Optical Measuring System TRITOP Used for Offshore Wind Turbine Setup

Optical Measuring System TRITOP Used for Offshore Wind Turbine Setup

The individual parts of wind turbines are normally produced at different places and often put together for the first time at the mounting site on the high seas. It is necessary to control the connections and mounting surfaces of towers and foundations independently before mounting, because problems arising on site make offshore mounting much more difficult. To guarantee a smooth setup of the offshore wind turbines, the optical measuring system TRITOP is used to check and verify the mounting surface and bolts. 

Wind Turbines

Inspecting Mounting Bolts in the Offshore Foundations

For the setup of offshore wind turbines, special concrete foundations are built on land. They are more than 20 meters high and have an upper platform with a diameter of approx. 10 meters. After completion, the foundations are tugged to their destination offshore and anchored to the sea bed with its upper edge of the platform 2–4 meters above the water surface. Wind turbines are very high, requiring their towers to be composed of several segments. These tower parts also need to be transported to their offshore destination and then constructed directly on site using a special floating crane. For mounting the lowest tower segment, 120 steel bolts positioned in two circles are recessed in the concrete foundation.

Concrete foundation anchored offshore

Concrete foundation anchored offshore.

Position of the mounting bolts in the concrete

Position of the mounting bolts in the concrete foundation and preparations for the measurement.

Since foundations and tower parts are produced at different places, a test setup ashore is not always possible. If the mounting bolts in the foundation do not fit the hole pattern in the lowest tower segment, time-consuming adjustments must be made on site. The tower mounting on the high seas is extremely difficult, not to mention additional on-site adjustment. As the floating crane is very expensive, such a situation causes extremely high additional costs and a large time lag.   
To avoid such problems, the optical measuring system TRITOP can be used to inspect and verify the bolts directly after the completion of the foundation ashore as well as after the anchoring on the high seas, with their position deviation controlled within the required accuracy of 1/10 millimeter.

Harsh conditions such as the limited space and measuring distance on the concrete foundations, strong wind or the lack of power supply do not pose any challenge to the mobile and compact TRITOP system. Wrongly positioned or tilted mounting bolts in the foundation can be identified fast and with the required accuracy, so that the position of bolts can be corrected before starting the tower mounting process.

Measurement of 120 mounting bolts

Measurement of 120 mounting bolts with the TRITOP system on the high seas.

Measuring with the Photogrammetric TRITOP System

For the measurement, gauging markers and two scale bars are placed directly on the foundation. In the meanwhile, customized adapters are applied for the measurement of bolts regarding cylinders, holes, spheres and border lines. The photogrammetric camera of the TRITOP system is then used to take pictures of the measuring area from different viewing angles.

During the measuring sequence, images are automatically transferred to a laptop. Based on all captured 2D images, the 3D coordinates of the gauge markers can be directly calculated by means of bundle adjustment. Two certified scale bars guarantee the accuracy of the measurement result, avoiding errors caused by picture stitching. Immediately after image transfer, the 3D coordinates of all 120 mounting bolts are calculated in the TRITOP software within a few minutes based on the unique dot pattern of the adapters. As the project is evaluated on site, it can be immediately checked for success or missing data.

Depending on the definition of the adapters, single points or the axis of a mounting bolt can be calculated to determine the position or the direction of each single mounting bolt. The TRITOP software enables the user to create measuring reports as well as exporting measuring data into tables. Report templates can be customized for individual measuring tasks.

Measuring report in TRITOP

Measuring report in TRITOP software with position of mounting bolts and GD&T details.

The TRITOP system is very mobile and flexible. The entire equipment, consisting of a camera case, a laptop and a scale bar case, can be easily carried by one person. The measuring procedure requires one operator only as well. The preparation for the measurement takes less than 30 minutes and the measurement itself approx. 10 minutes. Thus, including the transport by boat to the next platform, about one hour is required for each foundation.

The easily portable TRITOP measuring system allows precise measurement and verification of mounting bolts and surfaces. With this method, possible problems caused by wrongly positioned or tilted mounting bolts can be identified and eliminated before mounting. Thanks to the lightweight measuring equipment and simple measuring procedure, the inspection of over 120 mounting bolts per platform can be accomplished by one single person. The on-site data evaluation guarantees that all features are captured completely and correctly.

Using optical measuring technology for inspecting mounting surfaces ensures a smooth setup of offshore wind turbines, preventing high additional costs and saving time.

TRITOP

A portable CMM system measuring coordinates of three-dimensional objects

TRITOP