RE;ProfileSPDLinDirectSolver::solve() - aii < 0 (i, aii): (0,0)

[ryancwl95]

Hi,

I am trying to a model 1d consolidation problem following an example from : https://opensees.berkeley.edu/wiki/inde ... solidation.

After running the analysis, I'm faced with this notification. I was wondering if it is the cause of subsequent problems/failures in the analysis? could you give some advice?

Screenshot 2023-09-27 190947.png (58.35 KiB) Viewed 808 times

Also, below attached is a screen shot of the model. It has 10 elements in a grid size of 10units.

Screenshot 2023-09-27 191255.png (8.31 KiB) Viewed 808 times

I have checked with the node.tcl file of the model created by stko and it returned this:

Screenshot 2023-09-27 191608.png (50.58 KiB) Viewed 808 times

I was wondering if there is any problem with my modelling? As the X co-ordinates in the X column are correct, but the y-co-ordinates in the y column are incorrect for all nodes in the nodes.tcl file.

[STKO Team]

The error is saying that your model is singular.
What worries me is that your Y coordinates are all set to 0.
Are you sure you modeled your 2D elements in the X-Y plane?
Remember that a 2D model MUST be in the XY plane

[ryancwl95]

Hi,
Yes, it was done in a Z-X plane and I have rectify it. Now, the node numbering makes more sense, thank you.

I tired running the analysis again and i have this error. Could you please advise. Thank you!

WARNING NineFourNodeQuadUP: Determinant<=0 in tag 23Press any key to continue . . .

I started by drawing a 1 by 10units column using the Face3/4 command. Followed by adding the physical and element property on the surface created. next, adding the conditions and then setting up the mesh (resulting in the screen shot below). I am using 9-4quad up element.

[ryancwl95]

Hi,
For this error that I mentioned previously
: WARNING NineFourNodeQuadUP: Determinant<=0 in tag 23Press any key to continue . . .

I believe that the tag23 might be referring to the element Tag rather than the node Tag,. am I right?

Also, I have checked the script element.tcl and the nodetags for all the 9noded-quad elements are correct.

I also noticed that in this script the quad element tags do not begin with EleTag=1 but rather EleTag=23. Is there a reason for this?

Screenshot 2023-10-03 210339.png (34.24 KiB) Viewed 712 times

Secondly, I took a screenshot of the element tags under the "mesh tab" in STKO, showing the base of the 2d model.

Screenshot 2023-10-03 203835.png (17.48 KiB) Viewed 712 times

From the second image attached:

It seems that besides recognizing the "quads(squares)" as actual elements; they also recognize the lines on the left and right of the quad(square) as elements too (I'm not too sure). Is there something wrong with how I form the geometry? How do I address this issue?

Your advice will be appreciated, thank you!:)

[STKO Team]

Now you modeled it in the X-Y plane, but upsidedown!
The surface normal vector should point to the global +Z axis.
Otherwise the area of 2D elements will be negative (Jacobian < 0).
You can use the Reverse command to flip the local axes of surfaces.

[ryancwl95]

Now you modeled it in the X-Y plane, but upsidedown!
The surface normal vector should point to the global +Z axis.
Otherwise the area of 2D elements will be negative (Jacobian < 0).
You can use the Reverse command to flip the local axes of surfaces.

Thank you for your advice. ill give it a go.

Do you have any explanation for my second query:
"It seems that besides recognizing the "quads(squares)" as actual elements; they also recognize the lines on the left and right of the quad(square) as elements too (I'm not too sure). Is there something wrong with how I form the geometry? How do I address this issue?"

Screenshot 2023-10-03 203835.png (17.48 KiB) Viewed 680 times

[STKO Team]

It's normal, when STKO generates a mesh, it creates meshed for every geometry entity (also edges which are borders of faces, or faces which are border of solids).
But, if you do not assign an element property to them, they will not be converted into OpenSees elements