# ship motion analysis

Discussion in 'Software' started by aiix, May 7, 2010.

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### aiixNew Member

hye everybody..this is my second thread. now i am in progress with my final year project. it's about the motion prediction of trawler at sea. in order to do that, i need to determine the suitable formula to predict the behaviour of the trawler and using the MATLAB for analysis the motion. can anybody from here have ideas how to do that.for example the sequence that i should follow,the suitable method.(neglect the resistance)please help me. thank you

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### Tim BSenior Member

I'm fed up with these requests.

What are you in your final year of? It doesn't sound like you're on a Naval Arch course or you would have looked at a minimum of one approximation and a direct solution method for this already.

Do you even have a static stability model yet?

Which motions are you after? the full solution in six degrees of freedom? How are you going to determine coupling, damping, what wave options are you going to include? There are lots of good books about vessel dynamics around, and they all contain many formulae which may be suitable for your task.

We are not in the business of telling people how to do final year projects.

Tim B.

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### LyndonJSenior Member

You need the metacentric heights and the gyradius of rotation for both roll and pitch to do it by hand.

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### conceptiaNaval Architect

hey Tim we must not get fed up with these requests as the prime aim of this forum is knowledge sharing.
Linear wave theory along with a wave spectrum(look for Pierson Moscovitsch spectrum) will be the better input i guess. Radius of gyration(6X6 matrix) is also another input. Your aim must be to calculate the main offset of the vessel, load and motion RAO of the vessel, wave drift forces, added mass, stiffness matrix. I had done a MathCAD software 2 years back for the same, but I lost it while rebooting the PC.

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### frank2526244Junior Member

To predict the ship motion is not an easy task, it calls for strong relevant theory background. Current studies are most based on potential thoery which neglects the viscos effect of the fluid(water). Two major approach are optional, the 2D method and 3D method, and the later is much more popular. If you want to write codes to solve the problem on your own, one year is not enough wether you use MATLAB or other programming languages.

You can refer to Wamit(or other hydrodynamic software eg. Hydrostar Aqwa) User Manual to get more information about the method.

There are lots papers.

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### aiixNew Member

in this case, i need to focus hydrodynamic. i need to culculate the hydrodynamic forces acting on the trawler first.

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Hi Alix ....me too in final year ...doing my project
My project is in shallow water vessel response in an approach channel
i hv estimated siltation & water depth changes in the approach channel & now going to study vessel response in shallow water to get minimum under keel clearance...I m going to use ANASYS AQWA 12.1 ..i hv generated my hull form using FREEship 3.1 & taken it in IGES format to put in AQWA for analysis
AQWA inputs are water depth, mass , VCG, Radious of gyration abt X Y Z axis
Wave climate/directs etc
Plz let me know abt ur project progress
Best Luck

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### yipsterdesigner

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### ssaw005New Member

We need to calculate RAO’s for multiple drafts in AQWA. Is there any way to run batch processing in AQWA?

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