Experimental Study on the Effects of Various Scale Ratios of Physical Models on the Prediction of the Semi-Submersible Platform Dynamic Motions

From the beginning of recorded history, physical model testing has been regarded as the most reliable method to predict the dynamic responses of semi-submersible platform when subjected to environmental loadings. It is known that testing of floating structures requires very large model basins. As a matter of fact, physical model testing of deep water floaters is restricted due to the limitations of wave basins especially the water depth in the offshore testing facilities worldwide. Decades of research have focused on the methods to overcome the limitation of water depth in wave basin. However, little attention has been given to the scale effects on the responses of the physical model.
The aim of this study was to conduct a comprehensive experimental study on the effects of various scale ratios on the prediction of dynamic motions of the semi-submersible platform in UTP offshore wave basin. The geometry of the semi-submersible prototype has been chosen with similar configuration to the ocean ranger that had sunk to the bottom of the ocean with the loss of all 84 of its crew. Froude’s model law of similitude has been used to scale down the prototype to the scale of 1:100 and 1:300. The time series responses for the six degrees of freedom (6DOF) and response energy spectra for physical model tests were compared in the prototype scale with the numerical simulation that had been done using STAR-CCM+ software. The results showed a good agreement between the model test 1:300 and the semi-submersible platform compared to the model 1:100. This could be due to the size of the model. As a matter of fact, the smaller the model the lesser affected by the reflected waves from the walls of the wave basin facility. The objectives of the study were achieved.