When regular waves are incident to a long array of equally-spaced cylindrical columns, very large water-surface elevations among the columns and very large horizontal forces on the columns are expected in a certain critical wave-frequency range according to the linear potential theory. This is a kind of resonant phenomenon and closely related to the 'trapped waves' that may occur around a vertical cylinder placed in a narrow wave tank. Experimental facts suggest, however, actual water-surface elevations or horizontal forces are much smaller than the theoretical predictions. It has been found that the apparent contradictions between the linear potential theory and the experimental results can be attributed to the small energy dissipations induced in the viscous boundary layers that develop along the column surfaces. In fact, inclusion of tiny energy dissipations in the theory result in drastic change of the final results in the critical wave-frequency range, which agree quite well with the experimental results. This fact may have very important practical implications for the design of column-supported VLFSs (very large floating structures) in that the dynamic responses of the VLFSs could be quite different from those predicted by the linear potential theory, which is the subject of the present work.