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The problem of convergence of the residual plot in transient model of vessel

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Old   September 8, 2021, 01:58
Default The problem of convergence of the residual plot in transient model of vessel
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Lei Lv
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I constructed CFD transient simulations of human blood vessel to estimate the wall shear stress with turbulence models (k-omega) in CFX. However, no matter how I adjusted the mesh or modified the boundary conditions, convergence failed all the time, and the residual graph is shown in the figure below. How to solve this situation?
Detailed information:
1. The quality of meshes in the vessel were higher than 0.5 and the number of the mesh was about 2 million.
2. The inlet (velocity) and outlet (pressure) condition were based on the normal human measured value in a cardiac cycle, including density and viscosity of blood (constant). The wall was vessel wall which was no-slip.
3. Time duration was a cardiac cycle (0.8s), and timestep was 0.008s.
4. RMS<10e-6
Figures:
rp.png : The residual plot
vessel.png: the model of vessel (reconstructed by CTA)
Attached Images
File Type: jpg rp.jpg (95.4 KB, 10 views)
File Type: png vessel.png (27.6 KB, 11 views)
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Old   September 8, 2021, 03:19
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Frank Weise
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Your vessel size is a little to large. I do not know any creature with 25m vessel diameter . Maybe the right size could solve your problem.
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Old   September 9, 2021, 08:00
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Good catch!!!

Just for context, the largest Francis runner in the world is @11 m in diameter. Not sure about the diameter for the draft tube of such a machine, but I doubt you can fit two runners side by side.
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Old   September 13, 2021, 13:21
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Quote:
Originally Posted by FrankW View Post
Your vessel size is a little to large. I do not know any creature with 25m vessel diameter . Maybe the right size could solve your problem.
Thank you for your point out my defects. The problem has been solved.
Kind regard,
llalra
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Old   September 13, 2021, 13:23
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Quote:
Originally Posted by Opaque View Post
Good catch!!!

Just for context, the largest Francis runner in the world is @11 m in diameter. Not sure about the diameter for the draft tube of such a machine, but I doubt you can fit two runners side by side.
Thank you. I forgot to change my unit. The problem has been solved.
Kind Regards,
llalra
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boundary condition, cfx, convergence, residual, transient simulations

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