This paper investigates numerically a wave energy harness device-water interaction system excited by a wave maker motion in order to extract maximum wave energy. The model of the energy harness device consists of a moving coil connected to a magnetic body floating on the water surface of the towing tank. At one end of the towing tank, a wave maker produces waves to excite the device-water interaction system. The motion of the coil relative to the magnetic body produces an electromagnetic induction voltage added to an energy collection circuit, so that the kinetic energy of the coil motion is transformed to electric energy. To extract maximum energy from the wave requires a large relative motion between the coil and the magnetic body of the energy harness device. To this end, the natural frequency of the wave energy harness device should be so close to the wave frequency that a resonance of the wave energy device can be reached. Since the wave energy device floats on the water surface, its dynamic behaviour is affected by the water motion. Therefore, it is necessary to consider fluid-structure interactions to design an effective wave energy device. This problem is addressed in this paper. In this numerical simulation, the water is considered as a compressible fluid satisfying a wave equation in the water domain in association with the boundary conditions on the free surface, wall and bottom of the towing tank. The wave maker motion is simulated by a given boundary acceleration on the wet interface of the wave maker. The energy harness device is treated as a two masses connected by four springs between them. The spring stiffness can be adjusted to obtain an effective energy extraction device. On the interface between the magnetic body and the water, the equilibrium and motion consistent conditions are required. The governing equations describing the fluid-structure interaction dynamics of the integrated system are presented. A corresponding variational principle is formulated and a mixed finite element model is established. The developed computer program-FSIAP is used to complete the numerical simulations. Suitable parameters of the energy harness device are obtained. The dynamic responses of the integrated fluid-structure interaction system excited by the wave maker motions are calculated. It is shown that the designed energy harness device can extract maximum wave energy using the resonance principle. The results obtained are compared and discussed. Some guidelines for engineering applications are provided.

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