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-   -   Wave simulation in CFX (https://www.cfd-online.com/Forums/cfx/85990-wave-simulation-cfx.html)

solimcfd March 11, 2011 03:53

Wave simulation in CFX
 
Hi, I am simulating waves in CFX by specifying an inlet velocity profile obtained from linear wave theory. The waves I make start off nicely but then suffer substantial damping as they move along the grid. I have read some papers and this damping seems to be a common problem, but not to the same extent as in my simulations. Any ideas what this is due to? Is CFX capable of modelling such waves?

ghorrocks March 11, 2011 05:42

Yes, CFX should be capable of modelling waves with little dissipation.

Check your simulation is well converged, your mesh quality is good and you are running second order space and time differencing. For spacial differencing I would use hybrid with a blend factor of 1.0 as that is pure second order with no highly dissipative first order.

solimcfd March 16, 2011 18:46

I have done all of that but I am still experiencing excessive dissipation. Any other ideas on what i could do?

ghorrocks March 18, 2011 07:25

That's the basics covered, so time to start looking a bit deeper. Lots of things to look at. Here's a few ideas to start you off:
1) single versus double precision
2) free surface sharpening algorithm
3) mesh quality (have you tested on a hex grid with aspect ratio 1?)
4) mesh size
5) time step size

solimcfd March 18, 2011 07:47

Ok, so I'll have a look at these aspects! Thanks for the advice. I really appreciate it.

sorenasrn August 21, 2012 16:59

Wave Modeling in Ansys CFX
 
Hi
I need to generate wave in ansys cfx, but how can i model it???????
plz Help me

ghorrocks August 21, 2012 19:31

Do the free surface over a bump CFX tutorial.

sorenasrn September 5, 2012 12:05

Quote:

Originally Posted by ghorrocks (Post 378064)
Do the free surface over a bump CFX tutorial.

very thank 4 your advise.
i did this example, but i don't know how to simulate wave.

sorenasrn September 21, 2012 19:29

Tank Modeling
 
Hi
I want simulatie a tank that has 1.5 m height and 1m of it cover with water in ansys cfx. How can i do it?
Please Help

ghorrocks September 24, 2012 20:39

You have to adapt the tutorial example to your case. You can describe your wave with a CEL expression or other function. If you do not know how to do this then do more tutorials to learn CEL and other general functions.

Niru October 3, 2012 13:37

Regarding waves
 
I want to models waves in CFX or fluent. Can I get any tutorial file to do this?

evcelica October 3, 2012 15:57

Did you guys all just get the same homework assignment?

sorenasrn October 4, 2012 05:13

Quote:

Originally Posted by Niru (Post 384762)
I want to models waves in CFX or fluent. Can I get any tutorial file to do this?

I hadn't tutorial file.
but for wave simulation there are two main method:
1- velocity profile (u,w) in inlet
2- Inlet motion

sorenasrn October 4, 2012 05:30

Quote:

Originally Posted by Niru (Post 384762)
I want to models waves in CFX or fluent. Can I get any tutorial file to do this?

I hadn't tutorial file.
but for wave simulation there are two main method:
1- velocity profile (u,w) in inlet
2- Inlet motion

mystar November 29, 2012 06:50

Quote:

Originally Posted by sorenasrn (Post 384851)
I hadn't tutorial file.
but for wave simulation there are two main method:
1- velocity profile (u,w) in inlet
2- Inlet motion


Dear Sorenasrn !
Could you tell me more about making vWave by applying velocity in inlet,.. i have already tried many time but no result...

Brg

m.khatoonabadi October 22, 2015 03:02

Wave generation
 
Hi friends
I am trying to simulate a surface wave in CFX, but I do not know how I can generate a wave.
As far as I know we must write an expression( For example eta=a*sin(bt-cx)) and use it as an inlet velocity but I do not know how exactly?Is there any tutorial?

Best Regards

ghorrocks October 22, 2015 05:38

It is straight forward, just set the inlet velocity to your CEL expression. There are many examples of using CEL expressions in the CFX tutorials.

You can also do this with moving mesh (make an end wall move to generate waves) or with an initial condition (have a blob of fluid initially above the water level which splats down) or even a mass source term (to generate and consume fluid). There are lots of ways to do it.

highorder_cfd October 22, 2015 11:27

Hi All

Just to let you know (if you do not already know it), that in Fluent there is an open channel model with wave boundary conditions already implemented (from airy first order theory till 5th order theory). I hope this helps.

To give you an idea
http://www.ansys.com/Products/Simula...mpact+Analysis

m.khatoonabadi November 23, 2015 05:52

Hi
I am going to simulate a surface wave on a submarine. I am using the CFX software. For simulating the wave I want to utilize the velocity inlet way. Based on my wave profile the u and w velocities are uvel=exp(0.4z)*sin(2t) and wvel=exp(0.4z)*cos(2t). The mean velocity of water is 5 m/s.The length of the domain is 75 meters so I need 15 seconds ( 5*15=75) to ensure the created wave reaches to the outlet. I have some questions:

1- For input velocities I must use u=5+uvel and w=wvel and v=0???????

2= During simulation I set the timestep equal to 0.002. About 1.2 second, the simulation diverges because of the great change in w velocity. So if I use 0.001 as its timestep it takes about 2 weeks :confused:. What should I do?
Isn't 0.001 too small?

Tnx

ghorrocks November 23, 2015 06:07

1: That would seem to make sense.

2: These FAQs discuss the general approach in these situations: http://www.cfd-online.com/Wiki/Ansys...gence_criteria and http://www.cfd-online.com/Wiki/Ansys...do_about_it.3F


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