Propulsive Aspects of Dynamically Positioned Semi-Submersibles

With the help of an existing timedomain simulation program which is also applicable to semisubmersibles some aspects concerning the dynamic positioning (DP) performance of such vessels are investigated. To this end the basic assumptions underlying the program are discussed first, including an account of environmental forces and propulsive forces. After showing some correlation results obtained for monohulls the program is applied to a specific semisubmersible and a number of aspects which are important for the DP performance such as control coefficients, wind feed forward and phase lags originating from different sources, are covered. Finally a simple criterion for the extra power necessary to counter dynamic effects will be compared with results obtained with the time domain simulation program, as well as with measurements.