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Analysing loop propagation

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Merlin
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Re: Analysing loop propagation

#11

Post by Merlin » Mon Sep 14, 2020 9:36 am

Wave, energy or momentum, it depends of the type of approach, qualitative or quantitative.

I consider wave as a qualitative one. I agree that a mend is a transverse wave but the loop is not, the displacement is not perpendicular to the medium. The string analogy may be a trap since it does not handle “dynamics”. I mean that most of the time string studies refer to “stranded waves”, some type of “steady state” situation by opposition to a situation where accelerations and decelerations take place. The whip analogy looks better, but it is far from being that simple. Maybe the loop is a “longitudinal wave” in some aspect; anyway it is a strange wavy flying object.

If we aim at quantification then we have to use momentum variation in time (horizontal, vertical, angular) and energy balance. There must be a number of equations equivalent to the number of unknowns (among them: leg speeds, rod leg sag, line inclination at both ends of the loop, loop radius, etc. ) and you usually have to use simplifying assumptions or software able to handle a number of ODEs simultaneously. For example, morphing is included within the angular momentum problem but to make that easily usable for a simple model you assume that the loop does not morph. Such quantitative approach involves tension in the line, this tension varying along the line itself.

If you consider “tension” as something more global, then you are back into the qualitative approach (remember Berlin?).

You need something qualitative for teaching and it should ideally be based on a quantitative approach, as accurate as possible. Tension could be an example of a parameter linking both approaches.

You cannot solve the loop propagation technical problem by wave only, momentum only or energy only appraoches, IMHO.

Merlin
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Paul Arden
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Re: Analysing loop propagation

#12

Post by Paul Arden » Mon Sep 14, 2020 1:51 pm

Thank you. Those last couple of answer were very helpful for me :pirate:

I agree Merlin, wave length and frequency don’t make much sense applied to an unrolling loop. So in order to quantify it we need to use other methods.

Thanks, Paul
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gordonjudd
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Re: Analysing loop propagation

#13

Post by gordonjudd » Mon Sep 14, 2020 3:08 pm

A jerk is readable in Gordy's pull-back cast rod leg velocity and at the same time an opposite direction jerk is readable in the fly leg velocity - centripetal force explains it for me.
Dirk,
Not only is it readable, the jerk derived from the measured velocity profiles in that pull back cast can be calculated as shown below.
Image
Since the calculated correlation coefficient between those two jerk curves was only 12%, I don't think you can cherry pick a time range that fits with your centrifugal force theory while ignoring the 88% of the time when there is no correlation between the two jerk curves.

Invoking jerk as an explanation for the delay in the fly legs velocity increase relative to the start of the pull back is a derivative too far for me.

Gordy

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Graeme H
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Re: Analysing loop propagation

#14

Post by Graeme H » Tue Sep 15, 2020 9:29 am

Is this a loop or a wave?
Screen Shot 2020-09-15 at 5.28.51 pm.png
Screen Shot 2020-09-15 at 5.28.51 pm.png (25.01 KiB) Viewed 406 times
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Graeme
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gordonjudd
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Re: Analysing loop propagation

#15

Post by gordonjudd » Tue Sep 15, 2020 2:19 pm

Is this a loop or a wave?
Graeme,
For lack of a better term I would say it is an example of one of the many different shapes you see in a "fly wave."

It has a different shape than the "whip wave" that Dr. McMillan analyzed. However in both cases the mass of the medium is transported as the wave propagates down the medium.
Image

That mass transport does not happen in the many types of mechanical waves described in the literature. A transverse wave is a good example of a mechanical wave.
Image

Gordy

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Graeme H
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Re: Analysing loop propagation

#16

Post by Graeme H » Tue Sep 15, 2020 10:35 pm

gordonjudd wrote:
Tue Sep 15, 2020 2:19 pm
That mass transport does not happen in the many types of mechanical waves described in the literature. A transverse wave is a good example of a mechanical wave.
And yet in every static image we show of a mechanical wave, the medium is displaced, including the ones you've just posted. In the case of a transverse wave, we show the medium deviating from the centre line of the graph. If the medium has mass, then the mass has been momentarily transported perpendicular to the direction of wave propagation.
For lack of a better term I would say it is an example of one of the many different shapes you see in a "fly wave."
Well, yeah, that's not a great term. It means nothing to anybody.

Image

Is the picture showing a wave or is it a loop? Don't be too hard on yourself - I don't know how anybody can answer the question. I'm simply pointing out the inconsistency in the argument that every bend travelling along a fly line is called a transverse wave except one. In isolation, it is not possible to determine if I've shown a loop or a "real" transverse wave.

The fact that we are making this distinction between the two otherwise identical bends travelling through a medium means something is wrong with the model of a wave that we have in mind. That implies a change of perspective is required.

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Graeme
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Lasse Karlsson
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Re: Analysing loop propagation

#17

Post by Lasse Karlsson » Wed Sep 16, 2020 7:33 am

Graeme, quite difficukt to determine anything from your blown up picture, but I think I know where you want to go with it.

If a transverse wave displaces matter while it travels, but brings it back when it leaves, how can a loop be called a wave, when it moves matter from one point and leaves it at another?

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Graeme H
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Re: Analysing loop propagation

#18

Post by Graeme H » Wed Sep 16, 2020 10:59 am

Lasse Karlsson wrote:
Wed Sep 16, 2020 7:33 am
If a transverse wave displaces matter while it travels, but brings it back when it leaves, how can a loop be called a wave, when it moves matter from one point and leaves it at another?

Cheers
Lasse
I think you might have missed a post of mine earlier. The full cycle of the wave returns the fly to its starting point, as in a PUaLD cast.

But to answer your question: look at an aerial mend. when you land the line on the water, the line has a bend in it. That line was not returned to the starting point but we all agree that's a transverse wave.

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Graeme
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Graeme H
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Re: Analysing loop propagation

#19

Post by Graeme H » Wed Sep 16, 2020 11:00 am

Which of one of these actions marks the transition from a wave to a loop?



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Graeme
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Dirk le Roux
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Re: Analysing loop propagation

#20

Post by Dirk le Roux » Wed Sep 16, 2020 12:18 pm

Graeme,

I find the fly leg behaviour part of this clip extremely fascinating. Thanks for doing this one!

Cheers,
Dirk

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