滨海海底边界层对底栖微体化石仿真模拟的影响

doi:10.13745/j.esf.sf.2023.5.32

地学前缘 ›› 2024, Vol. 31 ›› Issue (2): 410-422.DOI: 10.13745/j.esf.sf.2023.5.32

滨海海底边界层对底栖微体化石仿真模拟的影响

张毅恒¹^,²(), 张涛¹, 雍媛媛², 鱼驰洋², 肖巨月¹, 何凯悦², 王邓², 王星³, 王宾¹, 杨晓光², 韩健²^,^*()

1.西北大学信息科学与技术学院, 陕西西安 710069
2.西北大学地质学系大陆动力学国家重点实验室/早期生命与环境陕西省重点实验室, 陕西西安 710069
3.临沂大学生命科学学院, 山东临沂 276000

收稿日期:2022-11-27 修回日期:2023-02-12 出版日期:2024-03-25 发布日期:2024-04-18
通讯作者: *韩健(1973—),男,研究员,主要从事动物门类的起源与寒武纪生命大爆发的研究。E-mail: elihanj@nwu.edu.cn
作者简介:张毅恒(1997—),男,硕士研究生,信息与通信工程专业。E-mail: zhangyiheng@stumail.nwu.edu.cn
基金资助:
中国科学院战略性先导科技专项(B类)(XDB26000000);国家自然科学基金项目(41672009);国家自然科学基金项目(41621003);国家自然科学基金项目(41720104002);国家自然科学基金项目(42172016);国家重点研发计划项目(2023YFF0803601)

Effect of boundary layer on simulation of benthic microfossils in coastal seabed

ZHANG Yiheng¹^,²(), ZHANG Tao¹, YONG Yuanyuan², YU Chiyang², XIAO Juyue¹, HE Kaiyue², WANG Deng², WANG Xing³, WANG Bin¹, YANG Xiaoguang², HAN Jian²^,^*()

1. School of Information Science & Technology, Northwest University, Xi’an 710069, China
2. State Key Laboratory of Continental Dynamics/Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi’an 710069, China
3. College of Life Science, Linyi University, Linyi 276000, China

Received:2022-11-27 Revised:2023-02-12 Online:2024-03-25 Published:2024-04-18

摘要/Abstract

摘要：

计算流体力学CFD(computational fluid dynamics)近年来在古生物学研究中已有大量应用。该方法在研究生物化石的个体形态、器官功能,以及其与生存环境之间的关系方面具有重要意义。目前古生物领域的CFD仿真对象多为厘米级别体型的生物,而对于毫米级别大小的微体生物的仿真则相对较少。区别于厘米级别的宏体生物,底栖型微体生物的生活环境局限于海床上方垂直高度较小的区域,受海底黏性边界层低流速区域的影响更为明显,因而在设置这类化石仿真的水流环境时应当考虑对于边界层流域水体流速以及海床表面地理环境的还原。本文基于随机表面生成的方法,构建了不平坦的滨海海床表面模型,并模拟了水流在海底边界层附近受海床表面地形影响的流动状态;基于获得的仿真流速数据,我们仿真了寒武纪微型底栖刺细胞动物化石Quadrapyrgite在起伏的海床表面环境中四个不同位置的受水流阻力情况。仿真结果显示,近海床表面处的水体流动可形成明显的低流速区域,且低流速区域的厚度随着入口速度增大而变薄。在起伏表面的凹凸区域中,凸起地带的迎水面形成的低流速区域较薄,流速变化较快;而在凸起地带背水面以及凹陷地带形成的低流速区域较厚,流速较缓且易形成涡旋。流速的差异体现在不同位置的Quadrapyrgite的受阻力大小不同上,其差值可达数倍到数十倍。这种量级的受阻力差值可以在毫米级到厘米级尺度上塑造、影响底栖型生物的分布甚至其自身的摄食行为。本文的研究为CFD方法模拟底栖微型化石的生存环境提供了更加深入的思路和方法。

关键词: 底栖微体化石, 计算流体力学, 海底边界层, 傅里叶变换, 随机表面产生方法

Abstract:

Computational fluid dynamics (CFD) has been used extensively in palaeontology in recent years. This method is important for the study of the relationships among individual morphology of fossils, function of organs, and their living environments. Currently, CFD methods in paleontology are mostly applied to simulate centimeter-sized organisms, while there are relatively few simulations on millimeter-sized microscopic organisms. In contrast to centimeter-sized macrofauna, microbenthos lived closer to the surface of the seabed and are more significantly influenced by the low velocity zone of the near-bottom viscous boundary layer, and therefore the reduction of the boundary layer basin environment needs to be taken into account in the simulation of these fossils. In this paper, a new model of an uneven coastal seabed surface is constructed using a random surface generation method, and the flow state of the bottom boundary layer is simulated as influenced by the topography of the seabed surface. Based on the velocity data obtained from this simulation, we carried out another simulation to analyze the drag forces of sedentary Cambrian cnidaria fossil Quadrapyrgite at four varied locations on the undulating seabed surface environment. The results illustrate that the flow near the seabed surface can form a distinct low-flow region, and the thickness of the low-flow region becomes thinner with the increase of the flow velocity. The bottom boundary layer is thinner in the upslope region of the waterward side where the flow velocity varies rapidly, and thicker, by contrast, in the downslope and gully regions of the backwater side where the flow velocity is slower and more prone to vortex formation. The influence of the difference in flow velocity is also shown in the amounts of drag forces of Quadrapyrgite at different locations, which can vary by a factor of 1-10 to several tens. This variation in drag forces can influence the distribution and feeding behavior of different microbenthos at the micrometer-centimeter scale. The work in this paper provides more in-depth ideas and methods for simulating the survival environment of benthic microfossils.

