# How can I obtain the flow coefficient of a flooding compartment?

Discussion in 'Boat Design' started by xichyu, Jul 1, 2016.

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### xichyuJunior Member

A ship was damaged. The ship rocked violently.
How can I obtain the flow coefficient of a flooding compartment?
How the flow coefficient influence the motion of the ship?

Practical problem！！！！！！！！！！！ A crew asked me yesterday. I am so sorry！！！

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### TANSLSenior Member

Probably the answer is very obvious to the experts but I am not able to guess. Could you explain what you mean by "flow coefficient" of a flooding compartment and what you want to use it for?.
Are you talking about "Cv" (see picture)?

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### rwatsonSenior Member

"The flow coefficient, or Cv, is a universal capacity index and is simply defined as “the number of US gallons of water per minute at 60F that will flow through a valve with a pressure drop of one psi. Sometimes “pressure drop” is described as pressure differential or “delta P”."

But the OP needs something more sophisticated
Heres my favourite sources from 2012, with the math

http://floodstand.aalto.fi/Info/Files/STAB2012_Ruponen_Larmela_Pennanen.pdf

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### TANSLSenior Member

Thanks, rwatson, I think both are talking about very similar things. By the way, very good article on your link.
As you already know, the Cv, which depends on the pressure, it is not a constant value but varies depending on how it does this pressure, which is not constant. Therefore, you should discuss the variation Cv compartment during flooding. Talking about the value of Cv, in my opinion, it is not correct. We must talk about the variation during the time of the flood.
Moreover, depending on the phenomenon the OP wants to study, you can respond on the influence of the "Cv (variable)" during that phenomenon or the convenience of studying some other more relevant parameter.

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### xichyuJunior Member

Thanks for your response！Would you tell me that where can I obtain the equation for calculating "Cv"？
Is it a book？

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### xichyuJunior Member

The depth of the hole(breach) is constantly changing.

http://screenshot.net/vxyoxbp

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### TANSLSenior Member

The pressure varies with the difference of the heights of the liquid inside and outside the tank. So, effectively, as the compartment is filled, or the draft of the ship changes for any circustance, pressure changes, and therefore the "Cv" varies. Perhaps you could use in your calculations mean value of Cv, half-sum of the initial and final values (final value = 0).
I do not know what you want to calculate but I'm sure it will be much more complicated than just determine the value of "Cv".
On the other hand, I do not know how "flow coefficient influences the motion of the ship". What motion do you mean ?.
In the exercise proposed in your link, you need to take into account also the air pressure inside the tank.

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### xichyuJunior Member

Thanks! I think the flow coefficient influences the flooding quantity of damaged compartment, which influence the motion of the ship.
When the ship damaged. The heeling angle is very big, so it need to be righted. But the ship rocked violently.

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