kW/m3s

10

Governmental funding of wave-power R&D from 1978.

UKNorwayTrondheimNTH

Those who cannot remember the past are condemned to repeat it.(George Santayana, 1863–1953, American philosopher. In 1905 in his treatise ”The Life of Reason”.)

No substantial increase in Norway during 1995-2008

6

11

Kjell Budal(1933-1989)

- initiated wave power research at NTH, Trondheim, 1973- already in 1977 made a theoretical study of wave-power

absorption by a group of interacting oscillating bodies- invented many different types of wave-power buoys- proposed latching control of phase (and amplitude)- advocated reasonably small power buoys, operating at

full capacity a rather large fraction of the year

12

• Absorption of wave energy from the sea may be considered as a phenomenon of wave interference. Then wave energy absorption may be described by an apparently paradoxical statement:

• To absorb a wave means to generate a wave • or, in other words:

• To destroy a wave is to create a wave.

A paradox?

7

13

Incident wave + reflected wave = standing wave

• Incident wave

• Wave reflected from fixed wall

• Interference result: Standing wave composed of incident wave and reflected wave

=

+

14

=

+

• Incident wave

• Wave reflected from fixed wall• Wave generation on otherwise

calm water (due to wall oscillation)

• Result: The incident wave is absorbed by the moving wall because the reflected wave is cancelled by the generated wave.

“To absorb a wave means to generate a wave”- or “to destroy a wave means to create a wave”.

8

15

Array of buoys in heave and in surge/pitch

incident wave

radiated by heave

radiated by surge/pitch

d = a+b+c, superposed

To absorb a wave means to generate a wave.

[Illustration from: Falnes, J. and Budal, K.: "Wave power conversion by point absorbers". Norwegian Maritime Research, Vol 6, No 4, pp 2-11, 1978.]

16

Two upper bounds PA og PB for the power P that can be absorbed by means of an oscillating body of volume V when the wave is sinusoidal with period T and amplitude H/2. [Figure 2 in the paper: Falnes, J. "A review of wave-energy extraction". Marine Structures, Vol 20, No 4, pp 185-201, 2007. (DOI: 10.1016/j.marstruc.2007.09.001)]

9

17

Budal's latching-controlled-buoy type wave-power plant

J. FALNES and P.M. LILLEBEKKENInstitutt for fysikk,

Noregs teknisk-naturvitskaplege universitet (NTNU),N-7091 Trondheim, Norway

Paper published inFifth European Wave Energy Conference: Proceedings of an International Conference held at University College Cork, Ireland, 17-20 September 2003. (Edited by Anthony Lewis and Gareth Thomas. Organised & Published by Hydraulics & Maritime Research Centre, Cork, Ireland, 2005, ISBN 0-9502440-5-8), pp. 233-244, [http://folk.ntnu.no/falnes/w_e/budal_latch_buoy_2003.pdf]and presented 2003-09-19 at the 5th European Wave Energy Conference:

Most of the presentation given 2003-09-19 is indicated on the following slides:

18

t

Optimal phase at resonance

Phase control by latching

[Reference: Falnes, J. and Budal, K.: "Wave power conversion by point absorbers". Norwegian Maritime Research, Vol 6, No 4, pp 2-11, 1978.]

10

19

Video clip A (mpg): Latching-controlled buoy models in wave channelReference: Budal, K., Falnes, J., Kyllingstad, Å. and Oltedal, G.: "Experiments with point absorbers". Proceedings of First Symposium on Wave Energy Utilization, Gothenburg, Sweden, pp 253-282, 1979. (ISBN 91-7032-002-0)

20Video clip C (mpg): Latching-controlled buoy of type E in wave tank

[Video clip on http://folk.ntnu.no/falnes/w_e/index.html]

11

21

Point absorber of "type E" with hydraulic machinery.

V1 - controllable valveV2, V3 - check valvesA1, A2, A3 - gas accumulatorsA1 is for latching controlA2 - high pressure accumulatorA3 - low pressure accumulatorM - hydraulic motor (turbine)

MC - mooring cable (or rod)PR, P - piston rod, pistonC - hydraulic cylinder

22

Building-up of latching-controlled buoy's heave oscillation to a stroke length of 0.8 m in wave of height 0.16 m and period 3.1 s. (Type E buoy model test)

12

23

Upper graph shows the force in the mooring strut varying over a 9-kN range.

Lower graph shows: Building-up of input energy Eb from 5.6 kJ to 11.4 kJ during 25 s when the incident wave has a height (0.18 ± 0.02) m and a period 3.1 s.

(Type E buoy model test.)

24Video clip D (mpg): Latching-controlled buoy of type M2 in wave tank


13

25

Point absorber of "type M2" with pneumatic machinery.

C, P, PR - cylinder, piston, piston rod RD - diaphragm seals, A2 - energy-storing gas accumulatorV2 and V3 - rectifying check valves AI and AO - air inlet and outlet pipesER - engine room containing turbo-generator. Mooring strut MS, connected to universal joint UJ, is pre-tensioned by pressure in accumulator A1.Relative motion of the buoy along piston rod PR may be latched/unlatched by activating/deactivating mechanism L. The system is provided with guiding rollers G, end stop buffers ES, ballast weight W, and rolling diaphragm seals RD.

26

Array of point absorbers (latching-controlled buoy of type N2)

Source: SINTEF, Trondheim, Norway, 1982.

[Illustration used in White paper: Om nye fornybare energikilder i Norge, St.meld. nr. 65 (1981-82), The Royal Ministry of Petroleum and Energy, Oslo, 1982,and in Budal, K., Falnes, J., Iversen, L.C., Lillebekken, P.M., Oltedal, G., Hals, T., Onshus, T. and Høy, A.S.: "The Norwegian wave-power buoy project". Proc. Second International Symposium on Wave Energy Utilization(H. Berge, ed), pp 323-344, 1982. Tapir, Trondheim, Norway. (ISBN 82-519-0478-1)]

14

27

Power buoy of type N2.

