Hunting and simulation - the hunt for the virtual pig

Why hunting is systemic and why the use of steel ammunition benefits the environment but not the hunted animal.

10/18/2022

The invitation read "Hunting is Systemically Relevant - But Not Unproblematic." The Economic Council's first face-to-face meeting after the 2020 Shutdown was held outdoors on October 8, 2020... followed by a three-course wild game dinner: Who can say no to that. I certainly can't.

And so board member Wolfgang Hauser had invited us to a joint tour of his hunting ground in Wiesensteig, directly opposite the Albaufstieg of the A8.

Here's a reason why I'm writing this blog two years later: What I wanted to show was not quite so simple in terms of simulation and, being unpaid, had to run alongside. Now, however, we at Merkle CAE Solutions have completed the "Pig" project and I can add to the last lines of the blog I wrote back then.

[Translate to English:]

Aber alles der Reihe nach.

Warum ist die Jagd überhaupt systemrelevant und welchen Nutzen hat die Gesellschaft davon, dass sich das Wild nicht ungestört ausbreiten darf?

Wenn man sich einen von einer Wildschweinhorde durchwühlten Maisacker anschaut oder einen frisch aufgeforsteten Wald betrachtet, dessen Schösslinge von Rehen abgefressen sind und nur verkrüppelte Bäume hervorbringt, hat man eine Vorstellung davon.

Neu war mir, dass der Jäger sowohl der Landwirtschaft als auch Forstwirtschaftschadensersatzpflichtig ist, wenn die Wildschäden ein gewisses Maß überschreiten. Und wenn die Population des Wildes zu groß wird, geht es an den eigenen Geldbeutel.

Es ist Aufgabe des Jägers, durch elektrische Zäune den Maisacker zu schützen. Und Wildschweine sind nicht blöd. Wenn sie erstmal begriffen haben, dass es Stromschläge nur dann gibt, wenn sie gleichzeitig den Boden berühren, dann springen sie über den Zaun und der Rest der Verwandtschaft lernt das und vererbt es an die eigenen Nachkommen weiter. Hier hilft nur die „Ausrottung der Wissenden“, so makaber das auch klingen mag.

[Translate to English:]

Neu war mir, dass der Jäger sowohl der Forstwirtschaft als auch Landwirtschaft schadensersatzpflichtig ist, wenn die Wildschäden ein gewisses Maß überschreiten. Und wenn die Population des Wildes zu groß wird, geht es an den eigenen Geldbeutel.

Part of the hunter's ethos is not to use a night scope, and so the animals learn that rooting in the moonlight is always dangerous. A cloud in front of the moon, on the other hand, provides the necessary protection to dwell in the cornfield like berserkers.

Also, from the standpoint of the herd, it is advisable to have high stands examined by experienced wild boars, who will warn their fellows with a whistle if a hunter is sitting here hidden.

We would not live in Germany if there were no sensible and often nonsensical regulations that do not make the hunter's job easier. And so the closed seasons are long, the regulations lush and it is not easy to keep game within reasonable limits.

Now to our actual topic.

One regulation states that the use of lead ammunition is only allowed to a very limited extent for reasons of water protection. Bullets made of steel penetrate the game body more easily, the impact is not great enough and the game still beats the bushes until it dies. This contradicts the equally sensible regulation not to let the shot game suffer.

This is again something that can be checked by simulation on a virtual pig, although unfortunately there are no ready-made computational models of animal bodies that I know of, and the failure criteria of tissue, bone and meat are also unknown for the time being, or rather we do not know them.

Since I have already lost the squeamish and the supposed animal rights activists at this point, who now write me nasty mails before you continue to buy your anonymous schnitzel in the supermarket, we can continue pragmatically among ourselves.

Bones behave similarly to hard wood and meat like a soft, hyperelastic rubber. A practical test on a cutlet shows a Young's modulus of 0.03 MPa and a tensile strength of about 10 N/mm².

If you want to be more specific, you can find a scientific article about the mechanical behavior of human muscles and bones at the following link: https://d-nb.info/974539120/34.

With this, something can already be done, even if humans and pigs, at least most of the time, have certain anatomical differences.

The geometry of the commonly used caliber 0.308 can also be obtained from the Internet. The material of the projectile, lead or steel, is also sufficiently studied to feed suitable material models for a finite element simulation FEA.

The geometry of the wild boar is more problematic. A CT scan of a wild boar is possible, but too expensive. In addition, we don't have a dead pig, since we already ate it two years ago, as described.

Figure 4 Bombardment with lead projectile

For this reason, the Merkle CAE Solutions team had to settle for purchased 3D anatomical data of a common domestic pig. A pig is a pig! But it contains everything that can be found in a sow (see Figure 2).

These detailed models are not easy to use for finite element analyses and have to be prepared first. We, i.e. Sören, first had to clean out the model down to the parts that were essential for us (skin, muscles, rind, heart and bones). But we didn't need the whole 2 years just for the meshing! You grow with your challenges, but I don't want to bore you with the details.

The finished FE model with transparent skin and rind is shown in Figure 3.

So the Merkle CAE Solutions pig is not just skin and bones, even if it may look that way at first glance!

Everything else is then classic craftsmanship of a calculation engineer:

To give the projectile made of lead and then the one made of steel the necessary speed and let it loose on the helpless FEM pig model.

Figure 5 Bombardment with steel projectile

The subsequent evaluation is not quite trivial. Some elements are deformed to such an extent that they can no longer be displayed reasonably. They are simply suppressed here from a certain strain.

You can see the results of the FEM simulation here:

In the case of the lead projectile, the entire heart is shredded and the exit channel is greatly enlarged. Due to the impact, shock occurs, which is usually sufficient so that the pig dies immediately.

When steel ammunition is used, on the other hand, there is a straight through shot. So if the heart or other vital organs are not hit accurately by the hunter, the wounded animal will strike the bushes and die there in agony if it cannot be found and redeemed by the hunter immediately.

The video below shows the behavior of the FEM model when fired with both types of ammunition.

Video 1: Bullet simulation with different ammunition

So what is well-intentioned in the ordinance for environmental reasons turns out to be more of a disservice to the wild boar. For the hunter, too, who has to spend hours searching for the injured animal in the undergrowth.

I hope I didn't strain your nerves with this blog. But you can see that the limits of simulation are far from being reached. Body models in particular are very complex in terms of modeling, but can deliver meaningful results even with good assumptions. Ultimately, everything is a question of effort and benefit.

Currently, we put virtual humans into protective clothing and expose them to hostile environmental conditions such as great heat, great cold or even vacuum in order to be able to build better protective clothing, e.g. astronaut suits. Because you won't find volunteers for this kind of experiments.

But that is another topic.

Your Stefan Merkle