浮游式黑潮渦輪發電機在波浪作用下的流體動力分析

Hydrodynamic Analysis for a Floating Kuroshio Turbine under Action of Waves

謝君彥(Jun-Yen Shieh)

指導教授 ： 邱逢琛

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703330

摘要

波浪是所有海洋結構物都會面臨到的外部環境因素，本研究的對象為浮游式黑潮發電渦輪機組(Floating Kuroshio Turbine；FKT)。當波長較長的波浪經過機組上方時，機組會受到波浪強制力與力矩的作用並且產生對應的運動反應。通常在較為嚴厲的天氣情況，長浪很容易隨之產生，此時位於水下的機組可能會產生劇烈的運動，不論對機組的運作或是壽命都會產生影響。本研究將針對波浪入流下機組所受到的波浪強制力與力矩進行分析，並對機組在波浪下可能產生的運動反應進行概略性的初步評估。
本研究使用的計算流體力學軟體為ANSYS FLUENT，在定速入流上加上不同波長的波浪，並以固定的波斜率輸入對應的波高，探討全機組在工作深度25m、雙轉子運作的情況下受到的波浪強制力與力矩，包含軸向力與垂向力以及俯仰矩。再分別利用快速傅立葉分析求出強制力振幅，利用模擬出的強制力結果評估在這兩方向的平移運動，並探討此俯仰矩作用下機組產生的縱搖運動。而後改變機組的深度至10m與40m觀察強制力與俯仰矩隨機組深度的變化。
本研究結果顯示在波浪作用下，強制力與力矩震盪的幅度會隨著波長與波高的增加而變大。另外在沒水深度較淺時，機組受到的波浪強制力與力矩振幅也會明顯增大。因此，長波來臨時FKT應盡可能下沉至足夠的深度以避開較大振幅的波浪強制力和力矩。本研究以CFD三維模擬的方式得到機組在波浪下的受力，未來的研究可以將本研究經由CFD算得較精確的波浪強制力與力矩結果作為模擬軟體OrcaFlex的外力輸入，進行機組在流與波浪同時作用下的運動模擬分析。另外本研究也在波浪的CFD模擬過程中進行了相當多的測試，未來在進行相似案例時，可以參考本研究的方式進行。

關鍵字

洋流 ； 浮游式黑潮渦輪發電機 ； 波浪 ； 波浪強制力 ； 計算流體力學

並列摘要

Waves are inevitable environmental factor to all marine structures. In the present study, we are going to study wave exciting forces and moment acting on a Floating Kuroshio Turbine (FKT) when long waves propagate over it. FKT will have corresponding motion responses due to the wave exciting forces and moment. In general, FKT needs to face the challenge when weather is severe. Long waves may make FKT do some violent movement, these movements will affect the performance and reduce service life of FKT. Therefore, we are going to analyze the wave exciting forces and moment, and make preliminary evaluation of the movements due to these forces and moment.
In the present study, the CFD software ANSYS FLUENT is used for dealing with the hydrodynamic problems. To simulate the situation that FKT under waves, we add different wavelength and wave height keeping wave slope constant at the inlet, and then calculate the wave exciting force in both x and y direction as well as moment in z direction when FKT working at the depth of 25 meters. Finally use Fast Fourier Transfer to get the amplitude of wave exciting forces and moment, and analyze the movement made by them. We will also calculate the pitch moment and evaluate the corresponding pitch motion. After that, we will change the depth of FKT, make it to the depth of 10 and 40 meters and compare the results to clarify the variation with depth.
The results show that the longer the wavelength or the higher the wave height will make the wave exciting forces and moment larger, and it is obvious that when FKT comes close to free surface, it will also enhance the forces and moment. Therefore, FKT should go deeper to avoid the large amplitude exciting forces and moment when long waves are coming. As a future work, the CFD calculated wave exciting forces and moment may introduced into OrcaFlex as external forces to simulate the motions of FKT with mooring line due to the combining influences of waves and current.

並列關鍵字

Ocean Current ； Floating Kuroshio Turbine ； Wave ； Wave Exciting Force ； CFD

參考文獻

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