Simulation Mechanical Forums (Read-Only)
Welcome to Autodesk’s Simulation Mechanical Forums. Share your knowledge, ask questions, and explore popular Simulation Mechanical topics.
cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

Reaction forces in steady fluid flow

5 REPLIES 5
Reply
Message 1 of 6
ptaffet
440 Views, 5 Replies

Reaction forces in steady fluid flow

 

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

 

 

5 REPLIES 5
Message 2 of 6
Joey.X
in reply to: ptaffet

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).

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
Message 3 of 6
ptaffet
in reply to: ptaffet

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

Message 4 of 6
Joey.X
in reply to: ptaffet

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.

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation
Message 5 of 6
ptaffet
in reply to: Joey.X

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!

Message 6 of 6
Joey.X
in reply to: ptaffet

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

Jianhui Xie, Ph.D
Principal Engineer
MFG-Digital Simulation

Can't find what you're looking for? Ask the community or share your knowledge.

Post to forums  

Autodesk Design & Make Report