# Calculations of the hull in the wave

Discussion in 'Software' started by TANSL, May 2, 2013.

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### TANSLSenior Member

For various reasons I had to develop a program that calculates the hydrostatic of a ship in a sine wave, given a certain displacement, for different longitudinal positions of the wave and at various angles of attack. Is anyone interested in it?.
The program is under debugging, and could be directed to specific calculations proposed by you.
Thanks.

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### DCockeySenior Member

Is it capable of different wave lengths and amplitudes?

How are you calculating the hydrostatics?

Is the variation of pressure with depth from the simple hydrostatic "density * gravity * depth" due to the wave included?

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### TANSLSenior Member

Is it capable of different wave lengths and amplitudes? : currently estimates a wave of length equal to the length between perpendiculars of the ship. The wave height is defined in terms of a table proposed by the ABS in the regulation ASSESSMENT ROLL OF PARAMETRIC, height not to be taken greater than the value: depth-draft.
Would be easy to adapt to any wavelength and any height.

How are you calculating the hydrostatics? : As always submerged body volume and center of buoyancy. It works on a solid model of the ship that is cut by the wave (Boolean algebra). The waterline area and moments of inertia of the same (here an approximation and, through the port and starboard half breadths at each frame, draw a "flat" surface, waterline projection on the horizontal plane)

Is the variation of pressure with depth from the simple hydrostatic "density * gravity * depth" due to the wave included? : NO

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### CrowsnestJunior Member

Hi TANSL

Hi:
Of course I'd be interested on testing your program. I've just finished a static stability and stresses calculator in any wave conditions, and am now working on the dynamic module.

Regards.

PD: I have no comercial interests. My soft is free.

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### daiquiriEngineering and Design

Tansl,
Keep on doing the good job. It could become a nice tool for estimating the effects of speed on the transverse static stability. I don't need it right now, but will be watching for further developments og your software. Thanks.
Cheers

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### TANSLSenior Member

Crowsnest and Daiquiri, thanks for your words.
If you think that an adaptation of my programs can be useful in your studies, please do not hesitate to tell me your suggestions. I will be happy to apply them.
Cheers

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### AlikSenior Member

This does not take running trim into account, thus not really suitable for small craft.

There is a method developed by Nachayev based on tank testing of trawler hulls. That one is used to estimate GM correction for Fn.

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### daiquiriEngineering and Design

Never heard of it Alik, but sounds very interesting. Can you point me to some paper or a book which deals with that method?

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### AlikSenior Member

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### daiquiriEngineering and Design

Thanks Alik, I will check it out.

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### TANSLSenior Member

When the wave motion is parallel to the longitudinal axis of the boat, trim calculation has no difficulty and the program does, though Alik say that it does not (how can you know that, my friend?). Actually it is laborious to calculate heel and trim at any instant, when the waves coming from the side. This does not, for now, the program.
Furthermore, this program, as well as any other, not mind too much the size of the vessel being studied. The calculations are exactly the same, for small boats or for super tankers.

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### daiquiriEngineering and Design

I was thinking about the fact that a vessel running at or near the "hull speed" (more likely a small craft than a cruiser or a tanker, by the way ) will not see sinusoidal waves around him, but something more similar to trochoidal waves (still an approximation though). Trochoidal waves are more unfavorable situation and will give a bigger reduction of stability, because their wave throughs are more extended than throughs of sinusoidal waves.

Perhaps you could implement the possibility to choose the wave type one wants to use for calculations?

Cheers

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### TANSLSenior Member

daikiri, of course, there is no problem in considering a trochoidal wave. The program creates a sinusoidal wave because it is this which considers the ABS, which was the reference Regulation for the calculations we were doing.

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### CrowsnestJunior Member

Dear TANSL:
May be, by running your soft through a whole wave phase, could return a X,Y,Z table/curve for the Center of Buoyancy shift.
This, as a collateral result can be useful for a component of torsion estimate, due to motion on waves. By giving a statistical number of cycles, may be also helpful for a fatigue approach as well.

Regards

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### TANSLSenior Member

Crowsnest, the program calculates the value of the various parameters of the hull, at a constant displacement indicated by the user, as the boat passes through the wave and also, if requested, it draws in AutoCAD the curves representing these variations.
Cheers
Ignacio

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