Modeling a pipe welded to a plate

kam33mitch

I am trying to model a mooring bitt where a 12" pipe is welded to a fixed base. The top of the plate has a cap welded to it to support the pipe. I've modeled this 6 different ways and cannot get the materials to behave properly. In the attached model, I drew the profile of the plate and pipe and revolved it to form the part but when the force is applied to the pipe it appears to ignore the top of the material with the pipe collapsing rather then bending. I had the same result using the bonded contact on the cap and pipe.

Any suggestions?

VMH

Hi, is the cap welded/attached to the pipe? Currently in your model, cap is not attached to anything so the pipe and cap will not interact together; therefore the pipe would want to collapse at the top open end instead of bending.

I bonded the cap to the pipe. See attached. I'm not sure if this is what you are trying to do.

VMH

Here's the model. For the elements, I would use quadratic elements (with midside nodes) for better results. I would also divide the pipe and cap more to get a better aspect ratio instead of having long strips.

kam33mitch

Yes, that is exactly what I thought I was doing. Thanks. I'll look at the attached to see what I did wrong.

kam33mitch

There's about 5 ways to model that cap. What I tried was to create a round plate mesh and extrude it. It looks like you revolved a rectangle, is that correct?

What I tried failed when trying to do the bonded contact and also gave material assignment errors I think. This led me to creating the inverted T shape and revolving that which was the model I submitted. For some reason the top collapsed on that shape as you indicated.

Just curious why your method works better so I can think with it when making parts in the future. It seems extruding/revolving created meshes is not the way to go.

VMH

I didn't model anything. It was all your model. I just defined the top cap as a new component which is not needed and created the bonded connection.

VMH

kam33mitch, the bonded contact didn't work for your model if you choose the pipe surface (smaller) as "master". You need to choose the cap surface (larger) as "master" for the bonded contact to activate. See youtube video below (click on the link). Also attached is the model used in the video.

kam33mitch

OK, I'm tracking now.

The more I play with this the better I understand the construction of things and how the nodes connect or don't connect to each other. It's coming together much quicker for me now. I was able to put together the underneath structure fairly easily now and have a great working model.

Thanks for your help.

VMH

I personally like to model 3D solid using FreeCAD and then export the .step file to be imported to Mecway. I have a few videos on it on my youtube channels. Due to someone keep download my videos and uploaded them to different sites for unknown reasons, I took down alot and kept a few.

kam33mitch

After digging in some more I see what you mean. FreeCAD was easier to model with overall when I was trying to put together the entire base.

VMH

There are other CAD softwares like Inventor, Catia, Solidworks, etc but they cost alot. FreeCAD is just one of many CAD modeling softwares out there and it's free. The workflow for larger project is generally modeling in the CAD software --> export geometry --> import geometry to FEA software --> etc. Software like Abaqus has this all these builtin so no need to use an external CAD software but it also costs alot.

Sergio

Hi, you can also use Onshape that is an online CAD suite, modeling is very similar to Solidworks or Unigraphics, and is free for small projects.

kam33mitch

Victor,

Could you take a look at the attached model. I am getting way different results/stresses between CCX and Mecway. Any ideas?

Victor

Hello kam33mitch, the file seems to be truncated. Could you please attach it again? If it has solution data, clear that to reduce the size - Right click Solution in the outline tree then click Clear.

kam33mitch

Sorry about that. try this one.

Victor

It's caused by the collapsed elements in the cap. They're hex8 but shaped like wedge6. I converted them to wedge6 using Mesh tools -> Correct collapsed elements. That has a side effect of removing their faces from the bonded contact so I also added that back in.

To find this problem, I first tried refining the mesh for the cylinder, which didn't help. Then I deleted components one by one until the two solutions matched.

Since the cap is apparently quite significant, you should also refine that until it stops affecting the solution.

VMH

kam33mitch, can you share your .step file for the base? Thanks

VMH

kam33mitch,

In addition to what Victor said above, I would use quadratic elements (with midside nodes) for solid elements subjected to bending to obtain more accurate results (It's usually recommended at least 3 to 4 layers thru the thickness when linear solid elements). You can search more on this subject online. I would also watch out for aspect ratios of your elements.

As for alot of elements generating locally at sharp edges, you can reduce that and have more uniform elements by using smaller value for "min. elements per edge" options in the meshing option.

See YouTube link below. Didn't see any differences in Mecway and CCX results after fixing possible elements quality issues.

German

Can you share Mooring base.step file?
Thank you

VMH

Sorry, I longer have the files...