[HMR]

Hi CFX users,

I am doing a transient simulation on stratified environment. I did lots of trial to fix my simulation but it was stopped in the middle of run and showed error.
I understand it may be numerical unstability but i modified my mesh area, discretization scheme etc but I can't overcome the problem. First after 100 time step CFX solver was stopped then it was stoped after 500 time when I modified finally it was stopped after 2500 time step after my third modification in mesh and descritization scheme. Could any body help me to figure out the problem.

I get the following message when CFX solver was stopped :

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 |
| G:/Re200Fr1-5_2740_Working/dp0/CFX-5/CFX/Work1/Fluid Flow CFX_002: |
| |
| 996.trn, 983.trn, 97.trn, 969.trn, 955.trn, 941.trn, 927.trn, |
| 913.trn, 900.trn, 886.trn, 872.trn, 858.trn, 844.trn, 830.trn, |
| 83.trn, 816.trn, 803.trn, 789.trn, 775.trn, 761.trn, 747.trn, |
| 733.trn, 720.trn, 706.trn, 692.trn, 69.trn, 678.trn, 664.trn, |
| 650.trn, 637.trn, 623.trn, 609.trn, 595.trn, 581.trn, 567.trn, |
| 554.trn, 55.trn, 540.trn, 526.trn, 512.trn, 498.trn, 484.trn, |
| 471.trn, 457.trn, 443.trn, 429.trn, 42.trn, 415.trn, 401.trn, |
| 387.trn, 374.trn, 360.trn, 346.trn, 332.trn, 318.trn, 304.trn, |
| 291.trn, 28.trn, 277.trn, 263.trn, 2560.trn, 2546.trn, 2533.trn, |
| 2519.trn, 2505.trn, 2491.trn, 249.trn, 2477.trn, 2463.trn, |
| 2450.trn, 2436.trn, 2422.trn, 2408.trn, 2394.trn, 2380.trn, |
| 2367.trn, 2353.trn, 235.trn, 2339.trn, 2325.trn, 2311.trn, |
| 2297.trn, 2283.trn, 2270.trn, 2256.trn, 2242.trn, 2228.trn, |
| 2214.trn, 221.trn, 2200.trn, 2187.trn, 2173.trn, 2159.trn, |
| 2145.trn, 2131.trn, 2117.trn, 2104.trn, 2090.trn, 208.trn, |
| 2076.trn, 2062.trn, 2048.trn, 2034.trn, 2021.trn, 2007.trn, |
| 1993.trn, 1979.trn, 1965.trn, 1951.trn, 194.trn, 1937.trn, |
| 1924.trn, 1910.trn, 1896.trn, 1882.trn, 1868.trn, 1854.trn, |
| 1841.trn, 1827.trn, 1813.trn, 180.trn, 1799.trn, 1785.trn, |
| 1771.trn, 1758.trn, 1744.trn, 1730.trn, 1716.trn, 1702.trn, |
| 1688.trn, 1675.trn, 1661.trn, 166.trn, 1647.trn, 1633.trn, |
| 1619.trn, 1605.trn, 1591.trn, 1578.trn, 1564.trn, 1550.trn, |
| 1536.trn, 1522.trn, 152.trn, 1508.trn, 1495.trn, 1481.trn, |
| 1467.trn, 1453.trn, 1439.trn, 1425.trn, 1412.trn, 14.trn, |
| 1398.trn, 1384.trn, 138.trn, 1370.trn, 1356.trn, 1342.trn, |
| 1329.trn, 1315.trn, 1301.trn, 1287.trn, 1273.trn, 1259.trn, |
| 125.trn, 1246.trn, 1232.trn, 1218.trn, 1204.trn, 1190.trn, |
| 1176.trn, 1162.trn, 1149.trn, 1135.trn, 1121.trn, 111.trn, |
| 1107.trn, 1093.trn, 1079.trn, 1066.trn, 1052.trn, 1038.trn, |
| 1024.trn, 1010.trn, 0.trn |
+--------------------------------------------------------------------+


+--------------------------------------------------------------------+
| The following user files have been saved in the directory |
| G:/Re200Fr1-5_2740_Working/dp0/CFX-5/CFX/Work1/Fluid Flow CFX_002: |
| |
| mon |
+--------------------------------------------------------------------+


+--------------------------------------------------------------------+
| Warning! |
| |
| After waiting for 60 seconds, 1 solver manager process(es) appear |
| not to have noticed that this run has ended. You may get errors |
| removing some files if they are still open in the solver manager. |
+--------------------------------------------------------------------+


This run of the ANSYS CFX Solver has finished.

I am using following CCL

This run of the CFX-13.0 Solver started at 18:51:18 on 30 Jan 2012 by
user jc218370 on 332Z5Q1 (intel_xeon64.sse2_winnt) using the command:

"C:\Program Files\ANSYS Inc\v130\CFX\bin\perllib\cfx5solve.pl" -batch
-ccl runInput.ccl -fullname "Fluid Flow CFX_002"

Setting up CFX Solver run ...


