Elmer Discussion Forum

Posted: **24 Jun 2015, 14:43**

Dear Elmer group
Hi
I’m working on a very simple axisymmetric model of tube with Navier-Stokes Solver.
I apply pressure=5000 pa in the inlet and pressure=0 pa in the outlet.
While the case seems really simple, it does not converge. Can you please help me solve this problem?
Thanks, Hamed

Posted: **24 Jun 2015, 15:24**

Hi Hamed,

I cannot help personally since I have never used the NS solver. But I think you should post your case here (mesh and sif files) in order to enable others with NS knowledge to have a look at it.

Matthias

Posted: **24 Jun 2015, 15:58**

Hi Matthias
Here is the test case.
Thanks for your help, Hamed

Posted: **25 Jun 2015, 15:06**

Hi Hamed!
Thetr was no second velosity component given for inlet.
See code below

Code: Select all

Header
  
Mesh DB "." "TubeMesh"

End



Constants

End



Simulation
  
Coordinate System = Axi Symmetric
  
Simulation Type = Steady State
Steady State Max Iterations = 50
Steady State Min Iterations = 2
Output Intervals = 1
Post File = "Stenosis.ep"

End



Body 1
  
Equation = 1
  
Material = 1

End



Material 1
   
Density = 1000.0
   
Viscosity = 0.004
   
End



Solver 1
  
Equation = Navier-Stokes
  
Stabilize = True
  
Linear System Solver = Iterative
  
Linear System Iterative Method = BiCGStabl
  
Linear System Preconditioning = ILU1
  
Linear System Max Iterations = 500
  
Linear System Convergence Tolerance = 1.0e-8
  
Nonlinear System Max Iterations = 10
  
Nonlinear System Convergence Tolerance = 1.0e-5
  
Nonlinear System Newton After Tolerance = 1.0e-5
  
Nonlinear System Newton After Iterations = 20
  
Nonlinear System Relaxation Factor = 0.7
  
Steady State Convergence Tolerance = 1.0e-4

End



Equation 1
  
Active Solvers(1) = 1  
End



! inlet
Boundary Condition 1
  
Target Boundaries = 1

Velocity 1 = 0
Velocity 2 = 1
Pressure = 5000.0
  
End



! outlet
Boundary Condition 2
  
Target Boundaries = 3  
Velocity 1 = 0.0

Pressure = 0.0
  
End






! symmetriy
Boundary Condition 3
  
Target Boundaries = 4  
Velocity 1 = 0.0
  
End

! Wall 
Boundary Condition 4
  
Target Boundaries = 2  
Velocity 1 = 0.0
Velocity 2 = 0.0  
End

Posted: **26 Jun 2015, 23:30**

Hi dmitry
Thanks for your comment. But the inlet velocity is not 1 or anything else prescribed. It's actually a part of solution.
I hope Peter read this post and help me.
Thanks, Hamed

Posted: **27 Jun 2015, 16:47**

Hi Hamed,
I cannot open the attached .rar file in my Ubuntu 14.04 desktop. can you attach it in .gz version (so that it would be convenient for your targeted commenters)?
I am thankful to Dmitry for making the SIF file available on behalf of Hamed. Cheers.

Yours Sincerely,
Anil Kunwar

Posted: **28 Jun 2015, 13:35**

Hi Anil
Thanks for your kind attention.
I attached the .tgz file.
Best regards, Hamed

Posted: **28 Jun 2015, 16:32**

Hi Hamed,
Your convergence issue is defined as:

