Learning Forum

[Ayelet]

Hi,

I have compered two input DAT files for AQWA , I don't find any difference between them, yet the output is deferent.

The model is a simple box that I created using Matlab and the deference that I get between the two files is that one box is starting from Z=0 and the other id starting somewhere lower (Z=-z).

I don't know how to continue and how to understand the problem since the only communication with AQWA is that DAT file which I can not see the deferent in.

The first:

[Yu Bi]

Hi, when the waterline height is different, the results will be different. You can check the ZLWL data record in the DAT file to see the waterline height on your structure.

[Ingrid Machecler]

To second Yu's comment, I would recommend you thoroughly check the difference between your 2 DAT files. There are small software applications which come in very handy to compare human readable files (such as text files). Meld in one of them. Google "file comparison tools ".

[Ayelet]

Hi, first of all thank you all for the response.
I already compared the files with comparison tool online, and I can't find any important difference. The few that came out were deferent y coordinates for some of the points due to change in the the mesh. In addition to that, I saw specifically that there are nodes with coordinate of Z=0 in the file but still the water line seems above.
I created the box around the main axis that is why I expected to see the elements as I ordered in the file. is there any chance that the periods of the waves I input can effect which elements I see in AQWAGS? It sounds far fetched but I noticed that sometimes when I change them I get a "normal picture" ..

[Yu Bi]

Hi, are all the nodes' z values the same between the two models? Are the nodes with the coordinate of z=0 used in the diffracting elements (i.e., DIFF TPPL or DIFF QPPL element)? What are the ZLWL data record values of the two models?

[Ayelet]

The elements are DIFF QPPL and I didn't define ZLWL as I thought that the water line define by the global axes-Z origin.

[Yu Bi]

What about the ZCGE data record? Do you have it in your DAT file? Which type of analysis/job is defined in the DAT file? Can you test adding in the ZLWL data record and give 0 value to it if the ZCGE data record is not defined?

[Ayelet]

ZCGE data record are both -12.1 and the analysis type is LINE.

[Yu Bi]

Hi, in the model's locate cooridate system, is the location of the centre of gravity the same?

[Ayelet]

Hi I Don't know how to check things in the local coordinate system. But I tried to wright the code again and I noticed that when there are errors and the simulation is not done the model is coming out OK but when the simulation run through to 100% the model jumps down under the water line.
Is there something that I can change like that the locations in the end of the simulation?
Thanks Ayelet.

[Yu Bi]

The adjustment of the ship position based on the ZCGE data record value happens during the program is running. So from what you observed, the centre of gravity of the two models must locate at different positions with respect to the ship surfaces, but your ZCGE value is the same, so they are moved to different positions. So either you can adjust the ZCGE value to make the drafts of the two models match (after run) or instead use the same ZLWL data record for the two models.

[Ayelet]

Hi again :) the problem is solved !
It was an error in the COG calculation... I knew it must be something simple .
Thank you for helping ! it is not easy understanding a problem from the "outside"
Thanks Ayelet.
P.S. : is there an AQWA course online I can take? My final project is based on AQWA simulation and I would like to know it better.

[Yu Bi]

Glad the problem was solved. Currently, we don't have Aqwa official training courses for students but we have it for the paid customers. So, you could request your university to get the Aqwa training materials via the Ansys customer portal.

[Ayelet]

OK I will try to get that option.
Thank you!