Judy Maksoud
International Editor
Offshore
Transportation can cause significant stress on the structures, according to Eero Lehtonen, competence center manager for PI Rauma, and has to be taken into account at the design stage. Lehtonen discussed the company's experience with spar design issues at the 24th annual Offshore Mechanics and Arctic Engineering conference in Greece. Finland's PI Rauma has been involved in many of the world's spar construction projects and has transported spars via heavy transport vessels from Finland to the Gulf of Mexico for completion.
"Analysis began at PI Rauma with the Genesis spar," Lehtonen said, and continues today. Analyses to date have included Genesis, Diana, Horn Mountain, Gunnison, the Holstein hard tank, Mad Dog, and Constitution, which is nearing completion in Finland, he said.
The company has performed analysis for each spar crossing from Finland to the GoM to gather the most comprehensive data, Lehtonen said.
One consideration is the size of the spar in relation to the transport vessel, Lehtonen said. To date, Dockwise has moved all of the Finland-constructed spars on either theMighty Servant I or Mighty Servant III, he said.
"There are overhangs on every transport," Lehtonen said. That means often that the soft tank of the spar makes contact with the water during transport, he explained.
It is critical to quantify loads that affect the soft tank during transport, Lehtonen said. In this case, no additional separation occurred at the truss support, he said, but designers need to know the stresses the spar will experience during transport, so the spar is not damaged en route.
PI Rauma carried out spectral analysis of load responses, fatigue analysis, and eigen-frequency analysis in evaluating the data gathered on spar transportation.
Though designed for the spar, present analysis procedures apply to all such transports, Lehtonen said, and can be used to verify the safety of heavy transport irrespective of the vessel's cargo.
06/16/05
