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Dynamic analysis and control of offshore

marine systems using OrcaFlex

A presentation to the SUPERGEN 7th

Doctoral Training Programme Workshop

‘Control of Wave and Tidal Energy Converters’

Lancaster University, LUREG, Room A74 Eng & Computer Rooms

by Steve Dalton and Sarah Ellwood, Orcina Ltd

26th February 2010

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OrcaFlex (latest release v9.3, Aug-09)

Contents

1. About OrcaFlex - Overview

2. Capabilities for modelling offshore marine systems

1. Companies using OrcaFlex to analyse marine RE systems

2. Types of marine energy systems modeled

3. Environmental modeling – waves, current etc

4. Example models

3. Current Problems and Some Solutions

4. How OrcaFlex can support SUPERGEN2 Marine

Consortium and other RTD into Marine Systems

5. Way Forward

www.orcina.com Slide 3 of 40

OrcaFlex (latest release v9.3, Aug-09)

1. About OrcaFlex

Our main product OrcaFlex is the world's leading

software package for the design and analysis of a

wide range of marine systems, including all types of:

– Riser systems: SCRs, TTRs, hybrids, flexibles, umbilicals,

hoses, bend stiffeners, bend restrictors etc.

– Mooring systems: spread, turret, SPM, jetty, etc.

– Installation planning with capabilities across the full range of

scenarios.

– Towed systems: bundle dynamics, seismic arrays, towed

bodies, etc.

– Defence, marine renewables, seabed stability and many

other types of system.

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OrcaFlex (latest release v9.3, Aug-09)

OrcaFlex- Visualisation

The GUI, visualisation and

automation facilities of

OrcaFlex are widely

recognised as best-in-class,

making OrcaFlex the most

productive line dynamics

environment to work with.

www.orcina.com Slide 5 of 40

OrcaFlex (latest release v9.3, Aug-09)

2. Capabilities for analysing Offshore

Marine RE Systems• Analysing the static and dynamic response of structures to simple to

complex environments

• Can import hydrodynamic data from diffraction (AQWA, WAMIT)

• Modelling structures – vessels (RAOs/ QTFs), buoys, shapes, links, winches, lines (pipe chain & rope, wire moorings, umbilicals, risers)

• 3D and 6D Buoys, Surface piercing, CALM, SPAR, Towed fish, wings.

• Modelling the environment - seabed, sea, current, wind, waves

• Full non-linear capabilities (material, geometric, loading regime, boundary conditions, friction, contact, release, buckling etc)

• Modal analyses of lines (natural frequencies and mode shapes)

• Time history and detailed fatigue analysis (regular & rainflow) options

• Both Implicit and Explicit solvers are provided to solve most problems

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OrcaFlex (latest release v9.3, Aug-09)

2.1 Companies and Academia using OrcaFlex

to analyse marine RE systems

• Some of our Clients that use OrcaFlex for the design and analysis of Marine Renewable Systems include:-– AWS Ocean

– Aquamarine

– Nemo Engineering

– OceanLinx

– Ocean Power Technologies

– Pelamis Wave (formerly OPD)

– Trelleborg (formerly CRP)

– Wavegen

– Several Universities (SuperGen Marine Programme) Edinburgh. University of Strathclyde , Herriot Watt.

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OrcaFlex (latest release v9.3, Aug-09)

2.2 Types of marine energy systems modelled

• Marine Renewable Devices include:-

– Wave Energy Converters (WECs)

– Energy harvesting Vehicles (e.g. Wave Glider, Wave Runner, SeaRaser)

– Tidal Energy Converters (TECs)

• Types of WEC devices include:-

– BMD-Buoyant Moored device

– HCD-Hinged Contour device

– OWC-Oscillating Water Column

• Types of TEC devices include:-

– Tidal Stream Systems normally using Horizontal or Vertical axis devices. Others include oscillating (hydrofoils) or Venturi effects

– Barrages making use of head (potential energy)

– Tidal Lagoons (making use of potential and kinetic energy of tides)

www.orcina.com Slide 8 of 40

OrcaFlex (latest release v9.3, Aug-09)

Main Types of WECs

• Current TechnologiesAttenuators and Point Absorbers:-

- BMD-Buoyant Moored Device. e.g. wavebob, wavehub, PowerBuoy (OPT), wave energy point absorber (OSU PMLG)

- HCD-Hinged Contour Device .

e.g. Pelamis, Waveroller

(OPD), WRASPA, Oyster, AWS.

