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Specialization in Ocean Energy. MODELLING OF WAVE ENERGY CONVERSION. António F.O. Falcão Instituto Superior Técnico, Universidade de Lisboa 2014. PART 4 MODELLING OF OWC WAVE ENERGY CONVERTERS. Basic approaches to OWC modelling. will be analized here. Basic equations.

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Presentation Transcript
slide1

Specialization in Ocean Energy

MODELLING OF WAVE ENERGY CONVERSION

António F.O. Falcão

Instituto Superior Técnico,

Universidade de Lisboa

2014

slide2

PART 4

MODELLING OF OWC WAVE ENERGY CONVERTERS

slide4

Basic equations

Volume flow rate of air displaced by OWC motion

  • Decomposeinto
  • excitationflow rate
  • radiationflow rate
slide6

Thermodynamics of air chamber

Assume compression/decompression process in air chamber to be isentropic (adiabatic + reversible)

slide7

Aerodynamics of air turbine

X

X

Dependence on Mach number Ma in general neglected, because of scarce information from model testing.

slide8

Frequency domain analysis

  • Linear turbine
  • Linear relationship air density versus pressure

Linearize:

Wells turbine

slide9

Frequency domain analysis

The system is linear

Decompose

Note: radiation conductance G cannot be negative

slide11

Frequency domain analysis

(deep water)

Axisymmetric body

(deep water)

slide13

Frequency domain analysis

Power

Power available to turbine =

pressure head x volume flow rate

Regular waves

Time average

slide14

Frequency domain analysis

Power

Turbine power output

Wells turbine

slide15

Exercise

Compute the turbine power ouput of the Pico OWC plant, for regular waves of period 10 s and amplitude 1.0 m.

The diameter of the turbine rotor is 2.3 m. The maximum alowable rotational speed is about 1500 rpm.

slide17

Frequency domain analysis

Dimensional analysis

slide18

Model testing: similarity laws for air chamber and air turbine

Correct dynamic similarity requires all terms in equation to take equal values in similar conditions at model size 1 and full size 2 .

1

2

air chamber

slide19

The two turbines are geometrically similar

Turbine dimensionless parameters (representing the turbine aerodynamic performance) take equal values for similar conditions of the air pressure cycle in the chamber of the model and the full-sized converter. We take such conditions as those of maximum air pressure .

Turbine size

Turbine rotational speed

slide20

Time-domain analysis of OWCs

The Wells turbine is approximately linear. So frequency-domain analysis is a good approximation.

Other turbines (e.g. impulse turbines) are far from linear. So, time-domain analysis must be used, even in regular waves.

This affects specially the radiation flow rate, with memory effects.

The theoretical approach is similar to time-domain analysis of oscillating bodies.

slide21

radiation flow rate

memory function

slide22

END OF PART 4

MODELLING OF OWC WAVE ENERGY CONVERTERS