# Seakeeping Analysis Computations

Discussion in 'Software' started by Silic0re, Mar 21, 2010.

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### Silic0reJunior Member

(First, sorry if this is the wrong forum, haven't gotten the layout quite down yet).

Let me explain what I'm trying to do...

I'm tasked with developing a piece of software that determines the environmental capability of a vessel. The software that I have developed can model the required thrust vectors for each thruster (azimuth, tunnel, props/rudders, etc) required to achieve a certain force requirement. What I have to do, is find out at what wind speed the vessel can no longer produce enough power to overcome the environment for arbitrary wind attack angles. It makes it a little easier that I can model the wind/waves/current as coincident forces all acting from the same angle.

I have a spectral model of the wave statistics for various locations around the world, JONSWAP, Pierson-Moskowitz, etc. I'm computing the wind loading forces according to OCIMF's MEG-3 publication, along with the current forces from the same publication. What I'm having problems with is the forces imparted on the vessel due to wave action.

I understand that there are two orders of forces imparted, the first order being oscillatory forces and the second order being the drift force. I need to calculate the drift force in the surge/sway/yaw frame.

So, what would really help out, is if you can point me towards some calculation methods for computing these? I've read about every piece of literature that I can get my hands on, including Fossen "Guidance And Control of Ocean Vehicles", which gives a formula in the time domain, that uses another formula in the frequency domain. I'm not an expert by any stretch (which is why I come here), so any help is greatly appreciated.

I'm thinking I may have to port PDSTRIP from it's wonderful FORTRAN base to something in the modern world, but as many others here have said, it's difficult to understand what the inputs and outputs of PDSTRIP are, and even worse that it's an abandoned project. I keep hearing about programs like SHIPMO from the Canadian Calderock agency, but I can't locate any code listings.

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### Silic0reJunior Member

I should also clarify, this is all for a vessel at zero speed.

Thanks

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### yipsterdesigner

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### Martijn_vEMarine software developer

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### Silic0reJunior Member

Thanks for the replies...

This has to be incorporated into our in-house software, so using a third party package such as maxsurf or seakeeper isn't going to work, which is why I was looking more for implementation specifics rather than software packages. I know utilities such as Maxsurf, SeaKeeper, ShipMo-PC, etc can perform these calculations, but I can't feed in my thruster model to determine station keeping ability at arbitrary wind/wave/current headings.

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