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Modelling underwater sea current

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Old   May 23, 2016, 16:39
Default Modelling underwater sea current
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shaman
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Hi all, i need to model thermal dilution of cold water discharge into seawater.
I have 3 question
1. How to model the seawater current which has a boundary layer like velocity profile... ie max at value A at surface and reduces as it reaches bottom. I have tried to model this as velocity inlet and outlet with same for domain initialization but the steady state analysis converge to a different solution. I need to maintain this current throughout the open sea domain. Can i use source.. if so how to maintain velocity profile.
2. My open sea domain is a hexagon 150m radius .. how to model translational periodics so my body of water represents d sea with underwater current mentioned above.
3. How to introduce scalar variable to track the behavior specific to the cold discharge water
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Old   May 23, 2016, 19:49
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1) You will only get your intended velocity when you set the simulation up such that it gives the profile - in other words you have an appropriate turbulence model, turbulence conditions and other variables. So if you don't get the right profile it is because you have not set the model up such that it gives you the profile.

2) Make the matching parallel faces translational periodic pairs. So you will have 3 pairs for your hexagon.

3) Simple way: use an additional variable with convection and diffusion. But this will not account for the variation in material properties due to the difference in composition. If you want to account for this (to model things like the density difference due to salinity content) then use a multicomponent mixture.
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Old   May 23, 2016, 19:55
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Tqvm.. ghorrocks..
The sea current i m looking to model is less complicated as compared to prevailing sea current with the earth movement..
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Old   May 23, 2016, 19:57
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I need a body of water moving at a velocity profile of my making vs depth.
The profile is from metocean study so it is reasonably accurate... and below 0.8ms-1.
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Old   May 23, 2016, 19:59
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Isnt it possible to introduce a source term to that body of water... n the discharge water resolved as normal
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Old   May 23, 2016, 23:57
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Yes, you can apply a source term. But if you apply a source term everywhere it will probably interfere with the flow around the region of interest to you. It could be better to put the source term on the periodic face only to pull the velocity to the profile.

If you know the velocity profile then why not forget about the periodic faces and just use an inlet with a prescribed velocity profile? Then you can specify the the profile easily.
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Old   May 24, 2016, 00:46
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Without source term wont the velocity at the discharge location diffuse due to large seabody. I could initialize the seabody with similar velocity profile. With no slip floor
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Old   May 24, 2016, 00:50
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If you have the correct turbulence model and conditions then the flow should not diffuse too much. This was my first point in the first post - you should try to make the physical model correct first, and then the need for a source term to enforce the desired velocity profile is greatly reduced.
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Old   May 24, 2016, 01:30
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Only have metocean data as ref for velocity profile.. have to make do with source term .. can the source term be velocity with function of height....and initialize sea body similarly
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Old   May 24, 2016, 06:26
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I do not understand what "metocean data as ref for velocity profile" means.

Yes, a source term can be a function of height (or just about anything else for that matter).
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Old   May 24, 2016, 07:38
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Metocean is d oceanographic study.. simulation conducted to simulate design criteria for specific return period ranging from 10... 50... 100 and in between.... it returns the most probable value with lowest potential of being exceeded
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Old   May 24, 2016, 07:38
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Anyhow.. fluent has a function of fixed velocity... is this applicable
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Old   May 24, 2016, 20:06
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I do not know what the fluent fixed velocity function means. Please explain what it does.
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Old   May 24, 2016, 20:09
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It fixed the velocity in a particular domain.... feedback from support.. need to verify this and seek equivalent in cfx
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Old   May 25, 2016, 01:54
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If you fix the velocity field then there is no point doing CFD as the velocity is fixed.

You can fix the velocity using a source term in CFX.
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Old   May 25, 2016, 02:03
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Thnks sir... wil explore and revert...
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Old   May 30, 2016, 06:21
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you should use a velocity profile at the inlet boundary using profile BC'S option in CFX. or create a user function for changing inlet velocity against depth. See the post non uniform velocity at inlet.
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