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August 7, 2009, 03:46 
Problem with split option

#1 
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Akshayy Garg
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Hi
I am having problem with splittind certain volumes. Here is the problem: There is a cylindrical reactor of dia 340mm and height 500 mm. In this a solid cubical substrate has to be kept whichis in form of combination of 100 parallel sheets, each of size 200X200X0.3 mm, kept at intervals of 0.2 mm between any two sheets(like a book in a jar). Now I want to split volume of reactor with that of each sheet because sheet is solid cube while reactor is fluid. But gambit is giving me the error for splitting more than one sheet and is crashing. Kindly help. I have to basically remove sheet volume from reactor and also keep the sheet inside. I tried with subtract with retain option that also is not working fine. Plz Help Akshayy Garg Last edited by akshayygarg; August 10, 2009 at 02:07. 

August 10, 2009, 01:13 

#2 
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Maxime Perelli
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Are your sheets full inside your reactor? (when you compare 200x200x0.3 with 133x500, I understand that sheets are also ouside from the reactors. Then you will have problem with the substract)
Maybe I didn't understand
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August 10, 2009, 02:11 

#3 
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Akshayy Garg
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Hi Thanks for reply. Sorry. I entered a wrong diameter. Its 340mm. I have corrected it. Akshayy Garg (IIT Delhi)


August 10, 2009, 03:31 

#4 
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Maxime Perelli
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Try to substract first just one sheet from your volume
And post the error
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December 5, 2013, 08:40 

#5 
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Hi
This is my first question here.Iam simulating the flow over solids(squares).For this, I created a domain(big rectangle) with solids squares inside.I have subtracted the square faces from the big rectangular face.I see the big surface getting distorted after I subtract one particular square face.I have easily subtracted all other faces. How to slove this? 

December 6, 2013, 02:00 

#6 
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Maxime Perelli
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a zoom of interested area may help to understand
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December 6, 2013, 04:42 

#7 
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Thank you Max for the response.
Please look in to the zoomed in view of the previous image thank you 

December 6, 2013, 04:58 

#8 
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Maxime Perelli
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this is just a bug on display (especially with shaded mode turned on)
Turne shaded mode off, and again on. Should be ok To be sure, just mesh the surface and you will see
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December 6, 2013, 06:13 

#9 
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Thank you for the reply.
You are right.I have easily meshed . thank you 

December 20, 2013, 02:18 

#10 
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hi
Iam simulating the flow over solids(squares).For this, I created a domain(big rectangle) with solids squares inside.I gave velocity inlet boundary condition at the entrance and pressure outlet at the exit.I have meshed it and transferred to fluent.I have applied periodic boundary conditions at the inlet making the outlet shadow. I have run the case for different grids with convergence criterion of 106.As I refine the grid the the curve goes flatter.Why is this happening? Which value is to be taken for further analysis?please find attached a pic of the grid independent study result. 

December 20, 2013, 03:13 

#11 
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Maxime Perelli
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please details more: display your model with BC, and also give more detail on your curves: what are you studying with grid independancy?
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December 20, 2013, 10:27 
Grid independent study

#12 
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Thanks for the response.
Please find the following files attached 1.Model with boundary conditions with out mesh 2.Model after mesh generation a.After mesh generation ,mesh is transferred to FLUENT. b.Periodic boundary conditions are applied at inlet making the outlet shadow.Convergence criterion is kept at 106. c.After convergence,a vertical rake exactly at the center of the model is created .Velocity magnitude along the rake is exported to excel sheet. Then the mesh is refined and send to FLUENT and steps (b) and (c) are repeated.I have done this with many(6) times.The velocity magnitude curves go flatter with refinement. If I change my convergence criterion to 107,all curves coincide how coarser or how finer I change my grid. What convergence should I take? Which curve value should I take for my study? I am confused.Why is this happening? Thank you 

December 20, 2013, 14:33 

#13 
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Maxime Perelli
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periodicity BC should be already defined in Gambit. It requires a linked mesh
Do you created it? on the doc file with the mesh, is the square at the center a solid body? If you create a rake exactly at the middle of your model, then it should cross also the solid bodies. And it means your rake should have discontinuities (at solid bodies) Display the velocity distribution around solid.
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December 23, 2013, 07:26 

#14 
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Thanks for the reply.
I did not apply linking the edges in GAMBIT.I have given the periodic boundary conditions in FLUENT.Is there any thing wrong if I follow this way?Now I have given liking the edges and I have to see if there will be a change. 

December 24, 2013, 07:55 

#15 
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Hi Max,
I have applied the edge link and applied the periodic conditions.I have run he case in fluent keeping the convergence criterion as 106.I want to compare the velocity profile.Now I have changed the grid and made so finer and very coarser .The velocity profile exactly overlaps on the reference what ever be the grid size.how to solve this? 

January 6, 2014, 01:39 

#16 
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Maxime Perelli
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First question is: is your periodicity ok
in Fluent you can display your results with periodicity. It can help you to know if your periodicity is well defined. check in Graphics Periodicity Panel > https://www.sharcnet.ca/Software/Flu...436.htm#273992
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January 21, 2014, 01:24 
Concept of periodic conditions

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Hi,
For the same problem mentioned above (flow over the solid particles),I have applied periodic conditions by specifying mass flow rate.Does this mean that I have applied fully developed flow conditions in this small domain? If I have applied fully developed conditions,the value of velocity along the length must not change.(du/dx=0). But in this case ,the velocity variation exists in the small domain but it is cyclic in the big domain.With periodic conditions Am I imposing no variation of velocity in the considered small domain? Thanking You Vijayalakshmi 

January 21, 2014, 01:48 

#18 
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Maxime Perelli
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on your post #12 (second picture), you seem to mesh the solid square.
Why? On your first picture, you displayed your BC. Can you also display the periodic BC
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January 21, 2014, 02:09 
Concept of periodic conditions

#19 
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Thanks for the response.
Please find attached the picture 4.1 which shows the full domain of the flow.The second picture(4.2) shows the region selected for simulation.Initially I meshed the squares region also.Now I have changed it and meshed only fluid region only. There will be a pressure drop in the flow.I want to specify mass flow rate at the inlet. My question is if I apply periodic conditions in fig 4.2,am I imposing fully developed conditions?If so, there will not be any variation in the velocity along the length in fig 4.2(du/dy=0).But what I wanted was the variation in velocity along the small domain,which repeats in the big domain.where am I going wrong? Please clarify. 

January 21, 2014, 02:13 
Concept of periodic conditions

#20 
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I think I did not attach the specified.Please look in to these pics.Domain.docx


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