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Offshore Center Danmark 

Newsletter ON/OFF 3 

August 2004 

Editor: 

Peter Blach pb@offshorecenter.dk 

Subscribtion: Anne-Marie Klestrup 

ak@offshorecenter.dk 

Graphic production: 

Jan C Design & Kommunikation 

Printing: 1000 

3 

Offshore wind 

energy—past, 

present and future 

Since the oil crisis in the 1970’s, electricity generation from wind 

energy has gained increasingly more focus from the Western 

World and Denmark in particular. Development activities have 

resulted in still more powerful wind turbines—today, new wind 

turbines are typically dimensioned to deliver an output of 2 MW 

or more, whereas 25 years ago the magnitude was much less. The 

dramatic growth in turbine size is expected to continue. 

Cont. page 2 

Newsletter to the offshore 

industry in Denmark 

ON/OFF 

Offshore wind energy—past, present 

and future .......................................... 1 

A Logistic Challenge ............................. 3 

Results from the development project 

“How to board an Offshore Wind Turbine” .. 4 

Blue Water Shipping—right in the middle 

of the Danish Offshore Centre ................. 6 

Foundation design considerations .......... 7 

Experiences at Horns Rev Offshore 

Wind Farm pilot project ........................ 8 

A2SEA A/S pioneers in offshore wind ...... 9 

Numerical Simulation of hydrodynamic 

Loads on Offshore Windmills ................10 

Research leading to new offshore 

design methods ..................................12 

Short News ........................................14 

Member questionnaire .........................15 

EUC Vest has introduced re-education 

entirely on the companies’ conditions ....16 

State-of-the-Art Design Standard 

specifically developed and applicable for 

Offshore Wind Turbine Structures .........18 

Materials in offshore wind turbine wings ..19 

www.offshorecenter.dk

Welcome 

– focus on Offshore Wind Energy 

Welcome to ON/OFF, the newsletter from 

Offshore Center Danmark to the Danish offshore 

industry and educational institutions. 

We have chosen in this issue to focus on 

news and topics related to offshore wind 

energy, an area with a good growth potential 

and an area where the Danish oil & 

gas offshore industry has vast experience, 

which can be shared also with the offshore 

wind industry. 

Onshore the cost ratio wind turbine/surrounding 

facilities is typically 80% / 20 %. 

Offshore this ratio changes dramatically, 

so that the two have almost the same cost 

share. This brings into focus issues like 

offshore foundations, mounting and landing, 

issues in which the offshore industry 

in Denmark has more than 30 years of 

experience. 

Offshore Center Danmark has recently 

held an offshore wind energy conference 

on this topic in Esbjerg and furthermore 

established a standing committee of 

members who will help to further develop 

offshore wind energy in Denmark. 

Future issues of ON/OFF will at times 

similar to this issue select a main offshore 

topic for closer investigation and will at 

other times, like the next issue be of a 

more general news-related nature. 

We hope you will find our newsletter of 

interest. 

Kind regards 

Peter Blach 

2 

Offshore Center Denmark 

Newsletter ON/OFF 3 - August 2004 

Location Year of Number Output pr Total output 

construction of turbines turbine [kW] [kW] 

Vindeby, Lolland (1) 1991 11 450 4,950 

Tunø Knob (2) 1995 10 500 5,000 

Middelgrunden (3) 2000 20 2,000 40,000 

Horns Rev (4) 2002 80 2,000 160,000 

Rønland (5) 2003 8 2,150 17,200 

Nysted (6) 2003 72 2,300 165,600 

Samsø (7) 2003 10 2,300 23,000 

Frederikshavn (8) 2003 3 2,300 & 3,000 7,600 

Total 214 1,978 (average) 423,350 

Cont. from page 1 

Traditionally, wind turbines have been placed 

throughout the country in windy locations 

such as hilltops and near the coastline. In 

1991 a new type of location was taken into 

use—offshore. In southern Denmark (1 mile 

off the coast of Lolland) the first offshore 

wind farm in the World was erected. The 

wind farm proved a success and since then, 

more and more wind turbines have been 

placed offshore. As of today, a total of 8 

offshore wind farms have been constructed in 

Danish waters. 

In addition to the existing 8 offshore wind 

farms 2 more, each of 200 MW, are currently 

being planned. One will be an addition to the 

existing Horns Rev offshore wind farm and 

both are expected to be fully operating by 

2007/2008. 

Currently, it’s possible to supply 20 % of 

the Danish energy demand by wind energy 

—offshore wind energy takes an increasing 

share of this: 

20% 

15% 

10% 

5% 

0% 

91 

92 93 94 95 96 97 98 99 00 01 02 03 jan-04 

Danish energy policy has a goal of major 

expansions of offshore wind farms. Thus it 

has been formulated that by the year 2030, 

¾ of all Danish wind energy (a ratio equivalent 

to 4,000 MW) must be produced by 

offshore wind farms. This is expected to 

result in the ability to cover half the Danish 

electricity demand through wind energy, 

under the assumption that the goal is met. 

Danish offshore wind farms 

Current (red) and planned/under construction 

(white) offshore wind farms. 

Worldwide, wind turbines with a total 

output of approximately 530 MW have been 

installed in offshore wind farms—Denmark 

is thus leading in the field, with 80 % of the 

total capacity. Only four other countries currently 

possess offshore wind farms: United 

Kingdom, Ireland, Sweden and Holland. 

Future prospects within offshore wind farms 

are vast. About 40 offshore wind farms, some 

as large as 1,000 MW, has been planned 

worldwide—the far majority located in 

North-West Europe. Within the next 4 years 

it is expected that the installed capacity will 

have grown to be approximately 20 times 

greater than the current 530 MW. Some of 

the biggest expansions planned, are located in 

United Kingdom and in Germany. 

Besides the offshore wind farms shown in 

above map, a number of farms are being 

planned in other locations—amongst these 

are: Cape Trafalgar (Gibraltar, Spain), Cape 

Cod (Massachusetts, USA), Long Island 

(New York, USA) and Queen Charlotte Islands 

(Canada—known as the Nai Kun wind farm). 

All in all, offshore wind energy is a market 

with a large potential, and a market where 

much of the technology is concentrated 

around Northern Europe and Denmark in 

particular. ■

A Logistic 

Challenge 

By Poul Skjærbæk, R&D Department, Bonus Energy A/S 

In October 2001, Bonus Energy was awarded the contract for the 

world’s largest offshore wind farm, the Nysted project in the Baltic Sea. 

The contract comprised a series of challenges. Bonus had previously 

installed other offshore projects, including the world’s first offshore 

wind farm at Vindeby with 11 450 kW turbines in 1991, the Middelgrunden 

offshore project with 20 2 MW turbines in 2000, and the 

Samsø offshore project with 10 2.3 MW turbines in 2002, but the 

sheer magnitude of the 72-turbine project at the Nysted Wind Farm 

was in a class of its own. 

Already at an early stage it was clear that this project was not “just 

another job”. The first challenge was to find suitable harbour facilities 

for the discharge of components. All harbours close to the wind farm 

site are either very small or subject to heavy ferry traffic which would 

put severe restrictions 

on the installation efficiency. 

The overall time 

frame for the project 

dictated that all 72 units 

should be installed over 

a period of maximum 80 

days, offering slightly 

more than one day per 

turbine including all 

downtime. This requirement 

and the restrictions 

on the local harbours 

called for a new installation 

set-up which could combine the use of a remote harbour and 

efficient installation at an attractive cost. 