+--------------------------------------------------------------------+
| |
| CFX Command Language for Run |
| |
+--------------------------------------------------------------------+

LIBRARY:
CEL:
EXPRESSIONS:
S = 0.31856 [K m^-1]
To = 300 [K]
Tst = To +S *Z Coordinate
END
END
MATERIAL: Air at 25 C
Material Description = Air at 25 C and 1 atm (dry)
Material Group = Air Data, Constant Property Gases
Option = Pure Substance
Thermodynamic State = Gas
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 1.185 [kg m^-3]
Molar Mass = 28.96 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1]
Specific Heat Type = Constant Pressure
END
REFERENCE STATE:
Option = Specified Point
Reference Pressure = 1 [atm]
Reference Specific Enthalpy = 0. [J/kg]
Reference Specific Entropy = 0. [J/kg/K]
Reference Temperature = 25 [C]
END
DYNAMIC VISCOSITY:
Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 2.61E-02 [W m^-1 K^-1]
END
ABSORPTION COEFFICIENT:
Absorption Coefficient = 0.01 [m^-1]
Option = Value
END
SCATTERING COEFFICIENT:
Option = Value
Scattering Coefficient = 0.0 [m^-1]
END
REFRACTIVE INDEX:
Option = Value
Refractive Index = 1.0 [m m^-1]
END
THERMAL EXPANSIVITY:
Option = Value
Thermal Expansivity = 0.003356 [K^-1]
END
END
END
END
FLOW: Flow Analysis 1
SOLUTION UNITS:
Angle Units = [rad]
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
ANALYSIS TYPE:
Option = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Automatic with Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 28900 [s]
END
TIME STEPS:
Option = Timesteps
Timesteps = 7.226 [s]
END
END
DOMAIN: Twin Fountain Stratified
Coord Frame = Coord 0
Domain Type = Fluid
Location = B20
BOUNDARY: Atm
Boundary Type = OUTLET
Location = F22.20
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Normal Speed = 0 [m s^-1]
Option = Normal Speed
END
END
END
BOUNDARY: Vent 1
Boundary Type = INLET
Location = F19.20
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 299.9575251 [K]
END
MASS AND MOMENTUM:
Normal Speed = 0.00429 [m s^-1]
Option = Normal Speed
END
END
END
BOUNDARY: Vent2
Boundary Type = INLET
Location = F18.20
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
HEAT TRANSFER:
Option = Static Temperature
Static Temperature = 299.9575251 [K]
END
MASS AND MOMENTUM:
Normal Speed = 0.00429 [m s^-1]
Option = Normal Speed
END
END
END
BOUNDARY: Wall
Boundary Type = WALL
Location = F21.20,F23.20,F24.20,F25.20,F26.20
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Buoyancy Reference Temperature = 300 [K]
Gravity X Component = 0 [m s^-2]
Gravity Y Component = 0 [m s^-2]
Gravity Z Component = 9.81 [m s^-2]
Option = Buoyant
BUOYANCY REFERENCE LOCATION:
Option = Automatic
END
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 1 [atm]
END
END
FLUID DEFINITION: Fluid 1
Material = Air at 25 C
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = Laminar
END
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cartesian
CARTESIAN VELOCITY COMPONENTS:
Option = Automatic with Value
U = 0 [m s^-1]
V = 0 [m s^-1]
W = 0 [m s^-1]
END
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = 1 [atm]
END
TEMPERATURE:
Option = Automatic with Value
Temperature = Tst
END
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = Default
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = Temperature,Velocity
OUTPUT FREQUENCY:
Option = Time Interval
Time Interval = 100 [s]
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
BODY FORCES:
Body Force Averaging Type = Volume-Weighted
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 5
Minimum Number of Coefficient Loops = 1
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Residual Target = 1.E-4
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 13.0
Results Version = 13.0
END
SIMULATION CONTROL:
EXECUTION CONTROL:
EXECUTABLE SELECTION:
Double Precision = Off
END
INTERPOLATOR STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
END
PARALLEL HOST LIBRARY:
HOST DEFINITION: host332z5q1
Remote Host Name = 332Z5Q1
Host Architecture String = winnt-amd64
Installation Root = C:\Program Files\ANSYS Inc\v%v\CFX
END
END
PARTITIONER STEP CONTROL:
Multidomain Option = Independent Partitioning
Runtime Priority = Standard
EXECUTABLE SELECTION:
Use Large Problem Partitioner = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARTITIONING TYPE:
MeTiS Type = k-way
Option = MeTiS
Partition Size Rule = Automatic
END
END
RUN DEFINITION:
Run Mode = Full
Solver Input File = Fluid Flow CFX.def
END
SOLVER STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARALLEL ENVIRONMENT:
Number of Processes = 1
Start Method = Serial
END
END
END
END


Regards

HMR

[ghorrocks]

Why do you say it could be numerical instability? You do not report a floating point error and have not included the residuals.

You have also forgotten the first thing to try when it does not converge - use a smaller time step. Also you have limited it to 5 coeff loops per time step. This should be more like 10 or 20.

[HMR]

Hi Glenn,

Thanks for your reply. In this stratified simulation case I considered 0.0001 residual. I understand what you mean for figure out this problem but I am not familiar about the floating point error.

[ghorrocks]

What makes you think your simulation has a numerical instability?

Also, have you tried smaller time steps?

[HMR]

Hi Gleen,

As I tried to carry on my simulation by changing modification in descretization and mesh but I am unable to find out the solution that's why I think may be problem in numerical instability. As departmnetal CFX license expires day before yesterday I am unable to do any simulation right now. I will modified this case according to your advice and let you know

Cheers

HMR

[HMR]

Glen,

My simulation is working good now. thanks for your response and advice.

Cheers

HMR