WTG Support Structures

Structural Design

WTG Support Structures

NIRAS is involved with design and engineering of steel foundations for large offshore wind farms including supports for wind turbine generators (WTG's). Design works includes hydrodynamic, structural and installation  design as well as cable protection, cable routing and cable dynamics analyses.

NIRAS provides support during all phases of the design of offshore wind turbine generator support structures, starting from site investigations, conceptual through to detailed design, detailed drawings, fabrication, transport, installation and in-service until decommissioning.

NIRAS provides the following services:

  • Conceptual and detailed design services for secondary and primary steel

  • MP detailed partly automated design program including the full geotechnical design

  • Pile driving analysis

  • Flange FEM analysis including detailed bolt modelling, pre-tensioning, driving, in-situ and fatigue utilization

  • Corrosion protection active/passive systems

  • Scour protection/analysis

  • Detailed fabrication drawings, monopile, jacket structures, bucket foundations

  • New solutions/innovative design

  • Special engineering: structural, hydrodynamics, cable dynamics/tie-in, geotechnical analysis

  • Example projects: Blyth Harbour, Scroby Sands, North Hoyle, Northwind, Rampion, Kriegers Flak, Vesterhav Nord/Syd, Dafeng, Changua, Xuven, Hai Long, and Dogger Bank

  • Review and evaluation on ad hoc basis

The TP-less Scroby Sands design featured and external cage structure and a hanging internal airtight platform (ATP). This ATP was onshore installed in a damped suspension arrangement prior to the offshore pile driving operation. Recently, we have developed a internal ATP with a Client (patent pending), which saved lots of time during offshore installation of the windfarm foundations.

WTG Support Structures

OHVS Support Structures

Offshore High Voltage Substations Support Structures

NIRAS carried out detailed design of a number of Offshore High Voltage Substations (OHVS), including monopile foundations (Northwind) and jacket structure foundations (Jieyang OHVS foundation shown bottom right picture) and jacket/concrete hybrid foundation (Anholt OHVS foundation shown on main picture and two top picture right).

NIRAS carried out installation engineering and site supervision of critical tasks for some projects.


Floating Wind

NIRAS is engaged with floating wind engineering. Our engagement has so far included technical review of proposed floater systems including turret systems (Dounreay Tri floater shown in picture top left) and conceptual design of various floater solutions. We have carried out   specialized structural analysis applying super nodes, solid and shell elements to find the stress level and fatigue performance of main members and special high load connection points (Tetraspar ANSYS FEM shown in picture right).

NIRAS has special knowledge within hydrodynamic analysis and determination of the structural response in time for a floating structure. Further to our in-house programs, we have a technical cooperation with the company Principia/Artelia and an agreement regarding use of their recognized program Deeplines. This program now includes a full hydrodynamic and aerodynamic model of the floating WTG system including the combined tower, nacelle and turbine blades response.

Other projects include analysis of the Sea Twirl system.

LIC Floating Wind

Other Structures

NIRAS has carried out various special design assignments within the offshore renewables sector. The works include detailed design of:

  • Steel supports for crane boom extension for a major installation vessel crane

  • Design, testing and supply of porpoise detector frames, deployed in German North Sea waters prior to windfarm construction. The frames including the subsea sensor and recording equipment were placed on dedicated locations on the seabed and retrieved after a year with an acoustically release retrieval bouy line

  • Sea fastening cradles for tower transport in standard cargo vessels

  • Sea fastening frames for deck support of nacelle, TP sections and blade racks

  • Engineering and pipeline/riser design for the wave piston prototype system installed offshore Gran Canaria

  • Offshore Metocean mast design, several projects

Other Structures LIC

Repair & Modification

NIRAS offers engineering services in relation to repair and modification of existing wind farms and related equipment. This also includes mechanical and hydraulic design where appropriate. Example of these works are listed below:

