Example 1: [control] [koordina]
Example 1 has an extremely coarse grid, which makes the computational time relatively short. However, this also means that the flow field is not resolved properly around the structure, and the scour depth becomes much smaller than it should be.
Some comments about the data set in the control file for Example 1:
1. The F 7 B option is used. This is an important parameter in reducing the critial shear stress of the particles as a function of the sloping bed. The algorithm has three empirical parameters, given on the F 109 data set. These parameters will affect the shape and depth of the scour hole.
2. The F 16 option is used to determine the bed roughness. The value of this data set should be equal to the effective roughness of the particles on the bed, for example 3 times d90.
3. There are far too few inner iterations specified on the F 33 data set (second parameter). A typical values to get good results is about 100-1000.
4. The transient free surface algorithm is used (F 36 2). This causes increased computational time. If the water surface is fairly horizontal so that its location does not affect the flow field significantly, the computational time can be shortened by removing this data set.
5. The F 56 parameter invokes a sand slide algorithm. The second parameter on this data set will affect the shape and magnitude of the scour hole.
Example 2: [control] [koordina]
Example 2 does not have any parameters for local scour. The example is given to show a much finer grid than Example 1. The grid intersections on the cylinder walls have been generated using a spreadsheet and the formula for x and y coordinates in a circle. The coordinates for the circle have been written from the spreadsheet to a koordina file, and this has been read after generating the initial grid. The same grid intersection points have been fixed by using the W 6 data sets in the control file, and then the elliptic grid generation algorithm has been used. Attraction towards the downstream part of the cylinder has been used.
Note that in this case the W 4 data set has been used to define the cylinder. It is recommended to use the G 13 data set instead, as shown in Example 1.
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