After a detailed analysis of available installation vessels, the special 

built installation vessel, Ocean Ady was chosen for the job. The 

Ocean Ady is a modified container ship, fitted with four supporting 

legs and a lattice boom crane. Previously, the Ocean Ady had been 

used for offshore wind turbine installation using a setup where two 

complete turbines were installed per round trip. In order to reach the 

required installation rate, the vessel was modified to meet a capacity 

requirement of 4 complete wind turbines. 

One of the modifications was a special rack for stacking four rotors 

on top of each other. Placed on the deck, the rack was more than 12 

meters high, requiring special attention to safe working conditions 

both during loading and installation off shore. In order to ensure that 

Project background: The Nysted Offshore Wind Farm is located on the North side of the Femarn 

Belt, approximately 10km from the Danish shore. The wind farm is located due south of a 

restricted Ramsar area, which limits the direct accessibility from the shore to the wind farm. All 

transports to and from the wind farm has to be carried via designated routes outside the Ramsar 

area. The project is owned by a consortium of Danish E2 and DONG and Swedish Sydkraft. For 

the construction of the wind farm, Per Aarsleff was awarded the contract for foundations, Bonus 

Energy the contract for the wind turbines, ABB the contract for the electrical infrastructure and 

Pirelli the cable connection to shore. 

all operations would work and that all working processes would be 

safe, a complete mock-up of the rotor rack was made well in advance 

of the start-up of the installation works. Based on the experiences 

from the mock-up, a series of modifications were introduced in order 

to obtain the best possible working environment. 

The port of Nyborg was 

selected as the base harbour 

for the discharge 

of components due to 

very good accessibility 

both by road and by sea. 

Furthermore, the port 

of Nyborg offered more 

than 60,000m2 of storage 

and assembly area 

right at the quayside, 

providing the basis 

for an optimum flow 

of goods throughout the vessel loading process. The total supply of 

turbines and equipment at the quayside required more than 700 truck 

loads, obviously requiring a high degree of flexibility at the unloading 

area. The only disadvantage of the port of Nyborg was that it was 

located more than 80 nautical miles from the wind farm site, resulting 

in an 11-hour run at favourable weather conditions. 

At the harbour area, a flow arrangement was established whereby 

pre-assembled tower sections, nacelles and blades would meet at the 

quayside in order to be ready for loading onto the installation vessel 

immediately upon arrival. 

When everything 

operated optimally, the 

installation vessel was 

loaded with 4 complete 

turbines in less than 12 

hours. 

On May 11th 2003, the 

first turbine installation 

commenced at Nysted 

Wind Farm, and after 

fine-tuning of the work 

procedures during the 

first two round trips, 

the installation pace reached the required 1 turbine installed per day. 

When the weather conditions were optimal, a round trip could be done 

in 72 hours, equalling 18 hours per turbine installed including trans- 

Offshore Center Denmark 3 

Newsletter ON/OFF 3 - August 2004

Cont. from page 3 

portation to and from the site and loading of the vessel. On the 79th 

day from the start up of the installation, the 72nd and last turbine was 

delivered to its final destination at Nysted Wind Farm. 

The commissioning works commenced as soon as the first turbine 

had been installed and proceeded on parallel to the installation. Grid 

connection was established in the beginning of July, 2003 and on July 

13th the first power was exported to shore. By the end of August, 

all turbines had been commissioned and were in automatic operation, 

and following a three-month adjustment and testing period, the 

project was taken over on December 1st 2003, one month ahead of 

schedule.■ 

Fact about Nysted Offshore wind farm: 

Owner: E2, DONG, Sydkraft 

Operator: E2, SEAS Transmission 

Project Rating: 165.6MW installed capacity 

Turbine type: Bonus 2.3MW Combistall 

Service provider: Bonus Energy A/S 

Key dates: 

October 8th 2001: Contract awarded to BONUS Energy A/S 

May 11th 2003: First turbine installed on site 

July 13th 2003: The first power is exported to shore 

August 31st 2003: All turbines are commissioned 

December 1st 2003: The wind farm is taken over by the owners 

4 Offshore Center Denmark 


Results from the 

development 

project “How to 

board an Offshore 

Wind Turbine” 

by Ulrik C. Jensen, RAMBØLL & Peter Blach, 


Offshore Center Danmark has, within a development project financed 

by the Danish Ministry of Science, Technology and Development 

(VTU), seized the initiative to review and develop suggestions for 

safe and economical methods to board offshore wind turbines. The 

results from the development project were not envisaged as the suggested 

solution for actual projects, but as a description of generic 

methods of landing including advantages and drawbacks, which later 

will be adapted to actual conditions. 

After a project period of one year, the results of the project were 

made available to the offshore wind turbine industry and the educational 

institutions, on a session June 10th at the “Offshore Wind 

turbine—Surrounding Facilities” conference at Aalborg University in 

Esbjerg. 

Offshore wind turbines are a segment of the wind turbine business 

growing rapidly these years. It is also a type of installation that holds 

great technical, environmental and economical challenges. A lot of 

knowledge from the offshore oil & gas related business can be used 

during the installation of offshore wind turbines, but the area also 

holds its unique challenges. An excellent example is boarding of the 

wind turbines, which is partly similar to what is known from oil drilling 

platforms, but partly has it own characteristic features. 

During the task of making offshore wind turbines a reliable and costeffective 

energy source, safe access to the installations is an essential 

component. 

In connection with the considerations to be made, it is vital to take 

into mind that the transfer of personnel and equipment to the wind 

turbines should be done as safely as possible taken into account the 

heavy sea conditions that often exist at an offshore wind farm.

Additionally the economic part of an optimal transfer mode is significant. 

Availability figures for an onshore wind farm is typically more 

than 97%, whereas the figures offshore can be substantially lower 

due to the relatively complex current and wave conditions at sea. In 

case the access conditions can be improved and hence the availability 

figures offshore, can be increased just a few percentages, this would 

have a direct impact to the earnings of the wind farm and the total 

pay-back period of the wind farm. Given that an offshore wind farm 

such as Horns Rev produces app. 2% of Denmark’s total electrical 

power consumption, this is a key element. 

A series of Danish and foreign firms have participated in the development 

project, with focus on boarding offshore wind turbines. During 

a panel discussion with the audience, the firms presented and argued 

for their solutions. 

One of the firms was Grumsens Maskinfabrik in Esbjerg, who has 

developed a crane for wind turbines. The crane has a hydraulic, pressure-compensated 

winch, which can catch and lift the service crew’s 

landing boat. Sales Engineer Per Mathiassen stated that he was positive 

on the project outcome and the possibilities he had been given to 

analyse the advantages and drawbacks of their method. 

Another company who made a presentation was the significant Danish 

supplier of Life-Saving Equipment for marine usage Viking Life- 

Saving Equipment. The company has recently bought a Norwegian 

company specialised in offshore evacuation and landing systems. It 

was within this company that an exciting solution of the problematic 

nature of secure and easy access to the offshore wind turbine 

was found. Viking manager Heine Johst stated: “The advantage of 

our development project is that is has been tested successfully over 

several years within the very demanding offshore oil & gas industry. 

During the course of the development project, we have made some 

adjustments in order to develop a more generic method, and it is this 

method we think can be used for offshore wind farms. “ 

A number of other methods were also presented, among these a boat 

with some quite incredible stability characteristics from the Danish 

company Sea Service. 

Finally, the Dutch company Fabricom gave a presentation of their 

OAS - Offshore Access System. This method had been successfully 

tested on an oilrig installation in Qatar, and the inventor Reinout 

Prins, informed the audience that the project had given him some 

valuable future input on down-sizing the solution to smaller scale 

offshore wind turbine installations. 

