Hi Ewan,

We were able to identify the added mass from free decay decay experiments. See Fig 16 of attached paper. Hope this helps.

https://www.researchgate.net/publication/277340024_Linear_parametric_hydrodynamic_models_for_ocean_wave_energy_converters_identified_from_numerical_wave_tank_experiments

Josh

Article Linear parametric hydrodynamic models for ocean wave energy ...

You can perform forced oscillation at any period requested using a hydraulic or electric moving arm forcing a vertical sinusoidal motion

Look at this doc it may be helpful for your topic. Good luck.

 You can read the classical reference about experimental hydrodynamic coefficients: Vugts (1970). It is available in here: http://repository.tudelft.nl/islandora/object/uuid%3Afe93e1b5-0f4a-46cd-beef-a5988146b8a2

I second forced oscillation tests suggested by Alain Ledoux. Basically, measuring the forces and the responses of the semi, then relating the radiation forces to the hydrodynamic coefficients will deliver you what is necessary at any frequency. Pick your frequencies carefully though.

Article The effect of asymmetric cross-sections on hydrodynamic coef...