WORKING AT HEIGHTS - Wind Energy Network

metmasts featureFoundation optionsTo date, several different foundations havebeen installed to support masts, including:monopiles, jackets, suction buckets andthe Keystone “twisted jacket”. There aremany factors that influence the selectionof foundation solutions, but the largestcost is that of installation. To keep costsas low, a flexible approach to installationvessel options is essential to securingcompetitive charter rates.The offshore environment is an onerousone and the mast and foundation mustbe designed for these conditions. Industryconcerns have been raised about thedurability of met masts offshore. Thelattice towers must also be checkedfor loads resulting from the foundationoscillating due to wave action. Theseoscillations induce a cyclic load effect inthe lattice, causing fatigue to its joints andmembers. These fatigue loads can besignificant and must be assessed duringthe design stage by using an integrateddesign process.Integrated model aboveIntegrationIntegrated design is as essential foroffshore meteorological masts as it isfor wind turbine structures. GL GarradHassan have performed assessments ofoffshore towers and foundations usingthe bladed fully dynamic simulationprogramme, the results of which haveestablished the importance of damping,the system’s resistance to oscillation. Thelevel of damping used in the integratedanalysis is critical to accurate calculationof the fatigue loads in the mast andfoundation. Damping sources aredescribed in the equations below:All about the dataWhen tackling the tricky early demandsof the project, it might be easy to forgetthat what really matters is the data comingfrom a few fragile instruments mounted onthe mast.Getting the specifications and detailedmounting arrangements right is crucial. AtGL Garrad Hassan we have analysed datafrom a large number of offshore mastsand found examples where this part ofthe design process has not been givensufficient attention. Some masts havedelivered data which failed to follow bestmeasurement practice, thereby impactingproject profitability. In delivering on the“hard part” of the meteorological mast,they failed to deliver on what is sometimesperceived to be the “easy part”.Data must also be complete and reliable.Probably the most common cause of datagaps are issues relating to the supply ofpower to the instruments. Delivering areliable power supply solution is alwaysworthwhile.An opportunitySavvy developers are starting tounderstand how challenging offshoremeteorological masts can be, butalso how crucial the data is to projectprofitability. They also recognise that manyof the issues encountered in their designand installation mirror future challengesthat projects will face.Investing the time and money needed tobuild a team with the competencies toovercome these challenges should be apriority for all developers.GL Garrad Hassanwww.gl-garradhassan.comGL Garrad Hassan found that omittingthe aerodynamic damping component inthe integrated analysis can overestimatefatigue loads in the mast by up to 30%.www.windenergynetwork.co.uk 103