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Dynamic mesh using profile

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Old   April 9, 2015, 21:59
Default Dynamic mesh using profile
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sanjeet Limbu
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I am trying to simluate the compression stroke by a piston using 2D axisymetric.
Currently i am trial s fo rthe 2D planner mesh using the dynamic mesh - profile mode, I created the profile by using the time and velocity for 1440 points from matlab taking time step as 0.000041667s.

But I am unable to get exact mesh motion. I got the zone motion correct.
The piston has crevice shape- I made two cellzone- body which defoems and crevice - as moving mesh.

I did the following: Cell zone- crevice .set as mesh motion type, and set write profile- having motion history points which also will be used for rigid bodies
Piston – as moving wall in boundary condition(piston is of two part its inteface with body and crevice both moving)
The dynamic mesh- piston as rigid body- profile selected,
Body- as deforming layering only, unchecked the remeshing and smoothening
Crevice as rigid body- profile selected.

I using the profile define to get the dynamic motion.. average velocity is 9m/s to max 14m/s
But when i using the preview mesh motion I am getting the negative volume error. even i tried to reduce the time step to 4.1667E-8, also getting the same error
Please tell how to do mesh


please help me I am not able to do anything ..
it seems that the crevice part get blocked by the body mesh as seperate and it donot reduce the volume
Attached Images
File Type: jpg dynamic mesh setting+_preview.jpg (47.6 KB, 61 views)
File Type: jpg dynamic mesh setting4.jpg (51.9 KB, 56 views)
File Type: jpg dynamic mesh setting.jpg (43.8 KB, 49 views)
File Type: jpg dynamic mesh setting3.jpg (60.3 KB, 42 views)
File Type: jpg dynamic mesh setting2.jpg (59.3 KB, 34 views)

Last edited by sanjeetlimbu; April 10, 2015 at 22:59.
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Old   April 10, 2015, 02:51
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sanjeet Limbu
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I am getting negative volume error during the dynamic mesh motion preview
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File Type: jpg Orthogonal_0.9_near partition.jpg (38.9 KB, 17 views)
File Type: jpg skewness_0.355.jpg (49.2 KB, 16 views)
File Type: jpg neg_volume error.jpg (45.9 KB, 15 views)
File Type: jpg mesh_negative.jpg (52.8 KB, 15 views)
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Old   April 11, 2015, 09:48
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sanjeet Limbu
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Please share some update on how to make it work....

I tried some simple case by removing the crevice part- just the cylinder- 2D rectangle, then using the edge sizing and mesh mapping... it size as 0.0001 mm.
I was able to do mesh motion preview for very small time step 4.16E-07s.

So the issue seem to be due to the mesh interface between the body and the crevice part at that wedge shape. Can you please tell how to make it work in dynamic mesh motion to avoid negative volume error
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Old   April 19, 2018, 09:49
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Andrés Cimino
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I think that your problem is that you are defining both a sliding mesh and a deforming mesh. As far as I know, that is not possible in FLUENT 18.

A sliding mesh does not change the shape of its cells, but it moves relative to another block of cells (e.g., when you model a turbomachine, using a static block of cells for the inlet and a block of cells fixed to the rotor, see FLUENT's theroy guide). Such meshes can be created using the tab moving mesh in cell zone conditions.


what seems to be happening is that the crevice's mesh is being superimposed to the other one because of its motion.

I gues you need to find a different approach.

Hope it helps
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