Mathematical
Tools in the
Design of Floating
Devices for Energy
Exploitation in
Marine
Environment
Vincenzo Nava Imanol Touzon Gonzalez Bilbao, BCAM Seminar, 18th October 2013
INDEX
About Tecnalia Marine Renewable Energies and Development of FloaAng Device Technologies Design of FloaAng Devices: An OperaAonal PerspecAve Resource Hydrodynamics and Dynamics of the Devices subject to Waves •  Case Study 1 : Hydrodynamics of an Offshore Wind Turbine Moorings And Aero-­‐HydroElasAcity Issues •  Case Study 2: System IdenAficaAon for CharacterizaAon of Moorings Energy Conversion Grid IntegraAon and Power Quality Conclusions Bilbao – 18th October 2013 – Vincenzo Nava ABOUT TECNALIA
Tecnalia is a no-profit private technological corporation, arising from the Basque
business environment.
Now it is an International benchmark in several field of expertise.
We all share a common operating model based on sector-focused Business Units
Generating GDP connecting scientific, applied and technological research.
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava ABOUT TECNALIA
To turn energy and environmental challenges into business opportunities
Smart Grids
Renewable Energies
Energy Storage and Electric Mobility
Marine Energy
Solar Energy
Future
Energy
Biorefinery and Bioenergy
System
Energy Efficiency
Energy
New Materials for a Low
Carbon Economy
and
Clearing up Uncertainties
Related to Weather and Climate
Sustainable and Resilient
Cities and Territories
Environment
Environment
and Climate
Forecasting Systems
Change
Sustainability
Water Cycle
as
Efficient Use of Resources
Waste valorisation
BCAM Seminar
Megatendency
Bilbao – 18th October 2013 – Vincenzo Nava ABOUT TECNALIA
Wave Energy
Offshore Wind
New concepts for high power electric generators. Reliable power converters based on advanced topologies and new devices. Structural materials for blades. Hydrodynamic analysis and performance of WEC Design of moorings systems and umbilical cables. Power converters and control systems Dynamic models for performance assessment and grid integraAon Materials Environmental Impact Studies for Marine Environment Site assessment and resource characterizaAon Grid connecHon of marine renewable parks BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
Renewable Energy in Marine Environment -  Sea as Resource •  Gradients of Salinity •  Temperature •  Tides and Currents •  Ocean Waves -  Sea as Environment •  Marine Geothermal •  Marine Biomass •  Offshore Wind •  Other sources Bilbao – 18 October 2013 – Vincenzo Nava BCAM Seminar
th
MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
Waves and Offshore wind may represent the most convenient choices to invest, despite the unavoidable technological and economic challenges of the sectors: -  Efforts distributed in a variety of devices -  Reliability and suitability of the conversion -  Hydrodynamic Modelling: energy losses, diffracAon/reflecAon -  Structural Issues (interacAon with mooring system) -  Aero-­‐HydroelasAcity (Offshore Wind) -  Survivability -  Economic feasibility BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
Oscillating Water Column (OWC)
Overtopping Devices
Oscillating Bodies (Point Absorbers & Surge Devices)
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
Why “being” FLOATING, then? -  Economically more convenient for deep water -  It could lead to greater availability of resource -  Reduced visual impact from seafront -  Seismically isolated -  Reduced risk due to solitons -  ExploitaAon of oil & gas already consolidated experience in conceptual design of the devices (with several differences) BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
APPROPRIATE MODELING IS MANDATORY
during all the phases of the design process
Mathematical Models hinge upon:
1)  Theories / Practical Considerations
2)  Empirical Assumptions (data from developers, previous
experience)
EXPERIENCE NOT YET MATURE !!! Mathematical Models must be validated through:
1)  Experimental Testing
EXPENSIVE !!! 2)  Numerical Tools (Monte Carlo Methods, approaches in time and
frequency domains).
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava MARINE RENEWABLE ENERGIES AND DEVELOPMENT OF FLOATING DEVICE
TECHNOLOGIES
A global model for marine energy devices involves multidisciplinary
aspects in several fields of engineering
Wind/wave climatology
Hydrodynamics (Fluid-body interaction)
Aerodynamics
Electric engineering
Hydraulics/Mechanics/Turbomachinery
Structural mechanics
Electronics
Cable dynamics
Each of these fields exploits one or more mathematical tools, from statistics
to probabilistic methods, perturbative and non perturbative techniques, but
also semi-analytical and numerical methods and computational procedures.
