In simple words you need to use ansys acoustics modules, for example, Harmonic Acoustics. There are other ways that includes adding that interaction through mass modeling.

It will probably depend on how detailed you want the analysis to be. But I agree with Arturo Ocampo , one way to do it is to rely on the Acoustic toolbox in workbench. Another way is to consider the effect of the water as added mass within the Transient/Harmonic toolbox. See this paper for instance:Article A NUMERICAL STUDY OF DAMAGE DETECTION OF UNDERWATER PIPELINE...

You should be aware of the widely used document in pipeline industry titled: "DNVGL-RP-F105 Free spanning pipelines". Then ANSYS can be used for a simple beam modal analysis if needed to determine the governing vibration frequencies and mode shapes which are used therein, with due account for the effective axial equilibrium force in the pipeline.