nigelswift
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Re: Stone Shifting 2
Aug 27, 2003, 21:06
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Berrlimey!!!
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FourWinds
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Re: Stone Shifting 2
Aug 27, 2003, 22:15
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It's a Friend of a Friend thing ... I'll see what I can do.
No promises :-)
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Steve Gray
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Re: Stone Shifting 2
Aug 27, 2003, 23:55
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I could set up a temporary website for pictures, etc. People could email them to me as attachments and I'll upload them. That's probably easier than trying to provide a direct upload capability. I have broadband, so the attachment size is no big deal. If I get a chance to set something up I'll post the details. Let me know if you're still have problems downloading the model, I could email it to you or send you a copy on CD.
When you do get the model try the following: tower height = 5.5m, offset = 1m, leave the other settings at default. I don't know how wide the blocks are (I assumed 1 m). If you increase the width (depth) of the block, it will increase the momentum, so you will have to reduce the offset or height to compensate. I suspect that the original Stonehenge uprights were erected from outside the circle and that the 45 degree slope was to allow the stone to arc into the hole, thus reducing the height requirement of the tower.
If you have already tried some practical experiments, see if the model behaves the same way with those settings. I would appreciate any feedback on this matter. Please bear in mind that the frictional coefficient of 0.8 is merely a guess. I haven't had time to assess it properly. The way to do it is to measure how much force is needed to drag a block of stone over a flat wooden surface. The coefficient is the force divided by the weight of the stone. So if it takes a pull of 7kg to move a 10kg stone the coefficient would be 0.7. You can do it with a spring balance or a string over a pulley with a weight pan on the end.
I have considered how to handle non-uniform blocks in the model. I would need a profile that approximates the block to a collection of small uniform cubes put together rather like a butcher's block. The moment of inertia of the entire block can then be computed as the sum of the moments of each of the small blocks. This can be done in advance of the real-time modelling, so computation time is not critical and hence we can use a very small block size, which will make the approximation quite accurate (how accurate it needs to be, I'm not sure).
My aim is to refine the model until it agrees with ALL our practical tests. Then we can use it to predict the appropriate parameters for the 10 tonner. If that works like a treat, then we can have some confidence that it will work for the 40 ton attempt.
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Steve Gray
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Re: Stone Shifting 2
Aug 27, 2003, 23:59
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Show him Gordon's website and the computer model in action. Use default settings, but change the tower height to 5.5m and the offset to 1m.
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Steve Gray
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Re: Stone Shifting 2
Aug 28, 2003, 00:09
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I have updated the model so that it uses default settings that give a good result. If you haven't already installed the model, just download and install Stoned.zip. If you have already installed it then just download the update and extract it to C:\Program Files\Stoned\Stoned.exe, overwriting the existing file.
Full model: http://www.swifttools.com/Stoned.zip (1.35MB)
Update only: http://www.swifttools.com/Update.zip (10KB)
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Steve Gray
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Re: Stone Shifting 2
Aug 28, 2003, 00:12
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I don't know what happened to the backslashes in the path name for that last post. I'll try the path again using double backslashes, but if it fails, I guess you can work out what I intended.
C:\\Program Files\\Stoned\\Stoned.exe
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baza
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Re: Stone Shifting 2
Aug 28, 2003, 02:34
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I think that we should be able to get rid of some of the variables.
The height of the uprights at Stonehenge varies. The outer circle is fairly constant, I`ve seen figures of between 13.5 - 16 ft for its height above ground. The inner horseshoe was higher, up to 22 ft. I presume that we`d be going for the lowest figure. I don`t know how deep the stones were set into the ground.
By depth, do you mean width? The width of the stone dragging on the tower? Or is that irrelevant once you know the coefficient of friction?
The figures that I`ve got are 7 ft wide and 3.75 ft deep for the outer uprights, with weight of 25-30 tons.
Can you tell me what the offset variable relates to, please? I don`t understand that one.
baz
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FourWinds
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Re: Stone Shifting 2
Aug 28, 2003, 06:55
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I'll have to look at your model at work cause I'm Mac at home. It sounds great.
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nigelswift
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Re: Stone Shifting 2
Aug 28, 2003, 07:16
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FW, Steve said: “I suspect that the original Stonehenge uprights were erected from outside the circle and that the 45 degree slope was to allow the stone to arc into the hole, thus reducing the height requirement of the tower.”
Although the 45 degrees may not be right, I do think it would be a great help to know if Steve’s correct about this because if he is it would be a strong indication of the exact height from which the original stones were tipped. It would be a great question to put to Mr Burl, as he might have an opinion on whether they were erected from inside or outside based on what he knows of the chronology and consequent constraints upon space.
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GordonP
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Re: Stone Shifting 2
Aug 28, 2003, 08:38
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Hi guys
Sounds like you're all having great fun with this computor model, I've still not got it out of the bloody box yet!!! I think I'll leave it there it might be useful if one of us remains in the stoneage.
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