I would put the yellow-brown liquid, and dark liquid in the tanks that are next to eachother, presuming they have fairly simular weights. I would put the blue liquid in the very front of the tank. Presuming that the first two filled tanks towards the rear, helped balance out its weight.
1:44 I would fill the tanks that are closest in maximum capacity, to the volume of the liquid being stored. Also taking into account the need for general weight ballance, ie: tank on one side is filled, its corresponding tank on the opposite side could be filled for general overall weight ballance.
Some example volumes, for tanks and liquids would have been useful. Just from looking at the video, it is impossible to say whether, for example, the ballast water would have filled the large center tank completely. Otherwise, great physical example for this problem.
I got the first two right! The third I was right, but I thought the rest would be in the port\starboard containers equally…..though I really didn’t know what I was doing.
Total non-engineer here. But I would think that storing liquids in several tall, relatively narrow cylindrical tanks evenly and widely distributed would render the issue quite moot. Might be a too great price to pay though in the weight of the tankage structure.
I agree on the oil and fuel tank use but I would have filled the two small tanks aft with ballast water since you want to run with stern trim and you would only be left with two slack tanks. Why wouldn’t this be better?
That is an interesting way to go. Your solution would produce the same level of free surface moment. From a stability perspective, it is equally valid. I happen to know that the two aft tanks are each half the volume of of the large tanks in the bow and stern. So if you completely filled them, there would still be some ballast water left over that needs to go in the bow or stern tank. It would still be the same level of free surface moment. The only thing I would debate is running with stern trim. This is a philosophical debate though. Nothing to do with safety. I once did a study for a client where I discovered even a little bit of aft trim added 1-2% to the fuel consumption rate. I know aft trim is recommended because it gives better steering control, and I would not stop anyone from using aft trim to operate safer. But, personally, I see it as a design flaw. The ship should not require aft trim to maintain good steering control.
Hi, does free surface moment also affect sloshing in ballast tanks? Also, is there free surface moment or sloshing if we were to use a piston cylinder system for ballast tanks...... For remotely piloted underwater vehicles.
It is more accurate to say that free surface moment and sloshing are totally different physical phenomena, but they depend on many of the same tank dimensions. As for a piston cylinder ballast tank, I believe you are describing a system which uses a piston to physically displace the water from a cylindrical ballast tank, and does not use compressed air. In this case, the water surface is contained by a solid barrier. That setup would not generate any free surface moment.
If a warship had U shaped tanks along the hull as part of its torpedo protection scheme, with each tank ending near the deck, port and starboard and one of those tanks was slack, how much free surface moment would it have?
That is a very clever question, which takes some math to get the exact numbers. For the simplified explanation, the U-tank is very similar to the example I provided in the video of a tank within a tank. Only in this case, the big tank extends the entire beam of the ship, and we have an air space (accommodations) inside a tank. We don't need to worry about the free surface moment of the 2nd tank, our air space. So what is the free surface moment of that big U-tank? Much more than if we divided that U-tank into two small separate tanks. But less than if we had one continuous tank across the entire beam. Interesting side note: U-tanks have another purpose. We will intentionally install them to help with the seakeeping of the ship and reduce its roll motions. By careful selection of the tank dimensions, we create a situation where the liquid in the tank sloshes in opposition to the ship roll motions. So the liquid in the U-tank always counterbalances the ship to reduce roll. That doesn't come for free. You still need to worry about the free surface moment of the U-tank. But it can be a relatively cheap way to improve seakeeping. (Cheap when compared to a computer controlled, hydraulic powered, retractable active control fin.)
![ละลาย (LALALYE) - DAOU PITTAYA ต้าห์อู๋ พิทยา [OFFICIAL MV]](http://i.ytimg.com/vi/wo6r9TgausI/mqdefault.jpg)
Appreciate the simplicity of the explanation, helpful to a non-naval architect to better understand
This is very, very good content.
Thank you for this information sir. Well done Nick.