Code: Select all

  IterSolver: Using iterative method: bicgstab
CRS_IncompleteLU: ILU(1) (Real), Starting Factorization:
CRS_IncompleteLU: ILU(1) (Real), NOF nonzeros:     81226
CRS_IncompleteLU: ILU(1) (Real), filling (%) :       137
CRS_IncompleteLU: ILU(1) (Real), Factorization ready at (s):     0.00
     1 0.1124E+05
       2 0.7514E+04
       3 0.5889E+04
       4 0.1708E+05
       5 0.3866E+04
       6 0.2429E+04
       7 0.2580E+04
       8 0.2275E+04
       9 0.3035E+04
      10 0.1031E+06
      11 0.2049E+04
      12 0.1822E+04
      13 0.2328E+04
      14 0.1327E+04
      15 0.1211E+04
      16 0.1222E+04
      17 0.1139E+04
      18 0.1130E+04
      19 0.1147E+04
      20 0.1106E+04
      21 0.1089E+04
      22 0.1182E+04
      23 0.1358E+04
      24 0.1402E+04
      25 0.1570E+04
      26 0.1381E+04
      27 0.1409E+04
      28 0.6168E+03
      29 0.5025E+03
      30 0.2913E+03
      31 0.3302E+03
      32 0.1333E+03
      33 0.1059E+03
      34 0.1962E+03
      35 0.8856E+02
      36 0.8878E+02
      37 0.9958E+02
      38 0.9659E+02
      39 0.3875E+02
      40 0.3510E+03
      41 0.3105E+03
      42 0.3118E+03
      43 0.3135E+03
      44 0.2634E+03
      45 0.7139E+02
      46 0.6194E+02
      47 0.6374E+02
      48 0.1161E+03
      49 0.5760E+01
      50 0.5687E+01
      51 0.1241E+01
      52 0.1185E+01
      53 0.1287E+01
      54 0.9660E-01
      55 0.1075E+00
      56 0.5053E-01
      57 0.3380E-01
      58 0.2505E-01
      59 0.2436E-01
      60 0.2422E-01
      61 0.1878E-01
      62 0.1883E-01
      63 0.1655E+00
      64 0.4446E-01
      65 0.1493E-02
      66 0.1373E-02
      67 0.1298E-02
      68 0.1621E-02
      69 0.1719E-02
      70 0.4436E-03
      71 0.5970E-03
      72 0.8140E-03
      73 0.1712E-03
      74 0.1372E-04
      75 0.2752E-04
      76 0.2608E-04
      77 0.2598E-04
      78 0.3635E-03
      79 0.3873E-04
      80 0.3631E-04
      81 0.9381E-04
      82 0.7828E-04
      83 0.1010E-03
      84 0.9913E-04
      85 0.9599E-04
      86 0.1026E-03
      87 0.3557E-04
      88 0.3782E-04
      89 0.4027E-04
      90 0.3586E-03
      91 0.8586E-05
      92 0.8552E-05
      93 0.7416E-05
      94 0.6277E-05
      95 0.1689E-05
      96 0.1410E-05
      97 0.1916E-05
      98 0.1727E-05
      99 0.1453E-05
     100 0.1964E-05
     101 0.1968E-05
     102 0.1677E-05
     103 0.3624E-06
     104 0.3147E-06
     105 0.3398E-06
     106 0.3393E-06
     107 0.3394E-06
     108 0.3979E-06
     109 0.3284E-06
     110 0.3265E-06
     111 0.2866E-06
     112 0.2866E-06
     113 0.2835E-06
     114 0.2844E-06
     115 0.2838E-06
     116 0.2838E-06
     117 0.2838E-06
     118 0.2838E-06
     119 0.2838E-06
     120 0.2838E-06
     121 0.2838E-06
     122 0.2838E-06
     123 0.2838E-06
     124 0.2838E-06
     125 0.2838E-06
     126 0.2838E-06
     127 0.2838E-06
     128 0.2838E-06
     129 0.2838E-06
     130 0.2838E-06
     131 0.2838E-06
     132 0.2838E-06
     133 0.2838E-06
     134 0.2838E-06
     135 0.2838E-06
     136 0.2838E-06
     137 0.2838E-06
     138 0.2838E-06
     139 0.2838E-06
     140 0.2838E-06
     141 0.2838E-06
     142 0.2838E-06
     143 0.2838E-06
     144 0.2838E-06
     145 0.2838E-06
     146 0.2838E-06
     147 0.2838E-06
     148 0.2838E-06
     149 0.2838E-06
     150 0.2838E-06
     151 0.2838E-06
     152 0.2838E-06
     153 0.2838E-06
     154 0.2838E-06
     155 0.2838E-06
     156 0.2838E-06
     157 0.2838E-06
     158 0.2838E-06
     159 0.2838E-06
     160 0.2838E-06
     161 0.2838E-06
     162 0.2838E-06
     163 0.2838E-06
     164 0.2838E-06
     165 0.2838E-06
     166 0.2838E-06
     167 0.2838E-06
     168 0.2838E-06
     169 0.2838E-06
     170 0.2838E-06
     171 0.2838E-06
     172 0.2838E-06
     173 0.2838E-06
     174 0.2838E-06
     175 0.2838E-06
     176 0.2838E-06
     177 0.2838E-06
     178 0.2838E-06
     179 0.2838E-06
     180 0.2838E-06
     181 0.2838E-06
     182 0.2838E-06
     183 0.2838E-06
     184 0.2838E-06
     185 0.2838E-06
     186 0.2838E-06
     187 0.2838E-06
     188 0.2838E-06
     189 0.2838E-06
     190 0.2838E-06
     191 0.2838E-06
     192 0.2838E-06
     193 0.2838E-06
     194 0.2838E-06
     195 0.2838E-06
     196 0.2838E-06
     197 0.2838E-06
     198 0.2838E-06
     199 0.2838E-06
     200 0.2838E-06
     201 0.2838E-06
     202 0.2838E-06
     203 0.2838E-06
     204 0.2838E-06
     205 0.2838E-06
     206 0.2838E-06
     207 0.2838E-06
     208 0.2838E-06
     209 0.2838E-06
     210 0.2838E-06
     211 0.2838E-06
     212 0.2838E-06
     213 0.2838E-06
     214 0.2838E-06
     215 0.2838E-06
     216 0.2838E-06
     217 0.2838E-06
     218 0.2838E-06
     219 0.2838E-06
     220 0.2838E-06
     221 0.2838E-06
     222 0.2838E-06
     223 0.2838E-06
     224 0.2838E-06
     225 0.2838E-06
     226 0.2838E-06
     227 0.2838E-06
     228 0.2838E-06
     229 0.2838E-06
     230 0.2838E-06
     231 0.2838E-06
     232 0.2838E-06
     233 0.2838E-06
     234 0.2838E-06
     235 0.2838E-06
     236 0.2838E-06
     237 0.2838E-06
     238 0.2838E-06
     239 0.2838E-06
     240 0.2838E-06
     241 0.2838E-06
     242 0.2838E-06
     243 0.2838E-06
     244 0.2838E-06
     245 0.2838E-06
     246 0.2838E-06
     247 0.2838E-06
     248 0.2838E-06
     249 0.2838E-06
     250 0.2838E-06
     251 0.2838E-06
     252 0.2838E-06
     253 0.2838E-06
     254 0.2838E-06
     255 0.2838E-06
     256 0.2838E-06
     257 0.2838E-06
     258 0.2838E-06
     259 0.2838E-06
     260 0.2838E-06
     261 0.2838E-06
     262 0.2838E-06
     263 0.2838E-06
     264 0.2838E-06
     265 0.2838E-06
     266 0.2838E-06
     267 0.2838E-06
     268 0.2838E-06
     269 0.2838E-06
     270 0.2953E-38
ERROR:: IterSolve: Failed convergence tolerances.

