Very large floating structures (VLFSs) of several kilometers long and wide are now considered as possible alternatives to land-based big facilities such as an airport. Many feasibility studies are now being carried out on the VLFSs and quite a few numerical methods have been proposed for an estimation of a response of the VLFS and a wave field around the VLFS. There are, however, few experiments that can be compared with the numerical results. One of the reasons is that the principal horizontal dimension of the VLFS is so large that the conventional experimental tanks can not comply with the appropriate similarity law. To overcome this difficulty, an attempt is made to carry out experiments in a very small water tank. With the use of the very small tank, an entire wave field around a model or an entire response pattern of the model in waves can be visualized by making use of certain techniques. Such visualization can not be achieved if the conventional water tanks are used.
In this study, we propose two techniques for visualizing and measuring wave fields which are around 1mm deformations. The first one is based on Moire's method. The second one is based on a picture analysis. Both techniques can fully inform on the very small deformation of the wave fields in widely and in simultaneously. Then we discuss the accuracy of the measurements of the wave fields by comparing with measurements by laser sensors.
