沿海声层析的同化和应用研究

发布时间：2018-04-28 09:04

本文选题：沿海声层析 + 流场反演　；参考：《浙江大学》2017年博士论文

【摘要】：沿海声层析(Coastal Acoustic Tomography,简称CAT)技术相比传统的测流方法,它仅在观测区域外围布置较少的站位即可对近岸快速变化的潮流实现大面积、长时间的同步观测。CAT适用于海湾、海峡和港口等航运繁忙、渔业活动频繁的近岸半封闭海区。CAT观测在站位选取、流场反演等方面仍有许多需要研究和改进的地方。本论文基于逆方法和数据同化方法对CAT的数据进行流场反演,并选取了三个典型的近岸海区(三门湾、舟山和琼州海峡)对潮流结构、余流动力机制等近海潮流动力学问题进行了讨论。论文用集合卡曼滤波方法将CAT数据同化到三角网格的海洋模式中。首先,我们建立了高空间分辨率三角网格,用于拟合近岸复杂的岸线边界;其次,我们通过声线与不规则网格的位置关系建立了传播时间差与模式状态向量在水平方向上的投影关系;最后,我们利用垂向平均的传播时间差数据进行数据同化,得到三维的流场结构。论文利用三门湾CAT观测数据,实现了三角网格的CAT数据同化。数据同化方法得到了 CAT观测区域内部杨礁附近的精细流场结构。数据同化方法得到的流场与三个定点ADCP的平均均方根误差为0.07 m s-1,优于逆方法(0.12 ms-1)和模式模拟(0.17 m s-1)的结果。数据同化方法得到了逆方法无法获得的流速垂向结构,与ADCP在垂向各层的均方根误差范围为0.02 m s-1至0.14 ms-1,同样优于模式模拟的结果(0.08 m s-1至0.27 m s-1)。这些结果表明数据同化方法得到的流场精度最高。进一步的敏感实验结果则表明,数据同化方法在声线数据缺失的情况下比逆方法更为稳定,精度更高。由此可见,相比于逆方法和模式模拟,基于非结构三角网格的CAT数据同化方法在近岸流场反演具有更好的效果。在对近岸非线性潮的研究中,我们利用连续27小时的15分钟滑动平均的舟山峙头洋湾的CAT数据,用逆方法反演得到了观测区域的主要的半日潮(M2)以及由M2产生的非线性潮M4和M6的潮流的水平结构。三者的空间平均的流速振幅比为M2:M4:M6=1.00:0.15:0.11。我们将M2的潮流代入到浅水方程的平流项和底摩擦项,通过理论推导计算得到了理论上M4和M6的潮流。对比观测和理论推导的结果,在水深大于60 m的深水区域,M4与平流项产生的潮流非常接近,表明峙头洋湾深水区域的M4主要由平流项作用产生。而对M6的研究则表明,M6在水深小于20 m的区域主要由底摩擦项的作用产生。我们还讨论了 M4和M6对峙头洋湾的潮流不对称性变形的影响,发现M4在观测区域对潮流的不对称性变形的影响大于M6。我们还利用一个M2周期内的动量方程对峙头洋湾的余流动力机制进行了讨论。结果表明,余水位的压力梯度项和余流的平流项占了潮流的平流项的75%,所以峙头洋湾的余流是由潮流的非线性作用所产生的。在琼州海峡为期15天的CAT观测实验中,我们利用CAT同步观测数据得到了潮流和余流的水平分布,并计算了通过琼州海峡的流量。结果显示,琼州海峡以全日潮为主,O1、K1、M2、S2和MSF五个分潮的流速振幅比为1.00:0.60:0.47:0.21:0.11。余流在海峡北部为西向,在海峡南部转为南向。余流流速在海峡北部区域较大,最大余流流速为西向12.4 cm/s。利用CAT数据估计的流量变化范围为-0.71 Sv到0.86 Sv,余流流量为-0.04 Sv(西向为负)。另外,对观测区域的动量分析结果显示,潮汐调整和海峡两端入口处的水位差对维持西向余流起重要作用。本文利用CAT的观测数据,得到了近岸主要的全日潮(O1和K1)、半日潮(M2和S2)、非线性潮(M4和M6)和余流的空间结构,并讨论了余流和非线性潮的动力机制。由此可见,CAT在近岸潮流的观测上具有独特的优势,可对潮流动力学研究发挥重要作用。
[Abstract]:Coastal Acoustic Tomography (abbreviated CAT) technology, compared with the traditional method of flow measurement, can achieve a large area of fast changing tidal current only in the periphery of the observation area. Long time synchronous observation of.CAT is applicable to the Bay, the Strait and the port and so on, and the close shore half closed to the frequent fishing activities. There are still many areas to be studied and improved in the.CAT observation of the sea area, such as site selection and flow field inversion. The inverse method and data assimilation method are used to invert the flow field of the CAT data, and three typical nearshore sea areas (Sanmen Bay, Zhoushan and Qiongzhou Strait) are selected for the tidal flow structure, the residual current dynamic mechanism and so on. In this paper, the problem of mechanics is discussed. In this paper, the CAT data is assimilated into the ocean model of triangular mesh by using the ensemble Kaman filter. First, we have established a high spatial resolution triangular mesh to fit the complex shoreline boundary of the near shore. Secondly, we establish the propagation time difference and mode through the relationship between the acoustic line and the irregular network lattice. In the end, we use the vertical average propagation time difference data to make data assimilation and get the three-dimensional flow field structure. In this paper, the CAT data assimilation of the triangular mesh is realized by using the CAT observation data of the Sanmen Bay. The data assimilation method gets the fine flow near the poplar reef within the CAT observation area. The mean square root error between the flow field and the three fixed-point ADCP is 0.07 m s-1, which is better than the inverse method (0.12 MS-1) and the model simulation (0.17 m s-1). The data assimilation method obtains the vertical structure of the flow velocity that the inverse method can't obtain, and the mean square root error range of the