Following a good and fruitful panel discussion, the conference moved 

forward to other topics, as described elsewhere in this newsletter. A 

report with the results of the development project together with all 

the presentations can be found on the web site of Offshore Center 

Danmark: www.offshorecenter.dk.■ 

5 



Blue Water Shipping—right in the 

middle of the Danish Offshore Centre 

By jb., Blue Water 

Situated at the quayside in the port of Esbjerg you will find a brandnew, 

two-storey office building. Locally it’s called the Black Diamond 

matching the famous King’s Library in Copenhagen. This is the new 

headquarters of Blue Water Shipping, a company with Danish roots 

now extended to include the whole world. 

Since the offshore industry came to Esbjerg—on the west coast of 

Jutland, Denmark—in the early seventies, Blue Water has taken part 

in the “North Sea Adventure”. The Blue Water freight forwarders and 

shipping people soon adopted the challenge of serving the offshore 

industry with international transport and logistic solutions. 

The offshore department grew rapidly and as a consequence branch 

offices were established in the oil and gas centres around the North 

Sea and later on in the Middle East, Central Asia, U.S.A., Brazil and 

East Asia. 

As the Danish windmill industry developed and became leading 

worldwide suppliers, Blue Water was an evident choice as a logistics 

partner. The company has developed great skill and experience 

in transport and handling of urgently required spare parts and large 

constructions. 

Actually Blue Water has become the leading expert in loading and 

discharging heavy wind mill sections to and from Danish ports. 

Among others Blue Water was an inevitable part in the erection of the 

offshore wind mill park outside Esbjerg during the years 2000-2003. 

The biggest in the world so far. 

Every week you will find large wind mill parts on the quays of 

Esbjerg—ready for shipment throughout the world. Even in the 

discharging ports, Blue Water’s own stevedore managers are taking 

over the responsibility. A special project and heavy lift department 

co-ordinates all shipments and the stevedore part is in safe hands of 

experienced marine navigators and engineers. 



Especially working for the oil and gas sector has contributed to the 

internationalisation of the Blue Water Shipping Group. An example of 

this is the landing of a major contract with Technip Coflexip covering 

transportation of a gas production platform “TPG500”—consisting 

of modules of up to 4,000 tons per section—from the Keppel Fels 

shipyard in Singapore to the Azerbaijan sector of the Caspian Sea. 

A similar heavy lift job was successfully carried out in 2001-2002. 

Securing such jobs is really making the boss—Kurt Skov—happy and 

proud. 

Blue Water Shipping is now present in 17 countries with 32 offices 

and a total staff of 530 employees. In Denmark Blue Water is represented 

in 10 main areas and abroad you will find Blue Water offices in 

Greenland, England, Scotland, Ireland, the Netherlands, France, Spain, 

U.S.A., Brazil, Russia, Georgia, Azerbaijan, Kazakhstan, United Arab 

Emirates, Singapore and China. The intention is to be an all-round, independent 

shipping- and freight forwarding company offering global 

clients a service within airfreight, sea freight, road and rail haulage. 

■

Foundation design 

considerations 

By Jørn H Thomsen, COWI A/S 

Off-shore wind mill foundation design may be defined as the noble art 

of developing sound and cost effective concepts, with due consideration 

of operational and environmental loads as well as hydrographic 

and geotechnical conditions—and notably fabrication, installation and 

logistics in the construction phase. 

It goes without saying that a close collaboration between the foundation 

contractor and the designers is imperative for optimisation of 

the designs with regard to the construction aspects. The design and 

construction of the gravity foundations for the Nysted Offshore Wind 

Farm, located some 10 km off the southern coast of Lolland, is a fine 

example of this approach. The foundation concept was developed 

jointly between the contractor P. Aarsleff A/S and the contractor’s 

consultant COWI A/S in the tender stage and detailed after award of 

the contract to P. Aarsleff A/S. 

The Client is the Joint Venture ENERGI E2 - DONG - Sydkraft 

Energy, with SEAS Energy Services as Client’s project manager. The 

project comprises 72 windmill foundations for 2.2 MW Bonus wind 

turbines. Height of hub above the sea is 68.8 meters and rotor diameter 

is 82.4 meters, giving a total height of 110 m. 

The windmills are founded at 6-12 m water depth and soil conditions 

are generally stiff moraine clay. 

It was immediately evident that a monopile solution was not feasible 

due to a high content of boulders. At the same time, these soil 

conditions were favourable for a gravity foundation, as generally high 

bearing capacity was met near the natural sea bed. 

In the course of the tender design, the contractor found that the most 

cost effective solution overall would be concrete foundations fabricated 

in Swinoujscie, Poland, where cheap and highly skilled labour was 

available. In turn, this required transport by barges to the site, where a 

floating crane would pick the units up and place them on pre-prepared 

stone beddings, thus maximising the effective time of the crane. 

The transport and installation procedures required that the weight of 

the concrete foundation units were minimised. This was achieved by 

the concept of a hexagonal base structure with six open cells, and 

a shaft and an ice cone at top. The base dimension is 15 m and the 

maximum height 16.25 m. By these means a concrete weight (in air) 

below 1300 t was achieved, allowing the marine operations. The necessary 

weight to provide stability against sliding and overturning was 

then provided by heavy duty olivine material filled in the cells and the 

shaft, adding another 500 t to the weight. 

The contractor together with the crane subcontractor Eide Marine 

designed a purpose built lifting device, shaped as a cone to fit the ice 

cone. The heavy lifting forces were thus distributed over a large area 

of the solid concrete ice cone, reducing the local installation stresses 

to a minimum. 

The actual performance proved the feasibility of the concept, as a 

production cycle for 4 foundations on one 10,000 t barge was carried 

through in 30 days or less, once teething troubles were overcome. 

With 3 barges in the line, 4 foundations were placed every 10 days, 

weather permitting. The project was carried out according to schedule, 

from contract award in March 2002 to all foundations in place in 

the summer of 2003, ready for reception of the wind turbines.■ 

7 



Experiences at Horns Rev Offshore 

Wind Farm pilot project 

By Jens W. Bonefeld, project manager, ELSAM 

For some time various technical problems have affected the wind 

turbines at Elsam’s huge Horns Rev Offshore Wind Farm pilot project. 

In the autumn of 2003, problems occurred on the transformers of the 

wind turbines and later production defects have been detected on a 

large number of generators. 

The operation of the wind farm can hence not be considered straight 

forward and valuable experience has been gained in the last year. 

Elsam’s supplier, Vestas, has acknowledged the problems and is 

making an energetic effort to solve them and ensure that the turbines 

return to satisfactory operation. 

The inclement weather conditions in the North Sea have made the 

work at Horns Rev difficult, and Vestas is considering it would be 

more expedient to dismantle all nacelles and bring them ashore to 

repair them under optimum conditions. This operation is carried out 

in during the summer of 2004 so that all wind turbines are operational 

by autumn 2004. 

Vestas is well under way with the planning of the project and only significant 

hindrances can stop the completion of the project. A number 

of turbines and rotors have thus been dismantled and transported 

to Esbjerg. These turbines and rotors will be inspected and used as 

preparation for the remaining works. 

Elsam appreciates that Vestas has demonstrated efficiency in their role 

as responsible supplier. Vestas has made an effort to ensure that the 

repairs necessary to make the wind turbines function technically correct 

are performed as quickly as possible 

Elsam has a contractual agreement with Vestas on availability and 

guarantee. Therefore the problems with the wind turbines will only 

have limited financial consequences for Elsam. 

