This topic is going to be my RnD place for paper simulation fx

How one would appproach creating paper sheet simulation?
For example, how to use the right scale or how to set up simulation, so it is in “correct” scale.

And also, is it possible to just simulate paper that is held in hand?

I have made a sample scene but it doesnt look quite right, I will post it a bit later, in the meantime I would love to hear some advice about this, so maybe I can do some changes to my scene before I post it.

Thanks in advance,
Tom

Now POPs are in DOP land. So I'll go with POP simulation then instance geometry on those.

I have prepared my first problem.

Basic scene with box and a paper. Paper is falling on the box.

Problem #1: It seems i cant get it to stop that flapping (I can only make it slover, but that doesnt resemble how actual paper would look )
I tried a lot of different settings, also these:
http://www.sidefx.com/docs/houdini14.0/cloth/clothrecipes [sidefx.com]
but still it's not giving desired results, specialy that non stopping flapping occurs. It looks like it doesnt lose energy or something.
It does look like a nice bird animation

https://www.youtube.com/watch?v=bhpVMz3VumM [youtube.com]

one example:




So, how can I get rid of that flapping?
I have also attached the scene.

P.s
Btw how can one embed video here so it would be possible to playback it in the forum?

simple cloth obj

Simple card sliding off a collision object . Not sure what your a re doing but it seems to me as you have been playing a bit to much with the retaliative stiffness in combination with some other parameters.

Thanks for the reply Rob!
What im trying to do is to make it look like paper.

Your first example:
rse_simple_paper_collision
I'm not sure if it looks like paper, more like fabric.
Here is simple reference I shot (sorry about the quality, cheap cam )




rse_simple_card_slide.hip
Your second example is more what I need. It seems that I have misunderstood how to use these values from this link:
http://www.sidefx.com/docs/houdini14.0/cloth/clothrecipes [sidefx.com]
In this help card -> Relative Stiffness it says:
http://www.sidefx.com/docs/houdini14.0/nodes/dop/clothobject [sidefx.com]

These values should lie between 0 and 1 and act as modifiers to the Overall Stiffness for specific types of deformation

Does that mean the values I put there (Relative Stiffness Tabs) are used as a multiplier with Overall Stiffness?

##########


And another thing… What is the actual difference between Week and Strong Bend? How do they work?

Cheers,
Tom

Problem #2:






As you can see from the images above, if I start with the paper sheet that has some custom form, it doesnt bend and become flat when its falling, like the real paper would do because of air resistance.

Decreasing Surface Mass Density on Cloth Object node didnt work.

What I'm trying to get is the proper behavior of paper, otherwise it just doesnt look like a paper and I cant figure it out on my own.

I have also updated the scene a little bit.

Does that mean the values I put there (Relative Stiffness Tabs) are used as a multiplier with Overall Stiffness?

They act as a subset of modifiers to the overall stiffness value

And another thing… What is the actual difference between Week and Strong Bend? How do they work?

The parameter help explains the function of both parameters.They work as stated above.

Your videos don't show here on the chrome browser. Altering the surface mass density is not going to effect the papers air resistance. Take a look at the drag tab .

Rob

circusmonkey
Take a look at the drag tab .

Rob

Hmm, I should play with those values a bit more, but they realy dont give desired result.
Or I should take couple days off from this problem and look at it with fresh head. I have a feeling I have missed something very basic, and because of that I try too much :roll:

Little more stiffness and drag force should work.

PradeepBarua
Little more stiffness and drag force should work.

Can you please show me how to work with the drag? (as stupid as this request may sound… but drag just slows it down…)

Maybe if I increase both drag and gravity it could work? Will try this one also later :mrgreen:

Thanks for the replys Rob and PradeepBarua

PradeepBarua
Now POPs are in DOP land. So I'll go with POP simulation then instance geometry on those.

Behaviour you are looking for can't be achieved with POPs. I was wrong, didn't see your reference. Cloth is best.

PradeepBarua
Behaviour you are looking for can't be achieved with POPs. I was wrong, didn't see your reference. Cloth is best.

No problem, I should have posted the reference with the first post.

toms993

PradeepBarua
Little more stiffness and drag force should work.

Can you please show me how to work with the drag? (as stupid as this request may sound… but drag just slows it down…)

Maybe if I increase both drag and gravity it could work? Will try this one also later :mrgreen:

Thanks for the replys Rob and PradeepBarua

You can animate drag value or activate it after certain frames when you want your paper to settle down.

PradeepBarua
You can animate drag value or activate it after certain frames when you want your paper to settle down.

Thanks for the suggestion.
I plan to do a bit more complex movements of paper, so Im not sure if animating drag would be realy usefull. Thats why I want to achieve as much as I can without doing much cheating.
Isnt that the point of FEM? (ofcourse with some limitations)

Im going to post a scene with more complex paper movements later.

A little tip for those who want to create falling paper.
More extreme drag values produce nice falling of paper:

Default:
Normal Drag - 1
Tangent Drag - 0.1



Custom:
Normal Drag - 10000
Tangent Drag - 10




P.s. This still doesnt mach the behavior of real paper what I'm aiming for, but it may be good enough, for this sort of effect.


Tom

Hi,

Some clarification about the Cloth Object parameters:

The Relative Stiffness settings for “Stretch”, “Shear”, “Weak Bend” and “Strong Bend” should all be picked between 0 and 1.
These act as *mulipliers* for the “Overall Stiffness”.
Combining a “Relative Stiffness Stretch” of 4000 with an “Overall Stiffness” of 2000 would result in an effective stretch stiffness of 8,000,000, resulting in the strange behavior you witnessed.

Some of the help documentation for cloth, for example the “cloth recipes”, still has tables that don't account for the Overall Stiffness multiplier. The cloth recipe's recommended settings will be corrected in tomorrow's build of 14.0.

For simulating paper, I'd start out with the defaults, change “Weak Bend” to 0 and change “Strong Bend” to 1. To increase the perceived thickness of the paper, you can increase the Overall Stiffness.

I hope this helps.

Michiel