Observation:
i.) Your linear system convergence tolerance setting is 1.0e-8.
ii.)The solver failed to converge in the 270th iteration, when the tolerance jumped from 1.0e-6 (within tolerance) to 1.0e-38 (far smaller tolerance width than the set 1.0e-8).

I express herein my rough guesses:
1. Try changing Linear System Preconditioning tools from ILU1 to others.
2. What is the fineness of your axisymmetric meshes?

For more information, you can view the following posts:
viewtopic.php?f=3&t=3920&p=13729&hilit= ... 5be#p13729
viewtopic.php?f=3&t=3372&p=13061&hilit= ... 5be#p13061

Yours Sincerely
Anil Kunwar

Posted: **28 Jun 2015, 16:45**

Hi Hamed,
1. I changed the keyword "Pressure" in BCs to the keyword "External Pressure" in your solver input file and the solver converged.

Code: Select all

!Inlet
Boundary Condition 1 
...
External Pressure = -1.01e5
...

Code: Select all

!Outlet
Boundary Condition 2 
...
External Pressure = -1.0e5
...

Results

: pressure distribution for external pressure; External_Pressure_P_Result.jpg (40.6 KiB) Viewed 7114 times

: veclocity distribution for external pressure; External_Pressure_v_result.jpg (36.51 KiB) Viewed 7114 times

Yours Sincerely
Anil Kunwar

Posted: **28 Jun 2015, 17:04**

Hi Hamed,
2. I applied Pressure (force) boundary conditions in BCs as:

Code: Select all

! inlet
Boundary Condition 1
  
Target Boundaries = 1
...
Pressure 1 = 30.0
Pressure 2 = 40.0
 ...
End

Code: Select all

! outlet
Boundary Condition 2
Target Boundaries = 3  
...
Pressure 1 = 0
Pressure 2 = 0
... 
End

And, then it converged.

The results are as following:

: Pressure Result; pressure.jpg (37.96 KiB) Viewed 7114 times

: velocity result; velocity.jpg (36.62 KiB) Viewed 7114 times

Please Note that:

Elmer_Models_Manual wrote:Boundary Condition bc id
...
External Pressure Real
An external pressure boundary condition directed normal to the surface.
...
Pressure i Real
A pressure force in the given direction i= 1,2,3 (It has a unit of Newtons/m^2. In Elmer, Force at boundary condition has the unit of N/m^2)
...

Yours Sincerely
Anil Kunwar

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