2D casting model

[Merlin]

Hi all

Here are the very first data coming out from a study of the role of the stiffness of a rod with my new 2D (2 dimensions) casting model. The base case is the simulation of the Paradigm cast.

I am using my current best guess of the Paradigm cast (thanks to Gordy for his help in providing the data), and I am only changing the stiffness of the rod. When doing so, some parameters of the rod are changing (e.g. equivalent mass, swing weight) and this is taken into account. I assume that the rods belong to the same series (same basic design, same non linearity).

Here are the tip trajectories:

There is no change in the input, which is a strong assumption. Most of the studies performed to analyze the role of the caster have shown that they adapt their input to the rod. So this is rather theoretical, but let’s sees what it tells.

The path for the softest rod suggest that the loop should be tailing (k = 0.55 N/m). In practice the caster should adapt his stroke and lowers the intensity of its input. The stiffness of the Paradigm is 0.75 N/m and it looks pretty straight. The 0.65 rod is at the limit of the tail, the stiffer ones have concave paths. The following table gives an idea of the theoretical performance of these rods:

stiffness effect.JPG (17.69 KiB) Viewed 5169 times

You can see that the maximum speed does not improve anymore from 0.85 N/m, but that one has to produce more torque to follow the input speed profile (figures represent the torque produced at hand level). This is due to the increase in swing weight of the rod. Ymin is the lowest vertical position of the rod tip and gives an indication of the loop size.

So these data could mean that the Paradigm (k 0.75) is well tuned for the line (which remains unchanged here), or that the caster is smart in using it at its best.

Merlin

[gordonjudd]

The stiffness of the Paradigm is 0.75 N/m and it looks pretty straight.

Merlin,
For comparison with your model here is the tip path that Grunde measured for the Paradigm cast from RSP0 to just past MCF for Mathias' elbow out casting style.


You can see the actual path is quite domed compared to the ideal straight line tip path that Dr. Gatti-Bono assumed in her first paper.


You model appears to be giving results that are very close the measured data. I will hope to learn how to use it.
Gordy

[Merlin]

Hi Gordy

The tip path I get for the Paradigm is flatter than the record, but the path is highly influenced by the various rotations of joints involved, and you know better than me that for this cast, it is really difficult to get precise data that can fit the idealized conception of the input in my model. I am still trying to improve the result but it might need a lot of time for a small result. Nevertheless one can live with that, the main objective being to make comparisons, and this is why I started with stiffness. Non linearity is scheduled for next time

Merlin

[Eagle Crest]

I look forward to your piece on non-linearity.

Steve

[Merlin]

Here it is Steve

All rods have the same length (9’), and I change the non linearity in the model. Here it is an “angular non linearity”, but for those who prefer the usual way of looking at it, you can divide those figures by the square of the length of the rod (after deducting the grip, something like 8 inches) and you will get the order of magnitude you are accustomed to.
I also changed the stiffness in some cases to cover a larger spectrum, because you will see that the differences in trajectories are small (less than 10 cm in height).

The reference case is always the same (k = 0.75; NL = 1.75), and corresponds to the blue line. If I increase non linearity (red line), several rod parameters follow this modification, and the trajectory is lower. This is due to the fact that increasing NL goes along with “tip action” and that the tip flexes first, while a “butt action” rod of same stiffness bends from the butt, so it exhibits a higher trajectory. This is counterintuitive but this is due to the fact that the stiffness is the same here. Our mental representation of “tip action” and “butt action” rods corresponds to a softer /slower butt action rod by comparison to the stiffer/faster tip action rod. If you add an adaptation of the cast on top of that, you realize that again several parameters can combined to explain the visible difference which we can read again and again in fishing books.

Then I increased the stiffness of the rod (0.9 N/m) with the higher NL value and this one has the highest trajectory (green line). No surprise here, this is the effect of a smaller bending. Then again I increased the non linearity and got a flatter curve (orange curve). Incidentally, we get in this case the highest maximum speed (23.7 m/s), while the lowest speed corresponds to the softer rod with less non linearity (in blue, 23.3 m/s). This is the effect of a higher speed/higher stiffness. So the lowest trajectory is the fastest one with the set of chosen characteristics for rods, and this is counterintuitive again.

Enough for today, it could be difficult to digest.

Merlin

[hshl]

Great Merlin,
Franz-Josef and I are looking forward. Redistribution effects (due to varying inertia) should be recognized by this new model too.
Regards Tobias

[Merlin]

Is the lever arm effect (longer arm for a tip action rod, shorter arm for a butt action rod) a myth?

Since I have started testing the model, the tip path is similar for two comparable rods of different action, and only the speed is higher for the faster rod. Even if deflections differ, their time history is different and this could be one of the explanations.

Another one could be that the model is unable to differentiate enough, but the model is able to see that if one overloads a rod, then he gets a tail (a downwards dip in the tip path).

Merlin

[Merlin]

Hi Tobias

The inertial effect is in the model (the intermediate component of the swing weight), but until now I do not see a large contribution in terms of speed (it is expected to be significant for light loads, as shown with the 1D model).

Merlin

[hshl]

Hi Merlin,
maybe the inertial effect benefits (reduces) the torque the caster has to apply in order to gain the speed ? However, I'm excited to see the next results ...
regards, Tobias

[Merlin]

Using the current 2D model, eliminating the inertial effects in the cast reduces the maximum speed by some 7% (Paradigm cast model).

When the new model dedicated to a specific rod is ready, I shall test this again, and this time for various load.

Merlin