- Heave, Pitch & Surge devices

OWC-Oscillating Water Column:- e.g. Oceanlinx, Wavedragon, Orecon, Limpet, Wavegen Near-shore

Overtopping devices e.g. (wavedragon)

Submerged differential pressure –normally hydraulic

Other types – e.g. wave rotor and flexible structures (shape/volume)

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OrcaFlex (latest release v9.3, Aug-09)

2.3 Wave Resource in UK waters

• The world ocean resource is

massive (Scotland alone is 60GW)

• Many studies carried out e.g Fugro

OCEANOR, Orecon, APBmer (UK

Marine RE Atlas), DTI, ETSU.

• Significant work already done

under SuperGen programme

The physical consequences of

energy extraction on marine

resources are now much more

quantifiable and resource

assessment before and after

device deployment can now be

more effectively conducted,

based upon firm scientific

principles.

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OrcaFlex (latest release v9.3, Aug-09)

Properties and Types of waves

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OrcaFlex (latest release v9.3, Aug-09)

Modelling Waves in OrcaFlex

Regular Waves (Hs & Tz)

• Airy

• Dean

• Stokes 5th

• Cnoidal

Irregular (Random) Waves

Setting up a random sea-state

• JONSWAP and ISSC Spectra,

• Ochi-Hubble Spectrum,

• Torsethaugen Spectrum,

• Gaussian Swell,

• User-Defined Spectrum.

OrcaFlex 9.4a22: default Jonsw ap.dat (modif ied 14:18 on 05/02/2010 by OrcaFlex 9.4a22)

Spectral Density for Wave Train 'Wave1'

Frequency (Hz)

0.250.20.150.10.050

Spectr

al D

ensi

ty (

m^2

/ H

z)

140

120

100

80

60

40

20

0

OrcaFlex 9.4a22: pretty Ochi.dat (modif ied 14:19 on 05/02/2010 by OrcaFlex 9.4a22)

Spectral Density for Wave Train 'Wave1'

Frequency (Hz)

0.70.60.50.40.30.20.10

Sp

ectr

al D

en

sity

(m

^2 /

Hz)

40

30

20

10

0

www.orcina.com Slide 12 of 40

OrcaFlex (latest release v9.3, Aug-09)

Wave Power Formula

• In deep water where the water depth is larger than half the wavelength, the wave energy flux is

• where

– P the wave energy flux per unit wave crest length (kW/m);

– Hm0 is the significant wave height (meter), as measured by wave buoys and predicted by wave forecast models. By definition, Hm0 is four times the standard deviation of the water surface elevation;

– Te is the energy period (second);

– ρ is the mass density of the water (kg/m3), and

– g is the acceleration by gravity (m/s2).

• The above formula states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meters, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter of wavefront length

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OrcaFlex (latest release v9.3, Aug-09)

Wave Power Calculation - example

• Example: Consider moderate ocean swells, in deep water, a few kilometers off a coastline, with a wave height of 3 meters and a wave period of 8 seconds. Using the formula to solve for power, we get

-

• meaning there are 36 kilowatts of power potential per meter of coastline.

• In major storms, the largest waves offshore are about 15 meters high and have a period of about 15 to 20 seconds. According to the above formula, such waves carry about 1.7 MW/m of power across each meter of wavefront and can be very destructive.

• An effective wave power device captures as much as possible of the wave energy flux. As a result the waves will be of lower height in the region behind the wave power device.

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OrcaFlex (latest release v9.3, Aug-09)

Wave energy and wave energy flux

• In a sea state, the average energy density per unit area of gravity waves on the water surface is proportional to the wave height squared, according to linear wave theory:

–

• where E is the mean wave energy density per unit horizontal area (J/m2), the sum of kinetic and potential energy density per unit horizontal area. PE=KE both contributing half to the wave energy density E, as can be expected from the equipartition theorem.

