Numerical analysis of force-feedback control in a circular tank

The advent of circular wave tanks, with wave-making segments all around the perimeter, brings potential advantages over standard, rectangular wave tanks where the wave-maker is confined to one or two adjacent sides of the tank. It is now possible to reproduce seas with full 360° directionality, enhancing the range of possible test scenarios. However, this additional capability also presents technical challenges: waves generated on “one side” of the tank must be absorbed on the opposite side, together with any waves reflected or radiated by the model under test, to prevent contamination of the wave field. This paper reviews the theory of wave generation and absorption in a circular tank, before proceeding to identify an appropriate control scheme for the University of Edinburgh's “FloWave” combined wave/current basin. Numerical simulations, based on linear multi-chromatic waves, are carried out using WAMIT to assess the suitability of wave-maker control schemes suggested in literature. For the first time a round tank's ability to reproduce sea spectra is assessed numerically. The simulations suggest that the generation of “peaked” spectra is possible to an accurate degree, with an overall standard deviation error of less than 2% over a designated “test zone”. However, there are difficulties in producing “wide” spectra, as effective dynamic wave absorption cannot be ensured over the whole frequency range. This may have important repercussions, not just for the usage of FloWave, but also in terms of the design of future round basins.