Vellum Inflate From Flattened State?

[Atom]

I have this sphere that I have deflated to a flattened state. I wrote that final frame out as a .bgeo.sc file. I have brought that into another simulation where I want to inflate the flattened sphere.

How do I configure vellum to inflate this object?

ap_inflate_sphere_101818.hiplc

[Noobini]

hmm...curly one, no success from me either....so....really Houdini still can't do simple Balloon pressure. In Max I can simply use negative pressure (not crushing it with a collider) , it works itself into a crumpled heap, then I used positive pressure to blow up the crumpled heap into its original shape (well, a puffy version of it anyway).

Only thing I can think of is have some omni wind blowing from inside the sphere to blow it up...(or fill it with liquid/particles ?)

Edited October 19, 2018 by Noobini

[Noobini]

here's how easy it is to achieve the effect in Max....really, 2 settings, Pressure and Gravity.

(Meanwhile, Houdini fanbois are too busy shouting....die Max/Maya die !!!)

 

[Skittixch]

Inflation is absolutely possible in vellum. See this hip file for one approach. Make sure you look in the vellum solver to see the magic.

Inflate.hipnc

[Noobini]

well...is that Pressure ? I think that's a 'morph' effect...

So, if you have Atom's collapsed sphere..can you apply internal Pressure to blow it up. As I said in the Max example....it won't get back its ORIGINAL shape....but a puffy version of it.....because there's actual Pressure inside.

While your example, I'm not technical enough to know what the gas solvers are doing...I'm guessing it just a blend/morph effect.

Edited October 19, 2018 by Noobini

[Noobini]

here's the jet effect if anyone feels up to the challenge...No, I didn't have to jump thru any hoop...it was just cut off the bottom and...sim

 

 

[Skittixch]

That video is very interesting. I haven't tried pressure with nonmanifold Geo... No morphs in my setup...I believe the sphere would inflate without that rest blend, I just threw that in to regain the original volume pre-squish, as the restlengths of the squished sphere would produce a smaller object than would be desirable in my opinion... Definitely things to experiment with though

[poncatoera]

I used sop solver inside the dop and only targeting the prims that has "pressure" constraint attribute in the constraint geom which is usually primnum 0 change the sop solvers data from Geometry to ConstraintGeometry

[Atom]

Thanks for looking into this and the example file. It does look like the effect needs an un-deflated rest state to work. Some others reported this effect could be accomplished by animating the @restlength parameter inside a geometry wrangle, but I have not got that to work yet.

if (s@type=="pressure") @restlength +=1.1;

 

[HM_2020]

Strange, you would think Vellum would have this... nCloth can do it easily too.  I imagine under the hood its just expanding rest lengths of the springs in Maya.

 

 

Edited October 19, 2018 by HowardM

[vtrvtr]

 

38 minutes ago, Atom said:

Thanks for looking into this and the example file. It does look like the effect needs an un-deflated rest state to work. Some others reported this effect could be accomplished by animating the @restlength parameter inside a geometry wrangle, but I have not got that to work yet.

if (s@type=="pressure") @restlength +=1.1;

 

Here's the hip with animating the restlength in a geometry wrangle

vellum_inflate_odf.hipnc

But you're correct you need some data to know when to stop, otherwise the length will just get bigger and bigger

[Noobini]

but to me...manipulating restlength......ie, edgelengths is just faking it. While for a balloon material that is rubber, yes agree it physically stretches/shrinks...but let's say it's made of non stretched cloth (or say a paper bag), if you blow air in or suck air out of it, it puffs up or crumples...but edgelengths do NOT change.

The only real proof is I guess if you cut a hole in the geo somewhere...does internal pressure escape and gives you the jet effect ?

[Noobini]

here's an illustration.....edgelengths of a paperbag don't change....a paperbag with no hole, pressure cannot escape...one with hole...can

 

Edited October 19, 2018 by Noobini

[anim]

what MAX seems to be doing (along with others, Maya, Marvelous) is simple old school force along N

you can easily implement it in Houdini, and while it's not a true pressure it creates an impression of inflating and even air leaking

not specific to Vellum, you can use this with FEM too and while a tiny wrangle is needed I wouldn't call it jumping through hoops

here is an example similar to boxes above

ts_N_pressure_force.hip

[Noobini]

agree...I wanted to see what Max was doing so I put a piece of cloth behind the jet stream to see what comes out....even tho the bag moves...there is NO physical airstream rushing out.

I've managed to mock something up in H17, again not true pressure but a fake effect...bit of a hack, upload soon.

[Noobini]

here's my hack:

 

 

vu_H17_Paperbag.hiplc

[Atom]

Thanks for all the feedback and solutions. I think the simplest way to handle this is to just record the collapsing geometry and play it backwards. I was hoping to get a little over inflate at the end and then a snap back to original size. But this can do for now.

[Noobini]

here's my little tute...(with crappy mic)

 

[Skittixch]

I think it's going to be about blending to the rest position of the un-deflated object, while changing rest length scale and bend stiffness all in the same keyframe...Tie them all together via relative channel expressions.  Not able to test at the moment, but I think that's gonna be the best of all worlds