deposition sediments

antonio · March 22, 2011, 08:58

Hi

I want to simulate the deposition of sediments in a free surface flow using the lagrangian particle tracking. As I am not interested in what happens in the air I would like to ask if I can use this approach considering only the dispersed phase water (with particles) and ignoring the air?

Thanks a lot

ghorrocks · March 22, 2011, 21:22

If you are talking about sedimentation in a river or something like that you could replace the free surface with a slip wall boundary.

What are you trying to model?

antonio · March 23, 2011, 08:58

Hi.

I basically pretend to see the the effect of a wall in the middle of a channel in the deposition of sediments. I was thinking doing this in a 2d simulation (for now), consider the water as the dispersed phase (with sediments) and to use a slip wall boundary at the top(at the water height), velocity at inlet and a relative static pressure = 0 at outlet. Do you see any inconvenient on this?

Thanks

ghorrocks · March 23, 2011, 17:48

Should work fine, but I have no idea what you are modelling so cannot say for sure.

Keep in mind that the particles will fall out of the flow and simply hit the walls and disappear. They will not build up to form a packed bed, CFX cannot model this.

antonio · April 5, 2011, 05:43

Hi all.I have changed my mind and I am trying to use the ASM model. Basically I have a channel with a specified water height and I want to inject in this channel of clean water a mixture of water+sediments. I want to see the effect of a simple obstacle in the deposition of the sediments. Can someone confirm me some points please:
1) In order to have an initial height of the water and a hydrostatic pressure distribution can I use identical expressions to those of the tutorial free surface over a bump?Cfx will "recognize" the meaning of DownH, UpH, UpPres and DownPres in this application?
2) I have defined a variable composition mixture with water and sediments (the constraint in this case is the water) and the buoyancy reference density = to the density of the water. In the tutorial U-Bend with Algebraic Slip Model is not defined a different density for the sediments(it´s equal to the water density). Why?Should I define explicitly the density of the sediments?
3) How can I see the variation of the deposition rate with time?

Many thanks

March 22, 2011, 08:58	deposition sediments	#1
antonio Senior Member Join Date: Jan 2010 Posts: 110 Rep Power: 17	Hi I want to simulate the deposition of sediments in a free surface flow using the lagrangian particle tracking. As I am not interested in what happens in the air I would like to ask if I can use this approach considering only the dispersed phase water (with particles) and ignoring the air? Thanks a lot

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March 22, 2011, 21:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,931 Rep Power: 145	If you are talking about sedimentation in a river or something like that you could replace the free surface with a slip wall boundary. What are you trying to model?

March 23, 2011, 08:58		#3
antonio Senior Member Join Date: Jan 2010 Posts: 110 Rep Power: 17	Hi. I basically pretend to see the the effect of a wall in the middle of a channel in the deposition of sediments. I was thinking doing this in a 2d simulation (for now), consider the water as the dispersed phase (with sediments) and to use a slip wall boundary at the top(at the water height), velocity at inlet and a relative static pressure = 0 at outlet. Do you see any inconvenient on this? Thanks

March 23, 2011, 17:48		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,931 Rep Power: 145	Should work fine, but I have no idea what you are modelling so cannot say for sure. Keep in mind that the particles will fall out of the flow and simply hit the walls and disappear. They will not build up to form a packed bed, CFX cannot model this.

April 5, 2011, 05:43		#5
antonio Senior Member Join Date: Jan 2010 Posts: 110 Rep Power: 17	Hi all.I have changed my mind and I am trying to use the ASM model. Basically I have a channel with a specified water height and I want to inject in this channel of clean water a mixture of water+sediments. I want to see the effect of a simple obstacle in the deposition of the sediments. Can someone confirm me some points please: 1) In order to have an initial height of the water and a hydrostatic pressure distribution can I use identical expressions to those of the tutorial free surface over a bump?Cfx will "recognize" the meaning of DownH, UpH, UpPres and DownPres in this application? 2) I have defined a variable composition mixture with water and sediments (the constraint in this case is the water) and the buoyancy reference density = to the density of the water. In the tutorial U-Bend with Algebraic Slip Model is not defined a different density for the sediments(it´s equal to the water density). Why?Should I define explicitly the density of the sediments? 3) How can I see the variation of the deposition rate with time? Many thanks