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[RanJ]

i have a 2D axisymmetry problem
and i have used the dynamic mesh with the option remeshing and smoothing
the inlet is a pressure inlet ( transient profile)
outlet (pressure 0Pa)
walls ( stationary)
a piston as a rigid body ( with stifness and preload)
i don't know what's wrong ?
any ideas?
thanks in advance

 

 

i get always that error :  WARNING: 53 cells with non-positive volume detected.

Error at host: Update-Dynamic-Mesh failed. Negative cell volume detected.

[RanJ]

i 'll appreciate ur help !!!

any idea could help

[Karthik R]

Hello,

Could you locate where you are seeing these negative cell volumes? Please create 'Cell Registers' for this and post the screenshot.

Also, how are you moving the piston? It is quite possible that your piston movement is quite large. Could you please reduce this and see? Also, could you please use the spring method and try?

Thank you.

Karthik

[RanJ]

the piston is a rigid body , that i have defined as a 1dof (1 translation ) with a preload (-877N) and a stiffness (k =78750N/m)

maybe it's too fast but that's the values i have for this simulation 

In the cell register what should i select ?

[RanJ]

as if it's not doing remeshing at all

[RanJ]

also , the presure in the inlet is a transient profile that increase and atteint 420000 Pa so it's supposed that the piston move to the right due to the pressure force

[RanJ]

there's someone who know how to manipulate those type of problem , i changed to the spring method using 0.1 , 0 , factor but i still have the same error

[Keyur Kanade]

Which version you are using? Please use latest 2020R1. 

What are geometry extents? 

Please reduce max length scale accordingly to say 0.01 or less. 

Change skewness to 0.5. 

The upper wall is very close to the piston. It has only 2 cells in between. If possible increase the gap or refine mesh further. 

Also as Karthik mentioned, your movement is too large. Please check by reducing it. 

Also please check 

Regards,

Keyur

 

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[RanJ]

 

hi , thank u for your answer.

i'm using 2019 R1

i reduce max length scale  0.002 but having the same problem

it's not possible to increase the gap between the wall and the piston , also i have checked those videos before  

 

[RanJ]

the piston should move to the right only 2mm and then it's constrained 

[Keyur Kanade]

Can you please test it with reducing preload. 

Please reduce time step. 

Choose a maximum time step size based on the length of the smallest cell and the maximum expected velocity of the moving boundary. 

Regards,

Keyur

 

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[RanJ]

preload won't change a big thing , i constrained the 1dof to not move to the left w to be able only to move 2mm to the right

the smaller cell size is 5e-4 m

and i i've set the time step : 1e-5 s 

should i reduce it more

 

[Keyur Kanade]

I see that you have transient profile at inlet. 

can you please try simple inlet conditions and check if it works. 

then you can add simple profile. see how it behaves. then you can add transient profile. 

please go step by step. 

Regards,

Keyur

 

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[Keyur Kanade]

Usually take approach as take simplified geometry and boundary conditions. See how simulation goes. It will give you good indication on how input parameters are affecting the results. Then add complexity step by step. 

Regards,

Keyur

 

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