## 2 Model Introduction and Verification  
### Hydrodynamic Model  
This paper uses FVCOM to simulate the ocean hydrodynamic forces, which is a prediction model for the ocean hydrodynamic environment in offshore areas and estuaries [29]. FVCOM adopts the finite volume method, uses unstructured triangular mesh to solve the original equation discretely, and encrypts the research area locally. On the one hand, the finite volume method can discretely solve the variables of the original equation. On the other hand, it can ensure efficient calculation when the equation is integrated, which fully uses the respective advantages of the finite element method and the finite difference method [30]. In the Cartesian coordinate system, the governing equations of FVCOMinclude the continuity equation, momentum conservation equation in three directions, temperature and salinity conservation equation, and density equation.  
\[\frac{\partial u}{\partial x}+\frac{\partial v}{\partial y}+\frac{\partial w}{ \partial z}=0 \tag{1}\]  
\[\frac{\partial u}{\partial t}+u\frac{\partial u}{\partial x}+v\frac{\partial u} {\partial y}+w\frac{\partial u}{\partial y}-fv=-\frac{1}{\rho_{0}}\frac{ \partial P}{\partial x}+\frac{\partial}{\partial z}(K_{m}\frac{\partial u}{ \partial z})+F_{u} \tag{2}\]  
\[\frac{\partial v}{\partial t}+u\frac{\partial v}{\partial x}+v\frac{\partial v }{\partial y}+w\frac{\partial v}{\partial z}+fu=-\frac{1}{\rho_{0}}\frac{ \partial P}{\partial y}+\frac{\partial}{\partial z}(K_{m}\frac{\partial u}{ \partial z})+F_{v} \tag{3}\]  
\[\frac{\partial P}{\partial z}=-\rho g \tag{4}\]  
\[\frac{\partial T}{\partial t}+u\frac{\partial T}{\partial x}+v\frac{\partial T }{\partial y}+w\frac{\partial T}{\partial z}=\frac{\partial}{\partial z}(K_{ h}\frac{\partial T}{\partial z})+F_{T} \tag{5}\]  
\[\frac{\partial S}{\partial t}+u\frac{\partial S}{\partial x}+v\frac{\partial S }{\partial y}+w\frac{\partial S}{\partial z}=\frac{\partial}{\partial z}(K_{ h}\frac{\partial S}{\partial z})+F_{S} \tag{6}\]  
\[\rho=\rho(T,S) \tag{7}\]  
Equation (1) is a continuity equation, where \(x\), \(y\), and \(z\) represent the positions in the east-west direction, north-south direction, and vertical direction in the Cartesian coordinate system. \(u\), \(v\), and \(w\) represent the velocity components in three directions in the Cartesian coordinate system. Equations (2)-(4) are momentum conservation in the east-west direction, north-south direction, and vertical direction, respectively, and \(F\) represents the parameter of geostrophic deflection force: \(\rho\) is the density of local seawater and \(\rho_{0}\) is the density of reference position: \(P\) is pressure; \(K_{m}\) is the vertical eddy viscosity coefficient; \(G\) is the acceleration of gravity; \(F_{u}\), \(F_{v}\), \(F_{T}\), and \(F_{S}\) are diffusion terms of momentum, temperature, and salinity in two horizontal directions, respectively. Equations (5)-(7) are the temperature equation, salinity equation, and density equation, respectively. \(T\) is temperature, \(S\) is salinity, and \(K_{h}\) is the vertical diffusion coefficient of turbulent kinetic energy.  
In the actual simulation process, the natural seabed terrain is often uneven. In order to avoid the false flow and diffusion caused by the rough bottom of the model, it is necessary to transform the \(\sigma\) coordinate vertically to smooth the bottom.  
\[\sigma=\frac{z-\xi}{H+\xi}=\frac{z-\xi}{D} \tag{8}\]  
Equation (8) is the conversion between the \(\sigma\) coordinate and Cartesian coordinate, where \(z\) is the specific position of the Cartesian coordinate system or the height of the water surface relative to the still water, \(H\) is the distance from the reference surface to the seabed, and \(D\) is the height of the total water column. Under the condition of this coordinate system, the variation range of \(\sigma\) is from 0, indicated by seawater, to \(-1\) at the bottom of the ocean, which avoids the unevenness of the bottom in the original Cartesian coordinate system.