Full Version: Root Fillet Example Model

Show messages:  1-12  13-27

this is the end goal of creating the cad model. stress evaluation and modal analysis. i attached some pics. fea model in mecway. load was 4600 rpm. the aero loads are very very small so they don't need to be modeled. i have checked that out previously. this is a delta computer case fan. the real part is much thinner and made with plastic. my part is aluminum and needed to be much thicker, because of that. this is just an example. i don't have the material properties for the real product.

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Hi Anthony, yes seam edges can be a problem in filleting with MoI as well. A fillet in MoI will not be able to cross over some other edge in the model that is not being filleted but that the fillet is going to run into. So that part is similar probably, sorry.

- Michael

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Hi Anthony, what about this version. This is with no fillet but exported out from MoI instead of from Rhino. Maybe it doesn't like something about MoI's STEP export. If this one does mesh ok then I guess it's something about the fillet that it doesn't like.

- Michael

Attachments:
moi_airfoil_no_fillet_stp.zip

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hi michael,

the last model you sent with no fllet will mesh with netgen but it hangs a little bit on a surface. not sure which one. i imported the rhino model with no fillet and it meshes faster without hanging. but both meshed without a fillet. this is for the solid with the projected curves from rhino. so no fix was done to those profiles. if i fix the profiles i can put a 1mm fillet on it. not really sure what to make of this. just another nurbs filleting oddity. i attached the step file from rhino.

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given the results of the last test, i went back to your 1mm model. i got it to mesh with netgen this time. not sure what's going on there. it seems to hang on an optimize surface step. last nite i left it there for a few minutes before killing it. today it hung but not for too long and finished meshing. i attached pics. i'll run it through fea just to be sure. but it looks like moi can create a quality step model, even using the messed up rhino projected airfoils.

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hi michael,

your model ran through fea fine. i attached the results. i'm not sure what was going on the first time i tried it. maybe the mesh settings i tried were too high. i'm going to try the first model you sent with the even bigger fillet radius. attached are the fea results for your 1mm fillet model.

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the first step model you sent has problems with netgen. on import a number of errors show up. it will mesh but in the area of the fillet seam the elements are all mangled. i tried two different mesh sizes and got mangled elements both times in that area. but your 1mm model worked and that was the goal. not really sure what to make of all this. it's kind of like what i was saying. you can follow the same process over and over but get different results. it's not clear what is causing the problems most of the time. so you end up just trying all sorts of things. so a matter of will power to get a good model out. but it seems like it's easier with moi. i look forward to trying it out.

netgen is free and available here, in case you want to play with it; https://ngsolve.org/news/releases

there isn't really decent help for it, but if you have questions, i can try to assist

i attached some pics of the error messages and of the mangled mesh fillet area. this was for the same exact mesh settings i used for your 1mm model.

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i had some ideas to test. i brought in all the models to netgen and checked to see if those warnings came up. they came up for all of the models you sent me. but two of your models meshed anyways. there were no warnings for the rhino no fillet model and the .08mm fillet model. Also, no warning for my correct 1mm fillet model. you may be getting affected by those bad projected curves that rhino created. i think i posted an updated file that has the fixed profiles in there. and the solid with the fixed profiles before and after filleting. if you try working with that model, the netgen errors should go away. but it seems like those errors don't indicate whether the model will mesh or not. however, netgen seems to work better if there are no errors present, the errors could explain the hanging i'm getting with the models you sent.

when i get moi v4, i will try making the projections in moi. if it does it better than rhino, there may be no issues with filleting and step export. rhino takes my two ellipses and two curves, that have been joined, and turns it into two curves. they break the ellipses up and merge parts of them with the curves. they also re-create the curves in a bad manner. so i have to go back split their two curves to get the ellipses back then rebuild all four curves and join them. the problem here is you loose accuracy doing the rebuild. plus it's yet another time suck. ideally, if the program could project the original curves and keep their structure. rhino can't do that apparently. not sure about moi.

