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Tension Discontinuity /DN

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Paul Arden
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Re: Tension Discontinuity /DN

#11

Post by Paul Arden »

Yes I think that the radius of the loop is very much tighter and the bottom of the loop begins and ends at the nose ie Tr should be there?

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Merlin
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Re: Tension Discontinuity /DN

#12

Post by Merlin »

The path of a particle in the line is something like a cycloid, and so what?
It's a fallacy to think the size of the loop influences the aerodynamics of the loop.
I guess this relates to alternative physics. :ninja:

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Re: Tension Discontinuity /DN

#13

Post by Graeme H »

Merlin wrote: Sun Jun 20, 2021 6:47 pm
I guess this relates to alternative physics. :ninja:

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Tension discontinuities? Yeah, I believe so.
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Re: Tension Discontinuity /DN

#14

Post by Graeme H »

Paul Arden wrote: Sun Jun 20, 2021 3:01 pm Yes I think that the radius of the loop is very much tighter and the bottom of the loop begins and ends at the nose ie Tr should be there?

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Can you rephrase that? I don't understand what you mean by "the bottom of the loop begins and ends at the nose".
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Re: Tension Discontinuity /DN

#15

Post by Paul Arden »

Basically I was wondering if this would be a better representation…
6A8EDFE1-4F6B-42F0-82F1-9E587B79746C.jpeg
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Re: Tension Discontinuity /DN

#16

Post by Merlin »

The wording "tension discontinuty" is inappropriate and comes from a mathematical discontinuity found when solving equations for a string shooter. It is not appropriate to reality and I much prefer a "tension singularity" which does not violate the fact that a string is a continuous medium. I am writing a paper on that and shall have reading test with Paul before posting.

On the other hand negating front drag for a loop can be classified as alternative physics, and tension discontinuity as well.

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Re: Tension Discontinuity /DN

#17

Post by Torsten »

For a single particle we can assume a combination of translation and rotation (like a rolling wheel) - that's why you're getting such a trajectory. A larger radius means that line more segments are exposed to form drag and thus have larger losses. So I'd still expect that this model produces plausible results, as long as the top and bottom legs are reasonable straight and the loop front is semicircular.

The alternative approach to solve this model with work/energy is here:

https://www.researchgate.net/publicatio ... g_dynamics
Gatti-Bono, Caroline & Perkins, N.. (2003). Comparison of numerical and analytical solutions for fly casting dynamics. Sports Engineering. 6. 165-175. 10.1007/BF02859893.

Daniel, you should get the same results, maybe you have compared them already.
Graeme H wrote: Sat Jun 19, 2021 4:04 am
Torsten wrote: Fri Jun 18, 2021 6:38 pm The disadvantage is the model itself, the assumption of a semicircular loop front is basically wrong - in the real world the line particles are not constrained to move along a circle.
The line particles never move along a circle even if the loop shape looks circular.
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Re: Tension Discontinuity /DN

#18

Post by Mangrove Cuckoo »

Graeme,

Thanks for the great videos!

It amazes me how frequently something obvious slaps me in the face and shows me how off target my incorrect suspicions are... and all I can do is bang my forehead and say "Duh!"

I have always been fascinated by gyroscopes (there is a toy one on my desk as I type this). And I had the idea that the unrolling loop had some similar properties, or at least half of 'em. Your videos show that the particle doesn't even travel in half a circle... maybe 1/4 at most?

I have been daydreaming about this shit ever since!
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Re: Tension Discontinuity /DN

#19

Post by gordonjudd »

A single point doesn't even follow a 1/4 circle in a normal "semi-circular loop". It has a sort of "1/4 parabolic" path, shedding forward velocity rapidly.
Graeme,
That is the case for an earth frame, but if you use an inertial frame (constant velocity in one direction) attached to the front of the loop the particles do appear to follow a quasi-semi-circular path. An example of what your clip 10 video would look like in a moving frame is shown below. Not sure why it is breaking up at the end using Vimeo.
[media]https://vimeo.com/manage/videos/566346145[/media]
a moving frame should give the same results as the ones you get earth frame, and is typically used in most analysis papers to make the analysis much more straightforward.
It's a fallacy to think the size of the loop influences the aerodynamics of the loop.
Can you give your reasoning for this statement?

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Re: Tension Discontinuity /DN

#20

Post by Merlin »

Hi Torsten

I did check with the work energy model from Gatti Bono. The set of momentum equations (horizontal and angular momentum) exactly matches the work energy one, with the same input data of course. That was a perequisite before moving forward and test pull back situations.

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