擷取水波能量的理論分析

Abstract

本論文以理論分析進行擷取流體表面或界面波能量的研究。我們在長方形盒中裝載單層或雙層流體，將PVDF雙層壓電片置於流體間的界面或自由表面上；並假設流體界面或表面的垂直方向位移與壓電片於垂直方向的位移分量相等，我們計算出整個系統最後之瞬時最大發電功率。單層流的分析考慮盒子受到側向施力或小角度搖擺運動兩種驅動模式。雙層流之分析則只考慮盒子受到側向施力驅動狀况，但壓電片可置於雙層流之表面或兩液體之界面。 計算結果發現，若想在低頻引發固流共振則必須將壓電片置於雙層流之界面。然而，若想在較高頻的情況引發固流共振則必須將壓電片置於雙層流表面。此外，對於單層流而言，盒子受到側向施力或搖擺運動，搖擺運動所產生的發電功率較高。

In this thesis, we perform a theoretical study on harvesting the surface or interface wave energy from layer(s) of liquid. Scavenging the vibration energy surrounding us is the core idea of this research. Such vibration energy is used as a source to exert force on a rectangular tank which is partial filled with liquid(s), and thus drives the wave motion. We consider two major cases; one is a tank containing a single-layer liquid exerted by either a lateral or pitching excitation. We harvest the surface wave energy at the free surface. The other is a tank consisting of the two layers of immiscible liquid exerted by a lateral excitation. There are two harvesting locations for the latter case, one at the free surface and one at the interface of the double-layer liquid. We place a PVDF bimorph on the interface between two liquids or on the free surface of the liquid. Under the assumption that the displacement of the PVDF bimorph along the gravitational direction is equal to the sloshing height of liquid at the interface or at the free surface, we calculated the power harvested in the PVDF bimorph. We found that if we want to resonate at a lower frequency, we have to place the PVDF bimorph at the interface of the liquid layers. However, if we intend to resonate at a higher frequency, putting the PVDF bimorph at the free surface can harvest more electric power. Moreover, the power output for the single-layer liquid is greater when it is under the pitching excitation case compared with the lateral excitation case.