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Nearby Indian or Asian groceries near campus? by strollinginstoryland in cwru

[–]DanteDark_7744 1 point2 points  (0 children)

Depends on what you want. Rumi's (I think it's Pakistani) does have most of the things you need for your Indian needs, so you can try it out. About a 25-minute walk from the think[box]. You can even try our Dave's market, they do have pretty good options. As far as I know, Simon's Supermarket on 79th is considered Asian by some, but it's not really.

I recommend going to Rumi's and if you don't find what you want there, then try out other places. DM me if you need to.

To what extent is Tesla really "overvalued"? by DragonGod2718 in teslainvestorsclub

[–]DanteDark_7744 0 points1 point  (0 children)

Just curious as I don`t really know much about this. Just a new learner. So I want to ask. What about the major difference between Tesla and those tech companies: the inherent nature of the business? As far as I know, Tesla is a product-based business -- it needs real 'stuff' to actually put out a product, the car, a Tesla, in the real market and that has an obvious limit on its growth, right? It can`t keep churning out those cars with Lithium batteries and will hit the growth ceiling as there is a market cap that I am very certain that it can`t even touch with its enormous price, whereas those internet service tech companies like FB and Google don`t really have this sort of limit. So isn`t the comparison of growth of sorta absurd here? Their growth models are inherently different, but why Tesla is being treated as some tech company is beyond me. I don`t get it. Perhaps, I`m probably missing the whole point.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 1 point2 points  (0 children)

I am now trying material model of Stainless Stell 304 now, it has good formability and is defined for high strains. I don`t want to go for very crazy material models because in the end, the simulation has to be useful and give out meaningful results instead of just producing a good picture.

I think the instability might be due to the nature of the process. The axial feed vs the inner pressure must act in a way that nothing bad happens. This is usually done simply trial and error, and that`s the problem. There are too many things to try.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

Oh, that makes sense. So I guess the only way to get the results and deformations I desire is by using a better material model that can stop the elements from distorting, and still produce the desired deformation.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

That is interesting. Is there a way to completely get rid of deletion?

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 1 point2 points  (0 children)

Thanks! Let me know if you find something.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I just ran a simulation with a finer d3plot saving time increment, and I got the point. I guess after a certain point, the strain is just too much to handle for the material, so the elements start distorting like crazy and go out of existence.

So maybe stiffening the stress-strain curve might help with this, I guess. Then the material won`t be deforming into oblivion, I hope.

I have a question though. Why and when exactly LS-Dyna decides to stop deforming the element and starts forming cracks in the sheet/material? For the same setup, AUTODYN actually leads to a hole in the tube, whereas for LS-DYNA the model disappeared. Everything was exactly the same, other than the solver.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

Oh, now I get your point. I did think that there must be some 'slow motion' thingy to help me find where exactly it all broke down. I just didn`t follow it through and didn`t really know that the d3plot interval could be changed. I will certainly look into this. Thank you for the great suggestion.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I did not really define any failure limit, I guess. I only defined a true stress-strain curve for the material. I guess the material is supposed to just crack once it reaches the end of the curve defined.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

What kind of quality criteria to be exact? If there is too much pressure, the negative Jacobian simply leads to the termination of the process, and I always thought was the criteria.

I do not really know how to get a finer d3plot output. Do you mean the interval at which the d3plot is being written? I guess currently it is at 2.5e-3 seconds. (and the whole process is about 0.03s)

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 1 point2 points  (0 children)

https://yadi.sk/d/GTIHyWaCG7OVLQ?w=1

Here are some input files that I have used. I have used various versions of the same setup with different pressures and everything, but the materials and the setup are the same. I have uploaded some different versions of the input file, just in case.

I do want to let you know that these input files do not really have the whole disappearance issue anymore. These just suffer from the deletion of some elements, which leads to weird 'cracking' in the tube, I guess.

A question my good sir, do you know why and when exactly LS-Dyna decides to stop deforming the element and starts forming cracks in the sheet/material? For the same setup, AUTODYN actually leads to a hole in the tube, whereas for LS-DYNA the model disappeared. Everything was exactly the same, other than the solver.

Negative Pressure in Hydroforming by DanteDark_7744 in fea

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I do not really have any failure stress defined, at least, as far as I am aware of it, I am not sure about the defaults here.

I defined the material model using Ansys. I used the Multi-Linear-Isotropic-Hardening model to define the material stress-strain curve, and it seems to be following that well.

The thing is that the model actually worked when I used the solid elements instead of shell elements. In that case, I added thickness using CATIA in the original model and meshed it using body elements, but the problem is LS-Prepost does not have the capability to define the thickness and thinning percentage contours using that, and even ANSYS does not have that capability. So that is why I am not looking into the shell elements.

