Structural Design of Wave Energy Devices – w

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Development of a Wave to Wire model: Hydraulic PTO system

implementation

Francesco Ferri Aalborg University

26-04-2012

Structural Design of Wave Energy Devices – w

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• System description

• System Implementation

• Numerical Result

• Future Steps

Presentation Contents

26-04-2012

Structural Design of Wave Energy Devices – w

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System Description

26-04-2012

• Double-acting hydraulic

cylinder

• Switch Valve

• Buffer system

(accumulators)

• Hydraulic Motor

Structural Design of Wave Energy Devices – w

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System Description

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• Floater diameter: 14m (Natural period ~ 6.2 s )

• Accumulators volume : 2.5m3 each one

• Motor swapt volume : 0.03m3/rev • Motor/generator inertia : 0.2 kgm2

• Hydraulic piston cross sectional area : 0.05m2

• Initial pressure HP reservoir : 100bar

Structural Design of Wave Energy Devices – w

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System Implementation

• Global State Space representation of the free floating behavior

• Expansion of the State Vector with two new states (p, N)

• Implementation of the PTO feedback force into the input vector (slide n.6 of the previous presentation)

26-04-2012

Structural Design of Wave Energy Devices – w

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,

and

Constrained Device: Moorings & PTO

State-Space Realization

State Vector

Global State-Space Representation

( ) ( ) ( )( ) ( )

excMX t AX t BF t

y t CX t

= +

=

( ) [ ]1 n

T

r rX t x x p N = ξ ξ

[ ]( ) ( ) [ ]

( )( )

1 1

1

0 0 0 0

0

0 0 0

0 0 0 1 0 0

0

0 0 0 0 , , 0

0 0 0 0 0 , ,

n n

n

r r

r r

r r m m

pto

pto g

A B

A B

AC C G f f

f N p

f p N T

= + ξ ξ Γ ξ

[ ]

0

00100

T

C

=

[ ]( )0

1 0 0 0 0 00

1 0 0 0 00 0 1 0 0 00 0 0 0 00 0 0 0 , 00 0 0 0 0 t

MM A

f VI

∞

= − +

ξ

[ ]

0

001

00

B

= −

The external constraints (PTO and mooring system) require in general a state expansion.

New States

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System Implementation

Structural Design of Wave Energy Devices – w

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System Implementation

PTO dynamic model:

High pressure reservoire dynamic

Hydraulic motor dynamic Approximations: • Isentropic transformation • Neglectible fluid compressibility • Neglectible valve dynamics • Neglectible losses (hydraulic rams, motor, generator, etc…)

Structural Design of Wave Energy Devices – w

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System Implementation Switch valve connection port between the floter and PTO system, regulated through the netto force acting on the piston and the actual displacement

Switch valve operation • Parallel flow • No flow • Cross flow

Structural Design of Wave Energy Devices – w

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Result T = 2s, H = 1m

Structural Design of Wave Energy Devices – w

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Result T = 2s, H = 1m

Structural Design of Wave Energy Devices – w

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26-04-2012

Result T = 2s, H = 1m

Structural Design of Wave Energy Devices – w

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Result T = 10s, H = 1m

Structural Design of Wave Energy Devices – w

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• Regular waves behavior

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Result T = 10s, H = 1m

Structural Design of Wave Energy Devices – w

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• Regular waves behavior

26-04-2012

Result T = 10s, H = 1m

Structural Design of Wave Energy Devices – w

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Future Steps and Collaborations

Hydraulic PTO system. • Collaboration with WavEC (WP4): implement the system in a floating device like Dexa. • Collaboration with WP3: increase the system complexity, ”reality” check.

26-04-2012

Funded by

The International Research Alliance

29-04-2012