ADCP in the vertical layers is 0.02 m s-1 to 0.14. MS-1 is also better than the result of model simulation (0.08 m s-1 to 0.27 m s-1). These results show that the data assimilation method has the highest precision of flow field. Further sensitive experimental results show that the data assimilation method is more stable and more accurate than the inverse method in the absence of acoustic line data. Simulation, CAT data assimilation based on unstructured triangular mesh has a better effect on inshore flow field inversion. In the study of near shore nonlinear tide, we use inverse method to retrieve the main semidiurnal tide (M2) of the observational region and the M2 produced by inverse method by using the CAT data of the Zhoushan Shi tou Bay, Zhoushan. The horizontal structure of the flow of the nonlinear tidal M4 and M6. The spatial average velocity amplitude ratio of the three is M2:M4:M6=1.00:0.15:0.11.. We substituting the flow of M2 into the advection term and the bottom friction term of the shallow water equation. The theoretical derivation is used to calculate the tidal currents of M4 and M6 in theory. The results of comparison and theoretical derivation are more than 60 in water depth. In the deep water area of M, M4 is very close to the flow generated by the advection term, indicating that the M4 in the deepwater area of the bay is mainly produced by the effect of advection. The study of M6 shows that M6 is mainly produced by the bottom friction term in the area less than 20 m in depth. We also discuss the influence of M4 and M6 on the asymmetrical deformation of the tidal current in the bay. It is found that the influence of M4 on the asymmetrical deformation of the tidal current is greater than M6.. We also use the momentum equation in a M2 period to discuss the dynamic mechanism of the residual current in the bay. The results show that the pressure gradient term of the residual water level and the advection term of the residual current account for 75% of the current advection term, so the residual current in the bay of Shi tou ocean is a tide. In the 15 day CAT observation experiment of the Qiongzhou Strait, we use the CAT synchronous observation data to obtain the horizontal distribution of the flow and residual flow, and calculate the flow through the Qiongzhou Strait. The results show that the Qiongzhou Strait is dominated by the full day tide, and the velocity and amplitude ratio of the five tides of O1, K1, M2, S2 and MSF is 1.00:0.60:. The 0.47:0.21:0.11. residual current is westward in the north of the Strait and southward in the south of the Strait. The residual current flow velocity is larger in the north of the Strait. The maximum flow velocity is 12.4 cm/s. West to 0.86 Sv using CAT data. The residual flow is -0.04 Sv (West to negative). In addition, the momentum analysis results of the observed area show the result of the momentum analysis. It is shown that the tidal adjustment and the water level difference at the entrance to the two ends of the Strait play an important role in maintaining the westward residual current. In this paper, we use the observation data of CAT to obtain the spatial structure of the main total diurnal tides (O1 and K1), semidiurnal tides (M2 and S2), nonlinear tides (M4 and M6) and residual currents in the near shore, and discuss the dynamic mechanism of the residual and nonlinear tides. Thus, it can be seen that CAT is in the near future. Shore tide observation has unique advantages and can play an important role in the study of tidal dynamics.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P714.1

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