含浮台矩形剛性儲存槽在地震下之結構-流體動力分析

Structural-Hydrodynamic Analysis of Rectangular Rigid Tanks with a Pontoon under Earthquakes

劉坤豐(Kun-Feng Liou)

指導教授 ： 王彥博

國立交通大學/工學院/土木工程系所/碩士(2020年)

摘要

台灣東西部海域地形差異懸殊，為支援離岸風電工程與水下技術發展，政府計畫打造出一座水深可變之深水池以滿足試驗所需。本研究旨在發展深水池於地震作用下之流體動力分析方法，俾便了解在設計地震力(PGA= 340 gal)下之池水與浮台振盪反應以供設計參考。本文以一座斷面為矩形之長方體深水池為標的，考慮池面有浮台並以鋼纜束制之條件下進行數值模擬分析，探討池面波動反應以及流體與浮台、鋼纜間之流體-結構互制行為。以剛性矩形儲存槽之流體動力分析理論為基礎，本研究並整合浮板轉動及鋼纜之束制行為而發展出完整的流體-結構互制動力方程。由於鋼纜只受拉不受壓之不連續力學行為，導致動力方程式不再為線性，因此本研究也發展了求解非線性運動方程式的數值方法。此外，為更深入探索深水池與浮台的流體-結構互制行為，本文亦完成一系列參數研究，探討震波強度、儲存槽高寬比、浮台重及鋼纜勁度等因子之影響。研究結果顯示，深水池的流體動力特性與高寬比(H/B)有關。高寬比愈小時，蓄水中參與對流運動的質量比例愈高；反之，則以隨槽體同步作剛體運動的比例愈高。深水池面之流體激盪反應具有地震相依性，與震波的頻率內涵有關。浮台對於波動反應的抑制效應與其重量有關，波動加速度隨浮台重量增加而有明顯趨緩之勢，但對於波高的抑制效應不顯著。鋼纜對於浮台的振盪反應有抑制效果，尤其是波高的部分。增加鋼纜數量(即勁度)對於流體激盪反應的控制效果會提升，但控制力也會隨著波高下降而漸趨飽和。

關鍵字

剛性矩形儲存槽 ； 地震 ； 浮台 ； 結構-流體互制 ； 非線性運動方程 ； 迭代過程

並列摘要

The topography in the Western and Eastern coasts of Taiwan divert drastically. To support development of offshore wind power and underwater technology, the government plans to build a deep water pool adaptive to variable water depth to comply with various experimental demands. The objective of this study is to develop a methodology for the hydrodynamic analysis of pools under earthquake excitations to get more insight on the slushing responses of water and the pontoon under earthquakes of PGA = 340 gal for design purpose. A rectangular storage tank with a floating pontoon constrained by cables is considered as the object in this thesis for numerical simulations to explore the surface slushing of the tank and the structural–hydrodynamic interactions between the water and pontoon along with the cables. Based on the theory of fluid dynamics for rectangular rigid tanks, this study integrates the pontoon in pitch motions and the constraints by the cables to devise a more completed dynamic equation of structural-hydrodynamic motion. The tension-only mechanical behavior of the cable causes discontinuity in the dynamic system and leads to a nonlinear dynamic equation. Therefore, a numerical method for solving the nonlinear equation of motion has also been developed in this study. Moreover, to further explore the structural–hydrodynamic interactions between the water and the pontoon, a series of parametric studies has been conducted to explore the influence of earthquake intensity, aspect ratio of the pool, pontoon weight, and cable stiffness. Results show that characteristics of the fluid dynamics of the pool are related to the aspect ratio (H/B). It is found that the smaller the aspect ratio, the higher participating ratio of the water mass is in the convective motion. And, oppositely for larger aspect ratios, higher proportion of the water will move synchronizedly with the tank in a rigid body mode. The sloshing responses of the deep-water pool is earthquake-dependent, which is related to the frequency contents of the earthquake. Effects of the pontoon on slushing response suppression depends on its weight. The slushing acceleration decreases with the increase of the weight of pontoon, while the trend is not obvious for the slushing displacement. The cable shows effective in depressing the oscillating response of the pontoon, in particular for the displacement responses. Increasing the number of steel cables (i.e. stiffness) will enhance the control effect on the sloshing responses, yet the control force will become saturated as the sloshing displacement decreases.

並列關鍵字

rigid rectangular tank ； earthquake ； pontoon ； structural–hydrodynamics ； non-linear equation of motion ； iterative process

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