[john881129]

Hi everyone! I got stuck in solving a 2-way FSI problem for my Final Year Project. Hope someone could please help me with it...
The project is to simulate the fluid flow around a 3D wing with a morphing wing structure installed. The final objective is to obtain the stress distribution in the mechanism. Before solving the real problem, I was planned to do a validation case to obtain a valid method. For the validation case, I chose a 3D straight wing with a NACA 0012 airfoil. In this case, CFX and Transient Structural are chosen as the CFD and structure solvers respectively. I've tested the problem settings on a simple cuboid in the case which the solver ran properly and was able to generate reasonable results. However, when I apply the same settings on my wing, the solver always terminated without any results generated. As shown in the CFX solver report, there are some problems with the mesh quality. However, I really cannot figure out the problem by myself... Could anyone please give me some suggestions that may help me to improve the mesh? Or are there any external meshers (like ICEM) that could be used for such a 2-way FSI problem?
(p.s. the attachment shows my previous mesh of the fluid field.)
Thanks and Best Regards,

[mvoss]

hi,
i am currently working on a quiet similar problem. what error shows up if the solver is crashing ?
i generally would suggest a hex-mesh since very fine tet/prism-elementation at the wing would cause very bad angles if the wing is moving.

neewbie

[john881129]

Originally Posted by neewbie

hi,
i am currently working on a quiet similar problem. what error shows up if the solver is crashing ?
i generally would suggest a hex-mesh since with very fine tet/prism-elementation at the wing would cause very bad angles if the wing is moving.

neewbie

Hi neewbie! Thanks for your reply. I'm quite new to CFX and FSI hence I'm not sure about what exactly is the problem in the project... Anyway, the solver report is shown like this (I marked the error messages in red and I made some notes in /*blue*/):

+--------------------------------------------------------------------+
| Job Information |
+--------------------------------------------------------------------+
Run mode: serial run
Host computer: MENTW121 (PID:6456)
Job started: Wed Jan 11 16:35:52 2012

+--------------------------------------------------------------------+
| Memory Allocated for Run (Actual usage may be less) |
+--------------------------------------------------------------------+
Data Type Kwords Words/Node Words/Elem Kbytes Bytes/Node

Real 5405.0 61.07 14.44 21113.4 244.28
Integer 7194.3 81.29 19.22 28102.6 325.15
Character 200.0 2.26 0.53 195.3 2.26
Logical 10.0 0.11 0.03 39.1 0.45
Double 265.5 3.00 0.71 2074.3 24.00
================================================== ====================
Interpolating Onto Domain "Default Domain"
================================================== ====================
Total Number of Nodes in the Target Domain = 88504
Bounding Box Volume of the Target Mesh = 3.57492E-03

Checking all source domains from the source file:
Target mesh is the same as domain "Default Domain".
Start direct copying of variables from domain "Default Domain".
+--------------------------------------------------------------------+
| Variable Range Information |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| Variable Name | min | max |
+--------------------------------------------------------------------+
| Velocity u.Beta | 1.97E-06 | 1.00E+00 |
| Velocity v.Beta | 8.94E-08 | 1.00E+00 |
| Velocity w.Beta | 1.04E-07 | 1.00E+00 |
| Courant Number | 3.22E+01 | 4.50E+03 |
| Mesh Coordinates | 4.61E-19 | 2.24E-01 |
| Effective Density at End of Timestep | 1.18E+00 | 1.18E+00 |
| Density | 1.18E+00 | 1.18E+00 |
| Mesh Diffusivity | 1.00E+15 | 1.00E+15 |
| Volume Porosity | 1.00E+00 | 1.00E+00 |
| Pressure.Gradient | 4.42E-01 | 9.28E+04 |
| Velocity u.Gradient | 1.77E-03 | 1.12E+04 |
| Velocity v.Gradient | 2.32E-02 | 9.47E+03 |
| Velocity w.Gradient | 3.61E-03 | 2.73E+03 |
| Mesh Displacement | 0.00E+00 | 1.99E-08 |
| Total Mesh Displacement | 0.00E+00 | 2.04E-07 |
| Absolute Pressure | 1.01E+05 | 1.01E+05 |
| Pressure | -6.51E+01 | 6.91E+01 |
| Total Pressure | -2.04E+01 | 7.15E+01 |
| Specific Volume | 8.44E-01 | 8.44E-01 |
| Shear Strain Rate | 2.19E-01 | 1.81E+04 |
| Turbulence Eddy Dissipation | 2.28E-01 | 2.05E+05 |
| Turbulence Eddy Frequency | 3.83E+02 | 1.91E+05 |
| Turbulence Kinetic Energy | 1.38E-03 | 1.34E+01 |
| Velocity Correlation uu | 9.96E-03 | 1.56E+02 |
| Velocity Correlation uv | -2.43E+01 | 5.97E+01 |
| Velocity Correlation uw | -1.54E+01 | 3.63E+01 |
| Velocity Correlation vv | 2.72E-11 | 4.90E+01 |
| Velocity Correlation vw | -1.08E+01 | 1.14E+01 |
| Velocity Correlation ww | 0.00E+00 | 2.26E+01 |
| Velocity | 2.66E-01 | 1.30E+01 |
| Dynamic Viscosity | 1.83E-05 | 1.83E-05 |
| Eddy Viscosity | 4.52E-08 | 1.82E-04 |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| CPU Requirements of Interpolation |
+--------------------------------------------------------------------+
Interpolation Step Time Percentage
(secs. %total)
----------------------------------------------------------------------
Tree Setup 1.40E-01 60.0 %
Interpolation 1.56E-02 6.7 %
Miscellaneous 7.80E-02 33.3 %
--------
Total 2.34E-01