• As the waves propagate, their energy is transported. The energy transport velocity is the group velocity. As a result, the wave energy flux, through a vertical plane of unit width perpendicular to the wave propagation direction, is equal to:-

• with cg the group velocity (m/s). Due to the dispersion relation for water waves under the action of gravity, the group velocity depends on the wavelength λ, or equivalently, on the wave period T. Further, the dispersion relation is a function of the water depth h. As a result, the group velocity behaves differently in the limits of deep and shallow water, and at intermediate depths.

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OrcaFlex (latest release v9.3, Aug-09)

Some WECs being designed, developed and/ or tested

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OrcaFlex (latest release v9.3, Aug-09)

Wave Energy Converters (WECs)• Over 80 companies globally developing different types of wave energy devices (see EMEC).

• A number of wave energy devices have been built but few have yet been developed up into commercial scale WECs because this of the very challenging environment & technicalities.

• A few devices have been built and tested at large scale and at least three types have been grid connected (Wavedragon, Pelamis, Oyster). These are still being optimised.

• Most have not been fully successful due to cost, complexity, reliability and harsh environment

• Major UK companies include the following covering the three main types of WEC device:-

– Aquamarine (Oyster-HCD/OWC)

– AWS Ocean (AWS-III-BMD)

– Carnegie Corporation (CETO-BMD))

– Finavera Renewables (AquaBuoy and Wave Buoy-BMD)

– Manchester Bobber (BMD)

– OceanLInx (OWC)

– OPT (Power Buoy-BMD) –Consortium with Japan

– Pelamis wave, formerly OPD (Pelamis-HCD)

– Protean Power (BMD)

– Trident Energy (BMD)

– WaveBob (BMD))

– Wave Dragon (floating slack moored OWC).

www.orcina.com Slide 17 of 40

OrcaFlex (latest release v9.3, Aug-09)

Example 3: Simulation of Cockerell raft

OrcaFlex 9.4a24: Cockerell raft.sim (modif ied 11:55 on 06/07/2004 by OrcaFlex 8.5a)

Time History: Pow er take-off 1-2 Length

Time (s)

20151050-5

Pow

er

take

-off

1-2

Le

ngth

(m

)

12

11.5

11

10.5

10

9.5

OrcaFlex 9.4a24: Cockerell raft.sim (modif ied 11:55 on 06/07/2004 by OrcaFlex 8.5a)

Time History: Pow er take-off 1-2 Tension

Time (s)

20151050-5

Pow

er

take

-off

1-2

Ten

sion

(kN

)

150

100

50

0

-50

-100

-150

www.orcina.com Slide 18 of 40

OrcaFlex (latest release v9.3, Aug-09)

Example 5: Operations on Articulated Jetty

OrcaFlex 9.4a20: articulated jetty - RMI version.dat (modif ied 00:28 on 05/10/2001 by OrcaFlex 7.5a34)

Time History: Float 1 Moment

Time (s)

3020100-10

Flo

at 1

Mom

ent

(kN

.m)

40000

35000

30000

25000

20000

15000

10000

5000

0

OrcaFlex 9.4a20: articulated jetty - RMI version.dat (modif ied 00:28 on 05/10/2001 by OrcaFlex 7.5a34)

Time History: Bow line 1 Effective Tension at End A

Time (s)

3020100-10

Bow

line

1 E

ffectiv

e T

ensi

on (

kN)

at

End A

30

20

10

0

-10

-20

OrcaFlex 9.4a20: articulated jetty - RMI version.dat (modif ied 00:28 on 05/10/2001 by OrcaFlex 7.5a34)

Time History: Float 1 Velocity

Time (s)

3020100-10

Flo

at 1

Velo

city

(m

/s)

2.5

2

1.5

1

0.5

0

www.orcina.com Slide 19 of 40

OrcaFlex (latest release v9.3, Aug-09)

