Abstract
Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices’ commercial applications. Therefore, the efficiency enhancement of wave energy converters has received much attention in recent decades. The reported research presents the double snap-through mechanism applied to a hemispheric point absorber type wave energy converter (WEC) to improve the energy absorption performance. The double snap-through mechanism comprises four oblique springs mounted in an X-configuration. This provides the WEC with different dynamic stability behaviors depending on the particular geometric and physical parameters employed. The efficiency of these different WEC behaviors (linear, bistable, and tristable) was initially evaluated under the action of regular waves. The results for bistable or tristable responses indicated significant improvements in the WEC’s energy capture efficiency. Furthermore, the WEC frequency bandwidth was shown to be significantly enlarged when the tristable mode was in operation. However, the corresponding tristable trajectory showed intra-well behavior in the middle potential well, which induced a more severe low-energy absorption when a small wave amplitude acted on the WEC compared to when the bistable WEC was employed. Nevertheless, positive effects were observed when appropriate initial conditions were imposed. The results also showed that for bistable or tristable responses, a suitable spring stiffness may cause the buoy to oscillate in high energy modes.
Highlights
Based on the above information, the present study introduces a simpler and more compact double snap-through mechanism that can be applied to work in a point absorber (PA)-wave energy converter (WEC), enables the occurrence of multi-stable states, and requires only a relatively compact space
Where X = [x1, x2, ⋯, xn]T is the nth order state vector; A′, B′, and C′ are the constant state space matrices that are calculated through the frequency domain identification (FDI) method discussed in Pérez and Fossen (2008, 2009); v is the buoy vertical velocity; and μ is the convolution term
A general mathematical formulation based on nondimensional parameters was used to calculate the time history
Summary
As an alternative to the conventional bistable potential adaptive, Younesian and Alam (2017) proposed a multi-stable mechanism composed of two oblique rigid links and two oblique springs (see Figure 1d) with additional potential wells introduced into the dynamic response. By adjusting the angle and initial spring lengths, the mechanical system can switch from monostable to bistable or tristable states, Their results have shown that bistable and tristable modes significantly improve the WEC efficiency, and the natural frequency can be shifted to a higher frequency range.
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