+--------------------------------------------------------------------+
| Job Information |
+--------------------------------------------------------------------+
Host computer: MENTW121 (PID:6456)
Job finished: Wed Jan 11 16:35:54 2012
Total CPU time: 2.340E-01 seconds
or: ( 0: 0: 0: 0.234 )
( Days: Hours: Minutes: Seconds )
Total wall clock time: 2.000E+00 seconds
or: ( 0: 0: 0: 2.000 )
( Days: Hours: Minutes: Seconds )

+--------------------------------------------------------------------+
| |
| Solver |
| |
+--------------------------------------------------------------------+


+--------------------------------------------------------------------+
| |
| ANSYS CFX Solver 13.0 |
| |
| Version 2010.10.01-23.02 Sat Oct 2 02:31:59 GMTDT 2010 |
| |
| Executable Attributes |
| |
| single-int32-64bit-novc8-noifort-novc6-optimised-supfort-noprof-nos|
| |
| Copyright 2010 ANSYS Inc. |
+--------------------------------------------------------------------+


+--------------------------------------------------------------------+
| Job Information |
+--------------------------------------------------------------------+
Run mode: serial run
Host computer: MENTW121 (PID:6508)
Job started: Wed Jan 11 16:35:57 2012

Connecting to the following master process:
Host Name : MENTW121
Port Number : 56220

+--------------------------------------------------------------------+
| Memory Allocated for Run (Actual usage may be less) |
+--------------------------------------------------------------------+
Data Type Kwords Words/Node Words/Elem Kbytes Bytes/Node

Real 38370.6 433.55 102.52 149885.1 1734.18
Integer 12594.9 142.31 33.65 49198.7 569.23
Character 3543.7 40.04 9.47 3460.7 40.04
Logical 80.0 0.90 0.21 312.5 3.62
Double 908.0 10.26 2.43 7093.8 82.08

+--------------------------------------------------------------------+
| ****** Notice ****** |
| The Total Centroid Displacement is being reinitialised using |
| the current mesh geometry. |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| Mesh Statistics |
+--------------------------------------------------------------------+
| Domain Name | Orthog. Angle | Exp. Factor | Aspect Ratio |
+----------------------+---------------+--------------+--------------+
| | Minimum [deg] | Maximum | Maximum |
+----------------------+---------------+--------------+--------------+
| Default Domain | 17.0 ! | 64 ! | 13 OK |
+----------------------+---------------+--------------+--------------+
| | %! %ok %OK | %! %ok %OK | %! %ok %OK |
+----------------------+---------------+--------------+--------------+
| Default Domain | <1 2 98 | <1 5 95 | 0 0 100 |
+----------------------+---------------+--------------+--------------+
Domain Name : Default Domain
Total Number of Nodes = 88504
Total Number of Elements = 374292
Total Number of Tetrahedrons = 311528
Total Number of Prisms = 62431
Total Number of Pyramids = 333
Total Number of Faces = 19838
+--------------------------------------------------------------------+
| User Defined Monitor Information |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ****** Notice ****** |
| |
| Monitor points have been defined in a moving mesh simulation. |
| Please note that the points are assigned to vertices located as |
| given below for the initial mesh. During the simulation, the |
| points may be re-assigned to other vertices but the new |
| positions are not reported in the output file. |
+--------------------------------------------------------------------+
Monitor Point: Monitor Point 1
Domain: Default Domain
User specified location (x,y,z) : 9.945E-01, 1.045E-01, 0.000E+00
Assigned vertex location (x,y,z): 1.550E-01, 4.650E-02, 0.000E+00
Distance to specified location : 8.415E-01