Buoy hull B, connected to submerged weight W, through cables C, is arranged to move along mooring strut MS

Buoy hull B, connected to submerged weight W, through cables C, is arranged to move along mooring strut MS, connected to universal joint UJ on anchor A. Hull B contains a latching mechanism and an OWC with rectifying valves, air turbine and electric generator.

28Video clip E (mpg): Latching-controlled buoy of type N2 in sea


15

29

Model (in scale 1:10) of power buoy of type N2. B – hull (diameter 1 m), open in the bottom, for providing communication with an internal OWC. BC – annular air chamber providing buoyancy. G –guiding rollers MS – mooring strutL – latching mechanismD – air duct O – calibrated orifice SS – supporting stay FW – flow-evening housing UJ – universal joint A – anchor

30

Experimental results from sea tests with N2 model.

Absorbed power Pa (measured) versus theoretical estimate Pt.The square points (red) obtained with modified buoy hull.

16

31

Modified hull

- larger opening

- larger radius of curvature

[Illustration used in 1993 paper # 111 as specified in the publication list http://folk.ntnu.no/falnes/w_e/publwave.html.]

32

Hs /m T-1 /s J /Wm-1 Latching strategy Pa /W (Pa /J)/m0.24 2.5 69 2 latchings/cycle 18 0.260.24 2.5 69 1 latching/cycle 16 0.230.22 2.5 58 Latched all time 7 0.12

Power absorbed for three consecutive runs of the N2-buoy model, with different latching strategies.

The significant wave height Hs was slightly reduced at the time when the third run was made.

Different latching strategies.

17

33

– upper graph –and one latching interval per oscillation cycle ("mode 2") –lower graph – .

Measured values (in metres) of the N2 model position relative to the strut, during 100 seconds. Two latching intervals per oscillation cycle ("mode 1")

34

Measurements from another "mode-2" run with the sea-tested N2 model.

Buoy velocity relative to the strut (in m/s) and of the hydrodynamic pressure (in kPa) at the collar on the strut, which pressure is a measure of the wave.

18

35

Acknowledgements.

Jørgen Halsdrew the illustrations used in slides 2, 5, 13, 14, 16 and 18 of this presentation.

Per Magne Lillebekkendrew the illustration used in slide 10, and from an existing analogue video, he also digitalised the video clips shown during the presentation (corresponding to present slides 19, 20, 24 and 28.)

36

Those who cannot remember the past are condemned to repeat it.(George Santayana, 1863–1953, American philosopher. In 1905 in his treatise ”The Life of Reason”.)

1

1

J. Hals: Power take-off systems for wave energy converters

Power take-off systems for wave energy converters

Jørgen Hals, PhD studentCentre for Ships and Ocean Structures (CeSOS)Norwegian University of Science and Technology (NTNU)Norway

NTNU Marinteknisk senter, 27 May 2007

2


Outline

Some aspects of wave power and its conversionThe three main roads to electricityProperties compared

Source

: Nati

onal

Ocean

ic an

d Atm

osph

eric A

dmini

strati

on, U

S

2

3


Scope...

limited to oscillating systems, not over-topping devicesconversion to electricity

Source: Hagerman

4


Power flow in wave energy conversion

3

5


The equation of motion- machinery force

( ) ( )m mF t R tη= − &

( ) ( ) ( )m m mF t R t S tη η= − +&

( ) ( ) ( ) ( )m m m mF t m t R t S tη η η= − + +&& &

( ) ( ) ( )m mF t R t tη= − &

( )( ) ( ), ( ), ( ), ( ),m eF t f t t t F t tη η η= & &&

( )( ) ( ) ( ) ( ) )( ) () (r r mem m t R t S t F t F tω η ω η η+ + + = +&& &

accelerated mass radiated waves buoyancyforce

waveexciation

force

machineryforce

|

PTO

R 5.0 m

η

z

x

( ) ( ) ( )m mP t F t tη= &

Useful power:

6


Instantaneous power

The minimum peak-to-average power ratio is 2, but in practice considerably higher → need for energy storageTypical machinery force in the order of 1 MN.

-10

10

30 Instantaneous power

0 5 10 15 20 25 30 35 40time {s}

-1-0.5

00.5

1Position

Source: Henderson., 2006

4

7


The three main roads to electricity(seen today...)

Air turbine (+generator)Hydraulic pump (+generator)Direct-coupled electric generator

8


Air turbines – used for OWCs

Wells turbineImproving performance through

– guide vanes– blade pitching– counterrotating turbines

Close to linear P/Q relationship

Impulse turbineImproving performance through

– guide vane design and pitching

Self-startingNo stallNonlinear P/Q relationship

Source: JAMSTEC, JapanSource: Setoguchi et al., 2001

Inherent energy storage in shaft rotationPneumatic gearing

5

9


Efficiency for air turbines

Average efficiencies in operated plants typically range from 35 to 50 %(pneaumatic to shaft power)

Source: Setoguchi et al., 2001Source: Richard Curran and Matthew Folley, 2008

10


Hydraulic systemsHydraulic pumps, rotary or linearFluid power equipment easilyavailable, but not optimised withregard to lossCan take large forces and largepowerHigh power densityNeed for lubrificationNon-linear force characteristicEfficiency in the range 0.5-0.8 (mechanical to motor shaft power)

Source: Jamie Taylor 2008

or

6

11


Emulating a linear PTO force- time series from the Pelamis device

Source: Henderson., 2006

12


Direct-coupled electric generators

Linear permanent-magnet generator, flat or tubularDemand for high force gives big machinesNon-linear force characteristic, but is easily controlledSimple; few moving componentsElectrical energy is storage a challenge

Source: Danielsson et al., 2008

7

13


Source: Danielsson et al., 2

008

Sour

ce:

Prad

o, 2

006

14


Half a wave cycle of linear generator operation

Source: Polinder et al., 2004

Efficiency(from mechanical to grid)

8

15


Source: Neumann et al., 2006

14:30 14:35 14:400

50

100

150

200

Time

Con

verte

d po

wer

[kW

]

Source: Henderson, 2006

Air turbine, Pico plant

Hydraulic PTO, Pelamis

Direct-coupled generator, AWS

16


Properties compared

SmallerLargerLargerSize (tendency)

Good (gasaccumulators)

DifficultModerate(shaft+flywheel)

Energy storage

Large forceLarge velocityLarge velocityForce or velocitypreference

HighLowHighNumber of components

0.5-0.8 (?)0.8-0.90.35-0.6Efficiency (average)

HydraulicsLinear generatorsAir turbines

9

17


So what is the best choise?

