| 摘要: | 先前的研究指出，歪型海膽是由侏羅紀早期的正型海膽演化而來。牠的生活習性逐漸從原本的海底基質之上演化為潛入泥沙中。相較於正形海膽的五輻對稱，歪形海膽的體軸演化為雙軸對稱。其成功躲過大滅絕事件的能力被歸因於其擁有潛沙的技巧，這也成為歪形海膽在新生代繁盛的重要原因之一。在這個背景下，我們提出了一個問題：為何歪型海膽能夠成功存活？是因為牠具備潛沙的能力，還是由於其獨特的外型構造呢？我們的假設是，歪型海膽獨特的外型可能有助於防止底部的沙子被沖走。若這一研究成功，未來或許能將其應用在減少橋墩局部沖刷的工程領域。
為了瞭解歪形海膽在大滅絕中的生存優勢，本研究以隸屬歪型海膽下綱的
Claviaster libycus作為研究對象，透過實驗和數值模式，探討其獨特外型所產生的局部沖刷效應。實驗方面，利用水槽執行蓄水深度為0.1公尺的潰壩水流來模擬大滅絕時產生的極端水流。數值模式則是使用Splash3D 進行模擬，透過求解Navier-Stokes方程式，結合本研究室開發之非連續雙黏性流模型(Discontinuous Bi-Viscous Model, DBM)，對水體流動和底砂運移之過程進行模擬和分析。
在探討歪形海膽在大滅絕事件中的生存優勢的基礎上，我們進一步將焦點轉向將其研究成果應用於減少橋墩局部沖刷的可能性。在進行實驗時，我們模擬了大滅絕時期極端水流對歪形海膽所造成的沖刷影響。這種模擬不僅有助於瞭解歪形海膽生存的機制，同時也提供了一個可行的思路，即是否能夠將歪形海膽的生存技巧應用在工程領域，特別是減少橋墩局部沖刷的工程挑戰。因此，我們也執行圓柱跟方柱橋墩的實驗和數值模擬，以了解造成局部沖刷之因素。
研究結果顯示當Claviaster libycus的生殖孔指向下游時，馬蹄形渦流並不明顯，確實有助於減少局部沖刷的發生，而這也驗證了本研究提出之假設：海膽從五輻對稱、不會潛沙，演化為雙軸對稱、會潛沙，對於穩定底部沉積物、減少局部沖刷發生是有幫助的。無論是圓柱還是方柱，都伴隨著明顯的局部沖刷，而方柱的沖刷深度尤其劇烈。進一步的分析指出，方柱由於其較大的迎水面積阻礙了水流，導致強烈的向下水流和馬蹄漩渦的形成。為減緩橋墩周圍的局部沖刷，建議應設計具有流線型形狀的橋墩。此外，Claviaster libycus的形態啟示將有望應用於開發橋墩的防護裝置。
;Previous research suggests that irregular echinoids evolved from the early Jurassic regular echinoids. Their lifestyle transitioned from residing on the seafloor substrate to burrowing into sediment. In contrast to the five-fold symmetry of regular echinoids, irregular echinoids exhibit bilateral symmetry. The survival capability of irregular echinoids during mass extinction events is attributed to their burrowing skills, a crucial factor in their prosperity in the Cenozoic era. In this context, a fundamental question arises: What enables the successful survival of irregular echinoids? Is it their burrowing capability or their distinctive morphological features? Our hypothesis posits that the unique morphology of irregular echinoids may aid in preventing the erosion of sediment from the seafloor. If successful, this study could be applied to mitigate local scour around bridge piers.
This study focuses on Claviaster libycus, a member of the irregular echinoid subclass, to understand the survival advantages of irregular echinoids during mass extinctions. We investigate the local scouring effects resulting from its unique morphology through experiments and numerical modeling. Experimental simulations involve dam-break flows with the impoundment depth of 0.1 meters to mimic extreme flow conditions during mass extinction events. Numerical simulations utilize the Splash3D model, solving the Navier-Stokes equations with the developed Discontinuous Bi-Viscous Model (DBM) to simulate and analyze water flow and sediment transport processes.
Building upon the insights gained from exploring the survival advantages of irregular echinoids, our attention shifts to the potential application of these findings to mitigate local scour around bridge piers. Experimental simulations mimic the scouring impact on irregular echinoids during extreme flows typical of mass extinction periods. This simulation not only aids in understanding the survival mechanisms of irregular echinoids but also provides a feasible approach to applying their survival techniques in engineering, particularly addressing the challenge of local scour around bridge piers. Consequently, experiments and numerical simulations are conducted on cylindrical and square column piers to understand the factors contributing to local scour.
The research results demonstrate that when the gonopore of Claviaster libycus is directed downstream, the formation of horseshoe vortices is not prominent, effectively reducing the occurrence of local scouring. This validates the hypothesis proposed in this study: sea urchins evolve from pentaradial symmetry, non-burrowing, to bilateral symmetry, burrowing, assisting in stabilizing bottom sediments and reducing the incidence of local scouring. Both cylindrical and square columns exhibit noticeable local scouring, with the square column experiencing particularly intense scouring depths. Further analysis indicates that the larger water-facing area of the square column hinders the flow, resulting in strong downward flows and horseshoe vortices. To mitigate local scouring around bridge piers, designing piers with streamlined shapes is recommended. Additionally, the morphological insights from Claviaster libycus have the potential for application in developing protective devices for bridge piers. |
