Question:

What does the COUPLE parameter do?

Answer:

SEAKEEPING gives users control over the coupling of the equation of motion. In short, coupling is the degree of interaction between the six modes of motion. For example, near the bow of a vessel much of the heave experienced is due to the coupling effects of pitch into heave. These coupling effects are included by computing certain coefficients in the equation of motion.

If a vessel is unappended and has port-starboard symmetry, the coefficients that couple the vertical modes (surge, heave, and pitch) to the horizontal modes (sway, roll, and yaw) will go to zero, making the equation of motion partially coupled. This is the default setting used by the SEA command.

However, if the vessel has non-zero heel or asymmetric geometry, all modes must be coupled. The COUPLE parameter will ensure that the SEA command uses a fully-coupled equation of motion by computing and retaining all coupling coefficients. Note that if a condition is symmetric and the COUPLE parameter is used, the results should remain the same.

The UNCOUPLE parameter does the opposite: it fully-uncouples the equation of motion by eliminating all hull component coupling coefficients.


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