Calculation of Semisubmersible RAOs using Morison Theory

Hi all,

Is it happen that someone of you have any paper or something which emphasises on this issue ? So far I have only found this (pages 89-97 in the attachment) is shown how the heave RAO is calculated, but I was wondering if some more detailed paper exists.

Thanks in advance!

P.S: I know that before the panel method the RAOs for semisubmersibles were calculated only using the morison theory, so I hope that it's explained in some paper.

 

I'd have to read it in more detail but using Morison's equations alone doesn't seem like enough. I usually see it for input forces on, say, 'tube' elements (riser elements, wave forces on certain cable elements, etc) in the hydro program AQWA, but not for more complicated geometries unless this is a specialized application. Indeed the paper table of contents addresses far more complex hydrodynamic phenomena, which is a good thing because otherwise my pet rat could be gunning for my job. She is, by the way, more competent than me most days.

What exactly do you need help with? Are you conducting research?

 

Go read reference 10 of the paper for a start.

Also you may want to get a copy of Mechanics of Wave Forces on Offshore Structures, Sarpkaya & Isaacson, Van Nostrand Reinhold, 1981, ISBN 0-442-25402-4; and Advanced Dynamics of Marine Structures, Hooft, John Wiley & Sons, 1982, ISBN 0-471-03000-7.

I haven't worked with semi-subs since I left school, they were all the rage then...lol....so up until the mid 1980's complete "real" RAO's were determined by model testing after the design had been spotted by a hand calculation. FWIW, make the demi-hulls dominate (i.e. small verticals) and the problem becomes much easier for a hand/automated calculation.

 

Morison Element Tube

Hi!

I'm studying a simple case that is the movement of a cylinder in frequency domain and time domain, considering also the moorings.
I want to put a viscous drag in surge movement, so I modeled a morison element (Tube). I don't know which is the right dimension of this element. For example, I inserted a very small tube con External ratio of 5 mm, thickness of 1 mm e length of 20 m, that is inside of the cylinder. But in this way I have a problem because in frequency domain, AQWA gives me error.
Does anybody know if is right my element morison modeling?

I attached also the file model.

Thank you very much!