Offshore wind power is a business area in embryo. At the end of 2003 

the offshore installed capacity only amounted to approx. 530 MW 

of which approx. 400 MW were in Danish waters. The total installed 

wind power capacity worldwide is 40,000 MW. However, particularly 

in Northern Europe and North America there are many ambitious 

projects in the making. It is expected that approx. 8000 MW will be 

installed offshore in the period between 2004 and 2008. This corresponds 

to approx. 15% of the total expected new wind power capacity. 

■ 



A2SEA A/S 

pioneers 

in offshore wind 

By Kurt E. Thomsen, Business Development Manager, A2SEA A/S 

When the Danish government decided to make a pledge to offshore 

wind, it was not clear to all how this would actually materialize. In 

the early 1990´s a number of smaller turbines had been installed in 

the Baltic and on locations in the sheltered waters of the east coast 

of Jutland. But now we were talking North Sea, exposed sites, major 

risks and clearly the number of sites and turbines were to be the driving 

factor in development of methods and equipment to deal with this 

new market. 

In 1999 the founder of A2SEA A/S handed in a patent application 

for the transport and installation concept which was later to be the 

backbone of the offshore wind industry, namely the crane ships which 

have been converted to perform offshore lifting of turbines. 

The idea was based on the specific environment that prevails on Horns 

rev and the idea was that if you could cope with the harsh environment 

out there, you could cope with all possible sites thereafter. 

The company was formally formed in July 2000 and the first task was 

to convince the client on Horns Rev—Vestas that A2SEA could actually 

do what it sets out to do, namely to safely transport and install 80 

2 MW turbines offshore within a short time frame. 

There were only four obstacles to overcome: 

1. The system had never been built before. 

2. No funds. 

3. No offshore experience. 

4. Never before actually lifted a wind turbine. 

The company in so many words started from a clean sheet of paper 

and developed from there. Fortunately the computer simulations and 

the scale model tests went very well and the company managed to 

persuade its client that it could carry out the contractual obligations 

safely and timely. 

The biggest vote of confidence therefore came as Vestas put the 

proposal forward to Elsam Engineering as the system they wanted to 

work with. And as the contract was awarded, the biggest challenge so 

far was approached with great vigilance by the three employees of the 

company, along with a retired naval architect. 

Within 6 months—albeit more than a month late, the first vessel was 

converted and ready for testing. Three months of teething problems 

later A2SEA carried out the first contract—namely the exchange of 

a blade damaged by lightning on the Blyth Offshore Wind farm, just 

prior to installing the first turbine on Horns Rev. 

This was an unusual test, as A2SEA had never before performed 

offshore work. A2SEA now had to position the vessel on a difficult 

rocky seabed, with also the tide up to 5 metres this proved to be quite 

a challenge. 

A2SEA managed to safely exchange the blade and return to Esbjerg 

in order to mobilize for the turbine installation on Horns Rev. 

The turbine installation started off in fairly rough weather but over 

time A2SEA managed to cope well with waves, swell, wind and currents. 

A2SEA’s was to load, transport and lift the turbines for Vestas to 

install and it was incredible to see how quickly all the crews managed 

to adapt to the new environment they were working in. This was also 

made easier due to the detailed planning of all offshore operations. 

Onshore however A2SEA suffered congestion in the harbour, a lesson 

also taken in well by Vestas and the next projects have all taken this 

fact into account and made provisions for very large staging areas since. 

The project suffered bad weather spells, but was blessed by superb 

weather conditions by July. 

The installation was finished on August 21st 2002 and this was effectively 

two weeks ahead of schedule. 

The two crane vessels stayed at the Horns Rev construction site for 

hook up and commissioning of the wind farm and these operations 

lasted the rest of the year and was finished in early December 2002. 

The contract for the Nysted wind farm was awarded shortly before 

Christmas 2002 and Bonus used Nyborg harbour as staging area for 

the 72 turbines. 

9 



The work started work in early May 2003 and by sailing four complete 

turbines per trip, the last turbine was installed in July 2003. 

A2SEA had learned quite a lot from the first project at Horns rev, and 

the most significant lesson learnt was to put great emphasis on the 

seabed conditions for jacking the vessel, as some base plates were 

lost at one occasion. 

The most significant upgrade was a sonar well fitted on the vessel in 

order for the jacking crew to see debris and other obstacles on the 

seabed. 

After completing the Nysted wind farm, the vessel Ocean Ady went 

on to Arklow Bank to install a met mast, and this was the first job 

installing monopiles. The project was carried out during October, 

and while Ocean Hanne was on Horns Rev for planned maintenance, 

Ocean Ady stayed on Arklow for commissioning of the seven GE 

turbines there. 

In December A2SEA was once again awarded a contract of installing 

offshore turbines, this time the Scroby Sands project, where 30 Vestas 

2 MW turbines were to be installed from March to May 2004. And 

this time the challenge was to cope with 5 knots of current in very 

shallow water. In fact some of the turbines would be dried out during 

Spring tides. 

During January a new set of base plates were designed, and fitted on 

to the legs of Ocean Ady and the vessel was mobilized during late 

February and early March. The reason for the new base plates was 

that A2SEA believed that in order to keep the vessel stable during 

jacking in the high currents, the company needed to penetrate the 

seabed to the maximum scour that would occur. This is not normal 



operation as you want to stay on top of the seabed for easy access and 

egress to each position, but the risk of underscouring a base plate was 

so big that it was decided—rightly—to install new tailor made plates. 

The installation of the turbines was split between A2SEA and Seacore 

—a British offshore contractor who in cooperation with A2SEA 

installed 6 of the 30 turbines on the shallowest locations. 

The contract was completed late May and again A2SEA has fulfilled 

a contract prior to the agreed time schedule to the client’s satisfaction. 

At the moment the company is busy at Horns Rev, as well as in the Baltic 

Sea, where a number of gearboxes on a wind farm will be replaced. 

In fact, A2SEA believes that the service and maintenance will be a 

major field in this industry, and A2SEA has already carried out more 

than 90% of the service contracts in the market so far. 

The company has grown from only one to 26 people employed today, 

and the offices located in Fredericia are perfect, being close to all 

major turbine manufacturers as well as the utility companies that are 

among the clients. Also for docking the vessel the location is good 

and A2SEA has now done further modifications in the local shipyard. 

All in all it has been an exiting four years since the company was 

founded and A2SEA takes great pride in the fact that it has installed 

the large majority of the offshore turbines in Europe and has serviced 

most of them always effective, always safe and always on time and to 

the agreed conditions. A2SEA thinks that this is their best recommendation 

for their future customers.■

Numerical Simulation of hydrodynamic 

Loads on Offshore Windmills 

By Erik Asp Hansen & Erik Damgaard Christensen, 

DHI, Water & Environment 

The costs for the foundations constitute a major part of the total 

investment for an offshore windmill. 

The hydrodynamic loads on the foundations give an important contribution 

to the total extreme and fatigue loads on the windmills. 

Today’s load estimation is primarily based on the relatively simple 

Morison Equation type formulations, which has been used in the offshore 

industry since the 1950’ties. In this formulation the loads on a 

structure are described by two empirical load coefficients, one for the 

drag load, CD and one for the inertia load, CM. The load calculations 

applied the undisturbed flow field, i.e. the flow field that would have 

been present without the structures. 

The Morison Equation cannot describe the forces from breaking 

waves, and cannot with adequate accuracy describe the forces on 

complex foundations, unless the empirical coefficients CD and CM 

are determined for the same type geometry and wave condition. 

