# Laboratory investigations on the resonant feature of `dead water' phenomenon

## TL;DR

This study experimentally investigates the internal wave phenomena behind ships in stratified fluids, identifying a resonant velocity that maximizes wave amplitude and drag, and compares observations with linear wave theories.

## Contribution

It provides new experimental data on internal wave excitation and validates linear theories for predicting wave behavior at critical velocities in stratified flows.

## Key findings

- Maximum wave amplitude occurs at a specific resonant velocity.
- Linear theories adequately describe wave transition and amplification.
- Internal wave characteristics depend on ship speed, length, and stratification.

## Abstract

Interfacial internal wave excitation in the wake of towed ships is studied experimentally in a quasi-two layer fluid. At a critical `resonant' towing velocity, whose value depends on the structure of the vertical density profile, the amplitude of the internal wave train following the ship reaches a maximum, in unison with the development of a drag force acting on the vessel, known in the maritime literature as `dead water'. The amplitudes and wavelengths of the emerging internal waves are evaluated for various ship speeds, ship lengths and stratification profiles. The results are compared to linear two- and three-layer theories of freely propagating waves and lee waves. We find that despite the fact that the observed internal waves can have considerable amplitudes, linear theories can still provide a surprisingly adequate description of subcritical-to-supercritical transition and the associated amplification of internal waves.