Software engineering

National Instruments’ Charlotte Nicolaou shows how software systems are helping to create installation tools as well as helping to design offshore wind systems in the renewables sector.

Houlder’s pile gripper arms.

A software environment, LabVIEW, created by Austin, Texas-based National Instruments (NI) is helping to ease the challenges faced by companies working in the offshore renewables space.

In the renewables sector, LabVIEW has been used to help control pile driving and to create control systems for new, floating offshore wind turbines.

When building new turbines, monopiles of up to 700-ton in weight, 75m-long and with a diameter of 7m need to be hammered into the seabed to act as the foundations for the turbines. Embedding these monopiles vertically into the seabed can be tricky, due to strong currents and ocean tides pulling the piles at different angles. If done incorrectly, they need to be fully removed and re-driven, which incurs significant costs.

Marine engineering firm Houlder developed a solution to this problem which consists of two, 70-ton hydraulic gripper arms that are used to hold a monopile in place while it is hammered into the seabed. With Houlder’s gripper arms mounted on the offshore vessel, any risk of uneven foundations is vastly reduced as they ensure the piles are vertical at all times.

A system of this magnitude requires a highly precise and robust control system. Houlder’s developers wrote the gripper arm software entirely in LabVIEW. This software sets the position of the gripper arms, translates that to the hydraulic cylinder length required and adjusts the hardware accordingly. It can implement safety limits, such as a minimum closing of the arms to avoid crushing the monopiles. It also monitors extensive analogue and digital I/O, allows for real-time control of the gripper arms using a joystick, has safety features to shut down the system if a fault is detected, and displays important information to the engineers via a user interface. This software is installed on an embedded device with a deterministic operating system allowing for fast and reliable responses from the software.

The SeaTwirl wind turbine.

Houlder, which has used the system since 2013, has added a second, larger set of gripper arms to help with the construction of the Rampion wind farm, off southern England, which is due to be completed in 2018.

While the traditional wind farms Houlder works with require hammering foundations into the seabed, two companies from Sweden, SeaTwirl and software developers WireFlow, teamed up to produce innovative floating wind turbine designs. The SeaTwirl wind turbine is one that is simple to install and can be deployed further from shore, where it is too deep to install standard turbines but where there are much stronger winds.

A huge difference in this design is that the entire body of the SeaTwirl turbine rotates to generate electricity, which means it can produce power no matter what direction the wind is blowing. It doesn’t need a yaw or pitch control system to get the blades in the correct position. Research shows that vertical axis turbines have a higher structural limit than their horizontal axis counterparts meaning they can be larger and therefore more cost-effective. The SeaTwirl turbines are still in the prototyping stage and their latest device is a 30kW turbine situated off the west coast of Sweden.

Despite being simpler in a lot of respects, this turbine design still needs a powerful control system and for that, SeaTwirl and WireFlow used LabVIEW as it was the fastest to program, high performance option they considered. Their software monitors the turbine and wind speed, controls the rotational speed to keep the power generation at optimal efficiency, logs important data and securely sends information back to the monitoring station, 70km away in Gothenburg. It also contains a number of fail-safes to protect the system in an emergency. As the system is still in development, all data is available for authorized engineers to access remotely. SeaTwirl plans to continue creating larger and more efficient wind turbines, with the help of LabVIEW.

Charlotte Nicolaou works as a marketing engineer looking after NI’s software products. In particular, she’s interested in data management for big analog data applications. She has a PhD in biophysics from the University of Sheffield.