# Trim calculation in wave condition

Discussion in 'Stability' started by bilgehan, May 5, 2010.

1. Joined: Aug 2009
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Location: istanbul

### bilgehanNew Member

Hi everybody.
I am a student in Istanbul Technical University (Turkey). I am trying to develop a software which can help us (students) for a longitudinal strength project.

At the moment, basicly all I want to do is positioning the wave on to the area curves taking trim into account for an exact draught.
Area curves are already being defined and threatened as functions in software and can give the area results for any given waterline height. On the other hand i have wave function.
Intersecting waterline and are curves, i evalute the areas for list condition multiplying them with station spacings and summing them i have buoyancy and try to have the wave condition sum same with the list condition.(waterline function as a line and wave function as a sine wave)

I found a way to rotate the function around an arbitrary point (lcf in this case) mathematically.

I am planning to iterate the position of the wave function on area curve funcitons and read them all.

The problem is any change in position of the wave function causes the lcf and lcb changes.

?? I wonder is there any mathematical way to position a wave onto ship (or ship onto wave. relative positioning.) just right (proving the trim angle and the buoyancy for the draught).??
??In other words what is the trim angle and vertical change of the ship for a specific wave given??
*LCG is known

Its been so long. Sorry about that i ve tried to make the stuation clear.
Thanks Everyboy.

2. Joined: Aug 2009
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Location: istanbul

### bilgehanNew Member

Nobody even said hello!
Here I got my way: first im gonna draw a LCF curve for the wave condition using the wave function besides the waterline. The Intersection of the wave function and LCF will be used the centre of rotation for the wave funciton. The iteration will start from the angle 0 and increase while the height of the wave function on area curves (not the waveheight) increases too. For every angle and height an sectional area curve will be created and LCB will be pointed. Then the longitudinal distance between LCG and LCB will be measured. Within iteration where the distance change the sign it will be meaing that the distance passed "0" once. Then the angle will be increased precisely untill the distance catches 0. A check will be made for the draught too. The case proves 0 distance between LCG-LCB and the exact draught will be the trimmed position of the ship in the wave condition.
It would be great If somebody have stg to say about this. Thanks.

3. Joined: Nov 2009
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Location: Houston

### conceptiaNaval Architect

First of all, i'd say it is a huge effort you are going to put in. I'd be interested to know if your software is capable to calculate the section area and hydrostatic data.
I dint notice your post on first place.

Last edited: May 10, 2010
4. Joined: May 2008
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Location: Australia

### LyndonJSenior Member

A very quick but useful first look at head on wave encounter wave encounter is to simply trim the vessel by some angle say -15 degrees longitudinally ( down by the bow) and re-float to the same displacement .

Then llok at what happens to both the waterplane centroid and the COB as they have different effects, WC is a dynamic COB is a static.

5. Joined: Nov 2009
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Location: Houston

### conceptiaNaval Architect

Ain't he talking about calculating the longitudinal strength. Wat is the significance of these CBs, n CFs inside this?
To my knowledge only thing he needs to calculate is the sectional area at each section for particular draft(for every possible trim angle). Make a sheet to interpolate the data to the given trim and wave. If he needs to check the stability, yes of course he needs to CBs and CFs, also CGs.
Correct me if gone wrong.

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6. Joined: Aug 2009
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Location: istanbul

### bilgehanNew Member

conceptia: Yes the program is capable of calculating sectional areas and hydrostatic data as well. To calculate the longitudinal strength in wave condition i also need to check the stability while we assume that the ship would be stabilised (nor triming neither sinking) in the wave.

LyndonJ: i agree when it comes to dynamics. I have to make some assumptions. I noticed that this is should be the calculation not a simulation

Thanks for helping

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7. Joined: Nov 2009
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Location: Houston

### conceptiaNaval Architect

ok then, the software is much complex now.. All the best with your work. This will give you complete knowledge about the concept of stability and longitudinal strength...

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