  This paper revisits the problem of tidal conversion at a ridge in a uniformly
stratified fluid of limited depth using measurements of complex-valued added
mass. When the height of a sub-marine ridge is non negligible with respect to
the depth of the water, the tidal conversion can be enhanced in the
supercritical regime or reduced in the subcritical regime with respect to the
large depth situation. Tidal conversion can even be null for some specific
cases. Here, we study experimentally the influence of finite depth on the added
mass coefficients for three diffierent ridge shapes. We first show that at low
forcing frequency the tidal conversion is weakly enhanced by shallow depth for
a semi-circular ridge. In addition, added mass coefficients measured for a
vertical ridge show strong similarities with the ones obtained for the
semi-circular ridge. Nevertheless, the enhancement of the tidal conversion at
low forcing frequency for the vertical ridge has not been observed, in contrast
with its supercritical shape. Finally, we provide the experimental evidence of
a lack of tidal conversion due to the specific shape of a ridge for certain
depth and frequency tuning.
