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## The pressure field beneath intense surface water wave groups

A weakly-nonlinear potential theory is developed for the description of deep penetrating pressure

fields caused by single and colliding wave groups of collinear waves due to the second-order nonlinear

interactions. The result is applied to the representative case of groups with the sech-shape of

envelope solitons in deep water. When solitary groups experience a head-on collision, the induced due

to nonlinearity dynamic pressure may have magnitude comparable with the magnitude of the linear

solution. It attenuates with depth with characteristic length of the group, which may greatly exceed the

individual wave length. In general the picture of the dynamic pressure beneath intense wave groups looks

complicated. The qualitative difference in the structure of the induced pressure field for unidirectional and

opposite wave trains is emphasized.