A Study on the Stability of Offshore Structures Built on a Nonhomogeneous Seabed

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基本資料

Project title

Code/計畫編號

MOST106-2221-E022-007

Translated Name/計畫中文名

在非均質海床上的離岸結構物之穩定性研究

Project Coordinator/計畫主持人

Chia-Cheng Tsai

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Marine Environmental Engineering,NKUST

Website

https://www.grb.gov.tw/search/planDetail?id=12240993

Year

2017

Start date/計畫起

01-08-2017

Expected Completion/計畫迄

31-07-2018

Bugetid/研究經費

770千元

ResearchField/研究領域

土木水利工程

自從 2011 年3 月11 日日本核災難後，可再生能源的發展變得越來越迫切。我們的政府也配合此一趨勢，投入更多的資源在可再生能源的發展。由於台灣是個島國，海洋豐富的能源資源，海洋能源技術急需積極的發展，如此不僅可供應國內需求，還可於未來進入全球的能源市場。據全國能源工作會議的結論，預計優先發展海上風電場，期望第一個海上風電場能在2017 年完成。歐盟等先進諸國目前均有規劃或建造中之離岸式風力發電廠多年，台灣目前尚無離岸風場開發之先例，加上離岸風場的開發，不論從技術、環境、營運條件等層面觀之，皆與陸域風場開發迥然不同，故所承受的風險亦相當大。但由於海域環境條件的不明確，加上時有颱風侵襲，有很多工程設計的分析需要進行。在這些問題中，我們將專注於波浪引起的海底不穩定性，包括剪切破壞和土壤液化。我們的考慮，將包含長時間作用的週期波和颱風引起的極端海象。由於海洋海底通常由非均質的土壤組成，其土壤響應與均質土壤的情況有很大的差別，因此也將一並考慮。大多數以前的研究著重在基樁附近的沖刷而忽視海底土壤的孔隙壓力變化。在本計畫中，我們將考慮流體、土壤與結構的互制。此海洋岩土工程問題將通過Biot 的孔隙彈性理論建模。以達西定律（Darcy’s law）來描述流體在多孔介質中的流動；並考慮孔隙流體和土壤的壓縮性；此外，土壤骨架的加速度也將一併考量。我們將發展一套無網格數值方法用於解上述孔隙彈性理論，此方法稱為局部徑向基函數配點法（LRBFCM）。部分的程式開發，將由計畫主持人共同指導澳大利亞格里菲斯大學博士班學生來完成，並邀請指導教授Prof. Dong-Sheng Jeng 來台訪問。當分析海上風電場的流體與結構的互制，傳統的數值方法受限於大量自由度而有其應用上的困難。在這本研究中，我們將以空間樹自適應模式來分析問題。程式將根據渦度的量質，自動在離岸基樁附近加密，可有效提升效率。爾後，將所得到的波浪壓力整合到前段所述的無網格數值模式，用來量化海床的響應，以期分析土壤的剪切破壞和液化。 After the Japan nuclear disaster on 11 March 2011, the development of renewable energy becomes more and more urgent. Our government also follows this tendency of clean energy explosion and implements development of the renewable energy source. Since Taiwan is an island nation with rich ocean energy resources, with the positive development of ocean energy technology it is not only possible to supply domestic demand but also can enter the future of the global marine energy market. According to conclusions of national energy conference, plans to the development of the offshore wind field need to be implemented appropriately. The producing power of wind farm needs to be expanded. It is expected that there is an offshore wind farm accomplished in 2017. In Europe, the offshore wind farm has been implemented for many years. However, Taiwan does not have any experience on the offshore wind farm. No matters from the viewpoints of technique, environment or commercial operation, risks of the offshore wind farm are larger than the wind farm located in the coastal area. To ensure the efficiency of power generating, we should avoid many uncertainties due to oceanic environment and typhoon attack. Among these issues, we will focus on the wave-induced seabed instability, including shear failure and liquefaction. Both regular long-term cyclic wave input and typhoon-induced extreme wave climate will be considered. Since marine seabed is often composed of non-homogeneous soil in various directions, its response to dynamic wave loading shows much difference from the case of homogeneous soil and will also take into consideration. Most of the previous studies focus on the scouring around the piles while neglecting the pore pressure in the seabed soil. In this project, we will solve the problem by considering the fluid-soil-structure interaction. The marine geotechnical problem will be modeled by the Biot’s poroelasticity theory. Darcy's law is used to describe the flow of a fluid through a porous medium. The compressibility of pore fluid and soil are considered. In addition, the acceleration of soil skeleton is also included. As a result, an u-p formulation will be adopted in this study and solved by implementing a meshless numerical method, naming the local radial-basis-function collocation method (LRBFCM) that based on the multiquadric type radial basis function. Some of the implementation will be accomplished by the co-advised Ph.D. students of Griffith University. In addition, their supervisor, Prof. Dong-Sheng Jeng, will visit Taiwan. When analyzing the fluid-structure interaction of an offshore wind farm, it is difficult to use traditional numerical methods since a large amount of degree of freedoms are involved. In this study, the wave pressure of the fluid-structure interaction will be modeled by using a spacetree-adaptive model. High resolutions will be adapted to the vicinity of the offshore piles during a simulation. The obtained wave pressure will be then integrated into the prescribed meshless numerical model to analyze the dynamics of the seabed. The instability of shear failure and liquefaction will thus be quantified.

DSpace CRIS

A Study on the Stability of Offshore Structures Built on a Nonhomogeneous Seabed

基本資料

Description