海床拖錨承載力之數值研究

Abstract

近年來，隨著環保意識的提升，各國積極推動綠色能源以減少碳排放。在各種綠色能源中，風力發電是台灣積極發展的領域之一。風力發電機的建設面臨許多挑戰，其中之一就是確保浮動平台的穩定性。本研究的目的是通過數值模擬評估拖曳式錨（Drag Embedment Anchor, DEA）的承載力。為了了解這種錨在海床中能夠提供多少承載力，必須了解錨在海床中的拖曳軌跡和行為。在本研究中，我們參考了美國船務局（American Bureau of Shipping, 2017）制定的方法，構建了錨在黏土海床中的軌跡和成載力的預測模型。然而，由於文獻和相關研究的有限性，目前尚無可靠的模型可用於預測錨在砂土中的拖曳軌跡。基於ABS方法預測的軌跡，本研究使用ABAQUS進行數值模擬，評估拖曳式錨在黏土地層中的成載力。結果表明，在不同深度、錨爪角度和土壤強度下，該數值模型具有良好的預測精度，這意味著該模型可能也適用於分析錨在黏土以外的地質材料組成的海床中的成載力。 本研究還考慮了地震載荷對拖曳式錨成載力的影響。具體而言，本研究探討了黏土的循環軟化對成載力的影響。循環軟化的程度取決於循環應變振幅和載荷循環次數。在本研究中，這兩個數值通過基於場地特定的地盤反應分析和基於Tsai等人（2014）的經驗模型來估算。隨後，進行數值模擬以評估拖曳錨在軟化後海床中的成載力。

Tsai et al. (2014)的方法是基於地表監測所得的地震參數如地震規模，PGA來進行折減分析，本研究還參考了Kishida and Tsai (2014)的方法，使用地盤反應分析所得的目標土層剪應力歷時，求得實驗室內的等值圈數以及剪應變值，直接對目標土層進行強度折減。

In recent years, environmental awareness has surged, and countries are actively promoting green energy to reduce carbon emissions. Among various green energy sources, wind power generation is an area that Taiwan has been actively developing. The construction of wind turbine is one of the challenges that need to be addressed. The research objective of this study is to evaluate the holding capacity of drag embedment anchor (DEA) through numerical simulation. To understand how much holding capacity this anchor can provide for securing the floating platforms, it is necessary to understand the drag trajectory and behavior of the anchor in the seabed. In this study, we refer to the methods specified in the American Bureau of Shipping (2017) to construct a prediction model for the trajectory and holding capacity of the anchor in clay seabed. However, due to limited literature and related studies, reliable models for predicting the drag trajectory in sandy soils are not readily available. Using the predicted trajectory based on the ABS method, numerical simulations were conducted using ABAQUS to evaluate the holding capacity of drag embedment anchor in clayey seabed. The results showed good predictive accuracy at different depths, fluke angles, and soil strengths, indicating that this numerical model may be used for analyzing the holding capacity of drag anchors in seabed composed of geologic materials other than clays. This study also considered the changes in the holding capacity of drag embedment anchors due to seismic loading. More specifically, this study examines the effect of cyclic softening of clays on the holding capacity. The amount of cyclic softening depends on the cyclic strain amplitude and the number of loading cycles. In this study, these two quantities were estimated by two methods, which are based on site-specific ground response analysis and an empirical model based on Tsai et al. (2014). Subsequently, numerical simulations were performed to evaluate the holding capacity of the drag anchor that were embedded in a softened seabed.