[joshcouch]

Hi,

I'm trying to model wave-breaking over a slope using STAR CCM+, using Cnoidal VoF waves.
My problem is that I'm not sure what water depth to specify for the waves. I initially tried to write a field function that calculated water depth throughout the tank as a function of x-position, but it seems to only accept a constant input. Should I set the water depth to the depth at which I expect it to break (or slightly deeper to prevent it breaking straight away, but whilst maintaining a shallow-water wave profile)? Am I correct in thinking that the way the wave 'feels' the bottom is through the no-slip condition set on that bottom? Should I be able to see the wave 'shoaling' as it gets shallower?

Thanks in advance,

Josh

[JB1989]

You should specifiy the water depth where the wave are initialized. If you are using a velocity inlet, simply adjust the water depth value to this depth. The wave shoaling should happen automatically provided your spatial and temporal resolution is fine enouigh to capture these effects.

[joshcouch]

Thanks JB, does the mesh need to be fine only in the area where I expect the water surface to be? Or should I make sure it's fine along the bottom too so as to capture bottom effects? Or should it be equally fine all over? Your help is much appreciated.

[JB1989]

Mesh refinements for wave is most important in region of the free surface (vertical and horizontal dimension). There are some recommendations like 80-100 cells per wavelength and 20 cells per wave height. If you want to model breaking waves you need a very fine mesh where the breaking accours. You can first do a check with a quasi 2D mesh (a 3d mesh with only one cell in thickness dimension) and see if everything works fine.

[joshcouch]

Ok, thanks!

[cesa]

Originally Posted by JB1989

Mesh refinements for wave is most important in region of the free surface (vertical and horizontal dimension). There are some recommendations like 80-100 cells per wavelength and 20 cells per wave height. If you want to model breaking waves you need a very fine mesh where the breaking accours. You can first do a check with a quasi 2D mesh (a 3d mesh with only one cell in thickness dimension) and see if everything works fine.

Could you please cite the paper that contains this info?

[Peresvet]

Originally Posted by cesa

Could you please cite the paper that contains this info?

I can only add one thing: if you violate the number of cells per wavelength and its height, then you will have to take into account one more rule. It is a mirror image of this article: the ratio of the wavelength to its height is no less than 18 times. I PERSONALLY SOLVE THIS PROBLEM WITH EITHER AN ADAPTIVE FREE SURFACE GRID OR A MULTISTEP SOLVER. Adaptive grid is good and requires less PC resources. There is a problem with joining with the overset mesh, especially when they are located one after the other inside each other. Refining does not prevent distortion at the boundaries. However, this is new for now and will be better.
Setting the depth is important for all cases where ship behavior and wave formation are studied. I studied this topic on my practical tasks and was convinced that in shallow water a displacement vessel sags and touches the bottom, in shallow water a planing vessel gets on planing easier and gains more speed than in depth, in shallow water the steepness and amplitude of the wave increases and as I walk on a ship, then I encounter all this every day when I go. Star-ccm+ does not give errors in such tasks.