I would put the yellow-brown liquid, and dark liquid in the tanks that are next to eachother, presuming they have fairly simular weights.
I would put the blue liquid in the very front of the tank. Presuming that the first two filled tanks towards the rear, helped balance out its weight.
1:44
I would fill the tanks that are closest in maximum capacity, to the volume of the liquid being stored.
Also taking into account the need for general weight ballance, ie:
tank on one side is filled, its corresponding tank on the opposite side could be filled for general overall weight ballance.
Some example volumes, for tanks and liquids would have been useful.
Just from looking at the video, it is impossible to say whether, for example, the ballast water would have filled the large center tank completely.
Otherwise, great physical example for this problem.
I got the first two right! The third I was right, but I thought the rest would be in the port\starboard containers equally…..though I really didn’t know what I was doing.
Thank you.
Total non-engineer here. But I would think that storing liquids in several tall, relatively narrow cylindrical tanks evenly and widely distributed would render the issue quite moot. Might be a too great price to pay though in the weight of the tankage structure.
this is fucking amazing! nick never fails to impress.
So where does the "surge" (volume and energy) of the mobile liquid come into play? Can Free Surface Moments be diminished with baffles?
Yes baffle plates are used for this purpose
You make my head hurt, but it's good pain
whats you take on Evergiven's steerage issues?
I agree on the oil and fuel tank use but I would have filled the two small tanks aft with ballast water since you want to run with stern trim and you would only be left with two slack tanks. Why wouldn’t this be better?
That is an interesting way to go. Your solution would produce the same level of free surface moment. From a stability perspective, it is equally valid. I happen to know that the two aft tanks are each half the volume of of the large tanks in the bow and stern. So if you completely filled them, there would still be some ballast water left over that needs to go in the bow or stern tank. It would still be the same level of free surface moment.
The only thing I would debate is running with stern trim. This is a philosophical debate though. Nothing to do with safety. I once did a study for a client where I discovered even a little bit of aft trim added 1-2% to the fuel consumption rate. I know aft trim is recommended because it gives better steering control, and I would not stop anyone from using aft trim to operate safer. But, personally, I see it as a design flaw. The ship should not require aft trim to maintain good steering control.
Why tanks don't have a kind of an air balloon inside to fill the empty volume?
Hi, does free surface moment also affect sloshing in ballast tanks?
Also, is there free surface moment or sloshing if we were to use a piston cylinder system for ballast tanks...... For remotely piloted underwater vehicles.
It is more accurate to say that free surface moment and sloshing are totally different physical phenomena, but they depend on many of the same tank dimensions.
As for a piston cylinder ballast tank, I believe you are describing a system which uses a piston to physically displace the water from a cylindrical ballast tank, and does not use compressed air. In this case, the water surface is contained by a solid barrier. That setup would not generate any free surface moment.
If a warship had U shaped tanks along the hull as part of its torpedo protection scheme, with each tank ending near the deck, port and starboard and one of those tanks was slack, how much free surface moment would it have?
That is a very clever question, which takes some math to get the exact numbers. For the simplified explanation, the U-tank is very similar to the example I provided in the video of a tank within a tank. Only in this case, the big tank extends the entire beam of the ship, and we have an air space (accommodations) inside a tank. We don't need to worry about the free surface moment of the 2nd tank, our air space. So what is the free surface moment of that big U-tank? Much more than if we divided that U-tank into two small separate tanks. But less than if we had one continuous tank across the entire beam.
Interesting side note: U-tanks have another purpose. We will intentionally install them to help with the seakeeping of the ship and reduce its roll motions. By careful selection of the tank dimensions, we create a situation where the liquid in the tank sloshes in opposition to the ship roll motions. So the liquid in the U-tank always counterbalances the ship to reduce roll. That doesn't come for free. You still need to worry about the free surface moment of the U-tank. But it can be a relatively cheap way to improve seakeeping. (Cheap when compared to a computer controlled, hydraulic powered, retractable active control fin.)
"Filling up the tank" aaah you cheated! :D