Depends onconceptfuture developments in each technologyend use (electricity or other)need for energy storage

1MARINTEK

Wave and wind power seminar at CeSOSMay 27 2008

Power production in a wave energy converter. Effect of controls and operational constraints

Karl E. Kaasen, MARINTEK

2MARINTEK

Topics

Heaving buoyFrequency domain modellingLinear power take-offIdeal world power maximisationRegular waves vs. spectral wavesConstrained maximisation

3MARINTEK

Vertically moving buoyCase studied

Z

Wamit panel model(50 % submergence)

Diameter: 3.5 mMass: 20 tonsHeight, top-bottom: 5.25 m

4MARINTEK

PTO as feedback from measured vertical speed

-

FE

FC

H(ω)

G(ω)

w

FE

FC

Theoretically optimal feedback:

G(ω) = 1/H(ω)*

(* = complex conjugation)

PTO dynamics

Buoy vertical velocity

Excitation forcefrom waves

Controlforce

Buoy dynamics

5MARINTEK

Electrical equivalent (simpler and more intuitive)

E

I Z+

U

ZL

U = E - Z·I

load

˜ Internal impedance

E ~ FeU ~ FCI ~ u

Optimal load: ZL = Z*

6MARINTEK

Power from a buoy in waves(J. Falnes)

21 1 12 2 2

21 12 2

(Available forcefor power generation)

Re{ } Re{ }

cos

exp( ), exp( )

, ,

e

e

e

e

e

e e F u

u F

F F Zu

P Fu F u Z u

F u R u

F F j u u j

Z R jX R B X A

γ

ϕ ϕ

γ ϕ ϕ

ω

= −

= = −

= −

= =

= −

= + = =(Z is the radiation ”impedance”)

7MARINTEK

Power as a function of velocity amplitude (1 m wave amplitude, ω = 1.0 rad/s)

0 5 10 15 20 25 30-5

-4

-3

-2

-1

0

1

2

3x 10

5

Amplitude of velocity (m/s)

Pow

er (W

)

gamma = 0gamma = 45 deg

8MARINTEK

Buoy in regular waves

10 20 30 40 50 60

-6

-4

-2

0

2

4

6

Phase = 0, no power

0 10 20 30 40 50 60

-6

-4

-2

0

2

4

6

Phase = pi/2, max power

9MARINTEK

Power maximisation

2 2

maxcos cos

for8 2

e eF FP u

R Rγ γ

= =

2

for cos 1,8 2e e

MAXF F

P uR R

γ= = =

Maximisation with respect to velocity amplitude, u:

Maximisation with respect to u and phase angle difference, γ:

10MARINTEK

Max power PMAX as function of frequency

Hypothetical (no constraints) for 3.5 m Ø buoy. 1 m wave amplitude

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2104

105

106

107

108

Frequency (rad/s)

Pow

er (

W)

11MARINTEK

Optimum amplitudes of velocity and position(but violating premise of linearity)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2100

101

102

103

104

Frequency (rad/s)

Velocity amplitude (m/s)Position amplitude (m)

Draught

12MARINTEK

Added mass and damping at various draughts

67 % draught 50 % draught

33 % draught 15 % draught

13MARINTEK

Excitation force at various draughts

0 5 10 15 20 25 300

20

40

60

80

100

Period T (s)

Hea

ve fo

rce

F 3 (k

N)

One egg alone

0 5 10 15 20 25 300

5

10

15

20

25

Period T (s)

Hea

ve P

hase

(deg

)

One egg alone

Draught 67 %Draught 50 %Draught 33 %Draught 15 %


14MARINTEK

Added mass and damping at various draughts

0 5 10 15 20 25 304

6

8

10

Period T (s)

Adde

d m

ass

Hea

ve A

33 (t

onn) One egg alone

0 5 10 15 20 25 300

2

4

6

8

Period T (s)

Dam

ping

Hea

ve B

33 (k

N/(m

/s))



15MARINTEK

0 0.5 1 1.5 2 2.50

0.5

1

1.5

2

2.5

3 x 104

Frequency (rad/s)

Mass, added mass, total mass

kg

Total massAdded massDry mass

(50 % draught)

16MARINTEK

Power absorption in spectral seas.How to choose controller characteristics?

0 0.5 1 1.5 2 2.5 30

0.5

1

1.5Jonswap spectrum, Hs=2.75, Tp=6.25, gamma=3.3

Frequency (rad/s)

17MARINTEK

Load control

zgzgzgF pvaC ++=

ωωγ

ωγω

ωγ

∀≈−≈−≈−

≈≈+

+

≠==

,0)(:,:controlconjugateComplex

0)(::control(reactive)Resonance

0)(:0,0:controlPassive

2

kgmg

gmgk

gg

aa

ppa

p

ppa

18MARINTEK

Constraints

Constraint on control force:

sigma_FC ≤ 50 kN (sigma = standard deviation)

Constraint on buoy motion:

sigma_z ≤ 0.5 m (absolute)or

sigma_zr ≤ 0.5 m (relative, zr = z – η)

19MARINTEK

Ga [kN/(m/s2) ]

Gv

[kN

/(m/s

)]

