damage

Discussion in 'Stability' started by jollyricard, Dec 27, 2010.

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jollyricardJunior Member

my question is:
How to set damage scenarios?
How do I determine the number of damage scenarios?
thanks

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Perm StressSenior Member

Plan a couple of weeks for damage stability chapter (reading only, I do not mean calculations here)

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klaasJunior Member

Well to give you a headstart:

light service draft (normally corresponding to your ballast arrival condition)
partial service draft (see rules)
deepest service draft (design draft)

The last two conditions are valid within a trim range of +- 0,5%Ls. If needed you have to add more conditions in order to cover the whole trimrange in which the ship operates.

Essential information for all conditions; draft, GM and trim

Way of setting of the damage scenarios depend on the program. Depending on the program is requieres more or less "handwork".

Altough in general the concept (in short) behind it is as follows:
The ship is divided in zone's and subzones (using transverse, longitudinal and vertical boundaries). The way you choose these (sub)zone's is completely free, however there are some tactics to follow in order to get good results.

The zone definition is linked to the the ships watertight geometry, this means that if damage occurs in a certain (sub)zone, this damage is translated to the damage of the watertight compartments overlapping or connected to this (sub)zone.

Generating damage cases:
To start you should decide how many adjacent zone's you want to calculate.
Afterwards the computer will generate the damage cases by calculating all the different combinations of adjacent zone's.

Index calculation:
For each of the zones the probability of damage is calculated in each loading condition.
For each damage case the probability of survival is calculated.

Multiplying the damage probability with the survival probability will give you the attained index for that case. Summation of all the attained indices (see the rules, for the formulae to apply!) give you the total attained index, this should be greater than the required index.

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ontwerpNaval Architect

What to do if Attained is less than Required

That was an excellent summary by klaas!

I just want to add a bit about what to do when the attained index is less than the required (which happens a lot in the beginning).

There are many things that can be adjusted to improve your results. Some of them are:
1. Raise the GM of your initial conditions.
2. Raise the critical points (openings).
3. Decrease the amount of trim in your DP and DS conditions (0 trim conditions generally give better results but then limit the operational trim range of your vessel)
4. Adjust the way your zones are defined so the critical compartments (hold, engine room, etc.) are better "protected". Although this is a tricky thing to do and requires some experience...and depending on the software you use may not be necessary.

One note that klaas didn't mention: when setting up your model for the stability calculation, make sure you define the variable permeability of the cargo holds according to the draughts of your initial conditions.

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tahtoh25Junior Member

could you send me any guide for how to make damage stability calculations according to solas i need it urgent

even a book name

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ontwerpNaval Architect

I don't know of a book or guide for damage stability...I am curious if there is one out there.

Normally the software you are using will include a section in their help files that explain how to do the calculation. I use NAPA and Delftship, they both have guides.

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klaasJunior Member

well thx ontwerp, got a good teacher on the subject...

As far tahtoh25's question, the best place to start is the rules together with the software guide. Probably even look into the guides of other programs.

All the rules you can find in SOLAS, additional there is MSC.281(85) with explanatory notes.

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tahtoh25Junior Member

thanks for your reply but i tried delft ship but i couldn't understand what exactingly the result also the help not contain any part for damage
if yoy can send me the pdf discrip this part it will be apperciated

napa i can't find it if you have the link for torrent or any shared file please send

autohydro is OK but the problem i have only the command to make the damage according to marpol not for solas if you can help please send because am now in very bad situation

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klaasJunior Member

Well damage stability according to Marpol is the deterministic way.
This is another way of calculating in which no probabilistic concepts are involved.

If you have got any to the point questions about Delftship I should be able to give you an answer. I've got no time to write a whole tutorial.

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tahtoh25Junior Member

i don't know how to determine the probabilistic damage as i told you if you have a paper say how to calculate it will be appreciated. because the solas only discrip the criteria

other wise you can extract the damage tutorial pages from dleft ship help and kindly send it to me

yahiarefaat@yahoo.com

is there any cracked napa copy free online??

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HReeveJunior Member

You're kidding, right?!?!

Nav Arch firms pay upwards of \$100,000 per year for software licenses (CFD, FEA, Stability, CAD, etc, etc).

Are you seriously asking professional engineers to give you an illegal copy of a program they likely paid a lot of money to use??

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tahtoh25Junior Member

first am not asking to give me that license second if you are talking about the cracked copy for soft wares i think better to make more search and u will find most the expensive soft wares is cracked and free online such as tribon m3 autoship etc

and my main questions regarding the tutorial for damage in freship professional

or what is the method for applying prob.dmage stability or books talking about it and i hope the professional designer can give me any thing regarding this in place of too much talking.

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HReeveJunior Member

That doesn't make it right or legal.

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nettersheimConsultant

Hello Tahto25,

I am interested in probabilistic damage stability for many years, and I confirm what has been said by Colleagues: there is no book on the matter at time (to my knowledge). You have to surf on internet and collect numerous articles produced on the subject and then do your own synthesis.

Francois-Xavier Nettersheim

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jollyricardJunior Member

ok, thanks

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