Example 6: Fish Model links

X

Z

5 m

X

Z

OrcaFlex 9.4a24: Fish model links.sim (modified 14:27 on 05/11/2007 by OrcaFlex 9.1a) (azimuth=270; elevation=0)Time: 20.0000s

OrcaFlex 9.4a24: Fish model links.sim (modif ied 14:27 on 05/11/2007 by OrcaFlex 9.1a)

Time History: Bow mooring Effective Tension at End B

Time (s)

20151050-5

Bow

moori

ng E

ffectiv

e T

ensi

on (

kN)

at

End B

1

0.95

0.9

0.85

0.8

0.75

0.7

0.65

OrcaFlex 9.4a24: Fish model links.sim (modif ied 14:27 on 05/11/2007 by OrcaFlex 9.1a)

Time History: Link 1X Tension

Time (s)

20151050-5

Lin

k 1

X T

en

sio

n (

kN)

20

15

10

5

0

-5

-10

www.orcina.com Slide 20 of 40

OrcaFlex (latest release v9.3, Aug-09)

Example 8: Simulation of Wave Glider UUV –

wave powered device - Liquid Robotics IncDistance covered by Wave Glider (model-9b)

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60

Time in seconds

Ho

rizo

nta

l d

ista

nce i

n m

etr

es

glider

Axial loads in tethers of Wave Glider (model-9b)

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 10 20 30 40 50 60

Time in seconds

Axia

l lo

ad

in

teth

ers

in

kN

glider

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OrcaFlex (latest release v9.3, Aug-09)

Wave Runner -A new propulsion system for

boats ditches the diesel?

Wave-powered boat finishes crossing

• A Japanese adventurer has completed a three-month journey from Hawaii to Japan in a boat powered by the energy of ocean waves.

The 4,800-mile voyage, which began in Honolulu in March, ended when Kenichi Horie's three-ton yacht docked in Wakayama in western Japan last night.

"The sea was so calm, and the weather was so great throughout my journey. That's why it took me so long," he said.

His boat, which relies on wave energy to move two fins at its bow and propel it forward, sailed at an average speed of 1.5 knots - slower than humans walk.

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OrcaFlex (latest release v9.3, Aug-09)

Tidal Resource in UK waters

The key advantages of tidal

Stream energy over other

renewable forms of generation

are:• High energy intensity smaller

cheaper rotors for a given power

• Predictable energy capture less project risk

• Energy to a timetable greater revenue per MWh generated

• Low environmental impact low development overheads

• Simple decommissioning low back-end risk and cost

www.orcina.com Slide 23 of 40

OrcaFlex (latest release v9.3, Aug-09)

Main Types of TECs

• Current Technologies– HAD-Horizontal Axis Device.

e.g. MCT, Open hydro, Torcado.

– VAD-Vertical Axis Device. e.g.Kobold by pontediarchemede

– Oscillating Hydrofoil Devices e.g. Pulse Tidal - Reduces water depth & size limitations over HAD

– Venturi Effect

– Other Designs

– Barrage and Lagoons

Using existing low head water turbine technology (Kaplan's) into large fixed, gravity of floating structures to generate electricity.

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OrcaFlex (latest release v9.3, Aug-09)

Methods to secure TECs to the seabed

There are several methods to securing TEC to the seabed (as defined on EMEC website):

i) Seabed Mounted / Gravity Base:This is physically attached to the seabed or is fixed by virtue of its massive weight. In some cases there may be additional fixing to the seabed.

ii) Pile Mounted:This principle is analogous to that used to mount most large wind turbines, whereby the device is attached to a pole penetrating the ocean floor. Horizontal axis devices will often be able to yaw about this structure. This may also allow the turbine to be raised above the water level for maintenance.

iii) Floating:Flexible mooring: The device is tethered via a cable/chain to the seabed, allowing considerable freedom of movement. This allows a device to swing as the tidal current direction changes with the tide.

Rigid mooring:The device is secured into position using a fixed mooring system, allowing minimal leeway.

