The free surface is abnormal after the mesh is thinner

Rong · May 11, 2021, 00:37

Hi guys!
I am calculating the total drag coefficient of a ship in calm water.
Two different grids are used.
The total drag coefficient converges with the coarse grid and the free surface is normal (Figure 1, 2).
But the fine grid is used. The total resistance coefficient of the calculation example does not converge, and the free liquid surface is abnormal (Figure 3, 4).
Can anyone tell me the reason for this?
I put these two case files below.

Rong · May 12, 2021, 04:27

Figure1

Figure2

Figure3

Figure4

pferro · May 15, 2021, 15:10

Hello,

It looks like your are using a too large time step for your fine grid.

Possible solution :
- decrease your time step.
- increase the number of outer correctors
- increase the number of sub cycle for the alpha.water resolution.

Good luck

May 11, 2021, 00:37	The free surface is abnormal after the mesh is thinner	#1
Rong New Member liqianrong Join Date: Jan 2021 Posts: 2 Rep Power: 0	Hi guys! I am calculating the total drag coefficient of a ship in calm water. Two different grids are used. The total drag coefficient converges with the coarse grid and the free surface is normal (Figure 1, 2). But the fine grid is used. The total resistance coefficient of the calculation example does not converge, and the free liquid surface is abnormal (Figure 3, 4). Can anyone tell me the reason for this? I put these two case files below.

May 12, 2021, 04:27	Figure1-4	#2
Rong New Member liqianrong Join Date: Jan 2021 Posts: 2 Rep Power: 0	Figure1 Figure2 Figure3 Figure4

May 15, 2021, 15:10	a bit of help	#3
pferro New Member Paulin FERRO Join Date: May 2021 Location: France Posts: 21 Rep Power: 5	Hello, It looks like your are using a too large time step for your fine grid. Possible solution : - decrease your time step. - increase the number of outer correctors - increase the number of sub cycle for the alpha.water resolution. Good luck

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