Shown in the following pictrue:

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Anytime you include WAVx in any load case, CAESAR II assumes "W" is "W+Buoy", for all load cases.
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if we do WAVx load case, "W" will be "W+Buoy", "WAVx" is the action force by wave and current.

i knew that, but the wave with small parameters should NOT have a great effect on the pipe. the tow force will mainly contribute to the interaction for pipe.