PES was awarded the Design and Build Subcontract to deliver Nautilus, a 3MW tidal turbine drive train test system at the National Renewable Energy Centre (Narec) in Blyth, UK. Nautilus is the first test rig of its kind in the world offering performance appraisal, reliability testing and certification of marine turbines at a low cost compared with sea trials. The £15m facility, built over an existing dry-dock, offers accelerated lifetime testing allowing developers to test and improve reliability. Two weeks of running can equate to four months of tidal sea trials without the associated costs of supporting an offshore test site.
In the beginning
Construction of the facility was complex; requiring heavily reinforced concrete, machined steel plates and a strong floor anchoring system to ensure the structures could withstand the forces exerted during testing. The floor of the facility was reinforced to a depth of 3.4m and approximately 7000 cubic metres of concrete was poured to withstand the weight and rigorous testing of the rig. The location on the North Sea coast threatened to hamper working conditions at times with an open-sided building, driving rain and freezing conditions; instrument selection was key.
Initial setting out within the building was carried out using the steel structure and construction datums using Leica TDA5005 total stations and Leica NA2 optical levels. Two Leica Absolute Tracker AT401s with SpatialAnalyzer® 3D metrology software were used to mark out nominal positions to ±1mm over the 45m site length. The PES supplied anchoring systems were installed using the digital readout to allow the engineers to obtain precise 3D locations of the base and upper opening of each anchor tube.
Controlling Uncertainty with USMN
18 permanent metrology nests were mounted on the steel columns within the building and a Unified Spatial Metrology Network (USMN) was generated using SpatialAnalyzer® Ultimate. This allowed PES to control and minimise the uncertainty of the measurements and allowed a tracker to be placed anywhere within the large facility. The USMN was updated monthly to maintain the strength of the network.
At ground level
Once the foundation had been cast, the strong floor, composed of 88 anchor positions each topped by a 150mm thick machined plate, was also positioned to ±0.25mm and levelled and grouted into position, achieving better than 1mm flatness over an area 18m x 6m. Machined bed plates 250mm thick were installed and levelled to a flatness ±0.1mm from 500 measured points over the three beds and grouted into position for the drive motor (70mt), the gearbox (130mt) and the Force Application System (110mt) to be secured to. The drive components were provisionally aligned to within ±1mm whilst 3rd parties completed their sub-assembly work. Once this had been completed the site was suitable for high accuracy measurements and the final alignment of the drive train was carried out.
Aligning to CAD
Final alignment of the key components was vital to maintaining the operating capabilities of the test rig. For this task an AT901 was used with a T-Probe allowing hidden features to be measured. Accuracy was improved as a result of being able to survey every side of a given feature. SpatialAnalyzer® offers native support for the main CAD formats making real-time comparison tonominal of the bores, shafts and faces possible. This significantly reduced the time required to carry out the alignment.
Using the instruments and techniques described allowed PES to install the drive train to an accuracy of greater than ±0.2mm. “The range of instruments we have means that we have total flexibility to solve complex measurement challenges”, explains Pete Beaumont, PES Head of Metrology, “our depth of experience makes PES a strong partner for diverse metrology needs.”
Following the successful completion of the facility, Shepherd Construction Limited’s onsite Project Manager stated, “Reviewing what PES UK has achieved on this site stands testimony to the professionalism and experience you and your team have in this nature of work. I can honestly say I could not think of another specialist contractor who could have achieved what you and your team have achieved to date.”