The Slow Drift Oscillations of a Moored Object in Random Seas

In this paper the phenomenon of the slowly varying drifting force on a moored object in a random sea will be explained and illustrated from the results of a number of model tests with a rectangular barge. These tests, conducted at the Netherlands Ship Model Basin, were an extension of an earlier executed program.It will be shown that, usIng the results of measured or calculated drifting forces on an object moored in regular waves, a predictIon can be made of the drifting forces Induced by wave trains consisting of regular wave groups.Also for an irregular wave train the drifting force on the barge could be computed as a function of time, which made it possible to calculate the surge motion of the barge. The results of tests and calculations show a reasonable agreement.