Tech-Marine involvement

Nysted offshore wind farm.

Tech-Marine involvement

 

 

Contractor  E2

Customer  Per Aarsleff A/S

Calculation  Tech-Marine Consulting ApS

 

 

The project concerned transport and placement of 73 concrete foundations for the Nysted Offshore Wind Farm, at the time, the second largest of its kind in the world.
The foundations diameter at the widest place were 10.3 m with heights ranging from about 11 – 16 meters and weight in the 1000-1300 ts range.
The foundations were produced onboard flattop barges at Ordra Port, Poland and towed 100 nautical miles to the Rødsand banks, Denmark, where the wind farm is located.

Tech-Marine undertook the following consultancy / production tasks for the main contractor Per Aarsleff A/S:

Tech-Marine Consulting ApS Tech-Marine Construction ApS     Environmental load calculation   Production of steel moulds   Analysis of barge motion   Production of supporting structure for the steel moulds   On-Hire survey of barges   Production of 73 Steel platforms for the foundations   Strength calculations for mooring system of the barges   Production of 73 set Guard Rails for the foundations   Required BHP calculations for the towing operation   Production of 73 boatlanding arrangements for the foundations   Loading manual   Production of securing arrangements for the foundations during towing   Approval of loading manual from class and maritime authorities   Production of emergency towing arrangements for the barges   Operation guidance for the barges, including loading and unloading sequence   Mobilisation of the barges   Design and calculations of securing arrangements for foundations       Design and strength calculation of the steel moulds       Design and strength calculations of supporting structure for steel moulds during casting

On behalf of Per Aarsleff A/S, Tech-Marine investigated the wind, current and wave impact on the mooring systems used for fixation of the barges during the unload sequence of the foundations at the wind farm. Tech-Marine calculated minimum requirements for the anchoring system and proposed methods to ensure safe operation.

For production and transport four barges, one of them a semi submersible, of the Nordsø type and one smaller barge for transport of the transformer foundation were chartered. In addition one tugboat were chartered for towing of the transport barges.

For the unloading procedure one additional barge was converted to a special crane barge.

Tech-Marine carried out on-hire survey of the barges on behalf of Per Aarsleff A/S, to ensure that the barges were in working condition and noted the general condition of the barges. Furthermore draft- and tank contents measurements were carried out as basics for the loading conditions.

The concrete foundations were cast in large steel moulds placed onboard the barges. All steel elements used in the casting process were designed by Tech-Marine Consulting ApS and produced by Tech-Marine Steel ApS.

During concrete casting it was important to maintain the same deck height above the pier. To achieve this, Tech-Marine produced a loading sequence for the ballast tanks during the concrete casting.

Model tests of the crane barge were carried out to determine the accelerations and vertical movements as basics of the calculation of the barge motion during the lifting operation.

Using the results of the test, Tech-Marine set the operational window for the crane barge.

Barges for transport:

Tech-Marine made stability calculations for the barges to be used for transportation of the foundations, from the production site to the site of the wind farm.

Each barge carried 4 foundations during the trip to the site.

Stability calculations were made for the voyage and separate calculations for the unloading procedure. During unloading it were of great importance that the stability of the barges always was sufficient to ensure safe operations.

Ballast operations were carried out using fixed and portable bilge pumps. Therefore the sequence of the ballast operations were carefully planned to minimize shifting of water.

To enable unloading of some of the highest foundations a semi submersible barge was used, which demanded special care during the stability calculations. During unloading a ¼ of the deck on the barge was submerged.

The arrangement and cargo distribution onboard the barges were of such an unusual character that approvals from the class and the maritime authorities were required. All documentation produced by Tech-Marine Consulting ApS were approved by the Classification societies and maritime authorities.

 

 

Nysted Offshore Wind Farm became fully operational 1.st of December 2003.

Photos: Jan Kofod Winther and Tech-Marine