Pow er as function of contro ller gains

0 20 40 60 80 100 1200

10

20

30

40

50

60

70

80

90

100

0

5

10

15

20

25

30

35

40

45

50

std X= 0,5 m

std Fc = 50 kN

3.5 m buoy, 20 t

Hs = 2.75 mTp = 6.25 s

Unconstrainedmax = 57 kW

Constrained max = 20 kW

Constrained optimum

Unconstrained optimum

20MARINTEK

Results – constraint on force and absolute motion

Wave: Hs = 2.75 m, Tp = 6.25 s, gamma = 3.3Energy transport [kW/m] : 20.6Buoy diameter [m] : 3.5

Constrained optimum:Power output [kW] : 20.4Velocity gain, gv [kN/(m/s)] : 79Acceleration gain, ga [kN/(m/s^2)] : 53Standard deviation of motion [m] : 0.50Standard dev. of rel. motion [m] : 0.77Standard dev. of control force [kN]: 49.3

Unconstrained optimum:Power output [kW] : 56.6Velocity gain, gv [kN/(m/s)] : 7Acceleration gain, ga [kN/(m/s^2)] : 67Standard deviation of motion [m] : 2.83Standard dev. of rel. motion [m] : 2.89Standard dev. of control force [kN]: 194.

21MARINTEK

Results - constraint on force and relative motion

Wave: Hs = 2.75 m, Tp = 6.25 s, gamma = 3.3Energy transport density [kW/m] : 20.6Buoy diameter [m] : 3.5

Constrained optimum:Power output [kW] : 18.7Velocity gain, gv [kN/(m/s)] : 32Acceleration gain, ga [kN/(m/s^2)] : 14Standard deviation of motion [m] : 0.69Standard dev. of rel. motion [m] : 0.50Standard dev. of control force [kN]: 27.5

Unconstrained optimum:Power output [kW] : 56.6Velocity gain, gv [kN/(m/s)] : 7Acceleration gain, ga [kN/(m/s^2)] : 67Standard deviation of motion [m] : 2.83Standard dev. of rel. motion [m] : 2.89Standard dev. of control force [kN]: 194.

22MARINTEK

Frequency response of velocity – unconstr. optimum

0 0.5 1 1.5 2 2.50

2

4

6

8Amplitude response of velocity

(1/s

)

0 0.5 1 1.5 2 2.5-100

-50

0

50

100Phase response of velocity

Frequency (rad/s)

Deg

rees

23MARINTEK

Velocity responseConstraint on abs. motion: sigma_z = 0.50 m

0 0.5 1 1.5 2 2.50

0.5

1Amplitude response of velocity

(1/s

)

0 0.5 1 1.5 2 2.5-50

0

50


Frequency (rad/s)

Deg

rees

(sigma_zr = 0.77 m)

24MARINTEK

Velocity responseConstraint on rel. motion: sigma_zr =0.50 m

0 0.5 1 1.5 2 2.50

0.5

1

1.5Amplitude response of velocity

(1/s

)

0 0.5 1 1.5 2 2.5-50

0

50


Frequency (rad/s)

Deg

rees

(sigma_z = 0.69 m)

1

1

Wind induced power – basic principles of power take-off

and equipment

Ole Gunnar DahlhaugDepartment of energy and process engineering

NTNU

2

Different types of wind turbines

• Drag-type turbines– Persian windmill– Chinese wind wheel– Saviounus

• Lift-type turbines– VAWT, Vertical Axis Wind Turbine

• Darrieus– HAWT, Horizontal Axis Wind Turbine

• The Danish concept• American multiblade• Grumman windstream

2

3

Drag-type turbines

The Persian windmill

The Chinese wind wheel

Savonious

4

Drag-type turbines

Ref: www.ifb.uni-stuttgart.de/~doerner/edesignphil.html

3

5

Lift-type turbinesVAWT, Darrieus

6

Lift-type turbinesVAWT, Darrieus

4

7

Ref: www.ifb.uni-stuttgart.de/~doerner/edesignphil.html

8

Lift-type turbinesHAWT, American Multiblade

5

9

Lift-type turbinesHAWT, Grumman Windstream

10

Lift-type turbinesHAWT, The Danish Concept

• The blades upwind the rotor• Constant speed on the rotor• Power output limitation

– Stall control

• Brakes– Mechanical– Aerodynamic

6

11

SPEED n 20 17 13 5 – 15 3 – 10 rpm

HE

IGH

T [M

]

Development of HAWT

12

Onshore Wind Turbines

7

13

Offshore Wind Turbines

14

Offshore Floating Wind Turbines

SWAY HYWIND

8

15

Wind power and energy

• Power output from wind turbines:

• Energy production from wind turbines:

ηρ ⋅⋅⋅= AcPower2

3

Energy Power Time= ⋅

C

A

16

Energy flux for wind turbines

ηρ ⋅⋅⋅= AcP2

3

Recommended literature: Wind Turbine Technology, David A. Spera, ISBN no. 0-7918-1205-7

Where:P = Power [W]ρ = Density [kg/m3]c = Velocity [m/s]A = Area [m2]η = Efficiency [ - ]

9

17

Global Installed wind power

Source: www.gwec.net

18

10

19


Installed wind power

20

Wind power capacity global forecast


11

21 Wind Power in Norwayper 1st January 2006

• Energy goal for 2010: 3 TWh

• Wind farms in operation:– Number of wind farms: 13– Number of wind mills: 165– Installed power: ca. 320 MW– Energy production: ca. 900 GWh

• Planned wind farms (License is given, but not built)– Number of wind farms: 15– Number of wind mills: 439– Installed power: 1214 MW– Energy production: 3866 GWh

• Planned wind farms (Applied for License)– Number of wind farms: 36– Number of wind mills: 1444– Installed power: 4496 MW

Hitra

22

12

23

HAWTHorisontal-Axis Wind Turbines

SMØLA

24

HAWTMain Components

• Foundation• Tower• Nacelle• Hub• Turbine blades

Ref. Wind Power Plants, R.Gasch, J.Twele

13

25

Towers

Guyed Pole Tower

Lattice tower Tubular steel towers,

Concrete tower

26

Tower designs


14

27

Nacelle and Yaw system

Ref. www.windpower.org

28

Yaw system

Ref. www.windpower.org

15

29

Nacelle

30

Nacelle

16

31

Nacelle Design


32

Nacelle Drive Trains


17

33

VESTAS V903 MW

108 TONS

34

18

35

36

19

37

Multibrid M5000 Power output: 5 MW

Diameter: 116 m.