  • Design of cable repair clamps for internal J-tubes

  • Design, testing and engineering to repair offshore cable protection system (CPS) on London Array wind farm, 175 J-tubes plus export cables

  • Repair of road transport equipment, several projects, testing, design, fabrication supervision fro repair of 150 T tower road transport vehicles. Structural reinforcement of equipment modification of vehicle bed, failure identification, vehicle dynamics, supervision of vehicle modification at local yard in Esbjerg

  • Design of mitigation solutions for MP/TP grouted connections on a series of offshore wind farms in the North Sea. The solutions included post-installed disc spring axial relief systems. The disc spring system was fatigue tested at a recognized technical authority in Germany

Repair & Modification LIC

Supply of Components

NIRAS has supplied various structures and components to the offshore and subsea industry.

NIRAS has supplied various structures and components to the offshore and subsea industry. The supply is mainly generated by Client request. NIRAS will typically apply one or more fabrication contractors which will typically be local Esbjerg yards and we work in close cooperation with the subcontractors. Typically, NIRAS will be involved directly in FAT, functional and integration testing. Furthermore, we engage with third party for weld control, testing services, witnessing and documentation. Examples on the supplies are:

  • Clawloks Bending Stiffener Latching Mechanism, LIC proprietary design (patent pending), approx. 25 sets (male + female units) supplied

  • Sling Tensioners for jack-up platform strengthening

  • Xmas tree support frames

  • Cross over flange for Xmas tree in temporary condition

  • Chemical injection system, prototype on-stream high-pressure injector developed, patented and tested

Supply Of Components

Testing Services

NIRAS has regularly been engaged to carry out testing services for offshore and onshore equipment. Work includes FAT testing of NIRAS supplied components, testing of cables to determin the structural properties, testing related to insurance and root cause investigations for structural failures and testing of malfunctioning transport equipment for onshore road transport of very heavy components.

NIRAS has a 12 m long horizontal testrig based in Esbjerg which allows us to carry out structural cable testing for wind farm offshore array and export cables. We also have possibilities for vertical suspension to determine cable dynamic behaviour. NIRAS has delivered testing sevices for a number of specific jobs relating to offshore/subsea cables in the North Sea. Some of the tasks have been:

  • Cable mechanical static properties and dynamic behaviour

  • Root cause identification for failed cables during pulling operations, cable twist

  • Testing of cable protection systems (CPS) including repair engineering

  • Cable clamp capacity

  • Clawloks connector, steel-steel connection system, CPS connection to J-tube/MP hole

  • Testing and design of external and internal J-tube systems

  • Integration testing including testing of Airtight platform (ATP) solutions

  • Subsea epoxy grouting tests

  • Scour tests

Testing Service

Mechanical Design

NIRAS has a wide range of research and development in mechanics ranging from various connectors to clawloks.

NIRAS' Research & Development of Mechanical Design

NIRAS has carried out a variety of research and development activities relating to mechanical. A selection of activities is listed below.

  • Flexible Riser Connector

  • Cable CPS Connector

  • Turner Tool

  • Internal Platform (ATP)

  • Flexible Riser Connector

  • Clawloks

  • Cable CPS Connector

  • Tower road transport

  • Mitigation solutions (disc spring fatigue testing)

  • Offshore high strength grouted connections (structural FEM analysis, evaluation)

  • ATP, airtight platfom for offshore windfarm monopile foundations

  • Bridge chord (pulling hydraulics)

  • Control of HPU working tandem (test rig)

  • Hydraulic levelling systems

  • Porpoise detectors (acoustic data aquisistion)

  • EFP bundle connectors in Grådyb

Transition piece line-up ready for offshore installation. LICengineering pioneered the design for the grouted connections at Blyth and North Hoyle offshore UK, as well as provided the first design of TP-less solutions – for the Scroby Sands windfarm.

Want to know more?

Thor Ugelvig Petersen

Thor Ugelvig Petersen

Vice President

Allerød, Denmark