Conservation Of Angular Momentum (COAM)

[VGB]

Daniel

You do not need to build a model to say that CoAM does not exist.Torsten gave the reasons why in his post Page 39 #382.

Almost everybody said that COAM didn't exist long before Page 39, Gordy appears to be hanging out there on his own still.

I denied the rise in speed because it is not supported by Graeme’s data (see Page 38 post #371) and since this is not an outcome of the model.

You were looking at the wrong slice of time. I asked for a birds eye view of the cast based on practical trials and casting experience, the birds eye view confirmed the observed rise in line speed. Your model outcome is nowhere near Graeme's tracker plot.

The late rise in speed you show in some posts is typical of a level line at the end of the rollover (typical taper of sinking tips). Without some taper and / or a leader the line is likely going to kick back, nearly all lines accelerate at the end of their rollover (observed by Graeme incidentally). Only light lines with a rather large loop may not show an acceleration.

The late rise in speed coincides with a large rise in rod leg tension and is not typical unless you throw a good cast into the overhang, you don't see it with the same lines if you don't go well into the overhang. Most lines accelerate later and at a lower rate in the cast.

I think you focus too much on what can happen with a pullback, a change in line density is not equivalent to a pullback in terms of physics. If I can find some day a technical reason and a mean to adapt the model for a speed change during or just after transition, I shall do it.

It has nothing to do with pullback, I introduced that concept into the discussion to try and help you understand the behaviour of the abrupt change of rod leg tension, because you cannot make the cast yourself. In a tethered cast, the change in rod leg tension when the slack is taken up with a multi density line is much more abrupt than pullback.

If I can find some day a technical reason and a mean to adapt the model for a speed change during or just after transition, I shall do it.

It appears to me that there is a blind spot in your models with respect to rod leg tension, I recall a similar discussion with the bouncing bomb casts lifting the rod leg off the ground. If you hit an abrupt stop, N3 comes into play between the rod and line, this is exactly the same.

Vince

[Merlin]

You were looking at the wrong slice of time

Disagree Vince, reread the posts:
#363

Hi Vince and Daniel,
The speed of the fly leg is always increasing albeit at a small rate during the early parts of the cast. It's very noisy data so seeing it amongst the noise is difficult. Ideally I'd have a better camera than the phone, good as it is.
The highlighted node is when the loop passes through the sinking line.

GH post 363.JPG (19.83 KiB) Viewed 413 times

I added a circle. There is a rise in speed followed by a drop to very low level (not visible here).

From my observations of this and many other casts in Tracker, the fly leg is always accelerating while we have tension in the cast. The acceleration is proportional to both the tension and the mass of the fly leg. Maybe something to do with one of those laws of motion some old bloke worked out...

And then

Sorry all - I stuffed this graph up. The chart starts as the transition between running and sinking line enters the rod leg. My bad.
I'll find another mark to post.
My apologies again. Here is Mk4 speed, The highlighted node is the time when the transition is at the loop nose. Unfortunately the frame noise is very large.

And this is the one with extra lines from me, using the new graph posted by Graeme (# 365).

GH transition speed.JPG (31.11 KiB) Viewed 413 times

The blue circle corresponds to the time when the transition is at loop nose. I added 0.06s, the time for the transition to move down to the rod leg (given the transition timing from Graeme’s data) and we are on the black line. Then I added twice 0.3s which is a typical time reaction to a pull back (blue line, then red one). No rise, so where is it? 0.6s is a long time for a rollover.

The late rise in speed coincides with a large rise in rod leg tension

Yes, and tension has increased because of line density (a crude assumption is the string formula)

It appears to me that there is a blind spot in your models with respect to rod leg tension

I doubt it. The bouncing bomb corresponds to a large acceleration of fly leg, the sag or slack in the rod leg is then severely reduced or canceled by dynamic conditions. Of course, one needs to know the ODE for dynamic sag to get a better understanding.

Merlin

[Walter]

I expect I’ll get chastised for this but, those charts you are all using for data are a joke right? This is the worst abuse of data science I’ve ever seen in my life.

Btw, what the heck is dynamic sag and how does it apply to am or coam?

[VGB]

Daniel, you are trying to analyse noise.

Yes, and tension has increased because of line density (a crude assumption is the string formula)

Agreed, the more sag you have in the rod leg, the longer it will take to pull taut and acceleration of the fly leg will be delayed. If I shoot the line, the acceleration may not happen at all. Not getting good turnover on these lines is very achievable.

The bouncing bomb corresponds to a large acceleration of fly leg, the sag or slack in the rod leg is then severely reduced or canceled by dynamic conditions. Of course, one needs to know the ODE for dynamic sag to get a better understanding.

To what external force do you attribute the large acceleration of the fly leg?

Dynamic sag -

Vince

[Walter]

Can we please try to stay close to the topic of COAM in this discussion?

Get back to the topic or I'll close this thread soon.

I withdraw my previous dissent. I think this thread has exceeded its expiry date.

[Graeme H]

Daniel,

That is noise in the data.

Cheers, Graeme

[Torsten]

Hi Daniel,

I've checked the Graeme's video and I'm not surprised that it's difficult to reproduce results with your analytical model - because of upward directed trajectory and the fly leg has a significant wave / tailing tendency, the "measurements" of the velocity look very noisy to me. The requirements are straight fly/rod legs parallel to the ground. Not really suited to verify your model for predicting of the the loop size. I remember when I've inserted a small dip in the tip path for my simulation, the result was a significant tail, there are some animations in the archive.

Actually too much off-topic here, please open up a new thread for your model; the scope is clearly defined:
(also @all!)

Can we please try to stay close to the topic of COAM in this discussion?

I think you have already shown for your model that angular momentum is not conserved.

@Gordy
If your system is a semicircular loop section, you need to consider *all* external loads, including the force from change of momentum of the fly leg. I don't think the torque from this force is cancelled, else the loop wouldn't accelerate if you neglect gravity, aerodynamics and material losses. The arrows in Graeme's drawing might be not representative. I think this is another reason why conservation of angular momentum is not applicable for this particular system.

On the other hand, you can always construct a larger system, where all conservation laws are fulfilled - e.g. our universe

Maybe someone has an idea how such a system needs to look like and could present a concept to answer Paul's question?

How about the question of COAM being responsible in part for loop morph?

Greetings,
Torsten

[Merlin]

I know Graeme, this is why I say there is no visible change in speed due to transition. The change at the end of rollover is obvious despite the noise.

For Vince

Change acceleration for high speed, which means high tension for a given (level) line.
If you want some explanation about dynamic sag in a rod leg (by opposition to static sag in a catenary), open a new thread otherwise I could be put in jail by some censor acting on the board. But I am not sure to answer, the board is invaded by lack of freedom, lack of tolerance and open mind attitude.

For Torsten

I already explained that Graeme’s video was not suitable for the model, nothing new under the sun.

I’m back in my cave waiting for a positive change in discussions. I am shocked by some comments.

Merlin

[Paul Arden]

Maybe someone has an idea how such a system needs to look like and could present a concept to answer Paul's question?
How about the question of COAM being responsible in part for loop morph?
Greetings,
Torsten

I like this part. Unfortunately I don’t have the required flyline here in the UK. I’m back for a funeral. I’ll be back in Malaysia 14Nov. It would be nice to go into these topics with the purpose of furthering understanding and arriving at commonly agreed results.

Cheers, Paul

[Graeme H]

I'll let someone else make a cast that matches the model. That's beyond my capabilities I think. (At least here on earth where gravity is a factor in casting a heavy line. )

Cheers,
Graeme