With today’s computer power and the development of advanced numerical 

algorithms it is now becoming possible to calculate the flow 

and associated pressure field around 3-dimensional structures exposed 

to combinations of waves and current. The total load, overturning 

moment etc. can thus be determined without the use of empirical 

coefficients and simplifying assumptions. 

To obtain accurate hydrodynamic loads, it is important to have advanced 

numerical schemes that can describe the change in water surface 

when the waves are moving past and interacting with a structure. 

Fig 1. Simulation of a large wave hitting 8 H-profiles placed in a row. 

Fig 2 shows an example where the horizontal loads on the windmill 

with ice-breaking conus have been studied by the use of NS3. 

The free surface algorithm in the DHI program NS3 belongs to this 

type of advanced models, and is based on the so-called VOF (Volume 

Of Fluid) concept. This programme has for example been used as a 

tool for studying the generation of turbulence below breaking waves 

and for loads on offshore structures. Fig 1 shows such an example for 

a series of H-beams being hit by a high wave crest. 

The loads on windmill 

foundations are fairly 

complex due to a number 

of phenomena: 

Most windmill foundations 

are placed in 

shallow waters, where the 

non-linearities of waves 

become pronounced 

and wave breaking can 

result. Furthermore, the 

presence of ice-breaking 

elements around the 

mean sea level or a scour 

protection on the seabed 

can influence the wave 

Fig 3 shows an example of the pressure 

distribution at the same instant as the 

free surface shown in figure 2. 

shape and hence the kinematics, and under some conditions local 

wave breaking may result leading to large load peaks. 

The tools for improving the accuracy in hydrodynamic load calculations 

are thus available as state-of-art numerical simulation programs. 

It is anticipated that such tools will become the state-of-practice 

within the next few years.■ 



11

Research leading to new 

offshore design methods 

By Helge Gravesen, Carl Bro Group 

The utilization of wind power has resulted in design of large offshore 

wind farms on still growing water depths. Technical challenges are met 

with research within a developed design basis including accurate description 

of the loads and dynamic responses. The results achieved from applied 

and basic research are immediately utilised in engineering projects. 

The experience drawn from the three large offshore pilot- and demonstration 

projects in Denmark, have formed the basis for developing new 

codes of practice including design in a technical border-area, in which 

different dynamic loads simultaneous are at work in a harsh offshore 

environment. At the same time, development is driven in search of limiting 

the costs, as costs in general are significantly higher for offshore 

than for onshore conditions, not at least due to an expensive sea-shore 

power cable connection. 

Research on loads to 

offshore wind turbines 

In connection with the demonstration projects, research programs were 

initiated within the framework of the energy research corporation, PSO. 

The programs concerned ice loads, wave loads, and combination of nature 

loads for offshore wind turbine foundations. The results from these 

research programs form the final basis for optimizing the construction 

of foundation and turbine tower beyond what can be achieved with 

traditional load combination. 

Within inner Danish waters and the Baltic Sea heavy ice is created 

each say 5 years. The foundations for offshore wind turbines should 

be designed taking this aspect into account as a vertical structure is 

exposed to quite substantial forces from drifting ice floes. Based on a 

model test programme defined by Carl Bro, Canadian Hydraulics Centre 

has carried out ice model tests (in scale 1:26). The test programme 

included different foundation geometries like double sided cones as 

well as down breaking and up breaking cones, which induce ice break- 



Ice model 

tests at 

structure 

with conus 

ing due to bending instead of crushing/buckling for a vertical cylinder 

geometry. 

The results of this research have proven that the ice loads to a sloping 

surface is much lower than that to a vertical structure and even lower 

than predicted in traditional models. In addition, significant improvements 

have been obtained in connection with the required vertical 

extension of the cone and the dynamic character of ice load for both 

vertical as well as sloping circular symmetrical structures. 

Introduction of a foundation with an ice cone results in increased wave 

loads to the foundation. Not at least the effect of steep, close to breaking 

waves has not been well described before. Wave flume model tests 

at Aalborg University have confirmed that traditional design principles 

based e.g. on the Morison equation have to be updated with due account 

to the steep and asymmetrical wave profile. On the other hand, 

it has been found that the phase shift induced by a complex foundation 

structure with an ice cone reduces the wave forces compared to 

traditional estimates. 

This knowledge has resulted in that the most recently developed, and 

up to now most accurate, 2-D waves, the Boussinesq model developed 

at the Technical University of Denmark, has been used to describe the 

time series for wave kinematics as well as the associated wave load 

time series. 

The calculation procedure has proven very robust and capable of 

simulating wave loads to even quite large and complex structures. It 

represents a significant improvement compared to traditional offshore 

practice on more shallow waters, which are typical for most new sites 

appointed to offshore wind farms. Based on the calculated pressure and 

velocity distribution, the wave load to arbitrary foundation geometries 

may be calculated. The results for the complex cone foundation have 

been verified by results from wave flume model tests. Through this, a 

key problem for offshore wind farms has been solved. 

Cone 

geometries 

Wave simulation 

around structure 

with cone 

Floating foundation, 

Spar-Buoy

Loads on wind turbine, tower and foundation need to be 

described as load time series, which due to varying frequency 

content and response may not be simply added to 

each other. Accordingly, a series of simulations including 

the complete turbine dynamics with simultaneous loads 

from wind and waves (or wind and ice) are carried out. 

The statistical output is then analysed and usually a 

simple robust combination rule for the loads verified 

by the simulations may be formulated. In this way the 

simulations may also be generalised to e.g. different 

water depths. The latest progress even allow for analysis 

of dynamic interaction between the wind and the wave load to rather 

flexible foundations on deeper water. 

The results mentioned above have been compared to a field test programme 

performed on Middelgrunden Offshore Farm. Even though 

the wave heights and associated loads were quite limited, the field 

tests showed a fine agreement with the predicted values. Even in the 

complex steel-concrete composite structure used as foundation for 

Middelgrunden the strains in the composite structure were measured to 

be close to the strains calculated during the design process with a very 

complex non-linear numerical model (ABACUS). 

By means of these improvements, a new level of understanding for 

design of offshore wind turbine foundations has been achieved. Outstanding 

aspects, where improvements are still required, include effects 

of non-linear damping from water, soil and ice, a direct wave load 

module superimposed on the Boussinesq modelling, better modelling 

of intensive breaking waves, better modelling of steep 3-D waves, and 

due account to risk of freak waves. 

Foundation at larger water depths 

When offshore turbines are located a larger water depths of 20-50 

m, the design and construction is dominated by the dynamic effects. 

However, the above-mentioned models have also been implemented for 

turbines at larger water depths even at sites with difficult foundation 

conditions. 

A detailed analysis of the conventional foundation concepts, including 

gravity structures, monopiles and tripods, has confirmed the need for 

an advanced dynamic analysis and an advanced wave load procedure. 

The extreme loads, both from stand still, from extreme operational 

loads, and fatigue loads are all very dependent upon the various modes 

of the total structure. The combined weight of nacelle and the wings 

is a key element for the first mode and the permitted lowest resonance 

frequency, so this is a key-determining factor. 

Foundations on larger water depths are also influenced by an increas- 

feasible. 

Tripod, Mode analysis, 

extreme load and fatigue 

load analysis 

ingly larger distance from nacelle to foundation level, 

which results in strong requirements for obtaining the 

required stiffness to limit the loads to a convenient level. 

