5 ms·

My "apples to apples" point is that density is not the only parameter to change when comparing ships to trains. 1. Assuming the same speeds. Ships go slower t

by graeham 14y ago

My "apples to apples" point is that density is not the only parameter to change when comparing ships to trains. 1. Assuming the same speeds. Ships go slower than trains (say 40kmph compared to 80kmph). 2. The frontal area is not the same as only part of the ship is underwater. Further, for a long train, the frontal area drag is likely less than the skin friction drag. 3. The coefficient of drag is not the same as the CD of a train is different than for a boat. 4. The amount of cargo on each is not the same, and would need to be normalized for a fair comparison. I'd be happy to take a quick look at your materials off-line, please send to jd2planks at hotmail

robomartin 14y ago
I really don't see it as even close. Moving anything through air requires far less power than moving the same thing through water. With regards to the rest of your comments, I've done some of those calculations. Again, there is no comparison. I need to repeat that the idea here is NOT to in ANY WAY use existing truck or cargo rail systems. They just don't perform. Here in the US you are lucky if you can get cargo trains moving on average at 20 to 30 miles per hour. In other words, the move just as slowly as cargo ships, except that they can't pull the same number of containers. The idea is that a new purpose-built system is the solution. Also, please keep in mind that the idea here isn't necessarily to search for the most efficient mode of cargo transportation in complete isolation of the realities of where they derive their energy from. Here's a very interesting paper on the aerodynamics of high-speed trains: http://ompldr.org/vMXlsOA/Aerodynamics_HSR02.pdf http://ompldr.org/vMXlsOA/Aerodynamics_HSR02.pdf Anyhow, I sent you all my files via a shared Dropbox folder. I'd be interested in what you have to say once you have a chance to look at it all. To be sure, there are huge issues with the idea that have absolutely nothing whatsoever to do with science and technology. I could not imagine the problems one might encounter in terms of the various special-interest groups that would get in the way of building such a thing, even if it was so good that it would save the world. I think the phrase "can't get out of our own way to save our lives" rings true in more than one way, at least in the US.
- leoedin 14y ago
  I think the problem is that you're imagining the same frontal area moving through two fluids. Certainly moving the same toyota camry through air and water will give vastly different results, but if you turned that toyota camry upside down and sealed all the holes, the actual wetted area that needed to be pushed through the water would be significantly less. I'd be happy to look at your calculations. My knowledge of hydrodynamics is somewhat limited, but I do have a fairly good understanding of aerodynamics and a lot of that stuff is transferable. I can't decipher your email riddle though - is [4:5] saying the 4th and 5th characters? Mine is leorampen (at) gmail.
  - robomartin 14y ago
    Sorry, that's a little Verilog. [4:9] means indeces [4][5][6][7][8][9], in other words, "martin". The camry example was just an illustration of the power relationship of something moving through water. Nothing more than that. The comparison of a container ship with 5,000 TEU (2,500 40 foot containers) vs. a train is, of course, different. And, of course, it isn't as simple as looking at cross-sectional area. That would be a gross oversimplification. Sometimes you have to assume that a cow is a uniform sphere of milk just to start to have some numbers to talk about. Imagine a train design to carry containers at 200 miles per hour. Single file. So, now, the cross sectional area is that of a single container, which is very small. If the train is designed to minimize parasitic drag and all of the frictional components of the rolling system it could be incredibly efficient when compared to a ship pushing some 4000 square feet (400 square meters) of cross sectional area of water at 20 miles per hour. And, as I have said multiple times, this isn't really solely about pure energy efficiency as much as a forward looking idea to that hopes to deal with the grotesque level of environmental pollution these ships produce as well as what might happen over the next 100 or 200 years with fossil fuels. One really has to start looking in at least a 50 to 100 year time scale to understand that what we are doing today is not sustainable in any way at all. To some extent, arguing the finer points of how much one displaces vs. the other and whether one solution is a few percent more efficient than the other is to miss the point. I'll go ahead and send you a link to the data.

by graeham 14y ago

robomartin 14y ago

I really don't see it as even close. Moving anything through air requires far less power than moving the same thing through water. With regards to the rest of your comments, I've done some of those calculations. Again, there is no comparison. I need to repeat that the idea here is NOT to in ANY WAY use existing truck or cargo rail systems. They just don't perform. Here in the US you are lucky if you can get cargo trains moving on average at 20 to 30 miles per hour. In other words, the move just as slowly as cargo ships, except that they can't pull the same number of containers. The idea is that a new purpose-built system is the solution. Also, please keep in mind that the idea here isn't necessarily to search for the most efficient mode of cargo transportation in complete isolation of the realities of where they derive their energy from. Here's a very interesting paper on the aerodynamics of high-speed trains: http://ompldr.org/vMXlsOA/Aerodynamics_HSR02.pdf http://ompldr.org/vMXlsOA/Aerodynamics_HSR02.pdf Anyhow, I sent you all my files via a shared Dropbox folder. I'd be interested in what you have to say once you have a chance to look at it all. To be sure, there are huge issues with the idea that have absolutely nothing whatsoever to do with science and technology. I could not imagine the problems one might encounter in terms of the various special-interest groups that would get in the way of building such a thing, even if it was so good that it would save the world. I think the phrase "can't get out of our own way to save our lives" rings true in more than one way, at least in the US.

leoedin 14y ago
I think the problem is that you're imagining the same frontal area moving through two fluids. Certainly moving the same toyota camry through air and water will give vastly different results, but if you turned that toyota camry upside down and sealed all the holes, the actual wetted area that needed to be pushed through the water would be significantly less. I'd be happy to look at your calculations. My knowledge of hydrodynamics is somewhat limited, but I do have a fairly good understanding of aerodynamics and a lot of that stuff is transferable. I can't decipher your email riddle though - is [4:5] saying the 4th and 5th characters? Mine is leorampen (at) gmail.
- robomartin 14y ago
  Sorry, that's a little Verilog. [4:9] means indeces [4][5][6][7][8][9], in other words, "martin". The camry example was just an illustration of the power relationship of something moving through water. Nothing more than that. The comparison of a container ship with 5,000 TEU (2,500 40 foot containers) vs. a train is, of course, different. And, of course, it isn't as simple as looking at cross-sectional area. That would be a gross oversimplification. Sometimes you have to assume that a cow is a uniform sphere of milk just to start to have some numbers to talk about. Imagine a train design to carry containers at 200 miles per hour. Single file. So, now, the cross sectional area is that of a single container, which is very small. If the train is designed to minimize parasitic drag and all of the frictional components of the rolling system it could be incredibly efficient when compared to a ship pushing some 4000 square feet (400 square meters) of cross sectional area of water at 20 miles per hour. And, as I have said multiple times, this isn't really solely about pure energy efficiency as much as a forward looking idea to that hopes to deal with the grotesque level of environmental pollution these ships produce as well as what might happen over the next 100 or 200 years with fossil fuels. One really has to start looking in at least a 50 to 100 year time scale to understand that what we are doing today is not sustainable in any way at all. To some extent, arguing the finer points of how much one displaces vs. the other and whether one solution is a few percent more efficient than the other is to miss the point. I'll go ahead and send you a link to the data.