Simulation Of Irregular Waves Research Articles

Maximizing output power of linear generators for wave energy conversion

SUMMARY The aim of wave energy converters is to extract energy from ocean waves and turn it into electricity. Since the earliest developments, optimal control strategy has been considered the one that optimizes the power extracted from the oscillating system. This technique requires energy exchanges between the oscillating system and an auxiliary storage energy system, and has been shown to be potentially capable of substantially increasing the amount of energy absorbed. Nevertheless, it requires very efficient devices due to the huge losses, which occur when operating conditions are far from the natural frequency of the oscillating system. Moreover, this optimization criteria cause large heave excursions in the oscillating system and high peak-to-average power ratios of the system. In this paper, a point absorber converter that uses a linear direct-drive generator and power electronics converters jointly is considered. This article presents a novel method of control, which optimizes the power transferred from the generator to the power electronic converter considering the copper losses in the electric generator. This approach of the optimization method allows a significant increase in the wave energy converter's capacity of energy conversion. Applying the proposed control strategy, power exchanges between the oscillating system and the generator can be reduced, and in consequence, system efficiency significantly increases. In addition, the oscillating system's heave excursions and the peak-to-average power ratio decrease. The formulation of the proposed method is presented as well as numerical simulations in irregular waves. Copyright © 2013 John Wiley & Sons, Ltd.

Simulation of Irregular Waves by CFD

Simulation of Irregular Waves by CFD

Internal generation of waves on an arc in a rectangular grid system

This paper presents a technique to generate waves at oblique angles in finite difference numerical models in a rectangular grid system by using internal generation technique [Lee, C., Suh, K.D., 1998. Internal generation of waves for time-dependent mild-slope equations. Coast. Eng. 34, 35–57.] along an arc-shaped line source. Tests were made for four different types of wave generation layouts. Quantitative experiments were conducted under the following conditions: the propagation of waves on a flat bottom, the refraction and shoaling of waves on a planar slope, and the diffraction of waves to a semi-infinite breakwater. Numerical experiments were conducted using the extended mild-slope equations of Suh et al. [Suh, K.D., Lee, C., Park, W.S., 1997. Time-dependent equations for wave propagation on rapidly varying topography. Coast. Eng. 32, 91–117.]. The fourth layout type consisting of two parallel lines connected to a semicircle showed the best solutions, especially for a small grid size. This technique is useful for the numerical simulation of irregular waves with broad-banded directional spectrum using conventional spectral wave models for the reasonable estimation of bottom friction and wave-breaking.

Numerical Methods to Predict Characteristics of Air Chamber for Fixed Terminator Type of Wave Energy Converter.

The numerical methods for analyzing a fixed terminator type of wave energy conversion device are described under the condition that the linear water wave theory is applicable. Two methods are proposed in order to calculate the device characteristics of an air chamber. One uses the flow rate and the gage pressure in the air chamber directly, because the interaction between the oscillating water column and the turbine is found to be controlled only by the flow rate and the pressure drop through the turbine in this system. The other method uses the equation of the floating body motion in a manner similar to the equivalent floating body approximation. The relations between these two methods are also examined. The hydrodynamic performance with frequency from zero to infinity is required in the simulation of irregular waves. However, resonances occur when the air chamber breadth is equal to an integral multiple of a half wavelength. Therefore the impulse response function is modified in order to eliminate the effects of the resonance frequency. Finally, it is confirmed that these solutions give good agreement with the experimental data.