engine and brakes

[Merlin]

Thus the effect of the front taper in a DT line is to slow the fly leg down, not speed it up a it does in a whip wave.

I'm sorry Gordy, but this not confirmed by simulations. Here is the speed description of the Scandi casts with the identification of the moment when FT is entering the loop:

Scandi 7.JPG (32.44 KiB) Viewed 3350 times

In these runs, the FT (normal way) or the BT (reversed) correspond to a speed increase. The deceleration takes place as the leader enters the loop.A deceleration may take place during the FT rollover at loop level, but only if its diameter is small. For the cast in the normal way, the line speed levels at the very end of the rollover of the FT, just before the leader enters the loop.

Merlin

[Walter]

Hi Walter,

In this plot, it's Velocity magnitude. I'll change the data being plotted when I get home to show both Vx and Vy for each point shown there.

I think you'd also enjoy looking at the same graphs for the Dolphin Nose casts. Some cool stuff going on in the fly leg leading into the loop. Vince and I are working through some options around that.

Cheers,
Graeme

I’ll look forward to the plots. Thanks in advance!

PS - Vince is a pretty bright guy.

[Merlin]

I'm seeing in most casts that the fly leg begins to accelerate as the front taper enters the loop.

Referring to my earlier mail, this observation from Graeme is in line with simulations. Things will vary from line to line, but the general trends are there. I shall run a level line case, just to see what it gives by comparison.

Merlin

[Merlin]

Here it is

Scandi 8.JPG (27.92 KiB) Viewed 3337 times

The level line has the same weight than the scandi.There is no kick since the model does not handle it. You can see an acceleration too, intermediate between the two others. Not surprizing.

Merlin

[Paul Arden]

Thanks Merlin. What I found interesting about Graeme’s video it appeared that the loop travelled at a fairly constant velocity and then accelerated as soon as the taper entered the loop.

Cheers,
Paul

[Graeme H]

I’ll look forward to the plots. Thanks in advance!

PS - Vince is a pretty bright guy.

That he is!

Here's the same information with velocity components split out. (Click on the image to see it in detail.) The little yellow text boxes show the instantaneous values at this frame in the video. The rod leg is moving forward at about 2 m/s.

What I found interesting about Graeme’s video it appeared that the loop travelled at a fairly constant velocity and then accelerated as soon as the taper entered the loop.

That is to be expected Paul. The loop travels at about half the fly leg speed in a tethered cast. If the fly leg speeds up then by definition, so does the loop. I'm trying to work out if the fly leg accelerates because the mass entering the loop is reducing or if the line remaining in the fly leg is now quite small (or both)

Cheers,
Graeme

[Paul Arden]

Ah yes that reminds me to see if I have two identical lines in the storeroom, one of which can have chop. In fact I can probably just take an old DT and chop the front taper off one end.

Cheers, Paul

[Merlin]

I'm trying to work out if the fly leg accelerates because the mass entering the loop is reducing or if the line remaining in the fly leg is now quite small (or both)

Graeme

The effect of the mass of line remaining in the fly leg is to affect the intensity of the acceleration or deceleration, but not the direction.

The reduction of mass of the fly leg is always creating an acceleration,but that can be more than canceled by drag forces at the end of the rollover.

Once you have the basic (and even simplified ODE), this is straightforward.

I am going to look at the "tension dilemna" on my side, because the acceleration or deceleration is not simply a question of linear density of the line.

Merlin

[Graeme H]

Hi Merlin,

I meant mass per unit length entering the fly leg. As that decreases, does the small tension force from the top of the loop have a greater effect on the velocity (F=ma) or is the acceleration due to there being less mass still to enter the loop in the fly leg (again, F=ma).

Or is it both?

Carry on though.

[Merlin]

Graeme

I'm not using linear density in my ODE, and this is why I want to make the bridge. For information, here is the speed history of a TT taper of "line" which starts with a 3 mm diameter and ends with a 0.3 mm diameter. The change in acceleration / deceleration is around 0.9 mm for the piece of line entering the loop. This is the time when drag forces outpace acceleration forces.

TT 1.JPG (23.01 KiB) Viewed 3308 times

For the fun, the relationship between fly leg speed and rholine (top of the loop) for the Scandi cast, normal way.

Rholine 1.JPG (21.38 KiB) Viewed 3308 times

Merlin