Turbine speed: 5,9 -14,8 rpm

Masses:

Blade: 16.500 kg

Hub: 60.100 kg

Nacelle: 199.300 kg

38

(tons)

20

39 Hydraulic transmission - 5 MW

P

M G

P = Hydraulic pump (Assumed weight 20 ton)

M = Variable displacement motor 8 x A4VSO1000

G = Generator placed at the bottom of the wind turbine

Weights in ton

40

Hub design

21

41

Hub design


42

Hub design


22

43 Blade Design


44

Design at different TSR


23

45

46

Energy Flux in the wind

AreacP ⋅⋅=2

3

ρ

Where:P = Power [W]ρ = Density [kg/m3]c = Velocity [m/s]

24

47

Wind velocity, power and energy

TimePowerEnergy ⋅=

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25

Velocity [m/s]

Tim

e [h

/yea

r]

0

100

200

300

400

500

600

0 5 10 15 20 25

Velocity [m/s]

Ener

gy [k

Wh/

m2 ]

ηρ ⋅⋅⋅= AcPower2

3

48

Power output

0

1 000

2 000

3 000

4 000

5 000

6 000

7 000

8 000

9 000

10 000

0 5 10 15 20 25

Wind Speed [m/s]

Pow

er [k

W]

Wind Power

Turbine Power

25

49

Aerodynamic brakes


50

Stall control


26

51

Turbine blade pitch system


52

Turbine blade pitch system

27

53

54

Links

• www.windpower.org/• www.ewea.org• www.nve.no• www.hydro.com/no/our_business/oil_energy/new_energ

y/wind/index.html• www.statkraft.no/pub/vindkraft/index.asp• www.gwec.net• http://ec.europa.eu/research/energy/nn/nn_rt/nn_rt_wind

/article_1101_en.htm

28

55

• Wind Power Plants, Fundamentals, Design Construction and Operation

– R. gasch, J. Twele, ISBN no. 1-902916-38-7

• Wind Turbine Technology– David A. Spera, ISBN no. 0-7918-1205-7

• Guidelines for design of Wind Turbines– DNV, RISØ, ISBN no. 87-550-2870-5

• Wind Energy Handbook– T. Burton, D. Sharpe, N. Jenkins, E. Bossanyi, ISBN no. 0-471-48997-2

• Aerodynamics of Wind Turbines– Martin O. L. Hansen, ISBN no. 1-902916-06-9

Recommended literature

1

Introduction by

Torgeir Moan, CeSOS

Session 2Dynamic analysis of floating systems

subjected to wave- and wind loads

CeSOS, May 27. 2008

2

Wind turbine concepts

tower

bladehub

nacelle

Wave energy converter

Rotor/flywheel for smoothing energy

Basic systems

3

Data, methods,criteria

Fabrication & Operation

data

Layout/Scantlings

Design for- serviceability &- producability- safety

Fabrication &installation- Fabrication plan -- Inspection/repair

Operation- Operation plan

Inspection/monitoring/ repair / maintenance

Removal and reuse

Reassessment

Life Cycle Phases of Marine Structures

Example: Spar wind turbine

+ Installation ofthe mooring system

4

Guidelines and standardsOffshore wind turbineso The IEC 61400-3 “Safety requirements for offshore wind turbines”,

International Electrotechnical Commission (2006). • Emphasis is given to the determination of load assumptions• Should be used in conjunction with the appropriate IEC/ISO standards

o Design of offshore wind turbines structures, Det Norske Veritas (DNV) (2004). • Consistent design philosophy in compliance with onshore wind turbine design • Strongly integrated with latest best practice offshore technology

o Guideline for the Certification of Offshore Wind Turbines, Germanischer Lloyd WindEnergie (2005). • Reflects state of the art offshore wind engineering• Covers all necessary requirements to support structures, blades and machinery.

Wave energy converters- No specific standard- Implement codes, standards and guidelines for offshore engineering(Det Norske Veritas: “Guideline on the design and operation of wave energyconverters”, Carbon Trust (2005)).

5 Design criteria for safety (with focus on structural failure modes)

System design checkAccidental collapse (ALS)- Ultimate capacity1) of

damaged structure with “credible” damage

Component design check depending on residual system strength andaccess for inspection

Fatigue (FLS)- Failure of welded joints

due to repetitive loads

Different for bottom – supported, or buoyant structures.Component design check

Ultimate (ULS)-Overall “rigid body”

stability- Ultimate strength of

structure, mooring or possible foundation

RemarksPhysical appearance offailure mode

Limit states

Collapsedcylinder

Totqlcollapse

Fatigue -fracture

6 Analysis for different criteria- different limit states (SLS, ULS, ALS, FLS)

Extreme displacement/stress, stress history in thestructure, mooring system, power off-take equipment

- assumed ”shut down” condition of moveable parts…(wind turbine, wave energy off-take system..)

- different fault conditions- account of automatic control

• SLS criteria : deflection criteria for turbine blade distance from tower• ULS criteria : different type of wave conditions for WEC,

combined wind and wavephenomena for WiEC- intact structure, including intentional ”shut down ”

conditionse.g. buoys of FO’s WEC in fixed upper or mean position

idle wind turbine• ALS criteria : fault conditions during power production and idle wind turbine• FLS criteria : combined long term wave and wind conditions

7

1330 Dynamic modelling of multi-body structures – for wave power generation by Reza Taghipour, CeSOS 1400 Dynamic modelling of wind turbines under combined wave and wind loading by Dr. Rune Yttervik, StatoilHydro 1430 Coffee break 1445 Mooring of floating plants by Dr. Zhen Gao, CeSOS 1515 Discussion: Challenges for the future. 1600 End of the day

Dynamic analysis of floating systems subjected to wave- and wind loads

Wave and Wind Power Seminar @ CeSOSMay 27. 2008

Dynamic Modelling of Multi-Body Structures for wave power

generation

R. Taghipour, A. Arswendy, T. Moan

CeSOS

Need among the state-of-the-art!

