1d_hydro.md

One dimensional hydrodynamic model

Explanations of model

For the one dimensional hydrodynamic models, the forces on netting are calculated based on individual twines. The twines are taken as a cylindrical elements. In practice, the force is usually decomposed into two components: normal drag force and tangential drag force (Cheng et al., 2020)

• is the fluid density.

• is diameter of the cylindrical element.

• is the length of the cylindrical element.

• is the undisturbed incoming flow velocity in the upstream of the net panel.

• is the velocity of the structure.

• The unit vectors $ and $ which are used to indicate the directions of forces are defined by the following equations ( is the unit vector of the cylindrical element):

• and are the normal drag and tangential force coefficients in the one dimension hydrodynamic models, respectively. These force coefficients are usually obtained from experiments that approximate the ideal conditions of a cylinder in an infinite flow field.

How to implement in code

Example code:

import hydroModules as hdm

rope = hdm.one_dimensional.line("M4",
                                meshinfo['Lines_rope'],
                                0,
                                caseinfo['Frame']['rope_sec_dia'],
                                caseinfo['Frame']['rope_sec_dia'])

model_index: [string] [-]. To indicate the model function, e.g., 'M1', 'M2', 'M3'.

hydro_element: [list] [-]. A python list to indicate how the lines are connected, e.g.., [[0,1],[1,2],[2,1]]

solidity: [float] [-]. The solidity of netting.

dw0: [float] [m]. The diameter of the physical net twines. It is used for the hydrodynamic coefficients.

dwh: [float] [m]. The hydrodynamic diameter of the numerical net twines. It is used for the force calculation (reference area).