Valid variables from output variable list:
Pressure
+--------------------------------------------------------------------+
| Initial Conditions Supplied by Fields in the Input Files |
+--------------------------------------------------------------------+
Domain Name : Default Domain
Absolute Pressure
Courant Number
Mesh Coordinates
Mesh Diffusivity
Mesh Displacement
Pressure
Pressure.Gradient
Shear Strain Rate
Specific Volume
Total Mesh Displacement
Total Pressure
Velocity
Velocity.Beta
Velocity.Gradient
Volume Porosity
+--------------------------------------------------------------------+
| Average Scale Information |
+--------------------------------------------------------------------+
Domain Name : Default Domain
Global Length = 1.5280E-01
Minimum Extent = 9.3000E-02
Maximum Extent = 2.4800E-01
Density = 1.1850E+00
Dynamic Viscosity = 1.8310E-05
Velocity = 9.2781E+00
Advection Time = 1.6469E-02
RMS Courant Number = 1.1615E+03
Maximum Courant Number = 4.5011E+03
Reynolds Number = 9.1752E+04

+--------------------------------------------------------------------+
| ERROR #002100004 has occurred in subroutine Out_Scales_Flu. |
| Message: |
| The Reynolds number is outside of the range expected based on the |
| Option selected for the TURBULENCE MODEL. Check this setting, |
| the values of the properties, mesh scale, consistency of units |
| and solution values in the input file. Execution will proceed. |
+--------------------------------------------------------------------+
/* For this problem, I'm sure that I selected the LAMINAR MODEL and the Reynolds number is far less than the critical transition Reynolds number. I don't know why this error pumped up...*/
+--------------------------------------------------------------------+
| Boundary Condition Data Supplied by External Solver Coupling |
+--------------------------------------------------------------------+

ANSYS Multi-field Solver : ANSYS
CFX Boundary : Wing
CFX Variable : Total Mesh Displacement
ANSYS Interface : 1
ANSYS Variable : DISP
+--------------------------------------------------------------------+
| Checking for Isolated Fluid Regions |
+--------------------------------------------------------------------+

No isolated fluid regions were found.
+--------------------------------------------------------------------+
| ****** Notice ****** |
| |
| The CFX results that are being used to initialise this |
| simulation were generated at a time value that is inconsistent |
| with the Coupling Initial Time value set in the CFX Input File. |
| Please review results carefully. |
| CFX results time : 1.0000E-01 |
| Coupling Initial Time : 0.0000E+00 |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| The Equations Solved in This Calculation |
+--------------------------------------------------------------------+
Subsystem : Mesh Displacement
X-Disp
Y-Disp
Z-Disp
Subsystem : Momentum and Mass
U-Mom
V-Mom
W-Mom
P-Mass

CFD Solver started: Wed Jan 11 16:36:10 2012

+--------------------------------------------------------------------+
| Convergence History |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| Writing transient file 0_CS.trn |
| Name : Transient Results 1 |
| Type : Selected Variables |
| Option : Every Coupling Step |
+--------------------------------------------------------------------+

================================================== ====================
| Timestepping Information |
----------------------------------------------------------------------
| Timestep | RMS Courant Number | Max Courant Number |
+----------------------+----------------------+----------------------+
| 1.0000E-01 | 999.99 | 999.99 |
----------------------------------------------------------------------
================================================== ====================
TIME STEP = 5 SIMULATION TIME = 1.0000E-01 CPU SECONDS = 1.948E+02
(THIS RUN: 1 1.0000E-01 4.368E+00)
----------------------------------------------------------------------
| COUPLING/STAGGER ITERATION = 1 |
----------------------------------------------------------------------
| SOLVING : Mesh Displacement |
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+
| X-Disp | 0.00 | 0.0E+00 | 0.0E+00 | 0.0E+00 OK|
| Y-Disp | 0.00 | 0.0E+00 | 0.0E+00 | 0.0E+00 OK|
| Z-Disp | 0.00 | 0.0E+00 | 0.0E+00 | 6.9 0.0E+00 OK|
+----------------------+------+---------+---------+------------------+