• Loads and response (wave-induced)

• Floating structure complexity

• Interactions

• Layouts

• Performance

Objective and Scope

Structural response analysis

Objectives: First order wave-induced motions and internal loads, displacements and stressesPower output

Case study: The FO3 WEC

Hydrodynamic Analysis

Motion AnalysisOriginal Modes of Motion:• Surge (platform and buoys )• Sway (platform and buoys )• Platform heave• Roll with sliding (platform and buoys)• Pitch with sliding (platform and buoys)• Yaw (platform and buoys)• Buoy #1~21 heave

i.e. total d.o.f.s = 27

Available Approaches:• Standard Approach: number of d.o.f.s to solve=132• Generalized Modes: number of d.o.f.s to solve=27

Assumptions

• First order hydrodynamic loads

• Power absorption mechanism model

Dynamic equilibrium:The equations of motions

Motions of each componentFollowing-Seas Waves (B=0)

Results show symmetrical properties resembling the physical problem symmetry.

Strong influence on motions from the power absorption mechanism.

Motions of each componentOblique-Seas Waves (B=45)

Results show symmetrical properties resembling the physical problem symmetry.

Wave EnvironmentJONSWAP-Mitsuyasu Spectrum

Power Absorption Statistics

Following-Seas Wave Condition Oblique-Seas Wave Condition

Wave is attenuated along its direction.Practically no power output from the buoys in the down-stream.Absorbed power was found independent of mean wave direction.The pattern of absorbed-power changes with wave direction.

Structural Analysis

The Interfacing Procedure

Validation for simplified case by comparison with analytical solution

Different Mesh Configurations

Stress along the column

FRF of the Axial Load and Bending Moment

FEA of FO3

Consistent hydrodynamic and structural models

Verification@ B=0

ΣFa=FPTO

ΣRF=0

The unbalance was found in practice to be 1.3% of the inertia force.

Comparative Study: Column-Deck Loads (Monochrome Following-Seas Wave B=0)

Axial Force-Amplitude Axial Force-Phase

Bending Moment-Amplitude (N.m.)

-1.0E+2

-6.0E+1

-2.0E+1

2.0E+1

6.0E+1

1.0E+2

1.4E+2

SC1 SC2 SC3 SC4

Columns Only FO3 WEC

0.0E+0

5.0E+4

1.0E+5

1.5E+5

2.0E+5

2.5E+5

3.0E+5

3.5E+5

SC1 SC2 SC3 SC4


-1.8E+2

-1.4E+2

-9.0E+1

-4.5E+1

0.0E+0

4.5E+1

9.0E+1

1.4E+2

1.8E+2

SC1 SC2 SC3 SC4

Column Only FO3 WEC

Bending Moment-Phase (N.m.)

0.0E+0

5.0E+8

1.0E+9

1.5E+9

2.0E+9

2.5E+9

3.0E+9

SC1 SC2 SC3 SC4


Comparative Study: Column-Deck Loads (Multiple Following-Seas Wave Range B=0)

0.E+00

5.E+04

1.E+05

2.E+05

2.E+05

3.E+05

3.E+05

4.E+05

0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3wave frequency (rad/sec)

FO3 WEC SC1FO3 WEC SC2Columns Only SC1Columns Only SC2

0.E+00

5.E+08

1.E+09

2.E+09

2.E+09

3.E+09

3.E+09

0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3wave frequency (rad/sec)

Full Platform-SC1Full Platform-SC2Only Platform-SC1Only Platform-SC2

Guide-Deck LoadsMonochrome Following-Seas Wave B=0)

Axial Force Bending Moment

• Significant load decrease along the direction of wave progression

0.0E+0

1.0E+3

2.0E+3

3.0E+3

4.0E+3

5.0E+3

6.0E+3

7.0E+3

8.0E+3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Guide Axial Force: Amplitude

-300

-250

-200

-150

-100

-50

0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Guide Axial Force: Phase

0.0E+0

2.0E+7

4.0E+7

6.0E+7

8.0E+7

1.0E+8

1.2E+8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Guide Bending Moment: Amplitude

-200

20406080

100120140160180

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Guide Bending Moment: Phase

Guide-Deck Loads(Multiple Following-Seas Wave Range)

Loads decrease as one moves towards the guides down streamWave is attenuated.Interaction/diffraction effects become dominant at the short wave range.

FRF in Oblique Seas Waves

Column-DeckBending Moment

Column-DeckAxial Force

1

Dynamic modelling of floating wind turbine under combined wind and wave loading

Wave and wind power seminar at CeSOS, Trondheim, 27.05.2008.

Rune Yttervik

2

Contents of presentation• Introduction / motivation

• Floating wind turbine – excitation mechanisms

• Floating wind turbine – damping mechanisms

• Floating wind turbine – dynamical properties

• H2SR analysis tool

• HYWIND Demo

– Purpose

– Main properties

• Issues of particular interest

3

Introduction / motivation• Dynamic response is determined by excitation

mechanisms, damping mechanisms and dynamic properties.

• Excitation mechanisms

– Ocean waves

– Wind field

– Ocean currents

• Damping mechanisms

– Mechanical damping

– Hydrodynamic damping

– ‘Electrical/aerodynamic damping’ (power production)

• Dynamic properties

– Mass

• Structural mass

• Added mass

– Stiffness

• Elastic stiffness (beams)

• Geometric stiffness (mooring system)

• Hydrostatic stiffness

4

Floating wind turbine – excitation mechanisms• Ocean waves

– Stochastic, irregular, linear, directional spreading.

