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Quote from: neptune on June 23, 2012, 10:25:12 AM
1. There is no disadvantage in bolting all the risers together as one unit. So that being the case, If the risers are being custom made, in a three layer system , we could fabricate the riser assembly from three concentric tubes and a single lid to which the 3 concentric tubes are welded/glued.

2.All the walls and the gaps are 0.2 inches . Therefore the volume of all the "pockets" of water in the system are not equal. This had been worrying me as I had this theory that they needed to be, and therefore gap widths would have to decrease as we moved from the inner layer to the outer. In a smaller model we could perhaps use gaps of less than 0.2, but precise construction would be essential. In this sense it is probably easier to build a large model than a small. But it costs more .

Hi Neptune,

I don't think a single lid would work as it would loose most of the Travis effect, each Riser would have a much smaller surface area and still seeing the same PSI. For instance, in my previous post of Wayne's latest size change, if it were one lid, Riser 2 SI needs to be subtracted from Riser 1 SI then multiply that by 2.6 and you can see the effect.

In the MTO the gap clearance can easily by adjusted by changing the 'Riser 4-Side Increase' variable.

Regards, Larry

Here you can see the effects of having a larger water gap around the Outer Riser.  The comparison is made for the case where 5.85 in^3 of water has been removed from the center Pod section of the model as compared to when it is completely "Full" and at a restrained full stroke.  The 5.85 value was used as this is right where the model with the smaller gap has lost enough buoyancy to overcome it's own weight and would begin to drop as the water level drops.

In the system with the bigger gap removing the same volume of water has a lesser effect on dropping the buoyancy on the Outer Riser.  It is still well buoyant beyond it's weight.  So only the inner two members will begin to drop as more water is removed.

Does this matter?  Probably not, if the system is designed to account for this.

But in the case of the smaller gaps (all around) you get a much larger change in effective water head in the system for smaller water volume changes.

Thanks,

M.

Edited to add:  Forgot to mention that the larger gap is achieved by replacing the 6 in OD x 3/16 in thick tube with a 7 in OD x 1/8 in thick tube that is also available through McMaster-Carr.

Quote from: mondrasek on June 23, 2012, 02:20:39 PM
Here you can see the effects of having a larger water gap around the Outer Riser.  The comparison is made for the case where 5.85 in^3 of water has been removed from the center Pod section of the model as compared to when it is completely "Full" and at a restrained full stroke.  The 5.85 value was used as this is right where the model with the smaller gap has lost enough buoyancy to overcome it's own weight and would begin to drop as the water level drops.

In the system with the bigger gap removing the same volume of water has a lesser effect on dropping the buoyancy on the Outer Riser.  It is still well buoyant beyond it's weight.  So only the inner two members will begin to drop as more water is removed.

Does this matter?  Probably not, if the system is designed to account for this.

But in the case of the smaller gaps (all around) you get a much larger change in effective water head in the system for smaller water volume changes.

Interesting observation. We may have to adjust the outer column to where the system would sink.

Regards, Larry

The outer column is a tradeoff depending on how you want to use the potential energy stored there.  The amount of potential energy should be a constant based on how high the column of water is raised vs the volume of water.  The potential energy stored would be an integral calculation.  The question would be how to use it without unbalancing the total amount of water in the closed loop system?