ON/OFF. Offshore wind energy past, present and future. Newsletter to the offshore industry in Denmark

Transcription

1 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: Newsletter to the offshore industry in Denmark ON/OFF 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 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

2 Location Year of Number Output pr Total output construction of turbines turbine [kw] [kw] Vindeby, Lolland (1) ,950 Tunø Knob (2) ,000 Middelgrunden (3) ,000 40,000 Horns Rev (4) , ,000 Rønland (5) ,150 17,200 Nysted (6) , ,600 Samsø (7) ,300 23,000 Frederikshavn (8) ,300 & 3,000 7,600 Total 214 1,978 (average) 423,350 Danish offshore wind farms 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 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% 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. 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.

3 A Logistic Challenge 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. 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 kw turbines in 1991, the Middelgrunden offshore project with 20 2 MW turbines in 2000, and the Samsø offshore project with 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 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

4 Cont. from page 3 Results from the development project How to board an Offshore Wind Turbine by Ulrik C. Jensen, RAMBØLL & Peter Blach, Offshore Center Danmark 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. 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. 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 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. 4 Offshore Center Denmark

5 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: Offshore Center Denmark 5

6 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. 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 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. 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 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. 6 Offshore Center Denmark

7 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 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. Offshore Center Denmark 7

8 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 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 MW will be installed offshore in the period between 2004 and This corresponds to approx. 15% of the total expected new wind power capacity. 8 Offshore Center Denmark

9 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 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. Offshore Center Denmark 9

10 The work started work in early May 2003 and by sailing four complete turbines per trip, the last turbine was installed in July 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 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. 10 Offshore Center Denmark

11 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. 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 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. 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. Fig 1. Simulation of a large wave hitting 8 H-profiles placed in a row. 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. Offshore Center Denmark 11

12 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 breaking 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. Ice model tests at structure with conus Cone geometries Wave simulation around structure with cone Floating foundation, Spar-Buoy 12 Offshore Center Denmark

13 Tripod, Mode analysis, extreme load and fatigue load analysis 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 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. feasible. Foundations on larger water depths are also influenced by an increasingly 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. Offshore Center Denmark 13

14 2 kurser i grundlæggende offshore teknologi Short News Short News Short News Short News Short News Short News Offshore Teknologi Efterår 2004 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 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 Kursus can be made via the homepage of Offshore Center Danmark 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. 14 Offshore Center Denmark

15 Member questionnaire Members of Offshore Center Denmark 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 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% Higher 60% Unchanged 36% OCD member s expectations for level of activity in the year international. 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 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 Higher 67% Unchanged 33% OCD member s expectations for level of activity in the year domestic. 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 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. Offshore Center Danmark Tel: Mail: info@offshorecenter.dk Offshore Center Denmark 15