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please help
Posted May 26, 2010, 10:47 p.m. EDT 6 Replies
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hi;
i was modeling limnear flow. but seem to me it looks like trublent one. the water was split every where .also i made the right side as outlet boundary, but as you see the arrow pointing in the opsite side !
any advice please
i was modeling limnear flow. but seem to me it looks like trublent one. the water was split every where .also i made the right side as outlet boundary, but as you see the arrow pointing in the opsite side !
any advice please
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6 Replies Last Post Jun 8, 2010, 3:57 a.m. EDT
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Posted:
1 decade ago
Hi
First note, it's written in the doc, inlet and outlet does NOTmean there is a one-way flow, that depends on your pressure in how it evolves in the model.
Too litle to tell exactly what you have as surprises, do you have any gravity (body load) to help "naturally" separate the fluids ? it could be that the results are correct, but the BC are not 100% as you expect.
Try to go over the settings once more
Good luck
Ivar
First note, it's written in the doc, inlet and outlet does NOTmean there is a one-way flow, that depends on your pressure in how it evolves in the model.
Too litle to tell exactly what you have as surprises, do you have any gravity (body load) to help "naturally" separate the fluids ? it could be that the results are correct, but the BC are not 100% as you expect.
Try to go over the settings once more
Good luck
Ivar
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Posted:
1 decade ago
hi Ivar
i am using 2D Axisumatry because of the buoy move in r axis its creats waves, so i just have only one BC , the outlet only. I try to apsorbe this waves but i couldnt.
I used this eaquation in source/ sinks , in Fz edit :(-9.81*if(phi<0,1.25,1000)). do u have any good ideas ?
i am using 2D Axisumatry because of the buoy move in r axis its creats waves, so i just have only one BC , the outlet only. I try to apsorbe this waves but i couldnt.
I used this eaquation in source/ sinks , in Fz edit :(-9.81*if(phi<0,1.25,1000)). do u have any good ideas ?
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Posted:
1 decade ago
Hi
I'm not a fluid specialist, seldom using that physics (so far I'm restudying the subject to use it too, but my fluidics books ar thick and lengthy and my reading time is very limited)
The way I see your image is that you have lets say water in the lower part (-z) and air in the top part (+z) and then a solid sphere moving down (-z) along r=0 in 2D axi.
Then from my understanding (but I might be wrong) you need some body load on the fluid to keep the "heavier water" in the lower part, if you are not considering yourself high up there, in free space ;) no ?
Then it could be an issue of time and speed (and time steps) that could avoisd those splashes.
Finally, the avoidance of reflections is indeed delicate, in ACDC we have the PML (perfectly matched layers) that mimics an infinitely long boundary, but limited in space so we do not need too many elements to cover it, but I'm not sure how this is done in fluidics, one need something that absorbs the incomong (horizontal in your case) energy.
Jean-Francois Leon answered somebody in one of the trheads about PML and fluidics, but they were referring to theory I'm not familiar with, so try a search on the forum, it could give you some other clues, one of these threads were, but I believe there is a couple other too around this subject:
www.comsol.eu/community/forums/general/thread/5687/
Good luck, and
have fun Comsoling, it's all just plain physics
Ivar
I'm not a fluid specialist, seldom using that physics (so far I'm restudying the subject to use it too, but my fluidics books ar thick and lengthy and my reading time is very limited)
The way I see your image is that you have lets say water in the lower part (-z) and air in the top part (+z) and then a solid sphere moving down (-z) along r=0 in 2D axi.
Then from my understanding (but I might be wrong) you need some body load on the fluid to keep the "heavier water" in the lower part, if you are not considering yourself high up there, in free space ;) no ?
Then it could be an issue of time and speed (and time steps) that could avoisd those splashes.
Finally, the avoidance of reflections is indeed delicate, in ACDC we have the PML (perfectly matched layers) that mimics an infinitely long boundary, but limited in space so we do not need too many elements to cover it, but I'm not sure how this is done in fluidics, one need something that absorbs the incomong (horizontal in your case) energy.
Jean-Francois Leon answered somebody in one of the trheads about PML and fluidics, but they were referring to theory I'm not familiar with, so try a search on the forum, it could give you some other clues, one of these threads were, but I believe there is a couple other too around this subject:
www.comsol.eu/community/forums/general/thread/5687/
Good luck, and
have fun Comsoling, it's all just plain physics
Ivar
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Posted:
1 decade ago
hi Ivar
actualy i am simulating a buoy in swiming pool,this buoy conected to mass. so I change the density for the buoy and add load to obtain the mass effect. I am using phase filed to study that.
what u mean by time step? should I increase it or reduce it ? i have new problem now! the buoy is hitting the ground like there is no fluied and keep sinking down.
I am working in time domain, could it be frequancy domain ?
thanks alot
actualy i am simulating a buoy in swiming pool,this buoy conected to mass. so I change the density for the buoy and add load to obtain the mass effect. I am using phase filed to study that.
what u mean by time step? should I increase it or reduce it ? i have new problem now! the buoy is hitting the ground like there is no fluied and keep sinking down.
I am working in time domain, could it be frequancy domain ?
thanks alot
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Posted:
1 decade ago
hi Ivar
actualy i am simulating a buoy in swiming pool,this buoy conected to mass. so I change the density for the buoy and add load to obtain the mass effect. I am using phase filed to study that.
what u mean by time step? should I increase it or reduce it ? i have new problem now! the buoy is hitting the ground like there is no fluied and keep sinking down.
I am working in time domain, could it be frequancy domain ?
thanks alot
actualy i am simulating a buoy in swiming pool,this buoy conected to mass. so I change the density for the buoy and add load to obtain the mass effect. I am using phase filed to study that.
what u mean by time step? should I increase it or reduce it ? i have new problem now! the buoy is hitting the ground like there is no fluied and keep sinking down.
I am working in time domain, could it be frequancy domain ?
thanks alot
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi
First note, it's written in the doc, inlet and outlet does NOTmean there is a one-way flow, that depends on your pressure in how it evolves in the model.
Too litle to tell exactly what you have as surprises, do you have any gravity (body load) to help "naturally" separate the fluids ? it could be that the results are correct, but the BC are not 100% as you expect.
Try to go over the settings once more
Good luck
Ivar
Hi Ivar,
Could you tell where it's witten in the doc inlet and outlet does not mean there is a one-way flow?
Thanks.
Thanon