Floating structure:This allows several turbines to be mounted to a single platform, which can move in relation to changes in sea level.

iv) Hydrofoil Inducing Downforce:This device uses a number of hydrofoils mounted on a frame to induce a downforce from the tidal current flow. Provided that the ratio of surface areas is such that the downforce generated exceeds the overturning moment, then the device will remain in position.

ORCAFLEX can model most of these in simple up to complex sea states

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OrcaFlex (latest release v9.3, Aug-09)

Modelling Currents & Tides in OrcaFlex

1. Multiple sets of current profiles can

be used, e.g. for 100yr, 1yr and

95% exceedance

2. Current can be ramped during

statics build-up

3. Vertical current variation by

Interpolation or power law

4. Tide cycles modelled if important

XY

Z

20 m

OrcaFlex 9.3c (azimuth=220; elevation=5)

No Depth (m) factor Rot (deg)

1 0 1 0

2 20 0.8 10

3 30 0.6 30

4 55 0.4 -5

5 85 0.3 40

6 100 0.25 35

OrcaFlex 9.3c

Vertical Current Prof ile

Speed (m/s)

10.80.60.40.20

Z (

m)

0

-20

-40

-60

-80

-100

www.orcina.com Slide 26 of 40

OrcaFlex (latest release v9.3, Aug-09)

Properties of Tides and Currents

Energy calculations

• Various turbine designs have varying efficiencies and therefore varying power output. If the efficiency of the turbine "ξ" is known the equation below can be used to determine the power output.

• The energy available from these kinetic systems can be expressed as:

• where:– ξ = the turbine efficiency

– P = the power generated (in watts)

– ρ = the density of the water (seawater is 1025 kg/m³)

– A = the sweep area of the turbine (in m²)

– V = the velocity of the flow

• Relative to an open turbine in free stream, depending on the geometry of the shroud shrouded turbines are capable of as much as 3 to 4 times the power of the same turbine rotor in open flow. .[36]

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OrcaFlex (latest release v9.3, Aug-09)

Tidal Energy Converters (TECs)• Over 30 companies globally developing different types of wave energy

devices (see EMEC).

• Companies involved in developing TEC devices include:-

– Aquamarine (Oyster-HCD/OWC)

– AWS Ocean (AWS-III-BMD)

– Carnegie Corporation (CETO-BMD))

– Finavera Renewables (AquaBuoy and Wave Buoy-BMD)

– Manchester Bobber (BMD)

– OceanLInx (OWC)

– OPT (Power Buoy-BMD) –Consortium with Japan

– Pelamis wave, formerly OPD (Pelamis-HCD)

– Protean Power (BMD)

– Trident Energy (BMD)

– WaveBob (BMD))

– Wave Dragon (floating slack moored OWC).

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OrcaFlex (latest release v9.3, Aug-09)

Example 9: Preliminary modelling of Rotor

energy take-off device- (tidal/current)

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OrcaFlex (latest release v9.3, Aug-09)

Example 10: Simulation of a Towed fish to

demonstrate PID control (of elevation)

OrcaFlex 9.4a20: E05 PID Controlled Tow ed Fish.dat (modif ied 14:25 on 04/12/2009 by OrcaFlex 9.2a24)

Time History: Survey Vessel Z

Time (s)

300250200150100500

Surv

ey

Vess

el Z

(m

)

6

4

2

0

-2

-4

-6

OrcaFlex 9.4a20: E05 PID Controlled Tow ed Fish.dat (modif ied 14:25 on 04/12/2009 by OrcaFlex 9.2a24)

Time History: Tow fish Z

Time (s)

300250200150100500

Tow

fish

Z (

m)

-85

-90

-95

-100

OrcaFlex 9.4a20: E05 PID Controlled Tow ed Fish.dat (modif ied 14:25 on 04/12/2009 by OrcaFlex 9.2a24)

Time History: Tow fish X

Time (s)

300250200150100500

Tow

fish

X (

m)

-435

-440

-445

-450

-455

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OrcaFlex (latest release v9.3, Aug-09)

3. Problems and Solutions

Modeling wave power extraction devices will help

engineers identify the best designs (MIT Dec 2009)

PROBLEM

• Ocean waves could theoretically generate an estimated 10 to 100 megawatts of renewable energy per kilometer of coastline. Several pilot installations already harvest wave power, and the first commercial wave farm began operating off the coast of Portugal in 2008, but has since been put on hold.

