Model Analysis

With model analysis, the mode shapes of the tether are obtained and any response is calculated as the sum of the responses of all the modes. This technique works reasonably well in shallow water, but there are cases where it obscures the fundamental mechanism of a motion at the top generating a travelling wave which travels down the tether.

For very deep water depth (>1000 meters) and high frequencies of top motion, these travelling waves are effectively damped before they reach the bottom and are reflected back to the top. Thus the tether does not behave in a modal maner (with tuned resonances) but rather as an energy sink. It may be important to account for this damping mechanism in calculating the ringing/springing response of a TLP.