A row of fifty identical, truncated vertical cylinders is submitted to regular head waves, with wave periods in a narrow range around the period of the so-called Neumann trapped mode. The free-surface elevation is measured at 14 locations along the array. Response amplitude operators of the free-surface motion are compared with numerical predictions from a potential flow model. Resonance effects, at wave periods equal to or larger than the critical one, are found to be much less than given by the numerical model. It is advocated that these discrepancies are due to dissipative effects taking place in the boundary layers at the cylinder walls. An artificial means is devised to incorporate dissipation in the potential flow model, whereby the cylinder walls are made slightly porous; the inward normal velocity of the flow is related to the dynamic pressure. The coefficient of proportionality is based on existing knowledge for circular cylinders in oscillatory flows. With this modification in the numerical code, excellent agreement is obtained with the experiments. The numerical model is further used for the case of a very long array composed of 1000 cylinders; it is found that with dissipation at the cylinder walls, the wave action steadily decreases along the array, even for wave periods substantially larger than the critical one. On the other hand, at wave periods less than the critical one, dissipation plays a negligible role; the observed decay is solely due to diffraction effects. Implications of these results for very large structures such as column-supported floating airports are discussed. In particular, it is concluded that scale effects may be an important issue in the experimental analysis of such multi-column structures.

In late years, the action for the environmental problem becomes more and more active in the world. The country like Japan, being surrounded by the sea, is rich in ocean energy. It is relatively easy to get wave energy among ocean renewable energies. The wave power generation device to collect wave energy has been studied in many countries of the world including Japan. There are a lot of electrical generating systems which use a turbine. But, the environment in ocean is different from that in land. Because the turbine is weak in ocean breeze, it is more difficult to maintain it. Therefore we proposed a new electrical generating system, which doesn't use a turbine, using the piezoelectric element and pendulums.

A linear electrical generator can be used on wave energy converter for converting the kinetic energy of a floating structure to the electricity. A wave farm consists of multiple wave energy converters which equipped in a sea area. In the present paper, a numerical model is proposed considering not only the interference effect in the multiple floating structures, but also the controlling force of each linear electrical generator. In particular, the copper losses in the electrical generator is taken into account, when the electrical power is computed. In a case study, the heaving motions and electrical powers of the multiple wave energy converters are estimated in the straight arrangement and triangle arrangement. In addition, the average electrical power is analyzed in different distances of the floating structures. The aim of this paper is to clear the relationship between the interference effect and electric powers from wave energy converters. This will be useful for deciding the arrangement of multiple wave energy converters.