Every self-propelled wind turbine installation jack-up has to deal with wind loads, whether it’s the journey from port to location or when operating at the offshore location itself. The wind loads acting on the topside structures is one of the critical environmental loads acting on these jack-ups for elevated condition, station keeping and stability purposes. An accurate prediction of the wind loads is therefore eminently important during the design processes of these types of jack-ups.
Existing empirical methods less accurate in predicting loads
During the design processes of these jack-ups, wind loads calculations are usually performed using empirical methods from classification societies and standards such as ISO and SNAME and scale models are also tested in wind tunnels. The first is less accurate, the second expensive and time consuming since a physical model must be built for the wind tunnel measurements. Moreover, there is always the question of how close these methods are to reality?
A new method to predict wind loads
The ability to predict the wind loads using Computational Fluid Dynamics (CFD) at the design stage is of interest. Because in CFD not only the wind loads can be predicted, but also valuable insights can be obtained into the flow behavior through visualization of the flow field which can be used to optimize the topside structures arrangement for minimum wind loads. Therefore, GustoMSC has been working hard on applying CFD method as a new method in the design process to predict the wind loads on self-propelled wind turbine installation jack-ups. The ability to predict wind loads using CFD at the design stage is an important step forward. The CFD method makes the design process more structured, saves costs during the development and construction of the jack-ups and makes the jack-ups more efficient when installing wind turbines.
CFD outcomes verified and validated
GustoMSC used the commercial software package from Siemens (i.e., STAR-CCM+) to apply CFD calculations to the topside structures of the jack-ups with and without deck load. The CFD results have been verified and validated by comparison with the Experimental Fluid Dynamics (EFD) results obtained at the German-Dutch Wind Tunnels (DNW) in Marknesse, The Netherlands. An atmospheric boundary layer profile was applied during the wind tunnel tests. The CFD calculated atmospheric boundary layer profiles were also validated and compared with those profiles measured in the wind tunnel.
Wind tunnel data used to validate CFD results
When developing the CFD approach, wind loads were calculated that act on the detailed topside structures of a typical GustoMSC designed self-propelled wind turbine installation jack-up. The applied atmospheric boundary layer profiles were maintained throughout the computational domain by applying an iterative method. The CFD results at the different flow angles were compared with and without the deck load present. A comparison was made between the CFD and the experimental results for the longitudinal force, lateral force, heeling moment, pitch moment and yaw moment coefficients. Examples of the wind loads results comparison for the longitudinal forces, lateral forces and heeling moments showed that the wind loads CFD results are in very good agreements with the EFD results.
Comparison between CFD and EFD results for the longitudinal force coefficients.
Comparison between CFD and EFD results for the lateral force coefficients.
Comparison between CFD and EFD results for the heeling moment coefficients.
Optimizing jack-up structure arrangement in design process
By applying CFD calculations it is possible to obtain comparable accuracy to wind tunnel model tests. The main advantage of using CFD is that it can provide useful information at the start of the design process, such as velocity quantities and pressure distribution on the surface of the top structures. These quantities can be useful in the design process as input for other design calculations. CFD can also provide physical insight into flow characteristics around the top structures, which can be used to optimize the construction of topside structures to achieve minimum wind loads early in the design process. Which makes it also possible to consult clients for an optimum deck arrangement for minimum wind loads. Examples of the flow field obtained from CFD calculations can be seen below for the topside structures with and without the deck load.
Unlocking the full potential of offshore units
There is a tendency to design ever larger jack-ups enabling the installation the ever lager offshore wind turbines. This makes stability and using accurate wind loads prediction even more important. Testing this with a scale model in the early design stage is expensive and time-consuming. Also, separate parts of the jack-up such as the legs, cranes and deck load cannot be accurately tested at model scale because of large scale effects involved. With GustoMSC’s CFD calculation method, it is also possible to calculate the wind loads acting on the components of the jack-up separately for wind loads even at full scale.
Less costs and more efficiency with the CFD method
By accurately predicting the wind loads on jack-ups and its components with the CFD method, the jack-up can be optimized at the beginning of the design phase. This not only results in significant cost savings, but also increases the efficiency of jack-ups. By using the CFD method in the design phase, more space can be created on the deck of the jack-up, allowing more cargo to be transported. In addition, a lighter jack-up also offers an advantage during transport from port to the offshore work location. A lighter jack up consumes less fuel and that results in a smaller industry footprint.
As a CFD Expert Engineer, Zana Sulaiman leads and carries out R&D and engineering projects that are focused on the aerodynamic and hydrodynamic performance of mobile offshore units (jack-ups, drill-ships, semi-submersibles). This includes resistance and propulsion calculations, shape optimization, and quantifying the environmental loads (current, wind, wave and breaking wave loads) for existing and new designs using CFD. Zana Sulaiman has been working at GustoMSC since 2014. He graduated in 2011 as Master of Science in Aerospace Engineering – Aerodynamics and CFD at Delft University of Technology.
Like to know more about CFD calculations?
Watch the recordings of the OMAE-Presentation: "Predicting Wind Loads on the Topside of a Self-Propelled Wind Turbine Installation Jack-Up Using CFD" at ASME Digital Collection.