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Resource
Modelling of the environmental input needed as:
1) Design input for the structural design
2) Forecasts in terms of Energy
2
/Hz) spectral density(m
Energy
Characterization of the resources as stochastic process
•  Model of the inputs as stationary, ergodic, Gaussian, non Gaussian processes.
•  Spectral representation of the input
•  Parameterization
6
Target spectrum (Bret.)
Minimum parameters:
5
• Hm0
4
3
• Te
2
• Energy flux J (kW/m)
1
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Frequency(Hz)
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Resource
Modelling of the environmental input
•  Space variability of the inputs:
Wave propagation from deep to intermediate and shallow water
Wave hindcast models
Wind forecasting
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Resource
Modelling of the environmental input
•  Analyses of the inputs
Long term and short term statistics of historical data
Probability analyses of the extremes
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Hydrodynamics and Dynamics of the Devices subject to Waves
Hydrodynamics and Hydraulics MoAon of the fluid inside the structure (sloshing phenomena, energy losses) Dynamics of the structures BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Hydrodynamics and Dynamics of the Devices subject to Waves
Loads due to ocean waves can be disAnguished into: • HydrostaAc Loads • Steady Current Loads • Wave Loads (PotenAal Theory) Linear Loads Non Linear Loads (2nd order components) Mean Dri_ Forces (2nd order components, which however can be calculated from linear potenAal) Low Frequency MoAon (to be included for the study of moored bodies) Higher Frequency MoAon (generally neglected in deep water and for floaAng devices) • Non Linear Viscous Effects (due to vortex formaAon, turbulence, dissipaAve loads) – Morison EquaAon BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Hydrodynamics and Dynamics of the Devices subject to Waves
PotenHal Theory / Linear Approach LinearizaAon of Navier-­‐Stokes equaAon, for inviscid, incompressible and irrotaAonal load yields to the existence of a velocity potenAal funcAon and therefore to Laplace equa5on: 2
coupled with the boundary condiAons: ∂φ ω2
− φ =0
∂z g
On the free surface (z=0) ∇ Φ=0
∂φ
=V
∂n
∂φ
=0
∂z
On the body surface Sb On the seabed (z=-­‐h) The soluAon is generally achieved by separaAng the potenAal into different components, respecAvely incident, diffracAon and radiaAon potenAal. φ = φI + φD + φR
•  SoluAon is obtained in an integral form exploiAng the results of Green’s Theorem •  PanelizaAon is very important (number, flat panels/lower order methods, curved panels/
higher order methods). BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Hydrodynamics and Dynamics of the Devices subject to Waves
ComputaHonal Fluid Dynamics Numerical SoluAon of the whole Navier Stokes equaAon, accounAng for the full free surface problem. ComputaAonally demanding. Really useful for solving specific classes of problems BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Case Study 1 : Hydrodynamics of an Offshore Wind Turbine
A full design of a floaAng offshore wind farm includes numerical models for: -­‐ economical viability; -­‐ stability and hydrodynamics of the pladorm; -­‐ mooring lines design -­‐ aero-­‐servo-­‐elasAc coupling -­‐ structural design (FEM). BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Case Study 1 : Hydrodynamics of an Offshore Wind Turbine
High Order Panel Method in Geometry DefiniAon Direct Solver Full DiffracAon SoluAon Heave plate modeled as a dipole BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Case Study 1 : Hydrodynamics of an Offshore Wind Turbine
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Case Study 1 : Hydrodynamics of an Offshore Wind Turbine
Mean Dri_ forces computed by means of Momentum ConservaAon BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Case Study 1 : Hydrodynamics of an Offshore Wind Turbine
QuadraAc Transfer FuncAon computed by means of Newman’s approximaAon BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Moorings And Aero-Hydroelasticity Issues
Coupled aero-­‐hydrodynamic models are sAll at a development stage and are absolutely needed for the development of the offshore wind industry Codes (i.e. for example FAST) are being developed taking into account coupled aerodynamics, aero-­‐elasAcity and hydrodynamics as response of offshore wind turbines frequently involves structural modes of vibraAon. Facts and Challenges: "   IntegraAon of structural modes into a mulA-­‐body approach "   Non negligible influence of the mooring lines "   Differences in control system for pitch and blades with respect to fixed turbines BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Hydrodynamics and Dynamics of the Devices subject to Waves