• Many wave-energy device designs involve floating buoys that bob in the waves to capture mechanical energy. The buoys’ bobbing motion acts like a piston, moving a magnet or activating a hydraulic system that generates electricity. Designs include large single-buoy units and arrays of units of many small buoys.

• Determining which design extracts the most energy from a broad range of wave frequencies that vary widely in time, and finding the optimal spacing and deployment of units present major challenges to widespread development of wave-energy extraction devices.

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OrcaFlex (latest release v9.3, Aug-09)

Modelling wave power – a solution?

SOLUTION

• MIT Professor Chiang Mei focuses on power extraction from short waves induced by wind, rather than from tides. To provide engineers with predictive tools, his team is developing theoretical models for both single-buoy units and arrays of smaller units. Most single-unit absorbers are designed to resonate in such a way that a given wave train produces the largest oscillation of the device to maximize energy extraction.

• In normal sea waves, isolated buoys must be large in order to resonate, but they do so only within a narrow frequency range. Smaller buoys, if appropriately separated, do not resonate in normal sea waves and can only be activated to moderate amplitudes by waves across a broad bandwidth.

• ORCAFLEX can do much of this and is an ideal tool for front end design, parametric studies and global analyses, but it does have a number of limitations to model WECs / TECs accurately.

www.orcina.com Slide 32 of 40

OrcaFlex (latest release v9.3, Aug-09)

4. Application of OrcaFlex to Marine Research

• Whilst most of the research themes and 13 work packages

under Phase 1 of the SuperGen Marine Energy programme are

complete, Phase 2 (SuperGen2) is now underway.

• OrcaFlex can complement aspects on 8 of the 12 work

packages under SuperGen2:-

– WP1: Numerical and physical convergence

– WP2: Optimisation of collector form and response

– WP3: Combined wave and tidal effects

– WP4: Arrays, wakes and near field effects

– WP5: Power Take Off and Conditioning

– WP6: Moorings and Positioning

– WP7: Advanced Control (non-linear modelling of ocean waves)

– WP8: Reliability

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OrcaFlex (latest release v9.3, Aug-09)

Current state of Wave Energy Research

• Hydraulic and hydrodynamic modelling using:-– CFD-FLOW-3D (WASPRA)

– AQUABUOY –E2I-EPRI

– SUPERGEN MARINE (CFD & WAMIT, MarinOPT)- HW/LANCS

– ORCAFLEX

• Hydraulic and hydrodynamic testing at various facilities using:-– Small to medium scaled models

– Large scale and Full-scale devices being designed using offshore Oil & Gas standard codes & practice e.g. Oyster (Aquamarine Power)

• Mooring systems (lines and anchors) are key to the design and implementation of most WEC’s

• Most WEC devices will have to be deployed in a series of arrays

• Most WEC’s are still small to modest scale prototypes which require much RTD, especially predictive modelling and harshness testing

• Some larger scale projects due for deployment and pre-commercial testing at EMEC and elsewhere over the next 5 years

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OrcaFlex (latest release v9.3, Aug-09)

UK Universities involved in WEC research

• University of Bristol

• University of Bath

• University of Plymouth

• University of Southampton (SOTON and SERG)

• University of Loughborough

• University of Manchester (UMIST)

• Manchester Metropolitan University (MMI)

• Robert Gordon University

• University of Lancaster (LUREG)

• University of Strathclyde

• University of Edinburgh

• University of Herriot-Watt

• Queens University- Belfast

• University of Newcastle

• University of Glasgow

These form the SuperGen

Marine Consortium

www.orcina.com Slide 35 of 40

OrcaFlex (latest release v9.3, Aug-09)

International Universities currently

involved in WEC research• MIT (Energy Initiative)

• University of Aalborg, Denmark (Wave Dragon)

• University of Agder, Norway (Wave Dragon)

• University of Uppsala, Sweden (Vattenfall)

