heave motion acting like a mirror

[akbarin]

Hi

I am doing a validation of spar floating platform against a refrence in ANSYS AQWA. All motions have a great agreement and my only problem is heave motion which is acting like a mirror. Can anyone help me how can I fix that or what can be my mistake?

That would be great if you can help me with that.Thanks, Naghmeh 

[mdti]

Hi @akbrain,

I assume along the horizontal axis your plot is time (s) and vertical axis shows distance in meters.

(1) To my understanding, the heave motions in the plots are shown at the centre of mass (CoM) of the body. So there is a mismatch between the vertical centre of mass of the 'reference' and 'Series 2'.

(2) At the begining of the simulation there could be some transient issue. For example, if you consider platform response after 250 s, the response of 'ref' and 'Series 2' look similar.

I hope your problem will be solved if you correct the first issue. If you have further questions, please post it here, I will try ot answer.

wish you all the best.

[akbarin]

Hi mdti

Thanks alot for your answer. my model and ref COG is the same (0 0 -89). and it is so strange for me that why my model is acting different. It has been a while that I am stuck with this issue. I was wondering that maybe my problem is the connection stiffness, bc it seems that it is not connected with time domain analysis, I turn on beta option and Include Linear Connection Stiffness Matrices in time domain analysis, but still does not see any changes,

Do you have any suggestions for me?

Thanks for your time

[mdti]

Dear @akbrain,

Did you try to find the mean of the both plots and set them as zero. This way you can be able to compare the dynamic part of the both plots. 

Please write here about the outcome. Good luck.