• Wind field

– Vertical shear.

– Stochastic atmospheric turbulence

– Mean speed and direction.

• Ocean currents

– Surface currents, variable speed and direction.

• Gravity

• Forces from interacting structure components

– Blade/tower

• Cyclic load on the cylinder structure

• Cyclic load on the rotor

• Steady load on the cylinder structure

• Steady load on the rotor

5

Wind field simulation• Three velocity components

• 3D random wind field

• Homogenous in space

• Spectral tensor

• Wave number & separation vector (as opposed to frequency and time difference)

• Duration : 10 min. !!

rrkrk diRijij exp)(8

1)( 3

References :

Jakob Mann, ‘Wind field simulation’, Prob. Engng. Mech. Vol. 13, No. 4, pp. 269-282, 1998.

A. G. Davenport, ‘Wind structure and wind climate’, Safety of Structures under Dynamic Loading, Volume 1, pp. 209-237, Norwegian Institute of Technology, 1977.

Davenport (1977)

6

Floating wind turbine – damping mechanisms• Passive damping mechanisms

– Mechanical damping

– Hydrodynamic damping

• Hull

• Mooring system

• Active damping mechanisms

– ‘Electrical/aerodynamic damping’ (power production)

7

Effect of different control strategies

0 200 400 600 800 1000 1200 1400 1600 1800-5

0

5

10

15

20

time [s]

tow

er to

p m

otio

n [m

]

CCADSCCWO

0 0.05 0.1 0.15 0.2 0.250

5

10

15

20

25

30

35

frequency [Hz]

sqrt(

Sf)

Tower Top Motion

CCADSCCWO

Active Damping Control with

Sea State Compensation

Active Damping Control with

Low Pass Filtering of Nacelle Velocity

Wind 17 m/s

Tint 10%

Hs 5m

Tp 12s0 200 400 600 800 1000 1200 1400 1600 1800

-5

0

5

10

15

20

time [s]

tow

er to

p m

otio

n [m

]

CCADC LP3WO

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

5

10

15

20

25

30

35

frequency [Hz]sq

rt(S

f)

Tower Top Motion

CCADC LP3WO

8

Floating wind turbine – dynamic properties• Mass

– Structural mass

• Hull

• Tower

• Mooring system

• Nacelle

• Rotor blades

– Added mass

• Hull

• Mooring system

• Stiffness

– Elastic stiffness

• Hull

• Tower

• Rotor blades

– Geometric stiffness

• Mooring system

– Hydrostatic stiffness

• Ballasting, stability

9

Floating wind turbine – stiffness propertiesElastic stiffness (cylinder structure & rotor blades) Geometric stiffness

(mooring system)

Hydrostatic stiffness

Ballasting

Waterplane areaPitch

Heave

Roll

Surge

Yaw

Sway

10

Floating wind turbine – dynamics summarized

SurgePitchHeave Yaw

Wave

Wind

1st, 2nd and 3rd elastic bending

1p 2p 3p

17)( rpm :n

[Hz] 60np1

11

Computer tool for analysis of dynamic response• HAWC2SIMORIFLEX (H2SR).

• HAWC2

– Wind field model

– Finite element structural modelling

– Aerodynamic modelling (Blade Element Momentum Method)

• SIMO

– Data exchange (position, velocity, acceleration, force).

• RIFLEX

– Wave field model

– Current field model

– Finite element structural modelling

– Hydrodynamic modelling (Morison)

HAWC2

RIFLEX

SIMO

12

Visualisation of computer simulation

Hs 11 m,

Tp 14 sek,

Uw 18.9 m/s

13

HYWIND Demo - purpose

• Document proof of the HYWIND concept.

• Develop a basis for commercial attractive solutions for future floating offshore wind farms.

• Verify and optimize the concept, by further develop cost efficient technical solutions for fabrication, assembly and installation methods during project execution.

14

HYWIND Demo - concept• Main data

– WTG: 2,3 MW

– Turbine weight: 138 tons

– Rotor diameter: 82,4 m

– Draft: 100 m

– Displacement: 5300 m3

– Diameter at water line: 6 m

– Diam. submerged body: 8,3 m

• Characteristics

– Steel tower

– Steel substructure

– 3 point mooring system

– Dynamic pitch regulation

– Completed at inshore site

– Towed upright to field

– Designed for extreme North Sea conditions

15

A common detailed test programme shall be carried out including:

• Testing of various control strategies of the turbine and investigate consequences for motions, fatigue loads, WTG performance and power production

• Testing of response to various failure modes

• Check of sensitivity to oblique wind and tilt

• Testing of alternative access systems

HYWIND Demo – test program

16

Issues of particular interest – future work• Definition of design codes to be used.

• Statistics of wind and waves, joint probability.

• Selection of load cases.

– ULS

– ALS

– FLS

– PLS?

• Analysis tool with full coupling of aerodynamic and hydrodynamic loading and response.

• Access offshore.

• Control algorithms for optimal combinations of power production, structural capacity and cost.