Even for a monopile on say water depth exceeding 30 m 

this results in the need for quite large dimensions, which 

is why foundation alternatives with a more material 

optimised structure like a tripod shows to be competitive. 

Further, the tripod structure, where the overall stiffness 

is highly influenced by the longitudinal stiffness of the 

supporting piles, has shown to be much less sensitive to 

weak bottom soil conditions. Accordingly, the local soil 

conditions determine which type of foundation is most 

The gravity structures require a heavy structure and a large foundation 

area, which should make this type of the foundation less competitive in 

deeper waters. The most recent experiences are that they up to now has 

proven to be competitive up to water depths of min. 20 m and possibly 

also for even deeper waters in case the soil conditions are favourable 

for this types of structures. 

Future offshore alternatives 

The development of the wind turbines to multi MW types has made it 

feasible to utilise offshore sites even though the associated cost from 

deeper foundations, establishment of a cable connection service and 

maintenance are far larger than onshore. The reduced requirements 

from noise and visual impacts etc. in addition to the larger wind resource 

and lower turbulence is favouring this development. 

Even more advanced alternative foundation systems have been considered 

on the basis of the vast experience within the offshore industry, 

including floating systems moored either by conventional cables or 

through tethers like in tension leg platform. A preliminary analysis 

indicates that such alternatives may only be feasible at water depths 

exceeding 60 m. There is still lacking substantial research, not to construct 

the foundations safely, but to find solutions, which are feasible 

with the limited economical margin for offshore wind farms. The additional 

fatigue loads to turbines needs still to be better addressed. 

The development of offshore wind power is at an early stage, but a 

strong and demanding process has been initiated. It is a challenging 

area demanding a high competence for all the players in the field. New 

development and unconventional engineering are required to obtain 

feasible structures and associated feasible projects. The wind industry 

needs to develop more cost effective solutions than those used in 

connection with the large bridge and offshore projects because the 

economical margins are much smaller. This is the challenge at deeper 

waters and at non-ideal soil conditions.■ 



13

Short News Short News Short News 

Short News Short News Short News 

Offshore Wind Energy 

Conference – Surrounding 

Facilities 

June 10th approx. 100 Offshore Center 

Danmark members, partners and interested 

parties were gathered at a conference at 

Aalborg University Esbjerg to discuss offshore 

aspects within the Danish wind energy 

industry. 

Speeches were made by organizations 

covering many aspects of offshore wind 

energy, including governmental authorities, 

certification companies, suppliers as well as 

wind turbine manufacturers. 

A case project based on development work 

finalized by Offshore Center Danmark, was 

also presented, please see elsewhere in this 

newsletter. 

The ideas brought forward on the conference, 

will be treated in the Offshore Wind 

Energy committee within Offshore Center 

Danmark, which had organized the conference.■ 

Offshore Technology 

Courses 

Following a questionnaire conducted by Offshore 

Center Danmark among its members, 

it has been decided to offer two new offshore 

technology courses during the fall of 2004. 

The two courses – Offshore Technology 

Basic Course 1 and 2 – have been designed 

for employees with a need for the most common 

techniques applied within offshore. 

More information as well as registration 



Offshore 

Teknologi 

2 kurser i grundlæggende 

offshore teknologi 

Efterår 2004 

Kursus 

can be made via the homepage of Offshore 

Center Danmark www.offshorecenter.dk 

using the menu Arrangementer / Interne arrangementer.■ 

Projects Development 

Offshore Center Danmark has initiated three 

new projects since this spring. The projects 

involve some 15 additional companies and 

educational institutions, bringing the total 

to 40 companies and institutions working 

within the seven development projects. The 

new projects are: 

- Crisis Management Simulator (internet 

based simulator covering oil spill accidents) 

- Scour problems for offshore wind turbines 

(erosion around offshore mono pile foundations) 

- Power project (international offshore wind 

energy project focusing on education) 

For a list of the projects already initiated by 

the center, please refer to earlier issues of 

ON/OFF.■ 

Offshore Windenergy – for 

the World 

As mentioned in the last issue of ON/OFF 

Offshore Center Danmark has during the 

last year worked intensively together with 

HIH-Vind to strengthen the technological 

as well as the commercial ties between the 

wind turbine manufacturers and the offshore 

industry. 

Following several workshops and many 

meetings, we are pleased to announce that 

this initiative is now materializing into a 

“Offshore Windenergy 

– for the World” 

large international offshore windenergy 

conference to be held in 2005, details soon 

to be announced. The Danish Ministry of 

Economics and Business Affairs is supporting 

the initiative. 

Please stay tuned to hear more in the next 

issues of ON/OFF.■ 

Yearly gathering of Offshore 

Center Danmark 

Early September Offshore Center Danmark 

members will be meeting for a 2-day 

conference at the castle Skarrildhus, close to 

Billund. 

Four main topics will be on the agenda, 

namely 

- board report and discussions with members 

- the future for the Danish oil reserves with 

view points from different actors 

- dinner and evening socializing 

- networking activity through inspiring 

exercise 

The conference is open only for members of 

Offshore Center Danmark.■

Member 

questionnaire 

Offshore Center Danmark has recently conducted 

a questionnaire among its members. 

The questionnaire has provided Offshore 

Center Danmark with valuable data about the 

industry—data which eventually will come 

to the benefit of the members. 

Part of the data is to be used in a new database 

which is expected to be launched in 

September (the URL is www.offshorebase.dk). 

Among other things, the questionnaire 

reflected a general optimism among the participants 

regarding the future. The diagrams 

below illustrate Higher the Unchanged expectations for the level 

67% 33% 

of activity in the future among the companies 

in the questionnaire. 

Lower 

4% 

OCD member’s expectations for level of activity 

in the year 2007 - international. 

Higher 

67% 

Higher 

60% 

Unchanged 

36% 

Unchanged 

33% 

OCD member’s expectations for level of 

activity in the year 2007 - domestic. 

Members of 


A2SEA 

ABB A/S, Offshore 

ABB Vetco Gray Denmark 

Amerada Hess A/S 

AM-gruppen 

AMPU 12 ApS 

AMU Center Vestjylland 

AN GROUP A/S 

BG bank, offshore afd. Esbjerg 

Billund Kommune 

Blue Water Shipping 

Blaabjerg Kommune 

Blåvandshuk Kommune 

BONUS Energy A/S 

Bramming Kommune 

Brørup Kommune 

BTM Consult ApS 

Bureau Veritas 

Carl Bro A/S, Havne og Vandbygnings afdeling 

Consulting Team Offshore 

COWI 

Dan-Equip A/S 

DAN-EX Electric A/S 

Danish Marine & Offshore Group 

Dansk Industri 

Deloitte, Offshore Afd. 

Denerco 

Det Norske Veritas 

DHI, Havne & Offshore Afd. 

DONG 

Enmaco Motorer A/S, offshore afd. 

Erhvervsuddannelsescenter Vest, EUC Vest 

Esbjerg Erhvervcenter 

Esbjerg Kommune 

Esbjerg Oilfield Services A/S 

Esbjerg Oiltool A/S 

Esbjerg Safety Consult 

Esvagt A/S 

EU Vest 

Fanø Kommune 

Fiskeri- og Søfartsmuseet 

Fjord & Fjord 

Force Technology 

Forskningsenheden for Maritim Medicin 

Gardit A/S 

GEUS, Danmarks og Grønlands 

Geologiske Undersøgelse 

Grindsted Kommune 

Gulf Offshore Leasing 

Gunnar Lund Olieservice 

How to become a member 

If you want to become a member of Offshore Center Danmark please fill out the 

registration form you find at our web-site www.offshorecenter.dk 

Click “Medlemslogin” 

Click “Indmeldelse” 

Fill out the registration form 

Click “Send” 

Membership fees can be found by clicking “Kontingentsatser” at the left. 

