This paper presents experimental and theoretical results obtained during the hydrodynamic study of a multi-cylinder system. The main focus of the study was to quantify hydrodynamic interactions between heaving vertical cylinders of a conceptual wave energy conversion system. Several identical circular cylinders representing platforms in an energy conversion system and a parabolic shaped wave reflector were tested in a wave flume tank. Wave heaving forces, radiation and diffraction effects were studied experimentally and numerically. The theoretical calculations were carried out for hydrodynamic coefficients, the radiation and diffraction effect analysis. Experimental results for multi-cylinders were compared with the numerical solutions by a panel-free method in the frequency domain. One main objective of the experimental tests was to calibrate the experimental set up, obtain validation data for numerical calculations. The diffraction studies showed that the hydrodynamic interactions could be constructive or destructive for heave wave forces. The positive magnification of the wave exciting force can be significant if a parabolic shaped reflector is used. It was observed that the wave force magnification and the wave energy absorption depend on incoming wavelength, and the cylinder to wavelength ratio. It has been found in the radiation tests that heave added mass and damping coefficients compare well with the calculations based on potential flow calculations.

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