MODEL YOUR MYOG DESIGNS IN 3D – SEE FABRIC STRESS – COOL SOFTWARE!!

Just what I've been waiting for for years, and has been holding back my tents designs. And clothing designs, come to that…

The apparent ability to do stressed surfaces looks brilliant. Or is this something you did in SketchUp (and if so, how?).

Many, many thanks for this.

Sadly, I think a lot of people will miss just how useful this might be, given the title. Is there any way the title can be changed to make its usefulness more obvious?

Oooohhh !!!!
Stress analysis of tunnel tents … oooohhhh!

VERY NICE!

Cheers

This can change the whole fabric MYOG world!

Glad you folks thought this might be interesting. The stressed surface was done in Marvelous Designer. The only things I did in sketchup for any of these were two bent poles for the tunnel tent and one straight pole for the mid. It's just a render option – either you can view the results of the 3D simulation "as fabric" (the other three pics) or you can see the stress plot, or some other options.

Roger – that tunnel tent was just for you, after reading your DIY tent pages.

I suppose the original title was not very informative for others. I don't know if there is a way to change it – I think maybe admins can…Roger??

Hi Andrew

> Roger – that tunnel tent was just for you, after reading your DIY tent pages.
I did wonder … :-) interesting stuff

I am not sure whether the title of the whole thread can be changed, but I will enquire.

Cheers

I've been looking at the pictures a bit more. Interesting, but I am not sure … So since you have the SW and can drive it, some Qs.

Looking at the teepee picture. The doors are bowed outwards in a way that does not happen in real life. Is it possible to stiffen the door edges? I would expect so, but how? Insert very stiff elastic? Or should one adjust the elasticity of the fabric? (The maths of that can be unbelievably complex in engineering terms!)

A similar (well, related) Q with the tunnel tent. Can one add guy ropes – or at least elastic constraints similar to them? And can one add elastic constraints to fixed points like the bottom ends of the tent poles – to stop them from pulling inwards when the ends re tightened?
(Explanation: I snapped a pole once when I pulled the end of the tent too hard, and that made the poles ends bow inwards too much. The pole was over-stressed anyhow and about to shatter. Fortunately, it was the LAST night of a 2-month trip!)

Yeah, I know: this is not NASTRAN or similar, just a fabric package for 2nd Life! But enquiring minds …

Very interesting stuff ! ! !

Cheers

Nice find Andrew! very cool!

Roger, those are great questions, and of primary importance if this package is going to be useful rather than just neat looking.

In that pic I actually have the fabric elasticity set to what I believe is the highest setting, which seems to be not really all that high. There's a slider bar from 0 – 99, and it's at 99. I found that you can make an edge "elastic" and input a (unitless) value for the elasticity though – see below. With the extra fiddling involved and the fuzzy physical properties, it starts to make me wonder how you can have confidence that any model will be at all realistic (aside from lots of testing, which is what my use of this software is trying to avoid!!). I suppose it might be possible to do some kind of standard stretch test on, e.g silnylon, and then find the fabric properties that best capture the real world behavior. Then try to make something a little more complex, cross your fingers, and see how it works out.

I should mention also that this SW appears to be currently under development. Just reading a little on the forums suggests lots of changes happening quickly. It's also worth noting that the forums are pretty active, and company reps even post a lot in response to questions there. I posted to ask about increasing the fabric elasticity past 99, so I'll let you know what I hear.

As for the tent poles, they are a solid, non-deformable structure in these models. The "avatar" (in my case, tent poles) in the SW is not modeled as a soft or deformable body – it is what it is and doesn't change. So you can't pull the ends together like you describe. You could definitely add guy lines just by sewing on very thin strips of material, with their edges set to "elastic" with high elasticity values.

Hi Andrew

> I should mention also that this SW appears to be currently under development.
Which means that right now is a really good time to ask for features!

> add guy lines just by sewing on very thin strips of material,
Yeah, I could see that in advance. But that is another place where a higher stiffness would be needed.

I wonder how they handle belts? Or can you make strips of very thick canvas? Is the elasticity a function of fabric thickness or weight? Ah, fun!

Cheers

I have to wonder how upgrades work. The license agreement doesn't really help, or makes it sound bad. It says that there are two types of licenses, perpetual and subscription. I see no option to buy a subscription, so that leaves perpetual. The perpetual license requires that upgrades be paid for, but since I don't see how much that costs, so maybe those don't exist either. It will be awfully expensive and heartbreaking to deal with weekly updates.

My question is

what happens if you have no catenary curve, a catenary curve of maybe 1 inch, or 2 inches

do you account for the fabric stretching?

> It's designed (I think) mostly for people to make digital clothing for their Second Life avatars

Surely this tool isn't just for Second Life? Why would you need to produce panel layups for a synthetic model?

No, I think it's genuinely for First Life applications. See some of the demo images: modelled garment vs real garment (on the other hand, they could be attempting to reverse-engineer existing garments into models for 2nd Life…)

I suspect the ability to do tensioned surfaces 'come for free' as part of the clothing drape analysis. It's useful to know where stressed seams are, even in clothing.

The Overview page gives a good, well… overview, discussing pattern block generation, drape analysis, material properties (let's hope it copes with anisotropic properties, e.g. warp/weft/bias).

I notice the $99 personal edition doesn't include 3D data sales. I'm not sure what that means… Does it mean all the lovely draping and analysis isn't provided?

Andrew, my comment about the title was an expression of regret, not complaint; I think this software is potentially very useful to a very wide range of MYOG types. Thanks for clarifying that it's MD doing the stress analysis. Your tunnel tent, did it use a circular hoop model?