You can always phone or mail us for help. 


Tel: +45 36 97 36 70 

Mail: info@offshorecenter.dk 

H.H. Consult A/S 

Hedeselskabet Miljø & Energi A/S 

Helle Kommune 

Holsted Kommune 

Hydropower A/S 

Jutlandia Terminal A/S 

Jørgen Kynde Isoleringsfirma 

Kommuneforeningen i Ribe Amt 

Kongstad Safeman 

LHJ Consult ApS 

LIC Engineering A/S 

Lindpro 

Madsens Maskinfabrik Aps 

Maersk Contractors, Esbjerg 

Maritimt Uddannelsescenter Vest 

Ministeriet for Videnskab, Teknologi og Udvikling 

Navicon 

Ocean Team Scandinavia 

Olesen & Jensen, Offshore 

Persolit 

Peter Harbo A/S 

PNE Teknik A/S 

Promecon 

QA Consulting 

Rambøll 

Randers Reb / Fyns Kran Lifting 

Ribe Amt 

Ribe Kommune 

Ribe Maskinfabrik 

Sanistål A/S 

Score Danmark A/S 

Semco Maritime 

Siemens 

Solar Offshore 

SURVIVAL A/S Training Center Esbjerg A/S 

Survival Training Maritime Safety (STMS) 

Syddansk Universitet 

Uni-Safe Electronics A/S 

Uniscrap A/S 

Valtor Offshore A/S 

Varde Kommune 

Vejen Kommune 

Vestas Northern Europe, Offshore Afd. 

Viking Life-Saving Equipment A/S 

Vindmølleindustrien 

VSB Industri- og Stålmontage A/S 

YIT A/S, Esbjerg + YIT Fredericia 

Ølgod Kommune 

Aalborg Universitet Esbjerg 



15

EUC Vest has introduced re-education 

entirely on the companies’ conditions 

By Poul-Arne Callesen & Steffen S. Nielsen, EUC Vest 

EUC Vest is the largest provider of re-education in the south-western 

part of Denmark. The centre is provider of a number of courses within 

service and crafts relevant for the offshore industry. 

The offshore industries demands for re-education are crucial to EUC 

Vest and the centre does its utmost at all times to meet the demands, 

which the companies have both for the contents as well as the form of 

re-education. 

As an example EUC Vest has just opened a new centre for Automation 

& Control in Esbjerg, based on the demands from the industry. 

By opening the centre, EUC Vest wished partly to strengthen the reeducation 

area within automatics and process technology and partly to 

make re-education more flexible. 



This meant, among other things, that EUC Vest now has said goodbye 

to a long-standing tradition of cancelling courses, due to lack of participants. 

In the “old days” a minimum of 10-12 participants was necessary 

for the centre to be able to go through with a course. Now it is 

guaranteed that the course will be carried out, and more courses will 

take place at the same time in the Centre of Automatics and Control. 

During 10 weeks in the spring and 10 weeks in the autumn, EUC 

Vest carries out five basic courses comprising hydraulics, pneumatics, 

electricity, and PLC. The centre still adheres to a combination of 

theory and practice, however, the students must be prepared to assume 

a greater responsibility than earlier and to work more independently. 

The Centre of Automatics and Control is a specially organized 

educational environment where the teacher goes from hydraulics to 

pneumatics to electricity and fault-finding. Thus, the students must

accustom themselves to be together with students who are attending 

other courses. This is viewed as an open and inspiring environment for 

students as well as for apprentices. 

The flexibility is reflected both in the enrolment as well as in the form 

and contents of the courses. Thus the students are offered to enrol on 

a Thursday and begin the course on the following Monday – in other 

words at a very short notice. Furthermore a week-course may be split 

up into a certain number of day-courses. The contents of the course are 

very much adapted to the demands the companies make on the students’ 

participation in a course. 

It is important, however, to emphasize that even though the centre is 

of course manned with qualified teachers, the whole concept calls for 

a high degree of independency and for the individual student to show 

initiative and energy. Self-instructing teaching materials and neighbour 

training are a natural part of the everyday life in the centre. 

The principle is that the individual student talks to the teacher on the 

first day about the course which has been chosen and about the qualifications 

the student possesses. For example the student may in fact be 

competent in a way which makes it possible to shorten the course for 

this particular student. 

Furthermore, because of the flexibility, the offshore industry has already 

shown a considerable interest in the concept, among other things due to 

the fact that it makes it easier for employees at sea or on platforms to 

attend courses while they are ashore. 

Kursus til medarbejderen med 

behov for indblik i grundlæggende 

offshoreteknologi 

Kursusprogram fås ved at ringe 36 97 36 70 

el. mail ak@offshorecenter.dk. Du kan også læse mere 

på www.offshorecenter.dk under interne arrangementer. 

The background of the centre is among other things a wide experience 

in instrumentation, regulation, and hydraulics in connection 

with ships and offshore installations. Those are typical examples 

of the demands which the offshore industry has for the employees. 

These courses will be held as ordinary courses at a duration of 3, 

5, or 10 days. But the concept will constantly be developed so that 

some of the courses which are held today as ordinary courses will be 

flexible in the future. 

The centre disposes of a modern equipment park that matches the 

demands, which the trade makes on automatics and process technology 

today and is constantly in contact with leading suppliers of stateof-the-art 

technological equipment for on- and offshore. 

The centre is also capable of offering courses aimed at new or existent 

equipment with a view to applying the customers own documentation 

material in connection with making repairs, preparation, 

running-in, logic fault-finding, and preventive maintenance. 

Company adapted courses can be held at a duration ranging from 

1/2 day to long-term courses. The courses can be held as normal day 

courses or – at request – as evening or weekend courses. 

If the centre becomes the success expected, the concept will be 

extended to other trades. In the future the centre will be the dynamo 

in the development of CBT, Computer Based Training, where the 

education is based on the Internet. 

■ 

Offshore 

Teknologi 

2 kurser i grundlæggende 

offshore teknologi 

Efterår 2004 

Kursus 



17

State-of-the-Art Design Standard 

specifically developed and applicable 

for Offshore Wind Turbine Structures 

The DNV services includes the Manufacturing, 

Installation and In-service Phase and 

the requirements are given with focus on the 

structural integrity of the installed structure 

Join our committees 

By Tove Feld, DNV Global Wind Energy 

The wind energy industry requires cost-effective 

design for offshore wind turbine 

structures in order to make the projects 

economically viable. A year ago none of the 

existing standards were truly applicable to 

offshore wind projects with a different loading 

scheme compared to the traditional oil 

and gas offshore structures, e.g. going from 

wave dominated to wind dominated. 

As a member of Offshore Center Denmark, you may also 

participate in the work of the four permanent working groups 

within the centre. 

The four committees each represent the interest of a number 

of members, who themselves have defined the groups 

The committees are: 

• Mobile & stationary offshore installations 

• Offshore Wind Turbines 

• HSEQ - Health, Safety, Environment & Quality 

• Decommissioning of offshore structures 



This let to the development of a new 

state-of-the-art offshore standard ‘Design 

of Offshore Wind Turbines Structures’, I 

DNV-OS-J101. (First edition issued June 1st 

2004), specific developed and applicable for 

offshore wind turbine structures. The new II 

standard is based on DNV´s experience from 

participation in more than 24 offshore wind 

projects and general rule development from III 

maritime and offshore industries for decades, 

resulting in a rational set of state-of-the-art 

rules allowing fit-for-purpose design. 