The dynamics can be described by the Cummins EquaAon: Where Fext can represent every non-­‐linear term, including PTO forces, moorings, drag and other terms. The convoluAon term represents a radiaAon memory effect, described by the radiaAon impulse response funcAon: • Realization theory (Hankel
SVD)
2∞
K (t ) = ∫ B(ω ) cos(ωt )dω • Prony method
π 0
• Direct Integration
Unless some specific phenomena must be studied, then it is much easier to apply linear soluAons (o_en in the frequency domain) and include nonlinear correcAons a_erwards! [
]
[
]
H (ω ) = M + M eq + A(ω ) ω 2 + B + Beq + B(ω ) jω + (K + K eq )
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Moorings And Aero-Hydroelasticity Issues
Analysis and design of the moorings of a floating system
Dynamic Approach Quasi-­‐StaHc Approach — appropriate for mean and low-­‐frequency — more appropriate for wave-­‐frequency displacements of the pladorm. pladorm displacements; — needs to take into account also hydrodynamic drag forces acAng on the mooring line components — more approximate approach — higher design safety factors. — the dynamic analysis must be linearized when coupled with frequency domains analyses BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Moorings And Aero-Hydroelasticity Issues
Analysis and design of the moorings of a floating system
Time Domain Frequency Domain — the effects of non-­‐linear funcAons of the wave —well suited for systems exposed to staAonary and moAon variables can be included. random loads. — equaAons of moAon are solved by direct — requires linear equaAons of moAon; numerical integraAon (Ame consuming) — linearity implies some inaccuracy in effects like drag loads, Ame varying geometry, variable surface elevaAon and horizontal restoring forces. However, in many cases these non-­‐lineariAes can be saAsfactorily linearized. BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Moorings And Aero-Hydroelasticity Issues
Analysis and design of the moorings of a floating system
BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Case Study 2: System Identification for Characterization of Moorings
Analysis and design of the moorings of a floating system
System IdenHficaHon Procedures The behaviour of the tension at the top of the mooring line is modelled as a dynamic system Fˆ (t ) = Ax`+C d x x + Kx
Fˆ (t ) = Ax`+ Bx + Kx
IdenAficaAon of the parameters is achieved by Fˆ (t )x(t ) = F (t )x(t )
Fˆ (t )x (t ) = F (t )x (t )
Principle of conservaAon of energy Or LSQ methods BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Case Study 2: System Identification for Characterization of Moorings
Analysis and design of the moorings of a floating system
System IdenHficaHon Procedures BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Case Study 2: System Identification for Characterization of Moorings
Analysis and design of the moorings of a floating system
System IdenHficaHon Procedures BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava INTEGRATION OF ENERGY CONVERSION AND MOORINGS
Energy Conversion
The problem of control
OpHmizaHon of power absorpHon CONTROL SYSTEM REAL – TIME CONTROL SEA – STATE CONTROL i. 
Change the phase of the moAon of the body conAnuously i. 
The control law is changed in correspondence of the sea state ii. 
Time domain analysis required ii. 
Frequency domain analysis required BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Energy Conversion
Linear Power Take Off Modelling: PM Synchronous Linear Generator
Can be approximated by a linear
damping coefficient in the Equation
of Motion
Design and model of a hydraulic PTO
Power conversion
Offshore grid
Buoy
HP acc
Hydraulic PTO
Vertical
movement
Compressibility of
the oil
Control
accumulators
LP acc
b
c
a1
d
a2
e
BCAM Seminar
Hydraulic motor
Electrical generator
Bilbao – 18th October 2013 – Vincenzo Nava DESIGN OF FLOATING DEVICES: AN OPERATIONAL PERSPECTIVE
Grid Integration and Power Quality Issues
StochasHc nature of the resource Strength of the grid Numerical Modelling for Power Quality Issues Efficient transport and control BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava CONCLUSIONS
Numerical and mathemaAcal modelling is a mandatory step in any engineering design process. Models serve to -­‐ describe the reality more or less reliably -­‐  allow scienAsts to understand phenomena, their implicaAon and their causes -­‐  provide to the designers powerful tools for the assessment of their objecAves. Importance of good modelling is increased especially when experience is not mature yet, as in the field of renewable in marine environment, especially when dealing with floaAng devices for wind and wave energy harvesAng. The appropriateness of these models may result in the success or failure of a concept or idea. BCAM Seminar
Bilbao – 18th October 2013 – Vincenzo Nava Thank you!
Vincenzo Nava TECNALIA – Marine Energy [email protected] 37