Integrated Modelling Methods used by Vestas Michael Høgedal & Tue Hald Loads Aerodynamics and Control, Technology January 2005
Introduction LAC-Offs...
Integrated Modelling Methods used by Vestas Michael Høgedal & Tue Hald Loads Aerodynamics and Control, Technology January 2005
Introduction LAC-Offshore is a group in Vestas Technology/LAC LAC Offshore shall actively contribute to optimal erection and operation of Vestas turbines on offshore sites by: •
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Affecting international code work to ensure correct basis for design of offshore support structures Coordinating project certification for offshore projects based on type approved turbines Providing cost-effective loads and ensuring structural integrity for tower and foundation Securing offshore suitable turbines through knowledge transfer to Turbine Programmes 2
Perspectives and trends Offshore wind energy: • A premature but rapidly developing business • Large room for reducing foundation costs • Moving into deeper water (now >20m, soon >40m, next ?) • ”New” foundation types will become cost-effective • Customers request turn-key projects with one contract holder, often the turbine supplier Some Vestas actions to stay in business: 1. Simulate and calculate structural response in integrated model to ensure structural integrity 2. Calibrate and improve our load tools to safely bring down construction costs of offshore support structures 3. Invent innovative foundation concepts to bring down construction, installation and operation costs of offshore support structures 3
Split of Responsibilities Area:
Loads
Design
Supply
Vestas
Contractor
Contractor
Contractor
Vestas
Vestas
CLIENT
Responsibility:
Environment
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Integrated Design Philosophy •
Vestas delivers design loads (wind and wave) down to mudline using an integrated structural model (Flex5)
•
Benefits: 1. Wind and wave loads are taken correctly into account 2. Overall structure can be fully optimized (utilization and costs) 3. Compliance with certifying body requirements Challenge: Cooperation form and split of responsibilities need to be well defined and clarified at an early stage
Flex5 simulation program Aeroelastic modelling tool • Structural model: - 36 DOF combined modal shape and multibody model - Each substructure treated using linear beam theory - Fundation model treated separately in FLEX5 • Aerodynamic model: - Blade element theory - Dedicated models for Turbulence (Veers model) Large yaw error Dynamic wake and stall (Stig Øye) • Effect control (Vestas) - Implemented directly in FLEX5 using DLLs • Hydrodynamic model - Morison equation - Wave kinematics (Irregular: up to 2nd order, Regular: Stream function)
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FLEX5 simulation program Some limitations with respect to offshore applications: • No soil-structure model implemented • Only possible to describe simple fixed cylindrical substructures above the sea bed (i.e. monopile) Future developments by Vestas: • Ability to model arbitrary foundations: - Tripod, Gravity, Bucket - Floating • Ability to model soil-structure interaction (p-y curves)
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Arbitrary Foundation Module
• FEM model of substructure using cylindrical beam elements • Craig-Bampton method: - Method for reducing the size of the FEM model to 6 DOF - LTM are used to transform from CB DOFs to physical DOFs - Combines motion of boundary points with modes of the structure assuming the the boundary points are held fixed - Similar to other reduction schemes
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Arbitrary Foundation Module The Craig-Bampton method: • Equation of motion (ignoring damping): •