• Oregon State University, USA (OH Hinslade Wave Research Lab)

• Ghent University

• University of Patras

• University of Delft

• University of Stellenbosch, South Africa (CRSES)

• University of Plymouth, Australia

• University of South Australia

• Kyushu University, Japan (wave powered impulse turbine)

• + a quite a few others –many involved in Tidal Energy Research

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OrcaFlex (latest release v9.3, Aug-09)

Other organisations & test facilities

• Department of Energy and Climate Change (DECC)

• Scottish Council for Development and Industry (SCDI)

• UKERC

• Supergen Consortium (5 UK Universities)

• BWEA - Marine

• Marine Institute

• Powertech Labs Inc.

• SWAY, Norway

• IEA- Ocean Energy Systems

• European Marine Energy Centre (EMEC) –Stomness, Orkney

• New and Renewable Energy Centre (NaREC), Blyth

• Wave energy tanks at PRIMaRE, University of Plymouth

• Ocean Energy Test Site, Galway

• Wave Energy Centre (WavEC), Lisbon, Portugal

• Wave Energy Technology Test Facility, South Africa (Saneri)

• Many more conferences and events being held e.g. ITE summit, ICMENE, BWEA, AWATEA, OTC, AE, OMAE, ISOPE, ICOE,REC, ICOE etc!

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OrcaFlex (latest release v9.3, Aug-09)

Deep and shallow ‘coastal’ water

characteristics and opportunities • Deep water corresponds with a water depth larger than half the

wavelength, which is the common situation in the sea and ocean.

• In deep water, longer period waves propagate faster and transport their energy faster. The deep-water group velocity is half the phase velocity.

• In shallow water, for wavelengths larger than twenty times the water depth, as found quite often near the coast, the group velocity is equal to the phase velocity.

• The regularity of deep-water ocean swells, where "easy-to-predict long-wavelength oscillations" are typically seen, offers the opportunity for the development of energy harvesting technologies that are potentially less subject to physical damage by near-shore cresting waves.

• ORCAFLEX can model complex irregular wave trains and perform non-linear structural response and rainflow fatigue assessment to these waves. However limitations include:-

– No capability to model detailed design of power take off (energy conversion)

– No capability to model complex fluid-structure interaction

– Breaking waves and local shore effects cannot be modelled easily

– It does not allow for wave field or tide effects to be modified by the device

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OrcaFlex (latest release v9.3, Aug-09)

Conclusions (1)• Marine renewables is clearly a very demanding and challenging field.

The success or failure of devices being developed and commercialised relies on good design & analysis, robust engineering, deployment and rigorous testing.

• A range of devices are being developed especially in UK, USA, Canada, Norway, Portugal BUT…

• Several large wave energy devices have recently sunk during being towed out to sea or have been destroyed in the first few weeks of operation or have failed due to poor reliability and durability problems. (e.g. Trident, Osprey, Pelamis). Therefore…

• More rigorous RTD (research, design, analysis, testing & development) is required to avoid these sort of problems. More Front End + Detailed Design/Analysis + Testing is essential!

• There are a lot of similarities with modelling WECs and TECs compared to offshore marine systems e.g. coupled response, (as well

as quite a few differences – energy extraction, wake effects etc).

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OrcaFlex (latest release v9.3, Aug-09)

Conclusions (2)• Main Advantages of using OrcaFlex as a FEED analysis tool !

– Very effective tool for modelling offshore/marine systems

– Simple to very complex modelling of the environment and the system

– Rapid model building, analysis and simulations can be undertaken

– Both Passive and Active (PID) control is provided – via algorithms and external functions.

– Full non-linear modelling capability is provided

– Very effective software tool for modelling FEED and for assessing and optimising the viability of global marine systems subjected to hostile environments

• The software is widely used in the offshore industry and is well validated for this purpose

• However there are some limitations with using OrcaFlex to simulate Marine RE systems– It does not model energy extracted from the sea by the device

– Wake effects between devices are not easy to model

– BUT improvements and new features are regularly being added!

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OrcaFlex (latest release v9.3, Aug-09)

Questions and Answers

Thanks for listening

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