IV 

DNV Project Certificate 

The challenge has been to establish a sound 

basis for development of projects both 

technically and economically that would be V 

recognized by all parties involved in offshore 

wind projects: owners, manufacturers, 

finance, insurance and authorities. Consequently 

the newly issued DNV-OS-J101 is VI 

a cost effective design standard, living up to 

safety levels required by authorities and other 

parties involved in offshore wind projects. 

In addition the standard account for the fact 

Certificate 

Maintenance 

that the structures are unmanned and the risk 

for pollution of the environment is limited, 

opposite the existing offshore standards. 

The new design standard has been chosen 

and is currently being used as Design 

standard on a number of Offshore Wind 

Projects around the world. The standard and 

the project certification serves the purpose 

of creating the trust and confidence between 

the parties that is needed for accelerating the 

development of offshore wind farms. ■ 

Design Basis 

Design 

Manufacturing 

Installation 

Commissioning 

In-Service 

Statement of Compliance 





Schematics over the DNV Project Certification 

Scheme 

Each group has appointed a chairman. 

To apply for membership of a committee please forward 

your request to Offshore Center Denmark, who will relay 

the request to the chairman.

Materials in offshore 

wind turbine wings 

by Birgit Kjærside Storm, Aalborg University Esbjerg 

The materials used in wind turbines wings must fulfil many requirements, 

as the wind turbines build today, are very large, and hence the 

wings get great tip space. At the same time the wind turbines are placed 

within environments, where also large chemical and wearing requirements 

to the materials are extreme. 

The key requirements set to the wing materials, are suitable rigidity and 

strength in bending out, and at the same time the materials must possess 

wearing qualities with regards to sand, hard rain, hail as well as salt and 

also be chemical resistant to water, bird droppings, insect’s blood and 

salt. Many other chemical influences to the wings are possible, but these 

mentioned are the most common. A high strength/weight scale is also 

required from the wing material. 

To fulfil the requirements and ensuring at the same time that the weight 

of the wing is as low as possible, almost solely composites are used for 

manufacturing of wind turbine wings. A composite is a piece of material 

that consists of a strengthening element as well as a matrix material 

which can “glue” the strength giving parts together. In wind turbine 

wings preferably fibre glass are used as strengthening element, but in 

the future many wings will be made with carbon fibres instead of or 

together with fibre glass. The carbon fibres are more rigid than the fibre 

glass. They have a higher strength/weight scale than fibre glass, but they 

are more costly than fibre glass. 

The matrix material is the material that surrounds the fibre material.The 

matrix material must be consistent with the fibres, as the fibres have to be 

moistening all over the surface in order to let the strength be transferred 

from the fibres to the matrices. In order to obtain a sufficient fastening 

between fibres and matrix materials, the fibres have to be coated so that 

moistening and fastening can be carried out. This coating is called a 

sizing. All wind turbine wings have a coating either as a gel coat or as 

painting on the surface. The coating is made in order to protect the wing 

material itself (the composite) against the wear and chemical attacks. 

The matrix material in wings is either hardening plastic polyester or a 

type of epoxy. Both non-saturated polyester and epoxy belong to the 

group hardening plastic materials. Being hardening plastic means that 

the materials during the hardening will cross bind. During the cross 

binding process strong primary bindings between the molecule chains 

are formed, and thereby a good strength and rigidity within the materials 

is obtained. By cross binding the chemical resistance of the materials is 

increased, as chemical substances cannot pass through a cross binding 

but have to find another route, in order to get in connection with an active 

group which can be influenced by the chemical substance. 

Epoxy and polyester each have advantages and disadvantages. They 

each have their own hardening method but the hardening course can 

be changed on the materials by inserting other chemical active groups 

in the materials during the polymerization process. Epoxy is used a 

lot in the so-called prepreg (pre-treated fibre glass in which the epoxy 

is found as pre-polymerized) which is put into a mould before it is 

hardened under thermal influence. By adding heat the hardening process 

is started, as a hardener is put in active condition and therefore can act 

with the epoxy group over which the cross binding can take place. The 

most commonly used epoxy type is DGEBA which cross binds with an 

amine. During heating the epoxy resin receives fluid by means of which 

it can moisten the fibres. 

Polyesters are mostly used as resines to be dissolved in the styrene. The 

styrene is used as dissolving material for the non-saturated polyester, 

but during the hardening process the styrene is activated by means of 

a peroxide and is used as cross binder in the non-saturated polyester. 

The hardening process can here be started at room temperature, as it 

is started by an initiator. The starting of the process can also happen in 

other ways, but an initiator (MEKP) is the most used method. 

The moistening of the fibre glasses is essential to get a good strength 

transfer from the fibre glasses to the matrix. The fibre glass is treated 

with different coupling agents depending of the type of resin (epoxy or 

polyester) to be used as matrices. To obtain good moistening the resin 

must have a suitable viscosity. If the viscosity of the resin is too high 

(the resin is too thick), the resin cannot float sufficiently easily over the 

fibres and therefore can not moisten the fibres. If on the other hand, if 

the resin has too low a viscosity (too thin) it will run off the fibres and 

therefore the moistening will be too low. 

Both epoxy and polyester are able to absorb water. This quality is unfavourable 

as adding water produces a risk of destroying the composite 

itself. Water can also reduce the binding between fibres and matrix 

materials. When wind turbines are placed offshore, they will be under 

almost constant influence from water and salt. Salt is a hygroscopic 

material and salt deposits on the surface of the wings are able to absorb 

water. Hence the requirements to the chemical resistance of the wing 

materials will be increased offshore. 

The wind turbine wing material of the future will probably still be 

composite materials with hardening plastic matrix material even though 

the hardening plastic can not directly be re-used. Hardening plastic possesses 

great strength and good chemical resistance and at the same time 

the moulding process can be done in as large dimensions as required. 

The fibre material will probably still partly be glass but carbon fibres 

will replace some of the glass. The matrix material will probably still be 

polyester and epoxy materials but new resin types such as polyimides and 

other strong and chemical very resistant plastic types can be envisaged. 



19


Niels Bohrs Vej 6 

6700 Esbjerg 

Tlf.+45 36973670 

info@offshorecenter.dk 

www.offshorecenter.dk 

The board of Offshore Center Danmark: 

Rambøll A/S, Force Technology A/S, Enmaco Motorer A/S, Aalborg Universitet Esbjerg, 

Esbjerg Kommune. 

Offshore Center Danmark was created through corporation between the Danish offshore 

industry, universities, Ribe County, the 14 municipalities in the county and the Danish 

ministry for Research, Technology and Development. 

New OffshoreBase 

A new database containing information 

about offshore companies is currently in the 

works. The database will serve as a profiling 

portal for offshore companies as well as 

a tool to find information about suppliers, 

vendors, consultants, educational institutions 

etc. 

Advanced search facilities will enable users 

to find relevant information about com- 

Your every day tool 

within offshore 

www.offshorecenter.dk is the place to find information 

of relevance to the Danish offshore industry. 

Here you will find a general presentation of Offshore 

Center Denmark and its services. 

panies with specific competences within 

specific geographic areas. 

The database is launched in September and 

is accessible through the URL 

www.offshorebase.dk. Members of 

Offshore Center Danmark are listed in the 

database free of charge. 

www.offshorecenter.dk

Read News Magazine (pdf) - Offshore Center Danmark

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