The question about the teepee, and boundary effects reminds me of methods I'd considered for previous thoughts at how to do stress analysis, and that is to provide a fixed edge as part of the model; like the curved hoop in the tunnel tent. e.g. insert a catenary curve boundary element to the 'avatar'. Or insert panels that won't be fitted in the final design (e.g. the teepee would have no door opening). They are workarounds that won't be 100% accurate, but they're likely to be better than nothing.

Modelling guyropes should be unnecessary, I think, provided your guys are inelastic; you'd specify the guy attachment points as fixed locations. Oh, hang on… ideally, you'd model the guying point on the ground, and model the guy as a inelastic bar, but with freedom to rotate about the guying point. You might even model the guy as a bungee loop (for ground pegging points, that is, not upper tent body guylines).

The 30 days from download is holding me back at the moment, as I won't be free for a while…

>Which means that right now is a really good time to ask for features!
Exactly!! They have a feature request forum and company reps seem to be pretty active on it.

Some more on fabric properties; here's what they have:
Stretching (warp) strength
Stretching (weft) strength
Shearing strength (not sure exactly what this means, because fabric will not "tear" no matter how much you stretch it)
Bending strength (make this higher for "stiff" guylines and a "belt")
Internal damping
Buckling Point (length ratio)
Density
Thickness

You can also save your own sets of properties as presets (e.g. save a "silnylon" and an "Xpac").

I don't know details on the license. I'm sure they would tell you pretty quickly on the forums though.

Jerry, I'm not sure I get what you're asking. Are you asking to see what cat cut vs. non-cat cut tarps would look like as a stress plot?

Kevin, I believe the no-data sales for the personal license means you can't sell your 3D clothing (that is, sell files…of models…I guess people actually buy virtual clothing). I'm pretty sure all of the capabilities I'm showing are available with the $99 personal license.

They also sell a package called CLO3D, which is a full blown textile modeling package intended more for making "real" textiles – they let you size the avatar up and down within the software, I believe you can add seam allowances in the software, basically everything a real clothing company would want to do. That one sells for…get ready…$7,000. A wee bit outside my budget.

A note since I mentioned seam allowances: you can export your pattern as a .obj file, import it into Google Sketchup (using a plugin you have to download), clean up the mesh (using a plugin you have to download), and then you can just click on each pattern face and do an offset to make your seam allowances. You can not add seam allowances and print directly from Marvelous Designer.

As for the tent, yes it was a circular hoop. Simple and quick for demonstration purposes.

And Kevin – no worries about the title thing. I understood, and you made a good point. :)

"Jerry, I'm not sure I get what you're asking. Are you asking to see what cat cut vs. non-cat cut tarps would look like as a stress plot?"

Yes

If you have a cat cut, is the maximum stress more or less or no difference?

Also, does it let you put in how much the fabric stretches in bot directions?

Ok, I took a guess. Let me know if you'd like it changed to something else!

> Stretching (warp) strength
> Stretching (weft) strength
> Shearing strength (not sure exactly what this means,

Stretching in warp and weft directions is pretty obvious of course. Assume that.

'Shearing' is more complex. Take a square of material and clamp two opposite sides. If you just pull the sides apart from each other you have 'stretch', but what happens if you pull the sides apart a fixed amount then try to move one edge sideways? That's shearing, and has a huge implication for fabric drape.

That gets into tensor or matrix analysis, and I am NOT going there!

Cheers

Never thought I would see the word "tensor" on this site.

+1 for tensors

Jerry, when I get the chance I'll model that and post the 3D stress plot. A fundamental question for tarp makers, for sure.

> Never thought I would see the word "tensor" on this site.

Too many PhDs … :-)

LOL, Cheers

Andrew
I think the distortion of the panels when stretched over the (infinitely) rigid support frame will not be cured by changing the elasticity of the fabric, I think it is due to the pattern panels being the wrong shape to start with. The software just stretches the fabric to fit, regardless of the forces involved. The edges of panels of real shelters are not simple geometric shapes, if this s/w is to be of any use it needs to allow you to create arbitrary shapes for the panels so there is no distortion when fitted over the frame.

It would be cool if the software could design the arbitrary shapes to minimize stress points.

Roger – still working on mine :)

Stuart – I'll have to disagree. The simulated fabric behaves very differently, at the highest "stretching strength", than my real world experience with a shelter made from the same shape panels. Another way to say that is in the real world, I've seen what a tensioned tarp of a certain design looks like, and when I model the exact same thing in the software (without "elastic" edges), the result is quite different. On the other hand, I mentioned but didn't clearly explain above that I can add "elastic" edges. The whole fabric is elastic but you can also simulate adding elastic ribbing to edges (or you might think of it as approximating a folded hem), and this gets rid of those big, unrealistic scoops on the seams and edges.

I think anyone who has made a tarp, pyramid shelter, or tunnel tent would agree that my basic shapes are the same basic shapes that "real world" shelters use. At the same time though, I'll readily admit they were just quick mockups, and I didn't get into the math required to get really exact fits and even out the stress distributions. To be sure, there are tools to make (or at least very closely approximate) any shape you want, so you could get very detailed if you want to.

Jerry – that would be cool indeed. I'm not holding my breath for that from the SW designer. If someone wants to get really ambitious and write an optimization plugin for it though, that would be great. Hmm, any takers?? Maybe retirees with time on their hands?? :)

I'm just a hand grenade throwing troll

don't want to do anything that would contribute

> To be sure, there are tools to make (or at least very closely approximate) any shape you want,

Could I import a spreadsheet of XY values for the edges? I design my tents that way – some heavy maths below the surface.

Cheers