Computational fluid dynamics modeling of fossil ammonoid shells
Computational fluid dynamics modeling of fossil ammonoid shells
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DOI：
10.26879/956
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发表时间：
2020-01-01
影响因子：
2
通讯作者：
Choi, YunJi
中科院分区：
文献类型：
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作者：
Hebdon, Nicholas;Ritterbush, Kathleen A.;Choi, YunJi
我们使用三维（3D）的数值模型来研究在灭绝的菊石头足类动物中发现的一系列壳形状的临界流体动力学特征。在化石记录中，菊石非常丰富，可能是古代海洋生态系统的主要组成部分。尽管它们的化石丰富，但我们缺乏重要的软体遗骸，这使得历史上很难调查这些生物的潜在生活模式和生态作用。通过采用数值工具来研究壳的形态如何影响菊石的流体动力学，我们可以为假设和测试生物体能力随时间的变化奠定基础。为了实现这一目标，研究分两个主要步骤进行。首先，我们应用了一些模拟方法，一个已知的问题，阻力系数的半球，选择最合适的建模方法，是准确和有效的。这些进一步检查对以前的实验结果菊石流体动力学。接下来，我们使用Blender和Zbrush制作了菊石壳的3D模型，其中每个壳模型模拟了特定的菊石化石，最近的鹦鹉螺，或通过系统地改变壳膨胀和脐暴露而创建的理想化壳形式。我们测试的假设，即整体壳膨胀和脐暴露将增加阻力经历了类似大小的菊石壳，因为它通过水移动相对于其他形态。采用ANSYS FLUENT软件进行了计算分析。我们进一步比较我们的模拟结果公布的实验测量菊石化石复制品和活鹦鹉螺的阻力。模拟结果提供的准确度在一个数量级的公布值，在测试范围内的水流速度（1 - 50厘米/秒）。模拟阻力测量结果表明，一阶灵敏度壳膨胀，与二阶效应脐带暴露。较大脐带缆暴露（壳体更渐屈）的影响在低速时最小，但在高速时很大。我们的结论是，整体壳体膨胀和脐带暴露影响单个壳体的阻力系数，因此，影响水动力效率。
We use three-dimensional (3D) numerical models to examine critical hydrodynamic characteristics of a range of shell shapes found in extinct ammonoid cephalopods. Ammonoids are incredibly abundant in the fossil record and were likely a major component of ancient marine ecosystems. Despite their fossil abundance we lack significant soft body remains, which has made it historically difficult to investigate the potential life modes and ecological roles that these organisms played. By employing numerical tools to study how the morphology of a shell affected an ammonite's hydrodynamics, we can build a foundation for hypothesizing and testing changes in the organism's capabilities through time. To achieve this goal, the study was carried out in two major steps. First, we applied a number of simulation methods to a known problem, the drag coefficient of a half-sphere, to select the most appropriate modeling method that is accurate and efficient. These were further checked against previous experimental results on ammonoid hydrodynamics. Next, we produced 3D models of the ammonoid shells using Blender and Zbrush where each shell model emulated a specific fossil ammonoid, recent Nautilus, or an idealized shell forms created by systematically varying shell inflation and umbilical exposure. We test the hypothesis that both the overall shell inflation and umbilical exposure will increase the drag experienced by a similarly sized ammonoid shell as it moves through water relative to other morphologies. ANSYS FLUENT was employed to execute the study. We further compare our simulation results to published experimental measurements of drag on ammonoid fossil replicas and live Nautilus. The simulation results provide accuracy within an order of magnitude of published values, across the tested range of water flow velocities (1 - 50 cm/s). The simulated drag measurements demonstrate a first-order sensitivity to shell inflation, with a second-order effect from umbilical exposure. The impact of a larger umbilical exposure (shells that are more evolute) is minimal at low velocities, but substantial at higher velocities. We conclude that the overall shell inflation and umbilical exposure influence an individual shell's drag coefficient, therefore, influence the hydrodynamic efficiency.