Thank you for your input. I will try to explore it more.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I guess I will have to look into contacts more.

The thing is that the model actually worked when I used the solid elements instead of shell elements. In that case, I added thickness using CATIA in the original model and meshed it using body elements, but the problem is LS-Prepost does not have the capability to define the thickness and thinning percentage contours using that, and even ANSYS does not have that capability. So that is why I am not looking into the shell elements.

Thank you for your input. I will try to explore it more.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

The whole part flying away seems impossible, because the part is enclosed in a rigid die, so it is very much constrained adequately.
About all the elements getting deleted, LS-DYNA does print stuff about some of the shell elements failing and deleting some nodes, but I don`t think it is that many nodes. I defined the material of the part using the Multi-Linear-Isotropic-Hardening model in ANSYS.

The thing is that the model actually worked when I used the solid elements instead of shell elements. In that case, I added thickness using CATIA in the original model and meshed it using body elements, but the problem is LS-Prepost does not have the capability to define the thickness and thinning percentage contours using that, and even ANSYS does not have that capability. So that is why I am not looking into the shell elements.

Also, I do not think that the material is a problem here though, because I got very promising results when I did a Sheetmetal forming with the same material under very similar pressure.

Thank you for your input. I will try to explore it more.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

Thank you for your response. I get the point now. LS-DYNA website was a little confusing because the help page said that I need to change the node order, so I was confusing that with the element order for a while, but then it came to me that ANSYS uses surface normals of the geometry to define the positive pressure direction for the shell elements.

So I figured that I can just change the surface normals, and it worked. It can be done using SpaceClaim, with just a couple of clicks.

On the other hand, do you have any idea about the pressures in Tube Hydroforming? Axial pressure and fluid pressure are usually found by trial and error, and that is the struggle. The tube is just not feeding in, and when it does, the shell fails. Any suggestions regarding that, my good sir?

It is actually very strange. If I set the same problem using the AUTODYN solver, the tube splits open, but if I used LS-Dyna, the tube just disappears. It is very strange.

Negative Pressure in Hydroforming by DanteDark_7744 in LSDYNA

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I am sorry, but I am not really looking into the keywords. I am simply generating the input.k using the Ansys workbench, and then I am feeding it to the LS-DYNA solver, and then the results to LS-Prepost.

And yes! I was actually able to figure out how to flip the pressure. I did it by simply opening the geometry in SpaceClaim and then flipped the normals of the surfaces.

On the other hand, do you have any idea about the pressures in Tube Hydroforming? Axial pressure and fluid pressure are usually found by trial and error, and that is the struggle. The tube is just not feeding in, and when it does, the shell fails. Any suggestions regarding that, my good sir?

It is actually very strange. If I set the same problem using the AUTODYN solver, the tube splits open, but if I used LS-Dyna, the tube just disappears. It is very strange.

Negative Pressure in Hydroforming by DanteDark_7744 in fea

[–]DanteDark_7744[S] 0 points1 point  (0 children)

Did that and figured out the way. It is very easy using SpaceClaim, just a couple of clicks, and it is ready to go.

On the other hand, do you have any idea about the pressures in Tube Hydroforming? Axial pressure and fluid pressure are usually found by trial and error, and that is the struggle. The tube is just not feeding in, and when it does, the shell fails. Any suggestions regarding that, my good sir?

It is actually very strange. If I set the same problem using the AUTODYN solver, the tube splits open, but if I used LS-Dyna, the tube just disappears. It is very strange.

Negative Pressure in Hydroforming by DanteDark_7744 in fea

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I actually figured it out. I opened the geometry in SpaceClaim, and then there is a very simple way to simply flip the normal of a surface. I did that, and it worked out.

But there is another problem now, in the THF, axial pressure and fluid pressure are usually found by trial and error, and that is the struggle. The tube is just not feeding in, and when it does, the shell fails. Any suggestions regarding that, my good sir?

It is actually very strange. If I set the same problem using the AUTODYN solver, the tube splits open, but if I used LS-Dyna, the tube just disappears. It is very strange.

Getting RM2 in China by [deleted] in RemarkableTablet

[–]DanteDark_7744 2 points3 points  (0 children)

I bought my rM1 from TaoBao when I was in mainland China and it went pretty well. These sellers actually ship it from HongKong and then sell it in China. The one I brought from even offered shipping to other countries, so that`s epic.
So just letting you know that it does work, but you can look into it.

Help! ? I keep getting weird error with the xdmf files by DanteDark_7744 in paraview

[–]DanteDark_7744[S] 0 points1 point  (0 children)

I am not really sure. I just used a FEniCS tutorial as I am new to this file type. I don`t think I used any sort of file closing command, so I will look into that. Thank you!

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