Hi,
I would like to calculate the forces (essentially of drag) on an object. I set up my simulation with a load curve that has 20 load cases. The curve ramps up the value of the fluid moving around the object because I heard that helped the solver find a convergence for the simulation. It seems load cases 0 and 1 are the only ones that ever complete. Load case 0 displays the reaction forces, but since the speed at time 0 is 0, the reaction forces are all 0 as well. Load case 1 shows velocity data but nothing for reaction forces. The Minimum and Maximum values are "Not Available"
Load cases 2 on show nothing for either, and the color scale disappears entirely (as opposed to being blank when I ask for reaction forces on load case 1). When I click the Last Result button, it takes me to load case 1.
Here is the end of the Summary:
**** Prescribed nodal velocities/forces
Node number DOF1 DOF2 DOF3 DOF4
3321 0.00000000E+00 0.00000000E+00 -2.50000000E+02 0.00000000E+00
3322 0.00000000E+00 0.00000000E+00 -2.50000000E+02 0.00000000E+00
3323 0.00000000E+00 0.00000000E+00 -2.50000000E+02 0.00000000E+00
3324 0.00000000E+00 0.00000000E+00 -2.50000000E+02 0.00000000E+00
**** Segregated Scheme Data
Select segregated scheme ................. = T
Solver for momentum equations ............ = Automatic
Solver for pressure equations ............ = Automatic
Velocity relaxation factor ............... = 7.000E-01
Pressure relaxation factor ............... = 5.000E-01
Inertial relaxation factor ............... = 1.000E+00
Apply automatic adaptive parameter control = T
ID of Detect stagnation due to oscillation = 1
The number of equations (U)............... = 289948
The number of equations (V)............... = 289948
The number of equations (W)............... = 287743
The number of equations (P)............... = 303182
**** Turbulence Model Data..................... = Off
**** Proceeding with Equal-Order Segregated Method
**** Iterative Solver Control Information
Global Solver Index = 7
Iterative Solver Selection = 1
EQ.1 PBiCGStab
EQ.2 PGMRes
EQ.3 PBiCG
EQ.4 PCGS
Pre-Conditioner Selection = 1
EQ.1 ILU(0)
EQ.2 SSOR
EQ.3 JACOBI
>>>>>>>> For multi time step interval # 1 <<<<<<<<
Time step number = 1
Current load fraction = 1.000E+00
--End of log
The current load fraction does not look right, but that may be because I set up my load curve wrong. The ID of Stagnation due to oscillation does not sound good either.
Thanks in advance!
Let me know if there is any other information that would be helpful.
This is from the HTML part
Load Curve 1 Index 1 Time | 0 |
Load Curve 1 Index 1 Multiplier | 0 |
Load Curve 1 Index 2 Time | 1 |
Load Curve 1 Index 2 Multiplier | 1 |
Load Curve 1 Index 2 Steps | 1 |
Load Curve 1 Index 2 Max Iterations | 15 |
Load Curve 1 Index 2 Turbulence | 0 |
Load Curve 1 Index 2 Upwind | 1 |
Load Curve 1 Index 2 Residual Type | 1 |
Load Curve 1 Index 2 Residual Tolerance | 0.0001 |
Load Curve 1 Index 2 Increment | 0 |
Load Curve 1 Index 2 Increment Tolerance | 1e-006 |
Load Curve 1 Index 2 Output Interval | 1 |
Load Curve 1 Index 2 Printout | 0 |
Load Curve 1 Index 2 Norm-V Type | 1 |
Load Curve 1 Index 2 Velocity Norm | 0.0001 |
Load Curve 1 Index 2 Norm-P Type | 1 |
Load Curve 1 Index 2 Pressure Norm | 0.0001
|
Did you turn on the UI option to output reaction force? the default is off.
If Yes, please upload log file with extension of .lgf(steady analysis) or .lgu(unsteady analysis).
I did set the UI option, and that's why I was able to see the reaction forces for load case 0 (even though they were all 0)
Here is the .lgf file I found in the solution folder.
I'm also attaching the Summary file.
Thanks for your help!
Philip
hi, Philip
Thanks for post the log file (.lgf), it indicates that the solution is not converged (reached maximal iteration #), that explains why the reaction force are zero.
There are multiple reasons for the solution convergence issue, here are some basic check list.
- Boundary conditions
- Mesh density, quality and boundary layer mesh
- Equation solver options
- Solution relaxation factors.
Sorry, I'm pretty new to this all. Is there any specific settings that you can see that I should change? I had to make the mesh pretty fine in order to make it mesh, so I don't know if that could have made an impact. On a side note, I tried it in Autodesk Simulation CFD before trying it in Autodesk Simulation Multiphysics, but it wouldn't mesh sucessessfully there.
I have no idea what the relaxation factors or solver settings should be, so if you could give me some advice on that, or at least point me to a page that explains everything, that would be very helpful.
Thanks for all your help!
For meshing issue, please start another thread to ask.
The solution relaxation factors could be set from
setup menu/Model seup/parameter/solution tab/Formulation >>button/segregated options/relaxation control