I am on a calculation in a FPSO and I am a first timer. I am a bit perplexed on how to combine the structure deflections due to the ship motion with the motion accelerations. could anyone confirm the following load cases ( suppose there is only one P/T and U and D represent acceleration and deflection respectively)

L1 W+P+T
L2 W+P+T+U+D
L3 W+P
L4 L2-L1
L5 L3+L4 (scalar) this case would have to be checked for fatigue as well.

if the above load cases are sound, I would like to know why I had to combine displacement with acceleration and check them as an occasional case. as far as I know displacement is always a secondary load, right?

DNV RP D101 is a very good document.

Regards,

Dan,

thanks for your tip, I think we had the same conversation a while back when I had just started this project; there I had refered to some of the load cases given in APpendix G of DNV D101 and I had been suggested by you or some other chap that the Appendix G was just an `example`. anyway my profound question is , would it be ok to consider the acceleration plus SUS as an occasional case while the deflection due to the acceleration was included in a secondary load case?

cheers

In this case, you know my opinion. The main difficulty is to segregate the effects. This is why some people will use the linear approach. In this case you do not have problems in identifying the type of loads. But you have the other problems (e.g. you can not use gaps, friction and so on)

The other approach is not to consider accelerations and displacements simultaneous. In fact the combined effect of accelerations and displacements, having the same direction, it will not be conservative.

Considering one at the time will allow you to construct proper loadcases.

Your loadcase L4 and L5 contain D so can not be a pure OCC.

Regards,