Rigids - Simple object blowing through fractured pieces

[SanJuan]

Hello all.

I've got what I think is a simple enough problem to solve, but I'm not quite sure how to go about it. Essentially I want to launch a solid object through a structure and for the solid object to completely blow through the fractured pieces. But when I try to sim it all, the solid will blow away a few pieces then come to a complete stop before falling to the ground.

Think of a giant canon ball blasting through a wooden beam.

I figured the issue might be that the density wasn't high enough, but even if I crank it up past a million it still gives me the same result. I'm not sure how to make that ball carry enough weight to not be stopped by splinters. Since I want it to fly through the scene and interact with the structure realistically, I'd prefer not to settle with animating the motion manually.

For the record, I'm using RBD packed objects for both the structure and the I'm using regular glue constraints at around 15 strength to hold the grain together, and another lower value to hold the beams in place. There are also -1 strength clustering of the end pieces, as well as 0.5% of the rest of the splinters.

 

Thank you.

[Noobini]

if the cannonball is godlike i guess, then why don't you just simply keyframe it and it will be unstoppable...well....only you can stop it...

Here I've got a simple setup, not same as yours but should illustrate the point, my tiny ball is keyframed to go left-right, set it to Create  Deforming Static...and it will blow those gigantic piece of concrete apart with ease...and the cannonball will stop in midair to admire its work too....

[SanJuan]

I get what you're saying, but I still wanted the objects in the scene to offer some resistance rather than the ball passing clean through. The wooden structure is just one element, I've also got bricks around it to form a whole tower. I want the ball to smash through the tower while still looking somewhat physically accurate.

 

If push comes to shove, I might settle for keyframing the motion myself, but I'd still much prefer to figure out this problem. Something tells me its an issue with the geo's density, but changing it on RBD packed object doesn't yield any different results.

[Noobini]

ok, so for my little scenario, if i don't use keyframe now...I simply increased my density as you've done, and that worked fine..have you also increased initial velocity ?

[SanJuan]

I Have. In RBD packed, I set the initial velocity to make it fly towards the structure, and I raised the density to about 100 million, and still nothing.

[Noobini]

hmm...for me I just increased my density by factor of 100 and that did wonders...plus a little extra speed...prolly easier for others to help you if you could upload the scene.

[SanJuan]

My scene is actually pretty large, with several file caches in between nodes. I usually don't see people sharing huge scenes, so I don't know how well posting that will go over. That being said, I pruned the file as a whole to lighten it up and keep the bare necessities for the sim. I've posted it on Google drive along with the cached geometry and constraints.

Be warned that there's a lot of elements in the scene, so the sim takes a while to start up. The problem becomes apparent around frame 12.

https://drive.google.com/drive/folders/1ykrv1E_ee7TwWXEZhAKq4xcs5rQeQWLx?usp=sharing

Edited December 19, 2017 by SanJuan
wrong link

[Noobini]

my first instinct was maybe your floor has an impenetrable invisible shape...but it looks ok...the blue proxy...I've also change the merge4 to mutual...just so the ball CAN affect the floor...then I tested the threshold, ie,. lowering the threshold to 0.1 coz I thought what if active was set at too high a level...none worked so far...

have also tried overwrite attribute active, since you did use a wrangle to set it...but didn't work...unless it needs to be unpacked ?

(threshold looks a bit sus tho...0.55 hmm...shouldn't it be like dunno say 5 or so ?)

Edited December 19, 2017 by Noobini

[SanJuan]

I don't think that's the issue. The non-active pieces are just there to create a base to the structure that'll never break, so as to support the whole thing. If you use a delete node to visualize the active pieces, you'll see that the height threshold is actually much lower than the ball's height.

As for the geometry itself, I figured it would be lighter to use packed geo. Besides, the constraint points share their respective piece's name attribute, so they are holding properly.

Maybe there is a way to ensure that when the traveling ball encounters any resistance it's velocity decays at a slower rate?

[SanJuan]

Here's a little follow-up...

I've sim'ed the ball to fly towards the tower and cached it out, then I made plugged the animated ball into my main sim as an animated static object. Then I use a SOP solver to turn it into an active object after it passes through the tower. Not the most accurate result but it's definitely easier to sim. I'll use this setup to figure out my constraint settings for now...