Learning Forum

[haruroslan]

Good day everyone,

[Mike Pettit]

The warning message '992 NON-DIFFRACTING ELEMENT(S)...' indicates that the structure is being considered as non-diffracting. In the details of the Surface Body object (the one inside the Part which is named as 'Surface Body'), please check that the Surface Type is set to 'Program Controlled' (make sure it is not 'Non-Diffracting').
The hydrostatics calculation does not differentiate between diffracting and non-diffracting elements, so you will get meaningful values in the Hydrostatic report. On the other hand, without any diffracting elements the diffraction calculation is not solving anything, so the RAOs will be zero.
Cheers, Mike

[haruroslan]

Hi Mike! Thanks for the response, I have just checked out my setting it was set as program-controlled as you mentioned, and still provided that error.
Also, I realize, I am getting this yellow box when I try to see the pressure and motion results "992 NON-DIFFRACTING ELEMENT(S) DETECTED WITH > 10% AREA BELOW THE WATER LINE. "-Does this error occur because of my model?
Do hope you could help me out on this!

[haruroslan]

Update I have solved the problem.


I simply separated my model along the waterline and reran the simulation.
Thanks nonetheless for the help!

[Mike Pettit]

Great, glad to hear that it is resolved. At the moment we do need to slice a part at the waterline so that it is made up of separate diffracting (wet) and non-diffracting (dry) surface bodies.
Cheers, Mike

[haruroslan]

Additionally, another error occurs from time to time when I try to include more data in my solutions.
"A problem has occurred while accessing the results. Check that the hydrodynamic output files are not already opened by another program, and contact Ansys support if needed."
Do hope this helps to clarify anyone else with similar problems.
Cheers Sharul Baggio

[Mike Pettit]

Please confirm that you do not have any of the hydrodynamics solver files open in another program (for example, the Aqwa restart file in AqwaGS).
Otherwise, please try closing the Aqwa Workbench editor, and use Windows Task Manager to confirm that there are no stalled instances of AnsysWBU.exe still running. Then re-open the Aqwa editor and try evaluating the results again.
Cheers, Mike

[haruroslan]

I have tried ensuring everything was closed, however unable to fix it.
Still given this error, I even remade the design. However, I was able to solve it without having any hydrodynamics graph added as seen here.
Is there any other way to generate the hydrodynamics graph, since this is causing the error?
Cheers mate!

[Mike Pettit]

That is a strange problem - has this started happening recently, i.e. have you used the software before without encountering this?
There are some alternative approaches you can use:
Read the Aqwa plotting files with the AqwaReader command line utility, which allows you to generate CSV files of Aqwa results. The manual for this is here: AqwaReader Manual (ansys.com)
Display Aqwa graphical results using the legacy AqwaGS software, which allows you to plot, post-process and export Aqwa results. The manual for this is here: Aqwa Graphical Supervisor User's Guide (ansys.com)
I hope this helps!
Cheers, Mike

[haruroslan]

Sorry, I am currently using a student account and won't be able to access those links, as I assume those are under ANSYS Customer Portal Hope there's another way to see it. (Edit: I have solved a way to manually plot it using the data from AqwaGS. Thanks for the tip Mike!)
And yes I have used this software with a similar setting for two separate designs, this error only came up here.

[Mike Pettit]

Sorry - of course you cannot access these help links without a customer number! I'm glad to were able to use AqwaGS anyway.
It is difficult to guess what might be causing the file access issue in your case - but if you have time you could try using Windows Resource Monitor, or the freely-available Process Monitor software, to check.
Cheers, Mike

[lzy080808]

I had the same problem , how can I fix it?

[Mike Pettit]

It is difficult to say what might be causing this issue, as it seems to be machine-dependent - I have certainly never seen it on my own machine. If possible, try running Windows Resource Monitor to see if you can find out which program/process is accessing the Aqwa results files, maybe there is some anti-virus running in the background?
To plot from the Aqwa results files you could try using AqwaGS, which you should find in the Ansys 2022 R1 folder from the Windows Start Menu.
Please let me know if you do manage to determine which process is preventing the Aqwa files from being accessed.
Cheers, Mike

[lzy080808]

Hi ´╝î
Thanks for your reply, I have solved this problem. I just closed all programs and restarted the computer, and finally the results can be calculated normally.
Also, I have a new problem.I just increased the frequency of the previously calculated successful cases in Hydrodynamic Diffration .However, the when I tried to solve for Hydrostatics, it stated that "Aqwa core solver stopped unexpectedly" and "solver aborted", without no explanation why. Right-clicking the error does not tell me where the error is. Please help.

[Mike Pettit]

Please check how much free space there is on your hard disk drive, particularly for the location of the temporary files folder (%TEMP%). Usually, if the Aqwa solver stops without any errors like this, it is because there is not enough space left on the disk. The amount of space required during the calculation also depends on the number of frequencies.
Cheers, Mike

[lzy080808]

Does the number of frequencies have an effect on the accuracy of the response calculation?

[Mike Pettit]

Generally yes, the number of frequencies in the Hydrodynamic Diffraction analysis will affect the accuracy of subsequent Hydrodynamic Response analyses.
Aqwa creates a database of hydrodynamic coefficients for each wave frequency/direction pair, and then interpolates between these coefficients in response calculations, so if you have more points in the database you will get better accuracy in the interpolation. This is particularly important around the natural modes of the structure/system where the coefficients may change rapidly with wave frequency.
If you are limited for disk space then you might try increasing the mesh element size (reducing the number of diffracting elements) a bit, which should allow you to include more frequencies - the memory requirement scales with the square of the number of diffracting elements.
I hope this helps.
Mike

[lzy080808]

Okay, I understand, thank you very much for your reply.