+--------------------------------------------------------------------+
| *** INSUFFICIENT MEMORY ALLOCATED *** |
| |
| ACTION REQUIRED : Increase the real stack memory size. |
| |
| Details : |
| Requested space : 324000 words |
| Current allocated space : 38370576 words |
| Current used space : 17850611 words |
| Current free space : 20519965 words |
| Number of free areas : 108 |
+--------------------------------------------------------------------+
/* It seems that the memory available is more than enough for what is required...*/
Fatal error generated in gCrdVxIp
Message :- FULL : Failed to make a data area for CrdVxIp
gCrdVxIp called by :- get_MVFLOW_ELIP
+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine gCrdVxIp |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. No results file |
| has been created. |
+--------------------------------------------------------------------+
End of solution stage.
+--------------------------------------------------------------------+
| The following transient and backup files written by the ANSYS CFX |
| solver have been saved in the directory |
| C:/Users/wang0537/AppData/Local/Temp/2-Way |
| validation_6048_Working/dp0/CFX/CFX/Work1/Fluid Flow CFX_004: |
| |
| 0_CS.trn |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| ANSYS Solver terminated with return code 3840 |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| The results from this run of the ANSYS solver have been written to |
| C:\Users\wang0537\AppData\Local\Temp\2-Way |
| validation_6048_Working\dp0\CFX\CFX\Work1\Fluid Flow CFX_004.ansys |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| Warning! |
| |
| The ANSYS CFX Solver has written a crash recovery file. This file |
| has been saved as C:/Users/wang0537/AppData/Local/Temp/2-Way |
| validation_6048_Working/dp0/CFX/CFX/Work1/Fluid Flow |
| CFX_004.res.err and may be an aid to diagnosing the problem or |
| restarting the run. More details should be available in the |
| solver output section of the output file. |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| The following user files have been saved in the directory |
| C:/Users/wang0537/AppData/Local/Temp/2-Way |
| validation_6048_Working/dp0/CFX/CFX/Work1/Fluid Flow CFX_004: |
| |
| mon |
+--------------------------------------------------------------------+

This run of the ANSYS CFX Solver has finished.

[mvoss]

according to the numbers the memory should be sufficient.... did you try to change the stack size e.g. to 1.1?

[john881129]

Originally Posted by neewbie

according to the numbers the memory should be sufficient.... did you try to change the stack size e.g. to 1.1?

No I didn't...Is it in the advanced mesh option?

[ghorrocks]

As newbie says, simply increase the memory allocation factors. You can do this on the solver manager under advanced.

Don't worry about the Re number warning. It is a warning, not an error and just a guide. If you are sure your flow is laminar then you have done the right thing.

[john881129]

Originally Posted by ghorrocks

As newbie says, simply increase the memory allocation factors. You can do this on the solver manager under advanced.

Don't worry about the Re number warning. It is a warning, not an error and just a guide. If you are sure your flow is laminar then you have done the right thing.

Thanks Glenn! There are three tabs that contains the option of increasing the memory allocation factor. Which I shall I change? (Sorry for keep asking such silly questions...)

[ghorrocks]

The error message tells you which one is the problem - the real stack. But I would change them all provided you have enough memory to do so. Once you have it running you can reduce them to what is really needed.

[stumpy]

I think he means the Solver, Partitioner and Interpolation tabs. It's the Solver tab you want in this case. Try increasing the Memory Allocation Factor to 1.2 or something similar.

[john881129]

Originally Posted by stumpy

I think he means the Solver, Partitioner and Interpolation tabs. It's the Solver tab you want in this case. Try increasing the Memory Allocation Factor to 1.2 or something similar.

Hi stumpy, I managed to run the solver this time by increasing the Memory Allocation Factor to 1.2. ^_^ However, it seems that there is still a problem in the mesh:
+--------------------------------------------------------------------+
| Mesh Statistics |
+--------------------------------------------------------------------+
| Domain Name | Orthog. Angle | Exp. Factor | Aspect Ratio |
+----------------------+---------------+--------------+--------------+
| | Minimum [deg] | Maximum | Maximum |
+----------------------+---------------+--------------+--------------+
| Default Domain | 23.4 ok | 172 ! | 20 OK |
+----------------------+---------------+--------------+--------------+
| | %! %ok %OK | %! %ok %OK | %! %ok %OK |
+----------------------+---------------+--------------+--------------+
| Default Domain | 0 3 97 | <1 5 95 | 0 0 100 |
+----------------------+---------------+--------------+--------------+

And the Orthog. Angle also seems undesirable... How can I improve these two factors?

[john881129]

Originally Posted by ghorrocks

The error message tells you which one is the problem - the real stack. But I would change them all provided you have enough memory to do so. Once you have it running you can reduce them to what is really needed.

Thanks Glenn~ I managed to run the solver by making these changes~ But it seems that there are still some problems in the mesh (shown above)...

[ghorrocks]

That is just a warning message, your simulation will still proceed. But pay attention to its advice - an expansion factor of 172 is pretty bad and you should try to do a better quality mesh.