An Algorithm for Analyzing Lagrangian Quasi-order Structure of 2D Ocean Current

Abstract

The invention relates to a two-dimensional ocean current Lagrangian coherent structure analytical algorithm. The algorithm is based on a Cauchy-Green right strain tensor, wherein the tensor is obtained in a way that a gradient obtained after particles move for a period of time in a flow field is calculated. Particle movement uses a Runge-Kutta 4 order integration method, and cubic interpolation is adopted for the flow field. In order to improve calculation accuracy, four neighbor points are added on each grid point to calculate the gradient by using a finite difference. The Cauchy-Green right strain tensor is provided with two real eigenvalues, wherein the local maximum value of the large eigenvalue and the local minimum value of the small eigenvalue are seed points of an LCS (Lagrangian Coherent Structure), and the Runge-Kutta 4 order integration is carried out in a non-corresponding characteristic vector field forwards and backwards to obtain a Lagrangian coherent structure. During integration, the direction discontinuity of a character vector is considered. The direction is always kept consistent with the direction of a previous point, and inversion is carried out if the direction differs more than 90 degrees. After one LCS is generated, the LCS seed points in a certain width range of the LCS are set to be ineffective, and an interval between the LCSs is controlled. The Lagrangian coherent structure is an important flow field topological structure, can be effectively applied to the range of ocean current, season-year changes and main flow and branch flow analysis.

Description

technical field [0001] The invention belongs to the field of flow field topology, and in particular relates to a two-dimensional ocean current Lagrangian quasi-order structure analysis algorithm. Background technique [0002] There are two concepts of stable manifold and unstable manifold (stable and unstable manifold) in the time-varying stable flow field. These two manifolds pass through a fixed point with a velocity of 0 in the flow field, and act as a boundary in the flow field: when particles move in the flow field, they will tend to the stable manifold and stay away from the unstable manifold, so that the flow can be The field is divided into different regions. In the unstable flow field, the corresponding concept is Lagrangian coherent structures (LCS), which are divided into attracting LCS and repelling LCS. [0003] The research on S has been developed in the last 20 years. As the dividing line of the unstable field for a certain length of time, the flow through t...

AI Technical Summary

Problems solved by technology

The first type of method is intuitive and simple, and is also used in some ocean current analysis, but its validity lacks strict proof

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