OWEC TOWER ASSetting The Standard For Deep Water Foundations

OWEC TOWER AS

GRAVITY BASED FOUNDATIONS FOR JACKETS

NORCOWE – Stavanger, 16 April 2015

Jordi Pascual Gilabert. Engineering Manager OWEC Tower AS

Leading Technology Company

• Pioneer company (2003) substructures for Offshore Wind• 1st jacket worldwide support WTG (Beatrice OWF – 45m wd)• Deepest installed jacket so far (Beatrice)• 1st develop pre-installed piles• World leading company track record• World leading expertise different Certification Bodies & Countries• Patented technologies• Continuous product development• Expert project management & interface management

Delivered 2 units

to Talisman

20062009

20102011

SCOTLANDGERMANY

Delivered 6 units

to DOTI

ENGLAND

Delivered 30 units

to Vattenfall

BELGIUM

Thornton Bank

Delivered 48+1

Units to C-Power

FRANCE

Delivered 1

Prototype to

STX/Alstom

Acquires 49.9% of OWEC

OWEC TOWER HISTORY

Proven Track Record

Proven Track Record

Cost Efficient

• Value engineering: concept to decommissioning

• Designed-to-build structures

• Rational & functional design:

1. Supply chain friendliness

2. Transport & Installation requirements

3. O&M friendly concepts

• Expertise Engineering & Management

• Proven Technology

• Flexibility wrt seabed & soil conditions

• Durable

• Life cycle focus: Fabrication, Transport &

Installation, Service, O&M, decomissioning

• Standardization & rationalized designs

• Large Installed Reference Base

• Wide Turbine Range

• Scalable & Adaptable

OWEC TOWER HIGHLIGHTS

OWEC TOWER AS

Reasons to Develop GBF substructures for jackets

• OWF developments to deeper sites (40+ m)

• Difficult soil conditions for piles (not feasible, too risky installation)

• Optimal structures = hybrid structures

• Reduced sea loading wrt full GBF

• (Local content)

OWEC TOWER AS

Hybrid jacket-GBF concept (I)• Scope of applicability

– Seabed adequate bearing capacity at surface levels– presence of hard soils or rock at intermediate depths (<30-50m)

not enough soil to resist pull loads, drilled piles required (drilled and driven deeper / drilled and grouted socket,…)

• Main idea behind– Previous soil conditions + intermediate to large water depth need

to reduce loading– Not a full GBF, hybrid structural concept– Hybrid structures = very efficient, structural elements adapted

optimally to function

OWEC TOWER AS

Hybrid jacket-GBF concept (II)

• Keep the jacket concept for substructure shaft, instead of a concrete shaft TRANSPARENCY TO SEA LOADS

• Using a gravity based structure for the foundation (i.e. GBF) STABILITY and LOAD TRANSFER TO SOIL at surface levels due to weight

OWEC TOWER AS

Hybrid jacket-GBF concept (III)

OWEC TOWER AS

Hybrid jacket-GBF main components (I)• GBF structure:

– Open top concrete caisson, filled with solid ballast

– Base slab: transfer allowable stresses to the soil

– Caisson: # external walls:

contain ballast; transfer shear coming from one leg to the opposite; provide adequate draft (floating tow)

# diagonal walls: transfer shear from diagonal loading; base slab stiffening; support eventual temporary buoyancy tanks to reduce required crane capacity

# anchor blocks: Allocate and enable connection jacket legs to caisson

OWEC TOWER AS

Hybrid jacket-GBF main components (II)• Ballast:

– Solid infill of GBF caisson

– Iron ore (magnetite) dry bulk density: 3ton/m3; heavy but expensive

– Hyperit; Olivine dry bulk density: 2.3ton/m3; lighter but still acceptable density; much cheaper

– Rock: 1.5-1.8ton/m3; much too light in general for these applications

– The heavier the ballast the lighter and smaller the GBF, but the more expensive the ballast Balance to considered transport and installation (lifting capacity) capacities and market price of ballast material supplied

– Type of ballast: PRIMARY DECISION, one key decision with high impact on design and project

OWEC TOWER AS

Hybrid jacket-GBF other components (I)• Underbase Skirts:

– Only required if sliding resistance is insufficient (larger and shallower caissons)– Generally not required in any of the concept designs performed

• Scour protection:– Filter and armour layer around the caisson– Scour protection of infill ballast generally not required

• Dredging & Gravel bed:– Depending of the regularity of the bathymetry and the bearing capacity of surface

soil, dredging and further filling with a gravel bed must be undertaken or not• Mechanical outfitting & cable interfaces:

– Attachements for cable routing between jacket and touchdown point– Cable routing that minimizes cable pull-in forces

OWEC TOWER AS

Hybrid jacket-GBF analysis remarks (I)• Load analysis:

– Loads on jacket drag dominated & Morrison equation

– Loads on GBF inertia dominated & Diffraction theory

– Essentially different nature of wave loading combined properly to obtain overall shear and bending moment at mudline

– Wave loading on the caisson add significant shear force; maximum bending moment is basically due to loads on the jacket.

– Exhaustive analysis (ca. 100 wave steps / period) to obtain accurately the response and the critical situations from geotechnical & stability point of view

OWEC TOWER AS

Hybrid jacket-GBF analysis remarks (II)• Load analysis:

– Vertical wave (heave diffraction) force on the caisson very significant, discharge can critically reduce the net submerged weight at some wave steps (impact on stability & bearing capacity)

– Loads on horizontal (top & bottom) and vertical (outer walls) planes size effects (diffraction, disturbed field theory), calibrated coefficients for relevant loading directions

– Loads underneath base slab: responsible for resulting net submerged vertical force, very related to soil and water flow (pore water pressure) Geotechnical interface in assessing flow conditions afecting wave loading on GBF

– Others: stiffness parameters for cyclic loading to assess WTG frequency constraints and WTG loading

OWEC TOWER AS

Hybrid jacket-GBF economy(I)• The total cost in a commercial wind farm is subject to many variables and assessment needs thorough analysis together with EPCI

companies for specific projects.

• Some of main topics influencing project economics listed.

• Production of concrete structure: on land / dry dock / floating submersible platform

• Jackets produced elsewhere, delivered to concrete production site (if onshore assembly) / to mating site (if offshore assembly)

• Lifting capacity considered when planning a dry weight lift (partial or total) and control of submergence of the flooded structure. 3000 to 4000 ton available nowadays

• Transport: self-floating tow vs transport on heavy lifting vessels

• Assembly concept: offshore vs onshore jacket connection to GBF

• Ballast: cost and impact in overall design

• Required seabed preparation, depending on the site

OWEC TOWER AS

Hybrid jacket-GBF development status• Engaged in many concept designs last 2 years

• Leading substructure design for Karmøy test site development

• Close cooperation with EPCI companies and project owners is key to develop most suitable concept(s)

• Ongoing activity, potential foreseen for OWEC’s hybrid jacket-GBF substructures in future offshore concession rounds

OWEC TOWER AS

Contact info OWEC Tower AS:Jordi Pascual Gilabert, Engineering ManagerJordiPascual.Gilabert@owectower.no

Johan Fredriksson, Chief Executive Officerjohan.fredriksson@owectower.no