Judy Maksoud
International Editor

LISBON, Portugal -- Deepwater semisubmersibles with more than fifty steel catenary risers (SCRs) and a vertical riser load equal to 15% of the hull displacement are being built. Fons Huijs of Marine Structure Consultants discussed the need for more analysis of semis with many SCRs at the International Offshore and Polar Engineering annual conference on July 4. "Vertical riser loads are large and have an effect on the motions of the semi," Huijs said.

Huijs described a numerical study carried out to determine the effects of steel catenary risers on the first order wave response of a semisubmersible. In this approach, Huijs said, the frequency domain method replaced the SCRs with damped mass-spring systems in the motion analysis of a semi with 50 SCRs.

Huijs' analysis used the frequency domain method to predict coupled motions. This approach takes considerably less time than the standard method, Huijs said. Though the method Huijs described is limited in that it does not take into account the current loads on moorings and risers, the normal diffraction analysis approach does not include current either, Huijs said.

Huijs believes the numerical study using the frequency domain method yields reliable results. "The approach takes much less time and yields results that are as useful as those produced by much more time intensive studies," he said.

July 4, 2007