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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
ww
.sdwed.civil.aau.dk
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• System description
• System Implementation
• Numerical Result
• Future Steps
Presentation Contents
26-04-2012
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
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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
26-04-2012
• 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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.sdwed.civil.aau.dk
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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
26-04-2012
System Implementation
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
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26-04-2012
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
ww
.sdwed.civil.aau.dk
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26-04-2012
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
ww
.sdwed.civil.aau.dk
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26-04-2012
Result T = 2s, H = 1m
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
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26-04-2012
Result T = 2s, H = 1m
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
(Replace logo with your own university/company logo)
26-04-2012
Result T = 2s, H = 1m
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
(Replace logo with your own university/company logo)
26-04-2012
Result T = 10s, H = 1m
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
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• Regular waves behavior
26-04-2012
Result T = 10s, H = 1m
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
(Replace logo with your own university/company logo)
• Regular waves behavior
26-04-2012
Result T = 10s, H = 1m
Structural Design of Wave Energy Devices – w
ww
.sdwed.civil.aau.dk
(Replace logo with your own university/company logo)
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
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