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Hi Anthony, sorry I just don't have any ideas right now on why netgen is having problems with some of those MoI exported files.

So one thing you have mentioned though is a problem with the projecting in Rhino. It might be good if I could see what is going on there. I guess probably the pieces to repeat the projection are in your file, but there are 284 objects in there and it's difficult for me to figure out what's going on. If you could make a simplified version that just has objects in it pertinent to one single projection that is getting messed up that may help yield a little more information on that part of things.

- Michael

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no problem michael, that's understandable. i don't know what the netgen errors/warnings mean either. it doesn't seem to stop it from meshing all of the time. but it does seem to make it hang on the surface optimization. that's about all i know there.

i tried to strip out what you don't need from the file. there are a lot of steps in making the model, so it's hard to take out everything. but what seems to be the root of the issue, in this particular case, is the projection step. after the projection you have to rotate the airfoils to set the sweep. but don't worry about all that. i saved the model for the projection at the tip. you have to set the cplane each time you do a projection onto a cylinder. the dark blue airfoils are before the projection. the cyan airfoils are after the projection. the red and green airfoils have the sweep set. so all those cyan airfoils that rhino creates seem to be the issue. i have to go and edit them all after the fact, then the fillet issues go away. if you look at the makeup of the red or blue airfoils, you will see they are two ellipses and two curves joined together. everything is fine if you use those. things go south if you use the cyan or green airfoils. the green airfoils are the final step with everything in the right position to do a loft. unfortunately rhino screws those up. so i finally figured out if i edit them, things work as expected. there are different layers to the file. i don't know if those are importing for you. that makes the file a lot clearer. if you aren't getting the layers, let me know, and i'll strip the file out more.

but the main step that seems to be the root of all the problems is going from the blue to cyan airfoils. the cylindrical surfaces are what you need to project onto. i believe the screencast shows the process. i should mention that i rotate those cylindrical surfaces to get the seams out of the way. if the seams enter into to any step then all hell breaks loose and i don't know why. i just figured it out by the school of hard knocks (i.e. rhino kicking me in the nards every change it gets).

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hi michael,

i stripped the file down all the way to the one operation i'm curious how moi handles. when rhino 5 does the projection onto the cylinder, the resulting closed curve is all messed up. i have to go and edit it after the fact. i'm wondering if moi keeps the original curve structure after the projection. i set the cplane to the appropriate one. all you have to do is project the dark blue closed curve onto the cylinder. the cyan curve is what rhino 5 generates, that's no good.

thanks,

anthony

ps; i deleted all the previous files i posted, to save server space

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Hi Anthony, I've attached the result of curve projection in MoI, the segmented structure of the curve is preserved in MoI.

- Michael

Attachments:
Anthony_Projected.3dm

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wow that's fantastic. i clearly made the wrong choice by sticking with rhino. i should have switched to moi when i evaluated it so many years ago now. i was under the impression that both programs were using the same kernel. but you have better filleting and projections. probably a lot more things too. thanks for checking into this. i will definitely be purchasing moi v4 instead of rhino v6.

anthony

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Hi anthony no they use different kernels, the part that is the same is they both use the .3dm file format as the main "native" format. But that's just for data storage not for any modeling calculations.

It is pretty useful to have both available, they each have different strengths and weaknesses. But yes many Rhino operations can tend to fuse segments together though which can be problematic. I've tried to avoid that with MoI.

With them both using the same storage format you can move objects back and forth between them easily.

- Michael

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thanks. i think when rhino first started out it may have been using the kernel you are. but then they started with their own kernel. i don't really recall. but whatever the case, moi seems much better at the basics. rhino does have a few features that i thought would be useful. but i'm willing to give those up to stop having modelling problems every single time i use the program. with moi v4 you are adding most of the missing things i was looking for. i think the only other thing is the zebra plots. it would be nice to have the cg location and inertia matrix. but i can live without it. the main thing is being able to make a model without having to do 20 attempts to get something usable. even then, it seems moi on the first attempt is still better than the rhino result.

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Show messages:  1-12  13-27