Key words: benthic microfossils, computational fluid dynamics, bottom boundary layer, Fourier transform, random surface generation

中图分类号:

张毅恒, 张涛, 雍媛媛, 鱼驰洋, 肖巨月, 何凯悦, 王邓, 王星, 王宾, 杨晓光, 韩健. 滨海海底边界层对底栖微体化石仿真模拟的影响[J]. 地学前缘, 2024, 31(2): 410-422.

ZHANG Yiheng, ZHANG Tao, YONG Yuanyuan, YU Chiyang, XIAO Juyue, HE Kaiyue, WANG Deng, WANG Xing, WANG Bin, YANG Xiaoguang, HAN Jian. Effect of boundary layer on simulation of benthic microfossils in coastal seabed[J]. Earth Science Frontiers, 2024, 31(2): 410-422.

图/表 9

图1 海底边界层流域在现代海洋中的位置(A,B据文献[10];D据文献[11]) A—海洋沉积相带的划分及滨、浅海空间范围;B—滨海环境波浪传播过程中的波形变化;C—流体力学中的边界层及其子层(斜线区域);D—放大显示滨海海底地形及边界层示意图。箭头长短代表流速大小。

Fig.1 Bottom boundary layer basin in the modern ocean. A and B adapted after [10], D adapted after [11].

图2 不同参数生成的二维随机表面

Fig.2 Two-dimensional random surfaces generated with different parameters A—A=0.1,N=1;B—A=0.02,N=5;C—A=0.008,N=10;D—A=0.004,N=20。

图3 不同参数生成的三维随机表面 A— β=1.9;B— β=1.6;C— β=1.3;D—β=1.0。每个生成的随机表面N=20,A=0.008。

Fig.3 3D random surfaces generated with different parameters

图4 仿真模型的构建 A—边界条件的设定以及仿真域和延长域的网格划分;B—模拟海底表面的网格划分。

Fig.4 Construction of the simulation model

图5 流域底部有Quadrapyrgites固着的仿真模型的构建过程 A—仿真域的生成过程,红框表示选取的海床表面区域;B—Quadrapyrgites模型;C—Q1-Q4在仿真域中位置及其代表区域的示意图。

Fig.5 The process of constructing the model with Quadrapyrgites fixed on the bottom

图6 不同入口速度下的模拟海床表面高度与流速分布俯视图右侧颜色图例代表图片中箭头的速度大小,下方的颜色图例代表模拟海床表面的高度。

Fig.6 Top view of simulated seabed surface height and flow velocity distribution at different inlet velocities. The color legend on the right represents the velocity magnitude of the arrows in the picture and the color legend below represents the height of the simulated seabed surface.

图7 不同入口速度下的模拟海床表面切面的流动形态左列图模拟海底表面的宏观流动,右列图示左列图红框区域的微观流动情况。箭头代表流动方向。每行箭头之间的高度差为0.005 m。

Fig.7 Flow patterns of simulated seabed surface sections at different inlet velocities. The left column shows the macroscopic flow at the simulated seafloor surface, the right row shows the microscopic flow shown in the red boxed area. The arrows represent the flow direction. The height difference between the arrows in each row is 0.005 m.

图8 固着有Quadrapyrgites仿真的可视化结果 A—水流流过Q1-Q4(从左至右)时的流场速度分布;B—Quadrapyrgites在Q1位置的流场速度分布;C—Quadrapyrgites在Q2和Q3位置的流场速度分布;D—Quadrapyrgites在Q4位置的流场速度分布。上方大箭头代表参考水流方向。图中颜色图例显示的流速范围为0~0.01 m·s-1;箭头的大小指示相对的流速大小,每行箭头之间的高度差为0.001 m。

Fig.8 Visualizations of the simulation with Quadrapyrgites fixed

表1 Quadrapyrgites在Q1-Q4所受阻力大小

Table 1 Drag forces of Quadrapyrgites at Q1-Q4

位置	阻力/N	绝对值与最大值(Q1)之比/%
Q1	5.872 8×10^-8	100
Q2	-5.280 5×10^-9	8.991
Q3	-4.085 8×10^-9	6.957
Q4	-1.341 7×10^-9	2.285

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滨海海底边界层对底栖微体化石仿真模拟的影响

Effect of boundary layer on simulation of benthic microfossils in coastal seabed

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