Modal test of Bishop Rock Lighthouse

STORMLAMP researchers from Exeter and Plymouth concluded a sequence of measurements on an offshore rock lighthouse in the South West with a modal test of Bishop Rock lighthouse.

Bishop Rock is a massive structure, built on a rocks four miles south west of the Scilly Isles, that sheer from 45m deep in the Atlantic Ocean. The first structure, completed in 1858, was strengthened in 1881 by building a new structure around the existing lighthouse and extending the height by 12m to 44m above mean high water.

The present structure is by far the largest of the the four lighthouses studied in the STORMLAMP project, which also include: Les Hanois ,Wolf Rock and Longships.

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On a very wet and windy September Monday, James Bassitt, Ian Moon (Exeter ian_james_selfie.jpg) and Alessandro Antonini (ale_daq.jpg) flew from St Just (Land’s End) airport to carry out a sequence of vibration measurements using accelerometers aligned horizontally at the top of the lighthouse.

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After an energetic exercise laying out, connecting and configuring the sensors, horizontal accelerations were measured in the lower entrance level, engine rooms, bedroom, kitchen, service and battery rooms, lantern level and helideck (ian_helideck.jpg).

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Response due to ambient conditions of strong winds and relatively benign waves was measured, as well as the effect of artificial excitation using a 140 N electro-dynamic shaker (shaker.jpg). Measurements started at around 1PM and were completed within two hours.

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Unfortunately, the strong winds were quickly followed by low visibility on Monday afternoon, shutting down Trinity House helicopter flights and stranding the team overnight. Happily the fog horn no longer operates at Bishop Rock, dining facilities were available (dinner.jpg) and the eerie effect of the powerful twin lantern beams

provided some entertainment. The team escaped when the fog lifted on the Tuesday afternoon.

dinner
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The modal test data are being used to evaluate the structure and provide the means for inverse identification of wave loads. The next STORMLAMP mission will be to Fastnet Lighthouse in December.

The video is by Peter Cox a wonderful landscape photographer based in Ireland.

http://www.petercox.ie