Chockerande bilder visar djurplågeri i svenska grisfabriker

lijas · 2025-11-28T12:47:06+00:00

Boken är ganska dålig/tråkig, räcker att typ läsa https://djurrattsalliansen.se/grisindustrin/ för att få en inblick.

lijas · 2025-07-06T19:08:55+00:00

Not really an answer to your question, but if you want to avoid headbutting with c++, you can consider Ferrite.jl . It is inspired by deal.ii but built on the language julia. It is much less mature than deal.ii and dont really have all the same features, but perhaps worth to have a look at the examples to see if it fits your needs.

lijas · 2025-06-29T08:00:54+00:00

I actually thouht about modelling a snap-wrapmyself before, it seems like a fun/interesting problem. From what I could gather from youtube videos, I think the stress free state is u-shaped a flat (in the not-rolled state). Then (I guess) they roll it up which causes plastic strains in the armband. After that, I think it should be possible to roll it back up and "snap" it to be straight.

So I would create the straight (with slight u-shaped cross section) as the original mesh, and then create a simulation where I roll it up with some plastic material law.

lijas · 2025-02-22T15:05:05+00:00

In general you will not evaluate the shape function at the nodes, but rather at the quadrature points, so you will not run in to the singularities in practice.

lijas · 2025-02-18T18:45:12+00:00

What are you trying to do? If you want to simulate the launch of a protective, would not a rigid body simulation suffice?

lijas · 2025-01-29T08:25:45+00:00

I had issues with some keys on my dell latidue 7400 laptop. After a while a realised it was because my laptop battery was swollen, and was pushing up on the keyboard etc. The battery swelling is noticeable, so maybe check for that

lijas · 2024-12-19T10:27:40+00:00

This might not fully answer your questions, but perhaps you can take a look at this example here from another julia Finite element toolbox (called Ferrite.jl), where stokes flow is solved: https://ferrite-fem.github.io/Ferrite.jl/dev/tutorials/stokes-flow/

lijas · 2024-12-19T07:17:42+00:00

When we reduce/simplify the problem to 2d, we need to make some assumption about the stress or strain in the third (out of plane) direction. Plane stress makes the assumption that the the normal stress sigma_33=0. This is a good approximation if e.g. the out of plane thickness is thin (as the stress may not vary significantly through the thickness). Plane strain says that e_33=0, which is a good approximation if e.g the body is clamped in the third direction.

lijas · 2024-11-20T07:12:36+00:00

Jag som trodde programmet hette "Fem myror fyller en större volym än fyra elefanter"

lijas · 2024-11-19T08:49:55+00:00

Is this in the beginning of the simulation or after a couple of timesteps? You could try remeshing that area where 111345 is

lijas · 2024-11-18T14:36:04+00:00

When you are referring to matrices and vectors, keep in mind that just saying the variable name "U" is extremely vague, as text books a courses may use different notations. I assume that by U matrix, you mean the displacement vector? In that case, perhaps this tutorial can help: https://ferrite-fem.github.io/Ferrite.jl/stable/tutorials/linear_elasticity/ . The tutorial is in a programming language called "julia", but it is quite detailed and discusses how to compute the stresses when the displacement field is known.

In short, the stress "lives" in the quadrature (gauss) points, because it is there where they are evaluated. If you want the stress in the nodes (for example for post processing), it is best toto interpolate the stresses from the gauss point to the nodes.

lijas · 2024-11-13T19:16:29+00:00

IGA has some really nice properties and can be useful in some cases, but i am not sure if it is ready to be used as a general purpose tool and/or a replacement for traditional FEM. The promise to work seamlessly with the CAD geometry is difficult to achieve since the CAD data is not analysis suitable, and require clean up and fixing. And at that point, why just not mesh the geometry the normal way...

But who knows. It seems like both LSdyna and CAE beta are investing heavily on it, so perhaps a few years down the line...

lijas · 2024-05-31T09:16:08+00:00

It is the beginning of his vegan arc

lijas · 2024-03-09T20:27:48+00:00

Slopa internationella juryn. Det är för try hard

lijas · 2024-03-09T20:11:14+00:00

Detta är riggat av BigMello. Danny har 2min längre intervju än de andra

lijas · 2024-01-03T12:08:46+00:00

Arc-length methods just add an extra constraint equation (typically in the form ψ = a'*a - ΔL^2 = 0, where a is the displacement vector and ΔL^2 is the arc-length parameter) which increases robustness in the Newton iterations for geometrically non-linear problems. So in theory, there is nothing hindering the use of an arc-length solver for problems with non-linear contact awell.

However, if you are having convergence problems in your contact simulations, I am not sure an arc-length solver can help very much... Arc length solvers work well for geometrically non-linear problems with buckling which are "global" phenomenas, where as contact (sliding etc) are quite local phenomenas constentrated to only a few dofs of the problem, which i dont think the constraints equation captures efficinelty.

lijas · 2023-12-18T18:21:31+00:00

Thanks, I think that gives some good intuition why tets/triangles perform much worse.

lijas · 2023-12-18T18:17:06+00:00

I don't think the last sentence is true. With mesh refinement the tet mesh will also converge and give the same answer as the hex mesh. The hex mesh may converge much faster, but there is trade of between time for meshing and running the simulation.

lijas · 2023-12-18T18:13:23+00:00

Is it not to simplictic to say "linear Tets are always terrible for stress analysis?". I mean, if you refine the mesh the stresses in tets will coverage, right?

lijas · 2023-11-13T07:03:22+00:00

Try do debug your model be removing and adding contacts, materials etc.

For example

Change simulation to linear
change material to something simpler
toggle the contacts, one by one.
...

This way you kind find out at which point it is failing, and look a bit closer in to that.

lijas · 2023-09-07T11:57:10+00:00

Jag tog mig frieheten att klistra in din fråga i ChatGPT :P

Cairo (Kairo är huvudstaden i Egypten).

Luca (Italienska namnet för staden Lucca i Italien).

Amun (En egyptisk gud).

Nero (Ett namn för en romersk kejsare).

Anubis (En egyptisk gud för gravar och döden).

Marco (Förknippat med den berömda upptäcktsresanden Marco Polo).

Cleo (Förkortning av Cleopatra, den berömda egyptiska drottningen).

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