1

CeSO

S

Mooring System for Wave Energy

Converter

Zhen GaoJu Fan

Torgeir Moan

May 27, 2008

2

CeSO

S

Contents

• The FO3 Wave Energy Converter• Objectives• Mooring analysis method• Hydrodynamic analysis (survival condition)• Comparison of the time- and frequency-domain results• Sensitivity study• Conclusions• Future work

3

CeSO

S

The FO3 Wave Energy Converter (WEC)

• The FO3 WEC model

4

CeSO

S

Objectives

• Investigate possible mooring systems– Components: polyester lines, buoys– Configuration: multiple WECs

• Study the effect of mooring system on WEC motions– Surge, sway and yaw– Heave, roll and pitch

• Mooring system analysis for multiple WECs in a farm

5

CeSO

S

Special considerations on WEC mooring systems (1)• Mooring system types

• Design considerations on WEC mooring systems– Shallow-water (70m)– Allowable vertical loads– Effect on vertical vessel motions– Farm design

a) b) c)Catenary Taut-line Taut-line with buoys

6

CeSO

S

Buoys

Special considerations on WEC mooring systems (2)• Farm design considerations• Standardized mooring components • Accessibility• Connection/Disconn.• Stability• Mooring design

on the boundary• Inspection plan• Failure analysis

Buoys

Clump weightBuoy

Clump weight

Buoy

Taut-line system Taut-line system with interior catenary lines

7

CeSO

S

Mooring analysis method

• Outline of mooring system analysis

• Frequency-domain analysis (uncoupled) • Time-domain analysis (coupled)

Wind

Wave

Current

OriginalPosition

MeanPosition

Dynamic Analysis (WF+LF)

Static Analysis

8

CeSO

S

• Survival condition– Hs=10.4m, Tp=14.4s, P-M; Uwind=29m/s; Ucurrent=2m/s– Env. Dir. 0 and 45

• Position of eggs:

Hydrodynamic analysis of the WEC

Operational condition

Survival condition

Still water

Deck

9

CeSO

S

Natural periods of WEC motions

• Hydrodynamic model (underwater part), WADAM

• Natural periods (sec)

(wave periods: 5-25 sec)

5510Roll (pitch)

136.2Heave

DeckStill water

10

CeSO

S

RAO of WEC motions

• Direct calculation by single-body analysis• Re-generated from multi-body analysis using generalized

modes, considering motion constraint between the platform and the eggs (Still water case)

• When the eggs are assumed to move freely along the guides.

Circular frequency (rad/s)0.0 0.5 1.0 1.5 2.0 2.5

RA

O -

Hea

ve (m

/m)

0.0

0.5

1.0

1.5

2.0

2.5SB_DeckSB_StillWaterGM_FreeGM_StillWater


RA

O -

Pitc

h (d

eg/m

)

0

1

2

3

4

5SB_DeckSB_StillWaterGM_FreeGM_StillWater

Heave RAO Pitch RAO

11

CeSO

S

The effect of viscous damping on RAO

Heave RAO Pitch RAO

• Viscous damping due to collars• 10%, 30% of critical damping


RA

O -

Hea

ve (m

/m)

0.0

0.5

1.0

1.5

2.0

2.50% of critical damping10% of critical damping30% of critical damping


RA

O -

Pitc

h (d

eg/m

)

0

1

2

3

4

50% of critical damping10% of critical damping30% of critical damping

12

CeSO

S

• Mooring system configuration– Four-line system, S1=57.2m, S2=40m– Polyester, D=125mm, Breaking strength=4811kN

D=150mm, Breaking strength=6927kN– Buoy, B=1000kN

Time-domain mooring analysis (1)

Mooring system layout

Dir. 0Dir. 45

Largest tension36 m

13

CeSO

S


• SIMO+RIFLEX– Coupled analysis (vessel motion + mooring line tension)– Nonlinear analysis

• Mean offset:

6.7-0.6013.7

(FD: 13.5)Dir. 45

11.7-0.3017.1

(FD: 15.5)Dir. 0

Pitch (deg)Heave (m)Surge (m)

14

CeSO

S


• Time series of the tension in the mostly loaded line:– Dir. 0:

Buoyancy– Dir. 45:

Line stretching

Dir. 0

Dir. 45

15

CeSO

S

Time-domain mooring analysis (4)• Spectral analysis (Dir. 0)

Surge

Heave Pitch

Tension

55 5555

55

2M

M AT

K Kπ

+=

+

ω ω

ωω

16

CeSO

S

Comparison of the T-D and F-D results

• Dynamic vessel motions: T-D (F-D)

• Mooring line tension at fairlead: T-D (F-D)

7.0 (6.0)2.3 (1.7)2.8 (3.8)0.8 (1.1)8.2 (6.9)1.6 (1.7)Dir. 45

10.6 (8.9)3.1 (2.5)2.9 (3.8)1.0 (1.1)11.6 (9.5)2.5 (2.4)Dir. 0

1-h ext.Std.1-h ext.Std.1-h ext.Std.

Pitch (deg)Heave (m)Surge (m)

4097 (3274)872 (/)759 (725)Dir. 45

1045 (850)521 (/)471 (453)Dir. 0

1-h ext.Std.Mean

Tension (kN)

17

CeSO

S

Sensitivity study• Buoyancy; Length of mooring line; Damping ratio in heave and

pitch; Position of fairlead• Horizontal length of anchor position: Dir. 0 (Dir. 45)

54 m 90 m 126 m

1004(4455)

36.4(25.8)

1200(5857)

34.3(24.2)

2658(8326)

35.2 (24.4)

B=500kN

900(1877)

24.8(19.9)

920(2124)

23.9(19.0)

850(3273)

25.0(20.4)

B=1000kN

1-h ext.tension (kN)

1-h ext.surge (m)


1-h ext.surge (m)


1-h ext.surge (m)

126 m90 m54 mFD results

18

CeSO

S

Conclusions

• Hydrodynamic analysis of the WEC in survival conditions.– Eggs are locked at the still water level– Eggs are locked under the deck

• Natural periods of the heave, roll and pitch motions are close to the important wave periods.

• Viscous damping due to collars needs to be considered in the calculation of motion RAO.

• Mooring line tension in the proposed configuration is mainly induced by surge (or sway) motion. Heave, roll and pitch motions are not significantly affected by mooring system.

• The frequency-domain method is practically acceptable compared with the time-domain simulations.

19

CeSO

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Future work

Buoys

Buoys

Clump weightBuoy

Clump weight

Buoy

Taut-line system Taut-line system with interior catenary lines

• Time-domain Multi-WEC mooring analysis

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CeSO

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Thank you !

wave and wind power seminar - cesos.ntnu.no · 1 introduction by torgeir moan, cesos wave and wind...

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